Homeostasis Flashcards
what does negative feedback regulate
the magnitude of correction required to bring a factor back within its normal range - as factor gets close to normal value , level of correction reduces
negative feedback process
- sensory receptor detects change eg. body temp too low
- coordination system - transfers info between different parts of body
- effector - carries out response to reverse the initial stimulus
positive feedback process
- the original stimulus produces a response that causes the factor to deviate from the normal range even more
- enhances the effect of the original stimulus
- eg. platelets in blood clotting, oxytocin release during childbirth
cell signalling
- coordinates activities of cells, either ones close together or far apart
- stimulus detected by receptor and converted into message by transduction, message is transmitted to effector to produce a response
paracrine signalling
signalling between cells that are close together
endocrine signalling
signalling between cells that are far apart - signalling molecule is transported in circulatory system
ectotherm
- organisms that rely on external sources of heat and behavioural activities to regulate their body temperature
- they have no internal mechanisms to regulate their temperature
- eg. reptiles, amphibians, fish
advantages of ectotherms
- require less energy intake to regulate temp
- they can use energy for growth rather than thermoregulation
disadvantages of ectotherms
- very dependent on their environment so can’t live in as many places
- basking and hibernation makes them vulnerable to predation
- have to rely on ambush predation rather than sustained
how do ectotherms regulate body temp?
- basking - orientate body to/away from sun
- stretch body arts to increase SA
- hide in burrow
- contract muscles to increase cellular respiration
- hibernation
- find shade
- press against cool stones
- have darker skin to absorb more heat
endotherm
- organisms that regulate their own body temp
- many chemical reactions in the body are exergonic - release energy in the form of heat
- eg. increasing rate of respiration in the liver to release heat - uses energy intake
endotherms advantages
- don’t rely on environment to regulate temp - can live in more places in the world
- can be active all year round - no hibernation
endotherms disadvantages
- lots of energy intake used on temperature regulation
- less energy can be used for growth
what detects changes in body temp in endotherms?
- thermoregulatory centre in hypothalamus monitors blood temp
- heat loss centre - activated when temp of blood increases - sends impulses through autonomic motor neurones to effectors in skin and muscles
- heat gain centre - activated when temp of blood decreases - sends impulses through autonomic NS to effectors in skin and muscles to raise body temp
physiological adaptations of endotherms to regulate temp
- sweat glands in skin: secrete/ don’t secrete sweat
- lungs, mouth and nose: pant/don’t pant
- hairs on skin: lie flat/stand on end
- blood vessels: vasodilation/vasoconstriction
- liver cells: lower respiration/ increase respiration
- skeletal muscles: don’t/do shiver
behavioural adaptations of endotherms to regulate temp
- move to shade/sunlight
- decrease/increase exposed SA
- remain inactive/move to generate heat in muscles
- hibernation
excretion
removal of metabolic waste from the body - by-products or unwanted substances from normal cellular process
what substances need to be excreted?
urea - from excess amino acids
carbon dioxide - from cellular respiration
bile pigments - from breakdown of haemoglobin
why do we need to remove carbon dioxide?
- high levels can lead to decrease of pH of blood leading to respiratory acidosis
- below pH 7.35 (optimum) - difficulty breathing, headache, drowsiness, restlessness, tremors, confusion
why do we need to excrete urea?
- urea is the breakdown of excess amino acids
- amino acids contain as much energy as carbohydrates but the body cannot store excess amino acids
how is urea formed?
Deamination:
- in liver, ammonia - toxic amino group is removed
- amino acid + oxygen = keto acid + ammonia
Formation of urea:
- ammonia reacts with carbon dioxide and urea is formed
- ammonia + carbon dioxide = urea + water
- 2NH3 + CO2 —> CO(NH2)2 + H2O
Urea is excreted from body in urine
where does blood flow through the liver?
- oxygenated blood to liver through hepatic artery and taken back to heart by hepatic vein
- hepatic portal vein supplies blood rich in products of digestion from intestines
- blood from hepatic artery and hepatic portal vein mixes in sinusoids to supply hepatocytes with enough oxygen
hepatic artery
- carries oxygenated blood from heart via aorta to the liver
hepatic portal vein
takes blood rich in products from digestion from intestines to liver
hepatic vein
rejoins to vena cava, takes products of liver metabolism away
bile duct
carries non-blood products out of the liver into the associated place eg. gallbladder, small intestine
hepatocytes
- cells that make up the liver
- secrete bile from breakdown of blood into canaliculi, bile then drains into bile ducts and taken to gall bladder
lobule
- repeating unit of the liver
- 6 sides - made up of tightly packed rows of hepatocytes radiating out from a central vein and surrounded by sinusoids
- branches of hepatic artery and hepatic portal vein allow blood supply through the central vein for lobules
- sinusoids - similar to capillaries but more porous endothelium so small/medium proteins can travel through walls
- arranged in irregular, branching plates surrounding central vein
- blood passes through sinusoids inwards
canaliculi
- channels in lobules carrying bile made by hepatocytes
- carry bile to bile ductules then to bile duct
- bile flows from centre of lobule outwards
kupffer cells
- specialised macrophages:
- destroy worn out red and white blood cells, bacteria and foreign matter arriving from digestive tract - Break down haemoglobin into bilirubin which is excreted in faeces - brown pigment
carbohydrate metabolism function of liver
- glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose into glycogen
- glucose levels fall, glucagon levels rise, hepatocytes convert glycogen to glucose
deamination function of liver
- transamination - conversion of one amino acid into another - overcomes problems in diet
- deamination - removal of amino group from amino acids, converting it to ammonia then to urea in ornithine cycle
detoxification function of liver
- toxic substances are detoxified and made harmless eg. alcohol, drugs
- breakdown of hydrogen peroxide:
hepatocytes contain catalase - splits hydrogen peroxide into oxygen and water - breakdown of alcohol:
hepatocytes contain alcohol dehydrogenase - breaks ethanol to ethanal, then to ethanoate used to build up fatty acids or used in respiration
renal artery
vessel supplying blood to kidney
(branches off aorta)
renal vein
vessel taking blood away from kidney (connects to vena cava)
capsule - kidney
dark red outer layer made from collagen and elastin
cortex - kidney
next layer in from capsule - dark
- where filtering takes place
- has dense capillary network to carry blood from renal artery to nephrons
medulla - kidney
next layer in from cortex - paler
- contains tubules of nephrons and collecting ducts
pelvis - kidney
next layer in from medulla - whitish
- where urine collects before passing down ureter
nephron structure and function
- tiny functional subunits in kidney
begins in cortex and extends to medulla - filters blood and removes nitrogenous waste products and balances mineral ions and water (ultrafiltration and reabsorption)
- Bowman’s capsule – proximal convoluted tubule – loop of Henle – distal convoluted tubule – collecting duct
podocyte cells
- have extensions called pedicels that wrap closely around capillaries of glomerous
- form slits ensuring cells, platelets and plasma proteins do not get into tubule
how is blood in the glomerulus separated from the glomerular filtrate?
- endothelium of blood capillary - small pores
- basement membrane - mesh of collagen fibres and glycoproteins - act as filter to prevent molecules with molecular mass over 69000 getting through
- podocytes - epithelial cells making up lining of renal capsule
ultrafiltration
- occurs in Bowman’s capsule
1. glomerulus supplied with blood through afferent arteriole from renal artery and blood leaves through narrower efferent arteriole - higher pressure in capillaries of glomerulus
2. this forces blood out glomerulus through slits in podocytes which passes through basement membrane to the bowman’s capsule
3. most plasma contents pass through basement membrane but blood cells and many proteins retained in capillary bc too big
4. the filtrate left behind in the glomerulus contains amino acids, water, glucose, urea and inorganic ions
adaptations of cells lining proximal convoluted tubule
- made up of tightly packed cuboidal cells with microvilli on the inside (increase SA for reabsorption)
- large no of mitochondria for active transport
selective re-absorption in proximal convoluted tubule
- most substances in glomeruler filtrate are required by the body so must be re-absorbed
- glucose, amino acids, vitamins, hormones, Na+ actively transported back to blood, Cl- follow passively to capillaries close to outer surface of proximal convoluted tubule
reabsorption in the loop of henle descending limb
- lower part is water permeable
- water moves out loop of henle to tissue fluid by osmosis, then down conc grad to surrounding capillaries
- no active transport
- filtrate entering is isotonic with blood
- fluid at bottom is hypertonic to blood
reabsorption in loop of henle ascending limb
lower part:
- very permeable to Na+ and Cl-
- fluid very concentrated
- Na+ and Cl- ions diffuse out into surrounding tissue fluid down conc grad
upper part:
- active transport of Na+ and Cl- ions out into surrounding tissue fluid
- increases water pot of fluid in nephron, decreases water pot outside
- impermeable to water so it can’t move out
reabsorption in distal convoluted tubule
- permeability of walls dependent on levels of ADH
- cells lining walls have many mitochondria for active transport
- if body lacks salt, sodium ions actively pumped out, chloride ions follow down conc grad
action of ADH when released
- made in hypothalamus and released from pituitary gland (where it’s stored) and carried in blood to collecting duct cells
- binds to receptors on cell membrane to trigger formation of cAMP - secondary messenger relaying signals received at cell surface receptors to molecules in cells
- vesicles in cells lining collecting duct fuse with cell membrane in contact with tissue fluid of medulla
- membranes of vesicles contain aquaporins - when inserted to membrane, makes it permeable to water
- this makes it easy for water to leave tubules, creating small amount of concentrated urine and maintaining water pot of blood
negative feedback control when water in short supply
- conc of inorganic ions in blood rises
- water pot of blood and tissue fluid decreases
- this is detected by osmoreceptors in hypothalamus
- they send nerve impulses to posterior pituitary, releases ADH to blood
- ADH picked up by receptors lining collecting duct, making the walls more permeable to water
negative feedback control in excess water
- blood becomes more dilute, water pot higher
- change detected by osmoreceptors in hypothaluamus
- nerve impulses sent to posterior pituitary are reduced or stopped
- release of ADH inhibited
- little reabsorption of water can take place as walls of collecting duct remain impermeable
making monoclonal antibodies for pregnancy test
- a mouse is injected with hCG (produced by pregnant women) so it makes the appropriate antibody
- B cells required to make the antibody are removed from the mouse and fused with a type of cancer cell that divides rapidly
how does a pregnancy test work?
- urinate on stick in morning (highest hCG conc)
- if pregnant, hCG binds to mobile monoclonal antibodies and forms hCG/antibody complex
- urine moves along test until it reaches the window where there are immobilised monoclonal antibodies arranged in + sign
- urine continues moving up test until a second window reached with immobilised monoclonal antibodies which bind to mobile antibodies regardless of whether they’re bound to hCG or not - line indicates test is working
kidney failure effects
- protein in urine - bowman’s capsule damaged - large proteins can fit
- blood in urine
- urea in blood
- high blood pressure - water balance of blood not regulated
causes of kidney failure
- high blood pressure (hypertension) - damages epithelial cells and basement membrane
- infection
- drug use
what does kidney failure and urea and mineral ions building up in blood cause?
- loss of electrolyte balance
- build up of toxic urea in blood
- high blood pressure
- weak bones - calcium/phosphorus balance in blood lost
-pain in joints - abnormal protein build up in blood - anaemia - kidney produce hormone that stimulates production of RBC - can cause tiredness and lethargy
haemodialysis
- involves dialysis machine - home or hospital
- blood leaves body and flows through machine - through partially permeable dialysis membranes (mimic basement membrane of bowman’s capsule)
- dialysis fluid on other side of membrane
- urea and excess mineral ions leave blood by diffusion
- blood and dialysis fluid move in countercurrent system to maximise exchange taking place
peritoneal dialysis
- takes place inside body
- dialysis fluid moves into abdomen by catheter
- urea and excess mineral ions move out blood capillaries to tissue fluid across peritoneal membrane (lining of abdomen), into dialysis fluid
dialysis fluid
- dextrose solution
- plasma levels of glucose so no net movement
- plasma levels of mineral ions so excess in blood can move down conc grad
- no urea so much can move out blood down steep conc grad
- not just water to prevent water entering blood and causing cells to swell or burst
disadvantages of kidney transplant
- risk of body rejecting donor organ
- antigens on donor differ from those on recipient
- immune system may recognise this and destroy the new kidney
- immunosuppressant drugs can be taken for the rest of their lives to counter this but the patient will not respond effectively to other infectious diseases
