Introduction to Animals and the Circulatory System: The Gap Between Life and Movement

Relevance of the Theme

Understanding the Animal Circulatory System is a crucial milestone in the study of Biology, as it allows for an in-depth view of the structure, function, and interaction of various parts of the body. It is a topic that connects several aspects of the animal kingdom, from the simplest animals with small organs to the most complex ones with highly developed circulatory systems. Through the analysis of this vital system, we become aware of the incredible diversity and complexity present in nature.

Contextualization

In the Biology curriculum, the study of the Animal Circulatory System comes after understanding the cell and tissues, allowing for a more global view of the organization of living beings. The relationship between the internal and external environment of organisms, the need for transport and distribution of substances, and cell nutrition are interconnected themes in the discipline.

Therefore, by studying the Animal Circulatory System, we are delving into the complex machinery of life, providing the key to understanding how animals are adapted to their environment, how they gain energy, and how they stay healthy. This knowledge also underpins other disciplines, such as Physiology, Biochemistry, and Medicine, making it essential for a range of future studies.

Theoretical Development

Components of the Animal Circulatory System

• Heart: A hollow, self-propelled muscular organ located inside the thoracic cavity, which acts as a central pump in the circulatory system, propelling blood through blood vessels. In most animals, the heart is divided into chambers that separate oxygen-rich blood (from the body) from oxygen-poor blood (to the lungs);

• Blood Vessels: Networks of tubes that extend throughout the animal's body, transporting blood. There are three main types: arteries (carry blood from the heart to tissues), capillaries (where exchanges of substances between blood and cells occur), and veins (transport blood from tissues back to the heart);

• Blood: Vital fluid that carries substances such as oxygen, nutrients, and hormones throughout the body. It varies in composition in different animals but is generally composed of red cells (erythrocytes), white cells (leukocytes), platelets, and plasma;

Key Terms

• Circulation: Constant and regulated movement of blood, transferring substances through the animals' bodies. It can be closed (when blood is always contained in vessels) or open (when blood can leave the vessels, coming into direct contact with tissues);

• Single Circulation: Type of circulation where blood passes through the heart only once in each complete cycle through the body, common in animals with simple structures;

• Double Circulation: Type of circulation where blood passes through the heart twice to complete the circulation of the body. Present in animals that need to separate oxygen-rich blood from oxygen-poor blood.

Examples and Cases

• Fish: Have a single circulation circulatory system. Blood flows from tissues to the heart, passes through the organ capillaries where it exchanges oxygen for carbon dioxide, and is pumped to the gills to be oxygenated again before being redistributed to tissues;

• Mammals: Have a double circulatory system. The right side of the heart receives blood from the body (low in oxygen) and pumps it to the lungs, where gas exchange occurs. Oxygenated blood returns to the left side of the heart and is then pumped to the body;

• Amphibians: Have a circulatory system with a mixture of single and double circulation. The heart has three chambers, with a partial mixture between oxygen-rich and oxygen-poor blood. Oxygenated blood from the lungs mixes with oxygen-poor blood from the body in the heart before being pumped to the rest of the body.

Detailed Summary

Relevant Points:

• Function and Structure of the Heart: The heart is a hollow, self-propelled muscular organ that propels blood through blood vessels. The structure and number of heart chambers vary among animals, with the hearts of mammals (4 chambers) and birds (4 chambers) being more complex than those of fish (2 chambers) and amphibians (3 chambers).

• Types of Circulation: There are two main types of circulation, single and double. In single circulation, blood passes through the heart only once during a complete cycle through the body. In double circulation, blood passes through the heart twice in each circulation cycle.

• Role of Blood Vessels: Blood vessels (arteries, capillaries, and veins) are like roads that carry blood throughout the body. Arteries carry blood from the heart to tissues, capillaries allow the exchange of substances between blood and cells, and veins transport blood from tissues back to the heart.

• Blood: Blood is a complex substance, composed of plasma, red cells (erythrocytes), white cells (leukocytes), and platelets. Its main function is to carry oxygen and nutrients to tissues and remove metabolic waste.

Conclusions:

• The structure and function of the animal circulatory system are closely linked. The complexity of circulation often reflects the complexity of the animal.

• Only a deep understanding of the circulatory system allows us to understand the relationship between different parts of the body and how they interact in the functioning of the organism.

• The circulatory system is essential for the survival of animals, allowing for the efficient transport of vital substances throughout the body.

Exercises:

1. Explain the difference between single and double circulation. Give examples of animals that have each type.

2. List and describe the main components of the circulatory system.

3. Develop a representative scheme of the blood circulation cycle of a mammal. Indicate the path the blood takes, identifying the structures of the circulatory system involved.