Heart Anatomy: Functions, Facts & Physiology

Heart

What is Heart?

Human Heart is a Hollow muscular organ that pumps the blood through the circulatory system by rhythmic contraction and dilation. In vertebrates there may be up to four chambers (as in humans), with two atria and two ventricles. The heart is located in the chest between the lungs behind the sternum and above the diaphragm. It is surrounded by the pericardium. Its size is about that of a fist. Heart anatomy

Heart Anatomy

It's average weight about is about 340grams in men and 255grams in women. The left half and the right half is divided by the wall called Septum. Each half, in turn, is divided into a upper chamber called Autrium or Auricle and a lower chamber called Ventricle. The Auricle receives blood from the veins and the ventricles pumps the blood into the arteries. ( Heart anatomy )

• Heartbeats in normal healthy Adult, the contraction and relaxation mechanism of the ventricles results in a heartbeat of about 70-72/min in males and 78-82/min in females .

• Situated in thoracic cavity in pericardial cavity close to its front wall.  It's broad base faces upward and backward. It's narrow apex faces downward, forward and slightly to the lest side and rests on diaphragm, below cardiac notch of left lungs.

• Wall of heart is made up of cardiac muscle fibre, connective tissues and tiny body vessels. Heart is situated in the chest between the lungs. Heart is hollow, muscular, somewhat, conical four-chambered force pump, enclosed in a fibrous bag.

Shape:  Some conical, like a inverted come.

Colour:  Dark red.

Chamber:  4 ( 2 auricles and 2 ventricles )

Size:  Roughly 12 x 9 cms.

Weight:  Average weight is about 300gm in male and 250gm in female.

Functions of the Heart

• The Heart supplies pure blood to the all parts of the body through arteries.

• It collects impure blood from organs / tissues through veins.

• It pumps impure blood into the lungs for purification. and

• It collects pure blood from the lungs to supply to the all parts of the body. 

Internal Structure of the Heart

Wall of auricles are thin than wall of ventricles, because they have to push the blood to ventricles only situated close to them.

Walls of ventricles are thick as they have to pump the blood quite far away. Wall of left ventricle is 3 times thicker as it has to pump the blood to complete body.
Heart anatomy

Heart has two pumps 

(i) Left pump : It leads oxygenated blood which is red in colour.

(ii) Right pump : It leads deoxygenated blood (purple in colour). Blood between two pumps does not mix directly. However in foetus there is an opening, so two pumps meet as lungs are not functioning. So foetus gets oxygen from mother but just before birth opening is closed. If the opening is not closed, then condition of blue baby is reached, and immediate surgery is required.

Auricle: Smaller in size and thinner muscular valves.

Ventricle: Larger in size and thicker muscular walls.

Left ventricle : Pumps oxygenated blood to rest of the body.

• Taller the person, lower the blood pressure in adult. 

• Male have lower blood pressure than female. In wall of ventricle, tendinous cords present.

• Inner wall of ventricle is raised into low muscular ridges as columnae carneae and few large muscular elavation as papillary muscles.

• Between ventricles inter ventricular septum present, bent to right side.

• Lumen of left ventricle is large and lumen of right ventricle is small and semilunar shape.

• Between auricles and ventricles A.V. node present.

• Between 2 auricles, inter auricular septum present. In emrbyo in it foramen ovalis aperture present, that converts into a fossae ovalis on birth time.

Right auricle : In this 2 opening present pre caval and post caval (in rabbit 3 openings).

• On opening of pre cavals eustachian valve present. Behind it coronary sinus opens on it the basius valve present. Right auricle opens into right ventricle.

Left auricle : In this pulmonary veins open by common aperture (without valve). It brings oxygenated blood from lungs into left auricle.

• Right auricle S.A. node or pace maker or heart of heart or node of Keith and Flack present. It is made up of cardiac muscles and stimulate heart beat. It is connected to vagus nerve.  Both auricles open into ventricles by auriculo ventricular valve.

• In right side, it is made up of three flaps

(i)tricuspid valve

(ii)lower edges of valve are fixed to papillary muscles of ventricle wall by chordae tendinae fibres.

• In left side it is bicuspid or Mitral valve.

Both valves are one way, i.e. allow blood from A to V not vice versa.

 Cardiac Cycle of Heart

The cardiac cycle consists of one heart beat or one cycle of contraction and relaxation of the cardiac muscle. During a heart beat, there is contraction and relaxation of atria and ventricles. The contraction phase is called systole while relaxation phase is called diastole. When both atria and ventricles are in diastolic or relaxed phase, this is joint diastole.

Heart Sounds

The beating heart produces characteristic sounds which can be heard by placing the ear against the chest or by using stethoscope (an instrument which magnifies sounds and conducts them to ear)ln a normal person, two sounds are produced per heart beat.

1. First sound.

This is caused partly by the closure of the closure of the bicuspid and tricuspid valves and partly by the contraction of the muscles in the ventricles. The first sound lub is low pitched not very loud and of long duration.

2. Second sound.

This is caused by the closure of the semilunar valves and marks the end of ventricular systole. The second sound dub is highly pitched, louder, sharper and shorter in duration.

Defects of Heart

1. Blue Baby syndrome (Cyanosis).:-

Due  to persisting foramen ovalis in atrial septum even after birth, the impure blood from right auricles comes to left auricle and then into left ventricle from where it is supplied to the body increasing the supplied to the body increasing the bluishness of the body.

2. Heart block (Cardiac arrest).:- 

If S-A node becomes defective it can not generate impulse properly and the heart beat becomes irregular or may stop. This is corrected by implanting artificial electronic pacemaker in the chest.

3. Murmuring heart:-

Due to defects in valves instead of the normal lub-dub sound, murmuring sound appears as the symptom.

4. Mitral stenosis.

Due to defect of mitral valve, passage of blood through A-V aperture, becomes improper.

5. Regurgitation.

Due to improper closure of A-V aperture, some blood during ventricular systole reenters the auricle. Cardiac valves may be defective by birth or may get damaged due to staphylococcal infection {rheumatic fever). This can be repaired or replaced surgically.

6. Angina pectoris.:- 

Due to blockage or thickening of coronary vessel's wall, there is inadequate blood flow to heart muscles associated with pain in heart during exertion or emotional tension.

The blockage may be due to deposition of cholesterol, smoking, diabetes or various other factors. Similar defect is also called coronary thrombosis when coronary vessels are blocked by blood clots.

7. Brown's heart disease (Brown's atrophy):-

Excess lipid (or lipofuschin) level in blood causes its deposition in coronary vessels which atrophy and causes symptoms as above.

8. Hooping heart.:-

Sometimes improper rhythms in heart beat occur, this is generally the indication of heart attack.

9. Myocardial infarction (Heart attack).:-

lnsufficient blood and 02 supply to part of cardiac muscles may cause death of that part. From damaged heart muscle cells, certain enzymes leak hence their presence in plasma is very simple diagnostic feature for heart attack, these enzymes are lactate dehydrogenase and transaminase.

10.Dextrocardia.:-

If heart is placed towards right side in the thoracic cavity as born defect.

11. Ectopia cordis.:- 

Sometimes heart becomes located outside the thoracic cavity as born defect.

Heart Beat

The spontaneous and rhythmic contraction and relaxation of heart to pump out and receive blood is called heart beat. So systole and diastole are collectively called heart beat.

Heart anatomy

Types

Heart beat is of two types.

1. Neurogenic :

Controlled by nerve:e.g.

lower animals - Arthropoda, Mollusca.

2. Myogenic :

By own muscles: e.g.

vertebrates including man and rabbit.

Some Facts

Neurogenic part is less. It is under control of upper part of medulla. Sympathatic accelerate heart beat. Para sympathatic or vagal inhibit heart beat. Adrenal, thyroxine increases heart beat.

Heart beat is

210/ minute in rabbit.

72 / minute in man.

500 / minute in mice.

800 / minute in shrew.

25 / minute in elephant.

8 / minute in belenoptera.

Origin of the HeartBeat

Mammalian heart is myogenic (myo = muscle, genic = originating from) i.e. heart beat originates from a muscle (however, it is regulated by the nerves). The heart beat originates from the sinoatrial node (SA node)-pace maker, which lies in the wall of the right atrium near opening of the superior vena cava. SA node is a mass of neuromuscular tissue. Sometimes SA node may become damaged or defective, so beat does not function properly. This can be remedied by the surgical grafting of an artificial pace maker in the chest of the patient. The artificial pace maker stimulates the heart at regular intervals to maintain its beat.

Conduction of Heart beat:-

Another mass of neuromuscular tissue, Atrioventricular node (AV node) is situated in the wall of the right atrium. AV node picks up the wave of contraction propagated by SA node. A mass of specialized fibres, bundle of His, originates from the AV node.

Bundle of His divides into two branches; One going to each ventricle. Within the mycocardium of the ventricles, branches of bundle of His divide into a net work of fine fibres called Purkinje fibres. The bundle of His and the Purkinje fibres convey impulse of contraction from AV node to the myocardium of the ventricles.

Regulation of Heart beat:-

The rate of heart beat is regulated by two mechanisms.

1 .Nervous regulation :

Cardiac centre lies in the medulla oblongata of the brain.

Cardiac centre is formed of two parts 

(i)Cardio-inhibitor

(ii)Cardio-accelerator

Cardio-inhibitor is connected with the heart through vagus nerve (it carries-parasympathetic nerve fibres) and cardio accelerator through sympathetic nerve fibres. Sensory fibres extend from the receptors present in the vena cava, aorta and carotid sinuses to the cardiovascular centre of in the medulla oblongata. Impulses received from the aorta and carotid sinuses decrease the heart rate, whereas impulses from the vena cava increase the heart rate.

2.HormonaI regulation:-

Adrenalin (epinephrine) and Noradrenalin (norepinephrine) hormones are secreated by medulla of the adrenal glands. Noradrenalin accelerates the heart beat under normal conditions while adrenalin does this function at the time of emergency. These hormones directly influence the SA node.

Thyroxine hormone secreated by thyroid gland increases oxidative metabolism of the body cells. This requires more oxygen and thus indirectly increases heart beat.

Heart rate

Pulse per minute is called heart rate.

Human heart beats about 72 times per minute in an adult person at rest, this is heart rate of that person. Heart rate increases during exercise, fever, fear and anger. Because smaller animals have the higher metabolic rate, their heart rate is higher than larger animals. An elephant has normal heart rate of about 25 per minute whereas mouse has a normal heart rate of several hundreds per minute.

Pulse

Pulse is rhythmic contraction and relaxation in the aorta and its main arteries. Thus pulse is a wave of increase which passes through arteries as the left ventricle pumps its blood into the aorta. Pulse is a regular jerk of an artery.

Therefore, it is also called arterial pulse.

The pulse rate is exactly same as the heart rate i.e. 72 because an artery pulses every time the heart beats. Pulse is usually taken on the radial and ulner artery in the wrist but it can be taken on any artery that flows near enough to the surface of the body to be felt like neck, temples and ankles.

Factors affecting Pulse rate:- 

 1. Pulse rate in children is more rapid than in adults.

2. Pulse rate is more rapid in the female than in the male.

3. When the person is standing up, pulse rate is more rapid than when he/she is lying down.

4. When any strong emotion is experienced, then pulse rate is increased
e.g. anger, excitement, fear etc.

5. Any exercise increases rate of the pulse.

Healthy Heart Slogans

Some facts about Heart

• Taller person has larger heart. 

• Human heart is fully developed about 8 week after conception (starts beating after 4 week of conception). 

• Birds and animals have 4 chambered heart (Highly developed). 

• In left ventricle pressure is 115-125 mm Hg.

• In right ventricle pressure is 25-30 mm Hg. 

• In man, cardiac cycle is of 0.8 sec. 

• Heart beat below normal is brachycardia. 

• Heartbeat above normal is Tachycardia.

• Fish have a two chambered heart:(i) Atrium (ii) Ventricle.