BIO 201 Unit 2: Integumentary and Skeletal Systems Study Notes

Integumentary System

Overview and Functions

The integumentary system is composed primarily of the skin, hair, nails, and associated glands. It serves as the body's first line of defense against environmental hazards and plays a vital role in homeostasis.

• Protection: Stratified squamous epithelial cells protect underlying tissues from trauma and pathogens.

• Melanin Production: Melanocytes produce melanin, which protects DNA from UV damage.

• Vitamin D Synthesis: The skin converts cholesterol into Vitamin D when exposed to sunlight, enhancing calcium absorption from the intestines.

• Immune Defense: The skin helps prevent illness, autoimmunity, and cancer by supporting immune system function.

• Sensory Reception: Specialized nerve endings in the epidermis detect itch, pain, and temperature; Meissner's corpuscles respond to fine touch/texture, while Pacinian corpuscles respond to deep pressure and vibration.

• Thermoregulation: Blood vessels constrict (vasoconstriction) to preserve heat when cold, and dilate (vasodilation) to release heat when hot. Sweat glands increase activity for evaporative cooling.

Layers of the Skin

The skin consists of multiple layers, each with specialized functions and cell types.

• Epidermis: Outermost layer, composed of stratified squamous epithelium. Contains the following sublayers (from superficial to deep):

  • Stratum corneum: Dead, keratinized cells providing a tough barrier.

  • Stratum lucidum: Clear layer found only in thick skin (palms, soles).

  • Stratum granulosum: Contains keratohyalin granules; cells begin to die.

  • Stratum spinosum: Provides strength and flexibility.

  • Stratum basale: Deepest layer; site of mitosis and stem cells, produces new keratinocytes and melanocytes.

• Dermis: Middle layer, composed of connective tissue. Contains:

  • Papillary region: Areolar connective tissue, forms fingerprints, contains Meissner's corpuscles.

  • Reticular region: Dense irregular connective tissue, provides strength and elasticity, contains Pacinian corpuscles.

• Hypodermis (Subcutaneous layer): Deepest layer, primarily adipose tissue, insulates and cushions the body.

Accessory Structures

Accessory structures of the skin include hair, nails, and glands, each contributing to the system's protective and regulatory functions.

• Hair: Produced by hair follicles, provides protection and sensory input. Types include:

  • Lanugo: Fetal hair, traps vernix caseosa for skin protection.

  • Vellus: Fine, lightly keratinized hair covering most of the body.

  • Terminal: Coarse, pigmented hair found on the scalp, face, and pubic regions.

• Arrector pili muscles: Cause goosebumps by contracting and raising hair.

• Nails: Composed of the hardest type of keratin. Key parts:

  • Eponychium: Produces the cuticle, protecting the nail matrix from infection.

  • Hyponychium: Seals the nail bed from injury.

• Glands:

  • Sebaceous (oil) glands: Secrete sebum, lubricating skin and hair.

  • Sudoriferous (sweat) glands:

    • Eccrine glands: All over the body, produce watery sweat for cooling.

    • Apocrine glands: Associated with hair follicles in groin and axilla, produce protein-rich sweat that can cause body odor.

Skin Color and Clinical Relevance

Skin color is determined by genetic and environmental factors, and changes can indicate underlying health conditions.

• Melanin: Produced by melanocytes; eumelanin (brown/black) and pheomelanin (red/yellow) determine skin, hair, and eye color.

• Hemoglobin: Red pigment in RBCs; oxygenated blood gives skin a pinkish hue.

• Bilirubin: Yellow pigment from heme breakdown; excess causes jaundice.

• Carotene: Orange pigment from foods; can tint skin if consumed in high amounts.

• Clinical color changes:

  • Erythema: Reddening due to increased blood flow (vasodilation), infection, or trauma.

  • Cyanosis: Bluish tint from deoxygenated hemoglobin.

  • Pallor: Whitish skin from reduced blood flow or low hemoglobin.

  • Jaundice: Yellowing from bilirubin buildup, often due to liver dysfunction.

Burns and Skin Injury

Burns are classified by depth and severity, affecting skin function and requiring clinical assessment.

• First-degree: Superficial, affects only the epidermis; redness and pain.

• Second-degree: Partial-thickness, affects epidermis and part of dermis; blisters and severe pain.

• Third-degree: Full-thickness, destroys epidermis and dermis; may be painless due to nerve damage, risk of infection and fluid loss.

• Rule of 9's: Used to estimate body surface area affected by burns for fluid resuscitation.

  Body Region	% of Total Body Surface Area
  Head	9%
  Each Arm	9%
  Torso (front and back)	36%
  Each Leg	18%
  Genitals	1%

Skin Cancer

Skin cancers arise from uncontrolled cell division in different layers of the epidermis.

• Basal cell carcinoma: Originates from stem cells in the stratum basale; most common, least dangerous.

• Squamous cell carcinoma: Originates from keratinocytes in the stratum spinosum; can metastasize.

• Melanoma: Originates from melanocytes in the stratum basale; most dangerous, high metastatic potential.

• ABCDE Rule for Melanoma:

  • Asymmetry

  • Border irregularity

  • Color variation

  • Diameter > 6mm

  • Evolving over time

Skeletal System

Bone Structure and Types

The skeletal system provides support, protection, and enables movement. Bones are classified by shape and internal structure.

• Long bones: Have a shaft (diaphysis) and two ends (epiphyses).

• Compact (cortical) bone: Dense outer layer, provides strength.

• Spongy (trabecular) bone: Less dense, contains trabeculae, site of hematopoiesis.

• Marrow:

  • Red marrow: Produces RBCs, WBCs, and platelets.

  • Yellow marrow: Stores adipose tissue.

Bone Cells and Remodeling

Bones are dynamic tissues, constantly remodeled by specialized cells.

• Osteoblasts: Build bone matrix by depositing calcium salts and collagen.

• Osteocytes: Mature bone cells residing in lacunae, maintain bone tissue.

• Osteoclasts: Break down bone matrix, releasing calcium into the blood.

Bone Development and Growth

Bone formation occurs through two main processes: endochondral and intramembranous ossification.

• Endochondral ossification: Most bones start as hyaline cartilage, which is gradually replaced by bone tissue.

• Intramembranous ossification: Flat bones (e.g., skull) develop directly from connective tissue membranes.

• Epiphyseal plate: Site of longitudinal bone growth; becomes ossified in adulthood.

Calcium Homeostasis

Blood calcium levels are tightly regulated by hormonal control.

• Parathyroid hormone (PTH): Released by parathyroid glands when calcium is low; stimulates osteoclasts to release calcium from bone.

• Calcitonin: Released by thyroid gland when calcium is high; stimulates osteoblasts to deposit calcium into bone.

Key Equations:

• $\text{PTH} \uparrow \Rightarrow \text{Osteoclast activity} \uparrow \Rightarrow \text{Blood calcium} \uparrow$

• $\text{Calcitonin} \uparrow \Rightarrow \text{Osteoblast activity} \uparrow \Rightarrow \text{Blood calcium} \downarrow$

Bone Repair

Bone healing after fracture involves several stages:

1. Hematoma formation (blood clot)

2. Soft callus formation by fibroblasts and chondrocytes

3. Hard callus formation (primary bone)

4. Remodeling to mature bone (secondary bone)

Timeframe: Complete healing typically takes 6-8 weeks.

Axial and Appendicular Skeleton

The skeleton is divided into axial (central) and appendicular (limbs and girdles) components.

• Axial skeleton: Skull, vertebral column, rib cage.

• Appendicular skeleton: Limbs, pectoral girdle (clavicle and scapula), pelvic girdle.

Special Features of Bones

• Sinuses: Air-filled cavities in skull bones (frontal, sphenoid, ethmoid, maxilla) that lighten the skull and add resonance to the voice.

• Fontanels: Soft spots in infant skulls allowing for growth and compression during birth.

• Vertebrae: Cervical vertebrae (atlas and axis) allow for nodding and rotation of the head.

• Pelvic differences: Female pelvis is wider and more circular for childbirth; male pelvis is narrower.

Common Bone Disorders

• Osteoporosis: Bone matrix deficiency, increased fracture risk, common in elderly and post-menopausal women.

• Brittle Bone Disease (Osteogenesis Imperfecta): Congenital disorder, insufficient collagen production, high fracture risk.

Summary Table: Skin Layers and Features

Layer	Main Cell Types	Key Features
Stratum corneum	Keratinocytes	Dead, keratinized, protective
Stratum lucidum	Keratinocytes	Clear, only in thick skin
Stratum granulosum	Keratinocytes	Keratohyalin granules, cell death
Stratum spinosum	Keratinocytes	Strength, flexibility
Stratum basale	Stem cells, melanocytes	Mitotic activity, pigment production

Additional info: Some details inferred and expanded for completeness, including clinical relevance, bone cell functions, and summary tables.