Digestive and Circulatory Systems in Animals

Digestive Systems in Animals

Models of the Digestive Apparatus

• A stomach cavity with one opening, e.g., Porifera.
• A digestive tract with two openings (mouth and anus), i.e., vertebrates.

Digestive Systems in Invertebrates

• Platyhelminthes: Flatworms have a blind tube with a single hole.
• Nematodes: A mouth and an anus appear.
• Annelids: In the digestive tract with a mouth and an anus, specialized structures like the esophagus, crop, and gizzard appear.
• Molluscs: The digestive tract has specialized regions and displays a body attached to the hepatopancreas.
• Echinoderms: The digestive tract has specialized regions in which Aristotle's lantern stands out among the sea urchins.
• Arthropods: They all possess a digestive tract with specialized regions and also other organs.

Digestive Systems in Vertebrates

Vertebrates have evolved a digestive apparatus that, in general, consists of a gastrointestinal tract, which consists of the mouth, pharynx, esophagus, stomach, and intestines, and attached glands, which are: salivary, liver, and pancreas.

Circulatory Systems in Animals

Transport of Nutrients

In less complex animals, such as Porifera, coelenterates, and some flatworms, there is no circulatory system, carrying out transport from cell to cell by diffusion or active transport. In complex animals, the circulatory system exists and consists of:

• Transport Liquids: It is considered a connective tissue composed of water, minerals, proteins, cells, and various pigments. There are several types of liquids:
  • Hydrolinfa: Proper to Echinoderms and lacks the capacity to transport gas.
  • Hemolymph: It is the fluid transport of many invertebrates. In molluscs and arthropods, it contains hemocyanin.
  • Blood: Present in vertebrates and annelids. Plasma has many cell types. It has platelets, and red blood cells with hemoglobin can transport gases.
  • Lymph: Present only in vertebrates. It transports fats and defense cells.
• Blood Vessels: These are tubes that form the vascular system along which fluid transport occurs. Types of blood vessels:
  • Arteries: They are thick and elastic; blood flows out from the heart through them.
  • Veins: They are thinner and heavier, and blood enters the heart through them.
  • Capillaries: They are the smallest of the vessels, and their walls consist of a single tissue endothelium.
• Heart: The heart is the organ responsible for delivering transport liquids through contraction and expansion movements. Types:
  • Tubular: Named as a pipe.
  • Accessory: Only responsible for accelerating circulation in specific areas.
  • Enclosed: They have chambers: atria, where blood enters, and ventricles, where blood exits.

Circulatory Apparatus

• Open: In this system, the transport liquid flows out of the vessels and bathes tissues directly. Typical of molluscs and arthropods.
• Closed: The liquid vessel never leaves; only the plasma, which is a part of fluid transport, does. It is characteristic of vertebrates and annelids.

Circulatory Systems in Invertebrates

• Molluscs: Open circulatory system with a septate heart and accessories called branchial hearts.
• Arthropods: Have an open tubular heart device.
• Annelids: Closed circulatory vessels and contractile cross hearts.