Integrating cells into tissues, organs and systems Flashcards
what is a tissue
a collection of cells that are adapted t perform a specific function
what is an organ
two or more tissues combined to create a structural unit that has a particular function that are a sum of its parts
what is an organ
two or more tissues combined to create a structural unit that has a particular function that are a sum of its parts
where are epithelial cells derived from
all three layers of trilaminar disc (ectoderm, mesoderm, endoderm)
what holds cells together
- cell-cell adhesion molecules
- extracellular matrix proteins (fibres)
- internal-external scaffolding
- close proximity (pressure effects)
epithelial tissue organisation
- epithelial cell sheets line all the cavities and free surfaces of the body
- epithelia rest on a supporting bed of connective tissues through a basement membrane
- the supporting bed attaches epithelial layer to other tissues e.g. muscle
- specialised junctions between epithelial cells make/form tissue barriers to inhibit movement of water, solutes and cells between compartments
epithelial cell adherence systems in the lateral surface
- join to similar types of epithelial cells
- tight junctions
- adherens junctions
- desmosome (adhesion plaque)
- gap junctions
- cell adhesion molecules
epithelial cell adherence systems in the basal surface
- hold epithelial cells to basement membrane
- hemi-desmosome
- focal adhesions
- integrins
- proteoglycans
- cell adhesion molecules
tight junctions
- always at very top of the cell nearest to lumen/apical surface
- relatively long cell-cell fusion point
- prevents movement of larger molecules through outer layer/lumen into deeper tissue layers of organ
- in the gut can open to allow small molecules to cross - paracellular transport
adhesion junctions
- 1/3 distance from luminal/apical surface
- found in pairs
- formed from intracellular actin filaments
- linked to E-cadherin proteins that cross intercellular space
- found throughout adhesion belt
- only epithelial and endothelial cells
- tissue stabilising factor and additional transport barrier
- interdigitate to hold cells together
desmosomes
- 1/2 way between top and bottom of cell
- strongest of all cell-cell adhesions
- random distribution pattern
- found in tissues that experience intense mechanical stress (cardiac muscle, bladder, GI mucosa, pregnant uterus)
- cytokeratin fibres intracellularly and E-cadherins intercellularly
- provides mechanical strength and prevents tissue destruction
- only cell-cell adhesion found in upper epidermal cells
gap junctions
- close to basal surface
- throughout cardiac and smooth muscle cells
- to quickly communicate changes in intercellular molecular composition
- allows free movement of small molecules between cells
- important in smooth muscle contraction - wave of electrical impulse
- consists of connexins (cylinders of proteins) arranged in a hexagonal pattern that open and close
- only motile cells like spermatazoa and RBCs don’t have gap junctions
hemi-desmosome
- only on basal surface
- attach to layer of extracellular matrix (e.g. fibronectin, collagen and laminin fibres)
- intracellular filaments of cytokeratin attached to laminin through integrins
- basal lamina attaches to connective tissue layer through elastin, fibrillin and collagen
- to anchor epithelial cells to basal lamina and prevent loss to external surface
focal adhesions
- attachment to basal lamina
- intracellular actin filaments binds to fibronectins through integrins
- when bound to fibronectin, conformational change results in binding to collagen fibres
integrins
- found throughout the body
- central to cohesive forces holding tissues together
- work as alpha-beta dimer
- weak binders of extracellular matrix as dimer pair
- phosphorylation by focal adhesion kinase produces heterotetramer with greater binding capacity so stronger bond
- e.g. skin, blastocyst attachment to endometrium
basement membrane layers
- basal lamina
- lamina reticularis
basal lamina
lamina lucida
- clear layer
- integrins
- laminins
- collagen IV and XVII
- dystroglycans
lamina densa
- dense layer
- collagen IV
- entactin/nidogen
- perlecan
- heparin sulfate proteoglycans
lamina reticularis
- even denser layer
- collagen I, III, V
- proteoglycans
collagen IV
- holds the layers of basement membrane together
- mutation = epithelial tissues fall apart
function of adherence proteins
- maintain survival and structure of cells and tissues
- prevent pathogens gaining entry to internal environment
function of tight junctions
seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
function of adhesion junctions
joins an actin bundle in one cell to a similar bundle in neighbouring cell
function of desmosome
joins intermediate filaments in once cell to those in a neighbour
function of gap junction
allows passage of small water-soluble ions and molecules
function of hemidesmosome
anchors intermediate filaments in cell to basal lamina
function of focal adhesions
anchors actin filaments in cell to basal lamina
cells to tissues to organs
- epithelial cells adhere to epithelial cell through cell surface proteins
- epithelial cells adhere to basal lamina through cellular adhesion molecules
- epithelial cells adhere to muscle cells through connective tissue fibres
- tissues adhere to other types of tissues through connective tissue fibres
- cells that touch each other communicate through gap junctions for effective functioning
what is the mucosal membrane
the moist, inner lining of some organs and body cavities
- lines all the moist, hollow internal organs of the body e.g. GI, urinary, respiratory and urogenital
- continuous with skin at various body openings e.g. eyes, ears, lips, vagina
- most secrete mucus (containing mucins, electrolytes, antiseptic enzymes, immunoglobulins, water)
layers of the GI tract
mucosa lining the lumen
- epithelial cell lining and supporting mesenchymal layer
muscularis mucosae
- thin discontinuous smooth muscle layer
submucosa
- connective tissue layer containing arteries and veins
muscularis externa
- smooth muscle layer with muscle fibres in two directions
- inner circular muscle and outer longitudinal muscle
serosa
- connective tissue layer containing collagen + elastin fibres, smaller arteries + veins, nerve fibres, outer layer of epithelial cells
layers of the oesophagus
mucosa
- epithelium - stratified squamous non-keratinised
- lamina propria
- muscularis mucosa
submucosa
muscularis externa
what is lamina propria
connective tissue found under thin layer of tissues covering a mucous membrane
what is the submucosa
subtending layer of connective tissue containing mucus-secreting glands (joins mucosa to muscularis externa)
what is the muscularis externa
smooth muscle layers that return organ to original dimensions - circular inner muscles and longitudinal outer muscle
layers of the stomach
mucosa
- epithelium
- very thin lamina propria
- muscularis mucosae
submucosa
muscularis externa
rugae
function of gastric mucosa
secerets acid, digestive enzymes and hormone gastrin
how many layers of smooth muscle in gastric muscularis externa
3 - oblique, circular, longitudinal
what are rugae (stomach)
folds of gastric mucosa forming longitudinal ridges in empty stomach
layers of the jejunum
mucosa
- simple columnar epithelium
- lamina propria
- muscularis mucosae
submucosa
muscularis externa
plicae circulares
what are plicae circulares (jejunum)
circular fold of mucosa and submucoase that project into gut lumen
layers of the large intestine (colon)
mucosa
- simple columnar epithelium (crypts of Lieberkuhn)
- thin lamina propria
- thin musuclaris mucosae
submucosa
- very big
muscularis externa
what are crypts of Lieberkuhn (colon)
- simple columnar epithelium
- produce mucus and supply cells to surface
function of mucosa in GI tract
- absorb substances from lumen
- prevent ingress of pathogens
- move contents and expel waste
lining of corpuscle (urinary tract)
squamous epithelium
lining of collecting ducts (urinary tract)
cuboidal epithelium
specialisation in proximal tubules
ciliated surface
layers of ureter
- lumen
- transitional epithelium (urothelium)
- lamina propria
- muscularis mucosa
- inner longitudinal muscle
- outer circular muscle
layers of bladder
- lumen
- transitional epithelium (urothelium)
- lamina propria
- muscular layer (detrusor muscle)
- adventitia (fat cells)
functions of urothelium
- distensibility
- produce mucus
- protects bladder from damage by acidic urine
- tight junctions and well packed to prevent leakage to inner cell layers
layers of urethra
- lumen
- stratified squamous epithelium
- lamina propria containing mucous epithelial glands
- smooth muscle
function of mucus glands (urethra)
produce lots of sticky mucus to prevent ingress of pathogens
function of urinary tract
- absorption of essential nutrients in kidney
- prevention of pathogen entry
- removal of waste products
2 parts of respiratory tract
conducting portion - nasal cavity to bronchioles
respiratory portion - respiratory bronchioles to alveoli
layers of pharynx
- stratified squamous non-keratinised epithelium
- lamina propria - elastic fibres
- striated muscle wall
- no muscularis mucosae or submucosa
layers of trachea
- pseudostratified ciliated columnar epithelium
- mucous membrane
- submucosa (seromucous glands)
- hyaline cartilage ring
- adventitia
layers of trachea and primary bronchi
mucosa
- epithelium - several cells deep and covered in cilia
- connective tissue
- thin lamina propria
- no longitudinal muscularis mucosa
submucosa
- connective tissue - collagen, elastin, fibroblasts
- seromucous glands - watery mucous thickens during infection
C-shaped hyaline cartilage
- perichondrium - fibroblasts lay down collagen fibres
- chondrogenic - cartilage is formed
secretions from epithelium and submucosal glands of trachea and bronchi
- mucins and water - make sticky mucus
- serum proteins - lubricates the surface
- lysozyme - destroys bacteria
- anti-proteases - inactivate bacterial enzymes
mucociliary escalator
materials are moved to oral cavity to be swallowed using the mucus and a cilia wave
goblet cells in trachea
produce mucus for mucociliary escalator
layers of secondary + tertiary bronchi
- pseudostratified ciliated epithelium
- smooth muscle
- seromucous glands in submucosa
- crescent shaped cartilage
structure of alveolus
capillaries lined with squamous epithelial cells (endothelium)
- attached to basal lamina with even thinner epithelial cells of air sac on opposite side
folds in basal lamina
- expansion of air sacs when air drawn into lungs
collagen at junction
- surrounded by layers of elastin fibres that provide elastic recoil to return sac to empty state when exhaling
connective tissue muscle layers in mucosa
- made from collagen and elastin fibres which are critical for normal lung function
