Download Chapter 8: Human Organization: Section 8.3

UNIT B: Human Body Systems
Chapter 8: Human Organization:
Section 8.3
Chapter 9: Digestive System
Chapter 10: Circulatory System and
Lymphatic System
Chapter 11: Respiratory System
Chapter 12: Nervous System
Chapter 13: Urinary System
Chapter 14: Reproductive System
UNIT B Chapter 8: Human Organization
Chapter 8: Human Organization
In this chapter, you will learn
about how the systems in our
bodies are connected and
work together to maintain a
relatively constant internal
environment.
What situations might disrupt the
internal state of the body?
How can alleviating stress improve
your health and quality of life?
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UNIT B Chapter 8: Human Organization
Section 8.3
8.3 Homeostasis
Homeostasis is the maintenance of a relatively constant
internal environment by an organism or single cell.
• Internal conditions in the body stay within a narrow
range (e.g., body temperature stays at 37ºC)
• The internal state of the body is a dynamic equilibrium,
since internal conditions are not absolutely constant
• Illness can result if the internal conditions change to a
great degree
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UNIT B Chapter 8: Human Organization
Section 8.3
Negative Feedback
Negative feedback is the main homeostatic mechanism that
keeps a variable close to a set point.
A homeostatic system has at least two components:
• Sensor: detects a change in internal conditions
• Control centre: directs a response that brings conditions back
to normal
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UNIT B Chapter 8: Human Organization
Section 8.3
Figure 8.5 Negative feedback mechanism. The sensor and control centre of a feedback
mechanism work together to keep a variable close to a particular value.
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UNIT B Chapter 8: Human Organization
Section 8.3
Examples of negative feedback
Regulation of room temperature
• Thermostat is set at 20ºC (set point)
• Temperature above set point:
o The sensor (thermometer in thermostat) detects the increase
in temperature
o The control centre (also in the thermostat) turns the furnace
off, and the room cools
• Temperature below set point:
o The sensor detects the decrease in temperature
o The control centre turns the furnace on, and the room warms
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UNIT B Chapter 8: Human Organization
Figure 8.6 Complex negative
feedback mechanism. When a
room becomes too warm,
negative feedback allows the
temperature to return to normal.
A contrary cycle, in which the
furnace turns on and gives off
heat, returns the room
temperature to normal when the
room becomes too cool.
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Section 8.3
UNIT B Chapter 8: Human Organization
Section 8.3
Regulation of body temperature
• The body temperature set point is 37ºC
• Temperature above set point:
o The sensor (hypothalamus in the brain) detects the
increase in temperature
o The control centre (also in the hypothalamus) directs
the blood vessels in the skin to dilate and activates
sweat glands
• Temperature below set point:
o The sensor detects the decrease in temperature
o The control centre directs the blood vessels in the
skin to constrict and inactivates sweat glands
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UNIT B Chapter 8: Human Organization
Section 8.3
Figure 8.7
Regulation of body
temperature. Normal
body temperature is
maintained by a
negative feedback
system.
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UNIT B Chapter 8: Human Organization
Section 8.3
Positive Feedback
Positive feedback is a mechanism that brings about an
even greater change in the same direction.
Example: blood clotting
• Injured tissues release chemical factors that activate
platelets
• Platelets initiate the clotting process and release factors
that stimulate further clotting
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UNIT B Chapter 8: Human Organization
Section 8.3
Homeostasis and Body Systems
All body systems contribute toward maintaining
homeostasis.
The Transport Systems
• Circulatory system: conducts blood to and away from
capillaries where exchange of gases, nutrients, and
wastes occurs; regulates tissue fluid composition
• Lymphatic system: collects excess tissue fluid, which is
returned via lymphatic vessels to the circulatory system
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UNIT B Chapter 8: Human Organization
Section 8.3
Figure 8.8 Regulation of
tissue fluid composition.
Cells are surrounded by
tissue fluid, which is
continually refreshed
because oxygen and
nutrient molecules
constantly exit, and carbon
dioxide and waste
molecules continually enter
the bloodstream.
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UNIT B Chapter 8: Human Organization
Section 8.3
The Maintenance Systems
• Respiratory system: adds oxygen and removes carbon
dioxide from the blood; regulates blood pH
• Digestive system: ingests and digests food, providing
nutrients to the blood to replace nutrients that are used in
body cells
• Liver: regulates blood glucose and removes toxic
chemicals
• Urinary system: kidneys regulate blood volume, salt
balance, and pH
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UNIT B Chapter 8: Human Organization
Section 8.3
The Support Systems
• Integumentary system: protects internal organs and
produces vitamin D
• Musculoskeletal system: protects internal organs, stores
minerals, and produces blood cells
The Control Systems
• Nervous system and endocrine system: work together to
control other body systems to maintain homeostasis
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UNIT B Chapter 8: Human Organization
Section 8.3
Disease
A disease is an abnormality in the body’s normal processes that
significantly impairs homeostasis.
• Systemic diseases: affect the entire body or several organ
systems (e.g., lupus)
• Localized diseases: affect a specific part of the body (e.g.,
dermatitis, arthritis)
• Acute diseases: occur suddenly and generally last a short time
(e.g., poison ivy dermatitis, influenza)
• Chronic diseases: develop slowly and last a long time (e.g.,
multiple sclerosis, most cancers)
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UNIT B Chapter 8: Human Organization
Section 8.3
Disease
Cancer is a group of disorders in which the controls of cell
division fail, resulting in the production of abnormal cells
that destroy healthy tissues.
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Carcinomas: cancers of epithelial tissue (most common)
Sarcomas: cancers arising in muscle or connective tissue
Leukemia: cancers of the blood cells
Lymphomas: cancers that originate in lymph nodes
UNIT B Chapter 8: Human Organization
Check Your Progress
1. Compare positive and negative feedback. Give an
example of each.
2. Describe how several body systems can interact to
maintain homeostasis.
3. List several specific diseases that result when a
particular body system fails to perform its function.
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Section 8.3
UNIT B Chapter 8: Human Organization
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Section 8.3