NEET MDS Lessons
Physiology
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 is a liquid tissue. Suspended in the watery plasma are seven types of cells and cell fragments.
- red blood cells (RBCs) or erythrocytes
- platelets or thrombocytes
- five kinds of white blood cells (WBCs) or leukocytes
- Three kinds of granulocytes
- neutrophils
- eosinophils
- basophils
- Two kinds of leukocytes without granules in their cytoplasm
- lymphocytes
- monocytes
- Three kinds of granulocytes
Carbohydrates:
- about 3% of the dry mass of a typical cell
- composed of carbon, hydrogen, & oxygen atoms (e.g., glucose is C6H12O6)
- an important source of energy for cells
- types include:
- monosaccharide (e.g., glucose) - most contain 5 or 6 carbon atoms
- disaccharides
- 2 monosaccharides linked together
- Examples include sucrose (a common plant disaccharide is composed of the monosaccharides glucose and fructose) & lactose (or milk sugar; a disaccharide composed of glucose and the monosaccharide galactose)
- polysaccharides
- several monosaccharides linked together
Examples include starch (a common plant polysaccharide made up of many glucose molecules) and glycogen (commonly stored in the liver)
Platelets
Platelets are cell fragments produced from megakaryocytes.
Blood normally contains 150,000 to 350,000 per microliter (µl). If this value should drop much below 50,000/µl, there is a danger of uncontrolled bleeding. This is because of the essential role that platelets have in blood clotting.
When blood vessels are damaged, fibrils of collagen are exposed.
- von Willebrand factor links the collagen to platelets forming a plug of platelets there.
- The bound platelets release ADP and thromboxane A2 which recruit and activate still more platelets circulating in the blood.
- (This role of thromboxane accounts for the beneficial effect of low doses of aspirin a cyclooxygenase inhibitor in avoiding heart attacks.)
ReoPro is a monoclonal antibody directed against platelet receptors. It inhibits platelet aggregation and appears to reduce the risk that "reamed out" coronary arteries (after coronary angioplasty) will plug up again.
1. Automatic control (sensory) of respiration is in - brainstem (midbrain)
2. Behavioral/voluntary control is in - the cortex
3. Alveolar ventilation -the amount of atmospheric air that actually reaches the alveolar per breath and that can participate in the exchange of gasses between alveoli and blood
4. Only way to increase gas exchange in alveolar capillaries - perfusion-limited gas exchange
5. Pulmonary ventiliation not effected by - concentration of bicarbonate ions
6. Central chemoreceptors - medulla - CO2, O2 and H+ concentrations
7. Peripheral chemoreceptors - carotid and aortic bodies- PO2, PCO2 and pH
8. Major stimulus for respiratory centers - arterial PCO2
9. Rhythmic breathing depends on
1. continuous (tonic) inspiratory drive from DRG (dorsal respiratory group)
2. intermittent (phasic) expiratory input from cerebrum, thalamus, cranial nerves and ascending spinal cord sensory tracts
10. Primary site for gas exchange - type I epithelial cells for alveoli
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.
(RDS) Respiratory distress of Newborn
1. hyaline membrane disease of the new born
2. decrease in surfactant, Weak, Abnormal complience of chest wall
3. Small alveoli, difficult to inflate, Alveoli tent to collapse, many of varied sizes
4. decrease in O2 diffusion area, lung difficult to expand, in compliance