Endocrine Glands Of the Neck--Chiaia

Question 1

Endocrine glands

Answer 1

Glands that facilitate intercellular communication between the cells of each organ and between different organs

Question 2

Why are endocrine glands necessary

Answer 2

They are necessary to maintain:

1) homeostasis of nutrients and vital substances in the cellular environment
2) coordination of growth/development
3) adaptation to environmental stresses

Question 3

What are the two communication systems to meet the needs of intercellular communication

Answer 3

• the nervous system (fast acting, specific)

- the endocrine system (slow acting, more pervasive less specific)

Question 4

Hormone

Answer 4

• organic, secreted in small amounts by endocrine cells
• exerts effect on distant tissues
• operates at very low concentrations

Question 5

Sites of action of hormones

Answer 5

1) circulating (distant)
2) local (paracrine, neighbor cells)
3) on self or same class of cells (autocrine)

Question 6

Functions of the thyroid gland

Answer 6

1) regulates tissue metabolism
2) regulates tissue growth (during development)
3) 2nd regulation of plasma Ca++

Question 7

Organization of thyroid gland

Answer 7

• two lateral lobes (right, left)
• lobes connected by narrow isthmus (over 2nd and 3rd tracheal rings)
• medial pyramidal lobe present during development

Question 8

Embryological development of thyroid

Answer 8

• foramen cecum of tongue
• lowered by thyroglossal duct (disappears)
• functional tissue is enclosed in dense irregular CT

Question 9

Follicles of the thyroid

Answer 9

• these are the structural and functional units
• single layer of simple cuboidal epithelial cells (follicular epithelial cells)
• cells make and release thyroid hormone into lumen where it is stored as a precursor (colloid)

Question 10

What envelopes the follicles of the thyroid lobules

Answer 10

A dense basket-like mesh work of fenestrated capillaries

-this is how the secretions end up in the bloodstream

Question 11

What are the two classes of cells that make up the thyroid follicles

Answer 11

1) follicular cells (simple cuboidal epithelial cells): these are the principal cells
2) parafollicular cells a.k.a “c-cells”

Question 12

Hyperactive follicular cells

Answer 12

• take cuboidal-columnar shape

- colloid is reduced and “scalloped border” forms

Question 13

Hypoactive follicular cells

Answer 13

• epithelial cells are inactive and have a squamous shape

- colloid is increased in follicle/lumen

Question 14

What is the major function of the thyroid gland

Answer 14

The synthesis and secretion of thyroid hormone

Question 15

What is thyroglobulin

Answer 15

It is a precursor glycoprotein a.k.a colloid from which thyroid hormone is made

Question 16

Synthesis of thyroid hormone

Answer 16

1) thyroglobulin made in the rER of follicular cells and processed in the golgi
2) tyrosine residues are added to thyroglobulin and compound is sent to apical surface of cell where it is exocytosed
3) thyroperoxidase is made by follicular cells and secreted into lumen close to microvilli
4) it catalyses the iodination of thyroglobulin in the lumen
5) T3 and T4 (thyroxine) are made

Question 17

Reuptake of iodinated thyroglobulin

Answer 17

• occurs at the apical surface to form colliod droplets (scalloped border)
• lysosomal digestion inside cell makes free T3 and T4
• **MIT and DIT serve as iodine carriers

Question 18

T3 and T4 out of cell

Answer 18

-they diffuse out of the basal surface and enter capillary circulation where they bind to plasma proteins on way to target tissue

Question 19

Anterior pituitary

Answer 19

• TSH released by anterior pit activates the thyroid gland
• binds to receptors on basal surface causing hypertrophy and hyperplasia of follicular cells, increased production and iodination of thyroglobulin, increased reuptake, increased secretion

Question 20

Thyroid hormone regulation

Answer 20

1) Low blood level of T3/T4 or low metabolic rate cases release of TRH from hypothalamus
2) TRH goes to ant pit to release TSH
3) TSH released into blood stimulate follicular cells
4) T3/T4 released into blood onto target tissue
5) T3/T4 increased levels feedback to hypothalamus

Question 21

Function of thyroid hormone

Answer 21

It is primarily concerned with cellular metabolism in all body tissues

1) metabolic effects
2) growth promoting effects

Question 22

Metabolic effects of thyroid hormone

Answer 22

1) calorigenisis: BMR; increased energy production/oxygen consumption
2) regulation of water and ion transport
3) regulation of protein, fat and carbs metabolism

Question 23

Growth promoting effects of thyroid hormone

Answer 23

1) acts synergistically with GH to promote normal skeletal development
2) controls moving and metamorphosis in lower vertebrates

Question 24

BMR

Answer 24

-BMR is measure of energy expenditure and cellular metabolism at rest (60%-70%)

1) BMR increases with exercise and fitness
2) decreases with dieting and age

Question 25

Hypothyroid

Answer 25

1) mentally and physically sluggish
2) low BMR
3) mental retardation
4) decreased glucose absorption in GI
5) weak heartbeat

Question 26

Hyperthyroid

Answer 26

1) restless, irritable, anxious
2) elevate BMR
3) mentally alert
4) increased glucose absorption in GI tract
5) tachycardia

Question 27

Cretinism

Answer 27

Hypothyroidism that occurs during development

Question 28

Myxedema

Answer 28

Hypothyroidism that occurs during adulthood

-lethargy along with mental deficiency

Question 29

Hashimoto’s dz

Answer 29

Hypothyroidism as a result of auto-immmune disorder, they kill follicular cells

Question 30

What is a goiter

Answer 30

Enlargement of the thyroid from hypertrophy and hyperplasia of follicular cells

Can result from:

1) iodine deficiency
2) graves dz

Question 31

Iodine deficiency

Answer 31

• less iodination so decreased T3/T4 output (hypothyroidism)
• less T3/T4 feedback so increased TRH and TSH resulting in compensatory follicular cell hypertrophy (parenchymatous goiter)

Question 32

Graves dz

Answer 32

• plasma igG “thyroid stimulating immunoglobulin” causes overstimulation of follicular cells (hyperthyroidism)
• goiter and protruded eyes (exopthalmos)

Question 33

Symptoms of graves dz

Answer 33

• anxiety irritability
• fine tremor of hands
• heat sensitivity
• weight loss
• goiter/exopthalamos
• rapid/irregular heartbeat
• increased T3/T4

Question 34

Parafollicular cells (c-cells)

Answer 34

Less numerous and are of neural crest origin

• they are larger and lighter stained and are usually between follicles but are insulated from the colloid
• secrete calcitonin (not under pit control)

Question 35

Calcitonin

Answer 35

• lowers plasma Ca++
  1) inhibits osteoclasts activity (decrease bone resorption and liberation of Ca++)
  2) promotes excretion of Ca++ from the kidney

Question 36

Parathyroid glands

Answer 36

Maintenance of appropriate plasma concentration of Ca++

• 4 masses behind the thyroid
• 2 superior(thyroid)/ 2 inferior (thymus)

Question 37

Parathyroid cells

Answer 37

• 2 types of cells
  1) chief cells (principal)
  2) oxyphil cells

Question 38

Chief cells

Answer 38

1) Secrete parathyroid hormone
- its half life is only 18 min
2) Light cell (inactive)
- Dark cell (active)
3) do not store a lot of PTH

Question 39

Function of PTH

Answer 39

-in response to low plasma Ca++, PTH released into circulation to increase Ca++

1) increases osteoclasts stimulating factor
2) promote Ca++ resorption by distal convoluted tubules of kidneys
3) promotes synthesis of 1,25 dihydroxycholecalciferol (vit D derivative) helps small intestine absorb calcium

***rate of PTH secretion directly controlled by plasma concentrations of Ca++

Question 40

Oxyphil cells

Answer 40

• larger than chief cells though less numerous
• acidophilic numerous mitochondria
• unknown function, don’t secrete hormones
• number of cells are increased in patients with chronic kidney dz