What is the definition of homeostasis?
The maintenance involving physiological control systems that maintain the internal environment within restricted limits
What is the internal envirnoment of an organism?
It is made up of tissue fluid
What does the tissue fluid do?
Bathe each ce;;,supplying nutrients and removing wastes
Why is it importance to maintain this tissue fluid at optimum levels?
- Protects the cells from changes in eztenral environment, therby giving the organism a degree of independence
What does homeostasis involve?
Trying to maintain the chemical make-up, volume and other features of the blood and tissue fluid within restrictied limits
What does homeostasis ensure?
Cells of the body are in environment that meets their requirements and allows them to function normally despite external changes
(this does not mean that there are no changes)
What is homeostasis abiility?
There is continous fluctuation brought by the variation in internal and external conditions, such as changes in temperature, pH and water potential
This changes occur around optimum point
Its ability to reutnr to optimum point so maintain organisms in balanced equilibrium
The importance of homeostasis
What are enzymes?
- Control the biochemical reactions within a cell and other proteins
- e.g such as channel proteins are sensitive to changes in pH and temperature
What happens if there is any changes to the factors?
This will reduce the rate of enzyme
or
may even prevent them from working altogether
eg by denaturing them
even small fluctuations in temperature or pH can impair the ability of enzymes to carry out their roles effectively
Why is it important to maintain a fairly constant internal enivornment for enzymes?
So reactions can take place at a suitable rate
What happens if water potential changes?
- Changes of water potential of blood and tissue fluids may cause cells to shrink and expand(even to bursting point) as a result of water leaving or entering by osmosis
- In both instances - cells cannot operate normally
Why is maintaing water potential in organisms important?
- The maintenance of constant blood glucose concentration is essential for constant water potential
- Constant blood glucose concentration also ensures a reliable source of glucose for respiration by cells
Why is it important for organisms ability to maintain a constant internal environment?
- More independent of changes in external environment
- May have wider geographical range
- greater chance of finding food,shelter etc.
- These type of mammals are found in hot arid deserts to cold frozen polar regions e.g penguins
Series of control mechanisms
control of self-regulating system features
- Optimum point
- Receptor
- Coordinator
- Effector
- Feedback mechanisms
What is the first step of control mechanisms?
- Optimum point is the point at which system operates best, this is monitored by a receptor
What is the second step of control mechanisms?
- Receptor which detects any deviation from the optimum point (i.e. stimulus) and informs the coordinator
What is the third step of control mechanisms?
- Coordinator, which coordinates information from receptors and sends instructions to an approriate effector
What is the fourth step of control mechanisms?
- Effector, often a muscle/gland which brings about the changes needed to return the system to an optimum point
- This returns to a normality creates a feedback mechanism
What is the fifth step of control mechanisms?
- Feedbackmechanisms - by whcih a receptor responds to a stimulus created by change to the system brought along by the effector
What is negative feedback?
- Change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
When does positive feedback occur?
- When there is a deviation from an optimum causes changes in result in an even greater deviation from the normal one
What is an example of positive feedback?
- Stimulus leads to a small influx of sodium ions
- Influx increases the permeability of the neurone membrane of sodium ions
- More ions enter causing a further increase in permability and even more rapid entry of ions
- (stimulus brings about large and rapid response)
What can change in water potential also effect?
Concentration of enzxyme and substrates as well as rate of reaction
Why do control systems have many receptors and effectors?
- Allows them to have separate mechanisms that each produce a positive movement towards optimum
- Allows a greater degree of control of particular cotrol factor being regulated
What is a general feature of homeostasis?
- Seperate mechanisms that control depatures from different directions from original state
An example
Importance of information is provided by receptors is analysed by the coordinator before action is taken
- Temperature receptors in skin may signal that the skin itself is cold and the body temperature should be raised
- However, information from regions in the hypothalamus in brain indicate blood temperature is above normal
- May happen during strenous exercise when blood temperature rises but sweating cools down the skin
- Control centre must coordinate the action of effectors
- e.g sweatubg would be less effective in cooling the body if not accompaind by vasodilation
What are endotherms?
Animals such as birds and mammals derive most of their heat from metabolic activities that take place inside their bodies
What are ecotherms?
Some animals obtain an proportion of their heat from sources outside of their bodies namely the enivrionment
Why do ectoherm’s body temperature fluctuate with the environment?
Many ecotherms gain heat from the environment
How do ecotherms adapt to the environment?
Control body temperature by adapting their behaviour to changes in external temperature
How do ecotherms
exposing themselves to the Sun
- In order to gain heat lizards orienate themseleves so the maximum surface area of the body is exposed to the warning rays of the Sun
What are examples of ecotherms?
- Reptiles e.g lizards
How do ecotherms adapt by taking shelter?
- Lizards will shelter in the shade to prevent over-heating when the Sun’s radiation at peak
- At night they retreat into burrows in order to reduce heat loss when external temperature i slow
How do ecotherms adapt by gaining warmth from the ground?
Lizards will press their bodies against areas of hot ground to warm tehmselves up
When required temperature is reached, they raise themseleves off the ground on their legs
What do most endotherms gain most of their heat from?
- Internal metabolic activities
Do their body temperature stay the same despite fluctuates in the external environment?
Yes
What is the importance of mammals having small surface area to volume raito in cold climates?
- They tend to have a small low surface area to volume raito
- In warmer climates they have ears , thick fur or fat layers to insulate the body
How do mammals adapt in cold climates using vasoconstriction?
- The diamter of the arterioles near the surface of the skin is made smaller
- This reduces the volume of the blood reaching the skin surface through the capillaries
- Most blood entering the layers of fat and so loses lttle heat to the environment
How do mammals adapt in cold climates using shivering?
- The muscles of the body undergo involuntary rhythmic contractions that produce metabolic heat
How do mammals adapt in cold climates raising of hair?
The hair erector muscles in the skin contract, raising the hairs on the body
This enables a thicker layer of still air , which is a good insulator to be trapped next to skin , insulation and conversing heat in mammals with thick hair
How do mammals adapt in colder climate by having an increased metabolic rate?
- In cold conditions, more of the hormones that increase metabolic rate are produced
- Respiration is increased so more heat generated
How do mammals adapt in cold climates decreased sweating?
- Sweating is reduced
- or
- ceases altogether in cold conditions
How do mammals adapt in cold climates using behavioural mechanisms?
- Sheltering from the wind, basking in the sun and huddling altogether help animals to mantain core body temperature
How do mammals in hot climates adapt using vasodilation?
- The diameter of the arterioles near the surface of the skin become larger
- Allows warm blood to pass close to the skin surface through capillaries
- Heat from body is then radiated away from the body
How do mammals in hot climates adapt using increased sweating?
- To evaporate water from the skin surface requires energy in the form of heat
- In relatively hairless mammals e.g humans is an effective way of losing heat
- Mammals with fur, cooling achievged by evaporation of water from mouth and tongue during panting
- High specific latent vaporisation makes water sweating an effective way to lose heat
How do mammals in hot climates adapt lowering the body hair?
- The hair erector muscles in skin relax and elasticity of skin causes them to flatten against the body
- This reduces the thickness of the insulating layer and allows more heat to be lost to the environment when the internal temperature is higher than external
How do mammals in hot climates adapt using behavioural mechanisms?
- Avoiding the heat of the day by sheltering in burrows and seeking out shade to help to prevent the body temperature from rising
