Chapter 4 The Tissue Level of Organization. Copyright 2009, John Wiley & Sons, Inc. What is a Tissue? A tissue is a group of cells Common embryonic

Chapter 4The Tissue Level of

Organization

Copyright 2009, John Wiley & Sons, Inc.

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

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4 Major Types of Tissues1. Epithelial

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

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

3. Muscular Generates the physical force needed to make body

structures move and generate body heat4. Nervous

Detect changes in body and responds by generating nerve impulses

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Cell Junctions

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

1. Tight junctions

2. Adherens junctions

3. Desmosomes

4. Hemidesmosomes

5. Gap junctions

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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

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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

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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

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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

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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

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Gap Junctions

Avascular tissues Lens and cornea

Developing embryo Nerve and muscle

Cardiac muscle Smooth muscle

GI Uterus

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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:1. Selective barrier that regulates the movement of materials

in and out of the body

2. Secretory surfaces that release products onto the free surface

3. Protective surfaces against the environment

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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

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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

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Epithelial Cells

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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)

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Covering and Lining Epithelium

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

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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

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

function1. Squamous

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

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

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Different Types of Covering and Lining Epithelium

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

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

and collapse to a smaller size

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Simple Epithelium

1. Simple squamous epithelium

2. Simple cuboidal epithelium

3. Simple columnar epithelium (nonciliated and ciliated)

4. Pseudostratified columnar epithelium (nonciliated and ciliated)

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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

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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

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Simple cuboidal epithelium

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

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Simple columnar epithelium

Column shaped cells Oval nuclei at or near base Nonciliated and ciliated

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Nonciliated simple columnar epithelium

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

Mucus secretion 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

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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

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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

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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 columnar epithelium Transitional epithelium

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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

Non-keratinized form does not contain keratin Found in mouth and esophagus

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Stratified Cuboidal Epithelium

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

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Stratified columnar epithelium

Very uncommon Columnar cells in apical layer only Basal layers has shorter, irregular

shaped cells Functions in protection and secretion

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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

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Glandular Epithelium

Endocrine Secretions, called hormones, diffuse directly into the bloodstream Function in maintaining homeostasis

Exocrine Secretions in ducts Mucus, sweat, oil, cerumen, saliva and digestive enzymes

Some mixed glands Pancreas, testes, and ovaries

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Functional Classification of Exocrine Glands Merocrine

Secretory vesicles Most exocrine glands Salivary glands and

pancreas Apocrine

Apical “pinching” Mammary glands Some question existence

Holocrine Rupture entire cell Sebaceous glands

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Connective Tissue

Most abundant and widely distributed tissues in the body

Consists of multitude of different cells, extracellular matrix and fibers

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

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Extracellular matrix of Connective Tissue

Extracellular matrix is the material located between the cells Consist of protein fibers and ground substance

Most connective tissues are quite vascular Good nerve supply Exceptions are cartilage and tendons, little or

no blood supply and no nerves

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Cells and Fibers in Connective Tissue

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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

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Connective Tissue Extracellular Matrix Ground substance

Between cells and fibers Fluid, semi-fluid, gelatinous, or calcified

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

Active role in tissue development, migration, proliferation, changing cell shape, and cellular metabolism

Complex combination of proteins and polysaccharides

Fibers Collagen fibers Elastic fibers Reticular fibers

Ground Substance

Water and assortment of macromolecules Glycosaminoglycans (GAGs) – polysaccharides

trap water for jelly-like consistency except hyaluronic acid GAGs a/w proteins to make

proteoglycans ( core protein and GAGs that project like bristles of bottle brush)

1. hyaluronic acid – viscous, slippery, binder, joint lubricant, shape of eyeballs

hyaluronidase – enzyme breaks down hyaluronic acid, enable sperm and WBC to move more easily, virulent factor in bacteria

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Ground Substance

2. chondroitin sulfate – support and adhesiveness of cartilage bone, skin and blood vessels

3. dermatan sulfate – skin, tendons, blood vessels, and heart valves

4. keratan sulfate – bone, cartilage and cornea5. fibronectin – adhesion proteins linking

components, binds collagen fibers and ground substance, attaches cells to ground substance


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Fibers collagen – most abundant protein, 25% of total

found in most types of connective tissue, especially bone, cartilage, tendons, and ligaments

strong, resistant to pulling forces, but not stiff allowing flexibility

often in parallel bundles elastic – consists of protein elastin and

surrounded by glycoprotein fibrillin stretchable up to 150% elasticity returning to original shape skin, blood vessels and lung tissue


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Fibers

reticular – collagen arranged in fine bundles coated by glycoprotein support in blood vessel walls and form network

around cells in selected tissues produced by fibroblasts forms stroma or supporting framework of many

soft organs such as spleen and lymph nodes


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Classification of Connective Tissues1. Embryonic connective tissue

Mesenchyme and mucous connective tissue

2. Mature connective tissueA. Loose connective tissue

1. areolar2. adipose3. reticular

B. Dense connective tissue1. dense regular2. dense irregular3. elastic

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Classification of Connective Tissues

C. Cartilage1. hyaline2. fibrocartilage3. elastic cartilage

D. Bone tissueE. Liquid connective tissue

1. blood 2. lymph

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Embryonic Connective Tissue

Mesenchyme gives rise to all other connective tissues irregular shaped cells, semi-fluid ground

substance, and delicate reticular fibers gives rise to mature connective tissue

Mucous (Wharton’s Jelly) found in umbilical cord of the fetus widely scattered fibroblasts, viscous jelly-like

ground substance, and loosely arranged collagen fibers


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Embryonic Connective Tissue


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Loose Connective Tissue: Areolar Most widely distributed in the body Contains several types of cells and all three fibers

embedded in semi-fluid ground substance sub-q skin, papillary dermis, around blood vessels, nerves

and organs, lamina propria of mucous membranes

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Loose Connective Tissue: Adipose Tissue

Contains adipocytes; storage of triglycerides

sub-q skin, around organs such as heart and kidneys, yellow marrow, padding around joints

Good for insulation and energy reserves

White (common) and brown adipose tissue

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Loose Connective Tissue: Reticular

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

nodes

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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

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Dense Irregular Connective Tissue

Collagen fibers are usually irregularly arranged Found where pulling forces are exerted in many

directions Reticular dermis of skin and heart

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Elastic Connective Tissue

Contain branching elastic fibers Strong and can recoil to original shape after

stretching Lung tissue and arteries

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Cartilage

Cartilage is a dense network of collagen fibers and elastic fibers firmly embedded in chondroitin sulfate Chondrocytes

Cartilage cells found in the spaces called lacunae Perichondrium

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

perichondrium

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Hyaline cartilage

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

articular cartilage) Provide flexibility and support. Reduces friction

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Fibrocartilage Chondrocytes are scattered among bundles of collagen

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

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Elastic Cartilage

Chrondrocytes are located within a threadlike network of elastic fibers

Perichondrium is present Provides strength and elasticity epiglottis, external ear

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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

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Bone composed of several different connective tissues:

(osseous) tissue, periosteum, and endosteum matrix: minerals and collagen functions:

support protection movement in conjunction with skeletal muscle mineral (calcium and phosphorus) storage red marrow – blood cell production yellow marrow – triglyceride storage


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Bone two types:

1. compact osteons or Haversian system

2. spongy lacks osteons spicules called trabeculae


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Compact Bone


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Spongy Bone


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Liquid Connective Tissue

Blood tissue (chapter 19) Connective tissue with liquid extracellular matrix called blood plasma Formed elements – WBC, RBC, and platelets Within blood vessels

Lymph (chapter 22) extracellular fluid in lymphatic vessels several types of cells in liquid extracellular matrix with lower protein content than plasma transports lipids and immune cells

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Table 6.11

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Epithelial 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

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Membranes

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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 Lamina propria contains very high concentration

of lymphocytes and particularly antibody secreting (IgA) plasma cells

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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

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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

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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 multiple peripheral nuclei arranged as parallel fibers motion, posture, heat and protection

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Muscular Tissue

Cardiac muscle tissue Have striations Involuntary movement or contraction is not

consciously controlled Intercalated disc (gap junctions) unique to

cardiac muscle tissue branching fibers single central “box-car “ nucleus

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Smooth Muscle Tissue

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

and intestines Nonstriated, spindle-shaped, central located

cigar-shaped nucleus, usually parallel Usually involuntary control: endocrine and/or

autonomic nervous system control

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Nervous Tissue Consists of two principle types of cells

Neurons or nerve cells Neuroglia

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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

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Tissue Repair: Restoring Homeostasis Granulation tissue

An actively growing connective tissue 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

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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

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Clinical Correlation

Basement membrane thickening Papanicolaou test Marfan Syndrome Autoimmune diseases

Sjogren’s Syndrome Systemic Lupus Erythematosus

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Medical Terminology

Atrophy a- -trophy

Biopsy bio- -opsy

Hypertrophy hyper-


Medical Terminology

Tissue rejection Tissue transplantation Xenotransplantation

xen-



End of Chapter 4

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Documents

Chapter 4 The Tissue Level of Organization. Copyright 2009, John Wiley & Sons, Inc. What is a Tissue? A tissue is a group of cells Common embryonic