Formation of Urine, the Kidney, and the Nephron

Question 1

Filtration

Answer 1

1. Blood moves from afferent arteriole (from renal vein) into glomerulus (cluster of tiny blood vessels)
2. Acts as a high pressure filter so that dissolved solutes pass through walls into Bowman’s Capsule moving from high to low pressure
3. Filtered blood moves out of glomerulus to efferent arteriole (to renal artery)

Question 2

What Can and Cannot be Filtered

Answer 2

Filtrate: ions - Na+ and Cl-, urea, uric acid, glucose, amino acids, water
Too Big to Filter: proteins, platelets, blood cells

Question 3

Reabsorption in Proximal Tubule

Answer 3

1. Na+ ions actively transported out of nephron into capillaries (using carrier molecules and ATP from the mitochondria lining nephron)
2. Cl- ions follow through passive transport due to attraction to Na+
3. Glucose and amino acids actively transported into capillaries (using carrier molecules)

Question 4

Threshold

Answer 4

Reabsorption occurs threshold level of substance reached - based off what body needs in moment –> excess solute remains in filtrate and excreted with urine (ex. high blood glucose results in excreting of excess sugar in urine)

Question 5

Reabsorption in Descending Loop of Henle

Answer 5

High amount of solutes being transported out and proteins in bloodstream result in high concentration of solute in outer medulla (“salty” medulla - very hypertonic), and osmotic gradient draws water out of descending Loop of Henle (very permeable)

Question 6

Reabsorption in Ascending Loop of Henle

Answer 6

After water reabsorption, remaining filtrate is too concentrated, so NaCl reabsorbed into outer medulla via passive transport (due to gradient) in ascending Loop of Henle (impermeable to water)

Question 7

Importance of Reabsorption

Answer 7

Reabsorption of water prevents huge amounts of water loss and large volumes of urine - without reabsorption, you would be peeing very frequently and would need a very large amount of water to stay hydrated

Question 8

Secretion

Answer 8

Movement of wastes from blood into distal tubule (nitrogen-containing wastes, H+ ions, some drugs) and movement of substances out of distal tubule into blood via active transport to maintain homeostasis (water, HCO3-, NaCl)
- Urine then travels down collecting duct to ureter

Question 9

Kidney Anatomy

Answer 9

Renal Vein, Renal Artery, Kidneys, Ureter, Bladder, Urethra
Inside Kidney: Renal Pelvis, Medulla, Cortex