Chapter 4

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4.
Epithelial
Connective
Muscle neural

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Includes epithelia and glands
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Epithelia – layers of cells that cover internal or external surfaces
Glands – secreting cells derived from epithelia
Important characteristics:
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Cells bound closely together
A free (apical) surface exposed to the environment or to some internal chamber or passageway
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Attachment to underlying connective tissue
 By a basement membrane
Epithelial cells that are damaged or lost at the exposed surface are continuously replaced

1.
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Provide physical protection
Protect exposed and internal surfaces
2.
3.
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Control permeability
Provide sensation detect changes in the environment and relay the information to the nervous system
4.
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Produce specialized secretions
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Gland cells
Glandular epithelium
Exocrine – secretions discharged onto the surface of the epithelium
Endocrine – secretions into the surrounding tissues and blood (hormones)

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Must remain firmly attached to a basement membrane and each other
Tight junction
 Lipid layers of adjacent cell membranes are tightly bound together by interlocking membrane proteins
Gap junction
 Two cells are held together by embedded membrane proteins.
 Form a narrow passageway to let small molecules and ions to pass through
Desmosome
 Cell membranes of two cells are locked together by intercellular cement and by membrane proteins connected to a network of intermediate filaments

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Have specialized structures that distinguish them from other body cells
Many that line internal passageways have microvilli on their exposed surface
 Increases surface area about 20 times
A cell with a ciliated surface has about 250 cilia that beat in a coordinated fashion to move materials across the surface of the cell
 Example: the respiratory tract

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A network of protein fibers
Lies between the epithelium and underlying connective tissues
Is a place of attachment for epithelial cells
Provides strength and resists distortion
Is a barrier between underlying connective tissues and the epithelium

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Epithelium must continually repair and renew itself
Are lost or destroyed by chemical or physical wear and tear
Stem cells
 Unspecialized cells
 Found deep in the epithelium near the basement membrane
 Continuously divide to replace dead or damaged cells in the epithelium

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Two types of layering:
1.
2.
Simple
Stratified
1.
2.
3.
Three Cell Shapes:
Squamous
Cuboidal
Columnar
Table 4 – 1 page 93

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Simple epithelium
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Single layer of cells covering the basement membrane
Line ventral body cavities, heart chambers and blood vessels
Where secretions or absorption occurs – thinness reduces diffusion time
Stratified epithelium
 Has several layers of cells over the basement membrane
 Provides more protection
 Found in areas subject to more mechanical or chemical stress

1.
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Squamous epithelium
Cells are thin and flat
Looks like fried eggs laid side by side
2.
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Cuboidal epithelium
Hexagonal boxes in 3D view, but in sectional view look like boxes
3.
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Columnar epithelium
Also hexagonal but taller and more slender
Nuclei are crowded in a narrow band close to basement membrane

 Found in protected regions where absorption takes place or where a slippery surface reduces friction
Simple Cuboidal Epithelium
 Provides limited protection
 Secrete enzymes and buffers in the pancreas and salivary glands
 Involved in the production of urine
Simple Columnar
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Provides some protection and allow for absorption and secretion
Lines the stomach, intestinal tract and many excretory ducts

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Nuclei are at varying distances from surface, it has a layered appearance
 Pseudostratified columnar epithelium
It is not stratified, all cells touch basement membrane
Typically possess cilia
Lines most of the respiratory tract

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Transitional epithelium
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Withstands considerable stretching
Lines ureters and urinary bladder
Stratified squamous epithelium
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Found where mechanical stresses are severe
Surface of the skin, lining of mouth, tongue and esophogus

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Produce exocrine or endocrine secretions
Exocrine
 Discharge products through a duct onto some internal or external surface
 Can be characterized as unicellular glands (goblet cells) or multicellular glands (secretory sheet)
Endocrine (hormones)
 Produced by ductless glands and released into blood or tissues

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Each glandular cell releases secretions by one of three mechanisms:
1.
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Merocrine secretion
Most common mode of secretion
Product released in vesicles by exocytosis
Mucus
2.
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Apocrine secretion
Involves loss of both cytoplasm and secretory product
Outermost portion of cytoplasm becomes packed with secretory vesicles and is the shed
3.
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Holocrine secretion
Entire sell becomes packed with secretions and then bursts apart and dies
 Sebaceous glands

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Exocrine glands can be categorized as serous, mucous or mixed
Serous Glands
 Watery solution containing enzymes
Mucous glands
 Secrete mucins that form a thick, slippery mucus
Mixed glands
 Contain both serous and mucous glands together

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All have three basic components:
1.
2.
3.
Specialized cells
Protein fibers
Fluid known as ground substance
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Protein fibers and ground substance form the matrix that surrounds the cells
Accounts for most of the volume of connective tissue

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Support and Protection
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Bony structural framework
Protect delicate organs
Transportation of materials
 Fluid connective tissues
Storage of energy reserves
 Adipose cells (fat)
Defense of the body
 Antibodies

1.
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Connective tissue proper
Many types of cells and matrix fibers in a ground substance
Tissue under skin, fatty tissue, and tendons and ligaments
2.
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Fluid connective tissues
Distinct cells in a watery ground substance with dissolved proteins
Blood and lymph
3.
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Supporting connective tissues
Matrix of dense ground substance and closely packed fibers
Cartilage and bone

 Some cells are “permanent residents,” and others are not always present because they leave to defend and repair areas of injured tissue

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Fibroblasts – most abundant cells
 Produce and maintain connective tissue fibers and ground substance
Macrophages – “big eater” cells
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Phagocytize damaged cells or pathogens
Mobilize immune system
Fat cells – adipocytes
 Large droplet of lipid that pushes nucleus and organelles to one side of the cell
Mast cells – found near blood vessels
 release chemicals to begin body’s defensive activities after an injury or infection
Antibodies, white blood cells and stem cells

1.
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Collagen fibers
Long, straight and unbranched
Strong and flexible, most common
2.
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Elastic fibers – contain protein elastin
After stretching return to original length
3.
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Reticular fibers – least common
Commonly form a branching, interwoven framework in various organs

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Fills spaces between cells and surrounds fibers
Clear, colorless and has consistency of maple syrup
 Slows movement of bacteria and other pathogens

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Areolar tissue
Contains all cells and fibers found in connective tissue proper
Extensive blood supply
Forms a layer that separates the skin from underlying muscles
 Provides padding and allowing movement

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Loose connective tissue containing large numbers of fat cells
Provides more padding and shock absorption for body
Insulation and energy storage

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Mostly collagen fibers
Two types: dense regular and dense irregular
Dense regular connective tissue
 Collagen fibers packed tightly, parallel to one another
 Tendons – attach muscle to bone
 Ligaments – attach bone to bone; often contain elastic fibers
Dense irregular connective tissue
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Interwoven network of collagen fibers
Provides support to areas subjected to stresses from many directions

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Blood and lymph
Proteins dissolved in watery matrix do not form fibers
Watery matrix is plasma in blood
 Red blood cell – makes up ½ of volume of blood
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 Transport oxygen
White blood cell – component of immune system
Platelets – cell fragments that function in blood clotting
Lymph forms as interstitial fluid enters small passageways, or lymphatic vessels
 Cells of immune system monitor the composition of lymph

 Cartilage and bone

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Matrix of a firm gel with embedded fibers
Chondrocytes – only cells found in matrix
 Live in small pockets called lacunae
Avascular – limits repair capabilities
Perichondrium
 Structure that separates cartilage from surrounding tissues

1.
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Hyaline cartilage – most common
Closely packed collagen fibers
Tough but flexible
Connects ribs to sternum, supports respiratory tract, and covers opposing bone surfaces
2.
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Elastic cartilage – numerous elastic fibers
Elastic flap of ear and epiglottis
3.
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Fibrocartilage – little ground substance, lots of collagen
Extremely durable and tough
Spinal column, between pubic bones and pelvis and in a few joints
Resist compression, absorb shocks and prevent damaging bone – bone contact

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Lacunae contain osteocytes (bone cells) and surround blood vessels
Canaliculi
 Branching network within bony matrix
Periosteum
 Covering of bone that has outer fibrous and inner cellular layers
 Table 4 – 3 page 105

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Form barriers or cover and protect structures and tissues
Four types:
1.
Mucous membranes
2.
3.
4.
Serous membranes
Cutaneous membranes
Synovial membranes

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 aka mucosae, line cavities that communicate with exterior
Kept moist at all times
Most lined by simple epithelia
 Also simple columnar, stratified squamous and transitional squamous
Line the digestive, respiratory, reproductive and urinary tracts

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Line the sealed, internal subdivisions of the ventral body cavity
Three kinds:
1.
Pleura – covering the lungs
2.
Peritoneum – lines organs of abdominal cavities
3.
Pericardium – covers the heart
Has parietal and visceral portions
Friction is reduced by water, serous fluid

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Skin
Covers surface of the body
Thick, relatively waterproof, and usually dry

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Joins or articulations are surrounded by a synovial membrane
Ends of bones are covered by hyaline cartilage and separated by viscous synovial fluid
Helps lubricate the joint and permits smooth movement

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Specialized for contraction
 Involves interaction between filaments of myosin and actin
Three types in the body:
1.
2.
3.
Cardiac
Skeletal
Smooth

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Contains large, multinucleated cells
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Are usually called muscle fibers
Produced through division of stem cells
Partial repairs can occur after injury
Marked by a series of bands called striations
Nervous system provides voluntary control over its activities
 Striated voluntary muscle

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Only found in the heart
Cells are interconnected at intercalated discs
 Specialized attachment sites containing gap junctions and desmosomes
Very limited ability to repair itself
Do NOT rely on nerve activity
 Specialized cells called pacemaker cells establish a regular rate of contraction striated involuntary muscle

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Walls of blood vessels, around hollow organs, and in layers around the respiratory, circulatory, digestive and reproductive tracts
No striations
Cells are able to divide
 Regenerate after injury
Nonstriated involuntary muscle

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Specialized for conduction of electrical impulses from one region of the body to another
Two types of cells:
Neurons – communicate through electrical events that affect their cell membranes
Neuroglia - provide physical support for neural tissue, maintain the chemical composition of the tissue fluids, supply nutrients to neurons and defend the tissue from infection

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Longest cells in your body (up to 39 in.)
Cannot divide – very limited ability to repair themselves
Contain three parts:
1.
Cell body – w/ large nucleus
2.
Dendrites – numerous branching projections
3.
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Axon – long and slender part, communicate with other cells
End at synaptic terminals

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Inflammation – area is isolated from healthy tissue while damaged cells are cleaned up.
 Swelling, warmth, redness and pain
Regeneration – second phase of following injury
 Fibroblasts produce dense network of collagen fibers known as
scar tissue or fibrous tissue
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Over time, scar tissue is remodeled and resumes normal appearance
Is more successful in some tissues than others
Permanent replacement of normal tissues is called fibrosis