BIOL EXAM 3 Pt. 3: Respiratory Physiology

Pulmonary ventilation

Pulmonary ventilation

• Bulk flow of air (movement of fluid)
• Gases moved to exchange areas

External respiration

• Diffusion (random motion of molecules)
• From lungs → blood

Transport of gases

• Bulk flow of blood (movement of fluid)
• In blood → tissues

Internal respiration

• Diffusion (random motion of molecules)
• Tissue gas use and production

External nose (nasus)

• Nostrils (nares)
• Main entrance at rest

Conchae

Scroll-like projections into cavity
• Inferior, middle & superior concha
• Create air turbulence

Respiratory mucosa

• Pseudostratified ciliated columnar epithelium
• Scattered goblet cells

Mucous & serous glands

- In underlying connective tissue (lamina propria)
- Numerous presence
- Secrete ~ 1 quart/day
- Mucus traps small particles

Cilia

- Move mucus toward throat
- Mucus swallowed & digested
- Sluggish when cold (thus runny nose)

Hyaline cartilage

• Forms 20 C-shaped rings
• Give strength & flexibility

Mucosa

- Pseudostratified ciliated columnar epithelium
- Contain goblet cells

Submucosa

- Connective tissue layer
- Contains seromucous glands
- Produce mucus “sheets”

- Cilia move mucus up (1-2 cm/min)

Smoking effects

• Paralyzes (eventually destroys) cilia
• No mucus movement to throat
• Moved by coughing instead

Primary (main) bronchi

• Right & left
• Branch from trachea before reaching lung lobes

Secondary (lobar) bronchi

Branch inside lobes

Tertiary bronchi

Divide repeatedly
• Progressively dec. in size

Bronchioles

< 1 mm diameter

Bronchioles: Epithelium

Simple cuboidal epithelium

Bronchioles: Smooth muscle

Abundant (no cartilage)

Terminal bronchioles

Smallest conducting airways

Respiratory bronchioles

dec. in smooth muscle
• Some alveoli (gas exchange)

Alveolar ducts

Diffuse smooth muscle rings (cells)
• Connective tissue fibers
• Outpocketing alveoli

Alveolar sacs

Groups of alveoli

Alveoli

Gas exchange surface
Inc. surface area

Thin diffusion distance to blood

Interconnected by alveolar pores

Alveolar epithelium: Type I Cells

Simple squamous epithelial
• Form alveolar lining

Alveolar epithelium: Basal lamina

Thin connective tissue layer

Alveolar epithelium: Type II cells

Cuboidal
• Located among type I cells
• Secrete surfactant

Alveolar epithelium: Macrophages

• Move freely over alveolar surface
• Scavenge and phagocytose debris

Air-blood barrier

• Type I cell
• Basal lamina
• Capillary endothelial cell
• Total thickness ~ 2 m

Capillaries

Form “cobweb” around alveoli
Shared basal lamina w/ type I cells

Radius effects (Law of Laplace)

• dec. in radius → inc. surface tension forces
• Tends to collapse alveoli

Surfactant

• Lipoprotein secreted by lung
• Reduces surface tension
• Decreases work of inflation

Lung gross anatomy: shape

Paired, cone-shaped

Lung gross anatomy: Hilus

• Pulmonary blood vessel entry & exit
• One for pulmonary artery & vein

Lung gross anatomy: Symmetry

Lungs differ in shape & size

Thoracic cavity: Pleura sac

• Fluid filled sac
• Surrounds each lung

Thoracic cavity: Visceral pleura

Against lung

Thoracic cavity: Parietal pleura

Against chest wall

Thoracic cavity: Pleural space

Inside pleural sac

Intrapleural pressure

• Negative pressure
• Holds lung open

Intrapulmonary pressure

Pressure inside lungs

@ Rest

Pip < Palv = Patm

-4 < 0 = 0

Inhale

Pip < Palv < Patm

-6 < -3 < 0

• Active (muscles contract)
• Diaphragm, external intercostals

Exhale

Pip < Palv > Patm

-3 < 3 > 0

• Passive
• May use diaphragm, internal intercostals

What happens in Pneumothorax?

Pip = Palv = Patm

Compliance

• Stretchiness (V/P)
• inc. by surfactant

Elasticity

• Tendency to retain shape
• Opposite of compliance

What happens in Emphysema (obstructive)?

• Lung tissue degenerates
• inc. in compliance
• Flimsy airways
• Collapse while exhaling

What happens in Fibrotic lung (restrictive)?

• Fibrous tissue permeates lung
• inc. in elasticity
• Limited lung volume

Static: Tidal volume (TV)

amt. of air in an average breath (0.5 L)

Static: Total lung capacity (TLC)

max air held by lungs (~6 L)

Static: Inspiratory reserve volume (IRV)

max. insp. on top of tidal insp. (~ 3 L)

Static: Expiratory reserve volume (ERV)

exp. ability in addition to normal exp. (~1.2 L)

Static: Residual volume (RV)

air in lungs following max. exp. (~1 L)

Static: Forced vital capacity (FVC)

max exp. following max insp. (~ 4.8 L)

Static: Functional residual capacity (FRC)

pool of air in lungs during TV (~2.4 L)

Dynamic: Forced expiratory volume (FEV1.0)

max. amount of air that can be exp. in 1 sec. following max insp. (~85% of FVC)

Vital capacity

Difference: max. inhalation & max. exhalation

Residual volume

Air remaining in lungs following max. exhalation

Ventilation

VE (L/min) = TV (L/breath) * F (breaths/min)

Alveolar ventilation (VA)

VA = (TV – DS) x frequency

• Breath portion stops in conducting airways
• Dead space (DS)
• ~ 0.15L of 0.5L TV

Atmospheric pressure (Patm)

760 mmHg

Atmospheric gas fractions

• 21% is O2
• 79% is N2
• 0.03% is CO2

Gas pressure (Pgas)

Pgas = gas fraction x Patm

PO2

= 0.21 x 760 = 159 mmHg

PN2

= 0.79 x 760 = 601 mmHg

Solid Diffusion

Determined by concentration gradient

Gases

Determined by gas pressure gradient

Pressure in alveoli determines Pressure in blood

Henry’s Law

Pressure of gas in solution is proportional to
pressure of gas over the solution

Pressures

Alveolar Pgas determines blood Pgas

Gas solubility

• O2 not very soluble in plasma
• CO2 is 30x more soluble

Temperature

inc. temperature → dec. in solubility

Hemoglobin (Hb)

• inc. O2 content of blood
• Dissolved O2 determines PO2

What is Hb built of…?

4 protein subunits (globin)
• 4 heme groups (bind O2)
• Binds 4 O2

Hb binding of O2

• Hb affinity for O2 affected by number bound
• As PO2 inc., Hb releases O2
• First falls off, others fall off more easily

O2 dissociation curve

• % Hb-O2 saturation vs. PO2
• Sigmoid (S) shape
• Shifts with varying Hb affinity for O2
• Due to cooperative O2 binding to Hb

As pH lvl inc. …

O2 affinity (Bohr effect) also inc. and vice versa

2,3–BPG

• Stabilizes deoxyHb
• inc. O2 affinity

As Temperature inc. …

O2 affinity dec.

Myoglobin

• In striated muscle
• Only one heme
• High O2 affinity
• Enables intracellular O2 storage

Dissolved CO2 (~10%)

• CO2 exits tissues
• Dissolves in plasma

Carbaminohemoglobin (~20%)

• CO2 enters RBC from plasma
• Attaches to amino group on Hb

Plasma bicarbonate (HCO3-) ~ 70%

• CO2 enters RBC from plasma
• Reacts with H2O via carbonic anhydrase

• HCO3- exits RBC to plasma
• Cl- enters RBC (chloride shift)

At the lung: PCO2 in lung < PCO2 in blood

CO2 + H2O ←→ H2CO3 ←→ (H+) + (HCO3-)

1. CO2 comes out of solution in plasma
2. Carbaminohemoglobin  CO2 + Hb
3. HCO3- goes back through pathway

Respiratory acidosis

(inc. CO2) + H2O ←→ H2CO3 →→ (inc. H+) + HCO3-

Hypoventilation

Respiratory alkalosis

(dec. CO2) + H2O ←← H2CO3 ←→ (dec. H+) + HCO3-

Hyperventilation

Metabolic acidosis

(inc. CO2) + H2O ←← H2CO3 ←→ (inc. H+) + HCO3-

• Ingestion of acids (amino acids, ascorbic acid)
• Alcohol ingestion
• Intense exercise (lactic acid)

Resp. Compensation: Hyperventilation

Metabolic alkalosis

(dec. CO2) + H2O ←→ H2CO3 →→ (dec. H+) + HCO3-

• Vomiting from stomach
• Ingestion of alkaloids

Resp. Compensation: Hypoventilation

Medullary respiratory centers

Locus of signal

Dorsal respiratory group

• Inspiratory neurons (fire during inspiration)
• Expiratory neurons (fire during expiration)

Ventral respiratory group (VRG)

Also has insp. & exp. neurons

pre-Bötzinger complex

• In VRG
• Thought to be rhythm generation center

Pontine respiratory group

Influences medullary respiratory centers
• Exact role uncertain

Peripheral

• Carotid body & aortic arch
• Stimulated by dec. O2, dec. pH, inc. CO2

Central (medulla)

Sensitive to dec. pH (inc. CO2)

Sensitivity

• Blood PO2 must be ~ 60 mmHg before VE inc.
• Inc. PCO2 by 2 mmHg will dramatically Inc. VE

Lung stretch receptors

• Hering-Breuer reflex
• Lung inflation inhibits inspiration

Proprioceptors

Muscle & joint

Sensory receptors

Touch, temperature, pain

Higher centers

Voluntary control