ch 4 lecture

Tissue

Tissue

A group of similar cells that usually have a similar embryological origin and are specialized for a particular function

Histology

The science that deals with the study of tissues

interstitial growth (cartilage)

Chondrocytes grow and divide, laying down more matrix inside the cartilage. This type of growth mainly occurs during childhood and adolescence.

appositional growth (cartilage)

Cartilage grows in diameter when new matrix is added to the surface of the existing tissue

Epithelial Tissue

• Covers body surfaces, lines hollow organs, body cavities, and ducts; forms glands

• Cells are tightly packed together with little or no extracellular matrix

• No blood vessels, so this is found directly adjacent to blood vessel rich connective tissue

• almost always form surface layers and are not covered by another tissue

General Features of Epithelial Tissue

• Arranged in sheets, in either single or multiple layers

• Consists mostly of closely packed cells with little extracellular material

• Many cell junctions are present, providing secure attachments among cells

• Has an apical surface-free surface and a basal surface attached to a base membrane

• Adhere firmly to nearby connective tissue via a thin extracellular layer, the basement membrane

• Avascular; exchange of materials between epithelium and adjacent connective tissue is by diffusion

• Have a nerve supply

• Have a high capacity for renewal (a high mitotic rate)
  

Major Functions of Epithelial Tissues

1. Serve as a selective barrier that limits or aids the transfer of substances into and out of the body

2. Serves as a secretory surface that releases products produced by the cells

3. Serves as a protective surface that resists the abrasive influences of the environment

Surfaces of Epithelial Cells

• Apical, Lateral, Basal

Apical Layer

Most superficial layer

Lateral Layer

Side of cell; the area where epithelial cells adhere to each other to form a sheet-like structure.

Basal Layer

Deepest layer

Basement Membrane Consists of…

1. Basal lamina (secreted by epithelial)

2. Reticular lamina (closer to connective tissue-fibroblasts

Roles of Epithelial Tissues

Protection, filtration, secretion, absorption, excretion

Layers of Epithelial Cells

• Simple (one)

• Stratified (several)

• Pseudostratified (one layer that appears as several)

Cell Shapes

• Squamous (flat)

• Cuboidal (cube-like)

• Columnar (rectangular)

• Transitional (variable)

Simple Epithelium

• Functions in diffusion, osmosis, filtration, secretion, and absorption

Pseudostratified Epithelium

Not all cells reach the apical surface

• Apical cells can contain cilia

• goblet cells secrete mucus

Stratified Epithelium

Two or more layers

Squamous Cells

Thin; rapid passage of substances

Cuboidal Cells

wide, cube or hexagons; function in either secretion or absorption

Columnar Cells

Taller than wider, function for secretion and absorption

Transitional Cells

Change cells from squamous to cuboidal and back (urinary bladder)

Epithelial Tissue Naming Combinations

Simple squamous, simple cuboidal, simple columnar, stratified squamous, stratified cuboidal, stratified columnar, pseudostratified columnar

Simple Squamous Epithelium

• composed of a single layer of flat cells resembling tiled floor

• Located in the air sacs of lungs, in the lining of blood vessels, the heart, lymphatic vessels, serous membranes

• Sites of filtration, diffusion, secretions

Simple Cuboidal Epithelium

• composed of a single layer of cube shaped cells

• located in the surface of ovary, lining of the kidney tubules, smaller ducts of many glands (like thyroid gland)

• Function: secretion and absorption
  

Simple Columnar Epithelium

• forms a single layer of column like cells

• ±cilia, ±microvilli, ±mucous (goblet cells)

Pseudostratified Columnar Epithelium

• Appears to have multiple layers due to nuclei which are at various depths. In reality, all cells are attached to the basement membrane in a single layer, but some do not extend to the apical surface

Stratified Squamous Epithelium

• Has an apical surface that is made up of flat cells

• The other layers have different shapes, but the name is based on the apical layer

• The many layers are ideal for protection against strong friction forces

Stratified Cuboidal Epithelium

• has an apical surface made up of two or more layers of cube-shaped cells

• Located in sweat glands, part of the urethra

Stratified Columnar Epithelium

Located in parts of the urethra, large excretory ducts of glands (esophageal gland), small areas of anal mucous membrane

Gland

A single cell or mass of epithelial cells adapted for secretion

Endocrine Glands

Ductless; their secretory products (hormones) enter the extracellular fluid and diffuse into the blood

Exocrine Glands

• sweat, oil, and digestive glands

• secrete their products into ducts that empty at the surface of covering and lining epithelium or directly onto a free surface

Mixed glands

Pancreas, ovaries, testes

Unicellular Gland

single-celled, such as the goblet cell

Multicellular Gland

composed of cells that form a distinctive microscopic structure or macroscopic organ, such as sweat, oil, and salivary glands

Categorization of multicellular glands

ducts and shape of the secretory portion

Ducts

are branched (compound) or unbranched (simple)

Shape of the secretory portion

Tubular (straight) and acinar (rounded)

Merocrine Glands

form the secretory products and discharge it by exocytosis

Apocrine Glands

• accumulate their secretary product at the apical surface of the secreting cell

• that portion then pinches off from the rest of the cell to form the secretion with the remaining part of the cell repairing itself and repeating the process

Holocrine Gland

accumulate the secretory product in the cytosol; when the cell dies, it and its products are discharged as the glandular secretion, with the discharged cell being replaced by a new one

Connective Tissue

• protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity

• Large amount of extracellular material separates cells

• Significant networks of blood vessels

• the most abundant and widely distributed tissue in the body.

• consists of two basic elements: cells and extracellular matrix (formed from ground substance and fibers)

• do not occur on free surface

• highly vascular(except for cartilage and tendons)

• except for cartilage, it contains nerve supply

• derived from mesenchyme
  

4 tissue types

Muscular, Nervous, epithelial, and connective

Muscular Tissue

Responsible for movement and generation of force

Nervous Tissue

Initiates and transmits action potentials (nerve impulses) that help coordinate body activities.

Cell Junctions

Points of contact between adjacent plasma membranes

Cell Junction Functions

1. Form fluid-tight seals between cells

2. Anchor cells together or to extracellular material

3. Act as channels, which allow ions and molecules to pass from cell to cell within a tissue

Five most important cell junctions

tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions

Tight Junctions

• Consist of weblike strands

• Form fluid-tight seals between cells

• Common among epithelial cells that line the stomach, intestines, and urinary bladder

• They inhibit the passage of substances between cells

Adherens Junctions

• Made up of plaque and anchor cells together

• Form the adhesion belt and keep tissues from separating as they stretch and contact

• Transmembrane glycoproteins called cadherins join the adjacent cells by insertion

Desmosomes

• composed of plaque and are linked by transmembrane glycoproteins that extend across a gap between adjacent cell membranes and link the cytoskeletons of cells together

• These spot weld-like junctions are common among the epidermis of the skin and cardiac muscle cells in the heart

Hemidesmosomes

• Half-welds that join cells to the basement membrane

• The transmembrane glycoproteins in these are called integrins, which attach to laminin in the basement membrane

Gap Junctions

• Allow cells in a tissue to rapidly communicate through connexins (tiny fluid filled tunnels; transmembrane protein channels that connect cells together)

• They are not fused together; only small ions and molecules pass through, proteins cannot

• Allow cell communication (nerve or muscle impulses)

Immature cells

• end in -blast (ex: fibroblast, chondroblast)

Mature Cells

• end in -cyte (osteocyte)

• reduced capacity for cell division and matrix formation and are mostly involved in maintaining the matrix

Fibroblasts

secrete fibers and matrix

Macrophages

also called histiocytes; develop from monocytes and are phagocytic (destroy bacteria)

Plasma Cells

develop into antibody- producing B lymphocytes or B-cells

Mast Cells

abundant alongside blood vessels and produce histamine)

Adipocytes

fat cells which store energy in the form of fat; found below skin and around organs

Leukocytes

white blood cells

Elastic Fibers

• Stretchable but strong fibers made of the proteins elastin and fibrillin

• found in skin, blood vessels, lung tissue

Eosinophils

White blood cells that migrate to sites of parasitic infection and allergic responses

Neutrophils

white blood cells that migrate to sites of infection and destroy microbes by phagocytosis

Ground Substance

• the material between cells and fibers

• made of water and organic molecules

• supports cells and fibers, binds them together, and provides medium for exchanging substances between blood and cells

Collagen Fibers

strong, flexible bundles of the protein collagen; the most abundant in your body

reticular fibers

• made up of collagen and glycoproteins

• provide support in blood vessel walls and form branching networks around various cells

ECM

• located in the spaces between connective tissue cells

• composed of fibers and ground substance

Three types of fibers embedded in the matrix between cells of connective tissues

collagen fibers, elastic fibers, reticular fibers

Collagen Fibers

composed of the protein collagen, are very tough and resistant to stretching, yet allow some flexibility in tissue; they are found in bone, cartilage, tendons, and ligaments

Elastic Fibers

composed of the protein elastin, provide strength and stretching capacity and are found in skin, blood vessels, and lungs

Reticular Fibers

consisting of collagen and glycoprotein, provide support in the walls of blood vessels and form a strong, supporting network around fat cells, nerve fibers, and skeletal and smooth muscle fibers

Embryonic Connective Tissue

present in the embryo or fetus

Embryonic Connective Tissue: Mesenchyme

• irregularly shaped mesenchymal cells embedded in semifluid ground substance that contains delicate reticular fibers

• Located exclusively under the skin and along developing bones of embryo; some in adult connective tissue, especially along blood vessels

• Forms almost all other types of connective tissue

Embryonic Connective Tissue: Mucous Connective Tissue

• widely scattered fibroblasts embedded in viscous, jellylike ground substance that contains fine collagen fibers

• located in the umbilical cord of fetus

• Function: support

Mature Connective Tissue

• exists in the newborn, has cells differentiated from mesenchyme, and does not change after birth

• Five Types: Loose connective tissue, Dense connective tissue, Cartilage, Bone tissue, Liquid connective tissue
  

Mature Connective Tissue; loose connective tissue: Areolar Connective Tissue

• one of the most distributed connective tissues; consists of fibers (collagen, elastic, reticular) arranged randomly and several kinds of cells embedded in a semifluid ground substance

• Located in and around nearly every body structure; in subcutaneous layer deep to skin; papillary region of dermis of skin; lamina propria of mucous membranes; around blood vessels, nerves, and body organs

• Function: support, strength, elasticity

Mature Connective Tissue; loose connective tissue: adipose tissue

• cells derived from fibroblasts, called adipocytes, that are specialized for storage of triglycerides as a large, centrally located droplet.

• White Adipose Tissue: in adults

• Brown Adipose Tissue: darker due to very rich blood supply and numerous pigmented mitochondria

• Located wherever areolar connective tissue is located

• Reduces heat loss through skin; served as an energy reserve; supports and protects organs

Mature Connective Tissue; loose connective tissue: Reticular Connective Tissue

• the fine interlacing network of reticular fibers and reticular cells

• located in the stroma of the liver, spleen, lymph nodes; red bone marrow; reticular lamina of basement membrane; around blood

• Forms stroma of organs; binds smooth muscle tissue cells; filters and removes worn-out blood cells in spleen and microbes in lymph nodes

Dense regular connective tissue

• consists of bundles of collagen fibers in a regular and orderly, parallel arrangement that confers great strength

• Forms tendons, ligaments

• Provides strong attachment between various structures

Dense irregular connective tissue

• contains fibers that are irregularly arranged and is found in parts of the body where tensions are exerted in various directions

• It usually occurs in sheets, such as the dermis of the skin

• It is also found in heart valves, the perichondrium, the tissue surrounding cartilage, and the periosteum

• Provides tensile(pulling) strength

Elastic Connective Tissue

• consists of elastic fibers and fibroblasts

• It is quite strong and can recoil back to its original shape after being stretched

• It is found in lung tissue and elastic arteries, allows stretching of various organs
  

Cartilage

• consists of a dense network of collagen fibers and elastic fibers embedded in chondroitin sulfate

• Its strength is due to its collagen fibers; its resilience due to the chondroitin sulfate

• surrounded by a dense irregular connective tissue membrane called the perichondrium

• Unlike other connective tissues, this has no blood vessels or nerves (except in the perichondrium),due to secretion of antiangiogenesis factor (a substance that prevents blood vessel growth)

• function: support, shock absorption, smooth movement of joints (no friction), and flexibility.

• three types: hyaline, fibrocartilage, and elastic
  

Perichondrium

a dense, fibrous membrane that covers cartilage and helps it grow, repair, and maintain its function

Hyaline Cartilage

• the most abundant but weakest type of cartilage and has fine collagen fibers embedded in a gel-type matrix. It affords flexibility and support. At joints, it reduces friction and absorbs shock.

• articular cartilage is a type

• surrounded by a perichondrium

Fibrocartilage

• contains bundles of collagen fibers in its matrix

• It does not have a perichondrium.

• Combining strength and rigidity, it is the strongest of the three types of cartilage

• the least flexible type of cartilage

• makes up intervertebral discs, menisci of knee

Elastic Cartilage

• contains a threadlike network of elastic fibers within the matrix.

• A perichondrium is present. It provides strength and elasticity and maintains the shape of certain organs.

Growth of Cartilage

• accomplished by interstitial (endogenous) growth (expansion from with) and appositional (exogenous) growth (from without)

Bone Tissue

• Bone is composed of bone or osseous tissue

• consists of a matrix containing mineral salts and collagenous fibers and cells called osteocytes, the periosteum, red and yellow bone marrow, endosteum

• Bone supports, protects, helps provide movement, stores minerals, and houses blood-forming tissue

• Bone is classified as either compact or spongy, depending on how the matrix and cells are organized

• The basic unit of compact bone is the osteon or haversian system, consisting of four parts

• Spongy bone has trabeculae rather than osteons
  

Four parts of bone tissue

1. lamellae

2. lacunae

3. canaliculi

4. central (haversian) canal

Lamellae

• “Little plates”

• concentric rings of matrix that consist of mineral salts that give bone its hardness and collagen fibers that give bone its strength

Lacunae

• small spaces between lamellae that contain mature bone cells called osteocytes

Canaliculi

• minute canals containing processes of osteocytes that provide routes for nutrient and waste transport

A central (haversian) canal

• contains blood vessels and nerves

Liquid Connective Tissue: Blood

• vascular tissue

• consists of a liquid matrix called plasma and formed elements suspended in the plasma

• formed elements include erythrocytes, leukocytes, and thrombocytes

Erythrocytes

• Red blood cells that function in transporting respiratory gases

Leukocytes

• white blood cells

• involved in phagocytosis, immunity, and allergic reactions

Thrombocytes

• Platelets that function in blood clotting

Lymph

• Interstitial fluid flowing in lymph vessels