Animal Transport Systems: From Hidrolinfa to Human Circulation
Transportation Systems
Acquired nutrients are distributed among all the cells in your body to ensure the proper functioning of animal metabolism. Waste products are expelled outside. Animals with simple structures do not need a transport system, since cells may acquire or expel substances from the environment in which they live. However, animals with highly complex needs require a circulating medium which serves to distribute nutrients and collect metabolic waste. In many cases, it also requires the presence of a booster pump to mobilize the blood supply throughout the body.
The Internal Environment
The internal environment is the fluid that transports nutrients. Its composition and color vary and may contain cells in many cases. The various internal resources that can be found in animals are hydrolipha, hemolymph, blood, and lymph.
Hydrolipha
This is the internal environment of Echinoderms. Its composition is very similar to that of seawater. It transports nutrients and waste but no oxygen-carrying pigment. It circulates through a system of tubes that connect to structures called tube feet. These structures serve to give movement to starfish and sea urchins. The ambulacral system works by hydrostatic pressure. The ambulacral foot sticks to the substrate when the internal hydrostatic pressure decreases due to the way it acquires, like a suction cup. There are ambulacral blisters that, when contracted, eject hydrolipha from within and go to the tube feet. For this reason, the hydrostatic pressure increases and the ambulacral foot comes off the substrate on which it is attached. The ambulacral system, by sharing this hydrolipha to different areas, allows the movement of the animal.
Hemolymph
Found in molluscs and arthropods. In molluscs and crustaceans, an oxygen-carrying pigment appears. In arachnids, millipedes, and insects, there is no need to carry oxygen around the internal environment, and their tracheal breathing system is not needed since the tracheae carry air directly to the body’s cells.
Blood
Annelids and Vertebrates have an internal environment with an oxygen-carrying pigment that gives it a red color. In vertebrates, the carrying pigment is called hemoglobin. Blood in vertebrates is particularly complex, with lots of functions and cells. These cells are erythrocytes, leukocytes, and platelets.
Lymph
It is present in vertebrates. It lacks oxygen-carrier pigments and consists of leukocyte-type cells.
Circulatory System in Humans
Humans have a closed circulatory system with a heart located in the thoracic cavity between the lungs and protected by the ribs. It consists of two atria and two ventricles. The heart beats about 72 times per minute, although this rate varies according to the activity that is taking place and the type of person. The heart rate is marked by a pacemaker comprising:
- Sinoatrial Node (SCN): Produces the initial impulse of heart rhythm. It is in the right atrial wall. Its fibers have a greater capacity for excitement than the rest of the heart. Therefore, it controls the heart rate.
- Internodal Fibers: These fibers connect one node to the next and expand the momentum generated by the heart fibrillation.
- Atrioventricular Node: A place where the impulse is delayed before exciting the ventricular contraction (0.11 s). It is located in the atrial septum that separates the right ventricle. It causes the ventricles to contract shortly after contracting the atria.
- Bundle of His and Purkinje Fibers: These fibers are found in the ventricular septum and encourage co-contraction of all muscle cells that form the ventricles.
Cardiac Movement
The heart’s motion is in a phase of systole and a phase of diastole. Systole is the contraction, and diastole is the relaxation. There is an atrial systole and a ventricular systole. This is due to delays incurred in the atrioventricular node. It generates an atrial diastole and a ventricular diastole. The relaxation of the atria allows blood to fill, which comes from the veins. Ventricular diastole allows the ventricles to fill with blood coming from the contracting atria. Cardiac motion is modified by the medulla as a function of the energy needs of tissues.
Types of Transportation Systems
Porifera and Cnidarians can use their internal cavity and distribution system. In addition, the outer cells exchange substances with water. In Platyhelminthes, substances are transported by diffusion from cell to cell. Animals with an internal transport system using a circulating fluid can pass through an open or closed circulatory system. The complexity of the circulatory system in vertebrates is highlighted. We observe an
Open Circulatory System
in arthropods and molluscs (excluding cephalopods). The blood supply is not always channeled. There are areas within the tissues where fluid called hemolymph accumulates. All the areas where extravasation of hemolymph occurs are called hemocoel. The driver of the hemolymph heart is open to the hemocoel through openings called ostioles. This heart has a tubular shape and is disposed in the back area of the animal. Hemolymph enters by suction and is expelled forward through an artery that branches and flows into the hemocoel. Lymph moves slowly, so animals that depend on this system to supply oxygen to cells cannot have rapid movements. Molluscs have accessory hearts, formed by blood vessels with contractility.
Closed Circulatory System
In this model of the circulatory system, the blood supply, called blood, always passes through blood vessels. It occurs in annelids, cephalopods, and vertebrates. In annelids, the heart is tubular and is located in the dorsal area of the animal. In vertebrates, the circulatory system achieves varying degrees of complexity as the level of evolution presented by the animal increases. The circulatory system can be single or double, with incomplete or complete circulation.
Simple Circulation
It appears in fish. In blood circulation, blood only passes once through the heart at every turn. The heart is tubular and shows a venous sinus that collects the blood, an atrium, and an impeller ventricle. The blood comes from the veins of the body charged with CO2 to the heart. The ventricle pumps blood to the gills to get oxygen flowing through arteries and distributed throughout the body. The return of blood to the heart is performed through veins.
Double Circulation
Blood flows through the heart twice per revolution of the circuit. Found in terrestrial vertebrates. The route is from the heart, leaving the left ventricle to the tissues of the body to re-enter the heart through the right atrium. This movement is called the greater circulation. The circuit continues from the right ventricle to the lungs to return again to the heart via the left atrium. This movement is the lesser circulation. The second circuit may have incomplete oxygenation of blood in amphibians and reptiles or complete oxygenation in birds and mammals.
Circulation in Amphibians
Tadpoles’ hearts function as the heart of a fish. In adult amphibians, they are septate, forming three chambers: two atria and one ventricle. The blood comes from CO2-filled tissue and enters the heart through the right atrium. It passes to the ventricle and is ejected out of the heart. The blood that goes to the lungs is oxygenated and returned by the pulmonary arteries to the heart again, entering the left atrium. In the single ventricle, a mixture of carboxylated and oxygenated blood is produced, so the system is inefficient, pumping oxygenated blood to the lungs and carboxylated blood to the body’s cells.
Reptiles
They also have a double and incomplete movement, such as amphibians. However, the ventricle is partially divided so that the mixture of carboxylated and oxygenated blood is lower and the heart’s efficiency is higher. Crocodiles have a heart with ventricles completely divided by a partition, like birds and mammals.
Birds and Mammals
They have complete double circulation. Carboxylated blood enters the heart through the right atrium and passes through the tricuspid valve to enter the right ventricle. It emerges from the heart through the pulmonary artery to the lungs, where it is oxygenated and returns to the heart through the pulmonary veins. It enters through the left atrium, passes through the mitral valve, and enters the left ventricle. From there, it goes to the body’s tissues, transporting the oxygen needed for the aerobic performance of the cells. Carbon dioxide is discharged into the blood and returns through the veins to the heart to enter again through the right atrium.