3.6.4 Homeostasis is the maintenance of a stable internal environment

Maintainance of an internal environment against external conditions

Mechanism used to restore any deviations from normal in a system back to its original state

Has a structure called Islets of Langerhans which has:
- Alpha cells which release glucagon
- Beta cells which release insulin

1) Spike is detected by beta cells in islets of langerhan
2) Beta cells release insulin
3)Liver cells become permeable to glucose.
4)Glucose removed from blood and converted to glycogen

Formation of glycogen from excess glucose mainly in liver

Breaking down glycogen into glucose in liver

Formation of glucose from non carbohydrate parts like amino acids in liver

In the nephrons which are long tubules surrounded by capillaries.

Renal artery > afferent arterioles > glomerelus > renal capsule/efferent arterioles(if big) > PCT > Loop of henle > DCT > CT

-Attaches to receptors on target cell- changing shape of channel proteins (more permeable)
-More protein channels inserted
- Activating glycogenesis enzymes

- Attaches to receptors on target cells and:
1)Causes a protein to convert into adenylate cyclase which causes ATP to cyclic AMP (cAMP) which cAMP activates protein kinase. This hydrolyses glycogen to glucose
2)Activating gluconeogenesis enzymes

Type 1:
Body doesnt produce sufficient amounts of insulin
Type 2:
Receptors in target cells become less responsive to insulin

1) Blood from afferent arterioles enters glomerulus (lots of capillaries)
2) Since the afferent arterioles diameter is larger than efferent theres a build up of hydrostatic pressure
3) This pressure pushes the small molecules out into the renal capsule. Forming glomerulus filtrate. Large molecules cant fit inside renal capsule

1) Gaps between capilary endothelium cells
2) Basement membrane
3) Gaps between podocytes

1)Na ions are actively pumped out of PCT into capillaries to decrease conc in PCT
2)Na ions diffuse down into PCT by a co-transporter which also transports glucose against gradient
3)Glucose then facilitates diffuse into capillaries and is reabsorbed

Walls much thinner and is permeable to water

Walls much thicker and isn't permeable to water

1)Na ions are actively transported out of loop into interstitial area with ATP( from mitochondria)
2)This lowers the WP so water from descending loop diffuse out and reabsorbed by capillaries
3)At the base some Na ions diffuse out as bottom is now diluted
- WP is highest at cortex inside and lowers as you go down medulla

1)Filtrate is very diluted (due to lots of Na ions being actively transported)
2)More water is diffused out of DCT however the amount is controlled by ADH
3)Urine is formed and passes out of collecting duct

1) Osmoreceptors detect this as water leaves causing it to shrivel
2)Hypothalamus releases ADH by pituitary gland
3)ADH binds to target cell(DCT/CT)
4) This causes DCT and collecting duct to become more permeable
5)More water is reabsorbed into blood and urine becomes more concentrated

1)ADH binds to receptors on DCT/collecting duct
2)This causes phosphorylase to activate
3)Phosphorylase causes vesicles with aquaporins to fuse with membrane

Water protein channels