Tissues

What are the 4 types of tissues?

-epitelial tissue

-connective tissue

-muscle tissue

-nerve tissue

What is the function and location of nervous tissue?

Function: internal communication

Location: brain, spinal cord and nerves

What is the function and location of muscle tissue?

Function: contracts to cause movement

Location: mucles attached to bone (skeletal), muscles of heart (cardiac), muscle of walls of hollow organs (smooth)

What is the function and location of epitelial tissues?

Function: forms boundaries between different environments, protects, secretes, absorbs, filters

Location: skin surface (epidermis), lining of GI tract organs and other hollow organs.

What is the function and loaction of connective tissue?

Function: supports, protects and binds other tissues together

Location: bones, tendons, fat and other soft padding tissue

Two main types of epitelial tissue (epitelium)

1. covering and lining epithelia: on external and internal surfaces

2. glandular epithelia: secretory tissue in glands

Characteristics of epithelial tissues...

1. cells have polarity -- apical (free, upper) and basal (lower, attached) surfaces. Apical surfaces may bear microvili or cilia. Noncellular basal lamina of glycoprotein and collagen lies adjacent to basal surfaces.

2. are composed of closely packed cells: continuous sheets held together by tight junctions and desmosomes.

3. supported by connective tissue reticular lamina (under the basal lamina)

4. avascular but innervated

5. high rate of regeneration

Simple squamous epithelium

(description, function & location)

*Description: single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of epithelia.

*Function: allows passage of materials through diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae.

*Location: kidney glomeruli; air sacs of lungs; lining of heart, blood vessels and lymphatic vessels; lining of ventral body cavity

Simple cubodial epithelium

(description, function, location)

*Description: single layer of cube-like cells with large spherical central nuclei

*Function: secretion and absorbtion

*Location: kidney tubules; ducts and secretory portions of small glands; ovary surface

 Simple columnar epithelium

(description, function, location)

*Description: single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (globlet cells)

*Function: absorbtion; secretion of mucus, enzymes and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action

*Location: nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes and some regions of the uterus

Pseudostratified columnar epithelium

(description, function, location)

*Description: single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting cells and bear cilia.

*Function: secretion, particularly of mucus; propulsion of mucus by ciliary action

*Location: nonciliated type in male's sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract

Stratified squamous epithelium

(description, function, location)

*Description: thick membrance composed of several cell layers; basal cells are cubodial or columnar and metabolically active; surface cells are flattened; in the keratinized type, surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers

*Function: protects underlying tissues in areas subjected to abrasion

*Location: nonkeratinized type forms the moist linings of the esophagus, mouth and vagina; keratinized variety forms the epidermis of the skin, a dry membrane

Transitional epithelium

(description, function, location)

*Description: resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous-like, depending on degree of organ stretch

*Function: stretches readily and permits distension of urinary organ by contained urine

*Location: lines the ureters, urinary bladder and part of the urethra

Stratified columnar epithelia

-quite rare in the body

-limited distribution in the body

-small amounts in pharynx, male urethra and lining some glandular ducts

-found in some sweat and mammary glands

typically two cell layers thick

-occurs at transition areas between 2 other types of epithelia

-only it's apical laye of cells is columnar

Glandular Epithelia

-a gland is one or more cells that make and secrete an aqueous fluid

-classified by: site of product release (endocrine or exocrine), relative number of cells forming the gland (unicellular or multicellular)

Endocrine Glands

• endocrine glands eventually lose their ducts, so they are often called ductless glands
• secrete hormones that travel through lymph or blood to target organs
• glands are structurally diverse, most endocrine glands are compact multicellular organs, but some individual hormone-producing cells are scattered in the digestive tract mucosa and in the brain resulting in diffuse endocrine system

Exocrine Glands

• more numerous than endocrine glands
• secrete their products onto body surfaces (skin) or into body cavities.
• unicellular glands secrete directly by exocytosis, whereas the multicellular glands secrete by an epithelium-walled duct that transports the secretion to the epithelial surfaces
• examples include: mucous, sweat oil and salivary glands

Multicellular exocrine glands

• composed of a duct and a secretory unit
• classified according to:

1. duct type (simple or compound)
2. structure of their secretory units (tubular, alveolar or tubuloalveolar)

Multicellualr exocrine glands: modes of secretion

• merocrine: products are secreted by exocytosis (example: pancreas, sweat and salivary glands)
• holocrine: products are secreted by rupture of gland cells (example: sebaceous glands)

Unicellular exocrine glands

• the only important examples of unicellular glands are mucous cells and globlet cells.
• in humans, such glands produce mucin, a complex glycoprotein that dissolves in water when secreted.
• once dissovled, mucin forms mucus, a slimy coating that both protects and lubricates surfaces.
• globlet cells: cuplike accumulation of mucin distends the top of the cell, making the cells look like a glass with a stem (this does not occur in mucous cells)

Connective tissue

• most abundant and widely distributed of the primary tissues.
• four main classes of connective tissue: (1) connective tissue proper (includes fat and fibrous tissue of ligaments). (2)cartilge (3) bone tissue (4) blood

Major functions of connective tissue 

• binding and supporting
• protection
• insulation
• transportation of subtances within the body

Characteristics of connective tissue

• common origin: all connective tissue arise from mesenchyme (embryonic tissue)
• degrees of vascularity
• cells separated by nonliving extracellular matrix (ground substance and fibers)

Structural elements of connective tissue:

ground substance

• medium through which solutes diffuse between blood capillaries and cells.
• components: intersitial fluid, adhesion proteins "glue", proteoglycans (protein core + large polysaccharides) (trap water in varying amounts, affecting the viscosity of the ground substance)

Structural elements of connective tissue:

Fibers

1. Collagen fibers: strongest and most abundant type, provides high tensile strength
2. Elastic fibers: network of long, thin, elastin fibers that allow for stretch
3. Reticular fibers: short, fine, highly branched collagenous fibers

Structural elements of connective tissue:

Cells

• mitotically active and secretory cells = "blasts"

• mature cells = "cytes"

                  -fibroblasts in connective tissue proper

                  -chrodrocytes & chondroblasts in cartilage

                  -osteoblast & osteocytes in bone

                  -hematopoietic stem cells in bone marrow

                  -fat cells, white blood cells, mast cells & macrophages

Connective tissue: mesenchyme

• embryonic connective tissue
• gives rise to all other connective fibers
• gel-liked ground substance with fibers and star-shaped mesenchymal cells

What are the three tyes of loose connective tissues?

• areolar
• adipose
• reticular

What are the three types of dense connective tissues?

• dense regular
• dense irregular
• elastic

Connective tissue proper: loose connective tissue  (areolar)

(description, function, location)

• Description: gel-like matrix with all 3 fiber types. Cells: fibroblasts, macrophages, mast cells and some white blood cells
• Function: wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid
• Location: widely distributed under epithelia of body (example: forms lamina propria of mucous membranes; packages organs; surrounds capillaries)

Connective tissue proper: loose connective tissue (adipose)

(description, function, location)

• Description: matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet
• Function: provides reserve food fuel, insulates against heat loss, suppors and protects organs
• Location: under skin in the hypodermis, around kidneys and eyeballs, within abdomen, in breast

Connective tissue proper: loose connective tissue (reticular)

(description, function, location)

• Description: network of reticular fibers in a typical loose ground substance, reticular cells lie on the network
• Function: fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells and macrophages
• Location: lymphoid organs (lymph nodes, bone marrow and spleen)

Connective tissue proper: dense connective tissue (dense regular)

• Description: primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast
• Function: attaches muscles to bones or to muscles, attaches bone to bone, withstands great tensile stress when pulling force is applied in one direction
• Location: tendons, most ligaments, aponeuroses

Connective tissue proper: dense connective tisse (dense irregular)

(description, function, location)

• Decription: primarily irregularly arranged collagen fibers; some elastic fibers; major cells is the fibroblast
• Function: able to withstand tension exerted in many directions, provides structural strength
• Location: fibrous capsules of organs and of joints, dermis of the skin, submucosa of digestive tract

Connective tissue proper: dense connective tissue (elastic)

(description, function, location)

• Decription: dense regular connective tissue containing a high proportion of elastic fibers
• Function: allows recoil of tissue following stretching, maintains pulsatile flow of blood through arteries, aids passive recoil of lungs following inspiration
• Location: walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes

What are the three types of cartilage?

• hyaline cartilage
• elastic cartilage
• fibrocartilage

Hyaline cartilage

(description, function, location)

• Description: amorphous but firm matrix; collagen fibers form an imperceptible network; chrondroblasts produce the matrix and when mature (chondrocytes) lie in lacunae
• Function: supports and reinforces, has resilient cushioning properties, resists compressive stress
• Location: forms most of the embryonic skeleton, covers the ends of long bones in joint cavities, forms costal cartilages of the ribs; cartilages of the nose, trachea and laryna

Elastic cartilage

(description, function, location)

• Description: similar to hyaline cartilage, but more elastic fibers in matrix
• Function: maintains the shape of a structure while allowing great flexibility
• Location: supports the external ear (pinna); epiglottis

Fibrocartilage

(description, function, location)

• Description: matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate
• Function: tensile strength with the ability to absorb compressive shock
• Location: intervertebral discs, pubic symphysis, discs of knee joint

Bone: Osseous tissue

(description, function, location)

• Description: hard, calcified matrix containing many collagen fibers; osteocytes lie in lacunae. Very well vascularized
• Function: bone supports and protects (by enclosing), provides levers for the muscles to act on, stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation (hematopoiesis)
• Location: bones

Blood

(description, function, location)

• Description: red and white blood cells in fluid matrix (plasma)
• Function: transport of respiratory gases, nutrients, wastes and other substances
• Location: contained within blood vessels

Nervous Tissue

(description, function, location)

• Description: neurons are branching cells; cells processes that may be quite long extend from the nucleus-containing cell body; also contribution to nervous tissue are nonirritable supporting cells
• Function: transmit electrical signals from sensory receptors and to effectors (muscles and glands) which control their activity
• Location: brain, spinal cord and nerves

Skeletal muscle

(description, function, location)

• Description: long, cylindrical, multinucleate cells; obvious striations
• Function: voluntary movement, locomotion, manipulation of the environment, facial expression, voluntary control
• Location: in skeletal muscles attached to bones or occasionally to skin

Cardiac muscle

(description, function, location)

• Description: branching, striated, generally uninucleate cells that interdigitate at specialized junctions (intercalated discs)
• Function: as it contracts, it propels blood into the circulation; involutary controlled
• Location: the walls of the heart

Smooth muscle

(description, function, location)

• Description: spindle-shaped cells with central nuclei; no striations; cells arranged closely to form sheets
• Function: propels substances or objects (foodstuffs, urine, a baby) along internal passageways; involuntary control
• Location: mostly in the walls of hollow organs

Epithelial membranes: (serous membranes)

• serosae-membranes (mesothelium + areolar tissue) in a closed ventral body cavity
• parietal serosae line internal body walls
• visceral serosae cover internal organs

What are the steps in tissue repair?

1. inflammation
2. organization restores the blood supply
3. regeneration and fibrosis effect permanent repair

What is the first step in tissue repair?

1. inflammation:

• release of inflammatory chemicals
• dilation of blood vessels
• increase in vessel permeability
• clotting occurs

What is the second step in tissue repair?

1. organization and restored blood supply

• blood clot is replaced with granulation
• epithelium begins to regenerate
• fibroblasts produce collagen fibers to bridge the gap
• debris is phagocytized

What is the third step in tissue repair?

1. regeneration and fibrous effect permanent repair

• the scab detaches
• fibrous tissue matures; epithelium thickens and begins to resemble adjacent tissue
• results in a fully regenerated epithelium with underlying scar tissue

Primary germ layers

• ectoderm, mesoderm and endoderm
• formed early in embryonic development
• specialize to form the 4 primary tissues: nerve tissue arises from ectoderm, muscle and connective tissue arise from mesoderm, epithelial tissue arise from all 3 germ layers.