Endocrine II

Question 1

How does the thyroid gland develop?

Answer 1

Develops as an evagination from the wall of the pharynx

Question 2

What is the thyroid gland?

Answer 2

Lies adjacent to trachea, posterior to larynx

Consists of two lobes connected by an isthmus and surrounded by a capsule (double layers of CT).

Question 3

What two cell types are found in the thyroid

Answer 3

Contains two types of hormone-secreting cells:

Follicle Cells = secrete thyroid hormones (T3 and T4)

Parafollicular Cells (C-cells) = secrete calcitonin

Question 4

basic structural unit of the thyroid

Answer 4

follicle - lined by simple cuboidal epithelium of follicle cells.

Question 5

What is colloid?

Answer 5

Colloid = acidophilic glycoprotein filling lumen of follicle, composed of thyroglobulin (thyroid hormone precursor) which undergoes extracellular iodination; serves as storage reservoir for thyroid hormones

Question 6

Outline the 7 steps of synthesizing colloid and thyroid hormones.

Answer 6

1. Synthesis of thyroglobulin
2. Release into follicle lumen
3. Iodination
4. Storage as colloid
5. Endocytosis of colloid in response to secretory stimulus (TSH from adenohypophysis)
6. Hydrolysis of thyroglobulin (produces T3 and T4)
7. Release of thyroid hormones into capillaries surrounding follicles

Question 7

What are follicle cells

Answer 7

low cuboidal when hypoactive; high cuboidal/low columnar when the gland is active; Hyperactive thyroid has little or no colloid in lumen of follicles. Follicle cells contain large nuclei, basophilic cytoplasm with fine granules, and numerous mitochondria, RER and lysosomes

Question 8

What are C cells

Answer 8

= lie adjacent to follicles but within basal lamina; larger than follicle cells with eccentrically placed nuclei, pale-staining cytoplasm, contain numerous membrane-bound granules (calcitonin)

Question 9

T3 and T4

Answer 9

increase metabolic rate and help maintain normal function and growth in tissues

Question 10

Calcitonin

Answer 10

decreases blood calcium by inhibiting bone resorption

Question 11

Describe the location and general anatomy of the parathyroid glands

Answer 11

Lie on border of thyroid, usually 4 glands in humans (range is 2-6); derived from endoderm of pharyngeal pouches.

Covered with a thin capsule and also enclosed in fascia of thyroid; septa extend inward from capsule, divide gland incompletely into lobules; septa carry blood vessels, lymphatics, nerves

Question 12

What cell types are in the parathyroid and what do they do?

Answer 12

Chief Cells = small, round, pale-staining cells with a spherical nucleus and indistinct cell borders. Secrete Parathyroid hormone

Oxyphil Cells = less common, larger with acidophilic cytoplasm, smaller darker nucleus, numerous mitochondria; increase in number after puberty. May represent non-secretory chief cells, but precise function is unknown.

Question 13

What is parathyroid hormone?

Answer 13

antagonistic to calcitonin, promotes bone resorption, increases blood calcium levels

Question 14

Describe the structure and location of the adrenal glands. Also, what hormones are secreted.

Answer 14

Paired glands located at cranial pole of each kidney; composed of 2 histological regions:

Cortex = outer region, secretory cells derived from mesoderm, produce corticosteroids

Medulla = inner region, secretory cells derived from neural crest tissue, produce catecholamines (epinephrine, norepinephrine)

Question 15

What are the three layers of the adrenal cortex?

Answer 15

zona glomerulosa
zona fasiculata
zona reticularis

Question 16

Describe the zona glomerulosa

Answer 16

Zona glomerulosa = narrow zone immediately beneath capsule (~15% of cortex), cells arranged into rounded clumps

Consists of pyrimidal or columnar cells with dark-staining spherical nuclei, acidophilic cytoplasm with some basophilic material, cytoplasm also contains lipid droplets

Produces mineralocorticoids (aldosterone and deoxycorticosterone) which control water and salt balance; aldosterone specifically increases kidney tubule resorption of Na+

Question 17

Describe the zona fasiculata

Answer 17

Zona fasiculata = thickest layer (~78% of cortex)

Consists of irregular cuboidal/polyhedral cells arranged in long radial cords; bordered by fenestrated capillaries.

Cells contain vesicular nuclei and basophilic cytoplasm with numerous lipid droplets (droplets larger than in zona glomerulosa)

Produces glucocorticoids (cortisol, corticosterone) which regulate carbohydrate, lipid and protein metabolism; part of stress response

Question 18

Describe the zona reticularis

Answer 18

Zona reticularis = composes ~7% of cortex volume

Cells form anastomosing network, separated by fenestrated capillaries

Cells in this region are smaller, the cytoplasm contains fewer lipid droplets and the nuclei are deeper-stained

Produces some glucocorticoids and very small amounts of sex hormones (dihydroepiandrosterone; physiologically relevant?)

Throughout the cortex, lipid droplets are associated with the synthesis of steroid hormones

Question 19

What cell type is found in the adrenal medulla?

Answer 19

chromaffin cells

Question 20

What is the function of the adrenal medulla?

Answer 20

Consists of anastomosing cords of cells known as chromaffin cells (due to specific staining of secretory granules with Chromium salts)

Secrete epinephrine (adrenaline), norepinephrine

Secretory cells of medulla innervated by sympathetic preganglionic fibers, so they are functionally equivalent to sympathetic ganglion cells.

Stimulation causes release of hormone by exocytosis. (Norepinephrine is the neurotransmitter of sympathetic postganglionic fibers).

Question 21

Where is the pineal body

Answer 21

Cone-shaped body attached by a stalk to the roof of the 3rd ventricle of the brain

Question 22

What does the pineal body do? What structure encapsulates it?

Answer 22

Produces melatonin which exerts a suppressive effect on gonadal function and regulates circadian and circannual rhythms, among other actions

Pia mater forms capsule around pineal body

Question 23

What are the cell types of the pineal body?

Answer 23

pinealocytes
glial cells
(also extracellular concretins)

Question 24

Pinealocytes

Answer 24

epithelial secretory cells (melatonin), irregularly shaped with branching processes; pale-staining cells with a large nucleus

Question 25

Glial cells of the pineal gland

Answer 25

= serve as supporting network; fewer in number, possess elongated deeply stained nucleus

Question 26

Extracellular concretions of the pineal gland

Answer 26

= lamellated bodies of calcified organic matrix; occur mainly in capsule and septa; unknown function, but increase in number with age