Excretion, communication and homeostasis

• What is excretion?


  Removal of metabolic waste from the body
• What is metabolic waste?


  Substance produced in excess by the metabolic processes in cells
• Why is metabolic waste a concern for the body?


  It may become toxic if not removed
• What is secretion?


  It is a wanted product
• What products must be excreted from the body?

  • Urea
  • CO2 from respiration
  • Nitrogen-containing compounds
  • Bile pigments found in feces
• How is urea produced in the body?


  Urea is made from excess amino acids in the liver through deamination
• Which organs are involved in excretion?


  Lungs, liver, and kidneys
• What role do the lungs play in excretion?


  They excrete CO2 passed from respiring tissues
• How does the liver contribute to excretion?


  The liver converts excess amino acids to urea in deamination
• What is the process of deamination?


  Amino acid + oxygen → keto acid + ammonia
• What happens to ammonia after deamination?


  Ammonia is converted to urea for transport to the kidneys
• What is the importance of excretion?


  • Prevents metabolic product build-up
  • Avoids enzyme inhibition
  • Maintains homeostasis
• How does carbon dioxide affect blood pH?


  It causes blood to become more acidic
• What is the role of carbonic anhydrase?


  It catalyzes the conversion of CO2 and H2O to carbonic acid
• What happens to oxyhemoglobin when CO2 levels increase?


  It dissociates to release oxygen
• How does excess CO2 affect hemoglobin's affinity for oxygen?


  It reduces hemoglobin's affinity for oxygen
• What is the effect of low pH on proteins in red blood cells?


  It can alter the shape of proteins
• What is erythropoietin?


  A hormone that stimulates the production of red blood cells
• What is renin?


  An enzyme that raises blood pressure
• What are the functions of the liver?


  • Regulates blood glucose, amino acid, and lipid levels
  • Synthesizes bile, plasma proteins, and cholesterol
  • Stores vitamins and minerals
  • Breaks down drugs and hormones
  • Destroys red blood cells
• What is the structure of the nephron?


  The nephron is the functional unit of the kidney
• What is ultrafiltration in the nephron?


  Filtration of blood at a molecular level under pressure
• How does blood enter the kidney?

  Through the renal artery
• What happens to urine after it is formed in the kidney?


  Urine is collected into the renal pelvis and travels down the ureter to the bladder
• What are the main functions of nephrons?


  1. Ultrafiltration in the glomerulus
  2. Reabsorption of water, glucose, and ions
  3. Regulation of blood pressure and volume
  4. Formation of urine
• What is the role of the proximal convoluted tubule?


  Reabsorption of all sugars, most mineral ions, and some water
• What occurs in the descending limb of the loop of Henle?


  Water potential of fluid decreases by removal of water
• What happens in the ascending limb of the loop of Henle?


  Water potential is increased as mineral ions are removed by active transport
• What is the function of the collecting duct?


  Water potential decreases by removal of water, forming urine
• What is the role of ADH in the kidney?


  ADH binds to the collecting duct to regulate water reabsorption
• How does the loop of Henle contribute to urine concentration?


  It creates a concentration gradient for water reabsorption
• What is the significance of the nephron's structure?


  It maximizes surface area for reabsorption and filtration
• What is the role of cotransporter proteins in the nephron?


  They transport glucose or amino acids from the tubule into the cell
• How does the reabsorption mechanism work in the nephron?


  It involves the movement of sodium ions creating a concentration gradient for water reabsorption
• What are the steps of the reabsorption mechanism in the nephron?


  1. Sodium ions are not actively pumped out of cells
  2. Concentration of sodium in cytoplasm decreases
  3. Sodium diffuses into the cell through cotransporter proteins
  4. Water moves into the cell via osmosis
  5. Glucose and amino acids are reabsorbed
• What is the function of the ascending limb of the Henle loop?


  It increases water potential by removing mineral ions through active transport.
• How does the collecting duct affect water potential?


  It decreases water potential by removing water.
• What is erythropoietin?


  A hormone that stimulates the production of red blood cells.
• What is renin?


  An enzyme that raises blood pressure.
• What is selective reabsorption in the kidneys?


  • Process where substances are reabsorbed from the tubule into the blood.
  • Involves microvilli to increase surface area.
  • Uses cotransporter proteins for glucose and amino acids.