16 - Homeostasis

Question 1

Define homeostasis.

Answer 1

The maintenance of a constant internal environment despite internal or external changes.

Question 2

Why is it important to maintain a stable temperature and pH?

Answer 2

Optimum enzyme activity
Rate of metabolic reactions

Question 3

Why is it important to maintain water potential?

Answer 3

Prevent cells bursting or shrinking

Question 4

Why is it important to maintain blood glucose concentration?

Answer 4

Allow cells to have access to the substrate for respiration while preventing cell damage by dehydration caused by higher concentrations.

Question 5

What is negative feedback?

Answer 5

Reversing a change so that it returns back to the optimum.

Question 6

What is positive feedback?

Answer 6

A derivation from the optimum which casuses changes resulting in an even greater deviation from the norm.

Question 7

Where is insulin released?

Type of cell + location

Answer 7

B-cells in the pancreas

Question 8

When is insulin released?

Answer 8

When blood glucose concentration rises

Question 9

How does insulin work?

Answer 9

• 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

Question 10

When is glucagon released?

Answer 10

When blood glucose concentration drops

Question 11

Describe the action of glucagon.

Answer 11

• 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)

Question 12

Where is adrenaline released?

Answer 12

Adrenal gland

Question 13

Describe the role and action of adrenaline.

Answer 13

• Binds to adrenaline receptor
• Activates adenylate cyclase
• Adenyl cyclase converts ATP to cAMP
• cAMP activates protein kinase
• Protein kinase converts glycogen to glucose

Question 13

How is Type 1 diabetes caused?

Answer 13

Autoimmune attack on B cells inhibits production of insulin

Question 14

How can Type 1 diabetes be treated?

Answer 14

Insulin injections

Question 15

How is Type 2 diabetes caused?

Answer 15

• Body produces insufficient insulin * Insultin receptors become less responsive

Question 16

How can Type 2 diabetes be treated?

Answer 16

• Losing weight and exercising
• Drugs to stimulate insulin production and reduce glucose absorption
• Insulin injections (severe cases only)

Question 17

Define osmoregulation.

Answer 17

Maintaining constant water potential of blood, despite changes in levels of water and salt intake

Question 18

Describe the structure of the nephron.

Answer 18

• Bowman’s capsule, containing glomerulus
• Proximal convoluted tubule
• Loop of Henlé
• Distal convoluted tubule
• Collecting duct

Question 19

Describe ultrafiltration.

Answer 19

• 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

Question 20

Describe selective reabsorption in the proximal convoluted tubule.

Answer 20

• Glucose is reabsorbed by activate transport (same method as ileum)
• Water reabsorbed by osmosis

Question 21

From where is sodium and chloride actively transported into the medulla?

Answer 21

Ascending Loop of Henle

Question 22

How is water reabsorbed into medulla?

Answer 22

• ADH makes collecting duct water permeable
• Water moves by osmosis from filtrate to medulla

Question 23

Which limb of the Loop of Henle is water permeable?

Answer 23

Descending

Question 24

How does ADH affect the permeability of the collectind duct to water?

Answer 24

More ADH = more permeable

Question 25

Describe the role of the hypothalamus in osmoregulation.

Answer 25

Contains osmoreceptors which cause release of ADH in presence of falling water potential

Question 26

Where is ADH released?

Answer 26

Posterior pituitary gland