M8IQ1- Homeostasis - Coggle Diagram
Stimulus and Response Process
- stimulus: something happens to cause change in the environment.
- receptor: change is detected by a receptor (chemo, thermo, mechano, photo, noci, etc) in the body (which operate according to the certain conditions).
- control centre: the receptor sends a signal to the control centre - hypothalamus in brain (central nervous system- brain + spinal chord) once a deviation from the body's set level is detected. the info from the receptors is compared to the normal/expected level.
- effector: control centre sends signal to appropriate effector (whatever is involved in fixing the imbalance- muscles which will expand or contract, or glands which will secrete hormones).
- the nervous and endocrine system transfer info from brain to effector; info travels via electrical impulses along nerve cells in nervous system, and via chemical messengers (hormones in blood) in endocrine system.
- response: effector restores body to original state.
What is it?
- the process by which organisms maintain a relatively stable environment with the use of nerves and hormones.
- many reactions inside the body only work under certain conditions, regardless of a changing outside environment.
- body temp, water availability, blood glucose levels, carbon dioxide concentration.
- there is a range for acceptable deviation from certain conditions called 'tolerance limits'. inside these limits, reactions proceed as expected, but outside there will be negative consequences on the organisms's health.
- to maintain homeostasis, organisms need to detect stimuli from both their internal environment and from the external environment.
- conditions within the body must be maintained at a constant level in order to achieve optimal metabolic efficiency.
- any change reinforces itself by causing more change in the same direction; eg, a fire growing larger.
- always causes a system to grow out of control, or shrink away into nothing- never stability.
- the monitoring reinforces and amplifies the situation, causing more of the same situation to take place.
- any change in a system causes a shift in the opposite direction - reversal of stimulus.
- causes a system to maintain stability.
- eg: body temperature too low (stimulus), receptor notifies hypothalamus > start shivering (response), get warmer.
- all regulation responds to fluctuations around a set point.
- sensitivity of the receptor, tolerance of the central nervous system to variation from the set point, and efficiency of the effector determine the size of the fluctuations from the set point.
- a sensitive receptor with an efficient effector mean smaller fluctuations around the set point.
- the internal regulation of an animal's body temp.
- humans have a preferred body temp of 37 C (reactions within body work best).
- endotherms creat heat by adjusting processes in our bodies (physiological sources of heat) ecotherms rely on external sources of temperature to cool down or heat up.
Body Temp in Humans (NEG FEEDBACK LOOP)
- body temp can change due to environment, exercise, etc.
- 2 types of receptors:
- skin- detects external changes, triggered frequently, and hypothalamus- temp-sensitive cells, monitor internal temp by measuring blood temp.
- regulatory response is initiated after detection of temp change, which affects the amount of heat we generate or lose.
- hypothalamus is also control centre for thermoregulation, so receptors send signals there.
- hypothalamus sends impulses to activate physiological responses to re-achieve balance.
Response to Cold
- hypothalamus detects drop in temp
- piloerection: goosebumps trap air close to skin, preventing heat loss via convection of air.
- vasoconstriction: blood vessels constrict so less blood travels near skin surface.
- shivering: muscle cells perform respiration to break down glucose and make energy > respiration releases heat.
- increasing metabolism: endocrine system can be used to influence the production of heat via metabolism.
- thyroid-stimulating hormone: secreted by pituary gland, acts on thyroid gland to release thyroid hormones triiodothyronine (T3) and thyroxine (T4) which regulate metabolic processes.
- seeking shelter, putting on clothing, voluntary movement, etc.
Response to Heat
- vasodilation: blood loses heat
through external environment.
- sweating: draws heat from the
skin to evaporate sweat.
- decreasing metabolism:
hypothalamus reduces the rate
of cellular respiration in internal organs.
- decreasing activity, covering
body in water, swimming in cool water,
removing clothing, moving into shade.
- stomata allow water vapour to escape (transpiration). without a steady water supply, transpiration can lead to water loss > plant cells lose their turgor (cell pressure), wilt and die.
- plants can close stomata when necessary (usually midday, and leaving them open all other times > maximise photosynthesis, reduce water loss). (done by decreasing water in guard cells).
- waxy cuticle: provides waterproof barrier to reduce water loss. thicker the cuticle, better they are at reducing water loss.
- vacuoles: organelles which store large amounts of water.
- xerophyte adaptations: may have fewer stomata to reduce potential for water vapour evaporation, or drooping/hairy leaves which trap air around the stomata causing the air to become saturated with water vapour, creating a humid microclimate where water isn't pulled it of the plant that easily.
- hydrophyte adaptations:
- increased stomata: many help to optimise gas exchange.
- large and flat leaves: large surface area to volume ration promotes water loss.
- mesophytes: land plants which are adapted to neither particularly dry nor particularly wet environments (roses, corn).
- xerophytes; plants that are specifically adapted to survive in arid regions (eucalyptus trees, banksia, spinifex grass).
- hydrophytes: plants adapted to wet environments (water lily).
- halophytes: plants that can survive in salty environments (mangrove trees).
- osmosis is the movement of water from high to low water concentration, across a semipermeable membrane.
- in salty environments, water within the roots will be more likely to move out of the plant and into the soil, and it is harder for the plant to 'suck up' water from the soil.
- excess salt can be toxic to cells.
- salt exclusion: special tissues in the roots and lower stem stop salt from entering, but allow water uptake.
- salt excretion: plant actively concentrates salt and excretes it through special glands on the leaves. salt crystalises and can be blown or washed away.
- salt accumulation: plant deposits salt in older tissues, leaves are shed by plant.
Glucose in Humans
- 1. blood glucose level rises
- beta cells in pancreas release insulin into the blood > liver takes up glucose and stores it as glycogen or body cells take up glucose > blood glucose level declines.
- 2. blood glucose level falls
- alpha cells in pancreas release glucagon > liver breaks down glycogen and releases glucose > blood glucose level rises.
- both result in homeostasis (glucose levels 90mg/100ml)
Water Balance- Humans
- life cannot exist without water. all living cells are about 75% water.
- water is the solvent of life
- water is involved in life chemistry
- water is involved in diffusion and osmosis
- water is involved in temperature regulation
- water supports and cushions cells and organs.
- if the balance of water and solutes in cells is not maintained at an optimal concentration, water may move into cells causing them to burst (lysis- animal cells) or too much water may move out, causing cells to shrink (plasmolysis) and the cytoplasm to become too concentrated for normal cell functioning.
- in response to decreased water levels:
- nervous system triggers and facilitates the thirst reflex (also done by hormones)
- pituitary gland releases ADH to increase reabsorption of water in kidneys.
- in response to increased water levels: nervous system stops the release of ADH by the endocrine system.