Hameostasis and excreation

2.  Keeping the conditions in the internal environment of the body relatively constant.
 Internal environment - the surroundings of the cells inside the body - Blood and Tissue fluids.
Homeostasis

3. Excretion
 getting rid of substances from the body (urine)

4. Tissue fluids
 It is a watery solution of salts, glucose and other solutes.
 It is formed by leakage from blood capillaries.
 Similar composition to blood plasma except plasma proteins
 Homeostasis of tissue fluid is important for optimum conditions for the cells.

5. Homeostasis of tissue fluid is important for optimum conditions for the cells.
 If too much solute in tissue fluid - the cells lose water by osmosis & become dehydrated (shrink).
 If less solute in tissue fluid - the cells gain water by osmosis & become swollen.
 Homeostasis of pH, temperature, waste products such as urea are also important.

6. Kidneys
 Play a major role in both homeostasis (osmoregulation) and excretion (of waste produce),

7. Urine
 The excretory product of the kidneys.
 Normal person - 1.5 dm3 (variable on drinking and sweating)
 waste product and salts- 40 g in dm3 of urine (40g/ dm3)
 Nitrogenous wastes (urea, ammonia & other)

8.  Sources - protein
 Body cannot store excess protein or
amino acids
 Liver converts them as glycogen and
urea which is excreted as waste produce
 Body stores excess carbohydrate as
glycogen in liver, and excess fats under
the skin and around other organs

9. The urinary system
 Blood supply of kidneys- renal artery from aorta and renal vein to vena cava
 Ureter - a tube from kidney to bladder
 Bladder - a muscular bag for urine
 Urethra - a tube from the bladder to outside
 close urine flow and hold urine in bladder
 Sphincter muscles - two ring-shaped muscles which contract to close urine flow and
hold urine in bladder
• Lower sphincter - voluntary control
• Upper sphincter involuntary control (relax when bladder is full of urine)

11. The kidneys
Outer cortex (darker region)
 contains many blood vessels and some
parts of kidney tubules (nephrons)
Inner medulla
 Contains other parts of kidney tubules
(nephrons) which join to form
pyramids and pelvis (funnel like
structure)
 Pelvic connects with ureter

12. Structure of the nephrons
 A million nephrons in each kidney
 1st & 2nd coiled tubules - "proximal" & "distal"*

13. Ultrafiltration in Bowman's capsule
 Bowman's capsule - a hollow cup of cells which surrounds a ball of blood capillaries
(glomerulus)
 Blood flow from renal artery - smaller arteries - smallest
 arteries (arterioles) - capillaries of glomerulus
 High pressure in capillaries filter small molecules (water, ions, glucose & urea) in blood into
the capsule through glomerulus
 3 layers of filter - two cell layers of capillary wall and capsule wall (coarse filtration) and
one basement membrane (fine filtration)
 Glomerular filtrate -the filtered fluid in capsule (fine filtration - ultrafiltration)

14. Changes in the filtrate in the rest of nephron
 Glomerular filtrate - 0.125dm3 per minutes
(180 dm" per day)
 1.5 dm' per day (So, kidneys concentrate
urine 120x)
 1% of filtrate - urine, 99% of urine -
reabsorbed

15. Take four samples of filtrate and compare
 Sample 1 - blood plasma
 Sample 2 - glomerular filtrate
 Sample 3 - end of 1& coiled tube
 Sample 4 - collecting duct

16. Flow rate
 A measure of how much water is in the tubule
Sample 1 Sample 2 Sample 3 Sample 4
Flow rate
100% 20%
1%
Protein (a)
a nil
nil nil
Glucose (b)
b b
nil nil
Urea (c)
c c 3c 60c
Na+ (d)
d d d 2d
Remarks Protein is not
filtered because of
their big sizes.
Reabsorb all
glucose, 80% of
water and 80% of
Na+ and some urea
Reabsorb 99% of
water, all glucose,
not all Na+, mostly
urea.