endocrine system Flashcards
how does cell communication occur
neuronal, autocrine, endocrine and paracrine
what are the actions of the endocrine system
- control metabolic rate
- regulation of blood ions and nutrients (Na, K, glucos-insulin/glucagon)
- growth and development
- emergencies (adrenaline, cortisol)
what are the major endocrine glands
pituitary glands, thyroid glands, adrenal glands
what does the pituitary glands do
- growth hormone stimulates growth
- tropic hormones control other endocrine glands
what does the thyroid gland do
hormones regulate metabolic rate & calcium
what does the adrenal gland do
stress hormones (cortisol regulates plasma glucose adrenaline heart rate)
what other organs have endocrine tissue
the gastrointestinal tract, kidneys, heart, adipose tissue (leptin) to suppress appetite
what are the three major classes of hormones
peptide hormones, steroid hormones, amino acid derivatives
what are peptide hormones
insulin, glucagon
what are steroid hormones
testosterone, oestradiol
what are amino acid derivatives
thyroid hormone, adrenaline
what are the 4 main hormone receptors
- g-protein-linked (beta-adrenoceptors)
- ion channel (nicotinic receptors Ach)
- steroid hormone (testosterone receptor)
- tyrosine kinase (insulin receptor)
what are hormones acting via g-protein linked receptors
largest class of receptors for many neurotransmitters/hormones.
all have similar serpentine structure (7 transmembrane spanning regions, but with very different amino acid sequences.
target for many drugs (eg. beta-blockers).
located in cell membrane
coupled to enzymes or ion channels via guanine nucleotide binding proteins (G-proteins).
what are the different G-proteins
Gs – activate adenylate cyclase (eg. β-adrenoceptors)
Gi – inhibit adenylate cyclase (some muscarinic receptors)
Gq – activates to phospholipase C (some muscarinic receptors)
what are adrenoceptors
These receptors (α & β) mediate the effects of adrenaline and noradrenaline
alpha-1, beta-1, beta-2, etc
Subtypes mediate different responses
e.g. β1 in heart; β-2 in lung bronchioles
Many drugs act at these receptors
what are nuclear receptors for steroids and thyroid
Receptors located in the cytosol (steroids) or nucleus (thyroid hormones) rather than on the cell membrane
ligand must first cross the cell membrane, then translocate to the nucleus
ligand binding leads to alteration in gene transcription and protein synthesis within cell
what are steroid hormone receptors
Group of hormones all synthesized from the lipid cholesterol
Includes male and female sex hormones
Small differences in structure result in very different effects
e.g. cortisol, estradiol, testosterone
what are tyrosine kinase receptors
Hormones that act through these receptors are peptide or protein hormones
Examples:
Insulin
Growth factors
Nerve growth factor (NGF)
what are ion channel receptors
Responses very fast and usually these are receptors for neurotransmitters rather than hormones.
The receptor structure itself is an ion channels
Number of transmembrane protein subunits
Form a cluster around a central pore
what is the regulation of hormone release
negative feedback by hormone or negative feedback by the substance being controlled
control of release by tropic hormones or control of release by the nervous system
what is the regulation of hormone concentration in the blood
Hormones bound to plasma proteins
- steroids - thyroid hormone
Free in plasma
most other hormones
the unbound hormone exerts its actions on cells
Excretion
Water-soluble can be excreted by the kidney
Others are broken down in the liver
what is the regulation of target cell sensitivity
Activation of the target cell depends on:
- Density of receptors
- Coupling of receptors to second messenger pathways
what are the types of coupling receptors to second messenger pathways
up-regulation: - gain receptors in response to hormone
down-regulation: - lose receptors in response to the hormone
what is permissiveness
can only act with another hormone present
synergism
hormones act together
antagonism
opposing action of another hormone
