Tissue organisation - cellular basis Flashcards
What are 3 forms of CT and how do they vary?
soft
semi-hard (cartilage)
hard (bone)
vary in ECM composition (determined by syn and secretion of components of matrix by supporting cells)
What is soft CT?
Consists of cells embedded in ECM – not together in sheets
What do cells of soft CT do?
synthesise and secrete components of ECM
Is composition of ECM always the same?
variable composition
- depends upon function of ECM
What does epithelium do?
Lines lumen
What is fibroblast?
Cell that syn + secrete proteins and proteoglycans - push them out into env where they get stabilised
List what is found in soft CT? (10)
Basal lamina Collagen fibre Capillary Mast cell Fibroblast Macrophage Hyaluronan Proteoglycans Glycoproteins Elastic fibre Adipose cells
How does soft CT function as space filler?
space filler between organs & provides mechanical support e.g. holding intestines in pos
What is function of soft CT in terms of organs?
attachment of organs to backwall of body/ where u can anchor organ &; protection of organ from impact
What is function of soft CT in terms of nutrients?
highway for nutrients in blood vessels – dissolved nutrients in plasma
What is function of soft CT in terms of storage?
fat (adipose cells) – build up reserve of these against future starvation & calcium for days when there’s not much calcium – need for nerve growth and growth conduction, muscle contraction – if low on calcium – top up level to what’s phys normal
What is function of soft CT in terms of immunological defence?
site of immunological defence – macrophages – where bacteria and parasites are so that’s where they need to be killed
What are 5 types of soft CT?
Mesenchyme Loose (areolar) Dense Reticular Adipose
What is mesenchyme?
specialised early connective tissue in embryo – setting down future organs for body
Where is loose (areolar) CT found?
mesentery, under dermis (hypodermis). v. flexible and open sponge-like – in places where lots of movement in parts of body are required so u don’t rip skin
Where is dense CT found?
Tendon at end of muscles, dermis – above hypodermis and underneath epidermis – gives tension and solidity to skin, capsules – organs e.g. kidney – CT surrounds it to hold it in place
Where is reticular CT found?
In bone marrow – stem cells and progeny have to held in place, lymph nodes – sim thing in lymph nodes
Where is adipose CT found?
Fat cell
How do types of soft CT vary?
in collagen & proteoglycan form
What does the ECM consist of?
Proteins – glycoproteins
Glycosaminoglycans – GAGs = sugars
Together these form large hydrated gel
What is role of collagen in ECM?
tensile strength of matrix
What is role of elastin in ECM?
elasticity of matrix
What is role of adhesive protein in ECM?
adhesion proteins for fibroblasts & other cells – proteins cells will attach to e.g. stem cells ion bone marrow, don’t float in space but have to attach to matrix to proliferate and diff properly
Which is most abundant protein in soft CT?
Collagen
What is structure of collagen?
Rod-shaped triple helix of polypeptides – up to 420 nm long. Not extensible – can’t pull it/no elasticity. Forms fibrils (group = fibres) of some type in ECM
What is function of collagen in soft CT?
Fibres and fibrils give strength to diff types of connective tissue
tensile strength of matrix tendons, dense CT (highest conc), ligaments
How many collagen proteins do humans have?
20
Size & shape of collagens vary according to function
How many types of fibrillar collagen are there?
4
What is Type I fibrillar collagen and where is it found?
tough In skin (dermis), bone, tendons – have to hold muscles in place during contraction/extension, dentine in teeth
What is Type II fibrillar collagen and where is it found?
thinner fibres
cartilage
What is Type III fibrillar collagen and where is it found?
Sheet collagens
blood vessels, skin (hypodermis which is more flexible)
What is Type IV fibrillar collagen and where is it found?
basement membrane
Why is cytoplasm in collagen III in dermis full of RER?
lots of syn and secretion of protein for export of collagen and proteoglycans
Where are elastic fibres found?
Prominent in skin, blood vessels & lung as lung vol has to increase as you breathe in and relax as you exhale – prevents ripping
What is structure of elastic fibres?
extensible (like rubber)
recoils passively after tissue is stretched.
What is function of elastic fibres?
the energy stored in elastic fibres pushes blood through circulation – peripheral blood vessels – relaxation helps pump blood through circulation
What happens to elastic fibres in the wall of aorta?
Fibrils – expand when blood pumped out of ventricle and the relax as systole contractions of ventricle pass by
What is structure of elastic fibres?
A composite material: a network of
fibrillin (protein) microfibrils embedded in a core of cross-linked elastin. Details unclear
What syn elastic fibres and what does this mean?
embryonic and juvenile fibroblasts
Adults make do with this – have all elastin u will ever have for rest of ur life; fibres are very
resilient, can withstand > 2 billion cycles of stretch-recoil before losing elasticity. Compare aged skin with juvenile, where UV irradiation damage is evident. Loss of elasticity and elastic fibre function with age
What is an adhesive protein?
ECM protein to which cells stick): cross-link cells of CT to collagen, bind to transmembrane receptors called integrins.
Anchor cell down to ECM so cell doesn’t float about
What is fibronectin?
abundant in all CT – fibroblast attached to it
What is tenascin?
produced at wounds, function obscure but helps fibroblasts migrate in skin to seal up cut and stop it being made again
What is laminin?
in basal laminae, binds epithelia to BM – along with collagen type IV
What is basement mem?
Separates CT from the epithelial layer
A physical barrier to cells, maintains the integrity of tissues
How are GAGs syn?
as proteoglycans – all have protein component except hyaluron
What are GAGs?
glycosaminoglycans, formerly known as mucopolysaccharides
100s of GAGs
Few common features, but do share common properties
What are GAGs arrangement?
70-200 sugars long, thin flexible sugar chains floating in water
high density of negative charge at phys pH
How do GAGs react with water?
Sugar chains are too stiff to fold into compact structures.
Also strongly hydrophilic
Tend to adopt highly extended shapes that occupy a huge volume
Water sucked into the matrix of GAGs by osmotically active ion cloud – dilute density of vol.
Cations e.g. Ca2+, K+ abundant in plasma + liquid phases attracted to –ve charge – get watery gel
How can ECM withstand compressional forces?
Water creates swelling pressure(turgor) that enables the ECM. Compare with collagen that resists stretch forces - opp.
What is structure of GAGs?
GAGs in CT constitute <10% of weight of the protein, but fill most of the volume as a porous hydrated gel.
Where would u find lots of GAGs and why?
Synovial joint
act as shock absorbers – walk, no pain as bones bang against each other
Proteoglycan vol of water acts as shock absorber
What are 2 classes of CT cells?
indigenous & immigrants
What are indigenous cells?
synthesis of ECM, lipid storage
What are immigrant cells?
immune system cells - Largely leukocytes (WBCs)
What are types of immigrant cells?
neutrophils monocytes/macrophages dendritic cells eosinophils basophils lymphocytes
What types of immigrant cells are phagocytic?
neutrophils
monocytes/macrophages
What are dendritic cells?
immune surveillance in tissues – wait for bacteria and grabs it and starts immune response
What are eosinophils?
function in parasitic infection
What are basophils?
obscure function
What are lymphocytes?
involved in antibody production, cell killing
