(2.71-2.79B) Excretory processes + Kidney

What is excretion?

The removal of metabolic waste products.

Why do waste products need to be removed from the body?

• Toxicity- if they become too concentrated, they could be harmful

• Osmotic effect- could ruin the balance of bodily processes

Define egestion.

Removal of food waste from the anus

What are the organs of excretion?

lungs

liver

kidney

skin

What do the lungs excrete?

carbon dioxide

water

What does the liver excrete?

urea

(from the breakdown of excess amino acids)

What does the kidney excrete?

water

urea

mineral ions

What does skin excrete?

urea

water

mineral ions

What are the functions of the kidney?

Osmoregulation

Excretion

What is osmoregulation?

The process of maintaining water + salt concentrations across membranes in the body

What are the functions of the urinary system?

Osmoregulation

Filter and expel waste products as urine

Describe the structure of the urinary system.

• 2 kidneys

• joined to:

• the bladder by 2 ureters

• aorta by renal artery

• vena cava by renal vein

Describe the structure of a kidney.

3 regions

• Cortex- outermost

• Medulla- inner

• Renal pelvis- tube to ureter

contains a million nephrons

• start in cortex

• loop into medulla

• back to cortex

• contents of nephron drains into renal pelvis

List the different parts of a nephron.

Bowman’s capsule around glomerulus

Proximal convoluted tubule surrounded by network of capillaries

Loop of Henle

Distal convoluted tubule

Collecting duct

What does a nephron do?

Ultrafiltration

Selective reabsorption of glucose

Selective reabsorption of water + salts

Where and how does ultrafiltration occur?

• arterioles branch off renal artery to each nephron, forming glomerulus in Bowman’s capsule

• capillaries narrow - increasing bp

• forces smaller molecules out of capillaries, into capsule forming filtrate

  • glucose

  • water

  • urea

  • salts

Where and how does selective reabsorption of glucose occur?

• filtrate travels to proximal convoluted tubule

• 100% of glucose is reabsorbed via active transport

Where and how does selective reabsorption of water occur?

• As the filtrate moves down the Loop of Henle

• salts and 80% of water exit via osmosis

Why is glucose reabsorbed at the proximal convuluted tubule?

It is the only place with the gates for active transport of glucose

How is water reabsorption regulated?

A negative feedback loop controlled by ADH

Describe the role of ADH in osmoregulation.

1. Deviation from the norm detected by hypothalamus- too much, too little water

2. Signal sent to pituitary gland to release more/less ADH

3. increased/decreased permeability of collecting duct and distal tubule

4. increased/decreased reabsorption of water into blood

5. little, concentrated/lots of dilute urine produced

What does urine contain?

water

urea

ions