Comprehensive Study Notes: Integumentary System, DNA Replication, Histology, Skeletal System, and Articulations

Integumentary System

Layers and Structure of the Skin

The integumentary system is composed of the skin and its associated structures. The skin consists of multiple layers, each with distinct functions and cell types.

• Layers of the Epidermis (from deepest to superficial):

  • Stratum basale (germinativum): Deepest, mitotically active layer; responsible for new cell production.

  • Stratum spinosum: Provides strength and flexibility.

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

  • Stratum lucidum: Present only in thick skin (e.g., palms, soles).

  • Stratum corneum: Most superficial; composed of dead, keratinized cells.

• Basement membrane: Separates the epidermis from the dermis.

• Dermis: Lies beneath the epidermis; contains connective tissue, blood vessels, nerves, and glands.

• Hypodermis (subcutaneous layer): Not part of the skin; consists mainly of adipose tissue.

Key Cell Types in the Epidermis:

• Keratinocytes: Most abundant; produce keratin for protection.

• Melanocytes: Produce melanin pigment; protect against UV radiation.

• Langerhans (dendritic) cells: Immune defense.

• Tactile (Merkel) cells: Sensory receptors for touch.

Skin Pigments:

• Melanin: Brown-black pigment; UV protection.

• Hemoglobin: Red pigment from blood; gives skin a pinkish hue.

• Carotene: Yellow-orange pigment from diet (e.g., carrots).

Skin Color Terms:

• Cyanosis: Blue tint due to low oxygen.

• Pallor: Pale appearance from reduced blood flow.

• Erythema: Redness from increased blood flow.

• Hematoma: Bruising (black-blue) from broken blood vessels.

Skin Cancer and Burns

• Basal cell carcinoma: Most common skin cancer; arises from stratum basale.

• ABCD Rule for Assessing Skin Cancer:

  • A: Asymmetry

  • B: Border irregularity

  • C: Color variation

  • D: Diameter > 6mm

• Types of Burns: Classified by depth and extent (first, second, third degree).

• Grafts for Third Degree Burns:

  • Autograft: From patient's own body.

  • Allograft: From another person.

  • Xenograft: From another species.

• Main concern in burn patients: Dehydration and fluid loss; treated with IV fluids.

Glands and Accessory Structures

• Sebaceous (oil) glands: Secrete sebum for lubrication.

• Sudoriferous (sweat) glands: Regulate temperature and excrete waste.

• Pilus: Hair shaft.

DNA Replication

Structure and Process

DNA replication is the process by which a cell duplicates its DNA before cell division. It is described as semiconservative, meaning each new DNA molecule consists of one old (parental) and one new strand.

• Base Pairing Rules: G-C, C-G, T-A, A-T (for DNA-DNA); DNA to mRNA uses A-U, T-A, G-C, C-G.

• Directionality: New strands are synthesized in the 5' to 3' direction.

• Antiparallel Strands: The two DNA strands run in opposite directions.

• Negative Charge: DNA is negatively charged due to phosphate groups.

Enzymes Involved:

• Helicase: Unwinds the DNA double helix.

• Primase: Synthesizes RNA primers.

• DNA Polymerase: Adds nucleotides to the growing DNA strand.

• Ligase: Joins Okazaki fragments on the lagging strand.

Leading vs. Lagging Strand:

• Leading strand: Synthesized continuously.

• Lagging strand: Synthesized in short fragments (Okazaki fragments), later joined by ligase.

Mutation: A change in the DNA sequence; can be caused by errors in replication or external factors.

Histology: Tissues

Overview of Tissues

A tissue is a group of cells with a common structure and function. The four main tissue types are epithelial, connective, muscular, and nervous tissue.

• Epithelial Tissue: Covers surfaces, lines cavities, forms glands. Avascular, relies on diffusion for nutrients.

• Connective Tissue: Supports, binds, and protects organs. Most abundant; has cells and a matrix (ground substance and fibers).

• Muscular Tissue: Responsible for movement.

• Nervous Tissue: Conducts electrical impulses.

Characteristics and Types

• Matrix: Non-cellular component; varies (liquid, gel, solid).

• Fibers in Connective Tissue: Collagen (strength), elastic (flexibility), reticular (support).

• Mesenchyme: Embryonic tissue from which all connective tissues derive.

Types of Epithelial Tissue

Type	Description	Location	Function
Simple squamous	One layer, flat cells	Lungs	Diffusion
Stratified squamous	Multiple layers, flat cells	Skin, esophagus	Protection
Pseudostratified ciliated columnar	Appears layered, has cilia and goblet cells	Trachea	Mucus secretion, movement
Cuboidal	Cube-shaped cells	Kidneys	Secretion, absorption

Types of Connective Tissue

Type	Description	Location	Function
Bone (osteon)	Hard matrix	Skeleton	Support, protection
Cartilage (hyaline, elastic, fibrocartilage)	Gel-like matrix, avascular	Trachea, ears, vertebrae	Support, flexibility
Blood	Fluid matrix	Blood vessels	Transport
Dense regular	Parallel fibers	Ligaments, tendons	Strength
Dense irregular	Irregular fibers	Dermis, areolar	Support
Adipose	Fat storage	Under skin	Energy storage, insulation

Cell Junctions

• Desmosomes: Strong, velcro-like attachments.

• Gap junctions: Allow communication between cells.

• Tight junctions: Prevent leakage between cells.

Glands

• Endocrine glands: Ductless; secrete hormones into blood.

• Exocrine glands: Have ducts; secrete substances (not hormones) like sweat, oil, enzymes.

Other Key Terms

• Apoptosis: Programmed cell death.

• Goblet cells: Produce mucus; found in columnar epithelium.

• Avascular: Lacking blood supply (e.g., epithelial tissue, cartilage, tendons, ligaments).

• Vascular: Has blood supply (most connective tissues).

Skeletal System

Divisions and Structure

The skeletal system provides support, protection, and movement. It is divided into two main divisions:

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

• Appendicular skeleton: Limbs and girdles (shoulder, pelvic).

Types of Bone Tissue:

• Compact bone (osteon): Dense, strong; forms outer layer.

• Spongy bone (trabeculae): Porous, lighter; found at ends of long bones.

Parts of a Long Bone:

• Diaphysis: Shaft.

• Epiphysis: Ends.

• Medullary cavity: Contains bone marrow.

• Periosteum: Outer membrane.

• Endosteum: Lines medullary cavity.

Bone Cells and Ossification

• Osteoblasts: Build bone.

• Osteoclasts: Break down bone.

• Osteocytes: Mature bone cells.

• Osteoprogenitor (stem) cells: Differentiate into osteoblasts.

Ossification: Formation of bone tissue.

• Endochondral ossification: Bone forms from hyaline cartilage (most bones).

• Intramembranous ossification: Bone forms from membrane (e.g., flat bones of skull).

Bone Shapes: Long (femur), short (carpals), flat (skull), irregular (vertebrae).

Bone Marrow: Red marrow (myeloid tissue) produces blood cells; found in medullary cavity.

Bone Growth and Disorders

• Appositional growth: Increases bone width from the outside.

• Interstitial growth: Increases bone length from within (at epiphyseal plate).

• Epiphyseal plate: Growth plate in children; becomes epiphyseal line in adults.

• Perichondrium: Membrane covering cartilage.

Bone Disorders:

• Osteoporosis: Decreased bone density, often due to low estrogen.

• Osteopenia: Reduced bone formation.

• Osteosarcoma: Bone cancer.

• Osteomyelitis: Bone inflammation.

• Rickets, Paget's disease: Other bone disorders.

Types of Fractures: Hairline, avulsion, greenstick.

Hormonal Regulation of Bone

• Calcitonin: Lowers blood calcium by stimulating osteoblasts.

• Parathyroid hormone (PTH)/Calcitriol: Raise blood calcium by stimulating osteoclasts; antagonistic to calcitonin.

• Estrogen: Maintains bone density.

• Human growth hormone (HGH): Stimulates bone growth.

Articulations (Joints)

Classification and Structure

Joints (articulations) are points where two bones meet. They are classified by structure and function.

• Structural Types: Fibrous, cartilaginous, synovial.

• Functional Types:

  • Synarthrotic: Immovable (e.g., sutures in skull).

  • Amphiarthrotic: Slightly movable (e.g., intervertebral discs).

  • Diarthrotic (synovial): Freely movable (e.g., knee, elbow).

Parts of a Synovial Joint:

• Articular cartilage

• Joint (synovial) cavity

• Articular capsule

• Synovial fluid

• Ligaments (bone to bone)

• Tendons (muscle to bone)

Types of Synovial Movements: Flexion, extension, abduction, adduction, supination, pronation.

Reflexes and Synapses

Reflex Arc

A reflex is an involuntary, rapid response to a stimulus, involving a specific neural pathway called a reflex arc.

• Five parts of a reflex arc:

  1. Receptor (sensory)

  2. Afferent (sensory) neuron

  3. CNS (integration center: brain/spinal cord)

  4. Efferent (motor) neuron

  5. Effector (muscle or gland)

Synapse: Junction where neurons communicate; involves chemical neurotransmitters but cells do not physically touch.

Lab and Anatomical Review

Major Bones and Landmarks

• Skull: Foramen magnum, sphenoid ("butterfly bone"), ethmoid, conchae, zygomatic process, mandible, occipital, styloid/mastoid, sutures, perpendicular plate, temporal, lacrimal.

• Hip bone: Ischium, pubis, ilium.

• Scapula: Glenoid cavity.

• Maxilla: Upper jaw.

• Carpal bones: Trapezium, etc.

• Clavicle: Collar bone.

• Humerus: Arm bone.

• Radius/Ulna: Forearm bones (radius by thumb, ulna by pinky).

• Femur: Thigh bone.

• Tibia/Fibula: Leg bones (tibia is larger, fibula is smaller and lateral).

Body Planes and Sections

• Coronal (frontal): Divides body into anterior/posterior (front/back).

• Transverse (horizontal): Divides body into superior/inferior (top/bottom).

• Sagittal: Divides body into right/left (midsagittal = equal, parasagittal = unequal).

Osmosis and Tonicity

Osmosis is the passive movement of water across a semipermeable membrane from high to low concentration.

Type	Description	Example	Effect on Cell
Hypertonic	More solute outside cell	2% NaCl	Cell shrinks (crenates)
Hypotonic	Less solute outside cell	Distilled water	Cell swells, may burst
Isotonic	Equal solute inside/outside	0.9% NaCl	No net movement

Key Terms and Definitions

• Antagonistic: Opposing actions (e.g., calcitonin vs. PTH).

• Sinus: Air-filled cavity in bone.

• Foramen: Hole in bone for passage of vessels/nerves.

• Hairline fracture: Thin break in bone.

• Endothelium: Epithelial lining of blood vessels.

Example Equations

• Osmosis (net movement of water): $J = -P (C_2 - C_1)$ Where: J = flux, P = permeability, C = concentration

• DNA Base Pairing: $\text{A} = \text{T}, \quad \text{G} = \text{C}$

Additional info:

• Some content was expanded for clarity and completeness, such as the details of bone growth, tissue types, and the reflex arc.

• Tables were reconstructed to summarize tissue types and osmosis effects.