Homeostasis

Homeostasis Homeostasis is the maintenance of a stable internal environment.

Homeostasis Homeostasis represents a state of DYNAMIC EQUILIBRIUM.

Homeostasis 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: Receptors (sensors) Monitors the environment & responds to a stimulus

Homeostasis All homeostatic mechanisms involve three components: 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: Control Center Determines the “set points” or range to be maintained

Homeostasis All homeostatic mechanisms involve three components: Control Center Determines the “set points” or range to be maintained Establishes the type of response

Homeostasis All homeostatic mechanisms involve three components: 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: Effector Mechanism for controlling the variable or response

Homeostasis All homeostatic mechanisms involve three components: Effector Mechanism for controlling the variable or response A reduced response is called a NEGATIVE FEEDBACK

Homeostasis All homeostatic mechanisms involve three components: Effector Mechanism for controlling the variable or response A reduced response is called a NEGATIVE FEEDBACK An increase in response is a POSITIVE FEEDBACK

Information sent along efferent pathway to effector. Figure 1.4 Interaction among the elements of a homeostatic control system. Output: Information sent along efferent pathway to effector. 4 Input: Information sent along afferent pathway to control center. 3 Control Center Afferent pathway Efferent pathway 2 Receptor Effector 5 Receptor detects change. Response of effector feeds back to reduce the effect of stimulus and returns variable to homeostatic level. 1 Stimulus produces change in variable. BALANCE

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?

Temperature-sensitive Temperature-sensitive Figure 1.5 Regulation of body temperature by a negative feedback mechanism. Control Center (thermoregulatory center in brain) Information sent along the afferent pathway to control center Information sent along the efferent pathway to effectors Afferent pathway Efferent pathway Receptors Temperature-sensitive cells in skin and brain Effectors Sweat glands Sweat glands activated Response Evaporation of sweat Body temperature falls; stimulus ends Stimulus Body temperature rises BALANCE Stimulus Body temperature falls Response Body temperature rises; stimulus ends Receptors Temperature-sensitive cells in skin and brain Effectors Skeletal muscles Efferent pathway Afferent pathway Shivering begins Information sent along the efferent pathway to effectors Information sent along the afferent pathway to control center Control Center (thermoregulatory center in brain)

Can you think of any examples? 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

1 occurs in blood vessel wall. Positive feedback cycle is initiated. 3 Figure 1.6 Summary of the positive feedback mechanism regulating formation of a platelet plug. Break or tear occurs in blood vessel wall. 1 Positive feedback cycle is initiated. 3 Released chemicals attract more platelets. 2 Platelets adhere to site and release chemicals. Positive feedback loop Feedback cycle ends when plug is formed. Platelet plug forms. 4

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?