NEET MDS Lessons
Physiology
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Partial Pressures of O2 and CO2 in the body (normal, resting conditions):
- Alveoli
- PO2 = 100 mm Hg
- PCO2 = 40 mm Hg
- Alveolar capillaries
- Entering the alveolar capillaries
- PO2 = 40 mm Hg (relatively low because this blood has just returned from the systemic circulation & has lost much of its oxygen)
- PCO2 = 45 mm Hg (relatively high because the blood returning from the systemic circulation has picked up carbon dioxide)
- Entering the alveolar capillaries
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While in the alveolar capillaries, the diffusion of gasses occurs: oxygen diffuses from the alveoli into the blood & carbon dioxide from the blood into the alveoli.
- Leaving the alveolar capillaries
- PO2 = 100 mm Hg
- PCO2 = 40 mm Hg
- Blood leaving the alveolar capillaries returns to the left atrium & is pumped by the left ventricle into the systemic circulation. This blood travels through arteries & arterioles and into the systemic, or body, capillaries. As blood travels through arteries & arterioles, no gas exchange occurs.
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- Entering the systemic capillaries
- PO2 = 100 mm Hg
- PCO2 = 40 mm Hg
- Body cells (resting conditions)
- PO2 = 40 mm Hg
- PCO2 = 45 mm Hg
- Entering the systemic capillaries
- Because of the differences in partial pressures of oxygen & carbon dioxide in the systemic capillaries & the body cells, oxygen diffuses from the blood & into the cells, while carbon dioxide diffuses from the cells into the blood.
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- Leaving the systemic capillaries
- PO2 = 40 mm Hg
- PCO2 = 45 mm Hg
- Leaving the systemic capillaries
- Blood leaving the systemic capillaries returns to the heart (right atrium) via venules & veins (and no gas exchange occurs while blood is in venules & veins). This blood is then pumped to the lungs (and the alveolar capillaries) by the right ventricle.
4. Emphysema
1. Permanent enlargement of airways with distension of alveolar walls
Thickened Bronchial Submucosa, Edema & Cellular Infiltration (loss of elasticity), Dilation of Air spaces, due to destruction of alveolar walls (Air trapped by obstruction)
2. Lower Respiratory tree destruction
Respiratory Bronchioles, Alveolar ducts, & Alveolar sacs
Types of Emphysema:
1. Centrilobular (Centriacinar) = Respiratory Bronchioles
Rarely seen in non Smokers, More in Men than Women, Found in Smokers with Bronchitis
2. Panlobular (Panacinar)
Hereditary, Single autosomal recessive gene. Deficient in 1-globulin (1-antitrypsin), Protects respiratory tract from neutrophil elastase (Enzyme that distroys lung connective tissue) , Aged persons, Results from Bronchi or Bronchiolar constriction
NOTE: Smoking = Leading cause of Bronchitis, Emphysema
Phases of cardiac cycle :
1. Early diastole ( also called the atrial diastole , or complete heart diastole) : During this phase :
- Atria are relaxed
- Ventricles are relaxed
- Semilunar valves are closed
- Atrioventricular valves are open
During this phase the blood moves passively from the venous system into the ventricles ( about 80 % of blood fills the ventricles during this phase.
2. Atrial systole : During this phase :
- Atria are contracting
- Ventricles are relaxed
- AV valves are open
- Semilunar valves are closed
- Atrial pressure increases.the a wave of atrial pressure appears here.
- P wave of ECG starts here
- intraventricular pressure increases due to the rush of blood then decrease due to continuous relaxation of ventricles.
The remaining 20% of blood is moved to fill the ventricles during this phase , due to atrial contraction.
3. Isovolumetric contraction : During this phase :
- Atria are relaxed
- Ventricles are contracting
- AV valves are closed
- Semilunar valves are closed
- First heart sound
- QRS complex.
The ventricular fibers start to contract during this phase , and the intraventricular pressure increases. This result in closing the AV valves , but the pressure is not yet enough to open the semilunar valves , so the blood volume remain unchanged , and the muscle fibers length also remain unchanged , so we call this phase as isovolumetric contraction ( iso : the same , volu= volume , metric= length).
4. Ejection phase : Blood is ejected from the ventricles into the aorta and pulmonary artery .
During this phase :
- Ventricles are contracting
- Atria are relaxed
- AV valves are closed
- Semilunar valves are open
- First heart sound
- Intraventricular pressure is increased , due to continuous contraction
- increased aortic pressure .
- T wave starts.
5. Isovolumetric relaxation: This phase due to backflow of blood in aorta and pulmonary system after the ventricular contraction is up and the ventricles relax . This backflow closes the semilunar valves .
During this phase :
- Ventricles are relaxed
- Atrial are relaxed
- Semilunar valves are closed .
- AV valves are closed.
- Ventricular pressure fails rapidly
- Atrial pressure increases due to to continuous venous return. the v wave appears here.
- Aortic pressure : initial sharp decrease due to sudden closure of the semilunar valve ( diacrotic notch) , followed by secondary rise in pressure , due to elastic recoil of the aorta ( diacrotic wave) .
- T wave ends in this phase
Lipids:
- about 40% of the dry mass of a typical cell
- composed largely of carbon & hydrogen
- generally insoluble in water
- involved mainly with long-term energy storage; other functions are as structural components (as in the case of phospholipids that are the major building block in cell membranes) and as "messengers" (hormones) that play roles in communications within and between cells
- Subclasses include:
- Triglycerides - consist of one glycerol molecule + 3 fatty acids (e.g., stearic acid in the diagram below). Fatty acids typically consist of chains of 16 or 18 carbons (plus lots of hydrogens).
- phospholipids - Composed of 2 fatty acids, glycerol, phosphate and polar groups , phosphate group (-PO4) substitutes for one fatty acid & these lipids are an important component of cell membranes
steroids - have 4 rings- cholesterol, some hormones, found in membranes include testosterone, estrogen, & cholesterol
Glomerular filtration
Kidneys receive about 20% of cardiac output , this is called Renal Blood Flow (RBF) which is approximatley 1.1 L of blood. Plasma in this flow is about 625 ml . It is called Renal Plasma Flow (RPF) .
About 20 % of Plasma entering the glomerular capillaries is filtered into the Bowman`s capsule .
Glomerular filtration rate is about 125 ml/min ( which means 7.5 L/hr and thus 180 L/day) This means that the kidney filters about 180 liters of plasma every day.
The urine flow is about 1ml/min ( about 1.5 liter /day) This means that kidney reabsorbs about 178.5 liters every day .
Filtration occurs through the filtration unit , which includes :
1- endothelial cells of glomerular capillaries , which are fenestrated . Fenestrae are quite small so they prevent filtration of blood cells and most of plasma proteins .
2- Glomerular basement membrane : contains proteoglycan that is negatively charged and repels the negatively charged plasma proteins that may pass the fenestrae due to their small molecular weight like albumin . so the membrane plays an important role in impairing filtration of albumin .
3- Epithelial cells of Bowman`s capsule that have podocytes , which interdigitate to form slits .
Many forces drive the glomerular filtration , which are :
1- Hydrostatic pressure of the capillary blood , which favours filtration . It is about 55 mmHg .
2- Oncotic pressure of the plasma proteins in the glomerular capillary ( opposes filtration ) . It is about 30 mm Hg .
3- Hydrostatic pressure of the Bowman`s capsule , which also opposes filtration. It is about 15 mmHg .
The net pressure is as follows :
Hydrostatic pressure of glomerular capillaries - ( Oncotic pressure of glomerular capillaries + Hydrostatic pressure of the Bowman capsule):
55-(35+10)
=55-45
=10 mmHg .
Te glomerular filtration rate does not depend only on the net pressure , but also on an other value , known as filtration coefficient ( Kf) . The later depends on the surface area of the glomerular capillaries and the hydraulic conductivity of the glomerular capillaries.
The Kidneys
The kidneys are the primary functional organ of the renal system.
They are essential in homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and the regulation of blood pressure (by maintaining salt and water balance).
They serve the body as a natural filter of the blood and remove wastes that are excreted through the urine.
They are also responsible for the reabsorption of water, glucose, and amino acids, and will maintain the balance of these molecules in the body.
In addition, the kidneys produce hormones including calcitriol, erythropoietin, and the enzyme renin, which are involved in renal and hemotological physiological processes.
Anatomical Location
The kidneys are a pair of bean-shaped, brown organs about the size of your fist. They are covered by the renal capsule, which is a tough capsule of fibrous connective tissue.
Right kidney being slightly lower than the left, and left kidney being located slightly more medial than the right.
The right kidneys lie just below the diaphragm and posterior to the liver, the left below the diaphragm and posterior to the spleen.
Resting on top of each kidney is an adrenal gland (adrenal meaning on top of renal), which are involved in some renal system processes despite being a primarily endocrine organ.
They are considered retroperitoneal, which means that they lie behind the peritoneum, the membrane lining of the abdominal cavity.
The renal artery branches off from the lower part of the aorta and provides the blood supply to the kidneys.
Renal veins take blood away from the kidneys into the inferior vena cava.
The ureters are structures that come out of the kidneys, bringing urine downward into the bladder.
Internal Anatomy of the Kidneys
There are three major regions of the kidney:
1. Renal cortex
2. Renal medulla
3. Renal pelvis
The renal cortex is a space between the medulla and the outer capsule.
The renal medulla contains the majority of the length of nephrons, the main functional component of the kidney that filters fluid from blood.
The renal pelvis connects the kidney with the circulatory and nervous systems from the rest of the body.
Renal Cortex
The kidneys are surrounded by a renal cortex
The cortex provides a space for arterioles and venules from the renal artery and vein, as well as the glomerular capillaries, to perfuse the nephrons of the kidney. Erythropotein, a hormone necessary for the synthesis of new red blood cells, is also produced in the renal cortex.
Renal Medulla
The medulla is the inner region of the parenchyma of the kidney. The medulla consists of multiple pyramidal tissue masses, called the renal pyramids, which are triangle structures that contain a dense network of nephrons.
At one end of each nephron, in the cortex of the kidney, is a cup-shaped structure called the Bowman's capsule. It surrounds a tuft of capillaries called the glomerulus that carries blood from the renal arteries into the nephron, where plasma is filtered through the capsule.
After entering the capsule, the filtered fluid flows along the proximal convoluted tubule to the loop of Henle and then to the distal convoluted tubule and the collecting ducts, which flow into the ureter. Each of the different components of the nephrons are selectively permeable to different molecules, and enable the complex regulation of water and ion concentrations in the body.
Renal Pelvis
The renal pelvis contains the hilium. The hilum is the concave part of the bean-shape where blood vessels and nerves enter and exit the kidney; it is also the point of exit for the ureters—the urine-bearing tubes that exit the kidney and empty into the urinary bladder. The renal pelvis connects the kidney to the rest of the body.
Supply of Blood and Nerves to the Kidneys
• The renal arteries branch off of the abdominal aorta and supply the kidneys with blood. The arterial supply of the kidneys varies from person to person, and there may be one or more renal arteries to supply each kidney.
• The renal veins are the veins that drain the kidneys and connect them to the inferior vena cava.
• The kidney and the nervous system communicate via the renal plexus. The sympathetic nervous system will trigger vasoconstriction and reduce renal blood flow, while parasympathetic nervous stimulation will trigger vasodilation and increased blood flow.
• Afferent arterioles branch into the glomerular capillaries, while efferent arterioles take blood away from the glomerular capillaries and into the interlobular capillaries that provide oxygen to the kidney.
• renal vein
The veins that drain the kidney and connect the kidney to the inferior vena cava.
• renal artery
These arise off the side of the abdominal aorta, immediately below the superior mesenteric artery, and supply the kidneys with blood.
Blood Groups
Blood groups are created by molecules present on the surface of red blood cells (and often on other cells as well).
The ABO Blood Groups
The ABO blood groups are the most important in assuring safe blood transfusions.
Blood Group |
Antigens on RBCs |
Antibodies in Serum |
Genotypes |
A |
A |
Anti-B |
AA or AO |
B |
B |
Anti-A |
BB or BO |
AB |
A and B |
Neither |
AB |
O |
Neither |
Anti-A and anti-B |
OO |
When red blood cells carrying one or both antigens are exposed to the corresponding antibodies, they agglutinate; that is, clump together. People usually have antibodies against those red cell antigens that they lack.
The critical principle to be followed is that transfused blood must not contain red cells that the recipient's antibodies can clump. Although theoretically it is possible to transfuse group O blood into any recipient, the antibodies in the donated plasma can damage the recipient's red cells. Thus all transfusions should be done with exactly-matched blood.
The Rh System
Rh antigens are transmembrane proteins with loops exposed at the surface of red blood cells. They appear to be used for the transport of carbon dioxide and/or ammonia across the plasma membrane. They are named for the rhesus monkey in which they were first discovered.
There are a number of Rh antigens. Red cells that are "Rh positive" express the one designated D. About 15% of the population have no RhD antigens and thus are "Rh negative".
The major importance of the Rh system for human health is to avoid the danger of RhD incompatibility between mother and fetus.
During birth, there is often a leakage of the baby's red blood cells into the mother's circulation. If the baby is Rh positive (having inherited the trait from its father) and the mother Rh-negative, these red cells will cause her to develop antibodies against the RhD antigen. The antibodies, usually of the IgG class, do not cause any problems for that child, but can cross the placenta and attack the red cells of a subsequent Rh+ fetus. This destroys the red cells producing anemia and jaundice. The disease, called erythroblastosis fetalis or hemolytic disease of the newborn, may be so severe as to kill the fetus or even the newborn infant. It is an example of an antibody-mediated cytotoxicity disorder.
Although certain other red cell antigens (in addition to Rh) sometimes cause problems for a fetus, an ABO incompatibility does not. Rh incompatibility so dangerous when ABO incompatibility is not
It turns out that most anti-A or anti-B antibodies are of the IgM class and these do not cross the placenta. In fact, an Rh−/type O mother carrying an Rh+/type A, B, or AB fetus is resistant to sensitization to the Rh antigen. Presumably her anti-A and anti-B antibodies destroy any fetal cells that enter her blood before they can elicit anti-Rh antibodies in her.
This phenomenon has led to an extremely effective preventive measure to avoid Rh sensitization. Shortly after each birth of an Rh+ baby, the mother is given an injection of anti-Rh antibodies. The preparation is called Rh immune globulin (RhIG) or Rhogam. These passively acquired antibodies destroy any fetal cells that got into her circulation before they can elicit an active immune response in her.
Rh immune globulin came into common use in the United States in 1968, and within a decade the incidence of Rh hemolytic disease became very low.