Topic 1: Introduction To Physiology

Question 1

What is Physiology?

Answer 1

Study of how the body functions.

Question 2

What is Homeostasis?

Answer 2

It is the ability ti maintain stable conditions in the internal environment (despite changes in the external environment)

Question 3

Conditions Controlled include (Homeostasis)

Answer 3

1) pH
2) Temperature
3) Blood Gases (CO2, O2)
4) Blood Pressure
5) Intracellular + extracellular fluid volumes
6) Etc.

Question 4

Homeostasis Information

Answer 4

• Cells can only survive within a narrow range of conditions - body conditions must be maintained within physiological limits
• Organ systems function together to maintain homeostasis
• Disease = failure to maintain homeostasis
• Nervous and/or endocrine systems control all other systems (control centres)
• They Act to:
  1) Maintain Homeostasis in a controlled manner e.g. pregnancy, growth, sudden fright

Question 5

Homeostatic Regulation

Answer 5

• Change in internal environment must be detected or anticipated
• Then nervous and/or endocrine system responds, altering systems responsible for that condition

Question 6

Types of NS/Endocrine Responses

Answer 6

1) Anticipatory Responses

2) Feedback Mechanisms

Question 7

Anticipatory Responses

Answer 7

E.g. Increasing respiratory rate at start of exercise –> proprioceptors (NS sensory receptors) signal movement before a change in internal conditions occurs (gases in blood)
- May also be learned or behavioural - E.g. put on coat

Question 8

Feedback Mechanisms

Answer 8

• Mechanisms that respond to a change in the system
• Consist of set points, receptors, control areas and effectors
• Set point = range of values of variable (e.g. body temperature) that does not bring about a response (Normal range)
• Variable is monitored by receptors –> info (input) fed back to control area (NS, endocrine gland) –> output to effector –> response

Question 9

Types of feedback

Answer 9

1) Negative Feedback

2) Positive Feedback

Question 10

Negative Feedback

Answer 10

• Most common homeostatic control mechanism
• Results of “output’ - variable moves back toward the set point i.e. in opposite (negative) direction to the change that triggered the response (“input”)

Question 11

Example of Negative Feedback

Answer 11

-Body temp. (= variable): set point = 36 - 37.8C.
- If increase in temp. (e.g. 40C)
- Hypothalamus thermostat cells (R) detect high temp. (stimulus) –>”input” Brain (NS) (Central area) –> “output” E= smooth muscle in blood vessels of skin relax (causing dilation) + sweat glands secrete sweat
- Results = core blood to skin surface and sweat evaporates
= increase heat loss and decrease temp. (opposite direction of stimulus)

Question 12

Second Example of Negative Feedback

Answer 12

Decrease in temp. –> shiver –> increase temp.

- Set point can change e.g. in fever

Question 13

Positive Feedback

Answer 13

• Less common - NOT homeostatic
• Output intensifies the input
• E.g. childbirth - labour
  uterine contractions –> NS –> Posterior Pituitary Gland (Releases)-> Oxytocin (hormone).
• Continues until endpoint (=baby born)