16 - Homeostasis Flashcards
Define homeostasis.
The maintenance of a constant internal environment despite internal or external changes.
Why is it important to maintain a stable temperature and pH?
Optimum enzyme activity
Rate of metabolic reactions
Why is it important to maintain water potential?
Prevent cells bursting or shrinking
Why is it important to maintain blood glucose concentration?
Allow cells to have access to the substrate for respiration while preventing cell damage by dehydration caused by higher concentrations.
What is negative feedback?
Reversing a change so that it returns back to the optimum.
What is positive feedback?
A derivation from the optimum which casuses changes resulting in an even greater deviation from the norm.
Where is insulin released?
Type of cell + location
B-cells in the pancreas
When is insulin released?
When blood glucose concentration rises
How does insulin work?
- Binds to insulin receptor
- More glucose enters cell as more channel proteins available
- More glucose used in respiration
- Activated enzymes convert glucose to glycogen (glycogenesis)
- Glucose level decreased
When is glucagon released?
When blood glucose concentration drops
Describe the action of glucagon.
- Binds to receptors on surface of target cells
- Activates enzymes to convert glycogen to glucose (glycogenolysis)
- Activates enzymes to convert glycerol + amino acids into glucose (gluconeogenesis)
Where is adrenaline released?
Adrenal gland
Describe the role and action of adrenaline.
- Binds to adrenaline receptor
- Activates adenylate cyclase
- Adenyl cyclase converts ATP to cAMP
- cAMP activates protein kinase
- Protein kinase converts glycogen to glucose
How is Type 1 diabetes caused?
Autoimmune attack on B cells inhibits production of insulin
How can Type 1 diabetes be treated?
Insulin injections
How is Type 2 diabetes caused?
- Body produces insufficient insulin * Insultin receptors become less responsive
How can Type 2 diabetes be treated?
- Losing weight and exercising
- Drugs to stimulate insulin production and reduce glucose absorption
- Insulin injections (severe cases only)
Define osmoregulation.
Maintaining constant water potential of blood, despite changes in levels of water and salt intake
Describe the structure of the nephron.
- Bowman’s capsule, containing glomerulus
- Proximal convoluted tubule
- Loop of Henlé
- Distal convoluted tubule
- Collecting duct
Describe ultrafiltration.
- Occurs in glomerulus
- Efferent (leaving) capillary narrower than afferent capillary
- Ions, water and glucose forced into glomerulus through pores between capillary endothelium and basement membrane
Describe selective reabsorption in the proximal convoluted tubule.
- Glucose is reabsorbed by activate transport (same method as ileum)
- Water reabsorbed by osmosis
From where is sodium and chloride actively transported into the medulla?
Ascending Loop of Henle
How is water reabsorbed into medulla?
- ADH makes collecting duct water permeable
- Water moves by osmosis from filtrate to medulla
Which limb of the Loop of Henle is water permeable?
Descending
How does ADH affect the permeability of the collectind duct to water?
More ADH = more permeable
Describe the role of the hypothalamus in osmoregulation.
Contains osmoreceptors which cause release of ADH in presence of falling water potential
Where is ADH released?
Posterior pituitary gland
