Urinary system

Urinary system consists of organs that produce store and remove urine from the body. It consists of two kidneys, a pair of ureters, a urinary bladder and the ureathra.

COMPONENTS OF URINARY SYSTEM

KIDNEYS

(PHYSIOLOGICAL ANATOMY OF KIDNEY)

Each kidney consists of:

Cortax, medulla, pyramid, Papilla and a pelvis.

1. Cortax

Cortax is the outer part of kidney.

2. Medulla 

Medulla is the inner part of kidney.

3. Pyramid

It contains straight collecting tubules.

4. Papilla

lt is perforated by openings of collecting tubules into minor calyx of pelvis.

5. Pelvis

lt leads into ureter.

FUNCTIONS OF KIDNEY

a. Kidneys excretes waste products especially nitrogenous and containing ends products of protein metabolism.

b. Kidneys eliminates drugs and tonic substance from the body.

c. Kidneys help in maintaining normal H+ ions concentration, PH of blood and acid base balance.

d. Kidenys help to mnaintain Na+ ion, K+ ion and electrolyte balance of the body.

e. Kidneys help to maintain water balance, plasma volume and ECF volume.

f. Kidneys helps to maintain osmotic pressure in blood and tissues fluids.

g. Kidneys helps to maintain blood pressure.

NEPHRON 

lt is the structural and functional unit of kidney which is capable of forming urine by itself is called nephron. Nephrons are in both normal kidneys are about 2.4 millions in both kidneys.

Composition of nephron

(1) Glomerulus

This device work as filter, though which fluid is filtered from the blood.

(2) Along renal tubule

Here the filtered fluid is converted into urine on its way to the pelvis of the kidney. It includes:

(a) Proximal convoluted tubule

(b) Loop of Henle having ascending and descending limbs.

(c) Distal tubule with diluted segments.

Function of Nephron 

Urine formation is the main duty of nephrons. They are responsible to clean or clear the blood plasma of unwanted substances, such as the ends products of metabolism like urea, uric acid etc. Urine formation occur in nephron. It can be completed by the fallowing three steps.

1. Glomerular filtration

This is the first step of urine formation and occurs when blood enters the glomerulus. The capillaries of the glomerulus offer resistance to the flow of blood and this blood pressure is setup. Due to glomerular B.P water with dissolved salts, glucose, drugs, urea, uric acid moves from the glomerulus to the inside of Bowman's capsule.

2. Selective reabsorption

The reabsorption process in the nephron is very selective. As the filtered fluid flows through the tubules. the Unwanted substances fail to be reabsorbed while the wanted materials required for body should be reabsorbed.

3. Tubular secretion

This is the mechanism by which substances are remove from the blood and are directly added to the tubular fluids. Hydrogen ion, Ammonium ion and drugs are some of the substances that move from blood into the distal tubule from Nephron. Hydrogen ion secretion is important in acid-base balance of the body.

Glomerular Filterate

Fluid that filters through the glomerulus into Bowman' s capsule is called "glomerular filtrate". 

Glonmerular Filtration Rate (GFR)

The quantity of glomerular filtrate formed in  each minute in all nephrons of both kidneys is called "glomerular filtration rate". It's average value is 125ml/min or 180 liters/day. 

URINE

lt is an amber color fluid of slightly acidic reaction excreted by kidney. Volume of urine is 600 to 2500 ml per 24hours. Color is pale yellow due to the presence of urochrome. Urochrome is a pigment derive from the break down of  hemoglobin.

Composition

Now let's have a look on the composition of urine. It is mainly composed of water, urea, uric acid, Ammonium compunds, creatinine and some kind of minerals.

URETER

Ureter is about 28 cm long and 3 mm in diameter.

Function of ureter

Ureter is responsible for  passing urine from the kidneys to the urinary bladder.

URINARY BLADDER 

lt is a pear shaped sac situated in the pelvic region of abdomninal cavity.

Function of urinary bladder 

It can stores urine before it is excreted out from the body through urethra. It can store about 0.5 to 1 litre of urine.

URETHRA 

Urethra starts from the neck of the urinary bladder and leads to the enterior.

Function of urethra 

In females it can carry only urine from the bladder out of the body. In males it can carries urine from bladder to outside of the body and as well as carry spermatic fluid.

Micturition 

The expulsion of urine from the body via the urethra is known as micturition. Although micturition is controlled by autonomic nervous system. Human learn to control it by voluntary nervous activity.