Respiratory System

Upper respiratory tract

• from nares to lungs

• nasal cavity, pharynx, larynx, trachea

• function: conducts air to/from lungs, modifies inspired air, thermoregulation, defense against harmful substances, olfaction

Tracheal sections

• cervical part: cricoid cartilage to thoracic inlet

• thoracic part: in thoracic cavity, ends at bronchi/base of heart

Tracheal components

• tracheal cartilage: incomplete hyaline cartilage rings

• tracheal muscle: smooth muscle connecting tracheal cartilages dorsally

• annular ligaments of trachea: fibroelastic tissue connecting consecutive tracheal rings

Tracheal bifurcation

• at T4/5 (dorsal to base of heart)

• splits into L + R primary bronchi

Tracheal carina

• crest inside tracheal bifurcation

Lungs

• passive function in mechanical act of breathing (expands according to volume of thoracic cavity)

• base adjacent to diaphragm

• apex at thoracic inlet

Lung surfaces

• costal: lateral, against ribs

• mediastinal: faces opposite lung

• diaphragmatic: against diaphragm

• interlobar: contact adjacent lobes of same lung

Lung lobes

• L: cranial (cranial + caudal parts), caudal lobe

• R: cranial, middle, caudal, accessory lobe

  • accessory passes dorsal to caudal vena cava

Cardiac notch

• fissure between cranial & middle lobes of R lung at intercostal space 4-5

• exposes R ventricle of heart to surface of thorax

• clinical significance: cardiocentesis

Hilus

• area where vessels & bronchi enter/leave lungs

Root of lung

• aggregation of structures which enter the lungs

Auscultation of lungs

• cranial: triceps + teres major mm.

• dorsal: back muscles/ribs 5-11

• basal/caudoventral: rib 6 at costochondral junction to dorsal rib 11