tissue level of organization

PHARM 314 Anatomy & Histology

The Tissue Level of Organization

Muhammad Ammar ZahidLecturer, SCPS, STMUIslamabad, Pakistan

What is a Tissue?

A tissue is a group of cells Common embryonic origin Function together to carry out specialized activities

Hard (bone), semisolid (fat), or liquid (blood) Histology is the science that deals with the

study of tissues. Pathologist specialized in laboratory studies

of cells and tissue for diagnoses

4 Types of Tissues Epithelial

Covers body surfaces and lines hollow organs, body cavities, duct, and forms glands

Connective Protects, supports, and binds organs. Stores energy as fat, provides immunity

Muscular Generates the physical force needed to make body

structures move and generate body heat Nervous

Detect changes in body and responds by generating nerve impulses

Development of Tissues

Tissues of the body develop from three primary germ layers:

Ectoderm, Endoderm, and Mesoderm Epithelial tissues develop from all three germ

layers All connective tissue and most muscle tissues

drive from mesoderm Nervous tissue develops from ectoderm

Cell Junctions

Contact points between the plasma membranes of tissue cells 5 most common types:

Tight junctions Adherens junctions Desmosomes Hemidesmosomes Gap junctions

Tight Junctions

Web-like strands of transmembrane proteins Fuse cells together Seal off passageways

between adjacent cells Common in epithelial

tissues of the stomach, intestines, and urinary bladder

Help to retard the passage of substances between cells and leaking into the blood or surrounding tissues

Adherens Junctions Dense layer of proteins called

plaque Resist separation of cells

during contractile activities Located inside of the plasma

membrane attached to both membrane proteins and microfilaments of the cytoskeleton

Transmembrane glycoproteins called cadherins insert into the plaque and join cells

In epithelial cells, adhesion belts encircle the cell

Desmosomes Contain plaque and

cadherins that extends into the intercellular space to attach adjacent cells together Desmosome plaque

attaches to intermediate filaments that contain protein keratin

Prevent epidermal cells from separating under tension and cardiac muscles cells from pulling apart during contraction

Hemidesmosomes

Resemble half of a desmosome Do not link adjacent cells

but anchor cells to the basement membrane

Contains transmembrane glycoprotein integrin

Integrins attach to intermediate filaments and the protein laminin present in the basement membrane

Gap Junctions Connect neighboring cells

via tiny fluid-filled tunnels called connexons Contain membrane proteins

called connexins Plasma membranes of gap

junctions are separated by a very narrow intercellular gap (space) Communication of cells

within a tissue Ions, nutrients, waste,

chemical and electrical signals travel through the connexons from one cell to another

Epithelial Tissues

Epithelial tissue consists of cells arranged in continuous sheets, in either single or multiple layers Closely packed and held tightly together Covering and lining of the body Free surface

3 major functions: Selective barrier that regulates the movement of materials

in and out of the body Secretory surfaces that release products onto the free

surface Protective surfaces against the environment

General Features of Epithelial Cells Surfaces of epithelial cells differ in structure and

have specialized functions Apical (free) surface

Faces the body surface, body cavity, lumen, or duct Lateral surfaces

Faces adjacent cells Basal surface

Opposite of apical layer and adhere to extracellular materials

General Features of Epithelial Cells Basement membrane

Thin double extracellular layer that serves as the point of attachment and support for overlying epithelial tissue

Basal lamina Closer to and secreted by the epithelial cells Contains laminin, collagen, glycoproteins, and proteoglycans

Reticular lamina Closer to the underlying connective tissue Contains collagen secreted by the connective tissue cells

Epithelial Cells

Epithelial Tissues Own nerve supply Avascular or lacks its own blood supply Blood vessels in the connective tissue bring in

nutrients and eliminate waste High rate of cell division for renew and repair Numerous roles in the body (i.e. protection and

filtration) Covering and lining epithelium

Outer covering of skin and some internal organs Glandular epithelium

Secreting portion of glands (thyroid, adrenal, and sweat glands)

Covering and Lining Epithelium

Normally classified according to: Arrangement of cells into layers Shapes of cells


Arrangement of cells in layers Consist of one or more layers depending on function Simple epithelium

Single layer of cells that function in diffusion, osmosis, filtration, secretion, or absorption

Pseudostratified epithelium Appear to have multiple layers because cell nuclei at different

levels All cells do not reach the apical surface

Stratified epithelium Two or more layers of cells that protect underlying tissues in

areas of wear and tear

Different Types of Covering and Lining Epithelium Cells vary in shape depending on their

function Squamous

Thin cells, arranged like floor tiles Allows for rapid passage of substances

Cuboidal As tall as they are wide, shaped like cubes or hexagons May have microvilli Function in secretion or absorption

Different Types of Covering and Lining Epithelium

Columnar Much taller than they are wide, like columns May have cilia or microvilli Specialized function for secretion and absorption

Transitional Cells change shape, transition for flat to cuboidal Organs such as urinary bladder stretch to larger size

and collapse to a smaller size

Simple Epithelium

Simple squamous epithelium Simple cuboidal epithelium Simple columnar epithelium (nonciliated and

ciliated) Pseudostratified columnar epithelium (nonciliated

and cilated)

Simple squamous epithelium

Single layer of cells that resembles a tiled floor on the surface Nucleus is centrally located and appears flattened oval or

sphere Found at sites for filtration or diffusion

Covering and Lining Epithelium Endothelium

The type of simple squamous that lines the heart, blood vessels, and lymphatic vessels

Mesothelium The type of epithelial layer of serous membranes

such as the pericardium, pleura, or peritoneum Unlike other epithelial tissue, Both are

derived from embryonic mesoderm

Simple cuboidal epithelium

Cuboidal shaped cells Cell nuclei round and centrally located Found in thyroid gland and kidneys Functions in secretion and absorption

Simple columnar epithelium

Column shaped cells Oval nuclei at near base Nonciliated and ciliated

Nonciliated simple columnar epithelium

Contains columnar cells with microvilli at their apical surface and goblet cells

Secreted mucus serves as lubricant for the lining of digestive, respiratory, reproductive and urinary tracts

Also prevents the destruction of the stomach lining by acidic gastric juices

Ciliated simple columnar epithelium Columnar epithelial cells

with cilia at the apical surface In respiratory tract,

goblet cells are interspersed among ciliated columnar epithelia

Secreted mucus on the surface traps inhaled foreign particles. Beating cilia moves particles to the throat for removal by coughing, swallowing, or sneezing

Cilia also moves oocytes to the uterine tubes


Pseudostratified columnar epithelium Appears to have several layers due to nuclei are

various depths All cells are attached to the basement membrane

in a single layer but some do not extend to the apical surface

Ciliated cells secrete mucus and bear cilia Nonciliated cells lack cilia and goblet cells

Stratified Epithelium

Two or more layers of cells Specific kind of stratified epithelium depends

on the shape of cells in the apical layer Stratified squamous epithelium Stratified cuboidal epithelium Stratified columunar epithelium Transitional epithelium

Stratified Squamous Epithelium

Several layers of cells that are flat in the apical layer New cells are pushed up toward apical layer As cells move further from the blood supply they dehydrate, harden,

and die Keratinized form contain the fibrous protein keratin

Found in superficial layers of the skin Nonkeratinized form does not contain keratin

Found in mouth and esophagus

Copyright 2009, John Wiley & Sons, Inc.

Stratified Cuboidal Epithelium

Fairly rare type of epithelium Apical layers are cuboidal Functions in protection

Stratified columnar epithelium

Also very uncommon Columnar cells in apical layer only Basal layers has shorten, irregular shaped cells Functions in protection and secretion

Transitional Epithelium Found only in the urinary system Variable appearance In relaxed state, cells appear cuboidal Upon stretching, cells become flattened and appear squamous Ideal for hollow structure subjected to expansion

Glandular Epithelium: Endocrine Glands

Secretions, called hormones, diffuse directly into the bloodstream

Function in maintaining homeostasis

Glandular Epithelium: Exocrine Glands

Secrete products into ducts that empty onto the surfaces of epithelium

Skin surface or lumen of a hollow organ Secretions of the exocrine gland include mucus, sweat, oil,

earwax, saliva, and digestive enzymes Examples of glands include sudoriferous (sweat) glands

Structural Classification of Exocrine Glands Multicellular glands are categorized

according to two criteria: Ducts are branched or unbranched Shape of the secretory portion of the gland

Simple gland duct does not branch Compound gland duct branches Tubular glands have tubular secretory parts Acinar glands have rounded secretory parts Tubuloacinar glands have both tubular and rounded

secretory parts

Structural Classification of Exocrine Glands

Functional Classification of Exocrine Glands

Connective Tissue

Most abundant and widely distributed tissues in the body

Numerous functions Binds tissues together Supports and strengthen tissue Protects and insulates internal organs Compartmentalize and transport Energy reserves and immune responses

Extracellular matrix of Connective Tissue Extracellular matrix is the material located

between the cells Consist of protein fibers and ground substance

Connective tissue is highly vascular Supplied with nerves

Exception is cartilage and tendon. Both have little or no blood supply and no nerves

Cells and Fibers in Connective Tissue

Connective Tissue Cells Fibroblasts

Secrete fibers and components of ground substance Adipocytes (fat cells)

Store triglycerides (fat) Mast cells

Produce histamine White blood cells

Immune response Neutrophil and Eosinophils

Macrophages Engulf bacteria and cellular debris by phagocytosis

Plasma cells Secrete antibodies

Connective Tissue Extracellular Matrix Ground substance

Between cells and fibers Fluid, semifluid, gelatinous, or calcified

Functions to support and bind cells, store water, and allow exchange between blood and cells

Complex combination of proteins and polysaccharides

Fibers Collagen fibers Elastic fibers Reticular fibers

Classification of Connective Tissues Embryonic connective tissue

Mesenchyme and mucous connective tissue Mature connective tissue

Loose connective tissue Areolar, adipose, and reticular

Dense connective tissue Dense regular, dense irregular, and elastic

Cartilage Hyaline, fibrocartilage, and elastic cartilage

Bone tissue Liquid connective tissue

Blood and lymph

Embryonic Connective Tissue Mesenchyme

Gives rise to all other connective tissues Mucous (Wharton’s Jelly)

Found in umbilical cord of the fetus

Loose Connective Tissue: Areolar Connective Tissue

Most widely distributed in the body Contains several types of cells and all three fibers

Loose Connective Tissue: Adipose Tissue Contains adipocytes

Good for insulation and energy reserves White (common) and brown adipose tissue

Loose Connective Tissue: Reticular Connective Tissue

Fine interlacing reticular fibers and cells Forms the stroma of liver, spleen, and lymph nodes

Dense Connective Tissue Dense connective tissue

Contains numerous, thicker, and denser fibers Packed closely with fewer cells than loose connective tissue

Dense regular connective tissue Bundles of collagen fibers are regularly arranged in parallel

patterns for strength Tendons and most ligaments

Types of Mature Connective Tissue: Dense Irregular Connective Tissue Collagen fibers are usually irregularly arranged

Found where pulling forces are exerted in many directions Dermis of skin and heart


Dense Connective Tissue: Elastic Connective Tissue

Contain branching elastic fibers Strong and can recoil to original shape after stretching Lung tissue and arteries


Types of Mature Connective Tissue: Cartilage Cartilage is a dense network of collagen

fibers and elastic fibers firmly embedded in chondroitin sulfate Chrondrocytes

Cartilage cells found in the spaces called lucunae Pericondrium

Covering of dense irregular connective tissue that surrounds the cartilage

Two layers: outer fibrous layer and inner cellular layer No blood vessels or nerves, except

pericondrium


Hyaline cartilage

Most abundant cartilage in the body Surrounding by perichondrium (some exceptions like

articular cartilage) Provide flexibility and support. Reduces friction


Fibrocartilage Chondrocytes are scattered among bundles of collagen

fibers within the extracellular matrix Lack a perchondrium Strongest type of cartilage Found in intervertebral disc (between vertebrae)


Elastic Cartilage

Chrondrocytes are located within a threadlike network of elastic fibers

Pericondrium is present Provides strength and elasticity


Repair and Growth of Cartilage Cartilage grows slowly When injured or inflamed, repairs is slow due

to its avascular nature. Two patterns of cartilage growth:

Interstitial growth Growth from within the tissue

Appositional growth Growth at the outer surface of the tissue


Bone tissue Bones are organs composed of several different

connective tissues: bone (osseous) tissue, periosteum, and endosteum.

Compact or spongy Osteon or haversian system

Spongy bone lacks osteons. They have columns called trabeculae


Liquid Connective Tissue

Blood tissue Connective tissue with liquid extracellular matrix called blood

plasma Lymph


Membranes


Epithelial Membranes

Mucous membranes Lines a body cavity that opens directly to the

exterior Epithelial layer is important for the body’s defense

against pathogens Connective tissue layer is areolar connective

tissue and is called lamina propria


Epithelial Membranes

Serous membranes or serosa Lines a body cavity that does not open directly to

the exterior. Also covers the organs that lie within the cavity

Consist of areolar connective tissue covered by mesothelium (simple squamous epithelium) that secrete a serous fluid for lubrication


Epithelial membranes: Mucous Membranes Membranes are flat sheets of pliable tissue

that cover or line a part of the body Epithelial membranes are a combination of

an epithelial layer and an underlying connective tissue layer Mucous, Serous, and Cutaneous membranes

Synovial membranes Lines joints and contains connective tissue but not

epithelium


Muscular Tissue

Consists of elongated cells called muscle fibers or myocytes Cells use ATP to generate force Several functions of muscle tissue Classified into 3 types: skeletal, cardiac, and

smooth muscular tissue


Skeletal Muscle Tissue

Attached to bones of the skeleton Have striations Voluntary movement or contractions by conscious control Vary in length (up to 40 cm) and are roughly cylindrical in

shape


Muscular Tissue

Cardiac muscle tissue Have striations Involuntary movement or contraction is not consciously

controlled Intercalated disc unique to cardiac muscle tissue


Smooth Muscle Tissue

Walls of hollow internal structures Blood vessels, airways of lungs, stomach, and intestines

Nonstriated Usually involuntary control


Nervous Tissue Consists of two principle types of cells

Neurons or nerve cells Neuroglia


Excitable Cells

Neurons and muscle fibers Exhibit electrical excitability

The ability to respond to certain stimuli by producing electrical signals such as action potentials

Actions potentials propagate along a nerve or muscle plasma membrane to cause a response Release of neurotransmitters Muscle contraction


Tissue Repair: Restoring Homeostasis When tissue damage is extensive both

stroma and parenchymal cells are active in repair Fibroblast divide rapidly New collagen fibers are manufactured New blood capillaries supply materials for healing

All of these process create an actively growing connective tissue called granulation tissue


Aging and Tissues

Tissue heal faster in young adults Surgery of a fetus normally leaves no scars Young tissues have a better nutritional state,

blood supply, and higher metabolic rate Extracellular components also changes with

age Changes in the body’s use of glucose,

collagen, and elastic fibers contribute to the aging process


End of Chapter 4

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tissue level of organization

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