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Students, you are required to read the textbook for the instructor to be able to teach the concepts the course encompasses. (From FOUNDATION SKILLS in the Biology Department Master Syllabus.) Do not just read these notes, to succeed in this class -- at least if you wish to have a high grade, you MUST use your textbook as a LEARNING TOOL! The textbook -- especially the figures, will help clarify things you did not understand in class or from reading the lecture notes.
MAIN TOPICS OUTLINE
16.1 ORGANISM REQUIREMENTS
16.2 HOMEOSTASIS
16.21 Examples of Homeostasis
16.22 Stages in Homeostasis
16.23 Components of Homeostasis
16.24 Mechanisms of Homeostasis
16.25 Evolutionary significance of Homeostasis
16.3 BODY TEMPERATURE REGULATION
16.31 Body temperature regulation when too warm
16.32 Body temperature regulation when too cold
16.4 REFLEX ARC
Reflex ArcLECTURE OBJECTIVES:
1. Understand how the human body maintains a rather constant internal environment despite changing external conditions.
2. Know the two stages, the three components, and the two feedback mechanism of homeostasis, and use body temperature regulation to describe the negative feedback mechanism.
3. Describe a negative and a positive feedback mechanism.
4. Describe a reflex arc.
5. Define selected key terms
Key Terms:def. Blood pressure: Force of blood pushing against the inside wall of blood vessels.
def. Effector: The component of a feedback mechanism, a muscle or a gland, that responds to output from an integrator (a nerve impulse from a control center).
def. Endocrine gland: Ductless organ, part of the endocrine system, that secretes hormones into the bloodstream.
def. Homeostasis (term used for multicellular organisms): A physiological state in which the physical and chemical conditions of the internal environment are being maintained within tolerable ranges.
def. Integrator: (Regulator Center, Control Center, Integrating Center) The component of a feedback mechanism, often the brain, that determines the point at which a controlled condition, such as body temperature, is maintained.
def. Interneuron: Neuron conveying messages between parts of the central nervous system.
def. Negative feedback: (A principle governing most control systems) a mechanism of homeostatic response in which a stimulus initiates action that reverses or reduces (suppresses and inhibits) the stimulus.
def. Neuron: A nerve cell, part of the nervous system.
def. Positive feedback: a mechanism of homeostatic response in which a stimulus initiates action that enhances (intensifies and increases) the stimulus.
def. Receptor: The component of a feedback mechanism, a specialized cell or part of a nerve cell, that responds to a specific stimulus.
def. Reflex: Automatic, involuntary response of an organism to a stimulus.
def. Reflex arc: Simple pathway of information flow without involving the brain. (Stereotyped movement made in response to a sensory stimulation.)
def. Stimulus: Change in the internal or external environment that a specific sensory receptor can detect, leading to a nerve impulse. (A stimulus is often something that stresses a controlled condition in the animal body.)
16.1 Organism requirements
1. Maintain internal operating conditions
- within tolerable range, even when the external environment changes (= response to the environment)
def. Homeostasis: (term used for multicellular organisms) A physiological state in which the physical and chemical conditions of the internal environment are being maintained within tolerable ranges.
2. Acquire nutrients, distribute nutrients (to the whole body), & dispose of waste
3. Protect
-- against injury and attack from harmful disease causing agents (bacteria, viruses, parasites).
4. Reproduce
- often help nourish and protect individuals
- egg (reptiles and birds)
- placenta, mammary glands (mammals)
16.2 Homeostasis
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def. Homeostasis: (term used for multicellular organisms) A physiological state in which the physical and chemical conditions of the internal environment are being maintained within tolerable ranges.
• Response to the environment to maintain internal operating conditions, within ranges most favorable for cell activities (even when the external environment change).
• Most organ systems in the body contribute to homeostasis.
• Controlled by the nervous system and to some degree by the endocrine system (“hormone” system).
• 16.21 Examples of homeostasis
i. Blood sugar (Glucose concentration in the blood) Å 0.1%ii. Blood pH (approximately 7.4)iii. Blood pressure ( approximately 120 / 80)iv. Body temperature (approximately 37°C (98.6°F))- - - - - - - - - - - - - - - - - - - - - - - - - - -
vi. Orgasm (at sexual reproduction)
• 16.22 Stages in homeostasis
Two (2) main stages:
1. Detection: A receptor detects the changes from the stable state
2. Counteraction: An effector counteracts the changes from the stable state
• 16.23 Components of homeostasis
Three (3) main components:
I. Receptor (receives a stimuli: detection)
II. Integrator (processes the information fr. the stimuli) -- "regulatory center"
III. Effector (carries out a response to the stimuli: counteraction)
• 16.24 Mechanisms of homeostasis
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Two (2) different mechanisms (body responses):
1. Negative feedback: cancels or counteracts original stimulus
(opposite present conditions), e.g., blood sugar balance, blood pH balance, blood pressure balance, body temperature "thermostat"
2. Positive feedback: increases original stimulus
in reproductive processes: child birth (labor), sexual reproduction (orgasm)
def. Negative feedback: (A principle governing most control systems) a mechanism of response in which a stimulus initiates action that reverse or reduce the stimulus.
def. Positive feedback: a mechanism of response in which a stimulus initiates action that enhances the stimulus.
• 16.25 Evolutionary significance of homeostasis
THE ABILITY OF THE BODY TO KEEP THE INTERNAL ENVIRONMENT WITHIN A CERTAIN RANGE ALLOWS HUMANS TO LIVE IN MANY HABITATS -- warm, cold, dry, wet.
16.3 Body Temperature Regulation
• 16.31 Body temperature regulation when too warm
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1. Controlled Condition (Homeostasis --- 37°C)
2. Stimulus (Stress --- Sunny, body becomes too hot Å37.2°C)
3. I. RECEPTOR (e.g., skin thermoreceptors) Registers that body is too hot
4. INPUT (sensory neuron impulse to the Integrator)
5. II. INTEGRATOR (brain --- hypothalamus)
6. OUTPUT (motor neuron impulse to the Effector)
7. III. EFFECTOR (e.g., sweat glands)
8. Response
i. Blood vessels dilate
ii. Increased blood flow to skin
iii. Sweat glands activated
iv. Sweating begins
v. Water from sweat evaporates
Result: Body temperature lowers
9. Return to Controlled Condition (Homeostasis --- 37°C)
• 16.32 Body temperature regulation when too cold
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1. Controlled Condition (Homeostasis --- 37°C)
2. Stimulus (Stress --- Cloudy, windy, body becomes too cold Å36.8°C)
3. I. RECEPTOR (e.g., skin thermoreceptors) Registers that body is too cold
4. INPUT (sensory neuron impulse to the Integrator)
5. II. INTEGRATOR (brain --- hypothalamus)
6. OUTPUT (motor neuron impulse to the Effector)
7. III. EFFECTOR (e.g., sweat glands, muscles)
8. Response
i. Blood vessels constrict
ii. Decreased blood flow to skin
iii. Sweat glands inactivate
iv. No sweating
v. Shivering
vi. Muscle friction generates heat
Result: Body temperature rises
9. Return to Controlled Condition (Homeostasis --- 37°C)
16.4 Reflex Arc
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def. Reflex: Automatic, involuntary response of an organism to a stimulus.
def. Reflex arc: Simple pathway of information flow without involving the brain. (Stereotyped movement made in response to a sensory stimulation.)
1. Controlled Condition
2. Stimulus (Stress --- put your hand on a hot stove)
3. I. RECEPTOR (skin pain receptors) Registers pain
4. INPUT (sensory neuron impulse to the Integrator)
5. II. INTEGRATOR (spinal cord --- interneuron)
6. OUTPUT (motor neuron impulse to the Effector)
7. III. EFFECTOR (muscles in the hand)
8. Response
Result: Hand is removed from the hot stove
9. Return to Controlled Condition
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