Resp structure and Function

Upper resp tract gross anatomy

nasal cav → nasopharynx

oral cav (hard and soft palate)→ oropharynx

soft palate separates: naso and oropharynx

nasopharynx + oropharynx = pharynx

oesphagus is dorsal to trachea

• cartilage rings are ventral

• trachealis muscle = dorsal

Horse upper resp tract

soft palate sits ventral to epiglottis

• complete separation of naso- and oropharynx

• air can only pass to trachea from nasopharynx

• no common pharynx

• obligate nasal breathers

Larynx (laryngeal cartiages) hangs from skull via hyoid apparatus

Stylohyoid

Epihyoid

Ceratohyoid

Basihyoid

Thyrohyoid

Some elephants can be terrifying (dorsal to ventral)

Laryngeal cartilages

Thyroid

Cricoid

Arytenoid

Inspiration

Inspiration: 

(diaphragm contract = volume increases BUT neg pressure → draws in air)

• Ribcage expands (external intercostals contract)

• Diaphragm contracts

• Overall size of pleural cavity is bigger

• Belly expands because diaphragm is pushing abdominal contents

• Often an animal’s abdominal movements will reveal respiratory rate

• Diaphragm = primary respiratory muscle

• External Intercostal Muscles = accessory respiratory muscles 

Horse (and Kangeroo) biphasic ventilation

• Locomotor-ventilation coupling

Passive inspiration → active inspiration

Passive expiration → active expiration

Front foot hits the ground → abdominal contents shifts forwards (momentum) → pushes on diaphragm → air forces out of lungs (expiration)

Inspiration - foot moves forward (stride) when cantering and galloping

• expansion of thoracic cavity when front feet extend

• larger pressure gradient → inspiration

Diffusion Distance

From alveolus → RBC

surfactant → type 1 alveolar epithelial cell → epithelial basal lamina → [connective tissue] → endothelial basal lamona → blood plasma → membrane of RB

Fick’s Law

Rate of transfer of gas through tissue PROPORTIONAL to difference in partial pressure either side of membrane

Rate of transfer INVERSELY P. to tissue thickness

Respiratory Quotient

(typically 0.8)

CO2 / O2 (exchange ratio)

Tissue pp gradients

arterial → tissue cells → venous mmHg

PO2: 95 → 23 → 40

Alveoli partial pressure gradients

arterial → venous (mmHg)

PO2: 40 → 104

PCO2: 45 → 40

Bronchus

• Spiral bands of bronchial smooth muscle

• Irregular plates of cartilage

• BALTs + mast cells

• Ciliated columnar epithelium + goblet cells

Bronchioles

• Conducting → terminal → respiratory

  • Gas exchange in respiratory

• Cuboidal epithelium + club cells

Alveolar ducts + alveoli

• Type 1 pneumocytes → 1 cell thick terminally differentiated blood gas barrier

• Type 2 pneumocytes → thicker, make surfactant

• Pores of Kohn between alveoli

Pleura

• Visceral → attached to lung surface, abundant elastic fibres for inflation

• Parietal pleura

  • Costal

  • Mediastinal

  • Diaphragmatic

• Pleural fluid

Mediastinum

• Continuous with neck, fascia, thoracic inlet, retroperitoneal space

• Contains:

  • Trachea

  • Thymus

  • Vagus

  • Left phrenic nerve

  • Oesophagus

  • Heart (pericardium)

  • Aorta

  • Cranial vena cava

  • Thoracic duct

  • Lymph nodes

Pleural lines of reflection

• Vertebral

• Costal

• Sternal

Within fold of parietal pleura → plica venae cavae

• caudal vena cava

• right phrenic nerve