NEET MDS Lessons
Physiology
Vital Capacity: The vital capacity (VC) is the maximum volume which can be ventilated in a single breath. VC= IRV+TV+ERV. VC varies with gender, age, and body build. Measuring VC gives a device for diagnosis of respiratory disorder, and a benchmark for judging the effectiveness of treatment. (4600 ml)
Vital Capacity is reduced in restrictive disorders, but not in disorders which are purely obstructive.
The FEV1 is the % of the vital capacity which is expelled in the first second. It should be at least 75%. The FEV1 is reduced in obstructive disorders.
Both VC and the FEV1 are reduced in disorders which are both restrictive and obstructive
Oxygen is present at nearly 21% of ambient air. Multiplying .21 times 760 mmHg (standard pressure at sea level) yields a pO2 of about 160. Carbon dioxide is .04% of air and its partial pressure, pCO2, is .3.
With alveolar air having a pO2 of 104 and a pCO2 of 40. So oxygen diffuses into the alveoli from inspired air and carbon dioxide diffuses from the alveoli into air which will be expired. This causes the levels of oxygen and carbon dioxide to be intermediate in expired air when compared to inspired air and alveolar air. Some oxygen has been lost to the alveolus, lowering its level to 120, carbon dioxide has been gained from the alveolus raising its level to 27.
Likewise a concentration gradient causes oxygen to diffuse into the blood from the alveoli and carbon dioxide to leave the blood. This produces the levels seen in oxygenated blood in the body. When this blood reaches the systemic tissues the reverse process occurs restoring levels seen in deoxygenated blood.
COPD and Cancer
A. Chronic Obstructive Pulmonary Disease (COPD)
1. Common features of COPD
a. almost all have smoking history
b. dyspnea - chronic "gasping" for air
c. frequent coughing and infections
d. often leads to respiratory failure
2. obstructive emphysema - usually results from smoking
a. enlargement & deterioration of alveoli
b. loss of elasticity of the lungs
c. "barrel chest" from bronchiole opening during inhalation & constriction during exhalation
3. chronic bronchitis - mucus/inflammation of mucosa
B. Lung Cancer
1. squamous cell carcinoma (20-40%) - epithelium of the bronchi and bronchioles
2. adenocarcinoma (25-35%) - cells of bronchiole glands and cells of the alveoli
3. small cell carcinoma (10-20%) - special lymphocyte-like cells of the bronchi
4. 90% of all lung cancers are in people who smoke or have smoked
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.
SPECIAL VISCERAL AFFERENT (SVA) PATHWAYS
Taste
Special visceral afferent (SVA) fibers of cranial nerves VII, IX, and X conduct signals into the solitary tract of the brainstem, ultimately terminating in the nucleus of the solitary tract on the ipsilateral side.
Second-order neurons cross over and ascend through the brainstem in the medial lemniscus to the VPM of the thalamus.
Thalamic projections to area 43 (the primary taste area) of the postcentral gyrus complete the relay.
SVA VII fibers conduct from the chemoreceptors of taste buds on the anterior twothirds of the tongue, while SVA IX fibers conduct taste information from buds on the posterior one-third of the tongue.
SVA X fibers conduct taste signals from those taste cells located throughout the fauces.
Smell
The smell-sensitive cells (olfactory cells) of the olfactory epithelium project their central processes through the cribiform plate of the ethmoid bone, where they synapse with mitral cells. The central processes of the mitral cells pass from the olfactory bulb through the olfactory tract, which divides into a medial and lateral portion The lateral olfactory tract terminates in the prepyriform cortex and parts of the amygdala of the temporal lobe.
These areas represent the primary olfactory cortex. Fibers then project from here to area 28, the secondary olfactory area, for sensory evaluation. The medial olfactory tract projects to the anterior perforated substance, the septum pellucidum, the subcallosal area, and even the contralateral olfactory tract.
Both the medial and lateral olfactory tracts contribute to the visceral reflex pathways, causing the viscerosomatic and viscerovisceral responses.
Phases of cardiac cycle :
1. Early diastole ( also called the atrial diastole , or complete heart diastole) : During this phase :
- Atria are relaxed
- Ventricles are relaxed
- Semilunar valves are closed
- Atrioventricular valves are open
During this phase the blood moves passively from the venous system into the ventricles ( about 80 % of blood fills the ventricles during this phase.
2. Atrial systole : During this phase :
- Atria are contracting
- Ventricles are relaxed
- AV valves are open
- Semilunar valves are closed
- Atrial pressure increases.the a wave of atrial pressure appears here.
- P wave of ECG starts here
- intraventricular pressure increases due to the rush of blood then decrease due to continuous relaxation of ventricles.
The remaining 20% of blood is moved to fill the ventricles during this phase , due to atrial contraction.
3. Isovolumetric contraction : During this phase :
- Atria are relaxed
- Ventricles are contracting
- AV valves are closed
- Semilunar valves are closed
- First heart sound
- QRS complex.
The ventricular fibers start to contract during this phase , and the intraventricular pressure increases. This result in closing the AV valves , but the pressure is not yet enough to open the semilunar valves , so the blood volume remain unchanged , and the muscle fibers length also remain unchanged , so we call this phase as isovolumetric contraction ( iso : the same , volu= volume , metric= length).
4. Ejection phase : Blood is ejected from the ventricles into the aorta and pulmonary artery .
During this phase :
- Ventricles are contracting
- Atria are relaxed
- AV valves are closed
- Semilunar valves are open
- First heart sound
- Intraventricular pressure is increased , due to continuous contraction
- increased aortic pressure .
- T wave starts.
5. Isovolumetric relaxation: This phase due to backflow of blood in aorta and pulmonary system after the ventricular contraction is up and the ventricles relax . This backflow closes the semilunar valves .
During this phase :
- Ventricles are relaxed
- Atrial are relaxed
- Semilunar valves are closed .
- AV valves are closed.
- Ventricular pressure fails rapidly
- Atrial pressure increases due to to continuous venous return. the v wave appears here.
- Aortic pressure : initial sharp decrease due to sudden closure of the semilunar valve ( diacrotic notch) , followed by secondary rise in pressure , due to elastic recoil of the aorta ( diacrotic wave) .
- T wave ends in this phase
Platelets
Platelets are cell fragments produced from megakaryocytes.
Blood normally contains 150,000 to 350,000 per microliter (µl). If this value should drop much below 50,000/µl, there is a danger of uncontrolled bleeding. This is because of the essential role that platelets have in blood clotting.
When blood vessels are damaged, fibrils of collagen are exposed.
- von Willebrand factor links the collagen to platelets forming a plug of platelets there.
- The bound platelets release ADP and thromboxane A2 which recruit and activate still more platelets circulating in the blood.
- (This role of thromboxane accounts for the beneficial effect of low doses of aspirin a cyclooxygenase inhibitor in avoiding heart attacks.)
ReoPro is a monoclonal antibody directed against platelet receptors. It inhibits platelet aggregation and appears to reduce the risk that "reamed out" coronary arteries (after coronary angioplasty) will plug up again.
Function of Blood
- transport through the body of
- oxygen and carbon dioxide
- food molecules (glucose, lipids, amino acids)
- ions (e.g., Na+, Ca2+, HCO3−)
- wastes (e.g., urea)
- hormones
- heat
- defense of the body against infections and other foreign materials. All the WBCs participate in these defenses