✨ Nursing Note A&P – Tissue Level of Organization✨

Tissue Level of Organization

Four tissue types

• Epithelial tissue: exposed surfaces, lines internal passageways and chambers, forms glands.

• Connective tissue: fills internal spaces, provides structural support for other tissues, transports materials within the body, stores energy.

• Muscle tissue: specialized for contraction and includes the skeletal muscles of the body, muscle of the heart, muscular walls of hollow organs.

• Neural tissue: carries information from one part of the body to another in the form of electrical impulses.

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Epithelial tissue

• Epithelia > cover internal or external surfaces (skin and line the digestive, respiratory, reproductive, urinary tracts)

• Glands > produce fluid secretions

Function of epithelial tissue

• Provide physical protection > maintain BT, blood fluid, against outside environment, infection, harm

• Control permeability

• Provide sensation > light tough, pressure, pain, thermoregulation

• Produce specialized secretions > glandular epithelium (gland cells)

Characteristics of epithelia

• Polarity > apical and basal surfaces attached

• Cellularity > cell junctions

• Attachment: basal lamina (base epithelium) > bound to a thin, noncellular basement membrane > complex structure (basal surface epithelium and the underlying connective tissue)

• Avascularity > lack blood vessels, get nutrients by diffusion, absorption

• Regeneration > repair via stem cells

Specializations of epithelial Cells

1. providing protection and lubrication > movement of fluids over the epithelial surface

2. control permeability > movement of fluids through the epithelium

3. production of secretions > provide physical protection or act as chemical messengers

• Microvilli: absorption and secretion > digestive system, kidneys

• Cilia: synchronized beating of the cilia moves substances over the epithelial surface. > respiratory tract

Maintaining the integrity of epithelia

Cell adhesion molecules (CAMs) > bind to each other and to extracellular materials.

• Gap junctions

  • two cells are held together by two interlocking transmembrane proteins

    > connexons: contain > six connexin proteins, cylinder with a central pore (narrow passageway lets small molecules and ions pass between the cells)

  • LOCATIONS: cardiac muscle tissue and smooth muscle tissue

• Tight junction (occluding junction)

  • CONTAIN: two lipid plasma membranes are tightly bound together by interlocking membrane proteins

  • FUNCTION: prevent water and solutes from passing between the cells

    stretching, bending, twisting, compression > protect mechanical stresses

• Desmosome

  • CONTAIN: CAMs and proteoglycans bind together

  • FUNCTION: very strong and can resist stretching and twisting

Glandular epithelia

produce secretions

• Endocrine glands (ductless glands)

  • FUNCTION: produces endocrine secretions (hormones) > release into interstitial > enter the bloodstream >> body.

  • ductless: not released into ducts

  • E.g., pancreas, thyroid gland, thymus, pituitary gland

• Exocrine glands

  • FUNCTION: produce exocrine secretions > release onto an epithelial surface through tubular ducts

  • E.g., digestive tract, perspiration (skin), tears (eyes), milk (mammary glands)

    • Serous glands > parotid salivary glands

    • Mucous glands > sublingual salivary glands, submucosal glands(small intestine)

    • Mixed exocrine glands contain > submandibular salivary glands

Modes of Secretion

• Merocrine secretion (common): released from secretory vesicles by exocytosis

  • Mucin: mixes with water to form mucus > lubricant, a protective barrier, a sticky trap for foreign particles and microorganisms

  • mucous (salivary glands): coat food and reduce friction during swallowing

  • sweat (merocrine sweat glands): produce the watery perspiration that helps cool on a hot day

• Apocrine secretion: loss of cytoplasm when secretory product

  • apical portion of the cytoplasm> becomes packed with secretory vesicles and is then shed.

  • Milk production (mammary glands): merocrine and apocrine secretions

• Holocrine secretion: destroys the whole gland cell when secretory product

  • Sebaceous glands (hair follicles)

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Connective Tissues

Classification of Connective tissues

• Connective tissue proper:

  connective tissues with many types of cells and extracellular fibers in a syrupy ground substance.

  • loose connective tissues / adipose tissue / fat

  • dense connective tissues / tendons

• Fluid connective tissues:

  • blood

  • lymph

  watery matrix that contains dissolved proteins

• Supporting connective tissues:

  • cartilage (gel with characteristics)

  • bone (mineral deposits)

  less diverse cell population

  matrix containing much more densely packed fibers

  protect soft tissues and support the weight of part or body

Function of connective tissue

• Establishing a structural framework for the body.

• Transporting fluids and dissolved materials.

• Protecting delicate organs.

• Supporting, surrounding, and interconnecting other types of tissue.

• Storing energy (triglycerides)

• Defending body from invading microorganisms.

Cells of connective tissue proper

• Fibroblasts: most abundant

  • secrete > hyaluronan (lock epithelial cells together) and proteins.

  • also secretes protein subunits > form large extracellular fibers

• Fibrocytes: second most abundant

  • spindle-shaped cells > maintain the connective tissue fibers of connective tissue proper

• Adipocytes (fat cells)

  • CONTAINS: a single, enormous lipid droplet > nucleus, organelles, cytoplasm (squeezed to one side)

• Mesenchymal cells (stem cells)

  • respond to local injury or infection by dividing to produce daughter cells > fibroblasts, macrophages, or other connective tissue cells.

• Melanocytes:synthesize and store the brown pigment melanin

• Macrophages: “big eater”

  • body’s defenses

  • When stimulated, they release chemicals

• Mast cells

  • small, mobile > common near blood vessels

  • cytoplasm of a mast cell > filled with granules containing histamine (released after injury or infection, stimulates local inflammation) and heparin

• Lymphocytes

• Microphages (neutrophils and eosinophils): phagocytic(吞噬) blood cells

  Connective tissue fibers

• Collagen fiber (common)

  long, straight, unbranched, flexible, a bundle of fibrous protein subunits wound together

  • Tendons > connect skeletal muscles to bones

  • ligaments > connect bones to bones

  • FUNCTION: withstand tremendous forces

• Reticular fibers (reticulum, network)

  • Thinner than collagen fibers

  • a branching, interwoven framework(stroma) > tough, flexible > stabilizes functional cells, parenchyma, organs /organ’s blood vessels, nerves, and other structures

• Elastic fibers (protein elastin)

  • a branching, wavy

  • After stretching, they return to the original length

  • e.g., interconnecting vertebrae

Ground Substance

• fills the spaces between cells and surrounds connective tissue fibers

• clear, colorless, and viscous (proteoglycans, glycoproteins)

• viscous > bacteria have trouble moving through (avoid bacteria, easier for phagocytes to catch)

Embryonic / Mesenchyme Connective Tissues

• first connective tissue to appear in a developing embryo

  • Star-shaped stem cells (mesenchymal cells): separated by a matrix with very fine protein filaments

  • Mucous connective tissue (Wharton’s jelly): loose connective tissue, in many parts of the embryo, e.g., umbilical cord

Loose Connective Tissues

fill spaces between organs, cushion and stabilize specialized cells in organs, and support epithelia.

surround and support blood vessels and nerves, store lipids, and provide a route for the diffusion of materials

• Areolar Tissue (areola, little space)

  • CONTAINS: all the cells and fibers of any connective tissue proper > in a very loosely organized array

  • open framework

  • viscous ground substance > provides mass and absorbs shocks

  • distort without damage

  • LOCATION: Within and deep to the dermis of skin, and covered by the epithelial lining of the digestive, respiratory, and urinary tracts; between muscles; around joints, blood vessels, and nerves

    • Elastic fibers > help returns to the original shape

    • capillaries: deliver oxygen and nutrients and remove carbon dioxide and waste products

      common injection site > extensive blood supply

• Adipose Tissue

  • provides padding, absorbs shocks >slow heat loss through the skin

  • LOCATIONS: Deep to the skin, especially at sides, buttocks, and breasts; padding around eyes and kidneys

  • Adipocytes (fat cells) account for most of the volume of adipose tissue

  • white fat(most): pale, yellow-white color

  • brown fat(infant):

    • lipid breakdown speeds up > create heat

  >> infant metabolic very quickly

• Reticular Tissue (see Reticular fibers)

  • reticular fibers form a complex three-dimensional stroma:

  • LOCATIONS: Liver, kidney, spleen, lymph nodes, and bone marrow

Dense Connective tissues

Collagenous: Fibers create most dense connective tissues

• Dense regular connective tissue

  collagen fibers are parallel to each other, packed tightly

  Provides firm attachment; conducts pull of muscles; reduces friction between muscles; stabilizes positions of bones

  • Collagen fibers

  • Fibroblast nuclei

    • LOCATION: Between skeletal muscles and skeleton (tendons and aponeuroses); between bones or stabilizing positions of internal organs (ligaments); covering skeletal muscles; deep fasciae

• Dense irregular connective tissue

  • no consistent pattern

  • CONTAINS: Collagen fiber bundles

  • LOCATIONS: Capsules of visceral organs; periostea and perichondria; nerve and muscle sheaths; dermis

  • FUNCTION: Provides strength to resist forces from many directions; helps prevent overexpansion of organs, e.g., urinary bladder

• Elastic tissue

  • CONTAIN: elastic fibers.

  • FUNCTION: help stabilize the positions of the vertebrae of the spinal column

Fluid Connective tissues

fluid matrix > surrounds the cells, includes many types of suspended proteins

• Blood: vessels of the cardiovascular system

  • plasma: watery matrix 

  • red blood cells, white blood cells, platelets

  • Lymph: interstitial fluid enters lymphatic vessels

    • immune system > monitor and respond to signs of injury or infection.

Supporting connective tissues

• Cartilage

  • matrix: firm gel (proteoglycans)

  • cells: chondrocytes

  • lacunae: small chambers

  • avascular > all exchange of nutrients and waste products by diffusion through the matrix

  • perichondrium

    have blood vessels > provide oxygen and nutrients to the underlying chondrocytes.

    • outer (fibrous region of dense irregular connective tissue) > support and protection and attaches the cartilage to other structures

    • inner (cellular layer) > the growth and maintenance of the cartilage

• Cartilage growth

  • Interstitial growth: enlarges the cartilage from within.

    • Chondrocytes in the cartilage matrix divide, and the daughter cells produce additional matrix

  • Appositional growth: adds new layers of cartilage to the surface

• Types of Cartilage

  • Hyaline cartilage (common)

    • FUNCTIONS: Tough, somewhat flexible > closely packed collagen fibers

    • LOCATIONS: connections between the ribs and the sternum

      • nasal cartilages > supporting cartilage, passageways of the respiratory tract

  • Elastic cartilage > yellowish color

    • Resilient and flexible (numerous elastic fibers)

    • FUNCTION: Provides support, but tolerates distortion without damage and returns to original shape

    • LOCATION: external flap (the auricle, or pinna) of the outer ear, a passageway to the middle ear cavity (the auditory tube), epiglottis, small cartilages (the cuneiform cartilages) in the larynx, or voice box.

    • articular cartilages, cover bone surfaces within joints > elbow and knee

  • Fibrocartilage

    • durable and tough (little substance, matrix)

    • FUNCTION: Resists compression; prevents bone-to-bone contact; limits movement

    • LOCATION: intervertebral discs

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Bone

Fasciae (body wall)

connective tissue layers and wrappings that support and surround organs

• Superficial Fascia (hypodermis, subcutaneous tissue)

  • CONTAINS: Areolar tissue and adipose tissue

  • LOCATION: Between skin and underlying organs

  • FUNCTION: provides insulation and padding, and lets the skin and underlying structures move independently

• Deep Fascia

  • each layer all the fibers run in the same direction

  • CONTAINS: dense irregular connective tissue

  • LOCATION: Bound to capsules, tendons, and ligaments

  • FUNCTION: Forms a strong, fibrous internal framework

  • helps the tissue resist forces coming from many directions

• Subserous Fascia

  • CONTAIN: Areolar tissue

  • LOCATION: Between serous membranes and deep fascia

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Tissue membranes

• Mucous Membranes

  • passageways and chambers > communicate with the exterior

  • FUNCTION: moist to reduce friction, facilitate absorption or secretion.

    • contain simple epithelia > perform absorptive or secretory functions

  • LOCATION: digestive, respiratory, reproductive, urinary tracts

• Serous membranes

  • CONTAIN: Very thin, but firm attached to body wall and organs / sealed, internal cavities of the trunk > not open to the exterior

  • FUNCTION: serous fluid to minimize friction between the surfaces >keep moist and slippery

  • LOCATION: pleura, pericardium, peritoneum,

• Cutaneous Membrane

  • CONTAIN: squamous epithelium, dense irregular connective tissue

  • FUNCTION: thick, waterproof, usually dry

  • LOCATION: skin

• Synovial Membranes

  • CONTAIN: areolar tissue (matrix of interwoven collagen fibers, proteoglycans, glycoproteins)

  • FUNCTION: lubricated to keep friction from damaging the opposing surfaces

  • LOCATION: Adjacent bones (joints, articulations)

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muscle tissue

• Skeletal muscle tissue (striated voluntary muscle)

  • long, cylindrical, striated, multinucleate

  • partially repair after injury

  • CONTAIN: muscle fibers (very large muscle cells—up to 0.3 m), several hundred nuclei,

  • myosatellite cells (satellite cells)>produce new muscle fibers

  • FUNCTION: Moves or stabilizes the position of the skeleton; guards entrances and exits to the digestive, respiratory, and urinary tracts; generates heat; protects internal organs

  • LOCATION: Combined with connective tissues and neural tissue in skeletal muscles > adjacent skeletal muscle fibers - tied together by collagen and elastic fibers - attached tendon or aponeurosis.

• Cardiac Muscle Tissue (striated involuntary muscle)

  • short, branched, striated, usually with a single nucleus

  • cells are interconnected by intercalated discs.

  • repair incomplete after damage

  • CONTION: Nuclei, Cardiac muscle cells (cardiocyte), Intercalated Discs, Striations

  • LOCATION: Heart

  • FUNCTION: Circulates, blood; maintains blood pressure

  • membranes are locked together by desmosomes, proteogly cans, and gap junctions.

• Smooth Muscle tissue (nonstriated involuntary muscle)

  • short, spindle-shaped, nonstriated, with a single, central nucleus

  • regenerate after an injury

  • Contain: small, spindle-shaped, with tapering ends and a single, oval nucleus

  • LOCATION: Found in hollow organs > the walls of blood vessels and in digestive, respiratory, urinary, and reproductive organs

  • FUNCTION: Moves food, urine, and reproductive tract secretions; controls diameter of respiratory passageways; regulates diameter of blood vessels

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Neural tissue

propagation (movement) of electrical impulses from one region of the body to another

control centers: brain and spinal cord

• Neurons

  • Cell body: contains nucleus and major organelles

  • Dendrites: contacted by other neurons, receive information from other neurons

  • Axon: send information to other cells

• Neuroglia (glial cells)

  • FUNCTION: support and repair neural tissue and supply nutrients to neurons

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Reference

Martini, F. H., Nath, J. L., & Bartholomew, E. F. (2018). Fundamentals of anatomy & physiology (11th ed.). Pearson.

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