Anatomy of the Digestive system

- Pharynx and Esophagus

Associate Professor Dr Farid Bin Ghazali

School of Health Sciences

Embryology

Components of

branchial/pharyngeal

apparatus:

1) Pharyngeal arches

2) Pharyngeal pouches

3) Pharyngeal

clefts/grooves

Pharyngeal (branchial) arches

Derived from neural crest cells

Resemble fish gills (branchia)

Begin to develop early in the 4th week

By end of 4th week, four pairs of arches are

visible on the surface (not 5th and 6th ) and a

buccopharyngeal membrane ruptures forming

communication between primitive oral cavity and

foregut

Pharyngeal arches (cont.)

Contribute to the

formation of the neck as

well as the face.

Visible structures at 42

weeks:

1st arch: mandibular

prominence, maxillary

prominences, and the

frontonasal prominence

Pharyngeal arches (cont.)

Core of mesenchymal tissue covered by surface ectoderm (outside) and by endodermal epithelium (inside)

Ectoderm -> skeletal

Mesoderm -> muscles with accompanying nerve

Arterial component (aortic arches)

Therefore, each arch carries nerve, muscle, bone and blood supply

First pharyngeal arch

Maxillary process (dorsal)

Premaxilla, maxilla, zygomatic bone, portion

of temporal bone

Mandibular process (ventral)

Contains Meckel’s cartilage which disappears

except for dorsal end (incus & malleus) and

mandible

First pharyngeal arch

Muscles of mastication, digastric (ant belly), mylohyoid, tensor tympani and tensor palatini

Therefore, the accompanying motor nerve is the mandibular branch of trigeminal (V2) and sensory are V1, V2, and V3

1st aortic arch practically disappears but forms the maxillary artery

Second pharyngeal arch

Reichert’s cartilage – stapes, styloid process,

stylohyoid ligament, lesser horn and upper part

of the hyoid

Muscles include: stapedius, stylohyoid, digastric

(post belly), auricular, and those of facial

expression

Facial nerve (CN VII)

2nd aortic arch – stapedial & hyoid arteries

Third pharyngeal arch

Cartilaginous contributions include greater horn

and lower part of hyoid

Sole muscle: stylopharyngeus

CN IX (Glossopharyngeal nerve)

3rd aortic arch (quite large): common carotid, 1st

portion of internal carotid (remainder dorsal

aorta), and external carotid

Fourth & sixth pharyngeal arch

Cartilaginous contributions to larynx derived from fusion: thyroid, cricoid, arytenoid, corniculate, and cuneiform

Muscles of 4th: cricothyroid, levator palatini, and pharyngeal constrictors are innervated by SLN (CN X)

Muscles of 6th: intrinsics of larynx are innervated by RLN (CN X)

4th aortic arch: L->arch of aorta & R->subclavian

6th aortic arch: L & R pulmonary with ductus arteriosus on left

Pharyngeal pouches (5)

1st:tubotympanic recess-> middle ear & eustacian tube -> TM

2nd palatine tonsil/fossa

3rd: inferior parathyroid (dorsal), thymus (ventral)

4th: superior parathyroid

5th: ultimobranchial body -> calcitonin producing C cells (parafollicular)

Pharyngeal clefts/grooves (4)

1st: external auditory

meatus

2nd-4th : epicardial

ridge and cervical

sinus (disappears)

The pharynx is that part of the digestive tube which is placed behind the

nasal cavities, mouth, and larynx. It is a musculomembranous tube,

somewhat conical in form, with the base upward, and the apex downward,

extending from the under surface of the skull to the level of the cricoid

cartilage in front, and that of the sixth cervical vertebra behind.

It is limited, superiorly above, by the body of the sphenoid and basilar part of

the occipital bone; inferiorly (below), it is continuous with the esophagus;

posteriorly, it is connected by loose areolar tissue with the cervical portion of

the vertebral column, and the prevertebral fascia covering the Longus colli

and Longus capitis muscles; anteriorly, it is incomplete, and is attached in

succession to the medial pterygoid plate, pterygomandibular raphé, mandible,

tongue, hyoid bone, and thyroid and cricoid cartilages; laterally, it is

connected to the styloid processes and their muscles, and is in contact with

the common and internal carotid arteries, the internal jugular veins, the

glossopharyngeal and vagus.

The Pharynx

Anatomy of the pharynx

Anatomy (cont.)

Extends from base of skull to inferior

border of cricoid cartilage anteriorly and

inferior border of C6 posteriorly

Widest portion (5cm) at hyoid

Narrowest portion (1.5cm) at caudal end

Divided into 3 parts: nasopharynx,

oropharynx, and laryngo(hypo)pharynx

Nasopharynx

Respiratory function

Anterior: choana (posterior nasal aperture)

Posterior: pharyngobasilar membrane and

superior constrictor muscle

Superior: basilar portion of occipital bone

Inferior: soft palate

Oropharynx

Digestive function

Anterior: anterior tonsillar pillar

Posterior: superior constrictor

Superior: soft palate

Inferior: base of tongue, superior epiglottis

Laterally: palatoglossal and palatopharyngeal arches

Hypopharynx

Lies posterior to the larynx

Superior: superior border of epiglottis and pharyngoepiglottic folds

Inferior: inferior border of the cricoid

Posterior/lateral: middle & inferior constrictors, bodies of C4-C6

Anterior: laryngeal inlet

Pharyngeal muscles

Pharyngeal muscles

External circular and internal longitudinal (opposite in remainder of GI tract)

External: 3 constrictors (CN XI via X and ELN/RLN for middle and inferior) function to constrict wall of pharynx during swallow

Internal: palatopharyngeus and salpingopharyngeus (CN XI via X) and stylopharyngeus (CN IX) act to elevate pharynx and larynx during speech/swallow

Pharyngeal muscles

Tensor veli palatini (V3) tenses soft palate

& opens Eustachian Tube during

yawn/swallow

Levator veli palatini (CN XI via X) elevates

palate during swallow/yawn

Palatoglossus (CN XI via X) approximates

tongue and soft palate

Pharyngeal muscles

Pharyngeal lymphatic drainage

Oral cavity

I, II, III

Oro/hypopharynx

deep II, III, IV

Nasopharynx

II, V, III

BLOOD SUPPLY TO PHARYNX:

Mostly from External Carotid Artery

1. Ascending Pharyngeal Artery directly off the External Carotid.

2. Maxillary ------> Descending Palatine Artery

3. Facial Artery branches:

Ascending Palatine Artery

Tonsillar Branch going to tonsils

4. Lingual Arteries and Ascending Pharyngeal arteries -- minor

contributions.

Pharyngeal vessels

Afferent innervation of pharynx

EUSTACHIAN TUBES: They equilibrate pressure between the middle ear and atmosphere, via the

throat.

1.Openings of the eustachian tubes are found in the Nasopharynx, at the posterolateral aspect.

2.Torus Tubarius: The tissue surrounding the eustachian tube.

TONSILS: WALDEYER'S RIM -- a "ring" of tonsils surrounding the naso and oropharynx.

1.Pharyngeal Tonsil -- Single lymph "node" on posterior of nasopharynx. It samples antigens breathed

in through the air and triggers an immune response.

ADENOID TONSILS: When enlarged or inflamed, it is termed an adenoid tonsil.

2.Palatine Tonsil -- between the palatoglossal and palatopharyngeal arches, on the posterior of the roof of

the mouth.

3.Lingual Tonsil -- on posterior third of tongue

4.Tubular Tonsil: Tonsils near the opening of the Eustachian tubes.

INFLAMED TONSILS: Glossopharyngeal Nerve can pick up referred pain from inflamed tonsils and

send the sensory pain to the middle ear.

DEEP CERVICAL LYMPH NODES: All tonsils of Waldeyer's Rim drain into deep cervical lymph nodes.

ARCHES: The palatine tonsil is located between the two arches.

1.Palatoglossal Arch: More anterior and more visible.

2.Palatopharyngeal Arch: More posterior.

Topography and constriction

of esophagus

Pharyngoesophag

eal junction

General structure of the digestive tract

A hallow tube with a lumen whose diameter varies

Surrounded by a wall made up of 4 principle layers

Mucosa layer / Mucous membrane

Contained epithelial layer and lamina propria

Submucosa layer

Composed of dense connective tissues, Blood vessels and lymph vessels and

Meissner's nerve plexus

Muscularis layer

Thin inner circular layer smooth muscle cells

Myenteric or Auerbach’s nerve plexus

Outer longitudinal layer smooth muscle cells

Serosa / Adventitia layer

Thin layer of loose connective tissue, rich in blood vessels and a simple squamous

covering epithelium (mesothelium)

The esophagus or gullet is a muscular canal, about 23 to 25 cm. long,

extending from the pharynx to the stomach.

It begins in the neck at the lower border of the cricoid cartilage, opposite the

sixth cervical vertebra, descends along the front of the vertebral column,

through the superior and posterior mediastinum, passes through the

diaphragm, and, entering the abdomen, ends at the cardiac orifice of the

stomach, opposite the eleventh thoracic vertebra.

The general direction of the esophagus is vertical; but it presents two slight

curves in its course. At its commencement it is placed in the middle line; but

it inclines to the left side as far as the root of the neck, gradually passes to

the middle line again at the level of the fifth thoracic vertebra, and finally

deviates to the left as it passes forward to the esophageal hiatus in the

diaphragm.

The esophagus also presents antero-posterior flexures corresponding to the

curvatures of the cervical and thoracic portions of the vertebral column. It is

the narrowest part of the digestive tube, and is most contracted at its

commencement, and at the point where it passes through the diaphragm.

Musculature Histology

Has an internal circular and external

longitudinal layer of muscle.

In the superior third, the external

layer is skeletal muscle.

The inferior third is composed

of smooth muscle.

The middle third is made up of

both types of muscle.

Blood supply of the Esophagus

– branches of the left gastric artery and the inferiorphrenic artery

• cervical part

– inferior thyroid branch of the thyrocervical trunk

• thoracic part

– branches of the descending aorta, bronchial arteries

• abdominal part

Nerve supply of the Esophagus

Nerve supply

• Cervical part

– parasympathetic - the recurrent laryngeal nerves

– sympathetic - the cervical sympathetic trunks

via the plexus around the inferior thyroid artery

• Thoracic part

– parasympathetic - vagus nerve via oesophageal plexus

– sympathetic - sympathetic trunk via greater splanchnic nerves

• Abdominal part

– parasympathetic - vagus nerve via anterior and posterior gastric nerves

– sympathetic - thoracic sympathetic trunk via greater and sometimes

Connects pharynx & stomach

Represents a transition

1.

2. Muscularis mucosae replaces elastic layer of pharynx

3. Muscularis – more regular

Tunica adventitia

Tunica muscularis (longitudinal)

Tunica musclularis (circular)

Submucosa

Muscularis mucosae

Lamina propria

Stratified Squamous Epithelium

Ske

leta

l m

usc

le

(Smooth muscle)

Esophagus – upper portion

Esophagus - high

Muscularis mucosae - smooth muscle

Submucosa – lax, elastic; 7 – 10 longitudinal folds; deep esophageal glands

Muscularis – 2 layers: inner = circular, outer = longitudinal; upper ¼ = skeletal, not regular; middle = mix skeletal/smooth; lower third = smooth (extent variable)

Epithelium – stratified squamous (25 cell layers – tall papillae indent lower surface

Lamina propria - – areolar C.T. – poor elasticity; superficial glands (extreme upper & lower ends - mucous – compound tubular)

Adventitia – loose, fibrous; blood vessels & nerves

Normally have four constrictions

1. At its beginning, 15 cm from the

incisor teeth caused by the

cricopharyngeus muscle (upper

esophageal sphincter).

2.Where it is crossed by the arch of

aorta, 22.5cm from the incisor teeth.

3.Where it is crossed by the left main

bronchus, 27.5 cm from the incisor

teeth.

4. Where it is passes through the

diaphragm, approximately 40 cm from

the incisor teeth.