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Physiology and Pharmacology > Epithelia and the Integumentary System > Flashcards

Epithelia and the Integumentary System Flashcards

1
Q

what are epithelial tissues?

A
  • they are at the boundaries of the body
  • they cover surfaces, line cavities and form glands
  • they separate controlled internal environment from uncontrolled external environment
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2
Q

where does epithelia develop from?

A

3 germ layers:

  • endoderm = GI lining
  • mesoderm = lining of cardiovascular system
  • ectoderm = epidermis/skin
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3
Q

what functions do epithelia perform?

A
  1. protection
    - skin is first defence against microbes
  2. diffusion
    - alveoli in lungs
  3. absorption
    - small intestine
  4. secretion
    - glands
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4
Q

what are the 4 common properties of epithelia?

A
  1. epithelial cells have polarity
  2. they have a basement membrane
  3. they are involved in cell adhesion and communication
  4. they are involved in cell replacement
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5
Q

what is the polarity of epithelial cells?

A
  • apical surface is to external environment (cilia, microvilli)
  • basolateral surfaces have specialised function for absorption
  • polarity determines specialisation
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6
Q

what is the basement membrane of epithelial cells?

A
  • separates epithelia from underlying tissue
  • allows access to nutrients, ions and proteins to regulate growth of cells
  • restricts migration and development of cancer
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7
Q

what are the 2 layers of the basement membrane and what are their roles?

A
  1. Basal lamina (BL)
    - provides mechanical support by tethering epithelial cells together to resist stretching and tearing
  2. Reticular lamina (RL)
    - reticular fibres anchor BL to underlying connective tissue via collagen and elastin
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8
Q

how are epithelial cells used in cell adhesion and communication?

A
  • gap junctions allow passage of water, ions and small molecules: lateral communication
  • modification of lateral membranes allow passage between cells
  • cell matrix attachments bond epithelial tissues to connective tissue beneath basal surfaces
  • adhesive junctions link cytoskeletons from cell to cell
  • adhering junctions form bundles of active filaments around cells
  • myosin filaments enable contractioon of cells
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9
Q

how are epithelia involved in cell replacement?

A
  • the more hostile the external environment, the greater the cell death
  • tissue homeostasis via cell replacement from stem cells

intestine epithelium renews within 5 days
interfollicular epidermis takes 4 weeks to renew
- lung epithelium takes 6 months to renew

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10
Q

what are gap junctions?

A
  • transmembrane claudins near the apical surface
  • control paracellular diffusion of materials between epithelia
  • claudins vary from cldn-18 to cldn-3
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11
Q

what are hemidesmosomes?

A
  • most prominent attachment between cell and cell-matrix
  • anchoring junction
  • anchors intermediate filaments in a cell to the ECM
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12
Q

what are integrins?

A
  • proteins which anchor the cell the laminin

- attach to extracellular keratin

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13
Q

what are adherens junctions?

A
  • connect actin filament bundle in one cell with the actin filament bundle of another cell
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14
Q

what are tight junctions?

A
  • they cell the gap between epithelial cells

- prevent paracellular transport

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15
Q

what are desmosomes?

A
  • connects intermediate filaments of one cell to those in the next cell
  • found in tissues under high amounts of mechanical stress
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16
Q

how is epithelial cell fate regulated?

A
  • switched expression of adhesion cadherins induces mesenchymal cells to form epithelium
  • epithelium is in close contact with mesenchyme
  • mesenchymal tissues control epithelial cell fate
  • formation of epithelium is reversible
  • epithelial-mesenchymal transitions are important in embryonic development and pathology e.g. cancer
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17
Q

what are the 4 major types of epithelium?

A
  1. simple: single layer of cell
    - lungs
  2. stratified: many layers
    - skin
  3. pseudostratified
    - upper respiratory tract
  4. transitional (urothelium)
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18
Q

what is simple squamous epithelia?

A
  • appearance of thin scales: flattened nuclei and cells

- facilitates rapid passage of molecules e.g. alveoli, serosa in intestine

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19
Q

what is simple cuboidal epithelia?

A
  • secretion and absorption of molecules requiring active transport
  • kidney tubules, ducts of glands
  • nuclei in centre of cell layer
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20
Q

what is simple columnar epithelia?

A
  • cuboidal presentation - elongation
  • with/without cilia/microvilli on apical surface
  • absorb/secrete molecules using active transport
  • majority of GI tract
  • ciliated surfaces line fallopian tube to move egg, and in respiratory tract to remove particulates
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21
Q

what is pseudostratified columnar epithelia?

A
  • single layer of cells with appearance of multiple layers due to nuclei at different levels and irregular nature
  • all cells contact the basement membrane
  • ciliated or unciliated
  • ciliated cells can be interspersed with goblet cells
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22
Q

what is stratified squamous epithelia?

A
  • most common type of stratified epithelia in the body
  • apical cells appear squamous (thin and flattened)
  • basal cells are cuboidal or columnar
  • top layer can be covered with dead cells containing keratin
  • areas of high abrasion
  • skin upper layers are keratinised, oesophagus layers are non-keratinised
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23
Q

what is stratified cuboidal epithelium?

A
  • less common

- found in ducts and glands

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24
Q

what is stratified columnar epithelium?

A
  • rare
  • found in conjunctiva, pharynx, male urethra and embryo
  • allows tissue to stretch and contract
  • contains goblet cells to secrete mucin for lubrication
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25
Q

what is transitional epithelia?

A
  • cells have round shape when relaxed

- allows change in shape distension without damaging epithelial lining

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26
Q

what is glandular epithelia?

A
  • they have complex ducts
  • contain single cell types of a variety of cell types
  • they secrete different substances:
mucus = mucus gland
protein = serous gland
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27
Q

what are the 2 types of gland?

A
  1. exocrine: secretion via ducts

2. endocrine: secretion without ducts

28
Q

what are unicellular goblet cells?

A
  • mucin-secreting glands

- scattered within simple epithelia, such as cuboidal, columnar, and pseudostratified epithelia

29
Q

what are multicellular acinar/acinus cells?

A
  • any cluster of cells

- acinar cells are found in the pancreas and have exocrine function

30
Q

what is the integumentary system?

A
  • skin and its accessory organs: hair, nails and cutaneous glands (sweat, sebaceous, mammary)
31
Q

what is skin?

A
  • largest organ in the body - 12-15% of body weight
  • barrier between internal and external environments
  • give insight to internal health via issues inside the body being displayed on skin
  • regulates loss of fluid, electrolytes and proteins
32
Q

what are the 3 layers of the skin?

A
  1. epidermis (uppermost)
  2. dermis
  3. hypodermis: areolar and adipose tissues between skin and muscles
    - not part of integumentary system
33
Q

what is the dermis?

A
  • connective tissue layer beneath epidermis
  • thicker than epidermis (0.2mm eyelids, 2mm palms)
  • contains collagen, elastic and reticular fibres
  • contain fibroblasts to produce laminin and fibronectin of the ECM
  • contains nerve endings, blood and lymphatic vessels
  • can induce arteriovenous anastomoses (thermoregulation)
34
Q

what are the 2 zones of the dermis?

A
  1. papillary layer
    - thin region of loose connective tissue (areolar)
    - allows mobility of leukocytes, mast cells and macrophages
  2. reticular layer
    - thick layer of dense, irregular tissue
    - less cells
    - contains adipocyte clusters
    - weight gain causes striae (stretch in skin)
35
Q

what is the dermal-epithelial boundary?

A
  • wave boundary of finger-like projections
  • dermal papillae: raised areas
  • epidermal ridges: sunken areas
  • less risk of sheering between layers
36
Q

what is the role of dermal papillae?

A
  • they facilitate nerve fibres reaching close to surface of epidermal layer in highly sensitive areas
37
Q

what is the epidermis?

A
  • keratinised stratified squamous epithelium
  • lacks blood vessels: diffusion of nutrients occurs from underlying dermal layer and connective tissue
  • self-generation throughout life every 2-4 weeks
38
Q

what are the 2 types of skin?

A
  1. thick skin
    - palms of hands and feet
    - no hair
    - contains 5 stratum layers
  2. thin skin
    - rest of body
    - contains hair
    - contains 4 stratum layers
39
Q

what are the 5 stratified epidermal layers, from base to uppermost?

A
  1. stratum basale
  2. stratum spinosum
  3. stratum granulosum
  4. stratum lucidum
  5. stratum corneum
40
Q

what are the cells of the epidermis?

A
  1. stem cells
  2. keratinocytes
  3. melanocytes
  4. langerhans cells
  5. merkel cells
41
Q

what are stem cells?

A
  • undifferentiated cells which can divide to form keratinocytes in deep layer of epidermis
  • the only cells in contact with basement membrane, so maintain their ability to replicate
42
Q

what are keratinocytes?

A
  • make up 80-90% of epidermis

- synthesise keratin which forms majority of upper surface

43
Q

what are melanocytes?

A
  • synthesise melanin pigment and release it
  • melanin is UV absorbant, antioxidant and protect skin from UV damage
  • melanin provides pigmentation but also depends on carotene pigments and the oxygen content of blood (red pigment from haemoglobin)
44
Q

how do melanocytes protect against UV radiation?

A
  1. melanosomes are phagocytosed by keratinocytes to surround the nucleus on the sun side
  2. melanocytes spread amongst keratinocytes and shed fragments containing melanin
  3. keratinocytes phagocytose the fragments, internalise them and accumulate melanin around their nucleus to protect from UV radiation
45
Q

what are langerhans cells?

A
  • dendritic cells of the skin
  • macrophages which originated from bone marrow and migrated to epidermis
  • density of 800 per mm2
  • immunological barrier to defend against pathogens and toxins that may penetrate the skin
  • maintain homeostasis and decide whether to launch an immune response
46
Q

what is the action of langerhans cells?

A
  1. migrate to lymph nodes for antigen presentation
  2. present antigens to skin lymphocytes
  3. skin lymphocytes circulate to the secondary lymphoid organs
  4. this activates an immune response
47
Q

what are merkel cells?

A
  • touch receptors
  • associate with dermal nerve fibres to form a Merkel disc
  • low numbers
48
Q

what is the stratum basale (germinativum)?

A
  • single layers of low columnal and cuboidal cells
  • consists of undifferentiated mitotically active keratinocytes
  • melanocytes give skin colour
  • merkel cells connected to nerves
  • dermal papilla dispersed with epidermal ridges at junction of tissues
  • hemidesmosomes anchor intermediate filaments in cells to cell-matrix (only found in this layer)
  • desmosomes also do this in all layers
49
Q

what happens to the undifferentiated keratinocytes in the stratum basale?

A
  • keratinocytes are attached to basement membrane and generate cells for superficial layers
  • the keratinocytes migrate up to replace layers of skin
50
Q

what are the two main melanin pigments?

A
  • pheomelanin = red soluble pigment

- eumelanin = brown insoluble pigment

51
Q

what is the stratum spinosum?

A
  • several layers of keratinocytes
  • usually thickest layer
  • deepest cells are mitotic and are pushed upwards
  • as cells get towards the surface they cease to divide
  • produce keratin filaments which cause cells to flatten and become squamous at surface
  • keratinocytes linked by desmosomes
  • tight junctions allow water retention in skin
  • dendritic cells are present
52
Q

what is the stratum granulosum?

A
  • 3-5 layers of flat keratinocytes
  • post-mitosis so cells no longer divide
  • dark-staining keratohyalin granules bind to cytoskeleton and convert to keratin
  • tight junctions prevent leakage of solutes to intracellular space
  • cells undergo apoptosis
  • produce glycolipid-filled vesicles which spread over cell surface to form waterproof barrier between spinosum and granulosum
53
Q

what is the stratum lucidum?

A
  • thin translucent zone
  • only exist in thick skin: hands and feet
  • densely packed keratinocytes which have no nuclei or organelles, hence translucent
  • protects areas prone to damage from mechanical stresses
  • continual layer - there are no distinct cell boundaries
  • granules of elerdin with proteoplasm (produce of keratohyalin)
54
Q

what is the stratum corneum (uppermost layer)

A
  • 15-30 layers
  • comprised of dead keratinocytes which flake off - stratum disjunctum
  • resistant to abrasion, penetration and water loss
  • cohesive
55
Q

what is in the cornified envelope of the stratum corneum?

A
  • keratins
  • enclosed with insoluble amalgam of proteins
  • cross-linked by transglutaminases
  • surrounded by lipid envelope
  • lamella bodies are secretory organelles packed with lipids to stop water loss
56
Q

what is the stratum disjunctum?

A

part of the corneum which flakes off:

  • layers of flattened corneocytes are cornified from expressing keratin that has been crosslinked by transglutaminase
  • corneo-desmosomes organise corneocyte adhesion to regulate desquamation
  • mitotic cells replace flaked-off cells
57
Q

what are the 3 accessory structures of the integumentary system?

A
  1. nails
  2. hair (pilus)
  3. glands
58
Q

what are nails?

A
  • derivatives of stratum corneum as it invaginates onto one side of finger
  • composed of dead cells densely packed with hard keratin fibres
  • new cells added by mitosis in the nail matrix, causing nail to lengthen
59
Q

how can appearance of nails show underlying health issues?

A
  • iron deficiency: nail becomes flat or concave

- long term hypoxemia (heart defect): nail becomes clubbed

60
Q

what is hair in the integumentary system?

A
  • slender filament of keratinised dead cells from follicle

- found almost everywhere in different densities: 50/cm2 in trunk, 100000/cm2 on scalp

61
Q

how does hair change during lifetime?

A
  1. lanugo: fine, downy, unpigmented
    - foetus
  2. vellus: fine, unpigmented, 2/3 women, 1/10 men
  3. terminal hair: longer, coarser, pigmented
    - eyebrows, eyelashes, scalp post-puberty, pubic, male facial
62
Q

what is the hair follicle?

A
  • hair bulb grows around bud of vascular connective tissue: dermal papilla
  • dermal papulla provides nutrients to cells of hair shaft
  • mitotically active hair matrix to push shaft up
medulla = loosely arranged cells
cortex = keratinised cuboidal cells
cuticle = surface layer of scaly cells
63
Q

what are 5 types of glands?

A
  1. merocrine sweat glands
    - watery perspiration, associated with myoepithelial cuboidal cells
  2. apocrine sweat glands
    - ducts lead to follicles
    - scent glands respond to stress and sexual stimulation
  3. sebaceous glands
    - oily sebum lubricating skin and hair
    - secrete lipids as antibacterial shield
    - holocrine: cells break down and are replaced by mitosis
  4. ceruminous glands: external ear wax
  5. mammary glands
64
Q

what is barrier function?

A
  • prevents water loss, physical injury and infection by microbes
  • cross-linked keratin layer upon a scaffold of keratinocytes
  • slightly acidic (pH 4-6)
  • bacteriocidal agents: saturated and unsaturated fatty acid inhibit growth of bacteria
  • lysozyme cleaves cross-linkages in bacterial cell walls
  • C6H inhibits induction of antibiotic resistance
  • immunological barrier
65
Q

how does the integumentary system regulate temperature?

A
  1. skin contains thermoreceptors in epidermis
  2. counter current heat exchange between arterial and venous blood flow in dermis
  3. arteriovenous anastomoses assists thermoregulation
  4. hypothalamus regulates temperature regulation
66
Q

how does the hypothalamus detect changes in temperature?

A
  • insulation by piloerection of hairs
  • cooling by sweating
  • vasodilation/vasoconstriction by anastomoses to control temperature

Physiology and Pharmacology (13 decks)

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