Unit 3: Homeostasis Chapter 7: Maintaining an Internal Balance

Unit 3: Homeostasis Chapter 7: Maintaining an Internal Balance

• The body’s attempt to adjust to a fluctuating external environment.

• Body maintains a constant balance or steady state.

• The system of balance requires: constant monitoring and feedback about body conditions.

What is Homeostasis?

Homeostatic Control Systems

The system has three functional components:

1.A monitor

2.A coordinating center

1.A regulator

What are the functions?1. Monitor• Located in the organs and signals a

coordinating center when it detects an organ is working outside its normal limit

2. Coordinating Center• Relays information to the corresponding

regulator3. Regulator • Works to restore the normal balance

Section 7.1: Pages 334-337Section 7.1: Pages 334-337

An Example: When you exercise… Carbon dioxide levels increase and 1. Chemical receptors in the brain are stimulated

Monitor2. Nerve cells from the brain relay the message

via impulses to the organ Coordinating Center

3. Muscles increase the depth and rate of breathing which flushes the excess carbon dioxide Regulator



Homeostasis is often referred to as dynamic equilibrium.

• The homeostatic mechanism ensures that all body systems function within a tolerable range.

• This includes monitoring and regulating fluctuations in blood glucose, body temperature, blood pressure and blood pH.



Feedback LoopsThere are two types of feedback systems that exists

within the body:a) Negative Feedback System – mechanism that makes

adjustments to bring body back to acceptable range b) Positive Feedback – mechanism that perpetuates the

system and moves the controlled variable even further away from its steady state

Think…(-) = resisting change or compensating (+) = reinforcing the change


Negative Feedback SystemSuppose you like your house a certain temperature…


Positive Feedback System: The Birthing Process


Thermoregulation


Thermoregulation: This describes the body’s ability to maintain a temperature range where cells can function

Ectotherms• Ectotherms depend on air

temperature to regulate metabolic rate activity is partially dependant on environment

• Ectotherms – most fish, amphibians, and reptiles

Endotherms• Endotherms maintain a

constant body temperature regardless of the surrounding temperature

• They increase cellular respiration to compensate for heat loss

• Endotherms – mammals and birds

The Hypothalamus• It is the region of the

vertebrate brain that is responsible for numerous nerve and hormone functions

• The “thermostat”• An example of the

coordinating center in the homeostatic control system.


How to deal with stress:

the hot and cold kind

How to deal with stress:

Quick Review:Section 7.2: Pages 338-341Section 7.2: Pages 338-341

The Importance of Excreting Wastes


Getting Rid of Wastes• Average Canadian consumes more protein than

is required to maintain tissues and promote cell growth

• Excess protein Converted into carbohydrates

• The proteins contain nitrogen which has two hydrogens attached = toxic


DeaminationSection 7.3: Pages 342-345Section 7.3: Pages 342-345

AMINO ACID

Deamination: Flushing it OutSection 7.3: Pages 342-345Section 7.3: Pages 342-345

There are three types of waste products: ammonia, urea and uric acid.

Deamination of amino acids results in NH3 (a toxic, water-soluble gas)

Ammonia plus carbon dioxide results in urea which is 100,000 times less toxic than ammonia

An additional waste product results from the breakdown of nucleic acids, such as DNA uric acid

Water BalanceSection 7.3: Pages 342-345Section 7.3: Pages 342-345

•The kidney helps maintain water balance when water is lost due to urine, perspiration, increased physical activity and exhaled air

•They are also responsible for filtering wastes from the blood.

Excretion for the Simple and Complex

• In unicellular and primitive multicellular organisms, wastes are expelled directly into the environment and carried away by water

How do primitive organisms maintain fluid retention?

The contractile vacuole maintains osmostic balance by pumping water out of the cell


Excretion for the Multicellular Triple-layered organisms such as insects, worms and

mammals, cannot directly expel wastes because:- not every cell interacts with the environment- not every cell is designed to remove wastes (cell specialization)

Resolution?- wastes are transported to cells that are capable of

excretion and removed or stored by the excretory system


Any Questions?

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Unit 3: Homeostasis Chapter 7: Maintaining an Internal Balance