Urinary System

• In many texts this is considered as part of the Excretory System.

• It is the system involved with cleaning the blood of the end products of metabolic activities.

• Also functions to adjust the composition of body fluids by selective re-absorption and secretion.

• secrete some bioactive factors-renin, erythropoietin

• The outside covering of the kidney is the renal capsule.

• Kidney is comprised of an outer region, the renal cortex and an inner region, the renal medulla.

• Renal medulla also contains the cup or funnel-like connective tissue calyces which open into the renal pelvis and exit by way of the ureter.

---hilum: BV, LV, N and ureters enter or out

*renal pelvis: funnel-shaped expension of upper end of ureter

*calyx: branches of renal pelvis

• Cortex contains all of the structure of cortical nephrons and part of the structure of juxta-medullary nephrons.

• Renal medulla contains parts of descending and ascending tubules and loops of juxta-medullary nephrons and the collecting tubules of all nephrons. Collecting tubules are arranged in bundles called pyramids.

• Spaces between pyramids called renal columns.• Nephrons are the structural and functional unit

of the kidney.• Cortical nephrons have short tubules and loops

of Henle and are retained within the cortex layer

• Juxta-medullary nephrons have much longer tubules and extend deep into medulla layer.

Nephron

• Major components of the nephron include:

• Renal corpuscle consists of glomerulus and capsules

• Proximal convoluted tubule

• Distal convoluted tubule

• Peritubular capillaries

Nephron

• Renal Corpuscle consists of the glomerulus and the capsule.

• Glomerulus is a capillary ball. Blood is supplied to the glomerulus by way of the afferent arteriole and leaves the glomerulus by the efferent arteriole.

• This is different in that blood travels from arteriole to capillary bed back to arteriole.

• The capsule consists of two layers of epithelium. The visceral layer fits like a glove over the glomerulus. This can not be seen with light microscope.

• Outer layer the parietal layer can be seen with light microscope.

Podocyte：cells with many processes ( primary and secondary processes-foot processes)Foot processes: interdigitated with each other and embraced the capillariesslit pore: -narrow intercellular space between foot processes -25 nm, with 4-6 nm diaphragm-slit membrane---function: produce filtrate by filtration (permeability)

* filtration barrier or membrane: the structure for filtration is called filtration barrier or membrane, including: fenestrated endothelial cell: negative ions basal lamina: type IV collagen, proteoglycan, laminin-negative ions (sulphate heparin) slit membrane-nephrin(size selective filter: negative ions

*intraglomerular mesangium: /mesangial cell: -small, irregular, with processes -small dark N -EM: RER, Golgi, lysosome, phagocytic vesicles, cytoskeleton-MF, MT,IF and secretory granules -functions: i.   produce ground substance ii.  phagocytosis iii. contract iv. secrete renin and enzymes

renal tubule:a. proximal tubule: 50-60um in D, 14 mm long---structure L/M: E/M:• pyramidal cuboidal• eosinophilic• round N• brush-liked border -------- microvilli(apical canaliculi)• longitudinal striation------- plasma membrane infolding• no clear boundary ------- lateral extension(rich in Na+ K+

ATPase) -------Function: i. Re-absorption : -85% Na+ ions and water -All of glucose, amino-acid, polypeptide, proteins and

vitamin -50% bi-corbonated salt and sulphate saltii. secrete H+, NH3, hippuric acid and creatinine

b. thin segment:

/10-15 um, simple squamous epi,

/facilitate the passage of water and ions

/reabsorb Na+ and Cl- and 5% water

c. distal tubule: ---structure: L/M E/M• cuboidal• slight-stained• round N• no brush-liked border --------------------------------- less microvilli• well-developed longitudinal striation -------plasma membrane infolding

---function:

i.    reabsorption of 8% water, Na+ ions

ii.   excretion of K+(potassium), H+(hydrogen),NH3 (ammonia)

iii. regulated by aldosterone(adrenal gland) and antidiuretic hormone (vasopressin) (pituitary gland)

 collecting tubule:• -simple cuboidal epi. to simple columnar epi. -slight –stained -have clear boundary -reabsorb 4% water

Juxta-glomerular apparatus

• Is consists of following components:• Juxtaglomerular cells: the tunica

media of the afferent arteriole has modified smooth mucle cells.

• Macula densa – a specialized segment of distal tubule, a ion sensor

• Extraglomerular mesangial cells:a signal sender

Function:• Allows to sample the composition of

blood as it enters nephron and as it is ready to leave.

• Plays important role in regulation of sodium excretion by kidney.

• Secretes hormone renin which then trigers the angiotensin II pathway

AngiotensinogenConverting enzyme

Interlobar arteries → Arcuate arteries →Interlobular arteries →Capsular cap. ↑ ↓ ↓Renal artery Afferent arterioles Afferent arterioles ↓ ↓ Juxtamedullary nephron Cortical nephron glomerulus glomerulus ↓ ↓ Efferent arterioles Efferent arterioles ↓ ↓ Vasa recta(artery and vein)← Capillary network Capillary network ↓ ↓ ↓ Renal vein←Interlobar vein← Arcuate vein ← Interlobular vein ← Stellate vein