Introduction to the Human Body

Chapter 1: An Introduction to the Human Body

Definitions

  • Anatomy

    • Definition: The study of structures of the body and the relationships among these structures, encompassing both microscopic (cells) and macroscopic (organs, systems) levels.

  • Physiology

    • Definition: The study of functions of the parts of the body, which is inherently dependent on anatomy. A body part is capable of performing a specific function due to its particular structure.

Levels of Body Organization

  1. Chemical Level

    • Atoms

      • Key Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P).

      • Atoms are made of subatomic particles: protons, electrons, and neutrons.

      • Atoms organize into molecules, which include DNA, phospholipids, and glucose.

  2. Cellular Level

    • Cells

      • Definition: The smallest structural and functional living unit capable of survival and reproduction. Cells are composed of molecules.

  3. Tissue Level

    • Definition: Groups of similar cells along with the materials surrounding them (interstitial/intercellular fluid).

    • Characteristics: Usually originate from the same embryological source and perform specialized functions.

    • Four Major Classes of Tissues:

      • Epithelial Tissue

      • Connective Tissue

      • Muscle Tissue

      • Nervous Tissue

  4. Organ Level

    • Definition: Composed of two or more different kinds of tissues that form structures with specific functions and recognizable shapes.

  5. System Level

    • Definition: Functionally related groups of organs working together to perform general functions.

  6. Organismal Level

    • Definition: The highest level of organization where all systems are integrated and function cooperatively to constitute a whole human being.

Body Systems Overview

  • 11 Systems in the Body (Table 1.2, p. 6):

    1. Integumentary System

      • Components: Hair, skin, fingernails

    2. Skeletal System

      • Components: Bone, cartilage, joints

    3. Muscular System

      • Components: Skeletal muscle, tendons

    4. Cardiovascular System

      • Components: Heart, arteries, veins

    5. Lymphatic & Immune System

      • Components: Tonsils, spleen, lymph nodes

    6. Nervous System

      • Components: Brain, spinal cord, nerves

    7. Endocrine System

      • Components: Adrenal glands, pancreas, ovaries

    8. Respiratory System

      • Components: Lungs, trachea, larynx

    9. Digestive System

      • Components: Stomach, esophagus, rectum

    10. Urinary System

      • Components: Kidneys, ureters, urinary bladder

    11. Reproductive System

      • Components: Ovaries, testes, vagina, prostate

Basic Anatomical Terminology

  • Anatomical Position

    • Description: A standard position used to ensure that directional terms are clear. The body is erect, the head is level, the eyes are forward, the feet are flat on the floor, and the upper limbs are at the sides with palms facing forward.

    • Variants:

    • Prone Position: lying face down

    • Supine Position: lying face up

Regional Names

  • Terms Given to Specific Regions of the Body:

    • Cephalic: head

    • Cervical: neck

    • Axillary: armpit

Planes and Sections

  • Plane

    • Definition: An imaginary flat surface that passes through the body. Common types include:

    • Sagittal Plane

    • Frontal or Coronal Plane

    • Transverse or Horizontal Plane

    • Oblique Plane

  • Section

    • Definition: The flat surface resulting from a body being "cut" along a specific plane.

    • Transverse/Horizonal/Cross-section

    • Frontal/Coronal Section

    • Sagittal Section

Sagittal Plane

  • Definition: Divides the body into left and right portions.

    • Midsagittal Plane: Divides the body into equal left and right halves.

    • Parasagittal Plane: Divides the body into unequal left and right halves.

Other Planes and Sections

  • Frontal or Coronal Plane: Divides the body into front (anterior/ventral) and back (posterior/dorsal) portions.

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

Major Directional Terms

  • Superior: Closer to the head

    • Example: The eyes are superior to the mouth.

  • Inferior: Away from the head

    • Example: The stomach is inferior to the heart.

  • Dorsal or Posterior: At the back of the body

    • Example: The brain is posterior to the forehead.

  • Ventral or Anterior: At the front of the body

    • Example: The sternum is anterior to the heart.

  • Medial: Nearer to the midline of the body

    • Example: The heart is medial to the lungs.

  • Lateral: Farther from the midline of the body

    • Example: The thumb is lateral to the ring finger.

  • Proximal: Nearer to the attachment of the limb to the trunk

    • Example: The knee is proximal to the ankle.

  • Distal: Farther from the attachment of the limb to the trunk

    • Example: The wrist is distal to the elbow.

Body Cavities

  • Dorsal Body Cavity

    • Cranial Cavity: Formed by cranial bones and contains the brain.

    • Vertebral (Spinal) Canal: Formed by the vertebral column and contains the spinal cord and the beginnings of spinal nerves.

  • Ventral Body Cavity

    • Defined as the cavity inferior to the abdominal diaphragm and subdivided into thoracic and abdominopelvic cavities.

    • Thoracic Cavity:

    • Contains the pleural and pericardial cavities, and mediastinum.

      • Pericardial Cavity: Surrounds the heart; associated serous membrane is the pericardium.

      • Pleural Cavity: Each surrounds a lung; the associated serous membrane is the pleura.

      • Mediastinum: Central portion between the lungs, extending from the sternum to the vertebral column and from the neck to the diaphragm; contains the heart, thymus, esophagus, trachea, and several large blood vessels.

    • Abdominopelvic Cavity:

    • Inferior to abdominal diaphragm, consisting of:

      • Abdominal Cavity: Contains stomach, spleen, liver, gallbladder, small intestine, and most of the large intestine; associated serous membrane is the peritoneum.

      • Pelvic Cavity: Contains urinary bladder, portions of large intestine, and internal reproductive organs.

Types of Serous Membranes

  • Definition: The organs (viscera) within thoracic and abdominal cavities and the cavity walls are lined with serous membranes, also known as serosa, which consist of two layers:

    • Visceral Layer: Covering the organs, tightly adhered.

    • Parietal Layer: Lining the inside walls of thoracic and abdominal cavities.

  • Serous Fluid: Provides lubrication between the two layers.

    • Pleural Cavities: Space between visceral and parietal pleura.

    • Pericardial Cavity: Space between visceral and parietal pericardium.

    • Peritoneal Cavity: Space between visceral and parietal peritoneum.

Abdominopelvic Regions & Quadrants

  • Nine Region System:

  • Four Quadrant System: More frequently used clinically with horizontal and vertical lines passing through the umbilicus, dividing the body into right/left and upper/lower quadrants.

Types of Serous Membranes

  • Definition and Composition

    • Serous Membranes (Serosa): Thin, double-layered membranes that line the ventral body cavities and cover the organs within them. They are distinguished from mucous membranes because they do not open directly to the exterior of the body.

    • Structure: These membranes consist of two layers: a sheet of simple squamous epithelium (called the mesothelium) resting upon a thin layer of areolar connective tissue.

    • Serous Fluid: The mesothelium secretes a watery lubricant called serous fluid into the space between the membrane layers. This fluid is essential for reducing friction as organs move, such as the heart's rhythmic expansion or the lungs' inflation during breathing.

  • The Two-Layer Arrangement

    1. Parietal Layer: The outer layer that lines the internal walls of the thoracic or abdominal cavities.

    2. Visceral Layer: The inner layer that covers and adheres directly to the external surface of the organs (viscera) within the cavity.

  • Specific Serous Membranes and Cavities

    • 1. The Pleura

      • Associated with the lungs within the thoracic cavity.

      • Visceral Pleura: The innermost layer clinging tightly to the lung surface.

      • Parietal Pleura: The layer lining the chest wall and the superior surface of the diaphragm.

      • Pleural Cavity: The fluid-filled space between the layers that ensures smooth movement during respiration (1212-2020 breaths per minute).

    • 2. The Pericardium

      • Associated with the heart within the mediastinum.

      • Visceral Pericardium (Epicardium): The layer forming the outer skin of the heart wall.

      • Parietal Pericardium: The layer lining the fibrous sac that surrounds the heart.

      • Pericardial Cavity: The space between these layers containing pericardial fluid, protecting the heart during its approximately 100,000100,000 daily contractions.

    • 3. The Peritoneum

      • The largest serous membrane, located in the abdominopelvic cavity.

      • Visceral Peritoneum: Covers most abdominal organs (e.g., stomach, spleen, liver).

      • Parietal Peritoneum: Lines the abdominal and pelvic cavity walls.

      • Peritoneal Cavity: The space between the two layers.

      • Retroperitoneal Space: A clinical term for the area behind the parietal peritoneum where organs like the kidneys and pancreas are located.

  • Summary of Function

    • The primary function is to minimize friction between the moving viscera and the body wall, preventing inflammation and tissue damage during physiological processes.