This document provides an overview of the structure and function of the urinary system. It discusses the key organs - kidneys, ureters, urinary bladder and urethra. It then focuses on kidney anatomy, including internal structures like the cortex, medulla and nephrons. Nephrons are described as the functional units that form urine, consisting of a glomerulus for filtration and renal tubules for processing. The mechanisms of blood filtration and urine production by nephrons are also summarized.

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The Urinary System:
Chapter 24

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Chapter 24 Overview
 Kidney Anatomy
Gross
Microscopic
Nephrons

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Urinary System Organs
• Kidneys
• Major filter organs
• Ureters
• Connect kidneys to bladder
• Urinary bladder
• Urine holding tank
• Urethra
• Exit tube

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Kidney Function
• Filters blood
• Removes toxins
• Metabolic wastes, excess ions from the blood
• Regulates blood chemistry
• Volume
• Composition (electrolytes)
• pH
• Endocrine function
• Erythropoetin production

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Kidney Location
• Retroperitoneal
• Superior lumbar region
• Right kidney lower than left
• Convex lateral surface, concave medial
surface
• Medial renal hilum
• Ureters, renal blood vessels, lymphatics, and
nerves enter and exit

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Kidney Anatomy
Layers of supportive tissue
1. Renal fascia
• Anchors kidney
1. Perirenal fat capsule
• fatty cushion
1. Fibrous capsule
• Adheres to kidney
• Prevents spread of infection

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Internal Kidney Anatomy
• Three regions
1. Cortex
2. Medulla
3. Pelvis

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Renal Cortex
• Superficial region of kidney
Renal medulla
• Cone-shaped “renal pyramids”
• Separated by renal columns, form lobes
• Produce urine
• Empty into minor calyces

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Renal Pelvis
• Funnel-shaped tube
• Continuous with the ureter
• Formed from minor calyces  major calyces

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Internal Kidney Anatomy
• Three regions
1. Lobe
2. Papilla
3. Minor calyces

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Internal Anatomy
• Lobe
• Pyramid and surrounding tissue
• Papilla
• Tip of pyramid

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Internal Anatomy
• Major calyces
• Branching channels of renal pelvis
• Collect urine from minor calyces
• Empty urine into the pelvis
• Urine flows from the pelvis to ureter

13. Copyright © 2011 Pearson Education, Inc. Figure 24.3
Renal cortex
Renal medulla
Major calyx
Papilla of
pyramid
Renal pelvis
Ureter
Minor calyx
Renal column
Renal pyramid
in renal medulla
Fibrous capsule
Renal
hilum
(a) Photograph of right kidney, frontal section (b) Diagrammatic view
Internal Kidney Anatomy

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Blood Supply
• Aorta  renal artery
• Renal artery… nephron blood vessels
• Afferent arteriole
• Glomerulus
• Efferent arteriole

15. Copyright © 2011 Pearson Education, Inc. Figure 24.4b
Aorta
Renal artery
Segmental artery
Interlobar artery
Arcuate artery
Cortical radiate artery
Afferent arteriole
Glomerulus (capillaries)
Nephron-associated blood vessels
(see Figure 24.7)
Inferior vena cava
Renal vein
Interlobar vein
Arcuate vein
Cortical radiate
vein
Peritubular
capillaries
and vasa recta
Efferent arteriole
(b) Path of blood flow through renal blood vessels

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Blood Supply
• Renal arteries deliver blood
• ~ 1
/4 (1200 ml) of cardiac output per minute
• All blood travels through glomerulus
• Filter structure
• Renal veins carry blood away

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FUNCTIONAL UNITS OF THE
KIDNEY:
NEPHRONS

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Nephrons
• Structural units, form urine
• ~1 million per kidney
Two main parts
1. Glomerulus: a group of capillaries
2. Renal tubule: process and filter urine
• Glomerular capsule
• Convoluted tubule

19. Copyright © 2011 Pearson Education, Inc. Figure 24.5
Nephrons

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Nephrons
• Renal corpuscle
• Glomerulus + glomerular capsule
• “Baseball + glove”
• Glomerular capillaries are fenestrated
• Allows material to pass
• Surrounded by podocytes

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Renal Tubule
• Proximal convoluted tubule (PCT)
• Cuboidal cells with dense microvilli and large
mitochondria
• Functions in reabsorption and secretion
• Confined to the cortex

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Renal Tubule
• Loop of Henle
• descending and
ascending limbs
• Freely
permeable to
water

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Renal Tubule
• Distal convoluted tubule
(DCT)
• Function to secrete
• Confined to the cortex
• Empties into the collecting
duct

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Collecting Ducts
• Receive filtrate from many nephrons
• Fuse together to form minor calyces
• Help maintain water and salt balance

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Nephron

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Nephrons
Two types
1.Cortical nephrons —85% of nephrons; almost
entirely in the cortex
2.Juxtamedullary nephrons
• Long loops of Henle
• deeply invade medulla
• Production of concentrated urine

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Nephron Capillary Beds
1. Glomerulus
• Afferent arteriole → glomerulus → efferent
arteriole
• Specialized for filtration – fenestrated
• High pressure

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Nephron Capillary Beds
2. Peritubular capillaries
• Formed from efferent arterioles
• Low-pressure
• For absorption
• Cling to renal tubules
• Empty into venules

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Filtration Membrane
• Porous membrane surrounding glomerulus
• Consists of
1. glomerular capillaries
2. glomerular capsule
• (podocytes with foot processes and filtration slits)
1. basement membrane

30. Copyright © 2011 Pearson Education, Inc. Figure 24.9a
Glomerular capillary
covered by podocyte-
containing visceral
layer of glomerular
capsule
Glomerular capillary
endothelium (podocyte
covering and basement
membrane removed)
Proximal
convoluted
tubule
Parietal layer
of glomerular
capsule
Afferent
arteriole
Glomerular capsular space
Fenestrations
(pores)
Efferent
arteriole
Podocyte
cell body
Foot processes
of podocyte
Filtration slits
Cytoplasmic extensions
of podocytes
(a) Glomerular capillaries
and the visceral layer of
the glomerular capsule

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Filtration Membrane
• Allows passage of water and solutes
• Most ions and salts can pass
• Most proteins too large
• blood cells too large

32. Copyright © 2011 Pearson Education, Inc. Figure 24.9c
(c) Three parts of the filtration membrane
Fenestration
(pore)
Filtrate in
capsular
space
Foot processes
of podocyte
Filtration slit
Slit diaphragm
Capillary
Filtration membrane
• Capillary endothelium
• Basement membrane
• Foot processes of podocyte
of glomerular capsule
Plasma