Anatomical Terminology, Body Organization, and Epithelial Tissue

Anatomical Terminology and Body Organization

Deep or Internal

Deep (internal) refers to structures that are located away from the surface of the body, toward the interior. For example, the lungs are deep to the ribs.

Regional Terms or Anatomical Landmarks

• Axial: Refers to the main axis of the body, including the head, neck, and trunk.

• Appendicular: Refers to the limbs and their attachments to the axis (arms and legs).

Body Planes & Sections

Body planes are imaginary lines used to divide the body into sections for anatomical study and medical imaging.

• Sagittal plane: Divides the body into right and left portions.

• Median or midsagittal plane: A sagittal plane that lies exactly in the midline, dividing the body into equal right and left halves.

• Parasagittal plane: Any sagittal plane that is offset from the midline, dividing the body into unequal right and left parts.

• Frontal (coronal) plane: Divides the body into anterior (front) and posterior (back) portions.

• Transverse (horizontal) plane: Divides the body into superior (upper) and inferior (lower) portions; also called a cross-section.

Body Cavities

The body contains several cavities that house and protect internal organs.

1. Dorsal body cavity: Protects the nervous system and has two subdivisions:

   • Cranial cavity: Encases the brain.

   • Vertebral (spinal) cavity: Encases the spinal cord.

2. Ventral body cavity (coelom): Houses the internal organs (viscera) and has two main subdivisions:

   • Thoracic cavity: Superior portion, divided into:

     • Right and left pleural cavities (each surrounds a lung).

     • Mediastinum: Central compartment, includes the pericardial cavity (encloses the heart).

   • Abdominopelvic cavity: Inferior to the thoracic cavity, separated by the diaphragm, and divided into:

     • Abdominal cavity: Contains digestive organs (stomach, intestines, spleen, liver, etc.).

     • Pelvic cavity: Contains urinary bladder, reproductive organs, and rectum.

Membranes of the Ventral Body Cavity

• Serous membranes (serosa): Thin, double-layered membranes that cover the walls of the ventral body cavity and the outer surfaces of the organs.

  • Parietal serosa: Lines the cavity walls.

  • Visceral serosa: Covers the organs within the cavity.

  • Serous cavity: The space between the parietal and visceral serosa, filled with serous fluid to reduce friction.

Serous membranes are named according to their location:

• Parietal pericardium: Lines the pericardial cavity.

• Visceral pericardium: Covers the heart.

• Parietal pleura: Lines the pleural cavity (lungs).

• Visceral pleura: Covers the lungs.

• Parietal peritoneum: Lines the abdominopelvic cavity.

• Visceral peritoneum: Covers the abdominal organs.

Abdominopelvic Regions and Quadrants

The abdominopelvic area is divided for clinical and anatomical reference.

• Abdominopelvic regions (nine regions):

  • Umbilical region: Center, contains the navel.

  • Epigastric region: Superior to the umbilical region.

  • Hypogastric (pubic) region: Inferior to the umbilical region.

  • Right & left inguinal (iliac) regions: Lateral to the hypogastric region.

  • Right & left lumbar regions: Lateral to the umbilical region.

  • Right & left hypochondriac regions: Lateral to the epigastric region.

• Abdominopelvic quadrants (four quadrants):

  • Right Upper Quadrant (RUQ)

  • Left Upper Quadrant (LUQ)

  • Right Lower Quadrant (RLQ)

  • Left Lower Quadrant (LLQ)

Tissues and Epithelial Tissue

Overview of Tissues

Tissues are groups of cells that are similar in structure and perform a common function. There are four basic tissue types:

• Epithelial tissue

• Connective tissue

• Muscle tissue

• Nervous tissue

Epithelial Tissue

Epithelium is a sheet of cells that covers body surfaces and lines body cavities. It is classified as either covering and lining epithelium or glandular epithelium.

• Functions:

  • Protection

  • Absorption

  • Excretion

  • Secretion

  • Sensory reception

Characteristics of Epithelial Tissue

• Polarity: Epithelial cells have an apical (upper, free) surface exposed to the body exterior or the cavity of an internal organ, and a basal (lower, attached) surface.

• Specialized contacts: Cells are closely packed and held together by tight junctions and desmosomes.

• Supported by connective tissue: The basal surface is attached to a basement membrane, which is an adhesive sheet of glycoprotein secreted by epithelial cells and connective tissue underneath.

• Avascular: Contains no blood vessels but is supplied by nerve fibers; nutrients diffuse from underlying connective tissues.

• Regeneration: High regenerative capacity due to frequent cell division.

Some apical surfaces are smooth, while others have microvilli (to increase surface area) or cilia (to move substances).

Classification of Epithelial Tissue

Epithelia are classified by two criteria:

1. Number of cell layers:

   • Simple epithelium: Single layer of cells; typically involved in absorption, secretion, and filtration.

   • Stratified epithelium: Two or more layers; mainly for protection.

2. Shape of cells (at the apical surface for stratified types):

   • Squamous: Flattened and scale-like.

   • Cuboidal: Boxlike, as tall as they are wide.

   • Columnar: Tall and column shaped.

Simple Epithelia

• Simple squamous epithelium: Very thin, allows for rapid diffusion and filtration. Found in air sacs of lungs, lining of heart, blood vessels, and lymphatic vessels.

• Special names:

  • Endothelium: Simple squamous epithelium lining blood vessels and the heart.

  • Mesothelium: Simple squamous epithelium found in serous membranes lining the ventral body cavity and covering its organs.

Summary Table: Body Planes and Cavities

Plane	Description
Sagittal	Divides body into right and left parts
Midsagittal (Median)	Divides body into equal right and left halves
Parasagittal	Divides body into unequal right and left parts
Frontal (Coronal)	Divides body into anterior and posterior parts
Transverse (Horizontal)	Divides body into superior and inferior parts

Body Cavity	Subdivisions	Contents
Dorsal	Cranial, Vertebral	Brain, Spinal cord
Ventral	Thoracic (pleural, pericardial, mediastinum), Abdominopelvic (abdominal, pelvic)	Lungs, Heart, Digestive organs, Urinary bladder, Reproductive organs

Additional info: Some explanations and definitions have been expanded for clarity and completeness, following standard Anatomy & Physiology textbook conventions.