omitted, except for the vasa recta. Cortical nephron most abundant type of nephron (80% this type) Juxtamedullary nephron long-looped nephron important in establishing the medullary vertical osmotic gradient (20% this type) Fig. 14-5, p. 509
Nephron-‐Tubular Component • Bowman’s capsule • Proximal tubule • Loop of Henle • descending limb • ascending limb • Distal tubule • CollecFng duct
Simple model of kidney func1on Filtra1on + Secre1on – Reabsorp1on = Excre1on 1 3 2 4 Fig 14-‐21
Afferent arteriole Efferent arteriole Glomerulus Bowman ’ s capsule Kidney tubule (entire length, uncoiled) Urine excretion (eliminated from the body) To venous system (conserved for the body) Peritubular capillary 20% of the plasma that enters the glomerulus is filtered 80% of the plasma that enters the glomerulus is not filtered and leaves through the efferent arteriole = Tubular secretion — selective movement of nonfiltered substances from the peritubular capillaries into the tubular lumen = Tubular reabsorption — selective movement of filtered substances from the tubular lumen into the peritubular capillaries = Glomerular filtration — nondiscriminant filtration of a protein-free plasma from the glomerulus into Bowman ’ s capsule GF TR TS Fig. 14-6, p. 510 GF 125 ml/min 180 L/day Ave plasma vol = 2.75L Therefore kidneys filter entire plasma vol ~65X/day TR: 178.5/180 L reabsorbed 125 ml/min fiiltered; 124 ml/ min reabsorbed
Glomeruli are beau1ful things
Glomerular Capillary Wall 1. A single layer of ﬂa^ened endothelial cells perforated by many pores. 2. Basement membrane is acellular and gela1nous composed of collagen and glycoproteins; the collagen gives structureal strength; the glycoproteins are nega1vely charged and repel albumin and other plasma proteins which are also nega1vely charged. Therefore plasma proteins are almost completely excluded from the filtrate. 3. Any plasma proteins that do slip into the filtrate are picked up by the proximal tubule by endocytosis-‐degraded into amino acids-‐returned to blood. 4. Thus-‐no proteins should be included in the urine!
Capillary pore (fenestration) Afferent arteriole Efferent arteriole Glomerulus Bowman ’ s capsule Lumen of Bowman ’ s capsule Outer layer of Bowman ’ s capsule Proximal convoluted tubule Inner layer of Bowman ’ s capsule (podocytes) Lumen of glomerular capillary Endothelial cell Basement membrane Basement membrane Podocyte foot process Filtration slit Filtration slit Endothelial cell Filtration slit Lumen of glomerular capillary Endothelial cell Capillary pore fenestration) Lumen of Bowman ’ s capsule Lumen of glomerular capillary Podocyte foot process Basement membrane 1 3 2 Fig. 14-7a, p. 511 Afferent arteriole to each Bowman’s capsule is wider than the narrow efferent arteriole (not shown below) which maintaines high blood P as a result of the blood damming up in the glomerular capillaries—it’s the major force producing glomerular filtraFon.
PODOCYTES of Bowman’s Capsule
Lumen of glomerular capillary Podocyte foot processes Filtration slit Capillary pore or fenestration Basement membrane Lumen of Bowman ’ s capsule Endothelial cell 1 2 3 Fig. 14-7b, p. 511
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- Fall '08
- Physiology, Nephron, Glomerulus, Blood Pressure