14.1 Homeostasis in mammals (Body Temp)

Question 1

Homeostasis

Answer 1

ability of the body or a cell to seek and maintain a condition of equilibrium or stability within its internal environment when dealing with external changes. This is done by negative feedback

Question 2

Factors controlled in mammals in homeostasis

Answer 2

• core body temperature
• metabolic wastes (CO2 and urea)
• blood pH
• blood glucose concentration
• water potential of the blood
• the concentrations in the blood of respiratory gases (oxygen and CO2)

Question 3

Internal Environment

Answer 3

All conditions inside the body in which the cells function. For a cell, its immediate environment is the tissue fluid that surrounds it.

Question 4

Features of Tissue Fluid

Answer 4

• temperature – low temperatures slow down metabolic
  reactions; at high temperatures proteins, including
  enzymes, are denatured and cannot function
• water potential – if the water potential decreases, water may move out of cells by osmosis, causing metabolic reactions in the cell to slow or stop; if the water potential increases, water may enter the cell causing it to swell and maybe burst
• concentration of glucose – glucose is the fuel for
  respiration, so lack of it causes respiration to slow or
  stop, depriving the cell of an energy source; too much
  glucose may cause water to move out of the cell by
  osmosis, again disturbing the metabolism of the cell.

Question 5

Negative Feedback

Answer 5

A mechanism by which a change in a particular factor brings about an action that reverses the change

Question 6

What does negative feedback involve

Answer 6

• the detection of changes in the internal environment or external environment by receptors
• passing of information of these changes to a central control area
• the dissemination of this information to different parts of the body by coordination systems
• a response to the information by effectors (muscles and glands) to bring the changed feature back to its set point

Question 7

What coordination systems are involved in homeostasis?

Answer 7

1) The Nervous System - made up of brain, spinal chord, nerves
2) Endocrine System - made up of a number of endocrine glands which secrete hormones into blood

Question 8

Thermoregulation

Answer 8

the control of body temperature (37 degrees humans)
- involves both coordination systems – nervous and
endocrine.

Question 9

Thermoreceptors

Answer 9

Receptors that detect a change in temperature.

• the ones found in the hypothalamus in the brain detect change in core temperature
• the ones found in skin detect changes in external temperature - skin temperature is first to change

Question 10

When there is a change in surrounding temperatures, which part of the body changes temperature first?

Answer 10

The Skin.

• The skin temperature is the first to change if there is a change in the temperature of the surroundings.
• These skin receptors give an ‘early warning’ about a possible change in core temperature.

Question 11

When a DECREASE in environmental temperature is detected by skin receptors or the central thermoreceptors, the hypothalamus sends impulses that activate the following physiological responses:

Answer 11

1) Vasoconstriction
2) Shivering
3) Raising body hairs
4) Decreasing the production of sweat
5) Increasing the secretion of adrenaline

Question 12

Vasoconstriction

Answer 12

• muscles in the walls of arterioles that supply blood to capillaries near the skin surface contract.
• This narrows the lumens of the arterioles and reduces the supply of blood to the capillaries so that less heat is lost from the blood.

Question 13

Shivering

Answer 13

the involuntary contraction of skeletal muscles generates heat which is absorbed by the blood and carried around the rest of the body.

Question 14

Raising body hairs

Answer 14

– muscles at the base of hairs in the skin contract to increase the depth of fur so trapping air close to the skin.
- Air is a poor conductor of heat and therefore a good insulator. This is not much use in humans, but is highly effective for most mammals.

Question 15

Decreasing the production of sweat

Answer 15

this reduces the loss of heat by evaporation from the skin surface.

Question 16

Increasing the secretion of adrenaline

Answer 16

this hormone from the adrenal gland increases the rate of heat production in the liver.

Question 17

When an INCREASE in environmental temperature is detected by skin receptors or the central thermoreceptors, the hypothalamus sends impulses that activate the following physiological responses:

Answer 17

1) Vasodilation
2) Lowering Body Hairs
3) Increasing Sweat Production

Question 18

Vasodilation

Answer 18

the muscles in the arterioles in the skin relax, allowing more blood to flow through the capillaries so that heat is lost to the surroundings.

Question 19

Lowering Body Hairs

Answer 19

muscles attached to the hairs relax so they lie fat, reducing the depth of fur and the layer of insulation.

Question 20

Increasing Sweat Production

Answer 20

sweat glands increase the production of sweat which evaporates on the surface of the skin so removing heat from the body.

Question 21

What does the hypothalamus do when temperatures decrease gradually?

Answer 21

• the hypothalamus releases a hormone which activates the anterior pituitary gland to release thyroid stimulating hormone (TSH).
• TSH stimulates the thyroid gland to secrete the hormone thyroxine into the blood. Thyroxine increases metabolic rate, which increases heat production especially in the liver.
• When temperatures start to increase again, the
  hypothalamus responds by reducing the release of TSH by the anterior pituitary gland so less thyroxine is released from the thyroid gland.