The Urinary System PDF

ANATOMY AND PHYSIOLOGY OF THE URINARY SYSTEM HES 029: Human Anatomy and Physiology with Pathophysiology Prepared by: Arwin Paul S. Avila, RMT Learning Objectives: 1. Discuss the different functions of the kidneys. 2. Identify the following regions of the kidney: hilum, cortex, medulla, m...

ANATOMY AND PHYSIOLOGY OF THE URINARY SYSTEM HES 029: Human Anatomy and Physiology with Pathophysiology Prepared by: Arwin Paul S. Avila, RMT Learning Objectives: 1. Discuss the different functions of the kidneys. 2. Identify the following regions of the kidney: hilum, cortex, medulla, medullary pyramids, calyces, pelvis, and renal columns 3. Describe the process of urine formation, identifying the areas of the nephron that are responsible for filtration , reabsorption , and secretion. 4. Describe the function of the kidneys in excretion of nitrogen-containing wastes. 5. Describe the composition of normal urine. 6. Describe the general structure and function of the ureters, urinary bladder, and urethra. 7. Compare the course and length of the male urethra to that of the female. 8. Explain the pathophysiology of renal disturbances. HES 029: Human Anatomy and Physiology with Pathophysiology THE RESPIRATORY SYSTEM  URINARY SYSTEM MAJOR EXCRETORY SYSTEM Filter and remove waste products and excess substances from the blood (production and excretion of urine). Four Main Components: Kidneys Ureters Urinary Bladder Urethra HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM FUNCTIONS OF THE URINARY SYSTEM 1. EXCRETION ○ Filter blood, reabsorb needed substances, and form urine to eliminate metabolic wastes, toxins, and excess ions. 2. REGULATION OF BLOOD VOLUME AND PRESSURE ○ Adjust blood volume and pressure by altering urine concentration based on hydration levels. 3. REGULATION OF BLOOD SOLUTE CONCENTRATIONS ○ Control the levels of major ions and other solutes in the blood. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM FUNCTIONS OF THE URINARY SYSTEM 1. Excretion 2. Regulation of Blood Volume and Pressure 3. Regulation of Blood Solute Concentrations 4. REGULATION OF EXTRACELLULAR FLUID pH ○ Manage the acidity of extracellular fluid by adjusting hydrogen ion secretion. 5. STIMULATION OF RED BLOOD CELL SYNTHESIS ○ Release erythropoietin to promote red blood cell production. 6. ACTIVATION OF VITAMIN D ○ Help regulate calcium levels in the blood. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM Anatomy and Histology of the Urinary System: KIDNEY HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM LOCATION AND SIZE Retroperitoneal; located in the posterior wall of the abdomen. Positioned between the T12 and L3 vertebrae. Right kidney slightly lower than the left due to the liver's position. About 4-5 inches long, 2.5 inches wide, and 1 inch thick. Adult male: 150 g Adult female: 135 g Bean-shaped; with a convex lateral surface and a concave medial surface. Anterior view showing urinary organs EXTERNAL ANATOMY Hilum: Medial indentation where the ureter, blood vessels, lymphatics, and nerves enter and exit the kidney. Renal Capsule: Outer connective tissue layer surrounding the kidney. Perirenal Fat Capsule: Fatty mass providing cushioning and support. Renal Fascia: Dense connective tissue anchoring the kidney to surrounding structures. EXTERNAL ANATOMY HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM INTERNAL ANATOMY Cortex: Outer region (1.4 cm thick), where most glomeruli are located. Medulla: Inner region made of renal pyramids, which are separated by renal columns. ○ Renal pyramids: Cone-shaped tissues; apex (papilla) leads to the minor calyx. ○ Renal columns: Tissues between the renal pyramids; support and separate them. Renal pelvis: Funnel-shaped cavity that collects urine and leads into the ureter. NEPHRONS Functional units of the kidney; responsible for filtering blood and forming urine. Each kidney contains over 1 - 1.3 million nephrons. Parts of a nephron: A. Renal Corpuscle B. Renal Tubules C. Collecting Duct Types: ○ Cortical Nephrons ○ Juxtamedullary Nephrons HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM NEPHRON ANATOMY: RENAL CORPUSCLE Located in the renal cortex. Consists of two main parts: ○ GLOMERULUS Tuft of fenestrated capillaries with small pores; allow fluid and small solutes to pass while retaining proteins and cells. Filters blood to form protein-free filtrate (blood plasma) and initiates urine formation by using blood pressure to drive water and solutes into Bowman’s capsule. ○ GLOMERULAR (BOWMAN’S) CAPSULE Cup-shaped structure surrounding the glomerulus, double-walled. Parietal layer: Simple squamous epithelium (structural support). Visceral layer: Made of podocytes (specialized epithelial cells); with filtration slits that regulate what enters the nephron. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM NEPHRON ANATOMY: RENAL CORPUSCLE JUXTAMEDULLARY APPARATUS Juxtaglomerular Cells: ○ Specialized smooth muscle cells surrounding the afferent arteriole ○ Detect changes in blood pressure. Macula Densa: ○ Group of specialized cells in the distal convoluted tubule ○ Sense sodium concentration in the filtrate. Main Function: ○ Plays a crucial role in regulating blood pressure and filtrate formation. ○ Secretes the enzyme renin when blood pressure is low or sodium levels are reduced, which triggers the renin-angiotensin-aldosterone system (RAAS) HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM NEPHRON ANATOMY: RENAL CORPUSCLE HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM RECALL: A B C HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM NEPHRON ANATOMY: FILTRATION MEMBRANE Barrier between the blood in the glomerulus and the filtrate in Bowman’s capsule. Consists of three layers: ○ Endothelial Cells of Glomerular Capillaries ○ Basement Membrane ○ Podocytes Basement Membrane: Gel-like layer between endothelial cells and podocytes that blocks large molecules and proteins, allowing smaller solutes and water to pass. NEPHRON ANATOMY: RENAL TUBULES PROXIMAL CONVOLUTED TUBULE (PCT) Located in the cortex. Connected to the Bowman's capsule; precedes the loop of Henle. Lining epithelium: Simple cuboidal with microvilli (increase reabsorption surface area) Major site of reabsorption: Water, ions (sodium, potassium, chloride), and nutrients (glucose, amino acids). Some secretion: Hydrogen ions and some waste products. Histological Features of the PCT HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM NEPHRON ANATOMY: RENAL TUBULES NEPHRON LOOP (LOOP OF HENLE) U-shaped loop extending into the kidney medulla. Consists of descending and ascending limb. ○ Descending Limb: Thin, permeable to water but not solutes, causing water reabsorption and filtrate concentration. ○ Ascending Limb: Thicker, impermeable to water, reabsorbs solutes (mainly Na+ and Cl-), creating a concentration gradient. Histological Features of the Nephron loop: Helps establish the medullary osmotic descending limb and thin ascending limb gradient, essential for urine concentration. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM NEPHRON ANATOMY: RENAL TUBULES DISTAL CONVOLUTED TUBULE (DCT) Follows the Loop of Henle and precedes the collecting duct. Lining epithelium: Simple cuboidal with fewer microvilli compared to the PCT. Primarily involved in secretion and fine-tuning reabsorption under hormonal control. ○ Reabsorbs ions and water. ○ Regulates blood pH by secreting hydrogen ions and reabsorbing bicarbonate. ○ Controls calcium, sodium, and potassium levels, influenced by hormones like Histological Features of the DCT aldosterone and PTH. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM NEPHRON ANATOMY: COLLECTING DUCTS Not part of the nephron, but closely associated. Receives filtrate from multiple nephrons. Traverses through the renal medulla. Converge into papillary ducts, draining into minor calyces and the renal pelvis. Involved in FINAL water and salt reabsorption, and acid-base balance. ○ Lined with principal cells (reabsorb sodium and water) and intercalated cells (manage acid-base balance). ○ Final adjustments to urine concentration and volume, influenced by ADH and Histological Features of the Collecting Duct aldosterone. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM TYPES OF NEPHRONS: CORTICAL NEPHRONS About 85% of nephrons. Located almost entirely within the renal cortex. Have shorter nephron loops; barely penetrate the medulla. Renal corpuscles are distributed throughout the cortex, closer to its outer edge. TYPES OF NEPHRONS: JUXTAMEDULLARY NEPHRONS About 15% of nephrons. Renal corpuscles are located near the medulla. Have long nephron loops that extend deep into the medulla. Crucial for water conservation and producing concentrated urine. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM RENAL BLOOD FLOW Kidneys receive one-quarter (20-25%) of total cardiac output. ○ Approx. 1200 mL/min or 600 mL/min/kidney Blood flow supports filtration, reabsorption, secretion, and fluid/electrolyte balance. Blood supply - Renal Artery Blood drainage - Renal Vein Carries blood TO the glomeruli Surround the PCT and DCT Carries blood FROM the glomeruli HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM ASSOCIATED CAPILLARIES PERITUBULAR CAPILLARIES ○ Surround the PCT and DCT of cortical nephrons. ○ Low-pressure, porous capillaries that are adapted for reabsorption of water and solutes from the tubules. VASA RECTA ○ Specialized capillary network that surrounds the nephron loops of juxtamedullary nephrons. ○ Plays a key role in maintaining the osmotic gradient in the medulla, essential for the kidney’s ability to produce concentrated urine. HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM URINE FORMATION HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM FILTRATION First step in urine production; occurs in the renal corpuscle. Passive process driven by hydrostatic pressure. Process of filtering blood and forming filtrate. ○ Filtrate: similar to plasma but lacks proteins and blood cells. FILTRATION Cardiac Output: 5600 mL/min (5-6 liters per minute). Renal Fraction: Approximately 21-25% of cardiac output. ○ Renal Blood Flow Rate: ~ 1200 mL/min ○ Calculation: Cardiac Output × Renal Fraction (5600 × 0.21 = 1176 mL/min) Renal Plasma Flow Rate: Renal blood flow rate multiplied by 55%. ○ Approximately 650 mL/min (1176 × 0.55); (Strasinger: 600-700 mL/min) Filtration Fraction: 19% of plasma is filtered by the glomerulus. ○ Filtrate Produced: Approximately 125 mL/min ○ Calculation: Renal Plasma Flow Rate × Filtration Fraction (650 × 0.19) Glomerular Filtration Rate (GFR): Amount of plasma entering the Bowman's capsule per minute, approximately 125 mL/min HES 029: Human Anatomy and Physiology with Pathophysiology THE URINARY SYSTEM FILTRATION MEMBRANE Allows water and small molecules to pass while blocking blood cells and filters larger proteins based on size and charge; minimal protein in healthy urine. FILTRATION MEMBRANE Separation based on size and charge; blocks molecules larger than 7 nm or molecular mass ≥ 40,000 daltons. ○ Strasinger: Glomerulus = Non-selective filter for plasma substances w/ MW