Urinary Systemppt.pptx

Urinary System Objectives • Name parts of the urinary system and list general functions • Trace pathway of blood within kidney • Describe the structure of the nephron and explain the process of urine formation. • Explain how various factors affect the rate of glomeular filtration Kidney Function...

Urinary System Objectives • Name parts of the urinary system and list general functions • Trace pathway of blood within kidney • Describe the structure of the nephron and explain the process of urine formation. • Explain how various factors affect the rate of glomeular filtration Kidney Functions • Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine • Regulate volume and chemical makeup of the blood • Maintain the proper balance between water and salts, and acids and bases Other Renal Functions • Gluconeogenesis during prolonged fasting • Production of rennin to help regulate blood pressure and erythropoietin to stimulate RBC production • Activation of vitamin D Other Urinary System Organs • Urinary bladder – provides a temporary storage reservoir for urine • Paired ureters – transport urine from the kidneys to the bladder • Urethra – transports urine from the bladder out of the body Urinary System Organs Figure 25.1a Kidney Location and External Anatomy • The bean-shaped kidneys lie in a retroperitoneal position in the superior lumbar region and extend from the twelfth thoracic to the third lumbar vertebrae • The right kidney is lower than the left because it is crowded by the liver • The lateral surface is convex and the medial surface is concave, with a vertical cleft called the renal hilus leading to the renal sinus • Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilus Internal Anatomy • A frontal section shows three distinct regions – Cortex – the light colored, granular superficial region – Medulla – exhibits cone-shaped medullary (renal) pyramids • Pyramids are made up of parallel bundles of urine-collecting tubules • Renal columns are inward extensions of cortical tissue that separate the pyramids • The medullary pyramid and its surrounding capsule constitute a lobe Internal Anatomy • Renal pelvis – flat, funnel-shaped tube lateral to the hilus within the renal sinus Internal Anatomy • Major calyces – large branches of the renal pelvis – Collect urine draining from papillae – Empty urine into the pelvis • Urine flows through the pelvis and ureters to the bladder Internal Anatomy Figure 25.3b The Nephron • Nephrons are the structural and functional units that form urine, consisting of: – Glomerulus – a tuft of capillaries associated with a renal tubule – Glomerular (Bowman’s) capsule – blind, cup-shaped end of a renal tubule that completely surrounds the glomerulus The Nephron – Renal corpuscle – the glomerulus and its Bowman’s capsule – Glomerular endothelium – fenestrated epithelium that allows solute-rich, virtually protein-free filtrate to pass from the blood into the glomerular capsule The Nephron Figure 25.4b Nephrons • Cortical nephrons – 85% of nephrons; located in the cortex • Juxtamedullary nephrons: – Are located at the cortex-medulla junction – Have loops of Henle that deeply invade the medulla – Have extensive thin segments – Are involved in the production of concentrated urine Nephrons Figure 25.5b Capillary Beds of the Nephron • Every nephron has two capillary beds – Glomerulus – Peritubular capillaries • Each glomerulus is: – Fed by an afferent arteriole – Drained by an efferent arteriole Capillary Beds of the Nephron • Blood pressure in the glomerulus is high because: – Arterioles are high-resistance vessels – Afferent arterioles have larger diameters than efferent arterioles • Fluids and solutes are forced out of the blood throughout the entire length of the glomerulus Capillary Beds • Peritubular beds are low-pressure, porous capillaries adapted for absorption that: – Arise from efferent arterioles – Cling to adjacent renal tubules – Empty into the renal venous system • Vasa recta – long, straight efferent arterioles of juxtamedullary nephrons Filtration Membrane • Filter that lies between the blood and the interior of the glomerular capsule • It is composed of three layers – Fenestrated endothelium of the glomerular capillaries – Visceral membrane of the glomerular capsule (podocytes) – Basement membrane composed of fused basal laminae of the other layers Filtration Membrane Figure 25.7a Filtration Membrane Figure 25.7c Mechanisms of Urine Formation • The kidneys filter the body’s entire plasma volume 60 times each day • The filtrate: – Contains all plasma components except protein – Loses water, nutrients, and essential ions to become urine • The urine contains metabolic wastes and unneeded substances Mechanisms of Urine Formation • Urine formation and adjustment of blood composition involves three major processes – Glomerular filtration – Tubular reabsorption – Secretion Figure 25.8 Glomerular Filtration • Principles of fluid dynamics that account for tissue fluid in all capillary beds apply to the glomerulus as well • The glomerulus is more efficient than other capillary beds because: – Its filtration membrane is significantly more permeable – Glomerular blood pressure is higher – It has a higher net filtration pressure • Plasma proteins are not filtered and are used to maintain oncotic pressure of the blood Glomerular Filtration Rate (GFR) • The total amount of filtrate formed per minute by the kidneys • Factors governing filtration rate at the capillary bed are: – Total surface area available for filtration – Filtration membrane permeability – Net filtration pressure