MDS PREP
What is the primary mechanism of the fight-or-flight response in the regulation of glycogenolysis?
1) Activation of glycogen phosphorylase by epinephrine
2) Inhibition of glycogen synthase by cortisol
3) Stimulation of glucose-6-phosphatase by thyroid hormones
4) Activation of hexokinase by norepinephrine
Answer: 1) Activation of glycogen phosphorylase by epinephrineExplanation: Epinephrine acts on the beta-adrenergic receptors of liver and muscle cells, which activate protein kinase. This kinase then phosphorylates and activates glycogen phosphorylase, an enzyme that breaks down glycogen into glucose-1-phosphate, which is rapidly converted to glucose-6-phosphate for use in glycolysis or for release into the bloodstream to maintain glucose levels during stress.
What is the function of the reticular formation in the regulation of sleep and wakefulness?
1) It initiates sleep
2) It maintains wakefulness
3) It is not involved in sleep-wake regulation
4) It initiates REM sleep
The reticular formation plays a crucial role in maintaining wakefulness by sending activating signals to the thalamus and cortex.
What is the primary action of endorphins on the body?
1) Inhibition of pain
2) Stimulation of growth
3) Regulation of mood and emotions
4) Increased blood pressure
E. Regulation of sleep-wake cycle
Endorphins, particularly ?-endorphin, are opioid peptides that act as natural painkillers. They are released during stress and pain and bind to opioid receptors in the brain and spinal cord to inhibit the transmission of pain signals. While they do have secondary effects on mood and stress response, their primary function is pain inhibition.
What happens when the corpus luteum regresses during the menstrual cycle?
1) It secrets more estrogen and progesterone
2) It stops secreting estrogen and progesterone
3) It starts secreting FSH and LH
4) It causes an increase in the thickness of the endometrium
Physiology
Answer: 2
The regression of the corpus luteum leads to a sharp decline in estrogen and progesterone levels, which in turn causes the endometrium to shed and results in menstrual bleeding.
Norepinephrine is stored at the
1. Preganglionic parasympathetic nerve endings
2. Postganglionic parasympathetic nerve endings
3. Preganglionic sympathetic nerve endings
4. Postganglionic sympathetic nerve endings
Physiology
Answer: 2
Norepinephrine is stored at the Postganglionic parasympathetic nerve endings
What is the primary mechanism by which the stomach protects itself from self-digestion by its own enzymes?
1) Mucus secretion by gastric mucosal cells
2) Presence of intrinsic factor in the gastric juice
3) High concentration of bicarbonate in gastric juice
4) Low pH of gastric juice inhibiting its own enzymes
E) The mucosal lining is impermeable to H+ ions
The stomach protects itself from the harsh acidic environment and its own digestive enzymes through the secretion of a thick layer of mucus by mucosal cells. This mucus barrier forms a physical and chemical barrier that shields the underlying tissue from the acid and pepsin. Additionally, the stomach lining has a high turnover rate and is continuously regenerated, and the enzymes in the gastric juice are inactive until they come into contact with food.
Which of the following statements about the sensory neurons and their pathways in the spinal cord is correct?
1) All sensory neurons synapse with motor neurons in the ventral horn to form spinal reflex arcs
2) Only pain and temperature sensations ascend to the brainstem for conscious perception
3) The axons of sensory neurons from the dorsal root ganglion may directly synapse with motor neurons or ascend to the brain
4) Sensory neurons only project to the reticular formation and thalamus for nonspecific arousal
The axons of sensory neurons from the dorsal root ganglion can follow three routes: forming spinal reflexes by synapsing with motor neurons, ascending to the brainstem for conscious perception, or relaying through the reticular formation and thalamus for general arousal.
Which of the following is the correct sequence of enzyme activation in the pancreatic juice?
1) Trypsinogen -> Chymotrypsinogen -> Procarboxypeptidase A -> Proelastase
2) Enterokinase -> Trypsinogen -> Trypsin -> Chymotrypsinogen -> Chymotrypsin
3) Procarboxypeptidase B -> Chymotrypsinogen -> Trypsin -> Procarboxypeptidase A
4) Proelastase -> Chymotrypsinogen -> Chymotrypsin -> Trypsinogen
E) Trypsin -> Chymotrypsinogen -> Chymotrypsin -> Procarboxypeptidase A
The activation of pancreatic enzymes involves a cascade. Enterokinase, an enzyme present in the brush border of the small intestinal epithelial cells, first cleaves trypsinogen into active trypsin. Trypsin then cleaves chymotrypsinogen into chymotrypsin. This process continues with chymotrypsin activating proelastase and procarboxypeptidase A and B into their respective active forms, which are essential for the complete breakdown of proteins in the small intestine.