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BIOL 237Human Anatomy

& Physiology I

© Jim Swan

These slides are from class presentations, and assigned reading. The content contained in these pages is also in the upcoming text: Human Anatomy and Physiology for the Health Sciences, A Focused Approach, by Jim Swan. If you are viewing this in Adobe Reader version 5 or above, and are connected to the internet you will also be able to access the “enriched” links to notes and comments, as well as web pages including animations, videos, and audio files.

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The Scope ofAnatomy & Physiology

Structure Function

Complementarity – the complementary and deterministic relationship between structure and function.

Complementarity is one of several broad principles essential to the study of biology in general and the human body in particular. It means that the structure and function of biological components determine one another. Complementarily is seen at all levels of biological hierarchy, from the cilia which allow cells to move fluid along the cell surface, to the different orientations of the elbow & knee joints which permit their different functions. Identify examples of complementarily in the tissues and organ systems you have studied so far.

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Structural Hierarchy of Living Organisms:

System-

Organ -

Tissue-

Cell-Simplest structure which can perform all living functions.

Cells working together to perform certain specific functions.

Tissues working together to perform specific functions.

Organs working together to perform specific functions.

specificity division of

labor

Living organisms are arranged in a hierarchy which facilitates division of labor for efficiency. According to the cell principle all living organisms are made up of cells. There is disagreement among biologists about the structures and functions necessary to qualify living organisms. By the qualities identified here, viruses are not alive! Many biologists would revise the definition of life to include viruses and possibly other structures such as prions. Think about how you would define life. By your definition, would viruses and prions be considered living? Explain your conclusion.

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The Functions of Life:

1. Maintaining boundaries and integrity of the organism.

2. Movement

3. Responsiveness, irritability, excitability

4. Intake of nutrients and digestion

5. Metabolism

6. Excretion

7. Growth and repair

8. Reproduction

Not all biologists subscribe to the cell principle for determining life, nor do all agree on the functions all living organisms must perform. But here is a list of functions which most agree characterize living organisms.1. - illustrated at the cellular level by the cell membrane and at the organism level by the skin. Other boundaries include all the semipermeable membranes in the body such as the walls of capillaries, and the linings of the gastrointestinal tract.2. - includes molecular transport, as in the exchange of nutrients and wastes by diffusion, and movement of the body or its parts. 3. - includes chemical, electrical, and physical responses to stimuli. Exemplified by chemical events at cell membranes and nervous control of muscle contraction and other body functions. 4. - all organisms must take in nutrients and process them. Nutrients include necessary gases such

as oxygen or carbon dioxide. 5. - the sum of energy producing and energy utilizing chemical reactions. Metabolism converts the

energy in nutrients to usable forms and couples that process with energy-requiring processes. 6. - removal of waste products which result from metabolism as well as toxic substances from other sources. 7. - organisms must be able to grow to maturity and to maintain and repair damaged tissue in order

to survive.

8 i t b bl t d i d t t t th i

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Homeostasis

-a dynamic balance of processes and materials in the internal environment;

- the ability to respond to stress to maintain balance.

constant, the same

steady

Homeostasis is the fundamental outcome of physiology. The body’s physiological processes act to maintain homeostasis and return to homeostatic balance after a stress or change occurs. Inability to maintain homeostasis over the long term results in death.

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Most homeostatic mechanisms utilize a control system known as negative feedback. Negative feedback works like a thermostat. A sensor responds to a variable stimulus. When that variable is outside the normal range the sensor notifies a control center, which then responds directly or triggers a response by an effector. The response has the effect of reducing or negating the original stimulus by bringing the variable back within the normal range. A negative feedback mechanism is self regulating, it turns itself off.

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7© 2006 Jim Swan

CO2Medulla oblongata

Carotid sinus

CO2

Respiratory Control

in blood

in blood

A good example of negative feedback is the control of respiration. The stimulus for controlling respiration is the level of carbon dioxide (CO2) in the blood. The sensors are located in the brain and in the carotid artery. They pick up an increase in CO2, such as might result from exercise. Input is sent from these receptors to the respiratory center, which sends stimuli to the respiratory muscles to increase respiration. Increasing respiration eliminates more CO2 from the blood and brings its level back to normal. When the level returns to normal the response, an increase in respiration, returns to normal too. A negative feedback mechanism is self regulating, it turns itself off.

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Positive Feedback

Positive feedback increases the original stimulus. It is used in certain situations to produce a rapid buildup of response.

Positive feedback is not self-regulating. Some external event is necessary to turn the response mechanism off.

Examples: blood clotting, labor (birth), digestion in the stomach.

Very few processes in the body involve positive feedback and those that do use it to produce a quick response. Some external mechanism is necessary to turn off the process. Examples of positive feedback include: blood clotting, the labor contractions of childbirth, digestion in the stomach.

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Four Basic Tissue Types:

Epithelial – lining and secretory tissue

Connective – supportive and nutritive tissue

Muscular – contracts to produce movement

Nervous – integration and control

Now that we have examined some basic principles important to human anatomy and physiology, we will apply these principles to the human body. You already know about cells and their characteristics from biology. Cells group themselves together into tissues. A tissue is a group of cells working together to perform one or more specific functions. There are four tissue types in the human body.

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The study of embryology shows us how the tissues arise. Understanding embryological development will help in understanding the functional relationships between the various cells and tissues. Here are some basic concepts:The primitive streak develops at about 15 days as the embryo begins to form. It's cells develop into the mesoderm and migrate to the interior of the embryo. Ectoderm forms: epidermis related structures and glands; the lining of the mouth, salivary glands, nasal passageways and anus; The nervous system including the brain and spinal cord; pituitary gland and adrenal medulla; the skull, pharyngeal arches, teeth. Mesoderm forms: dermis of the skin; lining of the body cavities; muscular, skeletal, cardiovascular and lymphatic systems; kidneys and part of the urinary tract; gonads and reproductive tracts; supportive connective tissues; adrenal cortex, reproductive endocrine tissue. Endoderm forms: most of the digestive system, liver, and pancreas; most of respiratory system; parts of urinary and reproductive systems; thymus gland, thyroid gland, parathyroid glands and pancreas.

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Characteristics of Epithelial Tissue

• Closely packed cells of a mostly uniform type

• Cells attached to a basement membrane

• Cells are joined by a junctional complex

•Tight junctions

• Desmosomes

• Gap junctions

The basement membrane consists of a basal lamina made of glycoprotein (similar to the glycocalyx on the apical surface) and a reticular lamina made of collagen.

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Tight junctions

Hemidesmosomes

Actin microfilaments

Keratin filaments

nucleus

Intercellular space

Desmosome

Desmosome

Gap junction

Adherens Junction

Epithelial cells, as well as certain muscle and connective tissue cells, have specialized connections between them, called a junctional complex. The junctional complex can be any combination of the junctions shown, each of which has a specific function.

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Tight Junctions

Diffusion between cells occurs through intercellular clefts.

Zona occludensAttached cells function as a

semipermeable membrane.

Attached cells function as a

semipermeable membrane.

Tight junctions, a.k.a. zona occludens, are most important in restricting transport between cells which form a semipermeable membrane, for instance in the wall of a capillary. They are composed of junctional proteins which run from the cell membrane of one cell to the cell membrane of the next cell. Tight junctions are not important in structural support. They vary somewhat in how "tight" they are depending on the extent and complexity of the fusions. Intercellular clefts are passageways through the tight junctions which allow water and small molecules to pass between cells in some locations (e.g. in the kidneys), while others allow very little to pass between them (e.g. in the brain).

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Keratin filaments Desmosomes

Hemidesmosome

Adherens junction(Zona adherens)

Actin filaments

Anchoring Junctions

a.k.a macula adherens - resist lateral stress, e.g. epidermis, urinary bladder.

a.k.a macula adherens - resist lateral stress, e.g. epidermis, urinary bladder.

Reticular lamina

Basal lamina

Desmosomes contain keratin filaments which run from one cell to the next, somewhat analogous to rebar used in building construction. These filaments often run across the cell laterally and are important in tissues where the cells are subjected to lateral stress, such as the skin or lining of the urinary bladder. Desmosomes are also known as macula adherens and are like spot welds between adjacent cells (macula is Latin for 'spot'). Hemidesmosomes (half-desmosomes) are small bundles of keratin filaments which anchor the basal membrane of an epithelial cell to the underlying connective tissue. There are also zona adherens (adherens junctions) which are more continuous adhesions composed of joining proteins that anchor cells to one another near the apical end. These molecules, known as cell adhesion molecules (CAMS) are called catenins and cadherin and also connect to the actin microfilaments of the cell's cytoskeleton.

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Gap Junctions

Gap junctions contain “connexons” which allow electrolytes to pass from one cell to another.

Gap junctions have channels called "connexons" which allow ions and, therefore, electrical impulses to pass from one cell to the next. Gap junctions are found in many tissues, but the best examples are 1) between cardiac muscle cells in the heart and smooth muscle cells in the intestine, and 2) between osteocytes in lamellar bone.

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The Epithelial cell

The Apical (free) surface

The basal surface

microvilli

Reticular lamina

Basal lamina

All epithelial tissues are attached to a basement membrane along a basal surface. The free or apical surface is open to the environment. The basal surface of all epithelium has a basement membrane. The basement membrane is composed of: 1) basal lamina – a “glue” similar to the glycocalyx, 2) reticular lamina – primarily collagen fibers which attach the cell to underlying connective tissue.

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Epithelium is named according to shape, structure, and arrangement of cells.

Shapes of Epithelium

•squamous - thin and flat cells

•cuboidal - cube shaped cells

•columnar - column shaped cells

The nuclei of epithelial cells varies in shape from one type to another. Nuclear shape and location can be important is differentiating some types of epithelial tissues. The shape and structure of epithelial cells has a complementary relationship with the function.

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Arrangement of Epithelial Cells•simple - single layer of cells

•stratified - multilayered cells

•pseudostratified - false stratified

•transitional – stretchable

•ciliated - cells possess cilia

In simple epithelium every cell has an apical and a basal surface, which is attached to the basement membrane. In stratified epithelium only the lowermost (basal) layer is attached to the basement membrane, and only the outermost layer has an apical surface.

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Simple Squamous Epithelium

Basementmembrane

Epithelium wraps to form tubes such as capillaries and alveolar sacs. The basement membrane remains on the outside.

Blood capillary

Simple squamous epithelium is the thinnest tissue in the body, often used where a semipermeable membrane allows transport, e.g. the respiratory gases across the alveolar membrane in the lungs, and gases, nutrients, wastes, and other molecules across capillary walls. Molecules can be transported through the intercellular clefts within the tight junctions, or through the epithelial cells themselves.

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Mesothelial Lining of Peritoneal Cavity

nucleus

cytoplasm

Plasma membrane

Simple squamous epithelium is also the epithelial tissue found in the membranes which line the peritoneal cavity and cover organs within the peritoneum. The peritoneum secretes mucus which acts as a lubricant and prevents tearing and abrasion as the organs move and shift. This tissue also forms the mesenteries which attach between abdominal organs to serve the same purpose.

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Functions of Simple Squamous Epithelium

• The thinnest tissue of the body.

• Forms semipermeable membranes in lungs and capillaries.

• Secretes serous fluid in serous membranes (e.g. pericardial and pleural membranes, mesenteries).

• Lines cardiovascular system, covers organs, forms glomerular capsules in kidney.

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Nucleus of simple squamous cell

Edgewise view of simple squamous cell

Bowman’s Capsule in the Kidney

capillaries

Simple squamous cells are so thin their nuclei are thicker than the rest of the cell. But the cells of the outer layer of Bowman’s capsule produce a wall which contains fluid filtering out of the capillaries.

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Simple Cuboidal Epithelium

Forms ducts, tubules and secretory cells in exocrine glands and in organs such as the kidney.

Basement membrane

Tissue wraps to form tubules and ducts of glands.

Tissue wraps to form tubules and ducts of glands.

Cuboidal epithelium forms the secretory units and ducts of most glands. A sheet of cuboidal epithelium will wrap to form an acinus (L. grape, ăs'ĭ-nŭs), a semicircular or circular group of secretory cells surrounding a cavity. The cavities from these groups unite to form the ducts of exocrine glands. When the sheet of epithelium wraps the basement membrane remains as an outer connective tissue covering of the duct or glandular tubule.

http://classvideos.net/anatomy/mp3/237histology23-5.mp3

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Convoluted Tubules of the Kidney

Nucleus of cuboidal cell

Lumen of tubule

The Virtual Microscope: http://webanatomy.net/microscope/microscope.htm

You are looking at numerous tubules scattered throughout the cortex (outer layer) of the kidney. These tubules appear as various shapes depending on their orientation to the plane of the section. The cuboidal epithelial cells make up the structure of the nephron tubules which perform the functions of the kidney in getting rid of wastes and retaining the substances you need to keep.

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Simple Columnar EpitheliumApical surface may have microvilli or cilia

Apical surface may have microvilli or cilia

Cell nuclei lie toward basal surface

Goblet cells secrete mucus

Columnar epithelium comes as short and tall columnar cells and lengths in between. Nuclei occur closer to the basal layer of the cells. It is non-ciliated in the GI tract, e.g. stomach and intestinal lining, ciliated in portions of the respiratory and genitourinary tracts. Columnar epithelium which is found in a mucous membrane has specialized goblet cells which secrete mucus, a protective and lubricating substance.

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Simple Columnar Epithelium in the Small Intestine

nucleus

Goblet cell

Lamina propriavillus

Villi are finger-like projections which line the small intestine. They are covered with simple columnar epithelial cells interspersed with goblet cells. The goblet cells secrete mucus which helps protect the GI lining from acid. Within the villi, beneath the epithelial layer, is a connective tissue called the lamina propria which contains capillaries and lymph vessels.

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Ciliated Simple Columnar Epithelium

Ciliated simple columnar is found in large bronchioles of the respiratory tract and in the genitourinary tract.

Link online to a video clip of ciliary action

Ciliated epithelia are found in locations such as the respiratory and genitourinary tract where the cilia beats in waves to move fluid along the passageways.

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Ciliated Simple Columnar of Fallopian Tube

cilia

Ciliated simple columnar cells

lumen

nucleus

connective tissue

In the female reproductive tract ciliary movement is used to transport the a fertilized egg down the fallopian tube.

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Pseudostratified Ciliated Columnar Epithelium (PCCE)

A non-ciliated pseudostratified epithelium is found in large glands and parts of male urethra.

A non-ciliated pseudostratified epithelium is found in large glands and parts of male urethra.

cilia

Nuclei

Primary lining of the Respiratory

tract

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P.C.C.E. in the Trachea

P.C.C.E.

Lumen of Trachea

nucleuscilia

Goblet cell

Basal cell

As in most all epithelia, basal cells undergo mitosis to produce new cells so that the

epithelium constantly exfoliates and is renewed.

Goblet cells are named based on their shape, like a glass goblet, with a wide mouth and a narrow base.

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Transitional Epithelium

Transitional epithelium lines the urinary tract where it provides stretchability.

4-5 cell layers non-distended3 cells stretched

basement membrane

Transitional epithelium lines the renal calyces, the ureters, the urinary bladder, and a portion of the urethra. Distension reduces the number of cell layers from 4 or 5 to 3. In the urinary bladder transitional epithelium allows expansion to accommodate increased urine, and in the ureters stretchability helps prevent excessive pressure on the kidneys when urination occurs.

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Stratified Squamous Epithelium

Basal layer

Intermediate layers

Cornified layer

Stratified squamous epithelium forms the outer layer or epidermis of the skin. Skin is found as the organ of the integument and also as the lining of the oral cavity, esophagus, anus and vagina. In the body’s external skin the epidermis is keratinized, i.e. the outer cells are impregnated with keratin which helps to produce a waterproof, protective layer. In the internal skin which lines cavities this keratinization is not present.

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Stratified Squamous in the Epidermis of the Skin

Flattened, cornified cells cover the surface as the stratum corneum.

epidermis of stratified squamous epithelium Stratum basale cells constantly

undergo mitosis.

dermis

In keratinized skin the outer layer of the epidermis becomes impregnated with keratin and the cells lose their living components. The cornified layer is a protective layer of dead cells.

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Non-keratinized Stratified Squamous Epithelium

Section of vaginal wall.

squamous surface cell

Stratified squamous epithelium

Connective submucosa

Non-keratinized skin is found in locations which are kept moist by secretions, such as the esophagus, mouth, anus, and vagina. Notice how the cells of the intermediate layers of the stratified squamous epithelium do not flatten and loose their nucleus as they do in keratinized epithelium (previous slide).

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Characteristics of Connective Tissues

• widely spaced cells – consist of various types

• intercellular matrix – a.k.a. ground substance

* These tissues are sometimes classified as

• connective tissue proper or true connective tissue

• cartilage and bone tissue.

*

Connective tissues are supportive tissues and are derived from mesenchyme stem cells, a product of the mesoderm. The cells of connective tissue are not usually close together and have a fluid intercellular matrix between them. The term extracellular matrix (ECM) can also be used, but usually is applied to the attachments of cells, including other cell types, not just those in connective tissues.

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Intercellular matrix components:

•loose or dense structure

•fibers - may be collagen (inelastic), elastin (elastic), or reticular.

• ground substance - a semiliquid containing water, glycoproteins, and other substances

The matrix may be loose, dense, or have other specialized characteristics, it may have one or more types of fiber, and has a ground substance with semi-solid to fluid gel or other materials. All of these features determine the structure and function of the variety of these tissues found throughout the body.

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Types of Fibers

• collagen fibers - high tensile strength with some flexibility found in inelastic types of tissues.

Collagen is actually a glycoprotein formed into a triple helix (called a fibril), and is found in as many as 19 different varieties in various tissues in the body.

Collagen is actually a glycoprotein formed into a triple helix (called a fibril), and is found in as many as 19 different varieties in various tissues in the body.

Collagen is braided, like a rope, to provide non-stretchable strength for tissues such as tendons, ligaments, etc.

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Types of Fibers (Contd.)

• elastic fibers - provide organs and tissues with the ability to stretch and recoil.

•Elastic fibers are thin and interwoven with collagen fibers to prevent tearing. Elastic fibers are made of the protein elastin (randomly coiled and covalently bound to form an elastic matrix), and glycoprotein microfibrils, formed into a cross-linked network within the tissue.

•Elastic fibers are thin and interwoven with collagen fibers to prevent tearing. Elastic fibers are made of the protein elastin (randomly coiled and covalently bound to form an elastic matrix), and glycoprotein microfibrils, formed into a cross-linked network within the tissue.

Elastic tissue is found where stretchability is important, such as the walls of arteries, and the internal support of the lung.

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Types of Fibers

• reticular fibers - made of the same molecules as collagen but thinner, they form an internal mesh-like network within organs.

• produces an endoskeleton or stroma for soft organs such as the spleen, liver, etc.

• produces an endoskeleton or stroma for soft organs such as the spleen, liver, etc.

Organs which are primarily composed of epithelial cells need an internal support to maintain shape and structure. They achieve this with an endoskeleton or stroma of reticular tissues.

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The Intercellular Matrix

• ground substance: a viscous, clear substance with a high water content

• composed of proteoglycans which are made of a protein core with attached glycosaminoglycans or GAGs.

Important GAGs are hyaluronic acid, chondroitin sulfate, heparan sulfate, keratan sulfate (produces keratin).

Important GAGs are hyaluronic acid, chondroitin sulfate, heparan sulfate, keratan sulfate (produces keratin).

The proteins fibronectin and laminin may also be part of the extracellular matrix. These are cell adhesion molecules (CAMS) which help to attach cells, connective as well as other types of cells, to the intercellular or extracellular matrix. They also have proven important in the movement of cells during embryonic development as well as in metastasis.

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A Proteoglycan

A proteoglycan from cartilage matrix actually contains about 30 keratan sulfate and 100 chondroitin sulfate chains

Keratan sulfate

Chondroitin sulfate

Core protein

Glycosaminoglycan chains (GAGs)

Most everyone has heard of chondroitin, glucosamine, and other glycosaminoglycans (GAGs). These are composed of molecules very similar in structure to disaccharides, with attached radicals containing nitrogen and sulfur. GAGs are the building blocks of proteoglycans which are the primary functional components of the intercellular matrix of connective tissues.

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Proteoglycan Complex

In the cartilage matrix, individual proteoglycans (in box, from before) are linked to a non-sulfated GAG, hyaluronic acid, to form a giant complex with a molecular mass of about 3,000,000. The box indicates one of the proteoglycans of the type shown in previous slide.

Hyaluronic acid.

Hundreds of proteoglycans (one is indicated by the green box) are attached to a central molecule called hyaluronic acid, also a GAG. Altogether this produces a proteoglycan complex, huge molecules which can actually be seen in the [electron microscope].

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• fibrocytes, or other generic cell for each tissue.

Cells Found in Connective Tissues

osteocytes for bone, chondrocytes for cartilage, adipocytes for adipose, etc.

osteocytes for bone, chondrocytes for cartilage, adipocytes for adipose, etc.

fibroblast - cell active in secreting the matrix. -clast (e.g. Osteoclast) a cell active in dissolving the matrix. -cyte is a mature cell.

fibroblast - cell active in secreting the matrix. -clast (e.g. Osteoclast) a cell active in dissolving the matrix. -cyte is a mature cell.

Fibrocyte (also fibroblast) - the generic or characteristic cell for each type of connective tissue. In the loose and dense tissues the name fibrocyte or fibroblast is used depending on the predominant action and stage of development of the cells. A fibroblast is actively secreting matrix, usually in growing tissue, while a fibrocyte is a mature cell, no longer active in building tissue, but still important in maintenance and managing homeostasis. The same designation is used for cells in other connective tissues, e.g. osteocytes and osteoblasts in bone, chondrocytes and chondroblasts in cartilage. A cell designated as a -clast is dissolving the matrix. For instance osteoclasts are important in bone remodeling by breaking down old matrix before it is replaced. These cells come from a different cell line than the -blasts and -cytes.

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• fibrocytes, or other generic cell for each tissue.

•Macrophages and other phagocytic cells.

• mast cells - like basophils in the blood, these cells secrete histamine and heparin which mediate inflammatory responses.

• plasma cells - a type of lymphocyte, they secrete antibodies.

Cells Found in Connective Tissues (contd.)

In addition to fibrocytes:macrophages - phagocytic cells derived from monocytes which are part of the body's first line of defense against invading microorganisms. These cells have a variety of names depending on the tissue such as histiocytes (lungs), Kupffer cells (liver), Langerhans cells (skin), microglia (nervous tissue). mast cells - similar to basophils in the blood, they play a role in inflammatory reactions by secreting histamine and heparin. Plasma cells – are activated lymphocytes which are actively producing antibodies against foreign antigens.

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Areolar Tissuethe Prototype Connective Tissue

Collagen fiber

Elastic fiber

Reticular fiber

Fibroblast

Macrophage

Plasma cell

Figure 4.7

Areolar is called the “prototype connective tissue” because it contains all the components such as fibers, cell types, ground substance, etc. typical of true connective tissues.

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Collagen fibers

Elastic fibers

Fibroblast

Mast cell

Reticular fibers

Found in outer dermis of skin, interstitial tissue, mesenteries and serous membranes.

Found in outer dermis of skin, interstitial tissue, mesenteries and serous membranes.

Areolar Tissue

Areolar, also known as loose connective tissue, is the most abundant connective tissue and is found in outer dermis of skin, interstitial tissue, mesenteries and serous membranes.One of its main functions is to contain blood vessels and nerves which serve nearby tissues and its spaces contain most of the bodies extracellular fluid.

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Reticular fibers

Fibroblast

Collagen fibers

Elastic fibers

Here is a photomicrograph of areolar tissue such as you will see in slides in the anatomy lab. Photomicrographs of relevant tissues such as this are available on the [Virtual Microscope].

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Adipose TissueLow Power

arteriole

Adipocytes

Connective matrix

Insulation and shock absorption; fatty pads around organs, subcutaneous fat.

Insulation and shock absorption; fatty pads around organs, subcutaneous fat.

Sometimes considered a specialized connective tissue rather than connective tissue proper, adipose is an exception to the general characteristics because its cells are closely packed and it has little matrix. The adipose cells store lipid in a large vacuole which fills each cell. Adipose is important for shock absorption and insulation and is found around many organs such as the heart, eyes, kidneys, spleen etc. as well as under the skin and in the medullary canal of long bones. Subcutaneous fat is a major stored fuel for aerobic activities. Adipose is also found associated with the serous membranes of the body.

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Adipose Tissuehigh power

nucleus of adipocyte

capillary

venule

nucleus of adjacent

fibroblast

Fat cells are virtually filled by the large lipid vacuole. This requires their nuclei and other organelles to be pressed against the plasma membrane, appearing sometimes as if they were outside the cell.

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Plasma membrane

Nucleus

Lipid vacuole

The cell membranes are just barely visible in this photomicrograph.

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Dense Irregular Connective Tissue

Nuclei of fibroblasts

Collagen fibers

High power

Low power

Found in the deep dermis of the skin and in the submucosa of the hollow organs.

Found in the deep dermis of the skin and in the submucosa of the hollow organs.

Dense irregular c.t. has few cells, mostly fibroblasts, and many fibers, principally collagen, arranged in an irregular pattern to provide strength and withstand stresses to which the organ may be subjected. It makes up the deep layer of the skin's dermis, and it produces the supporting submucosa of the hollow organs (e.g. GI tract), and the capsules of synovial joints.

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Dense Regular(Fibrous Connective Tissue)

collagen fibers

nuclei of fibroblasts

Found in tendons, ligaments, and fascia.

Found in tendons, ligaments, and fascia.

Tendon, l.s.Tendon, l.s.

Also known as fibrous or inelastic connective tissue, dense regular connective tissue forms the structure of tendons, ligaments, aponeuroses, fascia, and fibrous joints. It has almost entirely collagen fibers (certain ligaments, called elastic ligaments, have more elastic fibers) in densely packed arrays, with rows of cells between the fiber bundles.

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Elastic Connective Tissue

elastic fibers fibroblasts

Found in the stroma of the lungs and in the walls of the large arteries.

Found in the stroma of the lungs and in the walls of the large arteries.

Arterial wall

Arterial wall

Elastic connective tissue is found in the walls of the large arteries and in the stroma of the lungs and sparingly in certain elastic ligaments (e.g. those of the spinal column). It makes the arteries flexible to absorb the pulse pressure, and gives the lungs their recoil.

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Reticular Connective Tissue

High power

fibroblast

lymphocyte

reticular fibers

Forms the internal stroma of the soft organs such as the spleen and lymph nodes.

Forms the internal stroma of the soft organs such as the spleen and lymph nodes.

Section of

lymph node

Section of

lymph node

Reticular tissue is found as the internal support (stroma) of the kidneys, spleen, liver and many other soft organs. Has reticular fibers only.

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Cartilage

• intercellular matrix is more solid and gel-like, providing both flexibility and support

• cells located in spaces, the lacunae

• transport through matrix is slow (think of Jello) and tissue is avascular

• has the same types of fibers as other connective tissues.

Cartilage is considered a specialized connective tissue and not connective tissue proper. It has semisolid gel made principally of the glycosaminoglycans chondroitin sulfate and hyaluronic acid. The gel gives the cartilage a distinct shape, lots of water turgor, and flexibility. Cells in cartilage are found within spaces called lacunae. The lacuna allows the cell to be bathed in fluid from which itreceives nutrients and gets rid of wastes by diffusion. Substances diffuse very slowly through the gel and cartilage itself is avascular.

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Hyaline Cartilage

perichondrium

lacuna

chondrocytes

ground substance

Hyaline cartilage has organic collagen fibers but they are very finely divided and cannot be seen in the light microscope. Staining gives the matrix a texture which is referred to as the ground substance. Hyaline is the most common type of cartilage, found in the nose, attached to the ribs, as articular cartilage, and as the cartilage model for bone development. Cartilage has a fibrous covering called the perichondrium.

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Ground substance

Chondrocyte

Lacuna

The ground substance in hyaline cartilage stains because of the presence of very fine fibers, yet these fibers are not themselves visible.

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Elastic Cartilage

elastic fibers

chondrocytes

Epiglottis and the external ear

Epiglottis and the external ear

elastic cartilage - has dense bundles of elastic fibers and is rare, found only in the epiglottis and ear. Think about the difference in flexibility between the nose, made of hyaline cartilage, and the ear, made of elastic cartilage.

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Lacuna

Chondrocyte

Elastic fibers

The dark blue strands are the elastic fibers, found between the chondrocytes in their lacunae.

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Fibrocartilage

Intervertebral Disks and Pubic Symphysis,

The menisci of the knee

Intervertebral Disks and Pubic Symphysis,

The menisci of the knee

lacuna

chondrocytes

collagen fibers

fibrocartilage - has dense bundles of collagen fibers, it is the major component of the intervertebral disks and the symphysis pubis.

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Lacuna

Chondrocyte

Inelastic fibers

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Vascularization and Tissue Repair

There are two types of repair:

• functional or parenchymal repair in which the function of the replaced cells continues – usually refers to epithelial tissue.

• stromal repair or scar tissue in which fibrous tissue knits the damaged parts together but doesn't perform the tissues original function – occurs in connective tissue and muscle.

The ability of tissues to repair themselves is related to their blood supply. Tissues well supplied with blood capillaries can usually exhibit functional and rapid repair compared with poorly supplied tissues.

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Degree of Vascularization and RepairEpithelial tissue – continual replacement and functional repair; supplied with blood vessels from adjacent areolar tissue.

Bone tissue – well vascularized, constantly remodeled and replaced.

Areolar tissue – well vascularized, repairs via scar tissue

Adipose tissue – well vascularized, grows and repairs.

Dense regular and reticular c.t. – poorly vascularized, repaired with scar tissue.

Cartilage – avascular, scar tissue repair

Epithelial tissue generally exhibits functional repair. Most epithelial tissues exhibit rapid mitosis and the original function is normally retained. Although the tissue itself has no blood vessels, vessels are a short distance away in the supporting connective tissue which is usually areolar. Epithelial tissue in the skin, in the linings of organs in the GI and respiratory tracts, in the liver, many glands, and in blood vessels can all replace and repair themselves, the limiting factor generally being the degree of damage and other nutritive and health factors. Connective tissues with two notable exceptions have poor vascularization and therefore slow repair and replacement. And the repair of connective tissues (notwithstanding the two exceptions) is stromal repair, scar tissue which binds the organ but is not the same as the original tissue. The two exceptions are areolar, which is the route for blood supply in the skin and in many internal organs, and bone, which is richly supplied with blood vessels.

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Epithelial Membranes (Organ Membranes)

• Composed of epithelial tissue in combination with connective and, sometimes, smooth muscle tissue.

• Form the functional part of tubular organs in the gastrointestinal, respiratory, and genitourinary tracts.

Epithelial membranes are called organ membranes because they are organs in their own right, composed of two or more different tissues which work together to perform specific functions. In some cases, such as the GI tract, the membrane is, in fact, the organ.

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Serous Membranes

• squamous epithelium and areolar, dense irregular, or fibrous connective tissue

• secretes serous fluid as a lubricant

• locations:

peritoneal lining and covering of organs

mesenteries which attach to abdominal organs

pleural membranes, pericardial membranes

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peritonealcavity

liver

pancreas

duodenum

small intestine

mesentery

greateromentum

lesseromentum

transversecolon

rectum

urinary bladder

uterus

vagina

Mesenteries Greater omentum

colon

Small intestine

mesentery

Mesenteries are double-layered serous membranes which attach to the loops of intestine, the stomach, and other abdominal organs. The serous fluid, together with the fat present, act as lubricants to prevent tearing and abrasion as these organs move within the cavity. The greater and lesser omenta are large fatty mesenteries which protect the organs. Similar double-layered membranes surround the heart as the pericardium, and the lungs as the pleural membranes. The peritoneal membranes line the peritoneal cavity and cover the organs.

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The Mesenteries

Seen here is a loop of bowel attached via the mesentery.

The mesenteries help to connect and support portions of the GI tract, as well as to lubricate against damage from friction and abrasion when the organs move. Note the glistening surface due to the serous fluid secreted, as well as the numerous blood vessels which enter the bowel.

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Mucous Membranes

• Epithelium combined with areolar or dense irregular and smooth muscle

• Specialized cells (goblet cells) or glands secrete mucus, which acts as a lubricant.

• Locations:

respiratory tract (ciliated columnar or p.c.c.e.)

gastrointestinal (simple columnar)

genitourinary ( ciliated and non-ciliated)

Mucous membranes form the functional part of tubular organs in the respiratory, gastrointestinal, and genitourinary tracts.

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The GI Tract: A Mucous Membrane Covered by a Serous Membrane

serosa

Epithelial lining

Connective tissue

Smooth muscle layers

glands

Specialized glands, or cells called goblet cells, secrete mucus to protect the lining, lubricate the propulsion of food, and remove particulates form the respiratory tract.

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73© 2006 Jim Swan

submucosa

circular (transverse) smooth muscle

longitudinal smooth muscle

serosa

The Mucous Membrane

mucosa

The lining of the mucous membrane is a layer of epithelium, part of the mucosa which also includes a small amount of connective tissue. The epithelium is simple columnar in the GI tract, as shown here, and mostly pseudostratified ciliated columnar in the respiratory tract. Next is the submucosa, a layer of areolar and dense irregular connective tissue which contains glands, blood vessels, lymph nodes, and nerves. Then comes smooth muscle, usually composed of two layers. On the outside in the GI tract is a serosa, or serous membrane covering.

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Synovial Membranes

• Synovial membranes are not epithelial membranes

• Form joint capsules which lubricate joints, and bursae which lubricate the movements of tendons and ligaments – secrete synovial fluid.

• They are composed entirely of connective tissue.

We will examine the role of synovial membranes when we study arthrology in the next unit.

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Cutaneous Membrane: The Skin

• Epidermis composed of stratified squamous epithelium

• Dermis composed of areolar and dense irregular connective tissue

• Many specialized cells and glands

The skin is an organ since it is composed of different tissues working together. It is the organ of the integumentary system.