Endocrine Glands and Hormones Flashcards
History
in 1889, Prof. Brown-Séquard, aged 72:
Self-administration – 5 injections of dog testicle extract … 5 more from guinea pig testicle extract ….. “rejuvenated … increased his physical strength, improved his intellectual capacity, and increased his sexual potency”
Brown-Séquard. Lancet 1889
Glands
are epithelial tissue derivatives specialised for secreting
Secretion
is the biochemical release from a particular type of cell upon stimulation
Endocrine
endo’- internal crine’ - secretion…. Secretions enter bloodstream … ductless gland
compare with Exocrine (gland with ducts that channels its secretion)
Hormones definition
‘Chemical messengers’ secreted into blood by endocrine glands in response to an appropriate signal, and exerting their effects on target cells that have receptors that bind with the hormone.
classification of Hormones
- Based on their solubility
1. Hydrophilic or Water soluble
Peptides (e.g insulin) and catecholamines (adrenaline & noradrenaline)
2. Lipophilic or Lipid soluble
Steroids (e.g cortisol) and thyroid hormone - Based on their structure
1. Peptides – chain of specific amino acids
2. Amines - derivatives of amino acids, tryptophan or tyrosine (indoleamines, catecholamines, thyroid hormones)
3. Steroids – cholesterol derived lipids
PEPTIDES
Produced by normal protein synthesis machinery
Travel in blood in solution
Cannot enter cells
(lipid bilayer cell membrane)
Bind to cell surface receptor
Trigger event on inside surface of membrane
(second messenger system)
Fast acting
STEROIDS
Produced by modification of cholesterol molecule by enzymes
Travel in blood bound to plasma proteins
Enter cells easily
Intracellular receptor
Act on DNA to alter cell function
Slow acting (transcription delay)
Contraceptive pills and patches
contain oestrogen and progesterone which are steroids and can be absorbed through the skin and get into systemic circulation without being broken down in the GI tract
Thyroid hormones
are amines and are not broken down by enzymes in the GI tract and hence can be taken as tablets
Insulin
is a peptide hormone and should be administered through intravenous, subcutaneous or intramuscular routes
Human Endocrine Organs
Overall regulatory role of endocrine system
Metabolism, water and electrolyte balance
Stress response
Growth & development
Reproduction
Red cell production
Coordination of circulation
Coordination of digestion
Pituitary
Pea Size (1 cm2)
Weight 1g
Two lobes (anterior and posterior)
Connects to the hypothalamus via the pituitary stalk
all the HP- different axis
THE HYPOTHALAMUS, ANTEROR/ POSTEROIR PITUITORY GLANDS
Testes
Ovaries
function of testes
function of ovaries
HPG Axis – Regulation of Testicular Function
negative feedback
HPT Axis
Hypothalamus- Pituitary- Thyroid Gland
Thyroid Gland
Located in the neck area, over the trachea, and just below the larynx.
It is made of two lobes of endocrine tissue joined by an isthmus, a narrow part of the gland.
The hormone-secreting cells are arranged in hollow spheres called follicles.
Thyroid Hormones
Two hormones - Thyroxine (T4) and Triiodothyronine (T3)
The main ingredients are amino acid tyrosine and iodine (should come from diet)
Functions:
Increasing metabolic rate and heat production (calorigenic effect)
Sympathomimetic effect (permissive action)
Effect on cardiovascular system
Effect on growth and nervous system
Regulation of Thyroid Hormones
Parathyroid Hormone (PTH)
Calcium metabolism
Raises free plasma Ca2+
mobilises bone store
reduces urine loss
increases gut absorption
Adrenal Glands
(Suprarenal Glands)
- kidney secrets a hormone and hence is an endocrine gland.
- here are two adrenal glands and they are located one above each kidney and embedded in a capsule of fat.
Hormones Secreted By Adrenal Glands
The adrenal gland consists of two functionally different regions;
Adrenal Cortex
steroid hormones (cortisol, aldosterone and androgens)
Adrenal Medulla
catecholamines (adrenaline and noradrenaline)
adrenal cortex and medulla summaries
HPA Axis – Controls only Cortisol production from Adrenal Cortex
Integrated Stress Response
