Good Luck Daktari SECTION A: SHORT ANSWER QUESTIONS (Total – 60 Marks) Each question carries 5 marks. All questions are compulsory. - Gastrin is a peptide hormo
Good Luck Daktari SECTION A: SHORT ANSWER QUESTIONS (Total – 60 Marks) Each question carries 5 marks. All questions are compulsory. - Gastrin is a peptide hormone secreted by G cells in the antrum of the stomach. - Stimulated by peptides/amino acids, stomach distension, and vagal stimulation (via GRP) . - Increases gastric motility by enhancing contractions of the gastric smooth muscle . - Promotes gastric emptying by increasing the tone of the lower esophageal sphincter , relaxing the pyloric sphincter , and stimulating antral contractions . - Indirectly stimulates motility of the small intestine via increased gastrin-mediated secretions. - Enhances peristaltic movements , thus aiding in mixing and propulsion of gastric contents. - Excess gastrin (e.g., in Zollinger-Ellison syndrome ) can lead to hyper-motility and diarrhea . Inhibition of Pancreatic Autodigestion - Pancreatic enzymes are synthesized and secreted as inactive zymogens (e.g., trypsinogen). - Trypsinogen is activated only in the duodenum by enterokinase (enteropeptidase) . - The pancreas also secretes trypsin inhibitor (e.g., SPINK1 ) to prevent premature trypsin activation. - Compartmentalization of enzymes in zymogen granules within acinar cells prevents cytoplasmic exposure. - The ductal cells secrete bicarbonate , flushing enzymes into the duodenum and diluting them. - Any prematurely activated trypsin is rapidly inactivated by autolysis or inhibitors . - Disruption of these safety mechanisms (e.g., in pancreatitis) leads to autodigestion . Process of Digestion of Fats - Begins in the mouth (lingual lipase) and stomach (gastric lipase) – minor role. - Major digestion occurs in the small intestine , especially duodenum and jejunum . - Emulsification by bile salts increases surface area for enzyme action. - Pancreatic lipase (with colipase ) hydrolyzes triglycerides into monoglycerides and free fatty acids . - These products form micelles with bile salts for transport to the intestinal brush border . - Absorbed into enterocytes , where triglycerides are re-esterified . - Packaged into chylomicrons and transported via lacteals into lymphatics . Physiology Behind Satiety After a Heavy Meal - Stomach distension activates mechanoreceptors that signal the hypothalamus (satiety center) via vagal afferents . - Cholecystokinin (CCK) is released from the duodenum in response to fats and proteins, slowing gastric emptying and promoting satiety. - Insulin and GLP-1 rise postprandially and act on the arcuate nucleus of the hypothalamus to inhibit hunger. - Leptin (from adipose tissue) exerts longer-term satiety effects but contributes postprandially. - PYY from the ileum/colon also contributes to delayed gastric emptying and reduced appetite . - Serotonin (from enterochromaffin cells) contributes to early satiety by modulating enteric and central pathways. - Integration of neural and hormonal signals leads to inhibition of the lateral hypothalamic (hunger) center and activation of the ventromedial nucleus (satiety center) . Effects of Thyroid Hormones on the Cardiovascular System - Increased heart rate (positive chronotropic effect) : Thyroid hormones enhance the sensitivity of the heart to catecholamines, increasing heart rate. - Increased cardiac output : Both heart rate and stroke volume are elevated, leading to an increase in cardiac output. - Increased myocardial contractility (positive inotropic effect) : Thyroid hormones increase the force of myocardial contraction. - Peripheral vasodilation : Thyroid hormones cause vasodilation in peripheral vessels, lowering systemic vascular resistance. - Increased blood volume : Thyroid hormones increase sodium and water retention by the kidneys, contributing to increased blood volume. - Arrhythmias : Hyperthyroidism can lead to arrhythmias, including atrial fibrillation, due to increased myocardial excitability. - Enhanced oxygen consumption : Increased metabolic rate from thyroid hormones raises myocardial oxygen demand. Physiological Functions of the Pancreatic Hormone Glucagon - Increases blood glucose levels : Glucagon stimulates glycogenolysis in the liver, converting stored glycogen to glucose. - Promotes gluconeogenesis : Stimulates the liver to produce glucose from non-carbohydrate precursors (e.g., amino acids). - Stimulates lipolysis : Glucagon activates the breakdown of stored triglycerides into free fatty acids and glycerol. - Increases ketogenesis : In periods of fasting, glucagon stimulates the liver to convert fatty acids to ketone bodies. - Inhibits insulin secretion : Glucagon reduces insulin secretion to prevent hypoglycemia during fasting. - Enhances protein catabolism : Glucagon increases the breakdown of proteins to provide amino acids for gluconeogenesis. - Supports muscle energy needs : Although it has limited direct action on muscle, glucagon increases available glucose and fatty acids for energy. Countercurrent Multiplier System in the Kidneys (Short notes with diagram) DIAGRAM - Descending limb : Permeable to water, but not solutes; water is reabsorbed into the surrounding hypertonic medulla, concentrating the tubular fluid. - Ascending limb : Impermeable to water, actively transports Na+, K+, and Cl- out into the interstitium, diluting the tubular fluid. This creates a countercurrent multiplier effect that generates an osmotic gradient. - Vasa recta : Blood vessels that run parallel to the loop of Henle; they preserve the osmotic gradient by allowing water and solutes to exchange without disrupting the medullary concentration gradient. - Urea recycling : Urea contributes to the medullary osmotic gradient, further enhancing water reabsorption and concentrating urine. Diagram Explanation : - Descending Limb : Water moves out. - Ascending Limb : NaCl is pumped out. - Vasa Recta : Blood flow maintains osmotic gradient. - Urea : Contributes to the concentration of urine in the medulla. Hormones Secreted During Pregnancy - Human Chorionic Gonadotropin (hCG) :Produced by the placenta. - Supports the corpus luteum to maintain progesterone production in early pregnancy. - Basis for pregnancy tests . - Progesterone :Produced by the corpus luteum and later the placenta. - Maintains the uterine lining and suppresses uterine contractions. - Essential for pregnancy maintenance . - Estrogen (Estradiol) :Secreted initially by the corpus luteum, later by the placenta. - Stimulates uterine growth and prepares mammary glands for lactation. - Promotes vascularization of the endometrium . - Human Placental Lactogen (hPL) :Secreted by the placenta. - Modulates maternal metabolism to increase glucose availability for the fetus. - Promotes insulin resistance to ensure fetal nutrition. - Relaxin :Secreted by the corpus luteum and placenta. - Relaxes pelvic ligaments and softens the cervix for childbirth. - Inhibits uterine contractions in early pregnancy. - Prolactin :Secreted by the anterior pituitary and placenta. - Stimulates mammary gland development for lactation. - Levels rise progressively during pregnancy. - Cortisol :Secreted by the adrenal glands. - Regulates metabolism and helps in fetal maturation (especially lung development). - Increases blood glucose to meet maternal and fetal needs. - Oxytocin :Secreted by the posterior pituitary near labor. - Stimulates uterine contractions during labor. - Promotes milk ejection during breastfeeding. Phases of the Male Sexual Response The male sexual response can be divided into four main phases: - Excitement Phase :The excitement phase is initiated by sexual stimuli , such as visual, tactile, or psychological stimuli. - It leads to the erection of the penis , due to increased blood flow through the corpora cavernosa and corpus spongiosum . - Increased heart rate and blood pressure are observed as part of the body's physiological response to sexual arousal. - Testicular enlargement and scrotal elevation also occur. - Plateau Phase :The plateau phase is the period of sexual tension just before org