NEET MDS Synopsis
Pharyngeal Arch
Anatomy
Pharyngeal Arch
Arch Artery
Cranial Nerve
Skeletal elements
Muscles
1
Terminal Branch of maxillary artery
Maxillary and mandibular division of trigemenial (V)
Derived from arch cartilages (originating from neural crest):
From maxillary cartilages:
Alispenoid, incus
From mandibular:
Mackel’s cartilage, malleus
Upper portion of external ear (auricle) is derived from dorsal aspect of 1st pharyngeal arch.
Derived by direct ossification from arch dermal mesenchyme:
Maxilla, zygomatic, squamous portion of temporal bone, mandible
Muscles of mastication (temporalis, masseter, and pterygoids), mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini (originate from cranial somitomere 4)
2
Stapedius artery (embryologic) and cortiotympanic artery (adult)
Facial nerve (VII)
Stapes, styloid process, stylohyoid ligament, lesser horns and upper rim of hyoid (derived from the second arch cartilage; originate from neural crest).
Lower portion of external ear (auricle) is derived from 2nd pharyngeal arch.
Muscles of facial expression (orbicularis oculi, orbicularis oris, auricularis, platysma, fronto-ooccipitalis, buccinator), posterior belly of digastric, stylohyoid, stapedius (originate from cranial somitomere 6)
3
Common carotid artery, most of internal carotid
Glossopharyngeal (IX)
Lower rim and greater horn of hyoid (derived from the third arch cartilage; originate from neural crest cells)
Sytlopharyngeus (originate from cranial somitomere 7)
4
Left: Arch of aorta;
Right: Right subclavian artery;
Original sprouts of pulmonary arteries
Superior laryngeal branch of vagus (X)
Laryngeal cartilages (Derived from the 4th arch cartilage, originate from lateral plate mesoderm)
Constrictors of pharynx, cricothyroid, levator veli palatine (originate from occipital somites 2-4)
6
Ductus arteriosus; roots of definitive pulmonary arteries
Recurrent laryngeal branch of vagus (X)
Laryngeal cartilages (derived from the 6th-arch cartilage; originate from lateral plate mesoderm)
Intrinsic muscles of larynx (originate from occipital somites 1 and 2)
Digital Radiology
Radiology
Digital Radiology
Advances in computer and X-ray technology now permit the use of systems that employ sensors in place of X-ray ?lms (with emulsion). The image is either directly or indirectly converted into a digital representation that is displayed on a computer screen.
DIGITAL IMAGE RECEPTORS
- charged coupled device (CCD) used
- Pure silicon divided into pixels.
- Electromagnetic energy from visible light or X-rays interacts with pixels to create an electric charge that can be stored.
- Stored charges are transmitted electronically and create an analog output signal and displayed via digital converter (analog to digital converter).
ADVANTAGES OF DIGITAL TECHNIQUE
Immediate display of images.
Enhancement of image (e.g., contrast, gray scale, brightness).
Radiation dose reduction up to 60%.
Major disadvantage: High initial cost of sensors. Decreased image resolution and contrast as compared to D speed ?lms.
DIRECT IMAGING
- CCD or complementary metal oxide semiconductor (CMOS) detector used that is sensitive to electromagnetic radiation.
- Performance is comparable to ?lm radiography for detection of periodontal lesions and proximal caries in noncavitated teeth.
INDIRECT IMAGING
- Radiographic ?lm is used as the image receiver (detector).
- Image is digitized from signals created by a video device or scanner that views the radiograph.
Sensors
STORAGE PHOSPHOR IMAGING SYSTEMS
Phosphor screens are exposed to ionizing radiation which excites BaFBR:EU+2 crystals in the screen storing the image.
A computer-assisted laser then promotes the release of energy from the crystals in the form of blue light.
The blue light is scanned and the image is reconstructed digitally.
ELECTRONIC SENSOR SYSTEMS
X-rays are converted into light which is then read by an electronic sensor such as a CCD or CMOS.
Other systems convert the electromagnetic radiation directly into electrical impulses.
Digital image is created out of the electrical impulses.
The developing tooth bud -Bell stage
Dental Anatomy
Bell stage
The bell stage is known for the histodifferentiation and morphodifferentiation that takes place. The dental organ is bell-shaped during this stage, and the majority of its cells are called stellate reticulum because of their star-shaped appearance. Cells on the periphery of the enamel organ separate into three important layers. Cuboidal cells on the periphery of the dental organ are known as outer enamel epithelium.The cells of the enamel organ adjacent to the dental papilla are known as inner enamel epithelium. The cells between the inner enamel epithelium and the stellate reticulum form a layer known as the stratum intermedium. The rim of the dental organ where the outer and inner enamel epithelium join is called the cervical loop
Other events occur during the bell stage. The dental lamina disintegrates, leaving the developing teeth completely separated from the epithelium of the oral cavity; the two will not join again until the final eruption of the tooth into the mouth
The crown of the tooth, which is influenced by the shape of the internal enamel epithelium, also takes shape during this stage. Throughout the mouth, all teeth undergo this same process; it is still uncertain why teeth form various crown shapes—for instance, incisors versus canines. There are two dominant hypotheses. The "field model" proposes there are components for each type of tooth shape found in the ectomesenchyme during tooth development. The components for particular types of teeth, such as incisors, are localized in one area and dissipate rapidly in different parts of the mouth. Thus, for example, the "incisor field" has factors that develop teeth into incisor shape, and this field is concentrated in the central incisor area, but decreases rapidly in the canine area. The other dominant hypothesis, the "clone model", proposes that the epithelium programs a group of ectomesenchymal cells to generate teeth of particular shapes. This group of cells, called a clone, coaxes the dental lamina into tooth development, causing a tooth bud to form. Growth of the dental lamina continues in an area called the "progress zone". Once the progress zone travels a certain distance from the first tooth bud, a second tooth bud will start to develop. These two models are not necessarily mutually exclusive, nor does widely accepted dental science consider them to be so: it is postulated that both models influence tooth development at different times.Other structures that may appear in a developing tooth in this stage are enamel knots, enamel cords, and enamel niche.
Maintenance of Homeostasis
Physiology
Maintenance of Homeostasis
The kidneys maintain the homeostasis of several important internal conditions by controlling the excretion of substances out of the body.
Ions. The kidney can control the excretion of potassium, sodium, calcium, magnesium, phosphate, and chloride ions into urine. In cases where these ions reach a higher than normal concentration, the kidneys can increase their excretion out of the body to return them to a normal level. Conversely, the kidneys can conserve these ions when they are present in lower than normal levels by allowing the ions to be reabsorbed into the blood during filtration. (See more about ions.)
pH. The kidneys monitor and regulate the levels of hydrogen ions (H+) and bicarbonate ions in the blood to control blood pH. H+ ions are produced as a natural byproduct of the metabolism of dietary proteins and accumulate in the blood over time. The kidneys excrete excess H+ ions into urine for elimination from the body. The kidneys also conserve bicarbonate ions, which act as important pH buffers in the blood.
Osmolarity. The cells of the body need to grow in an isotonic environment in order to maintain their fluid and electrolyte balance. The kidneys maintain the body’s osmotic balance by controlling the amount of water that is filtered out of the blood and excreted into urine. When a person consumes a large amount of water, the kidneys reduce their reabsorption of water to allow the excess water to be excreted in urine. This results in the production of dilute, watery urine. In the case of the body being dehydrated, the kidneys reabsorb as much water as possible back into the blood to produce highly concentrated urine full of excreted ions and wastes. The changes in excretion of water are controlled by antidiuretic hormone (ADH). ADH is produced in the hypothalamus and released by the posterior pituitary gland to help the body retain water.
Blood Pressure. The kidneys monitor the body’s blood pressure to help maintain homeostasis. When blood pressure is elevated, the kidneys can help to reduce blood pressure by reducing the volume of blood in the body. The kidneys are able to reduce blood volume by reducing the reabsorption of water into the blood and producing watery, dilute urine. When blood pressure becomes too low, the kidneys can produce the enzyme renin to constrict blood vessels and produce concentrated urine, which allows more water to remain in the blood.
Lost Wax Process
Dental Materials
Lost Wax Process
The lost wax casting process is widely used as it offers asymmetrical casting withnvery fine details to be manufactured relatively inexpensively. The process involves producing a metal casting using a refractory mould made from a wax replica pattern.
The steps involved in the process or the lost wax casting are:
1 . Create a wax pattern of the missing tooth / rim
2 . Sprue the wax pattern
3 . Invest the wax pattern
4 . Eliminate the wax pattern by burning it (inside the furnace or in hot water). This will create a mould.
5 . Force molten metal into the mould - casting.
6 . Clean the cast.
7 . Remove sprue from the cast
8 . Finish and polish the casting on the die .
The lost-wax technique is so named because a wax pattern of a restoration is invested in a ceramic material, then the pattern is burned out ("lost") to create a space into which molten metal is placed or cast. The entire lost-wax casting process .
Wax pattern removal:
Sprue former can be used to remove the pattern. If not the pattern is removed with a sharp probe. Then the sprue former is attached to it. The pattern should be removed directly in line with the principle axis of the tooth or the prepared cavity. Any rotation of the pattern will distort it. Hollow sprue pin is advisable because of its greater retention to the pattern.
Duodenum
PhysiologyAs the contents of the stomach become thoroughly liquefied, they pass into the duodenum, the first segment of the small intestine. The duodenum is the first 10" of the small intestine
Two ducts enter the duodenum:
one draining the gall bladder and hence the liver
the other draining the exocrine portion of the pancreas.
From the intestinal mucosal cells, and from the liver and gallbladder. Secretions from the pancreas and bile from the gallbladder enter the duodenum through the hepatopancreatic ampulla and the sphincter of Oddi. These lie where the pancreatic duct and common bile duct join before entering the duodenum. The presence of fatty chyme in the duodenum causes release of the hormone CCK into the bloodstream. CCK is one of the enterogastrones and its main function, besides inhibiting the stomach, is to stimulate the release of enzymes by the pancreas, and the contraction of the gallbladder to release bile. It also stimulates the liver to produce bile. Consumption of excess fat results in excessive bile production by the liver, and this can lead to the formation of gallstones from precipitation of the bile salts.
The acid in the chyme stimulates the release of secretin which causes the pancreas to release bicarbonate which neutralizes the acidity
Methyl salicylate
Pharmacology
Methyl salicylate
also known as oil of wintergreen, betula oil, methyl ester) is a natural product of many species of plants Structurally, it is methylated salicylic acid It is used as an ingredient in deep heating rubs
Drugs Used in Diabetes -Megltinides
Pharmacology
Megltinides
nateglinide
repaglinide
Mechanism
binds to K+ channels on β-cells → postprandial insulin release
Clinical use
type 2 diabetes mellitus
may be used as monotherapy, or in combination with metformin