Thoracic Wall & Topographical Features Practical Flashcards
How many ribs does a dog have and how does this relate to the number of thoracic vertebrae present?
13 – same number of ribs as thoracic vertebrae
How many ribs does a horse, cow and cat have and how does this relate to the number of thoracic vertebrae present?
18, 13, 13 – same number as thoracic vertebrae
Why is the distal end of each rib cartilage and not bone?
To allow flexibility so the ribcage can expand and contract during respiration
Which structure attaches around the costal arch?
Diaphragm
How many intercostal spaces are there in the dog? What occupies these spaces in life?
- Intercostal muscles.
What important structures pass through the thoracic inlet in life?
Oespohagus, trachea, major blood vessels
What are the functions of the thoracic wall?
Respiration, protection & support of thoracic structures, muscle attachment
Does every pair of ribs have an intercapital ligament?
No – present ribs 1-10 only.
Which other ligament is the intercapital ligament very closely associated with?
Closely associated with the dorsal longitudinal ligament of the vertebral column.
Which vertebra(e ) does rib 5 articulate with?
Body articulates with body of T4 and T5 and tuberculum articulates with T5
Which vertebra(e ) does rib 11 articulate with?
T11 only
What is the function of the latissimus dorsi muscle and where does it get its nerve supply from?
Forelimb retractor and shoulder flexor. Nerve supply from brachial plexus
What is the main function of the pectoral muscles and where do they get their nerve supply from?
Forelimb adductor. Nerve supply from brachial plexus
What is the function of the external abdominal oblique muscle in relation to the thorax? Briefly explain the mechanism that results in this. By looking at an animal, how would you be able to tell that the external abdominal muscle was functioning in this way?
Accessory expirator muscle. Contraction results in the ribcage being pulled in a caudo-ventral direction which compresses the thoracic cavity / reduces the intrathoracic volume therefore helps force air from the lungs.
Increased movement of the abdominal wall / increased abdominal effort during respiration / heaving flanks
What is the function of the serratus ventralis muscle in relation to the thorax? Briefly explain the mechanism that results in this. By looking at an animal, how would you be able to tell that the serratus ventralis muscle was functioning in this way?
Accessory inspirator muscle. Contraction results in the ribcage being pulled in a cranio-dorsal direction which expands the thoracic cavity / increases the intrathoracic volume therefore helps draw air into the lungs.
Elbows slightly abducted to allow muscle to function in this way
What other functions does the serratus ventralis muscle fulfil?
Support of the trunk between the forelimbs (part of stay apparatus in horse)
Forelimb protractor and retractor
Lateral flexion of the neck region
What is the function of the intercostal muscles?
Link the movement of each rib to its neighbour so the ribcage functions as a single unit during inspiration and expiration
What are the main functions of the abdominal wall?
Support and protection of the abdominal contents; Abdominal press ; Movement of the trunk ;
Expiration
How would you describe the fibre direction of each of these muscles?
EAO – caudoventral ; IAO – cranioventral ; TA – dorsoventral ; RA - craniocaudal
What structures form the inguinal canal and where are they located ?
Superficial inguinal ring – slit in caudoventral region of aponeurosis of external abdominal oblique muscle
Deep inguinal ring – opening at caudoventral aspect of aponeurosis of internal abdominal oblique muscle
How does the sex of the animal influence what structures run through the inguinal opening?
Both sexes - External pudendal artery and vein; Genitofemoral nerve
Bitch – vaginal process
Dog – cremaster muscle, testicular artery and vein, spermatic cord
What are the cranial and caudal attachments of the linea alba?
Cranial attachment – sternum (last sternebra = xiphoid)
Caudal attachment –pelvis (pubic bone)
What are the layers that you would incise down through when making a surgical incision through the lateral aspect of the thoracic wall?
Skin, Cutaneous trunci muscle, superficial fascia & fat, muscle surrounded by deep fascia (which muscles depends on where incision is being made), intercostal muscles, pleura
Where is relation to the ribs would you make your incision and why?
Down the middle of the intercostal space to avoid the blood and nerve supply that run down the caudal and then both aspects of the ribs
What are the layers that you would incise down through when making a surgical incision through the ventral aspect of the abdominal wall? Which species would you routinely employ this approach with
Skin, superficial fascia & fat, (tunica flava abdominus – horse), linea alba, peritoneum.
Dogs, horses, cats
What are the layers that you would incise down through when making a surgical incision through the lateral aspect of the abdominal wall?
Skin, superficial fascia & fat, (tunica flava abdominus – cow), muscle surrounded by deep fascia (external abdominal oblique, internal abdominal oblique, transverse abdominis) , peritoneum
Cows and cats
Which specific rib has been labelled?
3rd rib
Which specific intercostal space has been labelled?
7th intercostal space
Cartilage should not be well visualised on radiographs yet some of the costal cartilages are visible on this radiograph – why do you think this is the case? Is this normal in dogs?
The costal cartilages become increasingly mineralised as the dog ages and therefore become visible on radiographs – this is therefore a normal finding
What structures form the thoracic inlet?
T1, 1st pair of ribs+ manubrium
Which ribs contribute to the costal arch in the dog? Where do the other ribs attach?
T10-12 form costal arch. T1-9 attach to sternum. T13 is ‘floating’
How is the mediastinum formed?
Reflection of the visceral pleura and endothoracic fascia from each side at the midline
What structure would normally occupy the mediastinal recess?
The accessory lobe of the right lung
By referring to the demonstration list the structures which lie out with the mediastinum
The lungs and the caudal vena cava (and accompanying right phrenic nerve!)
What structures are found within the plica vena cavae?
The caudal vena cava and the right phrenic nerve travel within this pleural fold
What is the functional relevance of pleural recesses?
These recesses represent the spaces into which the apex, base and ventral borders of the lung move into during inspiration
what are the 3 plueral recesses
- costomediastinal recess
- costodiaphragmatic recess
- cupulae
Name the serous membrane which covers a) the cranial and b) caudal surfaces of the diaphragm.
Cranial= pleural membrane; caudal surface= peritoneum
Explain where the aortic hiatus is located in relation to lumbar attachments of the diaphragm and to the oesophageal hiatus and caval foramen.
Aortic hiatus is between the right and left crus, and dorsal to the oesophageal hiatus which is positioned approximately in the midline within the right crus. The caval foramen is to the right of the midline in the tendinous centre.
List the structures which pass through each of the different openings in the diaphragm.
Azygous vein and aorta
Phrenic nerve and caudal vena cava
Oesophagus
What is the clinical significance of the Costodiaphragmatic line of pleural reflection?
This is the most caudal extent of the thoracic cavity. Caudal to this line is the abdominal cavity. This line therefore has surgical implications
Which major organ do the left and right phrenic nerves innervate?
The diaphragm
identify the structures within the mediastinum
identify 1-6
- latissimus dorsi muscle
- pectoral muscle
- serratus ventralis muscle
- external intercostal muscle
- internal intercostal muscle
- external abdominal oblique muscle
identify structures 6-11
- external abdominal oblique
- internal abdominal oblique
- transversus abdominus muscle
- rectus abdominis
- linea alba
- inguinal canal
what are the layers in the body wall
skin
- cutaneous trunci muscle
- superficial fascia
- deep fascia and muscle
- ribcage and intercostal muscles
thorax 5. pleura
abdomen 6. peritoneum
identify structures 1-11
- thoracic vertebrae
- rib
- costochondral junction
- costal cartilage
- intercostal space
- sternum/sternebrae
- 1st sternebrae = manubrium
- thoracic inlet
- costal arch
- diaphragm
what is going on in this dog
all of the soft tissue structures outside the thorax are mottled and streaked with black indicating the presence of gas in the body wall = subcutaneous emphysema
occurs when gas is introduced into body wall
it follows the path of least resistance and so tracks along the fascial planes
localized accumulation can occur if air is introduced through a bite or a with a foreign body but such extensive cases are rare and usually associated with being introduced from a rupture somewhere in the resp system
in this case the dog had a ruptured trachea which was forcing air into adjacent soft tissue and it was moving along fascial planes
once the rupture was repaired the dog recovered
what is occuring here
numerous soft tissue opacities with fluffy nodular pattern throughout the entire lungfield
when air within alveoli is replaced by either fluid or cells then the lungs are no longer radiolucent but become radio-opaque and produce the same opacity as soft tissue/fluid
the intervening air filled areas of the lung remain radiolucent which is why the lung field in this case contains a mix of light and dark areas
since the nodules in the lungs are the same opacity as the heart it is impossible to distinguish between the two which is why the heart appears to be obscured
metastatic tumour spread
what are the structures
- thoracic inleft
- thymus within cranial mediastinum
- pericardial sac which lies within the middle mediastinum
- caudal mediastinum (diverting to left)
- plica vena cava
- transversus thoracic muscle (lies on medial surface of ribs on ventral 1/3 of the thorax)
- mediastinal recess is formed between plica and caudal mediastinum
what are the lobes of the lung
what are the structures of the thoracic cavity
which of these sections (14,15,16 and 17 - cranial view) is represented of the a) cranial mediastinum b) middle c) caudal
14= cranial mediastinum
15 + 16= middle mediastinum
17 = caudal mediastinum
what structures are not found in the mediastinum
- lungs
- caudal vena cava
- right phrenic nerve
what does the cranial mediastinum contain (8)
- thoracic part of the longus colli muscles pass cranially through the cranial thoracic aperture
- thoracic part of esophagus lies to left of trachea prior to assuming a dorsal relation toward the tracheal bifurcation
- thoracic part of trachea terminating at its bifurcation
- large vessles brachiocephalic trunk and cranial vena cava supplying and draining the lateral thoracic wall, forelimbs, neck and head
- nerves: sympathetic trunks, vagus nerves, phrenic nerves, recurrent laryngeal nerves
- cranial mediastinal lymph nodes
- termination of thoracic lymph duct
- varying amounts of thymus gland (age + species)
what are the structures of the cranial mediastinum
what are the structures that are in the ventral part of the middle mediastinum
- heart
- pericardium
what are the components in the dorsal middle mediastinum (7)
- esophagus lying dorsal to trachea and crossing right side of aortic arch. termination of trachea in its bifurcation dorsal to base of heart
- pulmonary vessels associated with lungs
- aortic arch
- thoracic duct
- azygous vein
- middle mediastinal and bronchial lymph nodes
- vagus and phrenic nerves
what are the structures shown
what are the components of the caudal mediastinum
- aorta assuming dorsal position
- esophagus
- dorsal and ventral vagal trunks
- caudal mediastinal lymph nodes (one large node in the ruminant adjacent to esophagus, swelling may cause obstruction)
- left phrenic nerve (right phrenic nerve runs in the plica vena cava)
why is the caudal and cranial mediastinum displaced to the left
large volume of the apex of the cranial lobe of the right lung
what are the pleural recesses
- costomediastinal recess: The parietal pleura covering the costal surfaces and mediastinum
- Costodiaphragmatic recess: The parietal pleura covering the diaphragm and costal surfaces
- cupulae: The costal pleura reflects onto the Mediastinal pleura at the thoracic inlet
what are the pleural recesses
- costomediastinal recess: The parietal pleura covering the costal surfaces and mediastinum
- Costodiaphragmatic recess: The parietal pleura covering the diaphragm and costal surfaces
- cupulae: The costal pleura reflects onto the Mediastinal pleura at the thoracic inlet
what are the pleural recesses
- costomediastinal recess: The parietal pleura covering the costal surfaces and mediastinum
- Costodiaphragmatic recess: The parietal pleura covering the diaphragm and costal surfaces
- cupulae: The costal pleura reflects onto the Mediastinal pleura at the thoracic inlet
what are the attachments of the diaphragm in the cat
1=left crura of diaphragm attaching to lumbar vertebrae via the ventral longitudinal lig.
2 =attachment of the xiphoid cartilage to the diaphragm
What does 3 represent? Caudal vena cava
what is on the thoracic surface of the diaphragm
endothoracic fascia
pleural membranes (diaphragmatic pleura)
what is on the abdominal surface of the diaphragm
pericardium
liver predominantely on the right side
stomach on the left side (reticulum in ruminants)
intestine, spleen, pancrease, kidneys and adrenals
where do the sympathetic trunks and splanchnic nerves pass between on the diaphragm
left and right crura and psoas muscles on each side
what are the openings in the diaphragm (3)
- aortic hiatus: between the two crura ventral to the last thoracic vertebra (contains aorta, azygous vein and thoracic duct)
- esophageal hiatus: perforates the right crura near its junction with tendinous centre (contains esophagus, vagus –> dorsal and ventral branches)
- foramen vena cava: pierces the tendinous centre to the right of midline (contains the vena cava which is firmly attached to margin of the opening)
name the structures of the diaphragm
identify the structures/organs/recesses
1.
identify the structures
identify the structures
A. thymus
B. heart
C. aorta
D. esophagus
E. diaphragm
F. phrenic nerve
G. accessory lobe of the right lung (separated from other lobes of the right lung by the caudal vena cava and plica vena cava)
what is the large vessel in the right thorax labelled A and the pleural fold attached to it a?
A. caudal vena cava
a. plica vena cava (fold of pleura that connects the caudal vena cava to the mediastinum)
what is the cardiac notch
corresponds to where the heart is in direct contact with the thoracic body wall. The cardiac notch is usually larger on the left hand side due to the larger size of the right lung but in the dog the cardiac notch on the left hand side is limited to being between the two parts of the cranial lobe of the left lung. On the right hand side the cardiac notch is larger but is still restricted and lies between the cranial and middle lobes of the right lung.
identify the lobes of the right lung
A = cranial caudal
B = caudal
C = position of aorta leaving the middle of the base of the heart
D = pulmonary artery (entering the caudal lobe of the left lung)
F = venous return from the lungs enters the left atrium of heart
identify 1, 2, 3
- caudal vena cava burrows between the caudal and
- accessory lobe within the plica vena cava
- right phrenic nerve can be seen to accompany the caudal vena cava within the plica
identify the structures
A branch of the left pulmonary artery (D) is shown entering the caudal lobe of the left lung. The vessels labelled F represents where the venous return from the lungs enters the left atrium of the heart. From here the blood will enter the systemic circulation via the left ventricle and aorta.
structures of the thoracic cavity
