NEET MDS Lessons
Physiology
Heart sounds
Heart sounds are a result of beating heart and resultant blood flow . that could be detected by a stethoscope during auscultation . Auscultation is a part of physical examination that doctors have to practice them perfectly.
Before discussion the origin and nature of the heart sounds we have to distinguish between the heart sounds and hurt murmurs. Heart murmurs are pathological noises that results from abnormal blood flow in the heart or blood vessels.
Physiologically , blood flow has a laminar pattern , which means that blood flows in form of layers , where the central layer is the most rapid . Laminar blood flow could be turned into turbulent one .
Turbulent blood flow is a result of stenotic ( narrowed ) valves or blood vessels , insufficient valves , roughened vessels` wall or endocardium , and many diseases . The turbulent blood flow causes noisy murmurs inside or outside the heart.
Heart sounds ( especially first and second sounds ) are mainly a result of closure of the valves of the heart . While the third sound is a result of vibration of ventricular wall and the leaflets of the opened AV valves after rapid inflow of blood from the atria to ventricles .
Third heart sound is physiologic in children but pathological in adults.
The four heart sound is a result of the atrial systole and vibration of the AV valves , due to blood rush during atrial systole . It is inaudible neither in adults nor in children . It is just detectable by the phonocardiogram .
Characteristic of heart sounds :
1. First heart sound (S1 , lub ) : a soft and low pitch sound, caused by closure of AV valves.Usually has two components ( M1( mitral ) and T1 ( tricuspid ). Normally M1 preceads T1.
2. Second heart sound ( S2 , dub) : sharp and high pitch sound . caused by closure of semilunar valves. It also has two components A2 ( aortic) and P2 ( pulmonary) . A2 preceads P2.
3. Third heart sound (S3) : low pitched sound.
4. Fourth heart sound ( S4) very low pitched sound.
As we notice : the first three sounds are related to ventricular activity , while the fourth heart sound is related to atrial activity.
Closure of valves is not the direct cause for heart sounds , but sharp blocking of blood of backward returning of blood by the closing valve is the direct cause.
Hyperventilation
- Treatments :Rebreath air, hold breath (Increase CO2)
Give oxygen for Hypoxemia
The endocrine system along with the nervous system functions in the regulation of body activities. The nervous system acts through electrical impulses and neurotransmitters to cause muscle contraction and glandular secretion and interpretation of impulses. The endocrine system acts through chemical messengers called hormones that influence growth, development, and metabolic activities
The Cardiac Cycle: the sequence of events in one heartbeat.
systole - the contraction phase; unless otherwise specified refers to left ventricle, but each chamber has its own systole.
diastole - the relaxation phase; unless otherwise specified refers to left ventricle, but each chamber has its own diastole.
1) quiescent period - period when all chambers are at rest and filling. 70% of ventricular filling occurs during this period. The AV valves are open, the semilunar valves are closed.
2) atrial systole - pushes the last 30% of blood into the ventricle.
3) atrial diastole - atria begin filling.
4) ventricular systole - First the AV valves close causing the first heart sound, then after the isovolumetric contraction phase the semilunar valves open permitting ventricular ejection of blood into the arteries.
5) ventricular diastole - As the ventricles relax the semilunar valves close first producing the second heart sound, then after the isovolumetric relaxation phase the AV valves open allowing ventricular filling.
Functional Divisions of the Nervous System:
1) The Voluntary Nervous System - (ie. somatic division) control of willful control of effectors (skeletal muscles) and conscious perception. Mediates voluntary reflexes.
2) The Autonomic Nervous System - control of autonomic effectors - smooth muscles, cardiac muscle, glands. Responsible for "visceral" reflexes
The Nervous System Has Peripheral and Central Units
- The central nervous system (CNS) is the brain and spinal column
- The peripheral nervous system (PNS) consists of nerves outside of the CNS
- There are 31 pairs of spinal nerves (mixed motor & sensory)
- There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)
The pattern of innervation plotted on the skin is called a dermatome
The Nervous System Has Peripheral and Central Units
- The central nervous system (CNS) is the brain and spinal column
- The peripheral nervous system (PNS) consists of nerves outside of the CNS
- There are 31 pairs of spinal nerves (mixed motor & sensory)
- There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)
The pattern of innervation plotted on the skin is called a dermatome
Bleeding Disorders
A deficiency of a clotting factor can lead to uncontrolled bleeding.
The deficiency may arise because
- not enough of the factor is produced or
- a mutant version of the factor fails to perform properly.
Examples:
- von Willebrand disease (the most common)
- hemophilia A for factor 8 deficiency
- hemophilia B for factor 9 deficiency.
- hemophilia C for factor 11 deficiency
In some cases of von Willebrand disease, either a deficient level or a mutant version of the factor eliminates its protective effect on factor 8. The resulting low level of factor 8 mimics hemophilia A.