NEET MDS Synopsis
The Eye and Orbit
AnatomyThe Eye and Orbit
The orbit (eye socket) appears as a bony recess in the skull when it is viewed from anteriorly.
It almost surrounds the eye and their associated muscles, nerves and vessels, together with the lacrimal apparatus.
The orbit is shaped somewhat like a four-side pyramid lying on its side, with its apex pointing posteriorly and its base anteriorly.
Control of processes in the stomach
PhysiologyControl of processes in the stomach:
The stomach, like the rest of the GI tract, receives input from the autonomic nervous system. Positive stimuli come from the parasympathetic division through the vagus nerve. This stimulates normal secretion and motility of the stomach. Control occurs in several phases:
Cephalic phase stimulates secretion in anticipation of eating to prepare the stomach for reception of food. The secretions from cephalic stimulation are watery and contain little enzyme or acid.
Gastric phase of control begins with a direct response to the contact of food in the stomach and is due to stimulation of pressoreceptors in the stomach lining which result in ACh and histamine release triggered by the vagus nerve. The secretion and motility which result begin to churn and liquefy the chyme and build up pressure in the stomach. Chyme surges forward as a result of muscle contraction but is blocked from entering the duodenum by the pyloric sphincter. A phenomenon call retropulsion occurs in which the chyme surges backward only to be pushed forward once again into the pylorus. The presence of this acid chyme in the pylorus causes the release of a hormone called gastrin into the bloodstream. Gastrin has a positive feedback effect on the motility and acid secretion of the stomach. This causes more churning, more pressure, and eventually some chyme enters the duodenum.
Intestinal phase of stomach control occurs. At first this involves more gastrin secretion from duodenal cells which acts as a "go" signal to enhance the stomach action already occurring. But as more acid chyme enters the duodenum the decreasing pH inhibits gastrin secretion and causes the release of negative or "stop" signals from the duodenum.
These take the form of chemicals called enterogastrones which include GIP (gastric inhibitory peptide). GIP inhibits stomach secretion and motility and allows time for the digestive process to proceed in the duodenum before it receives more chyme. The enterogastric reflex also reduces motility and forcefully closes the pyloric sphincter. Eventually as the chyme is removed, the pH increases and gastrin and the "go" signal resumes and the process occurs all over again. This series of "go" and "stop" signals continues until stomach emptying is complete.
SINUS & FISTULA
General Surgery
Sinus
It is a tubular track lined by granulation tissue and open at one end which is at the surface,
eg. Tuberculous Sinus
Fistula
A tubular track lined by granulation tissue and open at both ends.at least one of which communicates with a hollow viscus. it can be internal or external.
Causes
1. Inadequate drainage
Abscess bursting at the non dependent part
Incision at the non-dependent part.
Narrow outer opening leading to collection of exudates in the cavity.
2. Presence of foreign body like sequestrum or slough.
3. Persistence of infection.
4. When the track is lined by epithelium
5. Specific causes, TB., Syphilis, etc.
6. Marked fibrosis of the wall with obliteration of blood vessels.
7. Poor general condition causing delayed healing.
Treatment
1. control of specific infection,
2. Thorough excision of track to open up the cavity. Removal of foreign body and scraping of the epithelium
3. Through Scrapping of the wall to expose healthy tissue
4. Wound laid open and allowed to heal from the bottom leaving no pocket,
Specific Agents
Pharmacology
Specific Agents
Hydralazine [orally effective]
MOA: Not completely understood. Seems to be partially dependent on the release of EDRF and perhaps partially due to K+-channel activation
- in clinical doses action is manifest primarily on vascular smooth muscle (non-vascular muscle is not much affected).
- Re: Metabolism & Excretion. In cases of renal failure the plasma half life may be substantially increased (4-5 fold). One mode of metabolism is
via N-Acetylation (problem of slow acetylators)
Side Effects
- those typical of vasodilation = headache, nasal congestion, tachycardia etc.
- chronic treatment with high doses > 200 mg/day may induce a rheumatoid-like state which may resemble lupus erythematosus.
Minoxidil (Loniten) [orally effective]
MOA: K+-channel agonist
- very effective antihypertensive. Used primarily to treat life-threatening hypertension or hypertension resistant to other agents.
Side effects - growth of hair
Diazoxide (Hyperstat) [used only IV]
MOA: K+-channel agonist
- Administered by rapid IV injection; action appearing after 3-5 min; action may last from 4 to 12 hours.
Nitroprusside (Nipride) [used only IV]
MOA: increase in cGMP
- unlike the other vasodilators, venous tone is substantially reduced by nitroprusside.
- rapid onset of action (.30 sec); administered as an IV-infusion.
- particularly useful for hypertension associated with left ventricular failure.
Digital Imaging
PedodonticsPhotostimulable Phosphors (PSPs) in Digital Imaging
Photostimulable phosphors (PSPs), also
known as storage phosphors, are materials used in digital imaging for the
acquisition of radiographic images. They serve as an alternative to
traditional film-based radiography.
Characteristics of PSPs
Storage Mechanism: Unlike conventional screen materials
used in panoramic or cephalometric imaging, PSPs do not fluoresce
immediately upon exposure to x-ray photons. Instead, they capture and store
the incoming x-ray photon information as a latent image.
Latent Image: The latent image is similar to that found
in traditional film radiography, where the image is not visible until
processed.
Image Acquisition Process
Exposure:
The PSP plate is exposed to x-rays, which causes the phosphor
material to absorb and store the energy from the x-ray photons.
Scanning:
After exposure, the PSP plate is scanned by a laser beam in a drum
scanner. This process is crucial for retrieving the stored image
information.
Energy Release:
The laser scanning excites the phosphor, causing it to release the
stored energy as an electronic signal. This signal represents the latent
image captured during the x-ray exposure.
Digitalization:
The electronic signal is then digitized, with various gray levels
assigned to different points on the curve. This process creates the
final image information that can be viewed and analyzed.
Advantages of PSP Systems
Image Quality: PSPs can produce high-quality images with
a wide dynamic range, allowing for better visualization of anatomical
structures.
Reusability: PSP plates can be reused multiple times,
making them a cost-effective option for dental practices.
Compatibility: PSP systems can be integrated into
existing digital imaging workflows, providing flexibility for dental
professionals.
Available PSP Imaging Systems
Soredex: OpTime
AirTechniques: Scan X
Gendex: Denoptix
These systems offer various features and capabilities, allowing dental
practices to choose the best option for their imaging needs.
COMPOSITE RESINS -Types
Dental Materials
COMPOSITE RESINS
Types
Amount of filler-25% to 65% volume, 45% to 85% weight
Filler particle size (diameter in microns)
Macrofill 10 to 100 µm (traditional composites)
Midi fill- 1 to 10 µm(small particle composites)
Minifill— 0.l to 1 µm
Microfill-: 0.01 to 0.1 µm (fine particle composites)
Hybrid--blend (usually or microfill and midifill or minifill and microfill)
Polymerization method
Auto-cured (self-cured)
Visible light cured
Dual cured
Staged cure
Matrix chemistry
BIS-GMA type
Urethane dimethacrylate (UDM or UDMA) type
TEGDMA-diluent monomer to reduce viscosity
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.
Classifications of epidemiologic research
Public Health Dentistry
Classifications of epidemiologic research
1. Descriptive research —involves description, documentation, analysis, and interpretation of data to evaluate a current event or situation
a. incidence—number of new cases of a specific disease within a defined population over a period of time
b. Prevalence—number of persons in a population affected by a condition at any one time
c. Count—simplest sum of disease: number of cases of disease occurrence
d. Proportion—use of a count with the addition of a denominator to determine prevalence:
does not include a time dimension: useful to evaluate prevalence of caries in schoolchildren or tooth loss in adult populations
e. Rate— uses a standardized denominator and includes a time dimension. for example. the number of deaths of newborn infants within first year of life per 1000 births
2. Analytical research—determines the cause of disease or if a causal relationship exists between a factor and a disease
a. Prospective study—planning of the entire study is completed before data are collected and analyzed; population is followed through time to determine which members develop the disease; several hypotheses may be tested at on time
b. Cohort study—individuals are classified into groups according to whether or not they pos- sess a particular characteristic thought to be related to the condition of interest; observations occur over time to see who develops dis ease or condition
c. Retrospective study— decision to carry out an investigation using observations or data that have been collected in the past; data may be incomplete or in a manner not appropriate for study
d. Cross-sectional study— study of subgroups of individuals in a specific and limited time frame to identify either initially to describe current status or developmental changes in the overall group from the perspective of what is typical in each subgroup
e. Longitudinal study—investigation of the same group of individuals over an extended period of time to identify a change or devel opment in that group
3. Experimental research—used when the etiology of the disease is established and the researcher wishes to determine the effectiveness of altering some factor or factors; deliberate applying or withholding of the supposed cause of a condition and observing the result