Capillaries

The microscopic blood vessels arranged in a network at the junction of arteries and veins are called capillaries. The capillary wall is composed of flattened endothelial cells. The wall is covered by a sheath made of collagen and reticular fibers. This is called the basal lamina. The capillary network carries blood from the aorta to the venules. The capillary network adjacent to the aorta is called the arteriole and the capillary network adjacent to the vena cava is called the venous network. Exchange of nutrients, respiratory air, excreta etc. takes place through capillaries.
Vasa vasorum are the fine blood vessels that supply nutrients to the walls of large arteries and veins.

Artery

The blood vessels that carry O2-rich blood from the heart to different parts of the body are called arteries. Arteriosclerosis is the hardening and loss of elasticity of the artery walls. In arteriosclerosis, calcium and cholesterol accumulate in the artery walls and the amount of fibrous tissue increases. Arteriosclerosis is the narrowing of the lumen of arteries and arterioles. Arteriosclerosis is caused by accumulation of fatty substances or cholesterol in the cavities of arteries and arterioles. Atherosclerotic plaque is the accumulation of fatty material caused by arteriosclerosis.

Blood vessels

The vessels through which blood travels from the heart to different parts of the body and back to the heart from different parts of the body are called blood vessels. There are three types of blood vessels. Arteries, veins and capillary network.
1. Artery: The blood vessels that carry O2-rich blood from the heart to different parts of the body are called arteries. Arteriosclerosis is the hardening and loss of elasticity of the artery walls. In arteriosclerosis, calcium and cholesterol accumulate in the artery walls and the amount of fibrous tissue increases. Arteriosclerosis is the narrowing of the lumen of arteries and arterioles. Arteriosclerosis is caused by accumulation of fatty substances or cholesterol in the cavities of arteries and arterioles. Atherosclerotic plaque is the accumulation of fatty material caused by arteriosclerosis.
Arterial properties
(i) Arterial wall is thick, strong and elastic
(ii) Its wall is divided into three layers. Tunica externa, tunica media and tunica intima.
(iii) It originates from the heart
(iv) Their lumen or cavity is small
(v) It does not contain kapatika
(vi) Arteries carry blood at high blood pressure
(vii) It carries O2 rich blood.
2. Veins: The blood vessels through which CO2-rich blood reaches the heart from different parts of the body are called veins.
Vein characteristics
(i) Vein wall is thin and inelastic
(ii) Its wall is divided into three layers. Tunica externa, tunica media and tunica intima.
(iii) It originates from body cells
(iv) Their lumen or cavity is large
(v) It contains kapatika
(vi) Arteries carry blood at low blood pressure.
(vii) It carries blood containing CO2
3. Capillaries: The microscopic blood vessels arranged in a network at the junction of arteries and veins are called capillaries. The capillary wall is composed of flattened endothelial cells. The wall is covered by a sheath made of collagen and reticular fibers. This is called the basal lamina. The capillary network carries blood from the aorta to the venules. The capillary network adjacent to the aorta is called the arteriole and the capillary network adjacent to the vena cava is called the venous network. Exchange of nutrients, respiratory air, excreta etc. takes place through capillaries.
Vasa vasorum are the fine blood vessels that supply nutrients to the walls of large arteries and veins.

Causes of heart failure

(i) In case of viral infection in the heart.
(ii) If inflammation occurs in the muscular layer of the heart.
(iii) Heart failure may occur due to genetic reasons.
(iv) Drugs like methylphenidate, tricyclic antidepressants, antipsychotics, dopamine agonists, TNF inhibitors, salbutamol, tamsulosin etc. cause heart failure.
(v) Drugs like cocaine, methamphetamine etc. cause heart failure.
(vi) Exposure to harmful substances like lead, cobalt, lithium etc. can cause damage to the heart.
(vii) Heart can become dysfunctional due to diseases like heart attack, heart failure, high blood pressure, diabetes, AIDS etc.
(viii) Diseases like amyloidosis, systemic erythematosus etc. increase the risk of heart failure.
(ix) The heart becomes dysfunctional when the cardiac muscle is atrophied.

Myogenic control, cardiac cycle control

Automatic regulation of cardiac activity without any external stimulus is called myogenic control. When the mammalian heart is dissected and placed in an O2-rich saline solution at 370C, the heartbeat continues without any external stimulation. The transformed muscle of the heart wall is responsible for its myogenic nature. Together they regulate the myogenic cycle.
According to Kitch and Flack, the SAN is located in the wall of the right atrium. It generates electrical signals automatically without any external stimulation. This electrical signal spreads to the wall of the right atrium. Then it reaches the left atrium from the right atrium. As a result, both atria contract simultaneously. Electrical signals then travel from the SAN to the AVN. Signal bundles from the AVN reach the Then the signal from the bundle of His reaches the Purkinje fibers of the ventricles. Impulses are transmitted to the ventricular wall via the Purkinje receptors. As a result, the ventricles contract.

Ventricular diastole

During this time the two ventricles are in dilated or relaxed state. Bicuspid and tricuspid cusps are open. But the semilunar eyelid remains closed. The pressure between the two ventricles decreases. As a result, blood containing CO2 enters the right ventricle from the right atrium and blood containing O2 enters the left ventricle from the left atrium. The duration of this dasha is 0.5 seconds.