Chemistry of Our World – The Human Body HOMEOSTASIS

What is Homeostasis? The ability of the Body to maintain a balanced internal environment that is within the normal range of health for that organism The organism must have this balance in order to thrive and survive

How it all Works Homeostasis involves a system of checks and balances to keep stability of the animal’s internal environment. The skin, kidneys, liver, endocrine system, nervous system and sensory system all play a part in maintaining the internal environment within narrow limits

Regulated Factors in the Body Some factors homeostatically regulated include: Concentration of nutrient molecules (food) Concentration of water, salt, and other electrolytes Concentration of waste products Concentration of O2 = 100mmHg and CO2 = 40 mmHg Average pH = 7.35 Blood volume 4-6 L and pressure 120/80 Temperature = 37o C (98.6 F) Heart Rate = Average 50-60 bpm

Effects of Homeostasis Homeostasis is continually being disrupted by External stimuli heat, cold, lack of oxygen, pathogens, toxins Internal stimuli Body temperature Blood pressure Concentration of water, glucose, salts, oxygen, etc. Physical and psychological distresses Disruptions can be mild to severe If homeostasis is not maintained, death may result

Maintaining Control In order to maintain homeostasis, the control system must be able to 1. Detect abnormalities from the normal range 2. Integrate this information with other body systems, external environmental factors, etc. 3. Make appropriate adjustments to restore the system to normal.

Control of Homeostasis

Two Types of Control Feedforward - term used for responses made in anticipation of a change Example: Salivation and release of extra stomach acid due to smell or sight of food Feedback - refers to responses made after change has been detected Two Types of feedback systems Negative Positive

Feedback Loops Negative feedback loop Positive feedback loop original stimulus reversed most feedback systems in the body are negative used for conditions that need frequent adjustment Examples: heart rate, blood pressure, temperature Positive feedback loop original stimulus intensified seen during normal childbirth

The Process:

Example: Body Temperature All mammals maintain a constant body temperature. Human beings have a body temperature of about 37ºC. E.g. If your body is in a hot environment your body temperature is 37ºC If your body is in a cold environment your body temperature is still 37ºC

Examples Sweating When your body is hot, sweat glands are stimulated to release sweat. The liquid sweat turns into a gas (it evaporates) To do this, it needs heat. It gets that heat from your skin. As your skin loses heat, it cools down

Sweating The skin

Examples Vasodilation Your blood carries most of the heat energy around your body. There are capillaries underneath your skin that can be filled with blood if you get too hot. This brings the blood closer to the surface of the skin so more heat can be lost. This is why you look red when you are hot!

This means more heat is lost from the surface of the skin If the temperature rises, the blood vessel dilates (gets bigger).

Vasoconstriction This is the opposite of vasodilation The capillaries underneath your skin get constricted (shut off). This takes the blood away from the surface of the skin so less heat can be lost.