6.4 – Gas Exchange

Causes and consequences of lung cancers Essential Idea: The lungs are actively ventilated to ensure that gas exchange can occur passively. 6.4 Gas Exchange Understandings: Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries   Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them Different muscles are required for inspiration and expiration because muscles only do work when they contract Applications: Causes and consequences of lung cancers Causes and consequences of emphysema External and internal intercostal muscles, and diaphragm and abdominal muscles are examples of antagonistic muscle action Skill: Monitor ventilation in humans at rest and after mild and vigorous exercise

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 3. Cellular Respiration – making ATP using glucose and O2, producing H2O and CO2

II. Structures Lungs – sponge like structures on either side of heart Divided into lobes – 2 on left, 3 on right side Air must be processed before it enters – filtered, cleaned, warmed, moistened

1. Hair in nostrils filters air by trapping dust, pollen, etc. Nose 1. Hair in nostrils filters air by trapping dust, pollen, etc. 2. Lined by mucous membrane to moisten and warm air 3. Cells have cilia which trap bacteria a. Get coated with mucus, swallowed, and destroyed by stomach acid

Pharynx (Throat) 1. Nose and mouth come together, divides into esophagus and trachea

Larynx (Voicebox) 1. Between pharynx and trachea 2. Made of muscle and ligaments (vocal cords) 3. Epiglottis – flap of tissue – if open, air flows to trachea, closes when you swallow to direct food to esophagus

Trachea (wind pipe) 1. Like a vacuum cleaner hose – rings of cartilage keep it strong 2. Contains mucus to trap debris and cilia to move it back up to throat so it can be swallowed

Bronchi – trachea divides into two tubes, one goes to each lung Bronchioles – bronchi branch into smaller tubes

Alveoli Small air sacs, about 300 million per lung Provide surface area for gas exchange Surrounded by capillary beds – O2 diffuses into blood, CO2 diffuses into alveoli to be exhaled

III. Anatomy of Ventiliation 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 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

IV. Mechanisms of Breathing A IV. 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.

D. 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.

V. Lung disorders A. Emphysema (COPD)– alveoli destroyed 1 V. 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