5.1.2 Excretion as an example of homeostasis Flashcards
substances that need to be excreted
carbon dioxide (from respiration)
nitrogen-containing compounds (ammonia, urea, uric acid)
bile pigments
excretion definition
removal of metabolic waste from the body
excretory organs
lungs (removal of CO2 from respiring tissue, brought from bloodstream mostly as HCO3- which diffuses into the alveoli to be breathed out)
liver (lots of metabolic roles e.g. deamination)
skin (not primary function, secretes ammonia, urea, uric acid (toxic), water and salt for homeostasis of body temperature and water potential)
why nitrogenous compounds are excreted
body cannot store excess amino acids
deamination: AA + oxygen -> keto acid + ammonia
formation of urea (less toxic and soluble than ammonia): ammonia + CO2 -> urea + H2O
NH4 + CO2 -> (NH2)2CO + H2O
urea transported to kidneys for excretion
keto acid used in respiration or converted to fat/carbohydrate for storage
why CO2 is excreted
excess CO2 is toxic as..
H+ ions from CO2 form haemoglobinic acid, competed with O2 for space on haem.
CO2 join with haemoglobin to form carbaminohaemoglobin (lower affinity for O2 than haemoglobin)
both result in less O2 carriage
if pH of blood drops too low, respiratory acidosis occurs
respiratory acidosis symptoms
slow breathing
headaches
confusion
rapid heart rate
structure of liver
divided into lobes
divided into lobules
structure of lobule
centre of lobule has hepatic vein
hepatic artery and hepatic portal vein run parallel into lobule
their blood mixes in sinusoid
Kupffer cells move around in sinuosood
canalicalus carries bile produced by hepatocytes to gall bladder
hepatic artery function + characteristic
brings oxygenated blood from heart to supply hepatocytes with oxygen needed for aerobic respiration
thicker wall, smaller lumen
hepatic portal vein function + characteristic
brings deoxygenated blood from intestines
may contain toxic compounds need detoxification or produces of digestion for storage
thin wall, larger lumen
bile canaliculus role + characteristic
bile made by hepatocytes secreted into bile canaliculi delivered to bile duct
stored in gall bladder until release in small intestine
enclosed space
bile function
emulsifies lipids
neutralises acid
why does blood mix in sinusoid
increase oxygen content for hepatocytes
Kupffer cell function
resident macrophage at sinusoid
breaks down RBCs
products of this breakdown released into bile duct to be sent into digestive system for excretion e.g. bilirubin from haemoglobin
liver functions
detoxification of alcohol
storage of glycogen (by converting glucose into glycogen)
formation of urea from excess amino acids (deamination)
detoxification definition
conversion of toxic molecules into less toxic or non-toxic molecules
why detoxification occurs
prevents accumulation of toxic substances which may kill us
detoxification in the liver
hydrogen peroxide (made by WBCs) by catalase
drugs by a group of enzymes called cytochrome P450
alcohol by ethanol dehydrogenase and ethanal dehydrogenase
detoxification of alcohol
ethanol dehydrogenated into ethanal (catalysed by ethanol dehydrogenase, NAD into NADH)
ethanal dehydrogenated ethanoic acid (catalysed by ethanal dehydrogenase, NAD into NADH)
ethanoic acid forms acetyl coenzyme A
why alcohol is detoxified
alcohol is toxic (depresses nerve activity)
can be broke down into useful products (contains chemical potential energy)
why too much alcohol ingested is bad
NAD accept hydrogen atoms in detoxification of ethanol
also used in oxidising and breaking down fatty acids for respiration
too much alcohol = not enough NAD = too many fatty acids
fatty acids -> lipids stored in liver cells -> liver cirrhosis
why freshwater fish secrete ammonia
highly toxic / very soluble in water
must be diluted in large volume of water
why mammals excrete urea
less toxic
can be more concentrated
less water needed to get rid of it
can be safely stored before being released from body
why birds excrete uric acid
loss of very little water
smaller mass of water is an advantage in flight
stages in making urea
deamination
ornithine cycle
why deamination occurs
amino acids can’t be stored (toxic)
can be used to release energy (waste to directly excrete them)
deamination
removal of the amine group from amino acid
forms a keto acid and ammonia
keto acid can be used directly in respiration
amino acid + oxygen -> keto acid + ammonia
why ornithine cycle happens
ammonia must be removed
too toxic and too soluble to transport and excrete
if excreted, large amount of water required and it would dehydrate us
urea less soluble and less toxic
ornithine cycle steps
ammonia + CO2 + ornithine combine to form citrulline + water in mitochondria
citrulline moves out into cytoplasm
converted to argininosuccinic acid then arginine and water by adding more ammonia (requires ATP -> AMP)
converted back to ornithine by adding water to arginine to remove urea and moves back into mitochondria
ammonia + CO2 -> urea + water
2NH3 + CO2 -> CO(NH2)2 + H2O
main function of kidney
remove waste from blood and make urine
urine passage through body
formed in kidney
through ureter
stored in bladder
moves out of body to urethra
nephron definition
functional unit of kidney
kidney structure
outside to inside
capsule (very outer layer)
cortex (dark outer layer where filtering takes place)
medulla (lighter in colour, collecting ducts)
branch of renal vein (deoxygenated blood without waste or excess water, leaves kidney)
branch of renal artery (oxygenated blood with waste and excess water, enter kidney)
pelvis (not the bone lol)
ureter (carries urine to bladder)
ultrafiltration definition
filtration at a molecular level smaller molecules (urea, water, glucose, amino acids, ions) filtered out of the blood into lumen of Bowman’s capsules
arterioles, glomerulus and Bowman’s capsule pressure in ultrafiltration
afferent arteriole lumen is wider than efferent arteriole lumen
provides hydrostatic ultrafiltration pressure needed for ultrafiltration
pressure in glomerulus higher than in Bowman’s capsule, forces substances from blood into Bowman’ capsule to form filtrate
filter of Bowman’s capsule
there are many gaps in between cells of the capillary (fluid can pass between these)
podocytes inside of Bowman’s capsule lifts cells away from the capillary to allow filtrate to pass beneath them rather than through them
why selective reabsorption occurs
a lot of molecules need to bereabsorbed in the blood (as they are vital)
around 85% reabsorbed
what happens to filtrate as it moves through the nephron method
glucose, amino acids, hormones, vitamins, Na+ actively transported out of filtrate at proximal convoluted tubule
filtrate is isotonic compared to blood in surrounding capillaries
water potential becomes less negative
water exits proximal convoluted tubule via osmosis
chlorine diffuses out of the convoluted tubule
more water moves out of filtrate at descending Loop of Henley (impermeable to ions)
concentration of Cl- and Na+ increases, filtrate is hypertonic compared to blood in surrounding capillaries
Na+ and Cl- ions leave the filtrate at ascending Loop of Henley (AT) (impermeable to water)
via diffusion initially, then active transport due to changing concentrations
filtrate is isotonic in comparison to blood in surrounding capillaries
H2O leaves at distal convoluted tubule via osmosis (controlled by ADH)
Na+ and Cl- leave (AT, then diffusion)
more H2O is reabsorbed at the collecting duct
ADH stands for
anti-diuretic hormone
where ADH is produced and secreted
produced in neurosecretory cells in hypothalamus
passes down axon of these cells to terminal bulb in posterior pituitary gland for storage
when ADH secreted
osmoreceptors in hypothalamus monitor water potential of blood
low w.p. = osmoreceptors shrink, triggers action potentials down axon of neurosecretory cells in hypothalamus
stimulates release of ADH into blood
how ADH makes cells of walls of collecting duct more permeable to water
ADH binds to receptor on cell
enzyme-controlled reactions caused a vesicle to be made containing aquaporins
vesicle fuses with membrane, more aquaporins = more permeable to H2O
water reabsorbed from collecting duct via osmosis into capillaries
ADH 6 marker perfect answer (hot days)
pituitary gland makes and secretes ADH
ADH travels in blood
target cells = cells lining collecting duct in nephrons of kidneys
ADH binds to receptors on cell surface membranes of target cells
triggers series of enzyme-controlled reactions
causes vesicles containing aquaporins to fuse with membranes
increases permeability to H2O
more ADH = more aquaporins = collecting duct is more permeable to water = more reabsorption of water from collecting duct (osmosis) = smaller volume of more conc. urine
ADH 6 marker model answer (cold days)
pituitary gland makes and secretes less ADH
less ADH travels in blood
target cells = cells lining collecting duct in nephrons of kidneys
less ADH binds to receptors on cell surface membranes of target cells
triggers series of enzyme-controlled reactions
causes less vesicles containing aquaporins to fuse with membranes
less permeability to H2O
less ADH = less aquaporins = collecting duct is less permeable to water = less reabsorption of water from collecting duct (osmosis) = larger volume of less conc. urine
advantages of kidney transplant
no need to dialysis (time-consuming)
diet less limited
better quality of life - can travel (not tied to hospital visits)
disadvantages of kidney transplant
may be rejected by the body
have to take immunosuppressants (increase likelihood of infections)
risks of major surgery (high likelihood of infection)
kidney failure causes
diabetes mellitus
hyper tension
infection
why kidney failure bad
build up of urea in blood (toxic to cells)
unable to regulate ion and water levels in blood
what protein in urine suggests has gone wrong
damage to basement membrane (caused by hypertension), allowing large substances like protein during ultrafiltration into nephron
haemodialysis method
blood from artery removed
blood pump keeps blood moving
heparin (anticoagulant) prevents clotting
blood passes into passed into machine with partially permeable artificial dialysis membrane
other side of membrane is dialysis fluid with correct conc. of glucose, ions, urea
blood and dialysis fluid flow in opposite direction to one another
urea diffuses from blood to dialysis fluid
air trap and air detector needed to remove any bubbles is returned to vein
takes 3-4 hours, 2-4 times a week
peritoneal dialysis method
tube surgically implanted into abdomen
bag connected, sends dialysis solution through tube into peritoneal cavity surrounding organs
abdominal membrane acts as filter
solution drained after few hours
adv. of peritoneal dialysis
treats kidney failure
keeps patients alive long enough to receive kidney transplant
can be done from home (better quality of life)
disadv of peritoneal dialysis
risk of infection post surgery
must carefully control diet
monoclonal antibodies method
inject mouse with target antigen to generate immune response
collect b-lymphocytes and combine with tumour cells to form hybridoma
produce lots of antibodies, collected and purified
pregnancy testing method
embryo secretes hCG, released during pregnancy
hCG (acts as antigen) binds to mobile monoclonal antibodies (anti-hCG) with coloured beads on them, complementary in shape
hCG-antibody complex moves along test strip with urine and binds to immobilised antibodies specific to the complex, producing blue line
control antibodies binds with any urine and bind to immobilised antibodies on control line to form coloured strip
indicates test is working
hCG stands for
human chorionic gonadotropin
assessing kidney failure
test urine for substances e.g. protein
measuring glomerular filtration rate (GFR)
GFR
glomerular filtration rate
sodium citrate
anticoagulant used in dialysis
removes calcium ions from blood
calcium ions are cofactor for blood clotting
why haemodialysis needs to be done for less time overall than peritoneal dialysis
removes more waste than peritoneal dialysis
fluids moves countercurrent flow (maintains steep concentration gradient)
dialysis fluid is constantly refreshed
instead of allowing fluids to reach equilibrium
where selective reabsorption occurs
proximal convoluted tubule
why longer Loop of Henle is advantageous
more ions can be actively transported out of the filtrate with a longer ascending limb
creates a steeper water potential gradient
more water can be reabsorbed via osmosis at the collecting duct
symptoms of lack of ADH
frequent need to urinate large volume of very dilute urine persistent feeling of thirst/excessive drinking electrolyte/mineral imbalance dehydration
ectothermic definition
organism that relies on external sources of heat to maintain body temperature
endothermic definition
organism uses heat from metabolic reactions to maintain body temperature
what ectotherms do when they are not warm enough
move into sunny area
move onto warm surface
expose larger SA to sun
what endothermic do when they are too warm
move out of sun
move underground
reduce body surface area to the sun
advantages of ectothermy
less food used up in respiration
more energy and nutrients gained from food can be converted to growth
need to find less food
survive for longer periods without food
disadvantages of ectothermy
less active in lower temperatures during which:
greater risk from predation (unable to escape)
cannot take advantage of food available
exergonic definition
releases energy as heat
behavioural responses of endotherms when too hot
hide away from sun (in shade)
orientated body to reduce SA exposed to sun
remain inactive and spread limbs out (enable greater heat loss)
wet skin (evaporation helps cool body)
behavioural responses of endotherms when too cold
lie in sun
orientate body to increase SA exposed to sun
move about (heat generated in muscles)
role into ball to reduce SA and heat loss
remain dry
physiological responses used by endotherms when too warm (skin)
sweat glands secrete fluid (evaporates using heat from blood)
hairs/feather lie flat (reduce insulation from air, greater heat loss)
vasodilation of arterioles near skin (more heat radiates away from body
physiological responses used by endotherms when too warm (gaseous exchange system)
some animals pant
increases evaporation of water from surface of lungs and airways
using heat from blood
physiological responses used by endotherms when too warm (liver/muscles)
less respiration/contraction
less heat released
physiological responses used by endotherms when too warm (blood vessels)
dilation of blood vessels at extremities
more heat can be a lost
physiological responses used by endotherms when too cold (skin)
less sweat secreted (less evaporation means less heat is lost)
hair/feathers stand erect to trap air (insulates body)
vasoconstriction of arterioles near skin surface (blood diverted away from skin surface, less heat loss)
physiological responses used by endotherms when too cold (gaseous exchange system)
less panting, less heat lost
physiological responses used by endotherms when too cold (liver/skeletal muscles)
increased respiration in liver cells (more heat released as byproduct)
spontaneous muscle contractions (shivering releases heat)
physiological responses used by endotherms when too cold (blood vessels)
constriction to limit blood flow to extremities (blood not cooled too much)
advantages of endothermy
maintain constant body temperature (no matter external temperature)
remain active even when external temperatures low (take advantage of prey available or escape from predators)
inhabit colder parts of planet
disadvantages of endothermy
use significant part of energy intake to maintain body temperature in the cold
need more food
lower proportion of energy and nutrients used for growth
may overheat in hot weather
role of peripheral temperature receptors
early warning that body temperature has changed helps hypothalamus respond more quickly
helps reduce variation in core body temperature
receptors in the skin monitor changes in temperate at extremities, which may affect core body temperature
similarities between ultrafiltration and formation of tissue fluid
- small molecules are filtered from/diffuse out of blood
- both processes occur in capillaries
- large molecules/proteins/cells remain in blood
- high hydrostatic pressure in both processes
- many molecules reabsorbed back into capillaries afterwards
- blood vessels become narrower to maintain hydrostatic pressure
- hydrostatic pressure greater than oncotic pressure in both
- neutrophils/lymphocytes can pass through in both
- both involve basement membranes
differences between ultrafiltration and formation of tissue fluid
- filtrate enters Bowman’s capsule then proximate convoluted tubule in kidney whereas tissue fluid enters intercellular space
- molecules not reabsorbed by capillaries form urine in the kidney but molecules not reabsorbed from tissue fluid will enters cells/form lymph
- blood filtered through 3 layers in ultrafiltration but only 1 layer in formation of tissue fluid
- knot of capillaries in ultrafiltration whereas a network of capillaries in formation of tissue fluid
