Exercise 43

Anatomy of the Urinary System

Functions of the kidney

Excretory Keeps the electrolyte balance Keeps the acid-base balance Keeps the water balance

Gross anatomy

Kidney The right kidney is in a lower position

than the left. Located at the superior lumbar region

of the dorsal body wall Hilus

Renal artery, vein and ureter

Figure 25.3

Gross anatomy

Capsules They hold the kidney in place and also

protect themAdipose capsuleFibrous capsule

Gross anatomy

CortexSuperficial kidney region immediate

bellow the capsuleLight color

MedullaDarker colorDeep to the cortex

Gross anatomy

Medullary pyramids• Base• Papilla or apex

Renal columnsCortical tissue between the pyramids

Minor calyces Major calyces

Gross anatomy

Renal pelvisCavity formed by the joining of the

major calyces and is continuous with the ureter

Blood flow to the kidneysAortaRenal arteriesSegmental arteries (5 branches)Interlobar arteries

Gross anatomy

Arcuate arteriesInterlobular arteriesAfferent arterioles

• Supply the nephronGlomerulus (capillaries)Efferent arterioles

Gross anatomy

Peritubular capillaries Interlobular veins Arcuate veins Interlobar veins Renal veins Inferior vena cava

There is no segmental veins

Gross anatomy

UretersDrain urine from the kidney to the

bladder Bladder

Trigone• 2 ureteral orifices• 1 urethral orifice

Gross anatomy

Detrusor muscleRugae

Parietal peritoneum

Gross anatomy Urethra

Drains urine from the bladderMales

• Belongs to the urinary and reproductive systems

• Prostatic, membranous, penile or spongy

Female• Belong to the urinary system only

Figure 25.18a

Gross anatomy

Internal urethral sphincter• Smooth muscle• Superior to the external one

External urethral sphincter• Skeletal muscle• Inferior to the internal one

Microscopic anatomy of the kidney Nephrons

Functional unit of the kidneys Formed by:

1) Glomerulus• Glomerular capsule or Bowman’s

capsule• Visceral layer with podocytes

cells that interdigitate with each other and cling to the endothelial cells. Pedicels

Microscopic anatomy of the kidney

• Capsular space• Parietal layer

Renal corpuscle Glomerulus + Bowman's

capsule 2) Renal tubules

Proximal convoluted tubules (PCT)• Simple cuboidal epithelium with

microvilli

Microscopic anatomy of the kidney

Loop of Henle• Descending loop

• Thick filament• Thin filament with simple

squamous epithelium and small number of microvilli

Microscopic anatomy of the kidney

• Ascending loop• Thick filament• Thin filament - simple

squamous epitheliumDistal convoluted tubule (DCT)

• Simple cuboidal epithelium

Microscopic anatomy of the kidney

Collecting ductsReceives urine from many nephronsRun through the medullary pyramids

Papillary ductsCollect urine from the collecting

ductsEmpty the urine into the minor

calyces

Microscopic anatomy of the kidney

Types of nephronsCortical

• Located within the renal cortexJuxtamedullary

• Locted at the cortex-medulla junction

• Loops of Henle penetrate the medulla

Figure 25.5a

Microscopic anatomy of the kidney

Renal circulation for the nephronGlomerular capillaries

• It produces the filtrate• It is a high hydrostatic pressure

capillary bed because:• It is fed by 2 arterioles• The afferent arterioles is larger

than the efferent

Microscopic anatomy of the kidney

Peritubular capillary bed• Low pressure capillaries• Porous walls• Absorbs contents of the filtrate

Microscopic anatomy of the kidney

In the cortical nephrons the efferent arterioles will form the peritubular capillaries. From there the blood will flow to the vein system

Microscopic anatomy of the kidney

In the juxtamedullary nephrons, the peritubular capillaries descend immediately into the medulla and give rise to the vasa recta. They run parallel to the loop of Henle and from there the blood will flow to the vein system

Microscopic anatomy of the kidney

Juxtaglomerular apparatus (JGA)Macula densa

• Specialized epithelial cells of the DCT

Juxtaglomerular cells• Specialized smooth muscle cells

of the wall of the arterioles

Figure 25.6

Urine formation

FiltrationFiltrate is forming by the passage of

fluid from the afferent arteriole to the Bowman’s capsule

ReabsorptionOccurs mainly in the PCTIt is passive for water It is active for many substances

Urine formation

SecretionSubstances pass from the tubular

cells or from the blood to the tubular lumen

It happens mainly on the DCT

Bladder For urine storage Micturition or voiding Mechanism of micturition

Urine is collected until it reaches 200 ml

Stretching of the bladder wallActivation of the stretching receptorsImpulse is sent through the

parasympathetic fibers

Bladder

Impulse reaches the CNS CNS sends motor command for the

bladder to contract Relaxation of the internal sphincter Urine passes to the posterior portion of

the urethra Voiding or not (voluntary action)

Bladder Incontinence

Lack of voluntary control of the external urethral sphincter

MicroscopyTransitional epitheliumDetrusor muscle

• Inner longitudinal layer• Central circular layer• Outer longitudinal layer

Microscopic Identification

KidneyCortex

• Renal Corpuscle• Glomerulus• Bowman’s capsule and space

MedullaRenal tubules

Kidney dissection

Whole kidneyHylusCapsule: fibrous and fat

Kidney dissection

Frontal cutCortexMedulla

• Pyramids• Papilla

ColumnsCalyces: major, minorPelvis

Cat Dissection

Urinary System Kidneys Ureters Bladder Urethra

38