Homeostasis Flashcards
Homeostasis
The maintenance of a constant internal environment
Importance of Homeostasis
Ensures that cells of the body are in an environment that meets their needs and allows them to function normally despite external changes.
Why is homeostasis important for enzymes?
pH and temperature sensitive -> reactions take place at a constant and predictable rate
Why is homeostasis important for water potential?
Water potential of the blood and tissue fluids may cause cells to shrink and expand due to osmosis.
What are the benefits of homeostasis for organisms?
Organisms are more independent of the external environment so have a wider geographical range.
The control of any self-regulation system involves a serious of stages that feature :
- Set point at which the system operates
- Receptor
- Controller coordinates information
- Effector
- Feedback loop, informs receptor of changes
Thermoregulation
Regulation of body temperature
Methods of gaining heat
- Production of heat -> metabolism of food during resp.
2. Gain of heat from environment (CCR)
Methods of losing heat
- Evaporation of water e.g. sweat
2. Loss of heat to environment (CCR)
Conduction
Transfer of energy through matter from particle to particle
Convection
Transfer of heat due to movement of warmed matter
Radiation
Transfer of heat through electromagnetic waves
Endotherms
Organisms that derive most of their heat from metabolic activities inside their body
Ectotherms
Organisms which obtain a large proportion of heat from sources outside the body
How do ectotherms control their body temperature?
- Exposing themselves to the sun
- Taking shelter
- Gaining warmth from the ground
- Generating metabolic heat
- Colour variations
Core body temperature of endotherms
35-44 C -> range is a compromise between having a higher temp. at which enzymes work more rapidly and the amount of energy needed to maintain that higher temperature.
Vasoconstriction
Diameter of the arterioles near the surface of the skin is made smaller. This reduces the volume of blood reaching the skin surface through the capillaries. Most blood passes beneath insulating layer of fat-> little heat loss
Response to cold environment
- Vasoconstriction
- Shivering
- Raising of hair
- Increased metabolic rate
- Decrease in sweating
- Behavioural mechanisms
Response to warm environment
- Vasodilation
- Increased sweating
- Lowering of body hair
- Behavioural mechanisms
How is hair raised?
Hair erector muscles in skin contract, raising hairs. This enables a thicker layer of still air, a good insulator, to be trapped next to skin, improving insulation and conserving heat in mammals with thick fur.
Two parts of thermoregulatory centre in hypothalamus
- Heat gain centre -> activated by a fall in blood temp.
2. Heat loss centre -> activated by rise in blood temp.
Thermoreceptors
In the hypothalamus + skin -> send impulses along the autonomic nervous system to the hypothalamus
Characteristics of Hormones
- Produced by glands which secrete hormone directly into blood
- Carried in the blood plasma to the cells on which they act -> target cells receptors on membrane that are complimentary
- Effective in very small quantities
Second Messenger Model
- The hormone is the first messenger, binding onto specific receptors on csm of target cells to form h-r complex
- H-r complex activates an enzyme inside the cell that results in prod, of a chemical that acts as a second messenger
- Second messenger causes a series of chemical changes that produce required response e.g. adrenaline -> glycogen to glucose
Pancreas
Large, pale-coloured gland that’s situated in the upper abdomen behind stomach
Islet of Langerhans
Hormone-producing cells consists of :
a cells -> larger and produce glucagon
b cells -> smaller and produce insulin
Sources of blood glucose
- Directly from diet
- From the breakdown of glycogen -> stored in the liver and muscle cells by glycogenesis
- Glucogenesis -> prod, of new glucose e.g. liver glycerol + amino acids
How is insulin secreted?
b cells of the islets of Langerhans in pancreas detect a rise in blood glucose level and respond by secreting insulin directly into blood plasma.
Insulin
Globular protein made of 51 amino acids
When insulin combines with glycoprotein receptors
- A change in tertiary structure of glucose transport protein channels, causing them to change shape and open, allowing more glucose into cell
- Increase in carrier molecules in csm
- Activation of enzymes that convert glucose to glycogen and fat
How is blood glucose level lowered?
- Increasing rate of absorption of glucose into cells
- Increasing respiratory rate of cells
- Increasing rate of conversion from glucose to glycogen in liver and muscle
- Increasing rate of conversion of glucose to fat
Glucagon
Only cells of the liver have receptors that bind to glucagon . They respond to fall in blood glucose by
- > activating an enzyme that converts glycogen to glucose
- > increasing conversion of amino acids and glycerol into glucose
Adrenaline raises the blood glucose level by:
- Activating an enzyme that causes breakdown of glycogen to glucose in liver
- inactivating an enzyme that synthesis glycogen from glucose
Diabetes
Chronic disease in which a person is unable to metabolise carbohydrate esp. glucose due to inability to control blood glucose levels from lack of insulin or loss of responsiveness
Type 1
Insulin dependant : may be result of autoimmune response against b cells of islets of Langerhans
Type 2
Insulin independent: Glycoprotein receptors on body cells lose responsiveness to insulin. Inadequate supply of insulin from pancreas. Usually over 40 and overweight.
Control of Type 1
Injections of insulin -> dosage should match glucose intake
blood glucose monitored by biosensors
Control of Type 2
Regulating intake of carbs in diet and matching this to amount of exercise. May be supplemented by insulin injection or by use of drugs that stimulate insulin prod. Other drugs slow down rate at which body absorbs glucose.
