NEET MDS Synopsis
Ketone Body
Biochemistry
During fasting or carbohydrate starvation, oxaloacetate is depleted in liver because it is used for gluconeogenesis. This impedes entry of acetyl-CoA into Krebs cycle. Acetyl-CoA then is converted in liver mitochondria to ketone bodies, acetoacetate and b-hydroxybutyrate.
Three enzymes are involved in synthesis of ketone bodies:
b-Ketothiolase. The final step of the b-oxidation pathway runs backwards, condensing 2 acetyl-CoA to produce acetoacetyl-CoA, with release of one CoA.
HMG-CoA Synthase catalyzes condensation of a third acetate moiety (from acetyl-CoA) with acetoacetyl-CoA to form hydroxymethylglutaryl-CoA (HMG-CoA).
HMG-CoA Lyase cleaves HMG-CoA to yield acetoacetate plus acetyl-CoA.
b-Hydroxybutyrate Dehydrogenase catalyzes inter-conversion of the ketone bodies acetoacetate and b-hydroxybutyrate.
Ketone bodies are transported in the blood to other tissue cells, where they are converted back to acetyl-CoA for catabolism in Krebs cycle
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.
Headgear orthodontic appliance
Orthodontics
High-pull headgear consists of a head cap connected to a face-bow. This appliance places a distal and upward force on the maxillary teeth and maxilla. These types of headgear have a more direct effect on the anterior segment of the arch.
Indications: Class II, Division I malocclusion that have an open bite
Cervical-Pull headgear is made up of a neck strap connected to a face bow. This appliance produces a distal and downward force against the maxillary teeth and the maxilla.
A major disadvantage of treatment using cervical headgear is possible extrusion of the maxillary molars Likely results include: opening the bite, first molars will move distally and forward growth of the maxilla will decrease.
Indications: Class II, Division I malocclusions.
Straigh pull headgear is similar to the cervical-pull headgear. However, this appliance places a force in strai ht distal direction form the maxillary molar. Like cervical-pull headgear,
Indications are Class II , Division I malocclusion (when bite opening is undesirable).
Reverse-pull headgear unlike all the other headgears above, the extraoral component is supported by the chin , cheeks, forehead or a combination of these structures.
Indications:
Class III malocclusions (where protraction of the maxilla is desirable).
Impression Materials - Types
Dental Materials
Impression Material
Materials
Type
Reaction
Composition
Manipulation
Initial setting time
Plaster
Rigid
Chemical
Calcuim sulfate hemihydrate, water
Mix P/L in bowl
3-5 min
Compound
Rigid
Physical
Resins, wax, stearic acid, and fillers
Soften by heating
Variable (sets on
cooling)
Zinc oxide-eugonel
Rigid
Chemical
Zinc oxide powder, oils, eugenol, and
resin
Mix pastes on pad
3-5 min
Agar-agar
Flexible
Physical
12-15% agar, borax, potassium sulfate,
and 85% water
Mix P/L in bowl
Variable (sets on
cooling)
alginate
Flexible
Chemical
Sodium alginate, calcium sulfate, retarders,
and 85% water
Mix P/L in bowl
4-5 min
Polysulfide
Flexible
Chemical
Low MW mercaptan polymer, fillers, lead
dioxide, copper hydroxide, or peroxides
Mix pastes on pad
5-7 min
Silicone
Flexible
Chemical
Hydroxyl functional dimethyl siloxane, fillers,
tin octoate, and orthoethyl silicate
Mix pastes on pad
4.5 min
Polyether
Flexible
Chemical
Aromatic sulfonic acid ester and polyether
with ethylene imine groups
Mix pastes on pad
2-4 min
Polyvinyl siloxane
Flexible
Chemical
Vinyl silicone, filler, chloroplatinic acid,
low MW silicone, and filler
Mix putty or use
two-component
mixing gun
4-5 min
Thiamin: Vitamin B1
Biochemistry
Thiamin: Vitamin B1
Thiamin, or vitamin B1, helps to release energy from foods, promotes normal appetite, and is important in maintaining proper nervous system function.
RDA (Required Daily allowance) Males: 1.2 mg/day; Females: 1.1 mg/day
Thiamin Deficiency
Symptoms of thiamin deficiency include: mental confusion, muscle weakness, wasting, water retention (edema), impaired growth, and the disease known as beriberi.
Garre’s Osteomyelitis
Oral Pathology
Garre’s Osteomyelitis (Chronic Osteomyelitis with Proliferative Perosteitis)
Chronic Non Suppurative Sclerosing Osteitis/ Periostitis Ossificans.
Non suppurative productive disease characterized by a hard swelling.
Occurs due to low grade infection and irritation
The infectious agent localizes in or beneath the periosteal covering of the cortex & spreads only slightly into the interior of the bone.
Occurs primarily in young persons who possess great osteogenic activity of the periosteum.
Clinical Features
Uncommonly encountered, described in tibia and in the head and neck region, in the mandible.
Typically involves the posterior mandible & is usually unilateral.
Patients present with an asymptomatic bony, hard swelling with normal appearing overlying skin and mucosa.
On occasion slight tenderness may be noted
pain is most constant feature
The increase in the mass of bone may be due to mild toxic stimulation of periosteal osteoblasts by attenuated infection.
Radiographic features
Laminations vary from 1 – 12 in number, radiolucent separations often are present between new bone and original cortex. (“onion skin appearance”)
Trabeculae parallel to laminations may also be present.
Histologic Features
Reactive new bone.
Parallel rows of highly cellular & reactive woven bone in which the individual trabeculae are oriented perpendicular to surface.
Osteoblasts predominate in this area.
D/D for Garre’s Osteomyelitis
Ewing's sarcoma
Caffey’s disease
Fibrous dysplasia
Osteosarcoma
Treatment
Removal of the offending cause.
Once inflammation resolves, layers of the bone consolidate in 6 – 12 months, as the overlying muscle helps to remodel.
If no focus of infection evident, biopsy recommended.
Headgear
OrthodonticsHeadgear is an extraoral orthodontic appliance used to
correct dental and skeletal discrepancies, particularly in growing patients. It
is designed to apply forces to the teeth and jaws to achieve specific
orthodontic goals, such as correcting overbites, underbites, and crossbites, as
well as guiding the growth of the maxilla (upper jaw) and mandible (lower jaw).
Below is an overview of headgear, its types, mechanisms of action, indications,
advantages, and limitations.
Types of Headgear
Class II Headgear:
Description: This type is used primarily to correct
Class II malocclusions, where the upper teeth are positioned too far
forward relative to the lower teeth.
Mechanism: It typically consists of a facebow that
attaches to the maxillary molars and is anchored to a neck strap or a
forehead strap. The appliance applies a backward force to the maxilla,
helping to reposition it and/or retract the upper incisors.
Class III Headgear:
Description: Used to correct Class III
malocclusions, where the lower teeth are positioned too far forward
relative to the upper teeth.
Mechanism: This type of headgear may use a
reverse-pull face mask that applies forward and upward forces to the
maxilla, encouraging its growth and improving the relationship between
the upper and lower jaws.
Cervical Headgear:
Description: This type is used to control the
growth of the maxilla and is often used in conjunction with other
orthodontic appliances.
Mechanism: It consists of a neck strap that
connects to a facebow, applying forces to the maxilla to restrict its
forward growth while allowing the mandible to grow.
High-Pull Headgear:
Description: This type is used to control the
vertical growth of the maxilla and is often used in cases with deep
overbites.
Mechanism: It features a head strap that connects
to the facebow and applies upward and backward forces to the maxilla.
Mechanism of Action
Force Application: Headgear applies extraoral forces to
the teeth and jaws, influencing their position and growth. The forces can be
directed to:
Restrict maxillary growth: In Class II cases,
headgear can help prevent the maxilla from growing too far forward.
Promote maxillary growth: In Class III cases,
headgear can encourage forward growth of the maxilla.
Reposition teeth: By applying forces to the molars,
headgear can help align the dental arches and improve occlusion.
Indications for Use
Class II Malocclusion: To correct overbites and improve
the relationship between the upper and lower teeth.
Class III Malocclusion: To promote the growth of the
maxilla and improve the occlusal relationship.
Crowding: To create space for teeth by retracting the
upper incisors.
Facial Aesthetics: To improve the overall facial
profile and aesthetics by modifying jaw relationships.
Advantages of Headgear
Non-Surgical Option: Provides a way to correct skeletal
discrepancies without the need for surgical intervention.
Effective for Growth Modification: Particularly useful
in growing patients, as it can influence the growth of the jaws.
Improves Aesthetics: Can enhance facial aesthetics by
correcting jaw relationships and improving the smile.
Limitations of Headgear
Patient Compliance: The effectiveness of headgear
relies heavily on patient compliance. Patients must wear the appliance as
prescribed (often 12-14 hours a day) for optimal results.
Discomfort: Patients may experience discomfort or
soreness when first using headgear, which can affect compliance.
Adjustment Period: It may take time for patients to
adjust to wearing headgear, and they may need guidance on how to use it
properly.
Limited Effectiveness in Adults: While headgear is
effective in growing patients, its effectiveness may be limited in adults
due to the maturity of the skeletal structures.
DAMAGE TO THE SPINAL NERVES AND SPINAL CORD
Physiology
Damage to Spinal Nerves and Spinal Cord
Damage
Possible cause of damage
Symptoms associated with innervated area
Peripheral nerve
Mechanical injury
Loss of muscle tone. Loss of reflexes. Flaccid paralysis. Denervation atrophy. Loss of sensation
Posterior root
Tabes dorsalis
Paresthesia. Intermittent sharp pains. Decreased sensitivity to pain. Loss of reflexes. Loss of sensation. Positive Romberg sign. High stepping and slapping of feet.
Anterior Horn
Poliomyelitis
Loss of muscle tone. Loss of reflexes. Flaccid paralysis. Denervation atrophy
Lamina X (gray matter)
Syringomyelia
Bilateral loss of pain and temperature sense only at afflicted cord level. Sensory dissociation. No sensory impairment below afflicted level
Anterior horn and lateral corticospinal tract
Amyotrophic lateral sclerosis
Muscle weakness. Muscle atrophy. Fasciculations of hand and arm muscles. Spastic paralysis
Posterior and lateral funiculi
Subacute combined degeneration
Loss of position sense. Loss of vibratory sense. Positive Romberg sign. Muscle weakness. Spasticity. Hyperactive tendon reflexes. Positive Babinski sign.
Hemisection of the spinal cord
Mechanical injury
Brown-Sequard syndrome
Below cord level on injured side
Flaccid paralysis. Hyperactive tendon reflexes. Loss of position sense. Loss of vibratory sense. Tactile impairment
Below cord level on opposite side beginning one or two segments below injury
Loss of pain and temperature