Either of the 2 (right and left) upper chambers of the heart that collect blood from the body and lungs respectively.
The atria open directly into the ventricles.
The atria open directly into the ventricles.
Shape and size In adults the heart is about the size and shape of a clenched ?st. One end of the heart is pointed (apex); the other is broad (base) and is deeply cleft at the division between the two atria. One groove running down the front and up the back shows the division between the two ventricles; a circular, deeper groove marks o? the atria above from the ventricles below. The capacity of each cavity is somewhere between 90 and 180 millilitres.
Structure The heart lies within a strong ?brous bag, known as the pericardium. Since the inner surface of this bag and the outer surface of the heart are both covered with a smooth, glistening membrane faced with ?at cells and lubricated by a little serous ?uid (around 20 ml), the movements of the heart are accomplished almost without friction. The main thickness of the heart wall consists of bundles of muscle ?bres, some of which run in circles right around the heart, and others in loops, ?rst round one cavity, then round the corresponding cavity of the other side. Within all the cavities is a smooth lining membrane, continuous with that lining the vessels which open into the heart. The investing smooth membrane is known as epicardium; the muscular substance as myocardium; and the smooth lining membrane as endocardium.
Important nerves regulate the heart’s action, especially via the vagus nerve and with the sympathetic system (see NERVOUS SYSTEM). In the near part of the atria lies a collection of nerve cells and connecting ?bres, known as the sinuatrial node or pacemaker, which forms the starting-point for the impulses that initiate the beats of the heart. In the groove between the ventricles and the atria lies another collection of similar nerve tissue, known as the atrioventricular node. Running down from there into the septum between the two ventricles is a band of special muscle ?bres, known as the atrioventricular bundle, or the bundle of His. This splits up into a right and a left branch for the two ventricles, and the ?bres of these distribute themselves throughout the muscular wall of the ventricles and control their contraction.
Openings There is no direct communication between the cavities on the right side and those on the left; but the right atrium opens into the right ventricle by a large circular opening, and similarly the left atrium into the left ventricle. Into the right atrium open two large veins, the superior and inferior venae cavae, with some smaller veins from the wall of the heart itself, and into the left atrium open two pulmonary veins from each lung. One opening leads out of each ventricle – to the aorta in the case of the left ventricle, to the pulmonary artery from the right.
Before birth, the FETUS’s heart has an opening (foramen ovale) from the right into the left atrium through which the blood passes; but when the child ?rst draws air into his or her lungs this opening closes and is represented in the adult only by a depression (fossa ovalis).
Valves The heart contains four valves. The mitral valve consists of two triangular cusps; the tricuspid valve of three smaller cusps. The aortic and pulmonary valves each consist of three semilunar-shaped segments. Two valves are placed at the openings leading from atrium into ventricle, the tricuspid valve on the right side, the mitral valve on the left, so as completely to prevent blood from running back into the atrium when the ventricle contracts. Two more, the pulmonary valve and the aortic valve, are at the entrance to these arteries, and prevent regurgitation into the ventricles of blood which has been driven from them into the arteries. The noises made by these valves in closing constitute the greater part of what are known as the heart sounds, and can be heard by anyone who applies his or her ear to the front of a person’s chest. Murmurs heard accompanying these sounds indicate defects in the valves, and may be a sign of heart disease (although many murmurs, especially in children, are ‘innocent’).
Action At each heartbeat the two atria contract and expel their contents into the ventricles, which at the same time they stimulate to contract together, so that the blood is driven into the arteries, to be returned again to the atria after having completed a circuit in about 15 seconds through the body or lungs as the case may be. The heart beats from 60 to 90 times a minute, the rate in any given healthy person being about four times that of the respirations. The heart is to some extent regulated by a nerve centre in the MEDULLA, closely connected with those centres which govern the lungs and stomach, and nerve ?bres pass to it in the vagus nerve. The heart rate and force can be diminished by some of these ?bres, by others increased, according to the needs of the various organs of the body. If this nerve centre is injured or poisoned – for example, by lack of oxygen – the heart stops beating in human beings; although in some of the lower animals (e.g. frogs, ?shes and reptiles) the heart may under favourable conditions go on beating for hours even after its entire removal from the body.... heart
(iii) blockage of the circulation of CSF. Such disturbances in the circulation of the ?uid may be due to congenital reasons (most commonly associated with SPINA BIFIDA), to MENINGITIS, or to a tumour.
Symptoms In children, the chief symptoms observed are the gradual increase in size of the upper part of the head, out of all proportion to the face or the rest of the body. The head is globular, with a wide anterior FONTANELLE and separation of the bones at the sutures. The veins in the scalp are prominent, and there is a ‘crackpot’ note on percussion. The normal infant’s head should not grow more than 2·5 cm (1 inch) in each of the ?rst two months of life, and much more slowly subsequently; growth beyond this rate should arouse suspicions of hydrocephalus, so medical professionals caring for infants use centile charts for this purpose.
The cerebral ventricles are widely distended, and the convolutions of the brain ?attened, while occasionally the ?uid escapes into the cavity of the cranium, which it ?lls, pressing down the brain to the base of the skull. As a consequence of such changes, the functions of the brain are interfered with, and in general the mental condition of the patient is impaired. Untreated, the child is dull and listless, irritable and sometimes suffers from severe mental subnormality. The special senses become affected as the disease advances, especially vision, and sight is often lost, as is also hearing. Towards the end, paralysis is apt to occur.
Treatment Numerous ingenious operations have been devised for the treatment of hydrocephalus. The most satisfactory of these utilise unidirectional valves and shunts (tubes), whereby the cerebrospinal ?uid is bypassed from the brain into the right atrium of the heart or the peritoneal cavity. The shunt may have to be left in position inde?nitely.... hydrocephalus
The brain has 4 ventricles: 1 in each of the 2 cerebral hemispheres; a 3rd at the centre of the brain, above the brainstem; and a 4th between the brainstem and cerebellum. These cavities are filled with cerebrospinal fluid.
The ventricles of the heart are its 2 lower chambers, which receive blood from each atrium and pump it to the lungs and to the rest of the body.... ventricle
In one part of the body there is a further complication. The veins coming from the bowels, charged with food material and other products, split up, and their blood undergoes a second capillary circulation through the liver. Here it is relieved of some food material and puri?ed, and then passes into the inferior vena cava, and so to the right atrium. This is known as the portal circulation.
The circle is maintained always in one direction by four valves, situated one at the outlet from each cavity of the heart.
The blood in the arteries going to the body generally is bright red, that in the veins dull red in colour, owing to the former being charged with oxygen and the latter with carbon dioxide (see RESPIRATION). For the same reason the blood in the pulmonary artery is dark, that in the pulmonary veins is bright. There is no direct communication between the right and left sides of the heart, the blood passing from the right ventricle to the left atrium through the lungs.
In the embryo, before birth, the course of circulation is somewhat di?erent, owing to the fact that no nourishment comes from the bowels nor air into the lungs. Accordingly, two large arteries pass out of the navel, and convey blood to be changed by contact with maternal blood (see PLACENTA), while a large vein brings this blood back again. There are also communications between the right and left atria, and between pulmonary artery and aorta. The latter is known as the ductus arteriosus. At birth all these extra vessels and connections close and rapidly shrivel up.... circulatory system of the blood
Form and position Each lung is a sponge-like cone, pink in children and grey in adults. Its apex projects into the neck, with the base resting on the DIAPHRAGM. Each lung is enveloped by a closed cavity, the pleural cavity, consisting of two layers of pleural membrane separated by a thin layer of ?uid. In healthy states this allows expansion and retraction as breathing occurs.
Heart/lung connections The HEART lies in contact with the two lungs, so that changes in lung volume inevitably affect the pumping action of the heart. Furthermore, both lungs are connected by blood vessels to the heart. The pulmonary artery passes from the right ventricle and divides into two branches, one of which runs straight outwards to each lung, entering its substance along with the bronchial tube at the hilum or root of the lung. From this point also emerge the pulmonary veins, which carry the blood oxygenated in the lungs back to the left atrium.
Fine structure of lungs Each main bronchial tube, entering the lung at the root, divides into branches. These subdivide again and again, to be distributed all through the substance of the lung until the ?nest tubes, known as respiratory bronchioles, have a width of only 0·25 mm (1/100 inch). All these tubes consist of a mucous membrane surrounded by a ?brous sheath. The surface of the mucous membrane comprises columnar cells provided with cilia (hair-like structures) which sweep mucus and unwanted matter such as bacteria to the exterior.
The smallest divisions of the bronchial tubes, or bronchioles, divide into a number of tortuous tubes known as alveolar ducts terminating eventually in minute sacs, known as alveoli, of which there are around 300 million.
The branches of the pulmonary artery accompany the bronchial tubes to the furthest recesses of the lung, dividing like the latter into ?ner and ?ner branches, and ending in a dense network of capillaries. The air in the air-vesicles is separated therefore from the blood only by two delicate membranes: the wall of the air-vesicle, and the capillary wall, through which exchange of gases (oxygen and carbon dioxide) readily takes place. The essential oxygenated blood from the capillaries is collected by the pulmonary veins, which also accompany the bronchi to the root of the lung.
The lungs also contain an important system of lymph vessels, which start in spaces situated between the air-vesicles and eventually leave the lung along with the blood vessels, and are connected with a chain of bronchial glands lying near the end of the TRACHEA.... lungs
Valsalva’s manoeuvre is involuntarily performed when a person strains to open his or her bowels: in these circumstances the passage of air to the lungs is blocked by instinctive closure of the vocal cords in the LARYNX. The resultant raised abdominal pressure helps to expel the bowel contents. The manoeuvre is also used in the study of cardiovascular physiology because the rise in pressure in the chest restricts the return of venous blood to the right atrium of the HEART. Pressure in the peripheral VEINS is raised and the amount of blood entering and leaving the heart falls. This drop in cardiac output may cause the subject to faint because the supply of oxygenated blood to the brain is reduced.... valsalva’s manoeuvre
Structure While of similar structure to an artery, veins have much thinner walls, with much less muscular tissue. Furthermore, most veins have one-way VALVES to ensure that the blood ?ows in the right direction. These are most numerous in the legs, then the arms, with few in the internal organs.
Chief veins Four pulmonary veins open into the left atrium of the heart, two from each lung. The superior vena cava returns the blood from the head, neck, and arms; while the inferior vena cava returns blood from the legs and abdomen. The large basilic vein that runs up the inner side of the upper arm is the vein usually opened in blood-letting (see VENESECTION). The great saphenous vein is of special interest, because of its liability to become distended or varicose. Within the abdomen, the inferior vena cava receives branches corresponding to several branches of the aorta, its largest branches being the hepatic veins, which return not only the blood that has reached the liver in the hepatic arteries, but also blood which comes from the digestive organs in the PORTAL VEIN to undergo a second capillary circulation in the liver.
There are several connections between the superior and inferior cava, the most important being three azygos veins that lie upon the sides of the spinal column, the veins on the front of the abdomen, and some veins that emerge from the abdomen at the navel and connect the portal system with those of the inferior and superior vena cava. (See also CIRCULATORY SYSTEM OF THE BLOOD.)... veins
Alternatives. Teas: Balm, Motherwort, Hawthorn flowers or leaves. Tablets: Hawthorn, Motherwort, Mistletoe, Valerian.
Tincture Lily of the Valley: 8-15 drops when necessary.
Broom: Spartiol drops. (Klein) 20 drops thrice daily.
Broom decoction. 1oz to 1 pint water gently simmered 10 minutes. 1 cup morning and evening. ... heart – extra beats
Ventricular ectopic beats may be detected on an ECG.
If there are frequent abnormal beats that cause symptoms, or beats that arise from more than 1 site in the ventricles, treatment with an antiarrhythmic drug may be required.... ventricular ectopic beat
It is caused by an abnormally fast heart-rate due to serious heart disease, such as myocardial infarction or cardiomyopathy.
It may last for a few seconds or for several days.
Diagnosis is confirmed by ECG.
Emergency treatment is with defibrillation and an antiarrhythmic drug.... ventricular tachycardia
Mitral disease leads to heart failure either by a narrowing of the orifice (stenosis) or a regurgitation blocks the passage of blood from the left atrium (auricle) to the left ventricle. The left atrium enlarges (hypertrophies) in an effort to counter the impediment. Real compensation – increased thrust of the blood – is provided by the right ventricle. In order to overcome a mitral impediment the right ventricle has to enlarge.
Sooner or later the right ventricle cannot enlarge any further and general heart failure sets in. Though caused primarily by a lesion of the mitral valve, it may be secondary to left ventricular failure (LVF), thyroid disorder (thyrotoxicosis), pericarditis, congenital heart disease, or any disease which weakens ventricular muscle.
Venous congestion and back pressure of RVF leads to congestion and accumulation of fluid in the lungs, cough and spitting of blood, painful swelling of the liver, nausea, loss of appetite and severe wasting.
Where the right ventricle fails to move the blood forward as it arrives from the systemic circulation, generalised dropsy sets in. Congestion of the kidneys leads to reduced urinary excretion and presence of albumin in the urine.
The picture is well known to the cardiac practitioner: blueness of the skin, congestion of the brain circulation with sleeplessness and delirium. Soon the tension of water-logged tissues results in pain and extreme anxiety. Feet are swollen and ankles pit on pressure; chest cavities fill with fluid and the abdomen swells (ascites).
Alternatives. Cardio-tonics would be given to strengthen the ventricle and diuretics to correct fluid retention: Lily of the Valley, Hawthorn, Motherwort, Broom. BHP (1983).
Due to rheumatic fever: Hawthorn.
High Blood Pressure: Mistletoe.
Effort Syndrome: Motherwort.
Tinctures. Combine, Lily of the Valley 2; Hawthorn 2; Motherwort 3. Dose: 1 teaspoon thrice daily after meals.
Diet. Low salt, low fat, high fibre. Restricted fluids, vegetarian protein foods, yoghurt. See also: DIET – HEART AND CIRCULATION.
Supplements. Potassium (bananas), Vitamin B6.
General. Stop smoking. Correction of overweight. Complete bed-rest with legs raised above level of the abdomen and patient propped-up to relieve difficult breathing. ... heart – right ventricular failure (rvf)
May be caused by anxiety, exercise, smoking, alcohol, caffeine, anaemia, thyroid disorder, a specific fever or presence of a ‘coronary’. Extra-systoles may be felt as a thumping in the chest. May also be caused by excessive digitalis therapy.
Treatment. Where due to shock (Passion flower), overstrain (Ginseng), flatulence (Chamomile), sense of oppression in the chest (Hawthorn), suffocation (Aconite), worse lying on the left side (Cactus), highly sensitive women (Pulsatilla), mental depression (Cactus), congestion of the lungs (Lobelia).
Tea. Combine equal parts – Motherwort and Passion flower. 1-2 teaspoons to each cup boiling water; infuse 15 minutes; 1 cup as necessary.
Tablets/capsules. Chamomile, Hawthorn, Lobelia, Mistletoe, Motherwort, Pulsatilla, Passion flower (Passiflora), Valerian.
Formula. Equal parts: Lily of the Valley, Passion flower. Dose: Powders: 500mg (two 00 capsules or one-third teaspoon). Liquid extracts: 1 teaspoon. Tinctures: 2 teaspoons. Thrice daily in water or honey. Practitioner. Tincture Aconite, BPC 1949. Dose: 0.12 to 0.3ml (2 to 5 drops). OR:– Spartiol (Broom) 20 drops thrice daily. (Klein).
Diet. See: DIET – HEART AND CIRCULATION.
Vitamin E. One 400iu capsule (or tablet) daily.
Minerals. Magnesium 300mg daily. ... palpitation
In sinus tachycardia, the rate is raised, the rhythm is regular, and the beat originates in the sinoatrial node (see pacemaker). Supraventricular tachycardia is faster and the rhythm is regular. It may be caused by an abnormal electrical pathway that allows an impulse to
circulate continuously in the heart and take over from the sinoatrial node. Rapid, irregular beats that originate in the ventricles are called ventricular tachycardia. In atrial flutter, the atria (see atrium) beat regularly and very rapidly, but not every impulse reaches the ventricles, which beat at a slower rate. Uncoordinated, fast beating of the atria is called atrial fibrillation and produces totally irregular ventricular beats. Ventricular fibrillation is a form of cardiac arrest in which the ventricles twitch very rapidly in a disorganized manner.
Sinus bradycardia is a slow, regular beat. In heart block, the conduction of electrical impulses through the heart muscle is partially or completely blocked, leading to a slow, irregular heartbeat. Periods of bradycardia may alternate with periods of tachycardia due to a fault in impulse generation (see sick sinus syndrome).
A common cause of arrhythmia is coronary artery disease, particularly after myocardial infarction. Some tachycardias are due to a congenital defect in the heart’s conducting system. Caffeine can cause tachycardia in some people. Amitriptyline and some other antidepressant drugs can cause serious arrhythmias if they are taken in high doses.
An arrhythmia may be felt as palpitations, but in some cases arrhythmias can cause fainting, dizziness, chest pain, and breathlessness, which may be the 1st symptoms.
Arrhythmias are diagnosed by an ECG. If they are intermittent, a continuous recording may need to be made using an ambulatory ECG.
Treatments for arrhythmias include antiarrhythmic drugs, which prevent or slow tachycardias.
With an arrhythmia that has developed suddenly, it may be possible to restore normal heart rhythm by using electric shock to the heart (see defibrillation).
Abnormal conduction pathways in the heart can be treated using radio frequency ablation during cardiac catheterization (see catheterization, cardiac).
In some cases, a pacemaker can be fitted to restore normal heartbeat by overriding the heart’s abnormal rhythm.... arrhythmia, cardiac
Sudden onset of atrial fibrillation can cause palpitations, angina, or breathlessness. The heart’s inefficient pumping action reduces the output of blood into the circulation. Blood clots may form in the atria and may enter the bloodstream and lodge in an artery (see embolism).
Diagnosis of atrial fibrillation is confirmed by ECG.
Digoxin or beta-blocker drugs may be given to control the heartrate.
Atrial fibrillation of recent onset may be reversed by defibrillation.
In most cases, anticoagulant drugs are given to reduce the risk of embolism.... atrial fibrillation
In the systemic circulation, oxygen-rich blood from the pulmonary circulation is pumped under high pressure from the left ventricle of the heart into the aorta, from where it travels through arteries and smaller arterioles to all parts of the body. Within body tissues, the arterioles branch into networks of fine blood vessels called capillaries. Oxygen and other nutrients pass from the blood through the capillaries’ thin walls into body tissues; carbon dioxide and other wastes pass in the opposite direction. Deoxygenated blood is returned to the heart via venules, veins, and the venae cavae.
Venous blood returns to the right atrium of the heart to enter the pulmonary circulation. It is pumped from the right ventricle through the pulmonary artery
to the lungs, where carbon dioxide is exchanged for oxygen. The reoxygenated blood then returns through the pulmonary veins to the heart and re-enters the systemic circulation.... circulatory system
The other fundamental difference in circulation is that most blood bypasses the lungs in the fetus through 2 special channels in the fetal heart.
Blood passes from the right atrium of the heart to the left atrium through the foramen ovale.
Another channel, known as the ductus arteriosus, allows blood to pass from the pulmonary artery to the aorta.
Both channels normally close after birth.
In rare cases, they fail to close, causing a congenital heart disorder (see heart disease, congenital).... fetal circulation
There are several grades of heart block, from a slight delay between the contractions of the atria (see atrium) and ventricles (called a prolonged P-R interval) to complete heart block, in which the atria and ventricles beat independently. Heart block may be due to coronary artery disease, myocarditis, overdose of a digitalis drug, or rheumatic fever. A prolonged P-R interval causes no symptoms. In more severe heart block, the rate of ventricular contraction does not increase in response to exercise. This may cause breathlessness as a result of heart failure, or chest pains or fainting due to angina pectoris. If the ventricular beat becomes very slow, or if it stops altogether for a few seconds, loss of consciousness and seizure may occur due to insufficient blood reaching the brain. If the delay is prolonged, a stroke may result.Symptomless heart block may not need treatment. Heart block that is causing symptoms is usually treated by the fitting of an artificial pacemaker. Drugs, such as isoprenaline, that increase the heart-rate and the strength of the heart’s contractions, may be given as a temporary measure.... heart block
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