Chapter 38-Excretory System

• Filtration
• Reabsorbtion
• Secretion

Filtration: water and small molecules pass, under high pressure, from blood into the nephron.

• Renal arteries divide into afferent arterioles and then divide into a capillary network- the glomerulus. This creates pressure.
• Smaller molecules are forced out of plasma by the pressure into the lumen of Bowman’s capsule- forming glomerular filtrate.
• Red blood cells and large proteins are too large to pass through.

Bowman’s capsule: a cup shaped funnel that surrounds each glomerulus.

Smaller molecules in blood are forced out of plasma by pressure created by the afferent arterioles dividing into the capillary network of the glomerulus.

Red blood cells and large proteins.

• High blood pressure
• Large surface area of the capillaries
• Large number of pores in the capillaries

Efferent arterioles are narrower than the afferent arterioles- force filtering the plasma.

Everything enters the glomerular filtrate except larger molecules eg. some hormones, platelets, large proteins, red and white blood cells.

• Some hormones
• Platelets
• Large proteins
• Red blood cells
• White blood cells

Reabsorbtion: molecules pass from the nephron back into the blood.

Food and water- glucose, amino acids, some salts and water.

Food molecules are taken back into the blood by active transport as they’re reabsorbed against the concentration gradient (so energy is required).

• Most water is reabsorbed by osmosis
• And in the loop of Henle and convoluted tubules.

• Active transport- requires energy
• Passive transport- doesn’t require energy

Food molecules are reabsorbed against the concentration gradient by active transport.