Chapter 4 Histology Flashcards
Histology
Study of normal structures of tissues
Tissues
Group of structurally and functionally related cells and their external environment, together perform common functions)
2 Components of Tissues
- Discrete population of cells; related in structure and function
- Extracellular matrix (ECM) - surrounding material
4 Primary tissue types
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue
Epithelial Tissue
-Cover and line all body surfaces and cavities.
-Tightly packed sheets of cells with no visible ECM
-Form glands that manufacture secretions
Connective Tissue
-Connect all other tissues to one another
-ECM is very prominent
-Cells are scattered out
-Bind, support, protect and allow for transportation of substances
Muscle Tissue
-Capable of generating force by contracting
-Little ECM between cells
Nervous Tissue
-Capable of generating, sending, and receiving messages
-Within unique ECM
Extracellular Matrix (ECM)
Substance in liquid, thick gel, or solid form that surround cells of tissue
2 Components:
1. Ground substance
2. Protein Fibers
Functions of ECM
–Provides tissue with strength to resist tensile (stretching) and compressive forces
–Directs cells to proper positions within tissue and holds those cells in place
–Regulates development, mitotic activity, and survival of cells in a tissue
Ground Substance
- Most of ECM
-Extracellular fluid (ECF or interstitial fluid) with water, nutrients, ions, and three families of macromolecules:
- Glycosaminoglycans (GACS)
- Proteoglycans
- Cell- adhesion molecules (CAMs)
Glycosaminoglycans (GACS)
chondroitin sulfate (small) and hyaluronic acid (enormous):
Negative charges of sugars in GAG attract positively charged ions in ECF
Ions create concentration gradient within ECF; draw water out of cells and blood vessels by osmosis
Effectively “trap” water in ECM; help ECM to resist compression; GradientsCore Principle
Proteoglycans
GAGs bound to protein core (resembles bottle brush):
Thousands of proteoglycans bind to very long GAG (such as hyaluronic acid); form huge proteoglycan “aggregates”
Make ECM firmer, more solid, and resistant to compression
Form barrier to diffusion of substances through ECM; protect underlying tissue from invading microorganisms
Cell adhesion molecules (CAMs)
Different types of glycoproteins:
Adhere to cell and cells to surroundings; hold everything in place within ECM
CAMs bind to cell surface proteins as well as protein fibers and proteoglycans; maintain normal tissue architecture
Protein Fibers
Embedded within ground substance; long molecules composed of multiple fibrous subunits with rope like structure; enormous tensile strength.
- Collagen fibers
- Elastic fibers
- Reticular fibers
Collagen Fibers
- Make up 20–25% of all proteins in body
- Composed of multiple repeating subunits
- Form white fibrous protein
- Resistant to tension (pulling and stretching forces) and pressure
Elastic Fibers
- Composed of protein elastin surrounded by glycoproteins
- Extensibility allows fibers to stretch up to one and a half times resting length without breaking. once stretched, fibers return to resting length (elasticity)
Reticular Fibers
- Thin, short collagen fibers; form meshwork or scaffold that supports cells and ground substance of many tissues
- Form weblike structure in organs such as spleen that helps trap foreign cells
Marfan Syndrome
Results from defects in gene that codes for glycoprotein fibrillin-I
Fibrillin
Component of ECM required for normal deposition of elastic fibers
Characteristics and symptoms of Marfan Syndrome
*Tall stature with long limbs and fingers; multiple skeletal abnormalities, recurrent joint dislocations, heart valve and lens (eye) abnormalities, and dilation of aorta
*Aortic dissection (rupture) – most lethal complication; layers of aortic wall separate and blood flows between them; leads to aortic rupture; ensuing blood loss is nearly always fatal if not caught and treated immediately
Cell Junctions
Another way cells bind to one another; neighboring cell’s plasma membranes are linked by integral proteins:
*Tight junctions *Desmosomes
*Gap junctions
Tight Junctions
(occluding junctions)
Holds cells closely together, space between is impermeable to movement of macromolecules
–Integral proteins of adjacent cell’s plasma membranes are locked together; form seal around apical perimeter of cell
–Seal may not be complete, allowing for leakage in some tissues
Example – between cells in blood vessels; prevent blood cells from exiting vessels
Desmosomes
Linking integral proteins; allow for materials in extracellular fluid to pass through space between cells
–Increase strength of tissue by holding cells together; mechanical stress is more evenly distributed
–Integral “linker” proteins are attached to intermediate filaments of cytoskeleton for structural reinforcement
–In tissues subjected to great deal of mechanical stress (epithelia of skin)
Gap Junctions
small pores formed by protein channels between adjacent cells; allow small substances to flow freely between each cell’s cytoplasm
–In between cells that communicate with electrical signals (cardiac muscle cells)
–Gap junctions illustrate Cell–Cell Communication Core Principle
Epithelial Tissues
On every internal and external body surface. It is the barrier between body and external environment (line organs and fluid filled cavities)
Functions of Epithelial Tissues
- Protection
- Immune defenses
- Secretion
- Transport into other tissues
- Sensation
Protection
Shield underlying tissues from mechanical and thermal injury
Immune defense
Form physical barriers; prevent invasion by microorganisms; specialized cells of immune system are scattered throughout epithelial tissues to protect underlying tissues
Secretion
Form glands that produce substances like hormones and oils; secreted into blood or through ducts respectively
Transport into other tissues
Selective permeable membranes; substances are able to cross these barriers by passive or active transport and enter other tissues
Sensation
Associated with rich nerve supply, detect changes in internal and external environments
Ex: tastebuds
Esophagus
Tubular organ that transports food from mouth to stomach.
Identifying a cell
Any structure that contains dark purple nucleus
Identifying Ground substance
Looks clear or has a slight tinge of color
Identifying protein fibers
Look like wavy or straight lines
Identifying Collagen fibers
Form bundles that resemble certain cell types.
- If bundles lack nuclei then it is most likely a collagen fiber
Sublingual gland
Salivary gland that produces saliva under tongue
-Contains clusters of small, light red round discs that lack nuclei
Discs
Red blood cells (erythrocytes), located in blood vessels
Classification of Epithelial Tissues
Consist of tightly packed cells linked together by tight junctions and desmosomes.
-Make sheets of cells impermeable and resistant to physical stresses and mechanical injury
Avascular
(Epithelial tissues are avascular)
-Lack blood vessels, must obtain oxygen and nutrients by diffusion from deeper tissues
ECM Location
Found beneath cells in think Basement Membrane
Basement Membrane
Two components/layers :
- Basal lamina
- Reticular lamina
-These two layers “glue” and provide barrier to epithelial tissue to underlying connective tissue, anchor underlying blood vessels in place.
Basal Lamina
ECM synthesized by epithelial cells
-Consist of collagen fibers and ground substance
Reticular Lamina
Synthesized by underlying connective tissue
- Consist of reticular fibers and ground substance
Epithelial Tissues, classified by
Number of cells layers and shape of cells
Simple epithelia
Single cell layer, adapted for transportation of substances between different tissues
-Some have microvilli
-Some have cilia
Stratified epithelia
More than one cell layer
Squamous Cells
Flattened
Cuboidal Cells
Short
Columnar Cells
Tall and elongated
Microvilli
Increased surface area
Cilia
Move substances through hollow organs
4 Types of Simple Epithelia
- Simple squamous Epithelium
- Simple Cuboidal Epithelium
- Simple Columnar Epithelium
- Pseudostratified Columnar Epithelium
Simple Squamous Epithelium
-Very thin single layer of cells; “fried egg” appearance
- Adapted for rapid diffusion of substances (oxygen, carbon dioxide, fluids, and ions)
- In air sacs of lung, specific segments of kidney tubules, and lining blood vessel
Simple Cuboidal Epithelium
- Single layer of cube-shaped cells with large central nucleus
- Thin enough for rapid substance diffusion
- In segments of renal tubules, respiratory passages, ducts of many glands, and thyroid gland
Simple Columnar Epithelium
- Single layer of rectangular-shaped cells with nuclei in basal portion of cell
- Often microvilli (small intestine) or cilia
- (uterine tubes and segments of respiratory tract) on apical plasma membrane
Pseudostratisfied Columnar Epithelium
- Appears layered because nuclei are at various heights
- Only one cell-layer thick with basal plasma membranes firmly in contact with basement membrane
- In segments of respiratory tract and nasal cavity; ciliated
Transports across simple epithelia
- Paracellular transportation
- Transcellular transportation
Paracellular transportation
Substances leak between cells in epithelial membrane; limited due to tight junctions that make spaces between cells nearly impermeable
Transcellular transportation
Substance enters cell by crossing plasma membrane; diffuses across cytosol; exits cell through plasma membrane at opposite side
Stratified epithelium
More than one layer of cells; best as protective barriers where subjected to high degrees of mechanical stress
Types of Stratified Epithelium
- Keratinized stratified squamous epithelium
- Non-keratinized stratified squamous epithelium
- Stratified cuboidal epithelium
- Stratified columnar epithelium
- Transitional epithelium
Keratinized stratified squamous epithelium
-Apical cellular layers are dead
-lack nuclei
-filled with protein keratin
-makes tissue tough and resistant to friction
-well adapted for outer layers of skin