Endocrine System (Troyer)

Question 1

Location of the Pituitary Gland?

Answer 1

IN the sphenoid bone of the skull

Question 2

Origin of the Pituitary Gland?

Answer 2

2 Parts

• ectoderm from roof of oral cavity that grows upward as Rathke’s pouch =becomes anterior pituitary
• neuroectoderm from diencephalon that grows downward = becomes posterior pituitary

Question 3

What is a portal system?

Answer 3

series of veins that are interposed between two sets of capillaries

Question 4

How does the hypothalamus “control” the adenohypophysis?

Answer 4

• Releasing and Inhibiting factors (hormones) are synthesized by special secretory neurons in hypothalamus
• Hormones are transported to and stored in axon terminals ending in the median eminence
• After receiving appropriate stimulus, hormones are discharged into capillaries and travel into hypophyseal portal system to capillaries in pars distalis

Question 5

What is the median eminence?

Answer 5

hypothalamic tissue extending into the pituitary (infundibular) stalk

Question 6

Pars distalis

Answer 6

parenchyma of cords or clusters of cells associated with sinusoids

part of adenohypophysis

Question 7

Where is the pars tuberalis?

Answer 7

forms collar around neural stalk of pituitary gland

Question 8

What is secreted by the pars intermedia?

Answer 8

• MSH - melanocyte stimulating hormone

- ACTH

Question 9

What does CRH release?

Answer 9

ACTH or corticotropin

Question 10

What does TRH release?

Answer 10

TSH or thyroid stimulating hormone

Question 11

What does GnRH release?

Answer 11

gonadotropins

Question 12

What does somatostatin do?

Answer 12

inhibits somatotropic hormone release

Question 13

Origin of the Thyroid?

Answer 13

outgrowth from the floor of the buccal cavity

Question 14

How many lobes are in the thymus?

Answer 14

two lobes that are usually connected by an isthmus

Question 15

T/F: Dogs have an isthmus

Answer 15

False

Question 16

Follicular Cells in the Thymus

Answer 16

• cuboidal epithelium
• microvilli on apical edge
• held together by tight junctions

Question 17

Parafollicular Cells in the Thymus

Answer 17

• found in isolated clusters beside the follicle
• larger, paler cells than follicular cells
• produce calcitonin which lowers serum calcium levels

Question 18

What does calcitonin do?

Answer 18

lowers serum calcium levels

Question 19

Function of the Thymus?

Answer 19

• endocrine

- ‘storage’ phases of production (unusual among endocrine glands)

Question 20

Follicular Cells and storage phases

Answer 20

synthesize and secrete thyroglobulin

Question 21

Where is thyroglobulin stored?

Answer 21

extracellularly in lumen of follicle, where it is partially iodinated

Question 22

Follicular Cells and endocrine phase

Answer 22

• stored thyroglobulin = taken up by follicular cells
• broken down by lysosomal enzymes to active thyroid hormone
• TH then released into blood

Question 23

What is T4?

Answer 23

• thyroxine or tetraiodothyronine
• prohormone = one iodine is removed to make T3
• most abundant form

Question 24

What is T3?

Answer 24

• triiodothyronine
• active hormone
• less abundant than T4

Question 25

Where can T4 become T3?

Answer 25

• liver, kidney, and muscles

- deiodinase removes one iodine

Question 26

What does T3 do?

Answer 26

• increases metabolic rate of target cells

- increases numer of mitochondria = hence mitochondrial respiration

Question 27

Colloid

Answer 27

• made up of thyroglobulin, a glycoprotein
• tyrosine amino acyl residues of thyroglobulin are iodinated
• represents storage phase of secretion

Question 28

Location of Parathyroid Glands

Answer 28

In or around thyroid gland

external parathyroids = vary from cranial to thyroids to level of thoracic inlet

internal parathyroids = embedded in, on, or near thyroid

Question 29

Structure of Parathyroid Glands

Answer 29

• capsule of internal parathyroids is areolar CT of thyroid

- parenchyma: cords, clusters w/ numerous capillaries

Question 30

What is the predominant cell type of the parathyroid glands? Are they subdivided in any way?

Answer 30

Chief cells

Yes = dark and light chief cells

Dark cells produce parathyroid hormone

Question 31

In what species are oxyphil cells found? What is the function?

Answer 31

Found in humans, ox, and horses

Exact function unknown

Question 32

What is the function of parathyroid hormone (PTH)? How is this function carried out?

Answer 32

raise blood calcium levels

increases osteoclast activity to tear down bone to release calcium

Question 33

Origin and location of adrenal gland

Answer 33

cortex = from mesoderm
medulla = from neural crest

Location: cranial pole of kidney

Question 34

Structure of the Adrenal Glands

Answer 34

capsule around adrenal sends trabeculae into the parenchyma

also fine reticular fibers within the parenchyma

Question 35

Three regions of adrenal gland cortex

Answer 35

• zona glomerulosa
• zona fasciculata
• zona reticularis

Question 36

What is produced in the zona glomerulosa of the adrenal cortex?
What’s the function?
How is it stimulated?

Answer 36

Mineralocorticoids

act on kidney to retain Na+ and water

Mostly stimulated by angiotensin

Question 37

What is produced in the zona fasciculata of the adrenal cortex?
How is it stimulated?

Answer 37

glucocorticoids

stimulated by ACTH

Question 38

What is produced in the zona reticularis?

Answer 38

weak androgens

Question 39

Secretions of the Pineal Gland?

Answer 39

• melatonin

- serotonin