Human body systems

Before starting to talk about the systems of the human body, it is important to clarify that according to the cell theory , the cell is the morphological and functional unit of all living beings. In the case of multicellular living beings (animals, plants and fungi), the cells specialize in carrying out different tasks, and are organized in levels of greater complexity .

Thus, cells with similar characteristics are organized in tissues . Organs are structures made up of two or more tissues that fulfill the same function. Taking into account the specific function of an organ or tissue, it is said to be part of a body system. In humans, up to twelve of these systems are distinguished . In this article we will explain in detail what they are and what is the function of each of the systems of the human body .

Systems of the human body

Digestive system

The best known human body system is perhaps the digestive system , responsible for processing food from the moment it enters the body to extract the nutrients contained in it, and subsequently expel the undigested waste.

It includes the mouth, esophagus, stomach, small and large intestines, as well as other associated organs, such as the liver and pancreas. Food undergoes a sequential crumbling process, culminating in the enzymatic digestion of its macromolecules to allow the absorption of its components in the intestine.

Circulatory system

The circulatory system is another of the systems of the human body. It is responsible for transporting nutrients and oxygen throughout the body, and removing carbon dioxide and metabolic waste produced by cellular respiration from cells. It is made up of the blood, the heart, and all the blood vessels in the body (arteries, veins, and capillaries). In the capillaries there is an exchange of substances between the blood and the cells.

Nervous system

The nervous system is made up of neurons and glial cells, its function is to generate nerve impulses, receive information through nerves and process this information.

It has two parts, the central nervous system is made up of the brain, the cerebellum and the spinal cord, while the peripheral nervous system is made up of the peripheral nerves. These are made up of sensory neurons, which gather information, and motor neurons, which send impulses to the muscles.

Respiratory system

The respiratory system allows gas exchange with the circulatory system. It is made up of the nose, pharynx, windpipe, and lungs. The diaphragm is a skeletal muscle that is located under the lungs and causes its contraction and expansion, facilitating the entry and exit of air, which is why it is also part of the respiratory system. Gas exchange occurs in structures called pulmonary alveoli, which are lined with capillaries.

Urinary system

The urinary system filters the blood and removes waste substances, in addition to regulating the concentration of salts within the body. It is made up of the kidneys, ureters, bladder, and urethra. In a broader sense, it can be considered to be part of the excretory system , responsible for eliminating waste from the human body, along with the sweat glands of the skin. 

Reproductive system

The reproductive system is, among the systems of the human body, responsible for fertilization and gestation. It is made up of the gonads, which produce eggs or sperm, and the external sexual organs, which allow internal fertilization. It also includes the uterus, where the gestation of the fetus occurs, as well as various muscles that play a role during delivery.

Muscular system

The muscular system is made up of skeletal striated muscles and tendons, which are a type of connective tissue that connects muscles to bones. Not all muscles in the human body belong to the muscular system.

Thus, the heart is composed of cardiac striated muscle tissue and belongs to the circulatory system, while other organs have one or more layers of smooth muscle tissue, which allows certain types of movements. For example, these smooth muscles facilitate the transit of food through the digestive system.

Skeletal system

The skeletal system is made up of bones and ligaments, which are a type of connective tissue that holds bones together. Together with the muscular system, it forms the locomotor system, whose function is to carry out the coordinated movement of the body, through the intervention of motor neurons associated with the muscles. Also, within the bones is the red bone marrow, where red blood cells are made.

Endocrine system

The endocrine system has the function of generating and releasing regulatory molecules of different body processes, called hormones, into the bloodstream. This system is made up of endocrine glands, which release products directly into the blood. The main glands of this type are the pituitary or pituitary (which regulates the activity of other endocrine glands), the thyroid, the adrenals (located in the kidneys), the pancreas, the parathyroids and the gonads. 

Immune system

The immune system is in charge of defending our body from pathogens. It is composed of the white blood cells found in the blood, also called leukocytes (the main types are neutrophils, eosinophils, lymphocytes, basophils and monocytes, each one fulfills a specific function), the thymus (which produces lymphocytes), the nodules lymphatics and lymphatic channels. These structures also belong to the lymphatic system.

Lymphatic system

The lymphatic system is similar to the circulatory system, it is composed of a series of nodules and channels that allow the synthesis and transport of lymph, the fluid that exists between the cells of the human body in different tissues. This system is closely related to the immune system, as it plays an important role in the distribution of lymphocytes throughout the body. The thymus, tonsils, and spleen are organs associated with the lymphatic system, which play a role in defense processes against microbes. The spleen is responsible for the destruction of those who have aged.

Integumentary system

Finally, the integumentary system is formed by the skin and its main function is to keep the body separated from the external environment, regulating the loss of water and minimizing any damage. In animals it includes hair, feathers or scales.

It also allows the regulation of body temperature through sweat and has associated sensory receptors that detect pain (nociceptors), pressure, temperature and surface texture. The skin is the largest organ of any animal, as it completely covers its body. In an adult human being it occupies an area of ​​2m ²  and weighs more than 4Kg.

Human body’s apparatus and systems

Some systems of the human body fall within a higher functional category, the apparatus, which can include one or more systems. Each device fulfills a specific function regardless of the type of tissues that are part of it. Thus, the locomotor system is made up of the skeletal system and the muscular system, coordinated by the nervous system. There is also a circulatory system, which encompasses the circulatory and lymphatic systems. The other functional systems of
the human body are the digestive, the excretory, the reproductive and the respiratory systems, each formed by the corresponding system.