Human Physiology, 14th edition (2016)

698 Chapter 19

2. The plasma concentrations of calcium and phosphate
   are also affected by absorption from the intestine and by
   the urinary excretion of these ions.
   B. Parathyroid hormone stimulates bone resorption and calcium
   reabsorption in the kidneys. This hormone thus acts to raise
   the blood calcium concentration.


3. The secretion of parathyroid hormone is stimulated by a
   fall in blood calcium levels.


4. Parathyroid hormone also inhibits reabsorption of
   phosphate in the kidneys, so that more phosphate is
   excreted in the urine.
   C. 1,25-dihydroxyvitamin D 3 is derived from vitamin D by
   hydroxylation reactions in the liver and kidneys.


5. The last hydroxylation step is stimulated by parathyroid
   hormone.


6. 1,25-dihydroxyvitamin D 3 stimulates the intestinal
   absorption of calcium and phosphate, resorption of
   bone, and renal reabsorption of phosphate.

D. A rise in parathyroid hormone, accompanied by the

increased production of 1,25-dihydroxyvitamin D 3 , helps to

maintain proper blood levels of calcium and phosphate in

response to a fall in calcium levels.

E. Calcitonin is secreted by the parafollicular cells of the thy-

roid gland.

1. Calcitonin secretion is stimulated by a rise in blood

calcium levels.

2. Calcitonin, at least at pharmacological levels, acts to

lower blood calcium by inhibiting bone resorption

and stimulating the urinary excretion of calcium and

phosphate.

Test Your Knowledge

Match these:

1. Absorption of a
   carbohydrate
   meal


2. Fasting

Match these:

3. Growth
   hormone


4. Thyroxine


5. Hydrocortisone


6. A lowering of blood glucose concentration promotes

a. decreased lipogenesis.

b. increased lipolysis.

c. increased glycogenolysis.

d. all of these.

7. Glucose can be secreted into the blood by

a. the liver.

b. the muscles.

c. the liver and muscles.

d. the liver, muscles, and brain.

8. The basal metabolic rate is determined primarily by

a. hydrocortisone. c. growth hormone.

b. insulin. d. thyroxine.

9. Somatomedins are required for the anabolic effects of

a. hydrocortisone. c. growth hormone.

b. insulin. d. thyroxine.

a. Rise in insulin; rise in glucagon

b. Fall in insulin; rise in glucagon

c. Rise in insulin; fall in glucagon

d. Fall in insulin; fall in glucagon

a. Increased protein synthesis;

increased cell respiration

b. Protein catabolism in muscles;

gluconeogenesis in liver

c. Protein synthesis in muscles;

decreased glucose utilization

d. Fall in blood glucose;

increased fat synthesis

REVIEW ACTIVITIES

10. The increased intestinal absorption of calcium is stimulated
    directly by
    a. parathyroid hormone.
    b. 1,25-dihydroxyvitamin D 3.
    c. calcitonin.
    d. all of these.


11. A rise in blood calcium levels directly stimulates
    a. parathyroid hormone secretion.
    b. calcitonin secretion.
    c. 1,25-dihydroxyvitamin D 3 formation.
    d. all of these.


12. At rest, about 12% of the total calories consumed are used for
    a. protein synthesis.
    b. cell transport.
    c. the Na^1 /K^1 pumps.
    d. DNA replication.


13. Which of these hormones stimulates anabolism of proteins
    and catabolism of fat?
    a. Growth hormone d. Glucagon
    b. Thyroxine e. Epinephrine
    c. Insulin


14. If a person eats 600 kilocalories of protein in a meal, which
    of these statements will be false?
    a. Insulin secretion will be increased.
    b. The metabolic rate will be increased over basal conditions.
    c. The tissue cells will use some of the amino acids for
    resynthesis of body proteins.
    d. The tissue cells will obtain 600 kilocalories worth of energy.
    e. Body-heat production and oxygen consumption will be
    increased over basal conditions.