M33: Endocrine System - thyroid, parathyroid and adrenal Flashcards
general anatomy of thyroid
- 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)
calcitonin function
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
explain synthesis of thyroid hormones
- IODIDE TRAPPING
- in blood: iodine -> IODIDE ions
- iodide taken into follicular cell lumen via secondary transport
- into lumen - SYNTHESIS OF TGP (thyroglobulin proteins)
- brought into lumen via secretatory vesicles & exocytosis - OXIDATION OF IODIDE
- a protein oxidizes iodide into IODINE (I2) - 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 - COUPLING OF T1 and T2
- T3 and T4 created by adding T1 and T2 together - 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 - SECRETION OF THYROID HORMONES
- T3/4 need transport pr- in blood because not water soluble (THYROXIN BINDING-GLOBULIN)
where are thyroglobulins synthesized in thyroid follicles?
- rough endoplasmic reticulum -> golgi complex -> secretatory vesicles -> follicle lumen via exocytosis
What is used more, T3 or T4? Why?
T3, more potent for receptors
but T4 is made more and is often converted into T3
colloid
TGP that has been iodinated
are T3 and T4 lipid or water soluble?
lipid soluble
largest endocrine gland
thyroid gland
what cell secretes calcitonin
parafollicular cell (C cell)
How long can thyroid store iodinated thyroglobulin?
2-4 months
T4 and T3 functions
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)
T3 and T4 regulation
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
goiter
- caused by not enough iodine in diet
- not able to produce thyroid hormones, results in constant production of TSH
- gland enlarges in size
4 sections of parathyroid gland
L and R superior parathyroid glands
L and R inferior parathyroid glands
2 cells that make up parathyroid glands
- CHIEF (PRINCIPLE) CELLS
- produce parathyroid hormone (PTH) - OXYPHIL CELLS
- don’t know what these do
Function of parathyroid hormone (PTH)
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
response when calcium levels are high
- 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
response when calcium levels are low
- 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
where are the adrenal glands located?
1 on top of each kidney, 2 total
general structure of adrenal gland and hormones it releases
3 layers, superficial to deep
- Capsule (CT)
- ADRENAL CORTEX
- ZONA GLOMERULOSA: mineralcorticoids (mainly aldosterone)
- ZONA FASCICULATA: glucocorticoids (mainly cortisol)
- ZONA RETICULARIS: androgens - 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
Which hormone lowers blood calcium levels?
calcitonin
Which hormone raises blood calcium levels?
parathyroid hormone (PTH)
calcitriol function
- made by kidney, stimulated by PTH
- active form of vitamin D
- increases calcium, magnesium and phosphate reabsorption in small intestine
What hormone does zona glomerulosa of adrenal gland release? function?
Mineralocorticoids
- major one is ALDOSTERONE
- Na+/K+ homeostasis (promotes Na+ absorption to increase BP)
- H+ excretion
- increase blood pressure/volume
2 things that can trigger aldosterone release
in general, low blood volume/pressure
- increased angiotensin II
- increased K+ in extracellular fluid (not enough being excreted via urine)
What hormone does the zona fasiculata in adrenal gland produce? function?
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
regulation of glucocorticoids
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
What hormones does the zona reticularis in adrenal gland produce? function?
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
What hormone does the adrenal medulla produce? function?
- 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
T4 is also called…
Thyroxine or teraiodothyronine
T3 is also called…
Triiodothyronine
name of centre band connecting R and L lobes of thyroid
isthmus
the pr- iodine binds to in the thyroid follicle lumen is called __________ and it forms a structure called a _________
thyroglobulin
colloid
name of pr- that transports T3 and T4 in blood
Thyroxin binding-globulin
