Regulating the Internal Environment Homeostasis is the maintenance of the body’s multicellular environment with the body’s external environment or any changes in activity caused. The bodies homeostatic response controls water concentration in the blood, body core temperature, blood glucose levels and heart rate by a process called negative feedback control.

Receptors and Effectors Any change to the environment will be detected by receptors found in the sensory organs and glands Effectors The receptor sends a message to the effector which alters the bodies response and returns it back to normal. Gland and muscular contraction, hormone and enzyme production are all effector responses.

Negative Feedback Control (Fig. 24.1)

Control of Heart Rate Although the pacemaker initiates heartbeats, the rate of heart beating is not fixed and can be altered as a result of nervous or hormonal activity. The autonomic nervous system regulates the heart, blood vessels, lungs, alimentary canal and sweat glands. This is when the body work automatically without the individual having to think about making the body do certain jobs.

Autonomic Nervous System (ANS)

Cardio Accelerator Cardio Inhibitor Centre Centre Medulla of Brain Cardio Accelerator Cardio Inhibitor Centre Centre Sympathetic Parasympathetic cardiac nerves cardiac nerves Antagonistic response Increase in Decrease in nerve impulses nerve impulses Increase in heart rate Decrease in heart rate

Hormonal Control of Heart Rate Adrenaline Adrenaline is produced in the adrenal glands which are situated above the kidneys. The sympathetic nervous system in a situation which would required adrenaline e.g. fight of flight situation, stimulates the adrenal glands to release adrenaline into the blood system. When it reaches the pacemaker it increases the heart rate

Exercise and Heart Rate When we exercise the muscle cells which are working are at a higher metabolic rate and therefore require a higher levels of oxygen and glucose. As a consequence they also produce higher levels of carbon dioxide. This all needs to be balanced.

Distribution of Blood During Exercise During exercise the heart rate (pulse) increases, the volume of blood (stoke volume) pumped through the heart in each contraction increases cardiac output = heart rate X stoke volume This increase in heart rate and stoke volume increases the rate of oxygen delivery to working cells and tissues. Not all organs require an increase in blood during exercise, only the ones which are doing the extra work: Increase in blood flow to tissue during exercise would be in the heart cardiac muscle, skeletal muscle and the skin where excess heat is lost. To help with this increase arteries and arterioles vasodilate to allow A larger volume of blood to pass through at a faster rate Decrease in blood flow to tissue during exercise would be in the kidneys, stomach, intestines etc.. The function of the kidneys to purify blood and the function of the intestine to digest and absorb nutrients are processes that can wait until exercise is complete. This decrease in blood is as a result of vasoconstriction of the arteries and arterioles carrying blood to these organs.

Control of Blood Sugar Levels Glucose is essential to all living cells as energy is released from Glucose. The liver stores excess glucose as glycogen so when it is needed there is a reserve.

The Pancreas and Sugar Levels Cells in the pancreas called the Islets of Langerhans produce two hormones – insulin and glucagon which help control blood glucose levels. These levels are controlled through negative feedback mechanisms. Insulin Glucose Glycogen Stored in liver Glucagon Glycogen Glucose

Diabetes Diabetes mellitus is a disorder in people and animals who do not have or have less functional insulin secreting cells in the pancreas. As a result of having little or no insulin, their blood glucose levels increase and are not stored in the liver. This can be detected in their urine as there is so much glucose in the blood that it is not reabsorbed but excreted in the urine. This used to be a fatal disease but with controlled administration of insulin by injection daily, their glucose levels can be maintained.

Control of Body Temperature The hypothalamus is the bodies temperature monitoring centre. Heat and cold thermoreceptors in the skin convey information to the hypothalamus. A body core temperature from the blood and body shell temperature form the skin triggers a response to return the temperature back to normal .

Sweat Glands Skin Arterioles Hair Erector Muscles Skeletal Muscles Hypothalamus Hypothalamus Receiving Information Core Blood Skin Temperature Thermoreceptors Sweat Glands Skin Arterioles Hair Erector Muscles Skeletal Muscles Sweating Vasodilatation ‘Goose bumps’ Shivering Vasoconstriction

Temperature Control in Infants Brown Fat Babies have a relatively large surface area to volume ratio and therefore loose heat more rapidly than an adult. When a baby is born its thermoregulation mechanisms are not fully developed. When it gets cold it involuntarily responds by vasoconstriction and brown fat generates heat as it is supplied with blood vessels.

Preterm babies, infants Hypothermia Hypothermia is when someone's body temperature is below what is considered a normal level. Preterm babies, infants and the elderly are at risk.