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Chapter 9 Excretory System consists of the kidneys, ureters, urinary bladder and urethra 1 The kidneys 2 How much do you know about your kidneys? http://www.betterhealth.vic.gov.au/BHCV2/BHC ARTICLES.NSF/pages/Quiz_The_urinary_syste m?OpenDocument 3 Answers to kidney quiz 1. 2. 3. 4. 5. 6. 7. 8. B B A A A C B A 4 URINARY SYSTEM - OVERVIEW http://www.youtube.com/watch?v=qxb2_d9ilEw 5 Kidney Structure human kidney 6 Functions of the kidneys • removal of metabolic wastes (urea, uric acid) from the blood and excretion to the outside of the body • regulation of blood pressure (aldosterone) • regulation of ion (Ca2+, Na+) absorption • regulation and conservation of water in the body 7 Fig. 36.8 1. There are approximately 1 million nephrons in each kidney. Why so many? 9 The nephron 4 STAGES OF URINE FORMATION 1. Glomerular filtration – into Bowman’s Capsule 1. Solute Reabsorption – from proximal tubule to capillary 3. Water Reabsorption – from proximal tubule and Loop of Henle to capillary 4. Tubular Secretion – from capillary to distal tubule Fig. 36.11 The nephron 12 Page 678 Urine Formation Urine is the final product of the processes of: • glomerular filtration: substances move from blood in glomerulus to the Bowman’s capsule • solute reabsorption: nutrients i.e. glucose, potassium and sodium ions, and many other substances the body can use • water reabsorption • tubular secretion 14 Step 1: Glomerular Filtration • The first step in urine formation is filtration of substances out of the glomerular capillaries into the Bowman’s capsule •Filtrate includes: water, sodium, chloride ions, glucose, amino acids, urea, other small solutes •Filtrate does NOT include: red and white blood cells, platelets, plasma proteins 15 Glomerular Filtrate and Urine average amounts over a 24 hour period 16 Step 2: Solute Reabsorption • sodium, chloride, glucose, amino acids are actively transported from the filtrate to the blood in the proximal tubule •There are many mitochondria in the cells of the proximal tubule (for ATP) 17 Step 3 WATER REABSORPTION •Water reabsorption begins in the proximal tubule (osmosis resulting from active transport of ions, glucose, etc from filtrate into blood) 18 Step 4: Tubular Secretion • transports substances (such as H+, K+, drugs, other solutes) from the capillary into the distal tubule • active transport – distal tubule has many mitochondria for ATP 19 Urine Composition • about 95% water • usually contains urea, uric acid, and creatinine (break down product from creatine phosphate used up in muscles) • may contain trace amounts of amino acids and varying amounts of electrolytes • volume varies with fluid intake, diuretics (caffeine & alcohol) and environmental factors (heat, humidity) 20 Ureters 21 Urinary Bladder • hollow, distensible, muscular organ located within the pelvic cavity, posterior to the pubic bone 22 Urinary Bladder 23 24 Urethra • tube that conveys urine from the urinary bladder to the outside of the body 25 Urine colour chart 26 Life-Span Changes • kidneys appear scarred and grainy • kidney cells die • by age 80, kidneys have lost a third of their mass • kidney shrinkage due to loss of glomeruli • proteinuria may develop (protein in urine) • renal tubules thicken • harder for kidneys to clear certain substances • bladder, ureters, and urethra lose elasticity • bladder holds less urine 27 ANIMATION REVIEW http://www.sumanasinc.com/webcontent/ani mations/content/kidney.html 28