VT 111 Lec. 2 Tissues & Body Membranes

Tissues

Are a collection of cells that are similar and that function together for a similar purpose.

• Used to build organs in animals

• Classification of tissues based on:

  • Structure of the cells

  • composition of the non cellular substance surrounding the cells (the matrix)

  • Function of the cells

Histology

The study of tissues

Cytology

The study of cells

Types of Embryonic Tissues

• Ectoderm: skin and adnexal structures (supporting appendages (structures/organs) near primary organs or systems), nervous system

• Endoderm: lining of G.I. tract, hollow organs (bladder)

• Mesoderm: bone, blood vessels, muscle, parenchyma of internal organs

Embryonic Tissues

• Tissues in the embryo that begin to form soon after fertilization

  • Day 13 or 14 in humans

  • 15 hrs in chickens

• Embryologic tissues are germinal layers because they can become different types of structures in the adult

• Types of Post Embryonic (Adult) Tissues

• Epithelial → covers & lines

• Connective (CT) → provides support

• Muscular → enables movement

• Nervous → controls work

Post Embryonic (Adult) Tissues

• All tissues formed from the germinal tissues

• Once the adult tissue is formed, its structural and functional fate is determined

  • Adult tissues are said to be differentiated (range of cell types with distinct structures/functions)

• Separate tissues have individual functions, but they all work together for survival of the organism.

Biopsy

The process of removing tissues for analysis from a patient

Epithelium: Where it’s Located

• Protective covering of the surface of the body

• Both inner and outer surfaces

• External surface made from ectoderm

• Internal surfaces made from endoderm

Characteristics of Epithelium

• Composed entirely of cells, lateral surfaces connected to neighboring cells by junctional complexes → very little extracellular matrix, if at all

• Some lack nerves but most are innervated → provide sensory input

• Specialized connections: tight junctions, desmosomes, gap junctions

• No blood supply, lacks blood vessels (avascular)

• Has polarity: apical vs. basal surface

  • Basement membrane that separates it from underlying connective tissue

  • Basal surface (side of the cell that faces the underlying connective tissue

  • Apical (side of the cell that faces the lumen (body cavity)

• Forms in sheets, covering or lining a structure

• Retains high mitotic rate among undifferentiated stem cells even in adult animals

Functions of Epithelium

• Protect, covers & lines underlying structures

  • skin, mucous membrane protects against abrasion

• Act as a barrier

  • epithelium prevents movement of substances through the epithelial layer, prevent entry of microorganisms

• Absorption/exchange/filter biochemical substances

  • exchange of respiratory gases, movement of nutrients, renal filter

• Excretion – substances that leave the body

  • Urine, feces, sweat

• Secretion – substances that stay in the body

  • mucous glands, sweat, etc.

• Provides sensory input

  • Smell, taste, sight

Cellular Attachments

• Plasma membranes

• Tight junctions

• Desmosomes

• Gap junctions

• Basement membrane/Basal lamina

Plasma Membranes

• Join to form specialized attachments

  • Junctional complexes → provide strength

Tight Junctions

• Formed by fusion of outermost layers of plasma membranes of adjoining cells

  • No leaks i.e tissues of the bladder or digestive tract

Desmosomes

• Connect plasma membranes of adjacent cells

• Strong mechanical coupling formed by filaments that interlock

  • Plaque (thickening)

  • Tonofilaments – intermediate filaments that extend from the plaque into the cytoplasm of each cell like anchors

• Found in tissues that undergo repeated tension & stretching

  • i.e skin, heart, uterus

Gap Junctions

• Cells linked by tubular channel proteins (transmembrane proteins)

  • Aka Connexons

• Extend from cytoplasm of one cell to the next

• Allow exchange and passage of ions and nutrients

• Role in cardiac and smooth muscle cells is to have the ability to quickly transport electrical signals between cells

Basement Membrane = Basal Lamina

• Foundation of the epithelial cell

• Nonliving network of fibers

  • Cements cells to underlying connective tissue

  • Varies in thickness

• Helps prevent cells from being torn off

• Partial barrier to underlying connective tissue

Surface Specialization

• Surfaces vary depending on their location and their role in the function of the tissue

• Smooth

  • Epithelia that line blood vessels is smooth to allow easy passage of blood cells

• Microvilli – fingerlike projections

  • Brush border – surface of a cell covered with microvilli; greatly increases surface area → increases absorptive ability; microvilli tend to occur on cells involved in absorption or secretion

• Cilia

  • Found on the free surfaces of cells and helps propel mucus and debris

  • Ex. Respiratory tract or urogenital tracts

• Keratin

  • Waterproof

  • Accumulation of keratin occurs when mature cells move from the basal layer to the superficial layer; keratinized epithelium

Classification of Epithelium

• # of layers of cells

  • Simple: single layer of cells (little protection to CT)

  • Stratified: multiple layers of cells (stronger)

  • Pseudostratified columnar: looks stratified but isn’t. Some cells tall, some short, all cells attached at basement membrane

• Shape of cell:

  • Classified by the shape of the cell on the luminal surface

  • Squamous = flat

  • Cuboidal = like a box

  • Columnar = taller than it is wide

• Presence of surface specializations

  • “cilia”, “keratinized” to indicate increased level of specialization

Types of Epithelia

Simple Squamous

Delicate, thin: inner lining of lung alveoli

Simple Cubodial

Central nuclei aligned in a row: ducts of liver, pancreas, salivary gland

Simple Columnar

Elongated cells; nuclei at base of cell: lining of GI tract

Stratified Squamous

Layers of cells: lining of the mouth or skin

Stratified Cuboidal

Generally 2 layers: sweat glands

Stratified Columnar

Rare: urethra

Pseudostratified Columnar

Cells of different heights; ciliated: trachea

Transitional

Ability to stretch: bladder

Squamous Epithelium

• Simple Epithelium

  • Delicate and thin

  • Flat and smooth

  • Found lining surfaces involved in passage of either gas or liquid

  • Mesothelium – epithelium of the serous membranes

  • Endothelium – epithelium that lines blood and lymphatic vessels

• Stratified Epithelium

  • Multilayered

  • Protect underlying tissues

  • Occurs in areas of body subject to mechanical and chemical stresses

    • Mouth, esophagus, vagina

  • Outer layer continually being worn off

  • Replaced at equal rate from cells in deeper layer

Cuboidal Epithelium

• Simple Cuboidal Epithelium

  • Single layer of cube-shaped cells

  • Nuclei aligned in single row

  • Found in areas where secretion and absorption occur

• Stratified Cuboidal Epithelium

  • Generally occurs in two layers

  • Protects underlying tissues

  • Found primarily along large excretory ducts

    • Sweat glands, mammary glands, salivary glands

Columnar Epithelium

• Simple Columnar Epithelium

  • Cells are elongated, closely packed together

  • Nuclei aligned in a row at base of cell

  • Some cells associated with absorption and secretion

  • Some ciliated on apical surfaces – simple ciliated columnar epithelia

  • Absorptive cells – covered in microvilli

  • Goblet cells – manufacture and store lubricating mucus onto luminal surfaces of epithelia

Columnar Epithelium Continued…

• Stratified Columnar Epithelium

  • Rare type of epithelia

  • In select parts of respiratory, digestive, and reproductive systems

  • Along some excretory ducts

  • Function in secretion and protection

• Pseudostratified Columnar Epithelium

  • Not truly stratified; rather simple

  • Nuclei at varying levels. not all cells reach luminal surface

  • Attach to basement membrane

  • Most are ciliated

  • In respiratory tract and portions of male reproductive tract

Transitional Epithelium

• Description:

  • Basal layer of cuboidal or columnar cells

  • Superficial layer of squamous cells

• Leak-proof membrane

• Found in regions required to expand and contract as part of their normal function

  • Ureters, urethra, bladde

Connective Tissue (CT)

• Derived from mesoderm

• Vascularized structural-type of tissue; found throughout body

• Most abundant and varied tissue

• Several types of CT

  • Bone, blood, fibrous tissue, cartilage, fat

  • Most (except fat) have more extracellular matrix than cells

• Classification scheme based on

  • Protein fiber type and orientation

  • Type of ground substance in the matrix

  • The fluid of the extracellular matrix

Types of Cells

➡

Fibrocytes

Maintain the general matrix of collagen

-blast type cells

cells that create the matrix

-clast type cells

cells that break the matrix down for remodeling

-cytes

cells that are maintenance type of

cells; cytes can convert back to blasts if

needed

Specialized Cells

➡

Chondrocytes

cells of the cartilage

Osteocytes

Cells of the bone

Adipocytes

Fat cells

Mast Cells

contain histamine, vasoactive chemicals

Leukocytes

White blood cells

Erythrocytes

Red blood cells

Macrophages

Phagocytic cells

Undifferentiated stem cells

Another type of specialized cell

Characteristics of Connective Tissue

• Unique single feature is that it consists of a living cellular component and a non-living matrix.

• Wide variety in ground substances, # and type of cells, and type of fibers allow for the many different kinds of CT

• The matrix is a combination of 3 basic components:

  1. Protein fibers (collagen, elastin, reticular)

  2. Ground substance (from liquid to gel to solid)

  • Water

  • Carbohydrates, simple sugars, ions, complex CHO’s

    • Hyaluronic acid, glycosaminoglycans, proteoglycans

  • Minerals

3. Cells can be fixed (adipose) or wandering (WBC, macrophage)

Ground Substances

• Medium through which the cells exchange nutrients and waste with blood

• Amorphous homogeneous material that ranges from liquid to gel to solid (glycoproteins)

• Shock-absorbing cushion that envelopes and protects delicate cells

• Effective obstacle for invading microorganisms (microbes)

Extracellular Fibers

• Collagenous fibers

• Reticular fibers

• Elastic fibers

Collagenous Fibers

• Most common; strong (immense tensile strength), thick strands of protein collagen

• Organized into bundles

• Varying density and arrangement of fibers

  • Loose CT surrounds organs

  • Dense CT around tendons & ligaments

Reticular Fibers

• Thin, delicate, branched networks of collagen

• Provide support for highly cellular organs

  • Endocrine glands, lymph nodes, spleen, bone marrow, liver

• Also found around nerves, blood vessels, muscle fibers, and capillaries

Elastic Fibers

• Composed primarily of the protein elastin

• Branched to form complex networks

  • Coiled microfibrils that can stretch & contract

• Occur in tissues subjected to stretching

  • Vocal cords, lungs, skin, walls of blood vessels

1. Major Cell Types

• Fixed cells

• Transient Cells

Fixed Cells

• Remains in connective tissue

• Involved in production and maintenance of the matrix

  • Fibroblast – manufacture & secrete fibers & ground substances of their matrix

  • Chondroblast

  • Osteoblast

  • Adipocyte – begin by looking like fibroblasts, but as they mature, fill with lipid & swell

  • Reticular cell – involved in immune response

Transient Cells

• Passes in and out of connective tissue = diapedesis

• Involved in repair and protection of tissue

  • Leukocyte – involved in immune response to kill invaders; can move through the walls of blood vessels through diapedesis

  • Mast cell – contain histamines and heparin; involved in inflammatory response,

  • Macrophage – involved in immune response to infection; phagocytes that engulf microbes, dead cells, and debris

Function of Connective Tissue

• Packaging, separating

  • Capsules around organs, holding layers to separate other tissues

• Connecting tissues to one another

  • Tendons, ligaments

• Support, movement

  • Bones, cartilage

• Storage

  • Nutrients, fat, minerals

• Cushioning, insulating

  • Adipose tissue

• Transportation/diffusion

  • Blood acts as a transport medium

  • ECF acts as a diffusion matrix for cells

• Protection

  • Cells of the immune system, bones protect underlying structures, et

Types of Connective Tissue

➡

Loose CT

• Packaging around organs attaches skin to underlying tissues

  • Areolar

  • Adipose

  • Reticular tissues

Dense CT

• Dense regular CT

  • Protein fibers oriented in one direction

    • tendons, ligaments, etc.

• Elastic CT

  • Contains collagen, elastin

    • vocal folds, nuchal ligament, external ear

    • elastic type: walls of arteries

• Dense irregular CT

  • Random oriented fibers (collagen)

    • Dermis, fibrous covering of organs

Cartalige

• Chondrocytes

• Classification depends on different types of ground substance

• Multiple functions

Hyaline Cartalige

• Most common cartilage

• Most rigid cartilage

  • Composed of closely packed collagen fibers and enclosed within a perichondrium

• Smooth, high amount of proteoglycans and collagen

• Articulating surfaces

  • Ends and growth plates of long bones, ribs, trachea, costal cartilage of ribs connecting to sternum

  • Fetal skeleton

Fibrocartilage

• Usually found merged with hyaline cartilage and dense connective tissue

• Contains thick bundles of hyaline cartilage

• No perichondrium

• More collagen than proteoglycans

• Slightly compressible, but very tough

• Takes a great deal of pressure

  • Menisci of knee

  • Between bones in pelvis

  • Intervertebral discs

Areolar Tissue

• Loose connective tissue; most common type of CT; found everywhere in the body

• Tangle of random fibers and cells suspended in thick ground substance

• Predominant cell is fibroblast

• Functions

  • Surrounds and supports

  • Provides nutrients

  • Present in all mucous membranes

• Pathological state

  • Loose CT fills with excessive body fluid -> Edema, pitting edema

Adipose Tissue = Fat

• Loose connective tissue

• Areolar tissue in which adipocytes (fat cells) predominate

• Located throughout body

• Highly vascular

• Very little extracellular matrix

• 2 main types

  • White adipose in the deep layers of the skin

  • Brown adipose found in newborn animals and those that hibernate

• Functions

  • Energy storehouse

  • Thermal insulator

  • Mechanical shock absorber

Reticular Tissue

• Loose connective tissue

• Thin, 3D network of loosely arranged reticular fibers and fibroblasts suspended in ground substance

• Forms framework for organs = Stroma

  • Spleen, lymph nodes, bone marrow

Dense Regular CT

• Tightly packed parallel collagen fibers

  • Fibroblasts form rows

• Immense tensile strength in one direction (fibers lie in the direction in which the force is exerted on them)

• Relatively avascular; slow to heal

• Locations

  • Tendons and ligaments

  • Sheets of fascia

Dense Irregular CT

• Thicker bundles of collagen than in dense regular

• Fibers interwoven into single sheet; can withstand forces from different directions

• Locations

  • Dermis of skin

  • Fibrous covering of organs

    • Kidney, testes, liver, spleen

• Tough capsule of joints

Elastic CT

• Composed primarily of elastic fibers in dense, branching bundles; along with collagen and proteoglycans

  • Parallel or interwoven pattern with fibroblasts and collagen

• Flexible

  • Withstands repeated bending

• Locations

  • Spaces between vertebrae

  • Body regions that require stretching

    • Ligaments

    • Walls of arteries, stomach, bronchi, bladder, heart

    • Epiglottis of larynx

    • External ears of animal

Specialized CT

• Cartilage

  • Based on type of fiber in matrix

• Osseous connective tissue = bone

  • Calcium phosphate salts

• Blood

  • Cells

  • Plasma is the extracellular fluid matrix

Bone CT

• Hardest and most rigid connective tissue

• Specialized matrix

  • Organic collagen fibers

  • Inorganic calcium salts

• Well vascularized

• Central haversian canal – vascular supply & nerve supply

• Canaliculi

• Locations

  • Skeletal fram

Blood CT

• Matrix

  • Ground substance = plasma

  • Fibrous component = protein

• Cells

  • Erythrocytes = RBCs

  • Leukocytes = WBCs

  • Thrombocytes = platelet

Cartilage = Gristle

• More rigid than dense connective tissue

  • More flexible than bone

• No innervation – can withstand a great deal of compression; avascular

• Cells

  • Chondrocytes in lacunae

• Matrix

  • Firm gel ground substance, tissue fluid, collagen, & elastic fibers

• Locations

  • Joints, ear, nose, vocal cords

  • Framework for bone formation

Muscle Tissue

• Primary characteristic: all muscle tissue is contractile

• Muscle only does work when it contracts

• Classification based on structure and function

• Striated, non striated

• Voluntary, involuntary

Muscle Tissue Continued…

• 3 different types

  • cardiac, smooth, skeletal

• Characteristics:

  • Contractile

  • Allows movement

  • Cells are long and either tubular or spindle shaped

  • Cells contain bundles of contractile proteins: actin and myosin

• Can be multinucleate

Cardiac Muscle

• Only in the heart

• Involuntary

  • Specialized pacemaker cells

• Striated

• Cells are "split“, terminate in “intercalated disks”

  • Way for cells to connect to one another

  • Disks pass excitation from one cell to the next

• Mononucleate

Skeletal Muscles

• Striated cells

  • Can be very large!!!!

• Voluntary- innervated by nerve cells

• Multinucleate, do not branch

  • Arranged like fibers surrounded by loose

Smooth Muscle

• Mononucleate

• Non-striated

• Involuntary

• Cells are spindle shaped

• Slow, sustained contractions

• Found in walls of hollow organs

  • bladder, uterus, intestines

Nervous Tissue

• Brain, spinal cord, peripheral nerves

• Only cells of the body that are normally excitable and conductive

  • Even longer cells!

• Different types of nerve and support cells

  • Neurons

  • Neuroglial cells (supporting) – more numerous

• Neurons - longest cells in the body

• Composed of 3 main parts:

  • Cell body – perikaryon; contain nucleus & controls cell metabolism

  • Short cytoplasmic extensions – dendrites; receive impulses from other cells

  • Long single extension – axon; conducts impulses away from the cell

Nervous Tissue Continued…

• Neurons: transport electrical signals

  • Neuroglia: support cells of the nervous system

• Feed the cells, maintain homeostasis of the extracellular fluid

• Insulative

• Protective

Membranes

• Thin, protective layers of tissue linked together that line body cavities, separate organs, and cover surfaces

  • Multicellular epithelial sheet bound to underlying connective tissue proper to form membranes; this epithelium bathed in mucous or in the case of the bladder, urine.

• 4 common types

  • Mucous membranes

  • Serous membranes

  • Cutaneous membranes

  • Synovial membranes

Mucous Membranes = Mucosae

• Line organs with connections to outside environment

• Composition

  • Stratified squamous or simple columnar epithelium; covers a layer of CT called lamina propria

  • CT layer, submucosa connects mucosa to underlying structures

• Generally produce large quantities of mucus

  • May contain goblet cells or multicellular glands

    • Mucus = water, electrolytes, and the protein mucin

    • Rich supply of antibodies helpful in trapping invaders/debris

• Some mucosae can also absorb

  • Epithelial layer in the intestine transfers nutrients to CT

• Controls what goes in and out of the body by forming a barrier