Medical Physiology Assorted SAQs — With OmpathStudy

Medical Physiology Assorted SAQs — With Answers (Past Paper Study Guide) Short-answer questions from various Medical Physiology past papers, University of Nairobi Level 1 (MBChB/BPharm), with model answers by Vincent Kipkorir and Fiona Nyaanga. A companion, questions-only version of a related set is published separately. --- 1. With a diagram describe the different components of a negative feedback system 2. Briefly describe two different modes of fluid movements between body fluid compartments. In the body, water moves through semi-permeable membranes of cells and from one compartment of the body to another by osmosis. Osmosis is basically the diffusion of water from regions of higher concentration to regions of lower concentration, along an osmotic gradient across a semi-permeable membrane. As a result, water will move into and out of cells and tissues, depending on the relative concentrations of the water and solutes found there. An appropriate balance of solutes inside and outside of cells must be maintained to ensure normal function. Endosmosis is movement of water into the cell while exosmosis is movement of water out of the cells. Cells can also take water into their intracellular compartment through pinocytosis. It's a mode of endocytosis in which small water particles are brought into the cell, forming an invagination, and then suspended within small vesicles. It's also called cell drinking. 3. State five functional differences between parasympathetic and sympathetic nervous systems SYMPATHETIC PARASYMPATHETIC --- --- Thoraco-lumbar outflow Cranio-sacral outflow Ganglia lie near the CNS and away from the effector Ganglia lie near the effector and away from the CNS Fight-or-flight: heart rate increases, respiratory rate increases, diverts blood to skeletal muscles, breaks down glycogen Rest-and-digest: involved in activities that conserve and restore energy Postganglionic fibres use norepinephrine as neurotransmitter Postganglionic fibres use acetylcholine as neurotransmitter Short cholinergic preganglionic and long adrenergic postganglionic fibres Long cholinergic preganglionic and short cholinergic postganglionic fibres Ratio of preganglionic to postganglionic fibres is 1:20 Ratio of preganglionic to postganglionic fibres is 1:3 Extensive divergence Limited divergence Activity involves mass discharge of the entire system Activity is normally localized to discrete organs 4. Describe how protein hormones stimulate protein synthesis Steroid hormones are lipid soluble and thus travel through blood with the help of a protein carrier. When they get to the target cell they detach from the carrier and traverse the cell membrane and enter the cell by simple diffusion. Receptors for steroid hormones are located inside target cells, in the cytoplasm or nucleus. The hormone will either bind to a cytoplasmic receptor and then enter the nucleus as a hormone-receptor complex or enter the nucleus to encounter its receptor. The receptors function as ligand-dependent transcription factors. That is to say, the hormone-receptor complex binds to promoter regions of responsive genes and stimulate or sometimes inhibit transcription from those genes. Thus, the mechanism of action of steroid hormones is to modulate gene expression in target cells. By selectively affecting transcription from a battery of genes, the concentration of those respective proteins are altered, which clearly can change the phenotype of the cell. When hormone binds to receptor, a characteristic series of events occurs: Receptor activation is the term used to describe conformational changes in the receptor induced by binding hormone. The major consequence of activation is that the receptor becomes competent to bind DNA. Activated receptors bind to "hormone response elements", which are short specific sequences of DNA which are located in promoters of hormone-responsive genes. In most cases, hormone-receptor complexes bind DNA in pairs, as shown in the figure below. Transcription from those genes to which the receptor is bound is affected. Most commonly, receptor binding stimulates transcription. The hormone-receptor complex thus functions as a transcription factor. 5. In relation to sensory physiology, describe adaptation, law of specific nerve energies and law of projection. Adaptation- occurs when sensory receptors change their sensitivity to the particular stimulus after being exposed to the same stimulus continuously for a long time. Law of specific nerve energies- the nature of perception is defined by the pathway over which sensory information is carried. Hence the origin of the sensation is not important but instead different sensations are differentiated from each other by the different nervous structures these stimuli excite. Law of projection - no matter where along the nerve is stimulated, the sensation will be felt at the site of the receptor. 6. Explain the difference between end plate potential, inhibitory post-synaptic potential and e