Histology Flashcards
Tissues
a group of specialized cells working together to perform a specific function
* four types:
- epithelial
- connective
- muscle
- nervous
Microscopy of human tissue
to be viewed under a microscope, human tissue must be:
- fixed
- sectioned
- stained
Microscopy: fixed
preserved with solvent
Microscopy: sectioned
cut into sections thin enough to transmit light
Microscopy: stained
to enhance contrast
Epithelial tissue/epithelium
- a sheet of body cells that covers surfaces and/or body cavities
- main functions: protect, absorb, filter, excrete, secrete, receive sensory input
- 2 main forms:
- covering/lining epithelium
- glandular epithelium
Covering/lining epithelium
lines the body’s internal and external surfaces
- ex: skin
Glandular epithelium
secretory tissue in glands
- ex: salivary glands
characteristics of epithelial tissue
5 distinguishing characteristics
- polarity
- specialized contacts (fit close together and form continuous sheets)
- avascular (no blood supply) but innervated (does have nerves)
- supported by connective tissue
- regeneration
polarity (characteristic)
epithelial tissue
(asymetrical arrangement of cell?)
- apical surface: free/upper side, contacts the cavity or external surface. usually smooth, sometimes covered in finger-like projections (not attached)
- basal surface: lower/attached side, faces inward to the body. attaches to the basal lamina - an adhesive sheet
- both surfaces differ in structure and function
specialized contacts (characteristic)
epithelial tissue
- epithelial tissues often form continuous sheets and require close contact between adjacent cells
- specialized contact points include tight junctions and desmosomes
Supported by connective tissue (characteristic)
epithelial tissue
all epithelial sheets are supported by connective tissue
- reticular lamina: deep to basal lamina, a network of collagen fibers (wax paper/sticker)
- basement membrane: made of basal + reticular lamina
* reinforces the epithelial sheet
* resists stretching and tearing
* defines the epithelial boundary
connective tissue is beneath (or deep to) basement membrane
avascular (characteristic)
epithelial tissue
- no blood vessels are found in epithelial tissue
- epithelial tissue is nourished from underlying connective tissue
- it is innervated (has nerves)
regeneration (characteristic)
epithelial tissue
- high regenerative capacity - frequent exposure to friction and/or damaging substances
- regeneration is stimulated by the loss of the apical - basal polarity/breaks in lateral contacts
- regeneration requires nutrients and mitosis (cell regen)
Clinical connection: pressure sores
- happens in immobile patients; bony parts (elbows, heels, etc.) are affected when there is pressure on these places for too long
- stage 1: epidermis affected (abrasion)
- stage 2: dermis (connective tissue)
- stage 3: hypodermis (fat)
- stage 4: muscle/bone
Classifying epithelial tissue
- two names: 1-# of cells, 2-cell shape
- ex: stratified squamous
layers - simple: 1 layer
- stratified: many layers of cells
cell shapes - squamous: flat, scale-like
- cuboidal: box-like
- columnar: tall, column-like
- in stratified tissue cell shape may vary - name is given based on apical (top) layer
pseudostratified columnar epithelia
when simple columnar epithelia appears stratified because the nuclei are seen at different levels/heights
- involved in secretion and movement of mucus
- many cells are ciliated
- ex: upper respiratory tract, ducts of the large glands, testicular tubes
simple squamous
- description: flattened, cytoplasm is sparse, disc shaped nucleus
- function: exist in places where rapid diffusion is essential
- ex: kidneys, lungs, endothilium, mesothilium
simple cuboidal
- description: cubed shaped, height = width, large central nucleus
- function: involved in secretion + absorption
- ex: kidney tubules, walls of glandular ducts
simple columnar
- description: tall, closely packed, height>width, microvilli, cilia, or goblet cells might be present. round/oval shaped nuclei
- function: involved in absorption + secretion of mucus, enzymes, other substances. cilia moves mucus
- ex: digestive tract, glandular ducts, gallbladder, bronchi, uterine tubes
stratified epithelia
- contains 2+ layers of cells
- new cells regenerate from below - basal cells divide and migrate towards the surface
- more durable than simple epithelia - function in protection / in places that we need protection
stratified squamous
most common
- description: thick epithelium, apical cells are squamous, apical cells are sometimes dead and full of keratin, basal cells are cuboidal/columnar and metabolically active
- function: protect underlying tissues in areas often subject to abrasion
- ex: moist linings of the esophagus, mouth, vagina, epidermis of the skin
stratified cuboidal
- description: quite rare, typically only 2 layers thick
- function: typically serves to transition tissue types
- ex: sweat glands, mammary glands
stratified columnar
- description: rare, only apical layer is columnar
- function: typically serves to transition tissue types
- ex: pharynx, male urethra, lining of glandular ducts
transitional epithelia
- forms the lining of the hollow urinary organs-found in bladder, ureters, urethra
- basal layers are cuboidal or columnar
- ability of cells to change shape allows for increased urinary flow an/or increased filling of the organs/storage
- think how the bladder expands to hold fluid
gland
1+ cell that makes and secretes an aqueous fluid - “a secretion”
glandular epithelia
classified by:
1. site of product release
- endocrine: (ex. thyroid gland)
- exocrine: (ex. sweat gland)
2. relative # of cells involved
- unicellular (ex. goblet cell)
- multicellular (ex. salivary gland)
endocrine glands
- ductless glands; glands lost in development
- secretions enter interstitial fluid and get picked up by cardiovascular system
- secrete hormones (messenger chemicals that travel through lymph/blood to reach target organs)
- ex. thyroid gland(secretes thyroid hormones), pituitary gland (secretes hormones like oxytocin and growth hormone)
- hormones enter blood through connection to blood vessels
exocrine glands
- secrete into ducts
- secretions are released onto body surfaces (like skin) or into body cavities
- more numerous than endocrine glands
- can be unicellular or multicellular
- ex. mucus, sweat, oil, salivary glands
unicellular exocrine glands
- found in epithelial lining of the inestinal and respiratory tracts
- produce mucin - a protein that dissolves in water to produce mucus
- mucus: slimy, protective, lubricating coating
- ex. mucous cells, goblet cells
- protects us from little particles we inhale
multicellular exocrine glands
- composed of a duct + secretory unit
- typically surrounded and divided by supportive connective tissue that supplies both innervation and blood
- classification by structure
1. simple: unbranched ducts; compound: branched ducts
2. tubular: secretory cells form a duct
3. alveolar: secretory cells form sacs - classification by mode of secretion
1. merocrine: exocytosis as products are produced
2. holocrine: accumulate products -> rupture
3. apocrine: accumulate products -> apex ruptures
Connective tissue
- most abundant and widely distributed type of tissue
- functions: binding, support, protection, insulation, reserve fuel, transportation of substance
- four classes
1. connective tissue proper
2. cartilage
3. bone
4. blood
qualities of connective tissue
- a common embryonic origin - all connective tissue arises from MESENCHYME
- varying degrees of vascularity (blood supply)
- cartilage = avascular, blood = highly vascularized
- cells are embedded/suspended in extra cellular matrix (ECM)
ECM
extra cellular matrix
- a sugar protein mesh that allows cells to bear weight and withstand tension
- fibers + ground substance
structural elements of connective tissue
3 main elements
- ground substance
- fibers
- cells
ECM = ground substance + fibers
- composition and arrangement of the 3 elements varies greatly between different types of connective tissue
ground substance
- unstructured, gel-like, fills space between cells
- medium through which solutes diffuse between blood capillaries and cells
components: - interstitial fluid
- cell adhesion proteins
- proteoglycans
- water (varying amounts)
connective tissue fibers
3 types
- collagen
- elastic
- reticular
Collagen
strongest and most abundant - high tensile strength
- would withstand “tug of war” but does not withstand twisting and pulling from axis
Elastic
networks of long, thin, elastin fibers
- allow for stretch and recoil
reticular
short, fine, highly branched fibers
- offer give
- makes tissue more pliable
connective tissue cells
- blast cells
- cyte cells
- fat cells
- white blood cells
- mast cells
- macrophages
blast cells
immature cells that actively secrete ground substance and ECM fibers
- fibroblasts: found in connective tissue proper
- chondroblasts: found in cartilage
- osteoblasts: found in bone
- hemocytoblasts: found in bone marrow
cyte cells
mature cells, less active than blast cells, become part of and maintain the ECM
fat cells
store nutrients
white blood cells
manage response to injury
- neutrophils, eosinophils, lymphocytes
mast cells
initiate inflammatory response against foreign microorganisms
macrophages
phagocytic cells that eat dead cells and microorganisms
Connective tissue proper
includes all types of connective tissue except bone, cartilage, and blood
- two subclasses
1. loose connective tissue (LCT)
- areolar
- adipose
- reticular
2. dense connective tissue (DCT)
- dense regular
- dense irregular
- elastic
Connective tissue proper
includes all types of connective tissue except bone, cartilage, and blood
- two subclasses:
1. loose connective tissue (LCT)
- areolar
- adipose
- reticular
2. dense connective tissue (DCT)
- dense regular
- dense irregular
- elastic
LCT: areolar connective tissue
- most widely distributed connective tissue - universal packing material
- supports/bonds other tissues
- contains fibroblasts that secrete a loose arrangement of collagen fibers
- loose fibers allow for increased ground substance - increased capacity for holding water/interstitial fluid
- macrophages and fat cells are contained in the spaces
LCT: Adipose connective tissue
White fat:
- like areolar tissue but greater nutrient storage
- cells = adipocytes
- minimal matrix (minimal space between cells)
- richly vascularized
- functions in shock absorption, insulation, and energy storage
Brown fat:
- contains abundant mitochondria - uses lipid fuel to generate heat (not ATP)
LCT: reticular connective tissue
- resembles areolar tissue, but the fibers are thinner
- reticular fibers form a mesh like stroma
- stroma acts as a support for free blood cells, macrophages, and mast cells in lymph nodes, the spleen, and bone marrow
DCT: Regular Connective tissue
- very high tensile strength
- closely packed bundles of thick collagen fibers that run parallel to the direction of the pull
- fibers appear white and slightly wavy
- fibroblasts manufacture collagen fibers and ground substance
- poorly vascularized
- ex. tendons (bone-muscle) and ligaments (bone-bone)
- clinical connection = ACL
DCT
- same elements as regular connective tissue but bundles of collagen are thicker and arranged irregularly
- forms sheets
- resists tension from many directions
- found in: dermis, fibrous joint capsules, fibrous coverings of some organs
DCT: elastic connective tissue
- some ligaments are very elastic
- ex. ligaments connecting adjacent vertebrae
- found in the walls of the large arteries
Cartilage
- stands up to both tension and compression
- 80% water, packed with collagen fibers and sugar proteins
- lacks innervation and is avascular - receives nutrients from surrounding membrane (perichondrium)
- matrix is secreted by chondroblasts during growth and by chondrocytes in adults
three types: - hyaline
- elsatic
- fibrocartilage
hyaline cartilage
- most abundant in gristle
- appears shiny, glassy, bluish
- found at tips of long bones, nose, trachea, larynx, ribs
elastic
- like hyaline but more elastic fibers
- found in ears and epiglottic
fibro cartilage
- properties in between hyaline cartilage and dense regular tissue
- found in knee and the invertebral discs
Bone
- also called osseous tissue
- osteons: individual structural units
- supports and protects body structures
- richly vascularized
- stores fat, synthesizes blood cells
- matrix has more collagen than cartilage plus inorganic calcium salts
- osteoblasts produce the matrix; osteocytes maintain the matrix
- LACUNAE: cavities within the matrix - where osteocytes reside
Blood
- most atypical connective tissue
- consists of blood cells surrounded by matrix
- red blood cells are most abundant
- fibers are soluble proteins that precipitate during blood clotting
- functions: transportation of nutrients, wastes, gases, and other substances
Muscle tissue
- highly vascularized
- responsible for most types of movement
- muscle cells possess myofilaments - elaborate networks of actin and myosin filaments
- myofilaments facilitate muscle contraction
3 types - skeletal muscle
- cardiac muscle
- smooth muscle
skeletal muscle
attaches to and creates movement of the bones
- voluntary (consciously controlled) muscle
cells = muscle fibers
- contain multiple nuclei
- appear striated or banded1
cardiac muscle
- found only in the walls of the heart
- involuntary muscle
- appears striated, but the fibers contain only one nucleus
- fibers are heavily branched and join the branches of the neighboring fibers
- intercalated discs: special joints where cardiac muscle cells are joined
smooth muscle
- mainly found in the walls of the hollow organs
- involuntary muscle
- no visible striations
- spindle-shaped cells with one nucleus
nervous tissues
creates components of the nervous system - the brain, spinal cord, and peripheral nerves
- regulated and controls the body functions
- two types of specialized cells
- neurons: nerve cells that generate and conduct nerve impulses
- glial cells: cells that support, insulate, and protect neurons
covering and lining membranes
composed of 2+ tissue types - epithelium bound to underlying connective tissue proper
- 3 types
1. cutaneous membranes
- mucus membranes
- serous membranes (lining cavities of the body and organ surfaces)
cutaneous membranes
skin
- keratinized stratified squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis)
- dry membrane
mucous membrane
- mucosae
- epithelial sheet lies over a layer of loose connective tissue called a lamina propria
- may secrete mucus
- lines the body cavities exposed to the external environment - digestive, respiratory, and urogenital tracts
- moist membranes - bathed by secretions
serous membranes
- serosae
- found in closed, ventral body cavities
- constructed from a simple squamous epithelium (called mesothelium) lying on a thin layer of areolar connective tissue
- ex. pleurae (lungs), pericardium (heart), peritoneum (abdomen)
tissue repair
when the body’s barriers are broken, inflammatory and immune responses are activated
- tissue repair starts very quickly
- repair is a function of the inflammatory process
- two methods of repair:
1. regeneration: destroyed tissue is replaced by the tissue of the same type; original function is restored
2. fibrosis: destroyed tissue is replaced by scar tissue (DCT); original function is lost
3 steps of tissue repair
- inflammatory stage
- inflammatory chemicals are released
- blood vessels dilate and become more permeable
- blood clots - organization restores blood supply
- blood clot is replaced with granulation tissue (new capillary-enriched tissue)
- epithelium regenerates
- fibroblasts produce collagen fibers to bridge the gap until regeneration is completed
- debris is phagocytized - regeneration and fibrosis
- scab detaches
- fibrous tissue matures
- epithelium thickens and begins to resemble adjacent tissue
- result = fully regenerated epithelium and underlying scar tissue
regenerative capacity
- high capacity: epithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, blood-forming tissue
- moderate capacity: smooth muscle, dense regular connective tissue
- low capacity: cardiac muscle, nervous tissue
