CH 18 - Respiratory System

respiratory organs

nose, pharynx, larync, trachea, primary bronchi, lungs

mucosa

Ciliated epithelial cells and goblet cells that secrete mucus. Same layers as GI tract.

mucociliary escalator

Mucus and particles trapped by cilia move up toward pharynx (throat)

air movement into lungs

Enters nose, pharynx, larynx, trachea, primary bronchi.

branching of respiratory tract

R/L primary bronchi → 2ndary bronchi (3R, 2L) → tertiary bronchi → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveoli

conducting zone

Everything up to terminal bronchioles. Warms, moistens, filters, and transports air to lungs. Mucus traps small particles; vocalization.

respiratory zone

Respiratory bronchioles, alveolar ducts, alveolar sacs. Area of gas exchange.

Lungs

Paired, cone-shaped organs in thoracic cavity covered by double-membrane (pleura). Contain most components of the respiratory tract; terminate at alveoli

alveoli

Single layer of epithelium; each one has a capillary bed for. Made of Type 1 and 2 cells.

Type 1 alveolar cells

Simple squamos hollow “tennis bal"l” shaped. Main site of gas exchange.

Type 2 alveolar cells

Septal cells that secrete surfactant - alveolar fluid that coats the hollow insides of alveoli.

Ventilation

Depends on difference between Patm, Palv, and P

Intrapleural pressure

P in the space between visceral and parietal pleura. Contains thin fluid lubricant layer. ALWAYS lower than P-atm and P-alv to keep lungs pushed up against thoracic wall—SUCTION CUP.

Boyle’s Law

P1V1 = P2V2. As volume increases pressure decreases.

Breathing cycle

Rest, Inspiration, Expiration

Inspiration (inhalation)

Air flows in when P-alv < P-atm by -3 mmHg.

Expiration (Exhalation)

Air flows out when P-alv > P-atm by +3 mmHg.

Diaphragm - normal/quiet inspiration

65-75% of incoming air (most important). Contracts to flatten and increase volume which decreases pressure to 758 mmHg. Lungs and thoracic cavity increase vertically.

External intercostals - normal/quiet

Raise rib cage. Increases diameter of lungs and thoracic cavity which increases volume and decreases pressure.

Forced inhalation

Scalenes raise ribs 1-2

Pectoralis minor raises ribs 3-5

Sternocleidomastoid raises sternum

Diaphragm - normal/quiet expiration

Relaxation raises; decreasing volume and increasing pressure to 762 mmHg. This lets air out. Thoracic cavity and lungs decrease vertically.

Internal intercostals - forced exhalation

Lower rib cage → decreases diameter and volume thus increasing pressure to push air out.

abdominal muscles - forced expiration

Rectus abdominus, external & internal oblique, transversus abdominus contract to push diaphragm up, compressing the thoracic cavity to expel air.

Factors affecting ventilation

Surface tension of alveolar fluid, lung compliance, airway resistance

Surface tension of alveolar fluid

Created by fluid film lining alveolar sacs. Surfactant reduces it, preventing lung collapse. Can be deficient in babies, causing respiratory distress syndrome.

Law of LaPlace

Pressure inside alveolus is directly proportional to surface tension within and inversely proportional to its radius. P = 2T/R

With surfactant

Air does not flow from smaller alveolus into larger one because pressure is the same in both alveoli. Due to surfactant reducing the surface tension.

Compliance

How much effort req’d to stretch the lungs and chest wall. High = easy, Low = difficult. Smoking decreases.

Airway resistance

Mostly encountered as air moves through bronchioles. Dilation decreases, Constriction increases. F = dP/R.

ventilation-perfusion ratio

High PO2 = pulmonary arterioles dilate.

Low PO2 = pulmonary arterioles constrict.

High PCO2 = bronchioles dilate.

Low PCO2 = bronchioles constrict.

Air flow at alveoli must be matched to perfusion (blood flow) for optimal gas exchange. Mismatch leads to inefficiency.

Tidal volume

Amt of air brought in/out with quiet breathing

Expiratory reserve volume

Amt. of air that can be forced out after tidal volume expiration

Inspiratory reserve volume

Amt. of air that can be forced in after tidal volume inspiration

Residual volume

Amt of air left in lungs after max expiration. This cannot leave the lungs.

Vital capacity - VC = IRV + ERV + TV

Max amt of air that can be forcefully exhaled after maximum inhalation

Total lung capacity - TLC = VC + RV

Amt of gas in lungs after maximum inspiration

Inspiratory capacity - IC = IRV + TV

Amt of gas that can be inspired after a normal expiration

Functional residual capacity - FRC = RV + ERV

Amt. of gas left in lungs after normal expiration

Gas exchange of O2 and CO2

Occurs via simple/passive diffusion, governed by two laws: Dalton’s law and Henry’s law. Depends on partial pressure difference (pressure gradient) of gases, surface area, diffusion distance, and molecular weight & solubility of gases.

Dalton’s Law

Each gas in a mixture exerts its own pressure as if there were no other gases present = Partial Pressure - Px

Henry’s Law

Quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility. O2 < CO2

O2 solubility

Has lower molecular weight, poor solubility. Only 1.5% of inhaled actually enters plasma.

O2 transport

PO2 determines how much binds to Hgb. Systemic arteries have PO2 = 100 mmHg. (97% oxy-Hgb)

Systemic veins have PO2 = 40 mmHg. (75% oxy-Hgb, 22% unloaded for tissues)

pH

Bohr effect = Hgb O2 affinity increases at high pH, decreases at low pH.

Exercise = increased CO2 = low pH = more O2 unloading, shifts curve right.

CO2

CO2 + H2O →← H2CO3 →← H+ + HCO3- . Exercise or DKA = increased CO2 = low pH = shifts curve right = more O2 unloading for tissues.

Severe vomiting/hyperventilation = decreased CO2 = high pH = less O2 unloaded to tissues

Temp

As temperature increases, O2-Hgb affinity DECREASES. This enhances O2 unloading to muscles during exercise, which increases temp via metabolism.

Low temp = more oxyHgb = less for tissues

Biphosphoglycerate (BPG)

Byproduct of ATP production via anaerobic glucose metabolism that INCREASES O2 UNLOADING FROM HGB to a lesser effect. Inhibited by oxyHgb.

CO2 transport

70% HCO3- ions, 23% carbamino compounds, 7% dissolved in plasma. Dissociates from bicarb in RBCs via carbonic anhydrase for exhalation.

Respiratory center

Cluster of neurons in medulla and pons - pneumotaxic area and apneustic area

Medullary respiratory center

Rhythmicity center. Contains dorsal and ventral respiratory groups.

Dorsal respiratory group of medulla

Controls resting inspiration. Sends APs to phrenic nerve → diaphragm and intercostal nerves → external intercostals.

Ventral respiratory group of medulla

Controls forceful breathing. Contains pacemaker cells that regulate DRG. Stimulate diaphragm, external intercostals AND ACCESSORY muscles for forceful inhalation.

Pneumotaxic area of pons

Sends inhibitory signals to DRG when lungs are super full — prevents overfilling by decreasing duration of inhalation, increasing RR.

Apneustic area of pons

Sends excitatory signals to DRG to prolong inspiration, resulting in long, deep inspiration.

Regulation of respiratory centers

Cortical (voluntary) influence, chemoreceptors, proprioceptors, limbic system, temp, pain, inflation reflex

Inflation reflex

Extra stretch in lungs lowers RR, stimulates exhalation

chemoreceptor breathing regulation

Central chemoreceptors in medulla oblongata, peripheral chemoreceptors in aortic bodies and carotid bodies. Detect CO2, H+, O2.

Inhibit DRG

Low CO2, High O2

Hypercapnia

Excess CO2 in the blood. Lowers pH = respiratory acidosis.