MDS PREP
The primary function of the afferent arterioles in the juxtaglomerular apparatus is to:
1) Constrict in response to increased sodium chloride delivery
2) Dilate in response to increased sodium chloride delivery
3) Secrete renin in response to decreased sodium chloride delivery
4) Constrict in response to decreased sodium chloride delivery
The afferent arterioles are part of the juxtaglomerular apparatus along with the macula densa and efferent arterioles. When the macula densa detects a decrease in sodium chloride delivery, it triggers the juxtaglomerular cells in the afferent arterioles to release renin, which is the initial step in the RAAS.
MCQ: The glomerular filtration barrier consists of:
1) Endothelial cells
2) Basement membrane
3) Podocytes
4) All of the above
The glomerular filtration barrier consists of endothelial cells, basement membrane, and podocytes, all of which work together to filter blood in the kidneys.
What is the significance of the pre-to-post ganglionic fiber ratio in the sympathetic nervous system?
1) It indicates the speed of nerve impulse transmission.
2) It reflects the number of synapses involved in the pathway.
3) It is unrelated to the function of the sympathetic nervous system.
4) It indicates the level of sympathetic nervous system activity.
In the sympathetic nervous system, the pre-to-post ganglionic fiber ratio of 1:20 to 1:100 indicates that there are fewer postganglionic fibers than preganglionic fibers. This ratio suggests that each preganglionic neuron synapses with multiple postganglionic neurons, thereby amplifying the sympathetic response to a given input.
Which of the following statements about glomerular filtrate is true?
1) It contains high levels of proteins.
2) It is isotonic to plasma.
3) It is essentially protein-free.
4) It has a higher concentration of glucose than plasma.
Glomerular filtrate is essentially protein-free, allowing for the passage of water, electrolytes, and small molecules while retaining larger proteins in the bloodstream.
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.
All of the following promote activation of muscle contraction EXCEPT
1. Binding of myosin to actin.
2. Opening of the sarcoplasmic reticulum Ca channel.
3. Ca2+ binding to troponin C.
4. Opening of Na channels.
Physiology
Answer: 1
Activation of muscle contraction is promoted by :
Opening of the sarcoplasmic reticulum Ca channel.
Ca2+ binding to troponin C.
Opening of Na channels
Ca2+ binding to the Ca2+-ATPase
What is the primary mechanism of action of the Na+/I+ symporter in thyroid cells?
1) Primary active transport
2) Facilitated diffusion
3) Secondary active transport
4) Osmosis
The Na+/I+ symporter (NIS) in thyroid cells uses the energy from the electrochemical gradient of sodium to actively transport iodide into the cells, which is an example of secondary active transport.
Which of the following statements is true about the regulation of the sympathetic nervous system?
1) The sympathetic nervous system is primarily regulated by the parasympathetic nervous system.
2) The sympathetic nervous system is mainly controlled by the hypothalamus.
3) The sympathetic nervous system is regulated by the spinal cord through the sympathetic chain ganglia.
4) The sympathetic nervous system is primarily regulated by the sympathetic chain ganglia.
Answer: 3) The sympathetic nervous system is regulated by the spinal cord through the sympathetic chain ganglia, which receive input from the hypothalamus and other higher centers.