Superficial vessels drain scalp, face and neck into superficial ring nodes. Deep vessels form left and right jugular lymphatic trunks. Superficial nodes form ring from chin to posterior head. Deep nodes form vertical chain near internal jugular vein
Mediastinum is located in the midline of the thoracic cavity. Divided into superior and inferior mediastinum, with inferior being larger. Extends from superior thoracic aperture to diaphragm
Axilla is a pyramidal space between upper limb and thorax. Apex bounded by neck root, first rib, clavicle, and scapula. Contains axillary artery, vein, brachial plexus, and lymph nodes. Contains muscles like coracobrachialis, pectoralis minor, and biceps brachii
Skin and mucus membranes form physical barriers against pathogens. Tears and saliva contain lysozyme that destroys bacterial cell walls. Stomach acids kill swallowed invaders
Esophagus is 25 cm muscular tube connecting pharynx to stomach. Length varies from 8-10 cm at birth to 23-37 cm in adults. Contains mucosa, submucosa, muscularis propria, and adventitia layers
Lymphatic system is part of immune system, complementing circulatory system. System consists of vessels, nodes, organs, tissue and lymph. Lymph is clear fluid carried back to heart for re-circulation. System is open, unlike closed circulatory system