The Respiratory System

Two Major Divisions  Upper Respiratory Tract – nasal cavity, pharynx, and larynx * External Respiration – exchange of gases between atmosphere and blood  Lower Respiratory Tract – trachea, bronchial tree, and lungs * Internal Respiration – exchange of gases between blood and body cells (Cellular respiration = breakdown of glucose) (Cellular respiration = breakdown of glucose)

Upper Respiratory Tract  Nose – 2 nostrils provide entrance to the nasal cavity; internal hairs to filter air

 Nasal Cavity – hollow space behind the nose; contains olfactory membrane; conducts air to the pharynx; blood vessels warm air; mucus traps particles and moisten incoming air

 Pharynx – back of throat; pathway for the respiratory and digestive tracts; aids in speech production

 Larynx – enlargement at the top of the trachea; known as the voice box; houses the epiglottis which keeps food from entering the trachea and the vocal cords

Lower Respiratory Tract  Trachea – windpipe; extends from the larynx to the primary bronchi; lined with pseudostratified ciliated columnar epithelium and mucus producing cells which filter air and move particles up to the pharynx

 Bronchial Tree – consists of the trachea and two primary bronchi which branch into smaller branches called secondary bronchi and then into tertiary bronchi and small bronchioles branch even further and divide into alveolar ducts into smaller branches called secondary bronchi and then into tertiary bronchi and small bronchioles branch even further and divide into alveolar ducts

 Alveoli – microscopic air sacs where oxygen and carbon dioxide are exchanged by diffusion between the air and the blood

Alveoli  Optimal diffusion of O 2 needed in organisms that require high levels of O 2 that cannot be obtained by diffusion alone.  1. Increased Surface Area – alveoli provide this  2. Decreased Tissue Thickness – easier for gases to pass through  3. Increased Concentration Gradient – between gases in organism and environment Fish respiratory system (gills) capitalizes on all three (lower amount of O 2 in water)Fish respiratory system (gills) capitalizes on all three (lower amount of O 2 in water)

 Lungs – soft, spongy organs in the thoracic cavity Left lung – divided into two lobes Right lung – divided into three lobes Lobes - divided into functional units called bronchopulmonary segments

Lungs

Lung Capacity  Total lung capacity – total amount of gas both lungs can hold; never completely empty; together they hold ~ 5-6 L of gas  Vital lung Capacity – maximum amount one can inhale or exhale

Efficiency  Lungs sacrifice respiratory efficiency to maximize H 2 O retention.  Decrease loss of H 2 O by eliminating one way flow of O 2  Always residual volume of air in lungs  Lungs not exposed to fully O 2 air  Some animals (i.e. birds) require more O 2 than a sac-like lung can provide.  Unidirectional flow of air through lungs eliminates dead volume and air is always fully O 2 (unlike mammals)  Also, flow of blood is opposite in direction to movement of air through lungs

Breathing Mechanism  Inspiration – inhalation a. Nerve impulses cause the diaphragm to contract b. Diaphragm moves downward and causes the size of the thoracic cavity to increase c. Intercostal muscles contract to raise ribs and increase thoracic cavity even more Alveolar pressure decreases d. Atmospheric pressure forces air into the respiratory tract e. Lungs become inflated

 Expiration – exhalation a. Diaphragm relaxes (rib cage falls due to gravity and other involved muscles relax) b. Alveolar walls collapse c. Alveolar pressure increases d. Air is squeezed out of the lungs and into the air passages

Muscles Involved In Breathing  The Diaphragm accomplishes very shallow breathing on its own.  External Intercostal Muscles are responsible for pulling up the rib cage during heavier breathing.  Neck Muscles are responsible for “gasping”

Regulation of Breathing  Rate of O 2 use (Cell activity) determines breathing rate Increased CO 2 in Blood  Message to Brain  Message to Respiratory Muscles  Increased Breathing Rate

Hemoglobin and Gas Transport Body TissuesLungs (low O 2 ) (High O 2 ) HbO 2      Hb      HbO 2 H+ CO 2 O2O2 CO 2 + H 2 O  HCO H+ Diffuses in plasma O2O2 CO 2 HCO H+  CO 2 + H 2 O * We exhale the CO 2 and the H 2 O

Respiratory Disorders  Emphysema - degenerative disease that destroys alveolar walls and is often caused by smoking or pollutants

 Bronchial Asthma – causes bronchioles to constrict so breathing becomes difficult and is commonly caused by allergic reactions

 Pneumonia – alveoli fill with fluids and blood cells due to bacteria or virus

 Tuberculosis – caused by bacteria that causes fibrous connective tissue to build up in the walls of the lungs; lung tissue becomes damaged and thickens to make gas exchange difficult