The Urinary SystemThe Urinary SystemCh 24Ch 24

Human Anatomy

Sonya Schuh-Huerta, Ph.D.Sonya Schuh-Huerta, Ph.D.

C. Babaian

Outline

• Historical perspective

• Kidney overview

• Nephron structure & function

• Ureters, Bladder & Urethra

• Hot research

• Disorders/diseases

Organs of the Urinary System

• Kidneys

• Ureters

• Urinary bladder

• Urethra

Why study the kidney?What does it do?

L. Da Vinci, 1508

The kidney: a vital organ with many functions

Filters the blood

-Removal of wastes & toxins

-Waste products: urea, uric acid, creatinine

-Production of urine

Homeostasis

-Body fluids & pressure

-Ions (Na+, K+, Cl-, Ca2+, HCO3-)

-Acid-base balance

-Blood sugar

Production of hormones

-Blood volume & pressure

-Calcium metabolism

-Red blood cell production

Kidney

Ureter

Bladder

• Historical interest in resolving urine’s composition & relation to health

• Alchemists of Medieval Europe thought urine contained gold!

• Urea isolated in 1773; 1st organic compound to be artificially synthesized

Urine color wheel

Gerrit Dou, 1617

What can urine tell us?

• Yellow color: breakdown products of hemoglobin

Urine color & components tella lot about a person’s health

What can urine tell us?

Modern-day urine color wheel

• Huge variation in amount & concentration of urine

• Kidney’s job: keep salt & water balanced (input = output)

• Maintain osmolarity of ~300 mOsmol/L

Salt & water balance

Matt Stonie, competitive eater

The kidneys

Renal artery

Renal hilum

Renal vein

Kidney

Ureter

Urinarybladder

Urethra

Location & gross anatomy

In almost all animals including humans

Paired, “kidney” bean-shaped organs

Located in the abdominal cavity: T12 – L3

Within the retroperitoneum

Left kidney behind spleen

Top of right kidney behind liver

Hilum opening where renal artery, vein, & ureter join kidney

Surrounded by fibrous capsule, fat & fasciaDorsal view

Position of the kidneys

12th rib

Body wall

Perirenalfat capsule

Renalartery

Renalvein

Inferiorvena cava

Aorta

Fibrouscapsule

Renal fasciaanteriorposterior

Supportivetissue layers

Body ofvertebra L2

PeritoneumPeritoneal cavity(organs removed)

Anterior

Posterior

Gross anatomy of the kidney

Renal cortex

Renalmedulla

Major calyx

Papilla ofpyramid

Renal pelvis

Ureter

Minor calyx

Renal column

Renal pyramidin renal medulla

Fibrous capsule

Gross anatomy of the kidney

medulla

hilum

renal capsule

renal pelvis

Cortical radiate vein

Cortical radiate artery

Arcuate vein

Arcuate artery

Interlobar veinInterlobar artery

Segmental arteries

Renal artery

Renal vein

Renal pelvis

Ureter

Renal medulla

Renal cortex

(a) Frontal section, posterior view, illustrating major blood vessels

Blood vessels of the kidney

Blood vessels of the kidneyAorta

Renal artery

Segmental artery

Interlobar artery

Arcuate artery

Cortical radiate artery

Afferent arteriole

Glomerulus (capillaries)

Nephron-associated blood vessels(see Figure 24.9)

Inferior vena cava

Renal vein

Interlobar vein

Arcuate vein

Cortical radiate vein

Peritubular capillariesand vasa recta

Efferent arteriole

(b) Path of blood flow through renal blood vessels

The kidney

• Contains ~1 million tubular structures = nephrons

• Carry out functions of the kidney

At the microscopic level

• Glomerulus & Bowman’s capsule

• Proximal tubule

• Loop of Henle

• Peritubular capilaries & Vasa recta

• Distal tubule

• Collecting duct

Nephron – the functional unit

Edward Sales

cortex

First part of the nephron

• Renal corpuscle Bowman’s capsule + glomerulus

• Glomerulus = tuft of porous capillaries • Bowman’s capsule = surrounds glomerulus

GlomerulusGlomerulus

Madelaine Dela Cruz

Glomerular filtration

• Holds back proteins & RBCs• Allows small molecules through:

WaterIons (Na+, Cl-, K+,

Ca2+, HCO3-)

GlucoseAmino acidsUrea & uric acid

Glomerular capillarycovered by podocytes

Proximalconvolutedtubule

Outer layerof Bowman’s capsule

Afferentarteriole

Glomerularcapsular spaceEfferent

arteriole

Glomerular filtration

• Glomeruli

– Porous capillaries– Fed & drained by

afferent & efferent arterioles

•Efferent arteriole has smaller diameter

– Filter 1 liter of fluid every 8 minutes!•180 liters of fluid per day•Total blood volume is filtered ~60X/day!

Filtration membrane

• Filter between blood in glomerulus & space of Bowman’s capsule

1. Endothelium of capillary

2. Basement membrane

3. Slits between foot processes of podocytes

Glomerularcapillary endothelium

Fenestrations(pores)

Podocytecell body

Foot processesof podocyte

Filtration slits

Cytoplasmic extensionsof podocytes

How does the nephron work?

1) Filtration– Blood filtrate leaves glomeruli

2) Reabsorption– Nutrients (glucose), H2O, & essential ions taken back into blood

3) Secretion– Active process of removing

undesirable chemicals from blood

– Dumping them into tubules

4) Excretion– Filtrate leaves as urine

Afferent arterioleGlomerulus

Efferent arteriole

Bowman’s capsule

Renal tubule

Peritubularcapillary

Urine

FiltrationReabsorptionSecretion

Different cell types & functions

Fenestrated endothelium of the glomerulus

Microvilli

Cortex

Medulla

Podocyte

Basementmembrane

Mitochondria

Highly infolded plasmamembrane

Proximal convolutedtubule

Distalconvolutedtubule

Descending limbLoop of Henle

Ascending limb

Glomerular capsuleRenal corpuscle

Glomerulus

Thick segment

Collectingduct

Intercalatedcell

Principal cell

Thin segment

Proximal convoluted tubule cells

Glomerular capsule: parietal layer

Glomerular capsule: visceral layer

Distal convoluted tubule cells

Nephron loop (thin-segment) cells

Collecting duct cells

Renal cortex

Renal medulla

Renal pelvis

UreterKidney

Glomerular Filtration Rate

• Glomerular Filtration Rate (= GFR)

Volume of fluid filtered by the glomeruli per unit time 180 L/day or 125 ml/min

– Can only be measured by compounds that are not reabsorbed or secreted

Coupling of water reabsorption to Na+ reabsorption

Tubule Cell PeritubularCapillary

Lumen

H2O

Na+

Na+

Na+

Na+

Na+

Na+ Na+ Na+

K+K+

H2O

H2O

H2O

H2O

H2O

H2O

Na+

H2O

H2O

Na+

ATPNaK

ATPase

low Na+

Na+

Na+Na+

Na+

Na+

Na+

Na+

H2O

H2O

H2OH2O

Proximal convoluted tubule

• Most solutes are reabsorbed here• All glucose is reabsorbed• Drugs/toxins are secreted• Filtrate is isoosmotic

Loop of Henle

• Ascending limb permeable to Na+, not H2O• Descending limb permeable to H2O, not Na+

• Concentrates medulla• Part of urine-concentrating system

Countercurrent multiplier system

Friedrich Henle, 1873

Countercurrent Multiplier System

• Fluids in adjacent tubes running in opposite directions – promotes the exchange of material

– Build-up of concentration– Movement of solutes– Examples in nature & mimicked in industry– Loop of Henle!

Loop of Henle

Corticomedullaryjunction

Afferent arterioleEfferentarteriole

Vasa recta

Peritubularcapillaries

Efferentarteriole

Cortical nephron Juxtamedullary nephron

• Cortical nephrons

• Juxtamedullary nephrons

–Loop of Henle plunges deep into medulla

–Vasa recta

–Set up the concentration gradient of medulla

–Create driving force for maximal H2O reabsorption from collecting ducts

Cortex

Medullahigh osmolarity

Collectingduct

The kidney cortex & medulla

Edward Sales

cortex

Benjamin Yates

medulla

Blood vessels of nephrons

• Peritubular capillaries– Capillary network of cortical nephrons– Adapted for absorption

• Low-pressure, porous capillaries

• Vasa recta– Capillary network of juxtamedullary nephrons– Thin-walled looping vessels

• Descend deep into the medulla

– Part of the kidney’s urine-concentrating mechanism

Adaptations of the kidney

• Desert animals conserve H2O

– Many long Loops of Henle– Highly concentrated urine (uric acid)– Urine “pellet”

Kangaroo ratBenjamin Yates

medulla

Distal convoluted tubule

• Permeable to (actively pumps) Na+ out of tubule• Impermeable to H2O• Filtrate hypoosmotic

Collecting duct

• Reabsorption of Na+ under hormonal control –Aldosterone (from adrenal gland)

• Reabsorption of H2O under hormonal control –Antidiuretic hormone, ADH (from posterior pituitary)

• The nephrons fine-tune the final concentration of urine based on body’s needs

How does the nephron fine tunethe reabsorption of Na+

and water?

Juxtaglomerular Apparatus

Red blood cell

Proximaltubule

Lumens of glomerularcapillaries

Efferentarteriole

Macula densa cells of the ascending limb

Granular cells

Extraglomerularmesangial cells

Afferent arteriole

Juxtaglomerularapparatus

Mesangial cellsbetween capillaries

• Regulates salt & fluid balance

• Special cells: granular cells & the macula densa

Juxtaglomerular Apparatus

• Macula densa Cells of distal ascending limb–Monitors solute concentration (Na+)

–When BP is low (GFR low) Na+ low signals granular cells to secrete renin

•Renin-Angiotensin System (RAS)

Regulates sodium & fluid balance (& BP)

• Granular cells Modified smooth muscle cells of aff. arteriole

–Make renin

Plasma Volume / Blood Pressure

GFR / Flow / NaCl

Macula densa

Renin

Granular cells

Angiotensin II

from Liver

Aldosterone

Adrenal gland

Sodium Reabsorption

Collecting ducts

Vascular & atrial pressure

Antidiuretic hormone

Posterior pituitary

Aquaporin channels

H2O Reabsorption

Collecting ducts

Excretion of salt & H2O

Fluid Volume / BP

• Many drugs interrupt steps of this system

• Used to treat high BP (hypertension), congenital heart disease, kidney disease, etc. diuretics

• Caffeine & alcohol also diuretics

Renin-Angiotensin System

Rest of the urinary system: Ureters

• Carry urine from the kidneys to the urinary bladder

• Oblique entry into bladder prevents backflow of urine

• Histology of ureter– Mucosa transitional epithelium– Muscularis 2 layers

• Inner longitudinal layer• Outer circular layer

– Adventitia typical connective tissue

Transitional Epithelium – Review…

• Description: – Has characteristics of stratified cuboidal &

stratified squamous– Superficial cells dome-shaped when bladder

is relaxed, squamous when full• Function: permits distension of urinary organs

by urine• Location: epithelium of urinary bladder, ureters,

proximal urethra

Transitional Epithelium(h) Transitional epithelium

Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous-like, depending ondegree of organ stretch.

Function: Stretches readily and permits distension of urinary organ by contained urine.

Location: Lines the ureters, bladder, and part of the urethra.

Photomicrograph: Transitional epithelium lining the bladder,relaxed state (390); note the bulbous, or rounded, appearanceof the cells at the surface; these cells flatten and becomeelongated when the bladder is filled with urine.

BasementmembraneConnectivetissue

Transitionalepithelium

Histology of the ureter

Lumen

Adventitia

Circularlayer

Longitudinallayer

Transitionalepithelium

Laminapropria M

uco

saM

usc

ula

ris

Urinary bladder

• A collapsible muscular sac

• Stores & expels urine– Full bladder spherical

• Expands into the abdominal cavity

– Empty bladder lies entirely within the pelvis

Urinary bladder

• Urachus closed remnant of the allantois

• Prostate gland– In males (not females!)

• Lies directly inferior to the bladder• Surrounds the urethra

Urinary bladder

Ureter notillustrated in (b)

Uterus

Urinary bladder

Ductus deferens

Pubic symphysis

Prostate gland

Vagina

Urethra

(a) Sagittal section through male pelvis, urinary bladder shown in lateral view

(b) Sagittal section through female pelvis

Urachus

Urinary bladder

• Urinary bladder is composed of 3 layers1. Mucosa transitional epithelium

2. Thick muscular layer detrusor muscle

3. Fibrous adventitia

Histology of the urinary bladder

Basementmembrane

Laminapropria

Transitionalepithelium

(a) Micrograph of the bladder wall (17X) (b) Epithelium lining the lumen of the bladder (360X)

Lumen of bladder

Adventitia(with fat cells)

Muscularlayer(detrusor)

Transitionalepithelium

Laminapropria

Urethra

• Epithelium of urethra– Transitional epithelium

• At the proximal end (near the bladder)

– Stratified & pseudostratified columnar mid-urethra (in males)

– Stratified squamous epithelium• At the distal end (near the urethral opening)

Urethra

• Internal urethral sphincter– Involuntary smooth muscle

• External urethral sphincter– Voluntarily inhibits urination– Relaxes when one urinates

Urethra

• In females– Length: 3–4 cm

• In males 20 cm in length; 3 named regions:– Prostatic urethra

• Passes through the prostate gland– Membranous urethra

• Through the urogenital diaphragm – Spongy (penile) urethra

• Passes through the length of the penis

Structure of urinary bladder & urethraUreter

Trigone of bladder

Prostate

Membranous urethraProstatic urethra

Peritoneum

Rugae

Detrusor muscle

Bladder neckInternal urethral sphincter

External urethral sphincterUrogenital diaphragm

Spongy urethra

Erectile tissue of penis

Ureteric orificesAdventitia

(a) Male. The long male urethra has three regions: prostatic, membranous, and spongy. External urethral orifice

Ureter

Trigone

Peritoneum

Rugae

Detrusor muscle

Bladder neck

Internal urethralsphincter

External urethralsphincter

Urogenital diaphragm

UrethraExternal urethralorifice

Ureteric orifices

(b) Female

Structure of urinary bladder & urethra

Micturition

Hypogastricnerve

Bladder

Pelvicnerves

Pelvicsplanchnicnerves

PonsPontinemicturitioncenter

Lower thoracicor upper lumbarspinal cord

Sacral spinalcord

Internal urethralsphincter External urethral sphincter

Inferiorhypogastricganglion

Visceral afferent impulses from stretch receptors in the bladder wall are carried to the spinal cord and then, via ascending tracts, to the pontine micturition center.

Integration in pontine micturition center initiates the micturition response. Descending pathways carry impulses to motor neurons in the spinal cord.

Parasympathetic efferents stimulate contraction of the detrusor muscle and open the internal urethral sphincter.

Somatic motor efferents to the external urethral sphincter are inhibited; the sphincter relaxes. Urine passes through the urethra; the bladder is emptied.

Sympathetic efferents to the bladder are inhibited.

(–)

(–)

(+)

(+)

Visceral afferentSympatheticSomatic efferentParasympatheticInterneuron

1

2

3

4

51

2

3

4

5

Hot Research• Adult reprogrammed cells (iPSCs) regenerate

entire kidney in vivo

(Usui et al., Amer J Path, 2012)

Disorders affecting the kidneys

• Diabetes mellitus (“flowing through” “sweet”)– Huge sugar load glucose in the urine & causes

osmotic diuresis; can result in low BP, coma & death

• Diabetes insipidus– Lack antidiuretic hormone (ADH)

massive amount of dilute urine & dehydration

• Renal calculi (kidney stones)– Too much salt, Ca2+, uric acid precipitates out of

solution & blocks urine flow; very painful

Disorders affecting the kidneys

• Renal Disease & Failure

–Glomerular dysfunction

–Slowed GFR, massive reabsorption of salt & water, severe hypertension, edema

–Dialysis & Kidney Transplants

Disorders of the urinary system

• Urinary tract infections– More common in females

– Burning sensation during micturition

• Bladder cancer– 3% of cancers more common in men

• Kidney cancer– Arises from epithelial cells of nephron tubules

Disorders of the urinary system

• Congenital defects of the urogenital tract – Hypospadias

–Abnormal placement of urethral orifice (opening); urethra opens anywhere

along the urethral groove on ventral side of penis or scrotum –One of most common birth defects in boys (~1 out of 125 boys) –More severe forms interfere with urination & sexual function! –Most forms are correctable with surgery

Disorders of the urinary system

• Pelvic Floor Disorders dropping down (prolapse) of the bladder, urethra, small intestine, rectum, uterus, or vagina, caused by weakness of or injury to the tissues of the pelvic floor

–Incontinence often develops –Only occurs in women –Incidence increases with age

(1 in 3 over age 65)

• Embryo develops 3 pairs of kidneys• Only 1 persists to become kidney• By fetal week 8 kidney & nephrons fully formed• Produces urine by fetal month 3• Contributes to amniotic fluid!

Gonad

Kidney

Urinarybladder

Urethra

Anus

Ureter Rectum

8-week fetus

Urinary system throughout life: fetus

• Kidney & bladder function declines with advancing age– Nephrons decrease in size & number– Tubules less efficient at secretion & reabsorption– Filtration declines – Recognition of desire to urinate is delayed– Loss of muscle tone in bladder & sphincters– Incontinence can develop

• And Yes,… exercise can help! Kegels

Urinary system throughout life: adult

Summary• Importance of the kidney & role in salt & water balance • Structure & function of the entire kidney, nephron, ureters, bladder & urethra

Questions…?

What’s Next?Lab: Urinary & Reproductive SystemsMon Lecture: Reprod & Endo Systems Mon Lab: Student Presentations & Potluck! & Endo SysWed Lecture: Finish Endo Sys & ReviewWed Lab: Lab Exam 5!

Madelaine Dela Cruz

Review: Anatomy of the Kidney

Review: Anatomy of the Nephron

(Boron & Boulpaep, Med Phys., 2003)

•Renal Clearance (= RC) Volume of blood plasma from which a particular substance (x) is completely cleared

– RC of creatinine & inulin = GFR– RC of glucose = 0 Why?

Renal Clearance

RCx = Ux · V

Px

Where Ux = concentration in urineV = flow rate of urinePx = concentration in plasma