Metazoans are called within the animal kingdom those heterotrophic and eukaryotic organisms , made up of several cells that unite in a coordinated way and with chemical interrelation, with specific morphology and determined functions, forming tissues that reunite cells with the same function, which will later form organs and these apparatuses, allowing vital functions such as respiration, nutrition, digestion, circulation, and relationship functions to be completed.
Summary
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- 1 General Features
- 2 Nutrition
- 3 Digestion
- 4 The circulation
- 5 Breathing
- 6 The relationship function
- 7 See also
- 8 External source
General characteristics
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Humans
Metazoans have their origin in a single cell, the zygote , which is then subdivided.
Cells that form a metazoan cannot individually capture food from the outside, nor can they, one by one, expel their waste products to the outside. For these functions, and for many others, the set of cells of a metazoan depends in each case on a few cells that specialize in performing a certain function.
For example, there are cells specialized in secreting enzymes that carry out digestion, there are cells that transport oxygen, there are cells that contract to produce animal movement, etc.
Other even more complex metazoans are chordates, which are classified into cephalochordates , urochordates and vertebrates . Within these we find the human being.
Nutrition
Metazoan nutrition consists of obtaining organic matter and transforming it into energy to keep all the cells in your body alive. It is done by mediating digestion, respiration, circulation, and excretion.
Digestion
Digestion is the reduction of food to small molecules, capable of joining cellular metabolism. This process is carried out by the so-called digestive enzymes. Digestion can be extracellular or intracellular, depending on whether it takes place outside or inside cells. Extracellular digestion can be internal or external, depending on whether the food is inside the body, in the so-called digestive system, or outside it, as happens, for example, in spiders, which pour their digestive enzymes on their prey. to then be able to ingest them by suction. In most metazoans, digestion is extracellular and internal and takes place in the following stages: 1. Mechanical grinding of the food. 2. Chemical digestion through the enzymes secreted by the different digestive glands. 3. Absorption of the resulting molecules, through the walls of the digestive system, into the blood stream. 4. Defecation, that is, expulsion of materials that could not be digested abroad. 5. In some metazoans, for example, in the coelenterates, in the flatworms and in the bivalves, the secretion of enzymes in their digestive systems is very low, so that food must pass into the cells to end their degradation. So they basically have intracellular digestion. reason why the food must pass into the cells to end its degradation. So they basically have intracellular digestion. reason why the food must pass into the cells to end its degradation. So they basically have intracellular digestion.
The circulation
Circulation is the distribution, to all cells of the body, of food molecules and also of oxygen, as well as the collection of carbon dioxide, water and ammonia or their derivatives, which are the waste products of cellular respiration . The ammonia formula is NH3. Sometimes pure ammonia is not expelled outside, but some derivative, such as urea or uric acid. A typical circulatory system consists of the heart, some beings have several of these organs, which propels a liquid called the internal medium, and a series of ducts or vessels through which the internal medium circulates. Depending on the direction in which the internal environment moves, there are two types of vessels: the arteries if it goes from the heart to the organs and the veins if it goes from the organs to the heart.
The breathing
In metazoans, oxygen does not usually reach the cells directly, but is transported from the respiratory system through the internal environment. The internal environment has special proteins, called respiratory pigments, that are capable of transporting oxygen, such as red hemoglobin, in vertebrates and annelids, or blue hemocyanin, in mollusks and crustaceans. The respiratory apparatuses can be branchial, pulmonary and tracheal. · The gillsThey are very thin folds in the skin and with a vascularization, or blood risk, through vessels of very little thickness, usually called blood capillaries, which are very abundant. They are typical of aquatic metazoans, which capture O2 molecules dissolved in water. They can be external, like amphibian larvae; or internal, as in fish. · The lungs are internal cavities with collapsed, humid and highly vascularized walls that capture oxygen from the air. Vertebrates except fish have lungs, and organs similar to lungs are terrestrial gastropods and arachnids. · The tracheas are waterproof ducts that go from the external surface of the animal to the cells. They are typical of arthropods. Tracheal breathing therefore does not require a circulatory system. Some metazoans lack a respiratory system, have skin respiration, that is, they take up O2 through the skin. For example, the earthworm, sponges, etc.
The relationship function
Relationship functions allow metazoans to know the internal environment of their own body and the external environment in which they move or perceive, integrate their variations or coordination, and emit the appropriate responses or response. · Perception is made by specialized nerve cells , called sensory cells or receptors, which are internal, if they collect stimuli from inside the body, or external, if they collect them from outside. The receptors can be: · Chemoreceptors: Gaseous substances or sense of smell are perceived by the antennae of insects and the nostrils of vertebrates. Liquid substances or sense of taste are captured by the tentacles of mollusks, the legs of insects and the taste buds of the tongue.
o Mechanoreceptors: Those sensitive to pressure or sense of touch are the tactile hairs of arthropods, the lateral line of fish or the tactile corpuscles of the skin. Those sensitive to gravity or balance are the statocysts of invertebrates, and the utricles and saccules with their otoliths in vertebrates. Those sensitive to sound or sense of hearing are the acoustic hairs of arthropods or the ears of vertebrates.
o Photoreceptors or sense of sight: They catch the eye spots of the planarians if there is light. The direction of light is captured by the eye vesicles of jellyfish and the ocelli of arthropods. The composite eyes of insects and the eyes of vertebrates capture images.
o Thermoreceptors: They capture the degree of heat in the corpuscles of the skin.
- Coordination consists of centralizing all the stimuli captured by the receptors and emitting adequate responses to each one of them. Vertebrates have organs specialized in coordinating responses, such as the brain, cerebellum, spinal cord, etc. · The responses ordered by the coordinating center, that is, the nervous system, can be of two types: movements and secretions. The movements, carried out by the locomotor system, are quick, punctual and brief responses. Secretions, made by the glands, are slow, sustained, and long-lasting responses.
