B4 revision

Homeostasis

An accelerated revision resource

A.Blackford

WARNINGThis PowerPoint is not a substitute for active revision using notes, the workbook and revision guide.

You also need to do plenty of past papers to get exam practice.

Good luck!

What is Homeostasis?

• Homeostasis is keeping the conditions inside your body constant

• In reality this means maintaining these features within a narrow range

• Examples are body temperature, water and salt, nutrients like glucose, oxygen and removing waste.

Why is this important?

• Remember MRS. GREN?• Cells need to be looked

after to work well!

Movement

Respiration

Sensitivity

Growth

Reproducti

on

Excretion

Nutrition

Oxygen and glucose

Glucose and other nutrients

Caron dioxide and urea

Feedback Controls the Systems

• Incubator example• There is an OPTIMUM (best)

temperature.• If the temperature gets too high it

must be reduced.• If the temperature gets too low it must

be increased• This is NEGATIVE FEEDBACK• Two systems needed with opposite

results; ANTAGONISTIC EFFECTORS

Incubator feedback control• Key words; Receptor, Processing Centre,

Effector, Negative Feedback, Antagonistic Effectors

ReceptorTemperature sensor

Processing CentreThermostat

Effector AHeater OFF

ReceptorTemperature sensor

Processing CentreThermostat

Effector BHeater ON

Required Incubator temperature 370C

Fall in temperature Rise in temperature

Fall in temperatureRise in temperature

Too Hot, Too Cold?

• Human core temperature 370C• Hands /feet often cooler• Heat produced from respiration• Liver and muscle make loads of

heat• Body temperature varies in the day

– Lower when we sleep– Higher when we are awake, eat or

exercise

Just Right (1)!

• The HYPOTHALAMUS the processing centre for body temp, water balance. Sleep ++

• The cerebral hemispheres are where we can make a conscious decision to get warmer or cooler

Hypothalamus

Cerebral hemispheres

Just Right (2)!

• Temperature receptor nerves in the skin are the receptors

• The hypothalamus is the processing centre

• The sweat glands, blood capillaries and hair erector muscles are the effectors. When we shiver the muscles are effectors as well

Temperature control• Key words; Receptor, Processing Centre,

Effector, Negative Feedback, Antagonistic Effectors

ReceptorNerves in skin

Processing CentreHypothalamus

Effector AVasodilatation/sweat

ReceptorNerves in skin

Processing CentreHypothalamus

Effector BVasoconstriction

Required body temperature 370C

Fall in temperature Rise in temperature

Fall in temperatureRise in temperature

Cooling Down When its Hot

• The body must LOSE energy– Sweating; evaporation uses energy – Vasodilation; more blood goes to the

surface of the skin, we look red and energy is lost to the environment. You can draw a feedback diagram for this.

– Fans, cool drinks, swimming or shade can all help (remember the cerebral hemispheres?)

Heating Up When Cold

• Our body must RETAIN heat– Reduce sweating– Vasoconstriction; less blood flows to the

surface so less energy is lost– Erector muscles make our hair stand up to

trap an insulating layer of air (works better for animals!)

– Also drink warm liquids, put on more clothes etc

• We can also produce more energy to heat us up by SHIVERING

Dangerously Hot• Heat Stroke

– 420C – hot dry skin (sweating has stopped)– Rapid Pulse (dehydration, stress,

increased metabolic rate) – dizziness and confusion– Nerve cell damage to the brain

• Treatment• Sponge with water• Wrap in wet towel• Use a fan• Put ice into armpits and groin

Dangerously Cold• Hypothermia

– The old and very young are most at risk– Below 350C Shivering , confusion, drowsiness,

slurred speech loss of coordination, poor

judgement – 300C Coma– 280C breathing stops

• Treatment– Insulate the body esp head, neck armpits and groin– Handle gently to reduce blood flow to extremities– Use warm towels– Give warm drinks– DO NOT give alcohol, food or hot water bottles

Keeping our Water Balanced!• We need to maintain our internal

liquids at a steady concentration. This means balancing our water gain with our water loss. Outputs

Exhaled airSweatUrineFaeces

InputsWater in foodWater in drinkWater from respiration

We need to drink about 1.5 litres of water a day

Sweating a lot or drinking too little = small volumes dark yellow urine

In the cold or drinking a lot = lots of pale yellow urine

How the Kidneys Work

• Kidneys are made up of millions of nephrons. These do the business of cleaning our blood and regulating our water content.– Blood high pressure filtered– Small molecules into capsule– Useful moles reabsorbed– Water controlled by ADH– Urea and other waste into bladder

down the collecting duct

Our Water Balance

• Kidneys regulate salt and water• Caffeine and alcohol makes us

produce lots of dilute urine• Ecstasy reduces the amount of urine• ADH is a hormone and controls how

much water is absorbed back into the blood– More ADH;

• more water reabsorbed = a little conc urine

– Less ADH;• less water reabsorbed = lots of dilute urine

What are Enzymes?

• Enzymes are proteins produced by living cells

• They are biological catalysts• They (usually) increase the rate

of chemical reactions in a cell• Most work best at 370C (optimum

temperature)• They each have an optimum pH

How Enzymes Work 1

• Enzymes have a 3D shape• A particular area is called the ACTIVE

SITE (a 3D hole)• The SUBSTRATE fits into this (Lock and

Key)• There is a change in shape of the

enzyme and PRODUCTS are produced• Enzymes emerge unchanged from the

process ready to work again

How Enzymes Work 2The reverse is also true. Two substrate molecules can be linked by an enzyme

This is a 3D diagram of our old friend catalase. Notice that is made up of a ‘ribbon’ of amino acids joined together. (B5 protein synthesis)

Temperature and Enzymes

Low energy, less collisions, less energetic, low rate of reaction

Higher temperature, more kinetic energy rate increasing

Optimum temperature enzyme stable maximum rate of reaction Heat denaturing

enzyme. Protein irreversibly damaged rate slows

Enzyme denatured active site irreversibly damaged no substrate can enter NO reaction

pH and Enzymes

This enzyme has an optimum pH of 8

A higher pH also causes the proteins in the enzymes to denature and the enzyme to stop workin

Pepsin in the stomach has an optimum pH of 2 (digests proteins)

Trypsin in the small intestine has an optimum pH of 8 (digests protein)

Salivary amylase has an optimum pH of around 7 (digests cooked starch)

A pH lower than the optimum causes the proteins in the enzymes to denature

Diffusion

• Random movement of molecules from an area of HIGH concentration to an area of LOW concentration until evenly distributed Potassium

permanganate diffusing in water

Changing the Rate of Diffusion

• Remember diffusion is a PASSIVE process, it doesn’t need energy.

• Temperature changes the kinetic energy of the molecules (hotter – they move faster and collide harder)

• Concentration more molecules move in any particular direction

• Small molecules diffuse faster than large ones

Osmosis

• The diffusion of water• Always takes place through a partially

permeable membrane • Concentrated solutions have relatively

less water than dilute ones• Water always moves from HIGH water

to LOW water i.e from DILUTE to CONCENTRATED

• Also a PASSIVE process

More on Osmosis

• Can you explain what is going on in this diagram?

Partially permeable membrane small molecules (like water) go through larger ones do not

Water molecule

Sugar molecule

Even More on Osmosis

Animal Cells

Plant Cells

(Why don’t they burst?)

Same as outside

Dilute outside

Concentrated outside

Compared to cell contents

Active Transport

• This needs ENERGY from respiration in the form of ATP

• Molecules move from a LOW concentration to a HIGH concentration

• Special carrier proteins in the cell membrane are responsible Outside

the cell

Inside the cell

ATPEnergy

Diffusion, Osmosis and Active Transport

Diffusion Osmosis Active

TransportOxygen into the lungs

Moving water into and out of cells

The last bit of glucose from the gut into the blood

Carbon dioxide and other waste out of cells

Water into freshwater animals

Potassium into nerve cells