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
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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

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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

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  • 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

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- 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

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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
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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
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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
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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
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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

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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

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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

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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

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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
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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 ***** in urine

hCG-antibody complex moves up ***** 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

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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

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Izzy Mason


Brilliant thanks :)



Only issue is that herapin on slide 14 should be heparin, otherwise very useful

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