integumentary system

Simple Squamous Epithelium – Single layer of flat, thin cells specialized for rapid diffusion and filtration

Simple Cuboidal Epithelium – Single layer of cube

shaped cells with central round nuclei, functions in secretion and absorption

Simple Columnar Epithelium – Single layer of tall, narrow cells (often with microvilli or cilia and goblet cells) specialized for absorption and secretion

Pseudostratified Ciliated Columnar Epithelium – Single layer of columnar cells whose nuclei appear at different heights (all cells touch basement membrane), often ciliated and containing goblet cells for mucus secretion and movement

Stratified Squamous Epithelium (Keratinized) – Multiple cell layers with flattened, dead, keratin

filled cells at the surface providing a waterproof, abrasion

Stratified Squamous Epithelium (Non

keratinized) – Multiple living cell layers with flat surface cells, kept moist, for protection against abrasion (oral cavity, esophagus, vagina, anus)

Transitional Epithelium – Stratified epithelium with dome

shaped apical cells when relaxed and flattened when stretched, allowing urinary organs to expand (bladder, ureters, part of urethra)

Areolar Connective Tissue – Loose connective tissue with gel

like ground substance and loosely arranged collagen and elastic fibers, cushions organs, holds interstitial fluid, and defends against infection (under epithelium, papillary dermis)

Adipose Tissue – Closely packed adipocytes with large lipid droplets, storing energy, insulating, and cushioning organs (hypodermis, around kidneys and eyeballs, in breasts)

Reticular Connective Tissue – Network of reticular fibers forming a soft internal skeleton (stroma) that supports free blood cells (lymph nodes, spleen, bone marrow)

Dense Regular Connective Tissue – Parallel bundles of collagen fibers with fibroblasts between, providing tensile strength in one direction for muscle

to

Dense Irregular Connective Tissue – Thick collagen fibers arranged irregularly to resist tension from multiple directions (reticular dermis, fibrous capsules of organs)

Elastic Connective Tissue – Connective tissue rich in coiled elastic fibers that allow recoil after stretching (walls of large arteries like the aorta, certain ligaments, walls of bronchi)

Hyaline Cartilage – Smooth, glassy matrix with fine, unnoticeable collagen fibers supporting and cushioning (articular cartilage of long bones, costal cartilages, trachea, nose)

Elastic Cartilage – Cartilage with abundant elastic fibers providing both support and flexibility (external ear/pinna, epiglottis)

Fibrocartilage – Cartilage containing thick, densely packed collagen fibers for tensile strength and shock absorption (intervertebral discs, knee menisci, pubic symphysis)

Bone (Osseous Tissue) – Hard, calcified matrix of collagen fibers organized into osteons with central canals, providing support, protection, leverage for muscles, mineral storage, and hematopoiesis (all bones)

Blood – Fluid connective tissue with plasma matrix and formed elements (erythrocytes, leukocytes, platelets) for transport of gases, nutrients, wastes, and immune defense (within blood vessels)

Epidermis (Stratum Basale) – Deepest epidermal layer of a single row of stem cells, attached to basement membrane

melanocytes, Merkel cells, and new keratinocytes form here

Epidermis (Stratum Spinosum) – Several layers of keratinocytes “spiny” in appearance due to desmosomes

contains Langerhans cells for immune defense

Epidermis (Stratum Granulosum) – 3–5 layers of flattened keratinocytes with keratohyalin granules, cells begin to die as organelles disintegrate

Epidermis (Stratum Lucidum) – Thin, translucent band of dead keratinocytes filled with eleidin

present only in thick skin (palms, soles)

Epidermis (Stratum Corneum) – Outermost layer of 20–30 layers of dead, flattened, keratinized cells without nuclei

constantly shed, forming a protective barrier

Dermis (Papillary Layer) – Areolar connective tissue with dermal papillae projecting into epidermis, containing capillaries that nourish epidermis and Meissner’s corpuscles for light touch

Dermis (Reticular Layer) – Dense irregular connective tissue with thick collagen bundles arranged randomly, housing blood vessels, sweat & oil glands, hair follicles, and Pacinian corpuscles for deep pressure

Hypodermis (Subcutaneous Layer) – Areolar connective tissue and adipose tissue anchoring skin to underlying structures, storing energy, and insulating

Eccrine (Merocrine) Sweat Glands – Coiled tubular glands distributed over most of the body that produce hypotonic sweat (99% water, salts, waste) for thermoregulation

Apocrine Sweat Glands – Larger sweat glands located in axillary and genital regions, secrete viscous, protein

and lipid

Sebaceous (Oil) Glands – Holocrine glands that secrete sebum (oil) into hair follicles, lubricating skin and hair and providing mild antibacterial protection

Hair Follicle & Shaft – Hair shaft is the visible, keratinized portion above the skin

hair root and bulb reside in the dermis, where dividing keratinocytes in the matrix produce hair

arrector pili muscle causes goosebumps

Nail Plate & Bed – Hard keratin covering dorsal surfaces of fingers/toes

nail bed is epidermis underneath

lunula is the whitish half

moon at the proximal base

cuticle (eponychium) overlaps proximal nail edge

Merkel (Tactile) Discs – Epidermal mechanoreceptors detecting light touch

Meissner’s Corpuscles – Dermal papillae receptors detecting fine, discriminative touch (fingertips, lips)

Pacinian (Lamellated) Corpuscles – Deep dermal receptors detecting deep pressure and vibration

Ruffini Endings – Dermal mechanoreceptors detecting stretch.