NEET MDS Lessons
Physiology
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.
Typical Concentration Gradients and Membrane Potentials in Excitable Cells
The Na Pump is Particularly Important in the Kidney and Brain
- All cells have Na pumps in their membranes, but some cells have more than others
- Over-all Na pump activity may account for a third of your resting energy expenditure!
- In the kidney the Na pump activity is very high because it is used to regulate body salt and water concentrations
- Kidneys use enormous amounts of energy: 0.5% of body weight, but use 7% of the oxygen supply
- Pump activity is also high in the brain because Na and K gradients are essential for nerves
- The brain is another high energy organ; it is 2% of body weight, but uses 18% of the oxygen supply
In the Resting State Potassium Controls the Membrane Potential of Most Cells
- Resting cells have more open K channels than other types
- More K+ passes through membrane than other ions- therefore K+ controls the potential
- Blood K+ must be closely controlled because small changes will produce large changes in the membrane potentials of cells
- Raising K will make the membrane potential less negative (depolarization)
- High blood K+ can cause the heart to stop beating (it goes into permanent contraction)
During an Action Potential Na Channels Open, and Na Controls the Membrane Potential
- Whichever ion has the most open channels controls the membrane potential
- Excitable cells have Na channels that open when stimulated
- When large numbers of these channels open Na controls the membrane potential
CNS PROTECTION
- Bones of the Skull Frontal, Temporal, Parietal, Sphenoid, Occipital
- Cranial Meninges Dura mater, Arachnoid Space, Pia mater
- Cerebrospinal Fluid
Secreted by Chroid Plexi in Ventricles
Circulation through ventricles and central canal
Lateral and Median apertures from the 4th ventricle into the subarachnoid space
Arachnoid villi of the superior sagittal sinus return CSF to the venous circulation
Hydrocephalic Condition, blockage of the mesencephalic aqueduct, backup of CSF, Insertion of a shunt to drain the excess CSF
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
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)
Exchange of gases takes place in Lungs
- A person with an average ventilation rate of 7.5 L/min will breathe in and out 10,800 liters of gas each day
- From this gas the person will take in about 420 liters of oxygen (19 moles/day) and will give out about 340 liters of carbon dioxide (15 moles/day)
- The ratio of CO2 expired/O2 inspired is called the respiratory quotient (RQ)
- RQ = CO2 out/O2 in = 340/420 = 0.81
- In cellular respiration of glucose CO2 out = O2 in; RQ = 1
- The overall RQ is less than 1 because our diet is a mixture of carbohydrates and fat; the RQ for metabolizing fat is only 0.7
- All of the exchange of gas takes place in the lungs
- The lungs also give off large amounts of heat and water vapor
Cells, cytoplasm, and organelles:
- Cytoplasm consists of a gelatinous solution and contains microtubules (which serve as a cell's cytoskeleton) and organelles
- Cells also contain a nucleus within which is found DNA (deoxyribonucleic acid) in the form of chromosomes plus nucleoli (within which ribosomes are formed)
- Organelles include:
- Endoplasmic reticulum : 2 forms: smooth and rough; the surface of rough ER is coated with ribosomes; the surface of smooth ER is not , Functions include: mechanical support, synthesis (especially proteins by rough ER), and transport
- Golgi complex consists of a series of flattened sacs (or cisternae) functions include: synthesis (of substances likes phospholipids), packaging of materials for transport (in vesicles), and production of lysosomes
- Lysosome : membrane-enclosed spheres that contain powerful digestive enzymes , functions include destruction of damaged cells & digestion of phagocytosed materials
- Mitochondria : have double-membrane: outer membrane & highly convoluted inner membrane
- inner membrane has folds or shelf-like structures called cristae that contain elementary particles; these particles contain enzymes important in ATP production
- primary function is production of adenosine triphosphate (ATP)
- Ribosome-:composed of rRNA (ribosomal RNA) & protein , primary function is to produce proteins
- Centrioles :paired cylindrical structures located near the nucleas , play an important role in cell division
- Flagella & cilia - hair-like projections from some human cells
- cilia are relatively short & numerous (e.g., those lining trachea)
- a flagellum is relatively long and there's typically just one (e.g., sperm)
-
- Villi Projections of cell membrane that serve to increase surface area of a cell (which is important, for example, for cells that line the intestine)