Tissue Level of Organization Flashcards
Identify the four types of tissue that make up the body and describe their roles.
Histology: the study of tissues.
- Cells working together form tissues, that is, collections of similar cells and cell products that perform a limited number of specialized functions.
Four types:
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Epithelial
- Covers exposed surfaces
- Lines internal chambers and passageways
- Forms secretory glands
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Connective
- Fills internal spaces
- Provides structural support
- Stores energy
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Muscle
- Contracts to produce movement
- Includes skeletal muscle, cardiac muscle, and smooth muscle.
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Nervous
- Conducts electrical impulses
- Carries information
Microscopes are used to study cells and tissues.
Describe three microscopy techniques.
Note: Magnifying power does not infer resolving power
Light microscopy: simple (one lense) and compound (more than one lense)
Transmission electron microscopy: electrons transmit through a cross-section of the sample onto a photographic plate
Scanning electron microscopy: whole sample coated with electron-dense material, then bombarded with electrons, some of which reflect back, producing a 3D image of the surface of the specimen.
Review: BIOL200 for more detail on microscopy
Epithelial tissue covers surfaces, lines cavities, and forms secretory glands.
Describe the two components of epithelial tissues.
- Epithelial tissues include both epithelia and glands:
- Epithelia are cellular layers that cover exposed surfaces and line internal cavities/passageways. They have no blood vessels and often contain secretory/gland cells.
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Glands are organized groups of cells/organs that contain epithelial-derived cells that synthesize substances for secretion. Two types:
- Exocrine glands secrete onto external surfaces or into internal ducts that connect to the exterior.
- Endocrine glands secrete hormones or their inactive precursors into the interstitial fluid that then enter the bloodstream for distribution.
Epithelial cells are extensively interconnected, both structurally and functionally.
Discuss the types and functions of intercellular connections between epithelial cells. [5]
Starting from the top in the diagram:
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Tight (occluding) junctions are characteristic of epithelial cells lining the intestinal tract
- They form a barrier that isolates the basolateral surfaces and deeper tissues from the contents of the lumen.
- Prevents passage of water/solutes between cells.
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Adhesion belts lock terminal webs of adjacent cells together.
- They strengthen the apical region and prevent distortion and leakage at tight junctions.
- Forms a band (dense proteins that are attached to microfilaments of the terminal web) that encircles each cell and binds it to its neighbours.
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Gap junctions permit chemical communication (diffusion of ions and small molecules).
- Coordinates the activities of adjacent cells.
- Two cells are held together by interlocking transmembrane proteins called connexons.
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Desmosomes provide a firm attachment between neighbouring cells by interlocking their cytoskeletons.
- Opposing plasma membranes are locked together.
- Strong and durable and help cells resist mechanical stress.
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Hemidesmosomes attach the deepest epithelial cells to the basement membrane.
- Locks the basal cytoskeleton to peripheral and transmembrane proteins that are firmly attached to a layer of extracellular protein filaments and fibers.
Describe the structure and function of squamous epithelium.
The cells in a squamous epithelium are flat and irregularly shaped.
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Simple squamous epithelium is the body’s most delicate epithelia
- Located in protected regions where absorption/diffusion takes place or where a slippery surface reduces friction.
- Found along passageways in kidneys, inside the eye, and at the gas exchange surfaces (alveoli) of the lungs.
- Mesothelium lines the pericardial, pleural, and peritoneal body cavities.
- Endothelium is the simple squamous epithelium lining the inner surface of the heart and all blood vessels.
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Stratefied squamous epithelium
- Located where physical/chemical stresses are severe.
- Form the surface of the skin and line the mouth, throat, esophagus, rectum, anus, and vagina.
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Keratinized squamous epithelium:
- On exposed body surfaces, where physical stress and dehydration are potential problems, apical layers of epithelial cells are packed with filaments of the protein keratin. Thus, superficial layers are both tough and water resistant. Keratinized epithelium is found at the surface of the skin, and in nails and hair.
- Nonkeratinized stratefied squamous epithelia are found in the mouth, pharynx, esophagus, anus, and vagina. These resist abrasion but will dry out and deteriorate unless kept moist.
Describe the structure, function, and locations of cuboidal epithelia.
- Cuboidal and transitional epithelia line several passageways and chambers connected to the exterior.
- Cuboidal epithelium resemble hexagonal boxes (or square when viewed in sections)
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Simple cuboidal epithelium provides limited protection
- Occurs where secretion or absorption takes place, such as the lining of portions of the kidney tubules, and linings of secretory chambers in the thyroid gland.
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Stratefied cuboidal epithelium are rare.
- Located along the ducts of sweat glands and in the larger ducts of mammary glands.
Describe the structure, function, and locations of columnar epithelia.
Columnar epithelia absorb substances and protect the body from digestive chemicals.
- Densely packed, hexagonal (taller/more slender than cuboidal); appear rectangular in sectional view.
- Elongated nuclei close to basement membrane.
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Simple columnar epithelium
- Found where absorption/secretion takes place.
- Line the small intestine, the stomach, gallbladder, uterine tubes, and ducts within the kidneys.
- May have microvilli which increase surface area for absorption
- May have motile cilia that move substances across the apical surface.
- In stomach and intestinal tract, simple columnar epithelial secretions protect underlying tissues against digestive chemicals.
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Pseudostratefied columnar epithelium includes several types of cells with varying shapes and functions.
- Appears stratefied, but is not truly, because the distance between the cell nuclei and exposed surface vary. In truly stratefied epithelia, all cells contact the basement membrane.
- Typically have motile cilia.
- Line naval cavities, the trachea (windpipe), and larger airways of the lungs. Also found along portions of the male reproductive tract.
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Stratefied columnar epithelium are not widely distributed throughout body.
- May have two or more layers. In the latter case, only the superficial cells are columnar in shape.
- Found in large ducts such as those of the salivary glands or pancreas.
Glandular epithelia are specialized for secretion.
What is the difference between endocrine and exocrine glands?
Compare the three different methods of exocrine secretion by glandular epithelia.
Collections of epithelial cells that produce secretions are called glands. They range from scattered cells to complex glandular organs. Some of these glands, called endocrine glands, release their secretions into the interstitial fluid. Others, exocrine glands, release their secretions into passageways called ducts.
Secretory cells of exocrine glands release their secretions into ducts using one of three methods:
- Merocrine: the product is released from secretory vessicles by exocytosis. Most common. Mucin is a merocrine secretion that mixes with water to form mucus. Mucus is an effective lubricant, a protective barrier, and a sticky trap for foreign particles/microorganisms.
- Apocrine: involves loss of cytoplasm as well as secretory product. The apical portion of the cytoplasm becomes packed with secretory vesicles and then shed. Milk production involves both method 1 & 2.
- Holocrine: destroys the gland cell. The entire cell becomes packed with secretory products and then bursts. Further secretion depends on cell replacement. Sebaceous glands, associated with hair follicles, produces an oily hair coating by means of holocrine secretion.
Explain how multicellular exocrine glands are classified by their structure.
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Simple glands have a single duct that does not divide on its way to the gland cells.
- Tubular
- Coiled
- Branched tubular
- Alveolar
- Branched alveolar
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Compound glands divide one or more times on its way to the gland cells.
- Tubular
- Alveolar
- Tubuloalveolar
- Unicellular exocrine glands are goblet cells that are scattered among aborptive cells in intestinal epithelia. They secrete mucin that hydrates to form mucus, which protects epithelial linings
Describe the general structure of connective tissue. [3]
All forms share three basic components:
- Specialized cells
- Extracellular protein fibers
- A fluid known as ground substance
- Cells make up the bulk of epithelial tissue, but the bulk of the volume of connective tissue is mostly matrix.
- 2 & 3 make up the matrix that surrounds the cells.
Loose connective tissues support other tissue types.
Describe the structure, function, and locations of areolar tissue, adipose tissue, and reticular tissue.
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Areolar: least specialized and most common.
- General packing material in the body.
- All of the cell types found in other forms of connective tissue proper can be found in areolar tissue.
- Adipose tissue forms a layer that provides padding within the orbit of the eyes, in the abdominopelvic cavity, and around the kidneys. Adipocytes account for most of the volume of the tissue.
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Reticular tissue is found in the liver, kidney, spleen, lympho nodes, and bone marrow, where it forms a tough, flexible network that provides support and resists distortion.
- Reticular fibers create a complex 3D supporting network known as a stroma.
Dense connective tissues are dominated by extracellular fibers whereas fluid connective tissues have an aqueous matrix.
Describe the structure, function, and locations of dense connective tissues.
Extracellular fibers make up most of the volume of dense connective tissues. There are three types:
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Dense regular found in tendons and ligaments that interconnect bones or stabilize the positions of internal organs.
- Forces applied to these cords and sheets arrive from a consistent direction: parallel to the long axis of the collagen fibers.
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Dense irregular connective tissue form an interwoven meshwork with no consistent pattern which strengthen and support stresses from many directions.
- Forms (1) a covering that sheathes visceral organs; (2) a superficial layer covering bones, cartilages, and peripheral nerves; and (3) a thick supporting layer in the skin (the dermis).
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Elastic tissue has elastic fibers that outnumber collagen fibers allowing it to tolerate cycles of extension and recoil.
- Found between vertebrae of the spinal column, in the walls of large blood vessels, in ligaments supporting transitional epithelia, and the erectile tissues of the penis.
Tissue membranes are physical barriers, and fasciae support and surround organs.
Describe the arrangements of epithelial and connective tissue in the four types of tissue membranes, and describe the structure and locations of the three types of fasciae.
Tissue membranes that line or cover body surfaces typically consist of an epithelium supported by connective tissue.
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Mucous membranes line passageways and chambers that communicate with exterior, including those in the digestive, respiratory, reproductive, and urinary tracts.
- Must be kept moist to reduce friction. Lubricated by either mucus (produced by golet cells or mucous cells) or fluids such as urine or semen.
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Serous membranes are extremely delicate and never directly connected to exterior.
- Consist of a mesothelium supported by areolar tissue.
- Lines the body cavities of the trunk: pleura, pericardium, peritoneum
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Cutaneous membrane covers the surface of the body.
- Consists of a stratefied squamous epithelium and a layer of areolar tissue reinforced by underlying dense irregular connective tissue.
- Thick, relatively waterproof.
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Synovial membrane lines freely movable joint cavities, but does not cover opposing joint surfaces. Referred to as epithelia, but not true epithelium because of four reasons:
- Developes within connective tissue.
- No basement membrane is present.
- Gaps of up to 1mm may separate adjacent cells
- Synovial fluid and capillaries are continuously exchanging fluid and solutes.
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Fasciae are connective tissue layers that support and surround organs. Three types:
- Superficial lies between the skin and underlying organs (areolar and adipose tissue)
- Deep forms a strong, fibrous internal framework which consists of dense regular connective tissue, and is continuous with or bound to capsules, ligaments, and other connective tissue structures.
- Subserous lies between serous membranes and deep fascia and consists entirely of areolar tissue.
Describe the relative proportions of muscle tissue and nervous tissue in the body.
Muscle tissue outweighs nervous tissue by 25:1
Describe the roles of inflammation and regeneration in response to tissue injury.
- Injury causes exposure to pathogens and toxins, causing mast cell activation which stimulates inflammation.
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Inflammation produces swelling, redness, heat, and pain.
- Increased blood flow
- Increased vessel permeability
- Increased local temperature
- Increased oxygen and nutrients
- Increased phagocytosis
- Removal of toxins and wastes
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Regeneration is the repair that occurs after the damaged tissue has been stabilized and inflammation subsides.
- Fibroblasts lay down a network of collagen fibers to stabilize injury, producing scar tissue.
- The permanent replacement of normal tissue by scar tissue is called fibrosis.
Describe the basic features of the cells of any epithelium.
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Apical surface, faces the exterior of the body or some internal space:
- Covered in motile cilia in portions of the respiratory and reproductive tracts.
- In epithelial cells that line internal passageways of the digestive, urinary, and reproductive tracts microvilli are often found on the apical surfaces.
- Basolateral surfaces include both the base, where the cell attaches to underlying epithelial cells or deeper tissues, and the sides, where the cell contacts its neighbours.
Summarize the classification of an epithelium based on cell shape and number of cell layers.
- Three basic shapes:
- Squamous
- Cuboidal
- Columnar
- If only one layer of cells is present, that layer is a simple epithelium.
- If several layers of cells are present, they are a stratified epithelium (e.g., surface of skin, lining of mouth)
Describe the basement membrane.
The basement membrane is a noncellular structure produced by the basal surface of the epithelium and the underlying connective tissue.
The basal lamina is an amorphous layer that contains glycoproteins. It is produced by the adjacent layer of epithelial cells.
The reticular lamina contains reticular protein fibers and ground substance secreted by underlying connective tissue cells. It gives the basement membrane its strength and acts as a filter that restricts diffusion between adjacent tissues and the epithelium.
Describe the structure, function, and locations of transitional epithelia.
- Cuboidal and transitional epithelia line several passageways and chambers connected to the exterior.
- Transitional epithelium are unusual stratefied epithelium.
- Tolerate repeated stretching without damage.
- Referred to as transitional because the appearance of the epithelium changes as stretching occurs.
- These epithelia line the urinary bladder, kidneys, the ureters, and the urine-collecting chambers within the kidneys, where large changes in volume occur.
Muscle tissue is specialized for contraction.
Describe the structure and function of skeletal muscle tissue.
- Skeletal muscle tissue is found in skeletal muscles, organs that also contain connective tissues and nervous tissue.
- The cells are long, cylindrical, and striated, with mutiple nuclei.
- This tissue moves or stabilizes the position of the skeleton; guard entrances and exits to the digestion, respiratory, and urinary tracts; generate heat; and protect internal organs.
Muscle tissue is specialized for contraction.
Describe the structure and function of cardiac muscle tissue.
- Cardiac muscle tissue is found in the heart.
- The cells are short, branched, and striated, usually with a single nucleus.
- The cells are interconnected at specialized intercellular junctions called intercalated discs, which help synchronize cardiocyte contractions.
- Cardiac muscle moves blood and maintains blood pressure.
Muscle tissue is specialized for contraction.
Describe the structure and function of smooth muscle tissue.
- Smooth muscle tissue is found throughout the body. (e.g., in the skin, the walls of blood vessels, and in many digestive, respiratory, urinary, and reproductive organs.
- The cells are short, spindle shaped, and nonstriated, with a single, central nucleus.
- Smooth muscle moves food, urine, and reproductive tract secretions; controls diameter of respiratory passageways; and regulates diameter of blood vessels.
