TSPSC JL & DL Special | Pumping System of Blood with Gases

July 3, 2023 / 04:31 PM IST

DOUBLE CIRCULATION

జూన్‌ 26 తరువాయి

As the ventricular pressure declines further, the tricuspid and bicuspid valves are pushed open by the pressure in the atria exerted by the blood which was being emptied into them by the veins.
The blood now once again moves freely to the ventricles.
The ventricles and atria are now again in a relaxed (joint diastole) state, as earlier.
Soon the SAN generates a new action potential and the events described above are repeated in that sequence and the process continues.
This sequential event in the heart which is cyclically repeated is called the cardiac cycle and it consists of systole and diastole of both the atria and ventricles.
As mentioned earlier, the heart beats 72 times per minute, i.e., that many cardiac cycles are performed per minute.
From this it could be deduced that the duration of a cardiac cycle is 0.8 seconds.
During a cardiac cycle, each ventricle pumps out approx imately 70 mL of blood which is called the stroke volume.
The stroke volume multiplied by the heart rate (no. of beats per min.) gives the cardiac output.
Therefore, the cardiac output can be defined as the volume of blood pumped out by each ventricle per minute and averages 5000 mL or 5 litres in a healthy individual.
The body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output.
For example, the cardiac output of an athlete will be much higher than that of an ordinary man.
During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope.
The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound (dub) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance.

ELECTROCARDIOGRAPH (ECG)

You are probably familiar with this scene from a typical hospital television show: A patient is hooked up to a monitoring machine that shows voltage traces on a screen and makes the sound “… pip… pip… pip…. peeeeeeeeeeeeeeeeeeeeee” as the patient goes into cardiac arrest.
This type of machine (electro-cardiograph) is used to obtain an electrocardiogram (ECG).
ECG is a graphical represe ntation of the electrical activity of the heart during a cardiac cycle.
To obtain a standard ECG, a patient is connected to the machine with three electrical leads (one to each wrist and to the left ankle) that continuously monitor the heart activity.
For a detailed evaluation of the heart’s function, multiple leads are attached to the chest region.
Here, we will talk only about a standard ECG. Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart.
The P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to the contraction of both the atria.
The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction.
The contraction starts shortly after Q and marks the beginning of the systole.
The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of the T-wave marks the end of systole.
Obviously, by counting the number of QRS complexes that occur in a given time period, one can determine the heart beat rate of an individual.
Since the ECGs obtained from different individuals have roughly the same shape for a given lead configuration, any deviation from this shape indicates a possible abnormality or disease. Hence, it is of a great clinical significance.

DOUBLE CIRCULATION

The blood flows strictly by a fixed route through Blood Vessels—the arteries and veins.
Basically, each artery and vein consist of three layers: an inner lining of squamous endothelium, the tunica intima, a middle layer of smooth muscle and elastic fibres, the tunica media, and an external layer of fibrous connective tissue with collagen fibres, the tunica externa.
The tunica media is comparatively thin in the veins.
As mentioned earlier, the blood pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta.
The deoxygenated blood pumped into the pulmonary artery is passed on to the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium. This pathway constitutes the pulmonary circulation.
The oxygenated blood entering the aorta is carried by a network of arteries, arterioles and capillaries to the tissues from where the deoxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium. This is the systemic circulation.
The systemic circulation provides nutrients, O2 and other essential substances to the tissues and takes CO2 and other harmful substances away for elimination.
A unique vascular connection exists between the digestive tract and liver calledhepatic portal system.
The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation.
A special coronary system of blood vessels is present in our body exclusively for the circulation of blood to and from the cardiac musculature.
Normal activities of the heart are regulated intrinsically, i.e., auto regulated by specialised muscles (nodal tissue), hence the heart is called myogenic.

REGULATION OF CARDIAC ACTIVITY

A special neural centre in the medulla oblangata can moderate the cardiac function through autonomic nervous system (ANS).
Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output.
On the other hand, parasym pathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.
Adrenal medullary hormones can also increase the cardiac output.

DISORDERS OF CIRCULATORY SYSTEM

High Blood Pressure (Hypertension)

Hypertension is the term for blood pressure that is higher than normal (120/80).
In this measurement 120 mm Hg (millimetres of mercury pressure) is the systolic, or pumping, pressure and 80 mm Hg is the diastolic, or resting, pressure.
If repeated checks of blood pressure of an individual are 140/90 (140 over 90) orhigher, it shows hypertension.
High blood pressure leads to heart diseases and also affects vital organs like brain and kidney.

Coronary Artery Disease (CAD)

Coronary artery disease, often referred to as atherosclerosis, affects the vessels that supply blood to the heart muscle.
It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which makes the lumen of arteries narrower.
Angina
It is also called ‘angina pectoris’.
A symptom of acute chest pain appears when no enough oxygen is reaching the heart muscle.
Angina can occur in men and women of any age but it is more common among the middle-aged and elderly.
It occurs due to conditions that affect the blood flow.

Heart Failure

Heart failure means the state of heart when it is not pumping blood effectively enough to meet the needs of the body.
It is sometimes called congestive heart failure because congestion of the lungs is one of the main symptoms of this disease.
Heart failure is not the same as cardiac arrest (when the heart stops beating) or a heart attack (when the heart muscle is suddenly damaged by an inadequate blood supply).

Dr.Modala Mallesh
subject expert
palem, Nakrekal
Ph.9989535675