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24 Cards in this Set
- Front
- Back
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Define the term connective tissue and cite examples to explain connective tissue functions.
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Connective tissue is an umbrella term used to describe a variety of tissue of medoderm embryonic origin. The tissue comprises of cells, fibres and ground substance. The cells are not contiguous like in epithelia. Connective tissue is dynamic which has a constant turnover and undergoes remodelling eg bone and re-organisation eg scar tissue.
Functions: Binding- of tissues to other tissues eg tendon binds bone to muscle Support- nearly all organs have a supportive framework of connective tissue eg blood vessels, Protection - of underlying tissue |
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List the common cell types found in connective tissue describing their function.
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Cells in connective tissue:
- Undifferentiated mesenchymal cells - Fibroblasts- synthesise extracellular matrix - Macrophages - phagocytose foreign material - Adipocytes - storage, in adipose tissue ( specialised CT) - Mast cells - alergic reaction, secrete histamine - narrow lumen of bronchioles, inflamation, leaky capillaires - oedema - plasma cells ( antibodies released from b lymphocytes) - blood cells - Specialised connective tissue ALSO chondroblasts - synthesise collagen, osteoblasts - synthesise bone, myoblasts - skeletal muscle |
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Describe and discuss the function of extracellular matrix.
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The extracellular matrix comprises of:
Ground substance - proteoglycans, glucosaminoglycans, water, lipids. Fibres - collagen fibres, reticular fibres, elastic fibres Function: Varying composition of ground substance changes the viscosity of the tissue. Thin gel - loose CT, thick gel - dense CT - density and fibre type decide if tissue is 1. primary mechanical importance eg tendon 2. loose packaging material eg adipose tissue |
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Explain the differences between loose and dense connective tissues, in terms of their cellular and extracellular components, relating these differences to tissue function.
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Loose connective tissue:
- loosely packed fibres seperated by abundant ground substance ( more than dense CT) - Thin gel of extracellular matrix - provides space packaging framework - septa and trabeculae inside organs. Not much fibrous support. - shock absorber when increase in fat cells - adipose tissue - can become greatly overcome by extracellular fluid - oedema. Dense connective tissue: - High density of extracellular fibres - firm gel of extracellular matrix - relatively low density of ground substance and cells - provides high tensile strength eg tendon - attaches epithelial tissue of skin ( epidermis) to underlying tissue. |
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What does loose connective tissue comprise of and where is it found?
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Loose areolar fibroelastic connective tissue
cells: fibroblasts, macrophages, mast cells ( granules) fibres: collagen most abundant, elastin fibres and very few reticular fibres. Positions: - just below skin - easily can move skin - below the mesothelial lining of the peritoneum, serosa - associated with adventitiia of blood vessels - stroma- septa and trabeculae, surrounds parenchyma of glands - submucosa ( immune cells present if adjacent epithelial cells are exposed to bacteria and foreign antigens eg respiratory tract) adipose and blood are also loose connective tissues. |
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Classify different types of embryonic connective tissue - mesenchymal connective tissue and mucous connective tissue
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Mesenchymal connective tissue: ( first loose connective tissue in embryo)
- mesenchymal cells surrounded by relatively fluid intercellular substance which over time in utero becomes more mucoid to form.... Mucous connective tissue ( whartons jelly) - only found in umbilical cord and subdermal CT of embryo. - cells: stellate fibroblasts , some marcrophages and lymphocytes. - extracellular: ground substance is soft jelly like, high conc of hyaluronic acid, fibres: fine collagen fibres. Mesenchymal core is present in limb buds surrounded by parietal layer of lateral mesoderm and overlying ectoderm. The distal ectoderm forms AER. |
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What is the structure and function of adipose tissue.
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Adipose tissue is a loose connective tissue where the majority of cells are adipose cells. Divided into lobules of fat cells by septa ( loose CT) which contain mast cells, and blood vessels. Each fat cell is invested by reticular fibres which in turn are anchored to collagen fibres of septa.
lipid dissolve during tissue processing but nuclei can be seen which are pushed to the cell periphery by lipid droplet. functions: - They synthesise and store fat - energy source - insulating material under skin - shock absorber around many joints - brown adipose tissue in neck and around vital organs of newborn babies generate heat ( UCPs- uncoupling proteins) and also in neck and upper chest of adults |
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What is the structure and function of reticular connective tissue?
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Reticular connective tissue
fibres are made of collagen type 3, fine branching threads. Fibroblasts lay down fibres. Function: Framework of lymphoid tissues (spleen, appendix) and liver. |
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Where are elastin fibres found in what is their function?
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Elastin fibres are present in the aleolar walls, where they form a basket-like supportive structure. They maintain the shape of the alveolar wall, protect it during distension and are responsible for non-forced exhalation
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Describe the different types of dense connective tissue
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Dense irregular connective tissue comprises of interwoven bundles of collagen which criss cross in many directions to overcome multidirectional forces.
Examples: capsules, large septa and trabeculae of many organs, deep fascia of muscle, the dermis of skin, periosteum around bone, perichondrium around cartilage, dura mater around brain and spinal cord. Dermis ( below the epidermis- epithelia) contains blood and lymphatic vessels, sensory nerves and nerve endings, skin appendages ( sweat glands, hair follicles, sebaceous glands), collagen bundles and elastin fibres ( elasticity of skin). Dermis and epidermis interdigitate to overcome shearing forces Dense regular connective tissue comprises of parallel fibre bundles to provide maximum tensile strength. - examples: tendons, ligaments and aponeuroses (flattened tendons) Tendon: connect muscle to bones. Parallel collagen bundles interspersed with rows of flattened fibroblasts. Fascles- bundles of of collagenous fibres and fibroblasts surrounded by endotendineum (loose CT). Peritendium holds groups of fascicles together. A fibrous sheath surrounds whole tendon. Ligament: connect bone to bone, like tendons collagen fibres interspersed with fibroblasts but elements are less regularly arranged. Elastic ligaments: ligament is mainly composed of elastin eg in neck and verterbrae. |
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Describe some disorders of connective tissue.
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MARFAN'S SYNDROME
- genetic defect in fibrillin gene causing underdeveloped elastic fibres in the body leading to tissue irregularities eg lax joints and fragile vascular walls ( predisposed to aorta rupture) symptoms: - very tall and thin, - legs and arms, fingers and toes may seem too long for the rest of their body, out of proportion. - cardiovascular problems eg rupture of aorta, valves not working - lung problems- alveoli colapse - sternal defects - dislocation of lens of eye Often homocysteinuria is misdiagnoses as marfans syndrome SCURVY Symptoms: bleeding gums and loose teeth due to vitamin C deficiency. Vit C is necessary for hydroxylation of proline for proper tropocollagen formation. The abnormal collagen produced lacks its usual strength and teeth don't remain in their bony sockets. Also associated with inability to heal wounds. LIPOMAS - usually benign tumours of fatty acids EHLERS-DANLOS SYNDROME - group of rare genetic diseases causing collagen fibre abnormalities of the dermis and tendons - joint dislocations and skin deformation. Osteogenesis imperfecta |
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Give an overview of collagen biosynthesis.
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1. Synthesis of polypeptide chain and then chain enters lumen of RER
2. Cleavage of signal peptide sequence 3. Hydroxylation of selected proline and lysine residues ( require Vit C to do this- Scurvy if deficiency) 4. Addition of N-linked oligosaccharides ( N glycosyl link between carbohydrate and amide nitrogen) 5. Addition of galactose to hydroxylysine residues 6. 3 chains align and disulphide bonds form between them. 7.Formation of triple-helical procollagen from C - to N- terminus and is transported via transport vesicle to convex side of golgi apparatus 8. O-linked glycosylation by addition of glucose ( glycosidic link betwen carbohydrate and hydroxyl group of Ser or Thr) 9. exocytosis of procollagen 10. In extracellular fluid N- &C- terminal propeptides are cleaved to form tropocollagen 11. Multiple tropocollagen molecules align and form covalent cross links between lysine and hydroxylysine residues. thus creating a colagen fibril 12. aggreagations of fibrils forms a colagen fibre |
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Describe the macroscopic structure of human skin and how this organ varies with site, sex, age, ethnicity and exogenous influence.
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HAIR- variations in distrubution and character according to body site, sex, age, ethnicity
THICKNESS of skin - varies depending on site, soles of feet and palms ( stratum corneum particularly thick) COLOUR - ethnicity, site , UV exposure LAXITY- variations according to site( superficial fascia Loose CT may be very mobile- dorsum of hand, surface of face but in other areas allows little movement - palm of hand), age, UV exposure OILINESS- puberty, site |
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Describe how some of these variations influence the susceptibility to and/or the manifestations of skin disease.
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Skin colour ( ethnicity)
- vitiligo: autoimmune dipegmentation, more conspicuous on dark skinned people. - UV induced acute sunburn, freckling, ageing, skin cancer in the fair skinned - especially those with red hair and blue eyes Oiliness: - acne - age - puberty Hair: - autoimmune hair loss ( alopecia areata - some hair, alopecia totalis- loss of hair from entire scalp) - gender - effects women more pschosociologicaly |
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Describe the microscopic and molecular structure of the epidermis.
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stratum corneum- horny layer
- layers of flattened, dead, keratinized cells, no nuclei or organelles but masses of keratin ( corneocytes) - Thickness depends on position, thicker at palms and soles of feet Stratum granulosum - Layers of squamous epithelial cells containing keratohyalin granules and are soon to be cornified ( keratinized) -lose plasmamembrane Stratum Spinosum - (prickle layer) layers of polyhedral epithelial cells which are daughter keratinocytes, that have moved up from basal layer. They undergo terminal differentiation and can no longer divide. They form prickle like desmosomes between each prickle cell. Stratum basale - simple cuboidal epithelial layer that undergo mitosis to replace surface cells. Touches basement membrane. |
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Describe epidermal dentritic(langerhans) cells and melanocytes.
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Langerhans cells ( epidermal dendritic)- derived from bone marrow, present antigen cells to T lymphocyte, mediate immune reactions - allergic contact dermatitis, Found in prickle layer ( stratum spinosum)
Melanocytes - dendritic cells which derive from neural crest, synthesise melanin- responsible for skin colour ( the number of melanocytes in whiter tones are the same in darker tones- less melanin produced in whiter) and deliver it to surrounding keratinocytes via dendrites. Found in basal layer ( stratum basale) of epidermis and in hair follicles. With age melanocytes stop working in hair follicles however they continue to work in epidermis. |
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Outline the disease which causes abnormal epidermis growth and differentiation.
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Psoriasis - Usually surface cells in epidermis are regenerated every 28-30 days. In psoriasis, an autoimmune condition, abnormal proliferation of the basale layer cells causes the development of new keratinized cells to reach surface before the surface cells can be shed. This results in a very thick prickle layer and many stratum corneum cells which causes scaling of the skin - raised patches of dead skin.
- heat loss, fluid loss, percutaneous absorption of exogenous materials, Erythrodermic psoriasis is the failure of vascular thermoregulation due to permanent vasodilation resulting in hypothermia. Treatment of psoriasis - corticosteroid creams - anti-inflammatory and prevent the acute inflammation which causes the intense proliferation of basal cells - methotrexate - antifolate - acts on cells in S phase to stop DNA synthesis and thus cell growth in rapidly dividing cells - cyclosporine - immunosuppresant |
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Briefly describe allergic contact dermatitis.
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Allergic contact dermatitis - Is caused by langerhans cells in prickle layer which mediate an immune response by presenting antegens to T lymphocyte. Antigen could be anything such as nickel, or perfum and the contact on skin causes this allergic reaction.
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Describe some diseases affecting melanocytes.
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Malignant melanoma: An aggresive neoplasm of melanocytes most common in skin. A retension of tumour cells abover epidermal basement membrane - good prognosis. Tumour cells penetrating the basement membrane - bad diagnosis. Moles are benign growths of melanocytes.
Vitiligo- Autoimmune destruction of melanocytes causing depigmentation, more conspicuous in dark skinned people. Symetrical depigmentaton -Unknown cause, potentially neural control as melanocytes have neural crest origin. |
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What is the dermo-epidermal junction?
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Basmement membrane -Layer between dermis and epidermis ( pink layer in histology slides). Used as prognosis of malignant melanoma, if tumour penetrates basement membrane - bad prognosis.
Dermis and epidermis intergitate to resist shearing forces. |
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Describe the dermis and it's constituents and any associated diseases.
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Dense regular connective tissue - abundant collagen fibres some elastin and reticulin. Flattened fibroblasts interspersed between bundles of fibres.
cells: fibroblasts ( synthesise extracellular matrix), macrophages, mast cells, blood vesels, and lymphatic vessels, nerves Extracellular matrix: collagen, elastin, reticulin, ground substance. Diseases: Fibroblasts and extracellular matrix: - keloids: grossly excessive production of scar tissue following wounding resulting in large skin marking. - striae: stretch marks, dammage to collagen and elastin, eg during pregnancy - solar elastosis - wrinking, damage to collagen and elastin by excessive UV exposure. BLOOD VESSELS: - vascular birthmarks ( port wine stain over skin) congenital malformation of dermal blood vessels ( superficial dermis- capillaries, deep dermis - larger blood vessels. LYMPHATIC VESSELS: - Lymphoedema: Mast cells: lie close to dermal blood vessels and during a hypersensitve allergic reaction release histamine which causes increased vascular permeability and become leaky --> oedema. - anaphylaxis - rapidly processing, life threatening allergic reaction. - urticaria - transcient appearances of elevated patches due to allergic reaction |
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Describe the skin appendages and problems associated.
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The pilosebaceous unit: hair follicle and sebacious gland ( holocrine secretion of oily sebum into hair follicle).
-alopecia -autoimmune attack of hair follicles, hairloss ( areata- patches, totalis- total hair loss on scalp) acne- abnormal differentiation of sebaceous gland causing obstruction of duct, increased production of sebum, infection with normally harmless skin bacteria. Differentiation occurs during puberty and more sebaceous glands on face. sweat gland - eccrine glands -sweat -hyperhidrosis (increased sweating at palms and soles) - apocrine sweat glands - protein- rich, odour less secretion which has no function and on digestion produces body odour. Nails - psoriasis- abnormal differentiation of epidermis basale layer cells. |
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Describe the position and function of subcutaneous fat.
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Adipose tissue ( loose areolar connective tissue) beneath the dermis, hypodermis- alows laxity of skin, to move around.
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Describe the main functions of the skin.
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Barrier function:
- Stratum corneum - prevents water loss, retains moisture, protects from some UV damage, prevents ingress of microbes, protection against abrasion - prevents percutaneous absorption of exogenous materials-must be overcome for percutaneous absorption of drugs Sensation: - feel external factors- pressure, pain, danger - diabetic sensory neuropathy - leprosy - bacterial infection Thermoregulation: - sweating - heat loss by evaporation of sweat - vasodilation (heat loss) and construction ( retain heat) of surface blood vessels. failure of vascular thermoregulation eg psoriasis - permanent vasodilation--> hypothermia Sociosexual communication eg tatoos |
