The excretory system removes waste from the body through various organs like the kidneys, lungs, gastrointestinal tract, and skin. The kidneys play a key role by filtering waste from the blood to produce urine. Urine volume is regulated by factors like water intake, salt intake, exercise, and hormones. Tests like urine analysis, kidney biopsy, and imaging scans are used to evaluate kidney function and diagnose issues like kidney disease. The countercurrent mechanism in the kidneys helps maintain a hyperosmotic medullary environment needed to concentrate urine.

1. A Presentation on
Excretory system

2. Excretory system
The excretory system is a system of organs that removes waste
products from our body, in order to maintain internal chemical
homeostasis and prevent damage to the body.
The organs are
 Kidneys
 Lungs
 GIT (Gastrointestinal tract)
 skin

3. Renal blood flow
• In the physiology of the kidney, renal blood flow is
the volume of blood delivered to the kidney.
• In humans, the kidney together receive 25%
• In average adult RBF 1.1 L/min
• PAH used for measurement of RBF
• RBF in the cortex is high than that in the medulla

5. Renin angiotensin system
• Renin is released into plasma
• low ECF Na or low ECV
• ↑ sympathetic (hypotension)
• ↓ afferent pressure
• Renin acts on angiotensinogen→angiotensin 1
• Angiotensin converting enzyme (ACE): Angiotensin 1→angiotensin 2
• Angiotensin 2 act on adrenal cortex→aldosterone secretion→ ↑ Na
reabsorption in distal and collecting duct of nephron
• ↑H and K secretion in exchange for Na

6. Function of kidney
• It excretes waste products , especially the nitrogenous and sulphur –
containing end products of protein metabolism .
• It helps to maintain the normal hydrogen ion concentration of body fluids &
electrolytes .
• It helps to maintain water balance of body and thereby plasma volume .
• It helps to maintain the optimum concentration of certain constituents of
blood .
• It eliminates drugs and various toxic substances from the body .
• It manufactures certain new substances –ammonia , hippuric acid , inorganic
phosphates . Ammonia helps in preserving acid-base equilibrium .
• It helps in maintaining the osmotic pressure in blood and tissues .
• It helps in the regulation of blood pressure during hypoxia in condition of
emergency through the liberation of renin from juxtaglomerular apparatus .

7. Countercurrent hypothesis
• It is a system by which renal medullary interstitial fluid
becomes hyper osmotic .
• Parts : Countercurrent mechanism has 2 parts
-Countercurrent multiplier : loop of Henley .
Function : production of high medullary osmolarity .
-Counter current exchangers : vasa recta
Function : preservation of high medullary osmolarity .

8. Countercurrent multiplier
Step 1 : loop of Henley is filled with fluid with a concentration of 300
mosmole/L .
Step 2 : active ion group pump of the thick ascending limb reduces the
concentration inside the tubule and raises the interstitial concentration ,
this pump establishes a 200 mosmole/L concentration gradients between
the tubular fluid and the interstitial fluid .
Step 3 : tubular fluid in the descending limb and interstitial fluid quickly
reach osmotic equilibrium because of osmosis of the water out of the
descending limb . The interstitial osmolarity is maintained at 400
mosmole/L because of continued transport of ions out of the thick ascending
limb

9. Countercurrent multiplier
• Step 4 : Additional flow of fluid into the loop of Henley from the proximal
tubule , which cause the hyperosmotic fluid previously formed in the
descending limb to flow into the ascending limb .
• Step 5 : once this fluid is in the ascending limb , additional ions are
pumped into to interstitial , with water remaining in the tubular fluid ,
until a 200 mosmole/L is osmotic gradient is established , with the
interstitial fluid osmolarity rising to 500 mosmole/L
• Step 6 : fluid I the descending limb reaches equilibrium with
hyperosmotic medullary interstitial fluid .
• Step 7 : interstitial fluid osmolarity ultimately rises to 1200 to 1400
mosmole/L

11. Countercurrent exchanger
two special features of the renal medullary blood flow contribute to the
preservation of the high solute concentrations :
1. Sluggish medullary blood flow .
2. vasa recta .
Blood enters and leaves the medulla by the by way of vasa recta at the boundary
of cortex and renal medulla . Vasa recta is highly permeable for highly
permeable to solute in the blood . As blood descends into the medulla towards
the papilla ,it becomes progressively more concentrated partly by solute entry
from the interstitium and partly by los of water into the interstitium .
As blood ascends back towards it becomes progressively less concentrated as
solute diffuse back out in the medullary intertitium & as water moves into vasa
recta .
Function : countercurrent mechanism plays a vital role in concentrated urine
formation

12. Countercurrent exchanger

13. kidney function tests
Serum creatinine test :
Creatinine is a waste product that comes from the normal wear and tear on
muscles of the body. Creatinine levels in the blood can vary depending on
age, race and body size.
A creatinine level of greater than 1.2 for women and greater than 1.4 for
men may be an early sign that the kidneys are not working properly. As
kidney disease progresses, the level of creatinine in the blood rises.
Urinalysis :
A urinalysis screens for the presence of protein and blood in the urine. An
excess amount of protein in the urine is called proteinuria. A positive
dipstick test (1+ or greater) should be confirmed using a more specific
dipstick test such as an albumin specific dipstick or a quantitative
measurement such as an albumin-to-creatinine ratio.

14. kidney function tests
Blood Urea Nitrogen (BUN)
• Urea nitrogen also is produced from the breakdown of food protein. A
normal BUN level is between 7 and 20 mg/dl. As kidney function
decreases, the BUN level increases.
Glomerular Filtration Rate
• This test is a measure of how well the kidneys are removing wastes and
excess fluid from the blood. It is calculated from the serum creatinine
level using age and gender with adjustment for those of African American
descent.
• Normal GFR can vary according to age (as you get older it can decrease).
The normal value for GFR is 90 or above. A GFR below 60 is a sign that
the kidneys are not working properly. Once the GFR decreases below 15,
one is at high risk for needing treatment for kidney failure, such as
dialysis or a kidney transplant.

15. Kidney Biopsy
A biopsy may be done occasionally for one of the following reasons:
• To identify a specific disease process and determine whether it will respond to
treatment
• To evaluate the amount of damage that has occurred in the kidney
• To find out why a kidney transplant may not be doing well
A kidney biopsy is performed by using a thin needle with a sharp
cutting edge to slice small pieces of kidney tissue for examination under a
microscope.
Creatinine Clearance
• A creatinine clearance test compares the creatinine in a 24-hour sample of
urine to the creatinine level in the blood, to show how many milliliters of
blood the kidneys are filtering out each minute (ml/min).

16. Imaging Tests
1.Ultrasound :
This test uses sound waves to get a picture of the kidney. It
may be used to look for abnormalities in size or position of the kidneys or
for obstructions such as stones or tumors.
2. CT Scan :
This imaging technique uses X-rays to picture the kidneys. It
may also be used to look for structural abnormalities and the presence of
obstructions . This test may require the use of intravenous contrast dye
which can be of concern for those with kidney disease.

17. kidney function tests
Indigo carmine test :
0.1 g of the dye is injected intramuscularly . It
should appear in the urine in 6-6 minutes . Any delay means renal
inefficiency .
Excretion is usually complete by 12-24 hours . This test may indicate which
particular kidney is wrong if ureteric catheter is used .
Iodoxyl test( intravenous pyelography ) :
this compound is rapidly excreted by kidney &
is opaque to X-ray . About 15 g of the substance in 20 ml of a 10% solution
of invert sugar , is given intravenously ,and a radiograph is taken . In
normal persons , a distinct pyelogram will be obtained in 2-10 minutes in
the renal deficiency it may be delayed for hours . This method is useful in
demonstrating the size & shape of kidney , renal pelvis , calyces , ureters ,
presence of stone etc.

18. Micturition
Micturition is the process by which urinary bladder
is emptied when filled . The process of emptying the urine into
the urethra is regulated by nervous signals, both from the
somatic and the autonomic nervous system. The autonomic
nervous system comprises both the sympathetic and the
parasympathetic nervous system.
Stimulus of Micturition :
Filling of bladder : 300 to 400 ml of urine .
.

19. Micturition reflex
It is a spinal reflex facilitated and inhibited by higher
brain center to avoid urine when it becomes filled .
Components of the reflex :
• Receptor : stretch receptor of the bladder wall.
• Afferent fiber : pelvic sphlancnic nerve .
• Center : S(2,3,4) .
• Efferent fiber : pelvic sphlancnic nerve .
• Effector : detrusor muscle .

21. Mechanism of micturition
Filling of urinary bladder
stimulation of stretch receptor
Afferent impulses via pelvic nerve
S(2,3,4)
Efferent impulses via pelvic nerve
Contraction of detrusor muscle and relaxation of internal sphincter
Flow of urine into urethra & stimulation of stretch receptor
Afferent impulses via pelvic nerve
Inhibition of pudendal nerve
Relaxation of external sphincter
Voiding of urine

24. FACTORS CONTROLLING VOLUME OF
URINE
• Water intake : Urine Volume is directly proportional to
the amount of taken. If no food or drink is taken the
urine volume diminishes to about 50 ml per hour.
• Elimination of water by other channels : Urine volume
is inversely proportional to the amount of water lost
through other channels . For instance , diarrhoea,
dysentery, cholera , excessive vomiting, etc.

25. FACTORS CONTROLLING VOLUME OF
URINE
• Rate of renal circulation : Urine volume is directly
proportional to the degree of renal circulation.
• Number of active glomeruli : It is obvious that, other
factors remaining constant , amount of filtration will
depend upon the number of active glomeruli .

26. FACTORS CONTROLLING VOLUME OF
URINE
• Available filtration pressure : Available filtration pressure is the
resultant of many opposing forces .
 Urine volume directly is proportional to the general blood
pressure.
 Urine volume is directly proportional to the glomerular pressure
.
 Urine volume is inversely proportional to the colloidal osmotic
pressure.
 Urine volume is inversely proportional to the concentration of
plasma proteins.

27. FACTORS CONTROLLING VOLUME OF
URINE
• Permeability of the filter bed : Urine volume is directly
proportional to the permeability of the filter bed.
• Degree of tubular re-absorption : Normally , the renal
tubules reabsorb water to about 90% from the capsular
filtrate . The degree of re-absorption depends upon the
anti-diuretic hormone secreted by the posterior pituitary
.The hormone increases the degree of reabsorption .

28. FACTORS CONTROLLING VOLUME OF
URINE
• Amount of solids to be excreted by the kidney :
Urine volume is directly proportional to the amount of solids
to be excreted by the kidney . Some such condition are as follows:
 Excess intake of salts
 Excess intake of sulphates , urea , etc.
 Excess protein diet produces more urea , hence more urine flow.
 Thyroxin increases the amount of urine .
 Hypo-function of adrenal cortex increases urine volume.
 In diabetes mellitus , urine volume increases.

29. Factors Affecting Formation Of Urine :
There are several factors which are affecting the
formation of urine. These factors are :
1) Water intake
2) Intravenous saline injection
3) Drinking saline solution
4) Effects of salt
5) Effects of water deprivation
6) Effects of exercise

30. Factors Affecting Formation Of Urine :
1) Water intake :
• When large quantities of water(1-2 litre) be taken the diuresis starts
after a latent period of about 15-30 minutes. The flow become
maximum in the second hour, when the output may be as high as
1300 ml per hour. Then it declines and comes back to normal in
about three hours time.
• Rise of blood volume, dilution of plasma and lowering of osmotic
pressure are very slight. The total solid loss per day is same.
• Secretion of antidiuretic hormone become reduced due to the dilution
of blood which reduce the reabsorption of water.

31. Factors Affecting Formation Of Urine :
2) Intravenous Saline Injection :
• If large volume of saline is given intravenously then
diuresis starts after a latent period of a few minutes.
• It becomes maximum in the second hour and then
gradually fall.
• The cause is mainly decrease in the tubular
reabsorption.

32. Factors Affecting Formation Of Urine :
3) Drinking saline solution :
• Isotonic salt solution does not give the same result as water
drinking. When about 1 litre is taken, urine volume may not
rise at all. When about 3 litres are taken in an hour,
moderate degree of diuresis take place.
• The maximum rate being only 300 ml per hour.
• But the output remain above normal for more than 24 hours.

33. Factors Affecting Formation Of Urine :
4) Effect of salt :
Increase salt intake :
*After ingestion of salt the urine flow is increase.
*The maximum concentration of salt in urine is found between
3rd & 12th hour.
*The rate of excretion become slower and water has to be taken
to dilute the retain salt.
* The excess fluid and salt are excreted in few days.

34. Factors Affecting Formation Of Urine :
Deprivation of salt :
* This can be produced in man by salt free diet & salt loss
through sweating.
• In this cases plasma Cl- level & Cl- excretion through the
urine progressively fall.
• * This situation can cause uraemia due to decrease of
glomerular filtration & clearance of urea.

35. Factors Affecting Formation Of Urine :
5) Effect of water deprivation :
A) In adult : If water is deprived then the fluid is drawn from
the tissue space which lead to body weight loss.
It also causes :
- Concentrated urine
- Uremic symptoms
B) In Children : Water deprivation causes :
- Uraemia
- Diarrhoea
- Vomiting etc.

36. Factors Affecting Formation Of Urine :
6) Effect of exercise :
Exercise reduce the urine volume because when
anyone takes exercise it will acting on hypothalamo-
pituitary mechanism which secrete antidiuretic
hormone.
This hormone will reduce the secretion of urine.

37. Glycosuria
• Glycosuria is a condition in which glucose is present in the urine in such
quantities as will reduce benedicts or Fehling's reagent.
• It is obvious that sugar may be present in the urine under two general
condition .
1. When the blood level goes above the renal threshold value of
sugar(0.18%) .
2. When the degree of tubular reabsorption of sugar is deficient .
All the different types of glycosuria can be put under these two groups
• First group is always attended to hyper glycaemia .
• In the second group blood sugar may be normal or even low .

38. Glycosuria due to hyperglycemia
i. Alimentary glycosuria :- When a large carbohydrate diet is taken ,
blood sugar may be rise and cause glycosuria . Alimentary glycosuria ,
therefore , is only possible in those subjects in whom power of sugar
utilization deficient & subjects should be considered as early cases of
diabetes .
ii. Nervous glycosuria :- Stimulation of sympathetic nervous to the liver or
of the splanchnic nerves breaks down liver glycogen & produce
hyperglycemia , which may lead to glycosuria .
iii. Piqure glycosuria : certain in

43. Factors affecting formation of urine
• Water intake