Human Body Systems: Anatomy and Functions Explained
The Circulatory System: Heart, Blood Vessels, and Blood
The circulatory system is the body’s vital transport network, powered by the heart.
The Heart: Engine of Circulation
The heart is the main organ of the circulatory system, acting as its ‘engine’. In humans, it is located in the mediastinum, in the middle of the chest. It is a hollow organ with strong, muscular walls, slightly larger than a clenched fist. The heart is divided by partitions into four chambers: two upper atria and two lower ventricles. To propel blood through the circulatory system, the heart performs two movements: a contraction phase (systole) and a relaxation phase (diastole).
Blood Vessels: Arteries, Veins, and Capillaries
Arteries: Carrying Blood Away from the Heart
Arteries are vessels that carry blood from the heart to other parts of the body, specifically from the ventricles. They possess elastic tissue that allows their walls to stretch and receive blood under high pressure from the heart.
Veins: Returning Blood to the Heart
Veins are channels through which blood returns to the heart after circulating through the arteries. Their walls are thinner and less elastic than arteries. They do not withstand high pressures because the blood returning to the heart has lower blood pressure.
Capillaries: Microscopic Connections
Capillaries are so named because they are as thin as a hair. They connect arteries and veins, forming vast networks around the body’s tissues, facilitating exchange.
Blood Circulation Pathways
Blood circulates through two main pathways: systemic (major) and pulmonary (minor) circulation.
Systemic Circulation (Major Pathway)
Oxygenated blood is propelled from the left atrium into the left ventricle, and from there, it goes to the aorta. As it circulates through the body, the blood becomes charged with carbon dioxide produced in the cells, thus becoming deoxygenated. Arterial capillaries extend throughout the tissues, connecting to veins. These veins carry the deoxygenated blood into the right atrium, where systemic circulation ends and pulmonary circulation begins.
Pulmonary Circulation (Minor Pathway)
Deoxygenated blood passes from the right atrium to the right ventricle and is then propelled into the pulmonary artery. This artery supplies blood directly to the lungs. In the pulmonary alveoli, gas exchange (hematosis) takes place, and the now oxygenated blood returns to the left atrium through the pulmonary veins, completing the pulmonary circuit.
Components of Blood
Red Blood Cells (Erythrocytes)
Red blood cells are blood cells that lack nuclei. Instead, they contain a protein called hemoglobin, which is responsible for transporting oxygen and carbon dioxide throughout our bodies.
White Blood Cells (Leukocytes)
White blood cells are cells with nuclei, allowing them to reproduce. An elevated count of white blood cells can indicate an infection in the body.
Platelets (Thrombocytes)
Platelets are crucial for blood clotting. Their function is to heal wounds and form a network with traces of red and white blood cells to stop bleeding.
Hematosis: Gas Exchange in the Lungs
Hematosis is the vital process that occurs in the alveolar-capillary wall within the lungs. In this process, oxygen from the alveoli enters the blood to be transported to the cells. Carbon dioxide from the blood is expelled into the alveoli, to then be eliminated from the body through exhalation.
The Respiratory System
The respiratory system is responsible for the process by which we inhale air into our body and exhale air rich in carbon dioxide. Its main components are the airways and the lungs.
The Airways: Path for Air
The airways include the nostrils, pharynx, larynx, trachea, bronchi, and bronchioles. The mouth also serves as an organ through which air can enter and leave the body.
Nasal Cavities
These are two cavities located above the mouth opening. They open to the outside through the nostrils and communicate with the pharynx at the back.
The Pharynx
Located below the nasal cavities and mouth, the pharynx is also part of the digestive system. Both food and air pass through it.
The Larynx
The larynx is located at the beginning of the trachea. It is a cavity formed by cartilage, which has a protrusion commonly called the ‘Adam’s apple’. Within the larynx are the vocal cords, which vibrate to produce voice.
The Trachea
The trachea is a tube about 12 cm in length, located in front of the esophagus. It serves as the main airway to the lungs.
Bronchi and Bronchioles
The bronchi are two tubes into which the trachea divides. They penetrate the lungs, where they branch multiple times, becoming progressively smaller until they form the bronchioles.
The Lungs: Sites of Gas Exchange
The lungs are two spongy organs protected by the ribs. While the right lung has three lobes, the left lung has two, with a space to accommodate the heart. The bronchioles end in tiny air sacs surrounded by capillaries, called alveoli. A membrane called the pleura surrounds and protects the lungs.
The Urinary System
The urinary system is responsible for removing toxic substances and waste products from our body. It consists of the kidneys and the urinary tract.
Kidneys: The Body’s Filters
The main organs of the urinary system are the kidneys. They are tasked with filtering waste substances from the blood and forming urine.
The Urinary Tract: Pathway for Urine
Urine is carried through two ducts, the ureters, into the bladder, and then expelled to the outside through the urethra. The ureters, bladder, and urethra make up the urinary tract.