Animal Circulatory and Respiratory Systems: A Detailed Look
Animal Transport of Nutrients
In less complex animals, such as Porifera, coelenterates, and some flatworms, there is no circulatory system. Nutrients are transported from one cell to another by diffusion or active transport. In complex animals, a circulatory system exists and consists of: transport fluid, blood vessels, and the heart.
- Transport Fluid: It is considered a connective tissue composed of water, minerals, proteins, cells, and various pigments. There are several types of fluids:
- Hydrolinfa: Found in echinoderms and lacks the capacity to transport gas (no respiratory pigments).
- Hemolymph: It is the transport fluid of many invertebrates. In mollusks and arthropods, it contains hemocyanin (a pigment that carries oxygen).
- Blood: Present in vertebrates and annelids. Plasma has many cell types (lymphocytes, red blood cells). It has platelets, and red blood cells can transport gases due to hemoglobin. Annelids possess, in addition to hemoglobin, hemoerythrin and chlorocruorin.
- Lymph: Present only in vertebrates. It transports fat cells and defenses.
- Blood Vessels: These are tubes that form the vascular system along which transport fluid circulates. Types of blood vessels:
- Arteries: They are thick, elastic, and carry blood away from the heart.
- Veins: They are thinner and carry blood towards the heart.
- Capillaries: They are the smallest of the vessels, and their walls are formed by a single tissue endothelium.
- Heart: The heart is the organ responsible for delivering transport liquids through contraction and expansion movements. There are several types:
- Tubular: Named because it is a tube.
- Accessory: Only responsible for accelerating circulation in specific areas.
- Enclosed: They have chambers: atria, where blood enters, and ventricles, where blood exits.
Circulatory System Models
According to the structure of the network of vessels:
- Open: In this system, the transport liquid flows out of the vessels and bathes tissues directly. Typical of mollusks and arthropods.
- Closed: The liquid never leaves the vessel; only the plasma, which is a part of the transport fluid, does. It is characteristic of vertebrates and annelids.
Examples
- Invertebrates – Snails: Open circulatory system and partitioned heart.
- Arthropods: They have an open, tubular heart unit.
- Annelids: Closed circulatory vessels and contractile cross hearts.
Branchial Respiration
Gill breathing is very effective in aquatic environments, where oxygen is sparse. It is typical of some annelids, aquatic mollusks, crustaceans, fish, amphibians, and insect larvae.
- Gills: Extensions of the body surface, highly vascularized. They can be laminar (crab), filamentous (fish), or tree-like (mollusks).
- Gill Position: They can be external or internal. The former are more vulnerable to injury and are typical of marine annelids, crustaceans, insects, and amphibian larvae. The latter are typical of mollusks, crustaceans, and fish.
- Gill Ventilation:
- Crustaceans: Most use the movement of their legs for ventilation.
- Lamellibranch Mollusks: Movement of the cilia that line the gills.
- Cephalopod Mollusks: Mantle contractions.
- Cartilaginous Fishes: Body movements.
- Bony Fishes: Continuous movement of the operculum, which protects the gills, helps move water through the gill slits.