4-1 Chapter 4 Histology: The Study of Tissues. 4-2 Tissue Level of Organization The classification of tissue types is based on the structure of cells;

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Chapter 4

Histology: The Study of Tissues

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Tissue Level of Organization

• The classification of tissue types is based on the structure of cells; the composition of noncellular substance surrounding cells (extracellular matrix) and the functions of the cells.

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Tissues and Histology

• Tissue Level of Organization– Epithelial – Connective– Muscle– Nervous

• Histology: Microscopic Study of Tissues

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Epithelium Characteristics

• Consists almost entirely of cells

• Covers body surfaces and forms glands

• Has free and basal surface

• Avascular• Undergoes mitosis

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Functions of Epithelia

• Protecting underlying structures

• Acting as barriers

• Permitting the passage of substances

• Secreting substances

• Absorbing substances

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Types of Epithelium

• Types of epithelium is based on the shape of the epithelial cells:

–Squamous: cells are flat or scale-like

–Cuboidal: cells are cube-shaped; about as wide as they are tall

–Columnar: cells are taller tan they are wide.

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Classification of Epithelium• Simple

– Squamous, cuboidal, columnar• Consists of a single layer of cells with each extending from the basement membrane to the free surface

• Stratified– Squamous, cuboidal, columnar

• Consists of more than one layer of cells, only one of which is attached to the basement membrane.

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Classification of Epithelium• Pseudostratified

–Columnar–Special type of simple epithelium–It appears to be stratified but it is not

(false – psuedo)–Consists of one layer of cells, with all

the cells attached to the basement membrane.

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Classification of Epithelium

• Transitional

–Cuboidal to columnar when not stretched and squamouslike when stretched

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Simple Squamous Epithelium

• Consists of a single layer of cells, with each cell extending from the basement membrane to the free surface.

• The nuclei appear as bumps when viewed as a cross section because the cells are so flat

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Simple Squamous Epithelium

• Function: diffusion, filtration, some protection against friction, secretion and absorption

• Location:lining of blood and lymphatic vessels (endothelium) and small ducts, alveoli of the lungs, loop of Henle in kidney tubules, lining of serous membranes (mesothelium) and inner surface of the eardrum.

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Types of Epithelium

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Simple Cuboidal Epithelium

• Cuboidal: cells are cube-shape; about as wide as they are tall.

• Single layer of cube-shaped cells, some cells have microvilli or cilia.

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Simple Cuboidal Epithelium

• Function: active transport and facilitated diffusion result in secretion and absorption by cells of the kidney tubules, secretion by cells of glands and choroid plexus, movement of particles embedded in mucus out of the terminal bronchioles by ciliated cells.

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Simple Cuboidal Epithelium

• Location: kidney tubules, glands and their ducts, choroid plexus of the brain, lining of terminal bronchioles of the lungs, and surface of the ovaries

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Types of Epithelium

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Simple Columnar Epithelium

• Single layer of tall, narrow cells. Some cells have cilia (in bronchioles of lungs, auditory tubes, uterine tubes and uterus) or microvilli (intestines).

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Simple Columnar Epithelium

• Function: movement of particles out of the bronchioles of the lungs by ciliated cells. It is partially responsible for the movement of the oocyte through the uterine tubes by ciliated cells. Secretion by cells of the gland, the stomach and the intestine. Absorption by cells of the intestine.

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Simple Columnar Epithelium

• Location: Glands and some ducts, bronchioles of lungs, auditory tubes, uterus, uterine tubes, stomach intestines, gallbladder, bile ducts and ventricles of the brain.

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Types of Epithelium

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Stratified Squamous Epithelium• Consists of more than one layer of

cells, only one of which is attached to the basement membrane

• Cells are cubodial in shape in the basal layer and progressively flatten toward the surface.

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Stratified Squamous Epithelium

• The epithelium can be moist or keratinized

• In most the surface cells retain a nucleus and cytoplasm.

• In keratinized stratified epithelium, the cytoplasm of cells at the surface is replaced by keratin, and the cells are dead

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Stratified Squamous Epithelium

• Function: protection against abrasion and infection.

• Location: moist-mouth, throat, larynx, esophagus, anus, vagina, inferior urethra, and cornea.

–Keratinized - skin

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Types of Epithelium

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Stratified Cuboidal Epithelium

• Multiple layers of somewhat cube-shaped cells.

• Function: secretion, absorption and protection against infection.

• Location: sweat gland ducts, ovarian follicular cells, and salivary gland ducts.

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Types of Epithelium

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Stratified Columnar Epithelium

• Multiple layers of cells, with tall, thin cells resting on layers of more cubodial cells. The cells are ciliated in the larynx

• Function: protection and secretion• Location: mammary gland duct,

larynx and a portion of the male urethra.

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Types of Epithelium

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Pseudostratified Columnar Epithelium

• Single layer of cells; some cells are tall and thin and reach the free surface and other do not. The nuclei of these cells are at different levels and appear stratified. The cells are almost always ciliated and are associated with goblet cells that secrete mucus onto the free surface.

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Pseudostratified Columnar Epithelium

• Function: synthesize and secrete mucus onto the free surface and move mucus (or fluid) that contains foreign particles over the surface of the free surface and from passages.

• Location: lining of nasal cavity, nasal sinuses, auditory tubes, pharynx, trachea and bronchi of the lungs.

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Types of Epithelium

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Transitional Epithelium

• Stratified cells that appear cubodial when the organ or tube is not stretched an squamous when the organ or tube is stretched by fluid.

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Transitional Epithelium

• Function: accommodates fluctuations in the volume of fluid in an organ or tube. Protection against the caustic effects of urine.

• Location: lining of the urinary bladder, ureter, and superior urethra.

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Types of Epithelium

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Cell Connections

• Functions– Bind cells together

– Form permeability layer

– Intercellular communication

• Types– Desmosomes

– Tight

– Gap

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Exocrine Glands

• Unicellular– Goblet cells

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Multicellular Exocrine Glands

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Exocrine Glands and Secretion Types

• Merocrine– Sweat glands

• Apocrine– Mammary

glands

• Holocrine– Sebaceous

glands

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Connective Tissue

• Abundant

• Consists of cell separated by extracellular matrix

• Diverse

• Performs variety of important functions

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Connective Tissue Cells

• Specialized cells produce the extracellular matrix–Suffixes

• -blasts: create the matrix• -cytes: maintain the matrix• -clasts: break the matrix down for remodeling

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Connective Tissue Cells

• Adipose or fat cells• Mast cells that contain heparin and

histamine• White blood cells that respond to

injury or infection• Macrophages that phagocytize or

provide protection• Stem cells

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Extracellular Matrix• Components

– Protein fibers• Collagen which is most common protein in body• Reticular fill spaces between tissues and organs• Elastic returns to its original shape after

distension or compression– Ground substance

• Shapeless background– Fluid

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Connective Tissue Categories

Adult– Loose– Dense– Connective tissue with special properties– Cartilage– Bone– Blood

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Functions of Connective Tissue

• Difficult to describe general properties of CT in the same way as epithelial tissue. 

• CT is so much more diverse. • Some of the characteristics may

not fit all of the CT types perfectly-- but they will fit most of them.

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Functions of Connective Tissue• Connective tissues are typically well-

vascularized • They can usually reproduce well (to

recover from injury)  • Exception:   They need a good

number of cells to help with this, and dense connective tissue has only sparse numbers of cells. they have a lot of noncellular material, called extracellular matrix material (or just matrix).

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Extracellular Matrix• The space between cells can be called

the extracellular space/material or the intercellular space/material. 

• "Extra-" means outside of, while "inter-" means between. We will use the term extracellular space to prevent other confusion

• That's because intercellular is easily confused with another term we will be using:  intracellular.  "Intra-" means within, and we will use intracellular to discuss what is inside the cell

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Extracellular Matrix• To the right, the extracellular space

is all in pink.   • The space is filled with material.  If

the material is only liquid, the tissue as a whole will be loose.  An example of that is in blood.  

• If the material in the extracellular space has some tough strands (called fibers) of protein in it, that gives the entire tissue a stronger consistency (because the cells are now sitting in a mesh of fibers).

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Ground Substance:• This is the liquid portion of the

extracellular matrix. 

• It is never entirely watery, but more gel-like. 

• A thin ground substance is seen in blood.   The ground substance is not just water, but it is also filled with many dissolved solute particles.

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Extracellular Matrix Fibers:

• The number, properties, and alignment of fibers in the extracellular matrix will help determine the properties of the connective tissue.  There are three main types of connective tissue fibers.  Two are made out of a protein called collagen, while the third is made out of a protein called elastin. 

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Extracellular Matrix Fibers:

• Collagen is a protein that forms a long strand.  If many of these strands are put together the large resultant bundle can be quite strong.  If only a few of these strands are intertwined, the small resultant bundle is only somewhat strong.  Collagen is has greater properties of strength than of elasticity. 

• Elastin, on the other hand, is not so strong, but has elastic properties.

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Extracellular Matrix Fibers:

• Reticular fibers:  Thin bundles of collagen. 

• They are very short, thin fibers that branch to form a network and appear different microscopically from other collagen fibers.

• Not as strong as most collagen fibers.

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Extracellular Matrix Fibers:

• Elastic fibers:  stretchy branching bundles of elastin.  Also called yellow fibers, because they tend to look yellower than collagen bundles do. 

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Extracellular Matrix Fibers:

• All of these types of extracellular matrix fibers can run together in different ways:

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Extracellular Matrix Fibers:

• as a mixture of fiber types mainly of one fiber type

                             OR

• loosely piled, with no one orientation

• densely piled, with no one orientation

• densely piled, all having the same orientation

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Connective Tissue Cell Types

• There are three main cell types in connective tissue.  These three cell types may appear in most of the types of connective tissue.  There are also cell types that are specific for certain connective tissues (and are only found there).

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The three main cell types are:

1. Fibroblasts

2. macrophages

3. mast cells

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fibroblasts

1. these important cells are the ones that lay down the extracellular matrix fibers! 

They tend to be elongate in

appearance

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macrophages

These cells are large and are derived from blood cells.  

A certain white blood cell can leave the blood and enter tissue, and is then called a macrophage. 

This cell is a scavenger in our connective tissues.  It chews up foreign particles in the tissue by phagocytosis, protecting and cleaning out our bodies.

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mast cells

these cells communicate chemically with our blood.

They signal our blood by releasing heparin and histamine, telling our blood when it should clot or allow inflammation of certain tissues. 

That means that these cells help begin a repair process, when needed, in tissue.

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Other cells that you may find in specific connective tissues are

1. osteocytes-- only found in bone

2. chondrocytes-- only found in cartilage (or developing bone)

3. adipocytes-- only found in adipose tissue for storing fat

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Other cells that you may find in specific connective tissues are

4. blood cells-- found only in blood (unless you are injured)

5. reticulocytes-- found only in reticular connective tissue.  Call them fibroblasts.

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If a connective tissue has plenty of cells within it, it is better at recovering after injury.  For example, if the skin is cut, and the dermis is thus cut, the mast cells will, of course, help get blood in the area to fill the hole left by the cut and then will also get the blood to begin clotting.  After that, however, we need to replace the clot with more dermis.

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This is possible because the fibroblasts in the remaining dermis begin dividing and secreting more fibers for the matrix.  As the fibroblasts make more dermal connective tissue, the macrophages start removing the clot.  And, voila!  The repair is done.

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If, however, a connective tissue has few cells (and/or blood supply is limited), it is more difficult to repair that connective tissue.  An example of this is in tendons and ligaments.

 It is difficult to repair tendons and ligaments after injury-- the healing time is much longer than for a broken bone

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Specific Types of Connective Tissue

•Loose connective tissue•Dense connective tissue•Cartilage•Bone

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Loose connective tissue

• It binds the skin to the underlying organs and fills spaces between muscles.

• This is composed of a mixture of collagenous and elastic fibers within the ground substance. 

• Fibroblasts, macrophages, and mast cells can be found within it.

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Loose Connective Tissue

• Also known as areolar tissue• Loose packing material of most organs and tissues• Attaches skin to underlying tissues• Contains collagen, reticular, elastic fibers and variety of cells

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Dense Connective Tissue• Dense regular

– Has abundant collagen fibers• Tendons: Connect muscles to bones

• Ligaments: Connect bones to bones

• Dense regular elastic• Ligaments in vocal folds

• Dense irregular• Scars

• Dense irregular collagenous• Forms most of skin dermis

• Dense irregular elastic• In walls of elastic arteries

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Dense connective tissue

• This tissue is made up of A LOT of fibers.  If it is regular dense connective tissue, it is mainly made up of parallel collagenous fibers.

• There is very little room for vascularization.

•   This is the type of tissue that makes up tendons and ligaments.

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Dense Regular Connective Tissue

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If it is irregular dense connective tissue, it is found making up the dermis of your skin. 

It has a lot of collagenous and elastic fibers

The fibers are not oriented in parallel bundles they are randomly arranged.

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Dense Irregular Connective Tissue

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Cartilage

• Composed of chondrocytes located in spaces called lacunae

• Next to bone firmest structure in body

• Types of cartilage– Hyaline– Fibrocartilage– Elastic

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Cartilage• This tissue contains chondrocytes,

and the extracellular matrix material was secreted by them. 

• They secrete a dense matrix, so dense that after they secrete it they end up stuck inside of it.

• There are different types of cartilage, each having its own appearance and elastic qualities.

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Hyaline Cartilage

• Found in areas for strong support and some flexibility– Rib cage and cartilage in trachea and bronchi

• Forms most of skeleton before replaced by bone in embryo

• Involved in growth that increases bone length

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Fibrocartilage

• Slightly compressible and very tough

• Found in areas of body where a great deal of pressure is applied to joints

– Knee, jaw, between vertebrae

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Elastic Cartilage

• Rigid but elastic properties

– External ears, epiglottis

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Connective Tissue with Special Properties• Adipose tissue

– Consists of adipocytes– Types

• Yellow (white)–most abundant, white at birth and yellows

with age• Brown

– found only in specific areas of body as axillae, neck and near kidneys

• Reticular tissue– Forms framework of lymphatic tissue– Characterized by network of fibers and cells

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Adipose Tissue

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Reticular Tissue

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Bone• Hard connective tissue that consists of living

cells and mineralized matrix

• Has an Organic and inorganic portion

• Types

– Cancellous or spongy bone

• Has spaces between trabeculae (plates of bones)

– Compact bone

• More solid (almost no space)

• Many thin layers

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Bone• This tissue contains osteocytes,

which are mature bone cells.  These cells also end up stuck inside the dense extracellular matrix that we think of as bone.  Because bone’s extracellular matrix is so dense, much more so than others, diffusion of nutrients through it is very difficult. 

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Therefore, osteocytes do not use diffusion to get their nutrients.  Instead, they extend tiny little processes to communicate with each other and with the blood; the development of these processes makes tiny little holes in the matrix, and these holes are called canaliculi.

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Cancellous Bone• Location: In the interior of the bones of

the skull, vertebrae, sternum and pelvis, also found in the ends of long bones.

• Structure: latticelike network of scaffolding characterized by trabeculae with large space between them filled with hemopoietic tissue. The osteocytes are located within lancunae in the trabeculae.

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Cancellous Bone

• Function: Acts as a scaffolding to provide strength and support without the greater weight of compact bone.

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Compact Bone• Location: Outer portions of all

bones and the shafts of long bones

• Structure: Hard, bony matrix predominates. Many osteocytes are located within lancunae that are distributed in a circular fashion around the central canals.

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Compact Bone

• Function: Provides great strength and support. Forms a solid outer shell on bones that keeps them from being easily broken or punctured.

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Bone

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Blood• Matrix between the

cells is liquid. Blood cells are free to move around

• Hemopoietic tissue

– Forms blood cells

– Found in bone marrow

• Yellow

• Red

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Blood

• Location: within the blood vessels. Produced by hemopoietic tissues. White blood cells frequently leave the vessels and enter the interstitial spaces.

• Structure: Blood cells and a fluid matrix.

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Blood

• Function: Transport oxygen, carbon dioxide, hormones, nutrients, waste products, ad other substances. Protects the body from infections and is involved in temperature regulation.

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Bone Marrow

• Location: within marrow cavities of bone. Two types: yellow marrow (mostly adipose tissue) in the shafts of long bones and Red marrow (hemopoietic or blood-forming tissue) in the ends of the long bones and in short, flat and irregularly shaped bones

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Bone Marrow

• Structure: Reticular framework with numerous blood-forming cells (red marrow)

• Function: Production of new blood cells (red marrow); lipid-storage (yellow marrow)

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Bone Marrow

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Muscle Tissue

• Characteristics– Contracts or shortens with force– Moves entire body and pumps blood

• Types– Skeletal

• Striated and voluntary

– Cardiac• Striated and involuntary

– Smooth• Nonstriated and involuntary

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Skeletal Muscle

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Cardiac Muscle

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Smooth Muscle

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Nervous Tissue

• Found in brain, spinal cord and nerves

• Ability to produce action potentials

• Cells– Nerve cells or neurons

• Consist of dendrites, cell body, axons

• Consist of multipolar, bipolar, unipolar

– Neuroglia or support cells

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Neurons

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Neuroglia

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Membranes• Mucous

– Line cavities that open to the outside of body

– Secrete mucus

• Serous– Line cavities not open to

exterior• Pericardial, pleural,

peritoneal

• Synovial– Line freely movable joints

– Produce fluid rich in hyaluronic acid

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Inflammation• Response when tissues

damaged or with an immune response

• Manifestations– Redness, heat, swelling,

pain, disturbance of function

• Mediators– Include histamine, kinins,

prostaglandins, leukotrienes

– Stimulate pain receptor and increase blood vessel permeability

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Tissue Repair• Substitution of viable cells for dead cells• Skin repair

– Primary union: Edges of wound close together• Wound fills with blood

• Clot forms

• Scab

• Pus

• Granulation tissue

• Scar

– Secondary union: Edges of wound not close• Clot may not close gap

• Inflammatory response greater

• Wound contraction occurs leading to greater scarring

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Tissue Repair

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Tissues and Aging

• Cells divide more slowly in older than younger people

• Tendons and ligaments become less flexible and more fragile

• Arterial walls become less elastic

• Rate of blood cell synthesis declines in elderly

• Injuries are harder to heal in elderly