Human Urogenital System 26-1
Urogenital System Functions Filtering of blood, Removal of wastes and metabolites Regulation of blood volume and composition concentration of blood solutes ph of extracellular fluid blood cell synthesis Synthesis of Vitamin D Reproduction and sexual function 26-2
Urinary System Anatomy 26-3
Location and External Anatomy of Kidneys Location Lie behind peritoneum on posterior abdominal wall on either side of vertebral column Lumbar vertebrae and rib cage partially protect Right kidney slightly lower than left External Anatomy Renal capsule Surrounds each kidney Perirenal fat Engulfs renal capsule and acts as cushioning and source of energy Renal fascia Anchors kidneys to abdominal wall, separates from abdomen Hilum Renal artery and nerves enter and renal vein and ureter exit kidneys 26-4
Internal Anatomy of Kidneys Cortex: Outer area Renal columns Medulla: Inner area Renal pyramids Calyces Major: Converge to form pelvis Minor: Papillae extend Nephron: Functional unit of kidney Juxtamedullary Cortical 26-5
The Nephron 26-6
Histology of the Nephron 26-7
Internal Anatomy of Kidneys Renal corpuscle Bowman s or Renal capsule Parietal layer Visceral layer Glomerulus Network of capillaries goes into another capillary bed called the peritubular Capillaries - Arterioles Afferent Blood to glomerulus Efferent Drains not into veinule but another arteriole Tubules Proximal (convoluted) tubule Loops of Henle Descending limb Ascending limb Distal (convoluted) tubules Collecting ducts 26-8
Renal Corpuscle 26-9
Kidney Blood Flow 26-10
Ureters and Urinary Bladder Ureters Tubes through which urine flows from kidneys to urinary bladder Urinary bladder Stores urine Urethra Transports urine from bladder to outside of body Difference in length between males and females Sphincters Internal urinary External urinary 26-11
Ureters and Urinary Bladder 26-12
Urine Formation 26-13
Filtration Filtration Renal filtrate Plasma minus blood cells and blood proteins Most (99%) reabsorbed Filtration membrane Fenestrated endothelium, basement membrane and pores formed by podocytes Filtration pressure Responsible for filtrate formation Glomerular capillary pressure (GCP) minus capsule pressure (CP) minus colloid osmotic pressure (COP) Changes caused by glomerular capillary pressure EFP = GCP CP COP Where Effective filtration pressure = EFP 26-14
Filtration Pressure 26-15
Tubular Reabsorption Reabsorption almost 90% takes place in Proximal tubule via Passive transport Active transport Cotransport Specialization of tubule segments Distal tubule and collecting duct affected by hormones like ADH & Aldosterone Substances transported Active transport moves Na + across nephron wall Other ions and molecules moved by cotransport Passive transport moves water, urea, lipid-soluble, nonpolar compounds 26-16
Reabsorption in Proximal Nephron 26-17
Reabsorption in Loop of Henle 26-18
Reabsorption in Loop of Henle 26-19
Tubular Secretion Substances enter proximal or distal tubules and collecting ducts H +, K + and some substances not produced in body are secreted by countertransport mechanisms 26-20
Secretion of Hydrogen and Potassium 26-21
Urine Production In Proximal tubules Na + and other substances removed Water follows passively Filtrate volume reduced In descending limb of loop of Henle Water exits passively, solute enters Filtrate volume reduced 15% In ascending limb of loop of Henle Na +, Cl -, K + transported out of filtrate Water remains In distal tubules and collecting ducts Water movement out regulated by ADH If absent, water not reabsorbed and dilute urine produced If ADH present, water moves out, concentrated urine produced 26-22
Filtrate and Medullary Concentration Gradient 26-23
Medullary Concentration and Urea Cycling 26-24
Urine Concentration Mechanism When large volume of water consumed Eliminate excess without losing large amounts of electrolytes Response is kidneys produce large volume of dilute urine When drinking water not available Kidneys produce small volume of concentrated urine Removes waste and prevents rapid dehydration 26-25
Urine Concentrating Mechanism 26-26
Hormonal Mechanisms ADH Secreted by posterior pituitary Increases water permeability in distal tubules and collecting ducts Aldosterone Produced in adrenal cortex Affects Na + and Cl - transport in nephron and collecting ducts Renin Produced by kidneys, causes production of angiotensin II Atrial natriuretic hormone Produced by heart when blood pressure increases Inhibits ADH production Reduces ability of kidney to concentrate urine 26-27
Effect of ADH on Nephron 26-28
Aldosterone Effect on Distal Tubule 26-29
Autoregulation and Sympathetic Stimulation Autoregulation Involves changes in degree of constriction in afferent arterioles As systemic BP increased, afferent arterioles constrict and prevent increase in renal blood flow Sympathetic stimulation Constricts small arteries and afferent arterioles Decreases renal blood flow 26-30
Clearance and Tubular Load Plasma clearance Volume of plasma cleared of a specific substance each minute Used to estimate GFR Used to calculate renal plasma flow Used to determine which drugs or other substances excreted by kidney Tubular load Total amount of substance that passes through filtration membrane into nephrons each minute Normally glucose is almost completed reabsorbed 26-31
Tubular Maximum Tubular maximum Maximum rate at which a substance can be actively absorbed Each substance has its own tubular maximum 26-32
Urine Flow and Micturition Reflex Urine flow Hydrostatic pressure forces urine through nephron Peristalsis moves urine through ureters Micturition reflex Stretch of urinary bladder stimulates reflex causing bladder to contract, inhibiting urinary sphincters Higher brain centers can stimulate or inhibit reflex 26-33
Micturition Reflex 26-34
Effects of Aging on Kidneys Gradual decrease in size of kidney Decrease in kidney size leads to decrease in renal blood flow Decrease in number of functional nephrons Decrease in renin secretion and vitamin D synthesis Decline in ability of nephron to secrete and absorb 26-35
Kidney Dialysis 26-36