Functions of Human Life

By the end of this section, you will be able to:
- Explain the importance of organization to the function of the human organism.
- Distinguish between metabolism, anabolism, and catabolism.
- Provide at least two examples of human responsiveness and movement.
- Compare and contrast growth, differentiation, and reproduction.

Different organ systems in the human body have unique functions contributing to human physiology.
Key functions defining human life are:
- Organization
- Metabolism
- Responsiveness
- Movement
- Development
- Reproduction

The human body consists of trillions of cells organized to maintain distinct internal compartments.
- Function of compartments:
  - Protect body cells from environmental threats.
  - Keep cells moist and nourished.
  - Separate internal body fluids from microorganisms.
  - Example: The intestinal tract houses more bacterial cells than human cells, yet they must remain outside the body’s circulation.
Cells have membranes (plasma membranes) that demarcate intracellular and extracellular environments.
Blood vessels protect blood in a closed circulatory system.
Nervous and muscle tissues are wrapped in connective sheaths.
Internal membranes separate vital organs in the chest and abdomen to ensure proper functioning.
The integumentary system (skin, hair, nails) serves as a barrier against microorganisms and toxins.

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed.
Overview of metabolic processes:
- Energy Consumption: Organisms ingest energy through food, converting it into usable forms for body functions and structure maintenance.
- Anabolism:
  - The process of converting smaller molecules into larger, complex substances, requiring energy.
  - Essential for building necessary chemicals from ingested nutrients.
- Catabolism:
  - The breakdown of larger substances into smaller molecules, releasing energy for cellular activities.
  - Allows the body to recycle parts of complex molecules to create structures needed for life.
Metabolism: The sum of all anabolic and catabolic reactions in the body, occurring simultaneously to support life.
Cells utilize adenosine triphosphate - A chemical compound (ATP) to store and release energy:
- Energy is stored through ATP synthesis (anabolism).
- ATP is broken down (catabolism) to release energy for cellular tasks.

Responsiveness: The ability of organisms to adjust to changes in internal and external environments.
- Example of external responsiveness: Moving towards food and water or away from danger.
- Example of internal responsiveness: Sweating and blood vessel dilation in response to increased body temperature (as illustrated by runners).

Human movement encompasses:
- Actions at joints, organ motion, and cell movement.
- Example: Blood cells circulate; muscle cells contract and relax for posture and vision; glands secrete regulating chemicals.
Coordinated muscle groups allow for:
- Breathing (air movement in/out of lungs).
- Circulation (pushing blood throughout the body).
- Digestion (propelling food through the digestive tract).
Conscious control permits voluntary skeletal muscle contraction for movement and daily activities.

Development: All changes the body undergoes throughout life.
- Involves differentiation, where unspecialized cells become specialized for specific functions.
Growth: Increase in body size—happens through:
- Increasing the number of cells.
- Expanding non-cellular material (e.g., mineral build-up in bones).
- Slight increase in size of existing cells.
Reproduction: Formation of new organisms from parental organisms, essential for continuation of species.
- Carried out by male and female reproductive systems.
Without reproduction, the lineage of complex organisms would cease.