Topic 18 -Endocrine system Flashcards
overview
- ductless glands and endocrine tissues within other organs
- secrete chemicals = hormones into blood
- transported via circulation and act on target cells
- target cell = cell with receptor specific for that hormone
hormone classes
steroids
hormones derived from amino acids
peptides and protein hormones
steroids
synthesized from cholesterol (lipid soluble)
- e.g. testosterone, estrogen, vitamin D
hormones derived from amino acids
e. g. derived from tyrosine
a) thyroxine /T4
- a thyroid hormone
- lipid soluble
- controls cellular metabolism, growth, development
b) epinephrine + norepinephrine (catecholamines)
- adrenal medulla hormones
- water soluble
- short term stress - part of fight-or-flight response
peptides and proteins hormones
- chains of amino acids held together by peptide bonds
- water soluble
- e.g. oxytocin, antidiuretic hormone (ADH), growth hormone (GH), insulin
pituitary gland
- suspended from hypothalamus
- lies in sella turcica of sphenoid bone
2 lobes: Anterior pituitary and posterior pituitary
anterior pituitary
epithelial tissue
- anterior pituitary hormone secretion regulated by hormones released from the hypothalamus
has metabolism and reproductive hormones
anterior pituitary metabolism hormones
i) Growth Hormone – promotes growth + metabolism
ii) Thyroid Stimulating Hormone (TSH)
- stimulates activity of thyroid gland
iii) Adrenocorticotropic Hormone (ACTH)
- stimulates secretion of adrenal steroids (adrenal cortex)
anterior pituitary reproductive hormones
i) Luteinizing Hormone (LH)
ii) Follicle Stimulating Hormone (FSH)
iii) Prolactin (PRL)
- stimulates milk formation
Posterior pituitary
- nervous tissue
- extension of hypothalamus
- hormones produced in hypothalamus, stored and secreted from post pituitary:
i) Oxytocin - stimulates uterine contraction and milk ejection
ii) Antidiuretic Hormone (ADH) - water reabsorption in the kidney
Thyroid Gland
- on anterior surface of superior part of trachea
- butterfly shaped
- thyroid histology:
a) follicles - walls = epithelial (follicular) cells
- produce mainly T4
- activated in other tissues to T3
b) parafollicular cells - between follicles - secrete calcitonin
- increases Ca++ uptake into bone (bone formation), which lowers blood Ca++
Parathyroid Glands
4 (usually) glands embedded in posterior thyroid
- secrete parathyroid hormone (PTH)
- increases blood Ca++ by:
a) ↑ Ca++ release from bone (= bone resorption) - activates osteoclasts
b) ↓ Ca++ loss in urine (kidney)
c) ↑ vitamin D activation (kidney) - vitamin D then ⇑ Ca++ absorption at the small intestine
Adrenal Glands
where are they and what are the parts
superior surface of each kidney
has two parts: adrenal cortex (outer) and adrenal medulla
adrenal cortex
what are the three zones
- epithelial tissue - secretes steroids only
- 3 layers (1 hormone type secreted by each):
i) zona glomerulosa - secretes mineralocorticoids (mainly aldosterone) - salt balance
ii) zona fasciculata
- secretes glucocorticoids (mainly cortisol)
- long-term stress hormone - carbohydrate metabolism
iii) zona reticularis
- secretes androgens (a small amount of testosterone)
- women - sex drive
- some converted in other tissues (e.g. fat) to estrogens
Adrenal medulla
- nervous tissue - 2 hormones: i) epinephrine (80%) ii) norepinephrine (20%)
