scienes

1. Biology SPM

3.  13.2.1 Identify the structure and functions of a kidney;
 13.2.2 Draw, label and explain the structure of a nephrone and
collecting duct;
 13.2.3 Describe the formation of urine:
 (i) ultrafiltration.
 (ii) reabsorption.
 (iii) secretion.
 13.2.4 Synthesise the concept of homeostasis by using negative
feedback mechanism in osmoregulation;
 13.2.5 Conduct an experiment to study the effects of different volumes
of water intake on urine formation.

4. Identify the structure
and functions of a
kidney;

6. Structure & function of the kidneys

7. Structure
of the
kidneys

8. THE FUNCTIONS OF KIDNEYS
a) EXCRETION
• The kidneys function in getting rid of nitrogenous
wastes such as urea.
b) OSMOREGULATION
• Maintaining water & salt balance in the body/
maintaining a constant osmotic pressure of blood.

9. Draw, label and explain the
structure of a nephrone and
collecting duct;

10. THE STRUCTURE OF NEPHRONE
Bowman’s capsule
Efferent arteriole
Glomerulus
Afferent arteriole
Renal artery
Renal vein
Loop of Henle
Distal convoluted
tubule
Proximal
convoluted tubule
Capillaries
Collecting duct

11. Excretory organ
Nitrogenous wastes (urea, uric acid,
ammonia & creatinine) are excreted from
the body by the kidneys through urine.

12. OSMOREGULATORY organ
 Control the total volume of water in body
fluids;
 Control the concentration of ions in body
fluids;
 Control BLOOD OSMOTIC PRESSURE;
 Control ELECTROLYTE CONTENT & pH
of blood & body fluids.

13. Describe the formation of
urine:
ultrafiltration.
reabsorption.
secretion.

14. FORMATION OF URINE
 The formation of urine involves 3 stages :
1. Ultrafiltration
2. Reabsorption
3. Secretion

15. ULTRAFILTRATION
 Blood containing urea & other
waste product  renal arteries
 kidneys
 Each renal artery branches
repeatedly  sending an
afferent arteriole  the
Bowman’s capsule of each
nephron.

16.  Bowman’s capsule: the afferent arteriole  a network of
capillaries (glomerulus)  join up again  the efferent
arteriole which leaves the Bowman’s capsule 
branches to form capillaries which surround the renal
tube.
 The afferent arteriole has a bigger diameter than the
efferent arteriole the blood in glomerulus is under high
hydrostatic pressure  forces out all the components of
blood except blood cells & plasma protein 
ultrafiltration (filtration under high pressure)

17.  The glomerular filtrate enters the capsular space through pores
in the wall of the Bowman’s capsule.

18. REABSORPTION
 The filtrate flows  the renal tubule  useful
substances are reabsorbed by blood capillaries
surrounding the renal tubule.
 All glucose & amino acids are reabsorbed from
proximal convoluted tubule by active transport.
 80~85% of water id also reabsorbed here by osmosis.

19. THE STRUCTURE OF NEPHRONE
Distal convoluted
tubule
Proximal
convoluted
tubule

20. SECRETION
 Occurs at the distal convoluted tubule.
 The cells at the wall of the DCT are capable of
absorbing certain substances from the blood capillaries
surrounding the tubule & then secreting them into the
tubule.
 K+, H+, NH4+, creatinine (a nitrogenous waste) & drugs
such as penicillin.
 Secretion of H+ helps to regulate the pH of blood.

21. THE STRUCTURE OF NEPHRONE
Distal convoluted
tubule

22.  After rebsorbtion & active secretion, the fluid
which emerges from the collecting duct is called
urine.
 Urine contains water (~96%), nitrogenous wastes
(~2.5%, mainly urea), mineral salts (Na+, Cl- &
K+ = ~0.15%) & traces of other substances such
as bile pigments (give urine its colour & odour).

23. Bloodin glomerulus
Filtratein tubule
urine
Ultrafiltration
Reabsorption of useful
substances from tubule
Active secretion of
waste into tubule

24. Synthesise the concept of
homeostasis by using
negative feedback
mechanism in
osmoregulation

25. OSMOREGULATION
 The kidneys help maintain the osmotic pressure of
blood by controlling & regulating the reabsorption of
water & salt from the distal convoluted tubule & the
collecting duct.
 The reabsorption of water at the DCT & the collecting
duct is controlled by the ADH.
 The reabsorption of salt at the DCT & the collecting
duct is controlled by aldosterone secreted by the adrenal
gland.

26. THE ROLE OF ANTIDIURETIC HORMONE
 Excessive intake of salt & perspiration (sweating)
 osmotic pressure of blood increase.  sensed
by hypothalamus  pituitary gland  ADH.
 ADH  the wall of the DCT & CT more permeable
to water  more water reabsorbed back from the
tubule & returned to the blood  osmotic pressure
decrease to normal.

27.  Too little salt/ drink too much water/ not perspire
(cold weather)  osmotic pressure decrease
(lower than normal)  hypothalamus not
stimulated  less ADH less water will be
reabsorbed  dilute urine  osmotic pressure of
blood increase to normal.

28. The Role of Aldosterone
 The salt content in blood is low (low osmotic pressure) 
pituitary gland stimulate the adrenal gland  produce more
aldosterone.
 Increasing the reabsorption of salt from the DCT.  salt returned
to the blood  increase the blood osmotic pressure to normal.
 Salt content high  less aldosterone will be produced  less salt
is reabsorbed  excrete through urine  blood osmotic pressure
restores to normal level.