Urinary system

Mrs. Dalia Kamal EldienMSC in Microbiology

Lecture NO 17

Objectives Organs of urinary systemFunctions of the urinary systemStructure of KidneyStructure of Ureter Structure of urinary bladderStructure of urethra

Functions of the urinary system

1. Excretion of waste products from the body. 2. Elimination of foreign substances3. Regulation the amount of water in the body4. Control the concentration of most compounds in the

extracellular fluid5. Functions as an endocrine organ:- Fibrocytes in the cortex release the hormone

Erythropoietin, which stimulates the formation of red blood cells.

Modified fibrocytes of the medulla secrete prostaglandins which are able to decrease blood pressure.

Organs of urinary system

Kidneys

Ureters

Urinary bladder

Urethra

1-Kidney

Two bean shaped kidneys are attached to the posterior abdominal wall, one on each side of the vertebral column.

Held in place by connective tissue [renal fascia] and surrounded by thick layer of adipose [perirenal fat]

The kidneys have a tough fibrous capsule (irregular dense connective tissue) for protection.

Main structures of the kidney:

1. Renal cortex

2. Renal medulla

3. Renal pelvis

Location of kidneys

Kidney

The kidney contains about 1 million functional units called Nephrons.

The nephrons are responsible for filtration, excretion, reabsorption, and they regulate ion balance, water content, help to stabilize blood pressure.

Functionally the processes can be divided into two steps, each of which have their anatomical correlate:

Filtration - glomeruli of the kidneySelective reabsorption and excretion - tubular system of

the kidneyGlomeruli and the tubular system are both part of the

basic functional unit of the kidney, the nephron

Glomruli (Renal corpuscle)

The renal corpuscle is consist of the glomerulus and the glomerular capsule (also known as Bowman’s capsule).

The glomerulus is the round (~0.2 mm in diameter) blind beginning of the nephron, consist of a bundled network of capillaries that increases the surface area of blood

Surrounding the glomerulus is the glomerular capsule, a cup-shaped double layer of simple squamous epithelium with a hollow space between the layers. Special epithelial cells known as podocytes form the Visceral layer of the glomerular capsule .

Podocytes work with the endothelium of the capillaries to form a thin filter to separate urine from blood passing through the glomerulus.

At the far end of the glomerular capsule, opposite the glomerulus, is the mouth of the renal tubule.

Renal tubules

A series of tubes called the renal tubule concentrate urine and recover non-waste solutes from the urine.

The renal tubule carries urine from the glomerular capsule to the renal pelvis.

 After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron. 

Renal tubules• The components of the renal tubule are:Proximal convoluted tubule: lies in cortex and

lined by simple cuboidal epitheliumLoop of Henle: U-shaped and lies in medulla

– Descending limb of loop of Henle– Ascending limb of loop of Henle

Distal convoluted tubule

2-Ureter

The mucosa consist of  stratified transitional epithelium and thick fibroelastic lamina propria.

There are no mucosal or submucosal glands.There is a layer of smooth muscle outside the

mucosaUrine is squeezed into the bladder by peristalsis.Outer adventitial layer has fibroelastic connective

tissue, with blood vessels, lymphatics and nerves.Folds of mucosa help to protect against reflux of

urine when the bladder is full.

3-Bladder

The bladder, also known as the urinary bladder, is an expandable muscular sac that stores urine before it is excreted out of the body through the urethra. It is located in the lower abdominal area near the pelvic bones.

 Urine enters the bladder via the ureters and exits via the urethra.

It's almost impossible to give an exact measurement for the volume of the human bladder, but different sources mention 500 mL

The mucosa is heavily folded - this helps to accommodate for large volume changes.

Bladder

Histology of the Urinary Bladder

• Upon examining the histology, it can be seen that the bladder wall has the same tissue layers as the renal pelvis and ureter.  The layers are:

MucosaMuscularis Serosa/adventita.

Mucosa

The innermost portion of the urinary bladder is the mucosa.  It is composed of transitional epithelium and connective tissue.  Six or more layers seen in the empty bladder The transitional epithelium has domed shaped cells on the

apical surface. The epithelial layer contains no blood vessels or lymphatic's. The basement membrane separates the epithelium from the

connective tissue. The epithelium lies upon connective tissue called the lamina

propria. The lamina propria is composed of areolar connective tissue. It contains blood vessels, nerves, and, in some regions, glands.

Muscularis

Consists of inner longitudinal, circular and outer longitudinal layers of thick muscle bundles

May also contain adipose tissue between muscle fascicles.

Muscle layers are distinct only near the bladder neck and in the remaining areas the longitudinal and circular layers mix freely without definite orientation

4-Urethra

The urethra conveys urine from the bladder to the exterior of the body.

It is similar in structure to the ureter, though shorter.

The lumen is kept closed, unless urine is being passed.

The female urethra is lined by psuedostratified columnar epithelium, with a few small mucosal glands that secrete mucus, and is bound to the anterior wall of the vagina by an external layer of fibrous connective tissue.

• IN FEMALESLength of 3–4 cmIN MALES 20 cm in length – three named regions

1. prostatic urethra is lined by transitional epithelium

2. membranous urethra psuedostratified columnar

3. penile urethra. psuedostratified columnar epithelium

which then transitions to stratified squamous epithelium

distally.

Sphincters keep the urethra closed when urine

is not being passed. There are two

Internal urethral sphincter : involuntary control

External urethral sphincter : voluntary control.

By this lecture we complete the Descriptive Histology course, I wish all of you luck and success