T14 Homeostasis Flashcards
homeostasis
the relatively constant internal state of an organism, even when the external environment is changing.
receptor role
detects a change in external stimuli and sends an impulse to the control centre
control centre role
receives impulse and coordinates a response by sending message to effector
effector response
responds to the message from the control centre and brings about the appropriate response
mechanisms operating to restore homeostasis after infection by pathogen
production of antibodies against antigens (humoral)
T cell production recognising antigens of the pathogen (cell-mediated)
inflammatory response
fever
antimoicrobial substance production
phagocytosis of pathogen
mechanisms to respond to stimuli
hormonal (endocrine glands)
nervous (direct stimulation of nerves by sensory receptor
mechanisms by which water and ion balance are maintained
digestive organs and hormones take in ions from food and drink to replace lost
kidneys regulate fluid and ions. ADH causes more water absorption by the kidneys and is released when blood volume is low
mechanisms by which respiratory gases are regulated during exercise
breathing rate increase (^^ loading and unloading)
heart rate increase
negative feedback in calcium homeostasis
Low Ca stimulates release of PTH from parathyroid glands which stimulates kidneys to reabsorb more calcium into blood from urine and release of Ca from bone.
PTH
parathyroid hormone
negative feedback in stomach emptying
food is eaten, and stretches stomach wall which activates stretch receptors and smooth muscle contracts, so is mixed and emptied from stomach and stretch receptors are deactivated
negative feedback mechanisms
self-correcting and counteracts change away from a set normal to reduce fluctuations to stabilise systems.
what does the hormone oxytocin do
intensifies contractions in childbirth and leads to milk release in mothers
interleukins
stimulate the hypothalamus to increase prostaglandin production which increases body temp
biological role of positive feedback loops
amplifies a physiological process to bring about a particular response
example of positive feedback loops
fever
oxytocin production
ovulation
why is positive feedback unstable
causes escalation in physiological response, pushing past physiological range vs negative feedback which is self-correcting
control of ovulation from feedback mechanisms
oestrogen released by the ovaries, stimulating the hypothalamus to release GnRH and pituitary to release LH
rise in LH stimulates release of more oestrogen from ovary and stimulates ovulation and rupured follicle forms a corpus luteum which secretes oestrogen and progesterone and GnRH release is inhibited
nervous system response
rapid, short-lived responses via electrical signals between adjacent cells
usually is the contraction of a muscle or secretion from a gland
endocrine system reponse
slow, long-lasting response through hormones in the blood.
usually is a change in metabolic activity in a target cell
where’s the temperature regulation centre found?
in the hypothalamus
set temperature of humans
36.7 degrees celsius
hypothalamus role in thermoregulation
detects movement away from optimum temp and coordinates responses to counteract the change in temp
mechanisms to reduce body temp
relaxation of erector muscles, increased blood flow to surface of skin, sweating, decreased metabolic rate
mechanisms to increase body temp
shivering, erector muscle contraction, increased metabolic rate, adrenaline and thyroxine release to release energy from the liver, decreased blood flow to skin
sweating
decreases temp by evaporation using body’s heat energy, is released by sweat glands to external layer of skin
how does temperature of vaporisation affect feeling on skin
lower temp of vaporisation allows for quicker heat absorption from skin
feedback mechanism regulating body temp
thermoreceptors (hot and cold) detect changes in temp below 35.8 or above 37.5 degrees celsius and send a message to the hypothalamus which then coordinates a response and sends an electrical signal to an effector (eg, blood vessels or sweat glands).
liver role in homeostasis
metabolises proteins and stores/detoxifies hormones/poisons.
aspects of protein metabolism in the liver
deamination/ transamination of amino acids, ammonia removal from the body by urea synthesis, amino acid synthesis, synthesises plasma proteins (eg, albumins, globulins, and blood clotting proteins
storage and detoxification in the liver
small intestine outputs hepatic portal blood to be used in haemoglobin breakdown (producing iron to blood). also produces minerals and vitamins to store. blood outputs toxins and hormones to be broken down by liver cells or detoxified.
protein metabolism in the liver
small intestine outputs amino acids which then goes on to be deaminised, transaminised or used in protein synthesis to produce urea, plasma proteins or new amino acids to be put into the blood.
deamination
removal of NH2
transamination
transfer of NH2
aspects of protein metabolism in the liver
deamination
transamination
protein
waste products from deamination
keto acids and an amino group is formed. the keto acids feed into the krebs cycle and are oxidised to form ATP and the amino group is converted to ammonia and reacts w carbon dioxide to enter the ornithine cycle to produce urea.
consequences of a faulty ornithine cycle
leads to a build-up of ammonia and could be fatal.
where does the kidney get a plentiful blood supply from?
the renal artery
urinary system role
filters the blood and removes waste, to produce urine.
nephron
selective filter element of kidney, filtering blood plasma.
comprises of a renal corpuscle and associated tubules and ducts, producing urine via ultrafiltration.
structure of the kidney
bean shaped organ surrounded by a fibrous membrane. divided into an outer cortex and inner medulla. renal pyramids end in small ducts (papillae which open into calyces of ollecting channels. with inner medullas alternated with renal pyramids and nephrons with collecting ducts facing inwards to the renal pelvis. a ureter drains out of the kidney leading to the bladder.
nephron role in excretion
produces filtrate of the blood, modifies the filtrate and produced a final excretory fluid as urine.
ultrafiltration
forcing fluid and dissolved substances through a membrane by pressure
where does ultrafiltration occur in the nephron
in the first part of the nephron, across the capillary membranes and the glomerular capsule.
effect of blood pressure and the formation of glomerular filtrate`
increasing pressure increases filtration rate, decreasing pressure decreases filtration rate
how is urine modified
via secretion and tubular reabsorption according to physiological needs
renal corpuscle
blood is filtered and filtrate enters convoluted tubule
filtrate contains water, glucose, urea, ions/ no cells or large proteins
proximal convoluted tubule
reabsorption of most of filtrate, including glucose and ions
loop of henle
salt transport and passive movement of water create salt gradient through kidney, water transported away by blood vessels around nephron.
distal convoluted tubule
filtrate further modified by active reabsorption and secretion of ions
collecting duct
water leaves the filtrate via osmosis, so is more concentrated. loop of henle salt gradient allows water to be removed along entire length of the collecting duct.
podocytes
specialised cells making up epitheliuim of bowman’s capsule, wrapping around capillaries of the glomerulus and plasma filtrate passes through filtration slits between them
role of glomerular filtration
produces initial filtrate of the blood that can be modified be modified later on
role of active secretion
allows to rid of unwanted substances and maintain salt gradient
role of osmosis in kidney nephron
allows urine to be concentrated
purpose of the salt gradient in the kidney
allows water to be withdrawn from the urine in order to maintain the osmotic gradient which withdraws water from the urine
how is the salt gradient produced by the kidney
via the active and passive movement of salt from the filtrate into the extracellular fluid in the medulla
hormones that affect the volume and composition of urine
ADH and aldosterone
where is ADH produced
the posterior pituitary gland
where is aldosterone produced
in the adrenal cortex
ADH function
regulates water reabsorption from the collecting duct
aldosterone function
regulates sodium absorption from kidney tubules
where are osmoreceptors found
in the hypothalamus
factors causing ADH release
low blood volume more negative water potential high blood sodium levels low fluid intake nicotine and morphine
factors inhibiting ADH release
high blood volume
less negative water potential
low blood sodium levels
alcohol
factors causing release of aldosterone
low blood volumes
mediated via complex pathway between osmoreceptors, kidney glomeruli and the hormone renin
process by which urine output is controlled
low blood volume (high osmotic pressure) stimulates osmoreceptors which send signals to neurosecretory cells to synthesise and release ADH from pituitary. arterioles constrict to increase blood pressure and sweat glands decrease activity and water reabsorption increases from collecting ducts. blood volume is restored and detected by osmoreceptors
what happens to urine and blood volume when ADH is released
urine vol decreases and blood volume increases
what happens to urine and blood volume when ADH is inhibited
blood volume decreases, urine volume increases
effect of aldosterone on nephron
increases reabsorption of sodium into the nephron kidney tubules so that theres is more sodium in the blood, maintaining the salt gradient so that the osmotic tendencies of the liver are maintained. also leads to more water being reabsorbed so the blood volume increases
minimum atomic mass required to go through membrane within nephron
69000 RPM
