Introduction to the endocrine system Flashcards
What is the endocrine system?
- a communication system based on chemical messengers called hormones
How are hormones distributed?
- hormones are distributed in the blood from their site of production to their site of action - endocrine mode of action
What are the main components of the endocrine system?
- endocrine glands ( secrete product directly into blood)
- hormones
- target tissue/cells
- hormone receptor ( on tissue or cells)
- 2nd messengers
What are neuroendocrine cells & give an example of one?
- cells that receive a neural input ( eg NT’s released by nerve cells or neurosecretory cells) and after input they release hormones into the blood
- interaction between the NS and the endocrine system
EXAMPLE - chromaffin cells in adrenal medulla
Compare the main differences between the NS and the ES
- nervous system - wired system with structural arrangement between neurons and target cells, NT’s released into cleft, rapid response
- endocrine system- wireless system, endocrine glands are widely dispersed and not structurally related to one another, hormones released into blood, slow response
What are the 6 major functions of the endocrine system?
- regulate organic metabolism eg glucagon, insulin
- regulate inorganic metabolism eg Ca2+, Na+
- regulate water and electrolyte balance
- promote linear growth and development eg growth hormone
- control sexual development eg estrogen, testosterone, FSH & LH
- adaptive response to stress eg adrenaline, cortisol
What is a simplified function of the endocrine system?
to maintain homeostasis - maintain physiological variables eg PH and temp within narrow range that is optimal for body function
What are the (8) major endocrine glands in the body?
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid gland
- Adrenal gland
- Pancreas
- Ovaries
- Testes
What hormones do the (8) major endocrine glands release?
- Hypothalamus - eg GHRH, TRH, GnRH
- Pituitary gland - eg oxytocin, vasopressin, growth hormone, FSH & LH
- thyroid gland - eg thyroid hormones T3 & T4
- Parathyroid hormones - eg parathyroid hormone
- Adrenal gland - eg cortisol, aldosterone
- Pancreas - eg insulin & Glucagon
- Testes - testosterone
- Ovaries - Estrogen & progesterone
What is the difference between endocrine and exocrine glands?
- Exocrine - maintain contact with body surface through a duct eg sweat gland & mammary glands
- Endocrine - do not have contact with body surface, they have no ducts.. they secrete hormones directly into blood
What are the 3 main classes of hormones?
- Peptide hormones
- Amines
- Steroid hormones
What are peptide hormones?
- hormones made of many amino acids linked together by peptide bonds
they are water soluble so they bind to receptors on outer surface - synthesized in rough ER and stored in secretory vesicles as they go through golgi apparatus
- examples : insulin and glucagon of the pancreas
What are amine hormones?
- hormones derived from amino acid tyrosine
- catecholamines - adrenaline and noradrenaline
- thyroid hormones - T4 & T3 ( note the number indicates the number of iodine’s)
What are steroid hormones?
- hormones that are derived from cholesterol
- corticosteroids ( includes glucocorticoids - cortisol & mineralcorticoids - aldosterone )
- sex steroids ( progesterone, androgens and estrogens)
What are androgens?
- natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics
What are the hypothalamus and the pituitary gland?
- 2 endocrine glands that control the production of and release of hormones of the other endocrine glands in the body
- each lobe of the pituitary gland ( anterior and posterior) secrete different hormones in response to signals from the hypothalamus
What stimuli can decrease or increase the production and release of a hormone?
- ions
- nutrients
- PH and temp
- neuron
- biological rhythms
What is the difference between positive and negative feedback regulation of hormone production?
- positive feedback increases the stimulus and increases productivity eg Ferguson reflex ( oxytocin causing uterine contractions in childbirth
- negative feedback reduces the stimulus and decreases activity eg testosterone release, FSH and inhibin
How many messengers are there in the endocrine system?
- 1st messengers - hormones
- signal is relayed to cells via hormone receptors eg G protein coupled receptor
- 2nd messengers - cAMP/cGMP or Ca2+/calmodulin, PIP3 and DAG
Compare up vs down regulation of receptor
- down regulation - high hormone conc - reduce the no of receptors to prevent overstimulation ie more degradation and lower gene expression
- up regulation - low hormone conc - increase no of receptors ie higher gene expression of receptors and more receptor synthesis
what is the sensitivity of a hormone usually defined as?
the concentration needed to produce a half maximal response
in this curve, B is normal curve response, but is A and C increased or decreased sensitivity?
- B = normal curve
- A = increased sensitivity - ie less hormone is required to produce a half maximal response
- C= decreased sensitivity - ie more hormone is requird to produce a half maximal response
