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The Urinary System p301-314

UNIT B. Chapter 13: Urinary System. Section 13.1. The urinary system is involved in excretion , which is the removal of metabolic wastes from the body. The function of the urinary system is to produce urine and conduct it outside the body. The Urinary System p301-314.

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The Urinary System p301-314

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  1. UNIT B Chapter 13: Urinary System Section 13.1 The urinary system is involved in excretion, which is the removal of metabolic wastes from the body. The function of the urinary system is to produce urine and conduct it outside the body. The Urinary Systemp301-314 TO PREVIOUS SLIDE

  2. Excretion • Excretion – removal of (harmful) waste from the body (excess water, salts, CO2, urea) • Secretion – Release of useful substance from cells within body • Defecation – Removal of undigested food and bacteria via anus. (these substances have never actually entered the body proper).

  3. UNIT B Chapter 13: Urinary System Section 13.1 1. Excretion of Metabolic Wastes mostly nitrogenous wastes: primarily urea, but also ammonium, creatinine, uric acid Urea is formed when ammonia released during amino acid breakdown combines with CO2 Some ammonia (NH3) is excreted as ammonium ion (NH4+) Creatinine is a breakdown product of creatine phosphate, a high-energy phosphate reserve molecule Uricacid is produced from the breakdown of nucleotides High concentration of uric acid in blood can precipitate out. Crystals may accumulate in joints: Gout Functions of the Urinary System TO PREVIOUS SLIDE

  4. UNIT B Chapter 13: Urinary System Section 13.1 2. Maintenance of Water-Salt Balance: Osmoregulation Salts can cause osmosis (diffusion of water) into the blood, causing blood volume and blood pressure to increase Kidneys also maintain levels of other ions, such as potassium (K+), bicarbonate (HCO3-), and calcium (Ca2+), in the blood 3. Regulation of Acid-Base Balance Kidneys monitor and keep blood pH at 7.4 by excreting hydrogen ions (H+) and reabsorbing bicarbonate ions (HCO3-) Urine is usually acidic TO PREVIOUS SLIDE

  5. UNIT B Chapter 13: Urinary System Section 13.1 4. Secretion of Hormones The kidneys secrete renin, an enzyme that stimulates the adrenal cortex to secrete the hormone aldosterone, which promotes the absorption of sodium ions (Na+) by the kidneys. Water is also reabsorbed along with sodium; which increases blood volume and therefore blood pressure Secrete the hormone erythropoietin (EPO) to simulate red blood cell production (erythropoiesis) when oxygen demand increases Help activate Vitamin D, a hormone-like molecule that promotes calcium (Ca2+) absorption from the digestive tract TO PREVIOUS SLIDE

  6. UNIT B Chapter 13: Urinary System Section 13.1 Ureters Small muscular tubes that transport urine from the kidneys to the bladder Peristaltic contractions in the ureters cause urine to enter the bladder TO PREVIOUS SLIDE

  7. UNIT B Chapter 13: Urinary System Section 13.1 Urinary Bladder Stores urine until it is expelled from the body Has three openings: two for the ureters, and one for the urethra, which drains the bladder Has two sphincters that lie close to where the urethra exits the bladder External sphincter is under voluntary control TO PREVIOUS SLIDE

  8. UNIT B Chapter 13: Urinary System Section 13.1 Urethra Small tube opening that extends from the bladder to an external opening Removes urine from the body Males: 20 cm long; urethra carries urine and semen Females: 4 cm long; urethra carries urine (not connected to reproductive system) TO PREVIOUS SLIDE

  9. UNIT B Chapter 13: Urinary System Section 13.1 When the bladder fills with about 250 mL of urine, stretch receptors send nerve impulses to the spinal cord Motor nerve impulses from the spinal cord cause the bladder to contract and sphincters to relax, allowing urination to occur The brain controls this reflex in older children and adults, allowing urination to be delayed Urination TO PREVIOUS SLIDE

  10. UNIT B Chapter 13: Urinary System Section 13.1 Kidneys: paired, bean shaped organs Highly vascular. Each covered by a tough connective tissue layer called a renal capsule Each has a depression (hilium) on the concave side where a renal artery enters and a renal veinand ureter exit TO PREVIOUS SLIDE

  11. Kidney: Internal Structure • Renal cortex (outer region) • where ultrafiltration takes • place. • Erythropoietin produced here. • Renal medulla (middle region) • collecting chamber, • contains cone-shaped masses • called renal pyramids • Renalpelvis(inner region) • funnel-shaped basin (cavity) • receives the urine from nephrons. Continuous with ureter. • .

  12. Renal cortex

  13. UNIT B Chapter 13: Urinary System Section 13.2 The kidney is composed of over 1 million nephrons, also known as renal or kidney tubules. Composed of urinary tubules and associated vessels Anatomy of a Nephron Figure 13.3 Anatomy of the kidney. b. An enlargement showing the placement of nephrons. TO PREVIOUS SLIDE

  14. Nephrons: Basic structural and functional unit of the kidney. • Function: Regulates concentration of water and solutes (like sodium salts) by • filtering the blood, • reabsorbing what is needed • excreting the rest as urine.

  15. UNIT B Chapter 13: Urinary System Section 13.2 Glomerularcapsule(Bowman’s capsule) Inner layer composed of cells called podocytes Spaces between podocytes allow small molecules from the glomerulus to enter the glomerular capsule (Glomerular filtration) Urinary Tubules TO PREVIOUS SLIDE

  16. UNIT B Chapter 13: Urinary System Section 13.2 Proximal convoluted tubule (PCT) Site of tubular reabsorption of water, glucose, amino acids, some salts, etc. into peritubular capillary network Lined with cuboidal epithelial cells that have packed microvilli to increase the surface area for reabsorption Many mitochondria to supply energy for activie transport (reabsorption) TO PREVIOUS SLIDE

  17. UNIT B Chapter 13: Urinary System Section 13.2 Loop of the Nephron (loop of Henle) descending limb - site of reabsorption of water (permeable to water) ascending limb Site of active and passive transport of salts into medulla tissue fluid creating an osmotic gradient. (impermeable to water) Parts of a Nephron – Urinary tubules TO PREVIOUS SLIDE

  18. UNIT B Chapter 13: Urinary System Section 13.2 Distal convoluted tubule (DCT) Helps move molecules (hydrogen ions, ammonia, creatinine, urea, drugs, etc. ) from the blood (peritubular capillary network.) into the tubule (tubular secretion) Many mitochondria No microvilli The DCTs of many nephrons enter one collecting duct Collecting ducts carry urine to the renal pelvis Parts of a Nephron – Urinary Tubules TO PREVIOUS SLIDE

  19. Parts of a Nephron – Urinary Tubules • Collecting ducts • Final reabsorption of water • and excretion of urine. • carry urine to the renal pelvis • Under control of ADH

  20. UNIT B Chapter 16: Urinary System Section 16.2 Each nephron has it own blood supply. Blood from the renal artery branches into afferent arterioles. Filtered blood returned to the inferior vena cava via renal vein. Two capillary regions: glomerulus (ball of capillaries inside the Bowman’s capsule) Peritubular capillary network (surrounds rest of nephron) Associated Vessels - Blood Supply in a Nephron Figure 13.4 Nephron anatomy. a. You can trace the path of blood through a nephron by following the black arrows. TO PREVIOUS SLIDE

  21. Associated Vessels - Blood Supply in a Nephron • Afferent Arteriole: brings blood to nephron • Glomerulus: site of pressure filtration • Efferent arteriole: takes blood from glomerulus to peritubular capillary network, before exiting through the renal vein

  22. Associated Vessels - Blood Supply in a Nephron • Peritubular Capillary Network: • Surrounds tubules of nephron and reabsorbs useful material. • Site of oxygen/carbon dioxide exchange (for kidney cells) • Drains into renal venules

  23. UNIT B Chapter 13: Urinary System Section 13.2 Urine formation is divided into the following processes: Pressure filtration (glomerular filtration) : water, salts, nutrients, and wastes move from the glomerulus to the inside of the glomerular capsule Selective (tubular) reabsorption: nutrient and salt molecules are actively reabsorbed from the convoluted tubules into the blood of the peritubular capillary network Tubular Secretion: certain molecules are actively secreted from the blood in the peritubular capillary network into the convoluted tubules Water Reabsorption Urine Formation TO PREVIOUS SLIDE

  24. UNIT B Chapter 13: Urinary System Section 13.2 Pressurefiltration occurs when blood enters the afferent arteriole and the glomerulus. pressure forces small molecules to leave the glomerulus and enter the glomerular capsule These filterable blood components form the glomerular filtrate 1. Glomerular (Pressure) Filtration TO PREVIOUS SLIDE

  25. UNIT B Chapter 13: Urinary System Section 13.2 Selctive reabsorption of useful materials begins in the proximal convoluted tubule into the blood of the peritubular capillary network. Water, glucose, amino acids and sodium. Na+ ions are actively reabsorbed into the blood, with Cl- ions following passively results in water moving passively from the tubule into the blood Glucose and amino acids are actively reabsorbed into the blood almost exclusively at the proximal convoluted tubule Some urea due to diffusion 2. Selective (Tubular) Reabsorption TO PREVIOUS SLIDE

  26. UNIT B Chapter 13: Urinary System Section 13.2 The glomerular filtrate that enters the proximal convoluted tubule is divided into two portions. Reabsorbed filtrate components: reabsorbed from the tubule into blood Nonreabsorbed filtrate components: continue to pass through the nephron to be processed into urine (become the tubular fluid that enters the loop of Henle) 2. Selective (Tubular) Reabsorption TO PREVIOUS SLIDE

  27. 2. Selective (Tubular) Reabsorption • Active Reabsorption • carrier proteins • Sodium, glucose, amino acids • Passive Reabsorption • diffusion • Cl- passively follow Na+ , increases osmotic pressure of blood • water • Some urea

  28. UNIT B Chapter 13: Urinary System Section 13.2 Second way substances are removed from blood in the peritubular capillary network and added to the tubular filtrate. Active transport of molecules out of blood and into Distal Convoluted Tubule Hydrogen ions, potassium ions, ammonium ions, creatinine, and certain drugs (antihistamines, penicillin) The resulting urine contains: Substances that have undergone glomerular filtration but have not been reabsorbed Substances that have undergone tubular excretion 3. Tubular Secretion TO PREVIOUS SLIDE

  29. UNIT B Chapter 13: Urinary System Section 13.3 The kidneys maintain the water-salt balance in the blood (osmoregulation). In this way, they also maintain blood volume and blood pressure. The excretion of a hypertonic urine (more concentrated than blood) depends on the reabsorption of water. This requires: Reabsorption of water Reabsorption of salt Establishment of a solute gradient Regulatory Functions of the Kidneys Osmoregulation TO PREVIOUS SLIDE

  30. Reabsorption of Water • Water is reabsorbed along length of nephron but excretion of hypertonic urine depends on action of Loop of Henle and Collecting Duct. • Loop of Henle is in Renal Medulla • Reabsorption of water out of loop and into blood depends on [NaCl] in renal medulla

  31. Loop of Henle • NaCl passively diffuses out of lower portion of ascending limb. • And actively transported out of upper, thick portion into tubule of renal medulla. • Results in high [NaCl] in renal medulla  osmotic gradient

  32. UNIT B Chapter 13: Urinary System Section 13.3 Figure 13.9 Reabsorption in the loop of Henle occurs through both active and passive transport. TO PREVIOUS SLIDE

  33. UNIT B Chapter 13: Urinary System Section 13.3 If the body is dehydrated (blood hypertonic), the pituitary gland releases antidiuretichormone (ADH) Promotes water reabsorption at collecting duct  more concentrated urine ADH does this by increases the number of aquaporins (water channels) of the collecting duct Blood volume and pressure rise As blood becomes more dilute, less ADH produced (neg feedback loophomeostasis) In the absence of ADH: collecting duct is impermeable to water, and urine is dilute Diuresis - increased amount of urine (decreased water in blood) Antidiruresis - decreased amount of urine (increased blood vol) Water Reabsorption depends on ADH TO PREVIOUS SLIDE

  34. 2. Reabsorption of Salt (depends on aldosterone) • Kidneys regulate salt balance by controlling excretion and reabsorption of ions: • Na +, K+, HCO3 –, Mg 2+ • Usually 98% of filtered sodium is returned to blood. • ~ 67% reabsorbed at proximal tubule • ~ 25% reabsorbed by ascending limb of loop of Henle • Remaining is reabsorbed from distal convoluted tubule and collecting duct Two hormones regulate the reabsorption of Na+ at the distal convoluted tubule: aldosterone and atrial natriuretic hormone (ANH)

  35. UNIT B Chapter 13: Urinary System Section 13.3 Aldosterone Secreted by adrenal cortex promotes reabsorption of Na+ reabsorption of water  Blood volume and BP increase Juxtaglomerular apparatus: secretes renin, an enzyme that leads to the secretion of aldosterone from the adrenal cortex Figure 13.6 Juxtaglomerular apparatus. The afferent arteriole and the distal convoluted tubule usually lie next to each other. The juxtaglomerular apparatus occurs where they touch. The juxtaglomerular apparatus secretes renin, a substance that leads to the release of aldosterone by the adrenal cortex. Reabsorption of sodium ions and water then occurs. Thereafter, blood volume and blood pressure increase. 2. Reabsorption of Salt TO PREVIOUS SLIDE

  36. Aldosterone • When blood volume decreases, so does BP • When BP is too low for glomerular filtration, • Jux Apparatus secretes renin • Renin converts angiotensinogen into angiotensin I, • Angiotensin-converting enzyme (in lung capillaries) then converts Angiotensin I  Angiotensin II, a powerful vasoconstrictor that also stimulates the adrenal cortex to release aldosterone, causing reabsorption of Na+ (and K+ to be excreted) resulting in reabsorption of water Increasing Blood volume and BP.

  37. UNIT B Chapter 13: Urinary System Section 13.3 Atrial natriuretic hormone (ANH) promotes the excretion of Na+(natriuresis) Secreted by the atria of the heart when cardiac cells are stretched due to increased blood volume Inhibits the secretion of renin and secretion of aldosterone  excretion of water into the urine  Blood volume and blood pressure decrease 2. Reabsorption of Salt TO PREVIOUS SLIDE

  38. Diuretics • Chemicals that increase flow of urine: • Alcohol inhibits the secretion of ADH  diuresis • Caffeine increases glomerular filtration rate and decreases tubular reabsorption of Na+ • Drugs (water pills) for high blood pressure inhibit active transport of Na+ at the loop of the nephron or at the distal convoluted tubule  decreased water absorption  blood volume  decreased blood pressure • Diuretics have been abused for quick weight loss (water loss), and by individuals attempting to pass a urine drug test • Side effects: electrolyte imbalances, dehydration, death

  39. UNIT B Chapter 13: Urinary System Section 13.3 Reabsorption of water at the loop of Henle and the collecting duct is due to the establishment of a solute gradient. Ascending limb: Salt (NaCl) is actively transported out of the ascending limb and into the renal medulla Less salt is available to transport as the fluid moves up the ascending limb, establishing a solute gradient that increases toward the inner medulla 3. Establishment of a Solute Gradient TO PREVIOUS SLIDE

  40. UNIT B Chapter 13: Urinary System Section 13.3 Urea moves out of the collecting duct, further contributing to the increasing solute concentration at the inner medulla Because of this solute gradient, water leaves the descending limb and the collecting duct and returns to the blood 3. Establishment of a Solute Gradient Figure 13.8 Reabsorption of water at the loop of Henle and the collecting duct. Salt (NaCl) diffuses and is actively transported out of the ascending limb of the loop of Henle into the renal medulla. Also, urea is believed to leak from the collecting duct and to enter the tissues of the renal medulla. This creates a hypertonic environment, which draws water out of the descending limb and the collecting duct. This water is returned to the circulatory system. (The thick black outline of the ascending limb means that it is impermeable to water.) The solute concentration is 300 mOsm/L in the glomerulus and peritubular capillary network. TO PREVIOUS SLIDE

  41. UNIT B Chapter 13: Urinary System Section 13.3 The normal pH of blood is 7.4. pH can be changed by the foods we eat and by metabolic processes (e.g., CO2 from cellular respiration combines with water to form carbonic acid) Several mechanisms in the body help maintain blood pH: Acid-base buffer systems Respiratory centre in the medulla oblongata Kidneys Acid-Base Balance TO PREVIOUS SLIDE

  42. UNIT B Chapter 13: Urinary System Section 13.3 Bicarbonate Buffer System in blood carbonic acid (H2CO3) and bicarbonate ions (HCO3-) When the blood is too acidic (excess H+ added): When the blood is too basic (excess OH- added): These reactions prevent any significant change in blood pH 1. Acid-Base Buffer Systems TO PREVIOUS SLIDE

  43. UNIT B Chapter 13: Urinary System Section 13.3 The respiratory centre in the medulla oblongata increases breathing rate if the H+ concentration of the blood rises. Increasing breathing rate rids the body of H+ because of the following reaction in the pulmonary capillaries: When CO2 is exhaled, the reaction shifts to the right, and H+ is reduced 2. Respiratory Centre TO PREVIOUS SLIDE

  44. UNIT B Chapter 13: Urinary System Section 13.3 The kidneys can rid the body of a wide range of acidic and basic substances to adjust pH. Slower than other two but more powerful effect on pH Reabsorb bicarbonate ions (HCO3-) and excrete H+ as needed to maintain blood pH Ammonia (NH3) produced in the tubule cells also helps to buffer and remove H+ in urine: 3. The Kidneys TO PREVIOUS SLIDE

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