Homeostasis CH5

Positive feedback

Response is to increase stimulus.Rarely occurs in homeostasis.

Negative feedback

Response is to reduce of eliminate stimulus.For example, when you are hot you sweat to reduce heat.


-Optimum temperature for humans is approximately 37 oC-Vital for this temperature to be maintained because the chemical reactions happening in every cell is heat sensitive.-To maintain this temp heat gain must equal heat loss.-Thermoregulation is the process of maintaining this constant temperature.

Heat production

Some energy is used for cellular processes but most of the energy is released in the form of heat.

Metabolic rate

The rate at which energy is released by the breakdown of food.

Factors that affect metabolic rate

•Exercise (can increase MR by 40)•Stress (sympathetic nervous system stimulates the increase of MR)•Body temperature (increase temp = increase in MR)

Peripheral thermoreceptors

•located in skin and mucous membrane.•Detect changes in the external environment and send information to hypothalamus

Central thermoreceptors

•Located in hypothalamus•Detect temperature of the internal environment

Two types of receptors within peripheral and central thermoreceptors

Cold receptors•Stimulated by temperature lower than normal•Hypothalamus receives information and stimulates heat production and heat conservation mechanismsHeat receptors•Detect temperatures higher than normal•Hypothalamus receives information and stimulates mechanisms that reduce heat and increase heat loss.

4 methods of heat loss

Conduction - transfer of heat by direct contact with particlesConvection - is the transfer of heat by the movement of a liquid or gas (eg moving air on body removes radiated heat)Radiation - transfer of heat in all directions, moves from hot to cold.Evaporation - process of a liquid forming a gas, which absorbs energy (eg sweat)

Physiological changes to maintain body temperature in cold environment

Vasoconstriction, shivering, release of thyroxine, release of adrenaline & noradrenaline, and behavioural response


-Hypothalamus stimulates blood vessels in skin to constrict, thus, decreasing the transfer of heat from internal body organs to the skin. less heat will then be lost from body surface.


-Hypothalamus sends stimuli to the parts of the brain that causes shivering.-Movement of skeletal muscles increases heat production

Release of Thyroxine

-Hypothalamus sends releasing factors to the anterior lobe of the pituitary to secrete TSH, which travels in the blood to the thyroids and stimulates the release of thyroxine into the blood. Thyroxine increases metabolic rate, thus, increasing body temperature.

Release of adrenaline & noradrenaline

-Hypothalamus stimulates the adrenal medulla secreting adrenaline and noradrenaline into the blood. These hormones increase cellular metabolism, thus, increase heat production. This helps maintain body temperature when there is rapid heat loss.

Behavioural response

-Putting extra jumpers on, reducing body surface area by folding arms, turning on heater etc.

Vasoconstriction feedback loop to prevent heat loss


Adrenal Medulla feedback look to prevent heat loss


Thyroxine feedback loop to prevent heat loss


Physiological changes to maintain body temperature in warm environment

Vasodilation, sweating, stop release of thyroxine, and behavioural response


-Hypothalamus stimulates vasodilation of skin arterioles increasing blood flow through the skin. skin becomes reddish, surface temperature rises, and there is greater heat loss through radiation and convection.


-Sympathetic nerves stimulate release of sweat. Heat is loss by the evaporation of sweat.

Stop release of thyroxine

-Hypothalamus will signal the anterior lobe of the pituitary to stop the release of TSH which will stop the thyroid releasing thyroxine, thus, metabolic rate decreases causing the decrease of heat production and body temperature.

Behavioural response

-Turning on a fan, taking off jumpers, reducing physical activity etc.

Temperature tolerance

•Temperature over 42 is dangerous•Temperature around 45 = death•High temperature usually cause by fever but can be environmental conditions

Heat stroke

-Difficulty for the body to lose heat which may be due to humidity causing the body temperature to rise and regulatory mechanisms to cease.-Can be fatal if brain cells are affected.

Heat stroke treatment

-Consists of cooling the body as quickly as possible by immersing the patient in cold water.-remove excess clothing, soak with water, fan the person. If available cool person in ice bath.

Heat exhaustion

•This condition occurs as a result of extreme sweating and vasodilation to lose heat.•The loss of water in sweating reduces the volume of blood plasma and vasodilation reduces causes blood pressure to reduce.•The output of blood from the heart decreases; therefore, the person may collapse.•Unlike heat stroke body temperature is almost normal.

Heat exhaustion treatment

drink fluids (water or sports drink)


•A person's core temperature falls below 330C, the metabolic rate is so low that heat production is unable to replace the heat loss and body temperature continues to fall.•Death can occur at core temperatures below 320C.

Hypothermia treatment

Move person out of cold environment and warm gradually.

Regulation of blood glucose

•Energy is released from glucose by cellular respirationGlucose + oxygen =Carbon dioxide + water + energy

Normal level of glucose in the blood

•90mg/100ml - this means 90 milligrams of glucose per 100ml of blood.•Or 5mmol/l

Regulation of blood glucose 2

The body's source of glucose is the food we eat. •Carbohydrates are broken down into glucose and absorbed into blood through the walls of the small intestine.•After a meal blood glucose levels can rise sharply.


Formation of glycogen from glucose.


Breakdown of glycogen into glucose.


Conversion of fats or proteins into glucose.


Production of lipids (this can be from glucose into lipids)


break down of lipids (eg break down of lipids to form glucose)

Liver's Role in regulation of blood glucose

After a meal breakdown of products, mainly glucose, are absorbed in the small intestine.Hepatic portal vein carries glucose to the liver.

Glucose may:

-Be removed from blood by the liver to provide energy for liver functioning.--Be removed by the liver and / or muscles and converted into glycogen for storage (glycogenesis).--Continue to circulate in the blood, available for body cells to absorb and use as a source of energy.--Be converted into fat for long-term storage (lipogenesis).

Glycogen storage

Liver•Available to convert into glucose to maintain blood sugar levelsMuscles•Provides energy for muscle activity.

The role of the pancreas

Islets of Langerhans - hormone secreting cells in the pancreas, there are two types:Alpha cells•Secrete glucagonBeta cells•Secretes insulin

The Role of the pancreas (Insulin - released when bgl is high)

Chemoreceptors in beta cells monitor blood glucose levels and will stimulate the release of insulin if levels are high.

Insulin from beta cells cause decrease in blood glucose levels by:

1.Accelerates glucose from blood to cells2.Accelerates glucose to glycogen (glycogenesis)3.Stimulates conversion of glucose to protein (protein synthesis)4.Stimulates conversion of glucose to lipids (lipogenesis)

Homeostasis feedback loop high blood glucose levels


The Role of the pancreas (Glucagon - released when bgl is low)

Chemoreceptors in alpha cells monitor blood glucose levels and will stimulate the release of glucagon if levels are low.

Glucagon from alpha cells increase blood glucose levels by:

1.Stimulating glycogenolysis2.Stimulating glycogenesis3.Stimulating effect on protein break down

Homeostasis feedback loop low blood glucose levels


The role of the adrenal glands

Adrenal cortex, adrenal medulla

Adrenal cortex

-ACTH released from anterior pituitary gland to stimulate the release of cortisol from the adrenal cortex-Cortisol regulates carbohydrate metabolism, stimulates glycogenolysis (break down of glycogen to glucose) and the transfer rate of amino acids to the liver for gluconeogenesis (conversion of fats and proteins into glucose).

Adrenal medulla

-Adrenal medulla secretes adrenaline & noradrenaline.-This elevates bgl's by stimulating break down go glycogen into glucose and production of lactic acid to be used by liver to manufacture glucose.