Introduction to the endocrine system Flashcards
The nervous system allows
Very rapid, focussed, precise communication between individual cells
The endocrine system allows
Very slow, sustained communication between groups of cells
Definition of a hormone
Chemical messengers carried in the blood from ductless glands
Act on cells possessing the appropriate hormone receptors
Each hormone may act on several target tissues
The pituitary gland
Situated below the brain, encased in skull
Sometimes called the master gland
The thyroid and parathyroid glands
Situated in the neck
Important in the control of metabolic rate and calcium homeostasis
The pancreas
Secretes digestive enzymes directly into the GI tract
Also secretes insulin in the blood
The adrenal glands
Lie on top of the kidneys
Divided into the outer cortex and inner medulla
Medulla is concerned with stress response
Cortex is concerned with stress, sodium and glucose homeostasis
The gonads (ovaries or testes)
Secrete the female and male reproductive hormones
Responsible for the development of secondary sexual characteristics and reproduction
Major types of receptors involved in hormone action
Steroid hormone receptors
G-protein coupled receptors
Tyrosine kinase receptors
Steroid hormone receptors
Hormone crosses the cell membrane and binds to a receptor which may be cytoplasmic or nuclear
Hormone receptor then binds to the hormone response element of DNA to influence gene transcription
G- protein coupled receptor
Hormone binds to the 7TM receptor to cause synthesis of a second messenger
Second messengers phosphorylate intracellular, regulatory protein to influence cellular activity
Tyrosine kinase receptor
Membrane bound enzyme which is a single strand of protein
Often two receptors must be present for hormone action
One hormone molecule binds to each receptor, the receptor then acts as an enzyme to phosphorylate tyrosine components of intracellular regulatory proteins
Two broad classes of hormones
Peptide hormones
Steroid hormones (and thyroid hormones)
Peptide hormones
Chains of amino acids, highly water soluble, susceptible to protease attack
Unable to cross the cell membrane without a carrier protein, act on membrane bound receptors
Rapid onset of action
Short plasma half life
Short duration of action
Steroid and thyroid hormones
Highly lipid soluble, poorly water soluble, must be transported in blood bound to plasma protein
Only unbound hormone biologically active
Able to cross the cell membrane and act on intracellular receptors
Slow onset of action
Long plasma half life
Ling duration of action
