2. The Kidney
11.3.1 Define excretion. Excretion is the removal
from the body of the waste products of metabolic
pathways.
11.3.2 Draw and label a diagram of the kidney.
(Include the cortex, medulla, pelvis, ureter and
renal blood vessels).
11.3.3 Annotate a diagram of a glomerulus and
associated nephron to show the function of each
part.
3. The Kidney
11.3.4 Explain the process of ultrafiltration,
including blood pressure, fenestrated blood
capillaries and basement membrane.
11.3.5 Define osmoregulation. Osmoregulation is
the control of the water balance of the blood, tissue
or cytoplasm of a living organism.
Aim 7: Data logging using colorimeters to
measure the response of blood cells to changing
salt concentrations is possible.
4. The Kidney
11.3.6 Explain the reabsorption of glucose, water
and salts in the proximal convoluted tubule,
including the roles of microvilli, osmosis and
active transport.
11.3.7 Explain the roles of the loop of Henle,
medulla, collecting duct and ADH (vasopressin) in
maintaining the water balance of the blood.
(Details of the control of ADH secretion are only
required in option H).
5. The Kidney
11.3.8 Explain the differences in the concentration
of proteins, glucose and urea between blood
plasma, glomerular filtrate and urine.
11.3.9 Explain the presence of glucose in the urine
of untreated diabetic patients.
6. Kidney Structure
The main parts of a kidney you need to know are:
Cortex
Medulla
Pelvis
Ureter
Renal Artery
Renal Vein
8. Processes of the Kidney
There are two main process that occur in the Kidney:
Ultrafiltration
Filtering out of the waste products from the blood
Reabsorption
Taking back into the blood of substances still needed by the body.
9. The Nephron
The Nephron is the functional unit of the kidney.
The parts of a nephron include:
The afferent and efferent blood vessels.
The glomerulus.
The Bowman's capsule.
Proximal and distal convoluted tubules.
Loop of Henle – descending and ascending limbs.
The collecting duct.
11. The Glomerulus
The function of the glomerulus is to produce a filtrate from
the blood.
This process is called Ultrafiltration.
It is passive.
It is unselective.
In the glomerulus, about 20% of the blood plasma escaped
through the walls of the capillaries into the bowman’s
capsule.
This is because of two reasons:
The blood pressure is very high in the glomerulus.
Efferent blood vessel has a much smaller diameter than the afferent.
The capillaries in the glomerulus are fenestrated.
They have many pores in them.
12. Structure of Part of a Glomerulus
Ref: IB Biology, Allott Ref: IB Biology OSC
13. Ultrafiltration
Ultrafiltration of solutes occurs through the fenestrations
(gaps) in the blood capillaries.
Large molecules in the blood are able to pass through the
gaps in the capillary cells, but are unable to pass through
the basement membrane.
The basement membrane is a protein membrane outside
the cells. It contains no pores and acts as a dialysis
membrane to stop the blood cells and large proteins
getting out of the blood vessel.
The capillaries are surrounded by podocyte cells, the cells
of the inner wall of the bowman’s caspule.
These cells wrap around the capillaries and have gaps
between them to allow the filtrate to pass through quickly.
14. Osmoregulation
Osmoregulation is the control of water (and hence solute)
levels in the blood, tissues or cytoplasm of a living
organism.
Osmoregulation is performed by the kidney.
The kidney controls the amount of water passed out of the
body in the urine.
15. Reabsorption in the Convoluted Tubule
As well as waste products, the glomerular filtrate contains
substances the body still needs.
Most of this selective reabsorption occurs in the proximal
convoluted tubule.
The inside of the PCT has microvilli, to increase the
surface area for re-absorption.
Glucose and salts are reabsorbed by active transport.
Water is reabsorbed by osmosis.
All glucose is reabsorbed (under normal conditions)
About 80% of water is reabsorbed leaving only about
20% to pass onto the loop of henle.
17. Reabsorption in the Loop of Henlé
Glomerular filtrate flows deep into the medulla in the
descending limbs of the loops of Henlé.
The cells of the ascending limb actively transport salt out.
In theory water should follow by osmosis, but the walls in
the ascending limb are impermeable to water.
The walls of the descending limb are permeable to water
and some leaves the descending limb due to the osmotic
gradient.
Thus the loop of Henlé acts to create an area of high
solute concentration in the medulla with an increasing
concentration deeper into the medulla
19. ADH and the Collecting Duct
If the water content of the blood is too low, the pituitary
gland (in the brain) secretes anti diuretic hormone (ADH).
This hormone makes the cells of the collecting duct wall
produce membrane channels called aquaporins, which
make the collecting duct more permeable to water.
The high solute concentration in the surrounding medulla,
causes most of the water in the filtrate to be re-absorbed
by osmosis into the medulla and then the blood vessels.
A small amount of concentrated urine is produced.
If the water content of the blood is high. ADH is not
secreted and water passes through into the pelvis.
A large amount of dilute urine is produced.
20. ADH and the Collecting Duct
Ref: IB Biology OSC
21. A Comparison of Blood
The blood in the renal artery is different from blood in the
renal vein.
Renal artery:
higher in urea, salt, water.
Renal vein:
lower in urea, salt, water.
Levels of glucose and blood proteins should be the same,
unless blood glucose levels are high and excess has been
removed in the kidney.
22. Comparing Glomerular Filtrate and Urine
Glomerular Filtrate:
High in glucose
Low in urea
Urine:
No glucose (it has been reabsorbed)
High in urea (it has been concentrated)
23. Diabetes
The urine of non-diabetic patients should contain no
glucose as it is selectively reabsorbed from the filtrate in
the proximal convoluted tubule
Diabetics have higher levels of blood glucose due to either
a lack of insulin secretion (type I) or insensitivity to insulin
secretions (type II)
Because of this, not all of the glucose in diabetics is
reabsorbed into the blood (protein pumps in tubule wall
become saturated)
This results in the presence of glucose in the urine of
untreated diabetics, which can be detected using test strips
24. IBO guide:
11.3.1 Define excretion. Excretion is the removal
from the body of the waste products of metabolic
pathways.
11.3.2 Draw and label a diagram of the kidney.
(Include the cortex, medulla, pelvis, ureter and
renal blood vessels).
11.3.3 Annotate a diagram of a glomerulus and
associated nephron to show the function of each
part.
25. IBO guide:
11.3.4 Explain the process of ultrafiltration,
including blood pressure, fenestrated blood
capillaries and basement membrane.
11.3.5 Define osmoregulation. Osmoregulation is
the control of the water balance of the blood, tissue
or cytoplasm of a living organism.
Aim 7: Data logging using colorimeters to
measure the response of blood cells to changing
salt concentrations is possible.
26. IBO guide:
11.3.6 Explain the reabsorption of glucose, water
and salts in the proximal convoluted tubule,
including the roles of microvilli, osmosis and
active transport.
11.3.7 Explain the roles of the loop of Henle,
medulla, collecting duct and ADH (vasopressin) in
maintaining the water balance of the blood.
(Details of the control of ADH secretion are only
required in option H).
27. The Kidney
11.3.8 Explain the differences in the concentration
of proteins, glucose and urea between blood
plasma, glomerular filtrate and urine.
11.3.9 Explain the presence of glucose in the urine
of untreated diabetic patients.
