Control & Regulation

Control & Regulation

Physiological Homeostasis

Mr G David

son

Saturday, April 22, 2023 G Davidson 2

Physiological Homeostasis We like to keep our living conditions

stable, e.g. in Autumn, we turn up the heating.

In some countries, in summer, air conditioning is used.

The aim is to keep indoors at the same temperature all the time.


Physiological Homeostasis Physiological homeostasis is the

process of maintaining a steady state in the body so cells can function effectively.

Our bodies automatically maintain a steady state.


Physiological Homeostasis In order to do this, there must be

detectors which detect any changes in state as well as a means of altering it.

Most systems work on a negative feedback basis.


General negative feedback system

Detected by8.

Control centres9.

Detected by3.

Control centres4.

Normal conditions6.

Normal conditions1.

Cause of Change2.

Cause of Change7.

Corrective mechanism5.

Corrective mechanism5.


OsmoregulationThis is the process of the body

maintaining the water, salt and iron levels at a proper level.

Should these levels alter they are detected by the osmoreceptors in the hypothalamus in the brain.


OsmoregulationThis stimulated the pituitary gland

into either releasing more or less ADH (anti-diuretic hormone).

The ADH takes effect in the kidneys and either more or less water is reabsorbed by the kidneys.


Osmoregulation

Osmoreceptors

Pituitary gland

Osmoreceptors

Pituitary gland

Normal conditions

Normal conditions

Increase in water

concentration of blood

Decrease in water

concentration of blood

Less water

reabsorbed into blood

More water

reabsorbed into blood


Control of blood sugar levelsThe blood sugar level is controlled in

the same way as the water concentration.

If too much glucose is found in the blood, the cells in the Islets of Langerhans in the pancreas, produce the hormone insulin.


Control of blood sugar levelsThis hormone is transported to the

liver where it brings about the conversion of glucose to glycogen, which is then stored in the liver.

If there is not enough glucose in the blood, the cells in the islets of Langerhans detect this and release another hormone glucagon.


Control of blood sugar levelsThis hormone is transported to the

liver where it brings about the conversion of glycogen back to glucose.

In emergencies, the adrenal glands produce adrenaline which overrides the process in order to release glucose for energy to deal with the emergency.


Mammalian body temperature

We are endotherms (warm blooded).

This means we can keep our body temperature constant, regardless of the external environment.



We have various methods at our disposal for achieving this, e.g. move into or out of the sun, change behaviour, put on or remove clothes, open windows, turn up heaters etc.

We also have physiological mechanisms at our disposal, e.g. when we are too hot, we sweat.



If we are cold, we shiver and our extremities may go “blue” or “white” as blood to them is reduced.

The skin can detect temperature changes and send information to thermoreceptors in the hypothalamus in the brain.



The hypothalamus responds accordingly, e.g. too hot

sweatinghairs lie flatred skin (due to increased blood flow)

Too coldshiveringgoose pimples (hairs erect)white skin due to decreased blood flow



Vasodilation:- when we are too hot, the arterioles to the skin surface dilate, allowing blood to the surface to lose heat.

Vasoconstriction:- when we are too cold, the arterioles constrict and blood is diverted along a “shunt” which keeps most of the blood away from the surface.


VasodilationEnvironment

skin

Much Heat Lost


VasoconstrictionEnvironment Little Heat

Lostskin


Ectotherm body temperature

In some animals, like fish, body temperature varies exactly as the environment varies, and there is no control of body temperature.

Others, like many reptiles and some insects, may use behavioural mechanisms to control their body temperature.

Both these groups are called ectotherms; “ecto” meaning outside.


Body temperaturesAnimal Body

TemperatureControl Mechanism

Endotherm Mouse 37o Homeostasis

Endotherm Camel 37o Homeostasis

Endotherm Bird 39o Homeostasis

Ectotherm Lizard Environmental Sunbathing

Ectotherm Frog Environmental Moves into shade

Ectotherm Snake Environmental

Retreats to underground

burrows


Energy uses at different temperatures

As enzyme activity depends on temperature, an animal which cannot control its body temperature will be inactive at low temperatures.

When the enzymes of the respiration reactions work slowly, an animal like a fly will have a low energy uptake and low food requirements.



In contrast, a small mammal in a cold environment uses a lot of energy to keep warm.

It may eat extra food and it will use extra oxygen.

This extra respiration provides heat to maintain a constant body temperature.



People used to eat more in winter. Central heating now makes that

unnecessary. Some animals which need a lot of

energy hibernate when conditions are difficult.

The body temperature drops, it is inactive and food stores in the body can last a long time.

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Control & Regulation