urinary system, urine formation

2. The urinary system is
the main excretory system
which consist of following
structure:-
1. 2 kidney which secrete
urine
2. 2 ureter that convey the
urine from the kidney to
the urinary bladder.
3. The urinary bladder which
collect & stores urine.
4. The urethra through which
urine leave the body.

3. The main function of kidney is to formation of urine,
maintaining water, electrolyte & acid base balance.
Excretion of waste products.
Production & secretion of erythropoietin the
hormone that stimulate formation of RBC.
Production & secretion of renin an important enzyme
in the control of blood pressure.

4. The kidney lies on the posterior
abdominal wall one on each side
of the vertebral column below
the diaphragm.
They extend from the level of
12 vertebra to 3rd lumber vertebra
The right kidney is slightly lower
then left due to space occupied by
the liver.
Kidney are bean shaped organ about 11 cm long, 6 cm
wide, 3 cm thick & weight 150g.
A sheath of fibrous connective tissue, the renal fascia,
encloses the kidney & renal fat.

5. The outer fibrous capsule surrounding the kidney.
The cortex a reddish brown layer of tissue immediately
below the capsule & out side the renal pyramids.
The medulla the innermost layer consisting of pale
conical shaped striation, the renal pyramids.
The hilum is the concave medial border of the kidney
where the renal blood & lymph vessel, the ureter &
nerve enter.

7. Urine form within the
kidney passes through a
renal papilla at the apex of a
pyramid in to a minor calyx.
Several minor calyces
merge in to a major calyx.
2 or 3 major calyces
combine forming the renal
pelvis, a funnel shaped
structure that narrow when
it leave the kidney as ureter.
The wall of the calyces &
renal pelvis are lined with
transitional epithelium &
contain smooth muscle.

8. The kidney contain about 1-2 million functional units
called nephrons & smaller number of collecting duct.
The collecting duct transport urine through the
pyramids to the calyces, giving the pyramids their
striped appearance.
The collecting duct are supported by connective
tissue, containing blood vessel, nerves & lymph vessels.

10. The nephron a tubule closed at one
that join a collecting duct at the other
end.
The close end is indented to form
cup shaped glomerular capsule which
also known as bowman’s capsule.
Bowmen capsule have network of
arterial capillaries.
Nephrone is about 3 cm long.
It has three part, those are:-
1. The proximal convoluted tubule.
2. The Medullary loop ( loop of Henle)
3. Distal convoluted tuble leading in
to a collecting duct.
the collecting duct unite
forming larger duct that empty in

11. The kidney receive about 20% of cardiac out put after
entering the kidney at the hilum.
The renal artery divided in to smaller arteries &
arterioles.
In the cortex an arterioles, the afferent arterioles enter
each glomerular capsule & then sub divided in to a
cluster of tiny arterial capillaries forming the glomerulus.
Between the capillaries loop are connective tissue
phagocytic mesangial cells which are the part of
monocytes macrophase defence system.
The blood vessel leading away from the glomerulus is
efferent arterioles.
The afferent arterioles has larger diameter then
efferent arterioles which increase the pressure inside the
glomerulus & drive filtration across the glomerular
capillary wall.

12. The wall of the glomerulus and glomerular capsule
consist of single layer of epithelial cell.
Glomerular wall are more permeable then those of
other capillaries.
The other part of nephron and collecting are formed
by single layer of simple squamous epithelium.
Renal blood vessel are supplied by both sympathetic
and parasympathetic nerve.
Which control renal blood vessel diameter & renal
blood flow independently of Autoregulation.

13. Formation of urine:-the composition of urine reflect
exchange of substance between nephron and the
blood in the renal capillaries .
The waste product of protein metabolism are
excreted , water and electrolyte level are controlled
& PH is maintained by excretion of hydrogen ion.
There are 3 process involve in the formation of
urine:-
1. Filtration
2. Selective reabsorption
3. secretion

14. This takes place through the semipermiable wall of
the glomerulus & glomerular capsule.
Water and small molecules pass through the
membrane.
Blood, plasma proteins, & other large molecules
are too large to filter through there fore remain in
the capillaries
Filtration takes place because there is a difference
between the blood pressure in the glomerulus
&pressure in the filtrate in the glomerular capsule.

16. Efferent arteriol is narrow then afferent arteriole,
capillary hydrostatic pressure is about 55mmHg build
up in the glomerulus.
This pressure is opposed by the oncotic pressure of the
blood provided by plasma protein about 30 mmhg.
By filtrate hydrostatic pressure is about 15 mmHg in
the glomerular capsule.
The net filtration pressure is there fore=
 55-(30+15)=10 mmHg

17. The volume of filtrate formed by both kidney each
minute is called the GFR(glomerular filtration rate)
In a healthy adult GFR is about 125 ml/min. .i.e 180
litres of filtrate are formed each day by two kidney.
Nearly all of the filtrate is later reabsorb from the
kidney tubule with less then 1% i.e 1-1.5 litres.

18. Autoregulation means renal blood flow is maintained
a constant pressure across a wide range of systolic
blood pressure( from around 80-200 mmHg) .
It operate independently of nervous control. Means if
the nerve supply to the renal blood vessel is interrupted
Autoregulation continue to operate.
It is stimulated by change in the renal arteries or
fluctuating level of certain metabolites e.g
prostaglandins.

19. Most reabsorption from the filtrate back
in to the blood takes place in the proximal
convoluted tubule
Its walls are lined with microvilli to
increase surface area for absorption.
Substance reabsorb in PCT are water, electrolyte organic nutrient
such as glucose.
Only 60-70% of filtrate reaches the Medullary loop
Water, sodium and chloride reabsorb in the loop.
Only 15-20% of the original filtrate reaches the distal convoluted
tubule.
More electrolyte s are reabsorb hear especially sodium, so
filtrate entering the collecting duct is quite diluted.
The main function of collecting duct to reabsorb as much as
water as body need.

20. The renal threshold is the concentration of a substance
dissolved in the blood above which the kidneys begin to
remove it into the urine.
When the renal threshold of a substance is exceeded,
reabsorption of the substance by the proximal
convoluted tubule is incomplete; consequently, part of
the substance remains in the urine.
Renal thresholds vary by substance – the low potency
poison urea, for instance, is removed at much lower
concentrations than glucose.
Ex:- the normal blood glucose level is 63-
144mg/100ml.
If this raise above the renal threshold about
160mg/100 ml glucose appear in the urine.

21. Serum albumin maintain oncotic pressure .
Oncotic pressure ensure blood will flow equal
amount every where in body.
It is a type of osmotic pressure drive
fluid to all the body part.
In osmosis water will migrate to the low solute solution to high
solute solution
In body tissue there is low solute then
blood vessel
When solute concentration is high water
will flow from low solute( cell or body cavity
or intra cellular space) to high solute
( blood vessel contain more albumin)
concentration.
This is the function of serum albumin to
draw water from body cavity & increase BP

22. 1. Parathyroid hormone:-
It is secreted by parathyroid gland & together with
calcitonin form the thyroid gland regulate
reabsorption of calcium & phosphate from the distal
convoluted tubule.
Parathyroid gland increase the blood calcium level &
calcitonin lower it.
2. Antidiuretic hormone:-
This is secreted by posterior pituitary. It increase the
permeability of the distal convoluted tubule &
collecting duct, increasing water reabsorption..
Secretion of ADH is controlled by negative feed beck
mechanism.

23. BLOOD OSMOTIC PRESSURE
RAISE
INCREASE REABSORPTION OF
WATER BY KIDNEY
OSMORECEPTER IN
HYPOTHALAMUS
STIMULATE POSTERIOR
PITUITARY
BLOOD OSMOTIC PRESSURE
LOWERED
INCREASE SECRETION OF ADH
+
-
INHIBITION
NEGATIVE
FEEDBECK
REGULATIO
N OF
SECRETION
OF ADH

24. 3. ALDOSTERONE:-secreted by the adrinal cortex
this hormone increase the reabsorption of
sodium & water & excretion of potassium.
4. Atrial natriuretic peptide:- this hormone is
secreted by atria of the heart in response to
stretching of arterial wall when blood volume is
increase.
It decrease the reabsorption of sodium and
water from the convoluted tubule & collecting
duct.

25. LOW RENAL BLOOD FLOW e.g DECERESE BLOOD VOLUME, PRESSURE, SODIUM
KIDNEY
SECRETION OF RENIN INCREASE BP
ANGIOTENSINOGEN---------------------ANGIOTENSIN1
HIGH BLOOD POTASSIUM ANGIOTENSIN 2 VASOCONSTRICTION
ADRINAL CORTEX
SECRETION OF ALDOSTERONE
INHIBITION KIDNEY TUBULE INHIBITION
INCREASE REABSORPTION OF SODIUM AND WATER
INCREASE EXCRETION OF POTASSIUM
INCREASE BLOOD SODIUM LEVEL
INCREASE BLOOD VOLUME
INCREASE BLOOD PRESSURE
ACE

28. Urine is a clear & amber colour due to the
presence of urobilin
The specific gravity is between 1020 & 1030
PH is around 6.
Quantity of urine per day is 1000-1500ml
The constituent of urine are :-
Water 96%
Urea 2%
Uric acid, Creatinin, ammonia, sodium,
potassium 2%
Chloride , phosphate, sulphate, oxalate is 2%

29. The balance between fluid intake & output is controlled
by the kidney.
The minimum urinary out put i.e the smallest volume
required to excrete body waste product is about 500 ml per
day.
Urinary volume in excess of this is controlled by anti
diuretic hormone.
Sensory nerve cells in the hypothalamus (osmorecepter)
detect change in the osmotic pressure of the blood.
Nerve impulse from the osmoreceptors stimulate the
posterior pituitary to release ADH.
When osmotic pressure is raised i.e the blood is becoming
more concentrated ADH out put increased as a result water
reabsorption by DCT & collecting duct increase.

30. When blood volume increase the stretch reeptors in
the arterial of the heart is stimulated & cardiac muscle
cell release atrial natriuretic hormone(ANP).
This reduce reabsorption of sodium & water by
proximal convoluted tubule & collecting duct.
More sodium and water excreted.

31. Renin-angiotensin –aldosterone mechanism maintain
concentration of sodium & potassium within physiologic limit.
sodium excretion regulated by the hormone aldosterone
secreted by adrenal cortex.
Cells in the afferent arteriol of the nephrone relese the
enzyme renin in response to sympathetic stimulation, low blood
volume or by low arterial blood pressure.
Renin convert the plasma protein angiotensinogen produced
by the liver to angiotension 1.
ACE convert angiotensin1 to angiotensin 2 which increase BP.
Renin & raised blood potassium levels also stimulate the
adrenal gland to secrete aldosterone.

32. The ureter is a tube that carries urine
from the kidney to the urinary bladder.
There are two ureters, one attached to
each kidney
The upper half of the ureter is located in
the abdomen and the lower half is located
in the pelvic area
The ureter is about 10 to 12 inches long
in the average adult. The tube has thick
walls composed of a fibrous, a muscular,
and a mucus coat, which are able to
contract.
Function:- sending urine towards the
bladder.

33. It is a cannel extending from
the neck of the bladder to the
exterior.
It is longer in mail then
female.
The female urethra is
approximately 4 cm long 6 cm
diameter.
Exterenal urethral orifl
urethral sphincter which is
under voluntary control.

34. When the volume of urine in the bladder reaches
about 250ml, stretch receptors in the bladder walls are
stimulated and excite sensory parasympathetic fibres
which relay information to the sacral area of the spine.
This information is integrated in the spine and relayed
to two different sets of neurones.
Parasympathetic motor neurones are excited and act to
contract the detrusor muscles in the bladder so that
bladder pressure increases and the internal sphincter
opens.
At the same time, somatic motor neurones supplying
the external sphincter via the pudendal nerve are
inhibited, allowing the external sphincter to open and
urine to flow out, assisted by gravity.