MDS PREP
Which of the following is a characteristic of the absolute refractory period during an action potential?
1) The membrane is fully depolarized.
2) The membrane is fully repolarized.
3) The membrane is inexcitable regardless of the strength of the stimulus.
4) The membrane is hyperpolarized.
E. The membrane is depolarized.
The absolute refractory period occurs during the initial phase of repolarization after an action potential. During this period, the membrane is inactivated and cannot be depolarized to generate another action potential, regardless of the stimulus strength. This ensures that action potentials are unidirectional and do not propagate backward along the axon.
What primarily determines the Glomerular Filtration Rate (GFR)?
1) Blood volume
2) Net filtration pressure and Kf
3) Renal blood flow
4) Urine output
The Glomerular Filtration Rate (GFR) is primarily determined by net filtration pressure and the glomerular capillary filtration coefficient (Kf), which reflects the permeability of the glomerular membrane.
What is the significance of the blood-brain barrier being absent in the circumventricular organs?
1) Allows free passage of hormones and neurotransmitters to the cerebrospinal fluid (CSF)
2) Enables direct interaction with the hypothalamus for osmoregulation
3) Facilitates the entry of pathogens and drugs into the brain
4) Necessary for the synthesis of neurotransmitters in these areas
The absence of the blood-brain barrier in circumventricular organs allows for the unimpeded movement of substances between the blood and the CSF, which is crucial for the regulation of various physiological processes, including osmoregulation.
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
The primary action of antidiuretic hormone (ADH) in the kidneys is to increase the permeability of water in the collecting tubules and ducts, promoting water reabsorption.
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.
What is the mechanism by which glucose is reabsorbed in the proximal tubules of the kidney?
1) Passive diffusion
2) Facilitated diffusion
3) Active transport
4) Osmosis
Glucose is reabsorbed in the proximal tubules of the kidney primarily through active transport mechanisms, utilizing sodium-glucose transporters.
MCQ: The average time required for spermatogenesis in humans is:
1) 30 days
2) 42 days
3) 74 days
4) 120 days
The average time required for spermatogenesis in humans is approximately 74 days, during which sperm cells develop from spermatogonia to mature spermatozoa.
MCQ: The gastrocolic reflex is:
1) The contraction of the stomach triggered by the presence of food in the duodenum
2) The contraction of the small intestine triggered by the presence of food in the stomach
3) The contraction of the rectum triggered by the presence of food in the stomach
4) The contraction of the gallbladder triggered by the presence of food in the small intestine
The gastrocolic reflex is the contraction of the colon triggered by the presence of food in the stomach, facilitating bowel movements.