TOPIC 2 - cells and tissues Flashcards
what is histology?
the study of cells and tissue by microscopy
what is histopathology?
the study of diseased tissues by microscopy
give 4 clinical applications of histology
- make a diagnosis
- determine prognosis (ie is it malignant or agressive)
- plan or confirm treatment
- predict or confirm response to some drugs
give additional benefits to histology
- audit of pathology services
- see how succesful a surgery was
- collect epidemiological data
- pathogenesis
- education
- can recognise normal tissue
give the 10 steps for histological preparation and examination
- tissue
- fixation
- cut up/ block section
- tissue processing
- section cutting and mounting
- section staining
- section scanning
- microscopy
- diagnosis
- prognosis prediction
what is step 1 of histology?
tissue - could be a surgical excision, biopsy etc
how do we stop the tissue degrading?
fixation (step 2)
- stop intrinsic autolytic enzyme action (autolysis)
- prevent bacterial contamination (putrefaction)
- increase mechanical strength to preserve structure/ morphology
give the general types of fixatives and their mode of action (4)
aldehyde - form protein covalent cross links
alcohol - denature proteins causing aggregation
oxidising - form protein cross links via oxidation
freezing - v quick but poor morphology
what is the most common fixative?
formalin (a formaldehyde solution)
- forms protein covalent cross links
- good penetration/ mechanical strength
- good tissue morphology preservation
- poor nucleic acid preservation
what fixative is used for electron microscopy?
glutaraldehyde
- larger molecule than formalin
- needs smaller tissue samples
- works well at low temperatures
what fixative is used for nucleic acid research?
ethanol
- fixes by precipitation
- reduces protein solubility –> precipitate
- used in cytology smears
what is step 3 of histology prep and examination
block section
- choosing what we want to see histologically
- cut up a larger section into smaller pieces
- can select area of interest
where do you place tissue slices (name of plastic box)
a cassette
what is step 4 of histology prep and examination
tissue processing
- aim - thin slice of tissue to examine under a microscope
what are the 4 steps of processing?
- dehydration (remove water with alcohol)
- clearing (replace acohol with xylene)
- wax infiltration (replace xylene with parrafin wax)
- embedding (orientate tissue to form a block)
what is the end product of tissue processing?
a parafin block
what does FFPE stand for
formalin fixed parafin embedded tissue
what is step 5 of histology prep and examination?
section cutting and mounting
- cut thin sections to be viewed under a microscope
what machine is used to cut the thin sections?
a microtome
what is step 6 of histology prep and examination?
section staining
- unstained tissue section is translucent
- make visible using dyes
- dyes can be specific
what is the H&E stain?
haematoxylin and eosin stain
- most common (95%)
what does haematoxylin stain?
PURPLE
basic dye = stains acidic structures
DNA - NUCLEI
what does eosin stain?
PINK
acidic dye = stains basic structures
PROTEINS - CYTOPLASM
what is PAS stain?
periodic acid schiff
- detection of mucin/ mucopolysaccarides
- detection of fungal organisms
- visualisation of basement membranes
what is DPAS?
PAS combined with diastase
- diastase removes glycogen
what stain is used on bacteria to see if gram + or-?
crystal violet and safranin counter stain
gram postive = purple
gram negative = pink (with counter stain)
what is the giesma stain?
H.Pylori bacteria and toxoplasma (and others)
- attaches itself to phosphate group of DNA
what is grocott’s stain?
fungi
- fungal walls go black
what is oil red O stain?
fat
- can only be used on frozen tissue not processed as alcohol fixation removes most lipids
what is orcein stain?
copper associated protein
elastin fibres
HEP B sAg
what is perl’s stain?
iron = blue
asbestos
what is ziehl neelsen stain?
mycobacterium
what does tinctorial mean?
relating to dying, staining or colouring
what is immunohistochemistry?
uses antibodies against a specific protein target (unlike tinctorial stains are not specific)
- can provide specific information on protein expression
- diagnosis - can tell you the origin of the cancer
- prognosis
- prediction of response to therapy
what are steps 7 and 8 in histology prep and examination?
section scanning and microscopy
what two drugs are used to treat breast cancer and the use of immunohistochemistry can predict reponse?
tamoxifen and herceptin
what is epithelilium?
layer or layers of cells that cover body surfaces (external and internal) or line body cavities
what are the 8 main features of epithelium?
- derived from endoderm/ mesoderm/ ectoderm
- line basically all body surfaces
- cellular
- sit on layer of connective tissue called basal lamina
- stuck tightly together (intracellular junctions/ complexes)
- polarity (composition of bottom and top different)
- avascular
- rapid turn-over
what are the 7 main functions of epithelium?
- absorption
- surface movement
- secretion
- gas exchange
- surface lubrication
- sensation
- protection of underlying tissue
what is a tight junction?
‘seal the cell’
- occludin/claudin seals to protein movement/ paracellular diffusion
- apical (at the top)
what is a adherens junction?
- transmembrane proteins connect across cell cytoskeletons
- below TJs
what is a gap junction?
- small channels that allow intercellular ion/ small molecule exchange
what is a desmosome?
- transmembrane proteins connect to others (linked to intermediate filaments) from adjacent cells
what is a hemi-desmosome?
- provide attachment to underlying basal lamina
what is the role of cell adhesion molecules?
critical for epithelium integrity, adherance to the underlying basal lamina and intrinsic function
what is the general approach for naming epithelia?
- number of layers of cells - single or more?
- shape of cells - flat, cuboidal or columnar?
- do the cells have any specialisation/ adaptations
what do you call a singular layer of epithelium?
simple
what do you call flat cells?
squamous
what do you called multi-layered epithelium?
stratified
how do you judge of the shape of stratified epithelial cells?
look at the top layer
what is the most common epithelium?
stratified squamous epithelium - skin, oesophagus, oral cavity etc
what is psuedo-stratified?
- single layer of columnar
- different heights
- but look like multiple layers
- upper airways - cilia/ goblet cells
what is transitional?
- multiple layers
- but changes shape (columnar and flat)
- distention (expands)
- only found in bladder/ urinary tract (uroethelial)
what 4 specialisations epithelial cells could have?
- cilia
- secretory
- microvilli
- keratinisation (ie when you scratch you skin and flakes come off)
how are epithelial cells adapted to protect?
prevent dehydration, chemical, mechanical damage covering of inter/outer surfaces multi-layered for strength (stratified) replicative to replace damaged cells tight seals between cells keritinisation
how are epithelial cells adapted for absorption?
lining of gut specialised for absorption (glucose, ions, water)
relies of cell polarity
brush border - increases surface area for absorption
how are epithelial cells adapted for surface movement?
cillia move in co-ordination to provide unidirectional movement
- airways (mucus)
- testes (sperm)
- fallopian tubes (ova)
how are epithelial cells adapted for gas exchange?
single layer of squamous cells that line blood vessles (endothelium) - minimal distance for gaseous diffusion
how are epithelial cells adapted for surface lubrication?
mesothelium is simple epithelium
lines all body cavities
potential spaces contain protein rich fluid (serous)
lubrication of surfaces that move against each other
how are epithelial cells adapted for sensation?
sensory organs are highly specialised epithelia
ectoderm - nervous system - all senses
how are epithelial cells adapted for secretion?
isolated epithelial cells (eg goblet cells)
organised multicellular glandular structures
- ducts open onto epithelial surfaces = exocrine
- ductless, straight into blood stream = endocrine
how do you classify exocrine glands?
- look at the duct
- unbranched = simple
- branched = compound - describe the gland
- tubular with coils
- tubular with branches
- alveolar (hollow)/ acinar (like a berry)
what are the 3 mechanisms of exocrine secretion?
merocrine
apocrine
holocrine
what is merocrine?
- protein product in intra-cellular vesicle
- vesicle membrane fuses with cell membrane
- protein product released by exocytosis
- fused plasma membrane recycled by endocytosis
- pancreatic enzymes in exocrine pancreas
what is apocrine?
- protein product in vesicle
- approaches apical membrane
- apical membrane pinches off with loss of some membrane
what is holocrine?
- secretory product accumulates in cytoplasm
- cell disintergrates to release product
- sebum in sebaceous glands
what is epidermolysis bullosa?
blistering skin disorder
- inherited gene mutation of adhesion molecules that stick epithelium to basement membrane
- abnormal anchoring of epidermis to dermis
- blisters
what is cystic fibrosis?
- mutations in CTFR gene
- defective chloride channel on apical surface of epithelial cells
- lungs but also exocrine glands eg pancreas
- less water in mucus –> thickened –> builds up –> infection
what is congenital ciliary dyskinesia?
- autosomal recessive
- abnormal cilia function –> secretion accumulation
- kartageners syndrome - bronchiectasis, sinusitis, situs inversus
what are mesenchymal tissues?
connective/supporting tissues
- blood, blood vessels, lymph system
- bone
- cartridge and joints
- muscle and fat
what are mesenchymal tissues derived from?
mesoderm (middle layer of embryo)
why do we need mesenchymal tissues?
- act as supporting structure to hold the body together
- give organs shape
- key metabolic function
- immune system
- tissue repair
- storage of fat (adipose tissue)
what makes up supporting tissue?
extracellular matrix and cells
what is the extracellular matrix?
- a gel like amorphous substance called ground substance (composed of glycosaminoglycans - hyaluronic acid and proteoglycans)
- percolating tissue fluid
- fibres of collagen (strength) and elastin (stretch and elastic recoil)
what composes the cell part of supporting tissue?
support cells
- fibroblast
- adipocytes
immune cells
what is the function of fibroblasts?
secretion of extracellular matrix
what is the function of adipocytes?
storage and metabolism of fat
what is ehlers-danlos syndrome?
rare inherited condition caused by defect in structure or processing of collagen
- joint hypermobility
- predisposition to joint dislocations
- skin laxity
- can cause life threatening heart complications
what is marfan syndrome?
rare inherited disorder with defect in gene that makes fibrillin
- marfanoid appearance (tall, thin
what are basophils?
- least common leucocyte
- have large blue (basophilic) granules
- similar to tissue mast cells
what is fibrilin essential for?
proper formation of the extracellular matrix (maintenance of the elastic fibres)
what defence cells are present in supporting tissues?
- tissue macrophages
- phagocytosis
- can join together to form multinucleate cells - mast cells
- produce histamine in allergy and anaphylaxis - wandering cells - all remaining leucocytes from the blood
how are leucocytes classified?
granulocytes (secretory granules in cytoplasm and multilobed nucleus)
- neutrophils, eosinophils, basophils
mononuclear (non-lobulated nuclei and can’t see granules)
- lymphocytes, monocytes
how much of plasma is water?
90%
what are neutrophils?
- multilobed (up to 5) single nucleus
- circulate in blood but enter tissues in response to disease/injury
- key in acute inflammation (phagocytosis)
what is pus?
defunct neutrophils
what is a myocardial infarction?
heart attack
- blood clot in one of the coronary vessels supplying the heart
- stops O2 supply to heart muscle - damage
- atherosclerosis (narrowing of coronary vessels)
what are lymphocytes?
- non-lobulated nuclei
- dense nuclei and minimal cytoplasm
- smallest leucocyte
- key role in all immune responses
- T and B cells
what are monocytes?
- largest leucocyte
- large nucleus at edge of cell
- circulate for 3-4 days then move into tissues as macrophages
- no role in blood
what are red blood cells?
- no nucleus
- biconcave
- haemoglobin
- highly adapted for oxygen and carbon dioxide transport
what is anaemia?
failure to maintain an adequate haemoglobin concentration
- shortness of breath
- pale
- lethargy
what makes up blood vessels?
arteries - eleastic and thick muscular walls
arterioles - terminal branches that supply capillaries
capillaries - v thin walled vessels to enable exchange of fluids, gases, nutrients and waste products
venules - capillaries to veins
veins - contain valves to stop backflow of blood, thin muscular walls with few elastic fibres
what are the three layers of blood vessels?
- tunica intima (inner lining)
- tunica media (muscular layer)
- tunica adventitia (outer connective tissue network)
what is deep vein thrombosis?
formation of blood clot in a deep vein (most common in leg)
- unilateral swelling
- redness
- pain
risk factors = cancer, recent surgery, obesity, pregnancy
- can cause PULMONARY EMBOLISM
- treat with anticoagulants
what are varicose veins?
weak or damaged valves in the superficial veins
risk factors = obesity, family history, pregnancy, leg trauma
- treat to reduce symptoms (mild pain) and appearance
what is the lymph vascular system?
drains excess fluid (lymph) from extracellular spaces and returns it to blood vascular system
- lymph passes through lymph nodes as it returns to blood
- lymphatic spread is important route of metastasis in cancer
what is lymphoedema?
localised swelling due to compromised lymphatics
- most common in upper limbs
- complication of surgery where sections of lymphatic system removed (eg breast cancer) = less drainage of lymph = swelling
why is bone important?
- structure
- protection
- movement
- haematopoiesis (maturation of leucocytes)
- maintaining calcium levels
what is bone made of?
collagenous extracellular matrix called osteoid
osteoblasts
osteocytes
osteoclasts
how does the bone have strength and rigidity?
osteoid is mineralised by deposition of calcium
what are osteoblasts?
synthesise osteoid and mediate the mineralisation with calcium
what are osteocytes?
inactive osteoblasts that get trapped within the formed bone
what are osteoclasts?
cells capable of eroding and resorbing bone - important in refashioning and turnover of bone
what are the two main forms of bone
woven (immature) - produced very rapidly in feotal development and fractures
lamellar (mature) - stronger and more resilient (all adult healthy bone)
what is paget’s disease?
haphazard and excessive osteoclast erosion of bone
- cause not known
- osteoblasts increase activity to attempt to replace bone
- new bone is weaker
- common in elderly
- pelvis, spine and skull
what is osteogenesis imperfecta?
brittle bone disease
- rare genetic disorder
- lack of type 1 collagen
- frequent fractures
- blue sclera
what is cartilage?
provides smooth articular surface at bone ends and structural support in pinna, trachea
what is cartilage made up of?
chondroblasts, chondrocytes and fibrous extraceullar material
what are chondroblasts?
synthesise and deposit ground substance and fibrous extracellular material
what are chondrocytes?
chondroblasts trapped in ground substance
what are the different types of cartilage and where are they found?
hyaline - nose, trachea, joints, end of ribs
elastic - ears
fibrocartilage - intervertebral discs, pubic symphisis
what are joints made up of?
bone cartilage synovium ligaments tendons muscles
what is rheumatoid arthritis?
autoimmune disease attacking synovium of joints
- common in hands, knees and ankles
- more common in women
- pain, swelling, stiffness
what is osteoarthritis?
wear and tear of cartilage in joints
- knees, hips, spine and hands
- joint pain, stiffness, swelling
- risk factors = age, obesity, family history
