1 Cells, Tissues, and Organs Flashcards
Describe how cells can differ from one another
- and what may cause them to be different
Cells are as they are due to their function
Relative amount of cellular components in a cells is dicated by the cell type
- e.g. decretory cells will have more rough and smooth ER, vesicles, with a higher activity of cell
Cells can also be specialised by membrane specialisations
OR
Specialised intracytoplasmic granules/filaments
- e.g. in muscles (actin)
Describe how cells can do movement and maintain their shape
This is often regulated by the Cytoskeleton
- filamentous components
Describe the cytoskeleton
whats its roles are
and what it is made up of
It can, for example:
- Used in movement - phagocytosis
- where actin filaments respond to the foreign body being detected and moves the cell membrane and cytoplasm to engulf it
Cells can take (or even become) different shapes due to the cytoplasm
It is made up of:
- Microfilaments
- Intermediate filaments
- Microtubules
- Thick filaments (myosin)
Describe microfilaments:
- what it is made of
- function
Microfilaments:
- Made of actin
Function:
- forming contractile skeleton in cell
- regulating cells shape and tactile activities (villous, movement to pinocytosis etc.)
Describe Microtubules:
- what it is made of
- function
Microtubules:
- made of tubulins (a and B)
Function:
- positioning of organelles
- cell shape changes
- used for the centrioles in cell division
- cilia formation
Describe intermediate fibres
- what it is made of
- function
Intermediate fibres:
- made from vimentin and cytokeratin
Functions:
- attaching organelles to each other and to the cell membrane
Useful in diagnosis as different ones are present in different tissue types
- e.g. vimentin in fibroblasts, cytokeratin in the epithelium
What is meant by cell surface specialisations?
Extension of the cell membrane and cytoskeleton
List some cell surface specialisations
- Cilia (and flagella)
- Microvilli (and sterocilia)
- Centrioles
Describe cilia (and flagella) as a cell surface specialisation
Cilia (and flagella)
- extensions of the microtubule cytoskeleton that actively move (flagella are longer)
- they have a microtubule core with a specific structure
> structure is a 9 + 2 configuration - they actively move (use ATP) - the role is to move things along their surface
If cilia go wrong (dynein arms or tubules don’t work - so it doesn’t waft properly)
- smoking can kill cilia - no wafting = coughing
Describe microvilli (and stereocilia) as a cell surface specialisation
Microvilli (and sterocillia)
- they are an extension of the actin microfilament cytoskeleton
- there is no active movement (more SA for more absorption)
- stereocilia are small cilia
Structure:
- an actin core and increased SA (20x)
- core runs into the cell
They are found in enterocytes, cells in the intestine where absorption is taking place
Describe centrioles as a cell surface specialisation
Centrioles are cylindrical structures
- found in animals cells
- as groupings of microtubules arranged in a 9 (triplets) + 0 pattern (like MTOC)
- they help to organise the assembly of microtubules during cell division
What are cell junctions, and what are the different types?
Cells must stick together in the epithelial layer
- to keep external fluids out, internal fluid in
There are different types of cell junctions:
- Tight junctions/barrier junctions (occluding)
- Adherens junctions
- Hemidesmosomes
- Gap junctions
Describe tight junctions/barrier junctions as a type of cell junction
They prevent the passage of substances between cells
- also help maintain the position of membrane proteins (polarity)
It is structured like a ‘seam’
- Outer leaflet of the cell membrane of one cell fuses with the outer leaflet of the membrane of the adjacent cell
- intercellular space is a space until you hit the tight junctions
- It creates a ‘seal’, so anything that tries to get from the basolateral layer must only go through the opening in + through the cells (not between the membranes)
2 types of tight junctions:
- Tight-tight junctions: let nothing through
- Leaky junctions - will allow some things through
Describe Adherens junctions as a type of cell junction
Adherens are a structural junction that attached cells to each other and to the cytoskeleton. 2 types:
- Zonula adherens (actin)
- Desmosomes (intermediate filaments)
They are not as tight as tight junctions
- it is a slight expansion of the cell membrane
- that is attached to actin
- which help to cause movements
Zonula adherens attach to actin
- which can contract and move (actin is attached to proteins that go into the cytoplasm - help to dissipate energy out)
- these are lateral - go all the way around the sides of the cells
Desmosome (Hemi) attach to intermediate filaments, -
- they don’t move
Describe a hemidesmosome as a type of cell junction
It is half a hemidesmosome
- on the basal surface - that stick the cells to the basement membranes
They are an anchoring junction
- made of integrins and laminin collagen
