Homeostasis

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Define homeostasis
The maintanance of a constant internal environment (within limits).
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Why is it important to maintain core body temp?
Too high and enzymes' active sites change shape and become denatured. Too low and metabolic reaction rate is slowed.
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Why is it important to maintain blood pH?
Too high or low pH denatures enzymes, the active site changes shape so it no longer works as a catalyst.
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Why is it important to maintain blood glucose levels?
If it is too low, cells cannot perform functions because there is not enough glucose to use for respiration to provide energy. Too much and cells shrivel up and die due to osmotic effects - water diffuses out.
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What is negative feedback?
Receptors detect the change in external or internal environment. Information is communicated via the nervous system to effectors. They respond to counteract that change and bring it back within limits.
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Advantage of multiple negative feedback mechanisms?
Quicker response and more control. You can actively increase and decrease a level to return it to normal.
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What is positive feedback?
A change is amplified - effectors respond to further bring levels away from normal e.g. hypothermia.
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State ways ectotherms control their body temp?
Basking, heat from the ground. moving into shade during peak heat, burrows at night.
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How can endotherms control their body temp?
Internally through homeostasis, heat from metabolic reactions. Activity level and internal temp largely independent of ext temp (unlike ectotherms).
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Heat loss in mammals?
Sweating, hairs lie flat, vasodilation.
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Heat produced in mammals?
Shivering, hormones - these increase respiration and metabolism so increase heat.
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Heat conservation in mammals?
Less sweating, hairs stand up (erector pili muscles contract), vasoconstriction.
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How is blood glucose levels controlled?
Controlled via a hormonal system from the pancreas. Cell clusters in the pancreas called Islets of Langerhan . Beta cells secrete insulin. Alpha cells secrete glucagon.
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How does insulin lower blood glucose?
Binds to specific receptors on the liver and muscle cells. Increases permeability of cells to glucose, activates enzymes that convert to glucose to glycogen. Increases rate of glycogenesis and respiration.
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How does glucagon raise blood glucose?
Binds to specific receptors on liver cells. Increases rate of glycogenolysis and gluconeogenesis. Activates enzymes that convert glycogen to glucose. Decreases rate of respiration.
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How does aldrenaline increase blood glucose concentration?
Aldrenaline binds to receptors in the liver cells. It activates glycogenolysis and inhibits glycogenesis. Activates glucagon secretion and inhibits insulin secretion.
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Describe the second messenger model.
Aldrenaline binds to the specific receptor and activates an ezyme called adenylate cyclase. Activated cyclase converts converts ATP into cAMP. This activates a cascade of reactions leading to glycogenolysis.
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What is type I diabetes?
The pancreas does not produce any insulin. If not controlled, glucose level can rise and stay high - hyperglycaemia. If too much insulin injected, then a sharp drop, hypoglycaemia.
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What is type II diabetes?
The body does not respond to its own insulin or B-cells do not produce enough. Controlled by diet and losing weight.
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What is the action of FSH?
Stimulates follicle to develop.
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What is the action of LH?
Stimulates ovulation and stimulates the development of corpus luteum.
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What is the action of Oestrogen?
Stimulates the thickening of the uterus lining.
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What is the action of Progesterone?
Maintains the thick uterus lining. And uterine milk.
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Describe and explain the action of hormones in the menstruation cycle.
1. High FSH conc. in blood. 2. Rising conc. of oestrogen. 3. Oestrogen peaks. 4.LH surge. 5. Rising levels of progesterone then falling levels as corpus luteum and then uterus lining breaks down.
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Negative feedback loop 1
FSH stimulates ovary to release oestrogen. Oestrogen inhibts further production of FSH.
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Negative feedback loop 2
LH stimulates corpus luteum to develop which then releases progestrone. Progesterone inhibts further production of LH.
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Positive feedback - Oestrogen
Oestrogen stimulates the anterior pituatry gland to release LH. LH stimulates ovary to release more oestrogen. Oestrogen further stimulates release of LH.
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Card 2

Front

Why is it important to maintain core body temp?

Back

Too high and enzymes' active sites change shape and become denatured. Too low and metabolic reaction rate is slowed.

Card 3

Front

Why is it important to maintain blood pH?

Back

Preview of the front of card 3

Card 4

Front

Why is it important to maintain blood glucose levels?

Back

Preview of the front of card 4

Card 5

Front

What is negative feedback?

Back

Preview of the front of card 5
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