M33: Endocrine System - thyroid, parathyroid and adrenal

Question 1

general anatomy of thyroid

Answer 1

• left and right lateral lobes
• centre region = ISTHMUS
• 50% of population has superior extension of isthmus = PYRAMIDIAL LOBE
• made of follicles

Cells
- FOLLICULAR CELLS (most abundant)
- in lumen of follicle: THYROGLOBULINS
- Basement membrane
- PARAFOLLICULAR CELLS (C cells)

Question 2

calcitonin function

Answer 2

decreases blood-calcium levels
- inhibits osteoclasts in response to elevated blood Ca2+
- ↓ Ca2+ uptake from SI
- ↓ Ca2+ release from kidney

often taken as osteoporosis medication

Question 3

explain synthesis of thyroid hormones

Answer 3

1. IODIDE TRAPPING
   - in blood: iodine -> IODIDE ions
   - iodide taken into follicular cell lumen via secondary transport
   - into lumen
2. SYNTHESIS OF TGP (thyroglobulin proteins)
   - brought into lumen via secretatory vesicles & exocytosis
3. OXIDATION OF IODIDE
   - a protein oxidizes iodide into IODINE (I2)
4. IODINATION OF TYROSINE
   - tyrosine is an amino acid on TBP
   - iodine binding onto tyrosine forms the COLLOID
   - depending on how many iodides added (1 or 2), colloid called T1 or T2
5. COUPLING OF T1 and T2
   - T3 and T4 created by adding T1 and T2 together
6. PINOCYTOSIS AND DIGESTION OF COLLOID
   - colloid packaged and taken back into follicular cell (reverse exocytosis)
   - LYSOSOMES digest colloid to separate tyrosines with iodides from rest of AA chain - T3 and T4 liberated
   - T3/4 lipid soluble, can move through plasma mem without transport
7. SECRETION OF THYROID HORMONES
   - T3/4 need transport pr- in blood because not water soluble (THYROXIN BINDING-GLOBULIN)

Question 4

where are thyroglobulins synthesized in thyroid follicles?

Answer 4

• rough endoplasmic reticulum -> golgi complex -> secretatory vesicles -> follicle lumen via exocytosis

Question 5

What is used more, T3 or T4? Why?

Answer 5

T3, more potent for receptors
but T4 is made more and is often converted into T3

Question 5

colloid

Answer 5

TGP that has been iodinated

Question 5

are T3 and T4 lipid or water soluble?

Answer 5

lipid soluble

Question 5

largest endocrine gland

Answer 5

thyroid gland

Question 6

what cell secretes calcitonin

Answer 6

parafollicular cell (C cell)

Question 7

How long can thyroid store iodinated thyroglobulin?

Answer 7

2-4 months

Question 8

T4 and T3 functions

Answer 8

Increased basal metabolic rate
- increased pr- synthesis
- increased fat and glucose utilization
- increased Na+/K+ ATPase synthesis
- Calorigenic effect (increase body temp). Helps regulate body temp.
- increase normal growth and development (nervous and skeletal)

Question 9

T3 and T4 regulation

Answer 9

Negative feedback system
1. Low T3 and T4 blood levels OR low metabolic rate stimulates release of TRH from hypothalamus
2. TRH carried via hypophyseal portal veins to AP, stimulates release of TSH by thyrotrophs
3. TSH released into blood stimulates thyroid follicular cells
4. T3 and T4 released into blood
high levels of T3 and T4 inhibits TRH and TSH

Question 10

goiter

Answer 10

• caused by not enough iodine in diet
• not able to produce thyroid hormones, results in constant production of TSH
• gland enlarges in size

Question 11

4 sections of parathyroid gland

Answer 11

L and R superior parathyroid glands
L and R inferior parathyroid glands

Question 12

2 cells that make up parathyroid glands

Answer 12

1. CHIEF (PRINCIPLE) CELLS
   - produce parathyroid hormone (PTH)
2. OXYPHIL CELLS
   - don’t know what these do

Question 13

Function of parathyroid hormone (PTH)

Answer 13

Basically the opposite function of calcitonin

• raise blood calcium levels
  
  • ↑ osteoclast activity and #
  • ↑ reabsorption of Ca2+ and Mg2+ by kidney
  • inhibits reabsorption of phosphate
  • promotes formation of CALCITRIOL (active vit D) by kidney - increases apsoption of calcium, phosphate and magnesium by intestinal tract

Question 14

response when calcium levels are high

Answer 14

• parafollicular cells increase calcitonin secretion
• parathyroid gland decreases PTH secretion
• CALCITONIN inhibits osteoclasts, decreasing bone reabsorption and Ca2+ uptake in intestine and kidneys
• homeostasis restored

Question 15

response when calcium levels are low

Answer 15

• parafollicular cells decrease calcitonin secretion
• parathyroid gland chief cells increase PTH secretion
• increased bone reabsorption and increased uptake of Ca2+ in intestine and kidney
• homeostasis restored

Question 16

where are the adrenal glands located?

Answer 16

1 on top of each kidney, 2 total

Question 17

general structure of adrenal gland and hormones it releases

Answer 17

3 layers, superficial to deep

1. Capsule (CT)
2. ADRENAL CORTEX
   - ZONA GLOMERULOSA: mineralcorticoids (mainly aldosterone)
   - ZONA FASCICULATA: glucocorticoids (mainly cortisol)
   - ZONA RETICULARIS: androgens
3. ADRENAL MEDULLA
   - CHROMAFFIN CELLS: epinephrine and norepinephrine

each layer of cortex named after cell structure: glomerulosa for round cells, fasciculata for fascicles, reticularis for branching network

Question 18

Which hormone lowers blood calcium levels?

Answer 18

calcitonin

Question 19

Which hormone raises blood calcium levels?

Answer 19

parathyroid hormone (PTH)

Question 20

calcitriol function

Answer 20

• made by kidney, stimulated by PTH
• active form of vitamin D
• increases calcium, magnesium and phosphate reabsorption in small intestine

Question 21

What hormone does zona glomerulosa of adrenal gland release? function?

Answer 21

Mineralocorticoids
- major one is ALDOSTERONE
- Na+/K+ homeostasis (promotes Na+ absorption to increase BP)
- H+ excretion
- increase blood pressure/volume

Question 22

2 things that can trigger aldosterone release

Answer 22

in general, low blood volume/pressure

1. increased angiotensin II
2. increased K+ in extracellular fluid (not enough being excreted via urine)

Question 23

What hormone does the zona fasiculata in adrenal gland produce? function?

Answer 23

Gluicocorticoids
- CORTISOL (95%), CORTICOSTERONE, CORTISONE
- released in response to physical & emotional stress

Functions
- pr- breakdown
- glucose formation
- lipolysis
triggers use of fats and pr- as energy to keep blood glucose levels stable
- resistance to stress
- anti-inflammatory (e.g. inhibit WBC)
- depression of immune response

Question 24

regulation of glucocorticoids

Answer 24

Negative feedback

Stimulus: low blood glucose and other stressors
- hypothalamus releases corticotropin releasing hormone (CRH)
- AP releases ACTH
- adrenal cortex secretes glucocorticoids
too many inhibits CRH

Question 25

What hormones does the zona reticularis in adrenal gland produce? function?

Answer 25

Androgens
- produce secondary sex characteristics in males

E.g. Dehydroepiandrosterone (DHEA)
- insignifigant in males
- may contribute to sex drive in females
- excess DHEA in females may led to extra facial and body hair
- secretion stimulated by ACTH

Question 26

What hormone does the adrenal medulla produce? function?

Answer 26

• Chromaffin cells (ANS controlled) produce EPINEPHRINE (80%) and NOREPINEPRINE (20%)
• sympathetic pre-galnglionic neurons stimulate release
• hormones mimic effect of SNS and cause fight/flight response

Question 27

T4 is also called…

Answer 27

Thyroxine or teraiodothyronine

Question 28

T3 is also called…

Answer 28

Triiodothyronine

Question 29

name of centre band connecting R and L lobes of thyroid

Answer 29

isthmus

Question 30

the pr- iodine binds to in the thyroid follicle lumen is called __________ and it forms a structure called a _________

Answer 30

thyroglobulin
colloid

Question 31

name of pr- that transports T3 and T4 in blood

Answer 31

Thyroxin binding-globulin