Urinary System Part 2 PDF

Urinary System Marie A. Román Martínez, PhD Department of Biology Office hours: by appointment Email: [email protected] Copyright-This presentation is intended for educational purpose only. No part of this presentation may be reproduced or transmitted in any form without written permission. Object...

Urinary System Marie A. Román Martínez, PhD Department of Biology Office hours: by appointment Email: [email protected] Copyright-This presentation is intended for educational purpose only. No part of this presentation may be reproduced or transmitted in any form without written permission. Objectives List the components of the urinary system. Describe the general functions of the urinary system. Describe the structure and functions of a nephron. Compare glomerular filtration, tubular reabsorption, and tubular secretion. Explain how urine is formed. Indicate the typical components of urine. Describe the structure and function of the ureters, urinary bladder, and urethra. Explain how water balance is maintained in body fluids. Explain how electrolyte balance is maintained in body fluids. Explain how pH balance is maintained in body fluids. Describe the common disorders of the urinary system. 2 Tubular Reabsorption and Tubular Secretion Involve both active and passive transport mechanisms. Passive transport depends upon: Permeability of renal tubule, peritubular capillaries, and vasa recta to a substance. Concentration gradient of the substance. 3 Events in Proximal Convoluted Tubule 65% of tubular fluid is reabsorbed. Actively reabsorption of glucose and amino acids, Na+, K+,Ca+2. Passive reabsorption of negatively charged ions (Cl- and HCO3-). ↑osmotic pressure in blood plasma causes H2O to be reabsorbed by osmosis. Tubular secretion: Moves metabolic wastes, drugs from blood plasma into tubular fluid. Helps regulate the pH by selectively removing H+, and HCO3-. 4 Events in the Nephron Loop Descending limb: Impermeable to solutes. Passive reabsorption of H2O by osmosis into the vasa recta. Ascending limb: Impermeable to water. Solutes are reabsorbed passively by diffusion. Actively (pumps) reabsorbs Na+. K+ and Cl- follow passively into the interstitial fluid. Some K+ reenters tubular fluid. 5 Events in the Nephron Loop Na+ and Cl- accumulate in interstitial fluid of renal medulla. ↑osmotic gradient → H2O reabsorption in the descending limb and collecting duct. 6 Events in the Distal Convoluted Tubule Hormone aldosterone causes active Na+ reabsorption. Cl- and HCO3- are passively reabsorbed through electrochemical attraction. H2O reabsorption occurs due to changes in osmotic pressure of tubular fluid→ under the control of ADH. PTH and active vitamin D cause active reabsorption of Ca+2. K+ are actively secreted in response to aldosterone. H+ are actively secreted to maintain normal blood pH. Drugs can be actively and passively secreted. 7 Water Conservation Tubular fluid leaving DCT is isotonic to blood plasma. Recall that Na+, K+, and Cl- have been moved into the interstitial fluid by the ascending limb in renal medulla. Results in passive H2O reabsorption by osmosis in collecting duct. Regulated by ADH→ causes the tubular fluid to become concentrated and hypertonic to blood plasma by the time it exits the collecting duct. The urine leaving the collecting duct has only 1% of the original glomerular filtrate volume. 8 Characteristics of Urine Average of 1.5-2.0 L/day Fresh urine of a healthy person: This Photo by Unknown Author is licensed under CC BY-NC-ND Pale yellow to light amber. Due to urochrome, a substance produced by the breakdown of bile pigments in the intestine. Slightly acidic (pH=6) but pH can vary with diet. Healthy pH (4.8-7.5) Specific gravity is greater than water. Substances not found in healthy urine: glucose, proteins, formed elements, hemoglobin, bile pigments. 9 Excretion of Urine Urinary Tract Includes renal pelvis, ureters, urinary bladder, and urethra. Structures function to carry urine from the kidneys to the external environment. Ureters Each ureter begins at the renal pelvis and enters the bottom of the urinary bladder. Wall has three layers: Outer fibrous layer: dense irregular connective tissue. Middle layer: smooth muscle cells Produce peristaltic waves to move urine. Inner layer: mucous Forms a flap that functions as a valve to prevent backflow of urine into ureter. 10 Urinary Bladder Hollow, muscular organ behind the pubic symphysis within pelvic cavity. Temporary storage of urine. Changes shape depending on how much urine it is holding. Trigone: Triangular area with three openings. Two ureteric orifices One urethral opening. 11 Urinary Bladder Four layers of urinary bladder wall: Inner layer: mucosa with transitional epithelium Submucosa: supports the mucosa. Loose connective tissue with elastic fibers, blood vessels, nerves. Muscular layer: detrusor Third and thickest layer. Smooth muscle that contracts to expel urine. Forms internal urethral sphincter at junction of urinary bladder and urethra. Outer layer: parietal peritoneum and dense irregular connective tissue. 12 Urethra Carries urine from bladder to the external environment. Wall contains smooth muscle cells and connective tissue. Inner lining mucosa. External urethral sphincter. External urethral orifice is external opening. Females: 1.5 in, opens in front of the vagina. Males: 6-8 in, opens at tip of penis. 13 Micturition Urination. Act of expelling urine from the urinary bladder. Urge to urinate begins at approximately 200 to 400 ml. Micturition reflex is triggered by bladder stretching. Baroreceptors in the urinary bladder wall are stimulated and trigger the reflex. Parasympathetic action potential cause detrusor to rhythmically contract. Internal urethral sphincter opens. Person becomes aware of the need to urinate. If voluntarily controlled external urethral sphincter relaxes, micturition occurs. If voluntarily controlled external urethral sphincter remains closed, micturition is denied. Cannot be postponed indefinitely. Micturition Reflex https://www.viddler.com/embed/1d40d02f/?f=1&autoplay=0&player=arpeggio&secret=90576092&loop 14 =0&nologo=0&hd=0 Healthy kidneys keep blood volume and composition constant. Despite changes caused by diet and cellular activity. Maintenance of Blood Plasma Composition The composition and volume of blood plasma are affected by diet, cellular metabolism, and urine production. Food and liquid intake provides the water and nutrient's that are absorbed into the blood. Cellular metabolism uses the nutrients and releases wastes into the blood. Urine production retains essential nutrients and minerals in blood plasma. Removes excess substances and wastes. 15 Water and Electrolyte Balance Two important components of blood plasma and other body fluids: 1. Water 2. Electrolytes Water intake is regulated by thirst center within the hypothalamus. Activated by: ↑solute concentration in blood. Angiotensin II when blood pressure declines significantly. Water intake must balance water loss, and this averages about 2,500 ml per day. 16 Water Balance By regulating the volume of water lost in urine, the kidneys have the ability to regulate the concentrations of water in blood plasma. Excessive water loss, ↑water reabsorption in renal tubule. Urine volume decreases (more concentrated). Minimal water loss, ↓water reabsorption in renal tubule. Urine volume increases (more dilute). Greater water intake, ↓water reabsorption, large volume of dilute urine. Low water intake, ↑water reabsorption, small volume of concentrated urine. 17 Water Balance Antidiuretic hormone Controls whether more or less water is reabsorbed. Increases permeability of DCT and collecting ducts. ↑water reabsorption. Natriuretic peptides. Increases GFR. More fluid moved from blood plasma into the glomerular capsule. Decrease Na+ reabsorption in DCT and collecting duct. Decreases water reabsorption. 18 Electrolyte Balance Important electrolytes in body fluids include ions of sodium, potassium, calcium, chloride, phosphate, sulfate, and bicarbonate. Na+ ions are the most important ions to be regulated because they compose about 90% of the cations in extracellular fluids. Certain hormones play important roles in maintaining electrolyte balance. Aldosterone Regulates the balance of Na+ and K+ in the blood plasma. Stimulates active reabsorption of Na+, and active secretion of K+ in the DCT and collecting duct. Hormone is produced by adrenal cortex in response to: Increase in blood K+→hyperkalemia Decrease in blood Na+→hyponatremia Angiotensin II 19 Electrolyte Balance Certain hormones play important roles in maintaining electrolyte balance (cont.) Natriuretic peptides—inhibits Na+ reabsorption in the DCT and collecting duct→ inhibits water reabsorption. Parathyroid hormone (PTH)—secreted by the parathyroid glands when blood Ca+2 concentration declines. Increases blood Ca+2 three ways: Increases Ca+2 reabsorption in DCT. Increases release of Ca+2 from bone tissue into blood. Activation of vitamin D→ increases absorption of Ca+2 from food in small intestine. Calcitonin– secreted by the thyroid gland when blood Ca+2 concentration increases. Decreases blood Ca+2. Promotes deposition of Ca+2 into bones. 20 Acid-Base Balance Healthy arterial blood pH is 7.35 - 7.45 Arterial blood pH below 7.35 → Acidosis Arterial blood pH above 7.45→ Alkalosis Cellular metabolism produces products that tend to upset the acid-base balance. Examples: lactic acid, phosphoric acid, and carbonic acid. Acids: Release H+ in water which ↓pH, and ↑acidity. The more H+ ions that are released, the stronger the acid. Bases: Release ions that combine with H+, when placed in water, and decrease their concentration in a solution. (e.g., OH- or HCO3-) Body fluids contain both acids and bases, and the balance between them determines pH. 21 Disorders of the urinary System Disorders are grouped into: Inflammatory disorders Noninflammatory disorders 22 Inflammatory Disorders Cystitis: Inflammation of urinary bladder often due to bacterial infection. Female more susceptible. Glomerulonephritis: Inflammation involving the glomeruli. Due to bacteria or bacterial toxins. Inflamed glomeruli are more permeable. Formed elements and proteins leak into glomerular filtrate and remain in urine. 23 Inflammatory Disorders Pyelonephritis: Inflammation of renal pelvis and nephrons. Pyelitis: just renal pelvis. Caused by bacterial infection. Urethritis: Inflammation of the urethra. Caused by various bacteria, such as Escherichia coli. More common in females. 24 Noninflammatory Disorders Diuresis (or polyuria): Excessive production of urine. Due to inadequate tubular reabsorption of water. Symptom of diabetes insipidus and diabetes mellitus. Renal calculi: Kidney stones. Crystallization of uric acid, Ca+2, or Mg+2 in renal pelvis. Painful, especially when moving through a ureter by peristalsis. Can use ultrasound therapy to break up stones, as an alternative to surgery. 25 Noninflammatory Disorders Renal failure: Reduction in urine production and failure to maintain healthy body fluid volume and composition. Can occur acutely or chronically. Causes uremia (a toxic condition caused by excessive nitrogenous wastes in the blood) and anuria (a cessation of urine production). Hemodialysis or kidney transplant may be needed. 26