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Biology OCR A A level > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

Define homeostasis

A

The maintenance of a stable equilibrium in the conditions inside the body

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2
Q

What do negative feedback loops aim to do?

A

Reverse the initial stimulus

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3
Q

What do positive feedbacks aim to do?

A

A change in the internal environment is detected by sensory receptors and effectors are stimulated to reinforce the change and increase the response

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4
Q

Define thermoregulation

A

Maintenance of a relatively constant core body temperature to maintain optimum enzyme activity

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5
Q

Define ectotherm

A

Animals that use their surroundings to warm their bodies so their core temperature is heavily dependent on outside environment

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6
Q

Define endotherm

A

Animals that rely on their metabolic processes to warm their bodies and maintain their core temperature

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7
Q

Draw a graph to show the effect of changes in the internal and external temperature on ectotherms and endotherms

A

External temperature on x axis
Body temperature on y axis
Ectotherm linear relationship not passing through the origin
Endotherm horizontal line around 37C

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8
Q

What are behavioural responses that some ectotherms have to changes in temperature?

A

Orientating themselves to have maximum exposure to the sunshine
Conduction by placing their bodies on the warm ground
Seeking shade to decrease temperature

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9
Q

What are 2 key physiological responses ectotherms have?

A

Colour changes in their skin

Alter heart rate to change metabolic rate

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10
Q

Where are peripheral temperature receptors in endotherms?

A

Skin

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11
Q

Where are the 2 temperature receptors found in the body?

A

Skin

Hypothalamus

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12
Q

What are the three mechanisms that endotherms have to cool down?

A

Vasodilation
Increased sweating
Reducing the insulating effect of hairs

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13
Q

Explain what vasodilation is and how it leads to cooling of the body

A

Arteries near the surface of the skin dilate
Forces blood through capillary networks near the surface of the skin
Skin flushes and cools as a result of increased radiation

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14
Q

Explain how sweating leads to heat loss

A

Sweat evaporates from the surface of the skin so heat is lost and the surface below cools

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15
Q

Explain how hair can be used to cool the body

A

The erector pilli muscles in the skin relax
Hairs lie flat on the skin
Avoids trapping an insulating layer of air

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16
Q

Describe the 4 processes that occur to warm up an endotherm

A

Vasoconstriction
Decreased sweating
Raising the body hair or feathers
Shivering

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17
Q

Explain how vasoconstriction causes warming in the body

A

Arterioles near surface of the skin constrict
Arteriovenous shunt vessels dilate so little blood flows through the capillary networks close to the surface of the skin
Little radiation occurs and warm blood is kept well below the surface

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18
Q

Explain the process of shivering within an endotherm

A

The rapid, involuntary contraction and relaxation of large voluntary muscles in the body

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19
Q

What are the two control centres in the control of thermoregulation?

A

Heat loss centre

Heat gain centre

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20
Q

Explain how the heat loss centre is activated

A

Temperature of the blood flowing through the hypothalamus increases
Sends impulses through the autonomic motor neurons to effectors in the skin and muscles triggering responses to lower core temperature

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21
Q

Explain how the heat gain centre is activated

A

Temperature of the blood flowing through the hypothalamus decreases
Sends impulses through the autonomic nervous system to effectors in the skin and muscles triggering responses to increase core temperature

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22
Q

How is oxygenated blood supplied to the liver?

A

Hepatic artery

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23
Q

How is deoxygenated blood removed from the liver?

A

Hepatic vein

24
Q

What is the role of the hepatic portal vein?

A

To carry blood containing the products of digestion straight from the intestines to the liver

25
Q

What are liver cells called?

A

Hepatocytes

26
Q

What are the key features of hepatocytes?

A

Large nuclei
Prominent golgi apparatus
Lots of mitochondria

27
Q

Where does the blood from the hepatic artery and portal vein mix?

A

In the sinusoid which is surrounded by hepatocytes

28
Q

What type of cell does the sinusoid contain?

A

Kupffer cells

29
Q

What is the role of a Kupffer cell?

A

Macrophage of the liver ingesting foreign particles and helping to protect against disease

30
Q

Hepatocytes secrete bile. Where does it go?

A

Into the canaliculi

Canaliculi then drains the bile into bile ducts which take it to the gall bladder

31
Q

What are the three major roles of the liver?

A

Carbohydrate metabolism
Deamination of excess amino acids
Detoxification

32
Q

How do hepatocytes aid carbohydrate metabolism?

A

When blood glucose levels rise the insulin levels rise and stimulate hepatocytes to convert glucose to glucagon
When blood glucose levels fall the glucagon levels rise and this stimulates hepatocytes to convert glycogen into glucose

33
Q

What is transamination?

A

The conversion of one amino acid into another

34
Q

Why is transamination important?

A

Diet doesn’t always contain the required balance of amino acids so this helps overcome this issue

35
Q

What is deamination?

A

The removal of an amine group from a molecule

36
Q

Explain what happens to excess amino acids that are absorbed by the liver

A

Amino acid molecules are split
The amino group combines with carbon dioxide to form urea
Urea is excreted via the kidneys
Rest of amino acid molecule is used in respiration

37
Q

What does the ornithine cycle show?

A

The enzyme controlled set of reactions that convert ammonia into urea

38
Q

Explain how the liver breaks down hydrogen peroxide

A

Hepatocytes contain catalase which splits hydrogen peroxide into oxygen and water

39
Q

Explain how the liver breaks down alcohol

A

Ethanol is the active agent in alcohol
Hepatocytes contain alcoholic dehydrogenase
Ethanol broken down into ethanal
Ethan is then converted into ethanoate which can be used to build up fatty acids or it is used in cellular respiration`

40
Q

What are the kidneys normally surrounded by?

A

A thick protective layer of fat and a layer of fibrous connective tissue

41
Q

What are the two crucial homeostatic functions of the kidney?

A

Excretion

Osmoregulation

42
Q

How does oxygenated blood arrive at the kidney?

A

Renal arteries coming from the abdominal aorta

43
Q

How does deoxygenated blood leave the kidney?

A

Renal vein into the inferior vena cava

44
Q

What liquid is produced by the kidneys?

A

Urine

45
Q

What tube does urine enter having left the kidney?

A

Ureter

46
Q

What are the three main areas of the kidney?

A

Medulla
Cortex
Pelvis

47
Q

Describe the structure and function of the kidney cortex

A

Dark outer layer
Dense capillary network carrying blood from renal artery to the nephrons
Filtering of blood occurs here

48
Q

Describe the structure and function of the kidney medulla

A

Lighter colour

Contains tubules of nephrons that form pyramids of the kidney and collecting ducts

49
Q

Describe the structure and function of the pelvis

A

Central chamber of the kidney where urine collects before passing out of the ureter

50
Q

Describe the structure of the Bowman’s capsule

A

Cup shaped structure that contains the glomerulus

51
Q

Describe the structure and function of the glomerulus

A

Tangle of capillaries

More blood enters the capillaries than leaves as ultrafiltration occurs

52
Q

Describe the structure and function of the proximal convoluted tube

A

First coiled region of tubule after the Bowman’s capsule
In the cortex of the kidney
Many substances needed by the body are reabsorbed into the blood

53
Q

Describe the structure and function of the Loop of Henle

A

A long tubule that creates a region with a very high solute concentration in the tissue fluid in the medulla

54
Q

Describe the structure and function of the distal convoluted tubule

A

Second twisted tubule where fine tuning of the water balance occurs
Permeability of the walls varies with levels of ADH in the blood
Ion and pH regulation occurs here too

55
Q

Where is ADH produced and secreted?

A

Produced in the hypothalamus

Secreted into the posterior pituitary gland

56
Q

How does ADH work?

A

Increases the permeability for the distal convoluted tubule and collecting duct to water

Biology OCR A A level (17 decks)

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