The Integumentary System

Sensory Receptors in the Skin

The skin contains various sensory receptors that detect environmental stimuli, especially those related to touch.

• Merkel cells: Detect light touch and pressure.

• Meissner's corpuscles: Sensitive to light touch, found in dermal papillae.

• Pacinian corpuscles: Detect deep pressure and vibration.

• Ruffini endings: Respond to skin stretch.

• Free nerve endings: Sense pain, temperature, and crude touch.

• Example: Meissner's corpuscles allow you to feel the texture of fabric.

Sebaceous Glands

Sebaceous glands are associated with hair follicles and secrete an oily substance called sebum.

• Function: Lubricates skin and hair, prevents drying, and has antibacterial properties.

• Example: Sebum production increases during puberty, sometimes leading to acne.

Epidermal Layers

The epidermis consists of several distinct layers, arranged from superficial to deep:

• Stratum corneum (most superficial)

• Stratum lucidum (only in thick skin)

• Stratum granulosum

• Stratum spinosum

• Stratum basale (deepest)

• Order from deep to superficial: Stratum basale → Stratum spinosum → Stratum granulosum → Stratum lucidum (if present) → Stratum corneum

Body's Natural Defenses Against UV Radiation

The skin protects against UV radiation primarily through the production of melanin by melanocytes.

• Melanin: Absorbs and dissipates UV rays, reducing DNA damage.

• Example: Increased melanin production leads to tanning after sun exposure.

Sweat Glands

There are two major types of sweat glands:

• Eccrine glands: Found throughout the body; produce watery sweat for thermoregulation.

• Apocrine glands: Located in axillary and genital areas; secrete thicker sweat, often associated with odor.

• Modified sweat glands: Mammary glands (produce milk) and ceruminous glands (produce earwax).

Types of Burns and Skin Layers Affected

Burns are classified by the depth of tissue damage:

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

• Second-degree: Involves epidermis and part of dermis; blisters, pain.

• Third-degree: Extends through dermis into deeper tissues; may be painless due to nerve destruction.

Homeostasis and Negative Feedback

The body maintains internal balance via negative feedback mechanisms.

• Example: Increased body temperature triggers sweat production, which cools the body.

The Skeletal System

Parts of a Bone and Terminology

Bones have distinct structural regions:

• Shaft (diaphysis): The long, central portion of a bone.

• Epiphysis: The ends of a bone.

• Metaphysis: Region between diaphysis and epiphysis, includes the growth plate.

• Periosteum: Outer fibrous covering.

• Endosteum: Inner lining of the medullary cavity.

Compact vs. Spongy Bone

Bones are composed of two major types of tissue:

• Compact bone (lamellar bone): Dense, organized in osteons; provides strength.

• Spongy bone (trabecular bone): Porous, contains trabeculae; found in epiphyses and inside flat bones.

• Example: Compact bone forms the outer layer of long bones; spongy bone is found at the ends.

Epiphyseal Plate and Bone Lengthening

The epiphyseal plate (growth plate) is a region of hyaline cartilage where bone lengthening occurs during childhood and adolescence.

• Location: Between epiphysis and diaphysis.

• Mechanism: Cartilage cells proliferate, then ossify, lengthening the bone.

Types of Ossification

Bone formation occurs via two processes:

• Intramembranous ossification: Direct formation of bone from mesenchyme; forms flat bones (e.g., skull).

• Endochondral ossification: Bone develops from a cartilage template; forms most long bones.

Hormones in Bone Health and Calcium Regulation

Several hormones regulate bone remodeling and calcium levels:

• Parathyroid hormone (PTH): Increases bone resorption, raises blood calcium.

• Calcitonin: Inhibits bone resorption, lowers blood calcium.

• Vitamin D: Promotes calcium absorption in the gut.

• Estrogen and testosterone: Influence bone growth and maintenance.

Bone Structure and Mechanical Stress

Bones adapt to mechanical stress through remodeling.

• Wolff's Law: Bone grows and remodels in response to the forces placed upon it.

• Example: Weight-bearing exercise increases bone density.

Cartilage Growth: Interstitial and Appositional

Cartilage grows by two mechanisms:

• Interstitial growth: Chondrocytes divide and secrete new matrix from within.

• Appositional growth: New layers added to the surface by chondroblasts in the perichondrium.

Types of Cartilage and Locations

Three main types of cartilage are found in the body:

• Hyaline cartilage: Most common; found in articular surfaces, trachea, and growth plates.

• Elastic cartilage: Flexible; found in external ear and epiglottis.

• Fibrocartilage: Strong, resists compression; found in intervertebral discs and meniscus.

• Example: The meniscus of the knee contains fibrocartilage.

Cartilage at the Growth Plate and Bone Lengthening Mechanism

The growth plate consists of hyaline cartilage, which allows for longitudinal bone growth.

• Mechanism: Chondrocytes proliferate, mature, and are replaced by bone tissue.

Growth Rates: Male vs. Female During Puberty

Growth rates differ between sexes, especially during puberty.

• Males: Generally experience a later, longer growth spurt.

• Females: Growth spurt occurs earlier, and growth plates close sooner.

Joints and Associated Bones

Naming Conventions for Joints

Joints are named based on the bones they connect.

• Example: The humeroulnar joint connects the humerus and ulna.

Immune Function in the Skin

Dendritic Cells

Dendritic cells (Langerhans cells) are immune cells found in the epidermis.

• Function: Phagocytose pathogens and present antigens to T cells.

• Example: Dendritic cells help initiate immune responses against skin infections.

Hair Growth and Loss

Hair Loss vs. Excessive Hair Growth

Hair loss (alopecia) and excessive hair growth (hypertrichosis) are distinct conditions.

• Hair loss: Can be caused by genetics, hormonal changes, or disease.

• Excessive hair growth: May result from hormonal imbalances or certain medications.

Summary Table: Types of Cartilage and Their Locations

Summary Table: Epidermal Layers

Key Equations

• Calcium Regulation:

Additional info: Academic context was added to clarify mechanisms, examples, and terminology for each topic.