7.5 Formation of Urine

Definitions:

• Filtration - Process by which blood or bodily fluids pass through a selectivley permeable membrane.
• Re-absorption - Transfer of glomerular filtrate from the nephron back into capillaries.
• Secretion - Movement of materials from the blood to the distal tubule. Products such as ammonia and some drugs.

• Water, NaCl, Glucose, amino acids, Hydrogen ions, Plasma proteins, red and white blood cells and blood platelets enter the glomerulus.

The following will NOT enter the Bowman's Capsule:

• Proteins
• Erythrocytes (Red and White Blood cells)
• Blood Platelets

Filtration:

1. Aorta
2. Renal Artery
3. Afferent tubule
4. Glomerulus - Capillary network
   - The location of filtration
   Blood enters at high pressure of 65mmHg (mm of mercury). This pressure causes the filtration.
   

Re-Absorption:

1. 600mL of blood passes through the kidneys per minute.
2. 120mL passes through the nephron.
3. 100mL is returned to the circulatory system
   -20mL will be controlled by the hypothalamus and pituitary gland.
   -ADH and Aldosterone released to increase H2O retention. 19 of the 20ML can be re-absorbed.
   

Passive Transport:

1. Osmosis - Water
2. Diffusion - materials within a solution

• Sodium ions move from kidney back into circulatory system. Proximal tubule to the peritubular capillary. Negative ions such as Carbonate and chlorine follow the sodium. Amino acids and glucose are also moved from the proximal tubule to the peritubular capillaries.

Active Transport:

• Amino Acids and Glucose must be completly retained to the circulatory system.
• Carrier molecules deliver remaining glucose and amino acids back into the blood.
• Creates an osmotic gradient so H2O moves back into capillaries.

-Brandon