Homeostasis Balancing the internal environment

External vs. Internal Environment What is the difference?

External environment: Your surroundings. The factors that cause your body to change in order to stay in homeostasis. (Cold outside, working out, bacteria)

Internal Environment Conditions within the fluid surrounding its body cells Comprised of self-regulating control systems – homeostatic mechanisms

Homeostatic Mechanisms Have three common components: Receptors – Set point – Effectors - provides information about specific conditions tells what a particular value should be Cause the response that alter conditions in the internal environment.

Response – Change Corrected Receptor Set Point Control Center Effectors Stimulus – change in external environment Homeostatic Mechanism

Negative vs. Positive feedback mechanisms

Negative Feedback Systems There is a change from the set point and negative feedback corrects this change or brings it back to normal. This correction reduces the action of the effectors until the body is back in homeostasis.

WAIT? WHAT? WAIT? WHAT? Think of the thermostat in your house.. You set the thermostat to 67 o F – this would be the Your house is warm due to the sun shining on it. If your house thermometer reads the temperature as 70 o F – the thermometer________________ that it is: Or What do you think the furnace does? There is a choice: or set point. senses. Too hot?Too cold? Turns on?Turns off?

WAIT? WHAT? WAIT? WHAT? Think of the thermostat in your house.. You set the thermostat to 67 o F – this would be the Your house is cool due to the sun setting If your house thermometer reads the temperature as 65 o F – the thermometer________________ that it is: Or What do you think the furnace does? There is a choice: or set point. senses. Too cold? Too hot? Turns off?Turns on?

Homeostatic Regulation of Body Temperature through Negative Feedback Your average body temperature is 98.6 o F – this would be the Your body becomes warm sitting in Ms. Neubert’s room. If your body temperature goes above 98.6 o F– the brain________________ that it is: Or What do you think your body does? set point. senses. Too hot?Too cold?

Answer… When your body senses that it is too hot the following will most likely happen: 1. Blood vessels in the skin dilate (blood vessels get larger) allowing heat to be closer to the surface of the skin and thus heat is released. 2. Nervous system will activate the sweat glands – evaporation of sweat helps to lower the body temperature. 3. Gradually, your body temperature will return to normal.

Homeostatic Regulation of Body Temperature through Negative Feedback Your average body temperature is 98.6 o F – this would be the Your body is cooled because Ms. Neubert’s room is too cold! If your body temperature goes below 98.6 o F– the brain________________ that it is: Or What do you think your body does? set point. senses. Too cold?Too hot?

Answer… When your body senses that it is too cold the following will most likely happen: 1. Blood vessels in the skin constrict (blood vessels get smaller) allowing heat to be conserved. 2. Nervous system will activate the skeletal muscles if the body temperature falls lower than normal– shivering helps to raise the body temperature by generating heat. 3. Gradually, your body temperature will return to normal.

Hyperthermia Heat receptors in the skin Hypothalamus Stress Sensors Control Center Increased activity of sweat glands Increased blood flow to the skin Effectors Perspiration evaporates cooling the skin Effect Stress is reduced shutting down mechanism Homeostatic Regulation of Body Temperature through Negative Feedback

Homeostasis Using a Neural Pathway Control center Many homeostatic mechanisms use a nerve pathway in which to produce their effects. These pathways involve an afferent path which brings sensory messages into the brain and an efferent path which carries outgoing nerve messages to effectors.

Positive feedback systems

Positive Feedback Systems Increasing change in the same direction. Deviation from the set point is accelerated No correction from the reaction of the effectors Body will shut down. however some positive feedback systems work in favor of the body – ie. Childbirth. however some positive feedback systems work in favor of the body – ie. Childbirth.

Positive Feedback Mechanisms Typical Positive Feedback Process Effector Intensifies Control Center Sensor Stress

Think of your body temperature throughout the day…. Your average body temperature is 98.6 o F – this would be the ________________________ Your body becomes hot due to an infection (feverish). If your body temperature goes above 98.6 o F– the brain________________ that it is: What do you think your body does? set point. senses. Too hot?Too cold?

But what if the effector message does not work? The fever will cause metabolic functions to change. The body does not cool down and continues to get hotter. When your body temperature reaches to 113 o F, the following will happen: Death due to cellular proteins breaking down (denaturing) at such high temperatures and metabolism will stop.

Think of your body temperature throughout the day…. Your average body temperature is 98.6 o F – this would be the _______________________ Your body is cooled because you are stuck outside in the cold weather! If your body temperature goes below 98.6 o F– the brain________________ that it is: What do you think your body does? set point. senses. Too cold?Too hot?

But what if the effector message does not work? The extreme cooling of your body will cause metabolic processes to slow down. The body does not warm up and continues to get colder. When your body senses that it is too cold the following will most likely happen: The first area to be affected by extreme loss of heat is the brain. You will become disoriented and tired. The first area to be affected by extreme loss of heat is the brain. You will become disoriented and tired. Loss of energy will NOT initiate voluntary muscle actions such as shivering to occur. Loss of energy will NOT initiate voluntary muscle actions such as shivering to occur. Eventually your respiratory and cardiovascular systems shut down and ultimately result in death. Eventually your respiratory and cardiovascular systems shut down and ultimately result in death.

Homeostatic Regulation of Child Birth through Positive Feedback Pressure of Fetus on the Uterine Wall Nerve endings in the uterine wall carry afferent messages to the Hypothalamus Production and Release of Oxytocin into the Blood Increasing strength of uterine contractions Intensifies The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk letdown and blood clotting.

Helpful Effects of Positive Feedback Positive feedback can be helpful. A specific example of these helpful outcomes would be: Childbirth, Childbirth, where there is an increased release of the hormone oxytocin when the head of the baby presses against the cervical opening in the mother. This pressure stimulates the sensory receptors. Oxytocin stimulates the uterus to contract and will continue to contract when the baby is born.

Blood clotting, where there is a break in the blood vessel wall and bleeding begins to occur. Damage cells release a chemical that initiates the clotting process. These chemicals will continue to be released until the bleeding has stopped.

Digestion in the stomach, where food enters stomach. As more food enters the stomach, the stomach stretches. A stretched stomach releases more pepsinogen. More pepsinogen means more pepsin which then means more protein breakdown. Gastrin levels increase, which control the acid released in the stomach. Thus more secretion occurs, more mucous, more histamine, increased peristalsis and the muscular layer become more active, until the food moves into the intestines.

Some examples of what your body can regulate: Body temperature Blood pressure Oxygen needed or Respiration Heart Rate (or blood delivered to heart) Glucose level or blood sugar level.