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excretion - Coggle Diagram
excretion
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human urinary system
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kidneys
contain numerous nephrons (tubules) which remove urea, excess water and heat from blood to form urine
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metabolism
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importance
get rid of waste products which are harmful and to ensure the maintenance of a steady state in the body
excretion
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excretory products
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excess water in urine, sweat and water vapour from kidneys, skin and expired air
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ultrafiltration
main idea: filter small, hold back big
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process
- renal artery splits into many arterioles, each leading into a nephron. the arteriole splitis into glomerulus
- the lumen of the afferent arteriole that brings blood into the glomerulus is wider than the efferent arteriole which bring blood away
- blood cells, platelets and large molecules like blood proteins and fats remain in blood which leaves the glomerulus via the efferent arteriole
- blood enters the glomerulus more readily through the wider afferent arteriole than it can leave through the narrower efferent arteriole. Hence, blood dams up in the glomerulus, creating a high blood pressure which forces blood plasma out of the glomerular capillaries into the Bowman's capsule along the entire length of the glomerulus
- the blood plasma forced out contains water and small molecules eg glucose amino acids minerals and nitrogenous products and it forms the filtrate in the Bowman's capsule
selective reabsorption
importance
in a normal adult, 120cm3 of filtrate is formed in the kidney every minute. if this volume fo filtrate is allowed to pass out as urine, the body will lose too much water and useful substances
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occurs at:
- PCT: all glucose, amino acids and vitamins are reabsorbed through the walls of the nephron into the surrounding capillaries
85% of the sodium ions, chloride ions and water are reabsorbed. the active uptake of sodium and other ions into the blood increases the water potential in the nephron, causing water to leave the nephron into the capillaries by osmosis
- loop of Henle: water is reabsorbed here
- DCT: water and smaller concentration of sodium ions and calcium ions are reabsorbed here
- collecting duct: remaining water needed by the body is reabsorbed here
composition of urine
water 96.0g, salts 1.8g, urea 2.0g, other nitrogenous substances 0.2g
might vary
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taking in more liquids/water rich food: larger volume of urine
water potential of the blood increases
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diabetes mellitus: large amount of glucose
unable to store excess glucose as glycogen in the body -> high conc. of glucose in the blood -> nephrons cannot reabsorb all the glucose fast enough -> lots of glucose passed out in urine
dialysis
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hemodialysis
done 2-3 times a week, 3-5h each session
how
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dialysis fluid introduced into dialyser and will be in contact with the tubing, where diffusion of waste materials form the blood into the dialysis fluid occurs
small molecules such as urea and other metabolic waste products diffuse out of the tubing into the dialysis fluid. bigger molecules remain in the tubing
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dialyser
features
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fresh dialysis fluid is in contact with the tubing where blood is about to enter the patient -> ensures no waste product enters the patient
dialysis fluid
contains same conc. of essential substances (eg glucose, amino acids and salts) as healthy blood so that essential substances will not diffuse out of the blood to the dialysis fluid
no metabolic waste products to set up suitable conc. gradient for waste products (urea, uric acid, creatinine, excess salts) to diffuse out of the tubing into dialysis fluid, maintaining the correct solute conc. and water potential of blood