University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

486

Pages:

24
Author:

hugdeigury7

Renal Corpuscle = glomerulus and Bowman’s capsule Podocyte Glomerular Filtration Membrane Glomerular Filtration Membrane • Fenestrated Endothelium – 0.08 micron pores exclude cells and large proteins like albumin • Basement Membrane – double layer of collagen from podocytes and endothelial cells is a selectively permeable membrane that only passes water, ions and small molecules, but not proteins – blood plasma has 7% protein but glomerular filtrate should only have about 0.03% protein • Filtration Slits – podocyte arms have interdigitating pedicels that form filtration slits that support the membrane and allow liquid to pass through. Filtration Pressure t Glomerular Filtration Rate (GFR) • • • • GFR = volume of filtrate formed per minute GFR = 150-180 L/day (50 x total blood volume) 99% of filtrate is reabsorbed, only 1-2 L urine excreted per day GFR is controlled by adjusting glomerular blood pressure through: – autoregulation: smooth muscle of afferent arteriole stabilizes glomerular BP over a range of 80 to 170 mmHg (systolic) •  BP stretches smooth muscle of afferent arteriole which responds by constricting and reducing blood flow. •  BP relaxes smooth muscle around afferent arteriole – sympathetic control: • acute stress triggers sympathetic neurons to constrict juxtaglomerular smooth muscle of afferent arterioles resulting in  GFR and urine production and redirect more blood flow to the heart, brain and skeletal muscles. Proximal Convoluted Tubule Sympathetic Nerve Fiber Juxtaglomerular smooth muscle cells Afferent Arteriole Distal Convoluted Tubule Collecting Duct Overview of Urine Formation Region of the Tubular Nephron Function Summary Proximal Convoluted Tubule Continuous, selective reabsorption of useful glomerular filtrates and returns them to the blood Descending Thin Limb Freely permeable to water which is removed from the of Loop of Henle urine and returned to the blood. Ascending Thick Limb of Loop of Henle Distal Convoluted Tubule Collecting Duct Actively and constantly pumps Na+, K+, and Cl- out of urine and returns it to the blood resulting in a dilute, hypotonic urine. Responsive to aldosterone which activates pumps that move Na+ from the urine and returns it to the blood and water follows. NaCl and water retention reduces urine output and helps maintain blood volume and pressure. Impermeable to water resulting in a large amount of dilute urine. Vasopressin (ADH) released due to dehydration increases collecting duct permeability resulting in water reabsorption and reduced urine output. A Summary of Renal Function Proximal Convoluted Tubule Reabsorption • Reabsorbs 65% of glomerular filtrate into peritubular capillaries including: – glucose (over 90%), amino acids, small proteins, vitamins, salts ( Na+, K+, Ca+2, Mg+2, Cl-), bicarbonate, water • PCT is a long tubule of cells with microvilli and abundant mitochondria for active transport. – PCT metabolism alone accounts for 6% of total calorie consumption at rest. • Transport Maximum: transport proteins of cell membrane can become saturated. – if blood glucose is extremely high, the PCT can not transport it all and some remains in urine (glycosuria). Proximal Convoluted Tubule Secretion • Waste secretion from blood and interstitial fluid into urine – urea, uric acid, ammonia, some hormones, many drugs and toxins • Acid-base balance - regulates pH of body fluids. – excretion of excess hydrogen ions (H+) into urine – reabsorption of bicarbonate (HCO3-) ions back into blood The Role of the Loop of Henle • Descending Limb of Loop of Henle – always freely permeable to water and urea – water follows gradient out of tubule • Ascending Limb of Loop of Henle – pumps Na+, K+, and Cl- out of urine into interstitial tissue constantly – maintains high osmolarity of renal medulla – always impermeable to water – tubular fluid becomes hypotonic Countercurrent Multiplier of the Loop of Henle The Effects of Aldosterone on the DCT Aldosterone (salt-retaining hormone) – Steroid hormone secreted by adrenal cortex in response to: • decreased amount of Na+ in the blood • drop in blood pressure – Causes cells of DCT to reabsorb Na+ from urine – Water is reabsorbed following the salt gradient. – Overall effect is  urine volume and  blood volume and  blood pressure. The Effects of Vasopressin (ADH) on the DCT and Collecting Ducts • Vasopressin is an antidiuretic hormone (ADH) – dehydration stimulates neurons in the hypothalamus that send axons into the posterior pituitary which releases vasopressin – vasopressin increases the permeability of DCT and CD to water by causing collecting duct cells to transfer aquaporin from storage vesicles in the cytoplasm to the cell membrane. Aquaporin is an integral membrane protein that lets water flow through cells from the urine back into blood. – overall effect is retention of water and decreased urine volume aquaporin The Effects of Vasopressin (ADH) on the DCT and Collecting Ducts The Role of Capillaries • Peritubular Capillaries and Vasa Recta – peritubular capillaries surround the PCT and DCT – vasa recta follow the loop of Henle – provide blood supply to cortex and medulla – absorb water and solutes secreted from the urine into the interstitial tissue – return water and useful solutes to systemic circulation Atrial Natriuetic Peptide (ANP) Atrial Natriuretic Peptide (ANP) is an antagonist to vasopressin: – High Blood Pressure stimulates cells in the right atrium to secrete ANP into the blood – ANP makes the collecting duct less permeable to water which results in: –  urine volume –  blood volume – inhibits renin/angiotensin/aldosterone pathway – Overall effect is lower Blood Pressure Renal Failure • Renal Failure may result from: – loss of blood flow to the kidney – blockage of urine flow – infection or other disease of the kidney • Renal Failure may lead to: – azotemia:  blood urea nitrogen (BUN) – uremia: toxic effects as nitrogenous wastes accumulate in the blood The Juxtaglomerular Apparatus Juxtaglomerular (JG) Cells • enlarged smooth muscle cells around the afferent arteriole regulate blood flow and GFR • contract or relax around the afferent arteriole in response to the macula densa cells and sympathetic neurons • also secrete renin in response to  BP (renin activates an endocrine response that raises BP) Mesangial Cells • connected by gap junctions to JG and MD cells • probably mediate communication between JG and MD cells Macula Densa Cells • epithelial cells at the beginning of the DCT • monitor flow and salinity of urine Renin-Angiotensin Control of Blood Pressure