Endocrine System Flashcards
exocrine glands
secrete products into ducts which empty into body cavities or surfaces
ex. sweat glands, sebaceous (oil) glands, goblet cells (secrete mucous)
endocrine glands
secrete hormones into interstitial space/bloodstream
- pituitary, thyroid, parathyroid, adrenal, pineal
other organs secrete hormones as a 2nd function:
- hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, placenta
general functions of hormones
- help regulate: fluid composition, metabolism, blood glucose, contraction or cardiac and smooth muscles, some immune functions
- growth and dev’t
- regulate reproductive systems
- circadian rhythms (sleep/wake cycle)
hormone receptors
- hormones are produced and released from endocrine cells
- they then bind to a specific receptor and the response to binding is different in different tissues
- this is handy because one hormone can create a whole body response with actions specific to the affected tissues
number of hormone receptors
the number of hormone receptors affects response and sensitivity to a hormone
down-regulation
when excess hormone is present, it can result in a decrease in the number of receptors causing a decrease in sensitivity to the hormone
up-regulation
deficiency in a hormone may cause an increase in the number of receptors, increasing sensitivity of that hormone
circulating hormones
most hormones are this type
- are released into blood supply and travel to target tissues by way of the circulatory system
local hormones
- when released, move through interstitial spaces, not blood supply
2 types: - paracrines
- autocrines
paracrine hormones
act on neighbouring cells, typically involving 2 different cell types
ex. endothelial cells release nitric oxide which acts on nearby smooth muscle cells in blood vessels causing vasodilation
autocrine hormones
act on the same cell that secretes them, can target itself, but often targets neighbouring cells that are the same as it
ex. WBCs and neighbouring WBCs are stimulated to replicate and have better immune function
mechanisms of hormone action
hormones bind to receptors on the cell surface (water soluble) or inside target cell (lipid soluble)
water soluble hormones
travel through blood and bind to receptors on the plasma membrane (doesn’t enter the cell)
- binding to the receptor is linked to a cascade of events happening inside the cell
lipid soluble hormones
enter the cell by travelling through plasma membrane and receptors are usually linked to something inside the cell such as our DNA or synthesizing proteins
possible hormone responses
each target cell responds to a hormone differently:
synthesis of new molecules
changing permeability of the cell membrane
transport of a substance into or out of the cell
altering the rate of metabolic actions
causing contraction of smooth or cardiac muscle
hormone regulation
- they are secreted in short bursts as needed
- secretion is regulated by:
signals from the nervous system
chemical changes in the blood
other hormones - often via negative, sometimes positive feedback
negative feedback in female reproductive system example
high levels of progesterone inhibit release of GnRH and LF which result in no more estrogen being secreted
positive feedback in female reproductive system example
high estrogen levels before ovulation stimulates release of GnRH (hypothalamus) which stimulates LH release (anterior pituitary) which builds corpus luteum which secretes more estrogen
the hypothalamus and pituitary gland
- neuroendocrine connections
- mastergland: release hormones that control the release of other hormones
hypothalamus
superior to pituitary, connected via nervous tissue connective stalk called the infundibulum
- receives input from cortex, hypothalamus and internal organs, and then uses the autonomic nervous system to adjust things like thirst, hunger, sex behaviour, flight or fight
- makes 9 hormones, controls pituitary gland with 7 releasing and inhibiting hormones
pituitary
hypophysis is another word for pituitary
- secretes 7 hormones and stores 2 for the hypothalamus
- sits in a saddle shaped indent in the sphenoid bone
anterior lobe of pituitary gland
aka adenohypophysis
- makes up 75% of the pituitary weight
- secretes 7 hormones, controlled by hypothalamus
posterior lobe of pituitary gland
aka neurophyophysis
- make up of neural tissue and releases 2 hormones made by the hypothalamus
neurosecretory cells
in the hypothalamus, make hormones and package into vesicles that travel down axons and the hormones are released into primary plexus of hypophyseal portal vein system
hypophyseal portal vein system
- primary plexus located at hypothalmic neurosecretory cells
- secondary plexus is located on top of anterior pituitary
- since the connection from the pituitary to the hypothalamus is so close, it keeps the hormones concentrated rather than dilute so we don’t need a lot to act on the anterior pituitary
superior hypophyseal arteries
carry regular arterial blood to hypothalamus, pick up hormones to carry to posterior pituitary
path of hypophyseal portal vein system
superior hypophyseal arteries
primary plexus of hypophyseal portal system (via infundibulum)
hypophyseal portal veins
secondar plexus of hypophyseal portal system (anterior pituitary)
path of blood flow to posterior pituitary
no portal network, has capillary network (plexus) instead
- supplied by inferior hypophyseal artery
what mechanisms control anterior pituitary secretions?
- neurosecretory cells
- negative feedback loops
neurosecretory cells and control of anterior pituitary secretions
hormones that come from the hypothalamus:
5 releasing hormones stimulate secretions
2 inhibiting hormones suppress secretions
negative feedback loops and control of anterior pituitary secretions
- either block releasing hormones or stimulate inhibiting hormones to be released
- when blood concentrations of a target gland’s hormone rise, the anterior pituitary secretion decreases
trophic cells
make hormones that regulate hormones
cells of the anterior pituitary
make 7 hormones for the AP
- somatotrophs
- thyrotrophs
- gonadotrophs
- lactotrophs
- corticotrophs
somatotrophs
secrete human growth hormone (hGH)
thyrotrophs
secrete thyroid stimulating hormone (TSH)
gonadotrophs
secrete follicle stimulating hormone and luteinizing hormone (FSH and LH)
lactotrophs
secrete prolactin, a hormone that is released to create milk supply after having a baby
corticotrophs
secrete adrenocorticotropic hormone (ACTH: targets adrenal cortex) and melanocyte-stimulating hormone (MSH: unsure of action in humans)
human growth hormone (hGH)
- released every few hours by somatotrophs, a lot at night while we’re sleeping
- most plentiful hormone in AP
- increases synthesis of insulin-like growth factor (IGF)
insulin-like growth factor (IGF)
a hormone that acts locally or targets other tissues via the blood stream
- common target cells are liver, skeletal muscle, cartilage and bone
functions: increases cell growth and repair, stimulates lipolysis (breakdown of fats), and slows glycolysis uptake into cells and its use in ATP production when blood glucose levels drop
