Thorax- respiration Flashcards
Diaphragmatic hernia
Liver (or other organ) herniated due to a torn diaphragm. Occupying the space where the lungs normally are.
General formation of the pleural and pericardial cavities
- Coelom is divided into right and left by dorsal and ventral mesocardium (future mediastinum)
- Pleuro-pericardial folds (mesoderm) separate lungs (pleural cavity dorsally) and the heart (pericardial cavity ventrally)
- The left and right pleural cavities will extend around pericardial sac
Pleuro-pericardial folds
- Mesoderm
- Separate the lungs (pleural cavity dorsally) and the heart (pericardial cavity ventrally)
Serous membranes
- Serosal fluid surrounds body cavities allowing them to slide around/move freely with body movements
- Flat mesothelial cells with underlying connective tissue
- Lungs= pleural serosal membrane (pleura)
- Heart= Serous pericardium
Muscles of the thoracic wall
- Scalenus
- Serratus ventralis (extrinsic)
- Serratus dorsalis
- Intercostals
- Rectus thoracis
- Transversus thoracis (inside thoracic cage)
- Diaphragm
Muscles of the thoracic wall purpose
Primarily for respiration
- Inspiratory- enlarging the thoracic cavity
- Expiratory- diminish cavity and expel air
Intercostal muscles
Arranged in 3 layers. Function to draw ribs together during respiration
External intercostal muscles- outermost, fibers run caudoventrally from rib to rib. Don’t meet the sternum. They fill the space until the costochondral junctions
Internal intercostal muscles- deeper, fibers run cranio-ventrally. Don’t occupy the most dorsal parts of the space, but they do meet the margin of the sternum.
Subcostal layer- weak, and inconsistent layer
Transversus thoracis
- Triangular sheet that arises from and covers the dorsal surface of the sternum
- Inserts on the costochondral junctions
Rectus thoracis
Placed over the lower ends of the first four ribs
Serratus dorsalis
- Lies over the dorsal parts of the ribs
- Origin from fascia of back and inserts on the ribs
- Plays a role in lifting ribs for inspiration (cranial part) and drawing the last 3 ribs caudally in expiration (caudal part)
Serratus ventralis
- Large, fan shaped muscle
- Origin on the neck, insertion on serrated face of scapula
Scalenus
- Attaches on first rib
- Stabilizes ribs during inspiration
Openings of the diaphragm
- Aortic hiatus
- Esophageal hiatus
- Caval foreman- caudal vena cava
What nerves supply the thoracic wall muscles?
- Diaphragm- supplied by phrenic nerves (somatic)
- Other muscles- supplied by intercostal nerves
Systemic circulation
- Left ventricle feeds into the aorta.
- The aorta branches into the dorsal intercostals, paired (left or right) subclavian, and the brachiocephalic trunk
- Subclavian artery supplies blood to the forelimb and to structures of the neck and cervicothoracic junction.
Branches:
- Axillary artery- To get to limb, it winds around the cranial border of the first rib and enters through the axilla, therefore becoming the axillary artery
- Vertebral artery- Also branches to become the vertebral artery which dives between the scalenus and longus colli muscles passing through the transverse foramina of the 6th to 1st vertebra
- Costo-cervical trunk- supplies the first few dorsal intercostal arteries and the deep cervical artery which ascends the neck
- Internal thoracic artery- curves ventrally within the mediastinum to pass between the transversus thoracic and the sternum. This one continues below the diaphragm into the abdomen
- Superficial cervical artery- the arises near the origin of the internal thoracic. Supplies the muscles of the ventral part of neck, cranial part of shoulder, and the upper arm
- Brachiocephalic trunk branches into the carotids (supply blood to the head) and the right subclavian (same as left on other side of body)
Brachiocephalic trunk
- In species other than the dog and pig, the brachiocephalic trunk is composed of both the left and right subclavian and the carotids.
- In the dog and pig, the left subclavian is separate
Nerves
- Nerve of each intercostal space divide into dorsal and ventral branches when emerging from the intervertebral foramen
– Dorsal branches enter the epaxial muscles, ventral branches descend into the intercostal space along the caudal border of each rib
Ventral branches
Become intercostal nerves which branch into the lateral cutaneous branch and the ventral cutaneous branch
- Lateral: Emerge at regular intervals between skin and supply cutaneous muscle, subcutaneous tissue, and skin
- Ventral: Emerge from deep pectoral after penetrating the ventral ends of intercostal spaces. They are the terminal branches of the intercostal nerves
Dorsal branches
- Enter epaxial muscles
- Medial and lateral branches
Axilla
- Space between the thoracic limb and the thoracic wall
- Bounded by pectoral muscles and the serratus ventralis
Lateral thoracic nerve
Provides motor to the cutaneous trunci
Axillary lymph node
The node where most of the afferent lymph vessels of the thoracic wall drain
Transversus thoracis
A flat muscle on the medial surface of the costal cartilages of ribs 2-8. From the costochondral junctions to the sternum
Diaphragm shape
Trefoil-shaped central tendon
Costa and sternum
2 crura from L1-L3 (right is bigger than the left)
- Tendinous structures that extend below the diaphragm to the vertebral column
Aponeurosis
- A sheet of fibrous tissue that takes the place of a tendon in flat muscles having a wide attachment area
- Eg. Diaphragm
Movement of diaphragm and ribs during inspiration and expiration
- Inspiration: diaphragm moves caudally to expand thoracic cavity, ribs will move forward
- Expiration: diaphragm moves cranially and ribs move caudally
Functional considerations of construction of the thorax
There is a compromise between locomotion and respiration. The advantages of a barrel-shaped chest are mostly sacrificed for the easier movement that is allowed when the scapula is flattened to the body. Also, less rib movement is chosen to give better support to the muscles that pass between the trunk and forelimb
Modes of breathing
- Normal respiration always involves contraction of the diaphragm but the involvement of other muscles is not certain depending on the mode
- 2 modes: diaphragmatic and costal
Diaphragmatic mode/breathing
- Accounts for ~70% of air flow
- Contraction and flattening of the diaphragm
- Caudal displacement of abdominal viscera
- Atmospheric pressure is greater than intra-thoracic pressure
Costal mode/breathing
- Muscle involvement is controversial
- Ribs move like a bucket handle
- Muscle contraction widens and shortens the rib cage
What are the main muscles for inspiration?
- Serratus ventralis
- Serratus dorsalis (cranial)
- Scalenus
- External intercostals
What are the main muscles for expiration?
- Passive recoil of lungs
- Abdominal muscles
- Internal intercostals (dorsal)
- Transversus thoracis
Result of loss of phrenic nerve function
- Resulted in little obvious loss of respiratory function
- Although diaphragm is important in respiration, there are other inspiratory muscles present and abdominal viscera present for respiration if nerve is lost.
Pleural cavities
Two pleura separated by the mediastinum. Pleura is separated into two serosas
- Parietal- covers the cavity wall
Separated into:
- Costal: borders cranial aspect of the pleura
- Diaphragmatic: borders diaphragm
- Mediastinal: borders mediastinum - Visceral/pulmonary pleura- directly covering the lung (organ)
Space between serosas
- Space between the organ and cavity wall
- Area in which pleurocentesis can be done or needle can be inserted to remove pneumothorax
Plica venae cavae
- A special fold of the right pleura which extends between the diaphragm and pericardium and carries the caudal vena cava in its free dorsal border
- Helps define a recess in which the accessory lobe of the right lung can fit
Cupula pleurae
- The point in which the costal and mediastinal serosa come together. May extend in front of the first rib
- Vulnerable to injury
Caudal mediastinum
- Not symmetrical; deflected to the left
- Due to the greater size of the base of the right lung
Species specific strength differences of the mediastinum
Thicker mediastinum allows for a greater pressure difference between pleura and the possibility of tolerating collapse of a lung (eg. Ruminants)
- Much weaker in cat, dog, horse and can rupture easily
- Horse mediastinum often has many small openings that allow both pleura to communicate
Costodiaphragmatic line
Where the lung parietal pleura and the diaphragm pleura meet
- Starts at top of ribs down to the sternum
Costodiaphragmatic recess
- The peripheral part of the diaphragmatic pleura rests against the costal pleura lining the chest wall
- Area of empty space in which the lungs will not reach
- Aiming for this space during thoracocentesis. Don’t listen for lung sounds here.
Line of pleural reflection- cat
Dorsal end at last rib- 13
Costochondral junction- 11
Ventral end- 9
Line of pleural reflection- dog
Dorsal end at last rib- 13
Costochondral junction- 9-11
Ventral end- 8
Line of pleural reflection- equine
Dorsal end at last rib- 17-18
Costochondral junction- 8
Ventral end- 6
Line of pleural reflection- ruminant
Dorsal end at last rib- 13
Costochondral junction- 8
Ventral end- 6
Line of pleural reflection- pig
Dorsal end at last rib- 13-14
Costochondral junction- 8
Ventral end- 5
Thoracocentesis in dog and cat
Done in ventral third of 4th to 7th intercostal space (usually just above the costochondral junction)
Reduction of pneumothorax
Aspiration through the dorsal part of space 7 or 8
Triangular zone of auscultation
- Triangle: line from olecranon to caudal angle of scapula then back to 2nd last rib
**Can’t hear more cranially because of musculature of limb and caudally because of diaphragmatic recess
