Integumentary System: Structure and Function

• The integumentary system performs eight key functions: protection, sensation, temperature regulation, vitamin D synthesis, excretion, immunity, water retention, and nonverbal communication.

Integumentary Definitions

• Transdermal administration involves delivering medication through the skin into the bloodstream.
• Vasoconstriction is the narrowing of blood vessels to conserve heat.
• Vasodilation refers to the widening of blood vessels to release heat.

Integumentary Layers

• The integumentary system consists of three layers: the epidermis, dermis, and hypodermis, from superficial to deep.
• The dermis has two layers: the papillary and reticular layers, from superficial to deep.

Primary Tissue Types

• The epidermis is composed of stratified squamous epithelium.
• The dermis consists of dense irregular connective tissue.
• The hypodermis is made up of adipose tissue and areolar connective tissue.

Epidermis Layers

• The epidermis has five layers (from superficial to deep): stratum corneum, stratum lucidum (only in thick skin), stratum granulosum, stratum spinosum, and stratum basale.

Epidermis Cells

• Keratinocytes produce keratin for protection.
• Melanocytes produce melanin for pigmentation and UV protection.
• Merkel (tactile) cells are sensory receptors for touch.
• Langerhans (dendritic) cells are immune cells protecting against pathogens.

Thick vs. Thin Skin

• Thick skin, found on palms and soles, has five epidermal layers (including stratum lucidum) and lacks hair or sebaceous glands.
• Thin skin covers most of the body, has four epidermal layers, and contains hair follicles and sebaceous glands.

Arrector Pili Muscles

• Arrector pili muscles are small muscles attached to hair follicles that contract, causing "goosebumps" and aiding in heat retention.

Sweat vs. Sebaceous Glands

• Sweat glands are found throughout the skin and secrete sweat for cooling.
• Sebaceous glands are located near hair follicles and secrete sebum (oil) for lubrication.

Burn Classifications

• First-degree burns affect the epidermis, causing redness, and are treated with cool compresses and aloe.
• Second-degree burns affect the epidermis and dermis, causing blisters, and are treated with wound care and pain management.
• Third-degree burns destroy all skin layers, appearing charred or white, and require skin grafts and infection control.
• Major concerns after a third-degree burn are infection and dehydration.

Nerve Receptors in Skin

• Meissner’s corpuscles detect light touch in the papillary layer of the dermis.
• Pacinian corpuscles detect deep pressure and vibration in the reticular layer of the dermis.
• Merkel cells detect light touch in the epidermis.
• Free nerve endings detect pain and temperature in the epidermis and dermis.

Compact vs. Spongy Bone

• Compact bone is the dense outer layer, providing strength.
• Spongy bone is porous, found inside bones, reducing weight and housing marrow.

Hyaline vs. Fibrocartilage

• Hyaline cartilage, found in joints, ribs, and the nose, provides smooth surfaces for movement.
• Fibrocartilage, located in intervertebral discs and menisci, absorbs shock.

Functions of the Skeletal System

• The skeletal system provides support, protection, movement, and mineral/energy storage.

Calcium and Phosphate

• Calcium is essential for muscle contraction, nerve function, and blood clotting.
• Phosphate is important for ATP production and DNA/RNA synthesis.

Bone Classes

• Long bones: femur, humerus.
• Short bones: carpals, tarsals.
• Flat bones: skull, ribs.
• Irregular bones: vertebrae, pelvis.

Periosteum vs. Endosteum

• The periosteum is the outer covering of bone, providing muscle attachment.
• The endosteum is the inner lining of the medullary cavity, involved in bone growth and repair.

Bone Regions

• Epiphysis: ends of long bones, containing articular cartilage for joint cushioning.
• Diaphysis: shaft of long bone, housing the medullary cavity with marrow.
• Metaphysis: between diaphysis and epiphysis, containing the epiphyseal plate/line (growth region).

Red vs. Yellow Bone Marrow

• Red marrow produces blood cells and is found in spongy bone of flat bones and ends of long bones.
• Yellow marrow stores fat and is found in the medullary cavity of long bones.

Bone Cells

• Osteoprogenitor cells are stem cells that develop into osteoblasts.
• Osteoblasts build bone by producing osteoid.
• Osteocytes maintain the bone matrix.
• Osteoclasts break down bone for remodeling and calcium release.

Bone Matrix

• The organic (osteoid) component consists of collagen and proteins, providing flexibility.
• The inorganic component consists of calcium and phosphate, providing hardness.

Osteon Structure

• The osteon (Haversian system) is a cylindrical structure for strength and nutrient transport in compact bone.

Bone Canals

• Canaliculi are small channels for communication between osteocytes.
• The central (Haversian) canal contains blood vessels and nerves.
• Perforating (Volkmann’s) canals connect osteons and the blood supply.

Hyaline Cartilage vs. Bone Tissue

• Hyaline cartilage lacks calcium, is avascular, and flexible.
• Bone tissue contains calcium, is vascular, and rigid.

Ossification

• Ossification is bone formation process.
• Intramembranous ossification forms flat bones (e.g., skull).
• Endochondral ossification forms long bones (e.g., femur).

Bone Growth

• Interstitial growth increases bone length and occurs at the epiphyseal plate.
• Appositional growth increases bone width and occurs at the periosteum.

Bone Remodeling

• Mechanical stress strengthens bone.
• Hormones regulate calcium levels and bone mass.

Hormones Affecting Bone

• Growth hormone, thyroid hormone, estrogen, testosterone, parathyroid hormone (PTH), and calcitonin influence bone growth and loss.

Calcium Regulation

• Calcitriol increases calcium absorption in the intestines.
• Parathyroid hormone (PTH) increases blood calcium by stimulating osteoclasts.
• Calcitonin lowers blood calcium by inhibiting osteoclasts.

Vitamin D Activation

• Skin: UV light converts precursor to vitamin D3.
• Liver: Converts to calcidiol.
• Kidneys: Converts to active calcitriol.

Rickets & Osteoporosis

• Rickets is a vitamin D deficiency in children, leading to weak bones.
• Osteoporosis is bone loss due to aging or hormonal changes, increasing fracture risk.

Axial vs. Appendicular Skeleton

• The axial skeleton (skull, vertebral column, thoracic cage) supports and protects vital organs.
• The appendicular skeleton (limbs and girdles) allows movement and flexibility.

Cranial vs. Facial Bones

• Cranial bones (8 bones) protect the brain (e.g., frontal, parietal, occipital).
• Facial bones (14 bones) form the face (e.g., maxilla, zygomatic, nasal).

Unique Mandible & Hyoid Features

• The mandible is the only movable skull bone, enabling chewing and speech.
• The hyoid bone does not articulate with other bones, supporting the tongue and aiding swallowing.

Suture Definition and Types

• Suture: Immovable joint in the skull.
• Coronal suture separates the frontal and parietal bones.
• Sagittal suture separates the left and right parietal bones.
• Lambdoid suture separates the occipital and parietal bones.

Auditory Ossicles

• The auditory ossicles (malleus, incus, stapes) are located in the middle ear and transmit sound vibrations to the inner ear.

Fontanelles

• The anterior fontanelle closes by 18–24 months, allowing skull growth.
• The posterior fontanelle closes by 2–3 months, aiding passage through the birth canal.

Vertebral Column Regions

• (Superior to Inferior): Cervical, thoracic, lumbar, sacrum, coccyx.

Vertebral Regions

• Cervical vertebrae (7): Small, flexible, with transverse foramina.
• Thoracic vertebrae (12): Articulate with ribs, with a downward spinous process.
• Lumbar vertebrae (5): Large, weight-bearing, with a short spinous process.
• Sacrum vertebrae (5 fused): Connects the spine to the pelvis.
• Coccyx vertebrae (4 fused): It is the vestigial tailbone.

Spinal Curvatures

• Thoracic and sacral curvatures are primary, present at birth.
• Cervical and lumbar curvatures are secondary, developing later for balance (cervical at 3–4 months, lumbar at 1 year).

Spinal Curvature Disorders

• Hyperkyphosis is excessive thoracic curvature ("hunchback").
• Hyperlordosis is excessive lumbar curvature ("swayback").

Thoracic Cage

• The thoracic cage consists of the sternum, ribs, and thoracic vertebrae.
• The function is to protect the heart and lungs and support breathing.

Types of Ribs

• True ribs (1–7) directly attach to the sternum.
• False ribs (8–10) attach indirectly via cartilage.
• Floating ribs (11–12) have no sternal attachment.

Limbs

• The upper limb is more mobile (e.g., shoulder joint).
• The lower limb is more stable for weight-bearing (e.g., thicker bones).

Pectoral Girdle

• The pectoral girdle consists of the clavicle and scapula, connects arms to the axial skeleton, and allows arm movement.

Winged Scapula

• Winged Scapula is caused by a weak or damaged serratus anterior muscle.
• Winged Scapula effects abnormal scapula protrusion, affecting shoulder function.

Upper Limb & Hand Bones

• The upper limb consists of the humerus, radius, ulna.
• The hand consists of carpals (wrist), metacarpals (palm), and phalanges (fingers).

Forearm Radius & Ulna

• Supination (palm up): radius and ulna are parallel.
• Pronation (palm down): radius crosses over ulna.

Colles’ vs. Smith’s Fractures

• Colles’s fracture: distal radius breaks from falling on an outstretched hand.
• Smith’s fracture: distal radius breaks from falling on a flexed wrist.

Pelvic Structure

• The pelvic bones (ilium, ischium, pubis) form the pelvis.
• The pelvic function supports body weight, protects pelvic organs, and anchors lower limbs.

Pelvic Girdle

• The pelvic girdle consists of two hip bones (coxal bones).
• The pelvic girdle connects the lower limbs to the axial skeleton and supports movement.