Oxygen to the Blood Why start here? When is someone dead? Alveoli—where the action is Diffusion--Gases and liquids Red Blood Cells and Hemoglobin Lung volume and Respiratory Rate Respiratory Control

Alveoli Key to lung function Where O2 enters blood, CO2 leaves blood Every alveoli is capillary covered sac Lining of sac is squamous epithelium Also cuboidal epithelial cells that secret surfactant (keeps surfaces from sticking) and cilia (to move mucous and particles up respiratory tree Unfold alveolar membranes in human lungs—tennis court!

Ventilating alveolus with perfusion of oxygen and non-ventilating alveolus with no perfusion Alveoli

Oxygen and CO2 Blood in capillaries around alveoli of lungs is: – Low/high in oxygen? – Low/high in CO2? Why? Drawing: – O2, CO2 molecules – Inside of alveolus – Alveolar membrane – Capillary membrane – Inside of capillary – Show net flow of gas molecules

Cells of alveoli Type I Pneumocytes—epithelial lining cells Type II Pneumocytes—make surfactant Dust Cells—macrophages that engulf dust

Diffusion—a reminder From higher concentration to lower concentration Only way substances can move in or out of a cell

Dissolved Gases Why “partial pressures?” Why “partial pressures?” Open a can of soda…what happens? Open a can of soda…what happens? Diffusion of O2 at from inside alveolus into capillary is also movement from air (gas) into plasma (liquid) Diffusion of O2 at from inside alveolus into capillary is also movement from air (gas) into plasma (liquid) Mass movement of oxygen into blood works because: Mass movement of oxygen into blood works because: – Differences in partial pressures are great – Distance is short – Oxygen is lipid soluble so it passes through membrane and coating (surfactant) – Surface area is huge—remember tennis court

Red Blood Cells (RBC) Fun Facts One drop of blood has 250 million RBC’s Adult human has total of 25 trillion RBC’s—1/3 of all cells in the body Each RBC lives about 120 days and travels 700 miles. Membrane rupture or other damage is noticed by phagocytes which then engulf the cell One percent of RBC’s are replaced each day at a rate of about 3 million per second Each RBC contains about 250 million Hb molecules So, number of Hb molecules in body is about equal to stars in the universe

Most O2 binds to Hb in RBC’s Hb is protein with four Heme groups— each has iron molecule at center which helps bind O2 Oxygen saturation for Hb is just right to bind with O2 in lungs and release in tissues CO binds more strongly and permanently with HB than O2—thus CO poisoning CO2 is carried in various forms in blood (see next slide) Red blood cells and Hemoglobin

Lung Capacity Total lung capacity: 4200 ml (f); 6000 ml (m) Resting tidal volume: 500 ml (f) Expiratory reserve (amount you can blow out after exhaling normally): 700 ml (f) Residual volume (amount you can never blow out): 1100 ml (f) Inspiratory reserve (amount you can breathe in after normal inhalation): 1900 ml (f) Rate of air exchange At rest: 500 ml/breath (tidal volume) x 12 breaths/min (resting respiratory rate) = 6 liters/min. Peak exercise: 4800 ml/breath (expanded tidal volume using most of reserves) x 50 breaths/min. (increased respiratory rate) = 200 liters/min. Lung Volume and Respiratory Rate

Respiratory control Great review of nervous system – Brainstem – Cranial nerves – Sensory and motor – Visceral versus somatic CO2 levels have more input during normal respiration Possible to blow off enough CO2 to pass out since low O2 doesn’t kick in on time—careful divers and swimmers!