5 - The endocrine system II: The thyroid and adrenal glands Flashcards
thyroid gland
• A large ductless gland in the neck that secretes hormones regulating growth and development through the rate of metabolism.
- produces hormones that regulate metabolism, body heat, and bone growth
thyroid hormones
T3 and T4
thyroid follicles
manufacture, store, and secrete thyroid hormones
follicle cavity
contains colloid
Colloid
contains thyroglobulin
C cells
produce calcitonin
C cells
produce calcitonin
thyroid hormone production
- Iodine move into the cell via transporter
- TPO reaction
- Oxidize Iodine
- incorporate iodine into thioglobulin
- results in MIT or DIT
- TPO causes more reactions with MIT and DIT
- T3 or T4 is formed
- Proteolysis and released into the cell
Most important enzyme = TPO - Thyroid Peroxidase
T4 is converted into T3 via - Deiodinase
Control of thyroid hormone production
low thyroid hormones (stimulus) –>
hypothalamus releases TRH (thyroid releasing hormone) through hypophyseal portal system into median eminence –>
anterior pituitary releases TSH into general circulation –>
thyroid gland produces T4 and T3 –>
target cells –>
blood levels controlled via negative feedback
functions of thyroid hormones
development + metabolism
function: development
- metamorphosis in frogs
– bone formation
– brain
function: metabolism
– increase metabolic rate
– increase ATP production (mitochondrial receptors)
– stimulate glycolysis
– increased heart rate and blood pressure
congenital hypothyroidism
condition present at birth that results in lack of thyroid hormones
- poor physical and mental development
- low metabolic rate + body temp
hypothyroidism in adults - myxoedema
- lethargy
- low body temperature
- muscle weakness
- subcutaneous swellings
- dry skin
- hair loss
- enlarged thyroid
- may be caused by low dietary iodine
Hyperthyroidism
- high metabolic rate
- high body temperature
- sweating
- high heart rate and high blood pressure
- central nervous system effects - excitability, restlessness, mood swings
Thyroid C cells (parafollicular cells) – release CALCITONIN
Calcitonin released in response to HIGH calcium levels in the blood
Inhibits osteoclast activity (bone breakdown),
Increases uptake of calcium into bone.
So DECREASES blood calcium level.
PTH and calcium homeostasis
- falling blood level
- stimulates Ca2+ uptake in kidneys
- stimulates Ca2+ release from bones
- increases Ca2+ uptake in intestines
- Blood Ca2+ level rises
- Homeostasis
Anatomy of parathyroid glands
- four small glands imbedded in posterior surface of thyroid
- chief or principal cells which secrete PTH
- oxyphil cell-function unknown
Adrenal gland anatomy
- Cortex (intermediate mesoderm) and Medulla (neural crest). Gland develops between dorsal mesentery and urogenital ridges
- Three main arteries supply each adrenal gland:
1) The superior suprarenal from the inferior phrenic artery
2) The middle suprarenal artery from the aorta
3) The inferior suprarenal artery from the renal artery
* 3. Blood supply: Cortex fed by three “zona” arteries which go to the medullary region. Medulla fed by ^ arteries and medullary arteriole.*
adrenal cortex
outer section of each adrenal gland; secretes cortisol, aldosterone, and sex hormones
Aldosterone
promotes the retention of Na+ by the kidneys.
- Na+ retention promotes water retention, which promotes a higher blood volume and pressure
Glucocorticoids
- stimulate glucose and glycogen synthesis
- stimulate release of fatty acids
- cause tissues to break down fatty acids and proteins
- immunosuppressive
- anti-inflammatory
Glucocorticoids
- stimulate glucose and glycogen synthesis
- stimulate release of fatty acids
- cause tissues to break down fatty acids and proteins
- immunosuppressive
- anti-inflammatory
adrenal medulla
secretes epinephrine and norepinephrine
adrenal medulla
secretes epinephrine and norepinephrine
general sympathetic activation
- breakdown glycogen to glucose
- changes in circulation
Ephinephrine and Norepinephrine
increase heart rate
adrenaline and noradrenaline
adrenaline and noradrenaline
adrenaline and noradrenaline
dilate air passages in lungs, increase respiratory rate
Stress and the adrenal gland
- short term response- epinephrine (adrenaline) and norepinephrine
- long term response- mineralocorticoids and glucocorticoids
