M5:S2 Excretion

• Excretion


  The removal of waste products from the body
• Metabolism


  The chemical reactions that happen in cells
• Metabolism produces waste products that are toxic and need to be removed from the body
• Excretion maintains normal metabolism and homeostasis
• Liver


  • Breaks down excess amino acids
  • Breaks down other harmful substances like alcohol and drugs (detoxification)
• Breakdown of excess amino acids in the liver

  1. Deamination (removal of amino groups)

  2. Organic acids can be respired or converted to carbohydrate

  3. Ammonia converted to urea

  4. Urea released into blood and filtered out by kidneys
• The liver stores glycogen from excess glucose
• Hepatic artery


  Supplies the liver with oxygenated blood
• Hepatic vein


  Takes deoxygenated blood away from the liver
• Hepatic portal vein


  Brings blood rich in digestion products to the liver
• Bile duct


  Transports bile produced by the liver to the gallbladder
• Liver lobules


  • Cylindrical structures made of hepatocytes arranged in rows
  • Central vein in the middle
  • Branches of hepatic artery, portal vein and bile duct connected
  • Blood flows through sinusoids past hepatocytes
• Kupffer cells


  Cells attached to sinusoid walls that remove bacteria and break down old red blood cells
• Hepatocytes produce and secrete bile into bile canaliculi
• Liver tissue can be examined under a microscope to identify structures like central vein, hepatocytes, sinusoids
• Kidneys


  Organs of excretion that filter waste products out of the blood and regulate water potential
• Excretion by the kidneys

  Blood enters through renal artery, filtered in nephrons, useful substances reabsorbed, remaining waste excreted as urine through ureter to bladder
• Nephrons


  • Long tubules with bundle of capillaries where blood is filtered (glomerulus in Bowman's capsule)
  • Afferent and efferent arterioles
  • Filtrate passes along nephron, useful substances reabsorbed
• Efferent arteriole


  Blood vessel that carries blood away from the glomerulus
• Nephron


  Functional unit of the kidney
• Urethra


  Tube that carries urine from the bladder out of the body
• Glomerulus


  Cluster of capillaries in the kidney where filtration occurs
• Afferent arteriole


  Blood vessel that carries blood to the glomerulus
• Cortex


  • Outer region of the kidney
• Collecting duct


  Tube that collects urine from the nephrons and transports it to the renal pelvis
• Renal artery


  Blood vessel that supplies blood to the kidney
• Renal vein


  Blood vessel that carries blood away from the kidney
• Bowman's capsule


  Cup-shaped structure at the beginning of the nephron that receives the filtrate
• Efferent arteriole is smaller in diameter than the afferent arteriole


  Blood in the glomerulus is under high pressure
• Ultrafiltration


  1. High pressure forces liquid and small molecules out of the capillary and into the Bowman's capsule

  2. Larger molecules like proteins and blood cells can't pass through
• Filtrate


  Liquid and small molecules that pass into the Bowman's capsule
• Filtrate flow


  1. Flows through the rest of the nephron

  2. Useful substances are reabsorbed along the way

  3. Remaining filtrate is urine that flows out through the ureter
• Proximal convoluted tubule (PCT)


  Part of the nephron where selective reabsorption occurs
• Distal convoluted tubule (DCT)

  Part of the nephron where selective reabsorption occurs
• Loop of Henle


  Part of the nephron where water is reabsorbed
• Selective reabsorption


  1. Useful substances leave the tubules and enter the capillary network

  2. Epithelium of the PCT has microvilli to increase surface area for reabsorption

  3. Glucose, amino acids, vitamins and some salts are reabsorbed by active transport and facilitated diffusion

  4. Some urea is also reabsorbed by diffusion

  5. Water is reabsorbed by osmosis
• Composition of urine


  • Water and dissolved salts
  • Urea
  • Other substances such as hormones and excess vitamins
• What urine doesn't usually contain

  • Proteins and blood cells
  • Glucose, amino acids and vitamins
• The volume of water in urine varies depending on how much you've drunk
• The amount of urea in urine varies depending on how much protein you've eaten