Tissue – Collection of cells that perform a common function.
Histology – Study of tissues.
Differentiation – Process where cells become specialized by inactivating specific genes.
Four Primary Tissue Types – Epithelial (covers), Connective (supports), Muscle (movement), Nervous (control).
Epithelial Tissue – A sheet of cells that covers surfaces and lines cavities.
Characteristics of Epithelial Tissue – Polarity (apical and basal surfaces), closely packed, avascular but innervated, highly regenerative.
Simple Squamous Epithelium – Single layer, flat cells; function: diffusion & filtration; location: air sacs of lungs.
Simple Cuboidal Epithelium – Single layer, cube-like cells; function: secretion & absorption; location: kidney tubules.
Simple Columnar Epithelium – Single layer, tall cells; function: absorption, mucus secretion; location: digestive tract lining.
Stratified Squamous Epithelium – Multiple layers; function: protection; location: skin, mouth, esophagus.
Transitional Epithelium – Changes shape; function: stretches; location: urinary bladder.
Endocrine Glands – Ductless, secrete hormones into blood.
Exocrine Glands – Have ducts, secrete onto surfaces (e.g., sweat glands).
Merocrine Secretion – Secretes via exocytosis (e.g., sweat glands).
Holocrine Secretion – Ruptures entire cell (e.g., sebaceous glands).
Connective Tissue Functions – Support, protection, insulation, transportation.
Types of Fibers in Connective Tissue – Collagen (strong), Elastic (stretchy), Reticular (supporting framework).
Areolar Connective Tissue – Cushions organs; found under epithelia.
Adipose Tissue – Stores fat, insulates; found under skin.
Hyaline Cartilage – Supports & cushions; found in joints, nose, trachea.
Fibrocartilage – Strong, absorbs shock; found in intervertebral discs.
Osseous Tissue (Bone) – Hard matrix; function: support & protection.
Blood Tissue – Fluid tissue; function: transport substances.
Skeletal Muscle – Voluntary, striated, multinucleated.
Cardiac Muscle – Involuntary, striated, branched, single nucleus.
Smooth Muscle – Involuntary, non-striated, spindle-shaped cells.
Nervous Tissue – Conducts electrical signals; found in brain, spinal cord.
Tissue Repair – Steps: Inflammation, organization, regeneration or fibrosis.
Integumentary System – Includes skin, hair, nails, and glands.
Epidermis – Outer layer, composed of keratinized stratified squamous epithelium.
Dermis – Middle layer, made of connective tissue.
Hypodermis – Subcutaneous layer, mainly adipose tissue.
Stratum Basale – Deepest layer, contains melanocytes and stem cells.
Stratum Spinosum – Several layers thick, contains desmosomes.
Stratum Granulosum – Where keratinization begins.
Stratum Lucidum – Only in thick skin, transparent layer.
Stratum Corneum – Outermost, dead keratinized cells.
Melanocytes – Produce melanin for UV protection.
Langerhans Cells – Immune response cells in epidermis.
Merkel Cells – Touch receptors.
Papillary Layer – Upper dermis, has dermal papillae (fingerprints).
Reticular Layer – Dense irregular connective tissue in the dermis.
Eccrine Sweat Glands – Found all over, regulate temperature.
Apocrine Sweat Glands – Found in armpits, groin; activated at puberty.
Sebaceous Glands – Secrete sebum (oil); associated with hair follicles.
Hair Function – Protection, sensory input, reduces heat loss.
Arrector Pili Muscle – Causes goosebumps.
Nail Matrix – Produces the nail.
Skin Functions – Protection, temperature regulation, sensation, vitamin D synthesis.
Burn Classifications – 1st-degree (epidermis), 2nd-degree (epidermis + upper dermis), 3rd-degree (full-thickness burn).
Basal Cell Carcinoma – Most common, least malignant skin cancer.
Squamous Cell Carcinoma – Grows rapidly, found in stratum spinosum.
Melanoma – Cancer of melanocytes, most dangerous.
Functions of Skeletal System – Support, protection, movement, mineral storage, blood cell formation.
Types of Skeletal Cartilage – Hyaline (most abundant), Elastic (ear), Fibrocartilage (intervertebral discs).
Perichondrium – Dense irregular connective tissue around cartilage.
Axial Skeleton – Skull, vertebral column, rib cage.
Appendicular Skeleton – Limbs and girdles.
Long Bones – Found in arms, legs; shaft with two ends.
Short Bones – Cube-shaped, found in wrists and ankles.
Flat Bones – Thin, flat, slightly curved; found in skull, sternum.
Irregular Bones – Complex shapes; vertebrae, pelvic bones.
Compact Bone – Dense outer layer.
Spongy Bone – Honeycomb-like, filled with marrow.
Diaphysis – Shaft of long bone.
Epiphyses – Ends of long bone.
Periosteum – Outer covering of bone.
Endosteum – Lines inner surfaces of bone.
Osteoblasts – Bone-forming cells.
Osteocytes – Mature bone cells in lacunae.
Osteoclasts – Bone-resorbing cells.
Haversian System (Osteon) – Structural unit of compact bone.
Canaliculi – Small channels for cell communication.
Bone Remodeling – Balance between osteoblasts and osteoclasts.
Wolff’s Law – Bone remodels in response to stress.
Osteoporosis – Bone resorption exceeds deposit; risk factors: low calcium, estrogen loss, immobility.
Rickets – Vitamin D deficiency, leads to weak bones.
Paget’s Disease – Excessive bone formation and breakdown.
Types of Fractures – Open (bone pierces skin), Closed (bone remains inside).
Stages of Fracture Healing – Hematoma, fibrocartilage callus, bony callus, bone remodeling.
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