Chapter 22 - Homeostasis

Question 1

Define homeostasis

Answer 1

The maintainance of a constant internal environment in the body cells.

Question 2

Describe the principles of negative feedback in homeostasis.

Answer 2

• Receptor cells detect changes and send a message (chemical or hormonal) to the brain.
• The brain gives new instructions
• The effectors receives the instructions and does corrective actions to bring the factor back to normal.
• The receptor cells then sends a feedback to brain on corrective actions.
• A negative message received from the receptor to effector prevents corrective actions of going too far.

Question 3

Can ectothermic animals regulate body temperature? Give reason for your answers.

Answer 3

• They cannot generate heat from within the body.
• Relatively low metabolic rates. Metabolic rate generates insufficient heat
• Rely on a external energy source. (sun, hot rocks.)
• ecto - outside
• therm - heat
• Body temperature is directly proportional to external temperatures.

Question 4

Give examples of ectothermic animals.

Answer 4

• Fish
• Reptiles
• Amphibians
• Crustacean

Question 5

How do ectothermic animals regulate their body temperature if it is cold?

Answer 5

• In low temperature, they bask in the sun to absorb its radiant energy.
• Some reptiles has a black pigment melanin in cells.
• If these cells relax, the pigment becomes more visible.
• The skin becomes darker in color and more energy is absorbed.

Question 6

How do ectothermic animals regulate their body temperature when it is hot?

Answer 6

• The cells containing melanin contracts, the pigment becomes more concentrated and invisible.
• The skin becomes lighter and more heat is reflected.

Question 7

Name the 5 regulations performed by homeostasis

Answer 7

• 1. It is responsible for thermoregulation ( temperature )
• Body needs to be kept between 36 - 37.5 ºC.
• Enzymes denature when too high, and become inactive when too low

2. Water balance is kept at 67%, other wise consequences.
3. Glucose levels are maintained by homeostasis.
   - 90-100mg/100cm3 per drop of blood (0.1% of blood)
4. Blood pH
   - Kept around 7.4, enzymes may denature at variations
5. Oxygen and CO2 is regulated. Shortage of O2, lower metabolic rate, excess CO2 decreases pH of blood.

Question 8

State some typical behavioral patterns of an ectothermic animal in cold temperatures

Answer 8

• Basking in the sun
• Black pigment called melanin becomes more visible when the cells relax, absorbing more heat energy
• Therefore, solar energy is used to increase body temperature
• Hibernation in some seasons, where all body processes slow down

Question 9

What happens to ectothermic animals like lizards when temperatures are high?

Answer 9

The cells contract, and the melanin pigments become less visible. The skin becomes lighter, reflecting more heat.
These animals also avoid unfavorable conditions by hiding under rocks or flicking sand over their bodies.

Question 10

Explain the term Aestivation

Answer 10

A state of dormancy due to dry summer conditions, occurs in some reptiles and toads.

Question 11

Define the term endothermic

Answer 11

Heat is generated within the body by cellular respiration high metabolism, and muscular contractions. In this way, a constant body temperature is maintained.

Question 12

State the optimum temperature for enzyme activity in humans

Answer 12

37ºC

Question 13

How is heat generated within the human body?

Answer 13

• Cellular respiration
• Increase in thyroxine and adrenaline secretions cause faster metabolic rate, faster respiration and more heat
• Heat can be absorbed from the environment (sun, hot drinks)

Question 14

Name and explain the four processes by which the body loses heat

Answer 14

• Radiation: Heat lost from warm body to cold environment
• Evaporation: Fluids (sweat) absorb energy and evaporate
• Convection: Hot air heated in the body rises, making space for cold air
• Conduction: Heat lost from warm body to cold object

Question 15

Name the six mechanisms which control body heat in endoderms
(These are really easy to remember, so they will not be asked seperately. Read through them in the textbook if you really want to)

Answer 15

• Vasoconstriction
• Vasodilation
• Hairs
• Sweat glands
• Shivering
• Exercise

Question 16

Describe the role of the hyothalamus in temperature regulation in humansin cold conditions

Answer 16

• Temperature receptors in the hypothalamus detects change
• Heat gain centre sends impulse to increase metabolism by shivering
• Also sends impulses to arterioles to perform vasoconstriction
• Sends impulse for erector muscles to contract and raise hair

Question 17

Describe the role of the hyothalamus in temperature regulation in humansin hot conditions

Answer 17

• Temperature receptors in the hypothalamus detects change
• Heat gain centre sends impulse to decrease metabolic rate
• Also sends impulses to arterioles to perform vasodilation
• Sends impulse to sweat glands to produce more sweat

Question 18

Explain how hypothermia occurs

Answer 18

• During extreme cold temperatures, the core temperature may drop below 35ºC
• Homeostatic control unable to cope
• Drop in blood temperature slows metabolic rate
• Reduces kinetic energy in enzymes, causing them to become inactive

Question 19

Annietjie wants to visit Antartica for her 87th birthday. Suggest some ways in which Annietjie could protect her her ancient body from falling into hypothermia

Answer 19

• She could heat her home
• Warm clothes
• Avoid being exposed to cold temperatures
• Eat sufficient carbohydrates for energy

Question 20

Why is Annietjie, as an elderly person, more succeptible to hypothermia?

Answer 20

• Less active, lower metabolism
• Generates less body heat
• Do not always eat enough carbohydrates
• She can not afford adequate heating
• She can not afford adequate clothing

Question 21

Annietjie did not follow your suggestions. Now she has hypothermia. Her son Jaco is panicking. What could he do to save her?

Answer 21

• Wrap the person in blankets
• Supply a hot water bottle
• Warm nourishing drinks
• Hot drinks (only later)
• Avoid excessive movements
• Provide a warm sheltered place
• DO NOT GIVE HER ALCOHOL
• Do not rub her (gross)
• Talk to her to keep the old bat mentally active

Question 22

What can happen to a person if glucose levels are too low?

Answer 22

Faint, coma, fatal

Question 23

What can happen to a person if glucose levels are too high?

Answer 23

Water may be drawn out of cells by hypertonic solution. Kidneys excrete, dehydration, fatal

Question 24

What happens in the body when glucose levels are too high?

Answer 24

• Beta cells in islets of Langerhans in pancreas secrete insulin
• Stimulates cells to uptake glucose
• Bloodstream transports insulin to liver
• Liver instructed to convert excess glucose into glycogen
• Glycogen stored in liver and body cells
• Insulin can increase rate of respiration

Question 25

What happens in the body when glucose levels are too low?

Answer 25

- Alpha cells in islets of Langerhans in pancreas secrete glucagon - Bloodstream transports glucagon to liver - Liver instructed to convert glycogen into glucose - Adrenaline can also be secreted by adrenal glands to stimulate this conversion - Glucagon can decrease rate of respiration

Question 26

Can diabetes mellitus be cured?

Answer 26

No. It is an autoimmune condition in which the beta cells of the pancreas are destroyed by the body's own antibodies. They are not able to secrete insulin anymore. This condition can be controlled by daily insulin injections

Question 27

What does the treatment of diabetes mellitus involve?

Answer 27

- Daily insulin injections - Regular measurement of blood glucose levels - A change in diet

Question 28

State the effects of diabetes mellitus not being treated correctly

Answer 28

Coma, brain damage, death

Question 29

Name the symptoms of diabetes mellitus

Answer 29

- Extreme thirst - Weight loss - Undiminished hunger - Frequent urination with glucose in urine - Blurry vision

Question 30

Osmoregulation: low levels

Answer 30

- special osmo-receptors in hypothalamus detect change - blood becomes more concentrated - hypothalamus send impulses to post pituitary gland - post pituitary releases ADH - renal tubules become more permeable to water - tubules reabsorbs more water - smaller volume of urine produced - urine becomes more concentrated

Question 31

Osmoregulation: high levels

Answer 31

- special osmo-receptors in hypothalamus detect change - blood becomes more dilute - hypothalamus send impulses to post pituitary gland - post pituitary releases ADH - renal tubules becomes less permeable to water - tubules reabsorbs less water - larger volume of urine produced - urine becomes more dilute