5.1.2 Excretion as an example of homeostasis

Question 1

substances that need to be excreted

Answer 1

carbon dioxide (from respiration)
nitrogen-containing compounds (ammonia, urea, uric acid)
bile pigments

Question 2

excretion definition

Answer 2

removal of metabolic waste from the body

Question 3

excretory organs

Answer 3

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)

Question 4

why nitrogenous compounds are excreted

Answer 4

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

Question 5

why CO2 is excreted

Answer 5

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

Question 6

respiratory acidosis symptoms

Answer 6

slow breathing
headaches
confusion
rapid heart rate

Question 7

structure of liver

Answer 7

divided into lobes

divided into lobules

Question 8

structure of lobule

Answer 8

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

Question 9

hepatic artery function + characteristic

Answer 9

brings oxygenated blood from heart to supply hepatocytes with oxygen needed for aerobic respiration
thicker wall, smaller lumen

Question 10

hepatic portal vein function + characteristic

Answer 10

brings deoxygenated blood from intestines
may contain toxic compounds need detoxification or produces of digestion for storage
thin wall, larger lumen

Question 11

bile canaliculus role + characteristic

Answer 11

bile made by hepatocytes secreted into bile canaliculi delivered to bile duct
stored in gall bladder until release in small intestine
enclosed space

Question 12

bile function

Answer 12

emulsifies lipids

neutralises acid

Question 13

why does blood mix in sinusoid

Answer 13

increase oxygen content for hepatocytes

Question 14

Kupffer cell function

Answer 14

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

Question 15

liver functions

Answer 15

detoxification of alcohol
storage of glycogen (by converting glucose into glycogen)
formation of urea from excess amino acids (deamination)

Question 16

detoxification definition

Answer 16

conversion of toxic molecules into less toxic or non-toxic molecules

Question 17

why detoxification occurs

Answer 17

prevents accumulation of toxic substances which may kill us

Question 18

detoxification in the liver

Answer 18

hydrogen peroxide (made by WBCs) by catalase
drugs by a group of enzymes called cytochrome P450
alcohol by ethanol dehydrogenase and ethanal dehydrogenase

Question 19

detoxification of alcohol

Answer 19

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

Question 20

why alcohol is detoxified

Answer 20

alcohol is toxic (depresses nerve activity)

can be broke down into useful products (contains chemical potential energy)

Question 21

why too much alcohol ingested is bad

Answer 21

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

Question 22

why freshwater fish secrete ammonia

Answer 22

highly toxic / very soluble in water

must be diluted in large volume of water

Question 23

why mammals excrete urea

Answer 23

less toxic
can be more concentrated
less water needed to get rid of it
can be safely stored before being released from body

Question 24

why birds excrete uric acid

Answer 24

loss of very little water

smaller mass of water is an advantage in flight

Question 25

stages in making urea

Answer 25

deamination | ornithine cycle

Question 26

why deamination occurs

Answer 26

amino acids can't be stored (toxic) | can be used to release energy (waste to directly excrete them)

Question 27

deamination

Answer 27

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

Question 28

why ornithine cycle happens

Answer 28

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

Question 29

ornithine cycle steps

Answer 29

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

Question 30

main function of kidney

Answer 30

remove waste from blood and make urine

Question 31

urine passage through body

Answer 31

formed in kidney through ureter stored in bladder moves out of body to urethra

Question 32

nephron definition

Answer 32

functional unit of kidney

Question 33

kidney structure

Answer 33

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)

Question 34

ultrafiltration definition

Answer 34

``` filtration at a molecular level smaller molecules (urea, water, glucose, amino acids, ions) filtered out of the blood into lumen of Bowman’s capsules ```

Question 35

arterioles, glomerulus and Bowman’s capsule pressure in ultrafiltration

Answer 35

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

Question 36

filter of Bowman’s capsule

Answer 36

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

Question 37

why selective reabsorption occurs

Answer 37

a lot of molecules need to bereabsorbed in the blood (as they are vital) around 85% reabsorbed

Question 38

what happens to filtrate as it moves through the nephron method

Answer 38

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

Question 39

ADH stands for

Answer 39

anti-diuretic hormone

Question 40

where ADH is produced and secreted

Answer 40

produced in neurosecretory cells in hypothalamus | passes down axon of these cells to terminal bulb in posterior pituitary gland for storage

Question 41

when ADH secreted

Answer 41

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

Question 42

how ADH makes cells of walls of collecting duct more permeable to water

Answer 42

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

Question 43

ADH 6 marker perfect answer (hot days)

Answer 43

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

Question 44

ADH 6 marker model answer (cold days)

Answer 44

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

Question 45

advantages of kidney transplant

Answer 45

no need to dialysis (time-consuming) diet less limited better quality of life - can travel (not tied to hospital visits)

Question 46

disadvantages of kidney transplant

Answer 46

may be rejected by the body have to take immunosuppressants (increase likelihood of infections) risks of major surgery (high likelihood of infection)

Question 47

kidney failure causes

Answer 47

diabetes mellitus hyper tension infection

Question 48

why kidney failure bad

Answer 48

build up of urea in blood (toxic to cells) | unable to regulate ion and water levels in blood

Question 49

what protein in urine suggests has gone wrong

Answer 49

damage to basement membrane (caused by hypertension), allowing large substances like protein during ultrafiltration into nephron

Question 50

haemodialysis method

Answer 50

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

Question 51

peritoneal dialysis method

Answer 51

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

Question 52

adv. of peritoneal dialysis

Answer 52

treats kidney failure keeps patients alive long enough to receive kidney transplant can be done from home (better quality of life)

Question 53

disadv of peritoneal dialysis

Answer 53

risk of infection post surgery | must carefully control diet

Question 54

monoclonal antibodies method

Answer 54

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

Question 55

pregnancy testing method

Answer 55

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

Question 56

hCG stands for

Answer 56

human chorionic gonadotropin

Question 57

assessing kidney failure

Answer 57

test urine for substances e.g. protein | measuring glomerular filtration rate (GFR)

Question 58

GFR

Answer 58

glomerular filtration rate

Question 59

sodium citrate

Answer 59

anticoagulant used in dialysis removes calcium ions from blood calcium ions are cofactor for blood clotting

Question 60

why haemodialysis needs to be done for less time overall than peritoneal dialysis

Answer 60

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

Question 61

where selective reabsorption occurs

Answer 61

proximal convoluted tubule

Question 62

why longer Loop of Henle is advantageous

Answer 62

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

Question 63

symptoms of lack of ADH

Answer 63

``` frequent need to urinate large volume of very dilute urine persistent feeling of thirst/excessive drinking electrolyte/mineral imbalance dehydration ```

Question 64

ectothermic definition

Answer 64

organism that relies on external sources of heat to maintain body temperature

Question 65

endothermic definition

Answer 65

organism uses heat from metabolic reactions to maintain body temperature

Question 66

what ectotherms do when they are not warm enough

Answer 66

move into sunny area move onto warm surface expose larger SA to sun

Question 67

what endothermic do when they are too warm

Answer 67

move out of sun move underground reduce body surface area to the sun

Question 68

advantages of ectothermy

Answer 68

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

Question 69

disadvantages of ectothermy

Answer 69

less active in lower temperatures during which: greater risk from predation (unable to escape) cannot take advantage of food available

Question 70

exergonic definition

Answer 70

releases energy as heat

Question 71

behavioural responses of endotherms when too hot

Answer 71

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)

Question 72

behavioural responses of endotherms when too cold

Answer 72

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

Question 73

physiological responses used by endotherms when too warm (skin)

Answer 73

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

Question 74

physiological responses used by endotherms when too warm (gaseous exchange system)

Answer 74

some animals pant increases evaporation of water from surface of lungs and airways using heat from blood

Question 75

physiological responses used by endotherms when too warm (liver/muscles)

Answer 75

less respiration/contraction | less heat released

Question 76

physiological responses used by endotherms when too warm (blood vessels)

Answer 76

dilation of blood vessels at extremities | more heat can be a lost

Question 77

physiological responses used by endotherms when too cold (skin)

Answer 77

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)

Question 78

physiological responses used by endotherms when too cold (gaseous exchange system)

Answer 78

less panting, less heat lost

Question 79

physiological responses used by endotherms when too cold (liver/skeletal muscles)

Answer 79

increased respiration in liver cells (more heat released as byproduct) spontaneous muscle contractions (shivering releases heat)

Question 80

physiological responses used by endotherms when too cold (blood vessels)

Answer 80

constriction to limit blood flow to extremities (blood not cooled too much)

Question 81

advantages of endothermy

Answer 81

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

Question 82

disadvantages of endothermy

Answer 82

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

Question 83

role of peripheral temperature receptors

Answer 83

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

Question 84

similarities between ultrafiltration and formation of tissue fluid

Answer 84

* 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

Question 85

differences between ultrafiltration and formation of tissue fluid

Answer 85

* 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