HideShow resource information


Excretion- removal of unwanted waste products of metabolism

Metabolic waste- waste substances toxic/produced in excess by reations inside cells

Deamination- removal of amine group from amino acid produce ammonia

2 main things excreted:

  • carbon dioxide (produced by respiration); passed from respiring cells to bloodstream, transported lungs, diffuses alveoli, excreted exhale

  • nitrogen-containing compounds ie. urea (produced in liver from excess amino acids): passed bloodstream, transported kidneys in solution, removed from blood = urine where stored until released


1 of 16

Why does Carbon Dioxide need to be removed?

in excess = toxic w/ 3 main effects

  • majority carried as Hydrogen Carbonate ions- makes H ions combine w/ haemog. compete w/ oxygen for space which can reduce oxygen transport

  • combines w/ haemoglobin = carbaminohaemoglobin = lower affinity for oxygen

  • excess = respiratory acidosis as when dissolves in plasma = carbonic acid = dissociates H ions

- H ions lower pH = acidic

- if change small= extra detected by respiratory centre in medulla oblongata increasing breathing rate helps remove excess

- if drops = slowed/difficult breathing, headache, drowsiness, restlessness, tremor + confusion, rapid heart beat, change blood pressure (respiratory acidosis)

- caused by diseases/conditions affect lungs ie asthma/chronic bronchitis/emphysema

2 of 16

Why does Nitrogenous compounds need to be removed?

  • body can't store proteins/ a. acids
  • a. acids lots energy so converted through deamination

  • forms very soluble & toxic ammonia 
  • converted less soluble & toxic urea transported to kidneys for excretion
  • remaining keto acid used directly in respiration/releases energy/converted to fat for storage

deamination; acid + oxygen makes keto acid + ammonia

forming urea; ammonia + carbon dioxide makes urea + water

3 of 16


  • supplied w/ blood from renal artery & drained renal vein
  • role to remove waste products from blood + produce urine
  • outer- cortex, inner- medulla, centre- pelvis leads to ureter
  • Nephron- tubules associated w/ blood capillaries starting @ cortex
  • has knot (glomerulus) & surrounded by bowman's capsule where blood pushed into (ultrafilt)
  • 4 parts; proximal convulated tubule, distal convulated tubule, loop of henle, collecting duct
  • as fluid moves along, composition altered achieved by selective reabsorption
  • substances reabsorbed back to fluid & capillaries w/ final product in CD = urine passes down pelvis, ureter to bladded

desc. limb LoH- Ψ fluid decreased by adding salts, removing water
Ψ increased, more salts removed

CD- Ψ decreased by removal water ensuring urine low water potential so higher concentration solutes

4 of 16


- blood flows into glomerulus from afferent arteriole (wider) & leaves via efferent arteriole

- differ in diameters = blood always under increased pressure which higher than pressure in Bc

- pressure difference tends push fluid from blood into Bc that surrounds glomerulus

barrier between blood in capillary & lumen Bc = 3 layers

  • endothelium of capillary; narrow gaps betw cells blood plasma & substances dissolved can pass
  • basement membrane; fine mesh collagen fibres & glycoproteins act as filter prevent passage molecules relative molecular mass > 69,000 (most proteins held glomerulus)
  • epithelial cells (podocytes); finger-like projections- major processes which ensure there's gaps between cells so fluid from blood glomerulus can pass between these into lumen Bc

Filtered out; water, amino acids, glucose, urea, inorganic ions

Left; blood cells & proteins

5 of 16

Selective Reabsorption

- as fluid moves along nephron substances removed from fluid & reabsorbed into blood

- most occurs in proximal convoluted tubule all gluc/a.a, some salts/water

  • membrane in contact w/ tubule fluid highly folded form microvilli increases SA reabsorp
  • co-transporter proteins transport gluc/a.a in association w/ Na ions from tubule into cell
    (f. diff)
  • oppo membrane, close tissue fluid, folded increase SA also sodium-potassium pumps
  • mitochondria indicates active process involved as makes lots ATP


  • sodium-potassium pumps remove Na ions from cells lining PCT reduce conc in cyto.
  • Na ions transported into cell along w/ gluc/a.a by f. diffusion
  • gluc/a.a conc rises inside cell diffuse out into tissue fluid diffuse into blood & carried away
  • reabsorption reduces water potential cell increasing it in tubule fluid so water in & reabsorb
  • larger molecules reabsorbed by endocytosis
6 of 16

Water Reabsorption (loop of henle) pt I

role LoH create low Ψ in medulla so water reabs from fluid in CD; desc med. asc cort.

  • arrangement allows salts transferred from asc to desc w/ overall effect increase conc salts in tubule fluid + consequently diffuse out from asc limb into surrounding medulla tissue
  • tissue fluid in medulla very low water potential


as fluid in tubule desc into medulla Ψ becomes lower (more neg);

  • loss water by osmosis to surrounding tissue fluid
  • diffusion Na/Cl ions into tubule from surrounding tissue fluid

as fluid asc towards cortex Ψ becomes higher (less neg);

  • base tubule- Na/Cl ions diffuse out tubule into tissue fluid
  • higher up tubule- Na/Cl ions a. transported out into tissue fluid
  • wall asc limb impermeable water so can't leave
  • fluid loses salts, not water as moves up asc
7 of 16

Water Reabsorption (loop of henle) pt II

arrangement = hairpin countercurrent multiplier

  • overall effect increase efficiency salt transfer from asc to desc = build-up salt conc tis fluid
  • movement salts asc to medulla = high salt conc in tis fluid of medulla so low Ψ = more neg
  • removal ions asc limb = top asc limb urine dilute
  • water reabsorbed from urine in distal tubules & CD
  • amount water reabsorb depends needs body so kidney = organ osmoregulation


  • top asc limb tubule fluid passes along short DCT a. transport used adjust conc various salts
  • fluid flows into CD where tubule fluid still lots water (high Ψ)  
  • CD carries fluid through medulla to pelvis & as passes CD water moves from tubule fluid to tissue
  • enters blood capillaries & carried away
  • amount reabsorbed depends on permeability walls of CD, when urine reaches pelvis low Ψ & conc urea + salts in urine higher than that of plasma
8 of 16

Osmoregulation pt I

Osmoregulation- control of water + salt levels in body

  • correct water balance between cells & surrounding fluid maintained prevent problems osmosis

water gain; food,drink, metabolism

water loss; urine, swear, water vapour in exhaled air, faeces

  • cool day = drunk lots = large volume dilute urine
  • hot day = drunk little = small volumes more concentrated urine

walls of collecting duct made more/less permeable according to needs of body

  • cool day = conserve less water = CD less permeable = less reabsorbed = more urine
  • hot day = conserve more water = CD more permeable = more reabsorbed = less urine
9 of 16

Osmoregulation pt II

Altering permeability

walls collecting duct respond to level antidiuretic hormone (ADH) in blood

cells have receptors bind ADH = ECR in cell

end result reactions insert vesicles contain water-permeable channels (aquaporins) into membr

makes walls more permeable water

more ADH = more aquaporins inserted = more water reabsorbed into blood = less urine 

less ADH = membrane folds inwards = new vesicles remove aquaporins = walls less permeable = less reabsorbed = more water passes out urine

10 of 16

Osmoregulation pt III

Adjusting concentration ADH in blood

water potential blood monitored by osmoreceptor in hypothalamus

cells respond effects osmosis, when water potential low osmoreceptor cells lose water = shrink & stimulate neurosecretory cells 

neurosecretory cells specialised neurons produce/release ADH; ADH made in cell body & flows down axon to terminal bulb in posterior pituitary gland where stored until needed

when stimulated send AP down axons & cause release ADH

ADH enters capillaries running through pituitary gland where transported + acts cells of CD

once water potential rises again, less ADH released

ADH slowly broken down w/ half life 20 minutes so ADH present in blood broken down & CD receive less stimulation

11 of 16

Kidney Failure pt I

occurs for number of reasons w/ most common:

  • diabetes mellitus
  • hypertension
  • infection

kidney fail- can't remove excess water/waste products can't regulate water/salts in body = death


Kidney transplant;

  • old kidneys left in place unless infection/cancerous & get kidney living relative/dead
  • major surgery as under anaesthesia implanted new organ attach blood supply + bladder
  • many feel better immediately but sometimes immune system = foreign new organ so given immunosuppresant drugs to prevent rejection

AD: freedom from time-consuming dialysis, diet less limited, better quality life, feel better physi

DISAD: need immunosuppresants, major surgery, frequent checks signs organ rejection

12 of 16

Kidney Failure pt II


dialysis- use of partially permeable membrane to filter blood

- remove waste/excess fluid + salt by passing over dialysis membrane

- partially-permeable allows exchange substances betw blood & dia fluid

- fluid = correct conc substances in plasma

- excess subst- diffuse across membrane into dia fluid

- too low conc- diffuse into blood from dia fluid

- dialysis combined w/ carefully monitored diet

13 of 16

Kidney Failure pt III

Treatment- Dialysis

2 types;


  • blood from vein passed into machine w/ artificial dialysis membrane
  • herapin added avoid clotting
  • bubbles removed before blood returns to body
  • performed @ clinic 3x week several hours
  • some learn to carry it out at home

peritoneal dialysis (PD)

  • filter = body own abdominal membrane
  • surgeon implants permanent tube in abdomen + dialysis solution added fill space
  • after several hours used solution drained
  • usually performed several consec sessions daily @ home/work
  • patient can walk around so sometimes called ambulatory PD
14 of 16

Testing Urine Samples

Pregnancy testing

once implanted in uterine lining, embryo secretes human chorionic gonadotrophin (hCG)

hCG rel small glycoprotein + found in urine as early as 6 days after conception

pregnancy tests today manufactured w/ monoclonal antibodies

antibody specific & binds only to hCG

when taken, soaks portion of test strip in urine

hCG-antibody complex moves up strip until sticks band of immobilised antibodies

all antibodies carrying blue bead & attached to hCG held in 1 place = blue line

always 1 control blue line to use for comparison, second = pregnancy

15 of 16

Testing Urine Samples pt II

Testing for anabolic steroids

anabolic steroids increase protein synthesis within cells = build-up cell tissue

non-medical uses controversial bc give advantage in competitive sports & dangerous side effects so banned by all major spoting bodies

half-life 16 hours, remain in blood days + relatively small & enter nephron easily

testing involves analysing urine sample in a lab using gas chromatography or mass spectrometry

gas chromatography- sample vaporised presence gaseous solvent & passed down long tube lined by absorption agent

each substance dissolves differently in gas & stays for unique, specific time (retention time)

analysed create chromatogram

standard samples drugs & urine run so drugs identified + quantified in chromatograms

16 of 16


Izzy Mason

Brilliant thanks :)

Similar Biology resources:

See all Biology resources »See all Excretion resources »