Flashcards in Session 5 Deck (84):
Define connective tissue and give examples
- Is found in a continuum throughout the body connecting muscle, nervous and epithelial tissue in a structural way, but also provides metabolic and physiological support
- Blood (gas transport and immune defence functions)
What are the functions of connective tissue?
- Provides substance and form to the body and organs
- Provide a medium for diffusion of nutrients and wastes
- Attach muscle to bone and bone to bone
- Provides a cushion between tissues and organs
- Defends against infection
- Aids in injury repair
What is connective tissue made up of?
- Extracellular matrix: ground substance (hyaluronate proteoglycan aggregates) and fibres (collagen, reticular and elastic)
How do connective tissues differ?
- Type of cells contained
- Abundance/density of cells
- Constitution of extracellular matrix: ground substance composition; fibre type, abundance and arrangement
What are the types of embryonic connective tissue?
What types of regular/proper connective tissue are there?
- Dense: regular; irregular
What are types of specialised connective tissue?
- Adipose Tissue
- Haemopoietic tissue
- Lymphatic tissue
Where does Mesenchyme cells come from?
- Proliferation and Migration of Mesodermal cells of the Middle germ layer (and a few ectoderm all cells)
What happens to the mesenchyme cells?
- Maturation and proliferation produces various connective tissue (eg cartilage, adipose, ligaments, tendons, bone and skeletal muscle), serous membranes, vascular and Urogenital systems and muscle
What type of cells does Mesenchyme consist of?
- Multipotent progenitor cells
What type of Mesenchyme cells are in the adult?
- Pluripotent cells that can produce new connective tissue cells for healing
What type of connective tissue is in the umbilical cord?
- Mucous connective tissue makes up the Wharton's jelly
Explain the structure of the hyaluronate proteoglycan aggregate in the ground substance
- Hyaluronic acid molecules have many proteoglycan monomers attached, which themselves are made up of a core protein with glycosaminoglycan (GAG) units attached
- The high density of negative charges on the GAGs attract water, forming a hydrated gel
Give examples of types of collagen
- Type I:most widely distributed; fibres aggregate into fibres and fibre bundles (eg in tendons, capsules of organs and skin dermis)
- Type II: Fibrils do not form fibres (in hyaline and elastic cartilage)
- Type III (Reticulin): Fibrils form fibres around muscle and nerves cells and within lymphatic tissues and organs
- Type IV: Unique form present in basal Lamina of Basement membrane
What are fibroblasts?
- Secrete procallagen from which collagen fibrils are assembled and are associated with the fibroblasts
What type of connective tissue is in the testis capsule?
- Dense irregular
What type of fibres are in a lymph node?
- Capsule contains collagen bundles
- Reticular fibres (collagen type III)
- Also contain lymphocytes
What are elastic fibres?
- Elastin is the main component of elastic fibres which is itself surrounded by microfibrils called fibrillin
- Occurs in most connective tissue but varies (eg is important in the dermis, artery walls and sites with elastic cartilage
What is Marfan's syndrome?
- An autosomal dominant disorder in which expression of the fibrillin gene is abnormal, causing the elastic tissue to be abnormal
- Sufferers are abnormally tall, exhibit arachnodactyly (abnormally long and slender fingers), have frequent joint dislocations and can be at risk of catastrophic aortic rupture
Describe the structure of a small elastic fibre
- Tunica intima (indistinct endothelial cells) (lumen side)
- Tunica media (elastin lamellae)
- Tunica adventitia (collagen) (outside)
Describe the structure of the aorta wall
- Tunica intima (thin layer)
- Tunica media (thick layer with many elastic lamellae): contains smooth muscle cells which produces elastin, collagen and extracellular matrix
Describe the structure of a mammary gland (masson's trichromatic)
- Glandular epithelium
- Loose irregular connective tissue (wispy collagen and many fibroblasts)
- Dense irregular connective tissue (thicker and more abundant collagen and fewer fibroblasts)
What type of connective tissue is in the Submucosa eg in the colon?
What is contained in loose connective tissue?
- Branching elastic fibres
- Collagen fibres
- Small blood vessel
- Nuclei of fibroblasts
- Mast cells
What type of connective tissue is the dermis?
- Dense irregular
- Bundles of collagen are densely packed but irregular arranged
- Can resist forces in multiple directions to prevent tearing
- Elastic fibres allow a degree of stretch and restores the original shape
What are capsules?
- Protect tissues that the connective tissue surrounds (eg adrenal gland, spleen, ovary, testis, prostate, joint)
- Type of Connective tissue varies depending on location from loose to dense irregular
What type of connective tissue makes up the tendon?
- Dense regular
- connects muscle to bone
- parallel densely packed collagen bundles with rows of elongated flattened fibroblasts between them
Describe the structure of myotendinous junctions
- Skeletal muscle fibres interdigitate with tendon collagen bundles
- Sarcolemma always lies between the collagen bundles and the muscles's myofilaments
Describe the structure of a short ligament
- Connects bone to bone
- Collagen bundles densely packed in parallel arrangement, are arranged in fascicles surrounded by loose connective tissue
What cells are commonly found in connective tissue?
- Mast cells
What is the function of fibroblasts?
- Synthesis and secrete ground substance and fibres that are in the ground substance
- Important in wound healing, are primarily responsible for the formation of scar tissue
Where do macrophages come from?
- Blood monocytes which move into loose connective tissue, especially when there is local inflammation
What is the function of macrophages?
- Are phagocytic: degrade foreign organisms and cell debris
- Are 'professional antigen presenting cells': present foreign material to T lymphocytes of the immune system
Where are mast cells found?
- Connective tissue near blood vessels
- Not found in CNS to prevent damaging effects of odema there
- What do mast cells contain?
- Abundant granules which contain:
~ Heparin (anticoagulant)
~ Histamine (increases permeability of blood vessel walls)
~ Substances that attract eosinophils and neutrophils
(part of immune system)
What is the function of mast cells?
- Are coated with Immunoglobulin E (IgE) (molecules that specifically bind allergens)
- The contents of the granules are rapidly released from the cell when an allergen cross-links with the surface-bound IgE molecules
- Granule secretions can result in immediate hypersensitivity reactions, allergy and anaphylaxis
How do adipose tissue cells develop?
- Mesenchymal cells develop into fibroblasts or preadipocytes (early lipoblasts)
- The early lipoblasts develop numerous lipid droplets in their cytoplasm
- In brown adipocytes the multiple lipid droplets remain separate, but in a mature lipoblasts (white adipocyte) the multiple lipid droplets fuse to form a single droplet that displaces all cell content to the cell periphery
Why do white adipocytes look empty in H&E stains?
- Toluene and xylene have dissolved the lipid
What is the function of white adipocytes?
- Contain fats which acts as a: fuel reserve; thermal insulator and shock-absorber
Where are brown adipocytes found?
- Near to scapula, sternum and axillae (especially in newborns)
- Also present in upper chest and neck of adults
What is the function of brown adipocytes?
- High respiratory capacity for the generation of heat (further promoted by uncoupling oxidative phosphorylation) as there is a rich vascular supply and abundant mitochondria
- Non-shivering thermogenesis is important for babies and hibernating animals
What are some variations in the macroscopic structure of human skin?
- Colour: Ethnicity; Site (lips,areole); UV exposure
- Hair: Site (hairy vs hair-free areas eg palms, soles, lips); Sex (facial and more profuse body hair growth in men); Age (baldness in men, greying in both sexes); Ethnicity (colour, character)
- Laxity/Wrinkling: Site; Age; Ultraviolet exposure
- Oiliness: Puberty; Site
How do some macroscopic variations of skin influence the susceptibility to and/or manifestations of skin disease?
- Vitiligo: psychosocial impact if it affects visible areas of darker-skinned individuals; less of a problem in fair-skinned people as not so visible
- Alopecia areata/Alopecia totalis (autoimmune response leading to hair loss): more psychosocial impact if it affects scalp, especially in women
- UV induced abnormalities: fair skinned people more susceptible to sunburn, freckling, ageing and skin cancer (eg basal cell carcinoma and malignant melanoma) especially in individuals with red hair
- Acne: more common during puberty
Describe the structure of the epidermis
- Consists of stratified squamous keratinised epithelium, made up of keratinocytes and their products
~ Horny layer (stratum corneum)
~ Granular layer (stratum granulosum)
~ Prickle cell layer (stratum spinosum)
~ Basal layer (stratum basale)
What happens in the basal layer?
- Keratinocytes mitosis
- Keratinocytes then move upwards to the prickle cell layer
What happens in the prickle cell layer?
- Terminal differentiation begins and keratinocytes loose thei ability to divide
- Keratinocytes synthesise keratinocytes (hetrodimeric fibrous protiens) which contribute to the strength of the epidermis, also the main constituent of hair and nails
What abrupt changes occur in the granular layer?
- Keratinocytes lose their plasma membrane (phospholipid bi layer)
- Keratinocytes begin differentiating into corneocytes (main cells of horny layer/stratum corneum)
What does the granular layer contain?
- Keratohyalin granules, which are aggregates of:
~ Other fibrous proteins (eg filaggrin, involucrin)
~ Enzymes which: degrade phospholipid bilateral (phospholipase); cross-link proteins eg filaggrin (aggregates proteins), involucrin (forms a major part of corneocyte envelope)
What is the structure and function of the horny layer (stratum corneum)?
- Layers of flattened corneocytes
- Major role in skin barrier function (eg prevents loss of water-water barrier function)
What is the transit time of a keratinocyte from the basal layer to the stratum corneum?
- 30-40 days
What other cells are in the epidermis?
- Langerhans cells
What are malanocytes?
- Dendritic cells of neural crest origin
- Occur at intervals along basal layer of epidermis (1/5 to 8 cells)
- Difficult to see histologically without special stains
- Produce melanin (pigment that gives skin colour)
- In dark-skinned individuals produce more melanin but are not increased in number
What are Langerhans cells?
- Dendritic cells of bone marrow origin
- Scattered throughout prickle cell layer
- Difficult to see histologically without special stains
- Highly specialised capacity to present antigens to T lymphocytes
- Mediates immune reactions eg allergic contact dermatitis
How is melanin transferred to neighbouring keratinocytes?
- Pigment donation: Phagocytosis of tips of dendritic processes to transfer mature melanosomes (organelles containing melanin)
How are prickle cells joined?
- Prickle-like desmosomes (intercellular junctions)
What are some disorders of epidermal components?
- Psoriasis (abnormal epidermal growth and differentiation)
- Allergic contact dermatitis (mediated by Langerhans cells)
- Malignant melanoma (malignant growth of malanocytes)
- Vitiligo (Autoimmune destruction of melanocytes)
What is psoriasis?
- Common skin disease (affects 2% of population)
- Cause unknown, but runs in families so is influenced by genetic factors
- Extreme proliferation of epidermal basal layer, causing gross thickening of prickle cell layer and production of excessive stratum corneum cells
- Manifests clinically as excessive scaling
- Can affect any area of the skin (can cover entire body surface)
What is malignant melanoma?
- An aggressive malignant tumour (neoplasm) of melanocytes, most commonly found in the skin
- Superficial spreading melanoma (tumour cells above epidermal basement membrane) has a good prognosis while penetrating, nodular melanomas have a poor prognosis
- Common moles are benign growths of melanocytes but can be difficult to distinguish from melanomas clinically
What is vitiligo?
- Autoimmune disease where the immune system attacks malanocytes, usually in symmetrical, localised areas of the skin causing depigmentation
- Is more visible in dark skin
- No explanation for symmetrical nature - could be under neural control as melanocytes are derived embryologically from neural crest
What is Alopecia areata?
- Autoimmune attack on hair follicles
Where is the dermo-epidermal junction? (Basement membrane zone)
- The epidermal basement membrane at the dermo-epidermal junction is below the basal layer of the basal layer of the epidermis
- Best seen with a PAS stain
What is the dermis?
- Dense irregular connective tissue
- Tough, fibrous and vascular layer
- Main component of leather
What does the dermis consist of?
- Extracellular matrix: collagen (especially type I); elastin; other extracellular matrix components
- Fibroblasts (synthesise extracellular matrix)
- Blood vessels
- Lymphatic vessels
- Mast cells
What can damage to collagen and elastin in the dermis cause?
- Solar elastosis (excessive UV exposure)
- Stretch marks (eg pregnancy)
- Keloids (excessive scar tissue following wounding - consists of mainly collagen synthesised by fibroblasts)
What are birthmarks (port wine stain) caused by?
- Congenital malformation of dermal blood vessels
Where are tissue mast cells found in the skin?
- Around dermal blood vessels
When and what happens when mast cells are activated?
- Type I immediate hypersensitivity (allergic) reactions
- Histamine is released
- Causes increased vascular permeability and leakage of plasma into extravascular sites
- Causes local oedema (swelling due to increased tissue fluid)
- In skin can cause urticaria and angio-oedema
- May have serious consequences in vital structures eg Upper respiratory tract
Describe the layout of blood vessels in the dermis
- Small blood vessels in the superficial dermis (mainly capillaries, small venules and arterioles)
- Larger blood vessels in the deeper dermis
Give examples of skin appendages
- Hair follicles ) pilosebaceous
- Sebaceous glands ) unit
- Sweat glands (eccrine (merocrine)/appocrine)
What type of secretion is used by sebaceous glands?
What is acne?
- Skin disease affecting sebaceous glands
What is acne caused by?
- Abnormal differentiation of sebaceous gland ducts which become obstructed
- Increased sebum production
- Infection with normally harmless skin bacteria
Why does acne normally occur on the face?
- Most abundant location of sebaceous glands
What are eccrine sweat glands?
- Major sweat glands of the body
- Use eccrine/merocrine secretion
- Found in most of skin
- Produce a clear, oderless substance consisting of water and NaCl (NaCl is reabsorbed in the duct to reduce salt loss)
- Active in thermoregulation and are controlled by the hypothalamus
What do eccrine glands consist of?
(Cuboidal epithelial cells)
- Intraepidermal spiral duct (acrosyringium)
- Straight dermal portion
- Coiler acinar portion in dermis
What is hyperhydrosis?
- Increased sweating
- Cause usually unknown
- May effect only palms and soles
What are apocrine sweat glands?
- Large sweat glands most abundant in axillae, genital and submammary areas
- No function of value
- Produce an oderless, protein-rich, apocrine secretion
- Digestion of this by cutaneous microbes causes body odour
What are the main functions of skin?
- Barrier function
- Psychosexual communication
What is the barrier function of the skin?
- Outer epidermis (stratum corneum) forms a barrier preventing percutaneous absorption of exogenous substrates
- Much studies as must be overcome in the percutaneous absorption of drugs
- May be seriously disrupted by many disease eg psoriasis
What does a poor barrier function lead to?
- Loss of fluid
- Loss of protein
- Loss of other nutrients
- Loss of heat
- Excessive absorption of
potential harmful exogenous
agents eg drugs
What is the sensation function of the skin?
- Sensory nerves in the skin allow sense of touch, temperature, tissue damage
- Affected by leprosy (disease of peripheral nerves) and diabetic sensory neuropathy
What is the thermoregulation function of the skin?
- Vascular thermoregulation (dilation/constriction of blood vessels) and thermoregulatory eccrine sweating (evaporation of eccrine sweat causes cooling) are critically important in maintenance of body temperature
- Failure of either can have serious consequences
What happens if vascular thermoregulation fails?
- Widespread vasodilation of erythrodermic psoriasis and the inability to vasoconstrict in a cold environment leads to heat loss
- Patients are often shivery and may become hypothermic