Physio Lect 4

Question 1

The primary effect of PTH on blood calcium and phosphate levels is to:
a) Decrease both calcium and phosphate
b) Increase both calcium and phosphate
c) Increase calcium and decrease phosphate
d) Decrease calcium and increase phosphate

Answer 1

c) Increase calcium and decrease phosphate

Question 2

In the nephron, PTH exerts its effects primarily at the:
a) Glomerulus
b) Proximal convoluted tubule
c) Distal convoluted tubule
d) Loop of Henle

Answer 2

c) Distal convoluted tubule

Question 3

The mechanism by which PTH increases calcium reabsorption in the distal convoluted tubule involves:
a) Increased paracellular transport
b) Stimulation of simple diffusion
c) Enhanced transcellular transport
d) Inhibition of calcium channels

Answer 3

c) Enhanced transcellular transport

Question 4

PTH increases blood calcium levels through its actions on:
a) Increased osteoblast activity and decreased osteoclast activity
b) Decreased osteoblast activity and increased bone mineralization
c) Increased osteoclast activity and increased calcium reabsorption in the kidney
d) Decreased osteoclast activity and decreased calcium absorption in the gut

Answer 4

c) Increased osteoclast activity and increased calcium reabsorption in the kidney

Question 5

The receptor for PTH on its target cells is best described as a:
a) Ligand-gated ion channel
b) Nuclear receptor
c) G-protein-coupled receptor
d) Receptor tyrosine kinase

Answer 5

c) G-protein-coupled receptor

Note: activates two signaling pathways:
1. Adenylate Cyclades —> cAMP
2. Phospholipase —> DAG and IP3

Question 6

Secretion of PTH from the parathyroid glands is stimulated by:
a) Elevated blood calcium levels
b) Decreased blood phosphate levels
c) Low blood calcium levels
d) High levels of active vitamin D3

Answer 6

c) Low blood calcium levels and high blood phosphate levels

Question 7

A patient with hypoparathyroidism is most likely to present with:
a) Hypercalcemia
b) Hypophosphatemia
c) Increased bone resorption
d) Hypocalcemia

Answer 7

d) Hypocalcemia

Question 8

The most common cause of hypoparathyroidism is:
a) Autoimmune destruction of the parathyroid glands
b) Benign tumors of the parathyroid glands
c) Accidental damage during thyroidectomy surgery
d) Dietary calcium deficiency

Answer 8

c) Accidental damage during thyroidectomy surgery

Question 9

In pseudohypoparathyroidism, the underlying defect involves:
a) Decreased secretion of PTH
b) Defective Gs-protein in the PTH receptor
c) Increased renal reabsorption of phosphate
d) Overactivity of osteoclasts

Answer 9

b) Defective Gs-protein in the PTH receptor

Increase PTH
Increase Phosphate.
Decrease Ca2+

Question 10

Primary hyperparathyroidism is most commonly caused by:
a) Chronic kidney failure
b) Vitamin D3 deficiency
c) An adenoma of the parathyroid gland
d) Long-term use of phosphate-binding antacids

Answer 10

c) An adenoma of the parathyroid gland

Question 11

A key clinical manifestation of hyperparathyroidism is:
a) Increased neuromuscular excitability
b) Decreased risk of kidney stones
c) Osteoporosis
d) Hypocalcemia

Answer 11

a) Increased neuromuscular excitability
(Nervous and skeletal system)

Also, Increase muscle cramps, twitches, and seizures.

Question 12

Humoral hypercalcemia of malignancy is characterized by:
a) Elevated plasma PTH levels
b) Decreased secretion of PTH-related peptide
c) Hypercalcemia with suppressed PTH levels
d) Hypocalcemia and hyperphosphatemia

Answer 12

c) Hypercalcemia with suppressed PTH levels

Other Effects:
Increase secretion of PTH related peptide
Hypercalcemia
Hypophosphatemia

Question 14

Hyperparathyroidism presents what clinical symptoms?

Answer 14

Kidney stones,
Weak, soft bones
GIT dysfunction
Emotional disorders
Neuromuscular disturbances

Question 15

The active form of vitamin D3, calcitriol, is produced through hydroxylation reactions in the:
a) Skin and adrenal glands
b) Liver and bones
c) Liver and kidney
d) Kidneys and intestines

Answer 15

c) Liver and kidney

Question 16

The synthesis of the active form of vitamin D3 in the kidney is stimulated by:
a) High plasma calcium levels
b) Low levels of PTH
c) Low plasma calcium and phosphate levels
d) High levels of calcitonin

Answer 16

c) Low plasma calcium and phosphate levels

Question 17

Calcitriol primarily increases calcium absorption in the:
a) Stomach
b) Pancreas
c) Small intestine
d) Large intestine

Answer 17

d) Large intestine (Duodenum)

Question 18

The mechanism of action of calcitriol in increasing calcium absorption involves:
a) Activation of ligand-gated calcium channels in the intestinal lumen
b) Stimulation of a nuclear receptor leading to increased synthesis of calcium transport proteins
c) Direct phosphorylation of calcium pumps in the enterocyte membrane
d) Increasing paracellular transport of calcium in the jejunum

Answer 18

b) Stimulation of a nuclear receptor leading to increased synthesis of calcium transport proteins

Question 19

Deficiency of calcitriol in children leads to which of the following conditions?
a) Osteomalacia
b) Osteoporosis
c) Rickets
d) Paget’s disease

Answer 19

c) Rickets

Small chest
Large head
Large abdomen
Curve femur, fibular and tibia

Question 20

Discuss the pathophysiology of the Rickets.

Answer 20

Decrease in Ca2+ and phosphate blood levels
Decrease in reabsorption of the bones
Thus signals the PTH to secrete to increase bone reabsorption —> increase Ca2+ levels.

Question 21

In adults, a deficiency of vitamin D3 typically results in:
a) Rickets
b) Osteomalacia
c) Hypercalcemia
d) Increased bone density

Answer 21

b) Osteomalacia

Question 22

Vitamin D3 resistance in chronic kidney failure is primarily due to:
a) Increased renal clearance of vitamin D3
b) Impaired intestinal absorption of vitamin D3
c) Inability of the kidney to convert inactive vitamin D3 to calcitriol
d) Downregulation of vitamin D3 receptors in target tissues

Answer 22

c) Inability of the kidney to convert inactive vitamin D3 to calcitriol

Due to absence of enzyme hydrolyze or kidney failure.

Question 23

The primary effect of calcitonin on blood calcium and phosphate levels is to:
a) Increase both calcium and phosphate
b) Decrease calcium and increase phosphate
c) Increase calcium and decrease phosphate
d) Reduce both calcium and phosphate

Answer 23

d) Reduce both calcium and phosphate

Decrease bone reabsorption as well as

Question 24

The target organs of calcitonin are the:
a) Bones and kidneys
b) Intestines and parathyroid glands
c) Liver and muscles
d) Brain and pancreas

Answer 24

a) Bones and kidneys

Question 25

Which of the following is a critical role of calcium in the body? a) Primary component of RNA b) Cofactor for all glycolytic enzymes c) Involvement in muscle contraction d) Regulation of insulin secretion by alpha cells

Answer 25

c) Involvement in muscle contraction Other roles: Bones and teeth Signaling pathways Promote blood coagulation

Question 26

The largest reservoir of calcium in the body is found in the: a) Blood plasma b) Intracellular fluid c) Bones and teeth d) Extracellular fluid

Answer 26

c) Bones and teeth

Question 27

Calcium plays an important role in intracellular signaling pathways and also: a) Inhibits blood coagulation b) Acts as a structural component of hemoglobin c) Serves as a cofactor in enzymatic reactions d) Promotes glycogenolysis in the liver

Answer 27

c) Serves as a cofactor in enzymatic reactions

Question 28

Phosphate is a crucial structural component of: a) Glycogen molecules b) Amino acids c) Cell membranes (phospholipids) d) Steroid hormones

Answer 28

c) Cell membranes (phospholipids)

Question 29

Compared to extracellular fluid, the intracellular concentration of phosphate is typically: a) Lower b) Equal c) Much higher d) Fluctuating widely

Answer 29

c) Much higher

Question 30

Urinary phosphate excretion is important for: a) Maintaining blood glucose homeostasis b) Regulation of blood pH (phosphate buffer) c) Synthesis of vitamin D3 in the kidney d) Preventing the formation of kidney stones

Answer 30

b) Regulation of blood pH (phosphate buffer)

Question 31

A patient presents with muscle cramps, perioral numbness, and a positive Chvostek's sign. The most likely underlying hormonal abnormality is: a) Excess parathyroid hormone b) Deficiency of vitamin D3 c) Deficiency of parathyroid hormone d) Excess calcitonin

Answer 31

c) Deficiency of parathyroid hormone

Question 32

The primary mechanism by which PTH reduces blood phosphate levels is by: a) Increasing intestinal phosphate absorption b) Decreasing bone resorption c) Inhibiting renal phosphate reabsorption d) Stimulating cellular uptake of phosphate

Answer 32

c) Inhibiting renal phosphate reabsorption

Question 33

The opposing effects of PTH on calcium and phosphate levels in the blood help to: a) Maximize bone mineralization b) Prevent precipitation of calcium phosphate crystals c) Enhance neuromuscular excitability d) Promote the formation of hydroxyapatite in soft tissues

Answer 33

b) Prevent precipitation of calcium phosphate crystals — kidney stones

Question 34

In bone, a rapid exchangeable pool of calcium allows for: a) Long-term storage of calcium for skeletal growth b) Minute-to-minute regulation of blood calcium levels c) Structural integrity that is resistant to resorption d) Calcium buffering primarily during periods of high dietary intake

Answer 34

b) Minute-to-minute regulation of blood calcium levels

Question 35

During periods of bone growth, intestinal absorption of calcium and phosphate typically: a) Decreases relative to urinary excretion b) Is balanced with urinary excretion c) Exceeds urinary excretion d) Is independent of hormonal control

Answer 35

c) Exceeds urinary excretion

Question 36

In osteoporosis, a bone disease characterized by increased bone resorption, there is often an increase in: a) Intestinal absorption of calcium and phosphate b) Bone formation markers in the blood c) Urinary calcium and phosphate loss d) Serum levels of vitamin D3

Answer 36

c) Urinary calcium and phosphate loss

Question 37

In chronic kidney failure, a common finding regarding calcium and phosphate balance is: a) Hypercalcemia and hypophosphatemia b) Hypocalcemia and hyperphosphatemia c) Increased renal absorption of both calcium and phosphate d) Decreased PTH levels due to impaired calcium sensing

Answer 37

b) Hypocalcemia and hyperphosphatemia

Question 38

Which hormone directly stimulates the conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 in the kidney? a) Calcitonin b) Parathyroid hormone c) Growth hormone d) Insulin

Answer 38

a) Calcitonin

Question 40

Increased levels of 1,25-dihydroxyvitamin D3 (calcitriol) would lead to: a) Decreased intestinal calcium absorption b) Increased bone resorption and increased intestinal calcium absorption c) Decreased PTH secretion d) Increased renal phosphate reabsorption

Answer 40

b) Increased bone resorption and increased intestinal calcium absorption

Question 42

Which of the following hormones has the most significant effect on increasing both blood calcium and phosphate levels? a) Parathyroid hormone b) Calcitriol (Vitamin D3) c) Calcitonin d) Glucocorticoids

Answer 42

b) Calcitriol (Vitamin D3)

Question 43

The action of PTH on bone leads to the release of: a) Primarily calcium with minimal phosphate b) Primarily phosphate with minimal calcium c) Both ionized calcium and phosphate d) Neither calcium nor phosphate directly

Answer 43

c) Both ionized calcium and phosphate

Question 44

Calcitonin's role in calcium regulation is generally considered: a) The primary regulator of daily calcium homeostasis b) More significant than that of PTH c) A protective mechanism against hypercalcemia d) Essential for bone growth and development

Answer 44

c) A protective mechanism against hypercalcemia Reduces both calcium and phosphate

Question 45

The rapid effects of calcitriol on calcium absorption in the duodenum suggest a possible mechanism involving: a) Nuclear receptor-mediated gene transcription b) Direct interaction with calcium channels in the cell membrane c) Increased synthesis of calbindin d) Enhanced paracellular transport

Answer 45

b) Direct interaction with calcium channels in the cell membrane

Question 46

In humoral hypercalcemia of malignancy, the secreted PTH-related peptide mimics the actions of PTH on: a) The parathyroid gland to inhibit PTH secretion b) The liver to increase vitamin D3 activation c) Bone and kidney to increase calcium levels d) The intestine to decrease calcium absorption

Answer 46

c) Bone and kidney to increase calcium levels