Intro to Histology: Epithelial 4.0-4.2 Flashcards
Histology
refers to the study of tissues
Tissues
Are a group of similar cells that are specialized to perform a specific function. Ex) nervous tissues are specialized to conduct nerve impulses
Stem Cells
Cells that are capable of becoming a variety of cells. Ex hemocytoblast
Toitpotent
The ability of a cell or group, to produce all tissues needed for development (zygote)
Pluripotent
The ability of a cell to produce a limited number of different cells. ( hemocytoblast makes seven different blood cells)
Differentiation
Cells specialize depending upon the environment.
Intracellular
Within a cell
Intercellular
Between cells
Apoptosis
programmed cell death ( statifed squamous epithelium of skin)
Nercorsis
Death of cells due to injury / diease
Hypertrophy
Increase in size of cells
Atrophy
Decrease in size or number of cells , Ex ( lack of excecise osteoporosis)
Hyperplasia
Increased in number of cells , anemia causes increase RBC
Metaplasia
Change in type of cell
Neoplasia
Change in cellular DNA, makes different and cancerous
Tissue Types
- Epithelia
- Connective
- Muscle
- Nervous
Epithelia Tissues
Covers all exposed surfaces inside and out Ex ( Lining of organs, glands, skin) Composed of covering or lining that lines skin, digestive, organ walls etc.
Glandular epithelium forms the glands.
Connective Tissues
Fills internal spaces, provides structural support, transports materials, stores energy Ex ( Bones, tendons, fats)
Muscle
Specialized for contraction
Nervous / Neural
Carriers information from one area in the body to another via electric impulses.
Epithelial Tissues Characteristics
- Cellularity:
- Polarity
- Attachment
- Avascularity
- Regeneration
Cellularity
highly cellular, tight junctions
Polarity
Epithelial have apical surface and basale surface and all is attached via the basement membrane.
Attachment
Base of epithelium bound to the connective tissue, known as basement membrane.
Epithelia tissues are bound via tight junctions and desmosomes. The basement membrane reinforces the sheet consists of two layers–> reticular lamina (deeper) and basal lamina.
Avasculairty
Lacks blood vessels, obtains nutrients absorption, it is still innervated and supplied via nerve fibers. Cells are nourished by substance diffusing from vessels into underlying connective tissues.
Regeneration
Constantly lost and replaced through cell division. Some cells are exposed to friction etc.
Epithelial Functions
- Protection ( epithelial protect exposed surfaces from abrasion, dehydration, destruction)
- Permeability ( substances that enters/ leaves), callus formation
- Sensation ( sensitive due to large neuron connections)
- Secretion ( gland cells that secrete protective secretions or chemical messengers in the inters.)
Glandular
Absorption
Protective
Secretory
Epithelial Specializations
- Specialized for the movement of fluids over the epithelial surface
- Fluids through the epithelium and production of secretions , absorption
Maintaining Integrity through Intercellular connections
- CAMS ( Cell adhesion molecules) are transmembrane proteins which bind to each other and to extra cellular materials.
- Intercellular Cement: thin layer of proteoglycans that contain polysaccharide derivatives called hyaluronic acid.
- Cell Junctions: specialized cells in the plasma membrane that attach a cell to another
Cell Junctions
- Gap Junctions: two cells joined via connexions, allow for communication.
- Occluding (tight) Junctions: bound memberous proteins membrane together. Do not allow water to pass through.
- Desmosomes: strong connections for mechanical stress. Cadherins proteins
- Hemidesosomes: resemble half a desmosome, found in basement membrane to attach extracellular filaments to basal lamina.
- Spot desmosomes : small discs found in intermediate filaments.
Attachment to Basal Lamina
- Basal Lauina
2 layers:
- lamina Lucida (clear layer): Layer contains glycoproteins, the permeability decreases through large proteins and molecules.
- Lamina Densa underneath (dense layer): Bundles of protein fibers give basement mem. strength and structure. Hemidesosomes attach the basement membrane to the epithelium.
Regeneration
Stem cells near basement membrane are called Gemative layers of cells that repair the epithelial structure.
Tissue Classifications
Named according to the arrangement and shape of cells in apical layer. Meaning you name based off of the top layer not the bottom or Basal layer.
1. Simple ( one layer) vs Stratified ( more than one layer thick) –> arrangement
2. Shape–> Squamous , Cuboidal, Columnar shape impacts nuclues
GAPS
Glandular
Absorption
Protective
Secretory
Know what tissues look like, found, function
Simple Squamous Epithelium
“one cell thick” and a squished appearance
Location: Lining of the alveoli, capillaries, lymph vessels, organs
Function: passive absorption ( diffusion) of gases. Secretes serous fluid to lubricate organs.
Endothelium ( lining of heart)
Mesothelium ( lining of ventral body cavities, serous membranes)
Serous Membranes –> reduce friction and secrete serious fluid.
Stratified Squamous Epithelium
Description: thick membrane of many layers
Cells near the basement membrane are cuboidal or columbar and alive
Cells near the surface are squamous and full of keratin and dead. Cells closer to the blood vessels can receive nutrients while as you move outward, they become depleted and die out.
Location: found in aread of high wear, tear ( skin, anus, mouth lining)
Kertain is tough, insoluble protein that accumulates in cells on surface.
Function: The epithelium protects from cuts, bacteria, scrapes and water proofs.
Simple Cuboidal Epithelium
Description: short, cube liked appearance with a large centred nucleus.
Location: glands, ovaries, kidney tubules
Function: cuboidal epithelium cells secrete substances in glands and in they kidney tubules they absorb water and solutes
Transitional Epithelium
Description: outer cells are rounded not flattened like stratified squamous. Layers of cuboidal and elongated cells held tightly. Outer cells alive
Location: Ureters, urinary bladder, part of urethra
Function: able to distend allows for expansion and contraction. Prevent the passage of urine into other areas.
Simple Columnar Epithelium
Description: elongated column shaped cells , one cell thick, nuclei are arranged near bottom of cells.
Location: Lines the digestive tract from stomach through to rectum. Found in gallbladder and oviducts.
Function: Absorption, secretion of mucous, movement of material (mucus and reproductive cells)
Goblet Cells: secrete mucus which protects and lubricates the tissues.
Brush Border: contains microvilli which vastly increases the surface area of the cell for absorption.
Pseudostratified Ciliated Columnar Epithelium
Description: Cells vary in height and only the tallest cells reach the free surface ( simple tissue)
Cell nucleus are at different heights which give it the false (pseudo) stratified look Cells are columnar shape
Location: trachea, upper resp tract, sperm ducts
Function: Secretes, absorbs substances. Protects the respiratory tract by sweeping dirt towards pharynx.
Cilia ( sweep dirt back towards pharynx)
Goblet cells ( secrete mucus which collect bacteria , moistness the resp. tract)
Glands
Endocrine and exocrine
Endocrine Glands
Have an intracellular effect ( inside cell)
Secretes hormones into the interstitial fluid–> blood
Ductless ( no ducts)
Exocrine glands
Secrete onto epithelial surface
Have ducts
Have extracellular effect
Ex (enzymes)
Glands Structure
Meocrine glands: most abundant, exocytosis, meocrine sweat glands
Holecrine glands: ( destroy cells) glands destroy whole cell in secretion. Ex (sebaceous glands –> sebum)
Aprocrine glands: apical surface is lost , milk glands
Secretion types
Serous Gland ( watery solution has enzymes ( parotid gland)
Mucous Gland (mucins that hydrate form mucus (sublingual gland)
Mixed Exocrine Glands ( contain more than 1 gland cell type and can produce two different exocrine secretions. ( submandibular gland)
