Respiratory System The Mechanics of Breathing

Breathing…. --also called VENTILATION --movement of air outside the body into the bronchial tree and alveoli --Involves Inspiration and Expiration

Inhalation/Inspiration – active process (muscle contraction) Diaphragm contracts (pulls lungs down) External intercostal muscles contract (pulls rib cage up and out). This increases the size of the thoracic cavity (and lungs) causing a drop in pressure inside the lungs (Boyle’s Law = volume pressure) At sea level, air pressure is 760 mm Hg. The change in size of the lungs causes the pressure inside to drop to about 758 mm Hg. Outside air rushes in to equalize the difference in pressure.

Forced Inhalation - active process (muscle contraction) – taking a deeper breath – requires stronger contraction of normal inspiratory muscles (diaphragm and external intercostals) --plus help of the pectoralis minor and sternocleidomastoid (SCM) muscle.

Exhalation/Expiration - elastic recoil – passive process (no muscle contraction) Muscles relax tissues return to their normal shape and size decrease size of the thoracic cavity (and lungs) increase pressure inside and forcing air out

Forced Expiration - active process (muscle contraction) Contraction of internal intercostal muscles (pulls rib cage down) -- abdominal muscles (pull sternum down and squeeze abdominal cavity – this forces more air out than normal

Review…. Why does air naturally move into the lungs ? Hint: mmHg What happens when we inhale? When we force inhalation, what muscles help with that? What happens when we exhale?

Gas Exchange Ventilation (inhalation and exhalation) brings air into the lungs Air contains oxygen, which diffuses from inside the alveoli into adjacent capillaries (both made of simple squamous epithelium). Carbon dioxide diffuses in the opposite direction. If you go up in elevation, the outside air pressure is less, so inhaled oxygen does not diffuse into the blood as easily.

Pressure of inhaled air is not enough by itself to inflate the individual alveoli of the lungs, which contain a very small amount of fluid. Fluid would normally cause the alveoli walls to stick together (b/c of surface tension) Body creates a chemical called surfactant, which disrupts surface tension inside alveoli, preventing them from sticking together. Surfactant - not made until the 7 th month of fetal life, therefore if born prematurely, alveoli will stick together and baby cannot breathe. This is RDS (Resp. Distress Syndrome). Baby is put on a ventilator and given artificial surfactant as long as needed

Transport of Gases Oxygen 98% - transported bound to the hemoglobin of a RBC (oxyhemoglobin) 2% - dissolved in plasma To stimulate the RBC to give up its oxygen to the tissues : increase in body temp. increase in breathing rate (hyperventilation) increase in CO 2 concentration

These three things are associated with exercise: an increase in CO 2 concentration results in blood that is more acidic (lower pH). To counter this, a person will hyperventilate – the rapid breathing is a way to help stimulate removal of CO 2 from the blood therefore lower the blood’s acidity (or raise the blood’s pH)

Carbon Dioxide 23% - transported bound to the hemoglobin of a RBC (carbaminohemoglobin) 7% - dissolved in plasma 70% - transported as a bicarbonate ion so it doesn’t adversely affect the pH of the blood it must undergo a chemical change from carbon dioxide to bicarb. ions

Review What type of tissue is found in the capillaries and alveoli? What molecule on the RBCs does oxygen and carbon dioxide attach to? What is that molecule called with Oxygen? With Carbon Dioxide? What could lead to the alveoli sticking together? How is that prevented? What substance is produced by the alveoli?

Review…. How much oxygen is transported by the RBCs? How much carbon dioxide is tranported by RBCs? What does CO 2 do to your blood pH? What is its effect on breathing?

Composition of Air Air is made up of a mixture of gases Nitrogen= 79%, Oxygen = 21% and CO 2 =.03% Air pressure is 760 mmHg of which each of the gases contribute to that total. Ex:.21[760]= 160 mmHg partial pressure of O 2

Nervous System Control Portions of your Spinal Cord control your breathing. pH sends impulse to Resp center which causes in breathing *CO 2 Medulla Oblongata Pons

Respiratory Volumes… SPIROMETRY- measurement of air volume in and out of the lungs

Tidal volume – least affected by missing all/part of a lung – since lungs are only filled to about half capacity after normal inhalation, air can be compressed to make up for missing part of lung. Other resp. volumes that require forced inhalation to measure (vital capacity, inspiratory reserve) cannot be made up for with missing all/part of a lung.