Introduction to Anatomy

• Anatomy studies the structure of living organisms.
• It examines the body's components, their organization, and their interrelationships.
• It is crucial for understanding bodily functions.
• It serves as the structural basis of physiological processes.

Subdivisions of Anatomy

• Gross anatomy (macroscopic anatomy) involves structures visible to the naked eye.
  • Systemic anatomy studies the body by organ systems, such as the skeletal, muscular, and nervous systems.
  • Regional anatomy studies the body by regions, for example, the head, thorax, and abdomen, relationships between structures are emphasized.
  • Surface anatomy focuses on external features in relation to deeper structures.
  • Clinical anatomy applies anatomical knowledge to medical practice.
• Microscopic anatomy studies structures not visible to the naked eye.
  • Histology is the study of tissues at the microscopic level.
  • Cytology is the study of cells.
• Developmental anatomy studies the changes in structure from conception to adulthood.
  • Embryology studies the development of an organism from fertilization to birth.
• Comparative anatomy compares anatomical structures across different species.

Anatomical Position and Planes

• Anatomical position serves as a standardized reference.
  • The body is erect, feet slightly apart, palms face forward, and thumbs point away from the body.
• Anatomical planes are used to divide the body for study.
  • The sagittal plane divides the body into right and left sections.
    • The midsagittal (median) plane is a sagittal plane along the midline, dividing the body into equal halves.
    • The parasagittal plane is any sagittal plane offset from the midline.
  • The frontal (coronal) plane divides the body into anterior (front) and posterior (back) sections.
  • The transverse (horizontal or axial) plane divides the body into superior (upper) and inferior (lower) sections.
• Oblique sections are diagonal cuts through the body.

Directional Terms

• Superior (cranial) means toward the head or upper part of the body; above.
• Inferior (caudal) means away from the head or toward the lower part of the body; below.
• Anterior (ventral) means toward the front of the body; in front of.
• Posterior (dorsal) means toward the back of the body; behind.
• Medial means toward the midline of the body; on the inner side.
• Lateral means away from the midline of the body; on the outer side.
• Intermediate means between medial and lateral structures.
• Proximal means closer to the origin or attachment point of a limb to the body trunk.
• Distal means farther from the origin or attachment point of a limb to the body trunk.
• Superficial (external) means toward the body surface.
• Deep (internal) means away from the body surface; more internal.

Body Cavities

• The dorsal body cavity protects the nervous system organs.
  • The cranial cavity encases the brain.
  • The vertebral cavity encases the spinal cord.
• The ventral body cavity houses internal organs (viscera).
  • The thoracic cavity contains:
    • Pleural cavities which surround each lung.
    • Mediastinum which contains the pericardial cavity and all thoracic organs except the lungs.
    • Pericardial cavity which encloses the heart.
  • The abdominopelvic cavity contains:
    • The abdominal cavity housing the stomach, intestines, spleen, liver, and other organs.
    • The pelvic cavity housing the urinary bladder, reproductive organs, and rectum.
• Serous membranes line the ventral body cavity and cover its organs.
  • The parietal serosa lines the cavity walls.
  • The visceral serosa covers the organs.
  • Serous fluid separates the parietal and visceral serosae, providing lubrication.

The Integumentary System

• Consists of the skin, hair, nails, and sweat and sebaceous (oil) glands.
• Provides protection against mechanical, chemical, and biological damage.
• Regulates body temperature through thermoregulation.
• Facilitates sensory reception for touch, pressure, pain, and temperature.
• Synthesizes vitamin D.
• Allows for excretion to eliminate waste through sweat.
• Skin layers are the epidermis, dermis, and hypodermis.
  • The epidermis is the outer layer of stratified squamous epithelium.
    • Keratinocytes produce keratin, a tough fibrous protein.
    • Melanocytes produce melanin, a pigment that protects against UV radiation.
    • Langerhans cells are immune cells that protect against pathogens.
    • Merkel cells are sensory receptors for touch.
  • The dermis is the inner layer of connective tissue.
    • The papillary layer is the superficial layer with dermal papillae projecting into the epidermis.
    • The reticular layer is the deeper layer with dense irregular connective tissue.
• The hypodermis (subcutaneous layer) is a layer of adipose tissue beneath the dermis.
• Melanin, carotene, and hemoglobin determine skin color.
• Skin appendages include hair, nails, and glands.
  • Hair provides insulation and protection.
    • Hair follicles produce hair.
    • Arrector pili muscles are smooth muscles that raise hair.
  • Nails protect the ends of fingers and toes.
  • Sweat glands produce sweat for cooling.
    • Eccrine sweat glands, found all over the body, produce watery sweat.
    • Apocrine sweat glands, found in axillary and genital areas, produce viscous sweat.
  • Sebaceous glands produce sebum (oil) for lubrication.

The Skeletal System

• Includes bones, cartilage, ligaments, and joints.
• Supports the body by providing a structural framework.
• Protects internal organs.
• Provides levers for movement via muscles.
• Stores minerals like calcium and phosphate.
• Is the site of hematopoiesis (blood cell formation) in red bone marrow.
• Stores fat in yellow bone marrow, for triglyceride storage.
• Bones are classified as long, short, flat, or irregular.
  • Long bones are longer than they are wide, such as the femur and humerus.
  • Short bones are cube-shaped, such as carpals and tarsals.
  • Flat bones are thin, flattened, and usually curved, such as skull bones and ribs.
  • Irregular bones have complex shapes, such as vertebrae and hip bones.
• Bone structure consists of compact and spongy bone, medullary cavity, epiphysis, diaphysis, periosteum, and endosteum.
  • Compact bone is the dense outer layer.
  • Spongy bone is the honeycomb-like inner layer.
  • The medullary cavity is the central cavity containing bone marrow.
  • The epiphysis is the end of a long bone.
  • The diaphysis is the shaft of a long bone.
  • The periosteum is the outer covering of bone.
  • The endosteum is the inner lining of bone.
• Bone cells include osteoblasts, osteocytes, and osteoclasts.
  • Osteoblasts are bone-forming cells.
  • Osteocytes are mature bone cells.
  • Osteoclasts are bone-resorbing cells.
• Bone development occurs through ossification (osteogenesis).
  • Intramembranous ossification is bone development from fibrous membrane (e.g., skull bones).
  • Endochondral ossification is bone development from hyaline cartilage (e.g., long bones).
• Joints (articulations) are sites where two or more bones meet.
  • Fibrous joints are immovable or slightly movable, such as sutures of the skull.
  • Cartilaginous joints are slightly movable or immovable, such as intervertebral discs.
  • Synovial joints are freely movable, such as the knee and shoulder.

The Muscular System

• Skeletal, smooth, and cardiac are the types of muscle tissue.
  • Skeletal muscle is voluntary and striated.
    • It is attached to bones and responsible for movement.
  • Smooth muscle is involuntary and non-striated.
    • It is found in the walls of internal organs and blood vessels.
  • Cardiac muscle is involuntary and striated.
    • It is found in the heart.
• Skeletal muscle functions include movement, posture maintenance, heat production, joint stabilization, and protection.
  • It moves bones and other structures.
  • It maintains body posture.
  • It generates heat during contraction.
  • It helps stabilize joints.
  • It protects internal organs.
• Skeletal muscle anatomy includes muscle fibers, myofibrils, sarcomeres, sarcoplasmic reticulum, and T tubules.
  • Muscle fibers (muscle cells) are elongated cells containing myofibrils.
  • Myofibrils are contractile units composed of sarcomeres.
  • The sarcomere is the basic contractile unit of muscle.
    • Actin are thin filaments.
    • Myosin are thick filaments.
  • The sarcoplasmic reticulum stores calcium ions.
  • T tubules transmit action potentials.
• Muscle contraction occurs via the sliding filament theory.
  • Actin and myosin filaments slide past each other, shortening the sarcomere.
  • The neuromuscular junction is the site where a motor neuron communicates with a muscle fiber.
  • A motor unit consists of a motor neuron and all the muscle fibers it innervates.
• Muscle actions include agonist, antagonist, synergist, and fixator roles.
  • The agonist (prime mover) produces the main movement.
  • The antagonist opposes or reverses the movement.
  • The synergist assists the agonist.
  • The fixator stabilizes a joint.