homeostasis - glucose and temperature (chapter 5)

• is the body’s ability to maintain relatively stable internal environment (a steady state) even with an outside world that’s constantly changing • a dynamic state of equilibrium (36.7), but within the range of 36.5 - 37.5

• core body temperature • pH and concentration of dissolved substances in the body fluid • concentration of glucose in blood • concentration of O2 and CO2 in blood and other body fluids • blood pressure • concentration of metabolic wastes

• is a type of sensor that detect and monitors changes in the environment = the stimulus • they send information to the modulator/control centre along efferent pathway

• it determines the level at which the variable is to be maintained, analyses the information it receives and then determines the appropriate response

• carries out response - information flows from the modulator to effector via efferent pathway (motor neuron) • the results of the response feedback to stimuli (to increase or decrease) • most homeostatic control mechanisms are negative, used to shut off stimulus or reduce its intensity

thermoreceptors: • central: located in the hypothalamus and detects the temperature of internal environment • peripheral: located in skin and some mucous membranes - it detects temperature changes in external environment and sends this information to the hypothalamus • cold: are stimulated by temperatures lower than normal - when they are stimulated, the hypothalamus receives the info and initiates heat conservation and heat production • heat: are stimulated by temperatures higher than normal, when they are stimulated mechanisms operate to reduce heat production and increase heat loss

• body processes: metabolism (cellular respiration) and exercise • illness • stress/emotions • increased thyroxine levels • medications • heat gained from environment: conduction or radiation

• evaporation: water/liquid from skin and lungs • warm air breathed out • voiding of warm urine and faeces • decreases in secretions og adrenaline (from adrenal medulla) • radiation of body heat to the cooler surroundings • heat loss to environment (conduction and convection)

radiation: - transfer of heat from an object to another without direct contact - e.g. gain heat when sitting in sun/loss when in cold room convection: - flow of warm, less dense air upwards, which is replaced with cooler, more dense air. The faster the flow the faster the cooling - e.g. electric fan helps to move warm air from our skin to be replaced with cool air conduction: - heat transfer to another object through physical contact (energy passes from molecule to molecule in contact) - e.g. placing hand in warm water evaporation: - heat is removed from the body when liquid turns into vapour (which carried with it the heat) - e.g. sweating

• shivering: involuntary contractions of skeletal muscles (increased activity produces heat) • vasoconstriction: decreases heat loss to surroundings via radiation • increased metabolic rate: increased production of thyroxine • increased secretion of adrenalin • decreased surface area: curls into ball • behavioural: wear thicker clothes, take warm shower, sit in front of heater and increase in voluntary activity.

• sweating: increases heat loss by evaporative cooling • vasodilation: increases heat loss by radiation • decrease in metabolic rate: decreased production of thyroxine • increased surface area: spreading limbs out • behavioural: wear less clothing, taking a cold shower, sit in shade, fan yourself, reduction of voluntary movement

vasodilation: - the arterioles’ diameter thicken, increasing blood flow closer to the skin (though the arterioles don’t move closer to the skin) vasoconstriction: - the arterioles’ diameter thin out, decreasing the blood flow close to the skin

stimulus: - a decrease in body temperature receptors: - the central (cold) thermoreceptors in hypothalamus - the peripheral (cold) thermoreceptors in skin modulator: - hypothalamus (nerve impulse sent to peripheral blood vessels in skin) effectors: - muscles in the walls of skin arterioles response: - vasoconstriction (muscles constrict away from surface, less heat lost by radiation and convection) negative reaction: - an increase in body temperature

stimulus: - an increase in body temperature receptors: - the central (hot) thermoreceptors in hypothalamus - the peripheral (hot) thermoreceptors in skin modulator: - hypothalamus (nerve impulse sent to peripheral blood vessels in skin) effectors: - muscles in the walls of skin arterioles response: - vasodilation (arterioles dilate and are closer to surface, increasing heat loss through convection and radiation) negative reaction: - a decrease in body temperature

stimulus: - an increase in body temperature receptors: - the central (hot) thermoreceptors in hypothalamus - the peripheral (hot) thermoreceptors in skin modulator: - hypothalamus (nerve impulse sent to sweat glands) effectors: - sweat glands produce and secrete sweat onto surface of skin response: - sweating (layer of sweat on skin will evaporate removing heat energy from skin with it) negative response: - a decrease in body temperature

stimulus: - a decrease in body temperature receptors: - the central (cold) thermoreceptors in hypothalamus - the peripheral (cold) thermoreceptors in skin modulator: - hypothalamus (nerve impulse sent to skeletal muscles) effectors: - skeletal muscles response: - shivering (muscles rhythmically contract and relax which create energy and heat) negative response: - an increase in body temperature

nervous system: - skeletal muscles (sympathetic): contraction of muscles - shivering - heat generation - blood vessels (sympathetic): muscles of arteriole walls - vasoconstriction - reduced heat loss through radiation endocrine system: - adrenal medulla: secrete adrenaline and noradrenaline - increased metabolic rate - increase body temperature - anterior pituitary gland: secretes thyroid stimulating hormone - increased production of thyroxine - increase in metabolic rate - increased body temperature behavioural: - wear thicker clothes - sit in front of heater - take warm showers etc.

nervous system: - skeletal muscles (sympathetic): sweat glands - sweating - increase heat loss through evaporation - blood vessels (sympathetic): muscles of arteriole walls - vasodilation - increased heat loss through radiation endocrine system: - adrenal medulla: decreased secrete adrenaline and noradrenaline - decreased metabolic rate - decrease body temperature - anterior pituitary gland: decreased secretion of thyroid stimulating hormone - decreased production of thyroxine - decrease in metabolic rate - decreased body temperature behavioural: - wear less clothes - find shade - take cold showers etc.

• a.k.a goosebumps • is a physiological reaction in mammals, triggered by various stimuli (like cold temperatures or arousal) • is contraction of small muscles (erector pili) which are attached to hair follicles (make hair erect) • works in other mammals due to the amount of fur (it is effective to trap body temperature) • though humans have sparse hairs covering their bodies, so it is ineffective

• most simple form of sugar in the blood (a simple carbohydrate) • main source of energy for all cells • absorbed in the small intestines • after a meal blood glucose levels can spike • cells require energy for activities such as reproduction, movement and synthesising molecules

glucose + oxygen = carbon dioxide + water + ATP

• glucose is stored as glycogen • it is a complex carbohydrate • can store up to 500g: - 100g in the liver - 400g in the skeletal muscles

• glycogen stored in the liver is a short-term energy supply • provides glucose for the body’s use for 6 hours if no other means of supply is available • occurs between meals (to maintain blood sugar levels) • conversion is stimulated by hormone glucagon glucose - glycogen (after a spike of glucose), then glycogen - glucose (after a decrease of glucose)

• converts glucose to glycogen for storage • converts glycogen to glucose for release into blood • majority of its blood supply comes from the hepatic portal vein directly from the stomach, spleen, pancreas, small and large intestines. glucose may: - be removed from blood by liver to provide energy for liver functions - be removed by liver and/or muscles and converted into glycogen for storage - continue to circulate in blood, available for body cells to absorb and use as a source of energy (cellular respiration) - be converted into fat for long-term storage, it’s in excess of that is required to maintain normal blood sugar and tissue glycogen levels.