Homeostasis Flashcards
How can organisms limit the external changes to cells?
By maintaining a relatively constant internal environment for their cells.
HOMEOSTASIS
The maintenance of a constant internal environment in organisms.
What is the internal environment made up of?
Tissue fluids that bathe each cell, supplying nutrients and removing wastes.
Maintaining the features of this fluid at the optimum levels protects the cells from changes in the external environment, thereby giving the organism a degree of independence.
What does homeostasis involve and ensure?
Involves maintaining the chemical makeup, volume and other features of the blood and tissue fluid within restricted limits.
Ensures that the cells of the body are in an environment that meets their needs and allows them to function normally despite external changes.
Why is homeostasis essential for the proper functioning of organisms?
- The enzymes that control the biochemical reactions within cells, and other proteins, such as channel proteins, are sensitive to changes in pH. Any changes to these factors reduces the efficiency of enzymes or may even prevent them working altogether, eg denaturing them. Even the smallest fluctuations in temperature or pH can impair the ability of enzymes to carry out their roles effectively.
- Changes to the water potential of the blood and tissue fluids may cause cells to shrink and expand as a result of water leaving or entering by osmosis. In both instances the cells cannot operate normally. The maintenance of constant blood glucose conc. is essential in ensuring a constant water potential. A constant blood glucose conc. also ensures a reliable source for resp. by cells.
- Organisms with the ability to maintain a constant internal environment are more independent of the external environment. Have wider geographical range and therefore greater chance of finding food, shelter, etc.
What does maintaining a constant internal environment mean?
Reactions take place at a constant and predictable rate.
What are the series of stages of control of a self regulating system?
THE SET POINT: which is desired level at which system operates.
RECEPTOR: which detects any deviation from the set point and informs the…
CONTROLLER: which coordinates information from various receptors and sends instructions to an appropriate…
EFFECTOR: which brings about the changes needed to return the system to the set point. This return to normality creates a…
FEEDBACK LOOP: which informs the receptor of the changes to the system brought about by the effector.
How are control mechanisms coordinated?
Systems normally have many receptors and effectors. It is important to ensure that the information provided by receptors is analysed by the control centre before action is taken. Receiving information from a number of sources allows a better degree of control.
Example of how control mechanisms are coordinated?
Temperature receptors in the skin may signal that the skin itself is cold and that the body temperature should be raised. However, information from the temperature centre in the brain may indicate that blood temperature is already above normal.
This situation could arise during strenuous exercise when the blood temperature rises but sweat cools the skin.
By analysing info from all detectors, the brain can decide the best course of action.
What else must the control centre do?
Coordinate action of the effectors so that they operate harmoniously.
E.g. sweating would be less effective in cooling the body if it were not accompanied by vasodilation.
Why must body temperature be regulated?
If too low- rate at which enzyme controlled reactions take place may be too slow for the organism to function properly.
If too high- Enzymes may be denatured and the organism may cease to function altogether.
What are two methods of gaining heat?
- Production of heat by the metabolism of food during respiration.
- Gain of heat from the environment by conduction (e.g. from ground), convection (e.g. from surrounding air or water) and radiation.
What are two methods of losing heat?
- Evaporation of water (e.g. during sweating)
- Loss of heat to the environment by conduction (e.g. to the ground), convection (e.g. to the surrounding air or water) and radiation.
CONDUCTION
Occurs mainly in solids and is the transfer of energy through matter from particle to particle. Heat causes the particles to vibrate and gain kinetic energy. These particles cause adjacent particles to vibrate and so the kinetic energy is transferred through the material.
CONVECTION
Occurs in fluids (gases and liquids) and is the transfer of heat as a result of the movement of the warmed matter itself. The heat causes the fluid to expand and move, carrying with it the heat that it has absorbed.
RADIATION
Energy transferred by electromagnetic waves. When these waves hit an object they normally heat up.
ECTOTHERMS
Gain most of their heat from the environment, so their body temperature fluctuates with that of the environment.
How do ectotherms control their body temperature?
By adapting their behaviour to changes in the external temperature.
Give an example of an ectotherm and explain why it cannot warm up by exercising.
Reptiles- e.g. lizards cannot warm up by exercising because, if their body temperature is low, they cannot respire fast enough to provide the energy for rapid movement.
What methods can ectotherms use to control their body temperature?
- EXPOSING THEMSELVES TO THE SUN. In order to gain heat lizards orientate themselves so that the maximum surface area of their body is exposed to the warming rays of the sun.
- TAKING SHELTER. Lizards will shelter in the shade to prevent over-heating when the Sun’s radiation is at its peak. At night they retreat into burrows in order to reduce heat loss when the external temperature is low.
- GAINING HEAT FROM THE GROUND. Lizards will press their bodies against areas of hot ground to warm themselves up. When the required temperature is reached, they raise themselves off the ground on their legs.
- GENERATING METABOLIC HEAT. Although not the main source of heat, respiration still provides a proportion of a lizard’s body heat.
- COLOUR VARIATIONS. Darker colours absorb more heat while lighter colours reflect more heat. Lizards in colder environments are generally darker in colour that those in warmer areas.
How do endotherms regulate their temperature?
Gain most of their heat from internal metabolic activities. Their body temperature remains relatively constant despite fluctuations in the external temperature.
Use behaviour to maintain a constant body temperature.
Shelter from cold wind or hot sunshine.
Curl up when its cold and spread out more when it is hot.
Also use a wide range of physiological mechanisms to regulate temperature.
What is the core body temperature of endotherms?
35-44C
This range is a compromise between having a temperature at which enzymes work more rapidly and the amount of energy needed to maintain that higher temperature.
What are the short term adaptations that mammals and birds in cold climates have evolved to have in order to survive?
-Body with a small surface area to volume ratio.
Within volume that heat is produced and from surface area that heat is lost.
Small SA:vol means the easier it is to maintain a high body temperature.
Mammals in cold climates are therefore relatively large, they also have smaller extremities, such as ears, and thick fur or fat layers for insulation.
Some of these features can be varied over a period of time, e.g. more fat in winter.
How do mammals make rapid changes to body temperature? (6)
VASOCONSTRICTION: The diameter of arterioles near the surface of the skin made smaller. This reduces the volume of blood reaching the skin surface through capillaries. Most of the blood entering the skin therefore passes beneath the insulating layer of fat and so loses little heat to environment.
SHIVERING: The muscles of the body undergo involuntary rhythmic contractions that produce metabolic heat.
RAISING OF HEAT: The hair erector muscles in the skin contract, thus raising the hairs on the body. This enables a thicker layer of still air, which is a good insulator, to be trapped next to the skin, thus improving insulation and conserving heat in mammals with thick fur.
INCREASED METABOLIC RATE: In cold conditions more of the hormones that increase metabolic rate are produced. As a result metabolic activity, including respiration, is increased and so more heat is generated.
DECREASE IN SWEATING: Sweating is reduced, or ceases altogether in cold conditions.
BEHAVIOURAL MECHANISMS: Sheltering from the wind, basking in the sun and huddling together all help animals to maintain their core body temperature.
What are long term adaptations to life in a warm climate?
Large SA:volume ratio (large extremities, such as ears)
Lighter coloured fur to reflect heat.
What are the rapid responses that enable heat to be lost when environmental temperature is high?
VASODILATION: The diameter of the arterioles near the surface of the skin becomes larger. This allows warm blood to pass close to the skin surface through the capillaries. The heat from this blood is then radiated away from the body.
INCREASED SWEATING: To evaporate water from the skin surface requires energy in the form of heat. In relatively hairless mammals, such as humans, sweating is highly effective means of losing heat. In mammals with fur, cooling is achieved by the evaporation of water from the mouth and tongue, which occurs when air is rapidly passed over these surfaces during panting.
LOWERING BODY HAIR: The hair erector muscles in the skin relax and the elasticity of the 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 the external temperature.
BEHAVIOURAL MECHANISMS: Avoiding the heat of the day by sheltering in burrows and seeking out shade help to prevent the body temperature from rising.
What are the two parts of the thermoregulatory centre in the hypothalamus?
- Heat gain centre- which is activated by a fall in blood temperature. This controls the mechanisms that increase body temperature.
- Heat loss centre- which is activated by a rise in blood temperature. This controls the mechanisms that decrease body temperature.
How is temperature regulation an example of homeostasis? (steps)
STIMULUS: a change in body temperature
Detected by RECEPTORS: Thermoreceptors
which pass the information to a
COORDINATOR: Hypothalamus in the brain, which then causes an EFFECTOR: the skin to produce the appropraiate RESPONSE: increase or decrease in core temperature.
HYPOTHALAMUS
Region of the brain adjoining the pituitary gland that acts as a control centre for the autonomic nervous system and regulates body temperature and fluid balance.
Describe the regulation of body temperature.
The hypothalamus monitors the temperature of the blood passing through it. In addition the thermoreceptors in the skin measure skin temperature. These thermoreceptors send impulses along the autonomic nervous system to the hypothalamus. They provide information on the environmental temperature and so give advanced warning of potential changes in the core body temperature. The animal can therefore take measure to conserve or lose heat as appropriate, before core temperature is affected.
The two sets of thermoreceptors (in the hypothalamus and the skin) interact to control temperature.
Of the two it is the core temperature, as measured in the blood passing through the hypothalamus, which is most important.
How does problems with the thyroid cause inability to regulate body temperature?
An overactive thyroid can cause a person to become too hot whereas an under active thyroid can cause people to become too cold.
The thyroid produces hormones that are able to influence how much blood vessels dilate, which in turn affects how much heat can escape from the body.
What is the regulation of blood glucose an example of?
How different hormones interact in achieving homeostasis.
What characteristics do hormones have in common?
- produced by glands, which secrete the hormone directly into the blood (endocrine glands).
- Carried in the blood plasma to the cells on which they act- known as target cells- which have receptors on their cell-surface membranes that are complementary to the hormone.
- are effective in very small quantities, but often have widespread and long-lasting effects.
How does the second messenger model of hormone action work?
- The hormone is the first messenger. It binds to specific receptors on the cell-surface membrane of target cells to form a hormone-receptor complex.
- The hormone-receptor complex thus produced activates an enzyme inside the cell that results in the production of a chemical that acts as a second messenger.
- The second messenger causes a series of chemical changes that produce the required response. In the case of adrenaline, this response is the conversion of glycogen to glucose.
PANCREAS
Large, pale coloured gland that is situated in the upper abdomen, behind the stomach.