Respitory System

alveolar structure

type I cells = simply squamous epithelium - gas exchange occurs here

type II cells = surfactant production

alveolar pores = equalize pressure; alternative route for air flow

alveolar macrophages = phagocytosis of cellular debris and pathogens

structures in respiratory zone

1. respiratory bronchioles

2. alveolar ducts

3. alveolar sacs

4. alveoli

function of respiratory zone

gas exchange

bronchial smooth muscle

controls airway diameter

elastic fibers

limits expansion of alveolus and helps w recoil

pulmonary capillaries

gas exchange

surfactant

• reduces surface tension to prevent lung collapse

• production begins at 24 wks and suffienct quantity at 34 wks gestation

• produced by type II cells

respriatory distress syndrome

premature babies who have difficulties breathing due to insufficient production of surfactant

alveolar-capillary (respiratory) membrane

• gas exchange occurs across membrane

• made of type I cells and pulmonary capillary

• plasma membranes are fused together

ventilation

movement of air in and out of the alveoli

respiration

gas exchange between

1. alveoli and pulmonary capillaries

2. systemic capillaries and systemic cells

gas exchange

• O2 and CO2 move in opposite directions across a membrane

• occurs in the lungs between the alveoli and the pulmonary capillaries – this is where the blood becomes oxygenated, and CO2 is removed from the blood and exhaled

• also occurs everywhere else in the body – this is where oxygenated blood gives up O2 to the cells of the brain, liver, etc. and transports the CO2 these cells produce to the lungs to get rid of it.

external respiration

gas exchange at lungs

internal respiration

gas exchange everywhere else

transport mechanism for gas exchange

simple diffusion. uses passive transport because the driving force behind gas exchange is a partial pressure gradient

daltons law of partial pressures

• The total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted by each gas in the mixture”

• air is a mixture of gases = ~21% O2 and ~79% N2

partial pressure of O2

in alveolus = 100 mmHg

venous blood = 40 mmHg

arterial blood = 100 mmHg

oxygen diffusion

O2 moves down partial pressure gradient from alveolus to pulmonary capillary (100-40 mmHg). continues to diffuse until partial pressures are equal

partial pressure of CO2

in alveolus = 40 mmHg

venous blood = 45 mmHg

arterial blood = 40 mmHg

CO2 diffusion

CO2 moves down partial pressure gradient from pulmonary capillary to the alveolus (45-40 mmHg). continues until pressures are equal

O2 transport in blood

1.5% dissolved in plasma

98.5% transported on the iron ions on the hemoglobin molecule

hypoxia

inadequate O2 delivery to tissues

4 types of hypoxia

1. hypoxemic hypoxia = caused by COPD, mountain climber will sometimes experience this

2. anemic hypoxia = too few normal RBC’s, sickle cell anemia

3. ischemic hypoxia = impaired circulation that causes heart failure

4. histotoxic hypoxia = cells cant use O2, created during release of cyanide gas in Hitlers gas chambers

CO poisoning

• odorless and colorless, leading cause of death during fires (early signs = nausea and headache)

• competes with O2 for Hb binding sites (affinity = 210X > O2)

• cyanosis is absent; fair skinned people = “cherry red”

• signs are dizziness, breathlessness, collapse, and loss of consciousness

cyanosis

bluish-gray coloring of mucosa and nail beds

CO2 transport in blood

10% dissolved in plasma

20% bound to hemoglobin

70% enters RBC where it reacts w H2O

• RBC produce carbonic anhydrase to rapidly convert CO₂ and H₂O into carbonic acid

• dissociates into H+ and bicarbonate ions where H+ is buffered by hemoglobin and bicarbonate enters the plasma to help neutralize metabolic acids

breathing mechanics

• pressure gradients cause air to flow in and out of lungs

• atmospheric pressure (barometric pressure)

• intrapulmonary pressure = pressure in alveoli

• inspiration = intrapulmonary P < atomospheric P (gradient exists and air flows into lungs)

• exhalation = intrapulmonary P > atomospheric P

boyles law

pressure and volume inversely related

muscles of inspiration

diaphragm = descends and flattens during contraction; pulls lungs down and increases lung volume

external intercostals = pull ribcage and lungs up and out, and increases lung volume

serous membrane called the pleura connects them

passive exhalation

• diaphragm and external intercostals relax - lung volume decreases, causes increase in intrapulmonary pressure

• Air will release once intrapulmonary pressure is larger than atmospheric pressure.

forced exhalation

requires contraction of abdominal muscles (pushes diaphragm up) and internal intercostal muscles (pulls ribcage down and inward). both decrease lung volume

carbon dioxide

• our primary stimulus to breathe

• only acid capable of crossing the blood-brain barrier and stimulating the central chemoreceptors

central chemoreceptors

• responds to hydrogen ions from only CO2

• located in the brainstem

hering-breuer reflex

• occurs during inhalation as the lungs expand when alveoli reach a critical level of stretch

• prevents over inflation of lungs

medulla oblongata

directly controls breathing and stimulates the contraction of the diaphragm and external intercostals

peripheral chemoreceptors

• found in aortic arch and carotid arteries

• stimulated by hydrogen ions from any acid

pons

modifies activity of medulla oblongata

stimulus to breathe

primary stimulus = increased CO2

other stimuli = decrease pH (acidosis) and decrease O2

Expiratory reserve volume (ERV)

amount of air that can be exhaled after a resting exhalation (1200 ml)

Inspiratory reserve volume (IVR)

amount of air that can be inhaled after a resting inhalation (3100 ml)

Residual volume (RV)

amount of air left in the lungs after a maximal exhalation (1200 ml), prevents lung collapse

Tidal volume (TV)

amount of air moving into and out of the lungs during resting breathing (500 ml)

Total lung capacity (TLC)

the maximum amount of air the lungs can hold (6000 ml)

Vital capacity (VC)

amount of air that can be exhaled after a maximal inhalation (4800 ml)

lobes of right lung

1. right upper (superior) lobe

2. right middle lobe

3. right lower (inferior) lobe

lobes of left lung

1. left upper (superior) lobe

2. left lower (inferior) lobe

which fissures separate what lobes

1. Horizontal fissure: RUL from RML

2. Right oblique fissure: RUL and RML from the RLL

3. Left oblique fissure: LUL from LLL

pleuras location and function

• parietal pleura lines the inside of the ribcage

• visceral pleura lines the surface of the lungs

• reduce friction as the lungs move

What is the function of the negative pressure between the two layers of the pleura (intrapleural pressure)

it helps prevent lung collapse

conducting zone function

provide passageways for air to reach the respiratory zone

structures of conducting zone

nose, pharynx, larynx, trachea, mainstem (primary) bronchi, lobar bronchi, 23 more generations of airway branching

last structure of conducting zone

terminal bronchioles

tracheobronchial tree

25 generations of airway breathing

• Trachea = generation 0

• mainstem (primary) bronchi = generation 1

• terminal bronchioles = generation 25

bronchiole

airway that has diameter <1mm

effect of sympathetic nervous system on bronchiole smooth muscle

contracts bronchiole smooth muscles thereby causing airways to constrict

are alveoli surrounded by smooth muscle

no, they are surrounded by pulmonary capillaries and elastic fibers

carina

ridge of cartilage at the bifurcation of the trachea