Introduction to Anatomical Terms

The Anatomical Position

• Definition: The standardized posture used in human anatomy to describe body structures, directional locations, and movements consistently.
• Key Standards:
  • The individual stands upright (erect) facing the observer directly.
  • Head, eyes, and toes face directly forward.
  • Upper limbs are placed at the sides of the body.
  • The palms face forward (anteriorly) with fingers extended.
  • The thumbs point laterally (away from the body midline).
  • The feet are parallel and point forward.

Anatomical Planes and Sections

• Definition of Plane: An imaginary flat surface that passes through the body to slice or section it for structural study.
• Frontal (Coronal) Plane:
  • Divides the body or an organ into anterior (front) and posterior (back) portions.
• Transverse (Horizontal) Plane:
  • Divides the body or an organ into superior (upper) and inferior (lower) portions.
• Sagittal Plane:
  • Divides the body or an organ vertically into right and left sides.
  • Midsagittal Plane: Passes directly along the midline, dividing the body into equal left and right halves.
  • Parasagittal Plane: Divides the body into unequal left and right halves.

Directional Terms and Orientation

• Directional Terms Table:
  • Ventral: Toward the front or belly. Example: The aorta is ventral to the vertebral column.
  • Dorsal: Toward the back or spine. Example: The vertebral column is dorsal to the aorta.
  • Anterior: Toward the ventral side. Example: The sternum is anterior to the heart.
  • Posterior: Toward the dorsal side. Example: The esophagus is posterior to the trachea.
  • Cephalic: Toward the head or superior end. Example: The cephalic end of the embryonic neural tube develops into the brain.
  • Rostral: Toward the forehead or nose. Example: The forebrain is rostral to the brainstem.
  • Caudal: Toward the tail or inferior end. Example: The spinal cord is caudal to the brain.
  • Superior: Above. Example: The heart is superior to the diaphragm.
  • Inferior: Below. Example: The liver is inferior to the diaphragm.
  • Medial: Toward the median plane / midline of the body; on the inner side of. Example: The heart is medial to the lungs.
  • Lateral: Away from the median plane / midline of the body; on the outer side of. Example: The eyes are lateral to the nose.
  • Intermediate: Between a more medial and a more lateral structure. Example: The collarbone (clavicle) is intermediate between the breastbone (sternum) and shoulder.
  • Proximal: Closer to the origin of a body part or point of attachment of a limb to the body trunk. Example: The elbow is proximal to the wrist.
  • Distal: Farther from the origin of a body part or point of attachment of a limb to the body trunk. Example: The fingernails are at the distal ends of the fingers; the knee is distal to the thigh.
  • Ipsilateral: On the same side of the body (right or left). Example: The liver is ipsilateral to the appendix.
  • Contralateral: On opposite sides of the body (right and left). Example: The spleen is contralateral to the liver.
  • Superficial (External): Toward or at the body surface. Example: The skin is superficial to the skeletal muscles.
  • Deep (Internal): Away from the body surface; more internal. Example: The bones/lungs are deep to the muscles/skin.

• Directional Differences in Quadrupeds vs. Humans:
  • In humans (bipeds), ventral and anterior are synonymous, as are dorsal and posterior.
  • In four-legged animals (quadrupeds):
  • Anterior refers to the leading portion of the body (the head).
  • Ventral refers specifically to the belly or underside (which is the inferior surface in quadrupeds).
  • Posterior refers to the tail/rear portion.
  • Dorsal refers specifically to the back surface (which is the superior surface in quadrupeds).

Divisions of the Skeletal System

• Axial Skeleton:
  • Forms the central vertical axis of the body.
  • Composed of the skull (head), vertebral column, and thoracic cage (ribs and sternum).
• Appendicular Skeleton:
  • Consists of the upper and lower limbs (appendages).
  • Includes the attachment girdles:
  • Pectoral (Shoulder) Girdle: Attaches upper limbs to the axial trunk.
  • Pelvic (Hip) Girdle: Attaches lower limbs to the axial trunk.

Body Regions

• Anterior Body Regions:
  • Cephalic: Head region.
  • Frontal: Forehead.
  • Orbital: Eye region.
  • Nasal: Nose region.
  • Buccal: Cheek.
  • Oral: Mouth.
  • Mental: Chin.
  • Cervical: Neck region.
  • Acromial: Point of the shoulder.
  • Axillary: Armpit region.
  • Brachial: Arm (upper arm).
  • Antecubital: Anterior surface of the elbow.
  • Antebrachial: Forearm.
  • Carpal: Wrist.
  • Palmar: Palm of the hand.
  • Digital: Fingers or toes.
  • Sternal: Breastbone area.
  • Pectoral / Thoracic: Chest area.
  • Umbilical: Navel region.
  • Coxal: Hip region.
  • Inguinal: Groin region.
  • Femoral: Thigh region.
  • Patellar: Kneecap (anterior knee).
  • Crural: Shin/anterior leg.
  • Tarsal: Ankle region.
  • Dorsum of Foot: Top surface of the foot.
  • Pes: Foot.

• Posterior Body Regions:
  • Cranial: Region surrounding the brain.
  • Auricular / Otic: Ear region.
  • Occipital: Base or back of the head.
  • Vertebral: Spine / vertebral column area.
  • Dorsal / Scapular: Shoulder blade / back region.
  • Cubital / Olecranal: Posterior elbow.
  • Lumbar: Lower back region between ribs and hips.
  • Gluteal: Buttock region.
  • Perineal: Region between the anus and external genitalia.
  • Popliteal: Hollow behind the knee (posterior knee).
  • Sural: Calf (posterior leg).
  • Calcaneal: Heel of the foot.
  • Plantar: Sole of the foot.

Body Cavities, Membranes, and Coeloms

• Cavities vs. Coeloms Distinction:
  • There are $7$ major body cavities in total, but only $3$ true coeloms.
  • All coeloms are cavities, but not all cavities are coeloms.
  • Coelom Definition: A fluid-filled body space lined with serous membranes (mesothelium/epithelium) that encloses internal organs and provides clearance for movement without friction.
• Dorsal Cavities (Lined by meninges; not true coeloms):
  • Cranial Cavity: Formed by cranial bones; contains the brain.
  • Vertebral Canal: Formed by the vertebral column; contains the spinal cord.
• Ventral Cavities:
  • Thoracic Cavity: Superior ventral cavity bounded by the chest wall; separated from the abdominal cavity by the diaphragm. Contains:
  • Pleural Cavities ($2$ coeloms): Enclose the left and right lungs.
  • Mediastinum: Central region between the lungs; contains the esophagus, trachea, thymus, and major blood vessels.
  • Pericardial Cavity ($1$ coelom): Encloses the heart within the mediastinum.
  • Abdominopelvic Cavity: Divided into:
  • Abdominal Cavity: Superior portion containing the stomach, intestines, liver, gallbladder, spleen, and pancreas.
  • Pelvic Cavity: Inferior portion containing the urinary bladder, internal reproductive organs, and rectum.
  • Scrotal Cavity: Found exclusively in males, accommodating the testes.

• Serous Membranes (Example: Pericardium):
  • Visceral Layer: Inner layer that adheres directly to the surface of the organ (e.g., visceral pericardium).
  • Parietal Layer: Outer layer that lines the inner wall of the body cavity (e.g., parietal pericardium).
  • Cavity Space: Fluid-filled potential space between the visceral and parietal layers.
  • Balloon Analogy: Pushing a fist into a flexible balloon models heart tissue surrounded by serous layers:
  • The fist represents the heart organ.
  • The inner balloon wall touching the fist represents the visceral pericardium.
  • The outer balloon wall represents the parietal pericardium.
  • The air space inside the balloon represents the fluid-filled cavity.

Abdominopelvic Quadrants and Regions

• Four Abdominopelvic Quadrants:
  • Formed by a vertical midline and horizontal transumbilical line crossing at the navel.
  • Right Upper Quadrant (RUQ): Contains the right lobe of the liver, gallbladder, right kidney, and portions of the stomach and intestines.
  • Left Upper Quadrant (LUQ): Contains the stomach, spleen, left lobe of the liver, pancreas, left kidney, and portions of the intestines.
  • Right Lower Quadrant (RLQ): Contains the cecum, appendix, right ovary/spermatic cord, and right ureter.
  • Left Lower Quadrant (LLQ): Contains the sigmoid colon, left ovary/spermatic cord, and left ureter.
• Nine Abdominopelvic Regions:
  • Grid Boundaries:
  • Vertical Lines: Midclavicular lines (drawn through the midpoint of each clavicle).
  • Superior Horizontal Line: Subcostal line (passes across the lowest boundary of the $10^{\text{th}}$ costal cartilage).
  • Inferior Horizontal Line: Intertubercular line (passes horizontally between the tubercles of the iliac crests).
  • Regional Breakdown:
  • Epigastric Region: Upper central region above the stomach.
  • Right Hypochondriac Region: Upper right region covered by the lower ribs.
  • Left Hypochondriac Region: Upper left region covered by the lower ribs.
  • Umbilical Region: Central region surrounding the umbilicus.
  • Right Lumbar Region: Right middle region adjacent to the lumbar vertebrae.
  • Left Lumbar Region: Left middle region adjacent to the lumbar vertebrae.
  • Hypogastric (Pubic) Region: Lower central region below the umbilical area.
  • Right Inguinal (Iliac) Region: Lower right region near the groin and iliac crest.
  • Left Inguinal (Iliac) Region: Lower left region near the groin and iliac crest.

Human Organ Systems Overview

• Integumentary System:
  • Major Organs: Skin, hair, nails, cutaneous glands.
  • Functions: Protection, water retention, thermoregulation, vitamin D synthesis, cutaneous sensation.
• Skeletal System:
  • Major Organs: Bones, cartilages, ligaments.
  • Functions: Support, movement lever systems, protection of internal organs, blood formation, mineral storage, acid-base balance.
• Muscular System:
  • Major Organs: Skeletal muscles.
  • Functions: Movement, stability, posture, heat production, communication, control of body openings.
• Nervous System:
  • Major Organs: Brain, spinal cord, nerves, ganglia.
  • Functions: Rapid internal communication, coordination, motor control, sensation processing.
• Endocrine System:
  • Major Organs: Pituitary, pineal, thyroid, parathyroid glands, thymus, adrenal glands, pancreas, ovaries, testes.
  • Functions: Hormone production, long-term internal chemical coordination and metabolism control.
• Cardiovascular System:
  • Major Organs: Heart, blood vessels.
  • Functions: Distribution of oxygen, nutrients, hormones, metabolic wastes, immune cells, and heat.
• Lymphatic System:
  • Major Organs: Lymph nodes, lymphatic vessels, thymus, spleen, tonsils.
  • Functions: Fluid recovery from tissues, immune defense, pathogen detection, cell absorption.
• Respiratory System:
  • Major Organs: Nose, pharynx, larynx, trachea, bronchi, lungs.
  • Functions: Oxygen absorption, carbon dioxide discharge, speech, acid-base balance.
• Urinary System:
  • Major Organs: Kidneys, ureters, urinary bladder, urethra.
  • Functions: Waste elimination, regulation of blood pressure/volume, electrolyte and acid-base balance.
• Digestive System:
  • Major Organs: Teeth, tongue, salivary glands, esophagus, stomach, small and large intestines, liver, gallbladder, pancreas.
  • Principal Functions: Nutrient breakdown and absorption.
  • Liver Specific Functions: Metabolism of carbohydrates, lipids, proteins, vitamins, and minerals; plasma protein synthesis; disposal of drugs, toxins, and hormones; blood cleansing.
• Male Reproductive System:
  • Major Organs: Testes, epididymides, ductus deferentia, seminal vesicles, prostate, bulbourethral glands, penis.
  • Principal Functions: Production and delivery of sperm; secretion of male sex hormones.
• Female Reproductive System:
  • Major Organs: Ovaries, uterine tubes, uterus, vagina, vulva, mammary glands.
  • Principal Functions: Production of oocytes, site of fertilization and fetal development, fetal nourishment, childbirth, lactation, secretion of female sex hormones.