Biology

• Excretory system

  • Two kidneys
  • Ureter takes urine to bladder
  • Bladder stores urine
  • Urethra excretes urine from body
• Structure of one kidney

  1. Ureter takes urine to bladder

  2. Renal artery brings blood to kidney

  3. Renal vein removes blood from kidney

  4. Medulla

  5. Pelvis

  6. Cortex

  7. Fibrous capsule
• Kidney


  • Cortex has vast blood supply
  • Medulla composed of collecting tubules that empty into renal pelvis
  • Pelvis drains urine into urethra
• Nephron


  • Filtration unit in kidney
  • Millions in each kidney
• Nephron structure


  1. Glomerulus

  2. Bowman's capsule

  3. Proximal convoluted tubule

  4. Loop of Henle

  5. Distal convoluted tubule

  6. Collecting duct
• Bowman's capsule


  • Site of ultrafiltration
• Proximal convoluted tubule


  • Site of selective reabsorption of water, glucose, ions
• Loop of Henle


  • Maintains sodium ion gradient in medulla
• Distal convoluted tubule


  • Site of water reabsorption
• Collecting duct


  • Site of water reabsorption
• Ultrafiltration


  1. High hydrostatic pressure in glomerulus forces small substances into Bowman's capsule

  2. Large proteins remain in blood
• Selective reabsorption


  1. Glucose, amino acids, water, ions reabsorbed in proximal convoluted tubule

  2. Cells have many mitochondria and microvilli to facilitate reabsorption
• Counter-current multiplier system


  1. Sodium actively transported out in ascending limb

  2. Water moves out by osmosis in descending limb

  3. Increases sodium concentration in medulla
• Osmoregulation


  1. Water moves out of distal convoluted tubule and collecting duct by osmosis

  2. Controlled by ADH which increases permeability
• Hypothalamus


  • Contains osmoreceptors that detect blood water potential
  • Produces ADH when water potential is low
• Posterior pituitary


  Secretes ADH into blood when signalled by hypothalamus
• Response to decreased water potential

  1. Hypothalamus produces more ADH

  2. Posterior pituitary secretes more ADH

  3. ADH increases permeability of collecting duct and distal convoluted tubule

  4. More water reabsorbed, smaller volume of more concentrated urine
• Response to increased water potential

  1. Less ADH produced

  2. Decreased permeability

  3. Less water reabsorbed, larger volume of dilute urine
• Digestive system


  • Esophagus
  • Stomach
  • Liver
  • Gallbladder
  • Duodenum
  • Small intestine (ileum)
  • Large intestine (colon)
  • Rectum
  • Anus
• Stomach


  • Mechanical and chemical digestion
  • Hydrochloric acid kills bacteria
  • Optimum pH for protease enzymes
• Pancreas


  • Exocrine glands secrete digestive enzymes into duodenum
  • Endocrine glands secrete insulin and glucagon into blood
• Gallbladder


  • Stores and releases bile
  • Bile neutralizes stomach acid and emulsifies lipids
• Duodenum


  • Site of neutralization of stomach acid using bile
• Ileum


  • Site of absorption of digestion products
  • Microvilli increase surface area
• Colon


  • Site of water reabsorption
• Starch digestion


  1. Salivary amylase hydrolyzes starch to maltose

  2. Pancreatic amylase continues hydrolysis in small intestine

  3. Maltase on epithelial cells hydrolyzes maltose to glucose
• Amylase


  Enzyme produced in salivary glands and pancreas that hydrolyzes starch to maltose
• Maltase


  Enzyme embedded in epithelial cell membrane that hydrolyzes maltose to glucose
• Glucose absorption


  1. Sodium ions actively transported out of epithelial cells

  2. Creates sodium concentration gradient

  3. Sodium-glucose cotransporter carries glucose into epithelial cells
• Digestion of starch


  1. Amylase in salivary glands and pancreas hydrolyzes starch to maltose

  2. Maltase in epithelial cells of ileum hydrolyzes maltose to glucose
• Amylase


  Enzyme produced in salivary glands and pancreas that catalyzes the hydrolysis of starch to maltose
• Maltase


  Enzyme embedded in epithelial cell membrane of ileum that catalyzes the hydrolysis of maltose to glucose
• Absorption of glucose


  1. Sodium ions actively transported out of epithelial cells by sodium-potassium pump

  2. Sodium-glucose co-transporter carries glucose into epithelial cells

  3. Glucose diffuses out of epithelial cells by facilitated diffusion
• Digestion of proteins


  1. Pepsin in stomach hydrolyzes polypeptides to shorter polypeptides

  2. Trypsin in duodenum hydrolyzes polypeptides to shorter polypeptides

  3. Exopeptidases in duodenum hydrolyze short polypeptides to amino acids

  4. Dipeptidase in epithelial cells of ileum hydrolyzes dipeptides to amino acids
• Pepsin


  Enzyme produced in stomach that has pH optimum of 2 and hydrolyzes polypeptides to shorter polypeptides
• Trypsin


  Enzyme released from pancreas that has pH optimum of 8 and functions in duodenum to hydrolyze polypeptides to shorter polypeptides
• Exopeptidases


  Enzymes produced in pancreas that function in duodenum to hydrolyze short polypeptides into amino acids
• Dipeptidase


  Enzyme found in epithelial cell membrane of ileum that hydrolyzes dipeptides into amino acids
• Digestion of lipids


  1. Bile salts emulsify lipids

  2. Lipase from pancreas and small intestine hydrolyzes lipids into monoglycerides and fatty acids
• Lipase


  Enzyme that hydrolyzes ester bonds in lipid molecules to produce glycerol and fatty acids