W6: the endocrine system Flashcards
what is homeostasis
maintains stable equilibrium of the internal environment of body
e.g. body temp, blood pressure and glucose
homeostasis maintained thru nervous and autonomic regulation:
ANS= causes rapid changed
endocrine system= unusually slower adjustments
definition of hormones and endocrine glands
hormones: chemical messengers secreted into blood by endocrine glands in response to appropriate signals and exert their effects on target cells that have receptors that bind with the hormone
endocrine glands: epithelial tissue derivatives specialised for secreting, ductless glands which secret hormones in blood
overall regulatory role of endocrine system
metabolism, water and electrolyte balance
stress response
growth and development
reproduction
red cell production
coordination of circulation and digestion
what are the primary endocrine organs
hypothalamus
pituitary gland - anterior and posterior
pineal gland
parathyroid gland (behind thyroid)
thyroid gland
thymus gland
adrenal gland
pancreas
ovaries
testes
secondary endocrine organs
heart
stomach
adipose tissue
small intestine
kidney
liver
placenta
what is the hypothalamus and PG
H and PG act as a unit
PG connect to H via the P stalk
described the pituitary
1cm^2
0.5-1g
2 lobes (ant and pos)
describe the posterior pituitary gland
- contains thin, nonmyelinated nerve fibres
- the nerve fibres are termination of modified nerve tracts whose cell bodies lie within the hypothalamus
ADH and oxytocin are:
- PRODUCED by H
- TRANSPORTED along nerve fibres to PPG via neuro-secretion
- STORED AND RELEASED into blood by PPG
ADH= KIDNEY
OXYTOCIN= BREAST AND UTERUS
describe the anterior pituitary gland
- CONNECTED to H via pituitary portal system
- TRANSPORT hormone from H to AP
- these hormones from H promote secretion and release of hormones from AP
- 5 different cell populations within the gland secrete 6 major hormones
what are the cell populations of the APG and what do they produce and how does the hypothalamus regulate it
SOMATOTROPHS: produces and releases GH,
REGULATED BY H: stimulated by growth hormone- releasing hormone, inhibited by somatoSTATIN
LACTOTROPHS: produces and releases PROLACTIN,
REGULATED BY H: stimulated by THYROTROPIN releasing hormone, inhibited by DOPAMINE (prolactin inhibiting factor)
CORTICOTROPHS: produces and releases adrenocorticotropic hormone,
REGULATED BY H: stimulated by corticotropin releasing hormone
THYROTROPHS: produces and releases thyrotropin
REGULATED BY H: stimulated by thyrotropin releasing hormone
GONADOTROPHS: produces and releases LH and FSH,
REGULATED BY H: stimulated by gonadotropin releasing hormone
what’s the meaning of tropin, tropic, troph and statin
statin: inhibit hormone release
troph: cells that produce and release the hormones (related to growth)
tropic: stimulates the cells to produce the hormone
tropin: stimulates the cells to release the hormone
what are the hypothalamic- pituitary hormonal axis
HPG- hypothalamic- pituitary-gonadal axis
HPT- hypothalamic- pituitary-thyroid axis
HPA- hypothalamic- pituitary- adrenal axis
describe the HPG axis
sex hormones:
testosterone in males
oestrogen and progesterone in females
trigger development of sexual characteristics
GnRH released to APG
LH and FSH released from APG to testes and ovaries
sex hormones now produced which trigger development
describe the HPT axis
thyroid gland:
highly vascular
consist of 2 lobes and composed of follicle cells
in front of larynx and trachea
thyroid gland and hormones: synthesised by follicle cells
thyroglobulin= secreted into follicular cells of the thyroid, and contains tyrosine amino acids (involved in synthesis and storage of thyroid hormones)
when these AA gets iodinated, it forms T3 & T4 hormones
thyroxine (T4) = contains 4 iodine ions
triiodothyronine (T3) = contains 3 iodine ions
T3 and T4 regulate metabolism on most cells of the body
describe the parathyroid glands
lie on posterior surface of each lobe of thyroid gland
parathyroid hormone is released
calcium metabolism is affected
raises free plasma Ca2+ to:
mobilise bone store (stimulate osteoclasts to move CA from bone to blood)
reduce urine loss (prevent CA loss in urine)
increase gut absorption (stimulate active vit D to promote calcium reabsorption from gut)
describe the adrenal glands and hormones
glands are enclosed in renal fascia- involved in stress response
consists of 2 different regions:
adrenal cortex and adrenal medulla
AC- steroids:
HORMONE SECRETED IS GLUCOCORTICOID= 1 cortisol = increases blood glucose and metabolic response to stress
HORMONE SECRETED IS MINERALCORTICOID= 1 aldosterone = fluid balance (na) and blood pressure maintenance
HORMONE SECRETED IS DHEA= weak androgens= release small amounts of testosterone (2nd sexual characteristics)
AM- catacholamines (fight or flight):
adrenaline (75-80% of medullary secretions)
noradrenaline (20-25% of medullary secretions)
how is the adrenal medulla and sympathetic nervous system related?
AM is a modified part of the SNS
- consists of modified postganglionic sympathetic neurones called chromaffin cells
- adrenaline/ noradrenaline are secreted in response to stimulation of sympathetic nerves
describe the pineal gland
- pinecone small shaped structure in centre of brain
- has specialised cells called pinealocytes and neuroglial cells
- secretes melatonin
- keep body circadian rhythm in sync with light and dark cycle
- modulation of wake/ sleep patterns
what hormones are involved in digestion of food in stomach?
lining of stomach (gastric mucosa) produces a hormone called gastrin in response to food (proteins) in stomach
G cells in gastric mucosa detect protein
gastrin released
stimulates partietal cells to then release HCl
chief cells release pepsinogen which turn into pepsin due to HCl
digestion of proteins begin
what hormones are secreted by the duodenum, jejenum and ileum
mucosa of small intestine secrets secretin and cholecystokinin (CCK)
DUODENUM and JEJENUM
1. after food is digest, turns into chyme (has acid)
2. acid in duodenum triggers secretin release
3. pancreas & liver produce bicarbonate rich secretion to neutralise
2a. fat in duodenum triggers CCK release
3a. gall bladder ejects bile salts and pancreas produces enzymes to emulsify digestion
ILEUM:
main incretin hormone is GLP-1 (glucagon- like peptide-1) is secreted from L-cells in ileum
what is the endocrine function of the pancreas
has both exocrine and endocrine functions
endocrine portions consists of isolated islands of cells called ‘islets of langerhans’
these cells make up about 1-2% of total pancreatic mass
how does the pancreas regulate blood glucose levels
insulin (secreted from beta cells):
lowers blood glucose, fatty acid and amino acid levels
promotes storage
glucagon (secreted from alpha cells):
opposed actions of insulin
promotes release of glucose into blood from storage organs
