Biology - Homeostasis + the Kidney

Parts of the excretory system

Kidney (2), ureter (2), bladder, urethra

Kidney use

Regulates water content and filters blood

Ureter use

Carries urine from the kidneys to the bladder

Bladder use

Stores urine

Urethra use

Carries urine from bladder to outsde of blody

How is blood supplied to the kidney?

By the renal artery under very high pressure

What happens to the blood in the kidney?

It’s filtered and leaves through the renal vein

Parts of the kidney

Renal capsule, medulla, renal artery, renal vein, cortex, ureter, renal pelvis

What is each kidney made up of?

Thousands of tubules called nephrons

What are the two halves of a nephron called?

Cortex (top) and medulla (bottom)

Parts of a nephron

Distal convoluted tubule, glomerulus, Bowman’s capsule, proximal convoluted tubule, capillary network, loop of Henle

Ultrafiltration definition

Filtration at the level of molecules

How does ultrafiltration work in the glomerulus

1. Blood arrives at the glomerulus in the Bowman’s capsule under very high pressure (input vessel wider than output vessel)

2. The walls of the glomerulus and Bowman’s capsule are 1 cell thick so molecules can diffuse into the tubule of the capsule. This fluid becomes known as glomerular filtrate

3. The glomerular filtrate contains water, glucose, urea, hormones and mineral ions

4. Large molecules (such as proteins) are too large to pass into the Bowman’s capsule so remain in the blood

What happens after ultrafiltration?

Selective reabsorption

How does selective reabsorption work?

1. The glomerular filtrate passes through the proximal convoluted tubule

2. Some molecules are reabsorbed into the capillary that runs alongside the proximal convoluted tubule

3. Some molecules are reabsorbed more than others hence selective reabsorption

4. Glucose, amino acids and some salts are reabsorbed here by active transport

5. Water is also reabsorbed here (mostly in the loop of Henle) by osmosis

What is the fluid like and what happens to it by the time it gets to the collecting duct?

It’s mostly water with urea and some salts dissolved in it. After passing through the collecting it is called urine and enters the bladder

Osomoregulation definition

The control of water in the blood

What happens when someone doesn’t drink enough water and their blood becomes too concentrated?

1. A decrease in blood water content is detected by the hypothalamus in the brain

2. This triggers the pituitary gland to release more ADH

3. The ADH travels in the blood to the kidney

4. The ADH increases the permeability of the collecting duct

5. More water is reabsorbed into the blood

6. Urine becomes darker (more concentrated) and decreases in volume

What happens when someone drinks loads of water and their blood becomes too dilute?

1. Increase in blood water content is detected by the hypothalamus

2. The hypothalamus triggers the pituitary gland to release less ADH (stops triggering)

3. Less ADH travels to the kidney

4. Decrease in ADH causes the collecting duct to become less permeable to water

5. Less water is reabsorbed into the blood

6. Urine becomes lighter (less concentrated) and increases in volume