chapter 16 - homeostasis Flashcards
What is homeostasis
It is the maintenance of a constant internal environment via physiological control systems. [Has the ability to return changes to an optimum and maintain a balanced equilibrium].
How is homeostasis brought about
Stimulus - causes a change to the system
Receptor – a change is detected in a living system/a detection of deviation from optimum.
Coordinator/CNS – operational information is stored here [hypothalamus/brain reacts to and analyses information from the whole body]
Effector - brings about a change to the system back to optimum via a muscle or gland.
Response - system returns to the optimum point.
describe what happens when temperature is too high
Proteins/enzymes will denature. Higher temperatures cause hydrogen bonds that maintain the enzymes structure to break this alters the enzymes active site therefore catalysis can no longer occur.
Describe what happens when temperature is too low
If the temperature falls below the optimum enzyme activity declines as there is not enough kinetic energy. This causes the rate of important reactions for example respiration to slow down.
What happens if there are deviations from pH
Deviations from optimal pH causes enzymes to denature. catalysis can’t occur
What happens if there is a high blood glucose concentration
if blood glucose levels are above optimum the water potential of the blood is reduced. This causes water to defuse into the cells in the blood. this leaves other cells surrounding the blood to become flaccid and they die.
What happens if blood glucose concentration is too low
When blood glucose concentration is too low there is not sufficient glucose for respiration therefore respiration rate declines and energy levels fall.
Define negative feedback
when a change is detected control mechanisms are turned off to bring rates back to an optimum.
Define positive feedback
A deviation from the optimum causes an even greater deviation from the optimum and control mechanisms remain turned on.
What is an ectotherm
They obtain a high proportion of the body heat from outside sources
What is an endotherm
They obtain a large portion of their body heat from metabolic activities and inside sources
Give examples of regulation of body temperature in ectotherms
eg lizards:
They expose themselves to the sun so maximum surface area is exposed to the heat.
They take shelter in shade to prevent overheating and at night time they retreat into borrows to reduce heat loss.
They press the bodies against the ground to warm up. When optimum is reached they raise themselves above the ground with their legs.
Examples of regulation of body temperature in endotherms
eg penguin/ polar bear:
They have a small surface area to volume ratio. In cold climates they reduce heat loss. They have smaller extremities for example: small ears, thick fur, fat layers to insulate the body, feathers.
Vasoconstriction - the diameter of arterioles nearer the skin surface is smaller this reduces the volume of blood near the skin surface by the capillaries. Most blood passes through insulating for layers and this reduces heat loss.
Raising hairs - Erector muscles contract. this causes hairs to rise. a thick layer of still work is formed which insulates the skin.
decrease sweating to reduce heat loss
Behavioral mechanisms - Sheltering from wind, huddling, basking in the sun to maintain core body temperature.
Give examples of ways endotherms and ectotherms lose heat in response to a warm environment
A large surface area to volume ratio increases heat loss as there is an increase in surface area
Lighter colour fur reflects more light and absorbs less light increasing heat loss
Vasodilation - Diameter of the arterioles nearer the skin increases so blood can pass more closely to the skins surface via the capillaries. blood heat is radiated out of the body.
more sweating - water evaporation needs energy in the form of heat. (high latent heat of vaporization) provides cooling effect.
less body hair- erector muscles relax. hairs relax/ flatten, there is only a thin layer of still air therefore a thin insulating layer. This increases heat loss from the skin.
Behavioral mechanisms - Avoiding the heat, sheltering in borrows/shade, prevents body temperature from rising.
what is glycogenesis
Where excess glucose is converted to glycogen by the liver
what is glycogenolysis
where excess glycogen is converted to glucose in the liver
happens when blood glucose conc is low.
what is gluconeogenesis
The production of glucose from sources other than carbohydrates. eg amino acids and glycerol.
happens when blood glucose conc is low
define the second messenger model
When the binding of an extra cellular molecule to a receptor causes molecules inside the cell to transmit signals intracellularly.
What is the best way to remember glucagon function
glucagon = ‘glucose is gone’
Describe in detail glucagon action.
receptors on cell surface membrane of a cells in the islet of the langerhans(pancreas) detect a fall in blood glucose conc.
a cells secrete hormone glucagon.
glucagon attaches to receptors on target cells
stimulates adenylate cyclade to convert ATP to cAMP (cyclicAMP)
cAMP activates kinase to hydrolyse glycogen to glucose (glycogenolysis ) and it also stimulates glyconeogenesis.
give an example of positive feedback (neurons)
When a stimulus causes a small influx of sodium ions to increase permeability that is a father entry of sodium ions therefore a build up of an action potential.
Give an example of positive feedback
hyperthermia
When the body gets too cold the temperature control system breaks down leading to positive feedback resulting in body temperature dropping even further.
What do alpha cells in the islet of langerhans (pancreas) do?
They secrete glucagon and adrenaline
What do beta cells in the islet of langerhans (pancreas) do?
they secrete insulin
What does insulin do
It’s acts to lower blood glucose
it’s a peptide hormone.
What does glucagon do
It increases blood glucose
What does adrenaline do
It’s increases blood glucose
What do islet cells act as?
Chemoreceptors
Because they act as both receptors and effectors
Receptor-it detects a stimulus of any deviation from the optimum
Effector - it brings about the corrective measures needed to return the system to optimum
