intro to histology Flashcards
why is histology important?
- provides structural basis for gross anatomy (and many of the life sciences)
- essential for understanding function and pathological change
what are the 4 categories of tissues recognized in histology?
- epithelial tissue
- connective tissue
- muscular tissue
- nervous tissue
what are the general functions of each of the 4 tissue categories?
- surface and glandular (epithelium)
- support (connective)
- contraction (muscular)
- innervation (nervous)
what is the structure of epithelial tissue?
cohesive sheets of cells
what are the specialized functions of epithelium?
- barrier between the internal and external environment
- mechanical protection
- absorption and secretion
what are the subdivisions of epithelial tissue?
- surface epithelium
- glandular epithelium
list the 3 factors that mediate the epithelial tissue functions
- structural modifications to the surface (microvilli, cilia)
- internal modifications (associated with manufacture of secretions and secretion)
- special types of junctional complexes between cells
what are cell-cell junctional complexes and what is their function?
they determine how and what can pass between cells
- function to link cells together but can also have functional implications
what are the 3 types of cell-cell junctional complexes?
- occluding (tight) junctions
- anchoring (adhering) junctions
- communicating (gap) junctions
all 3 are present in but varying amounts depending on the type of epithelium
what is the function of a tight junction?
to prevent diffusion of molecules between adjacent cells
- form a variously permeable barrier
what is the function of adhering junctions?
link cells together and provide mechanical strength
list some examples of adhering junctions
- belt demosomes
- spot demosomes
- hemi-demosomes
what is the function of gap junctions?
allow movement of molecules between cells
what are the three shapes of epithelial cells?
- squamous
- columnar
- cuboidal
what do squamous cells look like?
flat and sheet-like in appearance, often described as looking like fish scales
- large cells with small round nuclei
what do cuboidal cells look like?
cube-like shape (H=W=D) with a central nucleus, looks roughly like dice
what do columnar cells look like?
tall, rectangular column-like shape with nuclei usually located towards the bottom of the cell
what are the 3 classification criteria of surface epithelia?
- number of cell layers (simple or stratified)
- shape of surface cells (squamous, cuboidal, or columnar)
- surface specializations (keratin, cilia, microvilli)
what are the 3 types of simple epithelium?
- simple squamous epithelium
- simple cuboidal epithelium
- simple columnar epithelium
describe what simple squamous epithelium looks like and where is it located in the body?
- single layer of squamous cells
- functionally suited to surfaces where mechanical protection is not required
- e.g. lining of blood vessels, inside body cavities
describe what simple cuboidal epithelium looks like and where is it located in the body?
- single layer of cuboidal cells
- functionally suited to surfaces with an absorptive/secretory role
- e.g. secretory cells of exocrine glands, kidneys, ovaries
describe what simple columnar epithelium looks like and where is it located in the body?
- single layer of columnar cells
- functionally suited to surfaces with an absorptive role
- large surface area due to height of cells and microvilli
- e.g. digestive tract, uterus, reproductive system
what are the 3 types of stratified epithelium?
- (keratinized) stratified squamous epithelium
- stratified cuboidal epithelium
- stratified columnar epithelium
what does (keratinized) stratified squamous epithelium look like and where is it located in the body?
- functionally suited to surfaces where there is a varying amount of mechanical protection required
- stratified squamous epithelium: layers of squamous cells; living nucleated cells which flatten towards the surface
- e.g. skin, pharynx, esophagus
- keratinized stratified epithelium: live cells underneath layer(s) of flattened, dead, keratinized cells on the surface
- e.g. paw pads, tongue
what does stratified cuboidal/columnar epithelium look like and where is it located in the body?
- functionally usually associated with ducts (of glandular epithelium)
cuboidal: many layers of cuboidal cells
- e.g. sweat glands, mammary glands, salivary glands
columnar: many layers of columnar cells
- conjunctiva, pharynx
what are the 2 types of special surface epithelium?
- transitional epithelium (urothelium)
- pseudostratified cilliated columnar epithelium with goblet cells
appear to be stratified but all cells are in contact with the basement membrane
what does transitional epithelium (urothelium) look like and where is it located in the body?
- large ovoid surface cells
- functionally suited to surfaces which are required to stretch
- e.g. urinary bladder
what does pseudostratified ciliated columnar epithelium with goblet cells look like and where is it located in the body?
- one layer of columnar cells (nuclei at varying levels) with goblet cells and cilia
- functionally suited to surfaces involved in cleansing (cilia) and moistening
- e.g. upper and lower portions of the respiratory system, trachea
what are 2 important structures in glandular epithalial tissue?
- goblet cells
- single cells that retain connection with surface epithelial cells - secretory cells
- embedded in the underlying connective tissue
describe the structure of exocrine glands
- glandular epithelium with a duct to the surface
- widely distributed throughout the body systems
- produce mucus and serous secretions
describe the structure of endocrine glands
- glandular epithelium without a duct
- localized
- highly specialized functions
what shade of stain do serous secretory cells uptake?
dark stain
what shade of stain do mucus secretory cells uptake?
pale stain
what shade of stain do sero-mucus secretions uptake?
mix of pale and dark stain
what are the 4 classifications of connective tissue related to function?
- embryonic connective tissue
- general adult connective tissue
- adipose tissue
- special supportive connective tissue
what are the subtypes of general adult connective tissue?
- loose
- dense
- regular
- irregular
what is the function of general adult connective tissue?
support and connection between different tissues
what is the function of adipose tissue?
provides protection, insulation, and energy reserve
what are the subtypes of special supportive connective tissue?
- cartilage
- blood
- bone
what is the function of special supportive connective tissue?
provides a structural framework; a medium for transport; has a vital role in the healing process
what do all connective tissues consist of?
resident cells
- mesenchymal cells
- macrophages
- adipocytes
- fibroblasts
extracellular matrix
- protein fibers (elastic, collagen, reticular)
- amorphous ground substance
transient cell population
- plasma cells (antibodies)
- eosinophils (protection)
- neutrophils (protection)
- lymphocytes (protection)
the proportion and type of cells, fibers, and composition of the ground substance varies in different types of connective tissue
explain the spaghetti bolognese metaphor for connective tissue
- spaghetti = connective fibers
- sauce = ground substance
- meat/veggies = cellular matter
- the recipe may vary = different proportions of the elements
describe the characteristics of loose connective tissue
- more cells than fibers
- very little support
- designed for absorption
- covered in epithelium
- e.g. villi of small intestine
describe the characteristics of dense regular connective tissue
- more fibers than cells
- fibers are in alignment
- ribbon-like fibers
- one directional support (strength in one direction)
- e.g. tendons
describe the characteristics of dense irregular connective tissue
- more fibers than cells
- fibers arranged in multiple directions (irregular)
- multi-directional strength
- cells are usually fibroblasts or fibrocytes
describe the cells found in and the function of adipose tissue
main cell type:
- adipocyte
function:
- energy store (white fat)
- heat production (brown fat)
- protection
describe what adipose tissue looks like
- cytoplasm of each adipocyte is filled with a single lipid droplet
- nucleus is pushed to the periphery
what are the 3 main areas of the body where muscle is found?
- walls of all hollow organs
- muscles associated with the skeleton
- heart
what are the 3 types of muscle fibers?
- skeletal
- cardiac
- smooth
which types of muscle fiber are striated?
- skeletal
- cardiac
which muscle types are voluntary and which are involuntary?
voluntary:
- skeletal
involuntary:
- skeletal
- cardiac
list the key features of skeletal muscle in the transverse section?
transverse:
- multiple, peripheral nuclei
- cytoplasm packed full of myofibrils
- branches of connective tissue
- looks like tuna steaks
list the key features of skeletal muscle in the longitudinal section?
- peripheral nuclei
- striated
- long unbranched fibers
- limited amount of connective tissue between fibers
list the key features of cardiac muscle in the transverse section?
- single central nucleus present in sectioned fibers
- cross sections of fairly uniform size
- lots of connective tissue between fibers
list the key features of cardiac muscle in the longitudinal section?
- central nucleus
- striated
- short branched fibers
- intercalated discs join fibers (can be seen)
- abundant connective tissue between fibers
list the key features of smooth muscle in the transverse section?
- individual spindle shaped cells
- cross sections have variable diameter
- only a few central nuclei (dependent on where the cross section cuts each cell)
- cells are linked together
list the key features of smooth muscle in the longitudinal section?
- central nucleus
- non-striated
- short tapering fibers
- limited connective tissue between fibers
list some questions you can ask to distinguish between the 3 muscle types
- what is the orientation? longitudinal or transverse?
- if the orientation is longitudinal, is the muscle striated?
- do the muscle fibers consist of single cells or a single cell with multiple nuclei (which function as a coordinated unit)?
- is there a single central nucleus or multiple nuclei at the periphery?
- can you see any special types of cell-cell junctional complexes?
- is the section from an area where you would expect voluntary or involuntary control/contraction of muscle fibers?
what do the neurons, glanglions, and peripheral nerve bundles look like in a transverse section?
answer is picture bc nerve tissue will be discussed later
