Circulation in humans

Circulation in humans:

As we know our body is made up of cells and nutrients and oxygen needed to survive, and wastes need to be removed from them. transportation of nutrients, gases, wastes, and other substances from one part of our body to the other part, is carried out by blood. In simple words, transportation in humans is carried out with the circulation of blood. Since blood passes twice through the human heart, it is termed Double circulation

Function of transportation

• Transport of nutrients to the tissues for their utilization
• Transport of respiratory gases (O2 and CO2) to and from the cells.
• Collection of metabolic wastes from tissues and transporting them to excretory organs for their removal.
• Uniform distribution of heat in the body

Organs involved in transportation -Heart, Blood vessels, Blood, lymph nodes, and lymph vessels.

Structure and Function of the Human Heart

The heart of human:

The human heart is a mesodermally derived organ. It is a muscular organ made of cardiac muscle fibers. The human heart is situated in the thoracic cavity, in between the two lungs, slightly tilted to the left. It is protected by a double-walled pericardium, enclosing pericardial fluid.

Chambers of heart:

• The heart is a central pumping organ. It consists of 4 chambers, two upper chambers – the atria, and two lower chambers – the ventricles. A thin muscular wall – interatrial septum, separates the left and right atria, while a thick-walled inter-ventricular septum, separates the left and right ventricles.
• These chambers prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide.
• The heart performs its function by coordinating contraction and, relaxation and opening and closing of a number of valves present inside the heart.
• Ventricles consist of thick muscular walls for pumping blood to longer distances.

Pericardium: The heart is covered by a membrane known as the pericardium

Valve:

The valve inside the heart regulates the flow of blood by opening on one side to let blood flow out in one direction only and they prevent the backflow of blood. The name of the valves are:

• Right atrioventricular valve or tricuspid valve and
• Left atrioventricular valve or bicuspid valve.
• Semilunar valves are situated at the origin of the aorta and pulmonary artery.

A wave of contraction in the heart is conducted from the S.A. node to the A.V. node to the Bundle of HIS, and to Purkinje fibers.

Transportation process through the heart–

The process of transportation goes through various stages, these are: 

• The blood carries both oxygen and carbon dioxide so the chamber of the heart prevents the mixing of blood. The carbon dioxide-rich blood goes to the lungs and from here the CO2 gets removed.
• The oxygenated blood from the lungs is brought back to the heart. (oxygenated blood means oxygen-rich blood)
• Then this oxygenated blood is pumped throughout the body.

The mechanism/pathway of transportation in Humans:

The mechanism of whole transportation/ circulation takes place through the pathway:

1. The Oxygen-rich blood goes from the lung to the left atrium of the heart, on the time of receiving this blood The left atrium relaxes.
2. In the second step left atrium contracted bicuspid valve opened while the next chamber, the left ventricle, relaxes by this process blood is transferred to the left ventricle.
3. left ventricle contracts in its turn the blood is pumped out to the body.
4. The right atrium relaxes and then it receives Deoxygenated blood from the body.
5. When the right atrium contracts, the tricuspid valve opened the (lower chamber) and the right ventricle expands. By this transfers blood to the right ventricle, which pumps the blood to the lungs for oxygenation. As the process of circulation, oxygenated blood goes through the body.
6. Ventricles pump blood to various organs they contain thicker muscular walls than arteries.
7. During the contraction of the atria or ventricles, the valve prevents the backflow of blood.

Function Major arteries and veins

Veins play an important role in human circulation. The important functions of Arteries and Veins are given below:

1. The Superior Vena Cava brings deoxygenated blood from the head and shoulder region.
2. The Inferior Vena Cava brings deoxygenated blood from the lower parts of the body. These vena cava open in the right atrium Contraction of the right atrium forces this blood into the right ventricle.
3. Contraction of the right ventricle pumps blood into the pulmonary artery which transports blood to the lungs. Blood gets oxygenated in the lungs and returns to the left atrium through the pulmonary vein.
4. The left ventricle pumps blood into the aorta. The aorta distributes blood throughout the body.

The special function of Pulmonary Artery and Pulmonary Vein:

The pulmonary artery is the only artery that carries the deoxygenated (blood poor in O2) blood. It is called an artery as it carries blood away from the heart.

The pulmonary vein is the only vein that carries oxygenated blood (blood rich in O2). It is called a vein as it carries blood into the heart

Heart-Beat

Heartbeat- the beating of the heart goes on by itself as long as one is alive.

It starts with the contraction of the atria systole followed by relaxation or diastole. The lubb sound or 1st heart sound occurs due to the closure of atrioventricular valves, the atrial systole.

Important facts about heart-beat:

• Contraction of ventricles followed by relaxation accompanied by the dubb sound or the 2nd heart sound occurs due to the closure of semilunar valves.
• The flow of the blood in the arteries exerts pressure on their elastic walls. This pressure is called blood pressure. The pressure of blood at the time of ventricular contraction is higher and is called systolic pressure. When ventricles are relaxed and filled with blood, there is a drop in pressure. This lower pressure is called diastolic pressure.
•  The normal systolic pressure is about 120 mm of Hg and diastolic pressure is 80 mm of Hg Blood pressure is measured by an instrument called a sphygmomanometer.

ECG: Electro Cardiogram (ECG) is an instrument that records the conduction of a heartbeat. This helps in detecting heartbeat disorders

Blood vessels-:

The tubes transporting blood are called Blood Vessels. The wall of a blood vessel has three layers, tunica externa, tunica media, and tunica interna. There are three types of Blood Vessels:

(i) Artery

(ii) Capillary and,

(iii) Vein

Artery – Since the blood is carried from the heart under high pressure, the arteries have thick, elastic walls. Arteries are the vessels that carry blood away from the heart to various organs of the body

After reaching an organ or tissue the arteries divides into small vessels to get blood into cells.

The smallest vessels have walls that are one-cell thick and are called capillaries

Veins collect the blood from different organs and bring it back to the heart and there is no high pressure as the valve helps to prevent the backflow of blood. So in comparison to arteries, these are thin.

Blood-fluid connective tissue. The production of blood is called hemopoiesis which takes place in the bone marrow. Blood is composed of:

• Plasma – Plasma is a fluid part of the blood and is composed of 90% of water.
• Blood Cells-Red blood cells, white blood cells, and platelets constitute the solid part of the blood

{Read more about blood: https://pcsstudies.com/blood-definition-composition-and-function/}

maintenance by platelets–  to avoid continued bleeding blood has platelet cells that circulate around the body and plug these leaks by helping to clot the blood at these points of injury.

Lymph– The clear, colorless liquid moving out of the capillary wall is called Lymph. Lymph comes into direct contact with body cells. The spleen and tonsils are lymphoid organs.

Functions of lymph–

• Supplies nutrition and oxygen to those parts of the body where blood cannot reach
• Drains away, excess tissue fluid from extracellular spaces and pours back into the blood.
• Absorbs and transports fats absorbed from the small intestine (lacteals)
• Collects nitrogenous waste
• Lymphocytes and antibodies present in lymph help in removing bacteria

Circulation in some other animals 

Circulation in other animals:

• The circulatory system may be open or closed type Open circulatory system- Blood does not flow in closed vessels rather it flows through parts of the body cavity. It remains mixed with body fluid.
• For example- The circulatory system of cockroaches is of open type.

• Animals, like amphibians or many reptiles, have three-chambered hearts and they have a mixed stream of oxygenated and deoxygenated bloodstreams.
• Fishes have only a two-chambered heart, and the blood is pumped to the gills, gets oxygenated in the gills, and passes directly to the rest of the body. Blood goes only once through the heart in the fish during one cycle of passage through the body.
• In these organisms energy requirement is low, so there is no need of high efficiency of oxygen that’s why here single pathway or single circulation occurs.

Read more about blood ➡ 

Blood Groups- Types of Blood

Blood – definition, composition and Function

You can also read: 💡 

• Life Process – Nutrition
• Life Process- 2 Respiration
• Life Process-4 Excretion
• Blood – definition, composition, and Function
• Blood Groups- Types of Blood
• Blood – definition, composition, and Function

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