Biology - Chapter 9: Homeostasis & Hormonal control

What is the definition of homeostasis?

Homeostasis is the maintenance of a constant internal environment,

Internal environment?

Includes blood and tissue fluids that surround cells in the body.

Excludes lumen of the alimentary canal. (mouth to anus)

Why is homeostasis important?

1. Regulation of body temperature

2. Regulation of blood water potential

3. Regulation of blood glucose concentration

What happens when the body temperature is higher than normal?

As temperature increases above optimum temperature, enzhymes denature

Denatured enzhymes are premanently damaged and cannot catalyse chemical reactions anymore.

What happens when the body temperature is below normal?

As temperature decreases below optimum, enzymes become less active.

At freezing temperature, enzymes can be less active or inactive.

What would happen is the blood water potential is above normal?

1. when blood water potential is above normal than cytoplasms of tissue cells

2. Water molecules move out of tissue cells and into blood by osmosis. (From high water potential to lower water potential, down a water water potential gradient)

3. Tissue cells shrink and may become crenated

What happens when blood water potential is below normal?

1. Blood has lower water potential than cytoplasm of tissue cells

2. water molecules move out from blood into tissue cells by osmosis ( from high water potential to lower water potential ,down a water potential gradient)

3. Tissue cells swell and may burst

What does body temperature determine?

It determines the rate of chemical reactions catalysed by enzymes

What does the blood water potential determine?

It determines the proper functioning of tissue cells.

What does blood glucose concentration determine?

It determines the availability of glucose for cellular respiration

What happens when blood glucose concentration is low?

Low blood glucose concentration will result in insufficient glucose for cellular respiration.

Without glucose, cellular respiration cannot occur in tissue cells , hence insufficient energy will be provided for cells to perform their functions.

Organs may fail.

What happens when blood glucose concentration is lower than normal?

1. Insufficient glucose for cellular respiration.

2. Hence it cannot occur and

3. tissue cells will not have energy to perform their functions.

4. Organs may fail

What happens when blood glucose concentrations is higher than normal?

1. Water molecules will move out from tissue cells into blood by osmosis ( from higher water potential to lower water potential )

2. Tissue cells will shrink and become crenated

Name ALL 5 basic principles of homeostasis.

1. a normal levels

2. A stimulus which is a change in the environment away from the normal level

3. A receptor which is a nerve ending or an organ that can detect stimulus and transmit signals to control centre

4. A corrective mechanism which is a sequence of events to reverse the effects of stimulus

5. A negative feedback to reduce of stop the corrective mechanism as the condition returns to normal level

What are the parts of the skin involved in temperature regulation

1. thermoreceptors

2. skin arterioles, capillaries and shunt vessels

3. Sweat glands, sweat duct and sweat pore

What are thermoreceptors

Thermoreceptors are nerve endings

Where are thermoreceptors located at in the body?

1. Beneath the skin - to detect temperature changes in the external environment

2. In the hypothalamus - to detect temperature changes in the internal environment (blood)

What is the structure of an arteriole ?

Arterioles have a thick elastic muscular walll

What happens during vasoconstriction

1. lumen of arteriole becomes narrower

2. less blood can flow through arterioles

3. less blood will reach blood capillaries beneath skin

What happens during vasodilation

1. lumen of arteriole becomes wider

2. more blood can flow through arterioles

3. more blood will reach blood capillaries beneath skin

Where are skin capillaries

They are blood vessels that carry blood nearest to the skin surface

Why are skin capillaries placed nearest to the skin’s surface?

It is so that the skin can receive more blood - appearing red to provide more glucose to muscles to perform cellular respiration to provide more energy during/to

• vigorous muscular exercise

• consumption of hot food and drinks

• remain warm in a cold environment

How does the body release heat ?

Through metabolic activities (cellular respiration)

Where is most heat released in the body - by cellular respiration?

To all parts of the body, especially to muscles and liver

How the body loses heat

1. Through skin

2. Evaporation of water - from sweat on skin’s surface

3. In faeces and urine removed from the body

4. Exhaled air

Explain Thermoregulation - when the body’s temperature decreases below normal

• Stimulus: Body temperature decreases below normal

• Receptor: In skin and hypothalamus, detect decrease in body temperature then transmits signals to hypothalamus

• Control Centre: Hypothalamus is stimulated to begin the corrective mechanism

• Negative feedback - body temperature increases to normal

What types of corrective mechanism occur during thermoregulation when body’s temperature is below normal

1. Vasoconstriction of arterioles - less blood flow, less heat is lost through the skin,

2. Sweat glands become less active - less sweat is produced, less water evaporates from sweat, less heat is lost from evaporation of water in sweat

3. Metabollic rate increases - more heat is released within body

4. Shivering may occur - rapid contraftion and relaxation of skeletal muscles release more heat within the body

What is the definition of hormone?

A hormone is a chemical substance, produced in minute quantities by an endocrine gland. It is secreted directly into bloodstream and transported by blood to specific target organs where it exerts it effects. It is destroyed in liver and excreted from kidneys not in need.

What is the ductless gland?

Endocrine gland

What is the ducted gland?