Lecture 14 - Thyroid, Parathyroid and Adrenal Glands

Question 1

Thyroid structure and location

Answer 1

two lobes joined by an isthmus. Just below the larynx. anterior to the parathyroid.

Question 2

Thyroid development

Answer 2

developed by the foramen cecum (same as tongue). will be in place after 7 weeks, below the larynx.

Question 3

Colloid

Answer 3

gelatin like substance that fills the follicles of the thyroid. Is surrounded by follicular cells which secrete the colloid.

Question 4

Follicular cells shape

Answer 4

typically squamos to columnar

Question 5

Parafollicular cells (or C cells)

Answer 5

stain clearer. Produce calcitonin. can be embedded into the epithelium or can form bunches outside. Neural crest origin.

Question 6

Vascularity of thyroid cells

Answer 6

frequent capillary openings with fenestrated endothelium.

Question 7

Follicular cells contents

Answer 7

lots of RER, golgi, and microvilli

Question 8

Thyroid hormones

Answer 8

T3 (triiodothryonine) and T4 (thyroxine), calcitonin.

Question 9

T3 and T4

Answer 9

increase basal metabolic rate (T3 - mitochondrial number, cristae density and activity), influence body growth and nervous system development in the fetus. Stored in colloid. T4 most abundant. T3 most potent.

Question 10

Calcitonin

Answer 10

produced and secreted by parafollicular cells or C cells. induced by increases in blood calcium levels, lowers blood calcium by inhibiting bone resorption (osteoclasts)

Question 11

Iodine absorption in follicular cells

Answer 11

have iodide pumps (transporters) that concentrate iodide in the thyroid gland to make T3 and T4.

Question 12

Thyroglobulin

Answer 12

glycoprotein that is synthesized by RER and secreted into the colloid.

Question 13

Synthesis of thyroid hormones

Answer 13

Thyroglobulin produced, uptake of iodide by Na/I symporter on basolateral membrane, oxidation of iodine by thyroid peroxidase and transported into the follicle by pendrin, iodination by thyroid peroxidase occurs.

Question 14

Pendrin

Answer 14

anion transporter to get oxidized iodine into the follicle

Question 15

Thyroid peroxidase

Answer 15

oxidation of iodine in the cell and iodination of thyroglobulin in the follicle.

Question 16

Thyroid feedback loop

Answer 16

hypothalamus releases TReleasingH which stimulates the anterior pituitary gland to release TSH (thyrotropin). TSH causes a release of T3/T4 into the blood stream and target cells. Feedback to the anterior pituitary and hypothalamus inhibit TRH.

Question 17

Thyroid hormone secretion

Answer 17

upon stimulation of thyrotropin, follicular cells take up colloid by endocytosis. digested by lysosomal enzymes. Proteases free T3 and T4 to the cytoplasm and secreted basally into the blood. Rest is recycled.

Question 18

T or F: Thyroid produces there products extracellularly

Answer 18

True.

Question 19

Hyperactive thyroid follicle appearance

Answer 19

colloid is decreased. more of columnar epithelium.

Question 20

Hypoactive thyroid follicle appearance

Answer 20

lots of colloid present. squamous epithelium since pushed by the colloid.

Question 21

Parathyroid structure and location

Answer 21

4 small glands. posterior to thyroid.

Question 22

Parathyroid development

Answer 22

derived from the parapharyngeal pouches. Inferior come from 3rd pouch, superior come from 4th pouch.

Question 23

Two cell types of the parathyroid

Answer 23

chief (principal) cells and oxyphil cells

Question 24

Chief (principal) cells

Answer 24

produce parathyroid hormone which promotes bone reabsorption. dark staining. arranged in cords.

Question 25

Oxyphil cells

Answer 25

function is unknown, but abundance mitochondria. Light staining. accumulate in age, along with fat cells

Question 26

parathyroid hormone feedback loop

Answer 26

low blood calcium, stimulates parathyroid hormone secretion, PTH will cause bone to release calcium, kidneys to converse calcium, and intestine to increase absorption. Once calcium rises, PTH inhibited

Question 27

PTH 3 main targets

Answer 27

bone, kidney, and intestine

Question 28

PTH and bone

Answer 28

osteoblasts are the main target, which will produce osteoclast stimulating factor (paracrine mechanism) which induces the proliferation of osteoclasts - mobilizing calcium into the blood stream.

Question 29

PTH and kidney

Answer 29

kidneys conserve calcium in the tubule cells

Question 30

PTH and intestines

Answer 30

PTH induces the synthesis of vitamin D, which helps with the absorption of calcium.

Question 31

Adrenal structure and location

Answer 31

medulla, cortex, and capsule. two glands capping the kidneys but with no connection. Lots of adipose tissue but does not increase with age.

Question 32

Adrenal gland development

Answer 32

cortex - celomic epithelium (mesothelium) derived from mesoderm
medulla - neural crest cells derived from ectoderm

Question 33

3 layers of adrenal cortex

Answer 33

zona glomerulosa (15%), zona fasciculata (65%) with cords, and zona reticularis (7%)

Question 34

Zona glomerulosa

Answer 34

bent cords. interconnection between two segments. secrete mineralcorticoids.

Question 35

zona fasciculata

Answer 35

linear cord arrangement. Glucocorticoids and the androgens are secreted

Question 36

Zona reticularis

Answer 36

no specific cord arrangement. Lots of capillaries. also secrete glucocorticoids and androgens.

Question 37

Adrenal gland vascularization

Answer 37

highly vascularized. suprarenal vein in the medulla. arterial (via medullary arteries) and venous (via cortical veins) blood

Question 38

Aldosterone

Answer 38

(mineralcorticoid) secreted by columnar or pyramidal cells in the ZG. stimulates sodium reabsorption in the distal convoluted tubule of the kidney. Induced by angiotensin II.

Question 39

cortisol (hydrocortisone)

Answer 39

(glucocorticoid) secreted from ZF. increases blood sugar levels through gluconeogenesis. Suppress the immune system, and aid in fat, protein and carbohydrate metabolism.

Question 40

DHEA (dihydroepiandrosterone)

Answer 40

a weak androgen secreted by the ZR. converted into testosterone elsewhere in the body.

Question 41

Endocrine control of the ZF/ZR

Answer 41

hypothalamus is stimulated, induces ATCH from the anterior pituitary to the adrenal gland where it secretes glucocorticoids. Will feedback to hypothalamus and anterior pituitary

Question 42

Endocrine control of ZG

Answer 42

Aldosterone is controlled by angiotensin II (lung) which is derived from angiotensin I (kidney) which signal initially comes from the liver.

Question 43

Adrenal medulla

Answer 43

specialized postganglionic sympathetic neurons. produce epinephrine and norepinephrine

Question 44

Type of cells in the renal medulla

Answer 44

polyhedral parenchymal cells

Question 45

what is produced by medulla

Answer 45

epi, norepi, ATP, chromagranins, catecholamine-binding proteins, dopamine-B-hydroxylase, and enkephalins

Question 46

Staining of epinephrine and norepinephrine

Answer 46

epi: dark and regular/organized.
Noreip: very dark and irregular/disorganized.

Question 47

Fetal adrenal glands

Answer 47

much larger than in adults compared to body weight. secrete androgens and estrogens

Question 48

Short term response to stress of adrenal gland

Answer 48

epi and norepi released, heartbeat and blood pressure increase. blood glucose levels rise. muscles become energized.

Question 49

Long term response to stress of adrenal gland

Answer 49

glucocorticoids - protein and fat metabolism instead of glucose breakdown, reduction in inflammation, immune cells suppressed.
Mineralocorticoids - sodium ions and water are reabsorbed by kidney. blood volume and pressure increase.

Question 50

Hypophysectomy and the appearance of the adrenal cortex

Answer 50

removal of the hypothalamus causes cortical atrophy.

Question 51

Stress and appearance of the adrenal cortex

Answer 51

stress induces the hypothalamus and ACTH which causes thickening of the cortex.