CH4 Flashcards
how do the four types of tissues in the human body contribute to homeostasis?
provides diverse functions including protection, support, communication among cells, resistance to disease, etc.
what are the structure and properties of a specific tissue influenced by?
factors such as the nature of the extracellular material that surrounds the cells and the connections between the cells that compose the tissue
what are tissues?
group of cells that usually have a common embryonic origin and function together to carry out specialized activities
what are the four types of tissues?
epithelial, connective, muscular, and nervous
what are epithelial tissues?
tissues that cover body surfaces and lines hollow organs, body cavities, and ducts, and forms glands
what do epithelial tissues allow the body to do?
allows the body to interact with both its internal and external environments because they have a free/apical surface
what are connective tissues?
- tissues that protect and support the body and its organs
- bind organs together, store energy tissues as fat, helps the body by providing immunity to disease-causing organisms
what are muscular tissues?
tissues composed of cells specialized for contraction and generation of force, generates heat in the process that warms the body
what are nervous tissues?
tissues that detect changes in a variety of conditions inside and outside the body and responds by generating electrical signals called nerve action potentials/nerve impulses that activate muscular contracts and glandular secretions
what are some key differences in function among the four tissue types?
what is a biopsy?
removal of a sample of living tissue for microscopic examination
what do biopsies do?
procedure is used to help diagnose many disorders, especially cancer, and to discover the cause of unexplained infections and inflammations
why are biopsies sometimes conducted during surgery?
helps physician determine most appropriate treatment
ex: if thyroid tissue reveals malignant cells, surgeon can proceed immediately with most appropriate procedure
what are cell junctions?
contact points between plasma membranes of tissue cells
what are the four types of cell junctions?
- tight junctions
- adhering junctions
- desmosomes
- hemidesmosomes
- gap junctions
what are tight junctions?
junctions consisting of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells
what is the function of tight junctions?
- inhibits passage of substances between cells
- prevents contents of organs from leaking into blood or surrounding tissues
where can you find tight junctions?
where leakage is not desirable
- epithelial cells that line stomach, intestines, and urinary bladder
what are adhering junctions?
junctions that contain plaque and cadherins as well as actin microfilaments, often forming adhesion belts because they encircle the entire cell
what is plaque?
dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to actin microfilaments of the cytoskeleton
what are cadherins?
transmembrane glycoproteins
- inserts into the plaque from the opposite side of the plasma membrane, partially crosses the intercellular space, and connects to cadherins of an adjacent cell
what is the function of adhering junctions?
helps epithelial surfaces to resist separation during various contractile activities, like when food moves through the intestines
- to stick cells together
where can you find adhering junctions?
in the intestines
what are desmosomes?
- contain plaque and cadherins but the plaque does not attach to microfilaments and instead attaches to intermediate keratin filaments, plaque is discontinuous
- the keratin microfilaments extend from desmosomes on one side of cell across the intracellular fluid to desmosomes on the opposite side of the cell, contributing to stability of the cells and the tissue
what is the function of desmosomes?
prevents epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction
where can you find desmosomes?
common among cells that make up the epidermis and among cardiac muscle cells in the heart
what are hemidesmosomes?
- similar to desmosomes but do not link adjacent cells
- contains integrins which attaches to keratin on the inside of cell membrane
- integrins attach to laminin present in the basement membrane on the outside of cell membrane
what is the function of hemidesmosomes?
anchors cells not to each other but to the basement membrane
what are gap junctions?
- junctions where connexins form connexons that connect neighbouring cells
- plasma membrane are separated by narrow intercellular gap
what are connexins?
membrane proteins present in gap junctions
what are connexons?
tiny-fluid filled tunnels that connect neighbouring cells, present in gap junctions
what is the function of gap junctions?
- ions and small molecules can diffuse through connexons
- passage of large molecules such as vital intracellular proteins is prevented
- allows cells in a tissue to communicate with one another
- enables nerve or muscle impulses to spread rapidly among cells
where can you find gap junctions?
- avascular tissues such as the lens and cornea of the eye
- tissues where rapid communication is needed, such as parts of the nervous system and for the contraction of muscle in the heart, gastrointestinal tract, and uterus
- in developing embryo, where signals that regulate growth and cell differentiation travel through gap junctions
which types of gap junctions are found in epithelial tissue?
- adhering junctions
- hemidesmosomes
- tight junctions
which type of cell junction prevents the contents of organs from leaking into surrounding tissue?
tight junctions due to the lack of intercellular space
what are some major structural differences between an epithelial tissue and connective tissue?
in epithelial:
- cells tightly packed together
- avascular
- no extracellular matrix
- has a free/apical surface
in connective:
- cells far away
- vascular
- a lot of extracellular matrix
- no free/apical surface
why are epithelial tissues and connective tissues almost always found immediately adjacent to each other?
epithelial lacks blood vessels, so is next to vascular connective tissue, enables it to make exchanges with blood necessary for the delivery of oxygen and nutrients and the removal of wastes
why is there little intercellular space between adjacent plasma membranes of epithelial cells?
cells are closely packed together and are held tightly by many cell junctions
what are the two types of epithelial tissues?
- surface epithelium
- glandular epithelium
what is surface epithelium?
covers or lines a surface in the body exposed to the outside
where can you find surface epithelium?
- outer covering of skin and internal organs
- inner lining of blood vessels, ducts, body cavities
- lining of respiratory, digestive, urinary, and genital surfaces
what is glandular epithelium?
epithelial tissue that makes up the secreting portion of glands
what are the functions of glandular epithelium?
- protects
- secretes (mucus, hormones, enzymes)
- absorbs (nutrients in digestive canal)
- excretes (various substances in urinary tract)
where can you find glandular epithelium?
- thyroid gland, adrenal glands, sweat glands, digestive glands
what are the surfaces of surface epithelium?
- apical/free surface
- lateral surface
- basal surface
what is the apical surface?
- most superficial layer
the surface of an epithelial cell that faces the body surface, a body cavity, the lumen of an internal organ, or a tubular duct that receives cell secretions - may contain cilia or microvilli
what is the lateral surface?
- the surface of an epithelial cell that face adjacent cells on either side
- may contain tight junctions, adhering junctions, desmosomes, gap junctions
what is the basal surface?
- opposite to the apical surface, most deep layer
- deepest layer of epithelial cells adhere to extracellular materials like the basement membrane
- hemidesmosomes anchor epithelium to the basement membrane
how do basement membranes become thickened?
increased production of collagen or laminin, thickening in small blood vessels leads to reduced function
what is the basement membrane?
thin, extracellular layer that commonly consists of two layers, the basal lamina and reticular lamina
what is the function of the basement membrane?
- attaches and anchors the epithelium to the connective tissue
- forms a surface along which epithelial cells migrate during growth or wound healing
- restricts passage of larger molecules between epithelium and connective tissue
- participates in filtration of blood in kidneys
what is the basal lamina?
layer closest to, and secreted by, the epithelial cells
- contains laminin, collagen, glycoproteins, proteoglycans
what function does the protein laminin have in the basal lamina?
laminin adheres to integrins in hemidesmosomes and thus attaches epithelial cells to the basement membrane
what is the reticular lamina?
layer closest to connective tissue
- contains collagen produced by fibroblasts
what process allows for exchange of substances between epithelial tissue and connective tissue?
diffusion, does not require ATP and relies on kinetic energy of molecules
why is epithelial tissue constantly being renewed?
- epithelial tissues are subjected to physical stress and injury, thus they form boundaries within the body’s organs, or between the body and the external environment
- high rate of cell division allows them to constantly renew and repair by sloughing off dead/injured cells and replacing them with new ones
what happens when epithelial tissue and nervous tissue combine?
special organs are formed for smell, hearing, vision, and touch
what are some of the most important functions of epithelial tissue?
- protection
- filtration
- secretion
- absorption
- excretion
what is simple epithelium?
single layer of cells
- diffusion, osmosis, filtration, secretion, absorption
what is secretion?
production and release of substances such as mucus, sweat, enzymes
what is absorption?
intake of fluids or other substances such as digested food from the intestinal tract
what is pseudostratified epithelium?
simple epithelium, single layer of cells where cell nuclei lie at different levels and not all cells reach apical surface
what is stratified epithelium?
two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear
what are squamous cells?
thin, flat epithelial cells which allow for rapid passage of substances through them
what are cuboidal cells?
epithelial cells as tall as they are wide, shaped like cubes/hexagons
- may have microvilli on apical surface
- function in secretion/absorption
what are columnar cells?
epithelial cells much taller than wide, like columns
- protect underlying tissues
- may have cilia/microvilli
- often specialized for secretion/absorption
what are transitional cells?
epithelial cells that change shape
ex: cells in urinary bladder stretch/distend to a larger size and collapse to a smaller size
what is endothelium?
simple squamous epithelium that lines the cardiovascular and lymphatic system (heart, blood vessels, lymph vessels)
what is mesothelium?
simple squamous epithelium that forms epithelial layer of serous membranes of abdominal and thoracic cavities ( peritoneum, pericardium, pleura)
what are the two types of stratified squamous epithelium?
nonkeratinized and keratinized
which cell shape is best adapted for the rapid movement of substances from one cell to another?
squamous epithelial cells - flat and thin
what is simple squamous epithelium?
single layer of flat cells, centrally located nucleus that is flattened and oval or spherical in shape, resembles tiled floor when viewed from apical surface
what is the function of simple squamous epithelium?
present at sites of filtration or diffusion and at site of secretion in serous membranes
- not found in body areas subjected to mechanical stress
what is simple cuboidal epithelium?
single layer of cube-shaped cells, centrally located nucleus
what is the function of simple cuboidal epithelium?
secretion and absorption
where can you find simple cuboidal epithelium?
makes up secreting portion of some glands (thyroid) and ducts of some glands (pancreas)
what is nonciliated simple columnar epithelium?
single layer of nonciliated columnlike cells with oval nuclei near base of cells
- contains columnar epithelial cells with microvilli at apical surface and goblet cells
what are microvilli?
fingerlike cytoplasmic projections that increase surface area of plasma membrane, increasing cell’s rate of absorption
what are goblet cells?
modified columnar epithelial cells that secret mucus at their apical surfaces
where can you find nonciliated simple columnar epithelium?
- lines digestive canal (from stomach to anus)
- ducts of many glands
- gallbladder
what is the function of nonciliated simple columnar epithelium?
secretion and absorption
- secreted mucus lubricates linings of digestive, respiratory, and genital tracts and most of urinary tract
- helps prevent destruction of stomach lining by acidic gastric juice secreted by stomach
why are columnar cells capable of higher level of secretion and absorption than cuboidal cells?
larger, contain more organelles
what is ciliated simple columnar epithelium?
single layer of ciliated columnlike cells with oval nuclei near base of cells, goblet cells are usually interspersed
where can you find ciliated simple columnar epithelium?
lines some bronchioles of respiratory tract, uterine tubes, some paranasal sinuses, central canal of spinal cord, and brain ventricles
what is the function of ciliated simple columnar epithelium?
- cilia beat in unison, moving fluid across cell surfaces
- secretion of mucus also allows for lubrication of lining
what is nonciliated pseudostratified columnar epithelium?
- appears to have several layers, nuclei of cells are at various levels
- all cells attached to basement membrane but some do not reach apical surface
- lacks goblet cells
where can you find nonciliated pseudostratified columnar epithelium?
lines epididymis, larger ducts of many glands, and parts of male urethra
what is the function of nonciliated pseudostratified columnar epithelium?
secretion and absorption
what is ciliated pseudostratified columnar epithelium?
- appears to have several layers, nuclei of cells are at various levels
- all cells attached to basement membrane but some do not reach apical surface
- contains cells that extend to surface and secret mucus or bear cilia
what is the function of ciliated pseudostratified columnar epithelium?
secretes mucus that traps foreign particles, and cilia sweep away mucus for elimination from body
where can you find ciliated pseudostratified columnar epithelium?
lines airways of most of upper respiratory tract
what is stratified squamous epithelium?
two or more layers of cells, cells in apical layer and close to it are squamous
how is stratified squamous epithelium renewed?
- as basal cells divide, daughter cells arising from cell divisions push upward to apical surface
- as they move away from blood supply in connective tissue, they become dehydrated and less metabolically active
- tough proteins predominate as cytoplasm reduced, cells become tough hard structures that eventually die
what is keratinized stratified squamous epithelium?
stratified squamous epithelium that developed tough layer of keratin in apical layer of cells
- relative amount of keratin increases in cells as they move away from nutritive blood supply and organelles die
what is keratin?
tough, fibrous intracellular protein that helps protect skin and underlying tissues from heat, microbes, and chemicals
what is nonkeratinized stratified squamous epithelium?
stratified squamous epithelium that does not contain large amounts of keratin in apical surface
- constantly moistened by mucus from salivary and mucous glands
- surface cells do not die in epithelium, shed before they die