homeostasis and body organization

Homeostasis (Core Concept)

Definition:
Homeostasis = maintenance of a stable internal environment despite external changes.

Key Variables Maintained:

• Temperature (≈ 37°C)

• Blood glucose

• Water balance

• pH

Principle:

• Dynamic equilibrium (not static)

• Requires constant monitoring + adjustment

Homeostatic Regulation System

3 Components:

1. Receptor – detects change (stimulus)

2. Control Center – processes info (usually brain/endocrine)

3. Effector – carries out response

Flow:
Stimulus → Receptor → Control Center → Effector → Response

Feedback Mechanisms

Negative Feedback (MOST IMPORTANT)

• Opposes change

• Maintains stability

Examples:

• Blood glucose:

  • High glucose → insulin → lowers glucose

  • Low glucose → glucagon → raises glucose

• Body temperature:

  • Too hot → sweating

  • Too cold → shivering

AP Insight:

• Negative feedback loops = central to survival and regulation

Positive Feedback (RARE)

• Amplifies change

Examples:

• Digestive enzyme release (stomach)

• (AP classic: childbirth contractions, though not in your text)

AP Insight:

• Used for rapid, decisive processes, not stability

Levels of Organization (Hierarchy)

Order (must memorize):
Cells → Tissues → Organs → Organ Systems → Organism

Tissues (4 Types — HIGH YIELD)

1. Epithelial

• Tightly packed cells

• Functions:

  • Protection (skin)

  • Absorption

  • Secretion

• Found in:

  • Skin

  • Linings of organs

2. Connective

• Most abundant

• Functions:

  • Support

  • Transport

  • Protection

Types:

• Bone

• Blood

• Cartilage

• Adipose (fat)

• Lymph

3. Muscle

• Movement via actin + myosin

Types:

• Skeletal → voluntary

• Smooth → organs

• Cardiac → heart

4. Nervous

• Function:

  • Detect stimuli

  • Transmit electrical signals

Components:

• Brain

• Spinal cord

• Nerves

Organs (Composed of Multiple Tissues)

Examples + Functions:

• Skin → protection, temperature regulation

• Lungs → gas exchange (O₂ in, CO₂ out)

• Stomach → digestion

• Kidneys → filtration, water/pH balance

Organ Systems (Integrated Function)

Major Systems (know broadly):

• Nervous → control/coordination

• Endocrine → hormones

• Circulatory → transport

• Respiratory → gas exchange

• Digestive → nutrient breakdown

• Musculoskeletal → movement/support

• Immune/Lymphatic → defense

• Integumentary → protection + temp regulation

• Excretory → waste removal

• Reproductive → offspring

Key AP Concept:

• Systems are interdependent

• Example:

  • Respiratory + circulatory → oxygen delivery

Thermoregulation (Important Example)

Too Hot:

• Sweating (evaporative cooling)

• Vasodilation

Too Cold:

• Shivering (muscle activity → heat)

• Vasoconstriction

• Goosebumps (vestigial)

Adaptations in Mammals (Homeostasis Variations)

Energy Storage

• Whales → fat (blubber) for cold survival

Heat Regulation

• Camels → allow body temp to rise → conserve water

Hibernation

• Reduced:

  • Body temperature

  • Heart rate

  • Breathing

Example:

• Squirrels store fat + food, enter dormancy

AP Exam Emphasis (What to Focus On)

• Negative vs positive feedback (compare explicitly)

• Flow of regulation: stimulus → response

• Interactions between organ systems

• Structure → function relationships (tissues/organs)

• Real-world examples of homeostasis

Condensed Cheat Sheet

• Homeostasis = internal stability

• 3 parts: receptor → control center → effector

• Negative feedback = stabilizes (most common)

• Positive feedback = amplifies (rare)

• Organization: cell → tissue → organ → system

• 4 tissues: epithelial, connective, muscle, nervous

• Systems work together (not isolated)

• Adaptations = specialized homeostasis strategies