functions

Cell SA to Volume Ratio

Limits max cell size to maintain adequate surface area for exchange of O2, nutrient uptake, and waste removal.

Receptor

Transduces extracellular signals into intracellular responses.

Enzyme (Membrane)

Degrades chemical messengers/signaling molecules to terminate their signal.

Ion Channel

Allows passive movement of charged hydrophilic solutes across lipid bilayer.

Gated ion Channel

Regulates membrane permeability and ionic flow on demand.

Cell-Identity Marker

Distinguishes body's self-cells from foreign cells or pathogens.

Cell-Adhesion Molecule (CAM)

Anchors cells together and maintains structural integrity of tissues.

Facilitated Diffusion

Moves water and hydrophilic/charged solutes across membrane without AТР.

Simple Diffusion

Allows nonpolar, hydrophobic, lipid-soluble molecules and gases to cross membrane freely.

Filtration

Removes wastes from blood in kidneys; drives nutrients out of capillaries into tissue fluid.

Specificity (Carrier Transport)

Ensures selective permeability across membrane.

Hypertrophy /Location - Muscle growth via exercise, accumulation of body fat in adipocytes.

Basal Lamina

Anchors epithelium to underlying CT; consists of collagen, laminin, and fibronectin.

Tight Junctions

Seals off lateral intercellular spaces near apical side; prevents passage of solutes between cells.

Desmosomes

Resists intense mechanical stress; keeps cells from pulling apart.

Hemidesmosomes

Anchors basal epithelial layer to underlying basal lamina; prevents delamination.

Gap Junctions

Equilibrates internal conditions by allowing free diffusion of ions, glucose, and small solutes between cells.

Simple Squamous ET

Rapid diffusion, selective transport, filtration, secretes lubricating serous fluid.

Simple Cuboidal ET

Absorption and secretion.

Simple Columnar ET

Bulk absorption and bulk selective secretion (high mucus content).

Goblet Cells

Bulk synthesis and secretion of mucus (mucin proteins, water, ions).

PSCCE

Secretes and propels mucus along surface via ciliary action; barrier protection.

Keratinized Stratified Squamous ET

Abrasion resistance, prevents pathogen entry, minimizes water loss.

Non-Keratinized Stratified Squamous ET

Mild abrasion resistance, pathogen barrier; must be constantly kept moist.

Transitional ET

Allows stretching and recoil to accommodate fluid volume changes.

Exocrine Glands

Secretes products onto external or luminal surfaces (e.g., sweat, oil, digestive enzymes).

Endocrine Glands

Secretes hormones into blood (e.g., thyroid, adrenal, pituitary glands).

Fibroblasts

Synthesizes ECM protein fibers (collagen, elastin, reticular) and ground substance.

Macrophages

Phagocytizes pathogens/debris, recruits leukocytes to initiate immune response.

Mast Cells

Secretes heparin (inhibits clotting) and histamine (dilates blood vessels/causes inflammation).

Elastic Fibers

Allows tissue stretching and elastic recoil back to original shape.

Reticular Fibers Location/ - Forms stroma/framework for lymphatic organs (spleen, lymph nodes, bone marrow).

Glycosaminoglycans (GAGs)

Traps water and mobile ions to create gelatinous consistency in CT ground substance.

Proteoglycans (PGs)

Structural bonding between cell membranes, cytoskeletons, and ECM fibers.

Dense Regular CT /Locations - Resists predictable mechanical stress in one direction; forms all tendons and ligaments.

Dense Irregular CT /Locations - Resists unpredictable stress in multiple directions; reticular layer of dermis, organ capsules.

Loose Areolar CT /Locations - Nourishes overlying avascular epithelia via diffusion, provides leukocyte mobility; underlying almost every epithelium, papillary dermis.

Adipose Tissue /Location - Energy storage, thermal insulation, organ padding/shock absorption; hypodermis, surrounding kidneys/heart.

Chondroblasts

Actively secretes cartilage matrix (Type II collagen, GAGs); becomes trapped in lacunae to mature into chondrocytes.

Chondrocytes

Maintains surrounding cartilaginous matrix.

Perichondrium

Contains reserve chondroblasts for cartilage growth and repair (ABSENT in fibrocartilage & articular cartilage).

Hyaline Cartilage

Eases joint movements, maintains open airway, structural flexibility.

Elastic Cartilage /Locations - Provides high flexibility, stretch and recoil; external ear (pinna) and epiglottis.

Fibrocartilage

Resists compression, absorbs shock; lacks perichondrium (cannot regenerate easily).

Serous Membrane Structure/ - Simple squamous ET (mesothelium) over areolar CT; secretes watery serous fluid for lubrication.

Keratin

Forms anti-abrasive, waterproof physical barrier in skin, hair, and nails.

Acid Mantle

Inhibits bacterial and fungal growth on skin.

Hypodermis

Energy reservoir, body padding/shock absorption, thermal insulation, site for subcutaneous injections.

Stratum Basale Cells/ - Contains stem cells, living keratinocytes, melanocytes, and tactile (Merkel) cells; site of active mitosis.

Stratum Granulosum

Synthesizes and secretes glycolipid water barrier; cross-links keratin filaments.

Stratum Corneum

Resists abrasion, penetration, and water loss; apical cells exfoliate as dander.

Keratinocytes

Synthesize keratin, migrate apically, die and form protective outer stratum corneum barrier.

Melanocytes

Synthesizes melanin pigment in melanosomes and donates them to surrounding keratinocytes to protect nuclear DNA from UV.

Tactile (Merkel) Cells

Transduces fine touch sensations.

Dendritic (Langerhans) Cells

Phagocytizes invading pathogens and alerts lymphatic system.

Papillary Layer /Structures - Dermal papillae interdigitate with epidermal pegs; contains tactile (Meissner's) corpuscles and capillary beds to nourish epidermis.

Reticular Layer /Structures - Provides multi-directional tensile strength; contains Pacinian (lamellar) corpuscles, hair follicles, and sweat/sebaceous glands.

Tactile (Meissner's) Corpuscles

Senses light touch and texture.

Pacinian (Lamellar) Corpuscles

Senses deep touch, pressure, and vibration.

Hair Matrix

Growth center of hair shaft.

Arrector Pili

Contracts in response to cold/fear/tactile stimuli to pull hair upright ("goosebumps").

Merocrine Sweat Glands

Secretes watery perspiration for evaporative cooling and thermoregulation.

Apocrine Sweat Glands /Locations - Secretes thicker milky sweat rich in fatty acids/proteins responding to stress/sexual stimulation; axillary, groin, bearded regions.

Sebaceous Glands

Secretes oily sebum to lubricate skin/hair, prevent dryness, and contribute to acid mantle.

Ceruminous Glands

Combines with sebum and dead cells to produce cerumen (earwax) to waterproof canal and trap debris/bacteria.

Epiphyseal Plate

Site of interstitial growth allowing bone elongation during growth.

Periosteum Layers/ - Outer fibrous layer (Type I collagen, Sharpey's fibers) + inner osteogenic layer (osteoblasts/osteogenic cells); appositional growth and fracture repair.

Perforating (Sharpey's) Fibers

Anchors periosteum and attached tendons/ligaments firmly to bone.

Endosteum

Contains osteoblasts and osteoclasts for bone deposition and resorption/remodeling.

Osteogenic Cells

Continually divide via mitosis to give rise to osteoblasts.

Osteoblasts

Synthesize organic osteoid matrix (collagen) and deposit hydroxyapatite minerals to form new bone tissue.

Osteocytes

Maintains bone matrix, senses mechanical strain, relays signals to osteoblasts/osteoclasts for remodeling.

Canaliculi

Contains cytoplasmic extensions of osteocytes connected via gap junctions for nutrient/waste transfer.

Osteoclasts /Structure - Resides in resorption bays; uses ruffled membrane border and hydrogen pumps (pH ~4) + acid phosphatase to dissolve mineral/organic matrix.

Organic Bone Matrix Components/ - Collagen fibers, PGS, GAGs; gives bone flexibility and resists tensile/bending forces.

Inorganic Bone Matrix Components/ - 85% Hydroxyapatite (crystallized calcium phosphate), 10% calcium carbonate; gives bone compression strength and rigidity.

Perforating (Volkmann's) Canals

Connects blood vessels and nerves of periosteum to central canals and medullary cavity.

Spongy Bone /Locations - Lightens skeleton, provides shock absorption, houses red bone marrow; inside bone epiphyses, diploë of flat bones.

Calcitriol

Essential for raising blood calcium levels by strongly enhancing calcium absorption in small intestine.

Fontanels

Allows skull shifting during childbirth and rapid brain expansion during infancy.