BSC 1086C Lecture 15: Chapter 28- Urinary System

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Florida Gulf Coast University
Biological Sciences
BSC 1086C

Chapter 28- Urinary System Urinary System Organs - Kidneys are major excretory organs - Ureters transport urine from the kidneys to the bladder - Urinary bladder is the temporary storage reservoir for urine - Urethra transports urine out of the body Kidney Functions - Removal of toxins, metabolic wastes, and excess ions from the blood. - Regulation of blood volume, chemical composition, and pH - Gluconeogenesis during prolonged fasting - Endocrine functions o Renin: regulation of blood pressure and kidney function o Erythropoietin: regulation of RBC production - Activation of vitamin D Kidney Anatomy - Retroperitoneal, in the superior lumbar region - Right kidney lower than the left - Convex lateral surface, concave medial surface - Renal hilum leads to the renal sinus - Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilum - Layers of supportive tissue o Renal fascia ▪ The anchoring outer layer of dense fibrous connective tissue o Perineal fat capsule ▪ A fatty cushion o Fibrous capsule ▪ Prevents spread of infection to kidney Internal Anatomy - Renal cortex- Granular superficial region - Renal medulla- cone-shaped medullary (renal) pyramids separated by renal columns - Papilla- tip of pyramids; releases urine into minor calyx - Renal pelvis- funnel-shaped tube within the renal sinus - Major calyces- the branching channels of the renal pelvis that o Collect urine from minor calyces o Empty urine into the pelvis - Urine flows from the pelvis to ureter Blood and Nerve Supply - Renal arteries deliver ~ ¼ (1200 ml) of cardiac output to the kidneys each minute - Arterial flow into and venous flow out of the kidneys follow similar paths - Nerve supply is via sympathetic fibers from the renal plexus Nephrons - Structural and functional units that form urine - ~ 1 million per kidney - Two main parts o Glomerulus: a tuft of capillaries o Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus - Renal corpuscle= Glomerulus and its glomerular capsule - Fenestrated glomerular endothelium o Allows filtrate to pass from plasma into the glomerular capsule - Glomerular capsule o Parietal layer: simple squamous epithelium o Visceral layer: branching epithelial podocytes ▪ Extensions terminate in foot processes that cling to basement membrane ▪ Filtration silts allow filtrate to pass into the capsular space Renal Tubule - Proximal convoluted tubule (PCT) o Functions in reabsorption and secretion o Confined to the cortex - Loop of Henle with descending and ascending limbs o Thin segment usually in descending limb ▪ Simple squamous epithelium ▪ Freely permeable to water o Thick segment of ascending limb ▪ Cuboidal to columnar cells - Distal convoluted tubule (DCT) o Cuboidal cells with very few microvilli o Function more in secretion that reabsorption o Confined to the cortex Collecting Ducts - Receive filtrate from many nephrons - Fuse together to deliver urine through papillae into minor calyces - Cell types o Intercalated cells: Function in maintaining the acid-base balance of the body o Principal cells: Help maintain the body’s water and salt balance Nephrons - Cortical nephrons- 85% of nephrons; almost entirely in the cortex - Juxtamedullary nephrons o Long loops of Henle deeply invade the medulla o Extensive thin segments o Important in the production of concentrated urine Nephron Capillary Beds - Glomerulus o Afferent arteriole -> glomerulus -> efferent arteriole o Specialized for filtration o Blood pressure is h
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