NEET MDS Synopsis
Gabapentin
Pharmacology
Gabapentin (Neurontin): newer; for generalized tonic-clonic seizures and partial seizures (partial and complex)
Mechanism: unknown but know doesn’t mimic GABA inhibition or block Ca currents
Side effects: dizziness, ataxia, fatigue; drug well-tolerated and no significant drug interactions
Urine excretion
Physiology
Concentration versus diluting urine
Kidney is a major route for eliminating fluid from the body to accomplish water balance. Urine excretion is the last step in urine formation. Everyday both kidneys excrete about 1.5 liters of urine.
Depending on the hydrated status of the body, kidney either excretes concentrated urine ( if the plasma is hypertonic like in dehydrated status ) or diluted urine ( if the plasma is hypotonic) .
This occurs thankful to what is known as countercurrent multiplying system, which functions thankfully to establishing large vertical osmotic gradient .
To understand this system, lets review the following facts:
1. Descending limb of loop of Henle is avidly permeable to water.
2. Ascending limb of loop of Henly is permeable to electrolytes , but impermeable to water. So fluid will not folow electrolytes by osmosis.and thus Ascending limb creates hypertonic interstitium that will attract water from descending limb.
Pumping of electrolytes
3. So: There is a countercurrent flow produced by the close proximity of the two limbs.
Juxtamedullary nephrons have long loop of Henle that dips deep in the medulla , so the counter-current system is more obvious and the medullary interstitium is always hypertonic . In addition, peritubular capillaries in the medulla are straigh ( vasa recta) in which flow is rapid and rapidly reabsorb water maintaining hypertonic medullary interstitium.
In distal tubules water is diluted. If plasma is hypertonic, this will lead to release of ADH by hypothalamus, which will cause reabsorption of water in collecting tubules and thus excrete concentrated urine.
If plasma is hypotonic ADH will be inhibited and the diluted urine in distal tubules will be excreted as diluted urine.
Urea contributes to concentrating and diluting of urine as follows:
Urea is totally filtered and then 50% of filtrated urea will be reabsorbed to the interstitium, this will increase the osmolarity of medullary interstitium ( becomes hypertonic ). Those 50% will be secreted in ascending limb of loop of Henle back to tubular fluid to maintain osmolarity of tubular fluid. 55% of urea in distal nephron will be reabsorbed in collecting ducts back to the interstitium ( under the effect of ADH too) . This urea cycle additionally maintain hypertonic interstitium.
TetricEvoFlow
PedodonticsTetricEvoFlow
TetricEvoFlow is an advanced nano-optimized flowable composite developed by
Ivoclar Vivadent, designed to enhance dental restorations with its superior
properties. As the successor to Tetric Flow, it offers several key benefits:
Optimum Surface Affinity: TetricEvoFlow exhibits
excellent adhesion to tooth structures, ensuring a reliable bond and
minimizing the risk of microleakage.
Penetration into Difficult Areas: Its flowable nature
allows it to reach and fill even the most challenging areas, making it ideal
for intricate restorations.
Versatile Use: This composite can serve as an initial
layer beneath medium-viscosity composites, such as TetricEvoCeram, providing
a strong foundation for layered restorations.
Stability for Class V Restorations: TetricEvoFlow
maintains its stability when required, making it particularly suitable for
Class V restorations, where durability and aesthetics are crucial.
Extended Applications: In addition to its use in
restorations, TetricEvoFlow is effective for extended fissure sealing and
can be utilized in adhesive cementation techniques.
CARIDEX and CARISOLV
PedodonticsCARIDEX and CARISOLV
CARIDEX and CARISOLV are both dental
products designed for the chemomechanical removal of carious dentin. Here’s a
detailed breakdown of their components and mechanisms:
CARIDEX
Components:
Solution I: Contains sodium hypochlorite (NaOCl)
and is used for its antimicrobial properties and ability to dissolve
organic tissue.
Solution II: Contains glycine and aminobutyric acid
(ABA). When mixed with sodium hypochlorite, it produces N-mono
chloro DL-2-amino butyric acid, which aids in the removal of
demineralized dentin.
Application:
CARIDEX is particularly useful for deep cavities, allowing for the
selective removal of carious dentin while preserving healthy tooth
structure.
CARISOLV
Components:
Syringe 1: Contains sodium hypochlorite at a
concentration of 0.5% w/v (which is equivalent to
0.51%).
Syringe 2: Contains a mixture of amino acids (such
as lysine, leucine, and glutamic acid) and erythrosine dye, which helps
in visualizing the removal of carious dentin.
pH Level:
The pH of the CARISOLV solution is approximately 11,
which helps in the dissolution of carious dentin.
Mechanism of Action:
The sodium hypochlorite in CARISOLV softens and dissolves carious
dentin, while the amino acids and dye provide a visual cue for the
clinician. The procedure can be stopped when discoloration is no longer
observed, indicating that all carious dentin has been removed.
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
FLUORIDE
Biochemistry
FLUORIDE
The safe limit of fluorine is about 1PPM in water. But excess of fluoride causes Flourosis
Flourosis is more dangerous than caries. When Fluoride content is more than 2 PPM, it will cause chronic intestinal upset, gastroenteritis, loss of weight, osteosclerosis, stratification and discoloration of teeth
Membrane Potential
PhysiologyMembrane Potential
Membrane potentials will occur across cell membranes if
1) there is a concentration gradient of an ion
2) there is an open channel in the membrane so the ion can move from one side to the other
The Sodium Pump Sets Up Gradients of Na and K Across Cell Membranes
All cells have the Na pump in their membranes
Pumps 3 Nas out and 2 Ks in for each cycle
Requires energy from ATP
Uses about 30% of body's metabolic energy
This is a form of active transport- can pump ions "uphill", from a low to a high concentration
This produces concentration gradients of Na & K across the membrane
Typical concentration gradients:
In mM/L
Out mM/L
Gradient orientation
Na
10
150
High outside
K
140
5
High inside
The ion gradients represent stored electrical energy (batteries) that can be tapped to do useful work
The Na pump is of ancient origin, probably originally designed to protect cell from osmotic swelling
Inhibited by the arrow poisons ouabain and digitalis
Carbon Dioxide Transport
PhysiologyCarbon Dioxide Transport
Carbon dioxide (CO2) combines with water forming carbonic acid, which dissociates into a hydrogen ion (H+) and a bicarbonate ions:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3−
95% of the CO2 generated in the tissues is carried in the red blood cells:
It probably enters (and leaves) the cell by diffusing through transmembrane channels in the plasma membrane. (One of the proteins that forms the channel is the D antigen that is the most important factor in the Rh system of blood groups.)
Once inside, about one-half of the CO2 is directly bound to hemoglobin (at a site different from the one that binds oxygen).
The rest is converted — following the equation above — by the enzyme carbonic anhydrase into
bicarbonate ions that diffuse back out into the plasma and
hydrogen ions (H+) that bind to the protein portion of the hemoglobin (thus having no effect on pH).
Only about 5% of the CO2 generated in the tissues dissolves directly in the plasma. (A good thing, too: if all the CO2 we make were carried this way, the pH of the blood would drop from its normal 7.4 to an instantly-fatal 4.5!)
When the red cells reach the lungs, these reactions are reversed and CO2 is released to the air of the alveoli.