Circulatory system of gastropods
Encyclopedia
As in other molluscs, the circulatory system of gastropods is open, with the fluid, or haemolymph, flowing through sinuses
and bathing the tissues directly. The haemolymph typically contains haemocyanin, and is blue in colour.
is muscular and located in the anterior part of the visceral mass. In the great majority of species, it has two chambers; an auricle, which receives haemolymph from the gill
or lung
, and a ventricle
, which pumps it into the aorta
. However, some primitive gastropods possess two gills, each supplying its own auricle, so that their heart has three chambers.
The aorta is relatively short, and soon divides into two main vessels, one supplying the visceral mass, and the other supplying the head and foot. In some groups, these two vessels arise directly from the heart, so that the animal may be said to have two aortas. These two vessels in turn divide into many finer vessels throughout the body, and deliver haemolymph to open arterial sinuses where it bathes and oxygenates the tissues.
De-oxygenated haemolymph drains into a large venous sinus within the head and foot, which contains the nephridium
, an excretory organ with a function similar to that of the vertebrate kidney
. From here it passes into vessels within the gill, or into the capillary network of the pulmonate lung, before returning to the heart.
In some genera, such as the large marine snail Busycon
, the main anterior artery (which supplies the head and foot) includes an enlarged muscular region. This structure is effectively a secondary heart, and probably helps to maintain blood pressure in the vessels of the head.
and the lymph
, or interstitial fluid. As a result, the circulatory fluid is commonly referred to as haemolymph, rather than blood.
The majority of gastropods have haemolymph containing the respiratory pigment haemocyanin. This is a copper-containing protein that helps to carry oxygen, and gives the haemolymph a pale blue colour. In the freshwater Planorbid
snails, however, the haemocyanin is replaced by haemoglobin, and thus their haemolymph is red rather than blue. Some gastropods, such as the sea hare Aplysia
, appear to lack respiratory pigments altogether.
Regardless of whether they employ haemocyanin or haemoglobin, the pigments are dissolved directly in the serum
, with no equivalent of the red blood cell
s found in mammals. However, the haemolymph does contain amoebocytes, which may have a role in the immune system
.
Sinus (anatomy)
Sinus is Latin for "bay", "pocket", "curve", or "bosom". In anatomy, the term is used in various contexts.A sinus is a sack or cavity in any organ or tissue, or an abnormal cavity or passage caused by the destruction of tissue...
and bathing the tissues directly. The haemolymph typically contains haemocyanin, and is blue in colour.
Circulation
The heartHeart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
is muscular and located in the anterior part of the visceral mass. In the great majority of species, it has two chambers; an auricle, which receives haemolymph from the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
or lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
, and a ventricle
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
, which pumps it into the aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
. However, some primitive gastropods possess two gills, each supplying its own auricle, so that their heart has three chambers.
The aorta is relatively short, and soon divides into two main vessels, one supplying the visceral mass, and the other supplying the head and foot. In some groups, these two vessels arise directly from the heart, so that the animal may be said to have two aortas. These two vessels in turn divide into many finer vessels throughout the body, and deliver haemolymph to open arterial sinuses where it bathes and oxygenates the tissues.
De-oxygenated haemolymph drains into a large venous sinus within the head and foot, which contains the nephridium
Nephridium
A Nephridium is an invertebrate organ which occurs in pairs and function similar to kidneys. Nephridia remove metabolic wastes from an animal's body. They are present in many different invertebrate lines. There are two basic types, metanephridia and protonephridia, but there are other...
, an excretory organ with a function similar to that of the vertebrate kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
. From here it passes into vessels within the gill, or into the capillary network of the pulmonate lung, before returning to the heart.
In some genera, such as the large marine snail Busycon
Busycon
Busycon is a genus of very large edible sea snails, marine gastropod mollusks in the family Buccinidae. These snails are commonly known in the United States as whelks or Busycon whelks....
, the main anterior artery (which supplies the head and foot) includes an enlarged muscular region. This structure is effectively a secondary heart, and probably helps to maintain blood pressure in the vessels of the head.
Haemolymph
Because of the open circulatory system of gastropods and other molluscs, there is no clear distinction between the bloodBlood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
and the lymph
Lymph
Lymph is considered a part of the interstitial fluid, the fluid which lies in the interstices of all body tissues. Interstitial fluid becomes lymph when it enters a lymph capillary...
, or interstitial fluid. As a result, the circulatory fluid is commonly referred to as haemolymph, rather than blood.
The majority of gastropods have haemolymph containing the respiratory pigment haemocyanin. This is a copper-containing protein that helps to carry oxygen, and gives the haemolymph a pale blue colour. In the freshwater Planorbid
Planorbidae
Planorbidae, common name the ramshorn snails or ram's horn snails, is a family of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks....
snails, however, the haemocyanin is replaced by haemoglobin, and thus their haemolymph is red rather than blue. Some gastropods, such as the sea hare Aplysia
Aplysia
Aplysia is a genus of medium-sized to extremely large sea slugs, specifically sea hares, which are one clade of large sea slugs, marine gastropod mollusks. The general description of sea hares can be found in the article on the superfamily Aplysioidea....
, appear to lack respiratory pigments altogether.
Regardless of whether they employ haemocyanin or haemoglobin, the pigments are dissolved directly in the serum
Blood serum
In blood, the serum is the component that is neither a blood cell nor a clotting factor; it is the blood plasma with the fibrinogens removed...
, with no equivalent of the red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s found in mammals. However, the haemolymph does contain amoebocytes, which may have a role in the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
.