Flashcards in Chapter 4: Tissue Level Of Organization: Tissues And Homeostsis Deck (117)
What are cell junctions?
Contain points between the plasma membranes of tissue cells.. Tightly packed into functional units
What are the 5 most important types of cell junctions?
Tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions
What are tight junctions?
Weblike strands of transmembrane proteins that fuse to the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells. E.g., cells of epithelial tissue that lines the stomach, intestines, and urinary bladder. Inhibit the passage of substances between cells.. prevents contents from these organs from leaking into blood and surrounding tissues
What are adherens junctions?
Dense layer of proteins on the inside of the plasma membrane that attaches to both the membrane proteins and the microfilaments of the cytoskeleton.The transmembrane proteins are called CADHERINS and join the cells. Form adhesion belts in epithelial cells. Helps epithelial surfaces resist separation during contractile activities like food moving through intestines
What are desmosomes?
Contains plaque and have transmembrane glycoproteins that extend into intercellular space between adjacent cell membranes and attach cells to one another (similar to adherens). But unlike adherens junctions, the plaque of desmosomes doesn't attach to microfilaments but rather attaches to elements of the cytoskeleton called INTERMEDIATE FILAMENTS (consists of the protein keratin). Contributes to stability of cells and tissues. Common in cells that make up the epidermis and cardiac muscle cells. Prevents epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction.
What are hemidesmosomes?
Resembles desmosomes but don't link adjacent cells. Transmembrane glycoproteins are integrins rather than cadherins. On the inside of the plasma membrane, integrins attach to intermediate filaments (made of keratin). On the outside of plasma membrane they attach to the protein LAMININ which is in the basement membrane. Therefore, anchors cells to the basement membrane.
What are gap junctions?
Membrane proteins called CONNEXINS form tiny fluid-filled tunnels called CONNESNS that connect neighbouring cells. The plasma membranes of gap junctions are not fused together as in tight junctions but are separated by a narrow intercellular gap. Through the connexons, ions and SMALL molecules can diffuse from the cytosol of one cell to another. Transfer of nutrients and perhaps wastes in avascular tissues like the lens and cornea of the eye. Allows the cells in a tissue to communicate with one another. Enables nerve, muscle, and impulses to spread rapidly among cells.
What are the 3 differences between epithelial and connective tissue?
1) Epithelial cells have many cells tightly packed together so has little to no EC matrix. Connective tissue has a lot of EC matrix that separates cells. 2) Epithelial cells have no blood vessels and connective tissue does. 3) Epithelial cells almost always form surface layers and not covered by other tissue (except the epi lining of blood vessels)
Why are epithelial tissue located right next to connective tissue?
Since epi tissue lacks blood vessels and forms surfaces, it needs to be adjacent to blood vessel-rich connective tissue because it enables it to make exchanges with blood necessary to deliver O2 and nutrients and remove waste
What are the 3 main functions of epithelial tissues?
1) Selective barrier, 2) Secretory surface (releases products produced by cells onto its free surfaces), and 3) Protective surface
What is the apical, lateral and basal surface?
Apical is the most superficial epithelial layer. Faces the body surface, body cavity, lumen (interior space) of an internal organ, or tubular duct. Lateral surface faces the adjacent cells on either side. Basal surface is the deepest layer of cells. Adheres to EC materials like the basement membrane (so hemidesmosomes anchor epi to basement membrane)
What are the 2 layers of the basement membrane?
1) Basal lamina: Closer to epithelial cells. Contains proteins like laminin, collagen, glycoproteins, and proteoglycans... adheres to integrins in hemidesmosomes and therefore attaches epi cells to basement membrane. 2) Reticular lamina: Closer to the underlying connective tissue. Contains proteins and collagen produced by connective tissue cells called friboblasts.
What are some functions of the basement membrane?
1) Form a surface that epi cells migrate during growth/wound healing. 2) Restricts passage of large molecules between epithelium and connective tissue. 3) Participates in filtration of blood in kidneys
What are 2 types of epithelial tissue?
1) Covering and lining epithelium (outer surface of skin and some organs. Inner lining of blood vessels, ducts, body cavities, respiratory system, digestive system, urinary system, repro system). 2) Glandular epithelium (Secreting portion of glands... like thyroid, adrenal sweat glands).
Types f covering and lining epithelial tissue is classified according to these 2 characteristics:
1) Arrangement of cells in layers and 2) Cell shapes
What is simple epithelium?
Single layer of cells that function in absorption, secretion, diffusion, osmosis and filatration.
What is pseudostratified epithelium?
Multi layers of cells. Simple epithelium because all its cells rest on basement membrane. Cells that extend to apical surface may contain cilia... others (goblet cells) secrete mucus
What is stratified epithelium?
2 or more layers of cells that protect underlying tissues where there's considerable wear and tear.
What are the 4 shapes of cells?
Squamous, cuboidal, columnar, and transitional.
What are squamous cells?
Thin so allows rapid passage of substances
What are cuboidal cells?
Tall and wide. Shaped like cubes and hexagons. Many have microvilli at their apical surface and function in secretion/absorption.
What are columnar cells?
Taller than they are wide... protects underlying tissue. Their apical surfaces may have cilia or microvilli. Often specialized for secretion and abosorption.
What are transitional cells?
Change shape. Like in organs that stretch like the urinary bladder (stretches to a larger size and then collapses to a smaller size).
Name different types of simple epithelium
Simple squamous epithelium, simple cuboidal epithelium, simple columnar epithelium (non ciliated and ciliated), and pseudostratified columnar epithelium (non ciliated and ciliated).
What are the types of stratified epithelium?
Stratified squamous epithelium (keratinized when surface cells are dead and hardened, non keratinized when surface cells remain alive), stratified cuboidal epithelium, stratified columnar epithelium, and transitional epithelium.
What is the function of glandular epithelium?
Secretion. A gland may consist of a single cell or group of cells that secrete substances into ducts, a surface or into the blood
What are the two types of glands?
Endocrine and exocrine
Two types of exocrine glands?
Unicellular and multicellular
What are unicellular glands?
Single cell exocrine glands. Goblet cells are important unicellular exocrine glands that secrete mucus directly onto the apical surface of a lining epithelium