Circulatory System

Biology Doubts

Circulatory System Introduction

This system is concerned with the circulation of body fluids to distribute various substances to various body parts.

What are the functions of Circulatory System. 

The four most important functions of Circulatory System are 

1.Transport of various substances such as nutrients, waste products, respiratory gases, metabolic intermediates (Such as lactic acid from muscle to liver), vitamins hormones etc.

2.Regulation of body pH by means of buffer, body temperature homeostasis, water balance etc.

3.Prevention of disease by means of antibodies and antitoxins.

4.Support or turgidity to certain organs like penis and nipples. 

Types of Circulatory System. 

Circulatory system in various groups of animals can be classified as follows :

(i) Intracellular circulation : Occurs inside the individual cells where the distribution of substances is through cyclosis of cell cytoplasm. Example – Protozoans.

(ii) Extracellular circulation : When the distribution of the substances occurs inside the body through extracellular or intracellular fluids. This is of following types –

(a) Extra organismic circulation : When the water of the external environment circulate through body. This is also called as water circulation system. Example – canal system in porifera, water vascular system in Echinoderms and gastrovascular system in coelenterates.

(b) Intra-organismic circulation : It involves circulation of body fluids. It is of following types :

(1) Parenchymal circulation : In platyhelminthes, the fluid filled spaces present in the mesodermal parenchyma tissue between body wall and internal organs are used in the distribution of substances.

(2) Coelomic circulation : Coelomic fluid is concerned with the transport of substances. Example – pseudocoelomic fluid in the roundworms and haemolymph in Arthropods.

(3) Blood vascular system : It contains blood and a pumping structure (heart) for circulation of materials inside the body. It is of following types –

(i) Open circulatory system

(ii) Closed circulatory system

circulatory system

Circulatory system in multicellular animals 

(i) In protozoans : Distribution of nutrients takes place by cyclosis (streaming movement) of cytoplasm.

(ii) In poriferans : The vascular system of poriferans is the canal system. A simplest canal system involves ostia (mouth), spongocoel and on osculum (Anus). Route followed by water current in sponges :

(iii) In coelenterates :  Hydra has a single large internal cavity called coelenteron or gastrovascular cavity. It has single opening the mouth. It also extends into the hollow tentacles. It lacks a mesodermal epithelial covering (peritoneum) and a coelomic fluid. It is concerned with first extracellular and then intracellular digestion of food.

(iv) In platyhelminthes : Vascular system is absent but circulation occurs with the help of parenchyma hence called parenchymal circulation. Example – Fasciola hepatica.

(v) In annelids : Vascular system in annelids is a closed circulatory or blood vascular system which comprises four parts : blood, blood glands, blood vessels and hearts.

(a) Blood : Red, due to respiratory pigment haemoglobin dissolved in plasma. The blood cells are colourless and nucleated like the leucocytes of vertebrates.

(b) Blood glands : Reddish bodies present on alimentary canal in segments 4, 5 and 6 and are thought to produce blood corpuscles and haemoglobin.

(c) Blood vessels : Lack endothelium. The arrangement of blood vessels in first 13 segments is different from that is rest of the body. Ist 13 segments have five longitudinal vessels – dorsal, ventral, a pair of lateral oesophageal and a supraoesophageal vessel. Behind 13th segment has 3 longitudinal vessels – dorsal, ventral and subneural.

(d) Hearts : Four pairs, one pair in each of 7th, 9th, 12th and 13th segment. Two anterior pairs receiving blood from dorsal vessel only are called lateral hearts and two posterior pairs receiving blood from dorsal vessel as well as supra oesophageal vessel are called latero-oesophageal hearts. All hearts possess muscular pulsafile walls to pump blood into ventral vessel. Valves present to prevent back flow of blood.

Anterior loops : 2 pairs, one pair in each of the 10th and 11th segment, carry blood from lateral oesophageal vessel to supra oesophageal vessel.

Lymph glands : Two, small, whitish, located on each side of the dorsal blood vessel in each of the segments 26 and those behind it. They produce phagocytic cells which are occasionally liberated into the coelomic fluid to phagocytise harmful bacteria and other invaders.

Circulation in earthworm

circulation in earthworm


Ventral vessel : Distributing vessel.

Subneural vessel : Collecting vessel.

Lateral oesophageal : Collecting vessel.

Supra oesophageal : Collecting vessel.

Dorsal vessel : Distributing in 1st 13 segments and collecting in the region behind 13th segment.

(vi) In arthropoda : Blood vascular system in arthropods is ‘Open type’ or “Lacunar type”.

(a) Prawn : Blood vascular system of prawn includes pericardium, heart, arteries, blood lacunar/sinuses, blood channels and blood. Blood is colourless with phagocytic leucocytes and respiratory pigment haemocyanin dissolved in plasma. The blood has remarkable clotting properties. Heart is a muscular, triangular organ without auricle and ventricle but with ostia for inflow of blood into heart and arteries. Five of the arteries arise from the anterior end and one from the posterior end of heart. The prawn’s heart always contains oxygenated blood only and hence, also called as Arterial heart.

Circulation of blood in prawn 

Circulation in blood prawn


(b) Circulatory System. Cockroach : 

Cockroach has an open circulatory system. The body cavity is called haemocoel filled with a fluid haemolymph. The heart lies in the pericardial sinus of haemocoel. The heart is 13 chambered, tubular dorsal vessel, pulsatile with an anterior aorta. Each chamber is inverted funnel, shaped provided with valved lateral apertures called ostia. The heart is supported by 13 pairs of triangular fan like alary muscles. The blood sinuses are dorsal pericardial sinus, middle perivisceral sinus and the ventral perinural sinus or sternal sinus. These sinuses are separated from each other by dorsal diaphragm and ventral diaphragm. Blood or haemolymph is colourless contains haemcytes but is without respiratory pigment as it plays no role in respiration.

Circulatory System. Cockroach

Circulation of blood in cockroach :

circulation of blood in cockroach

(vii) In echinoderms : A true blood vascular system is absent. It is represented by a haemal system which is enclosed within a perihaemal system. haemal system includes oral haemal ring (a sinus), radical haemal sinuses or strands (present in the arms), axial glands, heart, brown glands (present within axial sinus of perihaemal system) and aboral haemal ring, from which arise, five pairs of genital haemal strands.

(viii) Blood circulation in vertebrates : Blood circulation was discovered by William harvey. In case of vertebrates, blood circulation is of closed type, which can be grouped into two categories :

(a) Single circulation (b) Double circulation

Differences between single and double circulation

Single and double circulation

Double circulation in mammals can be divided into three parts :

(1) Cardiac circulation : The amount of blood present in the heart. Its value is 7%.

(2) Pulmonary or lesser circulation : The amount of blood present in the surrounding of lungs and pulmonary blood vessels. Its value is 9%.

(3) Systemic or greater circulation : The amount of blood which circulates in the rest part of the body. Its value is 84%. It can be divided into three parts –

Arterial circulation – 15%

Capillary circulation – 5%

Venous circulation – 64%

Heart : The form, structure and function of heart exhibits much variation. The characteristics of heart of fishes, amphibians, reptiles, birds and mammals is presented in the following table.

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