Unit B4: Homeostasis

REVISION

UNIT B4: HOMEOSTASIS

Maintenance of a constant internal environment; Control systems;

Negative feedback; Function of cells

• Maintains Internal Temperature (37degrees)

< Heat stroke (Too hot)  - Rapid heart rate - Confusion - Dizziness - Increased Temperature - Increase in sweat leads to dehydration - Drink plenty of water

< Hypothermia (Too cold-35degrees) - Confusion - Violent Shivering - Weak pulse - Shallow breathing - Hairs stand up to trap heat - Warm blankets/drinks

• Maintains Water + Salt Levels - Maintained by Kidneys

< Gain water via food and drink - LOOSE water via sweating, faeces and urine

< Kidneys extract molecules from the blood, then restore the correct levels of salt and water back in to the body. The rest is excreted as urine.

< MORE dilute plasma, LESS ADH released-More dilute urine- Alcohol suppresses ADH - more dilute urine

< LESS dilute plasma (more concentrated), MORE ADH released -More concentrated urine- Ecstasy increases ADH production resulting in too much water in the body creating a more concentrated urine

• Receptors: Detect stimuli/Change in the environment - Nerve receptors
• Processing centre: Recieves information + co-ordinates response - Hypothalamus - Brain
• Effectors: Produce a response to the Stimulus - Muscles or glands

Central Nervous System helps to control homeostasis by detecting a stimulus, co-ordinating and producing a response

EXAMPLE:
STIMULUS: Room temperature decreases, Body temperature decreases
RESPONSE: Constriction of Blood vessels, Curling up, Shivering
RESULT: Heat production increases, Heat loss decreases, Body temperature regulates back to its optimum temperature of 37 degrees

Negative Feedback is the process in which changes are reversed inside the body. Negative feedback controls:

• Blood oxygen levels
• Salt levels
• Temperature

Examples of Negative Feedback:
Too Hot:
Vasodilation - Blood vessels become larger to lose heat/cool down
Sweating - Releases heat via excess water
Pilorelaxation - Hairs on skin flatten

Too Cold:
Vasoconstriction - Blood vessels become smaller to maintain heat
Shivering - Rapid, Involuntary muscle movement. Heat produced by respiration
Piloerection - Hairs on skin stand up

Cells depend on the movement of chemicals around the body via osmosis and diffusion:
Osmosis: type of diffusion with water
- Low concentration to high concentration through a partially permeable membrane

Diffusion: Spreading of particles
- High concentration to low concentration - "Moving down a concentration gradient"
- Diffusion in body = Digested food moves from gut to small intestine
- Diffusion in plants = Carbon dioxide moves from air spaces between mesophyll cells to the chloroplast

Enzymes:
- Work best at optimum temperature, maintained with Homeostasis
- If the temperature increases, so does the reaction rate (more collisions due to greater energy) Denature if too hot
- Active site of an enzyme is where the reaction occurs. Shape of Active site alters by pH and temperature
- Lock and key Model - Only molecules with the correct shape can fit into the enzyme - Only one type of enzyme can speed up a specific reaction