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Connective Tissue and More

Connective tissues, nervous, and muscle tissues

What is connective tissue?

Connective tissuesRepresent the most abundant by weight and most widely distributed type of tissue in the body

Generally:Bind structures togetherFill spaces in the bodyExamples: Connective tissue proper, Cartilage, Bone, Blood

Connective Tissue

Figure 4.6

Connective Tissues –general functions

Connect epithelium to the rest of the body (basal lamina)Have no contact with environment (usually covered by epithelium)Usually highly vascular (good blood supply)Also:

Protect delicate organsProvide structure and support (bone)Insulate and store energy (fat)Transport materials (blood)

Characteristics of Connective Tissues

Specialized cellsSolid extracellular protein fibers

Collagen, elastic, and reticularFluid extracellular ground substance

unstructured material that fills the space between cells

These latter two extracellular features are called Matrix

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The Matrix

The extracellular components of connective tissues (fibers and ground substance):

Makes up the majority of tissue volumeDetermines specialized function:

connective tissue proper syrupy liquidcartilage gel-like matrixblood fluid matrixbone crystalline solid

Matrix: ground substanceFills the spaces between cells and fibersFunctions as a molecular sieve through which nutrients diffuse between blood capillaries and cellsComposed of

interstitial fluidCell adhesion proteins: serve as glue for cells to attach to matrixProteoglycans: consist of a protein core with glycosaminoglycans (GAGs) such as chondroitin sulfate and hyaluronic acid which trap water and determine the consistency

Ground Substance: Proteoglycan Structure

Figure 4.7

Matrix: Protein Fibers

Collagen – tough but inelastic; provides very high tensile strength (greater than steel)Elastic – long, thin fibers that allow for stretch; composed of elastin which is similar to collagenReticular – branched collagenous fibers that form delicate networks, resist force in many directions

Elastic fibers allow a tissue to stretch Cells

Fibroblasts – connective tissue properChondroblasts – cartilage Osteoblasts – boneHematopoietic stem cells – bloodWhite blood cells, plasma cells, macrophages, and mast cells

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Other CTP cell types

MelanocytesAdipocytes – fat cells; insulation, energy, padding

Mesenchymal cells – stem cells; can differentiate into other mesodermal cell types

Fibroblasts

Stationary in the tissueSecrete the protein fibers and ground substance found in the matrix

Classification of Connective Tissues

Connective tissue proper:connect and protect

Fluid connective tissues:transport

Supporting connective tissues:structural strength

Classification of connective tissues

Connective tissue proper (CTP)

Contains many types of cells and extracellular fibers in a syrupy ground substanceLook at the cell types and the number and types of fibers to identify the type of tissue

Categories of Connective Tissue Proper

Loose connective tissue:more ground substance, less fibers e.g., fat (adipose tissue)

Dense connective tissue:more fibers, less ground substancee.g., tendons

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CTP: 3 types of LooseConnective Tissues Proper

The “packing materials” of the body Packing material, fills spacesContains mesenchyme cells – leftover from development, can differentiate into many of the other resident cell types3 types in adults:

areolaradiposereticular

Connective Tissue: Embryonic

Mesenchyme – embryonic connective tissueGel-like ground substance with fibers and star-shaped mesenchymal cellsGives rise to all other connective tissuesFound in the embryo

Loose CTP #1: AreolarAreolar connective tissue

Least specialized, open framework Viscous ground substance with all three connective tissue fibersFibroblasts, macrophages, mast cells, and some white blood cellsWraps and cushions organsWidely distributed throughout the bodySeparates skin from deeper tissuesHolds blood vessels and capillary beds:

Areolar Connective Tissue Model

Figure 4.8

Loose CTP #1: Areolar

Figure 4.9a

Loose CTP #2: Adipose

Adipose connective tissueMatrix similar to areolar connective tissue with closely packed adipocytesReserves food stores, insulates against heat loss, and supports and protectsFound under skin, around kidneys, within abdomen, and in breasts Local fat deposits serve nutrient needs of highly active organs

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Loose CTP #2: Adipose

Figure 4.9b

Loose CTP #2: Adipose

Contains many adipocytes (fat cells)

Figure 4–10a

Adipose Cells

Adipocytes in adults do not divide:expand to store fatshrink as fats are released

Mesenchymal cells divide and differentiate:to produce more fat cellswhen more storage is needed

Loose CTP #3: Reticular

Reticular connective tissueLoose ground substance with reticular fibersReticular cells lie in a fiber networkForms a soft internal skeleton, or stroma, that supports other cell typesFound in Reticular organs: lymph nodes, bone marrow, liver, and the spleen

Loose CTP #3: Reticular

Figure 4.9c

Loose CTP #3: Reticular

Provides support

Figure 4–10b

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CTP: 3 Types of DenseConnective Tissues

Connective tissues properTightly packed with high numbers of collagen or elastic fibers:

dense regular connective tissuedense irregular connective tissueelastic tissue

Dense CTP #1: Dense Regular

Dense Regular Connective TissueParallel collagen fibers with a few elastic fibersMajor cell type is fibroblastsAttaches muscles to bone or to other muscles, and bone to bone Found in tendons, ligaments, and aponeuroses

Dense CTP #1: Dense Regular

Figure 4.9d

Dense CT #1: Dense Regular

e.g. tendons, ligamentsAttachment and stabilization

Dense CTP #2: Dense Irregular

Dense Irregular Connective TissueIrregularly arranged collagen fibers with some elastic fibersMajor cell type is fibroblastsWithstands tension in many directions providing structural strengthFound in the dermis, periosteum, perichondrium, submucosa of the digestive tract, and fibrous organ capsules

Dense CTP #2: Dense Irregular

Figure 4.9e

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Dense CT #2: Dense Irregular Dense CT #3: Elastic Tissue

Made of mostly elastic fibers (elastin):e.g., elastic ligaments of spinal vertebrae

Figure 4–11c

Dense CT #3: Elastic Tissue Fluid Connective Tissues

Fluid connective tissues: blood and lymph

watery matrix of dissolved proteinscarry specific cell types (formed elements)

Fluid CT: BloodFormed elementsFormed elements are the cells plus the platelets (which aren’t technically cells) =

Red blood cells (erythrocytes) = majorityWhite blood cells (leukocytes)Platelets

Connective Tissue: Blood

Red and white cells in a fluid matrix (plasma)Contained within blood vesselsFunctions in the transport of respiratory gases, nutrients, and wastes

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Fluid Elements of Blood

Extracellular:Plasma – fluid portion of bloodInterstitial fluid – squeezed out of capillariesLymph – Int. fluid entering lymph vessels

Connective Tissue: Blood

Figure 4.9j

Flow of body fluids – A CyclePlasma in blood (without formed elements) squeezes out of capillaries due to blood pressure and small spaces between some epithelial cellsNow in tissue spaces it is called interstitial fluid. Passively enters lymphatic system.Now it is called lymph. Returns to blood through subclavian veins then to heartCycle repeats

Supporting Connective Tissues

Bone and Cartilage

What do supporting connective tissues do?

Supportive Connective Tissues

Function: Support soft tissues and body weightTypes:

cartilage: gel-type ground substancefor shock absorption and protection

bone: calcified (made rigid by calcium salts, minerals)for weight support

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Supporting CT #1: CartilageMatrix:

Proteoglycans derived from chondroitin sulfates (polysaccharide) makes it gel-likeDifferent cartilage types derive their properties from the number and type of proteoglycans and the number and type of protein fibers

Cells:chondrocytes, surrounded by lacunae (chambers)chondroblasts (progenitor of chondrocytes)

Cartilage Structure

No blood vessels:chondrocytes produce antiangiogenesis factor

Perichondrium (a dense irregular CTP):outer, fibrous layer (for strength)inner, cellular layer (for growth and maintenance)

Cartilage Growth - Interstitial

Interstitial growth (inside-out) by chondrocytes

Figure 4–13a

Cartilage Growth - Appositional

Appositional growth (adding to the outside) [Adults]

Figure 4–13b

The 3 Types of Cartilage Hyaline (glass) cartilage:

most commontranslucent matrix, packed collagenno prominent fibersjoint perichondrium

Elastic cartilage:tightly packed elastic fibers

Fibrocartilage:very dense collagen fibersjoint pads

Connective Tissue: Hyaline Cartilage

Amorphous, firm matrix with imperceptible (clear) network of collagen fibersChondrocytes lie in lacunaeSupports, reinforces, cushions, and resists compressionForms the costal cartilage (ribs)Found in embryonic skeleton, the ends of long bones, nose, trachea, and larynx

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Connective Tissue: Hyaline Cartilage

Figure 4.9f

Hyaline Cartilage

Reduces friction in jointsCover the end of long bones

Figure 4–14a

Connective Tissue: Elastic Cartilage

Similar to hyaline cartilage but with more elastic fibersMaintains shape and structure while allowing flexibilitySupports external ear (pinna) and the epiglottisMay be stacked up

Connective Tissue: Elastic Cartilage

Figure 4.9g

Elastic Cartilage

Flexible supportfound in external ear and epiglottis

Figure 4–14b

Connective Tissue: Fibrocartilage

Matrix similar to hyaline cartilage but less firm with thick collagen fibersProvides tensile strength and absorbs compression shockFound in intervertebral discs, the pubic symphysis, and in discs of the knee joint

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Connective Tissue: Fibrocartilage

Figure 4.9h

Fibrocartilage

Joints

Most joints have both hyaline cartilage and fibrocartilage in them

Connective Tissue: Bone (Osseous Tissue)

Hard, calcified matrix with flexible collagen fibers found in boneOsteocytes are found in lacunae and are well vascularized:

arranged around central canals within matrixsmall channels through matrix (canaliculi) access blood supply (no diffusion through matrix)

Supports, protects, and provides levers for muscular actionStores calcium, minerals, and fatMarrow inside bones is the site of hematopoiesis

Connective Tissue: Bone

Figure 4.9i

Bone

Very little ground substancematrix is 2/3 Calcium salts (phosphate, carbonate), 1/3 collagen

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Bone: what to look forOsteon (whole circular structure)Concentric lamellae (of matrix)Central canal (at center of lamellae)OsteoblastsOsteocytes in lacunaeCanaliculi – canals for diffusion

Close Up: ostocyte and canaliculi

Cytoplasmic extensions

Bone growth

Appositional only (outside)Osteocytes secrete matrix fibers and calcium salts, forms concentric rings

Comparing Cartilage and Bone

Table 4–2

Nervous Tissue

Also called neural or nerve tissue:Branched neurons with long cellular processes and support cellsspecialized for conducting electrical impulses rapidly senses internal or external environmentprocess information and controls responsesFound in the brain, spinal cord, and peripheral nerves

Nervous Tissue

Figure 4.10

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Muscle Tissue: Skeletal

Long, cylindrical, multinucleate cells with obvious striationsInitiates and controls voluntary movementFound in skeletal muscles that attach to bones or skin

3 Types of Muscle Tissue

Skeletal muscle:large body muscles responsible for movement

Cardiac muscle:found only in the heart

Smooth muscle:found in walls of hollow, contracting organs (blood vessels; urinary bladder; respiratory, digestive and reproductive tracts)

Muscle Tissue: Skeletal

Figure 4.11a

Muscle Tissue: Cardiac

Branching, striated, uninucleate cells interlocking at intercalated discsPropels blood into the circulationFound in the walls of the heart

Muscle Tissue: Cardiac

Figure 4.11b

Muscle Tissue: Smooth

Sheets of spindle-shaped cells with central nuclei that have no striationsPropels substances along internal passageways (i.e., peristalsis)Found in the walls of hollow organs

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Muscle Tissue: Smooth

Figure 4.11c

Developmental Aspects

Primary germ layers: ectoderm, mesoderm, and endoderm

Three layers of cells formed early in embryonic developmentSpecialize to form the four primary tissues

Nerve tissue arises from ectoderm

Developmental Aspects

Muscle, connective tissue, endothelium, and mesothelium arise from mesodermMost mucosae arise from endodermEpithelial tissues arise from all three germ layers

Body Membranes

Membranes:are physical barriers that line or cover portions of the body

Consist of an epitheliumAlways supported by connective tissues

4 Types of Membranes

1. Mucous2. Serous3. Cutaneous4. Synovial

Figure 4–16

Mucous MembraneMucous membranes (mucosae):

line passageways that have external connections:digestive, respiratory, urinary, and reproductive tractsGoblet cells secrete mucins mucus

Epithelial surfaces must be moist:to reduce frictionto facilitate absorption and excretion

Lamina propria:is areolar tissue

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Structure of Mucous Membrane

Figure 4–16a

Serous MembranesLine cavities not open to the outside; sealed internal subdivisions of ventral body cavity, e.g. peritoneumAre thin and transparent but strongHave fluid transudate to reduce friction

Epithelial part = Mesothelium (simple squamous)

Connective tissue part = areolar tissue

Structure of Serous Membrane

Figure 4–16b

Serous Membranes

Figure 4.12c

Double MembranesSerous membranes:

have a parietal (wall) portion covering the cavityand a visceral portion (serosa) covering the organs

Serous membranes: consist of parietal layer and visceral layer

Cutaneous Membrane

Cutaneous membrane:is skin, surface of the bodythick, waterproof, and dryMade up of epidermis and dermis (papillary and reticular layers). What types of tissues?

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Structure of Cutaneous Membrane

Figure 4–16c

Synovial Membranes

Line articulating (moving) joint cavitiesProduce synovial fluid (lubricant, nutrients to chondrocytes of articular cartilage)Protect the ends of bones (which themselves are covered in what?)Lack a true epithelium (incomplete, no basal lamina)

Structure of SynovialMembranes

Figure 4–16d

Summary: Inflammation and Regeneration

Figure 4–20

Aging

Epithelia get thinnerCT more fragile

So bruise easily, bones more brittle

Different PGs made by chondrocytes

Proteoglycans

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Summary

Connective tissues – structures and functionsCTP (loose, dense)Fluid (blood, lymph)Supporting (cartilage, bone)Nervous tissue – brief overview Muscle tissue overview (3 types)Membranes (4 types)