The hemolymph is a fluid having invertebrates. This transports the nutrients that feed the tissues and participates in the shedding of skin, among other important functions.
All animals have a circulating fluid responsible for transporting, with the help of the circulatory system, substances with respiratory pigments or organic molecules, made up of a protein and a particle that has an affinity for oxygen (darkbiologist, 2017).
In the different groups of animals, in addition to the hemolymph, there are other transport fluids; these are blood, lymph, and hydrolymph.
Blood is a fluid that has respiratory pigments, such as hemoglobin, which has iron ions that give it its characteristic red color. It is typical of annelids, such as the leech and earthworm, and of vertebrates.
Lymph is a fluid found only in vertebrates that allows fluids between cells to circulate.
On the other hand, hydrolymph is a colorless fluid, similar in composition to seawater, typical of echinoderms such as sea urchins and starfish (López, 2017).
Definition
Hemolymph is a fluid that has functions similar to those performed by blood in vertebrates, but is typical of the circulatory system of mollusks and arthropods (insects, arachnids and crustaceans).
Normally, the hemolymph represents between 5 and 40% of the individual's weight, depending on the species.
There are many differences in the way fluids circulate in vertebrates and invertebrates. One of the most significant is that the hemolymph does not carry oxygen to the organs from the lungs and brings carbon dioxide (Contreras, 2016).
This is because insects do not breathe through the lungs but, due to their small size, can passively exchange gases through the skin and tracheas, a system of channels open to the outside that run through their body.
The hemolymph does not directly irrigate all the cells and organs of the insect body, but the tegument that covers them has a basement membrane of connective tissue, whose properties control the exchange of materials between the cells and the hemolymph.
In the blood, the pigment that carries oxygen is hemoglobin, but as in insects the transport of oxygen is not of vital importance, the hemolymph does not have hemoglobin; that is why it is in other colors, or even transparent.
However, in both mollusks and arthropods, hemolymph has hemocyanin, an oxygen-carrying molecule that contains copper.
Due to the presence of hemocyanin, the circulatory fluid of these organisms turns blue-green when oxygenated; otherwise it is gray or colorless.
In contrast, vertebrate hemoglobin has iron, which makes it bright red when it carries oxygen, or dark red (brown) when it does not have oxygen (McCarthy, 2017).
Certain insects and some mollusks that live in low-oxygen environments also have circulatory fluid that contains hemoglobin, which gives it the red appearance of vertebrate blood.
In the hemolymph there are also the cells of the invertebrate immune system, which prevent them from infection, and also the cells involved in coagulation.
How is hemolymph transported?
In arthropods the circulatory system is open, there are no tubes or channels through which the hemolymph is distributed, but rather it exits through the anterior orifice of the circulatory system and is distributed throughout the body more or less freely. The organs are then bathed directly by it.
Circulation is normally induced by one or more tubular hearts. These are endowed with various lateral orifices, called ostioles, which help the hemolymph to enter them. The front part of the vessel is called the aorta and it is a straight tube without valves.
Body movements return fluid within the circulatory system to a cavity that surrounds the heart (s).
During expansion, the ostioles open and allow fluid to enter. Then they close, and the liquid is pumped out to the body again (Zamora, 2008).
The heart sucks the hemolymph from the abdominal cavity and expels it towards the head, through the aorta, from where it again filters through the tissues into the abdominal cavity. In some insects there are attached pumps in charge of irrigating towards the extremities and antennae.
Composition
The hemolymph is composed mainly of water in approximately 90%. The rest is made up of ions, a diversity of organic and inorganic compounds, lipids, sugars, glycerol, amino acids, and hormones (DeSalle, 2017).
It has a pigment for the transport of oxygen called hemocyanin, which is a conjugated protein that contains copper.
Its cellular part is made up of hemocytes, which are cells specialized in phagocytosis; that is, they are capable of assimilating or consuming other cells to destroy them.
They protect the body, expelling foreign bodies and preventing fluid from being lost through wounds.
Features
The main functions of the hemolymph are:
- Transport nutrients to feed the tissues and collect waste materials, which are carried to the excretory organs.
- Thanks to the hemocytes, it helps coagulation to close wounds.
- Prevents microbial invasion, helping defenses.
- It carries oxygen, mainly in water insects because, in general, oxygen is carried directly through the tracheal system, without the intervention of the circulatory system.
- Conducts hormones, performing important functions in metabolism.
- Due to pressure changes in the hemolymph, the molting process is triggered. When the exoskeleton reaches its maximum capacity, the impulses received by the brain cause hormones to be released to the hemolymph. An example is how the wings of butterflies unfold as the hemolymph irrigates them (Saz, 2017).
References
- Contreras, R. (May 27, 2016). The Guide. Obtained from Hemolinfa: biologia.laguia2000.com
- (2017). Monographs.com. Obtained from Animal circulatory system: monografias.com
- DeSalle, R. (2017). Scientific American, a Division of Nature America, INC. Retrieved from How is bug blood different from our own ?: scientificamerican.com
- López, MR (2017). Biosphere Project. Obtained from The animal kingdom - Transport systems.
- McCarthy, G. (2017). net. Obtained from Hemolymph: macroevolution.net
- Saz, A. d. (2017). Biosphere Project. Obtained from Horminas and growth in insects: resources.cnice.mec.es
- Zamora, JE (March 05, 2008). Welcome to OpenCourseWare. Obtained from Circulatory System: ocwus.us.es