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what is a tissue?
a collection of specialised cells that perform a particular function
list types of biopsy
- direct incision
how are tissues fixed?
why are tissues fixed?
maintains structure during handling and make cell parts visible
processing can lead to shrinkage artefacts
describe Hand E stain
- H=haematoxylin - a basic dye stains nuclei blue
- E = eosin - stains cytoplasm pink
what is the staining from the Periodic Acid Schiff reaction?
- blue nuclei
- pink collagen fibres
name different types of microscopy and their uses
- phase contrast - used to study cell cycle as not in a vacuum and doesn't require staining
- dark field - used for smears as it improves contrast of transparent unstained specimens
- fluorescence - early diagnosis of TB and meningitis
- confocal - used to build 3D images
what is the limit of resolution?
the minimum distance at which two points can be distinguished - electron microscopes have finer resolutions as electrons have a smaller wavelength than light
what is the difference between heterochromatin and euchromatin?
- heterochromatin - DNA not in active synthesis
- euchromatin - active in RNA synthesis
what is an epithelium?
sheet of contiguous cells of varied embryonic origin that cover the external surfaces of the body and line the internal surface
what are the 4 classifications of tissue?
how are epithelial cells classified?
- simple squamous - lining heart and blood vessels (endothelium), pleural and peritoneal cavities (mesothelium), and epithelium
- stratified squamous - found in oral cavity, vagina and oesophagus, can be keritanised - the skin
- simple cuboidal - line ducts of exocrine glands - kidney tubules and thyriod
- simple columnar - secretion of enzymes and mucus line the GI tract and large excretory ducts of glands
- pseudostratified ciliated - respiratory epithelia, upper resp tract, ear, nose.
- transitional - allows for distension and protection - bladder and ureter
regeneration of epithelial cells - rates?
they have the capacity to regenerate - eg. wound healing, replacement of skin, GI lining, uterine after menstruation
metaplasia - changing type - eg. resp epi - stratified squamous in heavy smokers
neoplasia - form carcinomas
where are mucous membranes found?
- lining the surfaces of open cavities
- the GIT, resp tract, reproductive and urinary tract
what are the typical 4 layer of a mucous membrane (mucosa)?
- basement membrane
- lamina (tunica) propria
- muscularis mucosa
lining of GIT?
- mucosa/mucous membrane - contains glands in SI
- submucosa - dense irregular CT with large vessels and nerves
- muscularis externae/ muscularis propria - inner circular and outer longitudinal layer - peristalsis
lining of the urinary tract?
- ureters urinary bladder and urethra transitional epi
- lamina propria - fibroelastic
- muscularis externae is thick
what is a gland?
an epithelial cell or an aggregation of epithelial cells specialised for secretion
what is the difference between endocrine and exocrine?
- endocrine secretion is straight in to the blood stream
- exocrine glands have ducts
divisions of exocrine glands?
- by STRUCTURE -
- - unicellular/multicellular
- - simple tubular/simple branched/simple coiled/simple acinar/simple branched acinar/ compound tubular/compound acinar
- by NATURE OF SECRETION -
- - mucus - high in mucins stain poorly with H&E
- - serous - high in enzymes, watery - stain pink with H&E
- by METHOD OF SECRETION -
- - merocrine - exocytosis
- - apocrine - non membrane bound structure ends up outside cell in a droplet
- - holocrine - disintergration of whole cell releases all contents this happens with sebaceous glands cells
what is transepithelial transport?
coupled endo and exocytosis
what is the function of the golgi?
packing, concentrating and modifying proteins from the RER
What is the purpose of glycosylation?
allows specificity by offering complex shapes
how is secretion controlled?
- negative feedback
examples of exocrine glands
- goblet cells in jejunum, colon
- salivary glands
- pancreas - enzyme part
examples of endocrine glands?
- parathyroid - chief cells secrete PTH
- adrenal gland
layers of adrenal gland
- - NA and A
- - zona reticularis - androgens
- - zona fasiculata - glucocorticoids - cortisol
- - zona glomerulosa - mineralocorticoids - aldosterone
what is connective tissue?
- mostly derived from mesoderm
- functions = support, defence, transport, repair
- mainly extracellular components with few cells
categories of connective tissue?
- embryonic - mesenchymal, mucous
- adult - loose, relicular, adipose, dense irregular, dense regular (collagenous/elastic)
- specialised - supporting (bone/cartilage), blood
describe embryonic mesenchymal connective tissue?
- cells - mesenchymal cells
- extracellular - fine reticular fibres (thin branching carbohydrate coated type III collagen) and small blood vessels
describe embryonic mucous connective tissue
where is it found?
- cells = fibroblasts
- extracellular = irregular collagen bundles
found deep to fetal skin and in the umbilical cord
describe adult loose/areolar connective tissue
where is it found?
- cells = fibroblasts, macrophages, plasma cells, mast cells, adipocytes
- extracellular = slender long collagen bundles, elastic fibres, reticular fibres, ground substance
ground substance is composed of GACs, proteoglycans and glycoproteins it forms a matrix for cell adhesion
found in superficial fascia/subcutaneous tissue, organs, between fasicles...
describe adult reticular connective tissue
where is it found?
- cells = reticular cells, lymphocytes and macrophages
- extracellular = reticular fibres
classic lymph tissue - lymph nodes
describe adult adipose tissue
where is it found?
cells = closely packed adipocytes separated by thin sheets of extracellular reticular and collagen fibres
describe dense irregular connective tissue
where is it found?
- cells = fibroblasts, macrophages
- extracellular = haphazard, thick, wavy collagen bundles and some reticular and elastic fibres
dermis, deep fascia, periosteum
describe dense regular collagenous connective tissue
where is it found?
- cells = parallel (few) rows of flattened fibroblasts
- extracellular = densely packed regularly arranged collagen fibres
describe dense regular elastic connective tissue
where is it found?
- cells = rows of flattened fibroblasts
- extracellular = bundles of thick elastic fibres - made from elastin
found in the lungs
what is marfans?
- genetic defect on chromosome 15
- underdevelopment of elastic fibres
- heart/blood vessels/eyes/skeleton
- long fingers...
what is Ehlers-Danlos syndrome?
- collagen abnormality > joint dislocations and hyperextensibility
- autosomal dominant inheritance
- dissecting aortic aneurysm at an early age
main structure of the skin
- main layers
- epidermal basement membrane
describe the structure of the epidermis
- epidermis has 4 layers -
- - stratum corneum - stacks of dead cells called squames key function = protection
- - the granular layer - contains keratohyalin granules and other fibrous proteins which degrade the phospholipid membrane and xlink proteins - this is where the keratinocytes lose their membrane and become cells of the stratum corneum
- - the prickle cell layer - daughter keratinocytes terminally differentiate and lose the ability to divide
- - the basal layer - keratinocyte mitosis
how long does it take for a keratinocyte to go from the basal layer to the stratum corneum
30 - 40 days
name two cells other than keratinocytes in the epidermis and their role
- melanocytes are dendritic cells of neural crest origin they occur at intervals along the basal layer and produce melanin in darker skin there are the same amount they are just more active
- langerhans cells are dendritic cells of bone marrow origin they are scattered through the prickle layer and are designed to present antigens to Tcells mediating the immune response
describe the structure of the dermis
- tough, fibrous, vascular layer, fibroblasts synthesis the
- extracellular matrix which contains collagens and elastin.
- The other main components = blood and lymph
- vessels. mast cells and nerves
list some skin appendages
- hair follicles
- sebacous gland
- sweat glands
list the main functions of the skin
- sociosexual communication
list some diseases of the skin
- diabetic sensory neuropathy
- alopecia areata
- allergic contact dermatitis
- basal cell carcinoma/malignant melanoma
where is cartilage found?
- fetal skeleton
- costal cartilages
- articulating surfaces of bone
- C-rings of the trachea
- pubic symphsis
what are the three types of cartilage?
describe hyaline cartilage
- most common
- can ossify in old age and disease
- makes up fetal skeleton remains in adult as costal cartilages, thyroid cartilage, articular cartilage, C rings of the trachea
describe elastic cartilage
- matrix is rich in collagen and elastin fibres
- doesn't calcify or ossify with age
- found in the ear canal and epiglottis
- irregular dense fibrous tissue with few chondrocytes
- found in symphsis, intervertebral discs, articular discs in the knee joint and the sternoclavicular joint
describe the structure of cartilage
- strong somewhat pliable
- firm proteoglycan matrix
- the cells are chondrocytes they form chondroblasts which secrete matrix trapping the cell in lacunae - they are then called chondrocytes
- most cartilage (NOT fibrocartilage) is surrounded by a dense irregular connective tissue called perichondrium which vasularises the cartilage by diffusion
how does cartilage grow?
- INTERSTITIAL GROWTH - chondrocytes divide within lacunae to form isogenous groups
- APPOSITIONAL GROWTH - is adding new cells to the surface but requires undifferentiated cells
can cartilage repair?
- little capacity to repair
- fibrous/scar tissue is laid down by the perichondrium
what is the make up of the bone matrix?
- 65% inorganic - calcium phosphate etc.
- 35% organic - mostly collagen
what are the types of bone?
what is the difference between spongy and compact bone?
- spongy bone has large open cavities surrounded by plates of bone
- compact bone is harder it has smaller cavities and thicker lamellar
- spongy bone contains bone marrow
describe the structure of bone
- bone is always covered and lined by soft connective tissues
- the marrow cavity is lined by endosteum
- the periosteum covering the bone has an outer fibrous layer of collagen fibres and fibroblasts and an inner osteogenic layer consisting of an osteoprogenitor layer and osteoblasts
- the periosteum is fixed to the bone by sharpeys fibres and damage/trauma to the periosteum is very painful
- bone matrix is formed by osteoblasts which are derived from osteoprogenitor cells as they lay down the matrix they become trapped in lacunae and are referred to as osteocytes.
- osteocytes have long processes which are housed in canaliculi which are tunnels that lead to haversian canals which contain blood vessels
- the osteocytes that join one haversian canal to another are known as osteons
- haversian canals are joined to each other by volkmann's canals
how does bone remodel after a fracture?
- bone is continuously being remodelled - osteoclasts break it down and osteoblasts rebuild it.
- 1. haematoma - fibrin clot and bone fragments
- 2. procallus - inflammatory cell influx debris cleared
- 3. callus - fibrocartilage
- 4. healing - osteoprogenitor cells from periosteum lay down sleeve of bone - starts as spongy bone
how is bone made?
bone forms from pre-existing tissue which is replaced
- there are two types of ossification:
- - intramembranous - bone development begins in highly vascularised CT, it begins at the primary centre of ossification and osteoblasts lay down osteoid - a non calcified matrix which later becomes calcified, the osteoblasts then become osteocytes.
- - cartilage is replaced, the primary centre is the diaphysis/shaft the secondary centres (the epiphyseal growth plates) occur at the epiphysis
give an example of where intramembranous ossification occurs
flat bones of the skull
give an example of endochondrial ossification
what is achondroplasia?
congential and often hereditary shortness of limbs - thin epiphyseal growth plates
what is osteogenesis imperfecta?
- brittle bones
- abnormal collagen synthesis
what hormones affect growth?
- low growth hormone - pituitary dwarfism
- high growth hormone - gigantism/acromegaly(inc. in diameter)
- sex hormone deficiencies - epiphyseal growth plates don't close - tall stature
- thyroid hormone deficiency - cretinism
- high PTH - decalcification > inc. # risk
how long do blood cells survive?
- RBCs - 120 days
- platelets - 10 days
- neutrophils - 2-4days
- lymphocytes - 1 day - years
what is haemopoesis?
progentitor stem cells in the bone marrow differentiate into myeloidblasts which are precursors for erythrocytes, granulocytes, monocytes and platelets. Lymphoblasts are precursors for lymphocytes
various cytokines regulate the rate of division and differentiation
what controls the production of RBCs?
erythropoetin released from pertitubular endothelial cells in the kidneys
- multi-lobed nucleus
- functions = chemotaxis and phagocytosis
- bilobed nucleus
- orange granules
- large dark purple granules
- release histamine and heparin
- mediate acute inflammation
- small round blue particles from cytoplasm of megakaryocytes in bone marrow
- activation leads to adhesion and aggregation and acts as a binding site for clotting factors
what are the three types of muscle?
describe skeletal muscle
- pink due to myoglobin and vascularisation
- fibres are long, multi-nucleated and cylindrical
- RED = slow lots of myoglobin
- WHITE = fast - easily fatigued
what determins power output of a muscle?
- number of fibres
- amount of hypertrophy
what is the structure of muscle
muscle > fascicle > fibre (cell) > fibrils packed in parallel with organelles organised between them, the sarcotubular system allows for depolarisation to be spread across the fibre by T tubules > myofibrils are made up of myofilaments which are actin and myosin
- the muscle sheath is epimysium
- surrounding each fascicle is perimysium
- surrounding each fibre is endomysium
describe the actin filament
- double helical strand
- troponin is distributed along it attached to tropomyosin
what is the sliding filament hypothesis?
- 1. a nerve impulse arrives at neuromuscular junction causing release of ACh, depolarisation of the end plate and release of calcium
- 2. calcium binds to troponin which changes its shape and moves tropomysin away from the binding site of the actin so that the myosin filaments can form a cross bridge
- 3. the breakdown of ATP releases energy so myosin can pull the actin - shortening/contracting the muscle
- 4. myosin detaches from the actin and the cross bridge is broken down when ATP binds to the myosin to the myosin head when the ATP is broken down by myosin ATPase the power strike can be repeated
how are muscles innervated?
nerves attach at the motor end plate, one per fibre
can muscle regenerate?
- skeletal muscle has a small regenerative capacity but gross damage is repaired by CT and leaves a scar
- in nerves or blood supply is interrupted muscle fibres degenerate and are replaced by fibrous tissue
describe smooth muscle
- non - striated
- found in walls of GI tract, resp tract, walls of ducts, glands, arteries, veins, large lymphatics and in the muscles of the eye
- the cells are long and spindle like often embedded in thin elastic fibres
- their contraction is slower than skeletal muscle and their actin and myosin arrangement is less ordered.
describe cardiac muscle
- found in the heart
- has elongated nuclei, which are central in the fibres, intercalated discs, fibres contain large numbers of sarcosomes, the T tubules lie at the Z bands
what are purkinjie fibres?
- ensure rapid spread of impulses
- contain fewer myofilaments, fibres and far fewer intercalated discs
can cardiac muscle regenerate?
NO repairs with fibro-connective scar tissue
how often are contractile proteins replaced?
- every two weeks
- muscle continuously remodels
- can atrophy and hypertrophy very quickly
what is myasthenia gravis?
- auto-immune destruction of end plate ACh receptors
- more common in females
- characterised by muscle weakness without sensory loss
treat with ACh esterase inhibitors
list conditions that affect the neuromuscular junction
- myasthenia gravis
- botulism - toxins block ACh release
- organophosphate poisoning - irreversible binding of AChE > asphyxiation
what is Duchenne MD?
- complete lack of dystrophin, muscle tears itself apart calcium enters and causes death and necrosis
- death in late teens from resp failure
- recessive defect on X chromosome
describe muscular dystrophies
- genetic disorders
- muscle weakness and wasting
- replaced by fat and CT
what are the main division of the nervous system?
- PNS > ANS > sympathetic/non-sympathetic
what is the structure of the CNS?
- vast numbers of neurones supported by neuroglia, components sorted into grey and white matter
- the CNS is the brain and the spinal cord
- most neurones in the CNS are multipolar
what is grey matter?
nerve cell embedded in neuroglia
what is white matter?
the processes is the processes of the nerve cells embedded in neuroglia
what is glia made up of?
- ependymal cells
what is the structure of the PNS?
- cranial and peripheral nerves made up of bundles fibres
- divided into motor/efferent and sensory/afferent
what happens in the pre-embryonic period?
- fertilisation > zygote
- cleavage > morula
- compaction > embryoblast/trophoblast/blastocyst cavity
- hatching > loss of zona pellucida
- beginning of implantation
- week 2 - trophoblast > syncytiotrophoblast + cytotrophoblast and embryoblast > epiblast + hypoblast (bilaminar disc)
- completion of implantation
- formation of primary yolk sac lined by hypoblast cells
- formation of secondary yolk sac from pinching off of primary yolk sac
what marks the start of the embryonic period?
formation of the primitive streak
what happens during the embryonic period?
- all major structures and systems formed
- GASTRULATION - primitive streak defines the axis it is made up of the pit, node and streak
- epiblast cells migrate towards the primitive streak and invaginate displacing the hypoblast cells and creating the trilaminar disc
- NOTOCORD - the epiblast cells that invaginate through the cranial part of the primitive pit form a solid rod of cells down the midline - this drives neuralation
- NEURALATION - formation of the neural plate and the neural tube - notocord causes thickening of overlying ectoderm and the edges fold round creating a tube.
- MESODERM - the paraxial mesoderm becomes organised into segments, in pairs called somites, there are 31 pairs
- FOLDING - cephalocaudal and lateral
what are the three layers of the trilaminar disc?
what do somites become?
- dermatome - skin section - dermis
- myotome - muscle section
- sclerotome - hard tissue section - bones
give rise to repeating sections such as vertebrae, ribs and intercostal muscles.
what are the derivatives of the ectoderm?
what are the derivatives of the mesoderm?
what are the derivatives of the endoderm?
- epithelium of the resp and GI tracts