MDS PREP
The average time required for spermatogenesis in humans is:
1) 30 days
2) 42 days
3) 74 days
4) 120 days
Spermatogenesis, the process of producing mature sperm cells from spermatogonia, takes approximately 74 days in humans. This includes the development of spermatids and their subsequent transformation into spermatozoa.
MCQ: The first sensation of bladder filling occurs at approximately:
1) 150 ml
2) 250 ml
3) 450 ml
4) 750 ml
The first sensation of bladder filling occurs at approximately 150 ml, signaling the need to void.
What is the primary mechanism responsible for the reabsorption of sodium in the distal tubules and collecting ducts of the nephron?
1) Sodium-hydrogen exchange
2) Sodium-glucose cotransport
3) Sodium-potassium-2-chloride cotransport
4) Sodium-phosphate cotransport
E) Sodium-chloride symport
The primary mechanism for sodium reabsorption in the distal tubules and collecting ducts is sodium-hydrogen exchange, which occurs through the NHE3 transporter. This allows for the reclamation of sodium while maintaining the acid-base balance by exchanging sodium for hydrogen ions, which are then secreted into the tubular lumen.
In the presence of which substance does vitamin B12 combine in the stomach to prevent its degradation by gastric acid?
1) Intrinsic factor
2) Pepsin
3) Gastric acid
4) Pancreatic amylase
In the presence of intrinsic factor, vitamin B12 combines in the stomach to prevent its degradation by gastric acid, ensuring its availability for absorption.
Which hormone is primarily responsible for the conversion of 7-dehydrocholesterol to cholecalciferol in the skin?
1) Parathyroid hormone (PTH)
2) Vitamin D
3) Ultraviolet B (UV2) light
4) 25-hydroxyvitamin D3
Ultraviolet B (UVB) light is primarily responsible for the conversion of 7-dehydrocholesterol to cholecalciferol (vitamin D3) in the skin.
What is the role of the sodium-calcium exchanger (NCX) in calcium homeostasis?
1) It transports calcium into cells
2) It transports sodium into cells and calcium out of cells
3) It transports sodium out of cells and calcium into cells
4) It has no role in calcium homeostasis
Physiology
Answer: 3
The sodium-calcium exchanger (NCX) is involved in the regulation of calcium levels in cells. It exchanges three sodium ions (Na+) for one calcium ion (Ca2+), thereby helping to maintain intracellular calcium homeostasis.
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
Vitamin E (tocopherol) is the most important antioxidant in the body, acting in the lipid phase of membranes to protect against oxidative damage.
What is the significance of the transport maximum for substances like glucose and phosphate?
1) It indicates the maximum amount that can be filtered by the glomerulus
2) It represents the maximum amount that can be actively reabsorbed by the tubules
3) It is the point at which the substance begins to be excreted in the urine
4) It is the point at which the substance becomes toxic to the body
The transport maximum for substances like glucose and phosphate represents the maximum amount that can be actively reabsorbed by the tubules before reaching saturation and being excreted in urine.