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

surfactant

reduces surface tension; prevents lung collapse. production begins at 24 wks and suffienct quantity at 34 wks gestation

alveolar-capillary (respiratory) membrane

gas exchange occurs across membrane

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 at lungs and cell of body

• occurs by simply diffusion

• driving force behind gas exchange = partial pressure gradient

daltons law of partial pressures

each gas in a mixture of gases exerts part of total pressure. 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 (100-40 mmHg) from alveolus to pulmonary capillary. 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

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

O2 transport in blood

1.5% dissolved in plasma

98.5% bound to hemoglobin

hypoxia

inadequate O2 delivery to tissues

4 types of hypoxia

1. hypoxemic hypoxia = impaired ventilation or CO poisoning

2. anemic hypoxia = too few normal RBC’s

3. ischemic hypoxia = impaired circulation

4. histotoxic hypoxia = cells cant use O2

CO poisoning

• odorless and colorless which is leading cause of death during fires

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

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

CO2 transport in blood

10% dissolved in plasma

20% bound to hemoglobin

70% as bicarbonate

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

• exhalation = intrapulmonary P > atomospheric P

boyles law

pressure and volume inversely related

muscles of inspiration

diaphragm = descends and flattens during contraction; pulls lungs down

external intercostals = pull ribcage and lungs up and out

contraction of muscles increases volume in lungs

passive exhalation

diaphragm and external intercostals relax - lung volume decreases, causes increase in intrapulmonary pressure. air will release once intrapulmonary pressure is larger than atomospheric

forced exhalation

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

control of breathing

medulla oblongata = stimulates contraction of diaphragm and external intercostals

pons = modifies medulla’s activity

hering-breuer reflex = stimulation of stretch receptors in lungs that prevents over-inflation

stimulus to breathe

primary stimulus = increased CO2

other stimuli = decrease pH (acidosis) and decrease O2

central chemoreceptors

located in medulla oblongata; respond only to H+ from CO2 - CO2 only acid that can cross blood-brain barrier

increase H+ → increase RR and depth breathing

peripheral chemoreceptors

located in aortic arch and carotid arteries; respond to increase in H (from any acid) to decrease in O2 - result = increase RR and depth breathing