Unit 1 Flashcards
(150 cards)
Characteristics of Four Basic Types of Tissue
1) Nervous-
- Cells-intertwining elongated processes
- ECM-none
- Main functions- transmission of nervous impulses
2) Epithelial-
- Cells-aggregated polyhedral cells
- ECM- very small amount
- Main f(x)n- lining of surface or body cavities, glandular secretion
3) Muscle-
- Elongated contractile cells
- ECM- moderate amount
- Main f(x)n- movement
4) Connective
- cells- several types of fixed and wandering cells
- ECM- abundant amount
- Main f(x)n- support and protection
The Preparation of Tissue for Light Microscopy
1) Fixation
- to preserve tissue morphology and molecular composition (12 h)
2) Dehydration in graded concentrated ethyl alcohol (70% up to 100%)
- to replace tissue water with organic solvents (6-24h)
3) Clearing in benzene, xylene or toluene
- to impregnate the tissues with a paraffin or a plastic resin solvent (1-6h)
4) Embedding in melted paraffin at 60 degrees C or plastic resin at room temperature
- paraffin or resin penetrates all intercellular spaces and even into the cells, making the tissues more resistant to sectioning (1-3h)
1) Fixation
2) Sectioning
3) Staining
Staining tissues
- used to localize and distinguish cell and tissue components
- Acidic stains (eosin) bind basic structures and components *cytoplasmic proteins
- Basic stains (hematoxylin) bind acidic tissue components (nucleic acids, RNA)
- the stain mixture of hematoxylin and eosin (H and E) is commonly used to distinguish the nucleus from the cytoplasm
Epithelium
- meaning upon nipple
- has closely coherent cells that form cellular sheets that cover and line the many surfaces and lumens of the body
- one can distinguish between covering epithelia and glandular epithelia
Functions of the Epithelium
- cover surfaces
- provide protection
- secrete and adsorb various substances
- transport particles
Thin, simple- transport
Thick stratifed-protection
Simple squamous
- lining of vessels (endothelium); serous lining of cavities; pericardium; pleura; peritoneum (mesothelium)
- fascilates the movement of the viscera (mesothelium), active transport by pinocytosis (mesothelium and endothelium), secretion of biologically active molecules (mesothelium)
Simple cuboidal
- covering the ovary, thyroid
- covering and secretion
Simple columnar
- lining of intestine, gallbladder
- protection, lubrication, absorption, secretion
Pseudostatified
- lining of trachea, bronchi, nasal cavitiy
- protection, secretion; cilia-mediated transport of particles trapped in mucus
Transitional: domelike to flattened,depending on the functional state of the organ (type of pseudostratified)
- bladders, ureters, renal calyces
- protection, distensibility
Stratified Squamous Keratinized
- epidermis
- protection; prevents water loss
Stratified Squamous (non-keratinized)
- mouth, esophagus, larynx, vagina, anal canal
- protection, secretion; prevents water loss
Statified Cubodial
- sweat glands, developing ovarian follicles
- protection, secretion
Stratified Columnar
- conjunctiva
- protection
General Features of Epithelial Cell Morphology
-polyhedral due to packing- columnar, cuboidal, squamous
- shape of nucleus corresponds to the shape of the cell
- most epithelial cells rest on CT
- digestive, respiratory, urinary system this underlying layer is called lamina propria
- irregularities in the contact area provide more area of contact
- small evaginations of the lamina propia are called papillae
Basal Lamina and Basement Membrane
- separates epithelial cells and CT
- composed of type IV collagen, laminin, entactin, and proteoglcans
- anchoring fibrils of type IV collagen attach the basal laminae to CT
- only visible with electron microscope, dense 20-100 nm of fine fibrils called lamina dense
- in some tissues, reticular fibers (type III collagen) are associated with the basal lamina forming a reticular lamina
- this thick layer of basal lamina and reticular lamina- basement membrane
Intercellular Adhesion and Intercellular Junctions
- the cohesion of epithelial cells is important for their function
- cadherins and interdigitations of lateral membrane contribute to this cohesion
- some epithelial (like in intestine) a junctional complex of zonula occludens (tight junction) and zonula adherens as well as desmosomes and gap junctions are found on the lateral surfaces
- zonulae occuludens play an important role in permeability
- hemidesmosomes help bind some epithelial cells to the basal lamina
Cell Specialization
- apical surface of many epithelial cells is modified to increase surface area or move particles
- microvilli are fingerlike extensions
- the microvilli and glycocalyx of small intestine are the striated border
- a slightly larger complex of microvilli of cells is on the proximal renal tubule and called the brush border
- sterocilia- long, nonmotile, extensions of apical surface in epidymis and ductus deferens
- cilia in respiratory system
- 9+2 arrangement of microtubules and are covered by cell membrane (5-10 microns long and 0.2 microns in diameter) and has basal body below plasma membrane
Rules for classifying epithelia
- all have two, some have three
- first: number of layers (simple, stratified, pseudostratifeid)
- second: shape of cells at most superficial layer (squamous, cubodial or columnar)
- third: if free surface of cell has cilia or kerain
Myoepithelial cells
-branched contractile cells found in secretory units of mammary, sweat and salivary glands
Endothelium
-simple squamous epithelium lining blood and lymphatic vessels
Mesothelium
-simple squamous epithelium lining body cavities such as the peritoneum
Epithelioid cells
-some tissues contain cells that are closely associated so that they resemble an epithelium
Epithelial Cell Renewal
- intestinal epithelial are renewed 4-6 days by mitotic activity of stem cells located in the lower portion of the intestinal glands (crypts of Lieberkuhn)
- skin cells are replaced in most sites 28 days and arise from stem cells in the basal layer of the epidermis
- in more complex glands can have longer lifespans