NEET MDS Synopsis
The Laryngopharynx
AnatomyThe Laryngopharynx
The laryngeal part of the pharynx lies posterior to the larynx.
It extends from the superior border of the epiglottis to the inferior border of the cricoid cartilage, where it narrows to become continuous with the oesophagus.
Posteriorly, the laryngopharynx is related to the bodies of C4 to C6 vertebrae.
Its posterior and lateral walls are formed by the middle and inferior constrictor muscles, with the palatopharyngeus and stylopharyngeus internally.
The laryngopharynx communicates with the larynx through the aditus or inlet of the larynx.
The piriform recess is a small, pear-shaped depression of the laryngopharyngeal cavity on each side of the inlet of the larynx.
Blood-Lymphatic Pathology
General Pathology
Blood-Lymphatic Pathology
Disorders of primary hemostasis
1. General characteristics of disorders of primary hemostasis (due to problems of blood vessels or platelets):
a. Occur early in life.
b. Unlike secondary hemostasis, bleeding occurs in more superficial areas such as skin and mucous membranes rather than in secondary hemostasis.
c. Signs include petechiae.
d. Can be caused by vascular and platelet abnormalities or alterations in the plasma proteins required for adhesion of platelets to vascular subendothelium.
e. Laboratory findings include prolonged bleeding time, as seen in platelet disorders.
2. Vascular abnormalities
Scurvy
(1) Caused by a vitamin C deficiency leading to decreased synthesis of collagen. Note: vitamin C is necessary for the formation of collagen via hydroxylation of lysine and proline.
(2) Symptoms include:
- Delayed wound healing.
- Petechiae and ecchymosis.
- Gingival bleeding, swelling, and ulcerations.
3. Platelet abnormalities
a. Thrombocytopenia
(1) Characterized by a decreased number of platelets.
(2) The most common type of bleeding disorder.
(3) Can be caused by a number of diseases, such as irradiation, acute leukemia, disseminated intravascular coagulation (DIC), or idiopathic thrombocytopenic purpura (ITP).
b. Thrombocytopenic purpura
(1) Idiopathic: An autoimmune disease characterized by the presence of autoantibodies against platelets, resulting in the removal of platelets by splenic macrophages.
(2) May also be drug-induced.
Disorders of secondary hemostasis
1. General characteristics of disorders of secondary hemostasis (due to problems with clotting factors):
a. Symptoms occur later in life.
b. As compared to disorders of primary hemostasis, bleeding occurs in deeper areas and larger vessels (i.e., joint spaces).
c. Laboratory findings include abnormal:
- Partial thromboplastin time (PTT)—measures the intrinsic and common clotting pathway (i.e., tests all coagulation factors except factor 7).
- Prothrombin time (PT)—measures the extrinsic pathway.
- Does not affect the bleeding time.
Hemophilia
a. Caused by a deficiency of particular clotting factor(s).
b. All types of hemophilia affect the intrinsic pathway of the clotting cascade.
c. Signs and symptoms include:
- Prolonged PTT.
- Continuous bleeding from cuts or trauma, which can lead to excessive blood loss.
- Bleeding into joint cavities (hemarthroses) and muscle.
Two types:
(1) Hemophilia A (classic hemophilia)
- Caused by a deficiency of factor 8 (antihemophilic factor).
- Transmission: sex-linked recessive—only occurs in males; however, females can be carriers.
(2) Hemophilia B (Christmas disease)
- Caused by a deficiency of factor 9 (plasma thromboplastin).
- Transmission: sex-linked recessive—only occurs in males; however, females can be carriers.
- Lower incidence rate than hemophilia A.
(3). Vitamin K deficiency
- Causes include malnutrition and malabsorption of fats.
- A decrease in clotting factors 2, 7, 9, and 10 and prothrombin is observed.
- Prolonged PT.
Disorders of both primary and secondary hemostasis
1. von Willebrand’s disease
a. Characterized by a defective von Willebrand’s factor (vWF). Defective vWF affects both primary hemostasis by affecting platelet adhesion to
endothelium, and secondary hemostasis, by a defective factor 8.
b. Genetic transmission: autosomal dominant.
It is the most common hereditary bleeding disorder.
2. Liver disease—disease of the liver results in a decreased production of coagulation factors and therefore can lead to problems with hemostasis.
3. Disseminated intravascular coagulation a condition in which clots form throughout the vasculature. This uses up all available clotting factors and platelets, resulting in problems with bleeding.
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.
The Pharynx
AnatomyThe Pharynx
The pharynx is the continuation of the digestive system from the oral cavity.
It is a funnel-shaped fibromuscular tube that is the common route for both food and air.
The pharynx is located posterior to the nasal and oral cavities, and the larynx.
For the convenience of description, the pharynx is divided into three parts: (1) the nasopharynx, posterior to the nose and superior to the soft palate; (2) the oropharynx, posterior to the mouth; and (3) the laryngopharynx, posterior to the larynx.
The pharynx is about 15 cm long.
It extends from the base of the skull to the inferior border of the cricoid cartilage anteriorly, and to the inferior border of C6 vertebra posteriorly.
It is widest (about 5 cm) opposite the hyoid bone and narrowest (about 1.5) at its inferior end, where it is continuous with the oesophagus.
The posterior wall of the pharynx lies against the prevertebral fascia, with the potential retropharyngeal space between them.
General chromosome abnormalities
General Pathology
General chromosome abnormalities
The normal human cell contains 46 chromosomes, including 22 homologous pairs of autosomes and one pair of sex chromosomes (XX for female and XY for male). A somatic cell is diploid, containing 46 chromosomes. Gametes are haploid, containing 23 chromosomes.
Aneuploidy
(a) Any deviation in the number of chromosomes, whether fewer or more, from the normal haploid number of chromosomes.
(b) Nondisjunction—a common cause of aneuploidy. It is the failure of chromosomes to pass to separate cells during meiotic or mitotic cell division.
(c) Often seen in malignant tumors.
Deletion: loss of a sequence of DNA from a chromosome.
Translocation: the separation of a chromosome and the attachment of the area of separation to another chromosome.
Histology of the Periodontal Ligament (PDL)
Dental Anatomy
Histology of the Periodontal Ligament (PDL)
Embryogenesis of the periodontal ligament
The PDL forms from the dental follicle shortly after root development begins
The periodontal ligament is characterized by connective tissue. The thinnest portion is at the middle third of the root. Its width decreases with age. It is a tissue with a high turnover rate.
FUNCTIONS OF PERIODONTIUM
Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)
The following cells can be identified in the periodontal ligament:
a) Osteoblasts and osteoclasts b) Fibroblasts, c) Epithelial cells
Rests of Malassez
d) Macrophages
e) Undifferentiated cells
f) Cementoblasts and cementoclasts (only in pathologic conditions)
The following types of fibers are found in the PDL
-Collagen fibers: groups of fibers
-Oxytalan fibers: variant of elastic fibers, perpendicular to teeth, adjacent to capillaries
-Eluanin: variant of elastic fibers
Ground substance
PERIODONTAL LIGAMENT FIBERS
Principal fibers
These fibers connect the cementum to the alveolar crest. These are:
a. Alveolar crest group: below CE junction, downward, outward
b. Horizontal group: apical to ACG, right angle
c. Oblique group: numerous, coronally to bone, oblique direction
d. Apical group: around the apex, base of socket
e. Interradicular group: multirooted teeth
Gingival ligament fibers
This group is not strictly related to periodontium. These fibers are:
a. Dentogingival: numerous, cervical cementum to f/a gingiva
b. Alveologingival: bone to f/a gingiva
c. Circular: around neck of teeth, free gingiva
d. Dentoperiosteal: cementum to alv. process or vestibule (muscle)
e. Transseptal: cementum between adjacent teeth, over the alveolar crest
Blood supply of the PDL
The PDL gets its blood supply from perforating arteries (from the cribriform plate of the bundle bone). The small capillaries derive from the superior & inferior alveolar arteries. The blood supply is rich because the PDL has a very high turnover as a tissue. The posterior supply is more prominent than the anterior. The mandibular is more prominent than the maxillary.
Nerve supply
The nerve supply originates from the inferior or the superior alveolar nerves. The fibers enter from the apical region and lateral socket walls. The apical region contains more nerve endings (except Upper Incisors)
Dentogingival junction
This area contains the gingival sulcus. The normal depth of the sulcus is 0.5 to 3.0 mm (mean: 1.8 mm). Depth > 3.0 mm is considered pathologic. The sulcus contains the crevicular fluid
The dentogingival junction is surfaced by:
1) Gingival epithelium: stratified squamous keratinized epithelium 2) Sulcular epithelium: stratified squamous non-keratinized epithelium The lack of keratinization is probably due to inflammation and due to high turnover of this epithelium.
3) Junctional epithelium: flattened epithelial cells with widened intercellular spaces. In the epithelium one identifies neutrophils and monocytes.
Connective tissue
The connective tissue of the dentogingival junction contains inflammatory cells, especially polymorphonuclear neutrophils. These cells migrate to the sulcular and junctional epithelium.
The connective tissue that supports the sulcular epithelium is also structurally and functionally different than the connective tissue that supports the junctional epithelium.
Histology of the Col (=depression)
The col is found in the interdental gingiva. It is surfaced by epithelium that is identical to junctional epithelium. It is an important area because of the accumulation of bacteria, food debris and plaque that can cause periodontal disease.
Blood supply: periosteal vessels
Nerve supply: periodontal nerve fibers, infraorbital, palatine, lingual, mental, buccal
Ichthyosis vulgaris
General Pathology
Ichthyosis vulgaris is a genetic disease characterized by increased cohesiveness of the cells in the stratum corneum, resulting up in a piling up stratum corneum (scales like a fish).
Surgical Gut (Catgut)
Oral and Maxillofacial Surgery
Surgical Gut (Catgut)
Surgical gut, commonly known as catgut, is a type of
absorbable suture material derived from the intestines of animals, primarily
sheep and cattle. It has been widely used in surgical procedures due to its
unique properties, although it has certain limitations. Below is a detailed
overview of surgical gut, including its composition, properties, mechanisms of
absorption, and clinical applications.
Composition and Preparation
Source: Surgical gut is prepared from:
Submucosa of Sheep Small Intestine: This layer is
rich in collagen, which is essential for the strength and absorbability
of the suture.
Serosal Layer of Cattle Small Intestine: This layer
also provides collagen and is used in the production of surgical gut.
Collagen Content: The primary component of surgical gut
is collagen, which is treated with formaldehyde to enhance its properties.
This treatment helps stabilize the collagen structure and prolongs the
suture's strength.
Suture Characteristics:
Multifilament Structure: Surgical gut is a
capillary multifilament suture, meaning it consists of multiple strands
that can absorb fluids, which can be beneficial in certain surgical
contexts.
Smooth Surface: The sutures are machine-ground and
polished to yield a relatively smooth surface, resembling that of
monofilament sutures.
Sterilization
Sterilization Methods:
Ionizing Radiation: Surgical gut is typically
sterilized using ionizing radiation, which effectively kills pathogens
without denaturing the protein structure of the collagen.
Ethylene Oxide: This method can also be used for
sterilization, and it prolongs the absorption time of the suture, making
it suitable for specific applications.
Limitations of Autoclaving: Autoclaving is not suitable
for surgical gut because it denatures the protein, leading to a significant
loss of tensile strength.
Mechanism of Absorption
The absorption of surgical gut after implantation occurs through a twofold
mechanism primarily involving macrophages:
Molecular Bond Cleavage:
Acid hydrolytic and collagenolytic activities cleave the molecular
bonds in the collagen structure of the suture.
Digestion and Absorption:
Proteolytic enzymes further digest the collagen, leading to the
gradual absorption of the suture material.
Foreign Body Reaction: Due to its collagenous
composition, surgical gut stimulates a significant foreign body reaction in
the implanted tissue, which can lead to inflammation.
Rate of Absorption and Loss of Tensile Strength
Variability: The rate of absorption and loss of tensile
strength varies depending on the implantation site and the surrounding
tissue environment.
Premature Absorption: Factors that can lead to premature
absorption include:
Exposure to gastric secretions.
Presence of infection.
Highly vascularized tissues.
Conditions in protein-depleted patients.
Strength Loss Timeline:
Medium chromic gut loses about 33% of its original
strength after 7 days of implantation and about 67% after 28
days.
Types of Surgical Gut
Plain Gut:
Characteristics: Produces a severe tissue reaction
and loses tensile strength rapidly, making it less useful in surgical
applications.
Applications: Limited due to its inflammatory
response and quick absorption.
Chromic Gut:
Treatment: Treated with chromium salts to increase
tensile strength and resistance to digestion while decreasing tissue
reactivity.
Advantages: Provides a more controlled absorption
rate and is more suitable for surgical use compared to plain gut.
Handling Characteristics
Good Handling: Surgical gut generally exhibits good
handling characteristics, allowing for easy manipulation during surgical
procedures.
Weakness When Wet: It swells and weakens when wet,
which can affect knot security and overall performance during surgery.
Disadvantages
Intense Inflammatory Reaction: Surgical gut can provoke
a significant inflammatory response, which may complicate healing.
Variability in Strength Loss: The unpredictable rate of
loss of tensile strength can be a concern in surgical applications.
Capillarity: The multifilament structure can absorb
fluids, which may lead to increased tissue reaction and complications.
Sensitivity Reactions: Some patients, particularly
cats, may experience sensitivity reactions to surgical gut.
Clinical Applications
Use in Surgery: Surgical gut is used in various
surgical procedures, particularly in soft tissue closures where absorbable
sutures are preferred.
Adhesion Formation: The use of surgical gut is
generally unwarranted in situations where adhesion formation is desired due
to its inflammatory properties.