THE BREATHING MECHANISM

THE MECHANISM OF BREATHING The action of breathing in and out is due to changes of pressure within the thorax, in comparison with the outside. INHALATION 1.  Diaphragm moves down, forcing air into airways 2.  Intercostal muscles contract, enlarging cavity even more 3.  Membranes move with the contractions 4.  Surface tension in alveoli and surfactant keep them from collapsing 5. Other muscles can force a deeper inhalation

THE MECHANISM OF BREATHING The action of breathing in and out is due to changes of pressure within the thorax, in comparison with the outside. EXHALATION 1.  Diaphragm moves up, forcing air out 2.  Intercostal muscles relax, shrinking the cavity 3.  Membranes move with the contractions 4.  Surface tension in alveoli keep them from collapsing 5.  Other muscles can force a deeper exhalation ATMOSPHERIC PRESSSURE = 760 mmHg Pressure is necessary for breathing, which is why it is difficult to breathe in high altitudes and also why a punctured lung can be dangerous.

INHALED AIR VS EXHALED AIR FACTORS INHALED AIR EXHALED AIR Oxygen [ ]  21%  16% Carbon Dioxide [ ]  .04%  5% Nitrogen [ ]  78% Dryness  Drier  Moist Temperature  Colder or Warmer than 37◦C  Warm ~37◦C Cleanliness  Dirtier Cleaner (May contain bacteria & viruses)

BREATHING VS RESPIRATION BREATHING: the act of bringing air in and out of lungs; consists of inhalation and exhalation ** Is an EXTERNAL mechanical process** CELLULAR RESPIRATION: when glucose and oxygen combine to produce carbon dioxide, water and ATP energy. ** Is an INTERNAL chemical process**

BREATHING RATE The rate at which we inhale and exhale is controlled by the respiratory center, the Pons Medulla, within the Medulla Oblongata in the brain. Inspiration occurs due to increased firing of inspiratory nerves and also the increased recruitment of motor units within the intercostal and diaphragm Our lungs are prevented from excess inspiration due to stretch receptors within the bronchi and bronchioles which send impulses to the Pons when stimulated. Exhalation occurs due to a sudden stop in impulses along the inspiratory nerves   Breathing rate is all controlled by chemoreceptors within the main arteries which monitor the levels of Oxygen and Carbon Dioxide within the blood. If oxygen saturation falls, ventilation accelerates to increase the volume of Oxygen inspired.

BREATHING & HOMEOSTASIS If oxygen saturation falls, breathing accelerates to increase the volume of Oxygen inspired. If levels of Carbon Dioxide increase a substance known as carbonic acid is released into the blood which causes Hydrogen ions (H+) to be formed. An increased [ ] of H+ in the blood stimulates increased breathing rates. Note: Breathing faster will increase the rate of oxygen is brought in and the rate at which cellular respiration occurs at. Carbon Dioxide levels primarily control the rate of breathing NOT oxygen.

BREATHING & HOMEOSTASIS Initial Condition 12-20 Breaths per minute Trigger/Cause Heavy Exercise Homeostatic Change: Oxygen in blood increases CO2 in blood decrease Homeostatic Change: Oxygen in blood decreases CO2 in blood increase Effector & what it does: Inspiratory nerves fire more often to increase the rate of breathing - causing an increase in breathing Sensors: Chemoreceptors in the Aorta/other blood vessels respond to increase in CO2 Coordinating Center: Pons Medulla

GAS EXCHANGE GAS EXCHANGE: This refers to the process of Oxygen and Carbon Dioxide moving between the lungs and the blood Occurs by diffusion* MOVEMENT OF OXYGEN Blood in the capillaries surrounding the alveoli has a lower concentration of Oxygen than the air in the alveoli which has just been inhaled. Both alveoli and capillaries have walls which are only one cell thick and allow gases to diffuse across them. MOVEMENT OF CARBON DIOXIDE The blood in the surrounding capillaries has a higher concentration of CO2 than the inspired air due to it being a waste product of cellular respiration. CO2 diffuses the other way  capillaries  alveoli exhaled

CONDITIONS NEEDED FOR GAS TRANSPORT MOIST So that gases can pass through the walls 2. THIN MEMBRANE So that gases can dissolve and pass into the blood and cytoplasm of cells 3. CONCENTRATION GRADIENT So that gases can move by diffusion (from high [ ] to low [ ] ) 4. PRESSURE GRADIENT So that gases can be pushed in the direction they need to move (from high press. to low press.)

GAS TRANSPORT O2 is needed for cells to undergo cellular respiration (Glucose + O2CO2 + ATP + Water) CO2 is a byproduct of cellular respiration & must be expelled from the body HEMOGLOBIN: Is a chemical found inside red blood cells that can carry gases. Hemoglobin has 4 binding sites where oxygen, carbon dioxide, hydrogen ions & carbon monoxide can be carried.

GAS TRANSPORT OXYGEN TRANSPORT Dissolved in the blood plasma (3%) Attached to hemoglobin as oxyhemoglobin (97%) Hb+O2  HbO2 CARBON DIOXIDE TRANSPORT Dissolved in the blood plasma (9%) Attached to hemoglobin as Carbaminohemoglobin (27%) Hb+CO2  HbCO2 As a combination of hydrogen ions dissolved in the blood or hydrogen ions on hemoglobin (64%)

GAS TRANSPORT CARBON MONOXIDE When given the opportunity, Carbon Monoxide (CO) will bind to hemoglobin 200x more tightly than Oxygen can, making it difficult for our body to acquire & transport what we need. Even if there is plenty of oxygen present, CO will be chosen over O2 by the hemoglobin, essentially leading to death. CO is a colorless, odorless gas that is a by-product of combustion reactions (starting your car, heating your home, fires)

NERVOUS CONTROL OF BREATHING