excretion in humans

• Antidiuretic hormone (ADH) regulates water loss by controlling the amount of water that passes out of the collecting ducts in the nephrons.
• Kidneys are responsible for excreting waste products such as urea, excess water, excess salts, carbon dioxide, and bile pigments
• Kidneys play a role in osmoregulation, which involves regulating the balance of water and electrolytes in the body
• Kidneys are crucial for urine formation through processes like ultrafiltration and selective reabsorption
• Excretion involves removing metabolic waste products and toxic substances from the body
• While most unicellular organisms excrete waste products via simple diffusion, larger organisms like humans have specialized excretory organs for excretion
• Examples of excretory organs found in mammals include the kidneys, ureters, bladder, and urethra
• Waste products excreted by humans include urea, excess water, excess salts, carbon dioxide, bile pigments, and various substances in sweat, expired air, and urine
• The human urinary system consists of the kidneys, ureters, bladder, and urethra, each with specific functions in the excretion process
• The structure of the kidney includes the cortex, medulla, renal pyramid, kidney tubules, ureter, fibrous capsule, renal artery, renal vein, and renal pelvis
• The basic functional unit of the kidney is the nephron, which consists of parts like Bowman's capsule, proximal and distal convoluted tubules, loop of Henle, and collecting duct
• Blood circulation at the kidney tubule involves the renal artery branching into arterioles, forming a glomerulus, and exiting through the renal vein
• Ultrafiltration and selective reabsorption are key processes in urine formation within the kidney tubule
• Ultrafiltration occurs at the renal corpuscle and involves the filtration of small molecules into Bowman's capsule due to high hydrostatic blood pressure and a partially permeable membrane
• Selective reabsorption involves reabsorbing useful substances like glucose, amino acids, water, and mineral salts from the glomerular filtrate back into the blood to prevent excessive loss
• General salts and nitrogenous waste are filtered from blood in the glomerulus to form glomerular filtrate, which eventually becomes urine
• Most of the glomerular filtrate is reabsorbed, but some substances are selectively reabsorbed back into the blood
• Structural features of the nephron for selective reabsorption:

  • Parts of the nephron are highly coiled to increase surface area and time for selective reabsorption
  • Dense network of capillaries around the nephron to increase surface area contact and maintain concentration gradient
  • Epithelial cells of coiled tubules contain many mitochondria to release energy for active transport
• On average, a person produces 1.5 to 2.5 litres of urine per day, depending on diet and health
• Urine color meanings:

  • Dark yellow: dehydration
  • Brownish orange: liver issues
  • Transparent yellow: normal
  • Pale yellow: normal
  • Transparent: normal
  • Pinkish red: possible blood presence
• Factors affecting urine composition:

  • The need for excretion
  • Excretory organs & products
  • Components of urinary system
  • Structure of the kidney
• Osmoregulation:

  • The regulation of blood plasma water potential
  • Controlled by anti-diuretic hormone (ADH) from the hypothalamus and pituitary gland
  • ADH increases reabsorption of water by the kidney tubules
  • Kidneys indirectly regulate blood pressure through osmoregulation
• Mechanism of dialysis in kidney failure:

  • Dialysis machine mimics kidney function
  • Blood is filtered and returned to the body
  • Dialysis fluid lacks nitrogenous waste to allow waste removal
• An individual can lead a normal life with one healthy kidney, as the remaining kidney compensates for the lost one
• Dialysis process:

  • Blood is drawn from a vein in the arm
  • Blood is pumped into the dialysis machine where it is filtered
  • Small molecules diffuse out of the tubing, while larger molecules remain
  • Filtered blood is returned to a vein in the arm
• Features enhancing dialysis process:

  • Dialysis fluid contains essential substances like glucose, amino acids, and mineral salts
  • Dialysis tubing is long, narrow, and coiled to increase exchange rate
  • Dialysis fluid flows countercurrent to blood flow to maintain a steep concentration gradient
• Blood enters the kidneys via the renal artery and leaves via the renal vein.
• The urinary bladder stores urine until it is excreted from the body.
• Ureters are tubes that carry urine from the kidneys to the urinary bladder.
• Urine formation involves filtration at the glomerulus, reabsorption of useful substances, secretion of certain substances, and concentration or dilution of urine.
• Nephron is the functional unit of the kidney responsible for filtration, secretion, and reabsorption processes.