Urinary System


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Contains both the Urine Formation Worksheet Review, and my own summary of the main textbook's chapter on the urinary system.

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Urinary System

  3. 3. Tubular Reabsorption <ul><li>Occurs in the proximal convoluted tubule </li></ul><ul><li>Microvili of the epithelial cells account for maximum reabsorption </li></ul><ul><li>It is the process by which nutrients are absorbed after they’ve already been through the intestines </li></ul>
  4. 4. Transport Mechanisms <ul><li>Lipid-soluble substances – moving down a concentration gradient for that substance </li></ul><ul><li>Sodium ions – active transport </li></ul><ul><li>Glucose – active transport through tubule walls </li></ul><ul><li>Water – osmosis through epithelium </li></ul><ul><li>Amino acids – active transport </li></ul><ul><li>Albumin – endocytosis </li></ul><ul><li>Lactic acid – active transport </li></ul>
  6. 6. Water and Sodium <ul><li>Water is transported through osmosis, and so tends to follow sodium ions into the proximal convoluted tubule until osmotic equilibrium is reached </li></ul><ul><li>Sodium transports water, because water diffuses passively but it carries the diffusion with its own active transport </li></ul><ul><li>They are closely associated because if one increases or decreases, so does the other </li></ul>
  7. 7. ADH (Antidiuretic Hormone) <ul><li>ADH controls water absorption in the collecting duct and the distal convoluted tubule of the kidney </li></ul><ul><li>It does this by stimulating the cells to insert “water channels” into the membrane, making the epithelium more permeable for water to diffuse through the cells </li></ul>
  9. 9. Tubular Secretion <ul><li>Process by which some substances move from the peritubular capillary into the renal tubule </li></ul><ul><li>H+ Ions – actively secreted throughout the entire renal tubule </li></ul><ul><ul><li>It regulates the pH balance, or acidity, of urine </li></ul></ul><ul><li>K+ Ions – passively transported through tubular epithelium into tubular fluid, then actively secreted </li></ul>
  11. 11. Permeability of Limbs of the Nephron <ul><li>Ascending Limb: </li></ul><ul><ul><li>Fairly permeable to water </li></ul></ul><ul><ul><li>Actively reabsorbs sodium and chloride ions </li></ul></ul><ul><ul><li>More hypotonic (less concentrated solutions in osmosis) </li></ul></ul><ul><li>Descending Limb: </li></ul><ul><ul><li>Very permeable to water </li></ul></ul><ul><ul><li>Somewhat permeable to solutes </li></ul></ul><ul><ul><li>More hypertonic (more concentrated solutions in osmosis) </li></ul></ul>
  12. 12. Countercurrent <ul><li>Mechanism – the process by which the kidneys concentrate the urine </li></ul><ul><li>Multiplier – the property where the urine becomes more concentrated each time a circuit is complete through the mechanism and filtration process </li></ul>
  14. 14. Antidiuretic Hormone <ul><li>ADH is produced in the pituitary gland </li></ul><ul><li>ADH prevents dehydration by stimulating the collecting ducts and the distal convoluted tubule to be more permeable to water, increases osmosis and allowing more water back into the body </li></ul><ul><li>When this happens, the sodium concentration in the medullary interstitial fluid increases as water leaves but sodium does not </li></ul>
  15. 15. Drinking Too Much Water <ul><li>On an incidental basis, drinking too much water simply dilutes the concentration of urine – too much causes water to seep out of the circulatory system and into the neighboring cells (causing headaches when this happens in the brain) </li></ul><ul><li>On a regular basis, it can damage the glomeruli as they overwork to process the excess water in the circulatory system </li></ul>
  17. 17. Renin-Angiotensin <ul><li>Renin is an enzyme secreted by the juxtaglomerular cells of the afferent arteriole </li></ul><ul><li>Renin </li></ul><ul><ul><li> breaks down angiotensinogen </li></ul></ul><ul><ul><li> becomes Angiotensinogen I </li></ul></ul><ul><ul><li> converted into Angiotensinogen II </li></ul></ul><ul><ul><li> stimulates aldosterone formation, which reduces the amount of sodium excreted in urine </li></ul></ul><ul><li>Macula Densa cells are sensitive to the sodium concentration in the distal convoluted tubule </li></ul>
  19. 19. KIDNEYS
  20. 20. Kidneys <ul><li>Bean-shaped organs in the lower-middle back on either side of the spinal column, help in place by adipose and connective tissue </li></ul><ul><li>Where urine is formed </li></ul><ul><li>Functions: </li></ul><ul><ul><li>Remove metabolic wastes </li></ul></ul><ul><ul><li>Regulate blood pressure, red blood cell production, and calcium ion absorption </li></ul></ul><ul><ul><li>Regulate volume, composition, and pH of blood </li></ul></ul>
  21. 21. Nephrons <ul><li>Functional unit of the kidney </li></ul><ul><ul><li>renal corpuscle </li></ul></ul><ul><ul><ul><li>Glomerulus </li></ul></ul></ul><ul><ul><ul><li>Glomerular capsule </li></ul></ul></ul><ul><ul><li>renal tubule </li></ul></ul><ul><ul><ul><li>proximal convoluted tubule </li></ul></ul></ul><ul><ul><ul><li>Nephron loop (ascending and descending limbs) </li></ul></ul></ul><ul><ul><ul><li>Distal convoluted tubule </li></ul></ul></ul><ul><li>Joins a collecting duct </li></ul>
  23. 23. Glomerular Filtration <ul><li>Urine formation begins when water and dissolved materials are filtered out of the glomerular capillary </li></ul><ul><li>Secretes renin to stimulate formation of aldosterone to hold onto sodium when the concentration of sodium decreases </li></ul>
  24. 24. Filtration Rate and Pressure <ul><li>Pressure – powered by hydrostic pressure in the glomerular capillaries </li></ul><ul><ul><li>Also affected by osmotic pressure </li></ul></ul><ul><ul><li>Blood vessels will constrict or relax when necessary to keep up same pressure </li></ul></ul><ul><li>Rate – varies with pressure </li></ul><ul><ul><li>Osmotic pressure increases, rate decreases </li></ul></ul><ul><ul><li>And vice-versa </li></ul></ul>
  25. 25. Tubular Reabsorption <ul><li>Substances selectively reabsorbed from the glomerular filtrate </li></ul><ul><li>Mostly happens in the proximal convoluted tubule, with help from microvili </li></ul><ul><li>Different materials reabsorbed in different ways </li></ul><ul><ul><li>Active transport – glucose, amino acids, sodium ions </li></ul></ul><ul><ul><li>Endocytosis – proteins </li></ul></ul><ul><ul><li>Osmosis – water (passively follows sodium) </li></ul></ul><ul><li>Excess substances released in urine </li></ul>
  26. 26. Tubular Secretion <ul><li>Transports some substances from plasma to tubular fluid </li></ul><ul><ul><li>Substances are actively secreted </li></ul></ul><ul><ul><li>This includes various hydrogen ions </li></ul></ul><ul><li>Potassium secreted both actively and passively in distal convoluted tubule and collective duct </li></ul>
  27. 27. Urine Regulation (Concentration and Volume) <ul><li>Most of sodium is reabsorbed before urine is excreted, as they are concentrated in a renal medulla by the countercurrent mechanism </li></ul><ul><ul><li>Water being reabsorbed helps it along, though it increases the concentration of sodium in the tubular fluid </li></ul></ul><ul><li>Distal convoluted tubule and collecting duct impermeable to water, so any water left is excreted through urine </li></ul><ul><ul><li>Unless ADH gets there, making them permeable to water, promoting water absorption and controlling sodium concentration </li></ul></ul>
  28. 28. Urea and Uric Acid Excretion <ul><li>Urea – byproduct of amino acid production </li></ul><ul><ul><li>50% is excreted through urine </li></ul></ul><ul><ul><li>Countercurrent mechanism involving urea helps water absorption </li></ul></ul><ul><li>Uric Acid – result of metabolism of nucleic acids </li></ul><ul><ul><li>Most reabsorbed by active transport </li></ul></ul><ul><ul><ul><li>Some secreted into renal tubule </li></ul></ul></ul>
  29. 29. Urine <ul><li>Composition – 95% water, and contains: </li></ul><ul><ul><li>Urea and uric acid </li></ul></ul><ul><ul><li>Creatinine </li></ul></ul><ul><ul><li>Trace amino acids </li></ul></ul><ul><ul><li>Varying electrolytes </li></ul></ul><ul><li>Renal Clearance – rate at which a chemical is removed from the plasma </li></ul>
  30. 30. NEPHRON COMPONENT FUNCTIONS (Kind of a summary of Urine Formation)
  31. 31. Renal Corpuscle <ul><li>Glomerulus – filters water and substances from plasma </li></ul><ul><li>Glomerular capsule – receives what’s filtered </li></ul>
  32. 32. Renal Tubule <ul><li>Proximal Convoluted Tubule – reabsorbs nutrients and substances </li></ul><ul><li>Descending Limb of Nephron Loop – reabsorption of water by osmosis </li></ul><ul><li>Ascending Limb of Nephron Loop – reabsorption of sodium, potassium, and chloride ions by active transport </li></ul><ul><li>Distal Convoluted Tubule – reabsorption of sodium and water, secretion of hydrogen and potassium </li></ul>
  33. 33. Collecting Duct – reabsorbs water <ul><li>Unrelated, but more on the Proximal Convoluted Tubule Reabsorption: </li></ul><ul><li>Active transport: glucose; amino acids, creatine; lactic, citric, uric, and ascorbic acids; phosphate, sulfate, calcium, potassium, and sodium ions </li></ul><ul><li>Endocytosis – proteins </li></ul><ul><li>Osmosis – water </li></ul><ul><li>Electrochemical Attraction – chloride and other negatively charged ions </li></ul>
  34. 34. ELIMINATION OF URINE (the Process of Peeing)
  35. 35. Ureters <ul><li>Tubes that extend from kidneys to bladder </li></ul><ul><li>Wall as mucous, muscular, and fibrous layers </li></ul><ul><li>Moves urine down through peristalsis </li></ul>
  36. 36. Urinary Bladder and Urethra <ul><li>Urinary Bladder </li></ul><ul><ul><li>Organ that stores urine and forces it into urethra </li></ul></ul><ul><ul><li>Internal urethral sphincter formed by detrusor muscle </li></ul></ul><ul><li>Urethra </li></ul><ul><ul><li>Tube through which urine exits the body </li></ul></ul>
  37. 37. Mincturition <ul><li>Process of expelling urine </li></ul><ul><li>Detrusor muscles contract, sphincter relaxes </li></ul><ul><li>Mincturition Reflex: </li></ul><ul><ul><li>The more urine in the bladder, the more the stretch receptors in it’s walls get stimulated, which send signals to the brain for you to do the pee-pee dance </li></ul></ul><ul><ul><li>Eventually, the signals override the voluntary muscular clenching reflex, resulting in urine being forcibly expelled (and causing traumatizing memories of preschool in the process  ) </li></ul></ul>