Railway Science (Biology – Circulatory System)

During ventricular diastole - Oxygenated blood enters from the left atrium to the left ventricle and deoxygenated blood enters from the right atrium to the right ventricle. During atrial diastole - Deoxygenated blood enters the right atrium through superior and inferior venae cavae and oxygenated blood enters the left atrium through the pulmonary veins.

Amphibians and reptiles have an incomplete double circulation. Double circulation is the sort of circulation where the blood goes to the heart twice. Some animals have complete double circulation: Fish, Alligator, Frogs, lungfish, Prawns, Egyptian plover (Crocodile birds), mammals.

Lymph is a colorless fluid consisting of salts, proteins, water, which transport and circulate digested food and absorbed fat to intercellular spaces in the tissues.
Platelets (thrombocytes, made in bone marrow) are small, colorless cell fragments in our blood that form clots and stop or prevent bleeding. Capillaries (smallest blood vessels, present in the lungs and muscles).
Causes of Hypertension include advancing age, obesity, high sodium diet, alcohol consumption.

Blood pressure - Pressure of circulating blood against the walls of blood vessels. A normal blood pressure level is less than 120/80 mmHg. Measuring instrument - Sphygmometer. Systolic pressure - Maximum pressure the heart exerts while beating. Diastolic pressure - The pressure in arteries when the heart rests between beats.

White blood cells are part of the body's immune system. They help the body fight infection and other diseases. Types of white blood cells are granulocytes (neutrophils, eosinophils, and basophils), monocytes, and lymphocytes (T cells and B cells). The normal number of WBCs in the blood is 4,500 to 11,000 WBCs per microliter (4.5 to 11.0 × 10⁹/L).

The wall between the chambers of heart is known as Septum. It separates the left and right sides of the heart. Pulmonary valve - Prevents blood from going backward from the pulmonary artery to the right ventricle.
Tricuspid valve - Prevent blood from flowing backward from the right ventricle to the right atrium. Aortic valve - Prevents backward flow from the aorta into the left ventricle.

In fishes, single circulation of blood occurs in which blood flows through the heart only once to complete the circuit. Double circulation - The mechanism in which blood circulates twice through the heart in one complete cycle. In most vertebrate groups, there is a double circulation of blood. It occurs in birds and mammals.

O Type blood group is referred as Universal Donor. Group O has neither A nor B antigens on Red Blood Cells (RBC) but both A and B antibodies are in the plasma. Basis on the presence or absence of 2 antigens, A and B, on the surface of RBC and protein called the Rh factor, which can be either present (positive) or absent (negative), creating the 8 blood types (A+, A-, B+, B-, O+, O-, AB+, AB-). Group A - has A antigen on RBC and B antibody in the plasma, Group B - has B antigen on RBC & A antibody in the plasma, Group AB has both A and B antigens on RBC (but neither A nor B antibody in the plasma) so it is referred as Universal Acceptor.

Spectrophotometer - an analytical instrument used for the objective calculation of visible light, UV light, or infrared light emission or reflection. Hemoglobin meter - A device used to measure the level of hemoglobin in a person's blood. Urinometer - A simple piece of equipment for determining urine specific gravity.

Three chambered hearts (have one ventricle and two atria) - Amphibians and reptiles.