NEET MDS Synopsis
The pancreas
PhysiologyThe pancreas
The pancreas consists of clusters if endocrine cells (the islets of Langerhans) and exocrine cells whose secretions drain into the duodenum.
Pancreatic fluid contains:
sodium bicarbonate (NaHCO3). This neutralizes the acidity of the fluid arriving from the stomach raising its pH to about 8.
pancreatic amylase. This enzyme hydrolyzes starch into a mixture of maltose and glucose.
pancreatic lipase. The enzyme hydrolyzes ingested fats into a mixture of fatty acids and monoglycerides. Its action is enhanced by the detergent effect of bile.
4 zymogens— proteins that are precursors to active proteases. These are immediately converted into the active proteolytic enzymes:
trypsin. Trypsin cleaves peptide bonds on the C-terminal side of arginines and lysines.
chymotrypsin. Chymotrypsin cuts on the C-terminal side of tyrosine, phenylalanine, and tryptophan residues (the same bonds as pepsin, whose action ceases when the NaHCO3 raises the pH of the intestinal contents).
elastase. Elastase cuts peptide bonds next to small, uncharged side chains such as those of alanine and serine.
carboxypeptidase. This enzyme removes, one by one, the amino acids at the C-terminal of peptides.
nucleases. These hydrolyze ingested nucleic acids (RNA and DNA) into their component nucleotides.
The secretion of pancreatic fluid is controlled by two hormones:
secretin, which mainly affects the release of sodium bicarbonate, and
cholecystokinin (CCK), which stimulates the release of the digestive enzymes.
Vitiligo
General Pathology
Vitiligo is an autoimmune destruction of melanocytes resulting in areas of depigmentation.
- commonly associated with other autoimmune diseases such as pernicious anemia, Addison's disease, and thyroid disease.
- common in the Black population
Types of Brain Injury
General SurgeryTypes of Brain Injury
Brain injuries can be classified into two main categories: primary and
secondary injuries. Understanding these types is crucial for effective diagnosis
and management.
1. Primary Brain Injury
Definition: Primary brain injury occurs at the moment
of impact. It results from the initial mechanical forces applied to the
brain and can lead to immediate damage.
Examples:
Contusions: Bruising of brain tissue.
Lacerations: Tears in brain tissue.
Concussions: A temporary loss of function due to trauma.
Diffuse axonal injury: Widespread damage to the brain's white
matter.
2. Secondary Brain Injury
Definition: Secondary brain injury occurs after the
initial impact and is often preventable. It results from a cascade of
physiological processes that can exacerbate the initial injury.
Principal Causes:
Hypoxia: Reduced oxygen supply to the brain, which
can worsen brain injury.
Hypotension: Low blood pressure can lead to
inadequate cerebral perfusion.
Raised Intracranial Pressure (ICP): Increased
pressure within the skull can compress brain tissue and reduce blood
flow.
Reduced Cerebral Perfusion Pressure (CPP):
Insufficient blood flow to the brain can lead to ischemia.
Pyrexia: Elevated body temperature can increase
metabolic demands and worsen brain injury.
Glasgow Coma Scale (GCS)
The Glasgow Coma Scale is a clinical tool used to assess a patient's level of
consciousness and neurological function. It consists of three components: eye
opening, verbal response, and motor response.
Eye Opening (E)
Spontaneous: 4
To verbal command: 3
To pain stimuli: 2
No eye opening: 1
Verbal Response (V)
Normal, oriented: 5
Confused: 4
Inappropriate words: 3
Sounds only: 2
No sounds: 1
Motor Response (M)
Obeys commands: 6
Localizes to pain: 5
Withdrawal flexion: 4
Abnormal flexion (decorticate): 3
Extension (decerebrate): 2
No motor response: 1
Scoring
Best Possible Score: 15/15 (fully alert and oriented)
Worst Possible Score: 3/15 (deep coma or death)
Intubated Cases: For patients who are intubated, the
verbal score is recorded as "T."
Intubation Indication: Intubation should be performed
if the GCS score is less than or equal to 8.
Additional Assessments
Pupil Examination
Pupil Reflex: Assess size and light response.
Uncal Herniation: In cases of mass effect on the
ipsilateral side, partial third nerve dysfunction may be noted,
characterized by a larger pupil with sluggish reflex.
Hutchinson Pupil: As third nerve compromise increases,
the ipsilateral pupil may become fixed and dilated.
Signs of Base of Skull Fracture
Raccoon Eyes: Bilateral periorbital hematoma,
indicating possible skull base fracture.
Battle’s Sign: Bruising over the mastoid process,
suggesting a fracture of the temporal bone.
CSF Rhinorrhea or Otorrhea: Leakage of cerebrospinal
fluid from the nose or ear, indicating a breach in the skull base.
Hemotympanum: Blood in the tympanic cavity, often seen
with ear bleeding.
WAR Lines - Impacted Mandibular Third Molars
Oral and Maxillofacial SurgeryWAR Lines in the Assessment of Impacted Mandibular Third Molars
The WAR lines, as described by George Winter, are a set of three imaginary
lines used in radiographic analysis to determine the position and depth of
impacted mandibular third molars (wisdom teeth). These lines help clinicians
assess the orientation and surgical approach needed for extraction. The three
lines are color-coded: white, amber, and red, each serving a specific purpose in
evaluating the impacted tooth.
1. White Line
Description: The white line is drawn along the occlusal
surfaces of the erupted mandibular molars and extended posteriorly over the
third molar region.
Purpose: This line helps visualize the axial
inclination of the impacted third molar.
Clinical Significance:
If the occlusal surface of the vertically impacted third molar is
parallel to the white line, it indicates that the tooth is positioned in
a vertical orientation.
Deviations from this line can suggest different angulations of
impaction (e.g., mesioangular, distoangular).
2. Amber Line
Description: The amber line is drawn from the surface
of the bone on the distal aspect of the third molar to the crest of the
interdental septum between the first and second mandibular molars.
Purpose: This line represents the margin of the
alveolar bone covering the third molar.
Clinical Significance:
The amber line indicates the amount of bone that will need to be
removed to access the impacted tooth.
After removing the soft tissue, only the portion of the impacted
tooth structure that lies above the amber line will be visible, guiding
the surgeon in determining the extent of bone removal required for
extraction.
3. Red Line
Description: The red line is an imaginary line drawn
perpendicular to the amber line, extending to an imaginary point of
application of the elevator, typically at the cementoenamel junction (CEJ)
on the mesial surface of the impacted tooth.
Exceptions: In cases of distoangular impaction, the
point of application may be at the CEJ on the distal aspect of the tooth.
Purpose: The length of the red line indicates the depth
of the impacted tooth.
Clinical Significance:
This measurement helps the surgeon understand how deep the impacted
tooth is positioned relative to the surrounding bone and soft tissue.
It assists in planning the surgical approach and determining the
necessary instruments for extraction.
Cardiac Output
Physiology
Cardiac Output:
Minute Volume = Heart Rate X Stroke Volume
Heart rate, HR at rest = 65 to 85 bpm
Each heartbeat at rest takes about .8 sec. of which .4 sec. is quiescent period.
Stroke volume, SV at rest = 60 to 70 ml.
Heart can increase both rate and volume with exercise. Rate increase is limited due to necessity of minimum ventricular diastolic period for filling. Upper limit is usually put at about 220 bpm. Maximum heart rate calculations are usually below 200. Target heart rates for anaerobic threshold are about 85 to 95% of maximum.
Terms:
End Diastolic Volume, EDV - the maximum volume of the ventricles achieved at the end of ventricular diastole. This is the amount of blood the heart has available to pump. If this volume increases the cardiac output increases in a healthy heart.
End Systolic Volume, ESV - the minimum volume remaining in the ventricle after its systole. If this volume increases it means less blood has been pumped and the cardiac output is less.
EDV - ESV = SV
SV / EDV = Ejection Fraction The ejection fraction is normally around 50% at rest and will increase during strenuous exercise in a healthy heart. Well trained athletes may have ejection fractions approaching 70% in the most strenuous exercise.
Isovolumetric Contraction Phase - a brief period at the beginning of ventricular systole when all valves are closed and ventricular volume remains constant. Pressure has risen enough in the ventricle to close the AV valves but not enough to open the semilunar valves and cause ejection of blood.
Isovolumetric Relaxation Phase - a brief period at the beginning of ventricular diastole when all valves are closed and ventricular volume is constant. Pressure in the ventricle has lowered producing closure of the semilunar valves but not opening the AV valves to begin pulling blood into the ventricle.
Dicrotic Notch - the small increase in pressure of the aorta or other artery seen when recording a pulse wave. This occurs as blood is briefly pulled back toward the ventricle at the beginning of diastole thus closing the semilunar valves.
Preload - This is the pressure at the end of ventricular diastole, at the beginning of ventricular systole. It is proportional to the End Diastolic Volume (EDV), i.e. as the EDV increases so does the preload of the heart. Factors which increase the preload are: increased total blood volume, increased venous tone and venous return, increased atrial contraction, and the skeletal muscular pump.
Afterload - This is the impedence against which the left ventricle must eject blood, and it is roughly proportional to the End Systolic Volume (ESV). When the peripheral resistance increases so does the ESV and the afterload of the heart.
The importance of these parameters are as a measure of efficiency of the heart, which increases as the difference between preload and afterload increases
Bleeding Disorders
PhysiologyBleeding Disorders
A deficiency of a clotting factor can lead to uncontrolled bleeding.
The deficiency may arise because
not enough of the factor is produced or
a mutant version of the factor fails to perform properly.
Examples:
von Willebrand disease (the most common)
hemophilia A for factor 8 deficiency
hemophilia B for factor 9 deficiency.
hemophilia C for factor 11 deficiency
In some cases of von Willebrand disease, either a deficient level or a mutant version of the factor eliminates its protective effect on factor 8. The resulting low level of factor 8 mimics hemophilia A.
Diphenoxylate
Pharmacology
Diphenoxylate (present in Lomotil)
A meperidine congener
Not absorbed very well at recommended doses.
Very useful in the treatment of diarrhea.
Eosinophilia
General Pathology
Eosinophilia:
Causes
-Allergic disorders.
-Parasitic infection.
-Skin diseases.
-Pulmonary eosinophilia.
-Myeloproliferative lesions and Hodgkin's disease.