Physiology of Thyroid Hormones

Question 1

Cuboidal epithelial cells in the thyroid are called ___ cells and they produce ___

Answer 1

Follicular cells

Produce thyroglobulin

Question 2

Colloid

Answer 2

A gelatinous substance
Made primarily of thyroglobulin
Found in the lumen of each follicle

Question 3

C cells

Answer 3

Responsible for the secretion of calcitonin

Question 4

Is T3 or T4 mostly released from the thyroid gland?

Answer 4

T4

But almost all of it is converted into T3 in the target tissues

Question 5

What mechanism facilitates the uphill uptake of I- into the cell?

Answer 5

Secondary active transport

So it is dependent on the Na/K pump

Question 6

Why do they thyroid hormones bind to proteins in the blood?

Answer 6

Enables transport and storage of relatively large quantities of hormones in an inactive form
Protects them from enzymatic metabolism
Can dissociate instantly, so free hormone is available at any time at any target tissue

Question 7

D1 and D2 deiodinase enzymes

Answer 7

Generate T3 by removing the iodine group from T4
D1 is most abundant, found in liver and kidneys mainly
D2 is main in the brain and pituitary gland

Question 8

TH hormone
1. Deficiency
2. Excess
on skin/hair

Answer 8

1. Pale, dry, puffy skin, dry brittle hair, brittle nails

2. Pink, warm, moist skin, onycholisis of nails

Question 9

TH hormone
1. Deficiency
2. Excess
on CV system

Answer 9

1. Decrease blood volume and CO, poorly contractile myocardium, sinus bradycardia
2. Positive chronotropic and ionotropic effects on the heart, increased CO, decreased PR, afib/tachycardia

Question 10

TH hormone
1. Deficiency
2. Excess
on resp system

Answer 10

1. Pleural effusions, alveolar hypotension when severe, sleep apnea
2. Decreased vital capacity due to myopathy of respiratory muscles

Question 11

TH hormone
1. Deficiency
2. Excess
on GI system

Answer 11

1. Modest weight gain, decreased motility/constipation, pernicious anemia
2. Increased appetite, weight loss, increased motility/diarrhea, pernicious anemia

Question 12

TH hormone
1. Deficiency
2. Excess
on CNS system

Answer 12

1. In childhood: poor neuronal development and myelination, mental retardation. In adulthood: slowed intellectual functions, ataxia, psychiatric disorders
2. Nervousness, emotional liability, hyperkinesia, tremor

Question 13

TH hormone
1. Deficiency
2. Excess
on the muscle

Answer 13

1. Stiffness and aching, tenderness, loss of Type 1 muscle fibers
2. Weakness and fatiguability, proximal myopathy, may be associated with myasthenia gravis

Question 14

TH hormone
1. Deficiency
2. Excess
on the skeleton

Answer 14

1. Poor growth and maturation of bone, decreased urinary excretion of Ca
2. Demineralization of bone, increased urinary excretion of Ca and phosphate, hypercalcemia

Question 15

TH hormone
1. Deficiency
2. Excess
on the kidney

Answer 15

1. Decreased renal blood flow, glomerular filtration as well as tubular resorption and secretion
2. Increased renal blood flow, glomerular filtration and tubular resorption and secretion

Question 16

TH hormone
1. Deficiency
2. Excess
on the bone marrow

Answer 16

1. Decreased red cell mass, normochromic/cytic anemia, pernicious anemia, macrocytic anemia
2. Increased red cell mass, pernicious and macrocytic anemia

Question 17

TH hormone
1. Deficiency
2. Excess
on the gonads

Answer 17

1. Childhood: delayed puberty, adulthood: menorrhagia, decreased libido, erectile dysfunction, infertility
2. Childhood: delayed puberty with normal development. Adult: increased libido, oligomenorrhea, spontaneous abortions

Question 18

Leptin

Answer 18

Long term regulator of body weight
Inhibits food intake and stimulates energy expenditure
Levels decrease during fasting
Low levels directly inhibits the expression and secretion of TRH (because you’re fasting)