12 Homeostasis Flashcards
Homeostasis ensures…
Cells in the body are in an environment that meets their needs and allows them to function properly.
Define homeostasis
the maintenance of a constant internal environment in an organism.
Homeostasis ensures enzymes can work by…
maintaining a constant pH and temperature
Homeostasis regulates water potential to ensure…
Cells don’t shrink or burst
Organisms with the ability to maintain a constant internal environment are…
more independent of the external environment therefore
have a wider geographical range
Five stages in a self-regulating system
Set-point Receptor Controller Effecter Feedback look
The set point is the…
desired level at week the system operates
The recepter
detects deviation from the set point
The controller
receives a signal about a change so it may send instructions to a effecter
the effecter
brings about changes needed to return the system to the set point
The feedback loop
informs the receptor of the changes to the system made by the effecter
Receiving information from a number of sources allows…
a better degree of control
If body temperature is too low…
the rate of enzyme-controlled reactions may be too slow
If the body temperature is too high
enzymes may be denatured and not function at all
The regulation of body temperature is…
thermoregulation
Methods of gaining heat…
production of heat
gain of heat from environment
Production of heat from…
metabolism of food during respiration
Gain heat from the environment by…
conduction
convection
radiation
Methods of losing heat
Evaporation of water…
Loss of heat to the environment
Evaporation of water to lose heat by
sweating
Loss of heat to the environment can occur by
Conduction
Convection
Radiation
Conduction:
Occurs in solids
Transfer of energy from particle to particle via kinetic energy
Convection
Occurs in fluids (gases and liquids)
Transfer of heat by the movement of the matter
Fluid expands + moves; carrying heat with it
Radiation
Transferred by electromagnetic waves
Ectotherm
an animal uses the environment to regulate its body temperature
Endotherm
an animal maintaining its body temperature by physiological mechanisms
An ectotherm’s body temperature will…
Fluctuate with the environment
Ectotherms control their body temperature by
adapting their behaviour to changes in the external temperature
Five ways an ectotherm might control their body temperature
Exposing themselves to the Sun Take shelter Gain warmth from ground Generate metabolic heat (minor) Colour variation
An endotherm’s body temperature…
remains reasonably constant despite changes in the external temperature
The temperature range of an endotherm is a compromise between..
Having a high temperature for enzymes to proceed faster
And the work needed to maintain the higher temperature
The smaller the surface area to volume ratio…
The easier it is to maintain a high body temperature
The higher the surface area to volume ratio
The harder it is to maintain a high body temperature
To make rapid changes in temperature, to warm up, 6 ways.
Vasoconstriction Shivering Raising of hair Increased metabolic rate Decrease in sweating Behavioural mechanisms
Rapid responses to lose heat (4)
Vasodilation
Increased sweating
Lowering body hair
Behavioural mechanisms
Vasoconstriction (3)
Diameter of arterioles near skin surface is made smaller.
Volume of blood reaching surface capillaries reduces.
Most blood therefore loses little heat to the environment
Raising of hair to increase body temperature (3)
Hair erector muscles in skin contract
Traps a layer of insulating air next to the skin
Lowering the temperature difference, reducing heat lost
Vasodilation (3)
Diameter of arterioles near skin surface increase
Warm blood passes close to skin surface capillaries
Heat from the blood is radiated away from the body
Lowering of body hair to reduce body temperature (3)
Hair erector muscles relax and hair flattens
Insulating air layer thickness is reduced
More heat is lost to the environment
Hypothalamus
The region of the brain that acts as the control centre for the autonomic nervous system and regulates body temperature/fluid balance
Autonomic nervous system
Part of the nervous system controlling muscles and glands that is not under voluntary control
The thermoregulatory centre of the hypothalamus has two parts…
Heat gain centre
Heat loss centre
Heat gain centre…
Activated by a fall in blood temperature
Controls mechanisms to increase body temperature
Heat loss centre…
Activated by a rise in blood temperature
Controls mechanisms to decrease body temperature
Two ways temperature is measured…
Hypothalamus monitors blood temperature
Skin thermoreceptors send impulses to hypothalamus
Two principle coordinating systems…
Nervous system (rapid) Hormonal system (slower)
Hormones are (3)
Produced by glands secreting into the blood
Carried in plasma to where they will act (target cells)
Effective in small quantities with widespread/longlasting effects
Second messenger model (5)
- Hormone is first messenger. Binds to specific receptors on membranes to form hormone-receptor complex.
- H-R complex activates an enzyme to produce a chemical for 2nd messenger.
- Second messenger causes chemical changes, producing response.
- For adrenaline, this is conversion of glycogen to glucose
Pancreas produces
Enzymes: protease, amylase, lipase
Hormones: insulin, glucagon
Groups of hormone producing cells in the pancreas
islets of Langerhans
Cells in islets of Langerhans, two types
alpha cells
beta cells
alpha cells of the islets of Langerhans;
larger and produce glucagon
beta cells of the islets of Langerhans
smaller and produce insulin
If blood glucose level falls too low…
cells will be deprived of energy and die, especially brain cells
If blood glucose levels are too high
The water potential of the cell is lowered
Causing osmotic problems that may result in dehydration
Three sources of blood glucose
Directly from the diet
From the breakdown of glycogen (glycogenolysis)
Gluconeogenesis
Glycogenolysis
splitting of glycogen into glucose
Gluconeogenesis
formation of new glucose from sources other than carbohydrates
Beta cells in the islets of Langerhans detect a rise in blood glucose levels and…
secrete insulin directly into the blood plasma
Insulin combines with glycoprotein receptors and… (3)
changes the tertiary structure of glucose transport proteins
increases the number of cell-surface carrier molecules
activates conversion of glucose into glycogen and fat
Changing the tertiary structure of glucose transport proteins…
causes them to change shape and open, allowing more glucose into the cells
Four ways blood glucose is lowered by insulin
- absorbed faster into cells especially muscles
- respiration rate increased
- conversion into glycogen (glycogenesis)
- conversion into fat
alpha cells in islets of Langerhans detect a fall in blood glucose,
secreting glucahon into the blood plasma
Glucagon binds to receptors in the…
liver
Liver cells respond to glucagon by.. (2)
- activating enzyme to concert glycogen into glucose
- increasing gluconeogeneis (conversion of amino acids and glycerol into glucose)
Adrenaline is produced by…
the adrenal glands in times of excitement/stress
Adrenaline raises the blood glucose level by (2)
- activating an enzyme that breaks glycogen into glucose in the liver
- inactivating an enzyme that synthesises glycogen from glucose
Insulin … the blood glucose level
lowerse
Glucagon … the blood glucose level
increases
A person affected by diabetes…
cannot metabolise carbohydrate (especially glucose) properly
Symptoms of diabetes (7)
high blood glucose, glucose in urine
increases thirst/hunger, need to urinate excessively
tiredness, weight loss, blurred vision
Type 1 diabetes is insulin…
dependent
Type 2 diabetes is insulin…
independent
Affect on cells in the liver with type 1 diabetes
Body’s immune system attacks the beta cells
In type 2 diabetes, (2)
glycoprotein receptors lose their responsiveness OR
there is an inadequate supply of insulin
Type 1 diabetes is controlled by
injections of insulin
Insulin must be injected as…
it is a protein and would be digested before it could be effective
