Respiration

Ventilation (breathing)

o How to get air in and out of lungs and capillaries
§ Air moves from higher to lower pressure.
§ Pressure differences between the two ends of the conducting zone occur due to changing lung volumes.
§ Compliance, elasticity, and surface tension are important physical properties of the lungs.

external respiration

o Gas exchange between blood and lungs and between blood and tissues
o Oxygen utilization by tissues to make ATP
o Ventilation and gas exchange in lungs = external respiration

internal respiration

o Oxygen utilization and gas exchange in tissues = internal respiration

respiratory zone

site of gas exchange, respiratory bronchioles, alveolar ducts, alveoli,
conduction air comes down to this

conduction zone

gets air to the respiratory zone

air travel pathway

§ down the nasal cavity Pharynx Larynx Trachea Right and left primary bronchi Secondary bronchi Tertiary bronchi (more branching) Terminal bronchioles Respiratory zone (respiratory bronchioles Terminal alveolar sacs

function of conduction zone

· Transports air to the lungs
· Warms, humidifies, filters, and cleans the air
o Mucus traps small particles, and cilia move it away from the lungs.
· Voice production in the larynx as air passes over the vocal folds
· Smoking stunts respiratory cilia. The large vocal folds in men allow for a lower pitch. Raising tension on the vocal folds raises pitch and lowerying tension on the vocal folds lowers pitch.

alveoli

o Simple squamous epithelial
o Air sacs in the lungs where gas exchange occurs
o 300 million of them
§ Provide large surface area (760 square feet) to increase diffusion rate

Thoracic cavity

§ Contains the heart, trachea, esophagus, and thymus within the central mediastinum
§ The lungs fill the rest of the cavity.

parietal pleura lines

thoracic wall

visceral pleura covers

lungs

intrapleural space.

The parietal and visceral pleura are normally pushed together, with a potential space between called

what separates the pleurae

layer of fluid

Atmospheric pressure

o pressure of air outside the body

Intrapulmonary pressure

o pressure in the lungs

Intrapleural pressure

pressure within the intrapleural space (between parietal and visceral pleura)
§ Lower than intrapulmonary and atmospheric pressure in both inhalation and exhalation always

Inhalation

§ Intrapulmonary pressure is lower than atmospheric pressure.

subatmospheric or negative pressure

pressure below that of the atmosphere

Exhalation

Intrapulmonary pressure is greater than atmospheric pressure.

transpulmonary pressure

difference between intrapulmonary and intrapleural pressure
· Keeps the lungs against the thoracic wall

collapsed lung caused by

Intrapleural pressure can rise because of a wound allowing atmospheric air into the intrapleural space

why is our breathing called negative pressure ventilation

o we create a negative (lower than atmospheric) pressure to inhale.

Lung Compliance

§ Lungs can expand when stretched.
§ Defined as the change in lung volume per change in transpulmonary pressure:
§ ΔV/ΔP
§ Reduced by infiltration of connective tissue proteins in pulmonary fibrosis

Elasticity

§ Lungs return to initial size after being stretched.
· Lungs have lots of elastin fibers.
Because the lungs are stuck to the thoracic wall, they are always under elastic tension

o Surface Tension

§ Resists distension
§ Exerted by fluid secreted in the alveoli
§ Raises the pressure of the alveolar air as it acts to collapse the alveolus
§ The fluid is mostly water, and water has surface tension.

Boyle's Law

o States that the pressure of a gas is inversely proportional to its volume
§ An increase in lung volume during inspiration decreases intrapulmonary pressure to subatmospheric levels.
· Air goes in.
§ A decrease in lung volume during exhalation increases intrapulmonary pressure above atmospheric levels.
· Air goes out.
o Increase lung volume, decrease pressure in lungs. Decrease lung volume, increase pressure in lungs.

- Law of Laplace

o Pressure is directly proportional to surface tension and inversely proportional to radius of alveolus.
§ Small alveoli would be at greater risk of collapse without surfactant.

- Lipoprotein surfactant secreted by

type II alveolar cells

lipoprotein surfactant

o Consists of hydrophobic protein and phospholipids
o Reduces surface tension between water molecules
o More concentrated in smaller alveoli
o Prevents collapse
o Production begins late in fetal life, so premature babies may be born with a high risk for alveolar collapse called respiratory distress syndrome (RDS)

- Pulmonary ventilation

o Breathing
o Also called pulmonary ventilation
§ Inspiration: breathe in
§ Expiration: breathe out
o Accomplished by changing thoracic cavity/ lung volume

Inspiration

§ Volume of thoracic cavity (and lungs) increases vertically when diaphragm contracts (flattens) and horizontally when parasternal and external intercostals raise the ribs.

Expiration

§ Volume of thoracic cavity (and lungs) decreases vertically when diaphragm relaxes (dome) and horizontally when internal intercostals lower the ribs in forced expiration

Spirometry:

o Subject breathes into and out of a device that records volume and frequency of air movement on a spirogram.
o Measures lung volumes and capacities
o Can diagnose restrictive and disruptive lung disorders

Vital capacity

o : maximum amount of air that can be forcefully exhaled after a maximum inhalation

Total lung capacity

o amount of gas in the lungs after a maximum inspiration

Inspiratory capacity

o amount of gas that can be inspired after a normal expiration

Functional residual capacity

o amount of gas left in lungs after a normal expiration

Tidal volume

o amount of air expired or inspired in quiet breathing

Expiratory reserve volume

o amount of air that can be forced out after tidal volume

Inspiratory reserve volume

o amount of air that can be forced in after tidal volume

Residual volume

o amount of air left in lungs after maximum expiration

restrictive disorders

o Lung tissue is damaged. Vital capacity is reduced, but forced expiration is normal.
§ Examples: pulmonary fibrosis and emphysema

obstructive disorders

o Lung tissue is normal. Vital capacity is normal, but forced expiration is reduced.
§ Example: asthma

Forced expiratory volume (FEV) Test

· Obstructive lung disorders are usually diagnosed by doing forced expiratory volume tests.

Asthma

· Symptoms: dyspnea (shortness of breath) and wheezing
· Caused by inflammation, mucus secretion, and constriction of bronchioles
· Often called airway hyperresponsiveness

allergic asthma

· triggered by allergens stimulating T lymphocytes to secrete cytokines and recruit eosinophils and mast cells, which contribute to inflammation
· Can also be triggered by cold or dry air
· Reversible with bronchodilator
o Albuterol

Partial pressure of gasses

pressure exerted by a particular gas in a mixture of gases.
Air= 79% N2, 20.93% O2, .03% CO2
changes with altitude

Dalton's Law

§ The total pressure of a gas mixture is equal to the sum of the pressures of each gas in it.

Partial pressure

§ the pressure of an individual gas; can be measured by multiplying the % of that gas by the total pressure
· O2 makes up 21% of the atmosphere, so partial pressure of O2 = 760 X 20% = 159 mmHg.

o Partial pressure of oxygen

§ Changes with altitude and location
§ Most people have need oxygen supplements above 20,000 feet.

gas exchange occurs

lungs and tissues

Gas exchange in the lungs occurs

§ via diffusion
§ O2 concentration is higher in the lungs than in the blood, so O2diffuses into blood.
§ CO2 concentration in the blood is higher than in the lungs, so CO2diffuses out of blood.

Role of gas exchange in alveoli

§ In the alveoli, the percentage of oxygen decreases and CO2increases, changing the partial pressure of each.

o Blood Gas Measurement

§ Only measures oxygen dissolved in the blood plasma. It will not measure oxygen in red blood cells.
§ It does provide a good measurement of lung function.
· If partial pressure oxygen in blood is more than 5 mmHg below that of lungs, gas exchange is impaired.

Pulmonary Circulation

§ The rate of blood flow through the lungs is equal to that through the systemic circuit (5.5 L/minute cardiac output).
§ The pressure difference between the left atrium and the pulmonary artery is only 10 mmHg.

Vascular resistance must be very low in pulmonary circulation

· Low pressure/low resistance pathway
· Reduces possibility of pulmonary edema

The resistance in the pulmonary circuit is

§ much lower than in the systemic circuit

Pulmonary arterioles constrict when alveolar partial pressure O2 is

low

pulmonary arterioles dilate when partial pressure O2 is

high

Blood flow to alveoli is increased when

they are full of oxygen and decreased when not

Opposite of systemic arterioles that constrict when partial pressure O2 in tissues is high.

· This ensures that only tissues that need oxygen are sent blood.

o Ventilation/Perfusion

§ The response of pulmonary arterioles to low oxygen levels makes sure that ventilation (O2 into lungs) matches perfusion (blood flow).

Oxygen toxicity

· : 100% oxygen is dangerous at 2.5 atmospheres.
Due to oxidation of enzymes

Nitrogen narcosis

occurs if nitrogen is inhaled under pressure; results in dizziness and drowsiness

Decompression sickness

· When a diver comes to the surface too fast, nitrogen bubbles can form in the blood and block small vessels.
· Can also happen if an airplane suddenly loses pressure

Automatic control of breathing is influenced by

feedback from chemoreceptors

chemoreceptors function

monitor pH of fluids in the brain and pH, PCO2 and PO2 of the blood

central chemoreceptors

located in the medulla

peripheral chemoreceptors

located in carotid and aortic arteries

§ Chemoreceptors in the Medulla

· When increased CO2 in the fluids of the brain decrease pH, this is sensed by chemoreceptors in the medulla, and ventilation is increased.
o Takes longer, but responsible for 70−80% of increased ventilation

§ Peripheral Chemoreceptors

· Aortic and carotid bodies respond to rise in H+ due to increased CO2 levels.
· Respond much quicker

Unmyelinated C fibers

· affected by capsaicin; produce rapid shallow breathing when a person breathes in pepper spray

Receptors that stimulate coughing

o Irritant receptors: in wall of larynx; respond to smoke, particulates, etc.
o Rapidly adapting receptors: in lungs; respond to excess fluid

Hering-Breuer reflex

· stimulated by pulmonary stretch receptors
· Inhibits respiratory centers as inhalation proceeds
· Makes sure you do not inhale too deeply

When ventilation is inadequate

CO2 levels rise and pH falls

carbon dioxide + water =

carbonic acid

In hyperventilation, CO2 levels

§ fall and pH rises.

Oxygen levels do not change as rapidly

because of oxygen reserves in hemoglobin, so O2 levels are not a good index for control of breathing.

Ventilation is controlled to maintain

constant levels of CO2 in the blood;
oxygen levels naturally follow

Effect of Blood PO2 on Ventilation

1) Indirectly affects ventilation by affecting chemoreceptor sensitivity to PCO2

2) Low blood O2 makes the carotid bodies more sensitive to CO2.

3) *Hypoxic drive - carotid bodies respond directly to low oxygen dissolved in the plasma (BELOW 70mmHg)*

the bends

Common name for decompression sickness.

Hemoglobin

o Most of the oxygen in blood is bound to hemoglobin.
§ 4 polypeptide globins and 4 iron-containing hemes
§ Each hemoglobin can carry 4 molecules O2.
§ 248 million hemoglobin/RBC
§ Carries oxygen in red bloods cells
§ Loaded in lungs and unloaded in the tissue
§ Decreased affintry in capillaries
§ No dna

Forms of Hemoglobin

oxyhemoglobin, methemoglobin, carboxyhemoglobin

Oxyhemoglobin/reduced hemoglobin

§ Iron is in reduced form (Fe2+) and can bind with O2.

Methemoglobin

§ Oxidized iron (Fe3+) can't bind to O2.
· Abnormal; some drugs cause this.

Carboxyhemoglobin:

§ Hemoglobin is bound with carbon monoxide.
§ really strong, and is stronger than oxygens bond

Carbon dioxide in blood

§ Dissolved in plasma
§ As carbaminohemoglobin attached to an amino acid in hemoglobin
§ As bicarbonate ions
§ Only 20% carbon dioxide carried by hemoglobin
§ 10% dissolved as carbonic acid
§ 70% is bicarbonate

Bicarbonate

· Enzyme that combines water with CO2 to form carbonic acid at high PCO2
· Occurs within RBCs in the capillaries of systemic circulation:
H2O + CO2 --> H2CO3

§ Formation of bicarbonate and H+

· Increases in carbonic acid favor dissociation into bicarbonate and hydrogen ions:
· H2CO3 --> H+ + HCO3−

% oxyhemoglobin saturation

% oxyhemoglobin to total hemoglobin

Measured to assess how well lungs have oxygenated the blood

Normal is 97%

Measured with a pulse oximeter or blood- gas machine

o Hemoglobin concentration

§ Oxygen-carrying capacity of blood is measured by its hemoglobin concentration.
· Anemia: below-normal hemoglobin levels
· Polycythemia: above-normal hemoglobin levels; may occur due to high altitudes
§ Erythropoietin made in the kidneys stimulates hemoglobin/RBC production when O2 levels are low.

Loading

§ when hemoglobin binds to oxygen in the lungs

unloading

§ when oxyhemoglobin drops off oxygen in the tissues

deoxyhemoglobin + O2

§ Direction of reaction depends on PO2 of the environment and affinity for O2.
· High PO2 favors loading.

Systemic arteries have a PO2 of

100 mmHg
· This makes enough oxygen bind to get 97% oxyhemoglobin.
· 20 ml O2/100 ml blood

Systemic veins have a PO2 of

40 mmHg
· This makes enough oxygen bind to get 75% oxyhemoglobin.
· 15.5 ml O2/100 ml blood

what percent of oxygen is unloaded in tissues

22%

At sea level oxygen unloading is

§ 100 mmHg 97-99% saturation

Oxygen remaining in veins serves as an

oxygen reserve

Oxygen unloading during exercise is even greater:

22% at rest
39% light exercise
80% heavy exercise