CHAPTER 4CHAPTER 4

TISSUESTISSUES

TYPES OF TISSUESTYPES OF TISSUESTISSUE- groups of cells having similar

structure and function

RECALL: HISTOLOGY- study of tissues

There are 4 primary kinds of tissues:

EPITHELIAL

CONNECTIVE

NEURAL

MUSCLE

- tissues combine to form organs of the body

EPITHELIAL TISSUEEPITHELIAL TISSUE

Epithelial tissue includes EPITHELIA and GLANDS

EPITHELIA (UM)- tissues that cover surfaces and line internal structures and cavities of the body

GLANDS- made up of secreting cells derived from epithelia

CHARACTERISTICS CHARACTERISTICS

- cells are close together

- free surface exposed to environment or some internal passageway

- attached to underlying connective tissue by a BASEMENT MEMBRANE

- are AVASCULAR- having no blood vessels; nutrients must be obtained from deeper tissues or exposed surfaces

Epithelia cover external and internal body surfaces:

- skin

- lining of digestive, respiratory, reproductive, and urinary tracts

Separates deep tissues from external environment

Epithelia also line internal cavities and passageways:

- chest cavity

- fluid-filled chambers in brain, eye, and inner ear

- inner surfaces of blood vessels and heart

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIA

Four essential functions:

1. Provide physical protection- protects exposed surfaces from abrasion, dehydration, destruction by chemical or biological agents

2. Control permeability- controls substances that enter and leave the body

3. Provide sensation- detect changes in the environment and relay info. to the nervous system

4. Produce specialized secretions- cells that produce secretions are called GLAND CELLS

- EXOCRINE secretions- discharged onto surface of the skin or other epithelial surface (Ex: perspiration)

- ENDOCRINE secretions- released into surrounding tissue and blood (hormones)

INTERCELLULAR INTERCELLULAR CONNECTIONSCONNECTIONS

To be an part of an effective barrier, epithelial cells must remain firmly attached to one another

- accomplished by CELL JUNCTIONS

3 TYPES OF JUNCTIONS:

TIGHT JUNCTIONS- cell membranes are fused together

GAP JUNCTIONS- proteins in the membranes bind and create channels between the 2 cells

DESMOSOMES- cells are attached by protein filaments

Junctions

SURFACE OF EPITHELIASURFACE OF EPITHELIA

Many epithelia have MICROVILLI- small, finger-shaped projections of the cell membrane

- increase the surface area of the cell

Some epithelial cells have CILIA- long, finger-shaped extensions of the cell membrane

- beat simultaneously to move materials across the epithelial surface

BASEMENT MEMBRANEBASEMENT MEMBRANE

Epithelial cells also must remained attached to the rest of the body

- BASEMENT MEMBRANE- lies between the epithelium and underlying connective tissues

- consists of a network of protein fibers (no cells)

- it provides strength, resists distortion, and provides a barrier

CLASSIFYING EPITHELIACLASSIFYING EPITHELIA

Epithelia are classified by the number of cell layers, and the shape of the exposed cells

2 TYPES OF LAYERING:

- Simple

- Stratified

3 CELL SHAPES:

- Squamous

- Cuboidal

- Columnar

LAYERSLAYERS

SIMPLE EPITHELIUM- single layer of cells covering the basement membrane

- thin

- only found in protected areas in the body- body cavities, interior of heart and blood vessels

STRATIFIED EPITHELIUM- several layers of cells above basement membrane

- found in areas subject to mechanical or chemical stresses

- surface of skin, linings of mouth and anus

CELL SHAPECELL SHAPE

1. SQUAMOUS- cells are thin and flat; cells look like fried eggs (due to nuclei) laid side by side

2. CUBOIDAL- cells appear square; nuclei lie near the center of each cell and form a neat row

3. COLUMNAR- also square, but taller and more slender; nuclei crowded into narrow band close to basement membrane

SIMPLE SQUAMOUS SIMPLE SQUAMOUS EPITHELIAEPITHELIA

- found in protected regions where absorption takes place or where a slick, slippery surface reduces friction

- linings of body cavities; lining of blood vessels and heart

Simple Squamous

SIMPLE CUBOIDAL SIMPLE CUBOIDAL EPITHELIAEPITHELIA

- provides limited protection and occurs in regions where secretion or absorption takes place

- secrete enzymes and buffers in the pancreas; line portions of kidneys involved in production of urine

Simple Cuboidal

SIMPLE COLUMNAR SIMPLE COLUMNAR EPITHELIAEPITHELIA

- provides some protection and may also occur in areas of absorption or secretion

- lines the stomach, intestinal tract, and many excretory ducts

Simple Columnar

PSEUDOSTRATIFIED PSEUDOSTRATIFIED EPITHELIAEPITHELIA

- columnar epithelia that appears layered because nuclei are situated at varying distances from the surface, but is not actually layered

- typically has cilia

- lines nasal cavity, trachea, bronchi, portions of male reproductive tract

Pseudostratified Ciliated

Stratified Columnar Ciliated

STRATIFIED SQUAMOUS STRATIFIED SQUAMOUS EPITHELIAEPITHELIA

- found where mechanical stresses are severe

- surface of skin, lining of mouth, tongue, esophagus, and anus

Stratified Squamous

CONNECTIVE TISSUECONNECTIVE TISSUE

- most diverse tissues of the body

All have 3 basic components:

1. Specialized cells

2. Protein fibers

3. Ground substance- a fluid that varies in consistency

- 2 and 3 make up the MATRIX that surrounds the cells

- connective tissues are made up mostly of this matrix

- never exposed to outside environment

FUNCTIONS:

- Support and protection

- Transport of materials

- Storage of energy reserves- fats

- Defense of the body- production of antibodies

CLASSIFYING CONNECTIVE CLASSIFYING CONNECTIVE TISSUESTISSUES

3 classes of connective tissue based on the physical properties of their matrix:

1. CONNECTIVE TISSUE PROPER- has many types of cells and fibers surrounded by a syrupy ground substance

- tissues underlying the skin, fatty tissue, tendons, and ligaments

2. FLUID CONNECTIVE TISSUES- have distinctive population of cells suspended in a watery ground substance containing dissolved proteins

- blood and lymph

3. SUPPORTING CONNECTIVE TISSUES- cartilage and bone

- less diverse cell population, dense matrix

CONNECTIVE TISSUE CONNECTIVE TISSUE PROPERPROPER

CELL TYPES:

1. FIBROBLASTS- most abundant; produce and maintain connective tissue fibers and the ground substance

2. MACROPHAGES- engulf damaged cells or pathogens

3. FAT CELLS- adipose cells; number varies from one connective tissue to another

4. MAST CELLS- contain chemicals that are released in times of defense

- WHITE BLOOD CELLS- produce ANTIBODIES when tissue is damaged

3 TYPES OF FIBERS IN CONNECTIVE TISSUE:

1. COLLAGEN FIBERS- long, straight, unbranched; most common; strong; flexible

2. ELASTIC FIBERS- contain protein elastin; branched and wavy; after stretching will return to original length

3. RETICULAR FIBERS- least common; thinner than collagen; form branching, interwoven network in organs

GROUND SUBSTANCE

- fills space between cells and surrounds connective tissue fibers

- normally clear, colorless, similar in consistency to maple syrup

CONNECTIVE TISSUE PROPER:CONNECTIVE TISSUE PROPER:

LOOSE CONNECTIVE TISSUELOOSE CONNECTIVE TISSUE- least specialized connective tissue in body

- contains all cells and fibers in connective tissue proper

- forms a layer that separates the skin from underlying muscles

- provides padding

Loose Connective

CONNECTIVE TISSUE PROPER:CONNECTIVE TISSUE PROPER:

ADIPOSEADIPOSE TISSUETISSUE- FAT

- loose connective tissue containing large numbers of fat cells

- loose connective tissue becomes adipose tissue when it is dominated by FAT CELLS

- more padding; shock absorption; insulation; energy storage

- skin of sides, buttocks; fills sockets behind eyes

Adipose

CONNECTIVE TISSUE PROPER:CONNECTIVE TISSUE PROPER:

DENSE CONNECTIVE TISSUEDENSE CONNECTIVE TISSUE- consists mostly of collagen fibers

TENDONS- cords of dense connective tissue that attach skeletal muscles to bones

LIGAMENTS- bundles of fibers that connect one bone to another

- contain elastic fibers and collagen fibers (stretchy)

Tendon

FLUID CONNECTIVE TISSUE:FLUID CONNECTIVE TISSUE:

BLOOD AND LYMPHBLOOD AND LYMPHBLOOD and LYMPH contain distinct collections

of cells in a fluid matrix

- RED BLOOD CELLS- account for more than ½ the volume of blood; transport oxygen

- PLASMA- watery matrix of blood

- WHITE BLOOD CELLS- important components of immune system

- PLATELETS- cell fragments that function in blood clotting

SUPPORTING CONNECTIVE TISSUE:SUPPORTING CONNECTIVE TISSUE:

CARTILAGE AND BONECARTILAGE AND BONE

- provide strong framework that supports the rest of the body

CARTILAGE

- firm gel containing embedded fibers

- only cells found within the matrix are CHONDROCYTES, which live in small pockets called lacunae

- cartilage is avascular

SUPPORTING CONNECTIVE TISSUE:SUPPORTING CONNECTIVE TISSUE:

CARTILAGECARTILAGE

There are 3 major types of cartilage:

1. HYALINE CARTILAGE- most common

- tough and somewhat flexible

- connects ribs to sternum, covers surfaces of bones within joints

2. ELASTIC CARTILAGE- contains numerous elastic fibers that make it very flexible and resilient

- outer ear, epiglottis (covering of larynx)

3. FIBROCARTILAGE- has little ground substance; dominated by collagen fibers

- extremely durable and tough

- between vertebrae of spinal column- resist compression, absorb shock

SUPPORTING CONNECTIVE TISSUE:SUPPORTING CONNECTIVE TISSUE:

BONEBONE- also called OSSEOUS TISSUE

- volume of ground substance compared to cartilage is very small

- matrix consists mainly of hard calcium compounds and flexible collagen fibers

- lacunae within the matrix contain bone cells, called OSTEOCYTES

- each bone is surrounded by a PERIOSTEUM- covering made of fibrous and cellular layers

Bone is constantly being remodeled throughout life

- complete repairs can be made even after severe damage

MUSCLE TISSUEMUSCLE TISSUE

Muscle tissue is specialized for contraction

- muscle cell contraction involves interactions between filaments of MYOSIN and ACTIN, which are proteins found in the cytoskeletons of cells

There are 3 main types of muscle tissue:

1. Skeletal

2. Cardiac

3. Smooth

MUSCLE TISSUEMUSCLE TISSUE::SKELETAL MUSCLE TISSUESKELETAL MUSCLE TISSUE

- contains very large, multinucleated cells

- skeletal muscles are long and slender, so are usually called MUSCLE FIBERS

- these fibers are not capable of dividing, but new ones are produced through the division of stem cells in muscle tissue some repair is possible after an injury

MUSCLE TISSUEMUSCLE TISSUE::SKELETAL MUSCLE TISSUESKELETAL MUSCLE TISSUE

- because of how actin and myosin filaments are arranged, skeletal muscle appears to have a series of bands called STRIATIONS

- skeletal muscle is described as STRIATED VOLUNTARY MUSCLE because the nervous system provides voluntary control over its activities

MUSCLE TISSUEMUSCLE TISSUE::CARDIAC MUSCLE TISSUECARDIAC MUSCLE TISSUE

- found only in the heart

- cells are much smaller than skeletal muscle fibers, and each cell usually has a single nucleus

- also have striations

- cardiac muscle cells are interconnected at INTERCALATED DISCS, special attachment sites that have gap junctions and desmosomes

- cells of cardiac muscle cannot divide; tissue cannot regenerate

- cardiac muscle cells do not rely on nerve activity to start a contraction; called STRIATED INVOLUNTARY MUSCLE

MUSCLE TISSUEMUSCLE TISSUE::SMOOTH MUSCLE TISSUESMOOTH MUSCLE TISSUE

- found in the walls of blood vessels, around hollow organs (urinary bladder), in layers around respiratory, circulatory, digestive, and reproductive tracts

- cells are small and slender, tapering to a point at each end; each has one nucleus

- actin and myosin filaments are scattered, so there are no striations

- cells can divide, so smooth muscle can regenerate after an injury

- nervous system does not provide voluntary control, so smooth muscle is known as NONSTRIATED INVOLUNTARY MUSCLE

Neural TissueNeural Tissue

- also known as nerve tissue; is specialized for the conduction of electrical impulses from one part of the body to another

- most of this tissue is concentrated in the brain and spinal cord

CONTAINS 2 TYPES OF CELLS:

1. NEURONS- control conscious and unconscious thought processes

2. NEUROGLIA- provide physical support for neural tissue, maintain the chemical composition of the tissue fluids, defend the tissue from infection

STRUCTURE OF A NEURON

- neurons are the longest cells in your body (up to 1 m in length)

- limited ability to repair because are unable to divide

- a typical neuron has a CELL BODY with a large nucleus

- extending from the body are several branches called DENDRITES and one AXON

- DENDRITES receive information from other neurons and AXONS carry that information to other cells

TISSUE INJURY AND REPAIRTISSUE INJURY AND REPAIR

Tissue repair involves 2 related processes:

1. INFLAMMATION

- the injured area is isolated from neighboring healthy tissue while damaged cells, tissue components, and dangerous microorganisms are cleaned up

- produces swelling, warmth, redness, and pain

INFECTION- inflammation resulting from presence of bacteria

2. REGENERATION

- damaged tissues are replaced or repaired to restore normal functioning

- fibroblasts produce a network of collagen fibers called SCAR TISSUE

- over time this scar tissue resumes a more normal appearance

- regeneration is most successful in epithelia and connective tissue

AGINGAGING

- there is a decrease in the speed and effectiveness of tissue repair

- epithelia get thinner; connective tissue gets more fragile

- individuals bruise more easily; bones become brittle

- cancer rates also increase with age