Homeostasis, thermoregulation and excretion

Question 1

What is homeostasis?

Answer 1

maintenance of a stable internal environment within restricted limits in organisms ensuring cells function normally despite environmental change

Question 2

Why is homeostasis important?

Answer 2

• keeps internal environment constant for metabolic reactions
• ensures cells function properly and avoid damage
• helps organisms respond + adapt to external change

Question 3

What is the role of a receptor in homeostasis?

Answer 3

sensory receptors = detect stimuli sending signals to the brain about changes in the environment (e.g blood pH and temp)

Question 4

What is the role of a coordinator in homeostasis?

Answer 4

coordinator = receives + interprets info from receptors and sends instructions to an appropriate effector

Question 5

What is the role of an effector in homeostasis?

Answer 5

effectors = muscles or glands that act on signals from the brain and cause responses to regain equilibrium (e.g sweating)

Question 6

What is a negative feedback system?

Answer 6

coordination between receptors and effectors to maintain optimum conditions

Question 7

How does negative feedback work?

Answer 7

• receptors detect a change in direction (e.g rising BG)
• signals trigger effectors to produce responses that reverse the initial change (e.g releasing insulin)
• conditions return to their set range

Question 8

Why is maintaing blood glucose concentration important and how is it achieved?

Answer 8

Important = glucose is needed for respiration but too much can affect water potential in blood cells

Achieved = insulin and glucagon adjust BG concentration to maintain a healthy glucose supply

Question 8

Why is maintaining blood PH important and how is it achieved?

Answer 8

Important = changes in PH can impair enzyme action

Achieved = adjustments are made to the acid-base balance in the blood to maintain optimum pH

Question 8

Why is maintaining water regulation important and how is it achieved?

Answer 8

Important = too much or little water in the blood and cells can cause cells to burst or shrink via osmosis

Achieved = water removed or reabsorbed from blood or tissue fluid to maintain optimum water potential

Question 8

Why is maintaining temperature important and how is it achieved?

Answer 8

Important = changes in temp can impair enzyme action

Achieved = adjustments made by sweating or shivering to maintain optimum

Question 8

What is a positive feedback system?

Answer 8

amplifies changes rather than reversing them a deviation from an optimum results in an even greater deviation from the optimum

Question 8

How does positive feedback work?

Answer 8

• initial change occurs (e.g release of clotting factors after injury)
• effectors are stimulated and enhance the change (e.g more clotting factors being released)
• change continues until an endpoint is met (e.g a fully formed clot)

Question 8

what are 2 examples of positive feedback?

Answer 8

Blood clotting = clotting factors activate further clotting

Childbirth = oxytocin stimulates more uterus contractions

Question 8

What is cell signalling?

Answer 8

process which cells communicate

can occur between adjacent cells or between distant cells

Question 8

How does cell signalling occur between distant cells?

Answer 8

• communicate by releasing hormones
• these hormones travel in the blood and signal to target cells
• cell-surface receptors enable cells to recognise and respond to hormones

Question 9

What is thermoregulation?

Answer 9

process of maintaining a relatively constant core body temperature important to maintain optimum enzyme activity

Question 10

What are ectotherms and give an example?

Answer 10

animals that use their surroundings to regulate body temp through behavioural changes like surrounding change

e.g reptiles and fish

Question 11

What are endotherms and give an example?

Answer 11

animals relying on their metabolic internal processes to control body temp

e.g mammals and birds

Question 12

How does thermoregulation reduce body temperature when it’s too high?

Answer 12

Sweating = effector sweat glands produce more sweat to promote evaporative cooling

Flattening hair = effector pili muscles relax flattening hairs to reduce insulation

Vasodilation = effector arterioles near the skin dilate, increasing blood flow to the skin and heat radiation from the skin surface

Question 13

How does thermoregulation increase body temperature when it’s too low?

Answer 13

Shivering = effector skeletal muscles contract to generate heat through increased cellular respiration (exothermicaly)

Minimising sweating = effector sweat glands produce less sweat helping to conserve body heat

Erecting hair = effector pili muscles contract raising hairs trapping a layer of warm air increasing insulation

Vasoconstriction = effector arterioles near the skin constrict reducing blood flow to the skin and heat radiation from the skin surface

Releasing adrenaline = effector glands release speed up cellular metabolism producing more heat

Question 14

How does the hypothalamus control body temperature?

Answer 14

1) collects info about body temperature from temp receptors in hypothalamus and about surface temp from peripheral receptors in the skin

2) this information is processed in the hypothalamus to detect deviations from normal levels in temp

3) hypothalamus sends signals to effectors like muscles and sweat glands

4) these effectors implement mechanisms to restore the ideal temp

Question 15

What 2 centres in the hypothalamus are involved in thermoregulation?

Answer 15

heat loss centre and heat gain centre

Question 16

How does the hypothalamus coordinate a response when temperature increases?

Answer 16

• impulses sent to the heat loss centre in the hypothalamus
• this sends impulses to the effector organs to increase heat loss
• the body temp returns to optimum

Question 17

How does the hypothalamus coordinate a response when temperature decreases?

Answer 17

• impulses sent to the heat gain centre in the hypothalamus
• this sends impulses to effector organs to reduce heat loss
• the body temp returns to optimum

Question 18

What is excretion and give an example?

Answer 18

process of removing metabolic waste from cells essential for maintaining normal metabolism and homeostasis

metabolic waste products (e.g urea) are metabolised in and excreted from liver cells

Question 19

What is detoxification?

Answer 19

breakdown of toxic substances (e.g alcohol, hormones and excess amino acids converting them into less harmful compounds that cells can excrete

Question 20

What are the stages of the liver breaking down amino acids?

Answer 20

1) amine groups removed from amino acids producing toxic ammonia and organic acids

2) organic acids either used for ATP production or stored as glycogen

3) ammonia combines with CO2 to form urea occurring partially in the mitochondria of liver cells

4) urea is then excreted from liver cells, enters the bloodstream, and is filtered out of the body via the kidneys as urine

Question 21

what other substances can the liver detoxify?

Answer 21

Alcohol = alcohol dehydrogenase breaks down ethanol to ethanal which is then converted to ethanoate to prevent cell damage

Hydrogen peroxide = catalase splits hydrogen peroxide into O2 and H2O preventing cell damage

Paracetamol - broken down to prevent toxicity to the liver and kidneys

Insulin = metabolised to help regulate BG

Question 22

What is the function of the liver in regulating blood glucose?

Answer 22

• glycogenesis converting excess glucose into glycogen for storage
• storing glycogen granules within its cells
• glycogenolysis breaking down glycogen into glucose when BG falls

Question 23

What is the function of the liver in breaking down red blood cells?

Answer 23

haemoglobin from old RBCs is broken down in liver cells into bile before excretion from the liver

Question 24

What are the key structures of the liver?

Answer 24

Hepatic artery = supplies oxygenated blood

Hepatic vein = carries away deoxygenated blood towards the heart

Hepatic portal vein = brings nutrient-rich blood from the intestines

Bile duct = transports bile to the gallbladder

Question 25

what is the structure of hepatocytes?

Answer 25

• large nuclei
• prominent Golgi apparatus
• several mitochondria

Question 26

What are the key cells and tissues in each liver lobule?

Answer 26

Hepatocytes = arranged along channels called sinusoids

Sinusoids = where O2-rich blood from the hepatic artery mixes with blood from the hepatic portal vein (rich in digestion products)

Branch of hepatic vein = located in the centre of each lobule to remove deoxygenated blood

Kupffer cells = ingest pathogens and other foreign particles helping protect against disease

Bile canaliculus = channel separate from sinusoids links to bile duct branches