Blood: Plasma, Blood Cells, and Platelets
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Components of blood. In the micrograph the dark red cells are red blood cells. Platelets are pink. The fuzzy gold balls are white blood cells. |
Blood is a connective tissue; it contains plasma, blood cells, and cell fragments called platelets. Adult women of average size have 4-5 liters of blood in their bodies; men have slightly more.
Plasma is the fluid part of blood. Roughly 55% of whole blood is plasma, which is mostly water. Plasma proteins perform a variety of tasks: Albumin is important in maintaining osmotic balance and transports chemicals such as therapeutic drugs. Other plasma proteins include protein hormones, as well as proteins involved in immunity, blood clotting, and the transport of lipids and vitamins. Plasma further contains ions, glucose, amino acids, signaling molecules, and dissolved gases.
Red blood cells carry oxygen and CO2. Erythrocytes, or red blood cells, (45% of whole blood) are biconcave disks. They contain hemoglobin, an iron-containing protein that binds with oxygen. They also carry a small amount of carbon dioxide. Red blood cells originate from stem cells in the bone marrow.
Click here for the Animation: Cellular Components of Blood. Please make sure that your sound is on and your volume is up.
How Blood Transports Oxygen
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Red Blood Cells |
Hemoglobin is the oxygen carrier. Only a tiny amount of oxygen is dissolved in blood plasma. Most of the oxygen is bound to the heme groups of hemoglobin; oxygen-bearing hemoglobin is called oxyhemoglobin. What determines how much oxygen hemoglobin can carry?
The amount of oxygen bound to hemoglobin changes as conditions in the tissues vary. Binding of oxygen is favored by conditions in the lungs: abundant oxygen, cooler temperature, and neutral pH. Release of oxygen is favored in the tissues where the oxygen levels are lower, temperatures higher, and pH more acidic. Hemoglobin also transports a small amount of carbon dioxide.
Click here for the Animation: Globin and Hemoglobin Structure. Please make sure that your sound is on and your volume is up.
Each hemoglobin molecule has four polypeptide chains (globin proteins), each of which possesses a heme group containing an iron molecule; each iron binds one molecule of oxygen.
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| The structure of hemoglobin. Recall that hemoglobin is a globular protein consisting of four polypeptide chains and four iron-containing heme groups. Oxygen binds to the iron in heme groups, which is one reason why humans require iron as a mineral nutrient. |
Hormonal Control of Red Blood Cell Production
Red blood cells form from stem cells located in red bone marrow. The hormone erythropoietin from the kidneys is the stimulus for stem cell division. Mature red blood cells have no nuclei and live for only about 120 days. Macrophages remove old blood cells from the bloodstream; amino acids are returned to the blood, iron is returned to the bone marrow, and heme groups are converted to bilirubin. Red cell counts remain rather constant at 5.4 million/microliter for males and 4.8 million for females.
A negative feedback loop stabilizes the red blood cell count. The kidneys monitor oxygen content of the blood; when it drops too low, the kidneys secrete erythropoietin. Erythropoietin stimulates bone marrow to produce more red blood cells; this increases the ability of the blood to carry oxygen. As oxygen levels rise, the information feeds back to the kidneys, which stop secreting erythropoietin.
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The feedback loop that helps maintain a normal red blood cell count. |
Blood Types – Genetically Different Red Blood Cells
All cells of the human body have surface proteins and other molecules that serve as “self” identification markers. Any protein marker that prompts a defensive action is called an antigen. The human body produces antibodies that recognize markers on foreign cells as “nonself” and stimulate immune reactions.
The ABO group of blood types includes key self markers on red blood cells. ABO blood groups are based on glycoprotein surface markers on red blood cells. Type A has A markers; type B has B markers. Type AB has both markers; type O has neither marker. Depending on ABO blood type, the body will also possess antibodies to other blood types; ABO blood typing is done to prevent incompatible blood types from being mixed.
Mixing incompatible blood types can cause the clumping called agglutination. Type A blood types do not have antibodies against A markers, but they do have antibodies to type B; Type B blood types do not have type B antibodies, but they do have type A antibodies, etc. A type A person cannot donate blood to a type B person because they are incompatible. When mixed, markers on the surface of red blood cells (not just the ABO markers) that do not match will cause the blood cells to undergo agglutination, a defense response where the blood cells clump.
Click here for the Animation: Genetics of ABO Blood Types. Please make sure that your sound is on and your volume is up.
Click here for the Animation: Transfusions and Blood Types. Please make sure that your sound is on and your volume is up.
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Clumped cells can clog small blood vessels, damage tissues, and cause death.
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Example of an agglutination reaction. This diagram shows what happens when type B blood is transfused into a person who has type A blood. |
h Blood Typing
Rh blood typing looks for an Rh marker. Rh blood typing looks for the presence (Rh+) or absence (Rh-) of antigen on red blood cells. An Rh- person transfused with Rh+ blood will produce antibodies to the Rh marker.
An Rh- mother who bears an Rh+ child can also become sensitized to the Rh antigen; secondary children may be at risk from maternal antibodies. In hemolytic disease of the newborn, too many cells may be destroyed and the fetus dies. Medical treatment (RhoGam) given to the mother after the birth of the first Rh+ baby can inactivate the Rh antibodies.
Click here for the Animation: Rh Blood Type and Pregnancy Complications. Please make sure that your sound is on and your volume is up.
There are also many other markers on red blood cells. Hundreds of different blood cell markers are known; most are widely scattered in the human population. To avoid problems with transfusions, blood undergoes cross-matching to exclude incompatible blood types from being used.
New Frontiers of Blood Typing
Blood + DNA: Investigating crimes and identifying mom or dad. Blood cell markers can be used to compare evidence from crime scenes to samples taken from possible perpetrators. Because blood groups are determined by genes, they are a useful source of information about a person’s genetic heritage. Blood typing can also be used to help determine the identity of a child’s father or mother.
For safety’s sake, some people bank their own blood. Even with screening, blood transfusions still carry the risk of being incompatible or potentially contaminated with infectious agents. In autologous transfusions, individuals pre-donate blood to themselves prior to surgeries in case transfusion is needed.
Blood substitutes must also avoid sparking an immune response. Blood substitutes have potential uses in situations where it is not feasible to perfectly match blood, such as in an ambulance or on the battlefield. To date, however, substitutes have been difficult to manufacture; OxygentTM is an oxygen carrier that has currently reached the final stages of clinical trials.
Hemostasis and Blood Clotting
Hemostasis prevents blood loss. Hemostasis is the process that stops bleeding to prevent excess loss of blood. Spasms of the smooth muscle in the damaged blood vessel stop blood flow for a few minutes by constriction of the vessel. Platelets clump to plug the rupture; they then release serotonin and other chemicals to prolong the spasm and attract more platelets. Finally, the blood coagulates to form the clot. Hemostasis can only seal tears and punctures that are relatively small.
Click here for the Animation: Hemostasis. Please make sure that your sound is on and your volume is up.
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How a Blood Clot forms |
Blood Disorders
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Normal red blood cell | Sickled red blood cell | A life stage of the microorganism that causes malaria, about to rupture a red blood cell. |
Anemias are red blood cell disorders. Anemias develop when red blood cells deliver too little oxygen to the tissues. Two types result from nutrient deficiencies: In iron-deficiency anemia, red cells contain too little hemoglobin, usually resulting from an iron-poor diet. Pernicious anemia is caused by a deficiency of folic acid or vitamin B12. Aplastic anemia results from a destruction of the red bone marrow and its stem cells.
Hemolytic anemias are caused by the premature destruction of red blood cells. Sickle cell anemia, a genetic disease, is one cause. Malaria is a major cause of hemolytic anemia and follows infection by a protozoan transmitted by mosquitoes. In thalassemia, individuals produce abnormal hemoglobin.
Carbon monoxide poisoning prevents hemoglobin from binding oxygen. Carbon monoxide (CO) is a colorless, odorless gas present in auto exhaust fumes and smoke from wood, coal, charcoal, and tobacco. CO binds to hemoglobin 200 times more tightly than oxygen, thus blocking oxygen transport to tissues.
Mononucleosis and leukemias affect white blood cells. Infectious mononucleosis is caused by the Epstein-Barr virus, which triggers overproduction of lymphocytes. Leukemias are very serious cancers in which there is an overproduction of white blood cells and destruction of bone marrow; chronic myelogenous leukemia is one type.
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Blood from person with chronic myelogenous leukemia |
Other viral infections, such as HIV (the human immunodeficiency virus), can also harm or destroy white blood cells. Toxins can destroy blood cells or poison the blood in other ways. Septicemia can occur when bacteria release toxins into the blood; Staphylococcus aureus (Staph A) is one important example. Toxemia happens when metabolic poisons accumulate in the body; toxemia can occur if the kidneys do not adequately filter the blood and remove these poisons.
The Cardiovascular System – Moving Blood Through the Body
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Human Cardiovascular system Click to enlarge |
The heart and blood vessels make up the cardiovascular system. The cardiovascular system has two major elements:
- The heart is the muscular pump that generates the pressure required to move the blood through the body.
- Blood vessels are the distribution tubes of varying diameters.
The route of circulation: heart >>> arteries >>> arterioles >>> capillaries >>> venules >>> veins and finally back to the heart.
Click here for the Animation: Major Human Blood Vessels. Please make sure that your sound is on and your volume is up.
Circulating blood is vital to maintain homeostasis. The cardiovascular system is the body’s internal rapid-transport system for oxygen, nutrients, secretions, and wastes via the blood. Homeostasis depends on the reliable supply of blood to all of the body.
The cardiovascular system is linked to the lymphatic system. Because of the pressure in the cardiovascular system, water and proteins leak out to become part of the interstitial fluid. The lymphaticsystem vessels pick up the fluid and return it to the general circulation.
The Heart: A Double Pump
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Location of the heart |
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The heart is a durable pump made mostly of cardiac muscle (myocardium). The heart is surrounded by a tough, fibrous sac (pericardium). The inner lining of the heart is the endocardium; it is composed of connective tissue and epithelial cells (endothelium).
The heart has two halves and four chambers. The septum divides the heart into two halves, right and left. Each half consists of an atrium (receiving chamber) and a ventricle (pumping chamber) separated by an atrioventricular valve (AV valve). The AV valve on the right is a tricuspid valve; the one on the left is the bicuspid, or mitral valve. Chordae tendineae (“heartstrings”) connect the AV valve flaps to the ventricle wall. Blood exits each ventricle through a semilunar valve.
Heart muscle cells are serviced by the coronary circulation; coronary arteries branch off the aorta, forming a capillary bed around the heart.
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In this drawing, you are looking down at the heart. The atria have been removed so that the atrioventricular (AV) and semilunar valves are visible. |
Click here for the Animation: Anatomy of the Human Heart. Please make sure that your sound is on and your volume is up.
In a “heartbeat,” the heart’s chambers contract, then relax. The cardiac cycle is a sequence of contraction (systole) and relaxation (diastole). As the atria fill, the ventricles are relaxed. Pressure of the blood in the atria forces the AV valves open; the ventricles fill as the atria contract. When the ventricles contract, the AV valves close, and blood flows out through the semilunar valves.
The cardiac output is the amount of blood each ventricle can pump in a minute; on average the output from each ventricle is about 5 liters. The heart sound “lub” is made by the closing of the AV valves; the “dup” sound is the closure of the semilunar valves.
Click here for the Animation: The Cardiac Cycle. Please make sure that your sound is on and your volume is up.
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Coronary arteries and veins. Click to enlarge | The Cardiac Cycle Click to enlarge | The heart's internal organization click to enlarge |
The Two Circuits of Blood Flow
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The pulmonary circuits for blood flow in the cardiovascular system. |
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The systemic circuits for blood flow in the cardiovascular system. |
The pulmonary circuit: Blood picks up oxygen in the lungs. The pulmonary circuit receives blood from the tissues, taking it through the lungs for gas exchange. The path of blood flow: blood from tissues enters the right atrium >>> tricuspid valve >>> right ventricle >>>right semilunar valve >>> pulmonary arteries >>> lungs >>> pulmonary veins >>> left atrium. Blood returning from the body tissues is high in carbon dioxide and low in oxygen; these concentrations are reversed after passage through the lung capillaries.
In the systemic circuit, blood travels to and from tissues. In the systemic circuit, oxygenated blood is pumped through the body. Blood moves from the left atrium >>> bicuspid valve >>> left ventricle >>>left semilunar valve >>> aorta >>> body tissues. Blood from the upper body travels through the superior vena cava; blood from the lower body travels through the inferior vena cava.
Blood from the digestive tract is shunted through the liver for processing. After a meal, blood laden with nutrients is carried from the digestive tract in the hepatic portal vein to the liver capillaries. There it passes through the liver capillary beds before leaving via the hepatic vein to return to the general circulation; oxygenated blood reaches the liver through the hepatic artery.
Click here for the Animation: Blood Circulation. Please make sure that your sound is on and your volume is up.
Click here for the Video: Heart Healthy. Please make sure that your sound is on and your volume is up.
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Distribution of the heart’s output in people napping. |
How Cardiac Muscle Contracts
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Intercalated discs |
Electrical signals from “pacemaker” cells drive the heart’s contractions. Cardiac muscle cells are linked by intercalated discs, which rapidly pass signals to contract throughout the heart. The cardiac conduction system consists of noncontractile cells that are self-excitatory (pacemaker cells). Excitation for a heartbeat is initiated in the sinoatrial (SA) node; it then passes to the atrioventricular (AV) node and on to the Purkinje fibers, which make contact with the muscle cells that result in ventricular contraction.
It is the action of the cardiac pacemaker (SA node) that produces our normal heartbeat. The nervous system adjusts heart activity. The nervous system can adjust the rate and strength of cardiac muscle contraction; stimulation by one set of nerves increases the rate and strength while stimulation by other nerves decreases heart rate. Centers for nervous control of the heart lie in the spinal cord and the brain.
Click here for the Animation: Cardiac Conduction. Please make sure that your sound is on and your volume is up.
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Cardiac Conduction System |
Blood Pressure
Blood exerts pressure against the walls of blood vessels. The force of blood against the vessel walls can be measured as blood pressure. Normal systolic pressure (peak pressure in the aorta) is 120 mm of Hg; normal diastolic pressure (lowest pressure in the aorta) is 80 mm.
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Blood pressure values give important clues as to the condition of the vessels and the flow of blood through them. In hypertension, the blood pressure is too high, which can lead to stroke or heart attack. In hypotension, the blood pressure is too low; loss of water or blood volume can lead to circulatory shock.
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Structure and Functions of Blood Vessels
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Artery |
Arteries are large blood pipelines. Because of their elastic walls, arteries tend to “smooth out” the pressure changes associated with the discontinuous pumping cycle of the heart (felt as a pulse). Because of their large diameters, arteries present little resistance to flow; blood pressure does not decrease very much in them.
Arterioles are control points for blood flow. Arteries branch into smaller arterioles, where the greatest pressure drop occurs. The wall of an arteriole has rings of smooth muscle over a single layer of elastic fibers. Arterioles serve as control points where adjustments can be made in blood volume distribution.
Capillaries are specialized for diffusion. A capillary is the smallest and thinnest tube in the path of circulation and is specialized for exchange of substances with interstitial fluid. Total resistance is less than in arterioles so the drop in blood pressure is not as great. Venules and veins return blood to the heart. Capillaries merge into venules. Venules merge into veins.
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Arteriole | Capillaries |
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Venule | Vein |
Veins are blood volume reservoirs (50-60% of blood volume) because their walls can distend or contract. Skeletal muscles adjacent to veins squeeze the walls to move the blood along on its way back to the heart; valves prevent backflow. Varicose veins can form when the veins have become overstretched, and the valves weakened.
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Valves in medium.sized veins prevent backflow of blood. | Skeletal muscles next to the vein contract, helping blood flow forward. | Skeletal muscles relax and valves in the vein shut—preventing backflow. |
Click here for the Animation: Skeletal Muscles and Fluid Pressure in a Vein. Please make sure that your sound is on and your volume is up.
Vessels help control blood pressure. The brain monitors signals from various arteries to determine the rate of heartbeat and any changes needed in vessel diameters. If the blood pressure increases, the arterioles are instructed to relax (vasodilation). If the pressure decreases, the diameter of the arterioles decreases (vasoconstriction). In the baroreceptor reflex, special receptors in the carotid arteries monitor changes in blood pressure and send the information to the brain for action.
Click here for the Animation: Structure of Blood Vessels. Please make sure that your sound is on and your volume is up.
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Changes in blood pressure in different parts of the cardiovascular system. |
Capillaries: Where Blood Exchanges Substances with Tissues
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Red blood cells moving single file in capillaries |
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Resin cast showing a dense network of capillaries |
A vast network of capillaries weaves close to nearly all living body cells. Capillaries comprise most of the cardiovascular system. The velocity of blood flow slows as the diameter of the vessels decreases. It is slowest in the capillaries to provide for maximum exchange.
Many substances enter and leave capillaries by diffusion. Diffusion is a slow process and is not efficient over long distances. Billions of capillaries ensure that all cells are near enough to a capillary to receive nutrients and give up wastes; blood flow is slow enough here to allow diffusion.
Some substances pass through “pores” in capillary walls. Water-filled, slitlike areas between the cells of capillary walls allow water-soluble substances to exit the blood due to pressure (bulk flow). This movement of fluids and solutes is important to homeostasis and maintaining blood pressure.
Blood in capillaries flows onward to venules. Precapillary sphincters regulate the flow of blood into capillaries. Capillaries are the “turnaround points” for the cardiovascular system.
Click here for the Animation: Capillary Forces. Please make sure that your sound is on and your volume is up.
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How substances pass through slitlike pores in the wall of a capillary | The "bulk flow" of fluid into and out of a capillary bed |
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The general direction of blood flow through a capillary bed. A pre.capillary sphincter wraps around the base of each capillary. | |
Cardiovascular Disorder
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Normal artery |
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| Artery with its lumen narrowed by a plaque |
Many factors may influence your chance of developing a cardiovascular disorder. Some risk factors include: family history, hypertension, obesity, smoking, or simply age. Inflammation, which leads to the production of C-reactive protein by the liver, may also play a role in cardiovascular disease.
Arteries can be clogged or weakened. Arteriosclerosis is a hardening of the arteries. When cholesterol and other lipids build up in these hardened arteries, atherosclerosis occurs. Atherosclerotic plaques can impede blood flow. Coronary arteries are narrow and vulnerable to clogging with these plaques; chest pain (angina pectoris) or heart attack may occur.
High blood levels of cholesterol can lead to atherosclerosis. Low-density lipoproteins (LDL or “bad” cholesterol) carry cholesterol into the arterial walls; high-density lipoproteins (HDL or “good” cholesterol) remove it. A total of 200 mg cholesterol per milliliter of blood or less is considered acceptable for most people. Surgery may be needed to clear blocked arteries. Coronary bypass involves using a large vessel from elsewhere in the body to bypass a completely blocked artery in the heart.
Laser angioplasty uses a laser to vaporize plaques while balloon angioplasty uses small balloons to flatten the plaques to open room in the artery; a wire “stent” may be inserted to keep the ballooned area open. Statins are drugs designed to reduce the amount of cholesterol in the blood. Disease, injury, or defects can weaken artery walls so they bulge outward due to blood pressure, forming an aneurysm; aneurysms can be fatal if the artery wall bursts.
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Coronary bypasses (in green). |
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(a) ECG of a normal heartbeat. The P wave is generated by electrical signals from the SA node that stimulate contraction of the atria. As the stimulus moves over the ventricles, it is recorded as the QRS wave complex. After the ventricles contract, they rest briefly. The T wave marks electrical activity during this period. (There is also an atrial recovery period “hidden” in the QRS complex.) (b) A recording of ventricular fibrillation. |
Heart damage can lead to heart attack and heart failure. A heart attack is damage to or death of heart muscle. In heart failure, the heart is weak and does not pump blood as efficiently.
Arrhythmias are abnormal heart rhythms. Electrocardiograms (ECGs) are recordings of the cardiac cycle and can be used to reveal irregular heart rhythms. Arrhythmias are irregular heart rhythms; bradycardia is a below normal rhythm, while tachycardia is an above normal rhythm. Ventricular fibrillation occurs when the ventricles contract haphazardly so that blood is not pumped correctly; this can lead to cardiac arrest.
Click here for the Animation: Examples of ECGs. Please make sure that your sound is on and your volume is up.
A heart-healthy lifestyle. Lifestyle changes can greatly reduce the risk of cardiovascular disease. Diets low in fat and cholesterol, regular exercise, and not smoking are three key strategies.
| Major Risk Factors for Cardiovascular Disease |
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Blood, Vascular System and the Heart
- Hemopoiesis
- Erythropoiesis – formation of Red Blood cells
- Erythropoietin – growth factor which stimulates the hemopoeitic stem cells in the bone marrow to produce red blood cells
- Thrombopoiesis – formation of platelets
- Thrombopoietin - growth factor which stimulates the hemopoeitic stem cells in the bone marrow to produce platelets
- Leukopoiesis – formation of white blood cells
- Colony stimulating factor (CSF)- growth factor which stimulates the hemopoeitic stem cells in the bone marrow to produce white blood cells
- Blood Coagulation – Hemostasis (See chart)
- Intrinsic Pathway – see coagulation cascade
- Extrinsic Pathway – see coagulation cascade
- Thrombin Formation – see coagulation cascade
- Fibrin Formation – see coagulation cascade
- Role of the Platelet
- Platelet structure
- Platelet Activation – Platelets can be activated by any one of the following
- ADP
- Thrombin
- Thromboxane A2
- Collagen
- von Willebrand's factor
- Bleeding Disorders
Note: Blood escapes from blood vessels and is often trapped in surrounding tissues. Accumulation may be visible and described as; - Petechiae = pinpoint hemorrhage.
- Purpura = larger, less regular areas of bleeding.
- Ecchymoses = areas of bleeding larger than 2 cm.
- Hematoma = large volume of blood trapped in soft tissue.
- Specific Disorders/Diseases due to platelets
- Thrombocytopenia
- Disseminated Intravascular Coagulation
- Specific Disorders due to Clotting Factor Deficiencies
- von Willebrand's
- Hemophilia A
- Hemophilia B
- Erythrocyte Disorders
- Polycythemia is a condition in which there is excess number of RBC’s
- Anemia is a condition in which there is a decrease in the number of RBC’s
- Hematocrit
- MCV
- MCHC
- Impaired production
- Pure red cell aplasia
- Pancytopenia
- Aplastic anemia
- Deficencies anemias
- Iron
- Vitamin B-12
- megaloblastic anemia due strictly to a deficiency of vitamin b-12.
- pernicious anemia due strictly to a deficiency of intrinsic factor, a protein formed in the stomach which is required for vitamin B-12 absorption.
- Folic acid
- Hemolytic Anemia (Clearance)
- Hemolysis
- Intrinsic Hemolytic Anemia
- Sickle Anemia
- Thalassemias
- Blood types – Genetically different Red Blood Cells
- ABO Groups
- Rh Factor
- Hemolytic disease of the newborn, also known as erythroblastosis fetalis
- Leukocyte Disorders
- Leukopenia
- Leukemias
- chronic myelogenous leukemia
- Neutrophilia
- Neutropenia
- Lymphadenopathy
- Infectious mononucleosis
The Respiratory System—Built for Gas Exchange
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Color enhanced scanning electron micrograph of cilia and mucus-secreting cells (in orange) in the respiratory tract |
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| Paired human vocal cords, where most speech sounds originate. The glottis (the gap between the vocal cords) changes when skeletal muscles act under the control of the nervous system. The sketches show what the glottis looks like when it is closed and opened. |
Airways are pathways for oxygen and carbon dioxide. The respiratory system brings in oxygen that each body cell requires and takes away carbon dioxide that every cell generates. Through the nasal cavities of the nose, air enters and leaves the respiratory system; the nasal cavities are separated by a septum of cartilage and bone. Hair and ciliated epithelium filter dust and particles from the air. Blood vessels warm the air and mucus moistens it. The paranasal sinuses lie just above the cavities and are linked to them by channels.
Air moves via this route: nasal cavities >>> pharynx >>> larynx >>> vocal cords (the gap between the cords is the glottis) >>> trachea >>> bronchi (one bronchus goes to each lung). The trachea leads from the larynx downward to branch into two bronchi, which are lined with cilia and mucus to trap bacteria and particles. The vocal cords at the entrance of the larynx vibrate when air passes through the glottis, allowing us to make sounds; during swallowing, the glottis is closed to prevent choking.
Click here for the Animation: Larynx Function. Please make sure that your sound is on and your volume is up.
Lungs are elastic and provide a large surface area for gas exchange. Human lungs are a pair of organs housed in the rib cage above the diaphragm; the two lungs are separated by the heart. Each lung is enclosed by a pair of thin membranes called pleurae (singular: pleura); the pleural membrane is folded in a manner that forms a pleural sac leaving an intrapleural space filled with a lubricating intrapleural fluid. Inside the lungs, bronchi narrow to form bronchioles ending in respiratory bronchioles. Tiny clustered sacs called alveoli (singular: alveolus) bulge out from the walls of the respiratory bronchioles. Together the alveoli provide a tremendous surface area for gaseous exchange, with the blood located in the dense capillary network surrounding each alveolar sac.
Click here for the Animation: Human Respiratory System. Please make sure that your sound is on and your volume is up.
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Components of the human respiratory system and their functions. Also shown are the diaphragm and other structures with secondary roles in respiration. |
Respiration = Gas Exchange
Respiration is the overall exchange of inhaled oxygen from the outside air for exhaled carbon dioxide waste. This exchange occurs in the alveoli; afterward, the cardiovascular system is responsible for moving gases in the body.
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Links between the respiratory system, the cardiovascular system, and other organ systems. |
The “Rules” of Gas Exchange
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Gas partial pressures. Hg is the chemical symbol for mercury. |
Respiratory systems rely on the diffusion of gases down pressure gradients. Air is 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, and 0.96% other gases. Partial pressures for each gas in the atmosphere can be calculated; for example, oxygen’s is 160 mm Hg. Oxygen and carbon dioxide diffuse down pressure gradients from areas of high partial pressure to areas of low partial pressure.
Gases enter and leave the body by diffusing across thin, moist respiratory surfaces of epithelium; the speed and extent of diffusion depends on the surface area present and on the partial pressure gradient.
When hemoglobin binds oxygen, it helps maintain the pressure gradient. Hemoglobin is the main transport protein. Each protein binds four molecules of oxygen in the lungs (high oxygen concentration) and releases them in the tissues where oxygen is low; by carrying oxygen away from the lungs, the gradient is maintained.
Gas exchange “rules” change when oxygen is scarce. Hypoxia occurs when tissues do not receive enough oxygen; at high altitudes the partial pressure of oxygen is lower than at sea level, so that hyperventilation may occur.
Underwater, divers must breathe pressurized air from tanks and avoid nitrogen narcosis, where nitrogen dissolves into the body, including the brain; divers must also ascend to the surface slowly to prevent nitrogen bubbles in the blood—the “bends” or decompression sickness.
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Breathing
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Inward Bulk Flow of Air Inhalation | Outward Bulk Flow of Air Exhalation |
Changes in the size of the chest (thoracic) cavity during a respiratory cycle. The X-ray image in (a) shows how taking a deep breath changes the volume of the thoracic cavity. Part (b) shows how the volume shrinks after exhalation. | |
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Lung volume during quiet breathing and during forced inspiration and expiration (“spikes” above and below the normal tidal volume). | |
When you breathe, air pressure gradients reverse in a cycle. The respiratory cycle is the continuous in/out ventilation of the lungs and has two phases:
- Inspiration (inhalation) draws breath into the airways.
- Expiration (exhalation) moves a breath out of the airways.
During the cycle, the volume of the chest cavity increases, then decreases, and the pressure gradients between the lungs and outside air reverse. This works because the air in the airways is the same pressure as the outside atmosphere. Pressure in the alveoli (intrapulmonary pressure) is also the same as the outside air.
The basic respiratory cycle. To inhale, the diaphragm contracts and flattens, muscles lift the rib cage upward and outward, the chest cavity volume increases, internal pressure decreases, air rushes in. To exhale, the actions listed above are reversed; the elastic lung tissue recoils passively and air flows out of the lungs. Active exhalation involves contraction of the abdominal muscles to push the diaphragm upward, forcing more air out.
Click here for the Animation: Respiratory Cycle. Please make sure that your sound is on and your volume is up.
How much air is in a “breath”?
About 500 ml of air (tidal volume) enters and leaves the lungs with each breath. A human can forcibly inhale 3,100 ml of air (inspiratory reserve volume) and forcibly exhale 1,200 ml (expiratory reserve volume). The maximum volume that can be moved in and out is called the vital capacity (4,800 ml for males, 3,800 ml for females).
A residual volume of about 1,200 ml remains in the lungs and cannot be forced out. Sometimes food enters the trachea rather than the esophagus; it can be forced out by the Heimlich maneuver, which forces the diaphragm to elevate, pushing air into the trachea to dislodge the obstruction.
Click here for the Animation: Lung Volume. Please make sure that your sound is on and your volume is up.
Click here for the Animation: Heimlich Maneuver. Please make sure that your sound is on and your volume is up.
How Gases Are Exchanged and Transported
Ventilation moves gases into and out of the lungs; it is different from respiration, which is the actual exchange of gases between the blood and cells. In external respiration, oxygen moves from the alveoli to the blood; carbon dioxide moves in the opposite direction. In internal respiration, oxygen moves from the blood into tissues and vice versa for carbon dioxide.
Alveoli are masters of gas exchange. Each alveolus is only a single layer of epithelial cells surrounded by a thin basement membrane and a net of lung capillaries, also with thin basement membranes. Between the two basement membranes is a film of fluid. Together the system forms the respiratory membrane. The partial pressure gradients are sufficient to move oxygen in and carbon dioxide out of the blood, passively.
Pulmonary surfactant is a secretion produced by the alveoli that reduces the surface tension of the film to prevent collapse of the alveoli; infant respiratory distress syndrome occurs in premature babies who lack the ability to make the surfactant.
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Gas exchange between blood in pulmonary capillaries and air in alveoli Click to enlarge | |||
Click here for the Animation: Structure of an Alveolus. Please make sure that your sound is on and your volume is up.
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Partial pressure gradients for oxygen and carbon dioxide through the respiratory tract. Remember that each gas moves from regions of higher to lower partial pressure. |
Hemoglobin is the oxygen carrier. Blood cannot carry sufficient oxygen and carbon dioxide in dissolved form as the body requires; hemoglobin helps enhance its capacity to carry gases by transporting oxygen. Oxygen diffuses down a pressure gradient into the blood plasma >>> red blood cells >>> hemoglobin where it binds at a ratio of four oxygens to one hemoglobin to form oxyhemoglobin. Hemoglobin gives up its oxygen in tissues where partial pressure of oxygen is low, blood is warmer, and pH is lower; all three conditions occur in tissues with high metabolism.
Click here for the Animation: Partial Pressure Gradients. Please make sure that your sound is on and your volume is up.
When tissues are chronically low in oxygen, red blood cells produce DPG (2,3-diphosphoglycerate), which decreases the affinity of hemoglobin for oxygen, allowing more oxygen to be released to the tissues. Hemoglobin and blood plasma carry carbon dioxide. Because carbon dioxide concentration is higher in the body tissues rather than in blood, it diffuses into the blood capillaries.
Seven percent remains dissolved in plasma, 23% binds with hemoglobin (forming carbaminohemoglobin) and 70% is in bicarbonate form.
Bicarbonate and carbonic acid formation is enhanced by carbonic anhydrase, an enzyme located in the red blood cells. Reactions that make bicarbonate are reversed in the alveoli where the partial pressure of carbon dioxide is low.
Click here for the Video: Bicarbonate Buffer System. Please make sure that your sound is on and your volume is up.
Homeostasis Depends on Controls over Breathing
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Controls over breathing. In quiet breathing, centers in the brain stem coordinate signals to the diaphragm and muscles that move the rib cage, triggering inhalation. When a person breathes deeply or rapidly, another center receives signals from stretch receptors in the lungs and coordinates signals for exhalation. |
A respiratory pacemaker controls the rhythm of breathing. Automatic mechanisms ensure a regular cycle of ventilation. Clustered nerve cells in the medulla coordinate the signals for the timing of exhalation and inhalation; the pons fine tunes the rhythmic contractions. The nerve cells are linked to the diaphragm muscles and the muscles that move the rib cage; during normal inhalation, nerve signals travel from the brain to the muscles causing them to contract and allowing the lungs to expand.
Normal exhalation follows relaxation of muscles and elastic recoil of the lungs. When breathing is deep and rapid, stretch receptors in the airways send signals to the brain control centers, which respond by inhibiting contraction of the diaphragm and rib muscles, forcing you to exhale.
CO2 is the trigger for controls over the rate and depth of breathing. The nervous system is more sensitive to levels of carbon dioxide and uses this gas to regulate the rate and depth of breathing. Sensory receptors in the medulla detect hydrogen ions produced when dissolved carbon dioxide leaves the blood and enters the cerebrospinal fluid bathing the medulla. The drop in pH in the cerebrospinal fluid triggers more rapid and deeper breathing to reduce the levels of carbon dioxide in the blood.
Changes in the levels of carbon dioxide, oxygen, and blood pH are also detected by carotid bodies, located near the carotid arteries, and aortic bodies, located near the aorta; both receptors signal increases in ventilation rate to deliver more oxygen to tissues.
Chemical controls in alveoli help match air flow to blood flow. When the rate of blood flow in the lungs is faster than the air flow, the bronchioles dilate to enhance the air flow and thus the rate of diffusion of the gases. When the air flow is too great relative to the blood flow, oxygen levels rise in the lungs and cause the blood vessels to dilate, increasing blood flow.
Apnea is a condition in which breathing controls malfunction. Apnea is a brief interruption in the respiratory cycle; breathing stops and then resumes spontaneously. Sleep apnea is a common problem of aging because the mechanisms for sensing changing oxygen and carbon dioxide levels gradually become less effective over the years.
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Sensory receptors that detect changes in the concentrations of carbon dioxide and oxygen in the blood. |
Disorders of the Respiratory System
Risks Associated with Smoking | Reduction in Risks by Quitting |
| Shortened life expectancy: Nonsmokers live 8.3 years longer on average than those who smoke two packs daily from the mid-twenties on. | Cumulative risk reduction; after 10 to 15 years, life expectancy of ex-smokers approaches that of nonsmokers |
| Choronic Bronchitis, Emphysema: Smokers have 4-25 times more risk of dying from these diseases than do nonsmokers. | Greater chance of improving lung function and slowing down rate of deterioration. |
| Lung Cancer: Cigarette smoking is a major contributing factor. | After 10 to 15 years, risk approaches that of nonsmokers. |
| Cancer of Mouth: 3-10 times greater risk among smokers. | After 10-15 years, risk is reduced to that of nonsmokers. |
| Cancer of Larynx: 2.9-17.7 times more frequent among smokers. | After 10 years, risk is reduced to that of nonsmokers. |
| Cancer of Esophagus: 2-9 times greater risk of dying from this. | Risk proportional to amount smoked; quitting should reduce it. |
| Cancer of Pancreas: 2-5 times greater risk of dying from this. | Risk proportional to amount smoked; quitting should reduce it. |
| Cancer of Bladder: 7-10 times greater risk for smokers. | Risk decreases gradually over 7 years to that of nonsmokers. |
| Coronary Heart Disease: Cigarette smoking is a major contributing factor. | Risk drops sharply after a year; after 10 years, risk reduced to that of nonsmokers. |
| Effects on Offspring: Women who smoke during pregnancy have more stillbirths, and weight of liveborns averages less (hence, babies are more vulnerable to disease, death). | When smoking stops before fouth month of pregnancy, rsik of stillbirth and lower birthweight eliminated. |
| Imparied Immune System Function: Increase in allergic responses, destruction of defensive cells (macrophages) in respiratory tract. | Avoidable by not smoking. |
| Bone Healing: Evidence suggests that surgically cut or broken bones require up to 30 percent longer to heal in smokers, possibly because smoking depletes the body of vitamin C and reduces the amount of oxygen interfere with production of collagen fibers, a key component of bone. Research in this area is continuing. | Avoidable by not smoking. |
Tobacco is a major threat. Smoking has both immediate effects (for example, loss of cilia function) and long term effects, such as lung cancer. Even one cigarette can cause you damage as well as hurt those around you through secondhand smoke. A variety of pathogens can infect the respiratory system.
Pneumonia occurs when inflammation in lung tissue and the buildup of fluids makes breathing difficult; pneumonia can sometimes occur when infections that start in the nose and throat, such as from influenza, spread. Tuberculosis arises from infection by the bacterium Mycobacterium tuberculosis; the disease destroys patches of lung tissue and can cause death if untreated. Histoplasmosis is caused by a fungus; treatment is possible, but the infection can sometimes spread to the eyes, causing impairment or blindness.
Irritants cause other disorders. Bronchitis, caused by air pollution, cigarette smoke, or infection, leads to increased mucus secretions, interference with ciliary action, and eventual inflammation and possible scarring of the bronchial walls.
If bronchitis progresses so that more of the bronchi become scarred and blocked with mucus, emphysema may result; here alveoli also begin to break down, further eroding the ability to breathe.
Asthma occurs in response to various allergens; smooth muscles in the bronchiole walls contract in spasms, mucus rushes in, and breathing becomes difficult. Steroid inhalers may be needed to relieve symptoms.
Click here for the Video: Clean Air Act. Please make sure that your sound is on and your volume is up.
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Examples of the kinds of particles that may be present in the air you breathe. | |||
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Normal human lungs (this lung tissue looks darker than normal because it has been chemically preserved). | Lungs from a person with emphysema | ||
The Challenge: Shifts in Extracellular Fluid
Extracellular fluid (ECF) is comprised of tissue fluid, blood plasma, and other fluids such as lymph that occurs outside of cells; intracellular fluid is the fluid inside cells. There is a constant exchange of gases and other materials between intracellular and extracellular fluid. The volume and composition of the ECF must remain stable for these exchanges to occur. The urinary system is responsible for maintaining relatively stable conditions in the ECF.
The body gains water from food and metabolic processes. Absorption of water from liquids and solid foods occurs in the gastrointestinal tract. Metabolism of nutrients yields water as a by-product. The body loses water in urine, sweat, feces, and by evaporation. Water leaves the body by excretion in urine, evaporation from the lungs and skin, sweating, and in feces. The body exerts the most control over urinary excretion, the production of urine. The least amount of water is lost in feces.
Normal Daily Balance between Water Gain and Water Loss in Adult Humans | ||||
Water Gain (milliliters) | Water Loss (milliliters) | |||
| Ingested in solids | 850 | Urine | 1,500 | |
| Ingested as liquids | 1,400 | Feces | 200 | |
| Metabolically derived | 350 | Evaporation | 900 | |
2,600 | 2,600 | |||
Solutes enter extracellular fluid from food, metabolism, and other ways. Solutes enter the body when nutrients and mineral ions are absorbed from the GI tract. Living cells secrete substances into tissue fluid and blood. The respiratory system brings oxygen into the blood; respiring cells add carbon dioxide.
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How activities of the urinary system coordinate with those of some other organ systems. |
Solutes leave the ECF by urinary excretion, in sweat, and during breathing. Respiratory exhalation rids the body of carbon dioxide; all other major wastes of metabolism leave in urine. Uric acid is formed in reactions that degrade nucleic acids; too much uric acid in the ECF crystallizes in joints, causing gout. Ammonia is formed when amino groups are removed from amino acids; it is turned into urea in the liver and either reabsorbed or excreted. Other products of protein degradation are also excreted.
The kidneys filter a variety of substances from the blood, including nitrogen, sodium, potassium, and calcium. Sodium, potassium, and calcium are called electrolytes because a solution in which they are dissolved will carry an electric current. Only 1% of the water that enters the kidneys is excreted in urine; most is returned to the blood.
Click here for the Animation: Water and Solute Balance. Please make sure that your sound is on and your volume is up.
The Urinary System - Built for Filtering and Waste Disposal
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Internal structure of a kidney. |
Each kidney is a bean-shaped organ about the size of a rolled up pair of socks. A kidney has several internal lobes; an outer cortex wraps around the central medulla. The whole kidney is wrapped in a coat of connective tissue called the renal capsule. The central cavity of the kidney is the renal pelvis.
Click here for the Animation: Kidney Structure. Please make sure that your sound is on and your volume is up.
Kidneys have several functions: They produce erythropoietin, which stimulates production of red blood cells. They aid in calcium absorption from food. Kidneys make renin, an enzyme that helps regulate blood pressure. Their main function is to remove metabolic wastes and maintain fluid balance. The urinary system also consists of tubelike ureters that carry urine to the urinary bladder for storage until urination; urine leaves the bladder through the urethra.
Click here for the Animation: Human Urinary System. Please make sure that your sound is on and your volume is up.
Nephrons are the kidney filters. Each lobe of the kidney contains blood vessels and over a million thin tubes called nephrons, which filter water and solutes from the blood. The wall of the nephron balloons around a cluster of blood capillaries called the glomerulus; the balloon is called the Bowman’s capsule; the rest of the nephron is a winding tubule. Filtrate from the Bowman’s capsule enters the proximal tubule, passes through the loop of Henle and into the distal tubule, and finally empties into a collecting duct.
Click here for the Animation: Structure of the Nephron. Please make sure that your sound is on and your volume is up.
Special vessels transport blood to, in, and away from nephrons. An afferent arteriole delivers blood to each nephron where it enters the glomerulus for filtration; the glomerular capillaries are much more permeable than other capillaries. Glomerular capillaries merge to form an efferent arteriole. The efferent arteriole splits to form the peritubular capillaries, which eventually carry filtered blood into venules and out of the kidneys.
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The urinary system and its functions. | The two kidneys, ureters, and urinary bladder are located between the abdominal cavity’s wall and its lining, the peritoneum. |
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The Urinary System – Built for Filtering and Waste Disposal Some parts of the nephron allow absorption of water and solutes, other parts do not. | Diagram of a nephron. Interacting with two sets of capillaries, nephrons are a kidney’s blood-filtering units. |
How Urine Forms: Filtration, Reabsorption, and Secretion
Filtration removes a large amount of fluid and solutes from the blood. In filtration, blood pressure forces filtrate out of the glomerular capillaries into the Bowman’s capsule, then into the proximal tubule. Blood cells, proteins, and other large solutes cannot pass into the capsule; water, glucose, sodium, and urea, however, are forced out of the blood.
Next, reabsorption returns useful substances to the blood. Reabsorption takes place across the walls of the proximal tubules. Water, glucose, and salt diffuse through the tubule wall; active transport then moves glucose and sodium ions into the tissue fluid. Negatively charged ions follow the sodium into the tissues; water also follows. Solutes are actively transported from the tissues to the peritubular capillaries, water follows, and reabsorption is complete. Any solutes and water remaining in the tubules become part of urine.
Average Daily Reabsorption Values for a Few Substances | |||
Amount Filtered | Percentage Excreted | Percentage Reabsorbed | |
| Water | 180 liters | 1 | 99 |
| Glucose | 180 grams | 0 | 100 |
| Amino acids | 2 grams | 5 | 95 |
| Sodium ions | 630 grams | 0.5 | 99.5 |
| Urea | 54 grams | 50 | 50 |
Secretion rids the body of excess hydrogen ions and some other substances. During secretion, urea, excess hydrogen ions, and excess potassium ions are returned to the nephrons to add to forming urine. This process maintains the body’s acid-base balance and also rids the body of drugs, uric acid, hemoglobin breakdown products, and other wastes.
Urination is a controllable reflex. The internal urethral sphincter (involuntary control) regulates urine flow from the bladder into the urethra during urination. The external urethral sphincter (voluntary control) opens to void urine from the body.
Click here for the Animation: Urine Formation. Please make sure that your sound is on and your volume is up.
Click here for the Video: Reabsorption and Secretion. Please make sure that your sound is on and your volume is up.
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Overview of the steps that form urine. | 1. Filtration- Water and sollutes forced out across the glomerular capillary wall collect in Bowman's capsule, which drains into the proximal tubule. |
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| 2. Reabsorption - As filtrate flows through the proximal tubule, ions and some nutrients are actively and passivley transported outward, into tissue fluide. Water follows, by osmosis. Cells of peritubular capillaries transport them into blood. Water again follows by osmosis. | 3. Secretion - Transport proteins move H+, K+, urea, and wastes out of peritubular capillaries. Transporters in the nephron tubule move them into the filitrate. |
How Kidneys Help Manage Fluid Balance and Blood Pressure
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Reabsorption of water and salt in the loop of Henle. |
The total volume of body fluids doesn’t vary much because the kidneys make adjustments to keep the volume of extracellular fluid, and blood in particular, in a normal range. Water follows salt as urine forms.
The loop of Henle pulls more water and salts from the filtrate to return it to the body. The descending part of the loop sits in salty tissue fluid; water is drawn out of the tube to be reabsorbed. The salt concentration of the remaining fluid in the loop rises until it matches the concentration of the surrounding tissues. In the ascending limb of the loop, water is inhibited from passing through the wall of the loop, but sodium is actively transported out of the loop. Salt continues to be removed in the distal tubule, but not water; as salt leaves the filtrate, salt gradients become steep, driving reabsorption of solutes into the peritubular capillaries. Urea helps boost the gradient by diffusion out of the collecting duct, taking water with it.
Hormones control whether kidneys make urine that is concentrated or dilute. Antidiuretic hormone (ADH) is secreted by the brain in response to a decrease in extracellular fluid; ADH causes the distal tubules and collecting ducts to become permeable to water, which moves back into the blood capillaries.
Decreases in the volume of extracellular fluid is sensed by cells in the efferent arterioles; these cells, part of the juxtaglomerular apparatus, release renin. Renin stimulates production of angiotensin I, which is converted to angiotensin II. Angiotensin II stimulates the adrenal cortex of the kidney to make aldosterone, which causes cells of the distal tubules and collecting ducts to increase reabsorption of salts. Caffeine and alcohol are diuretics, substances that promote loss of water.
A thirst center monitors sodium. When solute concentration in the extracellular fluid rises, the amount of saliva produced by the salivary glands drops; a dry mouth stimulates the thirst center of the brain. Stimulation of the thirst center and release of ADH cause liquid-seeking behavior.
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Where ADH and aldosterone act in kidney nephrons. | A negative feedback loop from the kidneys to the brain that helps adjust the fluid volume of the blood. |
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The juxtaglomerular apparatus and renin-secreting cells that play a role in sodium reabsorption. | A simplified flowchart for the steps by which aldosterone is released and then acts on distal tubules to regulate sodium reabsorption. |
Removing Excess Acids and Other Substances in Urine
The body’s acid-base balance, the relative amounts of acidic and basic substances in extracellular fluid, is maintained in part by the kidneys. Kidneys maintain acid-base balance by controlling the levels of bicarbonate in the blood. When the blood is too acid, water and carbon dioxide combine in cells in the wall of the nephron tubules to give rise to bicarbonate and H+. The bicarbonate enters the peritubular capillaries and from there it enters the blood to neutralize acid. The H+ in the tubules enters the filtrate to combine with phosphate, ammonia, or bicarbonate to be excreted. When the blood is too alkaline, less bicarbonate is reabsorbed into the blood.
Many other substances end up in urine once filtered from the blood: traces of drugs; excess glucose, which is a sign of diabetes; pus, a sign of infection; and even blood, a sign of infection, cancer, or injury.
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How the kidneys remove H+ from the body, preventing the blood from becoming too acidic. |
Kidney Disorders
Kidney stones are deposits of uric acid, calcium salts, and other substances that have settled out of urine and collected in the renal pelvis. Small stones can pass out during urination, but larger stones can inhibit urination. Lithotripsy uses sound waves to fragment the stones so they can pass out in the urine.
Inflammation of the bladder (cystitis) or kidneys (pyelonephritis) is the result of infections to the urinary tract; nephritis is general inflammation of the kidneys and can be severe enough to limit function. Polycystic kidney disease is an inherited disorder in which cysts form in the kidneys and gradually destroy normal tissue. Glomerulonephritis describes a variety of disorders that disrupt the flow of blood through the glomeruli of the kidneys.
Dialysis refers to the exchange of substances across a membrane between solutions of differing compositions; in hemodialysis, a machine is connected to an artery or vein, blood enters the tubes of the machine, and materials are removed from the blood before it is returned to the body.Respiratory and Renal
- Respiratory system
- Airways
- Lungs
- Respiration
- Rules of Gas exchange
- Breathing
- Exchange and Transport of Gases
- Alveolar exchange
- Hemoglobin and oxygen binding
- Hemoglobin and Carbon dioxide transport
- Formation of Bicarbonate (HCO3-) from CO2
- Regulation of Breathing
- Disorders of the Respiratory System
- Lung Cancer – highly correlated with smoking
- Risk to Smoking
- Benefits form stopping smoking
- Pneumonia and Influenza
- Tuberculosis
- Emphysema - highly correlated with smoking
- Bronchitis
- Acute
- Chronic
- Asthma
- Histoplasmosis
- Lung Cancer – highly correlated with smoking
- Renal System – Urinary Tract System
- Anatomy of the kidney
- Kidney cortex
- Kidney medulla
- Renal pelvis
- Renal Artery
- Renal vein
- Ureter
- Nephron – is the functional unit of the kidney
- Consist of:
- glomerulus
- Bowman’s capsule
- proximal tubule
- loop of Henle
- distal tubule
- collecting duct
- Consist of:
- Formation of Urine
- Filtration
- Reabsorption
- Secretion
- Regulation of urination
- Homeostasis of the body’s fluid balance
- ADH – Antidiuretic hormone
- Aldosterone
- Angiotensin II
- Thirst centers in the brain
- Homeostasis of blood acid-base balance
- Disorders of the Urinary tract system
- Kidney stones
- Cystitis
- Pyelonephritis
- Polycystic kidney disease
- Nephritis
- Glomerulonephritis
- Anatomy of the kidney
