thyroid/parathyroid

Question 1

thyroid gland consists of…

Answer 1

two lobes of endocrine tissue joined in middle by narrow portion of gland

Question 2

follicular cells

Answer 2

Arranged into hollow spheres
Forms functional unit called a follicle
Lumen filled with colloid
Serves as extracellular storage site for thyroid hormone

Question 3

thyroid gland produces

Answer 3

Produce two iodine-containing hormones derived from amino acid tyrosine
Tetraiodothyronine (T4 or thyroxine) Tri-iodothyronine (T3)

Question 4

c cells

Answer 4

Secrete peptide hormone calcitonin

Question 5

thyroid hormone ingredients

Answer 5

Tyrosine
Synthesized in sufficient amounts by body
Iodine
Obtained from dietary intake

Question 6

thyroid hormone synthesis

Answer 6

All steps occur on thyroglobulin molecules within colloid
• Tyrosine-containing thyroglobulin is exported from follicular cells into colloid by exocytosis
• Thyroid captures iodine from blood and transfers it into colloid by iodine pump
• Within colloid, iodine attaches to tyrosine
• Coupling process occurs between iodinated tyrosine molecules to form thyroid hormones

Question 7

thyroid hormone storage

Answer 7

remain in colloid until they are split off and secreted

Usually enough thyroid hormone stored to supply body’s needs for several months

Question 8

thyroid hormone secretion

Answer 8

Follicular cells phagocytize thyroglobulin-laden colloid
Process frees T3 and T4 to diffuse across plasma membrane and into blood
Most produced is T4 converted to T

Question 9

effects of TH (6 things)

Answer 9

• Main determinant of basal metabolic rate
• Influences synthesis and degradation of carbohydrate, fat, and protein
• Increases target-cell responsiveness to catecholamines
• Increases heart rate and force of contractionEssential for normal growth
• Plays crucial role in normal development of nervous system

Question 10

hypothalamus-pituitary-thyroid axis is regulated by negative feedback by which hormones

Answer 10

hypothalamic TRH, anterior pituitary TSH, and thyroid gland T3 and T4
- Feedback loop maintains thyroid hormones relatively constant

Question 11

hypothyroidism causes

Answer 11

Primary failure of thyroid gland

Secondary to a deficiency of TRH, TSH, or both Inadequate dietary supply of iodine

Question 12

cretinism

Answer 12

results from hypothyroidism from birth

Question 13

myxedema

Answer 13

Primary failure of thyroid gland

Secondary to a deficiency of TRH, TSH, or both Inadequate dietary supply of iodine

Question 14

hyperthyroidism most common cause is graves’ disease

Answer 14

Autoimmune disease
Body erroneously produces thyroid-stimulating immunoglobulins (TSI)
Characterized by exopthalmos

Question 15

treatment of graves’

Answer 15

Surgical removal of a portion of the over-secreting thyroid

Administration of radioactive iodine Use of antithyroid drugs

Question 16

six physiological processes of calcium

Answer 16

• Plasma Ca2+ must be closely regulated to prevent changes in neuromuscular excitability
- Excitation-contraction coupling in cardiac and smooth muscle
• Stimulus-secretion coupling
• Maintenance of tight junctions between cells
• Clotting of blood
• Bone formation

Question 17

hormones that regulate plasma calcium

Answer 17

PTH - parathyroid hormone
calcitonin
vitamin D

Question 18

hypercalcemia

Answer 18

reduces excitability

Question 19

hypocalcemia

Answer 19

Brings about overexcitability of nerves and muscles

Severe overexcitability can cause fatal spastic contractions of respiratory muscles

Question 20

PTH 4 function

Answer 20

parathyroid gland
Primary regulator of Ca2+
Raises free plasma Ca2+ levels by its effects on bone kidneys, and intestines
Essential for life
Prevents fatal consequences of hypocalcemia
Facilitates activation of vitamin D

Question 21

calcitonin

Answer 21

lower plasma ca
Hormone produced by C cells of thyroid gland
• Negative-feedback fashion
– Secreted in response to increase in plasma Ca2+ concentration
• Acts to lower plasma Ca2+ levels by inhibiting activity of bone osteoclasts
• Unimportant except during hypercalcemia

Question 22

vitamin D

Answer 22

• Stimulates Ca2+ and PO43- absorption from intestine
• Can be synthesized from cholesterol derivative when exposed to sunlight
– Often inadequate source
• Amount supplemented by dietary intake
• Must be activated first by liver and then by kidneys before it can exert its effect on intestines

Question 23

Endocrine Control of Calcium Metabolism
PTH
Vit D

Answer 23

PTH hypersecretion (hyperparathyroidism)
Characterized by hypercalcemia and hypophosphatemia
PTH hyposecretion (hypoparathyroidism)
Characterized by hypocalcemia and hyperphosphatemia
Vitamin D deficiency Children – rickets Adults – osteomalacia