The urinary system

Dr zubair

Urinary system• Kidney is compound tubular type of gland

• The tubules are URINIFEROUS TUBULES.

• Secreting tubules are known as NEPHRON

• Excretory tubules are known as COLLECTING

TUBULES.

• Uriniferous tubule is the structural unit of the kidney

while nephron is the functional unit of the kidney.

Urinary system• The two kidneys produce about 125 mL of

filtrate per minute; of this amount, 124 mL is

absorbed in the organ, and only 1 mL is released

into the ureters as urine.

• About 1500 mL of urine is formed every 24 h.

RENAL PARENCHYMA SURROUNDS A CAVITY

INSIDE THE KIDNEY, KNOWN AS RENAL

SINUS OPENS AT THE HILUS

RENAL SINUS

The renal

parenchyma

consists of an

outer zone known

as

CORTEX

CORTEX

The renal

parenchyma consists

of an inner zone

known as

MEDULLA

MEDULLA

Cortex is Granular in appearance while

medulla shows Radial striations.

Some regions of cortex appear granular due to presence of glomeruli and

convoluted tubules, are known as PARS CONVOLUTA or CORTICAL

LABYRINTH.

Pars convoluta are separated by regions which contain straight tubules and appear

as radiating columns are known as PARS RADIATA or MEDULLARY RAYS.

PARS CONVOLUTA/

CORTICAL LABYRINTH.

PARS RADIATA /

MEDULLARY RAYS

medullaConsists of

8-18 conical shaped lobes or

PYRAMIDS.

The pyramids are separated by regions known as the

RENAL COLUMNS or COLUMNS OF BERTINI.

PYRAMIDS.

RENAL COLUMNS

The apices of 2-3 pyramids unite to forma single PAPILLA.

Each papilla project into the MINOR CALYX.

MINOR CALYX.

Each pyramid with its associated overlying cortex is regarded as a

LOBE OF KIDNEY.

Photomicrograph of fetal kidney. Human fetal kidney shows

the cortex, the medulla, and two associated pyramids.

Note each surface convexity corresponds to a kidney lobe. During postnatal life the lobar convexities disappear and the kidney then exhibits a smooth surface.

A KIDNEY LOBULE consists of a medullary

ray at its center and half of the adjacent cortical labyrinth on

either side

KIDNEY LOBULE

Kidney Posses a connective tissue (capsule) frame work and renal parenchyma.

PARENCHYMA OF THE KIDNEY CONSISTS OF A LARGE NUMBER OF CLOSELY PACKED

URINIFEROUS TUBULES,BETWEEN WHICH ARE PRESENT BLOOD VESSELS AND A SCANTY AMOUNT OF INTERSTITIAL

CONNECTIVE TISSUE

URINIFEROUS TUBULE

Nephron (30-40 mm) long, derived from metanephric blastema,responsible for secretion of urine.

COLLECTING TUBULE (20mm) long, derived from ureteric bud, conveys urine to the renal pelvis.

types of nephrons

A long looped nephron

a short-looped nephron

. The inverted cone-shaped area in the cortex represents a

medullary ray.

The parts of the Uriniferous tubule are indicated by number:1 renal corpuscle including

the glomerulus and Bowman’s capsule;2, proximal convoluted tubule;

3, proximal straight tubule; 4, descending thin limb; 5,ascending thin limb;6, thick ascending limb (distal straight

tubule);7, macula densa located in the final

portion of the thick ascending limb;8, distal convoluted tubule;

9, connecting tubule;9*, collecting tubule that forms an arch (arched collecting tubule);10, cortical collecting duct;11, outer medullary collecting duct; and

12, inner medullary collecting duct.

Nephron

1. Bowman's capsule

2. Proximal convoluted tubule

3. Straight segment of the proximal convoluted tubule

4. Thin segment of Henles loop

5. Thick segment of Henles loop

6. Distal convoluted tubules

Collecting tubules

1. Arched collecting tubules

2. Straight collecting tubules

3. Papillary ducts

Location of nephron and collecting tubules in kidney

Cortical Portion of the kidney Portion of the tubule

Pars convoluta orcortical labyrinth

GLOMERULUS AND BOWMAN’S CAPSULE (renal corpuscle/ malpighian corpuscle)

PROXIMAL CONVOLUTED TUBULE

DISTAL CONVOLUTED TUBULES

ARCHED COLLECTING TUBULES

Pars radiata or medullary rays

Thick segment of Descending limb of Henles loopThick segment of ascending limb of Henles loop

Straight collecting tubules

Location of nephron and collecting tubules in kidney

Medulla of the kidney

Portion of the tubule

Outer zone

Thick segment of Descending limb of Henles loopThin segment of henles loop.Thick segment of ascending limb of Henles loop.Bends of short loop of henles.Straight collecting tubules

Inner zone

Thin segment of henles loop.Straight collecting tubulesPapillary ducts

Mesangial cellsIn addition to endothelial cells and podocytes, the glomerular capillaries have

Mesangial (Gr. mesos, middle, + angeion, vessel) cells adhering to their walls

Mesangial cells are contractile and have receptors for angiotensin II. When these receptors are activated, the glomerular flow is reduced.

Mesangial cells also have receptors for the natriuretic factor produced by cardiac atria cells. This factor is a vasodilator and relaxes the mesangial cells, probably increasing the blood flow and the effective surface area available for filtration.

They give structural support to the glomerulus Synthesize extracellular matrix, Endocytose and dispose of normal and pathological (immune complex)

molecules trapped by the glomerular basement membrane. Probably produce chemical mediators such as cytokines and

prostaglandins. In the vascular pole but outside the glomerulus, there are the so-called

extraglomerular mesangial cells that form part of the juxta glomerular apparatus

Proximal Convoluted TubuleThe proximal convoluted tubule receives the ultrafiltrate from the urinary space of Bowman’s capsule. The cuboidal cells of the proximal convoluted tubule have the elaborate surface specializations associated with cells engaged in absorption and fluid transport. They exhibit the following features:

• A brush border, composed of relatively long, closely packed, and straight Microvilli

• A junctional complex, consisting of a narrow, tight junction that seals off the intercellular space from the lumen of the tubule and a zonula adherens that maintains the adhesion between neighboring cells

• Plicae or folds located on the lateral surfaces of the cells, which are large flattened processes, alternating with similar processes of adjacent cells

• Extensive interdigitation of basal processes of adjacent cells .

• Basal striations, consisting of elongate mitochondria concentrated in the basal processes and oriented vertically

to the basal surface

Henle's Loop

Henle's loop is a U-shaped structure consisting of a thick descending limb, a thin descending limb, a thin ascending limb, and a thick ascending limb.

The thick limbs are very similar in structure to the distal convoluted tubule

In the outer medulla, the thick descending limb, with an outer diameter of about 60 m, suddenly narrows to about 12 m and continues as the thin descending limb.

The lumen of this segment of the nephron is wide because the wall consists of squamous epithelial cells whose nuclei protrude only slightly into the lumen .

Henle's Loop

Approximately one-seventh of all nephrons are located near the corticomedullary junction and are therefore called juxta medullary nephrons.

The other nephrons are called cortical nephrons.

All nephrons participate in the processes of filtration, absorption, and secretion.

Juxta medullary nephrons, however, are of prime importance in establishing the gradient of hyper tonicity in the medullary interstitium.

Henle's LoopOn the basis of the kidneys' ability to produce

hypertonic urine.

Juxta medullary nephrons have very long Henle's loops, extending deep into the medulla. These loops consist of a short thick descending limb, long thin descending and ascending limbs, and a thick ascending limb.

Cortical nephrons, on the other hand, have very short thin descending limbs and no thin ascending limbs

Distal Convoluted Tubule

• This tubule, like the ascending limb, is lined with simple cuboidal epithelium

• The distal convoluted tubules differ from the proximal convoluted tubules (both found in the cortex) because they have no brush border, no apical canaliculi, and smaller cells.

• Because distal tubule cells are flatter and smaller than those of the proximal tubule, more nuclei are seen in the distal tubule than in the proximal tubule.

Juxta glomerular Apparatus

• Adjacent to the renal corpuscle, the tunica media of the afferent arteriole has modified smooth muscle cells. These cells are called juxta glomerular (JG) cells

• Secretions of JG cells play a role in the maintenance of blood pressure.

• The macula densa of the distal convoluted tubule is usually located near the region of the afferent arteriole that contains the JG cells; together, this portion of the arteriole and the macula densa form the JG apparatus.

• Also a part of the JG apparatus are some light-staining cells. They are called extraglomerular mesangial cellsor lacis cells.