URINARY SYSTEM

Ján Líška DVM, PhD

Institut of Histology and Embryology, Faculty of Medicine, Comenius University

Urinary system• The kidneys are the organ with multiple functions:

• filtration of the blood

• excretion of metabolic waste products and related

removal of toxins

• maintenance blood volume

• regulation of acid-base balance

• regulation of fluid and electrolyte

balance

• production of the hormones

The other components of urinary system are accessory.

Their function is essentially in order to eliminate urine.

Urinary system - anatomy

• Kidney are located in the

retroperitoneal space

• The surface of the kidney

is covered by a fibrous

capsule of dense

connective tissue.

• This capsule is coated with

adipose capsule.

• Each kidney is attached to

a ureter, which carries urine to the bladder and

urine is discharged out through the urethra.

ANATOMIC STRUCTURE OF THE KIDNEY

CORTEX outer shell

columns

Excretory portion

MEDULLA

medullary rays

medullary pyramids

HILUMblood vessels

lymph vessels

nerves

ureter

RENAL PELVISmajor calyces

minor calyces

RENAL LOBES

Collecting system

Cortex is the outer layer surrounding the internal medulla.

The cortex contains renal corpuscles, convoluted parts of prox.

and dist. tubules. Renal column: the renal tissue projection

between two medullary pyramids which supports the cortex.

Renal pyramids: the conical segments within the medulla.

They contain the ductal apparatus and stright parts of the

tubules. They posses papilla - having openings through which

urine passes into the calyces. Each pyramid together with

the associated overlying

cortex forms a renal lobe.

minor calix

renal pyramid

minor

calyx

papilla

medulla

medullary rays

Medullary rays: are in the middle

of cortical part of the renal lobe,

consisting of a group of the straight

portiones of nephrons and the collec-

ting tubules (only straight tubules).

cortex

Cortex, medullary ray

Kidney cortex

(reticular fibers, Lillie)

NEPHRON the functional

unit of the kidney

parenchyma

Junqueira et al., 1999

proximal

tubule

distal tubule

Henle loopthin

limb

renal corpuscle

collecting

tubule

collecting

duct

Each nephron is composed of

an initial filtering component

- renal corpuscle and renal

tubules – specialized for

reabsorption of utltrafiltrate

produced by the renal corpuscle

and secretion.

RENAL CORPUSCLE

Gartner and Hiatt, 2003

Proximal tubule

Macula densa

Distal tubuleDistal tubule

BOWMANN

CAPSULE

parietal and vis-

ceral layers

afferent arteriol efferent arteriol

PODOCYTES

Bowman´s capsule

visceral layerGLOMERULUS

capillary tuft

urinary

space

Glomerular filtration barrier

•Fenestrated endothelium

•The common basal lamina

•Podocyte foot processes

The blood filter barrier.

consists of :

• Thin fenestrated endothelium of glomerular capillaries- the fenestrae lacking membrane

• The common basal lamina formed by fusion of thebasal laminae of the endothelium and the podocytes

• Filtration slits between adjacent secondary footprocesses – pedicels of the podocytes

Z. Tonar, 2005

Pedicles

- fused basal

laminae – glomeru-

lar basal lamina

with a central

electron - dense

layer and on each

side electron -

lucent layersFenestrated endothelium

- the fenestrae lacking

diaphragm

Diaphragm in the filtration slits

between pedicels

The blood filter barrier

Mesangial cells

Mesangial cells are similar

to pericytes – they contribute

to intraglomerular capillary

flow.

Mesangial cells provide

structural support to the

glomerular tuft, produce and

maintain mesangial matrix.

Mesangial cells release also

growth factors such as

VEGF .

Intraglomerular mesangial cells

• Fagocytic - cleansing

function

Mesangial cells are in

direct contact with the

glomerular endothelium

R.CIHAK, 1988

Columnar epithelium

Cuboidal epithelium

Cuboidal epithelium

Cuboidal epithelium with

brush border

Cuboidal epithelium

Squamous epithelium

podocytesbasement membrane

capillary

NEPHRON

Renal corpuscle - production of

primary urine.

Proximal convoluted tubule -

resorption of 75-80% glomerular

filtrate.

Henle's loop - in juxtamedular

nephron - long with flexion in a

thin segment - resorption of Na

and water - hypertonic urine.

Dist. tubulus - wider lumen,

active resorption of Na

(aldosterone) and water.

Proximal convoluted tubule (PCT)

• is lined by simple low columnar epithelium

• microvilli on the cell apex, forming a brush border

• lateral interdigitations with neighboring cells

• the cells have abundant membrane invaginations + concetrated mitochondria in their basal portions and

• acidophilic cytoplasm due to the presence of mitochondria

• most of the filtrate water and salts are in PCT reabsorbed

Proximal tubule

cell of nephron -

- basal labyrinth

concetrated mitochondria

in abundant membrane

invaginations

in the basal portion of cell

Kidney – mitochondria in proximal tubules (IH)

chondriom

mitochondria

Distal convoluted tubule

• larger lumen is lined by simple cuboidal epithelium

• the cells have less acidophilic cytoplasm

• the cells lack the brush border

• the cells have basal membrane invagi-

nations with concentrated mitochondria

and no significant lateral interdigitations mitochondria

Kidney - HE

glomerulus

JUXTAGLOMERULAR

APPARATUS and RENAL

CORPUSCLE

Specialized cells forming the macula densa

of the distal tubule, contact with the extra-

glomer. mesangial cells of the glomerulus

of the some nephron

Juxtaglomerular renin-producing cells

of the afferent arterioles

Stevens and Lowe, 2004

RENIN –ANGIOTENSIN –ALDOSTERON SYSTEM

Renin is produced by

juxtaglomerular cells to

produce angiotensin I from

an inactive precursor

angiotenzinogen (liver).

Angiotensin I is transformed

into lung to vasoconstrictor

angiotensin II - stimulates

the release of aldosterone –

- increase of Na resorption in

dist. tubule and collecting

duct.

Juxtaglomerular cells

produce also erythropoietin

important factor in the

regulation of blood

production.

CORTICAL NEPHRON

pars recta in

the medullary

ray

JUXTAMEDULLAR NEPHRON

- pars recta placed in medulla

In humans, about 15% of the nephrons

are juxtamedullary nephrons

and about 85% are cortical nephrons.

LOOP OF HENLE

U-shaped tubule consists of descending

and ascending limb with thick and thin segmentsDifferent sections of the loop of Henle

have different permeabilities.

medulla

LOOP OF HENLE

Active transport of sodium

and chloride ions leads to

the formation of a concen-

tration gradient in medulla -

water moves from the tubules

into the surrounding vasa

recta capillaries.

LOOP OF HENLE

Simple squamous epithelium lining the thin segment is

permeable to water and solute (NaCl and urea). Lumen of thin

segment is relatively wide, nuclei protruding into the lumen.

The thick segment of ascending limb lined by taller cells has

low permeability to water and to urea but actively transports

sodium and chloride into the peritubular fluid around both

limbs.

The interstitial fluid

becomes hyperosmotic

after active transport of

sodium chloride out of

the tubular fluid in the

thick ascending limb.

As a result, water

moves passively out of

the tubular fluid in the

descending limb into

the interstitial space.

Young et al.2006

NEPHRON

loop of Henle

Different origin of excretory (nephron) and collecting portions:

Metanephric mesoderm

(blastema) diferentiates

into excretory portion:

Bowman´s capsule

proximal tubules

loops of Henle

distal tubules

Ureteric bud forms

collecting portion:

renal pelvis

major calyces

minor calyces

collecting ducts

collecting tubule

COLLECTING TUBULES and DUCTS

- Descend from the medullary rays into the pyramid

- smaller - simple cuboidal epithelium

- larger - simple collumnar epithelium and distinct cell

boundaries

COLLECTING DUCTS

- transport the urine via the renal papillae into the renal calyx.

The final concentration or dilution of the urine occurs in the

collecting ducts.

Kidney – medulla (iH)

collecting ducts

Kidneys receive blood through the renal artery. An interlobar artery extends between the

renal lobes in renal column and then branches to form an arcuate artery that runs along

the corticomedullary junction. Arcuate artery branches into interlobular arteries that have

small branches that become afferent glomerular arterioles, which enter the renal

corpuscle and subsequently exit at the vascular pole as efferent glomerular arterioles.

Efferent arterioles close to the juxtamedullary region supply the blood for the medullary

peritubular capillary network inculding vasa recta.

vascular supply

Vascular supply of the kidney

Efferent arterioles close to the subcapsular region

supply vessels surrounding cortical segments of the

tubules and give rise to stelate veins.

Then continue into the interlobular vein,

through arcuate vein

and interlobar vein

and finaly to the renal vein.

Vascular supply of the kidney

Renal hilum: the opening in the middle of the concave medial

border for ureter, nerves, lymph and blood vessels to pass into

the renal sinus.

Renal pelvis: is formed at one end of kidney by the enlarged

upper portion of the ureter and at the other end is divided into

the major calyces - from these arise the minor calyces.

Ureter: passing from the renal pelvis

out of the hilus and conducts urine from

the kidneys to the urinary bladder by

means of peristalsis.

The wall: epithelium, lamina propria,

muscular layer, adventitia

Ureter (Trichrome)

muscular layer

mucosal folds

adventitia

urothelium

Ureter (HE)URETER (blue trichrome)

urothelium

lamina propria

tunica muscularis

URINARY BLADDER

(Vesica urinaria)

Wall of the urinary bladder -

epithelium, lamina propria,

muscular layer, adventitia

or serous peritoneum(upper

part of bladder)

Urinary bladder (Trichrome)

urothelium

l.propria

muscular layer

adventitia

URINARY BLADDER

Internal urethral orifice is the opening in the inferior wall of the urinary bladder,

surrounded by internal urethral sphincter and leads to the urethra.

Internal urethral sphincter - ring of the thickened smooth muscle, continuous with

the detrusor muscle, it is under the involuntary control of the ANS.

External urethral sphincter - the ring of skeletal muscle around the urethra. It is

under voluntary control.

Trigone - the smooth triangular area on the

inner surface of the urinary bladder, defined

by the internal openings of the ureters and

urethra.

It is of different origin than a bladder wall.

Trigone arise during development of the

urinary system when the ureters incorporate

into the wall of the bladder and ejacultory

ducts of the some origin incorporate into

the urethra (in male).

URINARY BLADDER

U.bladder

urethra

ureteric bud

mesonefric duct

Urinary bladder(Vesica urinaria)

Superficial umbrella cells

Intermediate (tennis racket)

cells

Urothelium - cells

Basal cells

Male urethra

• Preprostatic urethra - extends from the base of the bladder to the prostate.

• Prostatic urethra - passes through the substance of the prostate, closer to the anterior

than the posterior surface of the gland. In its posterior wall there is urethral crest with a

round swelling- colliculus seminalis in the middle. There are three openings - one median

for prostatic glands and two lateral for the ejaculatory ducts.

• Membranous urethra - the narrowest segment of male urethra.

It is having thickened circular

musc. sphincter urethrae

a voluntary external sphincter.

• Spongy (penile) urethra - lies within the bulb of penis, corpus spongiosum

and glans of penis - ends at the external urethral orifice. It contains openings

of the bulbourethral glands and also openings of many mucus glands.

Male urethra

The epithelium starts off

as transitional as it exits

the bladder.

Further there is pseudostratified

and stratified columnar,

then stratified squamous near the external

urethral orifice - opening located at the tip

of the penis.

Female urethra• It extends from the neck of bladder to the external urethral orifice

situated in front of the vagina and is about 4.0 cm long and 6mm

diameter.

The female urethra is surrounded by

the external sphincter urethrae in

anterior wall of vagina.

Female urethra

corresponds to the upper part of

prostatic urethra of males and is

covered by stratified squamous

epithelium, which becomes

transitional near the bladder -

membranous urethra, surrounded

by the intern. sphincter urethrae.

Urethral glands surrounding the

urethra are mucinous tubular and

they open in lacunae urethrales

between folds.

Thanks for attention

jan.liska@fmed.uniba.sk