Anatomy & Physiology: Skin, Bone, and Joint Study Guide

Skin and Integumentary System

Structure and Function of the Skin

The skin is the largest organ of the body and serves as a protective barrier, regulates temperature, and enables sensory perception. It consists of multiple layers, each with specialized functions.

1. Epidermis: contains these main types of cells(Keratinocytes, melanocytes, dendritic cells, tactile(Markel) epithelial cells) Outermost layer, composed of stratified squamous epithelial cells. Contains sublayers such as:

   stratum corneum:

   Outermost layer, 20-30 layers of dead cells.

   Provides protection and waterproofing

   Composed mainly of lipids

   no nuclei(anucleate cells)

   anucleated cells

   stratum lucidum:

   Present only in thick skin (e.g., palms, soles).

   Consists of dead keratinocytes.

   stratum granulosum:

   Contains flattened keratohyaline and lamellar granules.(possesses a waterproofing glycolipid that functions in preventing water loss)

   layer of the epidermis are keratinocytes too far from the dermal capillaries to survive

   stratum spinosum:

   Several layers of keratinocytes connected by desmosomes.

   Cells appear spiny due to the preparation process

   intermediate filaments, keratinocytes and dendritic (Langerhans) cells

   stratum basal:

   Deepest layer, attached to the dermis.

   Contains a single row of stem cells that divide to form new keratinocytes.

   Includes melanocytes, which produce melanin, keratinocytes, and tactile epithelial cells(work with nerve tissue to dated touch)

   Contains about 10-25% of melanocytes.prone to cancer in the form of melanoma

2. Dermis: Middle layer, contains dense irregular connective tissue, blood vessels, nerves, and appendages like hair follicles and sweat glands. Also composed of two sublayers:

   Contains mast cells, fibroblasts, macrophages, and white blood cells, such as neutrophils

   papillary dermis:

   Made of areolar connective tissue(loose)

   has capillaries, lymphatic vessels, and touch receptors(tactile/meissner corpuscles)

   Contains dermal papillae(friction ridges and fingerprints), which project into the epidermis, enhancing the connection between the two layers,

   Houses sensory nerve fibers and receptors.

   Contains phagocytes and other defensive cells

   Reticular Dermis:

   Composed of dense irregular connective tissue

   Contains a net like arrangement of collagen fibers, providing strength and elasticity.

   Includes structures like sweat glands, hair follicles, and lamellar / Pacinian corpuscles(pressure receptors)

   Cleavage lines(tension lines) happens when parallel orientation. how skin resist tension

3. Hypodermis (Subcutaneous Layer):

   Deepest layer, Not part of the skin but part of the integumentary system.

   Composed mainly of adipose tissue(loose), providing insulation, shock absorption, and energy storage

   Anchors skin to underlying structures, allowing flexibility.

Skin Accessory Structures:

• Hair Follicles and Hair Roots: Provide protection and sensory functions.

• Sebaceous (Oil) Glands: Secrete sebum to lubricate skin and hair.,found all over the body except the palms and soles

• Sweat Glands: Aid in temperature regulation and excretion.

• Arrector Pili Muscles: Cause hair to stand upright, aiding in thermoregulation.

Key Terms:

• Keratinized stratified squamous epithelium: Provides waterproofing and protection.

• Non-keratinized stratified squamous epithelium: Found in moist areas like the oral cavity.

Mode of secretion glands of the skin with examples:

Skin contains several types of glands that aid in thermoregulation and protection.

• Holocrine glands: Secrete products by rupturing the cell (e.g., sebaceous glands).

• Merocrine glands: Secrete via exocytosis without cell damage (e.g., eccrine sweat glands and pancreas).

• Apocrine glands: Secrete by pinching off a portion of the cell (e.g., apocrine sweat glands).

Burns and Burn Calculation

Burns are classified by depth and extent. The "Rule of Nines" is used to estimate the percentage of body surface area affected by burns, which is critical for fluid resuscitation.

• First-degree burns: Affect only the epidermis; redness and pain.

• Second-degree burns: Affect epidermis and part of dermis; blistering.

• Third-degree burns: Affect epidermis, dermis, and deeper tissues; may be painless due to nerve destruction.

Example Calculation:

• If both the anterior and posterior surfaces of both legs and the entire back are burned, use the Rule of Nines to estimate total body surface area affected.

Formula:

• $\text{Total Burned Area} = \text{Sum of affected regions according to Rule of Nines}$

Know skin pigments and causes of skin color changes: jaundice, tan, erythema, flushing, cyanosis

• Jaudice:Yellowish coloring of skin caused by an accumulation of the pigment bilirubin

• Tan:

• Erythema: redness

• flushing:

• cyanosis: blueness, Possible heart failure; possible respiratory disorders

Know the significance of cleavage line and flexure lines:

• Flexure Lines : form where the dermis is closely attached to the underlying structures.

  • Since the skin cannot slide easily to accommodate joint movement in such regions, the dermis folds and deep skin creases form

  • location:palms, soles, and joints of the hands and feet(Eccrine sweat glands are abundant)

• Cleavage lines:

  • Represent separations between underyling collagen fiber bundles in the reticular dermis.

  • Run circularly around the trunk and longitudinally in the limbs.

  • Surgical incisions parallel to cleavage lines heal better than those made across them

Know hair structures, type, color, and hair loss treatment

Terminal hair is located in all of the following areas, except the body hair of females.

Hirsutism is a condition characterized by females developing coarse terminal hairs in a masculine distribution

Bone and Skeletal System

Structure and Function of Bone

Function of Skeletal system: provide structural support, protect organs, enable movement, and serve as sites for hematopoiesis (blood cell formation).

• Types of bone tissue: Compact bone (dense), spongy bone (trabecular).

• Bone cells: Osteoblasts (build bone, initiates calcification, bone deposition, located in periosteum), osteoclasts (break down bone, concentrated in endosteum), osteocytes (maintain bone, found in lacunae). chondroblasts (secrete matrix, happens in endochondrial ossification ), chondrocytes(matrix becomes calcified, endochondrial ossification cartilage tissues features inside lacunae)

• Bone marrow: Red marrow (hematopoiesis), yellow marrow (fat storage).

Bone Growth and Ossification

Bones grow and develop through two main processes: intramembranous and endochondral ossification.

• Intramembranous ossification: Direct formation of bone from mesenchymal tissue (e.g., flat bones of the skull).

• Endochondral ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

  Appositital growth: growth/ repair. happens in the inner layer of the periosteum where osteblasts are created

  Interstitial growth: the lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within aka growing bone that adds length the process happens in the Metaphysis

Classification of Bones

• Flat bones: Thin, flattened, and usually curved (e.g., sternum, skull).

• Long bones: Longer than they are wide (e.g., femur, humerus).

• Short bones: Cube-shaped (e.g., carpals).

• Irregular bones: Complex shapes (e.g., vertebrae).

Bone Disorders

• Osteoporosis: Decreased bone density, increased fracture risk.

• Osteomalacia: Softening of bones due to vitamin D deficiency.

• Osteopetrosis: Abnormally dense bones.

Joints and Articulations

Classification of Joints

Joints are classified by structure and function.

• Fibrous joints: Bones joined by dense connective tissue; little or no movement, connected by ligaments (e.g., sutures in the skull).

• Cartilaginous joints: Bones joined by cartilage; limited movement (e.g., intervertebral discs).

• Synovial joints: Freely movable joints with a synovial cavity (e.g., knee, shoulder).

Types of Synovial Joints and Movements

• Ball-and-socket: Multiaxial movement (e.g., shoulder, hip).

• Hinge: Flexion and extension (e.g., elbow).

• Pivot: Rotation (e.g., atlantoaxial joint).

• Abduction: Movement away from midline.

• Adduction: Movement toward midline.

• Flexion: Decreasing the angle between bones.

• Extension: Increasing the angle between bones.

• Eversion/Inversion: Movements of the sole of the foot.

Ligaments and Tendons

• Ligaments: Connect bone to bone; stabilize joints.

• Tendons: Connect muscle to bone; transmit force for movement.

• Tendon sheath: Reduces friction between tendon and surrounding structures.

Common Joint Disorders

• Gout: Inflammatory arthritis due to uric acid crystals.

• Osteoarthritis: Degeneration of articular cartilage.

• Rheumatoid arthritis: Autoimmune inflammation of joints.

• Septic arthritis: Infection of joint space.

Table: Types of Epithelial and Connective Tissues

Type	Location	Function
Keratinized stratified squamous epithelium	Skin (epidermis)	Protection, waterproofing
Non-keratinized stratified squamous epithelium	Oral cavity, esophagus	Protection in moist areas
Adipose connective tissue	Hypodermis, around organs	Insulation, energy storage
Reticular connective tissue	Lymph nodes, spleen	Support for soft organs

Table: Types of Joints

Joint Type	Structure	Movement	Example
Fibrous	Dense connective tissue	Immovable	Sutures of skull
Cartilaginous	Cartilage	Slightly movable	Intervertebral discs
Synovial	Synovial cavity, ligaments	Freely movable	Knee, shoulder

Additional info:

• Some content inferred from standard Anatomy & Physiology curriculum, such as definitions and examples of bone and joint types.

• Rule of Nines for burn calculation: Each leg (anterior and posterior) = 18%, back = 18%. Total for both legs and back = 54% (but question options suggest 36% is correct for back and both legs).

• Practice questions and answer key included in the file were used to guide topic selection and explanations.