A & P 2 - Endocrine: Thyroid Gland

Front 1

What is the structure of the thyroid gland?

Back 1

Location: in front of lower larynx and upper trachea

Anatomy: two lateral lobes connected by an isthmus

Front 2

What is the structure and function of the thyroid follicle?

Back 2

single layer of epithelial cells with basement membrane

function:
-synthesis of thyroid hormones
-accumulation of Iodide
-synthesis of thryoglobulin (Tg)

Parafollicular (C) cells:
-synthesis of calcitonin

Front 3

What is difference between an active gland and inactive gland?

Back 3

inactive:
-follicles are large
-flattened
-colloid is abundant

active:
-small follicles
-cells increase in size
-colloid is reduced

Front 4

What are the thyroid hormones?

Back 4

called iodothyronines - derived from tyrosine

-T4 - 90 %
-T3 - 10 %
-rT3 - less than 1 %

secretion: T4:T3 = 10-20:1
T3 more potent than T4

rT3 has 2 iodines on outer benzyl ring, T3 has then on inner ring

Front 5

What are nutritional requirements for synthesis of thyroid hormones?

Back 5

dietary tyrosine

dietary iodine

Front 6

What are some steps in synthesis and release of thyroid hormones?

Back 6

1. iodide uptake

2. synthesis of Tg

3. oxidation of iodide to iodine (iodide cannot bind to tyrosine until oxidation)

4. iodination of Tg

5. coupling of T1 and T2 by TPO
-T4 = fast reaction, T3 = slow

6. pinocytosis of Tg

7. release of thyroid hormone by diffusion

Front 7

How are thyroid hormones transported?

Back 7

Bound to plasma proteins (Thyroxine-binding globulin TBG) - more than 99 %

Unbound:
-only unbound T4/T3 exert effect on target tissues and feedback effect on pituitary and HT

Front 8

What are some biological effects of thyroid hormone?

Back 8

increase basal metabolic rate


increase energy metabolism - calorigenic action and thermogenic

Carb metabolism:
-increase glucose turnover, uptake, oxidation, and synthesis

Fat metabolism:
-lipolytic effect

Protein metabolism:
-increase protein catabolism

Potentiation of action of catecholamines (increase HR)

Stimulation of growth and development:
-increase linear growth (deficiency = stunted growth)
-increase brain development (deficiency = mental retardation

Front 9

What affects thyroid hormone secretion?

Back 9

factors include increase ATP demand (pregnancy, cold, high altitude)

Front 10

What is an Endemic goiter?

Back 10

results from insufficient dietary iodide intake

low thyroid causes increase in TSH secretion causing enlargement of gland

Front 11

What is hypothyroidism in adults?

Back 11

Myxedema

signs:
-nonpitting edema: swelling of face and bags under eyes

pathology:
-increased hyaluronic acid and chondroitin sulfate bound with protein
-forms excessive tissue gel
-causes non pitting edema

Front 12

What is hypothyroidism in children?

Back 12

causes deformed dwarfism which is opposite to proportional dwarfism caused by hyposecretion of GH

causes cretinism - irreversible mental retardation

Front 13

What is Grave's Disease?

Back 13

Hyperthyroidism

pathology:
-bacterial and viral infections
-Low plasma TSH level due to suppression of pituitary leads to TSH secretion by feedback mechanisms

Front 14

What are some effects of Hyperthyroidism?

Back 14

exophthalmus - forward displacement of eyeballs

-pretibial edema

-diplopia

Front 15

What are properties of Calcitonin?

Back 15

stimulated by increased plasma Calcium level

increases CT secretion

effects:
-bone: promotion of bone calcification, lowers plasma Ca
-kidney: increases urinary excretion of Ca and phosphate, lowers synthesis of calcitrol
-Intestine: indirectly lowers calcitrol in kidney

Front 16

What is parathyroid hormone and what are some of its biological effects?

Back 16

secreted by chief cells

increases during decreased plasma Ca

biological effects:
-bone: increase bone resorption, increases Ca and phosphate in ECF
-kidneys: increase Ca reabsorption, increases urinary excretion of cAMP
-small intestine: indirectly increases formation of calcitrol and increase in calcium reabsorption

Front 17

What are characteristics of Vit D and biological effects??

Back 17

is a secosteroid - one ring has been opened

2 sources:
-D2 = diet
-D3 = synthesized in skin by UV

active metabolites:
-calcitrol - produced by kidneys

biological effects:
-small intestine: increase absorption of Ca, phosphate, and Mg
-kidney: increase reabsorption of Ca and phosphate
-bones: direct (increase blood Ca and phosphate), indirect (increase bone calcification

Front 18

What is Primary Hyperparathyroidism?

Back 18

increase PTH:
-hypercalcemia and hypophosphatemia
-increase urine cAMP
-increase Vit D production

-hypercalcinuria

resorption of bones

signs of hypercalcemia:
-low NM transmission and muscular weakness
-constipation

Front 19

What happens in Hypoparathyroidism?

Back 19

hypocalcemia and hyperphosphatemia

hypophosphaturia, low urinary cAMP

signs of low plasma Ca:
-tetanic contractions of hand and feet

Front 20

What are Rickets and Osteomalacia?

Back 20

-inadequate Vit D3 intake
-low ability of kidney to convert cacidiol to calcitrol

Rickets:
-low bone rigidity
-possibly tetany due to low Ca
-pigeon breast
-in kids

Osteomalacia:
-low bone mineralization --> low bone strength
-bowing of weight bearing bones does not occur