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CFoM > Days 1 +2: Tissues, Organs, & Epithelia (Membranes + Glands) > Flashcards

Days 1 +2: Tissues, Organs, & Epithelia (Membranes + Glands) Flashcards

1
Q

lumen

A

interior cavity of an organ

luminal / adluminal: free side of epithelium

abluminal: attached side of epithelium

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2
Q

components of mucous membrane (mucosa)

A
  1. epithelium (and its underlying basal lamina)
  2. lamina propria (loose connective tissue)
  3. muscularis mucosae (thin layer of smooth muscle
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3
Q

Deep to the mucosa

A
  • lumen
  • epithelium
  • lamina propria
  • muscularis mucosae
  1. submucosa : supportive (dense irregular) connective tissue
  2. muscularis externa (if an organ has no muscularis mucosae, it is just called the muscularis)
  • With respect to the long axis of the gut:
    • innermost layer: circular layer
    • outermost layer: longitudinal layer
  • Transverse secton of the gut:
    • innermost layer: smooth muscle circular layer sectioned longitudinal
    • outermost layer: longitudinal layer will be cut transverse
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4
Q

nervous tissue in the wall of an organ

A

visible as neuronal cell bodies

(of ANS that direct action of smooth muscles)

  • cell bodies are clustered in parasympathetic ganglia
    • located in two places:
      • submucosa
      • between the two layers of the muscularis externa
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5
Q

mesothelium

A

membrane that covers and protects most of the internal organs

different names:

  • peritoneum: abdominal cavity
  • pleura: lungs + chest cavity
  • pericardium: heart
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6
Q

serosa / serous membrane

A

mesothelium + subjacent connective tissue

permits low-friction movement of the surfaces against each other

outermost coat of an organ that lies in a body cavity

have a parietal + visceral layer

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7
Q

adventitia

A
  • organs embedded in the body wall don’t have a serosa*
  • outermost layer of organs that connects the organ to surrounding organs or body wall*
  • adventitia: the connective tissue layer located beyond the muscularis externa that connects directly with the tissues of the body wall
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8
Q

epithelium

A
  • located on free surfaces within and on the body
  • always attached to and supported by underlying connective tissue
  • renewable in some tissues (gut, skin, conditionally liver) and never in core of eye lens
  • most common source of cancers in adults
  • avascular: connective tissue carries bld vessels + nerves necessary for metabolic maintenance + proper functioning
  • tightly apposed cells: no extracellular matrix between epithelial cells

two broad types:

  • membranous
    • number of cell layers: simple, stratified, pseudostratified
    • cell shape: squamous, cuboidal, columnar
  • glandular
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9
Q

simple, stratified, pseudostratified epithelium

A

classification of epithelium based on cell layers

simple epithelium: single layer of cells

stratified epithelium: two or more layers of cells

pseudostratified epithelium: all cells contact the basement membrane, but not all cells extend to free surface; the nuclei are often located at different levels

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10
Q

squamous, cuboidal, and columnar epithelium

A
  • Cell shape epithelium classification*
    squamous: flat nucleus
    cuboidal: round nucleus
    columnar: tall oval nucleus
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11
Q

basement membrane

A

thin, specialized region of extracellular matrix produced by epithelial cells so it can bind to underlying connective tissue

  • cells attach by means of transmembrane linker proteins (link cell’s cytoskeleton to BM’s laminin)
  • in stratified epithelium, only the deepest layer of basal cells contacts the basal membrane
  • typically not visible under H&E stains, but is magenta with PAS stains

*known as the basement membrane under a light microscope, basal lamina under electron microscope

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12
Q

polarization of epithelium

A

polarization: having two different sides, in terms of function, location, morphology, etc.

Regarding individual epithelial cells:

apical surface: adjacent / oriented to outside air or organ lumen

basal surface: oriented toward/attached to underlying connective tissue

lateral surface: sides of the cell

Regarding epithelial surface as a whole:

free/luminal/adluminal surface: facing lumen of organ or vessel

abluminal (attached) surface: facing underlying connective tissue

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13
Q

pseudostratified epithelium

A

single layer made up of tall and short cells, all of which are in contact with the basement membrane

  • only the tall cells reach the free surface of the epithelium
  • distribution of the nucleus gives epithelium a striated appearance
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14
Q

stratified squamous epithelium

(nonkeratinized + keratinized)

A

basal layer cells may be cuboidal or columnar, but surface cells are squamous

if the cells are living: nonkeratininized

non-living cells: keratinized (nucleus and cytoplasm have been replaced by the intracellular intermediate filament keratin)

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15
Q

stratified epithelia

A
  • have two or more layers of cells
  • appearance of cells in deeper layers differ from surface
  • classified based on cell shape in most superficial layer
  • progenitor cells rest on the basement membrane, give rise to other cells
  • cells held together by intercellular adhering junctions
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16
Q

transitional epithelium

A
  • also known as urothelium (only found in the urinary system)
  • consists of a multilayer of cells that remain functionally and morphologically intact and stretch as the organs that it lines expand
  • transitions between stratified squamous and stratified cuboidal
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17
Q

metaplasia

A

epithelia produce progeny that are specialized, but not what is normally found in that location

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18
Q

dysplasia

A

abnormal differentiation results in altered size, shape, and organization of mature cells; may produce neoplasia

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19
Q

neoplasia

A

(ie, cancer)

occurs if cell proliferation is not controlled and results in an abnormal mass of proliferating cells (tumor)

benign (noncancerous, localized)

vs.

malignant (cancerous, metastatic)

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20
Q

carcinoma

A

malignant tumor of epithelial tissue

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21
Q

adenocarcinoma

A

glandular growth pattern of cells

22
Q

cytoskeleton

A
  • provides structural integrity, organizes cell spatially, and carries out coordinated intracellular movements
  • composed of 3 types of protein filaments:
    • actin
    • microtubules
    • intermediate filaments
23
Q

actin filaments

A

(microfilaments)

  • flexible, double-stranded helical polymer of one of several types of actin
    • globular g-actin monomers polymerize into filamentous f-actin (this change is necessary for cell movements/phagocytosis)
  • fibril diameter 5-7 nm
  • in non-muscle cells, actin microfilaments are highly concentrated beneath the plasma membrane
  • small bundles form the cores of microvilli
  • actin binding proteins: myosin, alpha-actinin, spectrin, fimbrin, filamin, gelsolin, talin
24
Q

microtubules

A
  • long, rigid, hollow polymeric cylinders; outer diameter 25 nm
  • polarized: rapidly growing + end, depolarizing - end (embedded in the centrosome)
    • subunits: tubulin heterodimers
      • ​one alpha tubulin, one beta tubulin
  • function to maintain cell shape, provide rigidity, regulate intracellular movement of organelles and vesicles, and comprise core of cilia + flagella​​
  • microtubule associated proteins: prevent depolarization, assist in intracellular movement of organelles and vesicles
    • motor proteins: ATPases that bind + transport organelles/large molecules
      • kinesins: towards + end
      • dyneins: towards - end
        • cytoplasmic: essential for cytosolic trafficking of vesicles
        • axonemal: involved in sliding microtubules necessary for the beating of cilia + flagella
25
Q

intermediate filaments

A
  • rope-like polymer fibers (10-12nm in diameter)
  • maintain cell shape + structural support
  • high tensile strength, protect cell from stresses + strains
  • occur throughout cytoplasm + sometimes attached to the cytosolic side of the plasmalemma
  • typically associate with specific cells
    • lamins: cell nuclei
    • keratins: epithelia + related structures
    • neurofilaments: neurons
    • vimentins: fibroblasts
    • glial fibrillary acidic proteins (GFAPs): glia
    • desmin: skeletal, cardiac, smooth muscle
26
Q

apical cell surface specializations

A

microvilli

stereocilia

cilia

27
Q

cilia

A
  • uniform, individually distinct, hair-like, 5 - 15 um length
  • composed of a highly-organized core of microtubules (axoneme) that inserts into the basal body (locted in the apical cytoplasm of the ciliated cell)
    • axoneme: complex of microtubules (9 +2) and MAPs
    • basal body: short cylinder of 9 microtubule triplets
  • moves material along the lumen parallel to the epithelia
28
Q

microvilli

A
  • core composed of actin filament bundles (25-30), inserts into the terminal web in apical cytoplasm
  • increases surface area of the cell
  • may be short, irregular bleb-like, or tall, closely-packed uniform projections
  • the number of shape of the cell’s microvilli reflect the cell’s absorptive capacity
29
Q

stereocilia

A
  • longest microvilli, uneven length, branching, often get clumped together
  • core of actin filaments
  • non-motile, limited distribution
30
Q

lateral cell specializations

(aka intercellular junctions)

A

junctions not restricted to epithelia

  • occluding:
    • zonula occludens (tight junctions)
  • adhering: transmembrane junctional proteins attach cytoskeletal filaments of one cell to cytoskeletal filaments of adjacent ones
    • zonula adherens (intermediate junction)
    • macula adherens (desmosome)
    • hemidesmosome
  • communicating:
    • gap junction/nexus
31
Q

zonula occludens

A

(tight junction)

  • prevents passage of material between adjacent cells
  • keeps apical membrane domain separate from basolateral membrane domain
  • rows of tight junction proteins fuse adjacent plasma membranes together (forms a belt around cell)
    • transmembrane proteins (claudins + occludins) bond at fusion sites
32
Q

zonula adherens

A

intermediate junction (adhering junction)

  • uniform intercellular gap of 15-20 nm
  • encircling attachment site; encircles cell near lumen
  • links cadherin complex and actin to that of adjacent cell
33
Q

macula adherens

A

(desmosome)

  • dense attachment plaque of ~12 proteins (including desmoplakins and plakoglobins) on cytoplasmic surfaces of opposing cell membranes
  • hairpin loops of tonofilaments (cytokeratin intermediate filaments) insert into + link the plaques, providing linked cells with resistance to shearing
34
Q

gap junction

(nexus)

A
  • disk-shaped communicating junction
  • very narrow (2nm) intercellular space
    • bridged by transmembrane connexons
      • ​each composed of 6 connexins
  • ​sites of electronic coupling (reduced resistance to ion flow)
  • regulated (open/close with signal)
  • permits intercellular passage of small molecules ( < 1kD)
  • essential in intercellular communication + coordination
35
Q

junctional complex

A

three intercellular junctions that arise in intestinal epithelial cells:

  • zonula occludens (tight junction)
  • zonula adherens (intermediate junction)
  • macula adherens (desmosome)

the junctional complex corresponds to the terminal bar of light microscopy

terminal web: dense mesh of apical cytoskeleton associated with the intercellular junctions

36
Q

hemidesmosome

A
  • half of a desmosome on the basal surface of some cells
  • links cytoskeletal intermediate filaments (tonofilaments) to transmembrane integrins
    • which links epithelium to basement membrane
37
Q

basement membrane (LM) & basal lamina (EM)

A
  • occupies th extracellular interface between an epithelium and its underlying connective tissue
  • LM: visible with PAS or silver staining
  • bases of epithelial cells (type IV collagen) are attached by binding sites (transmembrane integrins) to extracellular glycoproteins (ie, laminin)
  • two components:
    • lamina lucida: laminins, glycoproteins, proteoglycans
    • lamina densa: type IV collagen underlain by reticular fibers anchored by type VII collagen
  • functions:
    • attachment
    • filtration barrier (physical and polyanionic)
    • compartmentalization/separation of tissues
    • tissue scaffolding/structure
    • regulation & signaling (morphogenesis, development, wound healing)
  • ​referred to as external lamina surrounding muscle, adipose, Schwann cells
38
Q

basal infoldings (enfoldings)

A
  • deep invaginations of the cell membrane on the basal surface of epithelial cells; typically those forming the walls of ducts
  • enfolding membranes contain ion (Na-K ATPase) pumps to transport ions from the lumen to the underlying connective tissue (so it can return to the body)
  • enfoldings increase the surface area of the basal membrane, and thus the number of ion pumps
39
Q

classification schemes of epithelial glands

A
  • cell number (unicellular/multicellular)
  • mechanism of secretion (merocine/apocrine/holocrine/active transport)
  • control of secretion (regulated / constitutive)
  • direction of secretion (endocrine / exocrine)
  • product of secretion (mucous / serous / lipid / other)
40
Q

cell number:

unicellular vs. multicellular glands

A
  • unicellular: single cell
  • multicellular: many cells
    • simple: lack ducts / have unbranched ducts
      • tubular (U-shaped)
      • coiled tubular
      • branched tubular
      • branched acinar
    • compound: branched duct system
  • ducts are arranged in shape of a tube or acinus (grape-like)
  • both exocrine + endocrine glands can be uni/multicellular
41
Q

merocrine (eccrine) glands

A
  • secretions are released from membrane-bound secretory granules that fuse with the apical cell membrane, open, and release product onto the surface by exocytosis
    • often proteinaceous secretions
  • Most glands secrete in this manner
42
Q

apocrine secretion

A
  • released lipid product is surrounded by thin layer of cytoplasm surrounded by plasmalemma
  • mammary glands release the lipid component of milk this way
43
Q

active transport method of secretion

A
  • transports acids, salts, etc
  • parietal (acid-producing) cells of stomach actively transport H+ and Cl- across the cell membrane into the lumen of the gastric gland
  • osteoclast (resorbs bone): secretes H+
44
Q

holocrine secretion

A
  • product accumulates within maturing cell, secretory cell bursts, secreting entire content along with cell debris
  • sebacous glands secrete in this manner
45
Q

mucus vs. serous secretion

A

Mucus:

  • mucus cells and glands synthesize and secrete mucinogen
    • becomes mucin upon hydration
      • mucin: viscous secretion with high concentration of glycoproteins and low protein content

Serous:

  • secrete less viscous fluid, mostly proteins (enzymes/proenzymes) with low [glycoproteins]
46
Q

exocrine vs. endocrine glands

A
  • exocrine: toward lumen; release product onto epithelium surface either directly or through a duct
    • secrete apically
  • endocrine: toward the connective tissue (or the general circulation)
    • ductless, but highly vascularized
    • secrete basally
47
Q

regulated vs. constitutive secretion

A
  • regulated secretion:
    • cells secrete in response to external signals
    • soluble product is stored in high concentration in intracellular secretory vesicles (storage granules) until stimulated by extracellular signal
  • constitutive secretion:
    • membranes of transport vesicles move to + fuse with cell’s plasma membrane and contents of vesicle is immediately released into extracellular space
48
Q

external lamina

A

similar to the basal lamina, surrounds Schwann cells, muscle cells and fibers, and adipocytes

49
Q
A

simple tubular gland

50
Q
A

simple acinar (alveolar) gland

also a holocrine gland

51
Q
A

simple coiled tubular

(eccrine glands)

CFoM (7 decks)

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