Transcript External Respiration

The Respiratory System
Chapter 22
The Respiratory System
Processes of Respiration:
1. Pulmonary Ventilation –
movement of air into and out
of the lungs
2. External Respiration – gas
exchange at the lungs; O2
from lungs to blood, CO2
from blood to lungs
3. Respiratory gas transport
– use of blood to deliver O2
to the tissues and deliver
CO2 to the lungs
4. Internal Respiration – gas
exchange at the tissues; O2
from blood to tissues, CO2
from tissues to blood
Figure 22.1
The Respiratory System
Anatomy of Respiration:
•
Conducting zone – the
group of respiratory
passages that provide
passage of air to the lungs.
Includes nasal cavity,
pharynx, larynx, trachea,
bronchi, and bronchioles
•
Respiratory zone – the
microscopic lung structures
where gas exchange occurs.
Includes any structure with
air sacs, called alveoli.
Figure 22.1
The Nasal Cavity
Nasal Cavity - air passage that warms, moistens, and filters air, and also
contains olfactory receptors. Medially divided by the nasal septum.
External nares - the visible ‘nostrils’ that are the entrances into the nasal cavity
Conchae - bony protrusions into the nasal cavity that cause the air to flow
turbulently through the nasal cavity
Figure 22.3b
The Nasal Cavity
Respiratory mucosa – PSCCE with mucous and serous glands, producing a watery
mucus rich in lysozymes, enzymes that break down bacteria
Internal nares - the exits from the nasal cavity into the pharynx, located at the
posterior side of the nasal cavity
Paranasal sinuses - hollow spaces in the certain skull bones, lined with mucous
membrane. This mucus drains into the nasal cavity
Rhinitis –
inflammation of the
nasal mucosa
Sinusitis –
inflammation of the
paranasal sinuses
Figure 22.3b
The Pharynx
The Pharynx - air and food passage that connects the nasal cavity and mouth to the
larynx and esophagus. Commonly called the throat, divided into 3 regions:
1. Nasopharynx – posterior to nasal cavity, air only, lined with PSCCE
2. Oropharynx – posterior to oral cavity, air and food, lining is stratified squamous
3. Laryngopharynx – posterior to the epiglottis, air and food, lining is stratified
squamous
Figure 22.3b
The Larynx
The Larynx - air passage that connects the pharynx to the trachea, composed of
individual cartilages, mostly hyaline. Commonly called the voice box for its
additional function of voice production
Epiglottis - the only elastic cartilage, blocks entrance to the larynx during
swallowing, ensuring food only enters the esophagus
Figure 22.4a, b
The Larynx
Vocal Ligaments – elastic connective tissues in the lumen of the larynx. The
glottis is the opening between these ligaments. Lining epithelium switches from
stratified squamous to PSCCE below these ligaments.
• Vocal folds (true vocal cord) – vibrate to produce sound
• Vestibular folds (false vocal cords) - superior to vocal folds. Help close the
glottis when swallowing
Laryngitis – inflammation of the vocal ligaments
Figure 22.5
The Trachea
The Trachea - air passage from
the larynx to the bronchi,
commonly called the windpipe
Trachealis muscle - smooth
muscle on the posterior side of the
trachea, used in coughing
Trachea Layers in cross section:
• Mucosa – PSCCE with goblet
cells. Cilia sweep debris toward
throat for swallowing.
• Submucosa – connective tissue
layer containing mucous glands
• Hyaline Cartilage – c-shaped to
support air passage while also
allowing esophagus expansion
• Adventitia - connective tissue to
anchor trachea into surrounding
tissues
Figure 22.6
The Bronchial Tree
Bronchial Tree – the series
of branching air passages
leading to lung
compartments
Conducting zone
structures:
• Primary bronchi – branch
from trachea, one for each
lung
• Secondary bronchi –
branch from primary once
inside the lung, one for each
lung lobe
• Tertiary bronchi - branch
from secondary
• Bronchioles – when the
air passage diameter is
<1mm
• Terminal bronchioles –
when the diameter is
<0.5mm
Figure 22.7
The Bronchial Tree
Respiratory zone
structures:
• Respiratory bronchioles
– bronchioles with scattered
alveoli
• Alveolar duct – blindended passage lined by
alveoli
• Alveolar sac – a cluster of
alveoli at the end of a duct
• Alveoli – the individual
lung compartments where
gas exchange with blood
occurs
Figure 22.8
The Respiratory Membrane
Respiratory Membrane – the fusion of alveolar and capillary
walls, creating a 5µm thick membrane for gas exchange between
air and blood
Figure 22.9a, b
The Respiratory Membrane
Type 1 cells – squamous cells of the alveolar wall, fuse to endothelial cells
Type 2 cells - cuboidal cells that secrete surfactant, which reduces the surface
tension of water to prevent alveolar collapse
Alveolar macrophages - move amongst the respiratory membrane engulfing
cells and debris
Alveolar pores - small holes that connect adjacent alveoli
Figure 22.9c, d
The Lungs
Lungs - Paired organs that are highly compartmentalized into small air sacs
Right Lung - divided into upper, middle, and lower lobes by the horizontal
fissure and oblique fissure respectively
Left Lung - divided into upper and lower lobes by the oblique fissure, also has
the cardiac notch – an indentation for the heart’s apex
Figure 22.10a
The Pleurae
The Pleurae - a double layer of serous membrane producing serous fluid to
reduce friction during lung ventilation/movement
• Visceral pleura - the serous membrane layer that clings to the lung surface
• Parietal pleura - the serous membrane that is separated from the lungs, clings
to the internal surface of the thoracic body wall
• Pleural cavity - the space between the parietal and visceral layers, filled with
serous fluid
Figure 22.10c
Mechanics of Breathing
Pulmonary Ventilation - the
movement of air into and out
of the lungs based on the
interactions of pressures in
and around the body
• Inspiration - the movement
of air into the lungs
• Expiration - the movement
of air out of the lungs
Figure 22.12
Mechanics of Breathing
Involved pressures:
• Atmospheric pressure (Patm)pressure exerted by the air around
the body, 760 mmHg
• Intrapulmonary pressure (Ppul) the air pressure within the alveoli,
rises and falls (759-761 mmHg) but
eventually equalizes with Patm
• Intrapleural pressure (Pip) - the
pressure in the pleural cavity (756
or -4 mmHg), 4 mmHg less than
Ppul (must be a negative pressure
to prevent lung collapse)
• Transpulmonary pressure – the
difference between intrapleural and
intrapulmonary pressures, (Ppul Pip)… 760 – 756 = 4 mmHg
Mechanics of Breathing
Boyle’s law :
• P1V1 = P2V2
• When the volume of a chamber
increases, the pressure inside
that chamber decreases.
• When the volume of a chamber
decreases, the pressure inside
that chamber increases
Figure 22.13
Mechanics of Breathing
Inspiration:
• Contraction of diaphragm and external intercostal muscles increases the
volume of the thoracic cavity and lungs
• Volume increase lowers the Ppul to 759 mmHg (-1 mmHg)
• Air moves down its pressure gradient, into the lungs, until the Ppul
equalizes with the Patm
Figure 22.13a
Mechanics of Breathing
Expiration:
• Relaxation of the inspiratory muscles decreases volumes of thoracic
cavity and lungs
• Volume decrease raises Ppul to 761 mm Hg (+1 mmHg)
• Air moves down its pressure gradient, out of the lungs, until the Ppul
equalizes with the Patm again
Figure 22.13b
Mechanics of Breathing
• When Ppul is less than the
Patm , inspiration occurs and
lung volume increases
• As the lung volume
increases, so does pressure,
eventually equalizing with Patm
• When Ppul is greater than the
Patm , expiration occurs and
lung volume decreases
• As the lung volume
decreases, so does pressure,
eventually equalizing with Patm
Figure 22.14
Factors Affecting Ventilation
• Airway Resistance – friction of air
on walls of respiratory passages, is
insignificant in a healthy person
• Alveolar surface tension –
cohesion of water molecules would
cause alveolar collapse. Surfactant
from type 2 cells reduces this
• IRDS – infant respiratory
distress syndrome – an inability
to produce surfactant in
premature births
• Lung compliance – the ability of
the lungs to stretch as the thoracic
cavity expands
Figure 22.15
Respiratory Volumes and Capacities
Tidal volume - The volume of air ventilated during resting breathing (0.5 L)
Inspiratory reserve volume - additional air that can be forcefully inhaled beyond
tidal (2-3L)
Expiratory reserve volume - additional air that can be forcefully exhaled beyond
tidal (700-1200 mL)
Residual volume - volume of air always in lungs, prevents lung collapse (1.2L)
Figure 22.16a
Respiratory Volumes and Capacities
Vital Capacity - total amount of exchangeable air (3.1 - 4.8 L)
Total Lung Capacity - total air volume in lungs (4.2-6 L)
Dead spaces – areas where air is not involved in gas exchange
Anatomical dead space – volume of conducting zone structures (150 mL)
Alveolar dead space – volume of any nonfunctional alveoli
Figure 22.16a
Measuring Ventilation
• Spirometry – the measurement of lung volumes and capacities
• Alveolar ventilation rate (AVR) - measure of air volume flowing
into and out of alveoli
AVR = Breath frequency x (Tidal volume – dead space)
AVR = 12 breaths/min x (500mL – 150 mL)
AVR = 4,200 mL/min
Properties of Gases
Dalton’s Law - total pressure from a mixture of gases is the sum of
the partial pressures of each individual gas; this partial pressure is
proportional to the percentage of that gas in the mixture.
Example: Patm = PO2 + PCO2 + PN2
Henry’s Law – when a mixture of gases is exposed to a liquid, the
gases will dissolve in proportion to their partial pressures
Gas Exchange
External Respiration :
• The PO2 of the air in the alveoli is
greater than the PO2 of the blood
arriving at the alveoli
• Oxygen moves down its pressure
gradient from the alveoli into the
blood
• The PCO2 of the blood arriving at
the alveoli is greater than the PCO2
of the air in the alveoli
• Carbon dioxide moves down its
pressure gradient from the blood
into the alveoli
Figure 22.17
Gas Exchange
Oxygen moves from the
alveoli into the blood
until the partial
pressures equalize,
taking about 0.25 sec
Figure 22.18
Gas Exchange
Ventilation–Perfusion coupling –
• Areas of lung tissue whose alveoli are well supplied with air experience
dilation of local blood vessels
• Areas with relatively unventilated alveoli experience local vasoconstriction
Figure 22.19
Gas Exchange
Internal Respiration :
• The PO2 of the blood arriving at
the tissues is greater than the PO2
of the tissues
• Oxygen moves down its pressure
gradient from the blood into the
tissues
• The PCO2 of the tissues is greater
than the PCO2 of the blood arriving
at the tissues
• Carbon dioxide moves down its
pressure gradient from the tissues
into the blood
Figure 22.17
Oxygen Transport
• 1.5% of oxygen is transported
by being dissolved in the
blood’s plasma
• 98.5% of oxygen is
transported by being bound to
hemoglobin
• Hemoglobin is 100%
saturated with oxygen upon
leaving the lungs, and is still
75%saturated after delivering
to the tissues
• Bohr effect – increased PCO2
weakens the bond between
hemoglobin and oxygen
•Hypoxia – inadequate oxygen
delivery to body tissues
Figure 22.20
Carbon Dioxide Transport
• 7-10% of carbon dioxide is transport by being dissolved in plasma
• 20% of carbon dioxide is transported by being bound to hemoglobin
• 70% of carbon dioxide is transported as bicarbonate ions (HCO3-)
• Dissolved carbon dioxide reacts with water to form carbonic acid
(H2CO3) which then dissociates into hydrogen ions (H+) and bicarbonate
ions (HCO3-).
• Therefore, CO2 levels in the blood affect blood pH by affecting H+ levels
Figure 22.22a
Carbon Dioxide Transport
Carbonic acid-bicarbonate ion buffer system – the chemical reaction
involving carbon dioxide is reversible, allowing the prevention of drastic
changes of blood pH
Haldene effect - blood can transport more carbon dioxide when the PO2 is
lower
Figure 22.22b
Control of Respiration
Medullary Respiratory Centers – nuclei in
the medulla that regulate breathing rate and
depth
• Ventral respiratory group – generates the
breathing rhythm, inspiratory nerves from here
control the inspiratory muscles
• Dorsal Respiratory group – regulates the
breathing rhythm with information from
chemoreceptors in the blood
• Pontine respiratory group – regulates
smooth transitions between inhalation and
exhalation
Figure 22.24
Control of Respiration
Factors Affecting Breathing:
• Chemoreceptors – receptors for
CO2, O2 and H+ in the medulla and
major arteries. If carbon dioxide
levels increase (decreasing pH),
breathing rate and depth should
increase
• Higher brain centers – emotions
can affect breathing rate. The
cerebral cortex allows us to
voluntarily control breathing.
• Hyperpnea – increased breathing
rate due to metabolic need, as in
during exercise
• Other receptors – irritants or
excessive stretch inhibits ventilation
• Hyperventilation – increased
breathing rate beyond body needs.
Leads to vasoconstriction of
cerebral blood vessels and can
lead to fainting
Figure 22.25
Respiratory Disorders
Chronic Obstructive Pulmonary
Disorder (COPD) – any condition
involving a decreased ability to expel air
from the lungs. Symptoms include
dyspnea (labored breathing), coughing,
and hypoventilation
• Chronic bronchitis – excessive
mucous production in the respiratory
passages leading to frequent
infections
• Emphysema – a progressive loss
of the respiratory membrane and
decreased lung elasticity
Tuberculosis- bacterial infection spread
through aerosols; treated with 1 year
course of antibiotics
Cystic fibrosis – genetic disease
causing excessive, thick mucus
production causing major infections
Figure 22.28