Chapter 1: Communication

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Homeostatis Coordinating cell activities

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Homeostatis:Maintenance of a stable internal environment Factors: -Amount of water  (Osmosis)-Glucose (Affects respiration)-Temperature (Metabolism and denature)

Amount of water:Low temperature slows down metabolic reactionsHigh temperature can cause proteins to denature, causing damage to enzymes and to cell membrane.

Glucose:Lack of glucose = slow down respiration or halt. Cells has no energy source.Too much glucose = water can move out of cells by osmosis

TemperatureLow temperature = slow down metabolic reactionHigh temperature =  cause protein to denatureE.g. Cell membrane and enzymes.

Principles of homeostatis:The ability to control core temperature.Whatever temperature of he environment outside the body, the cells within it are kept at a temperature close to 37 degrees.

Why?:  To ensure that metabolic reactions are taking place inside the cells don't speed up or slow down due to external temperature changes

A negative feedback system requires a receptor and an effector and good communication between the two.

In control of temperature, the communication between effectors and receptors involves both the nervous and hormonal systemNervous system = Rapid, short-term effectsHormones = Slow, longer-term effects

On the other hand, there's positive feedback !Meaning:Positive feedback pushes a parameter further and further away from the norm, rather than keeping it constant.E.g. Person breathes in air with high concen. of carbon dioxide, producing high concen. of CO2 in blood and therefore increasing breathing rate.

Heat is conducted via:-Conduction-Convection-Radiation

Conduction: Heat passes from one particle to another if they are next to each other. The speed of transfer depends on how good the conductor is.

Convection:If a fluid (gas or liquid) such as air is warm, it becomes less dense so will rise through surrounding cooler air

Radiation:This is infrared radiation. All object emit infrared radiation. The hotter they are, the more they emit. This radiation travels in straight lines through the air, it is absorbed by solid objects in it path, warming them.Black objects absorb mostSilver surfaces reflect most

All mammals are able to generate heat within their bodies and so are said to be endothermic,Body temperature is controlled by ensuring a balance between heat input and outputIf external temperature rises above our internal, the only way to keep cool is via sweat.

Body temperature is determined by the balance between output and input

Input: -Generated by chemical reactions-Inside the body absorption of radiation from the sun or fire-Conduction from warmer substances


Output:-Radiation from the body-Conduction to colder substances-Conduction and convection in sweating.

Temperature receptorsThe hypothalamus receives information about temperature from other sources as well. The skin contains receptors that monitor the changes in skin temperature which is the first to change if there's  a change in enviromentHence, these peripheral (around the outside) receptors are able to give 'early' warnings about a possible change in temperature.

E.g  When you walk from a warm room into a cold one and 'feel cold' it is nerve impulses from these peripheral temperature receptors in your skin that you are responding to, Hence, no change in core temperature.

When core temperature might fall:-The hypothalamus sends electrical impulses along motor neurones (nerve cells) to some of the muscles and to the skin.-Nerve impulses causes muscles to contract and relax rapidly = shivering,-Cells respire, glucose is oxidised to release energy to make ATP.-Some of the energy is lost as heat, shivering therefore generates heat in the muscle.-Heat is then transferred into the blood as it passes through the muscles and then carried to the bloodstream (rest of the body)-Nerve impulses also affect the smooth muscle in the walls of arterioles that supply blood to capillaries near the skin surface.-The muscle contracts, narrowing the lumen of the arterioles and shutting off blood supply to the surface capillaries (Vasoconstriction)

Vasoconstriction: Ensures less heat is lost to the surrounding by radiation from the warm blood at the surface of the skin.-Sweat glands in the skin reduce their output of sweat-Erector muscles each attached to the base of a hair follicle, contract and pull the hairs up on end.Other mammals tend to increase the thickness of the layer of air trapped next to the skin. AAir is a poor conductor of heat and hence it insulates the body from changing temperature around it,we just get goosebumps

When core temperature might rise:The hypothalamus sends a different set of neurones. These impulses make all action just described but in the other way round-Arterioles supply blood to the skin now dilates as the smooth muscle in their wall relaxes, Vasodilation

Vasodilation: Allows more blood to flow close to the skin surface so that heat can radiate from it or be conducted with air. E.g. Pale skin turn pink in hot conditions-Sweat glands secrete more sweat-Plasma from the blood passing through the blood vessel that supply them is extracted in the sweat glands and passes up through the sweat ducts to skin surface.This liquid is mostly water but also contain main solutes in present in blood plasma (sodium ions, chloride ions and urea) As it lies on the surface of the skin, the water in it evaporates, water has a high latent heat of vaporisation and so it changes from liquid to gas, absorbing heat from skin

Behaviour can help too!We tend to wear fewer clothes on a hot day, we move into the shade . We drink iced drink and eat cool salads instead of hot food.

Hypothermia is a condition which the body temperature drops significantly below normal and the body can't regulate the temperatureCan be caused by extreme cold or people who are unwilling to spend money on heating.Hypothermia causes the body cells to slow down metabolic reactions and one who suffers it will feel sleepy and relaxed.Sugary drinks should not be given because the body won't be able to metabolise sugar if they're too cold.However, heart surgery needs the state of hypothermia. The heart will stop beating but yet slow down the metabolic rate of the cells, causing the person to still be alive. This avoids the use of a heart-lung machine to keep oxygenated blood moving to the body cells during the operation.

Mechanism for homeostatis: Negative feedback

How does it work?-Receptor monitors the factor that is being controlled-Effector causes an action that brings the factor back to normal

Animals that obtain heat from outside their bodies are known as ectotherms.They need lesser food then endotherms as they do use it to generate heat, they tend to be less active when they're in a cold environment because their cells are also at this cold temeperature and metabolic reactions take place slowly

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