Homeostasis Homeostasis is the maintenance of a stable
Homeostasis
Homeostasis is the maintenance of a stable internal environment.
Homeostasis represents a state of DYNAMIC EQUILIBRIUM.
Homeostasis represents a state of DYNAMIC EQUILIBRIUM. This means that adjustments are always being made to keep the variables within an acceptable range.
Homeostasis
Homeostasis All homeostatic mechanisms involve three components:
Homeostasis All homeostatic mechanisms involve three components: 1. Receptors (sensors) § Monitors the environment & responds to a stimulus
Homeostasis All homeostatic mechanisms involve three components: 1. Receptors (sensors) § § Monitors the environment & responds to a stimulus Transmits the stimulus (information) to a control center along a afferent pathway
Homeostasis All homeostatic mechanisms involve three components: 2. Control Center § Determines the “set points” or range to be maintained
Homeostasis All homeostatic mechanisms involve three components: 2. Control Center § § Determines the “set points” or range to be maintained Establishes the type of response
Homeostasis All homeostatic mechanisms involve three components: 2. Control Center § § § Determines the “set points” or range to be maintained Establishes the type of response Sends this information though a Efferent Pathway
Homeostasis All homeostatic mechanisms involve three components: 3. Effector § Mechanism for controlling the variable or response
Homeostasis All homeostatic mechanisms involve three components: 3. Effector § § Mechanism for controlling the variable or response A reduced response is called a NEGATIVE FEEDBACK
Homeostasis All homeostatic mechanisms involve three components: 3. Effector § § § Mechanism for controlling the variable or response A reduced response is called a NEGATIVE FEEDBACK An increase in response is a POSITIVE FEEDBACK
Figure 1. 4 Interaction among the elements of a homeostatic control system. 3 Input: Information 4 Output: Control Center sent along afferent pathway to control Afferent center. 2 Receptor pathway Receptor detects change. Efferent pathway Effector 1 Stimulus produces change in variable. Copyright © 2010 Pearson Education, Inc. Information sent along efferent pathway to effector. BALANCE 5 Response of effector feeds back to reduce the effect of stimulus and returns variable to homeostatic level.
Homeostasis Negative Feed Back is the major mechanism for controlling homeostatic responses.
Homeostasis Negative Feed Back is the major mechanism for controlling homeostatic responses. § The stimulus is either turned off or reduced in its intensity
Homeostasis Consider body temperature: � Temperature change in the body is the variable
Homeostasis Consider body temperature: � Temperature change in the body is the variable � The change in temperature up or down is the response Can you think of any other examples?
Figure 1. 5 Regulation of body temperature by a negative feedback mechanism. Information sent along the afferent pathway to control center Control Center (thermoregulatory center in brain) Afferent pathway Information sent along the efferent pathway to effectors Efferent pathway Receptors Temperature-sensitive cells in skin and brain Effectors Sweat glands activated Response Evaporation of sweat Body temperature falls; stimulus ends Stimulus Body temperature rises BALANCE Stimulus Response Body temperature rises; stimulus ends Effectors Skeletal muscles Body temperature falls Receptors Temperature-sensitive cells in skin and brain Afferent Efferent Shivering pathway Information sent begins along the efferent pathway to effectors Control Center (thermoregulatory center in brain) Copyright © 2010 Pearson Education, Inc. Information sent along the afferent pathway to control center
Homeostasis Positive Feed Back is a minor mechanism for controlling homeostatic responses and is used for only occasional events. The stimulus goes in the same direction as the response. One increases the other increases. Can you think of any examples?
Homeostasis Blood Clotting and Labor Contractions
Homeostasis
Figure 1. 6 Summary of the positive feedback mechanism regulating formation of a platelet plug. 1 Break or tear occurs in blood vessel wall. Positive feedback cycle is initiated. 3 Released chemicals attract more platelets. Positive feedback loop 2 Platelets adhere to site and release chemicals. Feedback cycle ends when plug is formed. 4 Platelet plug forms. Copyright © 2010 Pearson Education, Inc.
Homeostasis Disease occurs when the homeostatic mechanisms fail or are overwhelmed. Examples include: � Heart Failure � Anaphylaxis
Heart Failure Heart failure occurs when the heart muscle is damaged. As a result: Blood begins to back up into the lungs The lungs can not provided enough oxygen to the body Fluid backs up into the liver and abdominal cavity Fluid accumulates in the lower extremities How does it stop?
Heart Failure
Heart Failure
Anaphylaxis �This is a severe over reaction to an antigen. The arteries dilate causing the blood pressure to drop The heart rate speeds up The bronchioles of the lung constrict making breathing very difficult Skin becomes flushed and swollen How does it stop?
Anaphylaxis
Anaphylaxis
Homeostasis How about a cold or flu? How about cancer?
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