Hemolymph, or haemolymph, is a fluid, analogous to the
blood in
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph cells called
hemocytes
A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), a ...
are suspended. In addition to hemocytes, the plasma also contains many chemicals. It is the major tissue type of the
open circulatory system characteristic of
arthropods (e.g.
arachnid
Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegar ...
s,
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...
s and
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s). In addition, some non-arthropods such as
molluscs
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estim ...
possess a hemolymphatic circulatory system.
Oxygen-transport systems were long thought unnecessary in insects, but ancestral and functional
hemocyanin has been found in the hemolymph.
Insect "blood" generally does not carry
hemoglobin, although hemoglobin may be present in the tracheal system instead and play some role in respiration.
Method of transport
In the
grasshopper, the closed portion of the system consists of tubular hearts and an aorta running along the dorsal side of the insect. The hearts pump hemolymph into the sinuses of the
hemocoel where exchanges of materials take place. The volume of hemolymph needed for such a system is kept to a minimum by a reduction in the size of the body cavity. The hemocoel is divided into chambers called sinuses.
Coordinated movements of the body muscles gradually bring the hemolymph back to the dorsal sinus surrounding the hearts. Between contractions, tiny valves in the wall of the hearts open and allow hemolymph to enter. Hemolymph fills all of the interior (the
hemocoel) of the animal's body and surrounds all cells. It contains
hemocyanin, a
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
-based protein that turns blue when oxygenated, instead of the
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
-based
hemoglobin in
red blood cells found in vertebrates, giving hemolymph a blue-green color rather than the red color of vertebrate blood. When not oxygenated, hemolymph quickly loses its color and appears grey.
The hemolymph of lower arthropods, including most
insects
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...
, is not used for oxygen transport because these animals
respirate through other means, such as tracheas, but it does contain nutrients such as proteins and sugars. Muscular movements by the animal during
locomotion
Locomotion means the act or ability of something to transport or move itself from place to place.
Locomotion may refer to:
Motion
* Motion (physics)
* Robot locomotion, of man-made devices
By environment
* Aquatic locomotion
* Flight
* Locomo ...
can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...
relaxes, hemolymph is drawn back toward the heart through open-ended pores called ostia.
Note that the term "
ostia" is not specific to insect circulation; it literally means "doors" or "openings", and must be understood in context.
Constituents
Hemolymph can contain nucleating agents that confer extra cellular freezing protection. Such nucleating agents have been found in the hemolymph of insects of several orders, i.e.,
Coleoptera (beetles),
Diptera (flies), and
Hymenoptera.
Inorganic
Hemolymph is composed of
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
,
inorganic
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemist ...
salts (mostly
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
,
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
,
potassium,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, and
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
), and
organic compounds
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...
(mostly
carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or m ...
s,
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s, and
lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...
s). The primary oxygen transporter molecule is
hemocyanin.
Amino acids
Arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
hemolymph contains high levels of free amino acids. Most amino acids are present but their relative concentrations vary from species to species. Concentrations of amino acids also vary according to the arthropod stage of development. An example of this is the silkworm and its need for glycine in the production of silk.
Proteins
Proteins present in the hemolymph vary in quantity during the course of development. These proteins are classified by their functions: chroma proteins, protease inhibitors, storage, lipid transport, enzymes, the vitellogenins, and those involved in the immune responses of arthropods. Some hemolymphic proteins incorporate carbohydrates and lipids into the structure.
Other organic constituents
Nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
metabolism end products are present in the hemolymph in low concentrations. These include
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
,
allantoin
Allantoin is a chemical compound with formula C4H6N4O3. It is also called 5-ureidohydantoin or glyoxyldiureide. It is a diureide of glyoxylic acid. Allantoin is a major metabolic intermediate in most organisms including animals, plants and bacter ...
,
uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown ...
, and
urea. Arthropod
hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
s are present, most notably the juvenile hormone.
Trehalose
Trehalose (from Turkish '' tıgala'' – a sugar derived from insect cocoons + -ose) is a sugar consisting of two molecules of glucose. It is also known as mycose or tremalose. Some bacteria, fungi, plants and invertebrate animals synthesize it ...
can be present and sometimes in great amounts along with
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
. These sugar levels are maintained by the control of hormones. Other
carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or m ...
s can be present. These include
inositol,
sugar alcohol
Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, containing one hydroxyl group (–OH) attached to each carbon atom. They are white, water-soluble solids ...
, hexosamines,
mannitol
Mannitol is a type of sugar alcohol used as a sweetener and medication. It is used as a low calorie sweetener as it is poorly absorbed by the intestines. As a medication, it is used to decrease pressure in the eyes, as in glaucoma, and to lo ...
,
glycerol and those components that are precursors to
chitin.
Free
lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...
s are present and are used as fuel for flight.
Hemocytes
There are free-floating cells, the
hemocytes, within the hemolymph. They play a role in the arthropod
immune system. The immune system resides in the hemolymph.
Comparisons to vertebrates
This
open system might appear to be inefficient compared to the closed circulatory systems of the
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s, but the two systems have very different demands placed on them. In vertebrates, the circulatory system is responsible for transporting oxygen to all the tissues and removing carbon dioxide from them. It is this requirement that establishes the level of performance demanded of the system. The efficiency of the vertebrate system is far greater than is needed for transporting nutrients, hormones, and so on, whereas in insects, exchange of oxygen and carbon dioxide occurs in the
tracheal system. Hemolymph plays no part in the process in most insects. Only in a few insects living in low-oxygen environments are there hemoglobin-like molecules that bind oxygen and transport it to the tissues. Therefore, the demands placed upon the system are much lower. Some arthropods and most molluscs possess the
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
-containing
hemocyanin, however, for oxygen transport.
Specialist uses
In some species, hemolymph has other uses than just being a blood analogue. As the insect or arachnid grows, the hemolymph works something like a hydraulic system, enabling the insect or arachnid to expand segments before they are
sclerotized. It can also be used hydraulically as a means of assisting movement, such as in
arachnid locomotion. Some species of insect or arachnid are able to
autohaemorrhage when they are attacked by predators.
Queens of the ant genus ''
Leptanilla'' are fed with hemolymph produced by the
larvae.
[Genus ''Leptanilla'']
Australian Ants Online On the other hand, ''
Pemphigus spyrothecae'' utilize hemolymph as an adhesive, allowing the species to stick to predators and subsequently attack the predator; it was found that with larger predators, more aphids were stuck after the predator was defeated.
See also
*
Insect physiology
*
Respiratory system of insects
An insect's respiratory system is the system with which it introduces respiratory gases to its interior and performs gas exchange.
Air enters the respiratory systems of insects through a series of external openings called spiracles. These exter ...
References
Sources
* {{cite book , last=Chapman , first=R.F. , title=The Insects: Structure and Function , url=https://archive.org/details/insectsstructure0000chap , url-access=registration , publisher=Cambridge University Press , edition=4th , year=1998 , location=Cambridge , isbn=978-0-521-57890-5
External links
* ''
Boston Globe'
articleon hemolymph
Blue Squid Blood
Blood
Arthropod anatomy
Insect anatomy
Crustacean anatomy
Arachnid anatomy
Body fluids