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Collin College

BIOL. 2401 Chapter 4

Tissue Levels

CONNECTIVE TISSUE

•  Depending on the stimuli, mesenchyme develops into specific cells that give rise to the different C.T. types

•  The cells of each C.T. type secrete a surrounding matrix

•  The majority of connective tissue is the matrix; it is made out of•  ground substance•  extra-cellular protein fibers

•  Depending on the type of C.T., the matrix will be •  fluid and flexible with few or many cells•  solid and rigid with few or many cells

•  C.T. derives from Mesenchyme embryonic tissue.

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CONNECTIVE TISSUE

• Establishes structural frameworks • Transport fluids and dissolved materials • Protect delicate organs • Support, surround and interconnect tissues • Store energy reserves and minerals • Defend the body from microorganisms

Functions

CLASSIFICATIONS

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CLASSIFICATIONS

COMPOSITION AND ORGANIZATION

Contains largest variety of cells, has viscous ground substance and different fibers

Connective tissue proper

•  Fibroblasts – produce the fibers •  Macrophage – engulf pathogens •  Adipocytes – fat-storing cells •  Mesenchymal cells – stem cells

•  Melanocytes – pigment producers •  Mast cells – trigger inflammation •  Lymphocytes – attack foreign antigens •  Microphages – engulf cell remnants

Types of Cells

Types of Fibers•  Collagen fibers – flexible , high strength •  Elastic Fibers – coiled fibers with elastic properties •  Reticular – supporting network fibers

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•  Fibroblasts–  The most abundant cell type:

•  Found in all connective tissue proper•  Secrete proteins and hyaluronan (cellular cement)

•  Fibrocytes–  The second most abundant cell type

•  Found in all connective tissue proper•  Maintain the fibers of connective tissue proper

•  Adipocytes–  Fat cells : each cell stores a single, large fat droplet

•  Mesenchymal Cells–  Stem cells that respond to injury or infection

•  Differentiate into fibroblasts, macrophages, etc.

Cells of Connective Tissue Proper

•  Macrophages–  Large, amoeba-like cells of the immune system

•  Eat pathogens and damaged cells. Fixed macrophages stay in tissue, Free macrophages migrate

•  Mast Cells–  Stimulate inflammation after injury or infection

•  Release histamine and heparin •  Lymphocytes

–  Specialized immune cells in lymphatic (lymphoid) system•  For example, lymphocytes may develop into plasma cells

(plasmocytes) that produce antibodies

Cells of Connective Tissue Proper

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•  Collagen Fibers –  Most common fibers in connective

tissue proper–  Made from three amino acid chain

helices, bundled together into fibrils. In turn, many such fibrils from a collagen fiber.

–  They are long, straight, and unbranched

Fibers of Connective Tissue

–  Strong and flexible ; resist force in one direction –  For example, tendons and ligaments–  In skin for example, 90% of dermis is collagen. It can retain 8x its

weight in water…major moisterizing agent in your skin

•  Reticular Fibers –  Network of interwoven fibers (stroma)–  Strong and flexible as well ; resist force in many directions–  Stabilize functional cells (parenchyma) and structures–  For example, sheaths around organs

Fibers of Connective Tissue

•  Elastic Fibers –  Contain elastin–  Branched and wavy; return to

original length after stretching–  Found where function requires

elasticity and strenght ( Ex: elastic arteries)

Elastic fibers in 6 years old and 90 year old individual

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Ground Substance Connective Tissue Proper

•  Ground Substance–  Is clear, colorless, and viscous– Fills spaces between cells and slows pathogen

movement

•  Important note : fibers and ground substance are found in all connective tissues. Connective tissue proper just has a lot more variety of cells

Reticular fibers

Melanocyte

Fixed macrophage

Plasma cell

Blood in vessel

Adipocytes (fat cells)

Ground substance

Mast cell

Elastic fibers

Free macrophage

Collagen fibers

Fibroblast

Mesenchymal cell

Lymphocyte

CELLS AND FIBERS OF C.T. PROPER

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Mesenchyme

•  Mesenchyme Tissue is Embryonic Connective Tissues

LM × 136

Blood vessel

Mesenchymal cells

This is the first connective tissue to appear in an embryo.

•  Is not found in adults, but mesenchyme cells remain in many connective tissue proper

•  It can differentiate into new connective tissues when properly stimulated

Areolar Connective Tissue

•  Areolar Tissue•  Least specialized•  Open framework with Viscous ground substance•  Elastic and collagen fibers •  Found under many simple epithelial tissues (in lamina

propria)- holds blood vessels and capillary beds

LOCATIONS: Within and deep to the dermis of skin, and covered by the epithelial lining of the digestive, respiratory, and urinary tracts; between muscles; around joints, blood vessels, and nerves

FUNCTIONS: Cushions organs; provides support but permits independent movement; phagocytic cells provide defense against pathogens

Fibrocytes or fibroblasts

Macrophage

Collagen fibers

Mast cell

Elastic fibers

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ADIPOSE AND RETICULAR C.T.

Adipose Tissue•  Contains many adipocytes (fat cells)•  Two types of adipose tissue

1.  White fat•  Most common and Stores fat•  Absorbs shocks/Slows heat loss (insulation)

2.  Brown fat•  More vascularized tissue •  Adipocytes have many mitochondria•  When stimulated by nervous system, fat breakdown accelerates,

releasing energy •  Absorbs energy from surrounding tissues

Reticular Tissue•  Provides support via complex, three-dimensional network•  Supportive fibers (stroma) support functional cells (parenchyma)•  The form structural Reticular organs such as spleen, liver, lymph

nodes, and bone marrow

ADIPOSE AND RETICULAR C.T.

LM × 300

Adipose Tissue

LOCATIONS: Deep to the skin, especially at sides, buttocks, and breasts; padding around eyes and kidneys

FUNCTIONS: Provides padding and cushions shocks; insulates (reduces heat loss); stores energy

Adipocytes (white adipose

cells)

Adipose tissue

LM × 375 Reticular tissue

Reticular Tissue

LOCATIONS: Liver, kidney, spleen, lymph nodes, and bone marrow

FUNCTIONS: Provides supporting framework

Reticular tissue from liver

Reticular fibers

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•  Dense Regular Connective Tissue–  Tightly packed, parallel collagen fibers

•  Tendons attach muscles to bones•  Ligaments connect bone to bone and stabilize organs•  Aponeuroses attach in sheets to large, flat muscles

•  Dense Irregular Connective Tissue–  Interwoven networks of collagen fibers

•  Typical in the dermis of the skin•  Around cartilages (perichondrium) and bones

(periosteum)•  Form capsules around some organs (e.g., liver, kidneys)

DENSE C.T.

DENSE C.T.

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DENSE ELASTIC TISSUE

Made mostly of elastic fibersFor example, elastic ligaments between spinal vertebrae

FLUID CONNECTIVE TISSUE

–  Blood and lymph = a watery matrix of dissolved proteins–  Carry specific cell types (formed elements)

•  Formed elements of blood–  RBC’s(erythrocytes), WBC’s(leukocytes), Platelets

•  Lymphatic system returns extra interstitial fluid back to blood – fluid it monitored by immune system

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SUPPORTING CONNECTIVE TISSUE

Cartilage and bone support soft tissues and the rest of the body

Cartilages :

Matrix is a firm gel containing chondroitin sulfate and protein fibers •  Cells are called chondrocytes •  Cells are found in lacunae ( “living areas” ) •  Perichondrium separates cartilage from surrounding tissues •  Chondrocytes produce an anti-angiogenesis factor …… prevents the

development of blood vessels into cartilage ( they are thus avascular) •  Cannot get too thick – nutrients passage and healing factors are

dependent on diffusion •  Three types: hyaline, elastic and fibrocartilage

SUPPORTING CONNECTIVE TISSUE

Hyaline Cartilage

•  Stiff, flexible support – most common cartilage•  Reduces friction between bones and protects•  Found in synovial joints, rib tips, sternum, •  Keeps the trachea open•  Usually, lacunae are large and not touching, fibers not visible

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SUPPORTING CONNECTIVE TISSUE

Elastic cartilge

•  Supportive but bends easily•  Found in external ear and epiglottis•  Lacunae very close to each other with visible thin elastic

fibers between

Fibrocartilage (Fibrous Cartilage) •  Limits movement - Prevents bone-to-bone contact•  Found between pubic bones and intervertebral discs•  Lacunae are tiny and occur in small groups far apart•  Fibers sometimes visible as “smears”

Fibrocartilage

LOCATIONS: Pads within knee joint; between pubic bones of pelvis; intervertebral discs

FUNCTIONS: Resists compression; prevents bone-to-bone contact; limits movement

Fibrocartilage

Chondrocytes in lacunae

Fibrous matrix

LM × 400

LOCATIONS: Auricle of external ear; epiglottis; auditory canal; cuneiform cartilages of larynx

FUNCTIONS: Provides support, but tolerates distortion without damage and returns to original shape

Elastic cartilage

Chondrocytes in lacunae

Elastic fibers in matrix

LM × 358

Elastic Cartilage

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SUPPORTING CONNECTIVE TISSUE

BONE •  Has osteocytes located in lacunae •  In compact bone, they are located in concentric circles around

a central canal containing blood vessels •  Cells depend on diffusion through canaliculi for nutrients •  Little ground substance but dominating collagen protein fibers

provide limited flexibility within a dense mineralized matrix – hard to break unless changes occur within matrix

•  Surrounded by periosteum

Canaliculi

Osteocytes in lacunae

Matrix

Central canal

Blood vessels

LM × 375 Osteon

Osteon

Fibrous layer

Cellular layer

Periosteum

BONE CONNECTIVE TISSUE

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MUSCLE TISSUE

•  Specialized for contraction •  Three types

• Skeletal muscle : Striated and voluntary • Cardiac muscle : Striated and involuntary • Smooth muscle : not striated and involuntary

Striations in muscle are due to a very organized arrangement of the two contractile protein strands : actin and myosin

MUSCLE TISSUE

•  Very long/thin cells that are multinucleate •  They have a striated appearance •  They are our voluntary muscle •  Divide/regenerate via satellite cells

Striations

Nuclei

Muscle fiber

LM × 180 Skeletal muscle

Skeletal Muscle Tissue

Cells are long, cylindrical, striated, and multinucleate.

LOCATIONS: Combined with connective tissues and neural tissue in skeletal muscles

FUNCTIONS: Moves or stabilizes the position of the skeleton; guards entrances and exits to the digestive, respiratory, and urinary tracts; generates heat; protects internal organs

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MUSCLE TISSUE

•  Cardiocytes occur only in the heart •  Microscopic short cells that are branched and connect

via intercalated discs •  They are striated involuntary muscle •  Rely on pacemaker cells for regular contraction

MUSCLE TISSUE

•  They are not striated and short, tapered cells ---- involuntary muscle

•  Found everywhere motion is needed inside the body

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NEURAL TISSUE

•  Conducts electrical impulses •  Conveys information from one area to another •  CONTAINS TWO MAIN TYPES OF CELLS

•  Neurons • Transmit electrochemical signals •  Organized into a cell body, axon, and dendrites •  Dendrites receive the information and electrical

information is guided down the axon to other neurons

•  Neuroglia : Support neural tissue and help supply nutrients to neurons

NEURAL Tissue

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BODY SYSTEM MEMBRANES

• They Form barriers to protect organs • They are Composed of epithelium and

connective tissue

•  Four types •  Cutaneous •  Synovial •  Serous •  Mucous

Body membranes

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Cutaneous Membranes

•  Cutaneous membrane = skin–  A dry membrane–  Outermost protective boundary

•  Superficial epidermis–  Keratinized stratified �

squamous epithelium•  Underlying dermis

–  Mostly dense irregular �connective tissue

Mucous Membranes•  Lines passage ways that

communicate with the exterior

•  Must be kept moist to reduce friction

•  The epithelial layer is lubricated by mucus from goblet cells or via multi-cellular glands

•  The epithelial layer can be simple (ex : lining of intestine) or stratified (ex: lining of mouth)

•  The connective tissue layer under these membranes is called the lamina propria and is mostly areolar C.T.

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•  Line the sealed internal subdivisions of the ventral body cavity ( cavities that DO NOT open to the exterior)

•  3 main types of serous membranes are•  The pericardium•  The pleura•  The peritoneum

•  Each serous membrane has two layers to it•  The parietal portion : attaches to the inner surface of the body

cavity ( body wall)•  The visceral portion or serosa : covers the outer surface of

the organ involved. The epithelial layer is lubricated by mucus from goblet cells or via multicellular glands

Serous Membranes

Serous MembranesSerous layers are separated by serous fluid

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•  Composed out of only Connective tissue only

•  Lines fibrous capsules surrounding joints

Synovial Membranes

CONNECTIVE TISSUE FRAMEWORK

•  Layers of CT connect the organs within the dorsal and ventral body cavities

•  The layers provide strength, maintain position of organs and provide routing areas for bloodvessesl and nerves

•  Fasciae are connective tissue layers that support and surround organs•  Superficial Fascia or Subcutaneous layer

•  also called the Hypo dermis ( located under the dermis layer)•  areolar CT and fat

•  Deep fascia•  dense irregular CT

•  Subserous fascia•  layer of areolar CT between deep fascia and serous membranes

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CONNECTIVE TISSUE FRAMEWORK