Organisms response - Homeostasis

What is homeostasis?

The ability to maintain a relatively stable internal environment in an ever-changing outside world

Why is homeostasis important?

It maintains the conditions needed for enzymes to function at their optimum in order for bodily functions to be carried out

List examples of factors controlled by homeostasis.

- Core body temp

- Metabolic waste

- Blood pH

- Blood glucose

- Water potential of blood

- Respiratory gas concentration in blood

What are the systems in mammals that information for maintaining homeostasis are managed in?

- Endocrine system

- Nervous system

What is the endocrine system?

A collection of glands that produce hormones

What are the glands in the endocrine system?

Pituitary, thyroid, adrenal, ovaries/testes, pancreas

What is the difference between endocrine and exocrine glands?

- Endocrine - only hormone producing

- Exocrine - hormone producing glands that also produce non-hormone secretions e.g. pancreas

What cells do hormones target?

They target cells with receptors that are complimentary. They will not work on other cells

What make the endocrine glands well adapted?

- Good blood supply so hormones can easily enter blood stream

- Hormones only target cells with the right receptors

List the general qualities of hormones.

- Small molecules

- Have very specific shapes

- Secreted by endocrine glands

- Transported in blood in low concentrations

- Have widespread, slower affect

- Secreted fast

- Affects target cells

- Short life span in the body

Why is it important that hormones have a short life span in the body?

Because otherwise they would continue their action which would take the factor away from the optimum in the opposite direction

Understand the main differences between hormones and nervous responses.

See booklet page 72

How do the majority of homeostatic control mechanisms work?

They use negative feedback

What is negative feedback?

A response to a change in the body that counteracts or opposes the initial change (in either direction)

Describe how negative feedback works.

1. Receptor detects stimulus that is out of normal range or nearing this point

2. A coordination system transfers information between different parts of the body

3. An effector carries out a response

4. The response is monitored by receptors continuously to ensure it remains around the normal range

5. If the stimulus nears the other end of the range, another response will be initiated

What is a coordination system?

- Nervous system

- Endocrine system

Graph to show negative feedback.

What is positive feedback?

Feedback that can only initiate change in one direction

What is an example of positive feedback.

A nervous impulse. This is because an action potential can only depolarise a membrane, not anything else. It is only able to initiate change in one direction whereas negative feedback can cause something to increase or decrease depending on its current state

Why is negative feedback better than positive feedback for homeostasis?

The existence of separate mechanisms gives a greater degree of control because the body is able to return something to normal range regardless of the direction it has moved in e.g. if body temp goes to high it can be lowered and vice versa whereas positive feedback would only be able to lower the temperature continuously, not raise it if need be (control of both sides of the range)

Why is it very important to maintain a stable level of pH and temperature?

Otherwise, enzymes in cells would denature

How do low temperatures affect homeostasis?

- Molecules move slower

- Lower frequency of successful collisions

- Less ES complex formed

- Less likely for there to be energy for bonds to be broken or formed

How do high temperatures effect homeostasis?

- Molecules move faster

- Higher frequency of successful collisions

- More ES complex formed

- More likely for there to be energy for bonds to be broken or formed

BUT IF TOO HIGH...

- Bonds in the enzyme molecule begin to break and active site thus changes

- Enzyme denatured

What temperature is the human body usually at and why?

37 degrees as this is the opt temp for enzymes

What mechanisms does the body use to lower temperture?

- Vasodilation

- Sweating

- Relaxing of hair muscle

What mechanisms does the body use to raise temperature?

- Vasoconstriction

- Shivering

- Contraction of hair muscle (goosebumps)

- Adrenaline secreted

How does adrenaline increase body temperature?

It increases rate of metabolism and therefore heat production

Describe how vasodilation and constriction can raise and lower temperature.

- Dilate - arterioles relax so increased blood flow in capillaries to allow heat to be removed

- Constrict - arterioles contract so capillaries have reduced blood flow. Less heat lost by convection

What does the hypothalamus do?

Detect changes in pH and temperature and initiates response

Why do humans temperature vary throughout the day?

Increase as a result of physical activity and decrease when asleep

What does ectothermic animal mean?

Body temperature is regulated by the external environment

Describe ectothermic reptiles.

- No internal control of body temperature

- Internal temperature depends on external temperature

- Activity level depends on external temp

- Generate little of their own heat

- Have variable metabolic rate

- Behaviour changes as a result of temperature

What does endothermic mean for animals?

Body temperature is internally regulated

Describe endothermic mammals.

- Internal body temp controlled by homeostasis

- Internal temp less affected by external temp

- Activity levels are independent from external temp

- Have a consonantly high metabolic rate

How does pH away from the optimum effect homeostasis?

- Bonds in the enzyme molecule begin to break due to excess of H+ or OH- ions

- Tertiary structure changes so active site changes

- Enzyme denatured

What can indicate a bodily enzymes optimum pH?

Its location in the body, e.g. if it like acidic conditions it may be in the stomach

How does homeostasis control pH?

- There are pH buffers in the blood

- Respiratory regulation

How does respiratory regulation control pH?

If levels of CO2 become too high then carbonic acid can be made. If this is detected, a higher breathing rate and heart rate will be initiated causing O2 to be taken in and the CO2 to be removed