Anatomy Chapter Four: Tissue

Common Characteristics of Connective Tissue

1) Common origin: all connective tissues arise from mesenchyme (an embryonic tissue) 2) Degrees of vascularity: - Cartilage is avascular - Dense connective tissue is poorly vascularized - Other types of connective tissue have a rich supply of blood vessels 3) Extracellular matrix: all other primary tissues are composed mainly of cells, but connective tissues are largely nonliving extracellular matrix which separates, often widely, the living cells of the tissue. - Allows connective tissue to bear weight, withstand great tension, and endure abuses-such as physical trauma and abrasion-that no other tissue can tolerate

Macrophages

Phagocytic cells that eat dead tissue cells, foreign materials (dust), microorganisms (bacteria); function in the immune system Central actors in the immune system

Special Characteristics of Epithelial Tissues

Polarity Specialized contacts Supported by connective tissue Avascular but innervated High regeneration capacity (replace lost cells by rapid cell division)

Muscle Tissue Overview

Produces movement Function: Contracts to cause movement; responsible for most types of movement Muscle cells possess myofilaments made up of actin and myosin proteins that bring about contraction Highly vascularized Can be subdivided into 3 types

Fibrocartilage

Properties lay between hyaline and dense regular tissue - Rows of chondrocytes alternate with rows of thick collagen fibers (predominant; less firm than hyaline cartilage) Function: tensile strength allows it to absorb compressive shock Found in intervertebral discs (resilient cushions between the bony vertebrae), spongy cartilages of the knee (menisci)

Endothelium (Inner covering)

Provides slick, friction-reducing lining in lymphatic vessels, and in all hollow organs of the cardiovascular system (blood vessels and the heart) Capillaries are exclusively endothelium Allows efficient exchange of nutrients and wastes between the bloodstream and surrounding tissue cells

Stratified Cuboidal Epithelia

Rare in the body, mostly found in the ducts of some of the larger glands (sweat glands, mammary glands) Typically has 2 layers of cuboidal cells

Types of Muscle Tissue

Skeletal muscle (muscle attached to bones) Cardiac muscle (muscle of the heart) Smooth muscle (muscles of walls of hollow organs)

Skeletal Muscle Tissue

Skeletal muscle tissue is packaged by connective tissue sheets into organs called skeletal muscles that are attached to the bones of the skeleton (occasionally attached to skin) - AKA voluntary muscle - Skeletal muscles can be consciously controlled Attached to and causes movement of bones Functions: voluntary movement; locomotion; manipulation of the environment; facial expression; voluntary control Forms the flesh of the body Skeletal muscle cells are called muscle fibers - Long cylindrical cells - Are multi-nucleated (located peripherally) - Appear striated or banded (reflects alignment of myofilaments)

Organ

A group of tissues that perform a specific function or group of functions

Mast Cells

Initiate local inflammatory response against foreign microorganisms they detect Typically cluster about blood vessels Contain secretory granules with chemicals in cytoplasm that mediate inflammation

Epithelial Tissue (Epithelium)

A sheet of cells that covers body surfaces or cavities; forms boundaries between different environments, and nearly all substances received or given off by the body must pass through an epithelium - Highly specialized for selective secretion and absorption of ions an molecules Two main forms occur in the body: 1) Covering and lining epithelium: located on both internal and external surfaces of the body - Forms the outer layer of the skin (epidermis) - Lines the open cavities of the urogenital, digestive, and respiratory systems (any cavity that is exposed to the external environment) - Lines surfaces that separate body cavities from the outside environment (ex: the walls and organs of the closed ventral body cavity) - Lines the surface of internal organs 2) Glandular epithelium: secretory tissue found in glands ex: salivary glands

Dense Connective Tissue

AKA fibrous connective tissues All 3 have abundant fibers as their prominent element - Are tougher than loose connective tissue Dense regular connective tissue Dense irregular connective tissue Elastic connective tissue

Bone

AKA osseous tissue; firmest connective tissue (has more collagen fibers compared to cartilage) Functions: Supports and protects body structures (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) Stores fat and synthesizes blood cells in cavities Matrix: hard and calcified containing many collagen fibers - Has more collagen fibers compared to cartilage - Has inorganic calcium salts in the matrix - Osteoblasts produce matrix - Osteocytes maintain the matrix - Reside in cavities in matrix called lacunae Osteons: individual structural units Richly vascularized

Serous Membranes

AKA serosae Found in closed ventral body cavities; bodies that are closed to the exterior Constructed from simple squamous epithelium (mesothelium) resting on thin areolar connective tissue Parietal serosae line internal body cavity walls (exposed to outside of organ) Visceral serosae cover internal organs (exposed to inside of organ) Cavity between layers is filled with slippery serous fluid, so these are moist membranes; allows the layers to slide across each other easily Special names given to show location: -Pleurae (lungs) - Pericardium (heart) - Peritoneum (abdomen)

Loose Connective Tissue

All contain a sparse cytoplasm with loose arrangement of fibers (mostly collagenous) Areolar connective tissue Adipose tissue Reticular connective tissue

Special Characteristics of Epithelial Tissue: Supported by connective tissue

All epithelial sheets rest upon and are supported by connective tissue - Reticular lamina Reticular lamina: lays deep to the basal lamina; contains a fine network of collagen protein fibers that "belongs to" the underlying connective tissue - Forms the basement membrane with the basal lamina

Stratified Columnar Epithelia

Also has limited distribution in the body Small amounts found in the pharynx, the male urethra, and lining some glandular ducts - Also occurs at transition areas or junctions between 2 other types of epithelia Only its apical cells are columnar

Special Characteristics of Epithelial Cells: Avascular but Innervated

Although epithelium is avascular (has no blood cells), it is innervated (supplied by nerve fibers) Nourished by substances diffusing from blood vessels in the underlying connective tissue

Cutaneous Membranes

Another name for skin Keratinized squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis) Unlike other membranes, skin is a dry membrane

Columnar Cells

Are tall and column shaped - Nucleus is ellipsoidal and is usually located closer tot he cell base

First Name of Epithelia

Based on number of cell layers, epithelia can be: - Simple - Stratified

Second Name of Epithelia

Based on the shape of the epithelia cells within the layer(s) - In cross-section, all have 6 somewhat irregular sides (polyhedral shape); allows the cells to be closely packed Vary in height (also influences the shape of the nucleus, which conforms to the shape of the cell): - Squamous cells - Cuboidal cells - Columnar cells Simple epithelia are easy to classify by shape because the cells usually have the same shape In stratified eithelia, cell shape differs in the different layers - Named cording to the shape of the cells in the apical layer

Cuboidal Cells

Boxlike, approximately as tall as they are wide - Nucleus is spherical

Elastic Fibers

Branching networks of long, thin elastin (rubber-like protein) fibers in the extracellular matrix that allow for stretch and recoil Elastin allows these fibers to stretch and recoil like rubber bands Connective tissue can only stretch so much before the collagen fibers become taut; elastic fibers snap the connective tissue back to its normal length and shape when tension builds up Found where greater elasticity is needed ex: skin, lungs, and blood vessel walls

Adipose (Fat) Tissue

Cells called adipocytes, adipose, or fat cells Two types: white fat and brown fat Matrix as in areolar, but very sparse (has a scanty matrix); have nucleus pushed to the side Function: Provides reserve food fuel; insulates against heat loss; supports and protects organs (shock absorber), nutrient storage - Richly vascularized; high metabolic activity Location: under skin in subcutaneous tissue; around kidneys and eyeballs; within abdomen; in breasts; back of babies and scant areas of adults (brown fat)

Pseudostratified Columnar Epithelium

Cells vary in heigh and appear to be multi-layered and stratified as their nuclei lay at different levels, but all cells rest on the basement membrane (only the tallest reach the free surface of the epithelium) - Many contain mucus-secreting cells and bear cilia Function: Secrete substances, particularly mucus; propulse of mucus by ciliary sweeping action Location: mostly in upper respiratory tract (including trachea) ,ducts of large glands, and tubules in testes

Stratified Epithelia

Composed of 2 or more cell layers stacked on top of each other, are common in high-abrasion areas where protection is important, such as the skin surface and the lining of the mouth

Extracellular Matrix

Composed of ground substance and fibers

Dense Irregular Connective Tissue

Composed of the same elements as dense regular, but bundles of collagen are thicker and irregularly arranged (run in more than one plane) Forms sheets rather than bundles, and resists tension from many directions Found in: - dermis -fibrous joint capsules -fibrous coverings that surround some organs (exL kidneys, bones, cartilages, muscles, nerves)

Connective Tissue Proper Overview

Connective tissue proper can be divided into two main subclasses: loose connective tissue and dense connective tissue 1) Loose connective tissue - Areolar - Adipose - Reticular 2) Dense connective tissue - Regular - Irregular - Elastic Cells: fibroblasts, fibrocytes, defense cells, adipocytes Matrix: gel-like substance; contains all 3 fiber types (collagen, reticular, elastic) General features: - There are 6 different types of connective tissue - Functions as a binding tissue - Resists mechanical stress, particularly tension - Provides reservoir for water and salts - Nutrient (fat) storage

Structural Elements of Connective Tissue

Connective tissues have 3 main elements: - Ground substance - Fibers - Cells Differences in arrangement of these substances results in diversity of connective tissue that are each adapted to perform different functions in the body - Can be delicate and soft to form a soft padding around an organ - Can form "ropes" of incredible strength (ligaments and tendons) All subclasses of connective tissue are variants of the areolar connective tissue structural plan

Simple Epithelia

Consist of a single cell layer Typically involved in absorption, secretion, or filtration processes - Do not provide protection

Connective Tissue Proper

Consists of all mature connective tissues except bone, cartilage, and blood

Stratified Epithelia

Contain 2 or more cell layers; regenerate from below (basal cells divide and push apically to replace the older surface cells) Considerably more durable than simple epithelia; protection is a major role

Covering and Lining Membranes

Continuous multicellular sheets composed of at least 2 primary tissue types: an epithelium bound to underlying connective tissue proper layer - These membranes are simple organs Three types: - Cutaneous membranes -Mucous membranes - Serous membranes

Nervous Tissue Overview

Controls Main component of the nervous system (which includes the brain, spinal cord, and nerves) - Regulates and controls body functions Function: Allows internal communication within the body Made up of two specialized cells: - Neurons - Supporting cells

Epithelial Tissue Overview

Covers Functions: boundary formation between different environments, protection, absorption, excretion, secretion, filtration, and sensory reception Locations of epithelial tissue: - Lining of digestive tract organs and other hollow organs - Epidermis (skin surface)

Elastic Connective Tissue

Dense regular connective tissue containing a high proportion of elastic fibers Located in some ligaments - ex: certain ligaments connecting adjacent vertebrae within the vertebral column must be very elastic Also found in walls of many large arteries -arteries need to stretch when blood enters and recoil to push blood out Functions: allows tissue to recoil after stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration

Endocrine Glands

Ductless flands - Secretions are not released into a duct; are released into surrounding interstitial fluid, which is picked up by the circulatory system Internally secreting gland Secrete hormones by exocytosis

Connective Tissue Cells

Each class of connective tissue has a cell type that exists in immature and mature forms Immature form: undifferentiated cells; -blast; actively mitotic cells that secrete the ground substance and the fibers characteristic of their particular matrix - Primary blast cells by connective tissue class: - fibroblast: connective tissue proper - chondroblast: cartilage - osteolast: bone Mature form: once the blast cells differentiate the matrix, they assume their mature/less active mode; -cyte; maintain the health of the matrix; can easily revert to more active state to repair and regenerate the matrix when matrix is injured Connective tissue is also home to other cell types: - Fat cells - White blood cells -Mast cells -Macrophages

Classification of Epithelia

Each epithelium has 2 names: 1) Indicates the number of cell layers present (simple or stratified) 2) Describes the shape of its cells (squamous, cuboidal, columnar)

Types of Cartilage

Each type of cartilage is dominated by a different fiber type: Hyaline cartilage Elastic cartilage Fibrocartilage

Special Characteristics of Epithelial Tissues: Polarity

Epithelial cells exhibit apical-basal (top and bottom) polarity - All have an apical surface and an attached basal surface, which differ in both structure and function

Exocrine Glands

Externally secreting gland in which secretions are released onto body surfaces, such as the skin, or into body cavities More numerous than endocrine glands Secrete products into ducts ex: sweat, oil, mucous, and salivary glands Can be multicellular or unicellular - Unicellular secrete products through exocytosis - Multicellular secrete products through ducts, which transports it to the epithelial surface

Fascia

Fibrous membrane that warps around muscles, groups of muscles, blood vessels, and nerves, binding them together like a plastic sandwich wrap

Squamous Cells

Flattened and scale-like - Nucleus is also flattened

Basement Membrane

Formed by the basal and reticular lamina; reinforces the epithelial sheet, helps it resist stretching and tearing, and defines the epithelial boundary

Mesothelium (Middle covering)

Found in serous membranes in the ventral body cavity and covering its organs

Smooth Muscle Tissue

Found mainly in walls of hollow organs (other than the heart) - ex: digestive and urinary tract organs, uterus, blood vessels - Squeezes substances through these organs by alternately contracting and relaxing Involuntary muscle Has no visible striations Spindle-shaped cells with one nucleus

Cardiac Muscle Tissue

Found only in the walls of the heart Involuntary muscle Like skeletal muscle, contains striations; but cells only have one nucleus that is located centrally Cells can have many branches that join branches of other cardiac cells - Intercalated discs are special joints where cardiac cells are joined - Allows for synchronized movement during heart beat Functions: as it contracts, it propels blood into the circulatory system through the blood vessels to all parts of the body

Four Main Classes of Connective Tissues

Four main classes of connective tissues: - Connective tissue proper - Cartilage - Bone - Blood All classes of connective tissue consist of living cells surrounded by a matrix Mature connective tissue arise from a common embryonic tissue called mesenchyme - Fluid ground substance that contains mesenchymal cells - Arises during early weeks of embryonic development and eventually differentiates (specializes) into all other connective tissue cells - Some mesenchymal cells remain and provide a source of new cells in mature connective tissues

Tissues

Groups of cells that are similar in structures and perform a common or related function The body is made of four basic tissue types that interweave to form the body: - Epithelial tissue - Connective tissue - Muscle tissue - Nervous tissue Tissues are organized into organs; most organs contain all 4 tissue types, and their arrangement determines the organ's structure and capabilities

Dense Regular Connective Tissue

Has very high tensile strength; can withstand high tension and stretching Composed of closely packed bundles of thick collagen fibers that run parallel to the direction of pull - Fibers appear as white structures and have great resistance to pulling forces (tension) - Fibers are slightly wavy, so they are able to stretch to a small extent Fibroblasts manufacture collagen fibers and ground substance Very few cells and ground substance, mostly fibers Poorly vascularized Functions: attaches muscle to bones (tendons or aponeuroses) or to muscles (aponeuroses); attaches bones to bones (ligaments at the joint); withstands great tensile stress when pulling force is applied in one direction ex: tendons and ligaments, aponeuroses (flat, sheet-like tendons), fascia - Ligaments contain more elastic fibers than tendons and are more stretchy

White Blood Cells

Includes: neutrophils, eosinophils, lymphocytes Tissue response to injury

Aponeuroses

Layers of broad, flat, sheetlike tendons (tendons however are more cord-like and are an extension of the muscle) Attach muscle to muscle or to bone

Basal Surface

Lower surface that is attached to the apical surface of epithelia; faces inwards toward the body Attaches to basal lamina, an adhesive sheet that holds the basal surface of epithelial cells to underlying cells - Acts as a selective filter that determines which molecules diffusing from the underlying connective tissues are allowed to enter the epithelium

Hormone

Messenger chemical that are secreted by endocrine glands via exocytosis directly into the extracellular space Travel through lymph or blood to target specific organ(s) Prompts the target organ(s) to respond in some characteristic way

Hyaline Cartilage

Most abundant; AKA "gristle" -Appears as shiny bluish glass Contains a high number of collagen fibers that form an imperceptible network Function: supports and reinforce yet offers some pliability; serves as resilient cushion; resists compressive stress Found at tips of long bones, nose, trachea, larynx (supports most of the respiratory system passages), and cartilage of the ribs

Blood

Most atypical connective tissue because it is fluid - Consists of red or white blood cells surrounded by a fluid matrix (plasma) - Contained within blood vessels Red cells are the most common type - Also contains white blood cells and platelets - Fibers are soluble proteins that precipitate during blood clotting Functions in transport and in carrying nutrients, wastes, gases, and other substances

Gland

One or more cells that makes and secretes an aqueous fluid (usually containing proteins but has variation) called a secretion Classified by: - Site of product release (endocrine is internally secreting or exocrine is externally secreting) - Relative number of cells forming the gland (unicellular like goblet cells or multicellular like salivary) Unicellular glands are scattered within epithelial sheets ex: goblet cells

Areolar Connective Tissue

Most widely distributed connective tissue; universal packing material between other tissues Gel-like matrix contains all 3 fiber types; cells include fibroblasts (predominant form) - Fibroblasts that secrete loose arrangement of mostly collagen fibers - Loose fiber arrangement allows for increased ground substance, which can act as water reservoir by holding more interstitial fluid; all body cells obtain their nutrients from and release their wastes into this tissue fluid - Macrophages and fat cells are contained in spaces Function: Wraps and cushions organs; supports and binds other tissues while also allowing them to move freely over one another; macrophages defend against infection by phagotizing bacteria; plays an important role in inflammation; holds and conveys body tissue fluid; forms the subcutaneous tissue (cushions and attaches the skin to underlying structures) as it is the type of connective tissue that most epithelia rest upon Location: widely distributed under epithelia of body, packages organs (wraps small blood vessels, and nerves, glands), surrounds capillaries

Stratified Squamous Epithelium

Most widespread of the stratified epithelia; thick membrane composed of several cell layer; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous) and constantly being replaced by division of its basal cells; in the keratinized type, the 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 - Thick structure helps with protective role in body Location: areas of high wear and tear (ex: skin) - Non-keratinized type: found in moist linings: that of the esophagus, mouth, and vagina - Keratinized type: forms the epidermis of the skin (keratin is a tough, rough protein), a dry membrane, and extends a short distance into every body opening that is directly continuous with the skin

Supporting Cells

Nonconducting cells that support, insulate, and protect neurons

Reticular Connective Tissue

Resembles areolar tissue, but fibers are thinner reticular fibers Fibroblast cells are called reticular cells - Secrete reticular fibers made up of thin collagen Reticular fibers form a mesh-like stroma that acts as a support for blood cells in lymphoid organs (ex: lymph nodes, spleen, and bone marrow)

Transitional Epithelium

Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike depending on degree of organ distension (stretch) - When the organ is distended with urine, thins from about 6 cell layers to 3; domelike apical cells flatten to become squamouslike Function: stretches readily; ability to change shape permits stored urine to distend urinary organs (allows more urine to flow through tubes and too be stored) Location: Forms the lining of hollow urinary organs; lines the ureters, bladder, and part of the urethra

Reticular Fibers

Short, fine, highly branched collagenous fibers with a slightly different chemistry and form from collagen fibers - Continuous with collagen fibers and branch extensively, forming delicate networks that surround small blood vessels and support the soft tissue of organs Branching forms networks that offer more "give" than the larger collagen fibers Abundant where connective tissue abuts other tissue types, ex: basement membrane of epithelial tissues, around capillaries

Elastic Cartilage

Similar to hyaline cartilage but has more elastic fibers Function: maintains the shape of a structure while allowing great flexibility Found in the external ear (pinna) and epiglottis

Types of Epithelia

Simple Squamous Epithelium - Endothelium -Mesothelium Simple Cuboidal Epithelium Simple Columnar Epithelium Pseudostratified Columnar Epithelium Stratified Squamous Epithelium Stratified Cuboidal Epithelium (not in slides) Stratified Columnar Epithelium (not in slides) Transitional Epithelium (not in slides) Glandular Epithelium - Endocrine glands - Exocrine glands

Simple Cuboidal Epithelium

Single layer of cube like cells with large, spherical central nuclei Function: Secretion and absorption Forms the walls of smallest ducts of glands and many kidney tubules

Simple Squamous Epithelium

Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia; thin and often permeable Involved in absorption, secretion, or filtration processes Location: where filtration or the exchange of substances by rapid diffusion is a priority; where protection is not important - Kidney glomeruli (part of the filtration membrane) - Air sacs of lungs (forms the walls of the air sacs across which gas exchange occurs) Two types in the body that differ in function based on their locations: - Endothelium -Meothelium

Simple Columnar Epithelium

Single layer of tall, closely packed cells with round to oval uncle; some cells have microvilli and some have cilia; some layers contain music-secreting unicellular glands (goblet cells) Function: involved in absorption and secretion of mucus, enzymes, and other substances; ciliated type moves mucus (or reproductive cells) Location: digestive tract, gallbladder, ducts of some glands, bronchi, uterine tubes

Neurons

Specialized nerve cells that generate and conduct nerve impulses Branching cells with cytoplasmic extensions or processes that enable them to: - Respond to stimuli (via dendrites) - Transmit electrical impulses over distances within the body (via axons) from sensory receptors to effectors (muscles and glands)

Cartilage

Stands up to both tension and compression; has qualities intermediate between dense connective tissue and bone - Tough yet flexible material that lacks nerve fibers Avascular: receives nutrients from membrane surrounding it (perichondrium) - Perichondrium gives rise to chondrobasts and chondrocytes Matrix is secreted from chondroblasts (predominant cell type during growth) until the skeleton stops growing, and chondrocytes (in adults) - Chondrocytes (mature cartilage cells) found in cavities called lacunae - 80% water (helps it to rebound after compression), with packed collagen fibers and sugar proteins (chrondrotin and hyaluronic acid) Has 3 different subclasses

Fat Cells

Store nutrients

Collagen Fibers

Strongest and most abundant type Constructed of fibrous collagen protein Tough; provides high tensile strength (the ability to resist wing pulled apart) to the extracellular matrix (stronger than steel fibers of the same size)

Connective Tissue Overview

Supports Function: Supports, protects, insulates, stores reserve fuel, binds other tissue together (connects body parts), transports substances (blood) Locations: - Bones - Tendons -Fat and other soft padding tissue Most abundant and widely distributed of the 4 primary tissue types - Skin consists primarily of connective tissue Has 4 main classes

Histology

The study of tissue within the human body Forms the structural basis for understanding organ physiology in conjunction with gross anatomy

Types of Connective Tissue

There are four main types of connective tissue: - Connective tissue proper - Cartilage - Bone - Blood

Connective Tissue Fibers

Three types of fibers provide support within connective tissues: - Collagen -Elastic fibers - Reticular fibers Ground substance contains the fibers

Two Types of Adipose (Fat) Tissue

Two types: white and brown fat White fat: - Richly vascularized -Functions in shock absorption, insulation, and energy storage - Similar to areolar tissue but greater nutrient storage Brown fat: -Use lipid fuels to heat bloodstream rather than to produce ATP, as does white fat (contains abundant mitochondria) - Occurs mainly on the back of babies, scant amount on adult collar bones, neck, abdomen, and around spine

Apical Surface

Upper free surface of epithelia that is exposed to the body exterior or cavity of an internal organ Most apical surfaces are smooth, but some have specialized fingerlike projections of the plasma membrane called microvilli - Microvilli tremendously increase the exposed surface area - Microvilli are often dense in epithelia that absorb or secrete substances (ex: lining the intestine or kidney tubules)