Homeostasis and Blood Glucose Levels

Question 1

Homeosatsis

Answer 1

The maintenance of stable/constant internal environment

Within strict limits

Question 2

Importance of homeostasis

Answer 2

Maintaining a constant internal environment means enzyme controlled biological reactions take place at a constant optimum rate
So changes in the internal or external environment aren’t dangerous/deadly

Question 3

Why are organisms that control their own internal environment more independant of their environment

Answer 3

Greater geographical range so able to colonise more habitats and ecosystems
Greater chance of finding food, shelter and mates

Question 4

Explain an example of positive feedback (threshold potential)

Answer 4

Initial membrane depolarisation
Opening of voltage gated Na+ channels
Increased Na+ flows through the membrane
Further membrane depolarisation
Typically along unmyelinated axons

Question 5

Positive feedback

Answer 5

Occurs when a deviation from an optimum causes changes that result in an even greater deviation from the normal

Question 6

Negative feedback

Answer 6

When there is an increase/decrease from the set point, the opposite effect is instigated to produce a response that returns the value to normal

Question 7

Endotherms

Answer 7

Maintain body temperature by both physiological and behavioural means
Independant of area/environment so not relying on it
Can migrate to find a mate, reproduce all year round

Question 8

Ectotherms

Answer 8

All animals except mammals and birds
Maintain body temperatures by behavioural means only
Exposing themselves to sun or taking shelter
Gaining warmth from the ground

Question 9

Hypoglycaemia

Answer 9

Very low levels of glucose below the strict set range

Can be fatal

Question 10

Hyperglycaemia

Answer 10

Very high levels of glucose above the strict set range

Can be fatal

Question 11

What controls blood glucose concentration

Answer 11

Pancreas
Has glucose receptor cells that monitor the concentration of blood glucose
And endocrine cells called the islets of Langerhans which secrete hormones

Question 12

What are the Islets of Langerhans composed of

Answer 12

alpha cells which secrete the hormone glucagon

beta cells which secrete the hormone insulin

Question 13

Advantage of Islets of Langerhans having lost of capillaries

Answer 13

Can get the hormones straight into the blood so they can be transported

Question 14

Insulin

Answer 14

A peptide hormone secreted by beta cells in the pancreas
When blood glucose levels are too high
In order to help reduce blood glucose levels to the normal range

Question 15

How does insulin work

Answer 15

Binds to complementary receptors on cell surface membrane of target cells in liver
This controls the uptake of glucose by regulating the inclusion (addition) of glucose carrier proteins in the surface membranes of target cells so more glucose taken into cells
Insulin activates enzymes that stimulate glycogenesis
To decrease the blood glucose levels

Question 16

Glucagon

Answer 16

A peptide hormone secreted by alpha cells in the pancreas
When blood glucose levels are too low
In order to help increase blood glucose levels to the normal range

Question 17

How does glucagon work

Answer 17

Binds to receptors on the cell surface membrane of liver cells
Activates enzymes involved in the hydrolysis of glycogen to glucose (glycogenolysis)
Activates enzymes involved in the conversion of glycerol and amino acids into glucose (gluconeogenesis)

Question 18

Describe the role of glycogen formation and its role in lowering blood glucose levels

Answer 18

Glucose concentration in liver cells falls
Below that in the blood
Creating a glucose concentration gradient
Glucose enter the cells and leaves the blood via facilitated diffusion through carrier proteins

Question 19

Describe how blood glucose levels can be increased with hormones

Answer 19

Release of glucagon from alpha cells
Leads to formation of glucose in liver cells
From non-carbohydrates/amino acids/fatty acids

Question 20

Explain the changes to blood glucose levels after a meal

Answer 20

Glucose absorbed from the ileum into the hepatic portal vein
Blood glucose concentration increases
Detected by pancreas
Insulin secreted from beta cells
Causes glucose to be taken up by the liver and converted into glycogen
Reducing blood glucose levels
Detected by the pancreas
Stops secreting insulin
If levels fall to far, alpha cells secrete glucagon
Causes liver to hydrolyse some glycogen to store glucose
Glucose diffuses into the blood down a concentration gradient by facilitated diffusion
Increasing blood glucose concentration
Pancreas stops secreting glucagon

Question 21

Can insulin and glucagon be in the body at the same time

Answer 21

Yes