• Homeostasis is the regulation of the internal environment (chemical and physical) for the cells to function in an organisms
• Physical factors: temperature, blood pressure, and blood osmotic pressure
• Chemical factors: pH value, concentrations of minerals and blood sugar concentration
• The stimulus will reverse the reaction/response by initiating a corrective mechanism to achieve a normal state of homeostasis

In homeostasis, a number of organ systems coordinate and conduct a particular function:

• In the regulation of body temperature, nervous system, endocrine system, integumentary system, circulatory system, and muscular system coordinate and function to maintain body temperature within normal range.
• In the regulation of blood pressure and osmotic pressure, nervous system, endocrine system, circulatory system, and urinary system coordinate and function to maintain blood pressure and osmotic pressure within normal range.
• In the regulation of carbon dioxide partial pressure, the nervous system, respiratory system, and circulatory system coordinate and function to maintain carbon dioxide partial pressure within the normal range.
• In the regulation of blood pH, nervous system, endocrine system, respiratory system, and circulatory system coordinate and function to maintain blood pH within normal range
• In the regulation of blood glucose, the endocrine system and circulatory system coordinate and function to maintain blood glucose within normal range

• When body temperature falls below the normal range, thermoreceptors in the hypothalamus detect the changes and send stimuli to thermoregulating center in the hypothalamus via the nerves. The thermoregulating center triggered and send nerve impulses to the spinal cord via motor neurons to produce effectors, then returning the body temperature to normal range. The endocrine system is also functioning when the body temperature rises above the normal range.
• Thermoreceptors are found in the skin and hypothalamus:
  • Thermoreceptors in the skin detect the temperature change of the external environment.
  • Thermoreceptors in the hypothalamus detect the temperature change of the internal environment.

• The action of sweat glands:

• Sweat glands become inactive
• Less sweat is produced
• Less heat lost through evaporation

The action of blood capillaries on skin:

• The muscle in the afferent arterioles contract
• Vasoconstriction occurs
• Blood capillaries constrict, the diameter decreases
• Less blood flows through the blood vessels near the skin surface
• Heat eliminated through radiation decreases

The action of the hair erector muscles:

• Hair erector muscle contract
• Hair becomes erect
• A thick layer of air is trapped. Air is a good heat insulator
• Less heat is released

The action of skeletal muscles:

• Skeletal muscle contracts and relaxes repeatedly
• Shivering occurs
• Heat is generated

The action of adrenal glands:

• Adrenal glands are stimulated by the hypothalamus
• Adrenaline hormones are secreted
• Metabolism rate increases
• More heat is generated

The action of thyroid glands:

• Thyroid glands are stimulated
• Thyroxine hormone is secreted 
• Metabolism rate increases
• More heat is generated

• Blood sugar level (glucose) regulation is a homeostasis process that maintains the normal level of sugar in the blood.
• Two organs are involved:
  • Pancrease:
    • alpha cells secrete glucagon
    • beta cells secrete insulin
  • Liver:
    • Glucagon stimulates the liver cells to exchange glycogen into glucose
    • Insulin stimulates the excess of glucose into glycogen
• In a healthy human, the blood glucose level is regulated within a range of 75-110 mg glucose per 100ml blood

• Carbon dioxide produced by cells during cellular respiration
• In blood and tissue fluid, the amount of carbon dioxide is measured as the partial pressure of carbon dioxide
• The change in carbon dioxide partial pressure can be detected by peripheral chemoreceptor located at the aorta body and carotid bodies
• Central chemoreceptors located in medulla oblongata detect the pH change of cerebrospinal fluid
• The main effectors in regulating carbon dioxide partial pressure are intercostal muscles and diaphragm
• The intercoastal muscles and diaphragm contract and relax repeatedly and rapidly
• This increase the rate of breathing to remove excess carbon dioxide from the body and returning carbon dioxide partial pressure to normal level
• In the regulation of carbon dioxide partial pressure, the respiratory control center coordinates with the cardiovascular control center.
• The rates of oxygen uptake and carbon dioxide removal in the lungs increased with the high rate of heartbeat.

• Normal blood pressure for an adult is 120/80 mmHg
• Change in blood pressure from normal level can be detected by baroreceptor found in the aortic arch and carotid arteries
• The stimulated baroreceptors send nerve impulses to the cardiovascular control center and vasomotor control center in the medulla oblongata
• The main effectors in regulating blood pressure are sinoatrial node (SA node), smooth muscle of afferent arteriole and adrenal gland