NEET MDS Synopsis
ANTIGEN-ANTIBODY REACTIONS
General Microbiology
ANTIGEN-ANTIBODY REACTIONS
I. NATURE OF ANTIGEN-ANTIBODY REACTIONS
A. Lock and Key Concept
The combining site of an antibody is located in the Fab portion of the molecule and is constructed from the hypervariable regions of the heavy and light chains. Antigen-antibody reactions is one of a key (i.e. the antigen) which fits into a lock (i.e. the antibody).
B. Non-covalent Bonds
The bonds that hold the antigen to the antibody combining site are all non-covalent in nature. These include hydrogen bonds, electrostatic bonds, Van der Waals forces and hydrophobic bonds.
C. Reversibility
Since antigen-antibody reactions occur via non-covalent bonds, they are by their nature reversible.
II. AFFINITY AND AVIDITY
A. Affinity
Antibody affinity is the strength of the reaction between a single antigenic determinant and a single combining site on the antibody. It is the sum of the attractive and repulsive forces operating between the antigenic determinant and the combining site of the antibody .
B. Avidity
Avidity is a measure of the overall strength of binding of an antigen with many antigenic determinants and multivalent antibodies. Avidity is influenced by both the valence of the antibody and the valence of the antigen. Avidity is more than the sum of the individual affinities.
III. SPECIFICITY AND CROSS REACTIVITY
A. Specificity
Specificity refers to the ability of an individual antibody combining site to react with only one antigenic determinant or the ability of a population of antibody molecules to react with only one antigen. In general, there is a high degree of specificity in antigen-antibody reactions.
B. Cross reactivity
Cross reactivity refers to the ability of an individual antibody combining site to react with more than one antigenic determinant or the ability of a population of antibody molecules to react with more than one antigen.
Growth and spread of tumours
General Pathology
Growth and spread of tumours
Growth in excess of normal is a feature of all tumours but extension to tissue away from the site of origin is a feature of malignant tumours.
Modes of spread of malignant tumours
- local, invasion. This is a feature of all malignant tumors and takes place along tissue spaces and facial planes
o Lymphatic spread. Most often seen in carcinomas. This can be in the form of
o Lymphatic permeation: Where the cells extend along the lymphatics as a solid core
o Lymphatic embolisation: Where a group of tumour cells break off and get carried to the draining mode
-Vascular spread : This is a common and early mode of spread for sarcomas but certain carcinomas like renal cell carcinoma and chorio carcinoma have a predilection to early vascular spread.
Vascular spread is most often due .to invasion of venous channels and can be by permeation or embolisation.
Lungs, liver, bones and brain are the common sites for vascular metastasis but
different tumours have different organ preference for metastasis, e.g. : Bronchogenic carcinoma often spreads to liver and adrenals.
-Body cavities and natural passages
o Gastrointestinal carcinomas spread to ovaries (Krukenberg’s tomour)
Carbonic anhydrase inhibitors
Pharmacology
Carbonic anhydrase inhibitors
Acetazolamide, Dichlorphenamide, Methazolamide, Ethoxzolamide
Mechanism of Action
1. Carbonic anhydrase (CA) facilitates excretion of H+ and recovery of bicarbonate by the proximal renal tubule and ciliary epithelium of the eye. Sodium is recovered in exchange for H+.
2. Inhibitors block CA block sodium recovery. A very mild diuresis is produced (this is really a side effect of their use in glaucoma) because relatively unimportant mechanism for Na recovery and because proximal tubule site means that other sodium recovery mechansims continue to process their normal fraction of the sodium load.
Dautrey Procedure
General SurgeryDautrey Procedure
The Dautrey procedure is a surgical intervention aimed at
preventing dislocation of the temporomandibular joint (TMJ) by creating a
mechanical obstacle that restricts abnormal forward translation of the condylar
head. This technique is particularly beneficial for patients who experience
recurrent TMJ dislocations or subluxations, especially when conservative
management strategies have proven ineffective.
Indications:
The Dautrey procedure is indicated for patients with a history of
recurrent TMJ dislocations. It is particularly useful when conservative
treatments, such as physical therapy or splint therapy, have failed to
provide adequate stabilization of the joint.
Surgical Technique:
Osteotomy of the Zygomatic Arch: The procedure
begins with an osteotomy, which involves surgically cutting the
zygomatic arch, the bony structure that forms the prominence of the
cheek.
Depressing the Zygomatic Arch: After the osteotomy,
the zygomatic arch is depressed in front of the condylar head. This
depression creates a physical barrier that acts as an obstacle to the
forward movement of the condylar head during jaw opening or excessive
movement.
Stabilization: The newly positioned zygomatic arch
limits the range of motion of the condylar head, thereby reducing the
risk of dislocation during functional activities such as chewing or
speaking.
Mechanism of Action:
By altering the position of the zygomatic arch, the Dautrey
procedure effectively changes the biomechanics of the TMJ. The new
position of the zygomatic arch prevents the condylar head from
translating too far forward, which is a common cause of dislocation.
Postoperative Care:
Following the procedure, patients may require a period of recovery
and rehabilitation. This may include:
Dietary Modifications: Soft diet to minimize
stress on the TMJ during the healing process.
Pain Management: Use of analgesics to manage
postoperative discomfort.
Physical Therapy: Exercises to restore normal
function and range of motion in the jaw.
Outcomes:
The Dautrey procedure has been shown to be effective in preventing
recurrent TMJ dislocations. Patients often experience improved joint
stability and a better quality of life following the surgery. Successful
outcomes can lead to reduced pain, improved jaw function, and enhanced
overall satisfaction with treatment.
Principal heart sounds
Physiology
Principal heart sounds
1. S1: closure of AV valves;typically auscultated as a single sound
Clinical note: In certain circumstances, S1 may be accentuated. This occurs when the valve leaflets are “slammed” shut in early systole from a greater than normal distance because they have not had time to drift closer together. Three conditions that can result in an accentuated S1 are a shortened PR interval, mild mitral stenosis, and high cardiac-output states or tachycardia.
2. S2: closure of semilunar valves in early diastole , normally “split” during inspiration . S2: best appreciated in the 2nd or 3rd left intercostal space
Clinical note: Paradoxical or “reversed” splitting occurs when S2 splitting occurs with expiration and disappears on inspiration. Moreover, in paradoxical splitting, the pulmonic valve closes before the aortic valve, such that P2 precedes A2. The most common cause is left bundle branch block (LBBB). In LBBB, depolarization of the left ventricle is impaired, resulting in delayed left ventricular contraction and aortic valve closure.
3. S3: ventricular gallop, presence reflects volume-overloaded state
Clinical note: An S3 is usually caused by volume overload in congestive heart failure. It can also be associated with valvular disease, such as advanced mitral regurgitation, in which the “regurgitated” blood increases the rate of ventricular filling during early diastole.
4. S4: atrial gallop, S4: atrial contraction against a stiff ventricle, often heard after an acute myocardial infarction.
Clinical note: An S4 usually indicates decreased ventricular compliance (i.e., the ventricle does not relax as easily), which is commonly associated with ventricular hypertrophy or myocardial ischemia. An S4 is almost always present after an acute myocardial infarction. It is loudest at the apex with the patient in the left lateral decubitus position (lying on their left side).
Types of Head Injury
General SurgeryTypes of Head Injury
1. Extradural Hematoma (EDH)
Overview
Demographics: Most common in young male patients.
Association: Always associated with skull fractures.
Injured Vessel: Middle meningeal artery.
Common Site of Injury: Temporal bone at the pterion
(the thinnest part of the skull), which overlies the middle meningeal
artery.
Location of Hematoma: Between the bone and the dura
mater.
Other Common Sites
Frontal fossa
Posterior fossa
May occur following disruption of major dural venous sinus.
Classical Presentation
Initial Injury: Followed by a lucid interval where the
patient may only complain of a headache.
Deterioration: After minutes to hours, rapid
deterioration occurs, leading to:
Contralateral hemiparesis
Reduced consciousness level
Ipsilateral pupillary dilatation (due to herniation)
Imaging
CT Scan: Shows a lentiform (lens-shaped or biconvex)
hyperdense lesion between the brain and skull.
Treatment
Surgical Intervention: Immediate surgical evacuation
via craniotomy.
Mortality Rate: Overall mortality is 18% for all cases
of EDH, but only 2% for isolated EDH.
2. Acute Subdural Hematoma (ASDH)
Overview
Location: Accumulates in the space between the dura and
arachnoid.
Injury Mechanism: Associated with cortical vessel
disruption and brain laceration.
Primary Brain Injury: Often associated with primary
brain injury.
Presentation
Consciousness: Impaired consciousness from the time of
impact.
Imaging
CT Scan: Appears hyperdense, with hematoma spreading
diffusely and having a concavo-convex appearance.
Treatment
Surgical Intervention: Evacuation via craniotomy.
Mortality Rate: Approximately 40%.
3. Chronic Subdural Hematoma (CSDH)
Overview
Demographics: Most common in patients on anticoagulants
and antiplatelet agents.
History: Often follows a minor head injury weeks to
months prior.
Pathology: Due to the tear of bridging veins leading to
ASDH, which is clinically silent. As the hematoma breaks down, it increases
in volume, causing mass effect on the underlying brain.
Clinical Features
Symptoms may include:
Headache
Cognitive decline
Focal neurological deficits (FND)
Seizures
Important to exclude endocrine, hypoxic, and metabolic causes in this
group.
Imaging
CT Scan Appearance:
Acute blood (0–10 days): Hyperdense
Subacute blood (10 days to 2 weeks): Isodense
Chronic (> 2 weeks): Hypodense
Treatment
Surgical Intervention: Bur hole evacuation rather than
craniotomy.
Anesthesia: Elderly patients can often undergo surgery
under local anesthesia, despite comorbidities.
4. Subarachnoid Hemorrhage (SAH)
Overview
Causes: Most commonly due to aneurysms for spontaneous
SAH, but trauma is the most common cause overall.
Management: Conservative treatment is often employed
for trauma cases.
5. Cerebral Contusions
Overview
Definition: Bruising of the brain tissue due to trauma.
Mechanism: Often occurs at the site of impact (coup)
and the opposite side (contrecoup).
Symptoms: Can range from mild confusion to severe
neurological deficits depending on the extent of the injury.
Imaging
CT Scan: May show areas of low attenuation (hypodense)
or high attenuation (hyperdense) depending on the age of the contusion.
Treatment
Management: Depends on the severity and associated
injuries; may require surgical intervention if there is significant mass
effect.
Transpalatal Arch
OrthodonticsTranspalatal Arch (TPA) is an orthodontic appliance used
primarily in the upper arch to provide stability, maintain space, and facilitate
tooth movement. It is a fixed appliance that connects the maxillary molars
across the palate, and it is commonly used in various orthodontic treatments,
particularly in conjunction with other appliances.
Components of the Transpalatal Arch
Main Wire:
The TPA consists of a curved wire that spans the palate, typically
made of stainless steel or a similar material. The wire is shaped to fit
the contour of the palate and is usually 0.036 inches in diameter.
Attachments:
The ends of the wire are attached to the bands or brackets on the
maxillary molars. These attachments can be soldered or welded to the
bands, ensuring a secure connection.
Adjustment Mechanism:
Some TPAs may include loops or bends that can be adjusted to apply
specific forces to the teeth, allowing for controlled movement.
Functions of the Transpalatal Arch
Stabilization:
The TPA provides anchorage and stability to the posterior teeth,
preventing unwanted movement during orthodontic treatment. It helps
maintain the position of the molars and can prevent them from drifting.
Space Maintenance:
The TPA can be used to maintain space in the upper arch, especially
after the premature loss of primary molars or in cases of crowding.
Tooth Movement:
The appliance can facilitate the movement of teeth, particularly the
molars, by applying gentle forces. It can be used to correct crossbites
or to expand the arch.
Support for Other Appliances:
The TPA can serve as a support structure for other orthodontic
appliances, such as expanders or functional appliances, enhancing their
effectiveness.
Indications for Use
Space Maintenance: To hold space for permanent teeth
when primary teeth are lost prematurely.
Crossbite Correction: To help correct posterior
crossbites by repositioning the molars.
Arch Expansion: In conjunction with other appliances,
the TPA can assist in expanding the dental arch.
Stabilization During Treatment: To provide anchorage
and prevent unwanted movement of the molars during orthodontic treatment.
Advantages of the Transpalatal Arch
Fixed Appliance: Being a fixed appliance, the TPA does
not require patient compliance, ensuring consistent force application.
Versatility: The TPA can be used in various treatment
scenarios, making it a versatile tool in orthodontics.
Minimal Discomfort: Generally, the TPA is
well-tolerated by patients and does not cause significant discomfort.
Limitations of the Transpalatal Arch
Limited Movement: The TPA primarily affects the molars
and may not be effective for moving anterior teeth.
Adjustment Needs: While the TPA can be adjusted, it may
require periodic visits to the orthodontist for modifications.
Oral Hygiene: As with any fixed appliance, maintaining
oral hygiene can be more challenging, and patients must be diligent in their
oral care.
Management of H. Pylori Infection and ZE Syndrome
Pharmacology
Management of H. Pylori Infection
- Gram – rod
- Causes erosion of protective epithelial cells -> gastritis or peptic ulcer
H2 antagonist or PPI + Abx
- Metronidazole or amoxicillin/clarithromycin
- PPI + 2 or 3 antimicrobials is standard
- Ex: Ranitidine + Peptobismol + Clarithromycin + Amoxicillin 7-14 days
-Add bismuth if resistant H. pylori
- Ex: PPI + BMT (Bismuth + Metronidazole + tetracycline) 7days
Treatment for ZE Syndrome
- Gastrinoma of the duodenum or pancreas
-Elevated gastrin levels- Peptic/gastric ulcers
- Treatment
High dose PPI until resorting to surgery or chemotherapy for tumor removal