11.3 THE KIDNEY

Topic 11 Human Health & Physiology

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. • 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. • 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 in maintaining the

water balance of blood.• 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.

• Aim 7: Data logging using colorimeters to measure the response of blood cells to changing salt concentrations is possible.

Excretion• Excretion is the removal of waste products of metabolism• This is distinct from defecation, since in defecation the

waste is not products of metabolism

• What word did we use to describe defecation?

Kidney Structure• The main parts of a kidney you need to know are:• Cortex• Medulla• Pelvis• Ureter• Renal Artery• Renal Vein

Kidney Structure

Ref: IB Biology, Allott

A comprehensive animation

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.

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.

The Nephron

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.

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 capillaries are surrounded by podocyte cells, the cells of the inner wall of the bowman’s capsule.

• These cells wrap around the capillaries and have gaps between them to allow the filtrate to pass through quickly.

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.

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.

The collecting duct balances the water concentration of the blood, through hormonal control.

The collecting duct balances the water concentration of the blood, through hormonal control.

ADH and the Collecting Duct

Ref: IB Biology OSC

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)

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