Histology Flashcards
describe the three main components of connective tissue
ground substance
- semi solid clear gel
- made up of glycoproteins and glycosaminoglycans like hyaluronic acid
- water binding ability due to proteoglycans and glycosaminoglycans
- gives tissue volume
fibres
- collagen, elastin and reticular fibres.
- collagen is very strong, elastin is stretchy and reticular makes a network.
cells
- blasts and cysts to make up the connective tissue components.
- fibroblasts, osteoblasts, chondrocytes etc
- there are also immune cells in some, but not in cartilage tendons or ligaments
describe the criteria used to classify connective tissue
there are three classifications: proper, supporting and fluid.
proper
- loose, dense, or elastic
- dense regular and dense irregular
- dense regular is strong in one direction due to fibre arrangment, found in tendons and ligaments
- dense irregular is strong in many directions, like dermis of the skin.
- elastic is dense too, found in arteries.
- loose is areolar, adipose and reticular
- areolar holds together the GIT, anchors organs of the body
- reticular is found in spleen and lymphatics
- adipose is fat, helps with energy storage and shock absorption.
supporting
- bone and cartilage
- cartilage can be hyaline, elastic and fibrocartilage
- hyaline is joints
- elastic is epiglottis and ear
- fibrocartilage is vertebrae and meniscus of the knee
fluid
- blood
- important for transport and immunity
describe some connective tissue disorders with oral manifestations
scurvy
- lack of vitamin c affects collagen synthesis
- glycine, proline and hydroxyproline form collagen structure, and vitamin C is a co factor for forming this
- collagen supports blood vessels, tendons and skin. they are fragile without it
- causes teeth to become loose, haemorrhages and death
systemic lupus erythematosis
- autoantibodies attack host tissues like skin, bone, tendon and kidneys
- cause dryness, soreness, buccal and palatal lesions in the mouth
sjogrens
- autoantibodies affect glands producing tears and saliva
- dry eyes and mouth, make mouth susceptible to infection and caries
describe the relationship between the structure and function of connective tissues
all connective tissues have different structural arrangements for their function
tendons
- dense regular, helps tendon transfer the force of muscle contraction to bone
- connect muscle to bone
describe features common to all epithelial tissues
structurally:
- continous sheets of cells
- tightly bound together
- polarised
functionally:
- cover and line surfaces
- form a barrier
classify epithelial tissues
structure differs by shape of cell, number of layers, and apical specialisations
squamous are flat, cuboidal are square, and columnar are long, with nuclei at the basement membrane.
apical specialisations include cilia, keratin and microvilli
number of layers are either single, simple, or many, stratified, or single with nuclei at different levels, pseudostratified
list the functions of different epithelial classifications
simple squamous - passive diffusion, lungs and capillaries
simple cuboidal - small ducts involved in absorption or secretion, renal tubules and salivary glands
simple columnar - absorption - small intestine
cililated simple columnar - ovum from ovary to uterus, female reproductive tract
pseudostratified columnar ciliated - respiratory epithelium
stratified cuboidal - secretory - some glands and ducts
stratified columnar - secretory and protective - male urethra and glands
stratified squamous - protective, skin and oral mucosa
transitional - expansion and stretch, bladder only
disorders of epithelium in oral environment
ulcerations
- break in the continuity of epithelium
- can be infectious or not
oral squamous carcinoma
- dysplastic epithelium
- invades adjacent tissue
describe the organisation of skeletal muscle at the tissue level
composed of skeletal muscle cells
- elongated, cylindrical fibres with multiple peripherally located nuclei
- main type in skeletal muscle
individual muscles are organs, composed of muscle tissue, connective and nervous tissues.
each fibre is wrapped by endomysium. each fasicle of fibres is wrapped by perimysium, and each group of fasciles is wrapped by epimysium
describe the components of skeletal muscle fibres involved in contraction by sliding filament mechanism
myofibrils are arrangement to show a striated appearance
myofibrils are composed of myosin (dark bands) and actin (light bands), and the actin is bisected by z lines
it is the z lines that divide each myofibril into contractile units called sarcomeres
each sarcomere contains an A band, H band , M line, and a bisected I band.
A band - the entire length of the myosin filament
H band - the length of myosin not overlapping actin
M line - bisects the myosin
I band - the length of actin not overlapping the myosin
identify the components of the neuromuscular junction and the special adaptations of muscle fibres that support synchronous contraction of sarcomeres
skeletal muscle is innervated by somatic motor neurons
a motor unit is the single motor neuron and the muscle fibres it innervates
neuronal action potentials are converted into acetylcholine at the NMJ, which is detected by receptors on muscle fibres to stimulate action potential and contraction. this is excitation contraction coupling
excitation contraction coupling mechanism in detail:
- sarcolemma is the membrane, invaginates into the sarcoplasm (cytoplasm) to form t tubules that are continuous with the extracellular sapce
- sarcoplasmic reticulum is smooth endoplasmic reticulum containing calcium
- sarcolemma and SR support sarcomere contraction
identify the structural and functional differences between skeletal muscle and cardiac muscle cells
cardiac is found only in the heart to create autonomic contraction
elongated, branched cylindrical cells with one or two centrally located nuclei.
skeletal striated muscle has multiple, peripherally located nuclei.
both are striated.
cardiac muscle makes up the myocardium of the heart, the middle layer between the pericardium and the endocardium.
reticular connective tissue supports the cardiac muscle.
both cardiac and skeletal muscle have the same sarcomere arrangement, with t tubules and a sarcoplasmic reticulum. they both have a lot of mitochondria, glycogen and lipids. both contract by sliding filament mechanism.
however, cardiac is autonomic, the SR slowly leaks the calcium ions, and has intercalated discs to allow cardiac muscle cells to function as synctium.
skeletal contracts via motor neurons
cardiac contracts via sino atrial node and slow release of calcium ions. it is modulated by autonomic nervous system and hormones
identify the structural and functional differences between skeletal muscle and smooth muscle
smooth is elongated, spindle shaped cells
one nuclei, centrally located
no sarcomeres, which means there is no striation
comprises the gastrointestinal tract with inner circular and outer longitudinal
has actin and myosin like the skeletal, but arranged in criss cross lattice. when contracted it becomes shortened and globular.
skeletal is voluntary, smooth is involuntary. smooth is also non striated.
describe the main histological components of cartilage
ground substance with chondroitin sulphate
fibres like collagen and elastin
cells like chondroblasts and chondrocytes
hyaline cartilage contains collagen and ground substance, found in articulating bones
elastic cartilage is flexible and avascular, has elastic fibres concentrated around lacunae and collagen fibres
fibrocartilage is durable and tough, does not have much ground substance and is composed of dense irregular collagen and chondrocytes. found in vertebrae.
describe the histological components of cortical bone
compact bone, surrounded by periosteum, which is composed of an outer fibrous layer and an inner osteogenic layer.
layers of bone tissue are referred to as lamellae, and are arranged concentrically.
central canals run through the centre of each osteon to house blood vessels, nerves and lymphatics.
there is circumferrential lamellae that surrounds the entire cortical bone parallel to the periosteum.
describe the histological components of trabecular bone
- contains lemellar bone as well
- lamellae are found within trabeculae, which are the spikes in the bone.
- the spaces between the trabeculae are where the nerves, blood and lymphatics are found
- no osteons like seen in cortical bone
- lined by endosteum
describe the process of bone remodelling
remodelling can occur due to growth, mechanical stress, hormones and immunity
osteblastogenesis is bone formation, which should go in hand with osteoclastogenesis.
osteoblasts form bone
provide examples of disorders of bone and cartilage
periodontitis
- inflammatory disease
- chronic immune response to oral bacteria leading to destruction of host tissues
- immune mediated uncoupling of osteoblasto and osteoclastogenesis
- alveolar bone is destroyed
- teeth are lost
osteomalacia
- rickets
- failure of osteoid to mineralise
- due to dietary deficiency like lack of calcium and vitamin D
- bones are weak and fracture
dental abnormalities
- associated with osteomalacia
- enamel hypoplasia
- delayed eruption
describe the structure of skin
layers are epidermis, dermis and subcutaneous with associated structures like hair nails and glands
skin and mucosa have same structure
epidermis
- stratified squamous epithelium
- no vasculature
- 4-5 layers of it, from the outside in are stratum corneum, lucidum, granulosum, spinosum, basale
- cells include keratinocytes at 95%, langerhans, merkels and melanocytes. langerhans are found in spinosum, merkel and melanocytes are found in the basal layer.
- lucidum is only present in thick skin
dermis
- dense irregular connective tissue
- cells, vasculature, lymphatics, smooth muslce in some areas
- papillary and reticular layer
- papillary is interval with epidermis
- reticular is the dense connective tissue layer
describe the functions of skin
protection from pathogens
thermoregulation through blood and hair and sweat
water regulation by preventing loss of moisture
sensation through touch temperature and pain
absorption
storage and synthesis of vitamin D, fat, glucose water and salt
describe the function of mucous membranes
- specialised lining that produces a lubricating fluid with mucin to trap microbes and particles
- found in any region exposed to the external environment like mouth and nose
- protective for mouth, nose and oesophagus
- secretory for stomach
- sensation for small intestine
describe the structure of mucous membranes
epithelium and lamina propria constitute the mucosa
lamina propria is the areolar loose connective tissue that is found beneath mucosal epithelium and its basement membrane
gross types of oral mucosa are lining, masticatory, and gustatory.
masticatory mucosa has a stratum corneum, and rete ridges
describe the clinical considerations of skin
acne - overproduction of sebaceous glands
psoriasis - excessive turnover of epithelial cells
pemphigus - loss of desmoglein, cells are not well anchored, fluid forms blisters
vitiligo - loss of skin pigment due to destroyed melanocytes
basal cell carcinoma and squamous cell carcinoma where keratinocytes grow out of control
malignant melanomas - uv, moles, fair skin, sunburn
describe the clinical considerations of mucous membranes
cystic fibrosis - inherited autosomal recessive disease
chloride channel protein is abnormal, causes viscous secretions
can affect many areas of the body, including salivary glands
define histology and explain what tissues consist of
histology is the microscopic study of normal cells and tissues
disease is associated with disruption of normal structure and function
main types are:
- epithelium - barrier and lining tissue, forms outer layer of skin
- connective tissue - structural and functional support, cartilage, bone and blood
- muscle tissue is specialised for contraction
- nervous tissue which carries information through the body via electrical impulse.
describe the key differences between light and electron microscopy
they differ in optical resolution and magnification
LM - basic cellular structure, resolution of 0.2 micrometers, commonly used for routine histopathology
EM - reveals ultrastructure, resolution is 1 nanometer, 200 times greater resolution than LM.
describe the stages required to collect and prepare tissues for histological examination
- specimen collection
incision or punch biopsy, for skin and oral surfaces
needle biopsy for organs or lumps, use of x ray to guide biopsy
endoscopic biopsy through flexible tube and light
- fixation
preserves the structure by terminating biochemical reactions. use of formaldehyde and glutaraldehyde.
- dehydration
water removed using graded alcohol series, done gradually to prevent distortion.
- embedding
resin and paraffin to support the thin sections before being cut.
alcohol must be replaced by xylene in order to use paraffin as it is not compatible with alcohol.
- sectioning
done with a microtome, sections are 7 nanometres thick and mounted on glass slides
- staining
makes cells and components visible. many different stains can be used. most are aequeous, there has to be reversal of dehydration steps to remove the paraffin wax and replace with water.
- viewing
describe commonly used staining procedures
haemotoxylin and eosin
- H stains nucleic acids blue/purple as it is basic and stains acidic structures
- E is acidic and stains basic structures like cytoplasm red or pink
periodic acid schiff
- stains complex carbs magenta
- mucins produced by goblet cells are PAS positive and stain magenta.
- usually combined with H&E
masson trichrome
- stains connective tissues
- collagen stains green/blue
- nuclei stains purple
- cytoplasm stains red
- muscle and blood cells stain red
immunohistochemistry
- antibodies required, they are conjugated to enzymatic or fluorescent indicators
alcian blue
- stains mucin and cartilage blue
van gieson
- stains collagen red
- stains nuclei, erythrocytes and cytoplasm yellow
reticulin
- stains reticulin fibres black
- combined with H&E
describe the process of sliding filament mechanism
- action potential travels along the sarcolemma and reaches the t tubule
- DHP receptors are stimulated
- these receptors are connected to the ryanodine receptor on the sarcoplasmic reticulum
- when DHP is stimulated and changes shape, it causes the ryanodine receptor to open
- this allows calcium to flow into the sarcoplasm from the sarcoplasmic reticulum
- these float to the thin filament and bind to the c subunit of troponin
- this subunit changes shape
- this moves the tropomyosin out of the way, allowing the myosin head to bind to g actin proteins on f actin
- before myosin can bind to actin, it must power up
- the myosin head is an ATPase and releases energy to cock the head backward
- it then binds to an active site
- there is cross bridge formation, which is the trigger to release stored energy in the myosin head
- when this happens the myosin head launches toward the m line
- actin is pulled along with it
- this is the power stroke
- once the action potential ends, the calcium ions are pumped back into the reticulum, and the subunit is no longer bound to calcium, so the tropomyosin covers the actin once more
describe the different classifications of exocrine glands
unicellular
- goblet cells
multicellular
- secretory sheets - simplest multicellular gland
- pockets of gland cells set back from the epithelial surface
- simple tubular are found in the glands of the stomach and colon
- simple branched tubular are found in the lower portion of the stomach
- simple coiled tubular are found in the lower portion of the stomach and small intestine
- simple acinar are sebaceous glands of the skin
- simple branched acinar are sebaceous glands of the skin
- branched tubular are mucous glands of the duodenum
- complex branched acinar are mammary glands
- complex branched tubuloacinar are found inthe pancreas
branched exocrine galnds are surrounded by fibrous tissue capsules and the septa from the capsule will divide the parenchyma into interlobar septa
merocrine glands produce secretions in vesicles
apocrine glands produce secetory products in pinched off portions of the cell
holocrine glands produce secretory products when dying
describe the microscopic structure of branched glands
ducts extend along septa
interlobar ducts are lined by columnar stratified epithelium
interlobular ducts are lined by pseudostratified columnar epithelium
striated ducts and intercalated ducts have little connective tissue supporting them
striated ducts are lined by simple cuboidal which goes into columbar epithelium.
intercalated ducts are lined by simple cuboidal
myoepithelial cells lie between the secretory cells and basal lamina, they contract and squeeze the secretions from the acini along the duct
