3.4 - the respiratory system - physiology

functions

• provides gas exchange: body cells continually use O2 for metabolic reactions, generating ATP to breakdown nutrients, while releasing CO2 as a waste product

• regulate pH

• receptors for smell, filter inspired air, produce vocal sounds

• excretes small amounts of water and heat

conducting zone

air enters through the nose (nostrils and nasal cavity) or oral cavity to filter, warm, and humidify the air before it reaches the alveoli

• movement of air in a out, no exchange

• pharynx, larynx, trachea, and bronchi to terminal bronchioles

respiratory zone

movement of air through the respiratory bronchioles to alveoli for gas exchange

• site of gas exchange between air and blood

• O2 is diffused into the bloodstream, CO2 is diffused to alveoli to be breathed out

• trachea → right and left primary bronchi → bronchioles → alveoli

ventilation

mechanical flow of air into and out of the lungs using 3 pressures:

• changing the volume of thoracic cavity and lungs, pressure in lungs will also change

1) atmospheric pressure: 1 atm or 760 mmHg

2) alveolar pressure: air flows in and out the lungs due to pressure gradient from atm pressure (760 mmHg)

3) intrapleural pressure: the pressure in the pleural cavity, which is always lower than atmospheric pressure to act as a vacuum, and couples lungs to chest wall (756 mmHg)

inspiration

air is drawn into the lungs by contracting external intercostals up and out, and diaphragm pulls down

• atm pressure 760 mmHg, alveoli pressure 758 < 760 mmHg, intrapleural pressure 754 < 756 mmHg

• higher atm pressure going towards lower alveolar pressure

• increasing volume decreases pressure inside the thoracic cavity, allowing for airflow

• diaphragm: 75% of air entered during quiet breathing

• external intercostals: 25% of air entered during quiet breathing

expiration

expelling air out of the lungs by relaxing external intercostals and diaphragm naturally recoils back up into place

• atm pressure 760 mmHg, alveoli pressure 762 > 760 mmHg, intrapleural pressure 756 = 756 mmHg

• higher alveolar pressure going towards lower atm pressure

• decreasing volume of thoracic cavity spikes up pressure

boyle’s law

the pressure and volume are inversely related at a constant temperature

• high volume, low pressure

• low volume, high pressure

lung volumes

measure and assess pulmonary function

• generally larger in males, taller individuals, younger adults

• generally smaller in females, shorter individuals, elderly

• disorders can be diagnosed by comparing predicted and actual normal values (gender, height, age)

• lung capacities: combinations of lung volumes

• measured via spirometry

1) tidal volume

2) respiratory frequency

3) minute ventilation

tidal volume

volume of air inhaled or exhaled with each breath during quiet breathing (500 mL)

• smaller individual may have a smaller one than a larger individual

respiratory frequency

number of breaths per minute (12/min)

• pain/distress causes increase

minute ventilation

total volume of inhaled/exhaled air per minute (6 L/min)

• Rf * Vt

• Ex: 12 breaths/min * 500 mL/min = 6 L/min

respiration

the process of gas exchange in the body, O2 uptake and CO2 expulsion down their own pressure gradients

• external: pulmonary gas exchange between alveoli and blood

• internal: systemic gas exchange between systemic capillaries and tissues of the body

dalton’s law

each gas in a mixture of gases exert its own pressure as if no other gases were present

• partial pressurue: pressure of a specific gas in a mixture

• total pressure = all of partial pressures added

• earth’s atmosphere (760 mmHg): 78.6% N2, 20.9% O2, 0.04% CO2, ~1% water vapor

  • Ex: PN2 = 0.786 × 760 mmHg = 597.4 mmHg

• respiratory system depends on the medium of earth’s atmosphere to extract oxygen necessary for life

partial pressure

pressure of a specific gas in a mixture, determining the movement of O2 and CO2:

• between the atm and lungs

• between the lungs and blood

• between blood and body cells

diffusion of gas from a greater partial pressure area to lesser partial pressure

• greater difference in partial pressure = faster diffusion

alveolar air

alveolar air: less O2 and more CO2 than inhaled air

• CO2 content increases and decreases O2 content during gas exchange

• inhaled air is humidified, vapor content increases, percentage that is O2 decreases

exhaled air: more O2 and less CO2 than alveolar air

• some exhaled air did not participate in gas exchange, cuz it is a mixture of alveolar and inhaled air in dead space

henry’s law

the quantity of a gas that will dissolve in a liquid is proportional to the partial pressures of the gas and its solubility

• body fluids: ability of gas to stay in solution is greater than its partial pressure is higher and highly soluble in water

• higher partial pressure of a gas over liquid = higher solubility = more gases stay in solution

• more CO2 dissolved in blood plasma CO2 is 24x more soluble than O2

• we breathe in 79% nitrogen, but it is not soluble in blood plasma to dissolve and has no effect on body function

pulmonary gas exchange

diffusion of O2 from air in the alveoli of the lungs → to blood in pulmonary capillaries → and diffusion of CO2 in the opposite direction — all in the lungs

• deoxygenated blood from right side of heart to oxygenated blood, saturated with O2, and return to left side

• blood picks up O2 from alveolar air and unloads CO2 into alveolar air

• PO2 from 105 mmHg alveolar to 40 mmHg diffusion into pulmonary capillaries, continues to diffuse until capillary pressure meets alveolar pressure

• PCO2 from 45 mmHg deoxygenated blood into 40 mmMg alveolar air, continues to diffuse until alveolar pressure meets deoxygenated blood pressure

systemic gas exchange

the exchange of O2 and CO2 between systemic capillaries and tissues throughout the body

• O2 leaves bloodstream → converted to deoxygenated blood

• PO2 from 100 mmHg in capillaries into 40 mmHg tissue cells at rest, diffuses into tissue cells and PO2 drops to 40 mmHg exiting capillaries

• PCO2 from 45 mmHg tissue cells at rest to → interstital fluid → into 40 mmHg capillaries, until capillary pressure meets tissue cell pressure → return to heart and pumped to the lungs

gas exchange and exercise

more O2 diffuses from the blood into metabolically active cells and active cells use more O2 for ATP production

• PO2 in tissues drop (below 40 mmHg), increasing gradient for O2 diffusion

• deoxygenated blood would retain less than 75% of normal O2 content = enhances O2 unloading

• CO2 production increases (above 45 mmHg), and greater CO2 diffusion from tissues to blood, then alveolar air

gas exchange efficiency

1) substantial differences in partial pressures:

• bigger gradient encouragers faster diffusion, since differences between PO2 and CO2 are greater during exercise

• also depend on rate of airflow in and out the lungs

2) short distance for gas exchange: thin respiratory membrane and narrow capillaries

• buildup in interstitial fluid bt alveoli can slow down

3) total surface area is large: many capillaries participating in gas exchange

• pulmonary disorders decrease rate of exchange

4) coordinated blood flow and air flow: adjusting flow to match ventilation

• ex: one alveolus not receiving enough airflow, local O2 level drops, and redirect blood to better-ventilated alveoli where O2 levels rise in that area

5) molecular weight and solubility of gases: O2 lower molar mass than CO2, expected to diffuse faster, but CO2 solubility greater than O2

• CO2 out is 20 more rapid than O2 in

normal gas pressures

PO2: 40 mmHg venous blood, 100 mmHg arterial blood, 105 mmHg alveoli, 160 mmHg atmosphere

PCO2: 46 mmHg venous blood, 40 mmHg arterial blood, 40 mmHg alveoli, 0.3 mmHg atmosphere

O2 transport

with alveoli in lungs — does not dissolve easily in water — above 1.5% inhaled is dissolved in plasma and 98.5% bound to hemoglobin

1) dissolved O2: 1.5%

2) oxyhemoglobin: O2 + hemoglobin → ←binding of O2/dissociation→ ← HB-O2 (98.5%)

• most of it needs to bind to Hb (transport protein) thru blood (blood is watery, the gases are lipid soluble)

• hemoglobin: protein with four polypeptide chains and red pigment bounded to each

• high levels of O2 present, shifts towards formation of oxyhemoglobin

oxyhemoglobin dissociation curve (curve)

illustrates relationship between percent saturation of Hb by PO2 mmHg

• S shape: progressively easier for additional molecules to bind to hemoglobin

• pulmonary capillaries: PO2 high = Hb binds with large amounts of O2 and is almost 98% saturated

• tissue capillaries: PO2 low = Hb does not hold as much O2, and dissolved O2 unloaded via diffusion into cells

• basis: hemoglobin is 75% saturated with o2 at a PO2 of 40 mmHg, so PO2 between 60 and 100 mmHg indicates 90% saturation, why people perform well at high altitudes or with disease

• Hb is 90% saturated with O2 at a P O2 of 60-100 mmHg

  • large amts of O2 released from Hb in response to small decreases in PO2 (between 40 mmHg and 20 mmHg)

  • large percentage of O2 released from Hb in active tissues (< 40 mmHg) to provide more O2

  • High PO₂ (in lungs) = Hemoglobin binds more O₂ because there’s a large gradient.

  • Low PO₂ (in tissues) = Hemoglobin unloads more O₂ (but this is efficient around 40–20 mmHg).

• beneficial: pressure decreases the higher you go due to a smaller gradient, and gases don’t move as much, still able to load!

  • super high and u dead af: P O2 of 30 mmHg and Hb has 40% concentration of O2 – hard to unload O2

curve shifts

changing affinity of hemoglobin for O2 to maintain homeostasis to adjust to body activities and cellular needs

1) blood pH: as acidity increases (ph decreases), enhances unloading of oxygen from Hb

• pH decrease = curve shifts right; at any PO2, Hb is less saturated with O2

• bohr effect: increase in H+ (decreased pH) causes O2 to unload from Hb to tissues, also causes unloading of H+ from Hb

• Hb can act as a buffer to drive O2 off Hb and make more O2 for tissue cells

• pH increase = curve shifts left; increases affinity of Hb for O2 loading in lungs

2) temperature: metabolically active cells require more O2 amd liberate more acids and heat

• lowered body temp = need for O2 reduced = more remains bound to Hb and shifts to the left

• higher body temp = more need for O2 = less bound to Hb and shifts to the right

CO2 transport

CO2 transported in the blood (with tissue cells) in 3 forms:

1) dissolved CO2: 7% — into blood plasma, then upon reaching lungs, into alveolar air to exhale

2) carbamino compounds: 23% — with amino acids and proteins in blood

• Hb + CO2 → ← Hb-CO2

3) bicarbonate ions: 70% — CO2 diffusing in systemic capillaries reacts wth water to frm carbonic acid, dissociating into H+ and HCO3-

• HCO3- acts as a buffer to manage swings in pH

• more CO2 (metabolically active) produced, bicarbonate and H+ produced and helps unload O2 at the tissues

• also trade for Cl- into erythrocytes to maintain electrical balance (chloride shift)

haldane effect: removal of O2 from Hb increases affinity for CO2 to ride on

• lower Hb-O2, higher CO2 carrying capacity

ventilation control

action potentials from detecting size of thoracic cavity are sent from neuron clusters in medulla and pons of brain stem (respiratory center)

1) medullary respiratory center

2) pontine respiratory center

medullary respiratory center (medulla)

1) dorsal respiratory group (DRG): inspiratory neurons generate AP to diaphragm and external intercostal to contract for inspiration (quiet breathing)

2) ventral respiratory group (VRG): pre-botzinger complex with pacemaker cells to generate rhythm of respiration, containing both inspiratory and expiratory primarily invlved in forced breathing

• involved in forceful inhalation by sending APs to accessory muscles, DRG also active

• DRG inactive, VRG for forced exhale

pontine respiratory group

role in transition between inspiration/expiration, signaling medulla

• pneumotaxic area: upper pons to signal DRG to turn off before lungs have too much air

  • shorten duration of inspiration

  • more active area = breathing rate more rapid = overides apneustic area

• apneustic area: send excitatory signals to DRG to activate and prolong inspiration

  • long, deep inspiration

respiratory center regulation (RC regulation)

1) cortical influences

2) chemoreceptor regulation

3) along with limbic system, high temperature, and pain

cortical influence

• cerebral cortex connection allows voluntarily alteration of pattern breathing

• voluntary to orevent water or irritating gases in the lungs

• CO2 and H+ buildup prevents breathing ability, DRG strongly stimulated to send AP to inspiration muscles to continue breathing

• AP from hypothalamus and limbic allow emotions to alter respiration

chemoreceptor regulation

modulate how quickly and deep we breathe, maintain proper levels of CO2, O2, and H+ via negative feedback systems

• central: located in medulla in the CNS (cerebrospinal fluid), respond to H+ and CO2 when —

  • increase in P CO2 (via decrease pH)

  • ex exercise: breath more quickly and forcefully due to rising CO2

• peripheral: located in aortic arch and carotid bodies (arterial blood PNS), respond to PO2, H+, and PCO2 when —

  • increase in PCO2 (via decrease pH)

  • decrease PO2

  • decrease pH