Cellular Structures and the Circulatory System
Cellular Organization and Function
The cell is the basic unit of living matter. Depending on their structure and organization, cells are classified into different types of living organisms.
Prokaryotic Cells
Prokaryotic cells lack a distinct nucleus; their genetic material is located freely in the cytoplasm, along with the enzymes necessary for their maintenance and reproduction.
Eukaryotic Cells
Eukaryotic cells possess a distinct nucleus, where the genetic material is enclosed by a membrane, separating it from the cytoplasm. They contain internal membrane-bound structures called organelles, where cellular functions are performed.
Tissues
Tissues are groups of cells with a similar function, originating from a common initial cell.
Muscle Tissue
Muscles are tissues composed of specialized cells called myocytes, which are longer than they are wide, also known as muscle fibers.
There are three types of muscle tissue: smooth, striated, and cardiac.
Nerve Tissue
Nerve tissue is composed of neurons and glial cells.
Neurons, or nerve cells, transmit nerve impulses.
Glial cells are responsible for the care, nourishment, and protection of neurons.
Connective Tissue
Connective tissue is a diverse group of cell types that bind other tissues together, creating organizational structures within the body.
Epithelial Tissue
Epithelial tissue is formed by unspecialized cells that are strongly linked together, arranged in layers that cover the surface of hollow organs, skin, and mucous membranes.
Organs and Systems
Organs are composed of different tissues, each with a specific function, derived from the way their acting tissues are formed.
A system is a combination of parts working together in a coordinated and integrated manner to perform a specific function.
An apparatus is formed when multiple systems work in concert.
The Circulatory System
The circulatory system in humans is a closed system consisting of the heart, which acts as a pump, and blood vessels, including arteries, veins, and capillaries. Its primary function is to transport nutrients, oxygen, and other metabolic products to every cell in the body. Blood is the transport medium.
The Heart
The heart has four chambers: two atria and two ventricles. The two halves of the heart are separated. The atrium and ventricle on the same side are connected through openings fitted with valves, called atrioventricular valves. The right valve is called the tricuspid valve, and the left is the mitral valve.
Blood Vessels
Arteries are the vessels that carry blood away from the heart to all body cells. They branch into smaller vessels that reach all organs, called capillaries. These capillaries converge into veins.
Blood Composition
Blood consists of plasma, a liquid containing many dissolved substances, and cellular elements: red blood cells, white blood cells, and platelets.
Functioning of the Circulatory System
Blood, after cellular metabolism, enters the heart through the vena cava into the right atrium. The muscles of the atrium wall contract, pushing blood into the right ventricle. This blood is then sent through the pulmonary arteries to the lungs, where gas exchange occurs, removing carbon dioxide and enriching the blood with oxygen. This oxygen-rich blood returns through the pulmonary veins to the heart, entering the left atrium, which sends it to the left ventricle. From there, blood leaves the heart through the aorta and continues through the capillaries to reach the tissues, which take up oxygen and release carbon dioxide, starting a new cycle.
Circulation Circuits
There are two circulation circuits:
- Lesser or pulmonary circulation: venous blood, low in oxygen, is sent to the lungs for oxygenation.
- Greater or general circulation: oxygen-rich blood is sent from the heart to the body, allowing tissue cells to oxygenate.
Circulation in humans occurs within blood vessels, passing through the heart twice in each cycle, and is governed by…