Anatomy and Function of Human Organ Systems: Respiration, Circulation, and Urinary Tract

Human Body Systems: Circulation, Respiration, and Excretion

Pulmonary Circulation (Lesser Circulation)

In the Pulmonary Circulation (Minor Circulation), deoxygenated blood passes from the right atrium to the right ventricle and is then pumped into the pulmonary artery. This artery supplies blood directly to the lungs. In the pulmonary alveoli, where gas exchange, known as hematosis, takes place, the resulting oxygenated blood returns to the left atrium through the pulmonary veins. This completes the lesser circulation.

Hematosis: The Process of Gas Exchange

Hematosis is a vital process that occurs at the alveolar-capillary membrane. In this process, gas exchange occurs by diffusion. Specifically:

• Oxygen (O₂) that is in the alveoli passes into the blood to be taken to the cells where there is a lower concentration of oxygen.
• Carbon dioxide (CO₂) is released by the cells into the blood, which then passes into the alveoli to be expelled during exhalation.

The Respiratory System

The respiratory system is responsible for the intake of oxygen and the expulsion of carbon dioxide. Key components include:

Nostrils

Air enters through the nostrils, two ducts along the bottom of the nose. They comprise a nasal cavity with two outer holes separated by the nasal septum and covered with hairs that filter the air.

Pharynx

The air passes through the pharynx, an organ shared by the respiratory and digestive systems. It is a tube approximately 14 cm long that communicates with the nostrils, oral cavity, larynx, esophagus, and the Eustachian tube.

Larynx

The air is transferred to the larynx, a small tube protected by nine cartilages that hold it in place.

Trachea

The air moves through the trachea, a tube about 12 cm in length and 2 cm in diameter, located in front of the esophagus. It is composed of a series of flexible cartilages (C-shaped rings), whose ends are directed inwards and joined by smooth muscle fibers.

Lungs

Between the air circulating in the alveoli and the blood in the capillaries, there are only a few thin endothelial layers which can be easily crossed by gaseous particles, facilitating efficient gas exchange.

The Urinary System

The urinary tract is responsible for collecting waste and expelling substances outside the body. These organs include:

• Kidneys: Their function is to filter the blood to remove waste products and produce urine.
• Renal Pelvis: The innermost cavity that collects urine as it leaves the kidney.
• Ureters: Tubes that carry urine from the kidneys to the bladder.
• Bladder: A muscular, stretchable organ whose function is to store urine temporarily.
• Urethra: A tube that carries urine to the outside, being short in women and longer in men.