Module 10 ↑ ↓
Functions of respiratory system:
• Transport of oxygen from the air into the blood
• Removal of CO2 from blood into the air
• Control of blood acidity (PH)
• Temperature regulation
• Defense to airborne particles
Lungs located in thoracic cavity and surrounded by rib cage of the diaphragm
Airways: nasal cavity and mouth that join together at the pharynx
Pharynx leads into larynx (voice box) ▯ becomes trachea
Trachea divides into two main bronchi ▯ divide into smaller and smaller bronchioles
Bronchioles divide ad end in alveoli – site of gas exchange
Pulmonary artery (delivers deoxygenated blood to lungs) branches to from network of
capillaries around each alveolus. ▯Maximizes gas exchange
▯ Thin endothelial walls, large total cross sectional area, low blood velocity
In capillaries: O2 in CO2 out.
From capillaries: oxygen rich blood back to left side of heart through pulmonary vein
Structure of an alveolus
~300 million alveoli in healthy human lung ~ 0.3mm
Alveolar epithelial cells (type 1 cells): walls of alveoli ▯ one cell thick
Type 2: secrete surfactant that lines alveoli
Many capillaries surround alveoli
Respiratory Membrane: region b/w alveolar space and capillary lumen 0.3 microns narrow
gas exchange takes place here
Macrophages and lymphocytes (cells of IS): protect body from airborne particles
Fibers of elastin and collagen: present in walls of alveoli, around blood vessel and bronchi
Pressure of Lungs Intrapleural Pressure
• 2 thin pleural membranes:
Parietal pleura: lines and sticks to ribs Viceral Pleura: surrounds and stick to lungs
• 2 layers of that membrane form intrapleural space▯ contains pleural fluid
• Pleural Fluid: reduces friction b/w two pleural membranes during breathing
• Ribs tend to expand outwards while lungs tend to recoil and collapse
Alveolar and Atmospheric pressure
• Alveolar pressure: pressure inside the lungs (also called intrapulmonary pressure)
• Intrapleural pressure: pressure in intrapleural space
• Atmospheric pressure outside body: 760 mm Hg at sea level
• B/w breaths ▯ alveolar and atmospheric pressure is the same: 760 ▯ intrapleural space: 756
▯▯the chest wall and lungs moving in opp directions cause this lower intrapleural pressure.
Transpulmonary Pressure ▯ diff b/w alveolar and intrapleural pressures
▯ This diff in pressure holds the lungs open (very important)
▯Healthy lungs: transpulmonary pressure is +ve (outward) ▯ keeps lungs and alveoli open
• If both alveolar and intrapleural pressures were equal ▯
transpulmonary pressure= 0
• Thus , no pressure holding lungs open ▯ lungs would
• Occurs when intrapleural space is punctured ▯ creates equal
alveolar and intrapleural pressures (both 760)
• Usually, only one lung collapses ▯ b/c intrapleural space of
each lung is isolated from the other
Boyle’s Law: when volume of a container decreases,
pressure inside increases and vice versa
▯Pressure inversely proportional to volume
Inspiration and Expiration
• Moving air into lungs: pressure gradient ▯ air
pressure gradient • To move air into lungs▯requires high pressure outside and low pressure in alveoli
• To move air out▯requires high alveolar pressure and low atmospheric pressure.
• Can’t increase the outside atmospheric pressure▯alveolar pressure must change
Mechanisms of Inspiration
• To decrease alveolar pressure ▯ lung volume must increase ▯ diaphragm
contracts, moving downward and external intercostal
muscles of rib contract, lifting rib cage up and out.(vol
• Vol ↑ , ↓ alveolar pressure inside to ~759 ▯ pressure
gradient now exists: ↓inside lungs
• =Air now flows into lungs
• Contraction of these muscles ▯ active process that relies
on signals from the respiratory center in brainstem
Mechanisms of Expiration: depends on if you’re exercising or
• At rest ▯ diaphragm and external intercostal muscles relax: lungs recoil to original size.
Result: volume ↓, alveolar pressure ↑ above atmospheric pressure: pressure gradient reversed
and air flows out ▯ Passive process b/c no muscle contractions occur
• Exercise: air must be forced out of lungs ▯ needs contraction of abdominal and internal
intercostal muscles ▯ contracts…. volume of lungs: creates larger pressure gradient▯air out.
(pressure larger inside than outside)
▯Notice that as the "diaphragm" is pulled down, the volume increases, the pressure decreases, air rushes
in, and the "lungs" inflate. When the diaphragm relaxes, the volume decreases, the pressure increases, air
flows out, and the "lungs" deflate.
Pulmonary Compliance: stretchability of lungs ▯ the more stretchable the more compliant
• Defined: volume change that occurs as a result of a change in pressure
• Ex: 2 balloons: with pressure 0 inside and small initial volume ▯ when pressure added, each
balloon inflates to new volume: larger balloon is more compliant b/c its volume greater from
• Determines ease of breathing
• ↓ compliance: difficulty to inflate
• ↑ compliance: easy to inflate, hard to deflate
• Two factors influence compliance:
▯ mount of elastic tissue found in alveoli, blood vessels, bronchi
▯ urface tension of the film of liquid that is lining all alveoli. Pulmonary Compliance—Elastic Tissue Components
• Fibers of elastin and collagen in walls of alveoli, blood vessels, bronchioles.
• Elastin fibers are easily stretched—collagen fibers are not
• Arrangement contributes to ~ 1/3 of total compliance/”elastic behavior” of healthy lung.
• The more elastin, the less compliant lung (more thick rubber, less stretchable)
Pulmonary Compliance—Surface Tension
• Remaining 2/3 of elastic behavior: attributed to surface tension of liquid film lining of alveoli.
• Surface tension from the thin film tends to collapse the alveoli, decreasing compliance ▯ hard to
• Surface Tension: force developed at surface of a liquid ▯ due to attractive forces b/w water
molecules. • Water generates more tension at surface, b/c h2o molecules stick together tightly ▯no outward
balancing force ▯ forces b/w h2o inward
Pulmonary Compliance—Pulmonary Surfactant
• Pulmonary Surfactant: lipoprotein substance produced by type 2 alveolar cells and consists of
• Surfactant molecule has hydrophilic head that faces water and hydrophobic tail that faces away.
• When added to water ▯ lies on surface of airwater interface
• Heads attracted to water molecules and will balance inward forces with outward (disrupt
• Forces now equal in every direction and water drop will flatten out b/c of decreases surface
Pulmonary Compliance—Pulmonary Surfactant and Infant Respiratory Distress Syndrome
• Premature babies born before 36 weeks don’t produce enough surfactant
• Their alveoli tend to collapse ▯ hard to inhalinfant respiratory distress syndrome
• Use large amounts of energy inflating their lungs and can die from exhaustion
• To avoid: receive dose of surfactant directly into lungs @ birth
• Pulmonary surfactant is released from type 2 cells during deep breathing
Patients who have had open heart surgery find it painful to breath , instead choose to take small, rapid,
panting breaths▯ no surfactant is released and these patients can encounter complications and breathing
difficulties. This is why after any surgery in the thoracic cavity (Chest), patient is often given breathing
exercises that include deep breathing in order to stimulate surfactant release.
• Max air lung can hold:
~5 L /breath
• Doesn’t mean we breath
in that amount each
• Depends on: health, age, level of activity. Spirometer: device used to measure lung volumes and capacities ▯ also helpful in diagnosing
pulmonary diseases (asthma, bronchitis, emphysema)
• Consist of air filled chamber w/attached hose.
• As air is drawn out of chamber during inhalation, chamber falls and pulls on a chain attached to
a pen that rises.
• During exhalation, chamber fills, rises, and pen falls.
• As pen goes up and down, marks a path on a calibrated piece of paper that indicates lung vol.
Lung Volumes and Lung Capacities
• Tidal Volume: volume of air entering or leaving the lungs during one breath at rest= 500ml
• Inspiratory reserve volume: max amount of air that can enter lungs in addition to tidal
• Expiratory Reserve volume: Max amount of air that can be exhaled beyond tidal
• Residual Volume: remaining air in the lungs after max expiration=1200ml
• Inspiratory capacity: max amount of air that can be inhaled after exhaling the tidal volume
=tidal volume+ inspiratory reserve volume
• Functional residual capacity: amount of air still in lungs after exhalation of the tidal volume
=expiratory reserve volume+ residual volume
• Vital capacity: max amount of air that can be exhaled after a maximal inhalation
=inspiratory reserve+ tidal volume+ expiratory reserve volume
• Total lung capacity: Ma amount of air that lungs can hold= vital capacity+ residual volume
• Pulmonary ventilation (VE): amount of air that enters all of the conducting and respiratory
zones in one minute.
• Determines the amount of air ▯amount of oxygen that is available to the body.
• Conducting zone (anatomical dead space): area of lungs where no gas exchange occurs (b/c
no alveoli) • Respiratory zone: region of lungs where alveoli are located ▯ gas exchange
• @ rest: 7500 ml/min ▯ amount of air entering the
entire pulmonary system: conducting and
• Only air in respiratory zones (alveoli) will be
involved in gas exchange
• This volume: alveolar ventilation
Alveolar Ventilation: volume of air entering only the
respiratory zone each minute.
• Represents the volume of fresh air available for gas exchange.
• Anatomical dead space volume: volume remaining in
conducting zone ▯ estimated
• Dead space vol (healthy person) ~ equal to person’s body
• VA= VE—VD (VA: alveolar ventilation VE: pulmonary
ventilation VD: dead space volume)
Partial Pressure of Gases
• Partial Pressure: pressure exerted by that one gas in a mixture of
• Partial pressure= Total pressure of all gases X Fractional
concentration of the one gas
• PO2 is lower & PCO2 much higher
True values after gas exchange has occurred
• O2 and CO2 move down their concentration gradients ▯ partial
• PP can also describe amount of O2 or CO2 dissolved in plasma (b/c they dissolve in h20)
Partial pressures of Gases across the Alveoli—Diffusion
• Blood entering lungs: PO2 40 mmHg and PCO2 46mmHg
• Alveoli: P02 105 mmHg. PCO2 – 40 mmHg
• As blood moved past alveoli ▯ O2 and CO2 diffuse down PP gradient
• O2 will move from alveolar space to blood stream
• CO2 from blood to alveolar space • As blood leaves the PPs EQ with alveolar air
1. Blood leaving the lungs has a high PO2 (100 mmHg) and low PCO2 (40 mmHg).
2. Blood returns to the left side of the heart and is pumped to the systemic circulation.
3. Blood enters tissue beds with the same PO2 (100 mmHg) and PCO2 (40 mmHg).
4. Cells have a low PO2 (40 mmHg) and high PCO2 (46 mmHg) inside.
5. As blood flows through capillaries, oxygen diffuses into the cells and carbon dioxide diffuses out
down their respective partial pressure gradients.
6. Blood leaving the tissue will have equilibrated with cells; it will have a PO2 of 40 mmHg and PCO2
of 46 mmHg.
7. Blood returns to the right side of the heart to be pumped to the lungs, and the process repeats.
•Partial pressure of oxygen or carbon dioxide in the blood refers to the amount of these
gases dissolved in the plasma.
•Actually: there is very little O2 dissolved in plasma
• Oxygen is carried in the blood
dissolved in the plasma and
is carried in RBCs attached
to hemoglobin, which can carry
much more oxygen.
• Very little O2 is transported in blood dissolved in
plasma ▯can’t supply enough for body
▯1.5% of total O2 transported in blood
▯98.5% by hemoglobin Red blood cells and Hemoglobin
• Most of O2 is carried in RBCs attached to Hb▯each can carry 4 O2 molecules
• RBC’s also called erythrocytes: donut shaped w/o a hole ▯ large enough to squeeze through the
smallest of capillaries single file ▯ don’t contain a nucleus in mature form
▯ During early stage of development: have a nucleus
• Males: ~5.2 million RBCs/cubic mm ▯ more b/c of testosterone influence on RBS production
• Females: ~4.7 million/cubic mm
• Lifespan of 120 days ▯120 die and produced everyday
• Erythropoiesis: production of RBCs
▯ akes place in bone marrow &requires amino acids, iron,
folic acid, vit B12
▯Amino acids & iron: important components of Hb
▯Folic acid: essential for info of new DNA and for normal cell division
▯Small amounts of B12: b/c folic acid can’t do function w/o it
• RBCs are destroyed and removed by spleen and liver
• Erythropoietin (EPO): required for control of RBC production ▯
stimulates bone marrow to produce RBCs
• Adults: 90% secreted by kidneys, 10% by liver
• EPO is secreted in low amounts to ensure
that RBC production keeps up their daily
loss—250 million RBCs e