UNIT 5 BIOLOGY: HOMEOSTATIS

MAINTANENCE OF A CONSTANT INTERNAL ENVIRONMENT 

ENSURES BODY CELLS ARE IN AN ENVIROMENT WHERE THEY CAN FUCNTION PROPERLY AND EXTERNAL CHANGES DONT AFFECT THEM 

CONTINOUS FLUCTUATIONS BROUGHT ABOUT BY INTERNAL AND EXTERNAL FACTORS - TEMPERATURE PH AND WATER POTENTIAL - HOMESTATIS RETURN THESE BACK TO NORMAL AND SO MAINTAIN ORGANISMS BALANCED EQUILIBRIUM 

ENZYMES - SESNITIVE TO CHANGES IN PH AND TEMP - REDUCES EFFICENCY 

WATER POTENTIAL - CHANGES TO WATER POTENTIAL OF BLOOD AND TISSUE FLUID - CAUSES CELLS TO SHIRNK OR EXPAND - WATER LEAVING/ENETERING THROUGH OSMOSIS - CELL WONT FUNCTION PROPERLY 

ORANISMS WITH THE ABILITY TO MAINTAIN CONSTANT INTERNAL ENVIRONMENT ARE MORE INDEPENDENT OF THE EXTERNAL ENVIROMENT - WIDER GEOGRAPHICAL RANGE - GREATER CHANCE OF FINDING FOOD AND SHELTER - GREATER CHANCE OF SURVIVAL 

MAMMALS E.G. FOUND IN MOST CLIMATES 

• SET POINT - desired level
• RECEPTOR - picks up change from set point AND INFORMS THE.....
• CONTROLLER - coordinates info from receptors and sends instructions to an appropiate....
• EFFECTORT -  brings about changes needed to return system to set point, creating a....
• FEEDBACK LOOP - informs receptor of changes to the system 

METHODS OF GAINING HEAT:

• production of heat - metabolism of food during respiration 
• gain of heat from environment - by conduction (from ground), convection from air and radiation #

METHODS OF LOSING HEAT:

• evaporation of water - sweating 
• loss of heat to envionemnt - conduction convection and radiation  

mammals and birds - endotherms - gain heat from inside 

all others - ectotherms - gain heat from outside 

• EXPOSING THEMSELVES TO SUN - BASKING
• TAKING SHELTER 
• GAINING WARMTH FROM GROUND 
• GENERATING METABOLIC HEAT 
• COLOUR VARIATIONS - DARKER ATTRACTS MORE HEAT 

• VASCONTSRUCTION - diameter of arterioles near skin surface narrow, reduces volume of blood reaching the skin surface through the capillaries - less heat lost to enviro
• SHIVERING - produces metabolic heat 
• RAISING OF HAIRS - hair erector muscles contract - thick layer of still air gets trapped next to the skin - conserving heat 
• INCREASED METABOLIC RATE - more hormones that increase metabolism are produced - metabolic activity increases - more heat generated 
• DECREASE IN SWEATING
• BEHAVIOURAL MECHANISMS - shelter , huddling, basking 

• VASODILATION - diameter of arterioles near skin surface widen allwoing more blood to come to skin surface through capillaries - heat radiated away 
• INCREASED SWEATING 
• LOWERING OF BODY HAIR - hair erector muscles relax - less heat trapped
• BEHAVIOURAL MECHANISMS - sheltering, shade

BODY TEMP MAINTAINED BY HYPOTHALAMUS 

HYPOTHALAMUS RECIEVES INFO FROM INTERNAL AND EXTERNAL THERMORECEPTORS (SOME IN BLOOD SOME IN SKIN)

THERMORECEPTORS SEND IMPULSES ALONG SENSROY NEURONES TO HYPOTHALAMUS - WHICH SENDS IMPULSES ALONG MOTOR NEURONE TO EFFECTORS - MUSCLES AND GLANDS 

AUTONOMIC NERVOUS SYTEM - UNCONCIOUSLY 

2 PARTS - HEAT GAIN CENTRE, HEAT LOSS CENTRE 

• PRODUCED BY GLANDS
• CARRIED IN BLOOD PLASMA TO THE CELLS IN WHICH THEY ACT - TARGET CELLS - RECEPTORS ON CELL SURFACE COMPLIMENTARY TO HORMONE 
• ARE EFFECTIVE IN SMALL QUANTITIES 

SECOND MESSNEGER MODEL:

• hormone is first messenger, it binds to specific receptors on target cell - to form a hormone receptor complex
• the horm receptor complex activates an enzyme inside the cell that results in the production of a secondary messenger 
• second messenger causes a series of chemical changes that produce required resposne 

LARGE PALE GLAND SITUATED IN UPPER ABS BEHIND STOMACH 

PRODUCES ENZYMES FOR DIGESTION AND  HORMONES FOR REGULATING GLUCOSE

HORMAONAL SYSTEM CONTROLS BLOOD GLUCOSE USING TWO HORMONES INSULIN (B CELLS )AND GLUCAGON  (A CELLS)

BOTH OF WHICH SECRETED FROM A BUNDLE OF CELLS IN PANCREASE CALLED THE ISLETS OF LANERGHANS

IF BLOOD GLUCOSE LEVELS ARE TOO LOW - CELLS WILL BE DEPRIVED OF ENERGY AND DIE 

IF BLOOD GLUCOSE LEVELS ARE OO HIGH- IT LOWERS THE WATER POTENTIAL - CAUSE OSMOTIC ISSUES - DEHYDRATION

GLUCOSE COMES FROM 3 SOURCES: 

• diet
• breakdown of glycogen - glycogenolyisis
• from gluconeogenisis - production of new glucose - liver can make glucose form glycerol and amino acids 

B CELLS IN ISLETS OF LANGERHAN DETECT A RISE IN BLOOD GLUCOSE LEVEL AND RESPOND BY SECRETING INSULIN INTO BLOOD PLASMA 

INSULIN GLOBULAR PORTEIN 

WHEN INSULIN COMBINES WITH RECEPTORS :

• a change in tertiary structure of glucose transport protein channels - changes shape allowing more glucose into cells 
• increase in the number of carrier molecules in the cell surface membrane 
• activation of the enzymes that convert glucose to glycogen and fat 

BLOOD GLUCOSE IS LOWERED BY...

• increased uptake of glucos by cells
• incresing respiratory rate of cells - more uptake 
• increasing glycogeneis
• increasing the rate of conversion from glucose to fat 

A CELLS OF ISLATE OF LANGERHAN DETCT LEVELS OF BLOOD GLUCOSE FALLING AND SCRETE GLUCAGON DIRECTLY INTO THE BLOOD STREAM

ONLY CELLS OF LIVER HAVE RECEPTORS THAT BIND TO GLUCAGON - ONLY THEY RESPOND 

• activate enzyme that converts glycogen to glucose 
• increasing the conversion of amino acids and glycerol into glucose - gluconeogeneiss 

ADRENALINE ALSO INCREASES BLOOD GLUCOSE LEVEL =

• activates an enzyme that causes the breakdown of glycogen to glucose 
• inactivating enzymes that syntheisises gylcogen to glucose