1 a Homeostasis and Negative Feedback Control

8/13/2019 1 a Homeostasis and Negative Feedback Control

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Homeostasis and negative

feedback control


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Advantages of HomeostasisHomeostasis has survival value because itmeans an animal can adapt to a changingenvironment. It can deal with the temperaturedifference you face when you step out yourfront door.

The body will attempt to maintain a norm, thedesired level of a factor to achievehomeostasis. However, it can only work withintolerable limits, where extreme conditions candisable the negative feedback mechanism

In these instances, death can result, unlessmedical treatment is executed to bring aboutthe natural occurrence of these feedbackmechanisms


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Negative Feedback Control

In animals such as ourselves, the internalenvironment of our bodies must have certainconditions within tolerable limits to continue thehealthy functioning of us.

This is done by a process called negativefeedback control, where various receptors andeffectors bring about a reaction to ensure thatsuch conditions remain favourable.

In this PowerPoint, we investigate the control ofblood sugar concentrations, waterconcentrations and temperature


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The principle of negative

feedback control is illustrated by

the diagram below


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This occurrence is known as physiologicalhomeostasis, translating in layman's terms to thephysical equilibrium. It is essentially a correctivemechanism, consider the following scenario in a person

The level of glucose in the bloodstream drops

The person requires glucose in cells to meet the demand forATP

The body detects this with a particular receptor designed forthis function

These receptors release hormones, chemical messagesthat initiate the start of the feedback mechanism

The hormones travel to their target tissue and initiate acorrective response

In this case, the corrective response is the secretion of moreglucose into the bloodstream


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Requirement of Negative

Feedback ControlBecause mammals are warm blooded, theenzymes that are part of their make-up as a warmblooded animal require a certain temperature tooperate optimally. Also, the water concentration

of a cell and its chemical concentration mustremain at a certain level to allow normal cellularprocesses to occur.

In light of this, the feedback mechanism in suchwarm blooded animals is essential in regards toallowing the body to work in optimal conditions -so any change in from the norm in temperature iscorrected by the feedback mechanism.


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Osmoregulation

Osmoregulation is the regulation of water

concentrations in the bloodstream,

effectively controlling the amount of water

available for cells to absorb.


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Osmoregulation

The homeostatic control of water is as follows

A change in water concentration leads to active via negativefeedback control

Osmoreceptors that are capable of detecting water concentrationare situated on the hypothalamus next to the circulatory system

The hypothalamus sends chemical messages to the pituitarygland next to it.

The pituitary gland secretes anti-diuretic hormone (ADH), whichtargets the kidney responsible for maintaining water levels.

When the hormone reaches its target tissue, it alters the tubulesof the kidney to become more / less permeable to water

If more water is required in the blood stream, high concentrationsof ADH make the tubules more permeable.

If less water is required in the blood stream, low concentrations ofADH make the tubules less permeable.


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Evolutionary Adaptations in Water

Regulation

Evolutionary adaptations that organisms haveachieved through natural selection.

Ways in which both animals and plants can bebetter adapted to cope with extremeenvironments (desert or wetlands).

These changes can be behavioural, structuralor physiological, and in some way promote

water regulation. Both plant and animal adaptations are

investigated


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Blood Sugar RegulationTwo hormones are responsible for

controlling the concentration of glucose in

the blood. These are insulin andglucagon. The diagram illustrates the

principle of negative feedback control in

action involving blood/sugar levels.


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Pancreas ReceptorsThe receptors of the pancreas are responsible formonitoring glucose levels in the blood, since it isimportant in every cell for respiration.

Two types of cell release two different hormones fromthe pancreas, insulin and glucagon. These hormonestarget the liver, one or the other depending on theglucose concentration

In cases where glucose levels increase, less glucagonand more insulin is released by the pancreas and targetsthe liver

In cases where glucose levels decrease, less insulin andmore glucagon is released by the pancreas and targetsthe liver


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The LiverThe liver acts as a storehouse for glycogen, thestorage form of glucose. When either of the abovehormones target the liver, the following occurs

Insulin- Insulin is released as a result of an increase inglucose levels, and therefore promotes the conversionof glucose into glycogen, where the excess glucosecan be stored for a later date in the liver

Glucagon- Glucagon is released as a result of andecrease in glucose levels, and therefore promotes theconversion of glycogen into glucose, where the lackglucose can be compensated for by the new supply of

glucose brought about from glycogen


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DiabetesDiabetes insipidus is a condition where excessurine is excreted caused by the sufferers inabilityto produce ADH and promote the retention of

water.

Diabetes Mellitus is another form of diabetes wherethe sufferer does not have the ability to producesufficient insulin, meaning that glucose cannot be

converted into glycogen. Anyone who has thiscondition usually has to take injections of insulinafter meals and snacks to maintain their storage ofglucose needed in emergencies.


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Fight or FlightIn emergencies, adrenaline is released by the bodyto override the homeostatic control of glucose.This is done to promote the breakdown of glycogen

into glucose to be used in the emergency. Theseemergencies are often known as 'fight or flightreactions'.

Adrenaline is secreted by the adrenal glands. The

secretion of it leads to increased metabolism,breathing and heart rate. Once the emergency isover, and adrenaline levels drop, the homeostaticcontrols are once again back in place


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Temperature in

HomeothermsAnimals capable of temperature

regulation within a given range are

deemed homeotherms (alternativelyhomiotherms or homotherms). They

have the ability to regulate

temperature via negative feedbackcontrol.Temperature is controlled in a

variety of ways in these animals.


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Temperature in

HomeothermsThe hypothalamus once again

acts as a receptor in regulation,

by detecting fluctuations intemperature. These receptors

are better known as

thermoreceptors.


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Temperature in

HomeothermsSkin also possesses

thermoreceptors which can

detect the temperature of theexternal environment. This

information is relayed to the

hypothalamus which can in turntransmit nerve pulses for

corrective mechanisms to occur


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Corrective Mechanisms

in Temperature ControlIncreased sweating is a

corrective response aimed to

reduce the temperature of theorganism.


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in Temperature Control Vasodilationis a corrective response

where the blood vessels close to theskin surface become more dilated,

meaning there is a larger surfacearea for heat to be lost to theexternal environment from the bloodvessel carrying over-heated blood.

Vasoconstrictionis the opposite ofthis and occurs when temperaturesin an organism drop. The bloodvessels become constricted so that

minimal heat loss occurs.


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in Temperature ControlThe hairs on your body also play animportant role in temperatureregulation.

A corrective response can occurwhere the hairs 'stand on end', andtrap a layer of air between the hairand the skin. This insulation ofwarmer air next to the skin reducesheat lost, while a thin layer ofinsulation would increase heat loss.


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in Temperature ControlOther corrective mechanisms

are involved, such as a drop in

metabolic rate and shiveringwhen temperatures drop.

Documents

1 a Homeostasis and Negative Feedback Control