Question

With the help of a labelled diagram describe human excretory system.
How will you identify acute kidney injury by urine analysis? 

Answer 1

Excretory system of man consists of: 

A. Kidneys (a pair)
 B. Ureters (a pair)
 C. Urinary Bladder
 D. Urethra 

A. Kidneys:
Kidneys are a pair of dark red, bean shaped organs about 10 cm long, 5 cm wide and 4 cm thick. 

They are attached to the dorsal body wall at the level of 12th thoracic to 3rd lumbar vertebra in
the abdominal cavity. 

They are retroperitoneal as they have peritoneal covering only on the anterior surface.

They are situated on either side of the vertebral column.

The right kidney is slightly lower than left kidney due to presence of liver.

Left kidney is slightly back than right kidney due to the position of stomach in front of it. 

On the concave surface there is a notch called hilus or hilum.

Through the hilum, blood vessels, nerves, ureter, lymphatic vessels enter or exit.

Renal arteries enter in both the kidneys while renal veins leave the kidneys.

Each kidney is covered by three layers of tissues such as outer renal fascia, middle adipose tissue (perirenal fat) and inner renal capsule. 

Functions:

i. Removal of nitrogenous waste 

ii. Maintenance of water–salt balance [Homeostasis] 

iii. Removal of excess of foreign substances like drugs and pigments. 

iv. Osmoregulation. 

B. Ureters:

From the hilum of each kidney, a thin, narrow and muscular duct emerges out which is called as ureter. 
It measures about 40cm in length.
The ureters open into urinary bladder. 

Functions:

They carry urine from kidneys upto the urinary bladder by peristalsis. 

C. Urinary bladder:

It is single, large and pear shaped structure. 

It is located in pelvic cavity just behind the pubis bone.

It is thick-walled and highly muscular.

It has a layer of detrusor muscles.

These muscles help in the expansion during the time of storage of urine.

Functions:

It stores urine temporarily (500 ml to 1 litre of urine) and expels it at intervals through urethra. 

D. Urethra: 

It starts from the lower part of the urinary bladder and opens to the exterior.

Its opening is guarded by sphincter muscle called urethral sphincter. 

Through urethral sphincter micturition (urination) takes place. 

In males, urethra is long (20 cm) and has to pass through the penis. 

In females, it is short (4 cm) and opens in vestibule.

Acute kidney injury (AKI) is characterized by:

i. Oliguria (decreased urine production; < 400 ml per day in adults)
ii. Anuria (absence of urine),
iii. Accumulation of urea and other metabolic waste products,
iv. Body water and body fluid disturbances,
v. Electrolyte derangement.
If all of the above signs are seen in urine analysis, then the person may be suffering from Acute kidney injury (AKI).