Higher Human Biology

Unit 2

Regulating Mechanisms

Homeostasis

Control of blood sugar

• Insulin and glucagon are two hormones that control how much glucose (sugar) is in the blood

• These hormones are made in the pancreas, a gland that sits just behind the stomach.

Pancreas

• Your pancreas contains small groups of cells called the islets (or islands) of Langerhans.

Pancreas

• When you eat a meal, the amount of sugar in your blood rises. The cells in your pancreas react by making more insulin.

• When your blood sugar levels are low, the cells in your pancreas react by making more glucagon.

What does insulin do?

• After digestion, glucose enters your bloodstream.• The Islets of Langerhans in the pancreas detects an

increase in blood sugar level.• These cells produce the hormone insulin, which is then

transported to the liver in the bloodstream.• Insulin activates an enzyme to catalyse the reaction glucose glycogen

• This decreases the blood sugar level.• Glycogen, a long chain carbohydrate, is stored in the

liver until it is needed e.g. when you are sleeping

What does glucagon do?

• Glucagon stops your blood glucose level from dropping too low.

• When you exercise, your body uses the glucose in your blood to power your muscles. Your pancreas senses that you're using up your glucose supply.

• As your blood glucose level drops, your pancreas stops making insulin and your pancreas makes glucagon

• Glucagon activates an enzyme in your liver which catalyses the following reaction

Glycogen Glucose• These activities push up the amount of glucose in your

blood.

Control of blood sugar

Control of Body Temperature

• Core body temperature must remain at 37oC

• Careful control of the blood supply to the skin can do this by reducing blood flow to the colder extremities in cool conditions

Heat Stress

• The sympathetic nervous system directs the body’s attempts to regulate temperature by re-routing circulation and sweating

• Red skin indicates vasodilation and the collecting of blood near the surface for release of heat

• Sweating causes evaporative cooling• The individual reduces heat stress by lowering

physical activity levels, scheduling work during cool times of the day, wearing less clothes, using fans and air conditioning

Forms of heat loss

Temperature control system

Position of the Hypothalamus

Sweat glands

• Sweat glands dampen the skin. This loses heat by causing evaporation of the sweat

Sweating under pressure!

Sweating caused by heat

Sweating caused by muscular contraction

Nine Sweaty Facts

• Humans are the most prolific sweaters in the entire animal kingdom

• Sweating is accomplished through specialized sweat glands

• These glands are found in the dermis and epidermis, distributed all over the body, except for the margins of the limbs, sex organs, and ear drums

• They average between 150 and 340 glands/cm2 of skin for a total of between 2,000,000 and 5,000,000

• Add them all together and you get a hole the size of your mouth

• The sweat glands are innervated by the sympathetic nervous system

• When a rise in core temperature is detected by the hypothalamus, impulses to the sympathetic system cause an increase in sweat output

• The sweat gland consists of a deep coiled portion and a duct that opens on the skin

• The duct aids in the re-absorption of electrolytes, mainly sodium and chloride, in the sweat so that the fluid discharged onto the skin has had the electrolyte concentration reduced by a factor of about 20

Non-sweaty ways of cooling down may still use the evaporation of water

Heat Transfer by Circulation

• The peripheral (surface) circulation relies on beds of capillaries that transfer blood between the arterial and venous systems

• These changes in circulation can change the rate of blood flow from internal organs to the periphery by as much as 30%

• Vasoconstriction (reducing the diameter of the capillaries) reduces the blood flow from the core to the periphery. This reduces heat loss.

• Vasodilation (increasing the diameter) increases the flow of blood under the skin. This increases heat loss by radiation

Surface capillary

artery

vein

Cold Stress

• The body attempts to increase and conserve body heat by rerouting circulation, raising hairs to trap more insulating air, and shivering

• Vasoconstriction causes the blood to pool internally to conserve organ heat

• Shivering causes the temperature to increase due to muscular activity

• Individuals respond to cold stress by increasing muscular activity, wearing more clothes, or heating their living space

In cold conditions heat is made by shivering. This extra series of muscle contractions causes a rise in body temperature

Hair muscle

Contraction of this muscle makes the hair stand on end, trapping more insulating air.

hairSurface of skin

Coping with heat and cold

• Factors Affecting Thermal AcclimationAge• Both infants and elderly have lessened ability to

acclimatize to heat or coldBody size and shape• The surface area to weight ratio will affect the

level of acclimatization attainableBody composition• Subcutaneous adipose deposits (fat) insulate the

core and make it more difficult to dissipate heat in hot or easier to retain heat in the cold