An Introduction to Anatomy and Physiology Chapter 1 Homeostasis Slides 90-116 1.13_C_Homeostasis-Intro (Slides 1-9)

INTRO 1.13_C_Homeostasis-Intro

Homeostatic Regulation Ex: Household temperature control 1. Variable that is regulated 2. Receptor: monitors the variable (receives and transmits “stimulus”) 3. Control Center: integrates information and compares it to a “set point” (decides on appropriate response) & transmits command 4. Effector: receives & executes response to stimulus

Human thermostat

Pyrogens change the temperature control center “set-point” to a new higher level. Fever = higher body temperature, often accompanies bacterial or viral infections Blood flow shifted to core to conserve heat, shivering, increase in metabolic rate Chills stop when higher temp reached Benefits of a higher temperature: Inhibits bacterial growth Speeds up metabolic reactions for repair Increases delivery of white blood cells to infection sites

Negative Feedback: Blood glucose regulation

Negative Feedback: Fluid/Electrolyte balance

Negative Feedback Loop Restores Homeostasis (Temperature) In negative feedback systems the response of the effector negates or opposes the stimulus (shuts off the original stimulus) Too hot > effector leads to less hot (sweat, increase skin blood flow, decrease metabolism) Too cold > effector leads to less cold (shiver, behavioral changes, increase metabolism) Responses are often controlled by nervous and endocrine systems (e.g. brain regulates body temp) EXTRINSIC CONTROL but sometimes controlled at the cell and tissue level = AUTOREGULATION or INTRINSIC CONTROL

Negative Feedback: Regulation of Blood Pressure External or internal stimulus increase BP Baroreceptors (pressure sensitive receptors) Detect higher BP Send nerve impulses to brain for interpretation Response sent via nerve impulse sent to heart and blood vessels BP drops and homeostasis is restored Drop in BP negates the original stimulus

Homeostatic Regulation Homeostasis- The existence of a stable internal environment. Has 3 Parts: Receptor: a sensor that is sensitive to a particular environmental change or stimulus. Control Center: receives and processes the information supplied by the receptor. Effector: a cell or organ that responds to the commands of the control center and whose activity opposes or enhances the original stimulus.

Feedback System Cycle of events Three Basic components Body is monitored and re-monitored Each monitored variable is termed a controlled condition Three Basic components Receptor Control center Effector

Feedback Systems Receptor Body structure that monitors changes in a controlled condition Sends input to the control center Nerve ending of the skin in response to temperature change

Feedback Systems Control Center Brain Sets the range of values to be maintained Evaluates input received from receptors and generates output command Nerve impulses, hormones Brains acts as a control center receiving nerve impulses from skin temperature receptors

Feedback Systems Effector Receives output from the control center Produces a response or effect that changes the controlled condition Found in nearly every organ or tissue Body temperature drops the brain sends and impulse to the skeletal muscles to contract Shivering to generate heat

Paramecium eating pigmented yeast http://www.youtube.com/watch?v=l9ymaSzcsdY "As the paramecium stuffs itself with a meal of pigmented yeast, vacuoles form. As food particles are digested by acidic enzymes, the congo red will reveal the pH drop-color will shift from a more alkaline red, to a more acidic blue."

Blood Clot Formation http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structure/tr/m1/s7/trm1s7_3.htm

Body’s Internal Environment

Homeostatic Imbalances Normal equilibrium of body processes are disrupted Moderate imbalance Disorder or abnormality of structure and function Disease specific for an illness with recognizable signs and symptoms Signs are objective changes such as a fever or swelling Symptoms are subjective changes such as headache Severe imbalance Death

Positive Feedback Definition: enhances the original stimulus causing a greater deviation from the set point. Activates infrequent events that require immediate action Most are not related to the maintenance of homeostasis. Positive feedback often results in disease. Examples: Blood clot Uterine contractions in childbirth (stretch releases oxytocin from posterior pituitary), Cancer

Positive Feedback Systems: Normal Childbirth Uterine contractions cause vagina to open Stretch-sensitive receptors in cervix send impulse to brain Oxytocin is released into the blood Contractions enhanced and baby pushes farther down the uterus Cycle continues to the birth of the baby (no stretching)

Childbirth

Positive Feedback: Blood Loss Normal conditions, heart pumps blood under pressure to body cells (oxygen and nutrients) Severe blood loss Blood pressure drops Cells receive less oxygen and function less efficiently If blood loss continues Heart cells become weaker Heart doesn’t pump BP continues to fall

Positive Feedback -Disease

Two Types of Homeostasis Negative Feedback: when the effector(s) activated by the control center oppose or eliminate stimulus. Many examples; most common feedback system. Positive Feedback: initial stimulus produces a response that exaggerates or enhances its effects. Labor Contractions Blood Clotting

Negative Feedback Inhibitor Oppose change by creating response opposite in direction of initial disturbance change – temperature drop response – heat production initial disturbance – temp fall below normal set point Stabilize physiological variables Maintain constant internal environment Ex: goosebumps, sweating Positive Feedback Stimulatory Amplifies/reinforces change which can be harmful and disastrous Cause instability and disrupt homeostasis (continuous temp increase) Ex: sneezing, birth of baby, immune response to infection, blood clot

HOMEOSTASIS TUTORIALS & QUIZ 1.17_C_HOMEOSTASIS TUTORIALS_QUIZ