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Functions of Epithelial Tissue
Provide physical protection: Epitelia protect exposed and internal surfaces from abrasion, dehydration, and destruction by chemical or biological agents.
Control permeability: Any substance that enters or leaves the body has to cross an epithelium. Some epithelia are relatively impermeable, whereas others are permeable to compounds as large as proteins. Most are capable of selective absorption or secretion. The epithelial barrier can be regulated and modified in response to various stimuli.
Provide sensation: Sensory nerves extensively innervate most epithelia. Specialized epithelial cells can detect changes in the environment and convey information about such changes to the nervous system.
Produce specialized secretions: Epithelial cells that produce secretions are called gland cells. Individual gland cells are often scattered among other cell types in an epithelium that may have many other functions.
Covers exposed surfaces and line internal cavities and passageways; they often contain secretory cells, or gland cells, scattered among the other cell types.
Derived form epithelia, but secretory cells predominate; there are two types:
-Exocrine glands secrete onto external surfaces or into internal passageways (ducts) that connect to the exterior
-Endocrine glands secrete hormones or precursors into the interstitial fluid, usually for distribution by the bloodstream.
The region of the cell exposed to an internal or external environment. When the epithelium lines a tube, such as the intestinal tract, the apical surfaces of the epithelial cells are exposed to the space inside the tube, a passageway called the lumen.
Found on the apical surfaces of epithelial cells that line internal passageways of the digestive, urinary, and reproductive tracts.
cover the apical surfaces in portions of the respiratory and reproductive tracts. A typical ciliated cell contains about 250 cilia that beat in a coordinated fashion
Include both the basal surface, where the cell attaches to underlying epithelial cells or deeper tissues, and the lateral surfaces, where the cell contacts its neighbors.
-Gogli apparatus (faces apical surface)
-Endoplasmic reticulum (often extensive around the nucleus)
-Nucleus (in a tall cell, located closer to the base than the apical surface)
-Mitochondria (may be apical or basal, dependig on cell functions)
What is the probable function of an epithelial surface whose cells bear many cilia?
The presence of many cilia on the free surface of epithelial cells aids the movement of substances over the epithelial surface.
-Occluding junctions form a barrier that isolates the basolateral surfaces and deeper tissues from the contents of the lumen.
-Adhesion belt locks together the terminal webs of neighboring cells, strengthening the apical region and preventing distortion and leakage at the occluding junctions.
-Gap junctions permit chemical communication that coordinates the activities of adjacent cells.
-Desmosomes provide firm attachment between neighboring cells by interlocking their cytoskeletons.
Attach the deepest epithelial cells to the basal lamina. At a hemidesmosome, the basal cytoskeleton is locked to the peripheral proteins and to transmembrane proteins that are firmly attached to a layer of extra-cellular protein filaments and fibers.
Basal lamina, or basement membrane
A complex structure produced by the basal surface of the epithelium and the underlying connective tissue. Contains two layers:
Clear layer of Basal lamina
Contains glycoproteins and a network of fine protein filaments.
Dense layer of Basal lamina
Contains bundles of coarse protein fibers, and gives the basal lamina its strength and acts as a filter that restricts diffusion between the adjacent tissues and the epithelium.
The lipid portions of the two plasma membranes are tightly bound together by interlocking membrane proteins.
It prevents the passage of water and solutes between cells.
Continuous adhesion belt
Forms a band that encircles cells and binds them to their neighbors. The bands are dense proteins that are attached to the microfilaments of the terminal web.
Two cells are held together by interlocking junctional proteins called connexons
(channel proteins that form a a narrow passageway and let small molecules and ions pass).
- Gap junctions between epithelial cells are common where the movement of ions helps coordinate functions such as secretion or the beating of cilia.
- Gap junctions occur in other tissues as well; in cardiac muscle tissue, for example, they help coordinate contractions of the heart muscle.
At a desmosome,
the opposing plasma membranes are locked together. Desmosomes are very strong and resist stretching and twisting. Contain:
Cell adhesion molecules (CAMS)- transmembrane proteins that bind to each other and to extracellular materials.
Intercellular cement- A thin layer of proteoglycans that contain polysaccharide derivatives (hyaluronan)
Epithelial cells are avascular
They lack blood vessels. The cells forming the deepest layer of an epithelium must remain firmly attached to underlying tissues, because the blood vessels in those tissues nourish the entire epithelium.
Simple squamous epithelium
Most delicate type of epitelium. Located in protected regions where absorption and diffusion take place, or where a slick, slippery surface reduces friction.
Found: Along passageways in the kidneys, inside the eye, gas exchange surfaces(alveoli) of the lungs.
Simple squamous mesothelium
Lines each ventral body cavity.
Simple squamous endothelium
Lines the heart and blood vessels.
Stratified squamous epithelium
Located where mechanical or chemical stresses are severe.
Found: surface of skin and line the mouth, throat, esophagus, rectum, anus and vagina.
Tough and water resistant, and packed with filaments of the protein keratin. (Places where dehydration are potential problems)
Resists abrasion but will dry out and deteriorate unless kept moist. Found in the oral cavity, pharynx, esophagus, anus and vagina.
Found lining exocrine glands and ducts (passageways that carry secretions).
Stratified cuboidal epithelia
Rare. They are most common along the ducts of sweat glands, mammary glands, and other exocrine glands.
-Tolerates repeated cycles of stretching without damage.
-Lines the urinary bladder, the ureters, and the urine-collecting chambers withing the kidneys.
- Empty urinary bladder=relaxed (plump and cuboidal)
- Full urinary bladder = stretched (looks flattened)
Typically perform absorption or provide protection from chemical or environmental stresses.
Simple columnar epithelia
Found lining the stomach, intestine, gallbladder, uterine tubes, and ducts within the kidneys.
Pseudostratified columnar epithelium
Includes several types of cells with varying shapes and functions. Every epithelial cell contacts the basal lamina and typically possess cilia.
Found: lining the nasal cavities, the trachea, and larger airways of the lung. Also found along portions of the male reproductive tract.
Stratified columnar epithelium
Rare. May have two layers or multiple layers (only the superficial cells are columnar in shape)
Found: lining large ducts such as those of the salivary glands or pancreas.
The product is released from secretory vesicles by exocytosis. This is the most common mode of secretion
Involves the loss of cytoplasm as well as the secretory product. The apical portion of the cytoplasm becomes packed with secretory vesicles and is then shed. Milk production in the mammary glands involves a combination of merocrine and apocrine secretions.
Destroys the gland cell. The entire cell becomes packed with secretory products and then bursts, releasing the secretion and killing the cell. Further secretion depends on the replacement of destroyed gland cells by the division of stem cells.
- 1. Cell division replaces lost cells
- 2. Cells produce secretion, increasing in size
- 3. Cells burst, releasing cytoplasmic contents
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 and microorganisms.
A gland is simple if it has a single duct that does not divide on its way to the gland cells.
A gland whose cell form tubes are tubular.
A gland is branched if several secretory areas(tubular or acinar) share a duct.
Glands whose glandular cells from sac-like pockets are alveolar or acinar.
Simple gland locations
Simple tubular: Intestinal glands
Simple coiled tubular: Merocrine sweat glands
Simple branched tubular: Gastric glands
Simple alveolar: Stange in embryonic development of simple branched glands
Simple branched alveolar: Sebaceous glands.
A gland is compound if the duct divides one or more times on its way to the gland cells.
Glands whose secretory cells from both tubes and sacs are called tubuloalveolar.
Compound gland locations
Compound tubular: Mucous glands in mouth
Compound alveolar: Mammary glands
Compound tubuloalveolar: Salivary glands/ pancreas.
The individual secretory cells in epithelia that have independent, scattered gland cells.
Secrete mucin. The apical cytoplasm is filled with large secretory vesicles.
Connective Tissue Functions
-Establishing a structural framework for the body
-Transporting fluids and dissolved materials
-Protecting delicate organs
-Supporting, surrounding, and interconnecting other types of tissue
-Storing energy reserves
-Defending the body from invading microorganisms
Connective Tissue forms
1. Specialized cells
2. Extracellular protein fibers
3. Ground substance (fills the spaces between cells and surrounds connective tissue fibers)
Together, the extracellular fibers and ground substance constitute the matrix that surrounds the cells.
Connective tissue proper
Includes those connective tissues with many types of cells and extracellular fibers in a syrupy ground substance:
- Loose: fibers create loose, open framework + padding and support;
- Dense: extracellular fibers densely packed;
- -Dense regular
- -Dense irregular
Fluid Connective Tissue
Have distincitive populations of cells suspended in a watery matrix that contains dissolved proteins:
Blood: flows within cardiovascular system
Lymph: Flows within lymphatic system
Supporting Connective Tissue
Differ from connective tissue proper in having a less diverse cell population and a matrix containing much more densely packed fibers. Supporting connective tissues protect soft tissues and support the weight of part or all of the body.
- Cartilage: solid, rubbery matrix;
solic, crystalline matrix.
Most common form of connective tissue proper in adults. It's the 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.
Types of Fibers
Reticular: Strong and form a branching network (spider web)
Collagen: Thick, straight or wavy, and often form bundles (tree branches). Very strong and resist stretching.
Elastic: Slender, unbranching and very stretchy. They recoil to their original length after stretching or distortion.
Fixed Cells in connective tissue
Melanocyte: pigment cell that synthesized melanin, a brownish-yellow pigment.
Fixed macrophange: stationary phagocytic cell that englulfs cell debris and pathogens.
Mast cells: synthesize the extracellular fibers of the connective tissue.
Adipocytes (fat cells): store lipid reserves in large intracellular vesicles.
Wandering Cells in connective tissue
Plasma cell: active immune cell that produces antibodies.
Free macrophages: phagocytic cells that patrol the tissue, engulfing debris or pathogens (garbagemen)
Mesenchymal cells: stem cells that participate in the repair of damaged tissues.
Neutrophils/eosinophils: small phagocytic blood cells that enter itssues during infection.
Lymphocytes: cells of the immune system.
Found deep to the skin (buttocks and breasts). Forms layer that provides padding within orbit of the eyes, inthe abdominopelvic cavity and around kidneys.
Found in liver, kidney, spleen, lymph nodes and bone marrow, where it forms tough, flexible network that provides support and resists distoration.
Reticular fibers create complex 3D supporting network called stroma. Fixed macrophages and fibroblasts are present.
Dense regular connecive tissue
Found in tendons and ligaments that interconnect bones or stabilize the positions of internal organs.
Dense irregular connective tissue
Fibers form an interwoven meshwork in no consistent patter. These tissues strengthen and support areas subjected to stresses from many directions.
Dense irregular forms 1. a covering that sheathes visceral organs, 2. a superficial layer covering bones, cartilages and nerves, and 3. a thick supporting layer in the dermis
Has springy resilient nature that allows it to tolerate cycles of extension and recoil. Elastic tissue found between vertebrae of spinal column, in walls of large blood vessels, and in ligament supporting transitional epithelia and erectile tissue of the penis
Fluid Connective Tissue
Have a fluid matrix that includes many types of suspended proteins that under normal conditions do not form insoluble fibers. In blood, the watery matrix is called plasma. Contains blood cells and fragments of cells called formed elements.
Red Blood cells
Formed elements responsible for the transport of oxygen in the blood. They account for half the volume of whole blood.
White blood cells
Formed elements that help defend the body from infection and disease.
-Monocytes are phagocytes similar to free macrophages in other tissues.
-Lymphoctyes are uncommon in the blood but they are the dominant cell type in lymph.
-Eosinophils and neutrophils are phagocytes. Basophils promote inflammation.
Formed elements consisting of membrane-enclosed packets of cytoplasm.
Involved in the clotting response that seals leaks in damaged blood vessels.
Confined to vessels of cardiovascular system and contractions of heart keep it in motion. As blood flows through body tissues, water and solutes move from the plasma into the surrounding interstitial fluid.
- Arteries carry blood away from heart and into tissues
- Veins carry blood from capillary beds to heart
- Capillaries- smalles and most delicate blood vessels. All exchange between blood and interstitial fluid occurs at capillaries.
Formed as interstitial fluid drains into lymphatic vessels that begin in peripheral tissues and empty into the venous system.
The continuous recirculation of extracellular fluid is essential to homeostasis. It helps eliminate local differences in the levels of nutrients, wastes, or toxins; maintains blood volume and alerts the immune system to infections
Provides a flexible supporting framework. The matrix (firm gel) contains polysaccharide derivatives called chondroitin sulfates, that form complexes with proteins in the ground substance producing proteoglycans. Cartilage cells, or chondrocytes are the only cells in the cartilage matrix. They occupy small chambers known as lacunae.
Found between the tips of the ribs and the bones of the sternum, covering bone surfaces at mobile joints, supporting the respiratory passageways, and formin part of the nasal septum. It provides stiff but somewhat flexible support and reduces friction between bony surfaces.
supports the external ear and number of smaller internal structures. It tolerates distortion without damage and returns to original shape.
Found within knee joint, between pubic bones of pelvis, and in intervertebral discs of vertebral column. It resists compression, prevents bone-to-bone contact, and limits relative movement.
seperates cartilage from surrounding tissues. Two layers: 1. an outer fibrous layer of D. Irregular connective and 2. an inner, cellular layer.
Fibrous layer provides mechanical support and protection while cellular layer is important to growth and maintenance of cartilage.
Appositional and Interstitial Growth
Contains two-thirds of calcium salts and the rest of the matrix is collagen fibers. Makes the bone strong and somewhat flexible that is resistant to shattering.
Contains compact bone, the weight-bearing outer layer (organized), and spongy bone, lines the internal cavity.
Bone layers and arrangement
1. Mucous membrane (pg. 146)
2. Serious membrane
3. Cutaneous membrane
4. Synovial membrane
Connective tissue layers and wrappings that support and surround organs. Contain three types of layers:
- -The superficial fascia
- -The deep fascia
- -Subserous fasciapg. 147
Percentage Makeup of Tissues
- Neural tissue- 2%
- Epithelial tissue- 3%
- Connective tissue- 45%
- Muscle tissue- 50%
Specialized for contraction, which produces movement
Skeletal muscle tissue
- Move or stabilize the position of the skeleton
- guard entrances and exits to the digestive, respiratory, and urinary tracts
- generate heat and protect internal organs
Cardiac muscle tissue
Short, branched and striated. Interconnected at specialized intercellular junctions called intercalated discs. Moves blood and maintains blood pressure.
Smooth muscle tissue
Found throughout the body. Found in the skin, the walls of blood vessels, and in many digestive, respiratory, urinary and reproductive organs. Moves food, urine, and reproductive tract secretions; controls diameter of respiratory passageways and regulates diameter of blood vessels.
Specialized for conduction of electrical impulses from one region of the body to another. Found in brain and spinal cord.
Contains two types of cells: neurons and neuroglia. Pg. 151
Response to tissue injury
Involves inflammation and regeneration