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URINARY ORGANS

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The main function of the urinary system: to produce urine and Äclean´ the blood

Main parts: kidney (ren)

ureter urinary bladder (vesica urinaria)

urethra

The kidney is similar to

a thick-walled sac withnarrow lumen

Variations in species:

Renculi

Recessus

Rim-type (carnivores)

Unipapillar (insectivores, horse)

Multipapillar (pig, human)

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Kidney (r en, nephros):Parenchymal organ.

Stroma: capsule (fibrous, adipose)

interstitium: very weakPar enchyma: nephrons

collecting tubules

Blood supply:

 Arteria renalis

 Arteriae interlobares

 Arteriae arcuate

 Arteriae interlobulares

 Arteriae afferentes

Rete capillare

glomerulare

 Arteriolae efferentes

Peritubular capillaries

Vasa recta

Venulae rectae

Venae interlobulares

Venae arcuates

Vena renalis

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The nephron:Structural and functional unit of kidney parenchyma.

Main parts: renal corpuscle (Bowman¶s capsule,) glomerulus

tubulus renalis (proximal and distal convoluted tubules,

Henle¶s loop)

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Kidney glomerulus (renal corpuscle,Malpighian body, corpusculum renale Malpighi

LMLM

SEMSEMTEM

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Ultrafiltration apparatus: fenestrated endothelium of capillaries

basal lamina (molecular filter)

filtration slits between podocyte pedicels

Site of excr etion and r eabsorption:

Proximal convoluted tubule: pars convoluta

pars recta

Tubulus intermedius: thin segment pars descendens Henle¶s loop

pars ascendens

Distal convoluted tubules: pars recta

pars convoluta

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Proximal convoluted tubules

Light micrograph: simple cuboidal

epithelium with brush border 

Electron micrograph: microvillial surface,

basal striation, with many mitochondria:

energy demanding active transport across

the tubular epithelium

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Brush border with higher magnification

Basal striation: membrane invaginations and mitochondria

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Thin segmentum: simple squamous epithelium

Capillary

Collecting tubules

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Distal convoluted tubules:Shorter than the proximal (1/3). Lower and smaller cuboidal cells.

No brush border, only some irregular microvilli. Basal striation is well defined.

Dark cells appear between light ones.

No basal striation, but many

mitochondria

Role: regulation of acid-base household

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Collecting duct: no more secretion and reabsorption

One cell of the collecting duct:

No brush border, no basal

striation, still many

mitochondria

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Papillary duct: largest in diameter, lined by simple columnar epithelium.

Their epithelium is continuous with the epithelium of kidney papillae.

They open into the the renal calyces.

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Juxtaglomerular apparatus (JGA): macula densa, juxtaglomerular cells,

extraglomerular mesangial cells.

Macula densa (MD): the distal convoluted tubule (DC) returns to the vascular pole

of its glomerulus: there the tubular epithelium becomes higher, nuclei are arranged in

a dense group. Function: osmoregulation via sensation of Na+ cc. in the distal tubule.Juxtaglomerular cells (JG): strongly modified myoepithelial cells in the wall of the

afferent arteriole. They sense the decrease in blood pressure, then produce renin,

an enzyme catalysing the production of active angiotensin, a potent raiser of 

systemic blood pressure.

Extraglomerular mesangial cells:

Flat elongates cells forming fineMeshwork . Their function is obscure.

?Production of erythropoietin?

(stimulation of the erythropoiesis

in the red bone marrow)

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Interstitium of the kidney:Occupies very small volume, but it has importance in function.

 All transport processes take place across the thin interstitum.

Its amount is lowest in the cortex, increases in medulla, towards the papillae.

Main fibrous component: meshwork of fine reticular fibers around the tubular 

system.

Interstitial cells: fibroblasts, macrophages,dendritic cells, lymphocytes,

lipid-storing interstitial cells.

Erythropoietin (EPO): produced by intertubular fibroblast cells.Low oxygen tension stimulates the production of EPO.

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Reticular fiber system (blue) around a glomerulus and convoluted tubules

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Ur eter and urinary bladder 

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Female ur ethra

Tunica mucosa: folded

Lamina epithelialis: urothelium,

or stratified squamous keratinized

Lamina propria: loose CT with

wide lumened blood vessels

(cavernous tissue)Tunica muscularis:

Inner circular and outer longitudinal

smooth muscle layers

Tunica adventitia: loose CT,

blood and lymphatic vessels, nerves

Male ur ethra: see male genital organs