Heart Anatomy and Physiology-Physiology of Cardiovascular System
In this article you will know about the Structure of Heart, Heart Anatomy and Physiology, Physiology of Cardiovascular System. If you want to know more click here...
Heart is a Muscular organ situated in the mediastinum (space between two lungs) which pumps blood to all parts of the body.Precardium is the area of the chest that overlies heart. Cardiac and Coronary are terms that denote heart. Most of it lies on the left side of the midline (approximately two third) and only some part is situated in the right side of the midline.Size : 12x9x6 cm3 , about the size of one's fist Weight : Males 300 gm & Females 250 gm.
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| The Heart |
Anatomy of heart
Four chambers:
1. Right Atrium
2. Left Atrium
3. Right Ventricle
4. Left Ventricl
Four valves:
A. Atrio-ventricular valves: valves between atrium and ventricles
Two septa (plural of septum)
1. Inter-ventricular septum: septum between ventricles
2. Inter-atrial septum: septum between atria
Layers of heart
Heart has three layers:
1. Pericardium: covering of the heart
Pericardium has two layers:
- Outer- Fibrous pericardium
- Inner- Serous Pericardium
Serous pericardium again has two layers:
- Outer- Parietal layer
- Inner- Visceral layer
The space between parietal and visceral pericardium is called Pericardial cavity which contains pericardial fluid.
2. Myocardium: Middle layer which consists of Cardiac muscle. Cardiac muscle is a special type of muscle found only in heart. It contains intercalated discs at the junction of two muscle cells or muscle fibre which helps in fast conduction of electrical impulse. It has got following properties: Automaticity, Rhythmicity, Contractility, Conductivity, All or none law, Frank Starling‟s Law. Thickest wall of heart is that of Left ventricle because it has more cardiac muscle than anywhere else.
3. Endocardium: consists of squamous epithelium which lines the cavity of heart.
Note:
- Apical impulse: visible pulsation of heart.
- Apex beat: outermost and lowermost palpable point where the heart beat can be felt.
- Annulus fibrosus is insulator layer present between atrium and ventricles.
- Moderator band is present in right ventricle.
- Trabeculae carni are the irregular muscle ridges found in the wall of ventricles.
- Musculi pectini (pectinate muscle) are prominent ridges of atrial myocardium.
- Auricle: small conical pouch projecting from the upper anterior portion of each atrium of the heart.
- Heart has got apex and base.
Two large blood vessels originate from heart:
1. Pulmonary trunk: Arises from the right ventricle and gives branches pulmonary arteries to both lungs (3 branches to right lung and two branches to left lung).
2. Aorta: Arises from left ventricle and continues as ascending aorta, arch of aorta and descending aorta in the thorax, finally becoming abdominal aorta after piercing the diaphragm.
Blood is collected in the heart through three main veins
1. Superior venacava: from body parts above the heart
2. Inferior venacava: from body parts below the heart
3. Pulmonary veins: from right and left lung
Blood supply of heart
Heart receives blood from Coronary arteries which arise from the aorta. Aorta gives two branches Right and left coronary arteries just above the aortic valve. So, coronary arteries are the first branches of aorta.
The blood of heart is collected via the coronary veins which drain into coronary sinus which in turn drains into right atrium.
Nerve supply of heart
Heart is innervated by both Parasympathetic and Sympathetic Nervous System. Parasympathetic supply decreases the heart rate whereas Sympathetic supply increases the heart rate.
HEART AS A PUMP
Conducting System of Heart
Electrical activity of heart begins from SA node, from where impulse is transmitted to AV node by internodal fibres. Bundle of His arises from the AV node. Bundle of His then divides into two branches: Right and Left Bundle branch which branch into smaller Purkinje fibre and supply the muscle of the ventricle.
Sino-Atrial node (SA node) is also called Pacemaker of the heart because it is the main place where electrical impulse for heart is originated. It is present in the right atrial wall near the opening of superior venacava.
Atioventricular node (AV node) is also called Pace-setter of the heart because it maintains the pause between contraction of atrium and ventricle by delaying the transmission of impulse. It is present in the lower part of atrial septum.
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| Conducting System of Heart |
Cardiac cycle
Heart contracts and relaxes over and over forming a cycle of events. Contraction of heart is called Systole Relaxation of heart is called Diastole Heart takes 0.8 second to complete a Cardiac Cycle (1 contraction and 1 relaxation).
Atrium Systole 0.1 sec & Diastole 0.7 sec
Ventricle Systole 0.3 sec & Diastole o.5 sec
Heart Sounds
Sounds are produced in heart when valves close and blood hits the walls. Two heart sounds can be distinctly heard by stethoscope and are called 1st and 2nd heart sounds. 3rd and 4th heart sounds are rarely heard in normal people; when they are heard some pathology should be suspected.
1 st (Lub): low pitch loud sound (Closure of A-V valves)
2 nd (Dub): High pitch low loudness (Closure of semilunar valves)
Murmur: Abnormal sounds originating from the heart. It can occur due to regurgitation (backflow of blood through valves) or stenosis (narrowing of the valves).
Heart rate and Pulse
Heart rate is the number of heart beats per minute. Pulse is the wave produced in the wall of the blood vessels due to pumping of blood during each heartbeat. Pulse rate is usually measured in Radial Artery.
Normal heart rate
- Foetus 120-180 b/min
- Newborn 100-160 b/min
- Children 80-120 b/min
- Adults 60-100 b/min
Stroke volume (SV): It is the amount of blood pumped by each ventricle in each heartbeat. It is about 70 ml.
Cardiac Output (CO): It is the amount of blood pumped by each ventricle in one minute. It is about 5litre/minute. Mathematically, it can be calculated as
Cardiac Output = Stroke volume x Heart rate
Fick's Principle is used to measure Cardiac output.
Cardiac Output to different organs
- Liver-27%
- Kidney-25%
- Muscles-15%
- Brain-14%
- Heart-4%
Maximum Cardiac Output: Liver
Maximum Cardiac Output per gram: Kidney
Most vascular organ: Thyroid Gland
Avascular organs: Cornea, Cartilage, Epidermis
BLOOD PRESSURE
It is the pressure exerted by blood on the wall of the blood vessels. Blood pressure may be arterial or venous blood pressure. It may also vary as Systolic or Diastolic BP.
Systolic BP: when the heart contracts
Diastolic BP: when the heart relaxes
The blood pressure we generally measure is arterial blood pressure. It is measured in Brachial artery with Sphygmomanometer. It is measured in unit 'mm of Hg'. Sounds heard during measurement of blood pressure are called Korotkoff's sound (Note: 5 Korotkoff's sounds are heard).
Remember: Instruments required to measure BP are Sphygmomanometer and Stethoscope.
Pulse pressure:
It is the difference between Systolic BP and Diastolic BP. Its normal value is 40 mm of Hg. Pulse pressure= Systolic BP - Diastolic BP.
Mean Arterial Pressure (MAP):
It is a term used to describe an average blood pressure in an individual. It is the most important pressure in terms of perfusion (blood supply) of an organ. Its normal value is 93 mm of Hg.
MAP=Diastolic BP+1/3 pulse pressure
BLOOD CIRCULATION
Blood is distributed throughout the body by the pumping action of left ventricle of heart. In tissues smaller arteries called arterioles divide into capillaries through which exchange of various materials occur. Capillaries then unite to form venules (smaller veins) which form veins. Veins drain blood into the right side of the heart from where blood is taken to the lungs for oxygenation. Finally, blood returns to the left side of the heart and the same cycle is repeated.
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| Blood Circulation |
Here, we can distinguish two types of circulation:
A. Systemic circulation: Flow of blood from left side of heart till it returns to the right side after passing through various tissues of our body.
B. Pulmonary circulation: Flow of blood from the right side of the heart till it returns to the left side of the heart after passing through the lungs.
So, at any instant blood can be at three places:
1. Systemic Circulation: 84% of whole blood
- Arterial blood-20%
- Venous blood-9%
2. Pulmonary circulation: 9%
3. Heart: 7%
FOETAL CIRCULATION
The oxygenation of blood in foetus doesn't occur through lungs, as foetus doesn't respire. In fact oxygenation of foetal blood takes place in placenta through the blood of mother. Therefore there are certain differences in foetal blood circulation and blood circulation in humans after birth. There are three distinguishing feature of Foetal circulation:
1. Ductus Arteriosus: It is a blood vessel connecting Left Pulmonary artery to Arch of Aorta. After birth it becomes nonfunctional and persists as ligamentum arteriosum.
2. Ductus Venosus: It connects umbilical vein to the Inferior venacava. After birth it becomes non-functional and persists as Ligamentum venosum.
3. Umbilical cord: It contains 2 umbilical arteries and 1 umbilical vein. It forms the communication between foetus and the placenta. After birth it becomes umbilical ligament.
4. Foramen ovale: It is a foramen present between Right and left atrium. It closes after birth and remains as Fossa ovalis.
Note: If any of these four fail to close after birth, they form abnormal communication which can be life-threatening to the child.
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