MDS PREP
What is the primary action of antidiuretic hormone (ADH) in the kidneys?
1) Increases the permeability of water in the proximal tubules
2) Increases the permeability of water in the collecting tubules and ducts
3) Stimulates glomerular filtration rate
4) Inhibits sodium reabsorption
The primary action of antidiuretic hormone (ADH) in the kidneys is to increase the permeability of water in the collecting tubules and ducts, promoting water reabsorption.
The release of which hormone is triggered by the macula densa cells during tubulo-glomerular feedback?
1) Renin
2) Angiotensin II
3) Atrial Natriuretic Peptide (ANP)
4) Aldosterone
The macula densa cells respond to decreases in sodium chloride concentration in the tubular fluid by releasing renin, which initiates the renin-angiotensin-aldosterone system (RAAS). This leads to increased sodium reabsorption and water retention, thereby restoring the sodium chloride balance and blood volume.
Which of the following enzymes is involved in the digestion of proteins?
1) Ptyalin
2) Pepsin
3) Trypsin
4) Cholecystokinin
E) Gastrin
Pepsin is the primary enzyme responsible for the breakdown of proteins in the stomach during the gastric phase of digestion. It is secreted as pepsinogen by the chief cells of the gastric mucosa and is activated by hydrochloric acid to become pepsin.
Diabetic insipidus is due to the lack of
1 Insulin
2 Angiotensin.
3 Aldosterone.
4 A.D.H.
Physiology
Answer: 4
Diabetic insipidus is due to the lack of 4. A.D.H. (Antidiuretic hormone).
Explanation:
Diabetic insipidus (DI) is a condition characterized by the production of large
volumes of dilute urine due to the lack of the antidiuretic hormone (ADH) or the
body's inability to respond to it. It is different from diabetes mellitus, which
involves problems with insulin and blood sugar regulation.
1. Insulin: Insulin is a hormone produced by the pancreas that plays a critical
role in regulating blood sugar levels. A deficiency or resistance to insulin
leads to diabetes mellitus, not diabetic insipidus. Diabetes mellitus is
characterized by hyperglycemia (high blood sugar) and increased thirst and urine
production due to the inability of the kidneys to reabsorb glucose properly.
2. Angiotensin: Angiotensin is a hormone system that plays a role in the
regulation of blood pressure and fluid balance. It is involved in the
renin-angiotensin-aldosterone system (RAAS). While it is crucial for maintaining
blood pressure, it is not directly related to the pathophysiology of diabetic
insipidus.
3. Aldosterone: Aldosterone is a mineralocorticoid hormone produced by the
adrenal glands. It helps regulate sodium and potassium levels in the body, which
in turn affects fluid and blood volume. While it is essential for electrolyte
and fluid balance, it does not cause diabetic insipidus when lacking.
4. Antidiuretic hormone (ADH): ADH is a hormone produced by the hypothalamus and
stored in the posterior pituitary gland. It acts on the kidneys to increase
water reabsorption, which leads to the production of concentrated urine. In
diabetic insipidus, there is either a deficiency of ADH or the kidneys fail to
respond to it adequately. This results in the kidneys being unable to reabsorb
enough water, leading to the production of large volumes of dilute urine and
increased thirst.
There are two main types of diabetic insipidus: central and nephrogenic. Central
DI occurs when the pituitary gland does not produce enough ADH, while
nephrogenic DI results from the kidneys' inability to respond to ADH. Both types
lead to an imbalance in water regulation and can cause symptoms such as polyuria
(excessive urine production), polydipsia (excessive thirst), and dehydration if
not managed properly.
To treat diabetic insipidus, the underlying cause must be addressed. If it is
central DI, synthetic ADH (desmopressin) is administered to replace the missing
hormone. If it is nephrogenic DI, the treatment focuses on addressing the
kidney's response to ADH and managing symptoms such as maintaining fluid intake
and sometimes medications to reduce urine output.
What is the main difference between endopeptidases and exopeptidases?
1) Endopeptidases cleave internal peptide bonds, while exopeptidases act on the terminal peptide bonds.
2) Endopeptidases are inactive in the stomach, whereas exopeptidases are active in the stomach.
3) Endopeptidases are exclusively found in the pancreas, whereas exopeptidases are exclusively found in the intestinal mucosa.
4) Endopeptidases are exclusively activated by enterokinase, whereas exopeptidases are activated by other enzymes.
E) Endopeptidases are inhibited by acidic pH, while exopeptidases function best at acidic pH.
Endopeptidases, also known as endoproteinases, are enzymes that hydrolyze peptide bonds within the polypeptide chain, breaking down proteins into smaller peptides. Examples include pepsin, trypsin, and chymotrypsin. In contrast, exopeptidases, or exoproteinases, cleave peptide bonds at the ends of the polypeptide chain, either at the N-terminal (aminopeptidases) or C-terminal (carboxypeptidases). These enzymes are involved in the final steps of protein digestion and the degradation of small peptides into individual amino acids.
What is the effect of acetylcholine on the heart's sinoatrial (S1) node?
1) It increases the heart rate
2) It decreases the heart rate
3) It has no effect on the SA node
4) It causes arrhythmias in the SA node
Acetylcholine, released by the vagus nerve, acts on the SA node to slow down the heart rate by hyperpolarizing the membranes of the SA node cells and decreasing their automaticity.
What is the primary stimulus for the secretion of Secretin?
1) High blood glucose levels
2) Low pH in the duodenal lumen
3) The presence of fatty acids and amino acids in the duodenal lumen
4) Stretching of the duodenal wall
The primary stimulus for the secretion of Secretin is low pH in the duodenal lumen, which indicates the presence of acidic chyme.
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.