Chapter 2: General Anatomy & Radiographic Positioning Terminology

Detailed Chapter Overview

Chapter 2 provides the essential vocabulary and spatial framework required for all aspects of radiography. It establishes the universal language used by radiographers, radiologists, and other healthcare professionals to describe the body's structure, patient positioning, and the path of the x-ray beam. This chapter begins with the building blocks of the human body, from cells to systems, and provides a concise overview of skeletal anatomy (osteology) and joints (arthrology). The core of the chapter is dedicated to radiographic terminology. It meticulously defines the body planes (sagittal, coronal, axial) that are fundamental to understanding cross-sectional anatomy and CR alignment. Most importantly, it clarifies the critical distinction between a **projection** (the path of the central ray) and a **position** (the patient's posture). Mastering this terminology—including specific projections like AP, PA, and obliques, body positions like supine and Trendelenburg, and relational terms like medial/lateral and proximal/distal—is non-negotiable for accurate communication, precise positioning, and ultimately, the creation of diagnostic images that are free from distortion and correctly represent the patient's anatomy.

In-Depth Study Guide

Structural Organization of the Body

The human body is organized in a hierarchical manner, from the smallest chemical level to the whole organism.

• Cell: The basic structural and functional unit of all living tissue.
• Tissues: Cohesive groups of similar cells that perform a specific function.
• Organs: Complex assemblies of various tissues that are joined to perform a specific function (e.g., the stomach, the liver).
• System: A group or association of organs that have a similar or common function (e.g., the digestive system). The body has 10 individual systems.
• Organism: The 10 systems of the body functioning together make up the total organism.

The 10 Body Systems:

1. Skeletal: Provides framework, protection, and levers for movement.
2. Circulatory: Transports oxygen, nutrients, and waste; includes cardiovascular and lymphatic systems.
3. Digestive: Absorbs nutrients and eliminates solid waste.
4. Respiratory: Supplies oxygen and eliminates carbon dioxide.
5. Urinary: Regulates blood composition and eliminates liquid waste.
6. Reproductive: Enables reproduction of the organism.
7. Nervous: Regulates body activities with electrical impulses.
8. Muscular: Allows for movement.
9. Endocrine: Regulates bodily activity through hormones.
10. Integumentary: Protects the body and regulates temperature; includes the skin.

Osteology: The Study of Bones

The adult skeleton consists of 206 bones, divided into the axial and appendicular skeletons.

• Axial Skeleton (80 bones): Includes all bones on or near the central axis of the body (skull, vertebral column, ribs, sternum).
• Appendicular Skeleton (126 bones): Includes all bones of the upper and lower limbs and the shoulder and pelvic girdles.

Classification of Bones:

• Long Bones: Consist of a body (shaft) and two ends. Found only in the appendicular skeleton (e.g., humerus, femur).
• Short Bones: Roughly cuboidal in shape. Found only in the wrists (carpals) and ankles (tarsals).
• Flat Bones: Consist of two plates of compact bone with cancellous bone and marrow in between (e.g., skull cap, sternum, ribs).
• Irregular Bones: Have peculiar shapes that don't fit other categories (e.g., vertebrae, facial bones, pelvic bones).
• Sesamoid Bones: Small, oval bones that develop in and near tendons. The largest is the patella (kneecap).

Body Planes, Surfaces, and Lines

These are imaginary lines used to divide the body and describe locations.

Fundamental Cardinal Planes:

• Sagittal Plane: A vertical plane that divides the body into right and left parts. The **midsagittal plane** passes through the midline, dividing it into equal right and left halves.
• Coronal Plane: A vertical plane that divides the body into anterior (front) and posterior (back) parts. The **midcoronal plane** divides the body into equal anterior and posterior halves.
• Horizontal (Axial) Plane: A transverse plane at a right angle to the longitudinal axis of the body, dividing it into superior (upper) and inferior (lower) parts.
• Oblique Plane: A longitudinal or transverse plane that is at an angle or slant and is not parallel to the other cardinal planes.

Body Surfaces and Parts:

• Posterior or Dorsal: Refers to the back half of the body.
• Anterior or Ventral: Refers to the front half of the body.
• Plantar: Refers to the sole of the foot.
• Dorsal (Foot): Refers to the top or anterior surface of the foot.
• Dorsal (Hand): Refers to the back of the hand.
• Palmar: Refers to the palm of the hand (anterior surface).

Radiographic Positioning and Projection Terminology

This is the language of radiography. Precise use of these terms is essential.

Key Definitions:

• Position: The specific placement of the body part in relation to the radiographic table or image receptor. It is also used to describe the patient's overall posture, such as erect, supine, or prone.
• Projection: The path or direction of the Central Ray (CR) as it passes through the patient, projecting an image onto the IR. **This is the most accurate term for describing how a radiograph was taken.**

Common Projections:

• Anteroposterior (AP): CR enters the anterior surface and exits the posterior surface.
• Posteroanterior (PA): CR enters the posterior surface and exits the anterior surface.
• AP/PA Oblique: An angled projection where the CR enters from the anterior or posterior and the body is rotated. Described by the side closest to the IR (e.g., RAO, LPO).
• Mediolateral & Lateromedial: Named for the path of the CR through the side of a body part (e.g., a mediolateral projection of the ankle means the CR enters the medial side and exits the lateral side).

Common Body Positions:

• Supine: Lying on the back, facing upward.
• Prone: Lying on the abdomen, facing downward.
• Erect: An upright position, either standing or seated.
• Recumbent: Lying down in any position (supine, prone, or on the side).
• Trendelenburg: A recumbent position with the head lower than the feet.
• Fowler: A recumbent position with the head higher than the feet.
• Sims' Position: A recumbent oblique position with the patient lying on the left anterior side, with the right knee and thigh flexed.
• Decubitus (Decub): Lying down with a horizontal CR. Named according to the body surface the patient is lying on (e.g., dorsal decubitus, ventral decubitus, right/left lateral decubitus). Essential for demonstrating air-fluid levels.

Relational and Movement Terminology

• Medial vs. Lateral: Toward the midline vs. away from the midline.
• Proximal vs. Distal: Closer to the point of attachment/origin vs. farther from the point of attachment/origin.
• Superior (Cephalad) vs. Inferior (Caudad): Toward the head vs. toward the feet.
• Flexion vs. Extension: Decreasing the angle of a joint vs. increasing the angle of a joint.
• Abduction vs. Adduction: Movement of a limb away from the midline vs. toward the midline.
• Supination vs. Pronation: Rotating the hand so the palm is up vs. palm is down.
• Inversion vs. Eversion: Turning the foot inward vs. turning the foot outward.