CHAPTER 4 TISSUES

TYPES OF TISSUES TISSUE- 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 TISSUE

EPITHELIAL TISSUE Epithelial tissue includes EPITHELIA and GLANDS EPITHELIA (UM)- name given to those tissues that cover surfaces and line internal structures and cavities of the body GLANDS- made up of secreting cells derived from epithelia

CHARACTERISTICS - cells are close together - have a free surface exposed to environment or some internal passageway - attached to underlying connective tissue by a BASEMENT MEMBRANE - are AVASCULAR, meaning 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 EPITHELIA Four essential functions: 1. Provide physical protection- protects exposed surfaces from abrasion, dehydration, and 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 are discharged onto the surface of the skin or other epithelial surface (Ex: perspiration) - ENDOCRINE secretions are released into the surrounding tissue and blood (hormones)

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

SURFACE OF EPITHELIA Many epithelia have MICROVILLI - small, finger-shaped projections of the cell membrane - increases 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 MEMBRANE Epithelial cells also must remained attached to the rest of the body - performed by the BASEMENT MEMBRANE- lies between the epithelium and underlying connective tissues - consists of a network of protein fibers (no cells) - basement provides strength, resists distortion, and provides a barrier

CLASSIFYING 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

LAYERS 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 SHAPE Again, there are 3 basic cell shapes in the epithelium: 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 EPITHELIA - 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 CUBOIDAL EPITHELIA - 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 COLUMNAR EPITHELIA - provides some protection and may also occur in areas of absorption or secretion - line the stomach, intestinal tract, and many excretory ducts

PSEUDOSTRATIFIED EPITHELIA - 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

STRATIFIED SQUAMOUS EPITHELIA - found where mechanical stresses are severe - surface of skin, lining of mouth, tongue, esophagus, and anus

CONNECTIVE TISSUE

CONNECTIVE TISSUE - are the 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 - the protein fibers and ground substance 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 TISSUES There are 3 classes of connective tissue based on the physical properties of their matrix: 1. CONNECTIVE TISSUE PROPER- connective tissues with 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 PROPER CELL TYPES: FIBROBLASTS- most abundant; produce and maintain connective tissue fibers and the ground substance MACROPHAGES- engulf damaged cells or pathogens FAT CELLS- adipose cells; number varies from one connective tissue to another 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: LOOSE 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

CONNECTIVE TISSUE PROPER: ADIPOSE TISSUE - 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

CONNECTIVE TISSUE PROPER: DENSE 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)

FLUID CONNECTIVE TISSUE: BLOOD AND LYMPH BLOOD 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: CARTILAGE 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: CARTILAGE 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: BONE - 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 TISSUE

MUSCLE 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 TISSUE: SKELETAL 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 TISSUE: SKELETAL 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 TISSUE: CARDIAC 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 TISSUE: SMOOTH 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 TISSUE

Neural 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 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

AGING - 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