6.4 – Gas Exchange

Respiratory System A. Purpose is to take in oxygen for cellular respiration and get rid of CO2 made by it 1. Ventilation – act of breathing in and out using lungs a. Can’t get O2 by diffusion across surface b. Maintains concentration gradient for diffusion in lungs

2. Gas exchange – diffusion of O2 and CO2 B. Cellular Respiration – making ATP using glucose and O2, producing H2O and CO2

II. Anatomy of Ventilation

A. Process Air moves in through mouth or nasal passages Goes down trachea Separates into R & L bronchi Bronchi branch into bronchioles End in clusters of alveoli

Alveoli – air sacs, ~300 million/lung 1. Each one surrounded by capillary bed 2. Blood coming from heart high in CO2, low in O2 – relies entirely on diffusion based on concentration gradient Adaptation Advantage Spherical shape Large surface area Single cell thickness Less for gases to diffuse through Moist inner lining Efficient diffusion Capillary bed adjacent Short distance for diffusion

3.Composed of pneumocytes a. Type I – thin, large surface area, cannot be replaced b. Type II – produce and secrete a solution that acts as a surfactant (reduces surface tension) and prevents alveoli from sticking to each other, can be replaced if damaged

Mechanisms of Breathing A. There is no muscle in the lungs (can’t inflate/deflate on their own) B. Based on the inverse relationship between pressure and volume

Inhale - Diaphragm contracts (moves down) and external intercostals and abdominal muscles contract (expands rib cage) causing an increase in the volume of the thoracic cavity. Increase in volume leads to a decrease in pressure making pressure in lungs lower than air pressure outside body (partial vacuum) which sucks air into the lungs. Exhale – Diaphragm relaxes (moves up) and internal intercostals contract (shrinking rib cage) causing a decrease in volume of the thoracic cavity, increasing pressure, and pushing air out.

A. Emphysema (COPD)– alveoli destroyed 1. Causes – smoking, pollution Lung disorders A. Emphysema (COPD)– alveoli destroyed 1. Causes – smoking, pollution 2. Alveoli become large, irregularly shaped with gaping holes which reduces surface area for gas exchange Healthy

Lung Cancer 1. Prone to metastasize to brain, bones, liver, adrenal glands (high mortality rate) 2. Takes over space of healthy tissue 3. Often caused by smoking