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Urinary System AnatomyUrinary Section pages 5-8

Waste

• Metabolism produces waste products

• What is the primary waste product of cellular

respiration? How does the body dispose of it?

Urinary System

• Disposes of water soluble wastes

• Maintains fluid balance

• Regulates electrolytes

• Regulates acid-base balance

Urinary System

• Other functions

– Kidneys

• Renin stored and secreted

– Enzyme involved in

angiotensin II activation

• Erythropoietin

– Hormone that stimulates

RBC production

• Vitamin D activation

– Enzymes convert dietary and

manufactured vitamin D to

calcitrol

Nitrogenous Wastes

• Urine is about 95% water

• Second largest component is urea

– Urea derived from breakdown of amino acids

Nitrogenous Wastes

1. Dietary amino acids → NH2 removed → NH2 + H+ → NH3

– 500 ml of urine removes only 1 gram of nitrogen as ammonia

2. Ammonia can be converted to urea

– Requires energy

– 50 ml of urine removes 1 gram of nitrogen as urea

3. Ammonia can be converted to uric acid

– Requires lots of energy

– 10 ml of urine removes 1 gram of nitrogen as uric acid

TOXIC!

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Fill in the blanks…

Ammonia Urea Uric acid

Toxicity Very toxic

Energy Costs High = 3 ATP

Water Required 50 ml/g Nitrogen

Solubility Low

Examples Fish & aquatic

invertebrates

Urinary System

• Organs

– Kidneys

• Major excretory organs

– Urinary bladder

• Temporary storage reservoir for urine

– Ureters

• Transport urine from the kidneys to the bladder

– Urethra

• Transports urine out of the body

Figure 25.1

Esophagus (cut)Inferior vena cava

Adrenal gland

Hepatic veins (cut)

Renal artery

Renal hilum

Renal vein

Iliac crest

Kidney

Ureter

Urinary

bladder

Urethra

Aorta

Rectum (cut)

Uterus (part

of female

reproductive

system)

Figure 25.2a

Body wall

• Perirenal

fat capsule

Renal

artery

Renal

vein

Inferior vena cava

Aorta

• Fibrous

capsule

• Renal fasciaanteriorposterior

Supportivetissue layers

Body of

vertebra L2

PeritoneumPeritoneal cavity

(organs removed)

Anterior

Posterior(a)

Kidneys

• External anatomy

– Retroperitoneal position

– Embedded in pararenal fat

Kidneys

• External anatomy

– Hilus (or hilum)

• Where blood vessels, nerves,

and ureter pass

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Kidneys

• External anatomy

– 3 tissue layers surround & support

• Fibrous capsule

• Perirenal fat capsule

• Renal fascia

Hydronephrosis

• Backup of urine causes excess fluid in the

kidney

• Common causes

– Kidney stones

– Infection

– Enlarged prostate

– Blood clot

– Tumor

Kidneys

• Internal Anatomy

– Renal cortex

• Superficial region

• Renal columns extend into medulla

• Where urine is produced

Kidneys

– Renal medulla

• Cone-shaped medullary (renal)

pyramids

• Separated by the renal

columns

• Consist of tubules that

transport urine to the

calyces

Kidneys

– Renal medulla

• The papilla (point) of each

pyramid drains into a

minor calyx

• Several minor calyces

drain into one major calyx

• Major calyces drain into

renal pelvis

Kidneys

– Renal pelvis

• Funnel-shaped tube that collects

urine from calyces

• Continuous with ureter

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Figure 25.3

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

Kidneys

• Blood Supply

– Renal arteries deliver ~ 22 % of cardiac output (1.2

L/min)

• 90% directed to cortex

• Urine formation

Figure 25.4a

Cortical radiate vein

Cortical radiate artery

Arcuate vein

Arcuate artery

Interlobar vein

Interlobar artery

Segmental arteries

Renal artery

Renal vein

Renal pelvis

Ureter

Renal medulla

Renal cortex

(a) Frontal section illustrating major blood vessels

Figure 25.4b

Aorta

Renal artery

Segmental artery

Interlobar artery

Arcuate artery

Cortical radiate artery

Afferent arteriole

Glomerulus (capillaries)

Nephron-associated blood vessels

(see Figure 25.8)

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

Nephrons

• Structural and functional units that form

urine

• ~1 million per kidney

• Two main parts

1. Blood capillaries (glomeruli)

2. Renal tubule: begins as cup-shaped glomerular

(Bowman’s) capsule surrounding the glomerulus

Figure 25.5

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Nephrons

• Renal corpuscle

– Glomerulus + Bowman’s capsule

Nephrons

• Glomerular endothelium

– Fenestrated capillary endothelium

– Layer of highly branched and interlaced podocytes

– Allows filtrate to pass from plasma into the

glomerular capsule

Figure 25.8

Glomerulus

Glomerular capsule

Afferent arteriole

Efferent arteriole

Red blood cell

Podocyte cell body (visceral layer)

Foot processesof podocytesParietal layer

of glomerularcapsule

Proximaltubule cell

Lumens of glomerularcapillaries

Endothelial cellof glomerularcapillary

Efferent arteriole

• Macula densa cells

• Granular cells

• Extraglomerularmesangial cells

Afferent arteriole

Capsularspace

Renal corpuscleJuxtaglomerularapparatus

Mesangial cellsbetween capillaries

Juxtaglomerularapparatus

Figure 25.7a

Cortical nephron• Has short loop of Henle and glomerulusfurther from the corticomedullary junction

• Efferent arteriole supplies peritubularcapillaries

Juxtamedullary nephron• Has long loop of Henle and glomeruluscloser to the corticomedullary junction

• Efferent arteriole supplies vasa recta

Corticomedullary

junction

Ureter

Renal pelvis

Kidney

Cortex

Medulla

(a)

Afferent arteriole

Afferent arteriole

Collecting ductDistal convoluted tubule

Efferent arteriole

Vasa rectaLoop of Henle

Peritubular capillaries

Glomerular capillaries

(glomerulus)Glomerular

(Bowman’s) capsule

Renal

corpuscle

loop of Henle

Efferent arteriole

Proximal

convoluted tubule

Nephrons

• Renal tubules

– Proximal convoluted tubule (PCT)

• So-called because it is proximal to renal corpuscle

• Functions

– Major site of reabsorption (amino acids, glucose, water, Na+)

– Secretion (medications, nitrogenous wastes)

– Exchange of ions important for pH (H+, HCO3-)

• Confined to the cortex

Nephrons

• Renal tubules

– Loop of Henle

• Descends from the cortex to the medulla, turns, and comes

back to the cortex

• More later…

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Nephrons

• Renal tubules

– Distal convoluted tubule (DCT)

• Important site for secretion, aldosterone & ADH

activity

• Exchange of ions important for pH (H+, HCO3-)

• Reabsorption of some electrolytes such as Na+

• Confined to the cortex

Nephrons

• Renal tubules

– Collecting tubules (CT)

• Receive filtrate from many nephrons

• Fuse together to deliver urine through papillae into

minor calyces

• Functions

– Important site for secretion, aldosterone & ADH activity

– Site of reabsorption of water and electrolytes

– Exchange of ions important for pH (H+, HCO3-)

Figure 25.5

Fenestrated

endothelium

of the glomerulus

Microvilli

Cortex

Medulla

Podocyte

Basement

membrane

Mitochondria

Highly infolded plasma

membrane

Proximal

convoluted

tubule

Distalconvolutedtubule

• Descending limb

Loop of Henle

• Ascending limb

• Glomerular capsule

Renal corpuscle

• Glomerulus

Thick segment

Collecting

duct

Intercalated cellPrincipal cell

Thin segment

Proximal convoluted tubule cells

Glomerular capsule: parietal layer

Glomerular capsule: visceral layer

Distal convoluted tubule cells

Loop of Henle (thin-segment) cells

Collecting duct cells

Renal cortex

Renal medulla

Renal pelvis

Ureter

Kidney

Nephrons

• Juxtaglomerular Apparatus (JGA)

– Distal convoluted tubule and afferent arteriole

contact one another – modified at the point of

contact

• One per nephron

– Function

• Regulation of filtrate formation and blood pressure

Nephrons

• Juxtaglomerular Apparatus (JGA)

– 3 components

1) Macula densa

• Group of columnar cells on DCT

• Chemoreceptors that monitor NaCl

content of filtrate entering DCT

• Sense DCT flow and release

chemicals that alter diameter

of afferent arteriole

Nephrons

• Juxtaglomerular Apparatus (JGA)

– 3 components

2) Granular cells

• AKA juxtaglomerular cells

• In wall of afferent arteriole

• Enlarged smooth muscle cells

• Mechanoreceptors that sense blood

pressure in afferent arteriole

• Store and secrete renin in response

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Nephrons

• Juxtaglomerular Apparatus (JGA)

– 3 components

3) Extraglomerular mesangial cells

• Lie between arteriole and DCT

• Connected by gap junctions

• Pass regulatory signals between

macula densa and granular cells

Figure 25.8

Glomerulus

Glomerular capsule

Afferent arteriole

Efferent arteriole

Red blood cell

Podocyte cell body (visceral layer)

Foot processesof podocytesParietal layer

of glomerularcapsule

Proximaltubule cell

Lumens of glomerularcapillaries

Endothelial cellof glomerularcapillary

Efferent arteriole

• Macula densa cells

• Granular cells

• Extraglomerularmesangial cells

Afferent arteriole

Capsularspace

Renal corpuscleJuxtaglomerularapparatus

Mesangial cellsbetween capillaries

Juxtaglomerularapparatus

Nephron Capillary Beds

1. Glomerulus

– Afferent arteriole → glomerulus → efferent

arteriole

– Specialized for filtration

Nephron Capillary Beds

2. Peritubular capillaries

– Low-pressure, porous capillaries adapted for

absorption

– Arise from efferent arterioles

– Cling to adjacent renal tubules in cortex

– Empty into venules

Nephrons

• Cortical nephrons

– 85% of nephrons; almost entirely in the cortex

• Short loops of Henle extend barely into medulla

• Juxtamedullary nephrons

– Long loops of Henle deeply invade the medulla

– Extensive thin segments

– Important in the production of concentrated urine

• Much more on this later…

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Ureters

• Convey urine from kidneys to bladder

• Retroperitoneal location

• Enter base of bladder through posterior wall

– ↑ bladder pressure = distal ends of the ureters

close

• Prevents backflow of urine

– Mucus is protective

Urinary Bladder

• Muscular sac for temporary storage of urine

• On pelvic floor posterior to pubic symphysis

– Males—prostate gland surrounds the neck inferiorly

– Females—anterior to the vagina and uterus

Urinary Bladder

– Stretch receptors in bladder create desire to void

• Micturition

• Urge to void usually occurs with about 300ml urine

• Can hold up to about 500ml

Urinary Bladder

– Epithelium is specialized to accommodate stretching and recoil as bladder fills and empties

Figure 25.1

Esophagus (cut)Inferior vena cava

Adrenal gland

Hepatic veins (cut)

Renal artery

Renal hilum

Renal vein

Iliac crest

Kidney

Ureter

Urinary

bladder

Urethra

Aorta

Rectum (cut)

Uterus (part

of female

reproductive

system)

Urethra

– Sphincters

• Internal

– ANS control

• External

– Voluntary control

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Figure 25.21b

Ureter

Trigone

Peritoneum

Rugae

Detrusor

muscle

Bladder neck

Internal urethral

sphincter

External urethral

sphincter

Urogenital diaphragm

Urethra

External urethral

orifice

Ureteric orifices

(b) Female.

Figure 25.21a

Ureter

Trigone of bladder

Prostate

Membranous urethra

Prostatic urethra

Peritoneum

Rugae

Detrusor muscle

Bladder neck

Internal urethral sphincter

External urethral sphincter

Urogenital diaphragm

Spongy urethra

Erectile tissue of penis

Ureteric orifices

Adventitia

(a) Male. The long male urethra has three

regions: prostatic, membranous and spongy.

External urethral orifice

Figure 25.22

Somatic motor

nerve activity

External urethral

sphincter opens

Sympathetic

activity

Parasympathetic

activity

Urinary bladder

filling stretches

bladder wall

Spinal

cord

Promotes micturition

by acting on all three

spinal efferents

Inhibits micturition

by acting on all three

spinal efferents

Allow or inhibit micturition

as appropriate

Brain

Simple

spinal

reflex

Spinal

cord

Inhibits

Parasympathetic activity

Sympathetic activitySomatic motor nerve activity

Pontine micturition

center

Pontine storage

center

Higher brain

centers

Detrusor muscle

contracts; internalurethral sphincter

opens

Afferent impulses

from stretch

receptors

Micturition

Incontinence

• Damage to spinal cord

• Frequent micturition in infants

– Incontinence is normal: control of the voluntary urethral sphincter develops with the nervous system

Pathway of Urine Flow

Urine formed in nephrons

Calyces

Renal pelvis

Ureters

Bladder

Urethra