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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

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Figure 25.1 The urinary system.

Hepatic veins (cut)

Esophagus (cut) Inferior vena cava

Adrenal gland

Aorta

Iliac crest

Rectum (cut) Uterus (part of female

reproductive system)

Renal artery

Renal hilum

Renal vein

Kidney

Ureter

Urinary

bladder

Urethra

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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

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Figure 25.9 A schematic, uncoiled nephron showing the three major renal processes that adjust plasma composition.

Cortical radiate artery

Afferent arteriole Glomerular

capillaries

Efferent arteriole

Glomerular capsule

Renal tubule and collecting duct containing filtrate

Peritubular capillary

To cortical radiate vein

Three major

renal processes: Urine Glomerular filtration

Tubular reabsorption

Tubular secretion

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Figure 25.8 Juxtaglomerular complex (JGC) of a nephron.

Glomerular capsule

Efferent arteriole

Afferent arteriole

Glomerulus

Efferent arteriole

Juxtaglomerular

complex

Macula densa

cells of the ascending limb of nephron loop

• Extraglomerular

• Granular

cells Afferent arteriole

Parietal layer of glomerular capsule

Capsular space

Foot processes of podocytes

Podocyte cell body (visceral layer)

Red blood cell

Proximal tubule cell

Lumens of glomerular capillaries

Endothelial cell of glomerular capillary

Glomerular mesangial cells

Renal corpuscle Juxtaglomerular complex�

mesangial cells

•

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Figure 25.10 The filtration membrane.

Efferent

arteriole

Afferent

arteriole

Glomerular capillary

covered by podocytes

that form the visceral layer

of glomerular capsule

Parietal layer

of glomerular

capsule

Proximal

convoluted

tubule

Glomerular

capsular space Cytoplasmic extensions

of podocytes

Filtration slits

Podocyte

cell body

Fenestrations

(pores)

Glomerular

capillary endothelium

(podocyte covering

and basement

membrane removed)

Foot processes

of podocyte

Filtration slits

Podocyte

cell body

Foot

processes

Filtration slits between the podocyte foot processes

Capillary

Fenestration

(pore)

Plasma

Filtration membrane

• Capillary endothelium

• Basement membrane

• Foot processes of podocyte

of glomerular capsule

Filtration

slit

Slit

diaphragm

Three layers of the filtration membrane

Foot

processes

of podocyte

Filtrate

in capsular

space

Glomerular capillaries and the visceral layer of

the glomerular capsule

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Figure 25.5 Location and structure of nephrons. Renal cortex

Renal medulla

Renal pelvis

Ureter Kidney

Renal corpuscle

• Glomerular capsule • Glomerulus

Proximal

convoluted

tubule

Cortex

Medulla

Thick segment Thin segment

Nephron loop

• Descending limb • Ascending limb

Collecting duct

Glomerular capsule: parietal layer

Basement membrane

Podocyte

Fenestrated endothelium of the glomerulus

Glomerular capsule: visceral layer

Apical microvilli

Mitochondria

Highly infolded basolateral membrane

Proximal convoluted tubule cells

Apical side

Basolateral side Distal convoluted tubule cells

Nephron loop (thin-segment) cells

Principal cell

Intercalated cell

Collecting duct cells

Distal

convoluted

tubule

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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

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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

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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

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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

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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

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Figure 25.8 Juxtaglomerular complex (JGC) of a nephron.

Glomerular capsule

Efferent arteriole

Afferent arteriole

Glomerulus

Efferent arteriole

Juxtaglomerular

complex

Macula densa

cells of the ascending limb of nephron loop

• Extraglomerular

• Granular

cells Afferent arteriole

Parietal layer of glomerular capsule

Capsular space

Foot processes of podocytes

Podocyte cell body (visceral layer)

Red blood cell

Proximal tubule cell

Lumens of glomerular capillaries

Endothelial cell of glomerular capillary

Glomerular mesangial cells

Renal corpuscle Juxtaglomerular complex�

mesangial cells

•

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Figure 25.7 Blood vessels of cortical and juxtamedullary nephrons. Cortical nephron

• Short nephron loop

• Glomerulus further from the cortex-medulla junction

• Efferent arteriole supplies peritubular capillaries

Renal

corpuscle

Glomerulus (capillaries)

Glomerular capsule

Proximal

convoluted

tubule

Peritubular

capillaries

Ascending limb of nephron loop

Kidney

Arcuate vein

Arcuate artery

Nephron loop

Efferent

arteriole

Descending limb of nephron loop

Peritubular

capillary bed

Glomerulus

Efferent arteriole

Afferent

arteriole

Juxtamedullary nephron

• Long nephron loop • Glomerulus closer to the cortex-medulla junction • Efferent arteriole supplies vasa recta

Cortical radiate vein

Cortical radiate artery

Afferent arteriole

Collecting duct

Distal convoluted tubule

Afferent arteriole

Efferent

arteriole

Vasa recta

Cortex- medulla junction

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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

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