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2A.6 EXCRETION This is explained well in your textbooks – and the diagrams in here are great too So make sure to read through the Chapter & make your own notes!! Excretion There are many chemical reactions taking place in the body – these produce by-products, some of which are able to be used by the body, while others are wastes. Most wastes are toxic and would be harmful if allowed to accumulate. The removal of metabolic wastes from the body is called Excretion Removing wastes also allows the body to maintain equilibrium within the body (this is called Homeostasis) Organs of Excretion • Kidneys – filter blood to maintain a constant concentration of materials in the body fluids, excrete/remove nitrogenous wastes like urea, uric acid & creatinine • Liver – deamination & synthesis of urea • Lungs – CO2 • Skin – sweat glands secrete sweat (contains salts, urea & lactic acid) Kidney Objectives: • Label the components of the Urinary system & relationship with the CV system • Label structures of a kidney (cut-in half) • Label the nephron (the microscopic structure) • Explain the kidney’s function in relation to the nephron – filtration & selective reabsorption to form urine) • Use a table to show the composition of blood plasma & urine = to assess the kidney’s ability to filter & reabsorb some substances and let others pass out. Functions of the kidneys To rid the body of wastes, especially nitrogenous wastes such as urea. To regulate the balance of fluid, salt and pH. Functions of the kidneys They achieve these outcomes by filtering the blood as it passes through the kidneys. Waste substances are removed by the processes of filtration and tubular secretion. Useful substances are returned to the body by the process of selective reabsorption. Structure The major structural components of the urinary system are: Kidneys x2 Urinary bladder x1 Ureters x2 Urethra x1 Components of the urinary system & the kidney (external) US Govt - NIH What is the function of the…. Bladder? Ureters? Urethra? Frontal section through the kidney (*need to know) Renal artery supplies blood to kidney Renal vein takes blood away from kidney US Govt - NIH Nephron* • The functional (microscopic) unit of the kidneys is the nephron. • A nephron consists of a Bowman’s capsule, a renal tubule and their associated blood supply. • Each kidney contains approximately one million nephrons. The renal tubule (*need to know how to label) Bowman’s capsule Proximal convolute tubule (PCT) Common collecting duct Distal convolute tubule (DCT) Loop of Henle (LOH) Processes that occur in the production of urine 1. Filtration 2. Reabsorption (some is selective) 3. Tubular secretion (explained well in textbook – and there is a summary table as well!) The renal corpuscle Filtration takes place in the renal corpuscle. the renal corpuscle consists of the Bowman’s capsule and a mass of blood capillaries – the glomerulus. The renal corpuscle Afferent arteriole (blood coming in) Bowman’s capsule Efferent arteriole (blood leaving) Glomerulus Proximal convolute tubule 1. Filtration Urea Water, Glucose Amino acids Vitamins Salts (mainly sodium & chlorine) Filtration Process Structure Filtration Renal corpuscle Substance Active or passive Filtrate Water Urea, Glucose, Amino acids, Vitamins, Salts (mainly sodium & chlorine Passive (mass flow) Passive 2. Reabsorption Water, Glucose, Amino acids, Vitamins, Salts (mainly sodium & chlorine) Water Salts (mainly sodium & chlorine) Urine - Water - Urea - Salts The proximal tubule • Microvilli line the proximal tubule and create a brush border, which greatly increases the surface area for reabsorption. Microvilli L Slomianka ANHB - UWA Reabsorption Structure PCT Loop of Henle DCT Collecting duct Substance Active/passive Water (60-70%) Salts (60-70%) Glucose (100%) Amino acids (100%) Vitamins (100%) Water (25%) Na+/Cl- (25%) Water (5%) Na+/Cl- (5%) Passive (osmosis) Water (5%) Passive (osmosis) All active Passive (osmosis) Active Passive (osmosis) Active 3. Tubular secretion H+ NH4+ (ammonium) Creatinine Toxins Drugs Neurotransmitters Tubular secretion Process Tubular secretion Structure PCT & DCT Substance Mode H+ Active NH4+ (ammonium) Creatinine Toxins Drugs Neurotransmitters So, why is it well suited to its function? • Glomerular capsule surrounds the glomerulus to collect the fluid filtered out of the blood capillaries • The efferent arteriole leading out of the glomerulus has a smaller diameter – raising blood pressure – so that more fluid is filtered • The tubule has two sets of convolutions (PCT, DCT) and a loop so that each tubule has a large surface area for reabsorption and secretion • Each kidney has over a million nephrons so the total surface area available for reabsorption and secretion is extremely large Urine • Urine is a clear, transparent fluid. It normally has an amber colour (to presence of some bile pigments). • It is collected in the bladder and eliminated through the urethra. • The average amount of urine voided (passed) in 24 hours is about 1.5 litres (varies with diet, environment etc) Composition of urine • The composition of urine varies (usually due to diet/water intake) • Typically, urine contains: – approx. 95% water – approx 5% other solutes (incl. organic molecules such as urea, creatinine and uric acid), ions (mainly sodium & chloride ions) and other metabolic wastes. – There should be no blood cells in urine (too large to pass through glomerulus) – It does not normally contain proteins and glucose Terms • • • • Fluid intake Urine output Total Volume Concentration (concentrated or dilute) Impacts • If water intake is low, urine is very concentrated. (opposite = diluted) • Sleeping – kidney function slows down at night – so less urine produced (and therefore higher concentration in the morning) • If blood cells present in urine – could be sign of infection or disease (should not be present) • Alcohol – increases urine output • Read Kidney Failure and Kidney Dialysis (in textbook)