NEET MDS Synopsis
Nomenclature for stereoisomers
Biochemistry
Nomenclature for stereoisomers: D and L designations are based on the configuration about the single asymmetric carbon in glyceraldehydes
For sugars with more than one chiral center, the D or L designation refers to the asymmetric carbon farthest from the aldehyde or keto group.
Most naturally occurring sugars are D isomers.
D & L sugars are mirror images of one another. They have the same name. For example, D-glucose and L-glucose
Other stereoisomers have unique names, e.g., glucose, mannose, galactose, etc. The number of stereoisomers is 2 n, where n is the number of asymmetric centers. The six-carbon aldoses have 4 asymmetric centers, and thus 16 stereoisomers (8 D-sugars and 8 L-sugars
An aldehyde can react with an alcohol to form a hemiacetal
Similarly a ketone can react with an alcohol to form a hemiketal
Pentoses and hexoses can cyclize, as the aldehyde or keto group reacts with a hydroxyl on one of the distal carbons
E.g., glucose forms an intra-molecular hemiacetal by reaction of the aldehyde on C1 with the hydroxyl on C5, forming a six-member pyranose ring, named after the compound pyran
The representations of the cyclic sugars below are called Haworth projections.
Fructose can form either:
a six-member pyranose ring, by reaction of the C2 keto group with the hydroxyl on C6
a 5-member furanose ring, by reaction of the C2 keto group with the hydroxyl on C5.
Cyclization of glucose produces a new asymmetric center at C1, with the two stereoisomers called anomers, α & β
Haworth projections represent the cyclic sugars as having essentially planar rings, with the OH at the anomeric C1 extending either:
below the ring (α)
above the ring (β).
Because of the tetrahedral nature of carbon bonds, the cyclic form of pyranose sugars actually assume a "chair" or "boat" configuration, depending on the sugar
Hyoid Bone
Anatomy
U-shaped bone
Body
Greater horn
Lesser horn
Suspended by ligaments from the styloid process
Osteoradionecrosis
Oral Pathology
Osteoradionecrosis
Clinical features
A reduction in vascularity, secondary to endarteritis obliterans, and damage to osteocytes as a consequence of ionising
Radiotherapy can result in radiation-associated osteomyelitis or Osteoradionecrosis. The mandible is much more commonly affected than the maxilla, because it is less vascular. Pain may be severe and there may be pyrexia. The overlying oral mucosa often appears pale because of radiation damage. Osteoradionecrosis in the jaws arises most often following radiotherapy for squamous cell carcinoma.
Scar tissue will also be present at the tumour site, often in close relation to the necrotic bone.
Radiology
Osteoradionecrosis appears as rarefying osteitis within which islands of opacity (sequestra) are seen. Pathological
fracture may be visible in the mandible.
Pathology
The affected bone shows features similar to those of chronic osteomyelitis. Grossly, the bone may be cavitated
And discoloured, with formation of sequestra.
Acute inflammatory infiltrate may be present on a background of chronic inflammation, characterized by formation
Of granulation tissue around the non-vital trabeculae.
Blood vessels show areas of endothelial denudation and obliteration of their lumina by fibrosis.
Small telangiectatic vessels lacking precapillary sphincters may be present.
Fibroblasts in the irradiated tissues lose the capacity to divide and often become binucleated and enlarged.
Management
Prevention of Osteoradionecrosis is vital. Patients who require radiotherapy for the management of head and
neck malignancy should ideally have teeth of doubtful prognosis extracted at least 6 weeks prior to treatment.
The dose of radiation,
The area of the mandible irradiated and
the surgical trauma involved in the dental extractions.
Surgical management of Osteoradionecrosis is similar to osteomyelitis.
Movement Across Membranes
Physiology1 - Passive processes - require no expenditure of energy by a cell:
Simple diffusion = net movement of a substance from an area of high concentration to an area of low concentration. The rate of diffusion is influenced by:
concentration gradient
cross-sectional area through which diffusion occurs
temperature
molecular weight of a substance
distance through which diffusion occurs
Osmosis = diffusion of water across a semi permeable membrane (like a cell membrane) from an area of low solute concentration to an area of high solute concentration
Facilitated diffusion = movement of a substance across a cell membrane from an area of high concentration to an area of low concentration. This process requires the use of 'carriers' (membrane proteins). In the example below, a ligand molecule (e.g., acetylcholine) binds to the membrane protein. This causes a conformational change or, in other words, an 'opening' in the protein through which a substance (e.g., sodium ions) can pass.
2 - Active processes - require the expenditure of energy by cells:
Active transport = movement of a substance across a cell membrane from an area of low concentration to an area of high concentration using a carrier molecule
Endo- & exocytosis - moving material into (endo-) or out of (exo-) cell in bulk form
The Medial Wall of the Orbit
AnatomyThe Medial Wall of the Orbit
This wall is paper-thin and is formed by the orbital lamina or lamina papyracea of the ethmoid bone, along with contributions from the frontal, lacrimal, and sphenoid bones (L. papyraceus, "made of papyrus" or parchment paper).
There is a vertical lacrimal groove in the medial wall, which is formed anteriorly by the maxilla and posteriorly by the lacrimal bone.
It forms a fossa for the lacrimal sac and the adjacent part of the nasolacrimal duct.
Along the suture between the ethmoid and frontal bones are two small foramina; the anterior and posterior ethmoidal foramina.
These transmit nerves and vessels of the same name.
Ecological Succession of Biofilm in Dental Plaque
PeriodontologyEcological Succession of Biofilm in Dental Plaque
Overview of Biofilm Formation
Biofilm formation on tooth surfaces is a dynamic process characterized by
ecological succession, where microbial communities evolve over time. This
process transitions from an early aerobic environment dominated by gram-positive
facultative species to a later stage characterized by a highly oxygen-deprived
environment where gram-negative anaerobic microorganisms predominate.
Stages of Biofilm Development
Initial Colonization:
Environment: The initial phase occurs in an aerobic
environment.
Primary Colonizers:
The first bacteria to colonize the pellicle-coated tooth surface
are predominantly gram-positive facultative microorganisms.
Key Species:
Actinomyces viscosus
Streptococcus sanguis
Characteristics:
These bacteria can thrive in the presence of oxygen and play a
crucial role in the establishment of the biofilm.
Secondary Colonization:
Environment: As the biofilm matures, the
environment becomes increasingly anaerobic due to the metabolic
activities of the initial colonizers.
Secondary Colonizers:
These microorganisms do not initially colonize clean tooth
surfaces but adhere to the existing bacterial cells in the plaque
mass.
Key Species:
Prevotella intermedia
Prevotella loescheii
Capnocytophaga spp.
Fusobacterium nucleatum
Porphyromonas gingivalis
Coaggregation:
Secondary colonizers adhere to primary colonizers through a
process known as coaggregation, which involves specific interactions
between bacterial cells.
Coaggregation Examples:
Coaggregation is a critical mechanism that facilitates the
establishment of complex microbial communities within the biofilm.
Well-Known Examples:
Fusobacterium nucleatum with Streptococcus sanguis
Prevotella loescheii with Actinomyces viscosus
Capnocytophaga ochracea with Actinomyces viscosus
Implications of Ecological Succession
Microbial Diversity: The transition from gram-positive
to gram-negative organisms reflects an increase in microbial diversity and
complexity within the biofilm.
Pathogenic Potential: The accumulation of anaerobic
gram-negative bacteria is associated with the development of periodontal
diseases, as these organisms can produce virulence factors that contribute
to tissue destruction and inflammation.
Biofilm Stability: The interactions between different
bacterial species through coaggregation enhance the stability and resilience
of the biofilm, making it more challenging to remove through mechanical
cleaning.
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Subgingival and Supragingival Calculus
Overview of Calculus Formation
Calculus, or tartar, is a hardened form of dental plaque that can form on
both supragingival (above the gum line) and subgingival (below the gum line)
surfaces. Understanding the differences between these two types of calculus is
essential for effective periodontal disease management.
Subgingival Calculus
Color and Composition:
Appearance: Subgingival calculus is typically dark
green or dark brown in color.
Causes of Color:
The dark color is likely due to the presence of matrix
components that differ from those found in supragingival calculus.
It is influenced by iron heme pigments that are associated with
the bleeding of inflamed gingiva, reflecting the inflammatory state
of the periodontal tissues.
Formation Factors:
Matrix Components: The subgingival calculus matrix
contains blood products, which contribute to its darker coloration.
Bacterial Environment: The subgingival environment
is typically more anaerobic and harbors different bacterial species
compared to supragingival calculus.
Supragingival Calculus
Formation Factors:
Dependence on Plaque and Saliva:
The degree of supragingival calculus formation is primarily
influenced by the amount of bacterial plaque present and the
secretion of salivary glands.
Increased plaque accumulation leads to greater calculus
formation.
Inorganic Components:
Source: The inorganic components of supragingival
calculus are mainly derived from saliva.
Composition: These components include minerals such
as calcium and phosphate, which contribute to the calcification process
of plaque.
Comparison of Inorganic Components
Supragingival Calculus:
Inorganic components are primarily sourced from saliva, which
contains minerals that facilitate the formation of calculus on the tooth
surface.
Subgingival Calculus:
In contrast, the inorganic components of subgingival calculus are
derived mainly from crevicular fluid (serum transudate), which seeps
into the gingival sulcus and contains various proteins and minerals from
the bloodstream.
Cryosurgery
Oral and Maxillofacial SurgeryCryosurgery
Cryosurgery is a medical technique that utilizes extreme
rapid cooling to freeze and destroy tissues. This method is particularly
effective for treating various conditions, including malignancies, vascular
tumors, and aggressive tumors such as ameloblastoma. The process involves
applying very low temperatures to induce localized tissue destruction while
minimizing damage to surrounding healthy tissues.
Mechanism of Action
The effects of rapid freezing on tissues include:
Reduction of Intracellular Water:
Rapid cooling causes water within the cells to freeze, leading to a
decrease in intracellular water content.
Cellular and Cell Membrane Shrinkage:
The freezing process results in the shrinkage of cells and their
membranes, contributing to cellular damage.
Increased Concentrations of Intracellular Solutes:
As water is removed from the cells, the concentration of solutes
(such as proteins and electrolytes) increases, which can disrupt
cellular function.
Formation of Ice Crystals:
Both intracellular and extracellular ice crystals form during the
freezing process. The formation of these crystals can puncture cell
membranes and disrupt cellular integrity, leading to cell death.
Cryosurgery Apparatus
The equipment used in cryosurgery typically includes:
Storage Bottles for Pressurized Liquid Gases:
Liquid Nitrogen: Provides extremely low
temperatures of approximately -196°C, making it highly
effective for cryosurgery.
Liquid Carbon Dioxide or Nitrous Oxide: These gases
provide temperatures ranging from -20°C to -90°C, which
can also be used for various applications.
Pressure and Temperature Gauge:
This gauge is essential for monitoring the pressure and temperature
of the cryogenic gases to ensure safe and effective application.
Probe with Tubing:
A specialized probe is used to direct the pressurized gas to the
targeted tissues, allowing for precise application of the freezing
effect.
Treatment Parameters
Time and Temperature: The specific time and temperature
used during cryosurgery depend on the depth and extent of the tumor being
treated. The clinician must carefully assess these factors to achieve
optimal results while minimizing damage to surrounding healthy tissues.
Applications
Cryosurgery is applied in the treatment of various conditions, including:
Malignancies: Used to destroy cancerous tissues in
various organs.
Vascular Tumors: Effective in treating tumors that have
a significant blood supply.
Aggressive Tumors: Such as ameloblastoma, where rapid
and effective tissue destruction is necessary.
Types of Crying
PedodonticsTypes of Crying
Obstinate Cry:
Characteristics: This cry is loud, high-pitched,
and resembles a siren. It often accompanies temper tantrums, which may
include kicking and biting.
Emotional Response: It reflects the child's
external response to anxiety and frustration.
Physical Manifestation: Typically involves a lot of
tears and convulsive sobbing, indicating a high level of distress.
Frightened Cry:
Characteristics: This cry is not about getting what
the child wants; instead, it arises from fear that overwhelms the
child's ability to reason.
Physical Manifestation: Usually involves small
whimpers, indicating a more subdued response compared to the obstinate
cry.
Hurt Cry:
Characteristics: This cry is a reaction to physical
discomfort or pain.
Physical Manifestation: It may start with a single
tear that runs down the child's cheek without any accompanying sound or
resistance, indicating a more internalized response to pain.
Compensatory Cry
Characteristics:
This type of cry is not a traditional cry; rather, it is a sound
that the child makes in response to a specific stimulus, such as the
sound of a dental drill.
It is characterized by a constant whining noise rather than the
typical crying sounds associated with distress.
Physical Manifestation:
There are no tears or sobs associated with this cry. The child
does not exhibit the typical signs of emotional distress that
accompany other types of crying.
The sound is directly linked to the presence of the stimulus
(e.g., the drill). When the stimulus stops, the whining also ceases.
Emotional Response:
The compensatory cry may indicate a child's attempt to cope with
discomfort or fear in a situation where they feel powerless or
anxious. It serves as a way for the child to express their
discomfort without engaging in more overt forms of crying.