The tissue level of organization - Epithelia tissue Flashcards
Define tissues
Collections of specialized cells and cell products that perform specific functions
What is histology
is the study of tissues
What are the four types of tissue
- Epithelial
- Connective
- Muscle
- Nervous
Describe epithelial tissue
– Covers exposed surfaces
– Lines internal passageways
– Forms glands
Describe the connective tissue
Fills internal spaces
– Supports other tissues
– Transports materials
– Stores energy
Describe the muscle tissue
Specialized for contraction
– Skeletal muscle, heart muscle, and muscular walls of hollow organs
Describe the nervous tissue
– Carries electrical signals from one part of the body to another
Epithelial tissue includes
– Epithelia (singular, epithelium)
* Layers of cells covering internal or external surfaces
– Glands
* Structures that produce fluid secretions
What is the function of the epithelial tissue
- Provide physical protection
- Control permeability
- Provide sensation
- Produce specialized secretions
States some characteristics of epithelia
– Polarity (apical and basal surfaces)
– Cellularity (cell junctions)
– Attachment (basement membrane)
– Avascularity (avascular)
– Regeneration
Describe the specializations of epithelial cells
- Move fluids over the epithelium (protection)
- Move fluids through the epithelium (permeability)
- Produce secretions (protection and messaging)
Explain polarity
4-2 Epithelial Tissue
▪ Specializations of epithelial cells
1. Move fluids over the epithelium (protection)
2. Move fluids through the epithelium (permeability)
3. Produce secretions (protection and messaging)
▪ Polarity
– Apical surface
* Microvilli increase absorption or secretion
* Cilia on a ciliated epithelium move fluids
– Basolateral surface
Identify the structures of the epithelia
How is the integrity of the epithelia maintaned
- Intercellular connections
- Attachment to the basement membrane
- Epithelial maintenance and repair
What is the purpose for intercellular connections
– Support and communication
* Cell adhesion molecules (CAMs)
– Transmembrane proteins
* Proteoglycans act as intercellular cement
– Contain glycosaminoglycans such as hyaluronan (hyaluronic acid)
What is cell junctions
Form bonds with other cells or extracellular material
What are the types of cell junctions
- Gap junctions
- Tight junctions
- Desmosomes
Describe gap junctions
– Allow rapid communication
– Cells held together by interlocking transmembrane
proteins (connexons)
– Allow small molecules and ions to pass
– Coordinate contractions in heart muscle
Describe the tight junctions
– Between two plasma membranes
– Adhesion belt attaches to terminal web
– Prevent passage of water and solutes
– Keep enzymes, acids, and wastes in the lumen of the digestive tract
Describe desmosomes
– CAMs and proteoglycans link opposing plasma
membranes
– Spot desmosomes
* Tie cells together
* Allow bending and twisting
– Hemidesmosomes
* Attach cells to the basement membrane
Identify the cell junctions on the cell
What is attached to the basement membrane
– Basal lamina
* Closest to the epithelium
– Reticular lamina
* Deeper portion of basement membrane
* Provides strength
Explain the epithelial maintenance and repair
– Epithelial cells are replaced by continual division of
stem cells
* Located near basement membrane
Explain the classification of epithelia
- Based on shape
* Squamous—thin and flat
* Cuboidal—square shaped
* Columnar—tall, slender rectangles - Based on layers
* Simple epithelium—single layer of cells
* Stratified epithelium—several layers of cells
Describe the simple squamous epithelia
– Simple squamous epithelia
* Absorption and diffusion
* Mesothelium
– Lines body cavities
* Endothelium
– Forms inner lining of heart and blood vessels
Explain the function of Stratified squamous epithelia
- Protect against mechanical stresses
- Keratin adds strength and water resistance
Describe simple cuboidal epithelia
- Secretion and absorption
- Glands and portions of kidney tubules
Describe stratified cuboidal epithelia
- Relatively rare
- Ducts of sweat glands and mammary glands
Describe the transitional Epithelia
– Tolerate repeated cycles of stretching without damage
– Appearance changes as stretching occurs
– Found in the urinary bladder
Describe simple columnar epithelia
- Absorption and secretion
- Found in stomach, small intestine, large intestine
Describe pseudostratified columnar epithelia?
- Typically have cilia
- Found in nasal cavity, trachea, bronchi
Describe stratified columnar epithelia
- Relatively rare
- Provide protection in pharynx, anus, urethra
Define Gland
Glands are collections of epithelial cells that produce secretions
What are the two types of glands and describe
– Endocrine glands
* Release hormones that enter bloodstream
* No ducts
– Exocrine glands
* Produce exocrine secretions
* Discharge secretions through ducts onto epithelial surfaces
Gland structure has
– Unicellular glands
– Multicellular glands
Describe the unicellular glands
– Goblet cells are unicellular exocrine glands
* In epithelia of intestines
* Secrete mucin, which mixes with water to form
mucus
Describe the multicellular glands
are classified by
1. Structure of the duct
* Simple (undivided)
* Compound (divided)
2. Shape of secretory portion of the gland
* Tubular (tube shaped)
* Alveolar or acinar (blind pockets)
3. Relationship between ducts and glandular areas
* Branched (several secretory areas sharing one
duct)
State the three methods of secretion
- Merocrine
- Apocrine
- Holocrine
Describe Merocrine secretion
Released by secretory vesicles (exocytosis)
– Example: merocrine sweat glands
Describe Apocrine secretion
– Released by shedding cytoplasm
– Example: mammary glands
Describe Holocrine secretion
– Released by cells bursting, killing gland cells
– Gland cells replaced by stem cells
– Example: sebaceous glands
What types of secretions are produced by exocrine glands
– Serous glands
* Watery secretions
– Mucous glands
* Secrete mucins
– Mixed exocrine glands
* Both serous and mucous
