Thoracic Cavity, Viscera and VANs

Boundaries of the Thorax (Bones)

Dorsal - Thoracic vertebrae

Laterally - Ribs and costal cartilage

Ventral - Sternum

Thorax Muscles

Diaphragm

Internal/External intercostal muscles

• Fills spaces between ribs

  • Internal intercostal muscle = expiration

  • External intercostal muscle = inspiration

Transversus Thoracis

INSIDE of chest

Muscle of Expiration

Attaches to Sternum

Pulls sternum “in,” making chest cavity smaller

• Chest cavity smaller => Volume smaller/Pressure increase => Expiration

Diaphragm

Main muscle of inspiration

Caudal wall of thoracic cavity (divides thorax/abdomen)

Musculotendinous structure

Diaphragm cranial view (from thorax)

1. Central tendon

2. Costal part

3. Sternal part

4. Right crus- more developed

5. Left crus

6. Caval Foramen

7. Esophageal hiatus

8. Aortic hiatus

Diaphragm caudal view (from abdomen)

1. Central tendon

2. Costal part

3. Sternal part

4. Right crus- more developed

5. Left crus

6. Caval Foramen

7. Esophageal hiatus

8. Aortic hiatus

Serous membranes

every organ is surrounded by a serous membrane

inner wall = visceral

outer wall = parietal

Cavity

space between the visceral and parietal pleura

Pleura

Serous membrane for lungs

Pleural cavity

space between visceral/parietal pleura

Visceral pleura

directly on lungs

Parietal pleura

outer wall

Mediastinum

space between right/left pleural cavities

Pleural cavities

Left/right pleural cavities

Mediastinum between them

• contains heart, esophagus, trachea

Plica vena cava

on right sight surrounding caudal vena cava

Mediastinal recess

between plica vena cava and right mediastinal pleura

*contains accessory lobe of right lung

Regions of Pleura

1. Costal pleura

2. Mediastinal pleura

3. Diaphragmatic pleura

4. Visceral pleura

5. Pleural cupula

6. Costodiaphragmatic recess

   *pleural taps/thoracocentesis

Endothoracic fascia

“Glue” that holds parietal pleura to the throracic wall

Lungs

Heart on left side of chest, more room for lungs on right side

Right lung

4 lobes

Cranial, middle, caudal, and accessory lobes

Left lung

2 lobes

Cranial, caudal

Costal surface

touch ribs

Diaphragmatic surface

touch diaphragm

Basal margin

border of the base of the lungs

Hilus

where everything goes into the lungs

Bronchi

Pulmonary artery

Pulmonary veins

“Root of lung”

Pulmonary artery

carries deoxygenated blood

supplies lungs with blood

Pulmonary veins

carries oxygenated blood

drains lungs

Lung lung lobation

Cranial lobe

• cranial and caudal parts

Caudal lobe

Right lung lobation

Cranial lobe

Middle lobe

Caudal lobe

Accessory lobe (in mediastinal recess)

*right cardiac notch

Right cardiac notch

4th intercostal space (between ribs 4 and 5), between cranial and middle lobes

access to heart

Medial view of right lung

Accessory lobe: in mediastinal recess

has a groove for the caudal vena cava

Trachea

In mediastinum divides into two principal/main bronchi

Bronchi

Principal bronchi → Lobalar bronchi → Segmental bronchi, conducting air to lungs

Carina

where trachea branches into principal bronchi

Brochoesophageal artery

supplies bronchial tree

• actual nutritional blood that the lungs need

Tracheobronchial lymph nodes

lymph nodes associated with trachea and bronchi

Major Thoracic arteries

Aortic arch

• Brachiocephalic trunk

  • L/R common carotid aa

  • Right subclavian a

• Left subclavian

• Descending aorta

Left subclavian

own branch off of brachiocephalic trunk

Descending aorta

continuation of aortic arch to abdomen

Subclavian arteries (L/R)

R/L Subclavian aa. have identical branches but come off aortic arch differently

4 branches:

Costocervical trunk

Vertebral a

Superficial cervical a

Internal thoracic a.

Costocervical trunk

Supplies dorsal intercostal spaces 1-3, muscles of neck

Supplies ribs and neck

Vertebral a

shoots up neck through transverse vertebral foramina

Supplies brain and spinal corf

Vertebral a goes through vertebrae

Superficial cervical a

Supplies superficial structures of neck

Internal thoracic

Most important branch of subclavian a

Runs down to diaphragm

-Gives off: Ventral intercostal aa

-Musculophrenic a- to diaphragm

-Continues as cranial epigastric a

Branches off as the superficial cervical a

Veins of the thorax

Right azygos v

Caudal vena cava

Cranial vena cava

Right azygos v

drains thorax

in dogs, only have a right azygos

Ox has right and left azygos

Drains the coastal walls, the bronchial tree, and the esophagus

Caudal vena cava

drains caudal to thorax

drains pelvic limb, abdomen

Cranial vena cava

drains cranial to thorax

Drains head, thoracic limb

Thoracic duct

The largest lymphatic vessel in the body

Originates in the cisterna chyli in the abdomen

*Drains into the L brachiocephalic v, which drains into the cranial vena cava

Often see with right azygos v

Central Nervous System

Brain and Spinal cord

Brain: white matter central, gray matter out

Spinal cord: gray matter central, white matter outer

Integrating issuing commands

Peripheral Nervous System

Nerves and Ganglia

Sensory, motor output from CNS

Sensory

Afferent nerves, take impulse to CNS

Motor

Efferent nerves, take impulse away from CNS

Mixed Nerves

nerves seen carrying both sensory and motor fibers.

Spinal Nerves

Come from spinal cord/vertebrae

All spinal nerves are mixed

Motor/Efferent Nerves

Either visceral or somatic

somatic to voluntary skeletal/ striated muscle

• 1 neuron system

Visceral (Autonomic Nervous System)

• involuntary

• 2-neuron system

  • 1 in CNS and 1 in peripheral ganglion

Autonomic Nervous System/ Visceral Motor Nerves

2 divisions:

Parasympathetic and Sympathetic

Parasympathetic

Craniosacral system

• Nerves from cranial/sacral spinal cord

Sympathetic

Thoracolumbar system

• Nerves from thorax/lumbar spinal cord

Spinal Cord

Dorsal Root- Sensory

• Dorsal root ganglion (synapse)

Ventral Root- Motor

• No ganglion

Spinal Nerves

Mixed nerves: Motor and Sensory

Branches into: Dorsal ramus, Ventral ramus, communicating branch

Dorsal Ramus

to epaxial structures

Ventral ramus

to all other structures

Communicating branch

sympathetic trunk

Cervical Spinal Nerves

8 cervical nerves

CN1: comes out of lateral vertebral foramen of Atlas

CN2 out intervertebral foramen between Atlas/Axis

CN3 between Axis/C3

CN8 between C7/T1

*Vertebrae after nerve

Phrenic Nerve

Made from ventral branches of C5, C6, C7

Somatic motor and sensory to diaphragm

Left phrenic n crosses the heart

Thoracic/Lumbar Numbering

Different from Cervical

Nerve after vertebrae

TN1 between T1/T2

TN13 between T13/L1

Thoracic Nerves

Intercostal nerves

• located directly caudal to ribs

• run with intercostal arteries/veins

T13 - costoabdominal n

• makes sense - last nerve between ribs (costo) and abdomen

Lumbar Nerves

Innervate abdominal walls:

a. T13: Costoabdominal n

b. L1: Crainal iliohypogastric n

c. L2: Caudal iliohypogastric n

d. L3: Ilioinguinal n

e. L4: Lateral cutaneous femoral n.

Nerves on transversus abdominis

Sacral Nerves

S1 and S2: No intervertebral foramina (fused)

• Dorsal branches out of dorsal sacral foramina

• Ventral branches out of pelvic sacral foramina

S3 through intervertebral formina between sacrum and Cd1