Comprehensive Study Notes: Tissues, Integumentary System, and Skeletal System

Tissues

General Information

Tissues are groups of cells that work together to perform a specific function. In the human body, there are four primary tissue types, each with distinct structures and roles.

• Epithelial Tissue

• Connective Tissue

• Muscle Tissue

• Nervous Tissue

Epithelial Tissue

Epithelial tissue covers body surfaces, lines cavities, and forms glands. It is classified based on the number of cell layers and the shape of cells at the apical (top) surface.

• Traits: Closely packed cells, little extracellular material, avascular (no blood vessels), high regenerative capacity.

• Subclasses:

  • Simple Squamous Epithelium: Single layer of flat cells; allows diffusion and filtration (e.g., alveoli of lungs).

  • Simple Cuboidal Epithelium: Single layer of cube-shaped cells; secretion and absorption (e.g., kidney tubules).

  • Simple Columnar Epithelium: Single layer of tall, column-like cells; absorption and secretion (e.g., lining of digestive tract).

  • Pseudostratified Ciliated Columnar Epithelium: Appears layered but all cells touch the basement membrane; often ciliated (e.g., trachea).

  • Stratified Squamous Epithelium: Multiple layers; protects against abrasion (e.g., skin, mouth lining).

  • Stratified Cuboidal Epithelium: Rare; found in some ducts (e.g., sweat glands).

  • Stratified Columnar Epithelium: Rare; found in male urethra and some glands.

  • Transitional Epithelium: Stretches; found in urinary bladder.

• Glandular Epithelia:

  • Endocrine Glands: Ductless; secrete hormones into blood (e.g., thyroid gland).

  • Exocrine Glands: Secrete products into ducts (e.g., sweat, salivary glands).

Connective Tissue

Connective tissue supports, binds, and protects other tissues and organs. It is characterized by an abundance of extracellular matrix.

• Traits: Few cells, abundant extracellular matrix, varying vascularity.

• Parts:

  • Extracellular Matrix:

    • Ground Substance: Gel-like material; supports cells and binds them together.

    • Fibers:

      • Collagen Fibers: Strong, resist tension.

      • Elastic Fibers: Stretch and recoil.

      • Reticular Fibers: Form supportive networks.

  • Cells: Fibroblasts, chondrocytes, osteocytes, adipocytes, etc.

• Subclasses of Connective Tissue:

  • Connective Tissue Proper:

    • Loose Connective Tissue: Areolar, adipose, reticular.

    • Dense Connective Tissue: Dense regular (tendons), dense irregular (dermis).

  • Cartilage: Hyaline, elastic, fibrocartilage.

  • Bone: Compact and spongy bone.

  • Blood: Fluid connective tissue; transports substances.

Muscle Tissue

Muscle tissue is specialized for contraction, enabling movement of the body and its parts.

• Traits: Elongated cells (muscle fibers), contractile proteins (actin and myosin).

• Subclasses:

  • Skeletal Muscle: Voluntary, striated, attached to bones.

  • Cardiac Muscle: Involuntary, striated, found in heart, intercalated discs.

  • Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs.

Nervous Tissue

Nervous tissue is responsible for receiving, processing, and transmitting information through electrical impulses.

• Traits: Excitable cells, rapid communication.

• Cells: Neurons (transmit signals), neuroglia (support and protect neurons).

Integumentary System

Functions

The integumentary system (skin and its derivatives) protects the body, regulates temperature, and provides sensory information.

• Protection from mechanical, chemical, and biological damage

• Prevents water loss

• Regulates body temperature

• Excretes wastes

• Synthesizes vitamin D

• Sensory reception

Layers of the Skin

The skin consists of two main layers: the epidermis and dermis, with the hypodermis (subcutaneous layer) beneath.

• Epidermis: Superficial, avascular, composed of keratinized stratified squamous epithelium.

  • Cell Types:

    • Keratinocytes: Produce keratin, main cell type.

    • Melanocytes: Produce melanin pigment.

    • Langerhans’ Cells: Immune defense, migratory.

    • Merkel Cells: Sensory receptors for touch.

  • Layers (from deep to superficial):

    • Stratum Basale: Single row of stem cells; mitosis occurs here.

    • Stratum Spinosum: Several layers; contains pre-keratin filaments.

    • Stratum Granulosum: 3-5 layers; keratinization begins.

    • Stratum Lucidum: Thin, clear layer; only in thick skin (palms, soles).

    • Stratum Corneum: Many layers of dead, keratinized cells; protective barrier.

• Dermis: Deep, vascular, connective tissue layer.

  • Papillary Layer: Areolar connective tissue; forms dermal papillae (fingerprints).

  • Reticular Layer: Dense irregular connective tissue; provides strength and elasticity.

• Hypodermis: Not part of skin; adipose tissue; anchors skin to underlying structures.

Skin Coloration

Skin color is determined by three main pigments:

• Melanin: Brown-black pigment produced by melanocytes; protects against UV radiation.

• Carotene: Yellow-orange pigment from diet; accumulates in stratum corneum.

• Hemoglobin: Red pigment in blood; gives pinkish hue to fair skin.

Clinical Terms:

• Cyanosis: Bluish skin due to low oxygen.

• Erythema: Redness from increased blood flow.

• Jaundice: Yellowing from bilirubin buildup (liver dysfunction).

• Hematoma: Localized blood accumulation (bruise).

Hair

• Functions: Protection, sensation, reduces heat loss.

• Types: Vellus (fine, body hair), terminal (scalp, eyebrows, etc.).

• Parts:

  • Lengthwise: Shaft (above skin), root (within follicle).

  • Cross-section: Medulla (core), cortex (middle), cuticle (outer layer).

• Follicle: Structure in dermis from which hair grows.

Nails

• Function: Protects fingertips, aids in grasping.

• Tissue: Modified epidermis, hard keratin.

• Nail Bed: Underlying skin beneath nail plate.

• Eponychium: Cuticle; protects nail matrix.

• Hyponychium: Thickened skin under free edge; prevents infection.

Glands

• Sweat Glands:

  • Eccrine: Widely distributed; thermoregulation.

  • Apocrine: Axillary/genital areas; active at puberty; odor from bacterial action.

• Sebaceous (Oil) Glands: Secrete sebum; lubricates skin/hair.

• Ceruminous Glands: Modified sweat glands in ear canal; produce earwax.

Bone

Functions

• Support for body and organs

• Protection of vital organs

• Movement (leverage for muscles)

• Mineral storage (calcium, phosphate)

• Blood cell formation (hematopoiesis in red marrow)

• Triglyceride storage (yellow marrow)

Tissue Subtypes

• Compact Bone: Dense, organized into osteons (Haversian systems).

  • Osteon: Structural unit; concentric lamellae around central canal.

  • Perforating (Volkmann's) Canal: Connects blood vessels/nerves of periosteum to central canals.

  • Circumferential Lamellae: Extend around entire bone shaft.

  • Interstitial Lamellae: Fill gaps between osteons.

• Spongy Bone: Lattice of trabeculae; spaces filled with red marrow.

• Microscopic/Chemical Components:

  • Cells: Osteogenic cells, osteoblasts, osteocytes, osteoclasts.

  • Bone Matrix: Organic (collagen), inorganic (hydroxyapatite crystals).

Categories by Shape

• Long Bones: Longer than wide (e.g., femur).

• Short Bones: Cube-shaped (e.g., carpals).

• Flat Bones: Thin, flat (e.g., sternum, skull).

• Irregular Bones: Complex shapes (e.g., vertebrae).

Parts of a Long Bone

• Diaphysis: Shaft; compact bone surrounding medullary cavity.

• Epiphyses: Ends; spongy bone inside compact bone; articular cartilage covers joint surfaces.

• Periosteum: Double-layered membrane covering bone (except at joints).

  • Fibrous Outer Layer: Dense irregular connective tissue.

  • Osteogenic Layer: Contains bone-forming cells.

  • Sharpey's Fibers: Anchor periosteum to bone.

  • Nutrient Foramina: Openings for blood vessels.

• Endosteum: Lines internal bone surfaces.

• Articular Cartilage: Hyaline cartilage on joint surfaces.

Bone Markings

Bone markings are features that serve as sites of attachment, joint formation, or passage for nerves and blood vessels.

Category	Examples	Description
Attachments	Trochanter, Tuberosity, Tubercle, Crest, Line, Epicondyle, Spine	Projections for muscle/ligament attachment
Joints	Head, Facet, Condyle, Ramus	Projections that help form joints
Conduits (Holes)	Foramen, Meatus, Sinus, Fossa, Groove, Fissure	Openings for nerves, blood vessels, or other structures

Bone Development (Ossification)

• Intramembranous Ossification: Bone develops from fibrous membrane (e.g., flat bones of skull).

• Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

Bone Remodeling

• Purpose: Maintains bone strength, regulates calcium levels.

• Events:

  • Deposit: Osteoblasts build new bone matrix.

  • Resorption: Osteoclasts break down bone matrix.

• Hormonal Control: Parathyroid hormone (PTH) increases blood calcium by stimulating bone resorption; calcitonin lowers blood calcium.

• Osteoporosis: Disease where bone resorption outpaces deposit, leading to fragile bones.

Axial Skeleton

Skull

• Cranium (8 bones): Frontal (1), Parietal (2), Occipital (1), Sphenoid (1), Temporal (2), Ethmoid (1)

• Sutures: Immovable joints between skull bones.

• Facial Bones (14): Vomer (1), Mandible (1), Maxilla (2), Zygomatic (2), Nasal (2), Lacrimal (2), Palatine (2), Inferior Nasal Concha (2)

• Sinuses: Air-filled spaces in skull; lighten skull, resonate voice.

• Hyoid Bone: Not part of skull; supports tongue, no direct articulation with other bones.

Vertebral Column

• Ligaments: Hold vertebrae together.

• Discs: Intervertebral discs absorb shock.

• Vertebrae Structure: Body (weight-bearing), arch (encloses spinal cord), seven processes (muscle/ligament attachment).

• Divisions:

  • Cervical (7): Smallest, have transverse foramina.

  • Thoracic (12): Articulate with ribs.

  • Lumbar (5): Largest, bear most weight.

  • Sacrum: 5 fused vertebrae.

  • Coccyx: 3-5 fused vertebrae (tailbone).

• Abnormal Curvatures: Scoliosis (lateral), kyphosis (hunchback), lordosis (swayback).

Sternum & Ribs

• Sternum: Breastbone; manubrium, body, xiphoid process.

• Ribs: 12 pairs; true ribs (1-7), false ribs (8-12), floating ribs (11-12).

Appendicular Skeleton

Pectoral Girdle

• Clavicle: Collarbone; connects sternum to scapula.

• Scapula: Shoulder blade; provides attachment for arm muscles.

Arm and Forearm

• Humerus: Upper arm bone.

• Ulna: Medial bone of forearm (pinky side).

• Radius: Lateral bone of forearm (thumb side).

Wrist and Hand

• Carpus (Wrist): 8 carpal bones (mnemonic: Say Loudly To Pam Time To Come Home; from thumb side, proximal row first).

• Metacarpus (Palm): 5 metacarpal bones.

• Phalanges (Fingers): 14 bones per hand (proximal, middle, distal for each finger except thumb).

Bony Pelvis

• Coxal Bones: Ilium, ischium, pubis (fused in adults).

• Sacrum and Coccyx: Complete pelvic ring.

• Features: Acetabulum (big socket for femur), obturator foramen (big hole).

Lower Limb

• Femur: Thigh bone; largest bone in body.

• Patella: Kneecap; protects knee joint.

• Leg:

  • Tibia: Medial, weight-bearing bone.

  • Fibula: Lateral, non-weight-bearing.

• Foot:

  • Tarsals: 7 bones (ankle).

  • Metatarsals: 5 bones (foot).

  • Phalanges: 14 bones (toes).