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
Describe gap junctions as a type of cell junctions
Gap junctions are small holes between cells
- for direct communication between adjacent cells
- they allow the passage of ions, amino acids, sugars, second messengers, and metabolites to go between one cell and another
- they allow coordinated cell activity (e.g. in heart, muscle etc.)
They are made up of:
- 6 connexins, which make up 1 connexon/
- they form ‘tubes’ between cells, and connexons can form up quickly to allow the transport of information
- they can also quickly unalign and stop the gap between 2 cells
Good way of signalling
Describe a junctional complex
When all the junctions are grouped together, they are seen as a junctional complex
- all the different types of junctions can be seen
e. g.
- occluding (tight junctions)
- Zonula adherens
- desmosomes
- hemidesmosomes
- gap junctions
Define a cell
The basic unit of living life
Describe a simple tissue
It is a collection of similar cells
Describe a compound tissue
It is a mix of cells and ECM (extra-cellular matrix)
- ECM - a 3D network of extracellular macromolecules (collagen, enzymes, and glycoproteins) that provide structural and biochemical support to the surrounding cella
Define an organ
it is a distinct group of several tissues
Describe a system
it is a group of organs with a distinct role
Describe tissues:
Cells are arranged into tissues
- a collection of similar cells +/- support cells
They come from 3 embryonic primary germ layers:
- Ectoderm
- Mesoderm
- Endoderm
Describe the 3 embryonic primary germ layers
Ectoderm - gives rise to:
- nervous tissue, lens, skin, epidermis and derivatives, linings of oral, nasal, vaginal, and anal cavities, pituitary gland, adrenal medulla
Mesoderm - gives rise to:
- muscle, connective tissue, skin, blood vessels, internal reproductive organs, kidneys
Endoderm - gives rise to:
- epithelium of pharynx, auditory tubes, tonsils, lungs, bladder, digestive tract
Name the 4 basic tissue types
- Epithelium
- Connective
- Muscular
- Nervous
Describe the 4 basic tissue types
Epithelium
- sheet of closely-packed cells derived from one of the 3 germ layers, and which cover/line the surface of an organ
Connective
- comprising cells derived from the mesoderm, and producing an ECM of fibres and ground substance
Muscular
- also derived from mesoderm, and composed of cells (or multinucleated syncytia) whose cytoplasm contains filaments of contractile proteins (actin, myosin etc.)
Nervous
- they develop from neuro-ectoderm
- consist of cells of which the main type possesses processes called neurites (axons and dendrites) which conduct impulses when stimulated
Describe organs
Organs are composed of elements of some/all of the 4 main tissue types
They are distinct groups of (several) tissues, arranged to suit the function of the organ
- parenchyma - cells that perform the main function
- stroma - cells that act as supporting cells
(including connective tissue, blood vessels, nerves)
Name the 6 different systems
- Nervous system
- Respiratory system
- Circulatory system
- Digestive system
- Male reproductive system
- Female reproductive system
