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Kidney – Filters Blood, Allowing Toxins, Metabolic Wastes, and Excess Ions to Leave the Body in Urine

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Kidney – Filters Blood, Allowing Toxins, Metabolic Wastes, and Excess Ions to Leave the Body in Urine Urinary System Organs . Kidney – Filters blood, allowing toxins, metabolic wastes, and excess ions to leave the body in urine . 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 10/20/13 MDufilho 1 Figure 25.1 The urinary system. Hepatic veins (cut) Esophagus (cut) Inferior vena cava Adrenal gland Renal artery Renal hilum Aorta Renal vein Kidney Iliac crest Ureter Rectum (cut) Uterus (part of female reproductive system) Urinary bladder Urethra MDufilho10/20/13 2 Kidneys -Overview . Blood passes through kidney – filtration occurs at capillaries – 20% of plasma becomes filtrate . Filtrate passes through nephrons – water and electrolytes are reabsorbed . Some electrolytes, drugs and toxins may be secreted into filtrate by tubular secretion = Urine 10/20/13 MDufilho 3 Figure 25.9 A schematic, uncoiled nephron showing the three major renal processes that adjust plasma composition. Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery Glomerular capsule 1 Renal tubule and collecting duct containing filtrate Peritubular 2 capillary 3 To cortical radiate vein Three major renal processes: Urine 1 Glomerular filtration 2 Tubular reabsorption MDufilho 3 Tubular secretion 10/20/13 4 Figure 25.8 Juxtaglomerular complex (JGC) of a nephron. Glomerular capsule Glomerulus Foot Efferent processes arteriole Parietal layer of podocytes of glomerular capsule Podocyte cell body (visceral layer) Capsular Afferent space Red blood cell arteriole Efferent Proximal arteriole tubule cell Juxtaglomerular complex • Macula densa cells of the ascending limb of nephron loop Lumens of • Extraglomerular glomerular mesangial cells capillaries • Granular Endothelial cell cells Afferent of glomerular arteriole capillary Glomerular mesangial cells Juxtaglomerular complex Renal corpuscle MDufilho 10/20/13 5 Figure 25.10 The filtration membrane. Glomerular Efferent capsular space Cytoplasmic extensions arteriole of podocytes Filtration slits Podocyte Afferent cell body arteriole Proximal convoluted Glomerular capillary tubule covered by podocytes Parietal layer that form the visceral layer of glomerular Fenestrations of glomerular capsule capsule (pores) Glomerular capillaries and the visceral layer of the glomerular capsule Glomerular capillary endothelium (podocyte covering and basement Foot processes membrane removed) of podocyte Filtration slits Podocyte cell body Filtration membrane • Capillary endothelium Capillary • Basement membrane • Foot processes of podocyte of glomerular capsule Foot processes Filtration slit Slit Plasma diaphragm Filtrate in capsular space Foot Fenestration processes (pore) of podocyte MDufilho 6 Filtration slits between the podocyte foot processes 10/20/13 Three layers of the filtration membrane Figure 25.5 Location and structure of nephrons. Renal cortex Renal medulla Renal pelvis Glomerular capsule: parietal layer Basement membrane Ureter Podocyte Kidney Fenestrated endothelium Renal corpuscle of the glomerulus • Glomerular capsule Glomerular capsule: visceral layer • Glomerulus Distal convoluted Apical Mitochondria tubule microvilli Proximal Highly infolded basolateral convoluted tubule membrane Proximal convoluted tubule cells Cortex Apical side Medulla Thick Basolateral side Thin segment segment Distal convoluted tubule cells Nephron loop • Descending limb • Ascending limb Nephron loop (thin-segment) cells Collecting duct Principal Intercalated cell cell MDufilho10/20/13 Collecting duct cells 7 Renal Tubule . Proximal convoluted tubule (PCT) – composed of cuboidal cells with numerous microvilli and mitochondria . Reabsorbs water and solutes from filtrate and secretes substances into it . Reabsorbs 100% of glucose, amino acids, escaped proteins, some vitamins, 60-70% of Na+, K+, Cl-, Ca++ and water . Secretes H+, NH3 (ammonia), drugs, toxins, uric acid and histamine 10/20/13 MDufilho 8 Renal Tubule . Loop of Henle – a hairpin-shaped loop of the renal tubule . Descending Limb . Impermeable to electrolytes, permeable to water . 80% Water is absorbed, filtrate becomes hypertonic . Ascending Limb . Permeable to Na+ and Cl- but not water . Filtrate becomes hypotonic 10/20/13 MDufilho 9 Renal Tubule . Distal convoluted tubule (DCT) Reabsorbs: . Na+ directed by aldosterone . Water directed by ADH . Ca++ directed by PTH . Some HCO3-, depending on pH of blood Secretes: . NH3, K+, drugs, toxins, and creatinine . Some H+, depending on pH of blood 10/20/13 MDufilho 10 Collecting Tubule Reabsorbs . Na+ directed by aldosterone . HCO3- depending on blood pH . Urea to maintain hypertonic interstitial fluid around nephron tubules . Water directed by ADH 10/20/13 MDufilho 11 Capillary Beds of the Nephron . Every nephron has two capillary beds . Glomerulus . Peritubular capillaries . Each glomerulus is: . Fed by an afferent arteriole - larger . Drained by an efferent arteriole - smaller 10/20/13 MDufilho 12 Figure 25.8 Juxtaglomerular complex (JGC) of a nephron. Glomerular capsule Glomerulus Foot Efferent processes arteriole Parietal layer of podocytes of glomerular capsule Podocyte cell body (visceral layer) Capsular Afferent space Red blood cell arteriole Efferent Proximal arteriole tubule cell Juxtaglomerular complex • Macula densa cells of the ascending limb of nephron loop Lumens of • Extraglomerular glomerular mesangial cells capillaries • Granular Endothelial cell cells Afferent of glomerular arteriole capillary Glomerular mesangial cells Juxtaglomerular complex Renal corpuscle MDufilho 10/20/13 13 Figure 25.7 Blood vessels of cortical and juxtamedullary nephrons. Cortical nephron Juxtamedullary nephron • Short nephron loop • Long nephron loop • Glomerulus further from the cortex-medulla junction • Glomerulus closer to the cortex-medulla junction • Efferent arteriole supplies peritubular capillaries • Efferent arteriole supplies vasa recta Renal Glomerulus Efferent corpuscle (capillaries) arteriole Cortical radiate vein Cortical radiate artery Glomerular capsule Afferent arteriole Collecting duct Proximal convoluted Distal convoluted tubule tubule Afferent arteriole Efferent arteriole Peritubular capillaries Ascending limb of nephron loop Cortex- medulla Arcuate vein junction Kidney Vasa recta Arcuate artery Descending Nephron loop limb of nephron loop Peritubular capillary bed Glomerulus Afferent arteriole Efferent arteriole MDufilho 10/20/13 14 Hemodialysis . Diffusion of solutes through semipermeable membrane . Dialysis machine- group of tubules that act like a nephron . Membrane allows free passage of glucose, electrolytes and nitrogenous wastes . Filtration and production of filtrate is not required 10/20/13 MDufilho 15 .
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