Chapter 5 -Tissues Flashcards
What are the four primary tissue types
- epithelial – covers and lines
- connective – provides support
- muscle – enables movement
- nervous – controls work
What is histology
the study of the microscopic structures of tissues and organs.
List seven functions of epithelia cells
(1) protect, cover, and line other tissues
(2) filter biochemical substances
(3) absorb nutrients
(4) provide sensory input
(5) manufacture secretions
(6) manufacture excretions
(7) act as an interface layer that separates and defines the beginning and ending of different types of tissues.
What four attributes characterize epithelial tissue
- Epithelial cells are polar
- Epithelial cells have lateral surfaces that are connected to neighboring cells by junctional complexes.
- All epithelial cells lack blood vessels or capillaries.
- Although some epithelia lack nerves (for example, those in the stomach, intestines, and cervix), most epithelial cells are innervated and provide valuable sensory input.
Describe how epithelial cells are polar
They have a sense of direction relative to surrounding structures. Each epithelial cell has an apical surface and a basal surface, which are quite different from each other. The apical surface is the side of the cell that faces the lumen or body cavity, and the basal surface is the side of the cell that faces the underlying connective tissue.
Describe epithelial junctions
These junctions bring the cells into close apposition to one another, leaving little room for extracellular matrix. The matrix that surrounds epithelia therefore exists in very small quantities, if at all.
List 4 types of cellular junction
- Tight junction:
- Desmosome:
- Hemidesmosome:
- Gap junction:
Describe tight junction
Formed by the fusion of the outermost layers of the plasma membranes of adjoining cells. The matrix-filled space between cells is lost at the site of a tight junction. For centrally placed cells, the fusion occurs as a strip that wraps around the entire circumference of the cell In this way, an impenetrable barrier is formed that prevents the passage of substances from the luminal end to the basal end of the cell and vice versa.
Tight junctions are found in tissues in which there can be no leaks—for example, in the urinary bladder, where urine is held, or in the digestive tract, where tight junctions play a critical role in preventing the leakage of digestive enzymes into the bloodstream.
Desmones
A strong, welded plaque that connects the plasma membranes of adjacent cells. The bond is a mechanical coupling formed by filaments that interlock with one another like velcro. Intermediate filaments, may also extend from the desmosomic plaque into the cytoplasm of each cell like anchors. In this way, desmosomes form tough bonds between cells and therefore are found most commonly in tissues that undergo repeated episodes of tension and stretching, such as the skin, heart, and uterus.
Hemidesmosome:
junctions that look like half-desmosomes and link epithelial cells to the basement membrane.
Gap junction
Made of tubular channel proteins called connexons and extends from the cytoplasm of one cell to the cytoplasm of another. These transmembrane proteins allow the exchange and passage of ions and nutrients from one cell to another.
Gap junctions are most commonly found in intestinal epithelial cells, the heart, and smooth muscle tissue.
Not as important- The function of gap junctions in epithelial cells is not yet fully understood, but their ability to quickly transport electrical signals from one cell to another explains their presence in cardiac and smooth muscle cells, where they help coordinate contraction.
Explain how basement membrane acts as a partial barrier
It is a nonliving meshwork of fibers. Oxygen and nutrient molecules diffuse through the basement membrane from capillaries in the underlying connective tissue. Similarly, nutrient substances that are absorbed and waste that is excreted by the epithelium diffuse across the basement membrane into the blood supply of the connective tissue.
Role of cilia and microvilli in epithelial tissue
Microvilli increase the surface area of cells and allow more absorption and secretion. Ciliary movement occurs in coordinated “beats” that enable the efficient transport of material. In the trachea, cilia help propel mucus and debris up and away from the lungs toward the mouth. In the uterine tube, the beating motion of cilia encourages newly released ova into the oviduct, or infundibulum.
Where are cilia and microvilli found in epithelial cells
Microvilli are found on epithelial cells in the intestines and urinary tract. Cilia are found on the free surfaces of cells, usually in the respiratory and urogenital tracts.
Transitional epithelium is only found where
the urinary bladder
List the characteristics used to describe epithelial tissue
Number of layers and cell shape
What cells are generally rapidly dividing
epithelial
list the components of the neuron
Axon, dendrites and the perikaryon (body)
Epithelial cell shapes
Squamous
Cuboidal
Columnar
Epithelial cell layers
Simple - 1 layer
Pseudostratified 1 (modified simple, looks like more than 1)
Stratified - more than 1 layer
Transitional (more than one)
What are the two types of epithelial cells
sheets or glands
Describe the two poles of epithelial cells
Apical is towards the surface and Basal is towards the basement membrane
Basement Membrane
Foundation of epithelial cell
Nonliving network of fibers
-cements cells to underlying tissues
Helps prevent cells from being torn off
Parietal barrier to underlying tissue
Basal Lamina
Basement membrane
