Session 1: Homeo+cells Flashcards
Define the term ‘homeostasis’ with respect to water, temperature and pH balance
Homeo= sameness and stasis = standing still
“the ability or tendency of a living organism, cell, or tissue to keep the conditions inside it the same despite any changes in the conditions around it, or maintaining a state of internal balance”
Is in a state of dynamic equilibrium
Explain the concepts behind positive and negative feedback loops
Positive= An initial stimulus produces a response that accelerates or enhances the original change in conditions rather than opposing it
Positive stops when initiator stops
Negative stops when effector ceases
How does the body react differently to internal temperature increase and decrease?
Explain the positive feedback loop when a baby pushes against cervix
Explain positive feedback loop of blood clotting
Explain negative feedback loop of rising blood glucose level stimulus
Explain the importance of acid-base balance for normal human physiology
Importance; maintain within normal limits 7.35-7.45
Why?
To maintain homeostasis
Abnormal pH damage cells and tissues by breaking chemical bonds, changing the shpaes of proteins and altering cellular function
Whats acidosis and its causes, symptoms and treatment?
pH below 7.35
Causes?
Metabolic acidosis and respiratory acidosis
Treatment?
Infusion by bicarbonate solution (increase blood pH) and mechanical ventilation to drive out co2
Whats alkalosis?
pH above 7.45
pH above 7.8 generally causes uncontrollable and sustained skeletal muscle contractions
State the ‘normal range’ for pH in tissues including blood
7.35-7.45
State the ‘normal range’ for core body temperature
Recall the mechanism(s) (in broad terms) that regulate core body temperature
Two temperature sensors: one in skin (external body temp) and in hypothalamus (internal core temp)
Recall the mechanism(s) (in broad terms) that regulate pH
Carbonic acid- bicarbonate buffer: co2 in hemoglobin to bic (carbonic anhydrase), bic (leaves rbc) goes to lungs, converted back to co2 (by carbonic anhydrase) and leaves (low partial pressure of co2)
Recall the percentage of water in a ‘standard’ 70kg male
60%
State the body compartments where fluids accumulate
Compare and contrast water balance in males and females [and in early life and in older populations]
The older and more fat, the less h2o proportionally in body. Women more fat than men.
Outline the differences between dehydration and water toxicity
Water toxicity; Cells in hypotonic solution (environment) therefore cells swell and reach point where theres HIGHER osmotic pressure inside cell compared to outside. Cells swell, enzymes + proteins stop working. Cell keeps swelling until burst.
Dehydration; Osmolality increases (around cells)
Describe the process of oedema
Fluid retention
Hydrostatic Pressure greater than osmotic pressure
Whats Osmolality units?
mOsm/kg
Whats tonicity?
A description of how the solution affects the shape of the cell
(osmotic pressure=osmolarity)
How do we classify and analyse pH imbalances?
Arterial blood gas
Difference between osmolality and osmolarity?
What is the normal pH range for tissue survival?
6.8-7.8 limits of tissue survival.
Whats pyrexia and rigor?
Pyrexia is a fever.
Rigor occurs when “thermostat” in hypothalamus turned up. Hence shivers to warm self up. Increase in temperature helps immune system work optimally.
Protection of stomach wall from acid erosion, how?
Mucus secretion by goblet cells; provides a protective barrier
Bicarbonate secretion; neutralisation of acids
What treatments are used for regurgitation of stomach acids?
Treat with antacids.
Aluminium hydroxide ideal; longer lasting, milder, fewer side effects due to lower solubility profile (they are insoluble)
How can you work out hydrogen ion concentration without calc?
[H+] change by factor of 2 therefore 0.3 change in pH
pH7.4; [H+] =40nm
pH7.1; [H+]= 100nm
1 mmol/L of NaCl produces how many mOsm/kg?
2 mOsm/kg
Whats the role of a microscope?
is to magnify an image to a level at which the retina can resolve the information that would otherwise be below its limit of resolution
Whats the limit of resolution meaning? And resolving power
The smallest distance by which two objects can be seperated and still be distinguishable as two seperate objects.
Microscopes have greater resolving power than eye.
What determines limit of resolution?
The wavelength used (smaller wavelength smaller limit of resolution)
And the numerical aperature (NA): smaller =smaller limit of resolution)
the smaller the limit of resolution, the greater the resolving power.
Resolving power is a function of…
magnification
Compare light and electron microscopes
State the meaning of the term “tissue”, and provide an example of each of the 4 types
Tissue means woven in latin
Epithelial, Nerve, Muscle and connective
Explain why electron microscopes are capable of finer resolution than light microscopes
Smaller wavelength of EM beam compared to that of light microscope. Therefore the limit of resolution is smaller.
What are the differences between transmission electron microscopy and scanning electron microscopy?
Both: Fix with Glutaraldehyde
Embed in Epoxyresin
Stain (e.g.Osmium tetroxide)
TEM uses microtome with diamond knives to cut thins slices. Electrons pass through the specimen
SEM visualise surface of cells (no microtome). Electrons reflect off surface of cells.
Whats Freeze fracture EM?
The tissue is frozen to -160oC and fractured by
hitting with a knife edge. The fracture line passes through the plasma membrane exposing its interior which can then be
imaged
Resolving power of TEM how many times greater than light microscope?
1000 times
Describe the steps in obtaining a biological specimen to viewing it under a microscope:
1) Obtain the specimen
2) Fixation
3) Specimen dehydrated* and then embedded in paraffin wax or epoxy resin (can be stored now once cooled)
4) Slicing with microtome
5) **Rehydration and staining
*Dehydrated in series of alcohol solutions of ascending conc
** rehydrated in decending conc
Describe common biopsy techniques giving examples of tissues which can be sampled by each method
(1) surgery and then later dissection by the histopathologist; (2) the use of scraping methods (i.e. curettes, scalpel scrapes); (3) Sharp needles (i.e. Needle biopsy, pipelle, trephine, punch biopsy) or (4) direct venepucture (i.e. for blood smears and haematological disease assessment). Occasionally, body fluids are examined (i.e. sputum or semen), but these rarely need to be fixed and processed for histology.
.
Explain why tissue needs to be fixed and state which fixatives are commonly used
- terminate cell metabolism -prevent enzymatic degradation of cells and tissues by autolysis (self-digest) -kill pathogenic microorganisms -removes water and hardens the tissue -prevent putrefaction
Buffered formalin solutions (formaldehyde with NaCl) (TEM fixes with glutaraldehyde)
Why used a buffered isotonic fixation solution
Isotonic buffered formalin used, isotonic with the intracellular fluid and so allows better penetration of the formaldehyde, which reacts with the amino groups of amino acids within proteins and forms a methylated bridge between protein chains.
This preserves the general structure of the cells within a tissue or organ.
prevents tissue swelling.
Describe how tissue processing can lead to the formation of shrinkage and other artefacts
Need rapid fixation (1mm per hour), therefore biopsies are small.
Left in fixative for 24 to 48 hours only, longer times tend to cause the tissue to shrink due to dehydration and cause what are called ‘fixation artifacts
Artifacts can be generated in all stages of tissue prep e.g. improper equipment, defective microtome blade.
Discuss the value of histological staining and state the components of tissue stained by routine stains, such as Haematoxylin and Eosin (H&E) and specialist methods, such as immunohistochemistry and immunofluorescence
Staining is used to identify, give colour and distinguish parts of the specimen.
Haematoxylin is a basic dye and binds to acidic structures (DNA and RNA)
Eosin is acidic and binds to basic structures (intracellular and extracellular proteins (cytoplasm, collagen and elastic fibres)
Direct and indirect immunofluorescence. Indirect immunohistochemistry. High specificity; due to targeting antigens
Compare paraffin wax formalin fixed vs frozen section
Explain the value of histology in diagnosis
Invaluable, for example identifying the presence/absence and location of structures present in diseases such as progesterone receptors with breast cancer, visualised by immunohistochemistry or immunofluorescence
Outline the advantages conferred by phase contrast, dark field, fluorescence, and confocal light microscopy
Confocal microscope visualises the antibody (conjugated with dye) and antigen complex. This produces a 3D image. (clinically used for diagnosis of eye diseases too)
Phase contrast microscopes view live cells. Cells in culture can be manipulated and experiments to determine cells and tissue function.
Dark field; involving living cells too.
What chemicals are commonly used in each step of tissue preparation for a light microscope?
Fixation with formalin
Embedded in paraffin wax
Stain haematoxylin and eosin
From a simplified diagram of a cell, clearly label those ultrastructural components common to eukaryotic/animal cells
State how a cell functions by describing the structure and function of the major cell components and organelles
Whats are the colours elicited by H&E stains:
H is blue
E is pink
Whats not coloured by H&E?
elastic material, reticular fibers, basement membranes and lipids
