Lecture 3 Homeostasis

Question 1

Define Homeostasis

Answer 1

Homeostasis is the maintenence of a constant internal environment

Question 2

Define Negative feedback control mechanism

Answer 2

This is when a deviation from a set point/norm value will result in effectors being activated to restore the set point value. (eg effectors being muscle or gland)

Question 3

Give an example of a negative feedback control mechanism

Answer 3

Control of core body temperature via thermoregulation

Question 4

Define positive feedback mechanism

Answer 4

An initial stimulus produces a response that exaggerates or enhances the change in the original conditions, rather than opposing it. I.e a deviation from the set point results in processes that enhance that deviation further from the norm

Question 5

Give an example of a positive feedback mechanism

Answer 5

Childbirth

Question 6

.What are the two different systems employed in homeostatic regulation

Answer 6

Autoregulation

Extrinsic regulation

Question 7

Define autoregulation

Answer 7

This describes local level, cellular/tissue level response to environmental change. Eg a change in the oxygen concentration will triger chemicals that widen/dilate blood vessels.

Question 8

List the three components of a homeostatic regulatory mechanism

Answer 8

• Receptor, detects environmental stimuli
• Control center, recieves and processes information
• Effector, a cell or organ which responds to commands from control centre

Question 9

Define extrinsic regulation

Answer 9

This involves nervous/endocrine control. For example, during exercise, the nervous system issues commands to increase heart rate so blood circulates faster.

Question 10

Why is homeostatic regulation important

Answer 10

Because it is important to prevent harmful changes in body tissue fluid composition.

Question 11

Define set point

Answer 11

This is a value at which a controlled variable should be maintained.

Question 12

Define negative feedback control

Answer 12

aims to maintain a controlled variable at its set point. Controlled variable is some aspect of the internal environment, like blood pressure or plasma

Question 13

Describe briefly the process of thermoregulation

Answer 13

The set point core body temperature is 37 degrees.
If temperature rises above core temp, receptors fire to the control centre.

Control centre fires to 2 target effectors.

1) Muscle tissue lining the walls of the blood vessels
2) sweat glands.

Blood vessels dilate to increase the skin surface blood flow.

Skin acts as a radiator by loosing heat to environment via sweat. Sweat evaporates.

As the set point for temp is restored, blood flow to skin returns to normal levels.

Question 14

Explain the two ways in which heat loss is achieved in the event of elevated core body temperature ( >37.2 degs)

Answer 14

Increased blood flow to skin surface via skin capillaries.

Increased sweating

Question 15

The control of body temperature can also be thought of as a thermostat. Describe this process

Answer 15

Set point = normal room temp
Stimulus = room temperature rises (deviation from sp)
Receptor = thermometer (detects change and sends info to control centre)

Control centre = Thermostat, sends commands to the effector to switch on

Effector = AC. unit, which turns on. effector then acts to lower the temp, and restore the room temp to within normal range.

Question 16

Give an example of an effector

Answer 16

muscle or gland

Question 17

Give an example of a receptor

Answer 17

Sensory receptor cells.

Question 18

Describe how blood pressure is regulated via homeostasis

Answer 18

Baroreceptors detect fall in blood pressure

baroreceptors fire impulses to the c.c via the Glossopharyngeal nerve in medulla oblogata.

Medulla fires to the heart and blood vessels via autonomic to increase cardiac output and vasoconstriction

Effectors = heart and blood vessels which increase blood pressure and vasoconstriction.

Question 19

State the name of the nerve that baroreceptors fire impulses along to the medulla oblongata

Answer 19

Glossopharyngeal nerve

Question 20

In control of blood pressure, the medulla oblongata fires impulses to the heart and blood vessels along which nerves

Answer 20

The autonomic nerves.

Question 21

Explain positive feedback mechanisms

Answer 21

This is where initial stimulus causes a response which continually reinforces itself.

Question 22

Give some examples of positive feedback mechanisms

Answer 22

Action potentials in nerves

Ovulation

Blood clotting.

Question 23

Explain how the process of clotting is a positive feedback mechanism

Answer 23

Damage to blood vessel causes

activation of clotting factors

causes activation of thrombin

causes formation of a blood clot

Question 24

Which type of response is the nervous system involved in

Answer 24

Rapid, short term effectst hat last seconds usually

Question 25

Which type of responses/effects is the endocrine system involved in

Answer 25

Long term effects, (minutes to days)

examples include growth and metabolism

Question 26

What are thyroid hormones involved in

Answer 26

Metabolism control

Question 27

What are the features of nerves from the autonomic nervous system

Answer 27

CNS has a preganglionic neuron
Peripheral ganglion is called a post ganglionic neuron,
These both fire to a target cell.