NEET MDS Synopsis
Radiation Biology
Radiology
Radiation Biology
-X- and g -rays are called sparsely ionizing because along the tracks of the electrons set in motion, primary ionizing events are well separated in space.
Alpha-particles and neutrons are densely ionizing because the tracks consist of dense columns of ionization.
X-rays, gamma rays, electrons, and protons are all low LET forms of radiation in that their density of ionization is sparse. In general, they penetrate tissues deeply and result in less intracellular radiation injury.
High LET forms of radiation, such as heavy nuclear particles (e.g. fast neutrons), penetrate tissues less deeply and cause more radiation injury to biologic material.
Cells are most sensitive to Radiation when:
- they are actively proliferating.
- they are undifferentiated.
Exceptions to this Law:
- lymphocyte
- Oocyte
X-rays and gamma rays show latent injury that is residual tissue damage even after the initial radiation reaction is subsided.
Proteins tend to be more radiosensitive than carbohydrates and lipids.
Most radiosensitive tissue-small lymphocyte
Most radioresistant tissue- brain
Embryonic, immature or poorly differentiated tissues are more easily injured by radiation, but they also show greater recovery properties.
All cells show increased susceptibility to radiation at the time of mitotic division and if the cells are irradiated during the resting phase, mitosis is delayed or inhibited.
- In general, cells are most radiosensitive in late M and G2 phases and most resistant in late S.
- for cells with a longer cell cycle time and a significantly long G1 phase, there is a second peak of resistance late in G1
- the pattern of resistance and sensitivity correlates with the level of sulfhydryl compounds in the cell. Sulfhydryls are natural radioprotectors and tend to be at their highest levels in S and at their lowest near mitosis.
- To produce its effect. Oxygen must be present during the radiation exposure or at least during the lifetime of the free radicals (10-5 sec).
- Mandible is more ssceptible to radiation injury than maxilla due to the denser structure and poorer blood supply.
- Salivary glands though an organ with a low turnover rate, was unusually sensitive to radiation
- Liposarcoma tumors are the most radiosensitive soft tissue tumors
- Exophytic tumors are usually more easily controlled with radiation while infiltrative and ulcerative lesions are more radioresistant.
The infiltrative and ulcerative lesions are more likely to be larger than clinically apparent and contain a larger proportion of hypoxic cells.
Classification
Anatomy
Classification
Epitheliums can be classified on appearance or on function
Classification based on appearance
- Simple - one layer of cells
- Pseudostratified - looks like more than one layer but is not
- Stratified - more than one layer of cells
Simple epitheliums
Simple squamous epithelium
Cells are flat with bulging or flat nuclei. Lines the insides of lung alveoli and certain ducts in the kidney
Forms serous membranes called mesothelium that line cavities like: pericardial , peritoneal, plural
Lines blood vessels - known as endothelium
Simple cuboidal epithelium
It appears square in cross section, Found in: - Ducts of salivary glands, Follicles of the thyroid gland, Pigment layer in the eye, Collecting ducts of the kidney, In the middle ear is ciliated type.
Simple columnar
Lines the gastrointestinal tract from the stomach to the anal canal, Some columnar cells have a secretory function – stomach, peg cells in the oviduct, Some columnar cells have microvilli on their free border (striated border) – gall bladder, duodenum
Microvilli increase the surface area for absorption
Some columnar cells have cilia – oviduct, smaller bronchi
Cilia transport particles
Pseudostratified
Appears as stratified epithelium but all cells are in contact with the basement membrane. Has a thick basement membrane. Different cell types make up this epithelium, Cells that can be found in this type of epithelium are:
Columnar cells with cilia or microvilli.
Basal cells that do not reach the surface.
Goblet cells that secrete mucous.
Found in the trachea, epididymus, ductus deferens and female urethra
Stratified epithelium
Classified according to the shape of the surface cells
Stratified squamous epithelium
Has a basal layer that varies from cuboidal to columnar cells that divide to form new cells. Two types are found:
Keratinized: Mostly forms a dry covering, The middle layers consists of cells that are forming- and filling up with keratin. The superficial cells form a tough non living layer of keratin, Keratin is a type of protein, The skin is of this type has thick skin - found on the hand palms and soles of the feet, thin skin - found on the rest of the body
Non-keratinized: Top layer of cells are living cells with nuclei Forms a wet covering, The middle layers are polyhedral, The surface layer consists of flat squamous cells
Is found in: mouth, oesophagus, vagina
Stratified cuboidal epithelium
Found: - in the ducts of sweat glands
Stratified columnar epithelium
Found at the back of the eyelid (conjunctiva)
Transitional epithelium
- Sometimes the surface cells are squamous, sometimes cuboidal and sometimes columnar
- The superficial cells are called umbrella cells because they can open and close like umbrellas, when the epithelium stretch and shrink
- Umbrella cells can have 2 nuclei
- Found in the bladder and ureter
Muscles
PhysiologyThere are three types of muscle tissue, all of which share some common properties:
Excitability or responsiveness - muscle tissue can be stimulated by electrical, physical, or chemical means.
contractility - the response of muscle tissue to stimulation is contraction, or shortening.
elasticity or recoil - muscles have elastic elements (later we will call these their series elastic elements) which cause them to recoil to their original size.
stretchability or extensibility - muscles can also stretch and extend to a longer-than-resting length.
The three types of muscle: skeletal, cardiac, and visceral (smooth) muscle.
Skeletal muscle
It is found attached to the bones for movement.
cells are long multi-nucleated cylinders.
The cells may be many inches long but vary in diameter, averaging between 100 and 150 microns.
All the cells innervated by branches from the same neuron will contract at the same time and are referred to as a motor unit.
Skeletal muscle is voluntary because the neurons which innervate it come from the somatic or voluntary branch of the nervous system.
That means you have willful control over your skeletal muscles.
Skeletal muscles have distinct stripes or striations which identify them and are related to the organization of protein myofilaments inside the cell.
Cardiac muscle
This muscle found in the heart.
It is composed of much shorter cells than skeletal muscle which branch to connect to one another.
These connections are by means of gap junctions called intercalated disks which allow an electrochemical impulse to pass to all the connected cells.
This causes the cells to form a functional network called a syncytium in which the cells work as a unit. Many cardiac muscle cells are myogenic which means that the impulse arises from the muscle, not from the nervous system. This causes the heart muscle and the heart itself to beat with its own natural rhythm.
But the autonomic nervous system controls the rate of the heart and allows it to respond to stress and other demands. As such the heart is said to be involuntary.
Visceral muscle is found in the body's internal organs and blood vessels.
It is usually called smooth muscle because it has no striations and is therefore smooth in appearance. It is found as layers in the mucous membranes of the respiratory and digestive systems.
It is found as distinct bands in the walls of blood vessels and as sphincter muscles.
Single unit smooth muscle is also connected into a syncytium similar to cardiac muscle and is also partly myogenic. As such it causes continual rhythmic contractions in the stomach and intestine. There and in blood vessels smooth muscle also forms multiunit muscle which is stimulated by the autonomic nervous system. So smooth muscle is involuntary as well
Prognosis After Traumatic Brain Injury
Oral and Maxillofacial SurgeryPrognosis After Traumatic Brain Injury (TBI)
Determining the prognosis for patients after a traumatic brain injury
(TBI) is a complex and multifaceted process. Several factors can
influence the outcome, and understanding these variables is crucial for
clinicians in managing TBI patients effectively. Below is an overview of the key
prognostic indicators, with a focus on the Glasgow Coma Scale (GCS) and other
factors that correlate with severity and outcomes.
Key Prognostic Indicators
Glasgow Coma Scale (GCS):
The GCS is a widely used tool for assessing the level of
consciousness in TBI patients. It evaluates three components: eye
opening (E), best motor response (M), and verbal response (V).
Coma Score Calculation:
The total GCS score is calculated as follows: [ \text{Coma
Score} = E + M + V ]
Prognostic Implications:
Scores of 3-4: Patients scoring in this range
have an 85% chance of dying or remaining in a vegetative
state.
Scores of 11 or above: Patients with scores in
this range have only a 5-10% chance of dying or remaining
vegetative.
Intermediate Scores: Scores between these
ranges correlate with proportional chances of recovery, indicating
that higher scores generally predict better outcomes.
Other Poor Prognosis Indicators:
Older Age: Age is a significant factor, with older
patients generally having worse outcomes following TBI.
Increased Intracranial Pressure (ICP): Elevated ICP
is associated with poorer outcomes, as it can lead to brain herniation
and further injury.
Hypoxia and Hypotension: Both conditions can
exacerbate brain injury and are associated with worse prognoses.
CT Evidence of Compression: Imaging findings such
as compression of the cisterns or midline shift indicate significant
mass effect and are associated with poor outcomes.
Delayed Evacuation of Large Intracerebral Hemorrhage:
Timely surgical intervention is critical; delays can worsen the
prognosis.
Carrier Status for Apolipoprotein E-4 Allele: The
presence of this allele has been linked to poorer outcomes in TBI
patients, suggesting a genetic predisposition to worse recovery.
Osteomyelitis
Oral Maxillofacial Surgery
Osteomyelitis
Staphylococcus aureus causes osteomyelitis.
TYPES OF OSTEOMYELITIS
1.Suppurative Osteomyelitis - onset 4 weeks - Deep bacterial invasion into medullary & cortical bone - polymicrobial infection anaerobes such as Bacteriods, Porphyromonas or Provetella.
Staphylococci may be a cause when an open fracture is involved. Mandible is more prone than maxilla as vascular supply is readily compromised.
2.Focal Sclerosing Osteomylitis(Condensing osteitis) - Localized areas of bone sclerosis. Bony reaction to low-grade peri-apical infection or unusually strong host defensive response. Association with an area of inflammation is critical.
3. Diffuse Sclerosing Osteomylitis - Chronic intraosseous bacterial infection creates a smoldering mass of chronically inflammed granulation tissue.
4. Proliferative Periostitis(Periostitis ossificans & Garee’s osteomyelitis) - periosteal reaction to the presence of inflammation. Affected periosteum forms several rows of reactive vital bone that parallel each other & expand surface of altered bone.
- Radiopaque laminations of bone roughly parallel each other & underlying cortical surface. Laminations may vary from 1-12 in number. Radiolucent separations often are present between new bone & original cortex.
Conditions that weaken the immune system increase a person's risk for osteomyelitis, including:
Diabetes (most cases of osteomyelitis stem from diabetes)
Sickle cell disease
HIV or AIDS
Rheumatoid arthritis
Intravenous drug use
Alcoholism
Long-term use of steroids
Hemodialysis
Poor blood supply
Recent injury
Bone surgery, including hip and knee replacements, also increase the chance of bone infection.
Osteomyelitis in Children and Adults
In children, osteomyelitis is usually acute. Acute osteomyelitis comes on quickly, is easier to treat, and overall turns out better than chronic osteomyelitis. In children, osteomyelitis usually shows up in arm or leg bones.
In adults, osteomyelitis can be either acute or chronic.
Acute osteomyelitis develops rapidly over a period of seven to 10 days. The symptoms for acute and chronic osteomyelitis are very similar
Clinical features of chronic osteomyelitis are usually limited to :
- Pain and tenderness: the pain is minimal,
- Non healing bony and overlying soft tissue wounds with induration of soft tissues,
- Intraoral or extraoral draining fistulae,
- Thickened or “wooden” character of bone,
- Enlargement of mandible, because of deposition of subperiosteal new bone.
- Pathological fractures may occur,
- Sterile abscess (Brodie’s abscess), common to long bones is rare in jaws.
- Teeth in the area tend to become loose and sensitive to palpation and percussion.
METAPLASIA
General Pathology
METAPLASIA
A reversible replacement of one type of adult tissue by another type of tissue. It is usually an adaptive substitution to a. cell type more suited to an environment, often at the cost of specialised function.
(1) Epithelial metaplasia:
Squamous metaplasia. This is the commoner type of metaplasia and is seen in:
Tracheobronchial lining in chronic smokers and in bronchiectasis.
In Vitamin A deficiency.
Columnar metaplasia:
Intestinalisation of gastric mucosa in chronic gastritis.
(2) Connective tissue metaplasia:
Osseous-Metaplasia in :
Scars.
Myositis ossificans
Myeloid metaplasia in liver and spleen.
PFM Alloys
Dental Materials
PFM Alloys
Applications-substructures for porcelain-fused-to-metal crowns and bridges
Classification
o High-gold alloys
o Palladium-silver alloys
o Nickel-chromium alloys
Structure
Composition
o High-gold alloys are 98% gold. platinum. And palladium
o Palladium-silver alloys are 50% to 60% palladium and 30 to 40% silver
o Nickel-chromium alloys are 70% to 80% nickel and 15% chromium with other metals
Manipulation
o Must have melting temperatures above that of porcelains to be bonded to their surface
o More difficult to cast (see section on chromium alloys)
Properties - Physical
Except for high-gold alloys, others are less dense alloys
Alloys are designed to have low thermal expansion coefficients that must be matched to the overlying porcelain
Chemical-high-gold alloys are immune, but others passivate
Mechanical-high modulus and hardness
Water Acid Bases & Buffers -pKa
Biochemistry
Acids and bases can be classified as proton donors and proton acceptors, respectively. This means that the conjugate base of a given acid will carry a net charge that is more negative than the corresponding acid. In biologically relavent compounds various weak acids and bases are encountered, e.g. the acidic and basic amino acids, nucleotides, phospholipids etc.
Weak acids and bases in solution do not fully dissociate and, therefore, there is an equilibrium between the acid and its conjugate base. This equilibrium can be calculated and is termed the equilibrium constant = Ka. This is also referred to as the dissociation constant as it pertains to the dissociation of protons from acids and bases.
In the reaction of a weak acid:
HA <-----> A- + H+
the equlibrium constant can be calculated from the following equation:
Ka = [H+][A-]/[HA]
As in the case of the ion product:
pKa = -logKa
Therefore, in obtaining the -log of both sides of the equation describing the dissociation of a weak acid we arrive at the following equation:
-logKa = -log[H+][A-]/[HA]
Since as indicated above -logKa = pKa and taking into account the laws of logrithms:
pKa = -log[H+] -log[A-]/[HA]
pKa = pH -log[A-]/[HA]
From this equation it can be seen that the smaller the pKa value the stronger is the acid. This is due to the fact that the stronger an acid the more readily it will give up H+ and, therefore, the value of [HA] in the above equation will be relatively small.