MDS PREP
Which vitamin is the most important antioxidant in the body, acting in the lipid phase of membranes?
1) Vitamin C
2) Vitamin A
3) Vitamin E (tocopherol)
4) Vitamin B
Physiology
Answer: 3
Vitamin E is the most important antioxidant in the body, acting in the lipid phase of membranes and protecting against the effects of free radicals. It is crucial for maintaining the integrity and function of cellular organelles and the cell membrane by preventing the oxidation of unsaturated fats.
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.
The glomerular filtration barrier consists of:
1) Endothelial cells
2) Basement membrane
3) Podocytes
4) All of the above
The glomerular filtration barrier is a three-layered structure composed of endothelial cells of the glomerular capillaries, the basement membrane, and the podocytes (visceral epithelial cells of Bowman's capsule). These layers work together to filter blood, allowing small molecules to pass into the nephron while retaining larger ones.
An unstable membrane potential that will spontaneously depolarize is a property of which type of muscle?
1. Cardiac only
2. Cardiac and smooth
3. Skeletal and smooth
4. Skeletal and cardiac
Physiology
Answer: 1
The type of muscle that exhibits an unstable membrane potential that will
spontaneously depolarize is cardiac muscle.
Cardiac muscle cells, which are responsible for the contraction of the heart,
have an intrinsic ability to contract rhythmically without the need for external
stimulation. This is due to their unique property of automaticity, which is
mediated by the presence of the sinoatrial (SA) node and the subsequent
propagation of electrical impulses throughout the heart via the conduction
system. The SA node, often referred to as the "natural pacemaker" of the heart,
generates action potentials spontaneously and sets the heart rate.
The cardiac action potential involves a series of ionic currents across the cell
membrane that result in the depolarization and repolarization of the membrane.
During the resting phase, the membrane potential is maintained at a negative
value (around -90 mV) primarily due to the efflux of potassium ions (K+). When
the SA node initiates an action potential, voltage-gated sodium (Na+) channels
open, allowing an influx of sodium ions that leads to depolarization. Following
this, calcium (Ca2+) and more sodium ions enter the cell through voltage-gated
calcium (CaV) and sodium (Nav) channels, while potassium ions efflux through
various types of potassium (K+) channels, contributing to the plateau phase and
repolarization of the membrane.
The spontaneous depolarization of cardiac muscle cells is essential for the
coordinated contraction of the heart, which is critical for maintaining blood
circulation in the body. This property is not typically found in skeletal
muscles, which require an external signal from motor neurons to contract, nor in
smooth muscles, which are controlled by the autonomic nervous system and
hormones.
What is the primary effect of epinephrine on the gastrointestinal tract during the fight-or-flight response?
1) Increases motility and secretions
2) Decreases motility and secretions
3) Relaxes the gastrointestinal muscles
4) Dilates blood vessels in the GI tract
Answer: 2) Decreases motility and secretionsExplanation: Epinephrine decreases gastrointestinal motility and secretions as part of the fight-or-flight response. This is because the body's priority shifts from digestion to the preparation for immediate action, diverting blood away from the GI tract and reducing its activity to focus on more critical bodily functions.
Which of the following structures is associated with the control of voluntary eye movement?
1) Occipital lobe
2) Temporal lobe
3) Frontal eye field
4) Parietal lobe
The frontal eye field, located in the dorsolateral part of the frontal lobe, is involved in the control of voluntary eye movement. It is part of the motor system and helps in the planning and execution of saccadic movements.
The physiological capacity of the bladder, at which micturition is normally effected, ranges between:
1) 150 ml - 250 ml
2) 250 ml - 450 ml
3) 450 ml - 750 ml
4) 750 ml - 1000 ml
The physiological capacity of the bladder is the maximum intravesical volume tolerated without undue discomfort. It is usually between 250 and 450 ml. The bladder can stretch to hold more urine, but this is considered beyond the normal physiological capacity and can cause discomfort.
What is the primary inhibitory neurotransmitter in the central nervous system?
1) Dopamine
2) GABA (gamma-aminobutyric acid)
3) Glutamate
4) Acetylcholine
GABA is the main inhibitory neurotransmitter in the central nervous system, playing a crucial role in reducing the excitability of neurons and contributing to the regulation of neural circuits and synaptic plasticity.