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HomeostasisHomeostasis
Learning objectivesLearning objectivesThe human body needs to The human body needs to
maintain and regulate a maintain and regulate a steady state in order to steady state in order to function correctly function correctly
Homeostasis involves Homeostasis involves interactions between various interactions between various systems of the body systems of the body
Homeostasis Homeostasis ““the tendency of a system, esp. the the tendency of a system, esp. the
physiological system of higher animals, to physiological system of higher animals, to maintain internal stability, owing to the maintain internal stability, owing to the coordinated response of its parts to any coordinated response of its parts to any situation or stimulus tending to disturb its situation or stimulus tending to disturb its normal condition or function”normal condition or function” - - Dictionary.com Dictionary.com
Unabridged (v 1.1)Unabridged (v 1.1) ““The ability or tendency of an organism or The ability or tendency of an organism or
a cell to maintain internal equilibrium by a cell to maintain internal equilibrium by adjusting its physiological processes.” - adjusting its physiological processes.” - American Heritage Stedman's Medical DictionaryAmerican Heritage Stedman's Medical Dictionary
HomeostasisHomeostasisThere are several examples of There are several examples of
homeostasis and the processes involvedhomeostasis and the processes involvedWe have already looked at the We have already looked at the
reproductive hormones and how reproductive hormones and how oestrogen and LH are linked through oestrogen and LH are linked through NEGATIVE FEEDBACK NEGATIVE FEEDBACK – i.e. as one – i.e. as one gets more it causes the other to get lessgets more it causes the other to get less
Here are 3 more commonly used Here are 3 more commonly used examplesexamples
Temperature ControlTemperature ControlAlso known as Also known as THERMOREGULATIONTHERMOREGULATION The enzymes in our bodies work best at The enzymes in our bodies work best at
around 37around 37°C°Cwe need to be able to keep our bodies we need to be able to keep our bodies
as close to this temperature as possibleas close to this temperature as possibleThe body will react if it gets The body will react if it gets too hottoo hot or or
if it gets if it gets too coldtoo cold It will adjust the temperature back to It will adjust the temperature back to
where it should bewhere it should be
ThermoregulationThermoregulation
Involves receptors Involves receptors linked to the linked to the HYPOTHALAMUS HYPOTHALAMUS located in the brainlocated in the brain
Nerve impulses are Nerve impulses are sent from here to sent from here to the the SKINSKIN
Skin reacts to Skin reacts to change body change body temperaturetemperature
Too Hot…?Too Hot…?VASODILATIONVASODILATION – blood vessels near – blood vessels near
the skin get widerthe skin get widerThis allows more This allows more warm bloodwarm blood to flow to flow
near the surface and near the surface and lose heatlose heat, cooling , cooling you downyou down
Muscles controlling the hairs on your Muscles controlling the hairs on your skin skin relaxrelax – causing the hairs to lie – causing the hairs to lie flatflat
SweatSweat is secreted from sweat glands – is secreted from sweat glands – as it as it evaporatesevaporates, this cools you down, this cools you down
Too Hot…?Too Hot…?
Too Cold…?Too Cold…?VASOCONSTRICTIONVASOCONSTRICTION – blood – blood
vessels near the skin get smallervessels near the skin get smallerLessLess blood flows near the surface, blood flows near the surface,
keeping the heat keeping the heat closer to your closer to your body corebody core
Erector muscles Erector muscles contractcontract, pulling , pulling your hairs up on endyour hairs up on end
This traps This traps warmwarm airair close to your skin close to your skinSweat glands no longer secrete sweatSweat glands no longer secrete sweatShiveringShivering also helps to warm you up also helps to warm you up
– your muscles generate more heat – your muscles generate more heat through through respirationrespiration
Water ControlWater Control Also known as Also known as
OSMOREGULATIOOSMOREGULATIONN
Controlled by the Controlled by the hypothalamus hypothalamus using negative using negative feedbackfeedback
Involves the Involves the pituitarypituitary glandgland and the and the kidneyskidneys
Osmoregulation Osmoregulation Water is very important to the body, but Water is very important to the body, but
it must maintain the right amountit must maintain the right amount If there is a problem, it is spotted by If there is a problem, it is spotted by
OSMORECEPTORSOSMORECEPTORS in the in the hypothalamushypothalamus
A message is sent through nerve A message is sent through nerve impulses to the pituitary glandimpulses to the pituitary gland
This changes the amount of a particular This changes the amount of a particular hormone it releaseshormone it releases
The change in hormone level causes The change in hormone level causes the kidneys to reactthe kidneys to react
Not Enough Water..?Not Enough Water..?Hypothalamus signals the pituitary Hypothalamus signals the pituitary
glandglandPituitary increases its release of the Pituitary increases its release of the
hormone ADH (hormone ADH (ANTI-DIURETIC ANTI-DIURETIC HORMONEHORMONE))
More ADH enters kidney, stimulating it More ADH enters kidney, stimulating it to reabsorb more waterto reabsorb more water
Smaller amounts of Smaller amounts of more more concentratedconcentrated urine are produced urine are produced
OsmoregulationOsmoregulation
Too Much Water..?Too Much Water..?Hypothalamus signals the pituitary Hypothalamus signals the pituitary
glandglandPituitary slows down its release of Pituitary slows down its release of
the hormone ADH the hormone ADH Less ADH enters kidney, which then Less ADH enters kidney, which then
absorbs absorbs LESSLESS water waterMoreMore urine is produced urine is producedUrine is Urine is LESSLESS concentrated concentrated
Blood Sugar levelsBlood Sugar levelsWhen food is digested, sugar – When food is digested, sugar –
glucose – is producedglucose – is producedIt is important that blood sugar It is important that blood sugar
levels do not get too high – levels do not get too high – HYPERGLYCEMIAHYPERGLYCEMIA – or too low – – or too low – HYPOGLYCEMIAHYPOGLYCEMIA
It involves the hormone It involves the hormone INSULININSULIN
Too much glucoseToo much glucoseReceptors in the blood sense high levels Receptors in the blood sense high levels
of glucoseof glucoseNerve impulses sent to the Nerve impulses sent to the PANCREASPANCREAS Insulin is released into the bloodInsulin is released into the bloodTriggers an increase in glucose being Triggers an increase in glucose being
converted in converted in glycogen glycogen by the by the LIVERLIVERGlucose levels drop to normalGlucose levels drop to normal Insulin no longer produced and Insulin no longer produced and
degradesdegrades
Not Enough GlucoseNot Enough GlucoseReceptors in the blood sense Receptors in the blood sense low low
levelslevels of glucose of glucoseNerve impulses sent to the pancreasNerve impulses sent to the pancreas Insulin Insulin stopsstops being released into the being released into the
bloodbloodLessLess glucose is converted in glucose is converted in
glycogenglycogen by the liverby the liverLess glucose Less glucose absorbedabsorbed by the cells by the cellsGlucose levels return to normalGlucose levels return to normal
Glucose RegulationGlucose Regulation
Insulin crystals
Glucose RegulationGlucose Regulation People who cannot People who cannot
naturally control their naturally control their blood sugar levels blood sugar levels are called are called DIABETICDIABETIC
They must control They must control their blood sugar their blood sugar manuallymanually by by controlling their diet, controlling their diet, and by injecting and by injecting themselves regularly themselves regularly with insulinwith insulin