NEET MDS Synopsis
INNATE (NON-SPECIFIC) IMMUNITY
General Microbiology
INNATE (NON-SPECIFIC) IMMUNITY
The elements of the innate (non-specific) immune system include anatomical barriers, secretory molecules and cellular components.
Among the mechanical anatomical barriers are the skin and internal epithelial layers, the movement of the intestines and the oscillation of broncho-pulmonary cilia.
Associated with these protective surfaces are chemical and biological agents.
A. Anatomical barriers to infections
1. Mechanical factors
The epithelial surfaces form a physical barrier that is very impermeable to most infectious agents. Thus, the skin acts as our first line of defense against invading organisms. The desquamation of skin epithelium also helps remove bacteria and other infectious agents that have adhered to the epithelial surfaces.
2. Chemical factors
Fatty acids in sweat inhibit the growth of bacteria. Lysozyme and phospholipase found in tears, saliva and nasal secretions can breakdown the cell wall of bacteria and destabilize bacterial membranes. The low pH of sweat and gastric secretions prevents growth of bacteria. Defensins (low molecular weight proteins) found in the lung and gastrointestinal tract have antimicrobial activity. Surfactants in the lung act as opsonins (substances that promote phagocytosis of particles by phagocytic cells).
3. Biological factors
The normal flora of the skin and in the gastrointestinal tract can prevent the colonization of pathogenic bacteria by secreting toxic substances or by competing with pathogenic bacteria for nutrients or attachment to cell surfaces.
B. Humoral barriers to infection
Humoral factors play an important role in inflammation, which is characterized by edema and the recruitment of phagocytic cells. These humoral factors are found in serum or they are formed at the site of infection.
1. Complement system – The complement system is the major humoral non-specific defense mechanism (see complement chapter). Once activated complement can lead to increased vascular permeability, recruitment of phagocytic cells, and lysis and opsonization of bacteria.
2. Coagulation system – Depending on the severity of the tissue injury, the coagulation system may or may not be activated. Some products of the coagulation system can contribute to the non-specific defenses because of their ability to increase vascular permeability and act as chemotactic agents for phagocytic cells. In addition, some of the products of the coagulation system are directly antimicrobial. For example, beta-lysin, a protein produced by platelets during coagulation can lyse many Gram positive bacteria by acting as a cationic detergent.
3. Lactoferrin and transferrin – By binding iron, an essential nutrient for bacteria, these proteins limit bacterial growth.
4. Interferons – Interferons are proteins that can limit virus replication in cells.
5. Lysozyme – Lysozyme breaks down the cell wall of bacteria.
6. Interleukin -1 – Il-1 induces fever and the production of acute phase proteins, some of which are antimicrobial because they can opsonize bacteria.
C. Cellular barriers to infection
Part of the inflammatory response is the recruitment of polymorphonuclear eosinophiles and macrophages to sites of infection. These cells are the main line of defense in the non-specific immune system.
1. Neutrophils – Polymorphonuclear cells are recruited to the site of infection where they phagocytose invading organisms and kill them intracellularly. In addition, PMNs contribute to collateral tissue damage that occurs during inflammation.
2. Macrophages – Tissue macrophages and newly recruited monocytes , which differentiate into macrophages, also function in phagocytosis and intracellular killing of microorganisms. In addition, macrophages are capable of extracellular killing of infected or altered self target cells. Furthermore, macrophages contribute to tissue repair and act as antigen-presenting cells, which are required for the induction of specific immune responses.
3. Natural killer (NK) and lymphokine activated killer (LAK) cells – NK and LAK cells can nonspecifically kill virus infected and tumor cells. These cells are not part of the inflammatory response but they are important in nonspecific immunity to viral infections and tumor surveillance.
4. Eosinophils – Eosinophils have proteins in granules that are effective in killing certain parasites.
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.
Cells, cytoplasm, and organelles
PhysiologyCells, cytoplasm, and organelles:
Cytoplasm consists of a gelatinous solution and contains microtubules (which serve as a cell's cytoskeleton) and organelles
Cells also contain a nucleus within which is found DNA (deoxyribonucleic acid) in the form of chromosomes plus nucleoli (within which ribosomes are formed)
Organelles include:
Endoplasmic reticulum : 2 forms: smooth and rough; the surface of rough ER is coated with ribosomes; the surface of smooth ER is not , Functions include: mechanical support, synthesis (especially proteins by rough ER), and transport
Golgi complex consists of a series of flattened sacs (or cisternae) functions include: synthesis (of substances likes phospholipids), packaging of materials for transport (in vesicles), and production of lysosomes
Lysosome : membrane-enclosed spheres that contain powerful digestive enzymes , functions include destruction of damaged cells & digestion of phagocytosed materials
Mitochondria : have double-membrane: outer membrane & highly convoluted inner membrane
inner membrane has folds or shelf-like structures called cristae that contain elementary particles; these particles contain enzymes important in ATP production
primary function is production of adenosine triphosphate (ATP)
Ribosome-:composed of rRNA (ribosomal RNA) & protein , primary function is to produce proteins
Centrioles :paired cylindrical structures located near the nucleas , play an important role in cell division
Flagella & cilia - hair-like projections from some human cells
cilia are relatively short & numerous (e.g., those lining trachea)
a flagellum is relatively long and there's typically just one (e.g., sperm)
Villi Projections of cell membrane that serve to increase surface area of a cell (which is important, for example, for cells that line the intestine)
ENDOCRINE
Anatomy
ENDOCRINE
Endocrine glands have no ducts
They secrete into the blood from where the secretion (hormone) reaches a target cell
The following is a list of endocrine glands:
Hypophysis
Thyroid
Parathyroid
Adrenals
Islets of Langerhans
Pineal
Gonads
Hypophysis: Develops from oral ectoderm and nerve tissue, The oral part forms an upgrowth with an invagination (Rathke's pouch) The nervous part grows from the floor of the diencephalon - staying intact .The oral part separates from the mouth
Ectoderm – adenohypophysis - pars tuberalis
- pars distalis
- pars intermedia .
Diencephalon – neurohypophysis - pars nervosa .
- infundibulum
- median eminence
Rathke's pouch remains as Rathke's cysts
Pars Distalis: Forms 75% of the gland, The cells form cords, with fenestrated capillaries in-between
2 Cell types:
Chromophobes : 50% of the cells, do not stain lie in groups, they are resting chromophils
granules have been used
Chromophils: Stain
They can be subdivided according to their reaction with different stains
Acidophils (40%) :Cells have acidophilic granules in their cytoplasm. The cells are secretory.
They have a well developed EPR and Golgi apparatus.They have secretory granules.
subdivided into:
- Somatotropin cells: secrete somatotropin (growth hormone)
- Mammotropic cells: secrete prolactin
Basophils (10%) : These cells have basophilic granules in their cytoplasm and can be subdivided into:
Thyrotropin cells: secrete thyroid - stimulating hormone (TSH)
Corticotrophin cells: secrete adrenocorticotropic (ACTH)
Gonadotropic cells: secrete two hormones: Follicle stimulating hormone (FSH):
Stimulate follicle development and spermatogenesis
Luteinizing hormone (LH): Stimulate the formation of the corpus luteum and Leydig cells
Pars Tuberalis: Cells lie around the infundibulum . It is continuous with the pars distalis
Cells are cuboidal with no granules. Their function is unknown
Pars Intermedia: Poorly developed in the human. Follicles lined by cuboidal cells and filled with colloid are found Known as Rathke's cysts .There are also a few big basophilic cells
Their function is unknown
Pars Nervosa: Contains: - myelinated axons pituicytes, blood vessels
Axons:
The cell bodies of the axons lie in the supra-optic and paraventricular nuclei of the hypothalamus .From the cell bodies the axons go through the infundibulum forming the hypothalamohypophyseal tract to end in the pars nervosa
The axons have dilated blind endings filled with hormones (Herring bodies) coming from the cell bodies.
Two hormones are secreted:
Oxytoxin: - Cause contraction of the uterus
- Cause contraction of the myoepithelial cells of the milkgland
- The hormone is secreted by the paraventricular nuclei
Vasopressin :- Cause reabsorption of H2O in the kidney (also known as antidiuretic hormone ADH) The hormone is secreted by the supraoptic nuclei. A hypophyseal portal system exists
A primary capillary plexus of fenestrated capillaries form around the median eminence. Inhibitory hormones are secreted into these capillaries
The capillaries rejoin to form the portal veins that traverse the pituitary stalk
The portal veins break up into a secondary capillary plexus which lies close to the cells of the adenohypophysis
This portal system regulates the functions of the anterior pituitary function.
Pineal
Surrounded by pia which sends septae into the gland Cells are mainly pinealocytes and astroglial cells
Pinealocytes:Irregular shaped cells. with processes ending in flattened dilatations
Have a well developed smooth surfaced endoplasmic reticulum, Also a rough EPR not well developed, Lots of microtubules
Astroglial Cells: Elongated nucleus, Cells have long processes, They perform a supporting function
Hormones:
Melatonin - secreted during the night .suppress the onset of puberty
Serotonin - secreted during the day
In humans the pineal form concretions of calcified material called brain sand
Brain sand vary in size and number with age and is visible on X-rays
Mast cells are also found in the pineal and cause the high histamine contend of the gland
THYROID
Has a CT capsule that sends septae into the gland to divide it up into incomplete lobes and lobules. In the lobules are follicles, Follicles vary in size, They are surrounded by surrounded by reticular CT and capillaries
Cells of the Follicle:
Follicular Cells : Single layer of cuboidal cells, lie around the colloid, Follicular cells can become columnar when very active, Nucleus central, EPR has wide cisternae ,Golgi present
microvilli on the free surface
Parafollicular Cells: Also known as C-cells, Form part of the epithelium or form clusters between the follicles
- They never come into contact with the colloid
- Larger and stain less intensely than the follicular cells, Form 2% of the cells, Secrete calcitonin
Hormones: Thyroxine and thyriodothyronine - stimulate the metabolic rate, Calcitonin - lower the blood calcium
Parathyroid:
Has a CT capsule which send septae into the gland to divide it up into incomplete lobules, The CT contains fat which increase with age - may eventually be 50% of the gland, Glandular cells are arranged in cords
Glandular Cells:
Chief Cells: Small cells so their nuclei lie close together, Rich in glycogen, Biggest omponent
Secrete parathyroid hormone - essential for life
Oxyphil Cells:Develop at puberty, Bigger than the chief cells, Nuclei are smaller, Acidophilic
Hormones:
Parathyroid hormone - regulate calcium and phosphate ions in the blood
ADRENAL
- Thick CT capsule that do not send septae into the gland
Cortex:
Has 3 layers
Zona glomerulosa: 15% of the cortex, Directly under the capsule, Cells are columnar or pyramidal, Arranged in small groups or clusters, Wide fenestrated capillaries surround the clusters, Cells have an extensive smooth EPR
Zona Fasciculata: 78% of the cortex, Cells are arranged in cords ,1 to 2 cells wide perpendicular to the surface, Sinusoids lie between the cords, Cells are polyhedral with a central nucleus which is bigger than that of the zona glomerulosa, Lots of lipid in the cytoplasm cause the cells to stain lightly, Cells have a well developed smooth and rough EPR
The mitochondria in the cells are round with tubular or vesicular cristae
Zona Reticularis: 7% of the cortex, Cells form a network of cords with wide capillaries in-between The mitochondria in the cells are more ofte6n elongated than that in the zona fasciculate Degenerating cells with pyknotic nuclei are found. Cells contain numerous large lipofuscin granules. Cells of the cortex do not store their secretions but form and secrete on demand.
Hormones:
3 Groups:
Glucocorticoids (e.g. cortisol) - have an affection on carbohydrate metabolism
Mineralocorticoid (e.g. aldosterone) - control water and electrolyte balans
Androgens (e.g. dehyroepiandrosterone) - not very important
Medulla:
- Cells are big and oval and lie in groups and cords around bloodvessels
- Oxidising agents stain the granules in these cells brown - cells are therefore called chromaffin cells
- Granules contain adrenaline or non-adrernalin
- A few parasympathetic ganglion cells are also present
Hormones:
- Adrenaline - increase oxygen uptake
- increase blood pressure
- Noradrenaline - maintain blood pressure
Blood Supply:
- Blood vessel enter from the capsule to form the wide capillaries
- They flow into venules that form a central vein
- Between the endothelium of the capillaries and the glandular cells there is a subendothelial
- space.
- The glandular cells have microvilli protruding into this space.
ISLES OF LANGERHANS
Endocrine part of pancreas. The isles are round clusters in the exocrine tissue
- 100 - 200 µm
Islands consists of slightly stained polygonal or rounded cells, The cells are separated by fenestrated capillaries
- Autonomic nerve fibres innervate the blood vessels and the island cells
- 4 different cell types have been described
A cells : 20% of the cells, Bigger than B cells, Lie at the periphery, Have secretory granules ,Contain glucagon
B cells : 80%, Lie in the centre of the island, The cells are small with granules which are crystals, Granules are formed by insulin
D cells : Not numerous, Membrane bound granules, Store somatostatin (inhibit somatotropin)
F cells : Have membrane bound granules, Store pancreatic polypeptide, The hormone inhibits pancreatic exocrine secretion
Hepatitis D and E virus
General Pathology
Hepatitis D virus—can only infect cells previously infected with hepatitis B.
Delta hepatitis (HDV) is associated with a 35-nm RNA virus composed of a delta antigen-bearing core surrounded by HBV's Ag coat;
HDV requires HBV for replication.
Delta hepatitis can cause quiescent HBV states to suddenly worsened . Its transmission is the same as that of HBV.
Hepatitis E virus—a high mortality rate in infected pregnant women.
Hepatitis E (HEV) is caused by a single-stranded RNA virus. The disease is typically self-limited and does not evolve into chronic hepatitis; it may, however, be cholestatic.
Pregnant women may develop fulminant disease.
Transmission is by the fecal oral route.
HEV occurs mainly in India, Nepal, Pakistan, and Southeast Asia.
Types of Expansion
OrthodonticsExpansion in orthodontics refers to the process of widening the dental arch
to create more space for teeth, improve occlusion, and enhance facial
aesthetics. This procedure is particularly useful in treating dental crowding,
crossbites, and other malocclusions. The expansion can be achieved through
various appliances and techniques, and it can target either the maxillary
(upper) or mandibular (lower) arch.
Types of Expansion
Maxillary Expansion:
Rapid Palatal Expansion (RPE):
Description: A common method used to widen the
upper jaw quickly. It typically involves a fixed appliance that is
cemented to the molars and has a screw mechanism in the middle.
Mechanism: The patient or orthodontist turns
the screw daily, applying pressure to the palatine suture, which
separates the two halves of the maxilla, allowing for expansion.
Indications: Used for treating crossbites,
creating space for crowded teeth, and improving the overall arch
form.
Duration: The active expansion phase usually
lasts about 2-4 weeks, followed by a retention phase to stabilize
the new position.
Slow Palatal Expansion:
Description: Similar to RPE but involves slower,
more gradual expansion.
Mechanism: A fixed appliance is used, but the screw
is activated less frequently (e.g., once a week).
Indications: Suitable for patients with less severe
crowding or those who may not tolerate rapid expansion.
Mandibular Expansion:
Description: Less common than maxillary expansion,
but it can be achieved using specific appliances.
Mechanism: Appliances such as the mandibular
expansion appliance can be used to widen the lower arch.
Indications: Used in cases of dental crowding or to
correct certain types of crossbites.
Mechanisms of Expansion
Skeletal Expansion: Involves the actual widening of the
bone structure (e.g., the maxilla) through the separation of the midpalatine
suture. This is more common in growing patients, as their bones are more
malleable.
Dental Expansion: Involves the movement of teeth within
the alveolar bone. This can be achieved through the application of forces
that move the teeth laterally.
Indications for Expansion
Crossbites: To correct a situation where the upper
teeth bite inside the lower teeth.
Crowding: To create additional space for teeth that are
misaligned or crowded.
Improving Arch Form: To enhance the overall shape and
aesthetics of the dental arch.
Facial Aesthetics: To improve the balance and symmetry
of the face, particularly in growing patients.
Advantages of Expansion
Increased Space: Creates additional space for teeth,
reducing crowding and improving alignment.
Improved Function: Corrects functional issues related
to occlusion, such as crossbites, which can lead to better chewing and
speaking.
Enhanced Aesthetics: Improves the overall appearance of
the smile and facial profile.
Facilitates Orthodontic Treatment: Provides a better
foundation for subsequent orthodontic procedures.
Limitations and Considerations
Age Factor: Expansion is generally more effective in
growing children and adolescents due to the flexibility of their bones. In
adults, expansion may require surgical intervention (surgical-assisted rapid
palatal expansion) due to the fusion of the midpalatine suture.
Discomfort: Patients may experience discomfort or
pressure during the expansion process, especially with rapid expansion.
Retention: After expansion, a retention phase is
necessary to stabilize the new arch width and prevent relapse.
Potential for Relapse: Without proper retention, there
is a risk that the teeth may shift back to their original positions.
Endotracheal intubation (ETI)
Oral and Maxillofacial SurgeryEndotracheal intubation (ETI) is critical in trauma patients for securing the
airway, especially in cases of severe head injury or altered consciousness.
Statistics indicate that approximately 15% of major trauma patients require
urgent intubation, with rates varying widely from 2% to 37% depending on the
setting. Proper airway management is vital to prevent respiratory failure and
improve outcomes.
Importance of Endotracheal Intubation in Trauma Care
Endotracheal intubation (ETI) involves
placing a cuffed tube into the trachea to secure the airway, ensuring
adequate ventilation and oxygenation.
Prevalence: Studies show that between 9% and 28% of
trauma patients undergo ETI, highlighting its significance in emergency
medical care.
Consequences of Failure: The inability to secure a
definitive airway is a leading cause of preventable death in trauma cases.
Effective airway management is crucial for survival.
Indications for Endotracheal Intubation
Clinical Criteria: ETI is indicated in various
scenarios, including:
Severe head injuries with altered consciousness.
Respiratory distress or failure.
Hypoxia despite supplemental oxygen.
Hemodynamic instability (e.g., shock).
Guideline Recommendations: Current guidelines suggest
that ETI should be performed when specific clinical criteria are met, such
as:
Glasgow Coma Scale (GCS) < 9.
Persistent hypotension (systolic blood pressure < 90 mmHg).
Severe respiratory distress.
Challenges in Decision-Making
Complexity of Situations: The decision to intubate is
often complicated by factors such as:
The patient's overall condition and injury severity.
The presence of multiple indications for intubation.
The potential risks associated with the procedure, including
complications like hypoxemia and cardiovascular instability.
Variability in Practice: Despite established guidelines,
the actual intubation rates can vary significantly based on clinical
judgment and the specific circumstances of each case.
Outcomes Associated with Endotracheal Intubation
Impact on Mortality: Research indicates that patients
who undergo ETI may experience higher mortality rates, particularly if
intubation is performed in the absence of other indications. This suggests
that isolated shock may not be a sufficient criterion for intubation.
Length of Stay: Patients requiring ETI often have longer
stays in intensive care units (ICUs) and may experience more complications,
such as coagulopathy and multiple organ failure.
LIPIDS
Biochemistry
LIPIDS
The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, which are related more by their physical than by their chemical properties.
Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents.
Most membrane lipids are amphipathic, having a non-polar end and a polar end
Lipids are important in biological systems because they form the cell membrane, a mechanical barrier that divides a cell from the external environment.
Lipids also provide energy for life and several essential vitamins are lipids.
Lipids can be divided in two major classes, nonsaponifiable lipids and saponifiable lipids.
A nonsaponifiable lipid cannot be broken up into smaller molecules by hydrolysis, which includes triglycerides, waxes, phospholipids, and sphingolipids.
A saponifiable lipid contains one or more ester groups allowing it to undergo hydrolysis in the presence of an acid, base, or enzyme.
Nonsaponifiable lipids include steroids, prostaglandins, and terpenes
Nonpolar lipids, such as triglycerides, are used for energy storage and fuel.
Polar lipids, which can form a barrier with an external water environment, are used in membranes.
Polar lipids include glycerophospholipids and sphingolipids.
Fatty acids are important components of all of these lipids.