HOMEOSTASIS Flashcards
Homeostasis
Ability of an organism to maintain a constant internal environment
Negative Feedback
When a change to the normal initiates a response which reduces the effect of the change
Positive Feedback
change stimulates further change; can be dangerous if it is not natural; often associated with breakdown of control systems
Endotherms (warm blooded)
control their body temperature by physiological and behavioural means, thus keeping it constant
Ectotherms (cold blooded)
control their body temperature by behavioural means only, NO physiological cooling/heating mechanism, therefore usually Air Temperature = Body Temperature
Too Cold
When we are too cold, ‘heat gain’ centre in hypothalamus detects this via a receptor in the skin and inhibits the ‘heat loss’ centre, then the ‘heat gain’ centre sends nerve impulses to appropriate part of the body to do the following
Shivering: creates heat
Vasoconstriction: constriction of arteriole walls allows less heat in blood to be lost from skin
Making your hair stand on end: traps layer of insulating air
Increasing metabolic and respiration rate: achieved via hormones; respiration and metabolism releases heat
(REMEMBER: metabolic rate is measured by measuring the uptake of Oxygen or production of CO2)
Less blood flow to surface capillaries
Role of blood vessels in conserving heat
Vasoconstriction of arterioles
Therefore less radiation
Therefore less blood to the surface
Too Hot
When we are too hot, ‘heat loss’ centre in hypothalamus detects this due to a receptor in the skin via nervous impulses, and inhibits the ‘heat gain’ centre, then the ‘heat loss’ centre sends nerve impulses to appropriate part of the body to do the following
Sweating
Vasodilatation: dilation of arterioles, allowing heat in blood to be transferred to sweat
More blood flow to surface capillaries
Lowering of hairs causes less insulation
Decreasing metabolic rate and respiration rate
Why we produce heat during exercise
Respiration is carried out for muscular activity
However respiration is INEFFICIENT and therefore releases extra energy as heat
Why we get tired from exercise in hot conditions quicker than we do when it is cold
The heated conditions cause vasodilatation and cause more blood flow to the surface capillaries
This results in less blood flow to muscles requiring oxygen
Large mammals with small surface area to volume ratio will heat up a lot quicker than smaller animals as they have reduced heat loss through skin, therefore large animals will activate their ‘heat loss’ centre in hypothalamus a lot quicker than small mammals
As temperature increases, respiration rate increases in ECTOTHERMS, (in us it decreases), this is because
Increased temperature increases kinetic energy
Increased kinetic energy increases rate of reactions
More ATP is produced
Therefore more ATP used, therefore higher respiration rate required to remake lost ATP
Importance of maintaining a constant body temperature (i.e. importance of homeostasis)
If body temperature is too high, the excess heat denatures active sites of enzymes
Therefore substrate can no longer form a complex with it therefore reactions are ceased
If body temperature is too low, there is too little kinetic energy, therefore molecules move too slowly
Therefore few collisions and thus fewer enzyme-substrate complexes formed, therefore too slow reactions
Why the activity of Ectotherms that live in deserts varies so much
1) Their body temperature varies with that of environment
2) Temperature of desert fluctuates greatly
3) Metabolic reactions inside the Ectotherm are controlled by enzymes
4) Enzyme activity changes according to body temperature
5) Speed of bodily actions dependent on metabolic rate
6) Reptiles seek shade when hot and seek Sun when cool
Hyperglycaemia
too much glucose in blood, lowers water potential of blood and produces symptoms of thirst
Hypoglycaemia
too little glucose in blood, produce symptoms of dizziness, tiredness, etc. As the brain does not have glucose
Pancreas
Contains Islets of Langerhans that make two types of cells:
α-cells produce the hormone glucagon
β-cells produce the hormone insulin
Glycogenesis
the production of glycogen by the polymerisation of glucose
Glycogenolysis
the breakdown of glycogen to release glucose
Gluconeogenesis
the production of glucose from non-carbohydrate sources
If blood glucose levels too high
β-cells detect the rise and secret insulin (notice how the β-cells are the RECEPTORS and EFFECTORS.)( α-cells are inhibited)
Insulin fits into specific receptor proteins on membranes of cells
This causes extra glucose channels to open allowing glucose to enter cell via facilitated diffusion (this is done through the second messenger IRS) and allow it to become metabolised, in Liver cells, insulin causes IRS to activate glycogen synthase enzyme which causes glucose to be converted to glycogen (Glycogenesis)
Once glucose levels stabilise, β-cells reduce secretion of insulin
Type 1 Diabetes
body cannot make insulin; therefore glucose cannot pass from blood into cells, therefore starving the cells
Type 2 Diabetes
body does not make enough insulin or the receptors are not responding well to insulin, therefore glucose cannot be fully passed from blood into cells which is the job of the insulin
How diet and exercise may help maintain low glucose concentration in the blood of a type II diabetic person
Eat polysaccharides therefore slower digestion, therefore no surge in blood sugar level
Exercise increases respiration
If blood glucose levels too low
α-cells detect the low levels and secret glucagon
Glucagon fits into specific receptor proteins on membrane of cells that CONTAIN glycogen which are called liver cells
Glucagon activates an enzyme that converts glycogen to glucose (Glycogenolysis) and proteins/lipid to glucose (Gluconeogenesis), glucose can pass through cell membrane, therefore increasing glucose concentration of blood
Once glucose levels stabilise, α-cells reduce the secretion of glucagon
