physiology Flashcards
what is the hypothalamus
a neuroendocrine hormone as it releases neurone in the brain that travel in the blood to cells
another definition of endocrine gland
ductless gland
autocrine secretion
cells that secrete chemicals that bind to the same receptors on the cell that secreted it
what are ducted exocrine glands
deliver secretions to the external environment such as bile, sweat and saliva
paracrine secretions
chemicals diffuse in ECF to affect neighbouring cells and don’t travel in the blood
peptide/protein hormones
composed of chains of amino acids ( most common )
amine hormones
all derived from one or two hormones (tryptophan or tyrosine)
only melatonin comes from tryptophan)
steroid hormones
derived from cholestrol
stalk that connects the hypothalamus and pituitary gland
infundibulum
describe features of anterior pituitary
- connected to hypothalamus via capillary portal system
- treu endocrine tissue of epithelial origin
- makes up 2/3s of the gland
describe features of the posterior pituitary gland
- continuation of hypothalamus
- consists of axons and nerve terminals of hypothalamic neurone
- is neuroendocrine
what does non-tropic mean
neurohormones produced in the hypothalamus and travel to the posterior pituitary where they are released into the blood
what does tropic mean
neurohormones secreted into capillaries travelling to anterior pituitary and govern released of anterior pituitary hormones
name 2 hypothalamic non-tropic hormones
- vasopressin- ADH
- oxytocin- aids expression of milk from lactating breast
describe the hypothalamus-hypophyseal portal system
tiny vessels which transfer tropic hormones from hypothalamus to anterior pituitary. very rapid
what does trophic action mean
indirect effects in promoting growth
mechanics of action of peptide hormones
- mRNA binds amino acids onto peptide chain called preprohormone. Goes straight to ER.
- Enzyme in the ER chop off the signalling sequence creating an inactive prohormome
- Prohormone passes through the Golgi apparatus
- secondary vesicles containing prohormones and enzymes bud off the golgi and chop prohormones into active segments/
- secretory vesicles release content by exocytosis into extracellular space
- hormone moves in circulation for transport to target organ
what receptors do peptide hormones bind too
g-protein coupled receptor activate a 2nd messenger system and gives a rapid response
tyrosine kinase linked receptor alters gene expression and gives a slower but longer lasting response
mechanism of action of steroid hormones
lipophillicity allows steroid hormones to readily cross the plasma membrane.
2. Activation of intracellular receptors leads to change in gene expression at the level of the nucleus
3. genes control the synthesis of proteins so these hormones increase or decrease protein synthesis
describe half life of steroid hormones
hours to days
describe half life of peptide hormones
usually minutes therefore requires continued secretion
describe the glucostatic theory
food intake is determined by blood glucose
As blood glucose increases the drive to eat decreases
describe the satiety centre
promotes feelings of fullness by suppressing feeding centre
describe the lipostatic theory
food intake is determined by fat stores as fat stores increase the drive to eat decreases.
what does leptin do and what type of hormone is it
leptin is released by fat stores which depress the feeding centres reducing hunger and is a peptide hormone
what are the three categories of energy output
cellular work
mechanical work
heat loss
what is the only voluntary energy output
mechanical work by skeletal muscle
when do we enter the absorptive state
after eating when the ingested nutrients supply the body with energy and the excess is stored
anabolic phase
when do we enter the post-absorptive state
between meals and overnight as nutrients in plasma decrease and we rely on our bodies energy stores.
This is a catabolic phase
what is the normal BG levels
4.2-6.3mM
what is the level of BG for hypoglycaemia
<3mM
where are the hormones found in the pancreas
islets of langerhans
name the 4 types of langerhans cells
alpha cells- produce glucagon
beta cells- produce insulin
delta cells produce somatostatin
F cells- unknown function
simple function of insulin
stimulates glucose uptake by cells
how is insulin synthesised
- As a large preprohormone (preproinsulin) which is converted to proinsulin in the ER
- Proinsulin is then packaged into vesicles and stored until secreted
what form is excess glucose stored in the liver and muscle
As glycogen
what form is excess glucose stored in the liver and adipose tissue
as triglycerols
describe the primary action of insulin in terms of crossing into cells
1.insulin binds to tyrosine kinase receptors on the cell membrane of insulin dependent tissues to increase glucose uptake
- Stimulates mobilisation of GLUT 4 and it migrates to the membrane and able to transport glucose into the cell
name 2 tissues that are insulin dependent
muscle and fat
how do other tissues other than muscle and fat take up glucose
through other GLUT transporters which aren’t insulin dependent
stimuli which increase insulin release
- increased BG
- increased amino acids in plasma
- glucagon
- incretin hormones which control GI secretion
- vagal nerve activity
stimuli which inhibit insulin release
- low BG
- somatostatin
- sympathetic alpha 2 effects
4 stress e.g hypoxia
why take glucose orally vs IV
orally you have vagal stimulation which stimulates GI hormone release as well as insulin release
primary actions of glucagon
- increase glycogenolysis
- increase gluconeogenesis
- formation of ketones from fatty acids
All occur in the liver
stimuli that promote glucagon release
1.low BG <5mM
2. high amino acids
3. sympathetic innervation and epinephrine
4. cortisol
5. stress
stimuli that inhibit glucagon
- glucose
2 FFAs and ketones - insulin
- somatostatin
parasympathetic innervation on islet cells
increase insulin and decrease glucagon
sympathetic innervation on islet cells
increased glucagon, increase epinephrine and inhibition of insulin
function of pancreatic somatostatin
surpresses release insulin and glucagon
what happens if you have a SS secreting tumour
you have diabetes
effect of exercise on BG
glucose can be taken up independently of insulin
GLUT 4 transporters can migrate to membrane without insulin being present
what can hyperglycaemia cause
neuropathy
retinopathy
nephropathy
CVD
hormones that contribute to growth
GH
IGF-1
thyroid hormone
sex steroids
glucocorticoids
insulin
function of growth hormone
promote elongation of bones and increase height, weight and body mass
function of sex hormones in growth
close epiphyses and stop boner elongation
what happens in congenital hypothyroidism
babies are born of normal size but have retarded growth and development. They retain infantile facial features
what is IGF-1
also known as somatomedin C as it mediates the action of GH
Has insulin like qualities as it stimulates glucose uptake in muscle and bone
secreted primarily by the liver and controls GH through a negative feedback loop
things that stimulate GHRH (GH)
increased amino acids in the plasma
physical stress and illness
delta sleep
oestrogen and tesosterone
stimuli that increase GHIH (somatostatin secretion)
- glucose
- FFAs
- ageing
- cortisol
hypersecretion of GH
gigantism- excessive growth
acromegaly- enlarged hands and feet but long bones don’t increase
2 active forms of thyroid hormones
T3 and T4
2 types of cells present in thyroid gland
- C cells secrete calcitonin which is a calcium regulating hormone- fewer cells
- follicular cells which support thyroid hormone synthesis swell as thyroglobulin
what is a thyroid follicle
spherical structure whose walls are made of follicular cells and centre filled with colloid= sticky glycoprotein metric and contains 2-3 mths of TH
why does T4 have a longer half life than T3
thyroxine binding globulin has a high affinity for T4 releasing it slowly into the plasma
how much more T4 do you have than T3 in the plasma
50x more T4
key hormones in foetal development
thyroid hormone and insulin
thyroid hormone function
Bind to nuclear receptors in target cells were they change transcription and translation to alter protein synthesis
symptoms of hyperthyroidism
- increased metabolic rate and heat production
- increased protein catabolism- muscle weakness/weight loss
- altered nervous system function
- elevated cardiovascular function- increased HR
causes of hypothyroidism
Hashimoto disease- autoimmune attack on thyroid gland and can’t produce hormone
deficiency of dietary iodine
symptoms of hypothyroidism
weight gain and cold intolerant
brittle nails and thin skin
slow speech/ reflexes and fatigue
slow HR and weaker pulse
what does goitre mean
enlargement of thyroid gland
cause of hyperthyroidism
graves disease- antibodies produces that mimic TSH and continually activate thyroid gland
function of adrenal medulla (central part and neural in origin)
modified sympathetic ganglion
secretes catecholamines from the postganglionic cell
function of adrenal cortex
secretes 3 steroid hormones
1. mineralocorticoids
2. glucocorticoids
3. sex steroids
3 zones in the cortex
zona glomerulosa- aldosterone
zona fasciculata- glucocorticoids
zona reticularis- sex hormones
actions of cortisol on glucose metabolism
- gluconeogenesis
- proteolysis
- lipolysis
- decrease insulin sensitivity
