NEET MDS Synopsis
SENSORY PATHWAYS
Physiology
Sensory pathways include only those routes which conduct information to the conscious cortex of the brain. However, we will use the term in its more loosely and commonly applied context to include input from all receptors, whether their signals reach the conscious level or not.
LOCATION OF THE TEETH
Dental Anatomy
LOCATION OF THE TEETH
Normally, a human receives two sets of teeth during a lifetime.
The first (deciduous or primary) set consists of 20 teeth ("baby" teeth).
The second (permanent) set usually consists of 32 teeth. In each quadrant, there are eight permanent teeth: two incisors, one cuspid, two bicuspids, and three molars
The tooth positioned immediately to the side of the midline is the central incisor, so called because it occupies a central location in the arch.
To the side of the central incisor is the lateral incisor. Next is the cuspid, then the two bicuspids (the first bicuspid, followed by the second bicuspid). The last teeth are three molars. After the second bicuspid comes the first molar, followed by the second molar, followed by the third molar or more commonly called the "wisdom tooth."
Another method of describing the location of teeth is to refer to them as anterior or posterior teeth .
Anterior teeth are those located in the front of the mouth, the incisors, and the cuspids. Normally, these are the teeth that are visible when a person smiles.
The posterior teeth are those located in the back of the mouth-the bicuspids and molars.
Dark Field Microscopy
PeriodontologyDark Field Microscopy in Periodontal Microbiology
Dark field microscopy and phase contrast microscopy are valuable techniques
in microbiological studies, particularly in the field of periodontal research.
These methods allow for the direct observation of bacteria in plaque samples,
providing insights into their morphology and motility. This lecture will discuss
the principles of dark field microscopy, its applications in periodontal disease
assessment, and its limitations.
Dark Field Microscopy
Definition: Dark field microscopy is a technique that
enhances the contrast of unstained, transparent specimens, allowing for the
visualization of live microorganisms in their natural state.
Principle: The method uses a special condenser that
directs light at an angle, creating a dark background against which the
specimen appears bright. This allows for the observation of motility and
morphology without the need for staining.
Applications in Periodontal Microbiology
Alternative to Culture Methods:
Dark field microscopy has been suggested as a rapid alternative to
traditional culture methods for assessing bacterial populations in
periodontal plaque samples. It allows for immediate observation of
bacteria without the time-consuming process of culturing.
Assessment of Morphology and Motility:
The technique enables direct and rapid assessment of the morphology
(shape and structure) and motility (movement) of bacteria present in
plaque samples. This information can be crucial for understanding the
dynamics of periodontal disease.
Indication of Periodontal Disease Status:
Dark field microscopy has been used to indicate the status of
periodontal disease and the effectiveness of maintenance programs. By
observing the presence and activity of specific bacteria, clinicians can
gain insights into the health of periodontal tissues.
Limitations of Dark Field Microscopy
Analysis of Major Periodontal Pathogens:
While dark field microscopy can visualize motile bacteria, it is
important to note that many major periodontal pathogens, such as Aggregatibacter
actinomycetemcomitans, Porphyromonas gingivalis, Bacteroides
forsythus, Eikenella corrodens, and Eubacterium species,
are motile. However, the technique may not provide detailed information
about their specific characteristics or pathogenic potential.
Differentiation of Treponema Species:
Dark field microscopy cannot differentiate between species of Treponema,
which is a limitation when identifying specific pathogens associated
with periodontal disease. This lack of specificity can hinder the
ability to tailor treatment based on the exact microbial profile.
Limited Quantitative Analysis:
While dark field microscopy allows for qualitative observations, it
may not provide quantitative data on bacterial populations, which can be
important for assessing disease severity and treatment outcomes.
Nephron
Physiology
The nephron of the kidney is involved in the regulation of water and soluble substances in blood.
A Nephron
A nephron is the basic structural and functional unit of the kidneys that regulates water and soluble substances in the blood by filtering the blood, reabsorbing what is needed, and excreting the rest as urine.
Its function is vital for homeostasis of blood volume, blood pressure, and plasma osmolarity.
It is regulated by the neuroendocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone.
The Glomerulus
The glomerulus is a capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation. Here, fluid and solutes are filtered out of the blood and into the space made by Bowman's capsule.
A group of specialized cells known as juxtaglomerular apparatus (JGA) are located around the afferent arteriole where it enters the renal corpuscle. The JGA secretes an enzyme called renin, due to a variety of stimuli, and it is involved in the process of blood volume homeostasis.
The Bowman's capsule surrounds the glomerulus. It is composed of visceral (simple squamous epithelial cells; inner) and parietal (simple squamous epithelial cells; outer) layers.
Red blood cells and large proteins, such as serum albumins, cannot pass through the glomerulus under normal circumstances. However, in some injuries they may be able to pass through and can cause blood and protein content to enter the urine, which is a sign of problems in the kidney.
Proximal Convoluted Tubule
The proximal tubule is the first site of water reabsorption into the bloodstream, and the site where the majority of water and salt reabsorption takes place. Water reabsorption in the proximal convoluted tubule occurs due to both passive diffusion across the basolateral membrane, and active transport from Na+/K+/ATPase pumps that actively transports sodium across the basolateral membrane.
Water and glucose follow sodium through the basolateral membrane via an osmotic gradient, in a process called co-transport. Approximately 2/3rds of water in the nephron and 100% of the glucose in the nephron are reabsorbed by cotransport in the proximal convoluted tubule.
Fluid leaving this tubule generally is unchanged due to the equivalent water and ion reabsorption, with an osmolarity (ion concentration) of 300 mOSm/L, which is the same osmolarity as normal plasma.
The Loop of Henle
The loop of Henle is a U-shaped tube that consists of a descending limb and ascending limb. It transfers fluid from the proximal to the distal tubule. The descending limb is highly permeable to water but completely impermeable to ions, causing a large amount of water to be reabsorbed, which increases fluid osmolarity to about 1200 mOSm/L. In contrast, the ascending limb of Henle's loop is impermeable to water but highly permeable to ions, which causes a large drop in the osmolarity of fluid passing through the loop, from 1200 mOSM/L to 100 mOSm/L.
Distal Convoluted Tubule and Collecting Duct
The distal convoluted tubule and collecting duct is the final site of reabsorption in the nephron. Unlike the other components of the nephron, its permeability to water is variable depending on a hormone stimulus to enable the complex regulation of blood osmolarity, volume, pressure, and pH.
Normally, it is impermeable to water and permeable to ions, driving the osmolarity of fluid even lower. However, anti-diuretic hormone (secreted from the pituitary gland as a part of homeostasis) will act on the distal convoluted tubule to increase the permeability of the tubule to water to increase water reabsorption. This example results in increased blood volume and increased blood pressure. Many other hormones will induce other important changes in the distal convoluted tubule that fulfill the other homeostatic functions of the kidney.
The collecting duct is similar in function to the distal convoluted tubule and generally responds the same way to the same hormone stimuli. It is, however, different in terms of histology. The osmolarity of fluid through the distal tubule and collecting duct is highly variable depending on hormone stimulus. After passage through the collecting duct, the fluid is brought into the ureter, where it leaves the kidney as urine.
Nucleic Acids
PhysiologyNucleic Acids:
Two major types: DNA
RNA (including mRNA, tRNA, & rRNA)
Both types have code which specifies the sequence of amino acids in proteins
DNA = archival copy of genetic code, kept in nucleus, protected
RNA = working copy of code, used to translate a specific gene into a protein, goes into cytoplasm & to ribosomes, rapidly broken down
Nucleic acids are made of 5 nucleotide bases, sugars and phosphate groups
The bases make up the genetic code ; the phosphate and sugar make up the backbone
RNA is a molecule with a single strand
DNA is a double strand (a double helix) held together by hydrogen bonds between the bases
A = T; C= G because:
A must always hydrogen bond to T
C must always hydrogen bond to G
NITRIC OXIDE-DEPENDENT KILLING
General Microbiology
NITRIC OXIDE-DEPENDENT KILLING
Binding of bacteria to macrophages, particularly binding via Toll-like
receptors, results in the production of TNF-alpha, which acts in an autocrine
manner to induce the expression of the inducible nitric oxide synthetase gene (i-nos
) resulting in the production of nitric oxide (NO) . If the cell is also exposed
to interferon gamma (IFN-gamma) additional nitric oxide will be produced (figure
12). Nitric oxide released by the cell is toxic and can kill microorganism in
the vicinity of the macrophage.
Skeletal System Formation
Anatomy
Bones begin to form during the eighth week of embryomic life in the fibrous membranes (intramembranous ossification) and hyaline cartilage (endochondral ossification)
Hemorrhage
Oral and Maxillofacial SurgeryTypes of Hemorrhage
Hemorrhage, or excessive bleeding, can occur during and after surgical
procedures. Understanding the different types of hemorrhage is crucial for
effective management and prevention of complications. The three main types of
hemorrhage are primary, reactionary, and secondary hemorrhage.
1. Primary Hemorrhage
Definition: Primary hemorrhage refers to bleeding that
occurs at the time of surgery.
Causes:
Injury to blood vessels during the surgical procedure.
Inadequate hemostasis (control of bleeding) during the operation.
Management:
Immediate control of bleeding through direct pressure,
cauterization, or ligation of blood vessels.
Use of hemostatic agents or sutures to secure bleeding vessels.
Clinical Significance: Prompt recognition and
management of primary hemorrhage are essential to prevent significant blood
loss and ensure patient safety during surgery.
2. Reactionary Hemorrhage
Definition: Reactionary hemorrhage occurs within a few
hours after surgery, typically when the initial vasoconstriction of damaged
blood vessels subsides.
Causes:
The natural response of blood vessels to constrict after injury may
initially control bleeding. However, as the vasoconstriction diminishes,
previously damaged vessels may begin to bleed again.
Movement or changes in position of the patient can also contribute
to the reopening of previously clamped vessels.
Management:
Monitoring the patient closely in the immediate postoperative period
for signs of bleeding.
If reactionary hemorrhage occurs, surgical intervention may be
necessary to identify and control the source of bleeding.
Clinical Significance: Awareness of the potential for
reactionary hemorrhage is important for postoperative care, as it can lead
to complications if not addressed promptly.
3. Secondary Hemorrhage
Definition: Secondary hemorrhage refers to bleeding
that occurs up to 14 days postoperatively, often as a result of infection or
necrosis of tissue.
Causes:
Infection at the surgical site can lead to tissue breakdown and
erosion of blood vessels, resulting in bleeding.
Sloughing of necrotic tissue may also expose blood vessels that were
previously protected.
Management:
Careful monitoring for signs of infection, such as increased pain,
swelling, or discharge from the surgical site.
Surgical intervention may be required to control bleeding and
address the underlying infection.
Antibiotic therapy may be necessary to treat the infection and
prevent further complications.
Clinical Significance: Secondary hemorrhage can be a
serious complication, as it may indicate underlying issues such as infection
or inadequate healing. Early recognition and management are crucial to
prevent significant blood loss and promote recovery.