Unit – I A
Circulatory System and its Types
- Higher elements have higher metabolic activity, hence higher animals require an efficient and speedy supply of nutrients and oxygen for their tissues at the same time they require efficient and speedy disposal of respiratory products, nitrogen products.
- Hence such animals have developed a special fluid called blood in them and conducting system called circulatory system consisting of heart, vessels etc. This system is also called as vascular system. The circulatory system has two functional components viz. a) blood vascular system and b) lymph vascular system.
- The blood vascular system is of two types a) Open circulation and b) Closed circulation
Open Circulatory System:
- Open circulatory systems are the more basic type of circulatory system. They’re referred to as open because blood is not contained within an enclosed circuit of vessels.
- Blood flows from the heart through open-ended vessels and, when it reaches the end of the vessels, it flows directly over the tissues.
- While the tissues are bathed in blood, gas exchange occurs. Blood then freely flows back into vessels that direct the blood back to the heart.
- There are many organisms that have open circulatory systems, including grasshoppers, snails, and clams.
Characteristics of Open Circulatory System:
- Blood flows through large open spaces called lacunae and sinuses.
- No capillary system so tissues are in direct contact with blood (hemolymph)
- Exchange of nutrients and gases takes place directly between blood and tissue.
- The volume of blood flowing through tissues cannot be controlled as blood is flowing through open spaces.
- Blood flow is very slow.
- Found in higher invertebrates like most arthropods such as prawns, cockroach etc. and in some molluscs.
Circulatory System of Cockroach:
In cockroach, the blood does not remain confined to blood vessels but flows trough open spaces and channels in the tissues called lacunae and sinuses. Thus blood is in direct contact with tissues.
- The blood has a colourless plasma and contains numerous white blood corpuscles. The blood fills perivisceral cavity which is called haemocoel. Thus the organs are surrounded by blood.
- The heart of cockroach is a long elongated tube situated in the mid-dorsal line of the thorax and the abdomen immediately beneath the terga. The heart consists of thirteen chambers. The last two posterior chambers are very small. The chambers are separated from one another by deep constrictions. Thus each chamber contains two parts, a narrow tubular anterior aorta, and a posterior pulsating heart. The opening of each chamber into another is guarded with valves which allow blood from posterior to anterior end. Each chamber of heart is communicated to the anterior side by aorta and to the vesceral haemocoel by a pair of Ostia placed on either side of the heart. At the anterior end of the heart, the blood is given out into the anterior sinus or head sinus. Then it is passed to sternal sinus and then into pericardial sinus again.
Closed Circulatory System:
- William Harvey (1578-1657) discovered and published the first accurate description of the human circulatory system, based on his many years of experiments and observations as a scientist and physician.
- The humans have closed circulatory system. Unlike an open circulatory system, a closed circulatory system is more structured and controlled.
- The blood of a closed system always flows inside vessels. These vessels make up the vessel system of the body and can be found throughout the entire body.
Characteristics of Closed Circulatory System:
- Blood flows through closed system i.e. heart and blood vessels.
- Capillary system present so blood is not in direct contact with tissues.
- Nutrients and gases pass through the walls of capillaries to tissue fluid which is then taken up by the tissues.
- Blood flow is controlled by contraction and relaxation of muscles of blood vessels.
- Blood flow is rapid here.
- Found in some molluscs, annelids and all vertebrates.
Functions of Circulatory System:
- Respiration: Delivers oxygen to the cells and removing carbon dioxide from them
- Nutrition: Carries digested food substances to the cells of the body
- Waste Removal: Disposes of waste products and poisons that would harm the body if they accumulated
- Immunity: Helps protect the body from disease
- Cellular Communication: The circulatory system provides a mode of transport for hormones
- Thermoregulation: The circulatory system transports heat (can both warm and cool body)
Human Circulatory System:
- Most of the cells in the human body are not in direct contact with the external environment, so rely on the circulatory system to act as a transport service for them.
- Two fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the Cardiovascular System. The lymph, lymph nodes and lymph vessels form the Lymphatic System.
- The Cardiovascular System and the Lymphatic System collectively make up the Circulatory System.
- The system in which blood is circulated throughout the body is called circulatory system.
- The closed circulatory system was discovered by William Harvey.