Question

In veins, valves are present to check the backward flow of blood flowing
(a) Atmospheric pressure
(b) High Pressure
(c) Low Pressure
(d) All of these

Answer 1

The veins carry deoxygenated or the impure blood from the tissues back to the heart which flows at a very slow rate. This material moves to the different parts of the body with the help of liquid-like blood or in plants water plays a major role.

Complete step by step answer:
The veins which carry deoxygenated blood from tissue increase the possibility of the blood flowing backwards. The presence of valves prevents the flow of blood at low speed from flowing backwards.
In the arterial system, as resistance increases, the blood pressure increases and flow decreases. In the venous system, constriction increases pressure because it does in arteries; the increasing pressure helps to return blood to the heart.
So, the correct answer is, ‘Low pressure.’

Additional Information: Animals have blood which will act as the transport medium for a plethora of different processes. The transport and exchange of carbon dioxide is necessary for the removal of toxic Carbon dioxide from the blood. The digested food is to be transported to various organs of the body. The toxic wastes like urea are removed from the body by transporting it to the kidneys.
- Blood is circulated to various parts of the body by arteries and veins.
- Arteries carry oxygenated blood from the heart to various organs and tissues.
- Veins carry deoxygenated/impure blood from various organs to the heart.
- The blood vessels that carry arteries and veins are called capillaries.
- Walls of arteries and veins are made up of three layers i.tunica externa/tunica adventitia ii.tunica media and iii.tunica interna.
- Tunica externa or tunica adventitia is made up of fibrous connective tissue.
- Tunica interna is made up of endothelium and basement membrane.
- Tunica adventitia is the additional layer present between the tunica media and tunica externa. It helps in structural stability to the arteries and veins.
- Arteries and arterioles contain two elastic laminae on either side of the muscular layer i.e, tunica media. This elastic lamina is not found in the walls of veins.
- Endothelial layer in veins is double folded to form valves which direct the blood to the heart.

Note:
- Amphibians, reptiles, birds, and mammals have two types of circuits for blood flow - one through the lungs and back to the heart (pulmonary circulation) and the other throughout the rest of the body and all organs, including the brain (systemic circulation).
- Warm-blooded animals like mammals and birds have a more efficient system in the form of a four- chamber system (like the heart in human beings) where the oxygenated blood is completely separate from deoxygenated blood.