Download Thorax Thorax -Thorax is the Superior part of trunk betw neck and

Thorax
Thorax
-Thorax is the Superior part of trunk betw neck and abdomen
-Thoracic cavity surrounded by thoracic walls, and contains the thymus gland, heart, lungs,
bronchial tree, distal part of trachea, and most of the esophagus
-Thoracic wall consists of skin, fascia, nerves, vessels, musc, and bone
-Skeleton of the thoracic wall forms, the osteocartilaginous cage that protects the heart, lungs and
a portion of some of the abdominal organs (mainly the liver)
-Bony thorax includes the 12 thoracic vertebrae and intervertebral discs, the 12 pairs of ribs and
intercostal cartilage, and the sternum (plate 186-187)
Special features of thoracic vertebrae:
-They have costal facets on their bodies for rib articulation. They also has costal facets on their
transverse processes, for articulation for the tubercles of the ribs
-Has long spinous processes
-Ribs 2 thru 9, have superior demifacets for articulation with the vertebrae above them, and an
inferior demifacets for articulation with their own vertebrae
-Movement betw thoracic vertebrae is limited, which helps to protect thoracic viscera and the
visceral organs
-The bodies of T5-T8, are in contact with the descending thoracic aorta. The aorta often forms an
impression on the left side of T5 and T8, on the vertebrae them sleves, that is visible on an x-ray.
The aorta actually passes down the abdominal wall behind the diaphram, along the vertebral
column, not like the esophagus and the inferior vena cava.
The 12 pairs of ribs are narrowed, curved, flat bones:
-The first 7 pairs are called the True Ribs, clinically called Vertebro Sternal Ribs
because they attach to the vertebral colum posteriorly and the sternum anteriorly through
the costal cartilage
-Pairs 8, 9 and 10 are called the False Ribs, clinically called Vertebro Chondral
Ribs. becausue they attach to the vertebral column posteriorly and anteriorly through
their cartilage (chondro), to the cartilage of rib number seven and then to the sternum
-Ribs pairs 11 and 12 are called Free or Floating Ribs. because they both
posteriorly attach to the respective vertebrae but anteriorly, they end in the posterior
abdominal musculature
-The Costal Cartilage contributes to the elasticity of the thorax anteriorly, this can go
through a arthritic condition/degeneration where they become stiff making it difficult to
breath b/c loss of elasticity, it is called costal chondritis. The cartilage of ribs 7,8,9 an 10
ascend on either side to form the infrasternal angle (near the Xyphoid process, the angel
that is made by the cartilages meeting in the middle.) and costal margin (the cartilage
running from side to side on the lower ribs, making up the angle).
-Ribs are separated by intercostal spaces that contain intercostal muscles, blood vessels,
and nerves.
-The typical ribs, which are ribs 3 through 9, (plate 178-179) each have one wedgedshaped head with two articular facets, separated by a crest for articulation with the
vertebrae above and it’s own vertebrae (ex, thoracic 4 connects with 3 and 3)
-For articulation 3 to 9, they each have a neck that separates the head of the rib from the
tubercle from the junction at the neck and the shaft which has an articular facet for
articulation with the transverse process of the corresponding vertebrae.
-They each have a shaft that is thin and flat and that shaft has an angle at the point of
greatest curvature.
-Atypical ribs (#1,2,10,11,12):
-Rib #1 is the broadest, shortest and most curved of the true ribs. And it cannot be
palpated because it is under the clavicle.
- Rib #2 is thinner, longer and less curved than rib #1 and has two facets on its head for
articulation with T1 and T2.
- Rib# 10, is unique in that it only has only one facet on its head for articulation with T10.
- Rib pairs #11 and 12, floating ribs, are short ribs with only one facet and have no neck
nor tubercle.
Clinical associations with the Ribs:::
-The weakest part of any rib is just anterior to its angle (greatest curvature). Curve is just around
the thorax from front to back and any fracture will occur usually right in front of this.
-Rib fracture in infants and children are rare, due to the ribs elasticity
-Fractured ribs are very painful due to movement during ventilation, most of the time they can’t
be seen on x-ray
-Ribs 1 and 2 (due to their protection by the clavicle) and 11 and 12 (because they are floating)
are the least frequently fractured ribs
-Careful palpation based on an indiv’s complaints, can often reveal a rib fracture that might not
show up on a x-ray and can be extremely painful with palpation
-A flail chest, (which is also referred to as a stove-in chest) occurs when a large section of the
anterior and or lateral chest wall is freely movable due to multiple rib fractures. the chest will
move in with inspiration, and out with expiration. Allows chest wall to move paradoxically.
-Thoracotomy—any operation or procedure on the thoracic wall.
-Simplest to Remove (pus) empyema, from the pleural space
-Cervical ribs are sometimes present betw .5 and 1% of the population, they articulate with C7
and they are of no clinical significance unless neuro-vascular sypmtoms are reported, like
compression of the inferior trunk of the brachioplexus (which is formed from C5 to T1),
producing a tingling, or numb sensation on the medial surface of the forearm . It can also
compress the cervical artery, which can cause ischemia related pain primarily in the upper limb.
-In rare instances, just like cervical ribs, sometimes a lumbar rib could be present. If a lumbar rib
is present, it is VERY VERY very short and sometimes if confused with a fracture of the lumbar
spinous process. It is of no clinical consequence.
-Costal cartilages or Hyaline cartilage and the costal margin (formed by cartilage 7 thru 10) meet
to form the infrasternal angle at the xiphosternal joint.
The sternum:
is a long flat bone forming the middle anterior portion of the thorax (plate 185). The sternum has
three distinct parts, the manubrium on top and xiphoid process at the bottom, and the body in the
center between these two.
-Top of sternum, manubrium, is at the level of T3-T4. It is thick and has an indentation jugular
or suprasternal notch. On each side of the suprasternal notch (L&R) is called clavicular notch.
Rib 1 articulates with the manubrium just below the clavicular notch.
-The angle of Louis or Sternal angle is where the manubrium joins the body of the sternum. It
forms the manubriosternal joint. This sternal angle is located at the 2nd pair of costal cartilages,
and happens to be at the level of T4 and T5.
-The body of the sternum runs from T5 to T9,
-xiphoid process, which is the smallest and most variable (mobile) part of sternum
-Superior thoracic aperture:
is where the neck enters the thorax. Structures passing through include the trachea, esophagus,
blood vessels, nerves, lymphatics. The circle making up the superior thoracic aperture is bounded
by…posteriorly the 1st thoracic vertebrae, then the 1st pair of ribs anteriorly and then the
manubrium
-Inferior thoracic aperture:
is the border between the abdomen and thorax. It is covered by the diaphragm and it is bounded
by T12, 12 pair of ribs and then around the cartilages 7-10 and finally the xiphosternal joint
(where xiphoid attaches to the body of the sternum).
Anterior thoracic wall
Breast- contains mammary glands, located in superficial fascia of anterior thoracic wall
both sexes have breast tissue, mammary glands develope only in females from estrogen.
-the point of greatest prominence is the nipple surrounded by a pigmented area called the
aerola, post pubital, each breast contains up to 20 lactiferous glands each of which is
drained by the lactiferous ducts to the nipple.
-Circular base of female breast lies vertically from the 2nd to the 6th rib and transversely to
the lateral border of the sternum, to the midaxillary line.
-A small portion of the breast tissue, extends superiolaterally along the inferior border of
the pectoralis major muscle to form the axillary tail
-2/3 of the breast lies on the fascia of the pectoralis major musc and ½ of the breast lies on
the fascia of the serratus anterior musc
-between the breast and the deep fascia is a space called the retromammary space (bursa),
which allows for breast movement.
-the lactiferous glands are attached to the dermis of the skin (deep layer) by suspensory
ligaments (aka Cooper’s ligaments). These ligaments are best developed in the superior
part of the breast.
Vascular supply to the breast is via:
-the anterior intercostal arteries, which are branches of internal thoracic arteries (aka mammary
arteries) which are branches of the subclavian arteries.
-2nd oxygen rich blood supply comes from the Lateral thoracic artery and thoraco-acromial and
those are branches of the axillary artery
-lastly, blood supply from posterior intercostal arteries, which are branches of the thoracic aorta
Venous Drainage is via:
-the internal thoracic vein and the axillary vein
Lymph Drainage associated with the breast is via:
-lymph from the breast passes drains into a sub-areola plexus and from there 75% (the majority)
of the lymph drains into the axillary lymph nodes. Axillary lymph nodes are made up of 5
specific nodes: 1) pectoral nodes, 2)subscapula, 3)apical, 4)lateral and 5)central nodes. These
are all the axillary lymph nodes.
-The other 25% goes to the infraclavicular, supraclavicular and parasternal (along the sternum).
-A small amount of lymph can pass from one breast to the other.
Interference or blockage of lymph drainage (typically by cancer) produces a characteristic
leather-like appearance on the skin of the breast. It developes dimples like an orange, due to a
shortening of suspensatory (Cooper) ligaments because of the lack of lymph flow and ischemia.
Nerves of the breast are via, anterior branches of thoracic spinal nerves T4, 5, and 6. (Remember
every single spinal nerve is mixed, sensory and motor.)
LANDMARKS on the Thoracic Wall
Palpable clavicles,
jugular notch,
the manubrium,
sternal angle or angle of Lewis,
the mid-clavicular line,
infrasternal angle,
the xiphoid process and
costal margin
Major Muscles involved in Ventilation (in rest breathing) (external assoc with inspiration
and internal assoc with expiration)
-external intercostal musc.(inspiration) –when they contract, the anterior-posterior dimension
of the thorax increases
the diaphragm, when it contracts, it descends –and that increases the superior and inferior
dimension of the thorax
these actions collectively increase the volume of the thorax, which decreases the pressure
(Boyle’s Law) and air rushes in.
Nerves in the thorax, 12 pairs of thoracic spinal nerves. As soon as the nerves pass through the
intravertebral foramina, they divide into ventral and dorsal rami. Ventral rami goes into the
intracostal spaces to the ventral side of the body, while dorsal rami innervate the muscles, joints,
skin and bones of the back. *ALL SPINAL NERVES ARE MIXED, THE DORSAL ROOT
ARE ALL SENSORY AND VENTRAL ROOT ARE ALL MOTOR. Therefore the rami’s are
extensions of the spinal nerve.
Arterial supply to the thoracic wall
Oxygen or arterial supply to the thoracic wall via posterior intercostal arteries (come off thoracic
aorta). Anterior intercostal arteries come off the internal thoracic artery
Lateral thoracic (off the axillary) and there are some sub-costal arteries which come off the
thoracic aorta
Thoracic Cavity:
-Has 3 compartments: Two lateral compartments, each of which contained a lung and a central
compartment which contained everything else
-Each lung is surrounded by a pleural sac, 2 layers to a pleural sac: outer parietal layer which
adheres to the thoracic wall, and an inner visceral layer which covers the surface of the lungs and
invaginate into the fissures of the lung
-Pleural space, space between the two layers, is a potential space with only a thin layer of serous
lubricated fluid present
-The parietal pleura adheres to the thoracic wall, the mediastinum and the diaphragm. It is named
based on location
3 functions of the pleura
1)serous fluid acts as a lubricant for smooth lunch movement
2)pressure in plural space is sub atmospheric which causes lung to adhere to thoracic wall
3)pleura effectively isolates thoracic organs from the lungs.
The parietal pleura is named as follows:
-The costal pleura is all of the pleura that is against the thoracic wall
-The mediastinal pleura is the layer of pleura that runs from anterior to posterior against the
mediastinum (it lines the mediastinum on both sides)
-Diaphragmatic pleura runs against the superior surface of the diaphragm (covers the diaphragm)
-Cervical pleura which is sometimes called the pleura cupula, extends about 3 cm into the neck
and forms the dome/apex of the lung
*(can’t empty your lungs, air left over is residual volume)
Lungs
-Lungs are light soft spongy elastic, separated by mediastinum. They are attached to heart and
trachea by the root of the lung is the area of continuity between the visceral and parietal pleura
come together
-The hilum of the lung is the in and out doorway, and contains the main stem of the primary
bronchi, pulmonary vessels and nerves
-Described based on position and number of lobes: Right lung has a Horizontal and oblique
fissures divides it into 3 lobes (superior, middle and inferior), while Left lung only has oblique
fissures is 2 lobes (superior and inferior). Each lung has an apex at the top where pleura cubular
is located. Each one is explained as having 3 surfaces and 3 borders (where two surfaces meet)
Surfaces of the lung
-The costal surface, the largest surface, the part of each lung that is adjacent to the sternum and
in contact with the ribs
-The mediastinal surface is the surface of the lung that is next to the mediastinum running down
the midline from front to back, it runs from the sternum back to the vertebrae
-The diaphragmatic surface runs along the bottom, rests on diaphragm
Boarders of the lungs
-Anterior border is where the costal surface meets the mediastinal surface (right where internal
thoracic artery runs)
-Inferior border that surrounds the entire diaphragmatic surface
-Posterior border where the costal surface and the mediastinal surface meet posteriorly
RMB & LMB (right main stem bronchus, and left main brunchus: both also known as primary
bronchus)
-They cross Inferior-laterally (down and to the side) from the trachea
-The are also supported by C-shaped rings accept at the point at bifurcations where there is a
triangular piece of cartilage called the carina. The carina keeps the two primary bonchi properly
oriented. so the branches don’t close and squish the heart
-The right main stem bonchus, is shorter and more vertical and as a result, foreign objects are
more likely to lodge on the right side then the left
-The LMB passes below the arch of aorta and in front of the esophagus
-Each main stem bronchus divides into secondary bronchi, and each secondary bronchus supplies
one branch of a lobe, 3 secondary bronchi on the R side, and 2 on the left. and then divide into
tertiary branches which supply segments of each lung.
Vessels of the lung
-Each lung has a pulmonary artery, bringing oxygen deficient blood to it for gas exchange and
two pulmonary veins returning o2 rich blood to the left atrium
-The right and left pulmonary artery divides to send an individual branch to each lobe of each
lung.
-After supplying the lung pleura with their o2 and nutritional requirements the bronchial arteries
anastomose with the pulmonary arteries. The tissue of the lung gets its o2 rich blood and its
nutrition from the bronchial arteries. (nothing to do with pulmonary circuit). The right bronchial
veins on the right side drain into the azygos vein. The left bronchial veins drain into the
accessory azygos vein.
-There are two lymphatic plexuses in the lung and they communicate freely with each other:
Superficial lymphatic plexus, which is deep to visceral pleural, it drains lymph to the tracheal
bronchial lymph nodes which is located at the bifurcation of the trachea.
Deep lymphatic plexus of the lung which is located at the sub-mucosa of the bronchi. And that
plexus drains lymph to the pulmonary lymph nodes which is located on the surface of the main
stem bronchi. Due to the extensive lymphatic network, cancer can easily spread from one lung
to the other.
NERVES of the lung
-Parasympathetic nerves to the bronchi are associated with CN10 (all about the Vagus). When
they become active, it has three important effects:
1) cause broncho constriction because they are motor to the smooth muscle of the
bronchiole tree
2) inhibitory to the pulmonary vessels smooth muscle resulting in the vasodilation.
3) cause an increase in glandular secretion.
(Increase in parasympathetic nerves is NOT good for those that are hard of breathe)
-Sympathetic innervation does the exact opposite step by step
1)inhibitory to brochiol smooth muscle causing bronchiodilation
2)it is motor to the vascular smooth muscle, causing vasoconstriction.
3)Inhibit glandular secretion
Right vagus nerve
-enter the thorax in front of the subclavian artery where it gives rise to the right recurrent
laryngeal nerve. It then continues downward, to give rise to lots of branches from plexus’s and
then finally pierces diaphragm and enters the abdominal cavity.
Left vagus
- also descends down the artoa and gives rise to the left recurrent laryngeal nerve and then
continues down into the abdomen giving off many branches.
- all recurrent nerves supply all intrinsic muscles of the larynx: affecting the phonation
**Phrenic nerve are the only motor nerves to the diaphragm: 3,4,5, keeps a person alive
half are sensory and half are motor. Right side descends along IVC. And the left phrenic
descends right accross the left atrium and down the diaphragm.
Mediastinum -is the central part of thorax between the two pleural spaces
-extends from the superior thoracic aperture to the diaphragm and from the sternum (anteriorly)
all the back to the thoracic vertebrae (posteriorly)
-the structures in the mediastinum are surrounded by CT, nerves, blood, lymph vessels and fat
-functionally, the looseness of the CT in the mediastinum, coupled with the lungs elasticity is
what allows for volume changes in the thorax.
-clinically, The mediastinum is divided into:
- a superior region, which runs from the superior thoracic aperture down a plane and through
at the level of T4. This contains the thymus gland, arch of aorta, the SVC, vegas nerve, phrenic
nerves, brachiocephalic veins, and the trachea.
-The Inferior mediastinum, which runs from that same plane (sternal angle back to T4) all the
way down to the diaphragm. It is further broken down into an anterior, middle, and posterior
region
-The inferior middle mediastinum contains the heart and the great vessels (any vessel
that leaves/enters the heart)
-The anterior inferior mediastinum, anything in front of the heart, primarily fat, lymph,
nerves, vessels
-The posterior inferior mediastinum, back of heart
Pericardium—
double wall, fibroserous encasing. It is behind the sternum and runs anteriorly to the 2nd to the
6th costal cartilage and posteriorly from T5-T8
-the fibrous pericardium FUSES with the TUNICA EXTERNA (aka tunica adventicia) of the
great vessels. It is attached/adherent to the posterior surface of the sternum by the
sternopericardial ligaments. It protects the heart and gives it a mechanical advantage when it
contracts (because the heart doesn’t connect to any bone). The fibrous pericardium FUSES to
central tendon of the diaphragm.
-The inner layer, serous pericardium, its self, has an outer and inner surface. The inner layer is
visceral and the outer layer is parietal and attaches to the fibrous pericardium and between the
two is the pericardial space.
-fluid or inflammation of that space results in pericarditis, which produces cardiac tamponod.
Then results in pressure on the heart. Also causes distension of the veins in the face and neck
accumulation in pleural space is called pleurisy (jumped back to lungs)
superior mediastinum above the angle, the thymus gland, the arch of the aorta, the SVC (superior
vena cava), R&L recurrent laryngeal nerves
anterior inferior
posterior inferior is the thoracic aorta
Respiratory Sys, Pulmonology: has 5 basic functions
1) ventilation—movement of air into and out of the body, must have this for anything else to
occur
2) external respiration—gas exchange between the alveoli and the pulmonary capillary blood
3) gas transport—RBC transport hemoglobin which transports O2
4) internal respiration—gas exchange between systemic capillaries and metabolically active
tissues of the body
5) cellular respiration—metabolic use of oxygen by the cells to manufacture ATP, krebs (etc)
The anatomical structures of the respiratory system are categorized as either being in the
conducting division or the respiratory division:
-conducting division is composed of all the anatomical structures that provide a conduit/
pathway through which the air must travel in order to get to the respiratory division. Air with
in this space is considered Dead space.
-Respiratory division is where the external respiration takes place, gas exchange.
Pulmonary Ventilation:
Moving air into and out of the body at rest
Minute Ventilation VE = B.R x T.V
Breathing rate per minute x tidal volume
-Tidal volume is the Volume of air you breathe in or out with each breath
-Breathing rate is the number of breaths you take each minute
EX: for an adult
12 br/min x 500ml/br = 6020ml/min or 6 L/min
anatomical dead space = volume of air left behind in the respiratory tubes, can be estimated as
persons body weight in lbs expressed in milliliters
Alveolar Ventilation VA = B.R. x (T.V. – DS A) (how much air actually gets from minute to
alveolar)
*DS is dead space
EX: A 200 lbs person = 200ml… 3600 = 12 x (500 - 200)
If someone has a respiratory distress problem, allergic attack…. The faster you breathe, what
happens to the tidal volume? It decreases. (thus your alveolar ventilation will decrease) What
effect on alveolar ventilation?
EX: Same person, 200lbs… the breathing rate increases 30br/min, that means the TV will be
300ml/br
What happened to their minute ventilation? Ve = 30 x 300 = 9000ml/min (so moving more air
per minute)
What happened to their alveolar ventilation Va = 30 x (300-200) = 3000 (this decreases, and this
is the number that matters)
What structures are involved in the anatomical dead space?
Includes the volume of air in the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles,
respiratory bronchioles and alveolar ducts (we have entered the resp div) where the region of gas
exchange takes place. All of the air in the anatomical dead space, that air is said to be in the
conducting division of the respiratory system
Conducting div ends when we get to respiratory bronchioles… and the respiratory div starts at
the respiratory bronchioles, which lead to the alveolar ducts.
*** (know for another test, not this one) Mechanics of breathing is related to Boyle’s Law: as
pressure increases, volume decreases
At rest, resting muscles of inspiration (external intercostal expand) when they contract the
volume in the thorax increase. Inspiration is an ACTIVE PROCESS, meaning ATP is involved
(because muscles need energy to contract). Expiration at REST is a PASSIVE process, volume
decreases.
Ondines curse: automatic mechanism of breathing is lost, very rare.
Intrapulmonic pressure—is synonymous with intraalveolar pressure, These two are the pressures
inside the lung. When intrapulmonic pressure is less than atmospheric pressure, we get
INSPIRATION. During resting, inspiration and expiration, the intrapulmonary pressure varies
between -3 mmHg to +3 mmHg above atmospheric, resulting in inspir. and expir, contraction of
and relaxion of these muscles involved.
The lack of air in the intrapleural space (outside the lung between visceral and parietal pleura)
produces a sub-atmospheric pressure which is lower than the intrapulmonary pressure. This
arrangement produces what pulmonologists called a transpulmonary pressure across the
pulmonary lung—the mathematical pressure difference between the intrapulmonary and the
intrapleural space.Because of this transpulmonary pressure, the lungs adhere to the thoracic wall
and facilitates inflation of the lung moving the thoracic wall.
The elasticity of the lungs, elasticity is the property of a structure to return to it’s original size
after being distended. Healthy lungs are very elastic due to the high elastin content in a tissue
causes it to resist distension. Since the lungs are stuck to the thoracic wall, they are always in a
state of elastic tension. That tension increases during inspiration and decreases during expiration
(expiration allows them to rebound)
**The elastic tension, pulling the lungs away from the thoracic wall is called the recoil
tendency. The recoil tendency can be measured (esp in restrictive lung disease) as the amount of
negative pressure in the pleural space that is required to prevent the lung from collapsing. It is
caused by the elastin fibers and by the surface tension of the fluid lining the alveoli and on the
surface of the alveoli.
Surface tension (in the lungs, which contributes to elastin and recoil tendency)—is created due
to the fact that water molecules on the surface of the alveoli are attracted more to other water
molecules that to the air. This tension creates pressure inside the alveolus creating force on the
surface of an object that wants to make it collapse (not good). Glycoprotein, surfactant (surface
active agent) S&S by type II alveoli cells located in the call of the alveoli. Surfactant reduces the
Surface tension on the outside of the alveoli. Surfactant is not S&S until late fetal life, why there
is a huge concern with premies, give steroids to expecting mom’s to help start producing
surfactant. Surfactant reduces surface tension and allows them to expand (prevents alveoli from
collapsing)
Hyaline membrane disease, [looks like hyaline, but is NOT] due to a premature delivery and
surfactant is NOT being produced (premature babies). President Kennedy, Jackie kennedy, last
birth in white house, baby died from this.
Compliance—is the change in lung volume per mm change in trans-pulmonary pressure. (aka. is
the ability for it to expand when stretched) Healthy lungs are 100 times more distensible than a
latex balloon. Compliance of the lungs in reduced whenever there is resistance to distention.
Restrictive lung disease, pulmonary fibrous, lung tissue becomes stiff… the lungs don’t want to
stretch, it will resist being distended, the lungs are NOT compliant.
Inspired air from the alveoli, enters the alveoar ducts. Gas exchange occurs accross the walls of
the alveoli.
Alveoli are the final structures where the gases accumulate prior to diffusion into the pulmonary
capillary blood. the walls of the alveoli contain two types of cells. Type I alveolar cells are
specialized for the process of diffusion and Type II alveolar cells are S and S, surfactant (reduces
surface tension). In healthy mature lungs, there are about 350 million alveoli in each lung.
Lungs are completely dev around 8 or 9 years old.
Following effective ventilation: is the diffusion process.
Gas exchange is a passive process. This diffusion is enhanced because the alveolar membrane is
only one cell thick and the endothelium of the capillary is only one cell thick.
Gases are expressed by their partial pressure—that is the pressure that they exert in whatever
medium they exist and the units that are used on millimeters of mercury. The part of the total
pressure that is due to a different gas.
mmHg
pO2
pCO2
Alveoli
100
40
Oxygen Rich Blood
100
40
Oxygen deficient blood
40
46
The partial pressure of gases in the liquid, the partial pressure of gas in liquid is indirectly
related to the solubility of that gas in the liquid.
These numbers represent the numbers of partial pressure in a total number of gasses.
Blood coming from the lungs is deoxygenated. PO2 is 40 and PCO2 is 46. When it gets to the
alveoli the o2 moves from high concentration into the pulmonary veins where it is low in the
plasma and co2 moves from plasma in the pulmonary artery to the alveoli where the
concentration is low. Then oxygen dissolves in the plasma.
Oxygen Transport:
Oxygen is transporteed in two ways:
1) it is dissolved in plasma. (PO2 in blood is due, only to the O2 dissolved in the plasma)
The solubility of O2 dissolved in everyone 100 mL of blood (plasma contained in 100 ml of
blood) dissolved in 0.3 ml of O2/ 100 ml blood (@ pO2 100 mmHg) Is O.3 enough to keep me
alive? (to know this we must know the metabolic requirement)
BMR(basal metabolic rate)=200ml/mm
MET (metabolic equivalent) = how hard working relative to being at rest)–at rest this is 3.5
mlO2 / Kg of Body weight per min (1 MET, if 8 then that is you are working 8 times harder than
you are at rest)
EX: 70kg x 35 = 245 ml of O2 required
Cardiac output (Q or CO = flow): at rest for an adult is 5 L/min or 5000ml/min (every 100 ml of
this 5000 is carrying 0.3ml of O2) so 50 times .3 = 15 mlO2/min in the dissolved state. (this is
not enough to provide the body but is still extremely important. P02 in plasma is directly
associated to the 02 associated in plasma and gas exchange depends on a pressure difference.
(you must of 02 dissolved in plasma in order to have gas exchange because it gives a partial
pressure and need that partial pressure in order for gas exchange.) Once the O2 is dissolved in
plasma then, and only then can it enter hemoglobin.
2) the way oxygen is combined with hemoglobin (how much is transported by heme?)
OCC: oxygen carry capacity of the hemoglobin –maximum amount the hemoglobin can carry
= Amt of Hb x Amt of O2 Hb carries.
15 grams of hemoglodim/ 100 ml of blood x 1.34 mL of O2 / gram Hb = 20.1 mL o2/ 100 ml
blood *o2 carrying capacity.
The only time you are at o2 carrying capacity is if you are breathing pure O2
percent SO2 = amt of o2 actually combined with H
at rest breathing room air –20.9%
--------------------------------------------------------------------------CO2 Transport
hemoglobin at rest is 97% saturated
Blood in R Atrium is 75% saturated O2, how much O2 is being transported?
--any percentage of saturation x 20.1 =
at a cardiac output of Q = 5000 ml/min
Q = stroke volume x heart rate (SV x HR)
50 (100/ml packet) x 19.5 ml = about 975 (only need 200)
If were healthy, blood leaving the left ventricle has PO2 of 100, and is 97.5% saturated, and is
transporting 19.5 ml 02/ml blood. Blood back to RA has P02 of 40, and % SO2 of 75% (at rest)
and is trasporting 15mlO2/ml blood. Difference between two is A-V 02 difference.
A-V 02 difference –arterial venous o2 diff
Diff in ox content in o2 rich blood from the o2 def blood
19.5 o2 rich, and 15ml of o2 in o2 def
A-V O2 difference:: 19.5-15=4.5 ml O2/100ml blood
50 x 4.5=224 (meet our requirement)
Oxygen Association Curve (look at) –from Lung association.
Bohr Effect: conditions where there is an increase in pCO2 or an increase in body temperature or
a decrease in pH (variables in plasma). In any one or combo of these, hemoglobin more readily
gives up it’s oxygen. 75% sat, if factored changed, % may change to 60 meaning more O2 was
released from the hemoglobin. (ex: exercise)
3 ways CO2 is transported
1) Dissolved in plasma (7% of CO2 is transported in the dissolved state, more than O2)
2)establishes the partial pressure of CO2
pp is much lower because it is more soluble)
 93% Diffuses into the RBC
3)23% combines with a hemoglobin forming an carboxyHb
70% co2 trasported in blood is converted to carbonic acid by bicarbonate ion (CO3 + H2O
,H2CO3  H+ + HCO-3 ) SLOW REACTION
carbonic anhydrase speeds up rxn in RBC up to 200x
Chloride shift is the movement of negative Cl- ions from the plasma into the RBC to compensate
the loss of the HCO (bicarbonate ions) from RBC into the plasma
70% is transported as a bicarbonate [in Guyton]
Respiratory Controls:
two groups of neurons clustered in the medulla:
1) DRE dorsal respiratory group: located near root of CNX,
2)VRG: ventral respiratory group. network of neurons that runs in the brainstem from the
medulla all the way up to the medullary pontine (pons) boarder. It has both inspiratory and
expiratory neurons.
-Inspiratory neurons (at rest): fire and send impulses along phrenic and intercoastal
nerves innervating the diaphragm and external intercostal muscles. This is an active process.
-Expiratory neurons (at rest) in the VRG: they inhibit the inspiratory neurons which
stops the impulses to the respiratory muscles. This is passive
PLEASE understand this Concept::: expiration has no messages from neurons
-The DRG is responsible for integrating input from the peripheral stress receptors and from the
chemo receptors and sends that information to the VRG. The Pons influence and modify the
activity of the medullary neurons. Pons smooth out transition between inspiration and expiration.
2 pontine centers that influence the medullary center
1) Apneustic center promotes I by stimulating the I neurons in the medulla
2) Pneumotaxic center sends impulses to the VRG modifying your breathing rhythm. It
does this by antagonizing the apneustic center and thereby inhibits inspiration
inspiratory depth, is also influenced and determined by how active the respiratory center
stimulates the motor neurons serving the respiratory muscles. The greater the stim, the greater
the number of excited motor units and the greater the force of contraction of respiratory muscles.
Respiratory Rate: is determined by how long the inspiratory center is active and how quickly it is
turned off.
Chemical factors: **the most important factor influencing depth and rate are changing levels of
PCO2, pH and PO2 (in the plasma). The sensors responding to this stimuli are the
chemoreceptors located either in the medulla (central chemoreceptors) or the peripheral
chemoreceptors in the aortic arch, or in the carotid arteries where the bifurcate. PCO2 is
regulated to be 40mmHg in oxygen rich blood plus or minus 3 mmHg. When PCO2 rises, the
CO2 diffuses into the CSF where it combines with water to form carbonic acid which then
associated into bicarbonate ions and hydrogen ions. Since the hydrogen ions can’t be buffered
by the CSF it produces hypercapnia, decreasing the pH of the CSF which excites the central
chemoreceptors. The chemoreceptors synapse with the respiratory control centers in the medulla
and increase the rate and depth of breathing which flushes out the excess CO2 from the alveoli
returning PCO2 levels to normal. An increase in 5mmHg in PCO2, will double alveolar
ventilation even if pH and PO2 are normal. When Po2 and pH are below normal, the response to
elevated PCO2 is even greater. While PCO2, which is major player here, initiates response it’s
the hydrogen ion concentration that excites the central chemoreceptors. Cells that are sensitive to
PO2 are in the peripheral chemoreceptors. Normally, the affect of declining PO2 on ventilation
is minimal and actually is limited to enhancing the sensitivity of the peripheral chemoreceptors
to PCO2. oxygen levels are not prime stimuli for increasing ventilation unless PO2 falls to
60mmHg or below, when this happens the central chemoreceptors become hypoxic and their
activity decreases. At this point the peripheral chemoreceptors kick in and stim the central
receptors to increase ventilation. Decreasing pH will increase the rate and depth of breathing in
an attempt to rid the body of excess CO2 there by raising the pH even if the decrease in pH is not
due to CO2 elevation. Other causes for pH change: increasing lactic acid levels in blood, poor
fatty acid metabolism associated with DM,
Question: PCO2, pH and PO2, where are these variables located? These are variables that has to
do with the gases that are dissolved in plasma…
VE (minute ventilation) = BR x TV.
If HYPOventilation occurs PCO2 rises, pH falls, PO2 falls, but since this reflects on the O2
dissolved in plasma, total blood oxygen doesn’t change very much.
HYPERventilation  PCO2 falls, pH rises, PO2 rises, therefore PCO2, and pH are more
immediately effected by changes in ventilation than PO2.