23. Respiratory System Flashcards
Major Function of Respiratory System
supply the body with O2 and dispose of CO2
divide the respiratory system into: 2
Conducting Portion = from nostrils to bronchioles
- warm, moisten, cleanse (filter) incoming air
Respiratory Zone = respiratory bronchiole + alveolar duct + alveolar sac + alveolus
How many lobes in each lung
R lung has 3 lobes
L lung 2 lobes
Alveolii
- simple squamous epithelial cells
- Respiratory Membrane = Type I alveolar cell + Fused basement membrane + Endothelial cell of pulmonary capillary
- Gas exchange occurs across the respiratory membrane:
- alveolar cells secrete alveolar fluid (keeps surfaces moist + contains surfactant )
- Phagocytic alveolar macrophages wander the inner alveolar surfaces to remove dust and other foreign particles
Surfactant
- acts to decrease surface tension and prevents collapse of alveolus when exhale
- surface tension opposes expansion of water surface
- need to overcome surface tension to expand lungs
- surfactant decreases surface tension by disrupting hydrogen bonds among water molecules making it is easier to expand the lungs
Atmospheric Pressure
Intrapleural Pressure
Alveolar (Intrapulmonic) Pressure
Atmospheric Pressure
• Pressure exerted by air (gases) on the surface of the body (at sea level = 760 mmHg)
Intrapleural Pressure
• Pressure within the pleural cavity (between the pleurae) and is normally about 4 mmHg less than atmospheric pressure (approx. 756 mmHg)
Alveolar (Intrapulmonic) Pressure
• Air pressure within the alveoli (changes with the phases of breathing)
Boyle’s Gas Law
- that under constant temperature, the pressure exerted by a gas varies inversely with volume
- if ↑ volume, then ↓ pressure
- if ↓ volume, then ↑ pressure
- If compress a gas to ½ its original volume the pressure is increased 2x
Air is composed of a mixture of gases:
• Each individual gas in this mixture exerts its own pressure (partial pressure)
- 6% nitrogen (N2)
- 9% oxygen (O2)
- 04% carbon dioxide (CO2) 0.06% other gases
- 40% water vapor = 100% Total
Dalton’s Law
• that atmospheric pressure is equal to the sum of the pressure exerted by each individual gas
pN2 + pO2 + pCO2 + pH2O + p(other gases) = atmospheric pressure
Respiratory Physiology involves 4 events:
- Pulmonary Ventilation
- External (Pulmonary) Respiration
- Internal (Tissue) Respiration
- Transport of Respiratory Gases: Oxygen
- Pulmonary Ventilation
• gas exchange between atmospheric air and the alveoli of the lungs
At Rest:
- before inspiration, alveolar p = atmospheric p (760 mmHg)
- diaphragm is relaxed (dome-shaped)
Inspiration –
- diaphragm and external intercostals contract
thoracic cavity increases in size
- lungs expand
- pressure in lungs decreases from 760 to 758 mmHg
Expiration –
- diaphragm and external intercostals relax
- thoracic cavity decreases in size
- lungs recoil
- pressure in lungs increases from 760 to 762 mmHg
- External (Pulmonary) Respiration
• gas exchange between the alveoli and blood in the pulmonary capillaries
• O2 and CO2 diffuse down their pressure gradients
> Oxygen: alveolar (105 mmHg) → to the blood (40 mmHg)
> Carbon Dioxide: blood (45 mmHg) → to alveolar (40 mmHg)
• pO2 measurement – indicated amount of O2 dissolved in plasma NOT bound to Hb
• since O2 solubility is so low, we need an “extra” mechanism to transport O2 – role of hemoglobin
gas exchange is aided by: 3
- thinness of respiratory membrane
- extensive surface area of the alveoli
- numerous small pulmonary capillaries
how much gas dissolves in plasma depends on:
- partial pressure of the gas in air
2. solubility of the gas in water (Henry’s law)
- Internal (Tissue) Respiration
• gas exchange between the blood in the systemic capillaries and tissue cells
• O2 and CO2 diffuse down their pressure gradients
> Oxygen: blood (100 mmHg) → to tissue (40 mmHg)
> Carbon Dioxide: tissue (45 mmHg) → to blood (40 mmHg)
- Transport of Respiratory Gases: Oxygen
- 98% of O2 is transported bound to the iron in the heme group of hemoglobin
- 2% transported dissolved in plasma
- O2/heme binding reversible
- if pO2 increase, more O2 binds to Hb
- can reduce affinity of Hb for O2 to enhance offloading at the tissues, as the body O2 needs change
3 products of metabolism: ↑ p CO2 ↑ [H+] which will ↓ pH ↑ Heat All reduce affinity of Hb for O2
What is the Bohr effect?
Why Bohr effect?
at any given pO2 value, Hb releases more O2 when pH decreases
Why Bohr effect?
• a decrease in pH means there is more H+
• H+ binds to amino acid in Hb that alters Hb structure and decreases its O2 carrying capacity
• drives O2 off Hb so more O2 available to tissues
- Transport of Respiratory Gases: Carbon Dioxide
- 70% of CO2 is transported as bicarbonate ions (HCO3-) in the blood plasma
- 23% is transported by Hb (globin portion) in RBCs as carbaminohemoglobin
- 7% is dissolved in the blood plasma
The Respiratory Center can be divided into two principal areas:
1) the medullary respiratory center in the medulla oblongata
> dorsal respiratory group (DRG)
> ventral respiratory group (VRG)
2) the pontine respiratory group in the pons
1) Medullary Respiratory Center
• Controls basic rhythm of breathing. nerve impulses generated in DRG
• DRG inactive = passive expiration
• VRG inactive = quiet breathing
• VRG activated = forceful breathing
• Pre-Bötzinger complex: in VRG, generation of rhythm of breathing
composed of pacemaker cells that provide input to the DRG, driving the rate at which the DRG
neurons fire action potentials
2) Pontine Respiratory Group
- neurons are active during both inhalation and exhalation
- transmits nerve impulses to the DRG in the medulla
- MODIFIES the basic rhythm of breathing
Pre-Bötzinger complex
- in VRG
- generation of rhythm of breathing
- composed of pacemaker cells that provide input to the DRG, driving the rate at which the DRG
- neurons fire action potentials
Factors that Influence Breathing Rate/Depth
1) Higher brain inputs (cerebral cortex – voluntary control holding your breath)
2) Pulmonary irritants (presence of dust, smoke)
3) Inflation (Hering-Breuer) reflex (keep lungs from over-inflating)
4) Proprioceptor stimulation (monitor movement of joints and muscles)
5) Chemical factors (chemoreceptors monitor levels of CO2, O2 and H+ and provide input to respiratory center)
Homeostasis is Disrupted:
Homeostasis is Disrupted
Increased arterial pCO2 = Decreased pH in blood and CSF
Chemoreceptors Stimulated
stimulates
Medullary Respiratory center
Dorsal Respiratory Group
Inspiratory muscles
Increased respiratory rate (more CO2 expired)
Decreased arterial pCO2 = Increased pH of blood and CSF
Homeostasis is Restored
