Histology and tissues Flashcards
1
Q
Explain what histology is and how we study it
A
- Histology is the study of microscopic structure of organisms
- As the human eye is limited in it’s ability to resolve objects under a certain size scientists have developed new methods which create magnetised images of these tissues.
2
Q
Describe basic histology of tissues
A
- A basic tissue consists of cells which are adapted to form a similar function and their surrounding extracellular matrix.
- ECM consists of fibres and ground substance (this is dependent on the nature of the cells in the tissue
- Cells also contain specialised junctions which act to support tissues as well as allow for cell communication
3
Q
Describe basic principles of resolution and magnification in microscopy
A
- Magnification is the size under the microscope divided into the actual size of the tissue
- There is a limit of resolution between different imaging techniques
- Resolution is the ability to distinguish 1 object from another
o Human eye has a resolution of roughly 100-200um
o LM= 0.2um
o EM= 2nm
4
Q
Importance of plane in imaging analysis
A
- 4 different classifications of planes: o Sagittal (LR) o Frontal/Coronal (back and front) o Transverse (cross section) o Oblique (at an angle other than 90 - Different planes result in slightly different view points of an image
5
Q
Describe the basic organelles within a cell and their functions
A
- Nucleus
o Largest part of a cell nuclear envelope - Nucleosome
o Contains DNA (genetic information, important for protein encoding) - Endoplasmic Reticulum (smooth and rough)
o Rough is studded with ribosomes, large folded looking structure, important for synthesis, folding, modification, and transport of proteins - Mitochondria
o Sight of cellular respiration, production of ATP for energy - Ribosomes
o Site of protein production - Secretory Vessicles
o Proteins are stored in vesicles ready for release - Lysosomes
o Membrane enclosed organelles containing enzymes that are capable of breaking down a variety of debris and substances. Sometimes even pathogens - Golgi apparatus
o Package proteins and restructure ready for release or storage
6
Q
How do cells make up tissues and communicate?
A
- Cells are often joined together via tight junctions which prevent leakage and hold tissues together. They can communicate via gap junctions which consists of connexins from 2 cells which join to form a connexon. These allow for transport of electrons and chemicals between these cells which can trigger intracellular matrix. Cells can also interact by the release of hormones (paracrine) and neurotransmitters. These can interact with the cellular membrane on local cells which allows for the initiation of cascades within the cell.
7
Q
Describe Light in compared to Electron microscopy
A
- Electron microscopy provides a greater magnification and resolution than LM
- Light microscopy is useful for providing a good overall view of a tissue, whereas electron microscopy is more useful for fine details such as cellular junctions
- Electron microscopy requires a smaller tissue sample than LM
- EM uses a limited number of dyes (normally silver dyes), whereas there are a large array of dyes available for LM
- LM are generally cheaper pieces of equipment and preparation of tissues is less tedious.
8
Q
Identify common structures in LM and EM
A
- EM= organelles in cell
- Tissues: connective etc…blood vessel, nucleus
9
Q
Discuss the different types of fixative
A
- Fixation is incredibly important for producing good imaging of tissues
- Fixation is best done soon after death
- It is either carried out by perfusion or immersion
- Alcohol is common as it is good for speeding up the process of fixation (Carnoy’s fixative: mixture of formaldehyde and alcohol)
- Formaldehyde is the most common aldehyde fixative
10
Q
Explain basic H&E staining
A
- Hydration step with varying concentrations of alcohol
- Staining with haematoxylin, scotts, eosin respectively
- H=Acidic structures a purplish blue, S= to turn initial red nuclear staining to blue, E= basic structures pink
- Dehydration with varying alcohol concentrations
11
Q
Identify the subcellular features of an axo-dendritic synapse
A
- Space between the axons of the pre-synaptic and post synaptic neuron
- The pre-synaptic neuron can release neurotransmitters in response to a wave of depolarisation.
- The neurotransmitters interact with the post synaptic dendrite to cause an action potential which may or may not be propagated depending on whether a threshold is reached.
- Neurotransmitters taken back in by the presynaptic cell or other supporting cells
12
Q
Highlight the differences between excitatory synapses and inhibitory synapses
A
- If there is enough EPSPs the threshold potential is reached which is normally around -55mV
- This triggers a wave of depolarisation which runs into the positive +33mV. (action potential)
- Impulse travels along the axons to trigger the release of further excitatory neurotransmitters
- In IPSPs the neurotransmitter has the opposite effect on the post-synaptic neuron in creating a wave of hyperpolarisation.
13
Q
Summarise synaptic release of neurotransmitters
A
- Depolarisation of the membrane triggers calcium to enter the cell. The calcium increase promotes the fusion of synaptic vesicles which discharge neurotransmitter into the synaptic cleft. The is known as calcium mediated exocytosis. Following the depolarisation there is a refractory period in which no other action potentials can be reached a wave of hyperpolarisation occurs. This maintains the balance of the cells. There are drugs which cause rapid firing of presynaptic neurons such as cocaine.
14
Q
Summarise synaptic plasticity.
A
- The neuron is able to adapt the receptors on its surface which increases plasticity.
- Pre-synaptic neurons contain auto receptors which regulate neurotransmitter release. Retrograde signalling can also occur in which presynaptic receptors respond to signals from the post-synaptic neuron.
- Many receptors are not fixed to the membrane and can move laterally or can even remove completely from the membrane
- Protein synthesis within neuron can also be modified i.e., production of new synaptic receptors when required
- Gene expression can be controlled in the long term
- In the case of endocannabinoids local receptor signalling can result in the strength of synaptic transmission being altered short term.
15
Q
Explain the basic principles of cell communication
A
- Cells can communicate through several systems
- Autocrine (self)
- Juxtacrine (between cells)
- Paracrine (signals sent to cells in close proximity)
- Endocrine (Signals sent through the blood stream)
- Can also communicate via receptors on cell surfaces (useful in immune responses)
16
Q
How are receptors classified
A
- Receptors are proteins present on the surface of a cell which when activated can trigger a variety of intercellular responses. Receptors are generally specific to certain molecules which can bind to them causing a response.
- An example would be a G-protein coupled receptor. These receptors when stimulated will activate a G-protein which will in turn activate a 2ndary messenger which initiated a cascade of kinases which results in a change in gene expression.
17
Q
How does receptor structure effect it’s function?
A
- Membrane receptors are proteins which are found on the cellular/ nuclear membrane. Proteins themselves are amino- acid sequences which obtain a 3D structure held together by variety of intermolecular bonds and attractions. The confirmation of a protein determines it’s function and therefor it is essential that this structure is maintained. Membrane bound receptors have extra and intercellular domains. The extracellular domains are hydrophilic in nature and the intercellular domains are hydrophobic which maintains the confirmation in the membrane. Prior to interaction with stimuli these receptors are in an ‘inactive’ confirmation. When a molecule with specific chemistry to the receptor binds, it changes the inter molecular bonds within the receptor which in turn changes the receptors confirmation. The intercellular domain is usually linked to a messenger protein which is then activated causing an intercellular response or an ion channel which either opens or closes in response to binding.
18
Q
Discuss resting membrane potentials
A
- Is determined by the voltage between the membrane of the neural cell at rest. This put simply means it is determined by the concentration gradient of the ions and their membrane permeability.
- The ions primarily involved in a resting membrane are Na+ and K+. These move down their gradients using channels across the membrane to create a resting membrane potential
- K+ alone would establish an equilibrium potential o -90mV whereas Na+ would establish a potential of +60mV. The resting membrane is 25 to 30x more permeable to K+ than Na+ as it is closer to K+’s equilibrium potential.
- Na+ gradually leaks in making the interior slightly less negative which reduces the electrical gradient. K+ tends to leave the cell (less -ve to pull back). Leakage is counterbalanced by Na+/ K+ pumps which are powered by ATP.
