human heart
INTRODUCTION
Human circulatory system, also known as the blood vascular system consists of a muscular chambered heart, a network of closed branching blood vessels and blood, the fluid which is circulated
Structure of Human Heart
- Heart is located in the thoracic cavity, in between the two lungs, slightly tilted to the left. It is derived from the mesoderm and has the size of a clenched fist.
- Heart is protected by a double walled membranous bag called The pericardium consists of two layers, an outer parietal pericardium and an inner visceral pericardium attached to the heart. A space called pericardial cavity is present between the two layers which is filled with a fluid called pericardial fluid. The pericardium protects the heart from shocks and mechanical injuries.
- Our heart is divided into four chambers, two relatively small upper chambers called atria (singular, atrium) and two larger lower chamber called ventricles. The walls of the ventricles are much thicker than that of the atria. The right and the left atria are separated by a thin , muscular wall called the interatrial septum whereas the right and left ventricles are separated by thick-walled interventricular septum
- A thick fibrous tissue called the atrio-ventricular septum separates the atrium and the ventricle of the same side. However,, both of the atrio- ventricular septum are provided with an opening through which the two chambers of the same side are connected.
- The openings between the atria and the ventricles are guarded by atrioventricular (AV) valves . The AV valve between right atrium and right ventricle has three flaps or cusps and is therefore called the tricuspid valve. The AV valve between the left atrium amd left ventricle has two flaps or cusps and is thus called the bicuspid valve or mitral valve.
- Special fibrous cords called the chordae tendinae are attached to the flaps of the bicuspid and tricuspid valves at one end and their other ends are attached to the ventricular wall with the special muscles. The papillary muscles. The chordate tendinae prevent the bicuspid and tricuspid valves from collapsing back into the atrio during powerful ventricular contractions.
- Three semilunar valves (half-moon shaped pockets) are found at the points where the pulmonary artery (arising from the right ventricles and carrying deoxygenated blood to the lungs) and arota (large artery arising from left ventricle and carrying oxygenated blood to all parts of the body) leave the heart . These valves prevent blood from getting back into the ventricles.
- The right atrium receives deoxygenated blood through coronary sinus and two large veins called venae cavae (one superior vena cava and one inferior vena cava). Theleft atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins.
Physiological properties of cardiac (heart) muscle fibres:-
- Excitability and contractility.
- Obeys all-or-none principle.
- Has longer refractory period therefore it never develops failure.
- Does not show summation.
- Shows conductivity and rhythmicity.
Origin of heart beat:-
- A specialized cardiac musculature called the nodal tissue is also distributed in the heart. A patch of this tissue called the sino-atrial node (SEN) is present in the upper right corner of the right artrium and is called pacemaker. A wave of contraction originate from it and spreads other parts of heart. Another mass of this tissue called the atrio-ventricular mode (AVN) is present in the lower left corner of right atrium, close to the atrio-ventricular septum.
- A bundle of nodal fibres, i.e. atrio-ventricular bundle (AV bundle) continues from the AVN which passes through the atrio- ventricular septa to emerge on the top of the inter ventricular septum as bundle of His and immediately divides into right and left bundle.
These branches give rise to minute fibres called Purkinge fibres throughout the ventricular musculature of the respective sides.
- The nodal musculature has the ability to generate action potential without any external stimuli, i.e., it is autoexcitable. Action potential is short – lasting event in which the electrical membrane potential of cell rapidly rises and falls. Although all the heart muscle cells have the ability to generate the electrical impulses that trigger cardiac contraction, the SAN initiates it, simply because it generates the max. number of action potentials,i.e., 70-75 min.-1, and is responsible for initiating and maintaining the rhythmic contractile activity of heart.Therefore, it is called the pacemaker of the heart. Our heart normally beats 70-75 times in min. (average 72 beats min.-1,). This is called heart rate.
funfacts:-
- The heart’s electrical impulses create a tiny amount of electricity, measurable as an electrocardiogram (ECG or EKG).
- The heart can continue to beat even if separated from the body, thanks to its intrinsic electrical system.
- The heart’s chambers hold approximately 6 quarts (5.7 liters) of blood, which circulates the entire body in about one minute.
- Heartbeats are influenced by factors such as music; listening to music with a fast tempo can increase heart rate.
- The heart’s “lub-dub” sound is produced by the closing of its valves during contractions.
- Heart cells can regenerate, although this process is limited in humans, unlike some other animals.
- The heart’s largest artery, the aorta, is almost the diameter of a garden hose.
- Emotional stress can lead to a condition called Takotsubo cardiomyopathy, or “broken heart syndrome,” which mimics a heart attack.
- The heart pumps oxygen-rich blood to the body via arteries and receives oxygen-depleted blood through veins.
- Heart rate variability, the variation in the time interval between heartbeats, is a marker of cardiovascular health and can be influenced by lifestyle factors like exercise and stress management.
The heart is not controlled by the brain; instead, it has its own pacemaker called the sinoatrial node, which initiates each heartbeat.
Heart valves ensure that blood flows in one direction, preventing backflow and maintaining efficient circulation.
The heart can beat outside the body in certain conditions; for example, heart cells cultured in a lab can pulsate rhythmically.
Regular physical activity strengthens the heart muscle, reducing the risk of cardiovascular diseases like heart attack and stroke.
The heart’s size can vary depending on factors such as age, fitness level, and overall health; for instance, athletes often have larger hearts due to training-induced adaptations.
Blood carries oxygen, nutrients, hormones, and waste products throughout the body, ensuring proper functioning of organs and tissues.
The heart pumps blood through a network of blood vessels called arteries, veins, and capillaries. Arteries carry oxygen-rich blood away from the heart, while veins return oxygen-depleted blood back to the heart.
Blood consists of plasma, red blood cells, white blood cells, and platelets. Plasma is the liquid portion of blood, while red blood cells carry oxygen, white blood cells fight infections, and platelets help in blood clotting.
The lymphatic system is a network of vessels and organs that help maintain fluid balance in the body and defend against infections. It collects excess fluid from tissues and returns it to the bloodstream.
High blood pressure can be caused by factors such as genetics, diet, lifestyle, and underlying health conditions. Treatment typically involves lifestyle changes, medication, and sometimes surgery.
Dehydration reduces blood volume, making it harder for the heart to pump blood efficiently. This can lead to symptoms like dizziness, fatigue, and increased heart rate. Severe dehydration can be life-threatening.
Common signs include cold hands and feet, numbness or tingling in the extremities, swelling, slow healing of wounds, and changes in skin color or texture.
Hormones like aldosterone and antidiuretic hormone (ADH) regulate fluid balance by controlling the reabsorption of water and electrolytes in the kidneys. Other hormones, like adrenaline, can affect heart rate and blood pressure.
Exercise improves circulation by increasing blood flow, strengthening the heart muscle, and promoting the growth of new blood vessels. It also helps lower blood pressure, reduce inflammation, and improve overall cardiovascular health.
Maintaining a balanced diet, staying hydrated, exercising regularly, avoiding tobacco use, managing stress, and maintaining a healthy weight are all important for promoting healthy circulation and overall cardiovascular health.
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