The tissue level of organization a. Types of tissues



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THE TISSUE LEVEL OF ORGANIZATION

A. TYPES OF TISSUES
List three characteristics of a tissue?
1. Group of similar cells AND their extracellular matrices

2. Share a common embryological origin

3. Function together as a group to carry out particular functions
What determines the functions and properties of a tissue?
The functions and properties of a tissue are determined by the nature of the cells and the extracellular matrix, if present, created by and surrounding the cells.
List the four basic tissue types and give a brief description of each.
1. Epithelial tissues – cover the body surfaces; line hollow organs, body cavities, and ducts; form glands
2. Connective tissues – protect and support the body and its organs; binds organs together; store energy reserves as fat; provide resistance to disease in association with the immune system
3. Muscular tissues – responsible for movement and generation of force
4. Nervous tissue – initiate and transmit action potentials (nerve impulses) that help coordinate body activities
B. EPITHELIAL TISSUES

1. GENERAL FEATURES
Describe the general features of epithelial tissues.
1. Closely packed cells with little or no extracellular material between them

2. Cells arranged into continuous sheets, in either single or multiple layers

3. Epithelial cells have an apical surface that is exposed to a body cavity, lining of an internal organ, or the exterior of the body.

4. Epithelial cells have a basal surface that is attached to a basement membrane

5. The basement membrane (basal lamina) is a connective tissue matrix that attaches the overlying epithelium to the underlying connective tissue

6. Epithelia are avascular, meaning that they have no blood supply. They receive their nutrition by diffusion from the underlying connective tissues.

7. Epithelial have a nerve supply.

8. Since epithelia are subject to a certain amount of wear, tear, and injury, they have a high capacity for mitosis.


2. COVERING AND LINING EPITHELIA

a. ARRANGEMENT OF LAYERS

b. CELL SHAPES

c. CLASSIFICATION
Covering and lining epithelia are arranged into continuous sheets of cells consisting of one of three layer types depending upon the function of the tissue.
Covering and lining epithelia are also classified according to the shape of the cells that lie on the apical surface of the epithelium.
Describe the following:
1. simple epithelium – If the function is absorption or filtration, or the tissue is in an area of minimal wear and tear, the cells form a single layer, and is thus called a simple epithelium.
2. stratified epithelium – If the tissue is in an area with a high degree of wear and tear, then the cells are stacked into layers, and is thus called a stratified epithelium
3. pseudostratified epithelium – A third less common arrange-ment is the pseudostratified epithelium that has a single layer of cells, so it is simple, but some cells do not reach the apical surface, giving it a multilayered appearance.
Describe each of the following:
1. squamous cells – squamous cells are flattened and scale-like
2. cuboidal cells – cuboidal cells are usually cube-shaped in cross-section, being roughly as tall as they are wide
3. columnar cells – columnar cells are tall and cylindrical or somewhat rectangular, and generally taller than they are wide
4. transitional cells – Transitional cells readily change shape and are found where there is a continuous amount of stretching then relaxation, such as in the urinary bladder. The apical layer may range from squamous to cuboidal.
d. PHOTOMICROGRAPHS


tissue

location(s)

description

function(s)

simple squamous

lining heart (endocardium) and blood vessels (endothelium), lymphatic vessels, alveoli of lungs, glomerular capsule of kidneys, part of serous membranes

consists of a single layer of flattened, scale-like cells, much like a tile floor

diffusion, osmosis, and filtration

stratified squamous

keratinized form forms epidermis; nonkeratinized forms line mouth and tongue, pharynx, esophagus, anal canal, and vagina

consists of multiple layers flattened on surface; cuboidal to columnar in deepest layers

protection against wear-and-tear

simple cuboidal

lines kidney tubules and small ducts of many glands, covers ovary, forms pigmented epithelium of retina

consists of a single layer of cube-shaped cells, about as tall as they are wide

absorption and secretion

stratified cuboidal

relatively rare; lines larger ducts of some glands and part of the male urethra

consists of two or more layers of cells, the upper most being cuboidal in shape

protection

simple columnar

lines GI tract from stomach to anal canal, ducts of some glands, gallbladder; ciliated form lines oviducts, uterus, central canal of spinal cord

single layer of rectangular (columnar) cells, often has interspersed goblet cells

secretion and absorption

pseudostratified

lines much of lower respiratory system down to bronchiolar level; nonciliated form may be found in some gland ducts, epididymis, and part of male urethra

not truly stratified; all cells contact basement membrane, but not all reach apical; surface

secretion from goblet cells, movement of mucous across surface by ciliary action

transitional

urinary bladder, portions of ureters and urethra

variable; apical cells vary from squamous to cuboidal depending on degree of stretch of organ

allows distention of organ without causing an increase in tension in wall of organ



3. GLANDULAR EPITHELIA
Glandular epithelium forms the secretory portions of glands. Name the two major types of glands in the body and give a brief description of each.
1. Endocrine glands – endocrine glands are ductless; secrete hormones into the blood
2. Exocrine glands – exocrine glands secrete their product(s) either onto the apical surfaces of the cells or into ducts for transport to the free surface.
a. STRUCTURAL CLASSIFICATION
List the two major structural classifications of exocrine glands and give a brief description of each.
1. Unicellular glands – The best example of a unicellular gland is the goblet cell. This single cell secretes its product directly onto the free surface of many epithelia.
2. Multicellular glands – A multicellular gland consists of a secreting organ found deep to the free surface and attached to it via a duct.
b. FUNCTIONAL CLASSIFICATION
What is the basis for the functional classification of glands?
Functional classification is based on whether a secretion is a product of a cell or consists of entire or partial glandular cells themselves.
Describe each of the following:
1. holocrine secretion – In holocrine secretion the cells accumulate secretory product in their cytosol, die, and are discharged with their contents as the secretion.
2. merocrine secretion – In merocrine (eccrine) secretion the cells form a secretory product, store it in the cytoplasm in secretory vesicles, and release it by exocytosis.
3. apocrine secretion – In apocrine secretion vesicles with product accumulate in the apical portion of the cells. That portion pinches off from the rest of the cell to form the secretion.


C. CONNECTIVE TISSUES

1. GENERAL FEATURES
Name the three basic elements of all connective tissues.
1. cells

2. ground substance (ground substance is a more or less

homogeneous, amorphous, water-based background substance in which the specific differentiated elements of a connective tissue are suspended)

3. fibers


Name the three basic fiber types of the connective tissues.

1. collagen

2. elastin

3. reticular fibers


What is matrix?
Matrix is ground substance embedded with fibers that separate the cells.
2. CLASSIFICATION
Mature (adult) connective tissues are classified into five categories. List each of them, give their subdivisions, and the primary cell type of each.
1. loose connective tissues

areolar tissue (fibroblast)

adipose tissue (adipocyte)

reticular tissue (fibroblast)


2. dense connective tissues

dense regular connective tissues (fibroblast)

dense irregular connective tissues (fibroblast)

elastic connective tissues (fibroblast)


3. specialized connective tissues

cartilage

hyaline cartilage (chondrocyte)

elastic cartilage (chondrocyte)

fibrocartilage (chondrocyte and fibroblast)

bone (to be discussed later)



blood (to be discussed later)

3. PHOTOMICROGRAPHS


tissue

location(s)

description

function(s)

areolar

papillary dermis of skin, hypodermis, mucous membranes, blood vessels, nerves, and around body organs (i.e. everywhere)

loosely woven fibers embedded in ground substance; many different cell types wander through; fibroblasts form basic tissue

strength, elasticity, and support

adipose

hypodermis; around heart, kidneys, and eyes; yellow bone marrow; around joints

adipocytes that store fats, forming a characteristic “signet ring” appearance

provide insulation, energy storage, protection from mechanical injury

reticular

stroma of liver, spleen, lymph nodes; red bone marrow; basement membranes

net work of very short interlacing collagen fibers and fibroblasts

form framework of organs, binds together smooth muscle cells

dense regular

tendons, aponeuroses, and most ligaments

collagen fibers arranged in parallel bundles, with fibroblasts scattered between

provides strong attachments between parts

dense irregular

dense fascia, reticular dermis, perichondrium, periosteum, joint capsules, dura mater, membrane capsules, heart valves

collagen fibers randomly arranged and fibroblasts, forming a sheet

strength, support, and protection

elastic

lung, elastic arteries, trachea and bronchial tree, true vocal cords, vertebral ligaments, suspensory ligament of penis

elastic fibers that branch freely, forming sheets or ligaments

provides extensibility and elasticity to various organs that must be stretched

hyaline cartilage

articular surfaces of bones; anterior ribs; nose, parts or larynx, trachea, and bronchial tree; embryonic skeleton

Chondrocytes embedded in cartilage matrix rich in collagen fibers

resists compressive forces, provides smooth surfaces for articulation at synovial joints

fibrocartilage

pubic symphysis, intervertebral discs, menisci of shoulders and knees

consists of scattered Chondrocytes with hyaline cartilage matrix among bundles of collagen fibers

support, fusion (between pubic bones and between vertebrae), deepening of shoulder and knee joints

elastic cartilage

epiglottis, external ear, auditory tubes

Chondrocytes embedded in cartilage matrix rich in network of elastic fibers

allows structure to be semi-rigid and extensible; structure can return to resting shape

bone

comprises the bones of the skeleton

osteocytes embedded in a mineralized matrix of collagen fibers and ground substance

support, protection, storage, provides levers for movement; provides for blood cell formation

blood

within blood vessels and heart

formed cellular elements suspended ina liquid matrix (plasma)

transport of gases, immune function, blood clotting


D. MEMBRANES
What is a membrane?
An epithelial membrane is formed by a the combination of an epithelium and an underlying connective tissue layer.
Name the three true membranes and the one false membrane of the body.
mucous membrane (mucosa)

serous membrane (serosa)



cutaneous membrane (skin or integument)
synovial membrane (not a true membrane because there is no epithelium)
1. MUCOUS MEMBRANES
In general, where are mucous membranes found?
Mucous membranes line body cavities that open directly to the external environment.
What is the function of the epithelial layer?
The epithelial layer secretes mucous to protect the epithelium by lubricating it and trapping harmful agents.
Specifically, what body parts are lined by a mucosa?
Mucosae are found lining the respiratory tract, the digestive tract, and the genitourinary tract.
2. SEROUS MEMBRANES
In general, where are serous membranes found?
Serous membranes line body cavities that do not open to the exterior of the body and cover the external surfaces of the viscera.
What are the parietal and visceral layers of a serosa?
The portion of the serosa attached to the body wall is called the parietal layer and the portion attached to an organ is called the visceral layer.

What is serous fluid, where is it found, and what does it do?
Between the layers of the serosa is a small amount of serous fluid that lubricates the two layers and allows the organs to move freely within the cavity
3. CUTANEOUS MEMBRANE
The cutaneous membrane (epidermis) will be discussed with the skin.
4. SYNOVIAL MEMBRANE
Where are synovial membranes located?
They line the joint cavity of synovial (freely movable) joints.
Why are they not considered to be true membranes?
Synovial membranes are not true membranes because they do not contain an epithelial layer.
What is the structure of a synovial membrane?
Synovial membranes are composed of areolar connective tissue with elastic fibers and varying amounts of adipose tissue. The cells are synoviocytes that secrete synovial fluid.






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