1. Overall Function of Respiratory System exchange of O 2 and CO 2 from pulmonary capillaries thermoregulation phonation assistance in regulation of acidity elimination of water

2. Anatomy of Respiratory System horse cannot breath through the mouth upper and lower –upper includes nostrils, nasal passages, pharynx, larynx and trachea to thorax regulates temperature and humidity of air phonation protection of foreign bodies –lower - within the thorax lungs left and right bronchi bronchioles alveoli - surrounded by blood capillaries –site of gas exchange

3. nostrils - large, wide nostrils desirable –impaired by facial nerve damage nasal cavities - high vascularity –provide large surface area for heat and water exchange –cause airflow resistance sinuses - air filled cavities that open into nasal cavity pharynx - common passage for food and air –dorsal displacement of soft palate larynx - voice box –laryngeal hemiplagia trachea - non-collapsible tube with cartilage rings lungs –large alveolar density compared to other species –ribcage rigid compared to other species

4. Control of Breathing regulated by 3 factors: –chemical factors - increase CO 2 sends message to increase breathing frequency and breath more deeply –nervous control - natural flight response triggers increased rate of breathing –mechanical control muscle expand and contract ribcage force of front legs landing chemical and nervous control important at walk and trot mechanical control important at canter and gallop

5. Respiratory Mechanics muscular regulation inspiration and expiration regulated by muscular effort and elastic recoil –diaphragm - main muscle –contraction - flattened and back in body lengthens thorax, increasing volume and stimulating inspiration –relaxation - curved into thorax abdominal and thoracic muscle contract, decreasing width of thorax, causing expiration

6. resting point (of respiration) - opposing elastic forces are at equilibrium energy is required to increase or decrease volume of lungs and thorax passed resting point recoil returns lungs and thorax to resting point with out energy horse resting point –biphase - middle of breath inspiration - initially passive followed by contraction of diaphragm expiration - passive to resting point followed by abdominal muscle compression of ribcage (COPD)

7. Airway Resistance nostrils and larynx reduced by flaring of nostrils reduced by dilation of larynx neck and head in straight line

8. respiration rate - number of breaths per minute –rest : 12-20 /min –intense exercise : 150-180 /min –changes with exercise, pain and increased body temperature tidal volume - amount of air inhaled and exhaled with each breath –rest : 4-7 liters –exercise : 10 liters –alveolar ventilation - inspired air that reaches lungs –dead space ventilation - air that stays in airways and the part of lungs without gas exchange –alveolar volume - difference between tidal volume and dead space

9. dead space –resting horse 60-70% of tidal volume –intense exercise 20 % of tidal volume –prolonged steady exercise steady increase in dead space with increased respiration rate –thermoregulation –percent of dead space in horse at rest, twice as much as humans and dog minute volume - amount of air passing in and out per minute –minute volume = respiratory rate X tidal volume –rest 100 liters/min –maximal exercise1500 liters/min 7 fold increase in respiratory rate 2 fold increase in tidal volume

10. Functions at Rest and Adaptations of Respiratory System 1) ventilation (air into alveoli) - bulk movement of air into and out of lungs –minute volume 2) perfusion (how gas is removed from the lungs by the blood) –dependent on pressure difference between pulmonary artery, pulmonary vein, and vascular resistance 1% increase PCV results in 4% increase in pulmonary vascular resistance

11. 3) diffusion (how gas gets across the air blood barrier) –rate of diffusion pressure gradient diffusability of the gas –CO 2 very soluble, in and out of solution easily –O 2 low solubility, transported by hemoglobin thickness of membrane –all 3 processes increase during exercise to meet O 2 demands

12. Diffusion pulmonary diffusion –humans : 4-5 fold increase in pulmonary blood flow; expanding capillary blood volume 3 times –horse : 8 fold increase in pulmonary blood flow; even greater increase in capillary blood volume tissue diffusion –O 2 and CO 2 diffuse down the pressure gradient –PO 2 returning from muscle tissue following heavy exercise, only 16mm Hg increased driving pressure of O 2 from arterial blood into muscle –tissues with high aerobic needs are more vascularized greater surface area for exchange