UNIT B: Human Body Systems Chapter 8: Human Organization: Section 8.3 Chapter 9: Digestive System Chapter 10: Circulatory System and Lymphatic System.
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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
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.
UNIT B Chapter 8: Human Organization
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What situations might disrupt the internal state of the body?
How can alleviating stress improve your health and quality of life?
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
UNIT B Chapter 8: Human Organization
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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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Section 8.3
UNIT B Chapter 8: Human Organization
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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.
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 temperatureo The control centre turns the furnace on, and the room warms
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Section 8.3
UNIT B Chapter 8: Human Organization
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Section 8.3
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.
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 temperatureo 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 temperatureo The control centre directs the blood vessels in the
skin to constrict and inactivates sweat glands
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Section 8.3
UNIT B Chapter 8: Human Organization
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Section 8.3
Figure 8.7 Regulation of body temperature. Normal body temperature is maintained by a negative feedback system.
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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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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Section 8.3
UNIT B Chapter 8: Human Organization
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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.
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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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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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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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.
•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
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Section 8.3
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
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