The Respiratory System A Breathtaking Analysis of Structure and Function

Nose External nares = nostrils Vestibule – small hair-lined chamber Nasal cavity Divided by nasal septum Lined with nasal conchae to increase surface area ** Ciliated mucous membrane

Pharynx Nasopharynx – behind nose; air only Segments Nasopharynx – behind nose; air only Oropharynx – behind mouth; air & food Laryngopharynx – air & food

Larnyx AKA Voice Box Thyroid & cricoid cartilage Epiglottis – flap of tissue that closes over trachea when swallowing Vocal cords – elastic tissue UNCILIATED

WHY DO WE CLEAR OUR THROATS?

Trachea C rings of cartilage allow esophagus to expand Lined with ciliated mucous membrane

Bronchial Tree R & L primary bronchi Branching network Smallest tubes = Bronchioles Connect to alveoli Lined with surfactant to counteract surface tension of water

Lungs Spongy organs containing bronchial tree & alveoli

Diaphragm Separates thoracic cavity from abdominal cavity

Respiration Pulmonary ventilation – air in and out External respiration – gases between lungs & blood Internal respiration – gases between blood & body cells

Mechanics of Breathing

Background Information Pressure is basically the number of collisions between molecules Increasing the volume will… Decreasing the volume will…

Inspiration (Inhalation) Contraction of diaphragm & intercostals Thoracic cavity expands, increasing the volume Thoracic cavity pressure decreases

Inspiration (Inhalation) Lung surface pulls outward, increasing the lung volume Alveoli volume increases & pressure drops Air rushes in to restore equilibrium

Expiration (Exhalation) Diaphragm & intercostals relax Thoracic cavity reduces in size, increasing pressure Lung surface recoils to original shape, increasing pressure

Expiration (Exhalation) Volume of alveoli decreases Alveolar pressure increases Air flows out of alveoli

ASTHMA Tightening of bronchial tubes from spasms & mucus Chronic vs. exercise-induced vs. occupational Vary based on trigger/cause

                                                                                                                                                                                       

Exchange of Gases

Basic Information Partial pressures determine direction of movement of gases Only gases in the plasma affect the partial pressure Oxygen & CO2 diffuse independently of each other

External Respiration Between alveoli & bloodstream PO2 in alveoli > PO2 in plasma Most O2 entering blood is bound by Hb O2 goes to plasma only when Hb is saturated

External Respiration CO2 in opposite direction PCO2 in plasma > PCO2 in alveoli

                                                                                           

Internal Respiration Between capillaries & body cells PO2 in capillaries > cytoplasm PCO2 in cytoplasm > capillaries

But there’s a catch… CO2 has an affinity for Hb If CO2 binds to Hb, it blocks the binding sites for O2 If O2 can’t bind to Hb, we can’t bring nearly as much O2 into the blood

So… When CO2 enters the blood, it combines with water to form carbonic acid The carbonic acid immediately breaks down into Hydrogen ions (H+) & Bicarbonate ions (HCO3-)

Then… The H+ can’t be left in the plasma so it hitches a ride on the Hb The HCO3- just chills in the plasma and makes the trip to the lungs

In the lungs… H+ & HCO3- recombine to form carbonic acid and then CO2 & H2O The CO2 is exhaled and the H2O stays in the body

The formula… CO2 + H2O  H2CO3  H+ + HCO3-