13 Respiratory System

13.3

functions

__ of respiratory system

• provides oxygen

• eliminates CO2

• regulates H+ conc. (pH) with kidneys

• speech

• defends against inhaled microbes

• influences arterial concentrations of chemical messengers

• traps/dissolves blood clots from systemic veins

alveoli

site of gas exchange with blood

Airways

Tubes where air flows from external environment to the alveoli and back

Structures that make up the __ are:

• nose

• nasal cavity

• pharynx →common to both air + food

  • branches into the esophagus (digestive system) and the larynx

• larynx →houses the vocal cords

• trachea →branches into two bronchi

• bronchi (singular: bronchus)

• bronchioles →first airway branches that no longer contain cartilage

  • branches into terminal bronchioles → respiratory bronchioles

• alveoli →first appears in respiratory bronchioles

Conducting zone

Airways beyond the larynx can be subdivided into (1/2) zones

__ extends from top of trachea to end of terminal bronchioles. Contains no alveoli.

The __ provides low-resistance pathway for airflow

resistance regulated by:

• bronchiolar smooth muscle. constricts to prevent further particulate matters/irritants from entering site of gas exchange

• physical forces acting upon airways

Defends against microbes, toxic chemicals, and other foreign matter

• cilia, mucus, macrophages

Warms and moistens air

& Participates in sound production

Respiratory zone

Airways beyond the larynx can be subdivided into (1/2) zones

__ extends from respiratory bronchioles and down.

Where alveoli exchange gases with the blood.

Ciliary Mucuous escalator

Refers to the cilia (present from the airways to the end of the respiratory bronchioles) that constantly beat upward towards the pharynx

• mucous secreting glands + epithelial cells are present in oral and nasal cavities

  • particulate matter gets stuck in mucus; gets moved towards the pharynx by a “__” = Keeps lungs clear of matter and bacteria

• macrophages → phagocytize inhaled pathogens

A/N: Cilia is killed by noxious agents like tobacco smoke → smokers often cough up mucus

Alveoli

Tiny, hollow sacs whose open ends are continuous with the airways

• Type 1 alveolar cells: thick, flat epithelium. Lines the air-facing surface of alveolar wall

• Type 2 alveolar cells: specialized cells (produces a detergent-like surfactant: important for preventing collapse of alveoli) interspersed between the epithelial cells.

The following leads to a rapid oxygen-CO2 exchange by diffusion in the __:

Large SA of __ and capillary contact

as large as a tennis court

Thin interstitial space

sometimes absent altogether between capillary and __

Additionally, pores permit flow between adjacent __

pleura

Each individual lung is surrounded by a completely closed sac known as the pleural sac; it is made up of sheet cells known as __

• Visceral [__]: portion coating the surface of lung

• Parietal [__]: portion enclosing the (thoracic) cavity around lung

• has thin layer of intrapleural fluid in between → surrounds lungs and lubricates pleural surfaces to slide over each other during breathing

Respiratory cycle

constituted by a single

• inspiration: inhalation, movement of air from external environment to alveoli during breathing

• expiration: exhalation, movement of air from alveoli towards external environment

During the entirety of a __:

• 4L of air enters and leaves alveoli per minute

  • inc. 20 fold during heavy exercise

• 5L of blood (cardiac output) flows through pulmonary capillaries

  • inc. 5-6 fold

Respiration

__ has 4 steps:

1⃣ Pulmonary ventilation: exchange of air between atmosphere and alveoli by bulk flow

2⃣ Exchange of O2 and CO2 between alveoli and capillaries by diffusion → packaging of oxygen in pulmonary circulation

3⃣ Transport of O2 and CO2 thru pulmonary & systemic circulation by bulk flow

4⃣ Exchange of O2 and CO2 between capillaries and tissue cells by diffusion → drop off of oxygen in systemic circulation

760

All pressures in respiratory system are given relative to atmospheric pressure, which is __ mmHg at sea level

eg. when P_alv= 0 mmHg, P_alv = P_atm

P_atm = atmospheric pressure

• pressure surrounding body.

• decreases as altitude increases

P_ip= intrapleural pressure

• pressure outside lungs / intrapleural fluid surrounding lungs

P_alv= alveolar pressure

• pressure inside lungs / alveoli

flow

__ is directly proportional to pressure difference and inversely proportional to airway resistance

F = ( P_alv - P _atm) / R

A/N: equations comparing pressures follow pattern of P_inner- P_outer

• negative value (P_alv< P_atm) → inward flow (into) → inspiration

for transmural: inward pressure direction across lung/thorax (not into) = depression

• positive value (P_alv > P_atm) → outward flow (out of) → expiration

for transmural: outward pressure direction across lung/thorax = expansion

Transmural

Differences in pressures “across a wall” refer to “__” pressures.

P_tp: transpulmonary pressure = P_alv - P_ip

• __ pressure acting upon lung, opposing intrinsic collapsing of lung

• positive at rest → expansion of lungs. Normal (P_tp= -4 mmHg)

• negative → depression of lungs

P_cw: chest wall pressure = P_ip - P_atm

• __ pressure acting upon chest wall. opposing intrinsic expansion of thorax

• positive → expansion of thorax.

• negative at rest → depression of thorax. Normal (P_cw = 4 mmHg)

Intrapleural Pressure

__ (P_ip), or hydrostatic pressure of the intrapleural fluid causes lungs and thorax to move in and out together during normal breathing

Pneumotharx

Collapsing of lungs that occurs during surgery or trauma when chest wall is pierced without damaging lung and atmospheric air enters intrapleural space (P_ip= -4 mmHg → 0 mmHg)

i.e. P_ip = P_atm or P_ip becomes positive/higher pressure than P_alv

→ P_tp = P_alv - P_ip = + -(+) = 0 (eliminated)

→ moves across wall towards lower pressure (P_alv) → collapsing of lungs

elastic recoil

Defined as the tendency of an elastic structure to oppose stretching or distortion.

Why:

• lungs at rest/stretch tend to collapse.

• chest wall at rest/compression tends to expand

Tendencies of collapsing/expanding causes enlargement of intrapleural space between lung & chest wall

Maintained P_ip= -4 mmHg counteracts their tendency to collapse/expand

Inspiration

__ is initiated by contraction of diaphragm (phrenic nerve) and external intercostal muscles (motor neurons)

1. Enlargement of thorax

2. P_ip decreases due to Boyle’s law

3. P_tp = P_alv -( -P_ip) = more positive/inc.

4. Lungs expand

5. P_alv decreases

6. Air flows into lungs (as P_alv < P_atm )

Ceases __ when:

• P_alv = P _atm (equilibrium; no more pressure change needed for flow)

• P_tp= elastic recoil opposing it (can no longer expand lungs)

Expiration

__ is initiated by relaxation of diaphragm and external intercostal muscles (decreased firing of motor neurons)

1. Shrinking of thorax and diaphragm

2. P_ip increases

3. P_tp = P_alv -( + P_ip) = more negative/dec.

4. Lungs shrink as P_tp < elastic recoil of lungs

5. P_alv increases

6. Air moves out (as P_alv > P_atm)

Abdominal

During inspiration:

• diaphragm contracts down

• external intercostals (+pectoralis minor) pull ribs upwards and out

• Sternum is elevated by sternocleidomastoid and scalenes

During exhalation:

• diaphragm is relaxed and __ organs/wall/muscles press against diaphragm

• internal intercostals pull ribs downwards and inwards

• elasticity of lungs causes inward recoil

passive

Lungs are __ elastic structures and their volume depends on:

1. transpulmonary pressure P_tp: difference in pressure inside and outside lung

2. Lung compliance: how stretchable lungs are, determining how much they expand for given change in P_tp. proportional to P_tp

Lung Compliance

C_L and or __: magnitude of change in lung volume produced by given change in transpulmonary pressure.

Impacted by:

(1) stretchability of lung tissue

(2) surface tension of air-water interfaces in alveoli

• the greater the __, the easier it is to expand the lungs

→ more change in vol. with lesser pressure change (lungs not fully expanded)

• the lower the __, the harder (stiffer) it is for lung expansion

→ less change in vol. with greater P_tp (lungs already expanded from high P_tp)

• need more subatmospheric/smaller P_ip to make lung move overall

→ i.e,, it needs a smaller intrapleural pressure to cause the movement needed for further expansion (greater P_tp = P_alv -(-P_ip) = more expansion)

→ does NOT mean that it will make compliance higher (again, increased denominator makes lung less compliant because it is fully expanded!)

surface tension

inner alveolar cells’ moist water molecules attraction to each other.

• adds on additional force lungs have to overcome in order to stretch.

Surfactant (produced by Alveolar Type 2 Cells): detergent-like substance that lowers the __ → increases lung compliance

• mixture of lipids and proteins

• deep breaths stretch type II cells → increased surfactant secretion

• production occurs in late gestation in the fetal lung. stim. by increase of cortisol (glucocorticoid)

Law of Laplace

This law describes the relationship between:

r = alveolus radius

• decreased r → increased pressure

P = pressure

T= surface tension

• affected by presence of surfactant or not. more effective in small alveoli

  • with surfactant: no air flow. surfactant reduced T in smaller alveoli (b) such that T_b < T_a & small alveoli matches larger radius alveoli pressures (a)

  • without surfactant: air flow goes from high pressure (b) to low (a); small alveoli would be unstable and collapse

Respiratory distress syndrome of the newborn

Surfactant deficient disease when newborn is premature

• lacks developed Type 2 alveolar cells → can’t breath without strenous efforts

• Leading cause of death in premature infants

Asthma

Disease characterized by intermittent episodes of contracted smooth airway muscles from inflammation causing hyperresponsiveness → inc. airway resistance

Therapy for __ aims to:

• reduce inflammation with anti-inflammatory drugs (leukotriene inhibitors + glucocorticoids)

• reduce excessive muscle contraction with bronchodilator drugs

  • one class mimics epinephrine action on B-2 adrenergic receptor

  • another class blocks muscarinic cholinergic receptors → bronchoconstriction

chronic obstructive pulmonary disease

COPD. refers to either the following, or a combination of the two:

• emphysema: destruction and collapse of smaller airways

  • when there’s too much compliance, a decrease in P_tp can lead to lungs to collapse

• chronic bronchitis: excessive mucus production in bronchi; inflammation in airways → blockage by accumulation of mucus in airways; thickening of airways

last left off of 13.3 / L29