Characteristics of Living Organisms

Defining Features of Life

All living organisms share a set of fundamental characteristics that distinguish them from non-living matter. These features are essential for the maintenance, growth, and reproduction of life.

• Cellular Composition: The cell is the smallest unit capable of carrying out the functions of life. All organisms are composed of one or more cells.

• Metabolism: The sum of all chemical processes occurring in the body. Metabolism includes two main types:

  • Anabolism: Building up of larger molecules from smaller ones (e.g., muscle growth).

  • Catabolism: Breaking down of larger molecules into smaller ones (e.g., digestion).

• Growth: Occurs when anabolism exceeds catabolism, resulting in:

  • Increase in size of individual cells

  • Increase in the number of cells

• Excretion: Removal of waste products generated by metabolic processes to prevent toxicity.

• Responsiveness (Irritability): Ability to sense and react to environmental stimuli (e.g., touch, pain, light).

• Movement: Includes movement of the organism, movement of cells within the organism, and internal movement of substances.

• Reproduction: Ability to produce new cells (for growth and repair) and new organisms (offspring).

Levels of Structural Organization and Body Systems

Hierarchy of Organization

The human body is organized into a hierarchy of structural levels, each building upon the previous one.

• Chemical Level: Atoms and molecules form the basis of all matter.

• Cellular Level: Molecules combine to form cells, the basic units of life.

• Tissue Level: Groups of similar cells and their extracellular matrix perform specific functions as tissues.

• Organ Level: Two or more tissue types combine to form organs with specialized functions (e.g., heart, skin).

• Organ System Level: Organs work together in organ systems to perform broad functions (e.g., cardiovascular system).

Types of Anatomy and Physiology

Approaches to Studying the Body

• Systemic Anatomy: Study of the body by organ systems.

• Regional Anatomy: Study of specific regions (e.g., head, neck).

• Surface Anatomy: Study of external body markings.

• Gross Anatomy: Study of structures visible to the naked eye.

• Microscopic Anatomy: Study of structures requiring magnification:

  • Histology: Study of tissues.

  • Cytology: Study of cells.

• Neurophysiology: Study of brain and nerve function.

• Cardiovascular Physiology: Study of heart and blood vessels.

Anatomical Position and Regional Terms

Standard Reference Position

The anatomical position is the standard reference for describing body parts and regions: standing upright, feet shoulder-width apart, arms at sides, head and palms facing forward.

Body Regions

• Axial Region: Head, neck, and trunk.

• Appendicular Region: Upper and lower limbs.

Selected Regional Terms

• Trunk: Abdominal (abdomen), Cervical (neck), Gluteal (buttocks), Lumbar (lower back), Pelvic (pelvis), Thoracic (chest), Vertebral (spinal column)

• Head and Face: Cranial (skull), Cephalic (head), Frontal (forehead), Nasal (nose), Oral (mouth), Ocular (eye), Otic (ear)

• Upper Limb: Brachial (arm), Antebrachial (forearm), Carpal (wrist), Manual (hand), Digital (fingers), Palmar (palm), Pollex (thumb)

• Lower Limb: Femoral (thigh), Patellar (knee), Crural (leg), Tarsal (ankle), Pedal (foot), Plantar (sole), Hallux (great toe)

Body Planes and Sections

Describing Internal Organization

• Sagittal Plane: Divides body into right and left sections.

  • Midsagittal (Medial) Plane: Equal right and left halves.

  • Parasagittal Plane: Unequal right and left sections.

• Frontal (Coronal) Plane: Divides body into anterior (front) and posterior (back) sections.

• Transverse (Horizontal) Plane: Divides body into superior (upper) and inferior (lower) parts.

• Oblique Plane: Cuts at an angle, useful for examining complex structures.

Organization of the Human Body: Cavities and Membranes

Body Cavities

Body cavities protect internal organs and allow for their movement and expansion.

• Posterior Body Cavity:

  • Cranial Cavity: Contains the brain.

  • Spinal Cavity: Contains the spinal cord.

  • Both are filled with cerebrospinal fluid for protection and buoyancy.

• Anterior Body Cavity:

  • Divided by the diaphragm into:

    • Thoracic Cavity: Contains pleural cavities (lungs), mediastinum (heart, vessels, trachea, esophagus), and pericardial cavity (heart).

    • Abdominopelvic Cavity: Contains abdominal cavity (digestive, lymphatic, urinary organs) and pelvic cavity (reproductive, digestive, urinary organs).

Abdominopelvic Quadrants and Regions

The abdominopelvic cavity can be divided for clinical and anatomical reference:

• Four Quadrants: Right Upper (RUQ), Left Upper (LUQ), Right Lower (RLQ), Left Lower (LLQ).

• Nine Regions: Right/Left Hypochondriac, Epigastric, Right/Left Lumbar, Umbilical, Right/Left Inguinal (Iliac), Hypogastric.

Serous Membranes

Serous membranes line certain body cavities and cover organs, producing serous fluid to reduce friction.

• Visceral Layer: Contacts the organ.

• Parietal Layer: Attaches to surrounding structures.

• Serous Fluid: Lubricates and prevents friction.

Additional info: Organs located behind the parietal peritoneum are termed retroperitoneal (e.g., kidneys).

Medical Imaging Techniques

Non-invasive Visualization of Internal Structures

• X-ray: Uses ionizing radiation to produce images of dense structures (e.g., bones, chest cavity).

• Computed Tomography (CT): Uses ionizing radiation and computer processing to create 3D images, especially useful for soft tissues.

• Magnetic Resonance Imaging (MRI): Uses magnetic fields and radio waves to generate detailed images of soft tissues.

Core Principles in Anatomy and Physiology

Homeostasis and Regulation

Homeostasis is the body's ability to maintain a relatively stable internal environment despite external changes. This is achieved through coordinated physiological processes.

• Feedback Loops: Mechanisms that regulate variables by responding to changes:

  • Negative Feedback: Opposes initial change, stabilizing the variable (most common).

  • Positive Feedback: Reinforces initial change, amplifying the response (less common).

• Structure-Function Relationship: The form of a body part determines its function.

• Gradients: Differences in concentration, pressure, or temperature drive physiological processes.

• Cell-Cell Communication: Cells coordinate activities via chemical or electrical signals.

Examples of Gradients

• Temperature Gradient: Heat moves from warmer to cooler areas.

• Concentration Gradient: Substances move from areas of higher to lower concentration.

• Pressure Gradient: Fluids and gases move from high to low pressure regions.

Common Misconceptions about Homeostasis

• Negative feedback is not inherently 'bad'; it is essential for stability.

• Homeostasis does not mean a static internal environment; variables fluctuate within normal ranges.

• Regulatory mechanisms are not simply 'on' or 'off'; they operate dynamically.

• Not all physiological variables can be controlled; only those with appropriate sensors and effectors.

Key Terms and Definitions

• Regulated Variable: A variable maintained within a normal range (e.g., body temperature, blood glucose).

• Controlled Variable: A process manipulated to maintain homeostasis of a regulated variable.

Summary Table: Levels of Organization

Example: Negative Feedback Loop (Blood Glucose Regulation)

• Increase in blood glucose detected by pancreas (sensor).

• Pancreas releases insulin (effector).

• Cells take up glucose, lowering blood glucose to normal range.

Additional info: Feedback loops are essential for maintaining homeostasis and preventing disease.