Renal Physiology PDF

Renal Physiology Chapter 11 The Urinary System The urinary system is composed of the kidneys, ureters, urinary bladder, and the urethra. The urinary system is constantly working to maintain the purity and health of the body’s fluids by removing unwanted substances and r...

Renal Physiology Chapter 11 The Urinary System The urinary system is composed of the kidneys, ureters, urinary bladder, and the urethra. The urinary system is constantly working to maintain the purity and health of the body’s fluids by removing unwanted substances and recycling others. The kidneys contribute to homeostasis by regulating plasma composition through the elimination of metabolic wastes, toxins, excess ions, and water. Where are the kidneys located? ______________________________________________ ______________________________________________ Functions of the Kidney  Regulation of  Volume, composition, and pH of the body fluids  Acid-base homeostasis (via the production of ammonia)  Energy metabolism via gluconeogenesis during fasting conditions  Plasma osmolarity through the control of aquaporin receptors within the collecting duct  Detoxification of metabolic wastes through excretory mechanisms  Conversion of vitamin D3 into its active form  Synthesis and conversion of important hormones such as erythropoietin and renin. Anatomy of the Kidney Renal Blood Flow Reabsorption Secretion/Reabsorption The Nephron The main functional unit of the kidney responsible for urine formation Cortical nephron  Shorter loops of Henle  About 80-85% of nephrons in humans Juxtamedullary nephron  Longer loops of Henle that extend down the renal medulla  Only 15-20% of nephrons in humans The nephron is composed of  Renal corpuscle = Bowman’s capsule + glomerulus  Renal tubule with three distinct parts:  Proximal Convoluted Tubule  Loop of Henle  Distal Convoluted Tubule Mechanism of Urine Production 2/3 Reabsorption 2/3 Secretion/Reabsorption Glomerular Filtration Initial stage for urine formation The endothelium of these capillaries are very porous. They allow fluid, waste products, ions, glucose, and amino acids to pass from the blood into the capsule. It blocks out bigger molecules like blood cells and proteins so they stay in the blood and exit through the vasa recta. All the “stuff” that get squeezed out of the blood into the capsule is called filtrate which is then sent along the renal tubule. Glomerular Filtration RPF = renal plasma flow Glomerular Filtration Rate (GFR) - volume of filtrate produced by both kidneys per minute Physiological indicator of renal function Glomerular filtration is determined by Starling’s pressures GFR = Kf [ (PGC – PBS) - πGC ] Kf =Filtration coefficient PGC =Hydrostatic pressure in glomerular capillary PBS =Hydrostatic pressure in Bowman’s space πGC =Oncotic pressure in glomerular capillary No filtration occurs Physiology, Physiology, 5th edition 5th edition Berne and BerneLevy, and2003 Levy, 2003 Proximal Convoluted Tubule Cell walls are made up of cuboidal epithelial cells containing mitochondria to power pumps that pull sodium ions (Na+) from the filtrate using active transport Microvilli to increase surface area to help reabsorb as much of the “good stuff” as possible  Glucose, amino acids, proteins, vitamins, lactate, urea, uric acid, Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, H₂O The vast majority of renal reabsorption occurs in the proximal convoluted tubule (PCT).  Approximately 67% of Na+ and 67% of water (H₂O) reabsorption (equal proportions = isosmotic)  This mechanism is essential for the maintenance of the chemical integrity of the extracellular fluid composition and general homeostasis. © Learneo, Inc. 2024  Proximal Convoluted Tubule In a healthy individual there will be ~100% reabsorption of glucose When plasma glucose is below 200 mg/dL most if not all filtered glucose is reabsorbed Renal threshold for glucose = 200 mg/dL If the blood glucose concentration is higher than 200 mg/dL but lower than 400 mg/dL, what can be said regarding reabsorption and excretion? _________________________________________ ________________ If the blood glucose concentration is higher than 400 mg/dL what can be said regarding reabsorption and excretion? _________________________________________ Loop of Henle Counter-current multiplication The kangaroo rat https://www.endangeredspecieslawandpolicy.com/kangaroo-rat-from-endangered-to-threatened OpenStax College, CC BY 3.0 Loop of Henle Counter-current multiplication The kangaroo rat The ascending portion actively pumps out salt and is impermeable to water The high concentration of salt in the interstitial fluid of the medulla causes water to passively flow in the descending portion via osmosis https://www.endangeredspecieslawandpolicy.com/kangaroo-rat-from-endangered-to-threatened OpenStax College, CC BY 3.0 Loop of Henle Counter-current multiplication The kangaroo rat The ascending portion actively pumps out salt and is impermeable to water The high concentration of salt in the interstitial fluid of the medulla causes water to passively flow in the descending portion via osmosis https://www.endangeredspecieslawandpolicy.com/kangaroo-rat-from-endangered-to-threatened OpenStax College, CC BY 3.0 Distal Convoluted Tubule Responsible for the reabsorption of sodium (Na+), chloride (Cl-), bicarbonate (HCO3-), some water (H₂O), and the secretion of ammonium (NH₄⁺) Na+ reabsorption regulated by aldosterone (steroid hormone made in the adrenal cortex - gland) Parathyroid hormone (PTH) acts on the DCT to stimulate calcium (Ca+) reabsorption when Ca+ is low Empties into the collecting duct Collecting Duct Contains aquaporins which aid in the reabsorption of water into the blood Involved in Na+ reabsorption and potassium (K+) excretion © Learneo, Inc. 2024 Important Hormones Renin-Angiotensin-Aldosterone System  Low blood volume activates the juxtaglomerular apparatus in a variety of ways to make it secrete renin (secreted by extraglomerular mesangial cells).  Renin > angiotensin I > angiotensin converting enzyme (ACE) > angiotensin II.  Angiotensin II has a variety of effects, but it also causes the release of aldosterone from the adrenal cortex Aldosterone  Promotes sodium reabsorption in the DCT and collecting duct  Promotes the retention of water and sodium  Stimulates thirst  Increase blood volume and thus increase in blood pressure ADH or vasopressin  In the presence of high ADH the renal mechanisms produce hyperosmotic (concentrated) urine.  In the absence of ADH the renal excretion mechanisms produce hyposmotic (diluted) urine.  ADH increases the permeability of water of the distal convoluted tubule and collecting duct (by adding aquaporins), which are normally impermeable to water. This effect causes increased water reabsorption and retention, decreasing the volume of urine produced. Urinary Bladder Micturition – medical term for urination There are two sphincters, or muscular valves, that separate the bladder from the urethra.  The sphincters must open before the urine can flow into the urethra.  The internal sphincter is under involuntary control and the external sphincter is under voluntary control (pudendal nerve, S2,3,4). Volume of Urine  Bladder typically “feels full” around 150 - 200 mL  Perceiving a sense of urgency around 300 – 400 mL  >600 mL – involuntary urination Clinical Applications Urinary Tract Infection Most often occurs in sexually active women. Intercourse drives bacteria from the vagina and the anus through the nearby opening of the short urethra. The use of spermicides (found on condoms) magnifies the problem because they also kill the natural, “healthy” bacteria and allow pathogenic bacteria to colonize. Symptoms include a burning sensation during micturition, increased urgency and frequency of micturition, fever, and sometimes cloudy or blood-tinged urine. The elderly are also susceptible to UTIs due to weakness of the bladder, incontinence, poor bladder emptying, and retention of urine. Symptoms of a UTI in the elderly include mental changes and confusion. Renal Calculi – “Kidney Stones”  4 different types – Calcium oxalate is the most common  Patients experience severe pain  Risk factors – family history, chronic dehydration, obesity, certain diets (such as those with high in protein and/or salt)  Stones less than 5mm in diameter will likely pass without intervention  Stones >5 mm may become lodged in the ureter blocking the flow of urine and increasing intrarenal pressure  Lithotripsy – uses shock waves to break up stones