Chapter 4- The tissue level of Organization PDF

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CHAPTER 4: THE TISSUE LEVEL OF ORGANIZATION LEARNING OBJECTIVE: 4-1

Identify the four major types of tissues in the body and describe their roles.

4-2

Discuss the types and functions of epithelial tissue.

4-3

Describe the relationship between structure and function for each type of epithelium.

4-4

List the specific function of connective tissue and describe the three main categories of connective tissue.

4-5

Compare the structures and functions of the various types of connective tissue, proper, and the layers of connective tissue called fasciae.

4-6

Describe the fluid connective tissue blood and lymph and explain their relationship with interstitial fluid in maintaining homeostasis.

4-7

Describe how cartilage and bone function as supporting connective tissues

4-8

Explain how epithelial and connective tissues combine to form four types of tissue membranes and specify the functions of each.

4-9

Describe the three types of muscle tissue and the special structural features of each type.

4-10

Discuss the basic structure and role of nervous tissue.

4-11

Describe how injuries affect the tissues of the body.

4-12

Describe how aging affects the tissues of the body.

4-1 IDENTIFY THE FOUR MAJOR TYPES OF TISSUES IN THE BODY AND DESCRIBE THEIR ROLES     

Cells working together form tissues- collections of specialize cells and cell products that carry out a limited number of functions Histology- The study of tissues Epithelia Tissues- Covers exposed surfaces, lines internal passageways and chambers and forms glands Connective Tissue- Fills internal spaces, provides structural support for other tissues, transports materials within the body, and stores energy. Muscle Tissue- Specialized for contraction and includes the skeletal muscles of the body, the muscle of the heart and the muscular walls of hollow organs.

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Nervous tissue- Carries information from one part of the body to another in the form of electrical pulses

4-2 EPITHELIAL TISSUE COVERS BODY SURFACES, LINES, INTERNAL SURFACES, AND SERVES OTHER ESSENTIAL FUNCTION  

Epithelial Tissue- Surface of your skin and tissue includes epithelia and glands. Glands- Are structure that produce fluid secretions. They are attached to or derived from epithelia

Epithelial covers every exposed surface of the body  Form the skin  Line the digestive, respiratory, reproductive, and urinary tracts o Lines all passageways to the outside world  Delicate epithelia line internal cavities and passageways, such as the chest cavity, fluidfilled spaces in the brain, the inner surface of blood vessels, and chamber of the heart. Functions of Epithelia Tissue    

Provide Physical Protection- Abrasion Control Permeability- Any substance that enters or leaves your body must cross an epithelium Provide Sensation- Epithelia extremely sensitive to stimulation because they have a large sensory nerve supply. Provide Specialized Secretions- Epithelia cells that produce secretions are called glands cells.

Characteristics of Epithelial Tissue  Polarity- An epithelium has an exposed surface, either facing the external environment or an internal space and a base which is attached to underlying tissues. o Term Polarity refers to the presence of structural and functional differences between the exposed and attached surface  Cellularity- Epithelia are made almost entirely of cells bound closely together by interconnections known as cell junctions.  Attachment- The base of an epithelium is bound to a thin, noncellular basement membrane. o This basement membrane is formed from the fusion of several successive layers, ( the basal lamna and reticular lamina) a collagen matrix and proteoglycans (intercellular cement).  Avascularity- Epithelia are avascular which means that they lack blood vessels. They get nutrients by diffusion or absorption across either the exposed or the attached epithelial surface.

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Regeneration- Epithelial cells that are damaged or lost at the exposed surface are continuously replaced through stem cell divisions in the epithelium

Specializations of Epithelial Cells 1). The movement of fluids over the epithelial surface, providing protection and lubrication 2). The movement of fluids through the epithelial to control permeability 3). The production of secretions that provide physical protection or act as chemical messenger *The specialized epithelial cell is often divided into TWO functional regions, which means the cell has a STRONG POLARITY 1). Apical Surface- Where the cell is exposed to an internal or external environment 2). Basolateral Surfaces- Which include both the base (basal surface0 where the cell attaches to underlying epithelial cells or deeper tissues, and the sides (lateral surfaces), where the cell contacts its neighbors. 

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Many epithelial cells that line internal passageways have microvilli on their exposed surfaces. Microvilli are especially abundant on epithelial surfaces where absorption and secretion take Motile chilia are characteristic of surfaces covered by ciliated epithelium

Maintaining the Integrity of Epithelia 

To be effective as a barrier, an epithelium must form a complete cover or lining. Three factors help maintain the physical integrity of epithelium: (1) intercellular connections, (2) attachment to the basement membrane, and (3) epithelial maintenance and repair.

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1). Intercellular Connections- Involved either extensive areas of opposing plasma membranes or specialized attachment sites called cell junction

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o Cell adhesion Molecules (CAMs) which bind to each other and to extracellular materials. Cell Junctions- Are specialized areas of the plasma membrane that attach a cell to another cell or to extracellular materials. The three most common types of cell junction are (1) gap junctions, (2) tight junctions, and (3) desmosomes, (4) hemidesmosomes

Gap Junctions  Some epithelial functions require rapid intercellular communication.  Gap Junction- Two cells are held together by two embedded interlocking transmembrane proteins called connexons. ONLY gap junctions allow the diffusion of ions and molecules between cells.

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o Each connexon is composed of six connexins proteins that form a cylinder with a central pore. o Gap junctions are common among epithelial cells, where the movement of ions helps coordinate functions such as the beating of cilia. In cardiac and smooth muscle tissues, they are essential for coordinating muscle cell contractions. Tight Junction- ( Occluding junction) Encircle the apical regions of epithelial cells. The lipid portions of the two plasma membranes are tightly bound together by interlocking membrane proteins. Tight junctions largely prevent water and solutes from passing between the cells. Desmosomes- CAMS and proteoglycans link the opposing plasm membranes. They are very strong and can resist stretching and twisting. For example, desmosomes are abundant between cells in the superficial layers of the skin. o Two types of desmosomes:  Spot desmosomes are small discs connected to bands of intermediate filament. The intermediate filaments stabilize the shape of the ell  Hemidesmosomes resemble half of a spot desmosome. Rather than attaching one cell to another, a hemidesmosome attaches a cell to extracellular filaments in the basement membrane. This attachment helps stabilize the position of the epithelial cell and anchors it to underlying tissues.

Attachment to the Basement Membrane  Not only do epithelial cells hold onto one another, but they also remain firmly connected to the rest of the body. o Epithelial cells must be attached to other cells or they will die. o Basement membrane composed of basal lamina and a reticular lamina.  Basal Lamina- Is an amorphous, ill-organized layer though to function as a selective filter. Its secreted by the adjacent layer of epithelial cells. It restricts the movement of proteins and other large molecules from the underlying connective tissue into the epithelium  Reticular Lamina- Deeper portion of the basement membrane consist mostly of reticular fibers and ground substance. Epithelial Maintenance and Repair 

Epithelial cells lead hard lives. The only way the epithelium can maintain its structure over time is by the continual division of stem cells. Most epithelial stem cells are located near the basement membrane in a relatively protected location.

4-3 CELL SHAPE AND NUMBER OF LAYERS DETERMINE THE CLASSIFICATION OF EPITHELIA 

Recall that epithelial tissue includes epithelia and glands. The glands are either attached to or derived from epithelia

CLASSIFYING EPITHELIA

Classification of epithelial tissues (epithelia) Epithelia are classified by the: 

1. Number of cell layers  

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– Simple = one layer of cells only – Stratified = more than one layer of cells

2. Shape of the cells at the free (apical) surface   

– Squamous = flat – Cuboidal = cube/square shaped – Columnar = tall and thin like a column/rectangle

Glandular epithelia

• Endocrine glands–secrete hormones into the interstitial (extracellular) fluid; the hormones then diffuse into the bloodstream – They are ductless glands – See Ch. 18 (The Endocrine System) for more details

• Exocrine glands–secrete their products through ducts onto the exposed surface of an epithelium – They can be classified by their secretion type: • Serous – watery; contains enzymes (e.g. pancreatic juice) • Mucous – mucin + water = mucus • Mixed – serous/mucous

– They can also be classified by their method (mode) of secretion (see the next slide). Exocrine methods (modes) of secretion   

Merocrine- The product of released via exocytosis o E.g. sweat glands, salivary glands, mammary glands. Aprocrine- Both the product and some cytoplasm are released o E.g. mammary glands Holocrine- The entire cell bursts and all of the cytoplasm is released o E.g. sebaceous (oil) glands

Characteristics of connective tissues (CTs) 

They’re diverse structurally and functionally (but all CTs originate from the same embryonic tissue = mesenchyme)

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They’re found everywhere in the body, but they are never exposed to the outside environment

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Vascularity varies greatly among the different types

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In general, the cells are less densely packed than in epithelia

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They typically have lots of intercellular matrix (the nonliving or noncellular part of CT) = ground substance + extracellular fibers 

– The matrix is typically secreted by cells called fibroblasts

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– The special characteristics of the specific matrix produced by each type of CT leads to structural and functional diversity (e.g., consider bone vs. cartilage)

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– The ground substance may be fluid (e.g. plasma in blood), gel (e.g. chondroitin sulfate in cartilage), or solid (e.g. CaPO4 salts in bone)

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– There are 3 main extracellular fiber types:

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Collagen fibers–are relatively thick, long, straight, unbranched, and strong

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Reticular fibers(a thinner collagen variant)–form a branched network

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Elastic fibers–are thin, branched, and springy

Connective Tissue functions  Support and interconnections (binding) – Both physical (e.g. bone, cartilage, areolar tissue, dense CT, etc.) AND physiological (e.g. blood) support

 Transportation (e.g. blood) of heat, hormones, nutrients, wastes, gases, etc.  Protection of delicate organs (e.g. bone, cartilage, and adipose)  Storage – e.g. lipid energy (adipose) and calcium (bone)  Defense of the body from microorganisms (e.g. blood and lymph) Classification of adult CT : Connective tissue Connective Tissue Proper

LOOSE: Fibers create loose, open framework

DENSE: Fibers densely packed

Fluid Connective Tissues

BLOOD: Contained in circulatory system

LYMPH: Contained in lymphatic system

Supporting Connective Tissue

CARTILAGE: Solid, rubbery matrix

BONE: Solid, crystal-line matrix

Areolar Tissue Adipose Tissue Reticular Tissue

Dense regular CT Dense irregular CT Elastic Tissue

Hyaline cartilage Elastic cartilage Fibrocartilage

Connective tissue proper   

Contains a variety of cells and extracellular fibers The ground substance is a clear, viscous fluid Includes loose connective tissues and dense connective tissues (see the next two slides)

4-4 Connective tissue has varied roles in the body that reflect the physical properties of its 

Connective tissue- diver group of supporting tissues o Recall that the reticular lamina layer of the basement membrane of all epithelial tissues is made up of connective tissue components. o In essence, connective tissue connects the epithelium to the rest of the body. Other types of connective tissue include bone, fat, and blood...