cells and tissues Flashcards
Definition and roles of cells, tissues, organs, and organ systems
Living organisms are made of cells; different types of cells tend to be grouped into organised tissues, with specific functions
Organisation and appearance of cells in tissues relates to function and results in easy identification
Different tissues in different positions with different functions:
Outside, in contact with environment
Inside, in contact with body cavities
In the middle between the two
Different tissues can be organised into specific organs with particular function
Organ systems are assemblies of different organs associated with a particular process: Eg the digestive system consists of mouth, pharynx, oesophagus, stomach, intestine, rectum and anus
The basic tissues of plants: dermis/dermal tissue/epidermis
function:
protect plant tissue and prevent water loss
Dermal tissue - pavement cells, guard cells & subsidiary cells
around stomata, trichomes (hair cells)
A complete layer of cells, entry and exit controlled via stomata
Cuticle: On outside of epidermis
1) Transpiration barrier – water loss controlled by stomata
2) Developmental roles
3) Interaction with microorganisms
The basic tissues of plants: plant ground tissue: parenchyma, collenchyma, sclerenchyma
makes up bulk of plant in stem, roots and leaves
Parenchyma: most of the cells that make up the body of the
plant contained within the epidermis, that aren’t vascular
Thin, uniform cell walls, large vacuoles
Form photosynthetic cells in leaves and stems (chlorenchyma)
They are the only dividing cells (so found in meristems)
+ used in wound repair
They form storage cells in roots, stems, seeds (starch)
May be air filled tissue in floating plants
Collenchyma: structural support in growing shoots & leaves
Living cells, thickened cell walls – thickness depends on
mechanical stress on the plant – may be doubled
Beneath epidermis of stems & leaves
-4 different types, relating to exactly how cells interact with one
another and how the walls are thickened.
Sclerenchyma: main structural support for a plant
Long, slender cells bundled together
Thick cell walls; cells themselves are dead
Develop in association with xylem & phloem
eg tough strands in celery sticks!
Commercially important: fibres for fabrics:
eg flax for linen, hemp for rope & fabric, cotton fibre, etc
The basic tissues of plants: vascular
xylem transports water
phloem transports sugars
Xylem: water transport
transpiration, root pressure
Phloem: organic nutrients, mostly sucrose
The basic tissues of plants: meristem
cell division to produce new growth-in tips of roots and shoots in buds, around stem of woody plant
Sites of growth
Undifferentiated parenchymal cells (similar to animal stem cells in roles)
Generate new cells which can then differentiate into new cell types as the developing structure matures
Apical for growth of roots and shoots, modified to form flowers
Primary: increase in length/height, derived from apical
Secondary – vascular cambium, makes new xylem & phloem
throughout life - wood formation
The basic tissues of animals: muscle
muscles - Force generation by contraction
cardiac - Involuntary, striated
skeletal - 600+ skeletal muscles
smooth muscle - Involuntary:
Control of gut movements
Blood vessel diameter
Uterine contraction in childbirth
Etc.
extracellular matrix composition
Fibres embedded in “ground substance”
Fibres:
collagen – tensile strength-don’t stretch or branch
elastic fibres – stretch and then recoil, branched
Ground substance:
complex glycosaminoglycans
attached to proteins - proteoglycans
compression resistance
Fibre and glycosaminoglycan/proteoglycan composition
gives the extracellular matrix its mechanical properties:
Fibres give tensile strength and elastic recoil,
ground substance gives compression resistance
Connective tissue cells:
a) Make the matrix
b) Sense loading on matrix
c) Modify matrix according to load
BONE:
Extracellular matrix, has lots of collagen, but is calcified: calcium phosphate
High compression resistance due to calcification, resilient and tension, resistant due to collagen
The basic tissues of animals: connective tissue
Tissues with cells embedded in an extensive extra cellular matrix(ECM)
Mechanical function - strength
Support
Wrapping & binding
Packing & space filling
Wound healing
Infection control
May form structures in their own right – eg bones, tendons etc, Or be a major part of other tissues and organs, forming a strengthening and organisational framework
types of connective tissue:
1.Connective tissue proper
Tendon/ligament/dermis, loose CT,
Pigmented CT, blood
May be on its own or be part of other
structures
2. Cartilage, skeletal, supportive
3. Bone skeletal, supportive
Assembly of tissues and organs into larger scale structures
Tissues, organs and organ systems - animals
Tissue: collection of cells and/or extracellular materials specialised for a particular function
mostly grouped in a well-ordered arrangement
- easily recognisable microscopically
- organisation associated with function
Organ - A distinct, discrete functional unit formed from 2 or more tissues
What are epithelia? Basic functions
Epithelial cover and line all body surfaces-anything that has a link from outside to inside
Epithelium-completely cellular layer
Avascular
Sits on top of basement membrane
Usually over a vascular connective tissue
Controls entry+exit of all materials to and from body tissues
Not just surfaces but also structures derived from them Eg. Glands-grows as tube into underlying surface
general functions:
Protection
Secretion
Absorption
Dialysis-filtration
Sensation-sensory/communicate with NS
Types – classification: simple/stratified // squamous, cuboida, columnar // pseudostratified, transitional
- Number of layers of cells
Simple-1
Stratified-many - Shape of top layer
Squamous-thin/wide
Cuboidal-small cubes
Columnar-taller than wide - Stratified squamous epithelium have 2 varieties:
Keratinized - anucleate cornified(dead cells)
Non-keratinized - living nucleated
MISCELLANEOUS:
Pseudostratified ciliated columnar epithelium - Found in the trachea
-All cells in contact with basement membrane-but different shapes/sizes
-Cilia-energy intensive process-waft mucus up/down from the goblet cells
-Fuel source from basement membrane
transitional
-In urinary system-lines bladder and shifts between stretched/collapsed as bladder empties and fills
General features of epithelia
Cellularity: entirely cellular
- separate internal and external environments
- cellular monitoring of transfer
Specialised intercellular contacts
desmosomes, adherens junctions,
tight junctions, gap junctions
Polarity: top surface is different to bottom surface
Top-contacts external environment
Bottom-basement membrane and the body
(May be modified-cilia, microvili, basal striations)
Basement membrane: 2 parts
Basal lamina-from epithelium
Reticular fibres(=collagen)-from connective tissue
Functions of stratified epithelia
Stratified epithelia:
most common - stratified squamous
protection from damage-surface cells can be lost and replaced from underneath
Toughest-stratified squamous keratinised epithelium of the skin
Surface cells fill up with keratin, lose nuclei-> become tough, dead, waterproof covering(to stop leaking out)
Next toughest-stratified squamous non-keratinised epithelia:
Cells are alive all the way to the surface
Inner body surfaces
Oral cavity, oesphagus, vagina
Kept moist by glandular secretions
Functions of simple epithelia
Occur where substances must be transported across the epithelium – stratified would make this impossible
Columnar and cuboidal cells – cells have roles in active transport and modification of materials that pass through them – eg gut cells - plenty of cell “machinery” mitochondria, lysosomes, golgi etc
Other cells in epithelia – goblet cells, lymphocytes
Columnar epithelia may contain other cell types Eg.
Goblet cells-in simple columnar Pseudostratified columnar
Lymphocytes-monitor epithelia for immune system
extracellular matrix - defintion
Materials made by cells, released to the exterior of the cell
(i.e.outside the plasma membrane) which assemble into a
3 dimensional extracellular structure with structural,
and often other, functions
common features - plants + animals
Structurally complex
Fibrous framework embedded in a gel-like background matrix
Plants:
Polysaccharide fibres-cellulose, hemicellulose and proteins embedded in matrix of highly charged pectin polymers
Animals:
Fibrous protein fibres (eg collagens) embedded in matrix of highly charged glycosaminoglycans
Animal ECM
Fibre and glycosaminoglycan / proteoglycan composition gives the extracellular matrix its mechanical properties
plant cell wall-purpose
Gives rigidity and strength
– although mostly itself is not especially rigid
Works in association with turgor pressure from it’s cell osmosis draws water in; cell wall resists this and becomes stretched in the process –has high tensile strength
Plants wilt without enough water – pressure in cell drops, so cell walls aren’t loaded and structure loses its strength
Some parts of plants are reinforced with extra cell wall components so become stronger & not dependent on water pressure
3 layers in between cells(extracellular matrix):
middle lamella: first component secreted after cell division; glues cells together, allows plasmodesmata to form
primary cell wall: synthesised second
secondary cell wall: synthesised last, but only after cell will no longer divide, so not always made
middle lamella
uniform and continuous layer between adjacent cell walls
Made of pectins and some protein:
Mostly pectic acid, some pectin: polysaccharides
- polymer of about 100 galactouronic acid molecules
- highly charged and hydrated, forms gels with Ca++ and Mg++
pectic acid: Long charged sugar chains form hydrated gel in presence of Ca++, MG++
primary cell walls
first cell wall produced, pushes middle lamella away from plasma membrane
Properties:
a) expandable, to allow for cell growth
b) semi-permeable: nutrition, respiration
Components: cellulose, hemicellulose and pectin
Cellulose:
straight chain glucose polymer; polymer chains held together with hydrogen bonds to form larger assemblies, fibrils and fibres.
Form on the outside of the plasma membrane and arranged in to highly ordered structures
Hemicellulose:
many different sugar monomers, branching chains. Cross-link cellulose fibrils together, tensile strength of the wall
Pectin:
gel contains fibres and gives compression resistance to wall
(R)Proteins - small quantities:some alter mechanical properties of wall structure, eg stretching in cell growth.
Others enzymes – formation, remodelling, breakdown of wall components - fruit ripening, leaf fall etc
secondary cell wall
Forms between plasma membrane and primary cell wall
made after the primary is finished & cell has stopped expanding
mostly fibres – cellulose, lignin (wood), pectins not always present; no proteins
may be very thick & cause death of cell; however thickness gives the region of the plant very high tensile & compressive strength
- eg woody components
support tissue in vertebrates (human=connective tissue)
Loose connective tissues: wrapping and space-filling
sometimes called areolar connective tissue
Tendons and ligaments: connecting , force transfer
regular dense fibrous connective tissues
Dermis: strong component of skin: reinforcing, force transfer
irregular dense fibrous connective tissues
Bone and cartilage
skeleton and its joints – support, movement, protection
loose connective tissue
space filling, energy storage, cushioning, planes of movement, immune function
Fibres: collagen and elastic fibres for stretch resistance and elastic recoil
Ground substance GAGs: hold water – jelly: hyaluronan
- prevents spread of infection
resident cells in loose CT:
fibroblasts-make matrix
fat cells-energy storage, space filling, cushioning
mast cells-immune function, swellin, inflamation, anaphylaxis
endothelial cells
pericyte-stem cell around capillaries
immigrant cells loose in CT:
monocyte
macrophages
lymphocytes
plasma cells
cartilage: hyaline, elastin, fibrocartilage
hyaline:
Joint surfaces - adult
Foetal Skeleton
Tracheal rings
glass like-no visible fibrous structure; lots of fibres present, but obscured by huge amounts of GAG and PG
- appositional interstitial growth
elastin:
Just like hyaline, but with loads of elastic fibres in matrix
fibrocartilage:
Intermediate between hyaline cartilage and dense fibrous connective tissue
Visibly fibrous, high GAG content
-Intervertebral disc, tendon/ligament attachment to bone
-Tempormandibular joint
Collagen – tension resistance
Collagen fibres are upright deep in the tissue then curve over, forming “arcades”; more-or less parallel to the surface at the top
surface-collagen fibres resist shear forces
Elsewhere-pressurised by the proteoglycans, drawing water into their GAG chains & swelling
In combination they resist compression
GAGs/proteoglycans – compression resistance
- jelly
- lubrication
Glycoproteins: connectors & signallers
bone structure/cells
highly vascular, innervated, Living tissue
Osteoblasts: make new bone
Osteoclasts: remove old bone
Osteocytes: sense mechanical loading & control the other cell types
Bone has mineralised extracellular matrix : brittle calcium phosphate mineral (compression resistant) reinforced by flexible type I collagen (tenson resistant) to form strong composite material
Intramembranous ossification
Mesenchyme: Embryonic connective tissue
Cells in sparse extracellular Matrix; vascular
Condensation: cells come together to form a dense mass
Differentiation: cells become osteoblasts and secrete bone Matrix; then become embedded as osteocytes; new cells add on the outside and become Osteoblasts
Appositional growth
canaliculi???
Endochondral ossification; cartilage model/anlagen/rudiment Primary & secondary centres, articular cartilage and growth plate
Growth plate: cartilage cells, vascularisation & bone formation
Vascular invasion; brings osteoprogenitor cells
Bone formation on calcified cartilage; erosion of old cartilage
Epiphyseal plate & longitudinal growth of bone
