MDS PREP
What is the primary mechanism by which thyroid hormones increase metabolic rate?
1) Stimulation of the sympathetic nervous system
2) Increased expression of uncoupling proteins
3) Increased activity of the sodium-potassium ATPase pump
4) Stimulation of mitochondrial oxidative phosphorylation
Answer: 4) Stimulation of mitochondrial oxidative phosphorylationExplanation: Thyroid hormones, particularly T3, increase metabolic rate by enhancing the activity of mitochondrial oxidative phosphorylation. This leads to increased ATP production and overall cellular energy metabolism.
What is the primary neurotransmitter responsible for the contraction of the pupillary sphincter muscle?
1) Acetylcholine
2) Norepinephrine
3) Epinephrine
4) GABA
Answer: 1) AcetylcholineExplanation: The pupillary sphincter muscle is innervated by the parasympathetic nervous system, which uses acetylcholine as its primary neurotransmitter. Contraction of this muscle leads to pupil constriction, or miosis, which occurs in low-light conditions or when focusing on near objects.
Which of the following statements about Secretin is true?
1) It is structurally similar to insulin.
2) It is structurally similar to glucagon.
3) It stimulates the release of hydrochloric acid by the stomach.
4) It is secreted in response to high blood glucose levels.
Secretin is structurally similar to glucagon, which is involved in glucose metabolism and regulation.
What is the threshold for phosphate excretion in the urine?
1) 0.10 mM
2) 0.50 mM
3) 1.00 mM
4) 2.00 mM
The threshold for phosphate excretion in the urine is approximately 0.50 mM, above which phosphate begins to appear in the urine.
What is the primary effect of insulin on lipolysis?
1) Stimulation
2) Inhibition
3) No effect
4) Stimulation in the presence of glucose
Answer: 2) InhibitionExplanation: Insulin inhibits lipolysis by decreasing the activity of hormone-sensitive lipase in adipose tissue. This helps to maintain energy homeostasis by reducing the mobilization of fatty acids during periods of sufficient glucose availability.
What type of receptors are found in the heart that are stimulated by the parasympathetic nervous system?
1) Adrenergic receptors
2) Muscarinic receptors
3) Nicotinic receptors
4) GABAergic receptors
The parasympathetic nervous system acts on muscarinic receptors (specifically M2 receptors) in the heart to decrease the heart rate and atrial contractility, thereby contributing to a resting state and energy conservation.
The macula densa is found in:
1) The proximal convoluted tubule
2) The loop of Henle
3) The distal convoluted tubule
4) The collecting duct
The macula densa is a specialized group of epithelial cells located in the distal convoluted tubule at the junction with the afferent and efferent arterioles. It plays a role in the tubulo-glomerular feedback mechanism to regulate renal blood flow and glomerular filtration rate.
Which sleep stage is associated with the lowest body temperature, decreased heart rate, and decreased muscle tone?
1) Stage 1 NREM
2) Stage 2 NREM
3) Stage 3 NREM
4) REM sleep
Stage 3 NREM, also known as slow-wave sleep, is characterized by delta waves on EEG and is associated with the lowest body temperature, decreased heart rate, and decreased muscle tone, indicating a deep restorative sleep state.