MDS PREP
What is the primary function of the pyloric sphincter?
1) To regulate the flow of chyme into the small intestine
2) To mix and churn food in the stomach
3) To secrete intrinsic factor for vitamin B12 absorption
4) To secrete mucus for the protection of the gastric mucosa
E) To produce hydrochloric acid
The pyloric sphincter, also known as the pylorus, is a ring of smooth muscle that connects the stomach to the duodenum. It relaxes to allow small, controlled amounts of chyme to pass from the stomach into the duodenum. This regulation is important to prevent the rapid emptying of the stomach and the potential overwhelming of the small intestine with food and acid.
What is the equilibrium potential for sodium (Na+) ions in a typical neuron?
1) -60 mV
2) -90 mV
3) +60 mV
4) +90 mV
Answer: 3) The equilibrium potential for sodium (Na+) ions in a typical neuron is +60 mV.
What is the primary action of antidiuretic hormone (ADH) in the kidneys?
1) Increases the permeability of water in the proximal tubules
2) Increases the permeability of water in the collecting tubules and ducts
3) Stimulates glomerular filtration rate
4) Inhibits sodium reabsorption
Physiology
Answer: 2
ADH acts on the distal tubules and collecting ducts of the kidney to increase the permeability of the tubular epithelium to water. This results in the reabsorption of water and the concentration of urine, thereby reducing urine volume and increasing blood pressure.
What is the main mechanism by which the intestinal phase inhibits gastric acid secretion?
1) By releasing hormones that inhibit gastrin release
2) By promoting the release of somatostatin
3) By reducing vagal input to the stomach
4) By increasing the pH of gastric contents
E) By reducing the activity of the myenteric plexus
The intestinal phase of gastric acid secretion is mainly responsible for inhibiting gastric secretion. This is primarily achieved through the release of hormones like secretin and cholecystokinin (CCK) in response to the presence of acidic chyme in the duodenum. These hormones act on D cells in the stomach to reduce gastrin secretion, which in turn decreases acid production by parietal cells. Additionally, the presence of food in the intestine triggers an enterogastric reflex that inhibits the vagal nerve's excitatory effects on the stomach.
Which of the following is the correct statement regarding mammalian nerve fibers?
1) A-alpha fibers have the lowest conduction velocity and are responsible for pain and temperature sensation.
2) A-beta fibers have the highest conduction velocity and are responsible for motor supply to skeletal muscles.
3) A-gamma fibers are heavily myelinated and have the fastest conduction velocity.
4) C fibers have a large diameter and are responsible for fine motor control.
Answer: 2) A-beta fibers have the second highest conduction velocity after A-alpha fibers and are responsible for touch, kinesthetic sense, and pressure sensation, not motor supply to skeletal muscles. A-alpha fibers have the highest conduction velocity and are indeed responsible for motor supply to skeletal muscles.
What is the significance of the intestinal phase of gastric acid secretion?
1) It is responsible for the majority of acid secretion
2) It is primarily responsible for the inhibition of acid secretion
3) It is only triggered by the thought of food
4) It is not a significant phase of gastric acid secretion
Physiology
Answer: 2
The intestinal phase plays a minor role in stimulating gastric secretion. However, it is crucial for inhibiting gastric secretion and motility once food enters the duodenum. Factors such as acidity, fatty acids, and osmolality of the duodenal contents trigger the release of hormones like secretin and cholecystokinin, which in turn inhibit gastric acid secretion.
What is the function of calcidiol in the body?
1) It is the active form of vitamin D
2) It is the precursor to calcitriol (active vitamin D)
3) It has no known function
4) It inhibits calcium absorption
Calcidiol is the precursor to calcitriol (active vitamin D) and plays a role in calcium absorption and bone health.
In which part of the male reproductive system does spermatogenesis occur?
1) Seminal vesicles
2) Epididymis
3) Prostate gland
4) Seminiferous tubules
Spermatogenesis occurs in the seminiferous tubules of the male reproductive system, where sperm cells are produced and matured.