C29 - The Principles and Importance of Homeostasis Flashcards
What’s homeostasis?
The control and maintenance of an organism’s physiological conditions within narrow limits.
Why is the maintenance of a stable internal environment (homeostasis) important?
Optimum conditions for enzymes and proteins within the body are maintained.
The water potential of oxygen and tissue fluid is also kept within the correct range. This prevents cells shrinking due or expanding due to osmosis.
Organisms are not as dependent on the temperature of their external environment. This enables mammals and birds to inhabit a wider range of ecosystems, from arid deserts to cold polar environments.
What’s negative feedback?
A corrective mechanism (part of a control system) which allows only small fluctuations (e.g. of temperature, pH etc.) around a set point.
It inhibits the original stimulus.
What does a control system do?
(Homeostasis)
Detect changes in internal conditions and produce required responses to reverse the changes.
What features must a control system have?
A set point - the desired value which the negative feedback operates around.
Receptors - detect stimuli and deviations from the set point
Controller (communication pathway) - coordinates information from the receptors and sends instructions to the effectors. (Nervous and normal systems act as controllers)
Effectors - produce the changes required to return the system to the set point
Feedback loop - the return to the set point creates a feedback loop that informs the receptors of the changes to the system
What’s positive feedback?
A mechanism which enhances the original stimulus.
It’s used in action potential generation, blood clotting and child birth.
What are endotherms?
Organisms able to maintain a core body temperature (at 35-44°C).
What parts of the body are involved in thermoregulation?
Temperature-sensitive neurones (thermoreceptors) locates in the hypothalamus. (This part of the hypothalamus is called the thermoregulatory centre). - thermoreceptors detect changes in the temperature of blood flowing through the brain.
Peripheral temperature receptors located in skin and outer organs. - these thermoreceptors pass info to the hypothalamus. (This provides an early warning system).
The hypothalamus then sends nerve impulses to various effectors e.g. hair erector muscles, sweat glands, blood vessels etc. to reverse the detected change.
What happens when the body is too hot?
Once temperature is above a set point, the hypothalamus initiates a response via negative feedback.
Vasodilation allows blood to flow close to the surface of the skin, and heat is lost to the air by conduction and radiation.
Sweat glands secrete sweat, which evaporates from the skin.
Hairs lie flat, providing little insulation.
What happens when the body is too cold?
Once temperature is below a set point, the hypothalamus initiates a response via negative feedback.
Vasoconstriction shuts off blood supply to capillaries near skin surface.
Smooth muscle in the arterioles wall contracts, which narrows the arteriole lumen.
Less heat is lost from skin surface.
Hairs are pulled to vertical position by erector muscles to create air pockets and insulate the body.
When muscles receive nervous input from hypothalamus, they contract, generating heat from increased rate of respiration (shivering).
What’s a metabolic rate?
The rate at which biochemical reactions occur in cells.
Adjustments to metabolic rate can adapt body temperature.
What is thyroxine?
Where is it released?
The hormone that governs metabolic rate.
Thyroxine increases metabolic rate.
It’s secreted from the thyroid gland, situated in the neck.
What happens when a temperature decrease is detected (by the hypothalamus)?
The hypothalamus secretes thyrotropin-releasing hormone (TRH).
TRH stimulates production of thyrotropin (thyroid stimulating hormone TSH) from the anterior pituitary gland.
TSH is responsible for stimulating secretion of thyroxine.
Thyroxine passes into the nucleus of cells. It increases rate of transcription of several specific genes (e.g. for mitochondria production & respiratory enzymes).
Rate of respiration is increased, which increases heat production.
(This is a slow response).
What’s hypothermia?
Lowering of the body’s core temperature outside it’s normal range, below 35°C.
When this happens, metabolic reactions slow because molecules have less Ek.
This creates a positive feedback effect, so less metabolic heat is released, and this further reduces body temperature.
What are the causes of hypothermia?
Exposure to cold weather / immersion in cold water.
Fuel poverty (when a household would need to spend more than 10% of their household income on fuel to keep their home a satisfactory temperature).
