Physiology

Question 1

What is a stem cell?

Answer 1

A stem cell is a cell that (1) is able to divide many times, making identical copies of itself; (2) is able to differentiate into other specialised cell types.

Question 2

What are the features of pluripotent and tissue restricted stem cells?

Answer 2

Pluripotent stem cells:
- Have unlimited ability to proliferate in vitro (in the lab)
- Can make all the cells in the body
Tissue restricted (adult) stem cells:
- Have restricted ability to proliferate in vitro
- Can make only one or a few specialized cell types

Question 3

Give examples of pluripotent stem cells.

Answer 3

(1) Embryonic stem cells

2) Induced pluripotent stem cells ( i.e. reprogrammed’ somatic cells

Question 4

Give examples of tissue restricted stem cells.

Answer 4

(1) Haematopoietic stem cell

(2) Intestinal stem cells

Question 5

What are the pros and cons of using human embryonic stem cells?

Answer 5

Pros:
- the stem cells are able to differentiate into cells of any type
- it is possible to produce disease-specific cells to study disease
Cons:
- ethical concerns
- clinical use may require immunosuppression to avoid rejection

Question 6

What are the pros and cons of using induced pluripotent stem cells?

Answer 6

Pros:
- Possibility of patient-specific stem cells
- Minimize the need for immunosuppression
- Does not require destruction of an embryo
Cons:
- Less economically viable than using embryonic stem cells

Question 7

What are the 4 main ways heat is lost from the body into the environment?

Answer 7

Radiation
Conduction: loss through physical contact with another object
Convection: loss by air moving over the body
Evaporation: loss by evaporation of sweat

Question 8

How does sweat cause heat loss?

Answer 8

Sweating by eccrine sweat glands is an important way of controlling body temperature. The cooling effect is due to the conversion of liquid water to water vapour.

Question 9

How does the body detect temperature?

Answer 9

Peripherally, the body has skin thermoreceptors.

Centrally, neurons in the pre-optic anterior hypothalamus are able to sense temperature.

Question 10

How does the body regulate body temperature?

Answer 10

The body detects temperature by peripheral thermoreceptors in the skin and centrally by neurons in the preoptic anterior hypothalamus. These detectors send this information about temperature to the hypothalamus, which activates a negative feedback mechanism. When temperature rises, heat loss mechanisms are stimulated. When temperature decreases, heat gain mechanisms are stimulated. This attempts to return the body temperature to the hypothalamic set point.

Question 11

What mechanisms does the body have to increase its temperature?

Answer 11

Skin: vasoconstriction of the arterioles in the skin, no sweating, contraction of erector pili muscles to raise hairs of the skin in an attempt to trap warm air around the body.
Skeletal muscle: shivering
Adrenal and thyroid glands: increase metabolic rate to generate heat
Behaviour: curl up, find shelter, put on a jumper

Question 12

What mechanisms does the body have to decrease its temperature?

Answer 12

Skin: vasodilation of arterioles in the skin, stimulation of sweating, relaxation of erector pili muscles.
Skeletal muscle: no shivering
Adrenal and thyroid glands: less secretion, decreased BMR –> less heat production
Behaviour: find shade, swim, remove clothes

Question 13

Which type of sweat gland is involved in temperature balance?

Answer 13

Eccrine sweat glands

Question 14

Define homeostasis.

Answer 14

Homeostasis is the tendency of an organism to regulate its internal environment, usually by a system of feedback controls, to stabilise its health and ability to function.

Question 15

Explain the function of enzymes.

Answer 15

Enzymes increase the speed of reactions by lowering activation energy.