Anatomy Essentials: Epithelium, Ligaments, and Circulation
Epithelium
The epithelium is tissue formed by one or several layers of cells joined together to coat all free surfaces of the organism. It constitutes the inner lining of cavities, organs, hollow tubes of the body, and skin. Epithelium also forms the mucous glands and the parenchyma of many organs, including the liver.
Connective Tissues
Ligaments
A ligament is a tough, fibrous band that provides stability to a joint.
Synovial Fluid
Synovial fluid is a clear, viscous fluid found within joints.
Labrum
The labrum is a ring that may surround a joint surface to deepen it.
Articular Cartilage
Articular cartilage functions to:
- Cushion pressure overload of the articular surfaces.
- Allow movement of bone surfaces without causing friction.
Circulation
Systemic Circulation
Systemic circulation begins with oxygenated blood leaving the left ventricle of the heart. It travels through the aorta and its arterial branches to the capillary system, where it delivers oxygen. Veins then carry oxygen-poor blood back to the heart, flowing into the superior and inferior vena cavae, which drain into the right atrium.
Pulmonary Circulation
Pulmonary circulation begins with oxygen-poor blood leaving the right ventricle through the pulmonary artery, which divides to serve each lung. In the pulmonary alveolar capillaries, blood is oxygenated. The four pulmonary veins then carry oxygen-rich blood to the left atrium of the heart.
Respiratory System
Upper Airway
The upper airway consists of:
- Nostrils: Two large cavities that allow air entry. The air is moistened, filtered, and heated to a specific temperature by structures called turbinates.
- Pharynx: A muscular, membranous structure that helps direct air into the lower airways.
The upper respiratory tract extends from the nose to the trachea. The conducting zone is from the trachea to the terminal bronchioles. The respiratory zone, where gas exchange occurs, extends from the respiratory bronchioles to the alveolar sacs.
The upper airway has three main functions: to heat incoming air to a specific temperature, to humidify the air (saturate it with water vapor), and to filter the air.
Lower Airway
The lower airway consists of:
- Larynx: A tube that filters inspired air and allows air passage into the trachea and lungs. It closes during swallowing to prevent food passage and also functions as the phonetic organ, producing sound.
- Trachea: Provides an open pathway for air inhaled and exhaled from the lungs.
- Bronchi and their ramifications:
- Bronchus: Carries air from the trachea to the bronchioles.
- Bronchiole: Carries air from the bronchi to the alveoli.
- Alveolus: Site of hematosis (gas exchange), where carbon dioxide is removed from the blood and oxygen is absorbed.
- Lungs: The lungs facilitate gas exchange with the blood. The alveoli are in close contact with capillaries to enable this process.
Heart
The heart is the main organ of the circulatory system. It is a conical, muscular organ located in the chest cavity. It functions as a pump, pushing blood throughout the body. It is divided into four chambers: two upper chambers called the right atrium and left atrium, and two lower chambers called the right ventricle and left ventricle.
Systole refers to the contraction of the heart (either an atrium or a ventricle) to eject blood into the tissues.
Diastole refers to the relaxation of the heart to receive blood from the tissues.