Digestive System Development

Development of the Digestive System

• The digestive system develops from the endoderm.
• The primitive gut is divided into three parts: cephalic, middle, and caudal.

Cephalic (Foregut)

• Contains:
  • Oral cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Proximal part of the duodenum
  • Spleen
  • Pancreas
  • Gall bladder
  • Liver

Middle (Midgut)

• Contains:
  • Distal part of the duodenum
  • Jejunum
  • Ileum
  • Cecum with the vermiform appendix
  • Ascending colon
  • Two-thirds of the transverse colon

Caudal (Hindgut)

• Contains:
  • Last one-third of the transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum
• The stomach develops during the 4th week of gestation.
• The pancreas develops in the 4th month.
• The duodenum develops in the 4th month.
• The liver develops in the 3rd week.
• The esophagus develops in the 5th week.
• The midgut develops during the 5th to 12th week of gestation.
• After the 12th week, the hindgut begins to develop.
• The stomach is intraperitoneal.
• The duodenum has superior, horizontal, ascending, and descending parts, and is retroperitoneal.
• The jejunum is intraperitoneal.
• The ileum is intraperitoneal.
• The cecum is intraperitoneal.
• The vermiform appendix is intraperitoneal.
• The ascending colon is mesoperitoneal.
• The descending colon is intraperitoneal.
• The transverse colon is intraperitoneal.
• The sigmoid colon is intraperitoneal.
• The superior one-third of the rectum is intraperitoneal.
• The middle one-third of the rectum is mesoperitoneal.
• The inferior one-third of the rectum is retroperitoneal.
• The liver is intraperitoneal.
• The pancreas is retroperitoneal.

The Mouth

• The lips are formed by the orbicularis oris muscle.
• The lips are bounded superiorly by skin and inferiorly by the mucous membrane.
• The upper and lower lips connect at the sides through the labial commissure.
• The skin of the lip is continuous with the mucous membrane to the surface of the gums, forming the frenulum of the upper and lower lip.
• The oral cavity is found behind the teeth.
• The hard palate is superior to the oral cavity, and the tongue is interior.
• The mucosa of the tongue extends to the inferior surface of the tip of the tongue and forms the frenulum of the tongue on the midline.
• The oral vestibule is the space bounded externally by the lips and cheeks, and internally by the teeth and gums.
• The oral vestibule opens into the external environment through the oral fissure.
• The hard palate is formed by the palatine process of the maxilla and the horizontal plate of the palatine bone.
• The anterior part of the soft palate is attached to the posterior end of the hard palate.
• The parietal part of the soft palate hangs down freely.
• The midline of the soft palate has an elevation called the uvula.
• The axillary, facial, and lingual arteries, as well as the ascending pharyngeal artery, supply blood to the mouth. All of these are branches of the external carotid artery.
• The pharyngeal plexus provides nerve supply to the mouth.
  • Cranial nerves 5, 7, 9, and 10 are involved.

The Teeth

• Humans have two sets of teeth in their lifetime: deciduous and permanent.
• Each tooth is made up of three parts: crown, neck, and root.
  • The crown is above the alveolus.
  • The neck is for the attachment of the gingivae or gums.
  • The root is located inside the alveolus.
• Tooth development begins on the 7th week of embryonic life.
• The deciduous teeth consist of incisors, canines, and molars.
• The permanent teeth consist of incisors, canines, premolars, and molars.
• I = Incisors
• C = Canine
• P = Premolar
• M = Molar
• The deciduous dental formula is 2, 1, 0, 2 = 20.
• The permanent dental formula is 2, 1, 2, 3 = 32.
• Deciduous teeth eruption starts at 6-8 months.
• The first tooth to erupt is the central or lateral incisor.
• By the age of 1 year, a baby has a set of 8 incisors.
• After 1 year, the first molar, then canine, and then 2nd molar appear.
• All sets of 20 deciduous teeth appear at 2 years of life.

Eruption Time of Permanent Teeth

• The 1st permanent molar erupts at 6 years.
• The 1st premolar erupts at 9 years, and the 2nd premolar erupts at 10 years.
• The canine erupts at 11 years.
• The 2nd molar erupts at 13-16 years, and the 3rd molar erupts at 18-30 years.
• The superior and inferior alveolar arteries supply blood and originate from the maxillary artery of the external carotid artery.
• The superior and inferior alveolar nerves provide nerve supply.

The Tongue

• The tongue's development begins at the 4th week of embryonic life.
• The tongue consists of two parts: the base, which has the apex, and the root.
• Between the body and root is a U-shaped sulcus called the terminal sulcus.
• On the midline of the body is the median sulcus.
• The tongue develops in three parts: the single root and two halves of the body.
• At the junction of the anterior and posterior parts of the tongue on the midline is the foramen cecum, resulting from thyroid gland development.
• The root has lingual tonsils.
• The dorsal surface of the body has many projections of mucosa called papillae.
• Foliate papillae are located on the margin of the tongue.
• Filiform papillae are the smallest and located on the superior surface of the anterior part of the tongue.
• Fungiform papillae are fewer in number and located on the dorsal surface of the tongue.
• Vallate papillae are the largest, located in front of the foramen cecum and terminal sulcus. There are 7-12.
• The lingual artery provides the blood supply to the tongue.
• The glossopharyngeal nerve, chorda tympani of the facial nerve, and hypoglossal nerve provides the nerve supply.
• The regional lymph nodes include:
  • Submandibular
  • Submental
  • Superior cervical
  • Inferior deep cervical

The Sublingual Salivary Gland

• Positioned above the mylohyoid muscle.
• Located on the floor of the oral cavity, covered by mucous membrane.
• Forms a sublingual fold between the tongue and the inner surface of the mandible
• The gland is a mucous gland with an alveolar-tubular structure.
• Has 18-20 ducts.
• Smaller salivary glands open in the oral cavity.
• Principle ducts open via a single opening common to both sublingual and submandibular ducts.
• The sublingual branch of the lingual artery provides blood supply.
• The facial nerve supplies nerve.

The Submandibular Salivary Gland

• Located in the submandibular fossa.
• Emerges from under the border of the mandible.
• Covered by skin, platysma muscle, and fascia of the neck.
• It is a mixed gland with a compound alveolar-tubular structur
• The 2nd largest gland
• Consists of 10 lobules.
• The submandibular duct opens in the caruncula sublingualis.
• The sublingual branch of the lingual artery provides blood.
• The facial nerve provides nerve.

The Parotid Salivary Gland

• Located on the lateral side of the face.
• In front of and slightly below the ear.
• Penetrates into the retromandibular fossa.
• Its surface extends upward to the zygomatic arch, downward to the mandibular angle, in front on the masseter muscle, and in back to the external acoustic meatus and anterior border of the sternocleidomastoid muscle.
• It is the largest salivary gland and a serous gland.
• Consists of 7 lobules.
• The parotid duct is 5-6 cm long.
• It arises from the anterior border of the gland and passes on the surface of the masseter muscle.
• Curves around its anterior border.
• Pierces the buccinator muscle.
• Enters the oral cavity under the mucous membrane.
• Opens into the vestibule of the mouth through small openings opposite the 2nd upper molar.
• The superficial temporal artery (external carotid artery) provides the blood.
• The auriculotemporal nerve provides the nerve supply.

The Pharynx

• Part of the digestive and respiratory tracts.
• The space within that area is the pharyngeal cavity.
• Approximately 12-15 cm long.
• Behind the nasal cavity is the nasopharynx.
• Below the oral cavity is the oropharynx.
• From the larynx is the laryngopharynx.

The Nasopharynx

• Communicates anteriorly with the choanae.
• The formix of the pharynx is the superior wall of the pharynx.
• At the junction of the anterior and posterior walls of the pharynx is the pharyngeal tonsil.
• The lateral wall contains the pharyngeal opening of the auditory tube, called the torus tubarius.

The Oropharynx

• Middle part of the pharynx
• Its function is mixed because the alimentary and respiratory tracts intersect here.
• Posteriorly is the cervical vertebrae.
• Anteriorly is the base of the tongue.
• The superior wall is the inferior surface of the soft palate (uvula).

The Laryngopharynx

• In a state of rest when there is no swallowing, the anterior and posterior walls of this area remain in contact and separate only if food passes through it.
• Anteriorly, there is an opening into the larynx in front of the epiglottis and on sides by aryepiglottic folds.
• On either side of the fold, is a pear-shaped fossa in the pharyngeal wall called the piriform fossa.
• The ascending pharyngeal artery and facial artery supply blood to the pharynx.
• The glossopharyngeal nerve and the superior laryngeal nerve (of the vagus nerve), and the vagus nerve provide nerve supply to the pharynx.
• Regional lymph nodes include:
  • Retropharyngeal lymph nodes
  • Jugulodiagastic lymph nodes
• The pyrogott's ring has 6 lymphoid structures:
  • 3 in the nasal part and 3 in the oral part
• The areas include:
  • Pharyngeal (superior)
  • Tubal (above auditory opening)
  • Palatine (on each side)
  • Lingual (inferior)

The Esophagus

• Topography:
  • From the cervical 6th-thoracic 11th vertebrae
  • Situated in three cavities: cervical, abdominal, and thoracic
  • Syntopy:
    • Cervical part:
      • Anterior: trachea
      • Lateral: common carotid artery
    • Thoracic part:
      • Anterior: trachea
      • Posterior: vertebral column
    • Abdominal part:
      • In front and to the right: the left lobe of the liver
      • In front and to the left: covered by peritoneum
• External structure:
  • A hollow tube-like organ that connects the pharynx to the esophagus
  • Length of the adult esophagus is 25-27 cm.
  • Begins at C6-T111 and enters the stomach at T11-T12
  • Consists of three cavities: cervical, thoracic, and abdominal
    • Cervical
    • Thoracic
    • Abdominal
• Internal Structure:
  • Mucous
    • Has mucous gland
    • Submucosa
    • Mucosa contains longitudinal folds.
  • Muscular
    • Outer layer contains longitudinal fibers.
    • Inner layer contains circular fibers.
  • Adventitia or serous
    • Loose connective tissue
• Constrictions:
  • The esophagus has three constrictions:
    • Pharyangeal(at the beginning of the esophagus)
    • Aortobrachial (at the level of the Trachea)
    • Diaphramgmatic (where the esophagus pierces through the diaphragm)
• Blood supply:
  • Esophageal branch of the thoracic aorta
    • C.P. - inferior thyroid artery
    • T.P - brachial artery, aorta - A.P. - Left gastric artery - Inferior phernic artery
• Nerve supply
  • Inferior Cervical cardia of Recurrent laryngeal nerve.
    • Thoracic vagus nerve

The Stomach

• Dilation of the tube has a sac-like structure.

• Lies between the esophagus and duodenum.

• Has anterior and posterior walls.

• Has a greater curvature and lesser curvature.

• Cardia orifice as inlet; pyloric orifice as outlet.

• Lies between the esophagus and the stomach small cardiac notch.

• Near the lesser curvature is the angular notch.

• Portions:

  • Above the cardia notch is the fundus
  • Near the lesser curvature is the cardiac
  • Between and through the angular notch is the Body and Pylori
  • Pyloric part subdivides into the pyloric antrum and pyloric canal
  • mucous
    • Innermost layer
    • Gastric galnd
  • submucosa
    • vascular cob
  • muscular
    • Outer longitudinal layer
    • middle circular layer
    • inner oblique layer
    • serous
    • Outermost layer
    • cderived from pentoneum (intapevitoreally) Extends between T1111-L1 or LL1

• lies in left lateral hypochondrium and middle epigastric,

• Sytappy

  • Ant - abdominal wall below liver drib

• post- upper fan of kidney. Suprarenal galand

• sup- LeH lobe of liver

• inf _ Lower Pant traverse colon Blood supply: Right And Leit gastri a Righf And Ceft castors - epiploic a Nerve supply ; Ant And Port guagu munk. Burn abdominal part of vagus n Redona/ lymph nodes: Right gastra LN. Left casfñc LN. Celia LN

The Small Intestine

• Parts consist of Duodenum, Jejunum, Ileum
• Skeletery extends between ThX11 - area of right iliac fossa
• Hulotopy lies in abdominal cavity Occipies epigoshlum Nesogastrium And parfly hypogashum
• suntopy large inte dundenum pancreas, /wer lies arond It
• Position according to peritoneum
• Duodenum retroperitoneum
• Jejumun Intra perritoneam
• Ileum
• Structure is Wall's - Mucosa. Simple colunan.
  • Surmucosa Smoot m inner circular layer outer logitudinal layer Serosa
• Blool supply.

celtic Trunk up mesenterica Nerve supply

• Vagus N. Regionol lymph rodes
• Common ilde L.N The dundenum - its parts super part
• Decendirg part
• Horizontal part Ascenairg p.

structure

Exlernal structure Duudeno Jaurun Hexus where intestinou tube be down shoorply Passes down onl to Lett constst suspensory Intemal structure- Mucous coat. is innermst coat. Has mucous galand secretes mucosa

• intestinai villi desc part has 2 duodenal tapilla mayor & miner Corcular frond Submucosa assloor connective tiusure
• muscular cocht - inner celular layer oufer longitudinal layen
• serous cocet as cutermost coat b denved prom peritoneum Topography skelelopy EXtends bl Li - Llll Hololopy- suph part - Eigashrim Dec Paht- Right hyhochondrical negion How port - umbalcal region Asce - e- E gas hime

Blood supply

• gasmodudena/ a sup&mle pareaficododenal a mesennica

Jejunum and Ileum

• External structure- invested in peritoneum. Attached to post all B to abdominal womb B' mesentry. .leje unum is large and thick situated in mesegasmium and hypogasticum region Jeje unum is left to malne & Fleum is Right fo malrne
• structure - .mucous coat Innermost coat Has mucous galnal Screats mucosa intestinal vild
• In festinal Grand secretes intestinal juicees solitary LNS Agging ated Ln creauiar folds submucosar vascular coab Muscula coat: Inner Circalar layer

Outer longitudinal layer serous coat = outermost layar 6 Derved from penteoneum Blood supply

Intestinial asup mesentic cu Heocolic a Nerve supply · Pust vaged tank from abdominal port of vagus N

The Large Intestine

• The following are its parts:
  • Cecum Vermilorm Appendlx Colon rectum Their topography: cecum -R1 late region/ Dv app git anl 9b wally post illopsous as/Colon Rt lat. ragion,Rt. hypochonchium region Trons colon -Rt Hypliconchium, margin blur epgasmice & am bilia region

U hypchonclum Dec codon: lh lol Region, Lt. Hy/s/shonchiam Sigmcelon

Sigmoid Redum - hyaugashum . Positions see to pentoneum; Ceeum - interaperitoneally App, as colon mesoperitoneally dee colon Trans colon - inhalperttoncally Sig colin Rectum Super 3'3 inhalertoneally mid 4mesopentoneally . Int Ys - Tet ropentoneally Structure External Shuchure:Taenia cou: Bundle of lungitudinal m. Free tapala mosenteric taenia omental tucnia / Nausha Appendees epiprocae

Internel Sirveluse-

muu tavestment cont as Has sur cous grand Semibinar falds - intestinal Galal coliany impatetic nudules - Muscular coal · as a inner Circular layer - by extemal longitudinal layer - serous coat - as outer most coal " - denved trom penteneam Blood aupply: The cohle a. Righa colic a " mid colt, a from susp mesentie a · - 2). Leh cahie a sigmoid colic a from indy mosentiz ce "" Mane upply: purf vagal bank from abdominoi patt of vagus l "Regional amph nodes:" Sup Mosentie EN - M1 LM Que 14 The cecum: * Strivelere.First segment of large intestine from its origin

• Sac The ahveluese is 6323 to m Right Iliae fossa - Int. surface adjoins with and abdominal wall = 2. 4 Al the Junction of small intestine & large intestine Hiscal. ilica valines presen * The ge valves allows parser ge of 1000 fom small to large intestine vii. semdunar folds viii. Illao onfice lies on tapilala · Position ace, to pentoneum. "7 inhaperitoneally: Topography of the vermiform appendia: “ = all and abdominal wall post = iliopreas onl +positions of vermilorm appendix

Aspesending position (0-4556, casas) lateral (255) - Mleal_-(174) - Ascendirg (131) Blood supply * Appendicular brandh of loeoeel a of sup. mesentine Merge supply. - Past branch of vagul bank of abdominal branch of vagus

The Rectum

• structure- External structure Rectum is divided by sigmoid color at level of promontory . i has 2 parts upper part. amplellu 4 lower part - anal canal 2
• Repeals shape of sacrum then go back rom appex of coceur · bet S-shaped 2 Racale female relation in male and from tectum - unmary bladder seminal vescides. Doublin Deferense Prostate galna à in temaler : Uterus and vagina upp Internal struelusea Maceas coal Innmust layer by secreles mucous gland cupper part has transverse folds lower par how Longitudinal folis Submucosa " a gvasiular coal B "internal Rectal venous plexus. Diease Hemorrhoidon Piles