NEET MDS Synopsis
Glomerular filtration
Physiology
Glomerular filtration
Kidneys receive about 20% of cardiac output , this is called Renal Blood Flow (RBF) which is approximatley 1.1 L of blood. Plasma in this flow is about 625 ml . It is called Renal Plasma Flow (RPF) .
About 20 % of Plasma entering the glomerular capillaries is filtered into the Bowman`s capsule .
Glomerular filtration rate is about 125 ml/min ( which means 7.5 L/hr and thus 180 L/day) This means that the kidney filters about 180 liters of plasma every day.
The urine flow is about 1ml/min ( about 1.5 liter /day) This means that kidney reabsorbs about 178.5 liters every day .
Filtration occurs through the filtration unit , which includes :
1- endothelial cells of glomerular capillaries , which are fenestrated . Fenestrae are quite small so they prevent filtration of blood cells and most of plasma proteins .
2- Glomerular basement membrane : contains proteoglycan that is negatively charged and repels the negatively charged plasma proteins that may pass the fenestrae due to their small molecular weight like albumin . so the membrane plays an important role in impairing filtration of albumin .
3- Epithelial cells of Bowman`s capsule that have podocytes , which interdigitate to form slits .
Many forces drive the glomerular filtration , which are :
1- Hydrostatic pressure of the capillary blood , which favours filtration . It is about 55 mmHg .
2- Oncotic pressure of the plasma proteins in the glomerular capillary ( opposes filtration ) . It is about 30 mm Hg .
3- Hydrostatic pressure of the Bowman`s capsule , which also opposes filtration. It is about 15 mmHg .
The net pressure is as follows :
Hydrostatic pressure of glomerular capillaries - ( Oncotic pressure of glomerular capillaries + Hydrostatic pressure of the Bowman capsule):
55-(35+10)
=55-45
=10 mmHg .
Te glomerular filtration rate does not depend only on the net pressure , but also on an other value , known as filtration coefficient ( Kf) . The later depends on the surface area of the glomerular capillaries and the hydraulic conductivity of the glomerular capillaries.
Blood Transfusions
PhysiologyBlood Transfusions
Some of these units ("whole blood") were transfused directly into patients (e.g., to replace blood lost by trauma or during surgery).
Most were further fractionated into components, including:
RBCs. When refrigerated these can be used for up to 42 days.
platelets. These must be stored at room temperature and thus can be saved for only 5 days.
plasma. This can be frozen and stored for up to a year.
safety of donated blood
A variety of infectious agents can be present in blood.
viruses (e.g., HIV-1, hepatitis B and C, HTLV, West Nile virus
bacteria like the spirochete of syphilis
protozoans like the agents of malaria and babesiosis
prions (e.g., the agent of variant Crueutzfeldt-Jakob disease)
and could be transmitted to recipients. To minimize these risks,
donors are questioned about their possible exposure to these agents;
each unit of blood is tested for a variety of infectious agents.
Most of these tests are performed with enzyme immunoassays (EIA) and detect antibodies against the agents. blood is now also checked for the presence of the RNA of these RNA viruses:
HIV-1
hepatitis C
West Nile virus
by the so-called nucleic acid-amplification test (NAT).
The Nerve Impulse
Physiology
The Nerve Impulse
When a nerve is stimulated the resting potential changes. Examples of such stimuli are pressure, electricity, chemicals, etc. Different neurons are sensitive to different stimuli(although most can register pain). The stimulus causes sodium ion channels to open. The rapid change in polarity that moves along the nerve fiber is called the "action potential." In order for an action potential to occur, it must reach threshold. If threshold does not occur, then no action potential can occur. This moving change in polarity has several stages:
Depolarization
The upswing is caused when positively charged sodium ions (Na+) suddenly rush through open sodium gates into a nerve cell. The membrane potential of the stimulated cell undergoes a localized change from -55 millivolts to 0 in a limited area. As additional sodium rushes in, the membrane potential actually reverses its polarity so that the outside of the membrane is negative relative to the inside. During this change of polarity the membrane actually develops a positive value for a moment(+30 millivolts). The change in voltage stimulates the opening of additional sodium channels (called a voltage-gated ion channel). This is an example of a positive feedback loop.
Repolarization
The downswing is caused by the closing of sodium ion channels and the opening of potassium ion channels. Release of positively charged potassium ions (K+) from the nerve cell when potassium gates open. Again, these are opened in response to the positive voltage--they are voltage gated. This expulsion acts to restore the localized negative membrane potential of the cell (about -65 or -70 mV is typical for nerves).
Hyperpolarization
When the potassium ions are below resting potential (-90 mV). Since the cell is hyper polarized, it goes to a refractory phrase.
Refractory phase
The refractory period is a short period of time after the depolarization stage. Shortly after the sodium gates open, they close and go into an inactive conformation. The sodium gates cannot be opened again until the membrane is repolarized to its normal resting potential. The sodium-potassium pump returns sodium ions to the outside and potassium ions to the inside. During the refractory phase this particular area of the nerve cell membrane cannot be depolarized. This refractory area explains why action potentials can only move forward from the point of stimulation.
Factors that affect sensitivity and speed
Sensitivity
Increased permeability of the sodium channel occurs when there is a deficit of calcium ions. When there is a deficit of calcium ions (Ca+2) in the interstitial fluid, the sodium channels are activated (opened) by very little increase of the membrane potential above the normal resting level. The nerve fiber can therefore fire off action potentials spontaneously, resulting in tetany. This could be caused by the lack of hormone from parathyroid glands. It could also be caused by hyperventilation, which leads to a higher pH, which causes calcium to bind and become unavailable.
Speed of Conduction
This area of depolarization/repolarization/recovery moves along a nerve fiber like a very fast wave. In myelinated fibers, conduction is hundreds of times faster because the action potential only occurs at the nodes of Ranvier (pictured below in 'types of neurons') by jumping from node to node. This is called "saltatory" conduction. Damage to the myelin sheath by the disease can cause severe impairment of nerve cell function. Some poisons and drugs interfere with nerve impulses by blocking sodium channels in nerves. See discussion on drug at the end of this outline.
Maxillary Third Permanent Molar
Dental Anatomy
Maxillary Third Permanent Molar
They are the teeth most often congenitally missing
Facial: The crown is usually shorter in both axial and mesiodistal dimensions. Two buccal roots are present, but in most cases they are fused. The mesial buccal cusp is larger than the distal buccal cusp.
Lingual: In most thirds, there is just one large lingual cusp. In some cases there is a poorly developed distolingual cusp and a lingual groove. The lingual root is often fused to the to buccal cusps.
Proximal: The outline of the crown is rounded; it is often described as bulbous in dental literature. Technically, the mesial surface is the only 'proximal' surface. The distal surface does not contact another tooth.
Occlusal: The crown of this tooth is the smallest of the maxillary molars. The outline of the occlusal surface can be described as heart-shaped. The mesial lingual cusp is the largest, the mesial buccal is second in size, and the distal buccal cusp is the smallest.
Root Surface:-The root may have from one to as many as eight divisions. These divisions are usually fused and very often curved distally.
Blood
PhysiologyBlood is a liquid tissue. Suspended in the watery plasma are seven types of cells and cell fragments.
red blood cells (RBCs) or erythrocytes
platelets or thrombocytes
five kinds of white blood cells (WBCs) or leukocytes
Three kinds of granulocytes
neutrophils
eosinophils
basophils
Two kinds of leukocytes without granules in their cytoplasm
lymphocytes
monocytes
The External Nose
AnatomyThe External Nose
Noses vary considerably in size and shape, mainly as a result of the differences in the nasal cartilages and the depth of the glabella.
The inferior surface of the nose is pierced by two apertures, called the anterior nares (L. nostrils).
These are separated from each other by the nasal septum (septum nasi).
Each naris is bounded laterally by an ala (L. wing), i.e., the side of the nose.
The posterior nares apertures or choanae open into the nasopharynx.
Proper Pin Placement in Amalgam Restorations
Conservative DentistryProper Pin Placement in Amalgam Restorations
Principles of Pin Placement
Strength Maintenance: Proper pin placement does not
reduce the strength of amalgam restorations. The goal is to maintain the
strength of the restoration regardless of the clinical problem, tooth size,
or available space for pins.
Single Unit Restoration: In modern amalgam
preparations, it is essential to secure the restoration and the tooth as a
single unit. This is particularly important when significant tooth structure
has been lost.
Considerations for Cusp Replacement
Cusp Replacement: If the mesiofacial wall is replaced,
the mesiofacial cusp must also be replaced to ensure proper occlusal
function and distribution of forces.
Force Distribution: It is crucial to recognize that
forces of occlusal loading must be distributed over a large area. If the
distofacial cusp were replaced with a pin, there would be a tendency for the
restoration to rotate around the mesial pins, potentially leading to
displacement or failure of the restoration.
Structure of gypsum products
Dental Materials
Structure of gypsum products
Components
a. Powder (calcium sulfate hemihydrate = CaSO4½H2O)
b. Water (for reaction with powder and dispersing powder)