7.3.1 - Homostasis

Question 1

What Is Homostatsis?
(2 Points)

Answer 1

~ Control systems that keep the internal environment of the body, within narrow limits.

~ The body is kept within a state of dynamic equilibrium.

Question 2

What Is Meant By A State Of Dynamic Equilibrium?

Answer 2

Where the internal environment of the body, is kept fluctuating around a specific normal level.

Question 3

Why Is Homostasis Important In Terms Of Temperature?
(3 Points)

Answer 3

~ Ensures the maintenance of optimal conditions for enzyme action and cell function.

~ If temperatures exceed 40°C, enzymes would begin to denature.

~ Meaning metabolic reactions are less efficient.

Question 4

Why Is Homostasis Important In Terms Of Blood Glucose?
(3 Points)

Answer 4

~ Cells need a constant supply of energy, in the form of ATP.

~ Glucose is respired to supply this ATP.

~ Cells in the pancreas need to monitor and control blood glucose concentrations.

Question 5

Why Is Homostasis Important In Terms Of Water?
(3 Points)

Answer 5

~ Water is essential to keep the body functioning, so the amount of water in the blood needs to remain constant.

~ Water is lost in urine and sweat.

~ Kidneys need to therefore monitor and regulate, water concentrations in the blood.

Question 6

What Is The Mechanism Called, Which Keeps A Constant Internal Temperature & What Does It Involve?
(2 Points)

Answer 6

~ Thermoregulation.

~ Involves both cooling and warming mechanisms.

Question 7

What Are The Cooling Mechanisms, Which Maintain Body Temperature?
(3 Points)

Answer 7

~ Vasodilation.

~ Sweating.

~ Flattening of hairs.

Question 8

Describe Vasodilation, As A Cooling Mechanism
(4 Points)

Answer 8

~ When its hot, arterioles near the surface of the skin dilate.

~ Therefore more blood flows through the capillaries, in the surface layers of the dermis.

~ Meaning more heat is lost from the skin, by radiation.

~ Lowering temperature.

Question 9

Describe Sweating, As A Cooling Mechanism
(3 Points)

Answer 9

~ When its hot, more sweat is secreted by sweat glands.

~ The water in the sweat evapourates from the surface of the skin, taking the heat from the body.

~ The skin is therefore cooled.

Question 10

Describe Flattening Of Hairs, As A Cooling Mechanism
(3 Points)

Answer 10

~ When its hot, the hair erector pili muscles in the skin relax, causing the hairs to lie flat.

~ Stopping them from forming an insulating layer of trapped air, allowing air to circulate over the skin.

~ Heat then leaves the skin via radiation.

Question 11

What Are The Warming Mechanisms, Which Maintain Body Temperature?
(5 Points)

Answer 11

~ Vasoconstriction.

~ Boosting metabolic rate.

~ Shivering.

~ Erection of hairs.

~ Less sweating.

Question 12

Describe Vasoconstriction, As A Warming Mechanism
(4 Points)

Answer 12

~ When its cold, arterioles near the surface of the skin contrict.

~ Therefore less blood flows through the capillaries, in the surface layers of the dermis.

~ Instead blood is diverted through shunt vessels, deeper in the skin.

~ Therefore heat is not lost through radiation.

Question 13

Describe Boosting Metabolic Rate, As A Warming Mechanism
(2 Points)

Answer 13

~ When it cold, the body releases adrenaline and thyroxine.

~ Increasing the basal metabolic rate (BMR), increasing heat production in the body.

Question 14

Describe Shivering, As A Warming Mechanism
(3 Points)

Answer 14

~ When its cold, muscles begin to contract in spasms.

~ Making the body shiver, therefore producing more heat, from increased respiration.

~ Warming the blood and raising the core body temperature.

Question 15

Describe Erection Of Hairs, As A Warming Mechanism
(3 Points)

Answer 15

~ When its cold, the hair erector pili muscles in the skin contract, causing the hairs to stand on end.

~ Forming an insulating layer of trapped air, stopping heat loss via radiation.

~ Warming the body.

Question 16

Describe Less Sweating, As A Warming Mechanism
(3 Points)

Answer 16

~ When its cold, less sweat is secreted by sweat glands.

~ Reducing the amount of heat loss via evapouration.

~ The skin is therefore warmed.

Question 17

What Are Themoreceptors?
(4 Points)

Answer 17

~ Found on the skin and mucous membranes.

~ They send impulses along sensory neurones to the hypothalamus.

~ The hypothalamus then sends impulses along motor neurones to effectors.

~ Effectors then restore body temperature back to normal.

Question 18

What Is The Normal Body Temperature?

Answer 18

37°C.

Question 19

Describe The Process Of Thermoregulation, When There Is An Increase In Body Temperature
(4 Points)

Answer 19

~ High temperatures are detected by thermoreceptors.

~ Hypothalamus then sends signals to effectors.

~ Cooling mechanisms occur.

~ More heat is lost and less heat is produced by the body.

Question 20

Describe The Process Of Thermoregulation, When There Is A Decrease In Body Temperature
(4 Points)

Answer 20

~ Low temperatures are detected by thermoreceptors.

~ Hypothalamus then sends signals to effectors.

~ Warming mechanisms occur.

~ More heat is produced and conserved by the body.

Question 21

What Is Negative Feedback?
(2 Points)

Answer 21

~ Keeps things around the normal level, body temperature is usally kept within 0.5°C above or below 37°C.

~ Negative feedback only works within certain limits, if the change is too big effectors may be unable to return temperature to the normal level.

Question 22

Describe The Negative Feedback Control Loop
(4 Points)

Answer 22

~ Receptors detect when a level is too high or too low.

~ A coordination systems transfers information between different parts of the body, either via the nervous or hormonal system.

~ An effector then carries out a response, bringing the level back to normal.

~ The factor which changes is continously monitored by receptors, so that it fluctuates around a ideal value.

Question 23

What Is Positive Feedback?

Answer 23

Amplifies an initial change.

Question 24

What Are Positive Feedback Loops?
(3 Points)

Answer 24

~ Are useful to quickly activate a process. E.g A blood clot after an injury.

~ Can also occur when homostatic mechanisms break down.

~ They do not maintain a constant internal environment, so are not involved within homostasis.

Question 25

How Can **Hormones Inside Cells**, **Alter Gene Transcription**? (2 Points)

Answer 25

~ Hormones which can cross the cell surface membrane, are able to enter the nucleus and bind to transcription factors present. ~ E.g. Steriod and thyroid hormones.

Question 26

How Can **Hormones Outside Cells**, **Alter Gene Transcription**? (4 Points)

Answer 26

~ These hormones (protein hormones) cannot cross the cell membrane, instead they bind to receptors in the cell membrane. ~ The binding, activates messenger molecules in the cytoplasm of the cell. ~ These messenger molecules activate enzymes, called protein kinases, which trigger a cascade inside the cell. ~ The cascade may result in changes to the activity of transcription factors, which may affect gene expression.

Question 27

What Is Meant By A **Cascade**?

Answer 27

A chain of reactions.