Anatomy & Physiology Study Notes: Integumentary and Skeletal Systems

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Integumentary System

Structure and Layers of the Skin

The skin is the largest organ of the body and serves as a protective barrier. It consists of multiple layers, each with distinct functions and cell types.

Epidermis: The superficial layer of the skin composed of stratified squamous keratinized epithelium. It is avascular and relies on diffusion of oxygen and nutrients from the underlying dermis.
Dermis: The deeper layer of skin made of loose and dense irregular collagenous connective tissue. It provides structural support and houses blood vessels, nerves, and glands.
Hypodermis: The layer of adipose tissue beneath the dermis, also known as subcutaneous tissue. It insulates the body and stores energy.

Glands of the Skin

Skin contains specialized glands that aid in thermoregulation and excretion.

Eccrine Sweat Glands: Most numerous glands that produce watery sweat for temperature regulation. Active in all ages.
Apocrine Sweat Glands: Located in the axillae, anal area, and areola. Secrete thick sweat rich in proteins, which bacteria can metabolize to produce odor. Become active at puberty.

Functions of the Integumentary System

The integumentary system performs several vital functions:

Protection: Acts as a barrier against mechanical injury, pathogens, and UV radiation.
Sensation: Contains sensory receptors for touch, pressure, pain, and temperature.
Thermoregulation: Regulates body temperature via sweat production and blood flow.
Excretion: Eliminates wastes and toxins through sweat.
Synthesis of Vitamin D: Skin synthesizes vitamin D when exposed to sunlight, which is essential for calcium absorption.

Negative Feedback Loop for Body Temperature Regulation

Body temperature is regulated by a negative feedback mechanism involving the skin and hypothalamus.

If body temperature rises, thermoreceptors in the skin detect the change and send signals to the hypothalamus, which stimulates sweating and vasodilation. When temperature normalizes, sweating and vasodilation decrease.
If body temperature drops, thermoreceptors detect the decrease and signal the hypothalamus, which stimulates vasoconstriction and redirects blood to deeper tissues.

Layers of the Epidermis

The epidermis consists of several layers, each with specific cell types and functions. Thick skin (palms, soles) has five layers; thin skin has four.

Stratum basale: Deepest layer; site of most mitosis.
Stratum spinosum: Thickest layer; provides strength.
Stratum granulosum: Cells fill with keratin.
Stratum lucidum: Only in thick skin.
Stratum corneum: Outermost layer; cells migrate here in 40-50 days.

Mnemonic: "Come Let's Get Sun Burned" (Corneum, Lucidum, Granulosum, Spinosum, Basale)

Cell Types in the Epidermis

Keratinoctyes: Make up 95% of epidermal cells; produce keratin for toughness and water resistance.
Dendritic (Langerhans) cells: Immune system phagocytes.
Merkel cells: Detect light touch and discriminate shapes/textures.
Melanocytes: Produce melanin pigment for UV protection.

Dermis Structure

Papillary layer: Superficial; loose connective tissue.
Reticular layer: Deep; dense irregular connective tissue.

Sensory Receptors and Skin Patterns

Lamellated (Pacinian) corpuscles: Detect pressure and vibration.
Epidermal ridges: Patterns in thick skin that enhance grip and produce fingerprints.

Skin Pigments

Melanin: Brown-black to orange-red pigment; protects from UV radiation.
Carotene: Orange pigment from diet (carrots, sweet potatoes).
Hemoglobin: Iron-containing pigment in red blood cells; gives skin a pink hue.

Skin Color Changes and Clinical Signs

Cyanosis: Blue appearance due to lack of oxygen.
Erythema: Redness from increased blood flow (e.g., exercise, fever).
Pallor: Pale color from decreased blood flow.

Hair and Nails

Hair: Filamentous structures covering most of the body except thick skin, lips, and parts of external genitalia. Arrector pili muscles cause hair to stand on end.
Types of hair: Lanugo (fetal, thin, non-pigmented), Vellus (thin, non-pigmented), Terminal (thick, coarse, pigmented).
Nails: Composed of the nail plate, nail bed, eponychium (cuticle), hyponychium (anchors distal end), and lunula (half-moon shaped region).

Skin Injuries and Burns

Wound: Disruption in skin integrity.
First-degree burn: Least severe; redness and pain, no permanent damage.
Second-degree burn: Partial thickness; blisters, may require skin grafts.
Rule of nines: Divides body into sections (each 9%) to estimate burn severity.

Skin Cancer

Basal cell carcinoma: Cancer of basal cells; least likely to metastasize.
Squamous cell carcinoma: Cancer of keratinocytes; more likely to metastasize than basal cell carcinoma.
Malignant melanoma: Cancer of melanocytes; most likely to metastasize.
ABCDE rule: Used to identify skin cancer:
- A - Asymmetry
- B - Border
- C - Color
- D - Diameter
- E - Evolving

Skeletal System

Functions of the Skeletal System

The skeletal system provides structure, protection, and support for the body, and is involved in movement, mineral storage, and blood cell formation.

Protection: Shields vital organs.
Mineral storage: Stores calcium and phosphorus.
Acid-base homeostasis: Buffers blood pH.
Blood cell formation: Occurs in bone marrow (hematopoiesis).
Fat storage: Yellow bone marrow stores fat.
Movement and support: Provides attachment for muscles and supports body weight.

Classification of Bones

Long bones: Longer than wide; have a shaft (diaphysis) and two ends (epiphyses). Example: femur.
Short bones: Cube-shaped. Example: carpal bones.
Flat bones: Two layers of compact bone with spongy bone in between. Example: cranial bones.
Irregular bones: Irregularly shaped. Example: vertebrae.
Sesamoid bones: Located within tendons. Example: patella.

Structure of Long Bones

Periosteum: Covering of the diaphysis.
Diaphysis: Shaft of the bone.
Epiphysis: Ends of the bone; contains spongy bone.
Spongy bone: Honeycomb-like structure; resists force from many directions.
Epiphyseal line: Remnant of the growth plate.
Red bone marrow: Produces red blood cells.
Yellow bone marrow: Stores fat.
Extracellular matrix: Contains inorganic (strength, resistance to compression) and organic (flexibility) components.

Bone Cells

Osteoblasts: Bone-forming cells.
Osteocytes: Mature bone cells.
Osteoclasts: Bone-resorbing cells; have a different origin than other bone cells.

Microscopic Structure of Bone

Osteon: Structural unit of compact bone; concentric rings called lamellae.
Lacunae: Small cavities between lamellae where osteocytes reside.
Canaliculi: Small channels connecting osteocytes for communication.
Trabeculae: "Ribs" of spongy bone.

Bone Formation and Growth

Intramembranous ossification: Forms flat bones (e.g., skull).
Endochondral ossification: Forms bones below the head (except clavicles); occurs in hyaline cartilage scaffold.
Longitudinal growth: Increase in length.
Appositional growth: Increase in width.
Epiphyseal plate: Growth plate with zones for reserve cartilage, proliferation, hypertrophy, calcification, and ossification.

Hormonal Regulation of Bone Growth

Testosterone: Increases appositional growth.
Estrogen: Increases longitudinal growth and induces closure of growth plate.

Bone Remodeling and Repair

Compression: Stimulates bone deposition.
Tension: Stretching force.
Calcium ion homeostasis: Regulated by parathyroid hormone and calcitonin.
- If blood calcium is low, parathyroid hormone increases osteoclast activity to release calcium from bone.
- If blood calcium is high, calcitonin promotes calcium deposition in bone.
Bone healing: Hematoma forms, fibroblasts and chondroblasts create a soft callus, osteoblasts build a bone callus, and bone is remodeled. Repair takes 6-8 weeks.

Types of Fractures

Simple fracture: Skin and tissue around fracture remain intact.
Compound fracture: Skin and tissue around fracture are damaged.

Axial and Appendicular Skeleton

Axial skeleton: Skull, vertebral column, thoracic cage.
Appendicular skeleton: Limbs and girdles.

Skull Bones and Sutures

Cranial bones: 8 total (2 parietal, 2 temporal, 1 frontal, 1 occipital, 1 sphenoid, 1 ethmoid).
Facial bones: 14 total (mandible, vomer, 2 nasal, 2 palatine, 2 lacrimal, 2 zygomatic, 2 maxilla, 2 inferior nasal conchae).
Sutures: Coronal, lambdoid, squamous, sagittal.
Keystone bone: Sphenoid; articulates with every other cranial bone.
Ethmoid bone: Located deep in anterior cranium between eyes and behind nasal bones.

Vertebral Column and Thoracic Cage

Vertebrae: 7 cervical, 12 thoracic, 5 lumbar.
Atlas (C1): Articulates with skull.
Axis (C2): Contains dens for head rotation.
Thoracic vertebrae: Articulate with ribs.
Lumbar vertebrae: Largest; bear most weight.
Spinal curvatures: Primary (thoracic, sacral) and secondary (cervical, lumbar).
Abnormal curvatures: Scoliosis (sideways), lordosis (swayback), kyphosis (hunchback).
Intervertebral discs: Pads of fibrocartilage for shock absorption.
Sternum: Breastbone; consists of manubrium, body, xiphoid process.

Pectoral and Pelvic Girdles

Pectoral girdle: Clavicle (collar bone) and scapula (shoulder blade).
Glenoid cavity: Articulates with head of humerus.
Acromion: Forms point of shoulder.
Humerus: Only bone of the arm.
Radius: Forearm bone along thumb side.
Ulna: Forearm bone along pinky side.
Carpals: Wrist bones (scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate).
Metacarpals: Bones of the hand.

Pelvis and Lower Limb Bones

Pelvis: Composed of ilium, ischium, and pubis.
Male vs. female pelvis: Female pelvis has a wider opening, shorter sacrum, more movable coccyx, and tuberosities point more laterally.
Acetabulum: Deep socket for femur head.
Femur: Largest and strongest bone.
Tibia: Shinbone.
Tarsals: Ankle bones (calcaneus, talus, navicular, medial/intermediate/lateral cuneiform, cuboid).
Metatarsals: Numbered I-V from medial to lateral.
Phalanges: Toe bones; each toe has three except the big toe (hallux), which has two.

Bone Markings and Features

Epicondyle: Small projection near a condyle.
Foramen: Hole in bone.
Suture: Narrow joint between bones.
Condyle: Rounded end that articulates with another bone.
Spine: Sharp process.
Tubercle: Small rounded projection.
Trochanter: Large projection (only on femur).
Fossa: Indentation in bone.
Crest: Ridge or projection.

Key Formulas and Processes

Calcium Homeostasis:
Rule of Nines (Burns):

Table: Comparison of Skin Glands

Gland Type	Location	Secretion	Function
Eccrine	All over body	Watery sweat	Thermoregulation
Apocrine	Axillae, anal area, areola	Thick, protein-rich sweat	Odor production, active at puberty

Table: Types of Bone Cells

Cell Type	Function
Osteoblast	Bone formation
Osteocyte	Maintain bone tissue
Osteoclast	Bone resorption

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for college-level Anatomy & Physiology students.