Digestive System

Dr: Azza Zaki

The Digestive System The

digestive system is concerned with the:  uptake  digestion  and absorption of food  excretion of non-digested food. The digestive system :divided into A- Gastro-intestinal tract B- Digestive glands Dr: Azza Zaki

Digestive tract (alimentary canal): is continuous tube with 2 openings, the mouth and the anus. it includes the following: Mouth  pharynx  oesophagus stomach  small intestine  & large intestine. Digestive glands include: Salivary glands  liver & pancreas

Dr: Azza Zaki

•Most of the organs of the digestive system lie in the abdominal cavity, except: Mouth cavity, pharynx and salivary glands which lie in the head region. Oesophagus which traverses the neck and thorax. The abdominal cavity: is bounded superiorly by the diaphragm which separates it from the thoracic cavity and continuous inferiorly with the pelvic cavity.

Dr: Azza Zaki

Abdominal Regions the abdominal cavity is divided into 9 regions by:  2 vertical planes  right & left. Each one extends from the mid-clavicular point to the midinguinal point.  2 horizontal planes  1. Upper horizontal plane: level of 3rd lumbar vertebra. 2. Lower horizontal plane: level of 5th lumbar vertebra.

Dr: Azza Zaki

Dr: Azza Zaki

The Peritoneum •

The abdominal cavity is lined by the Peritoneum which is the largest serous membrane in the body, and it consists of a double layer: A. Outer layer: is called the parietal peritoneum, lines the abdominal cavity. B. Inner layer: is called the visceral peritoneum, covers the abdominal viscera. The space between the 2 layers is a potential space and contains small amount of fluid (peritoneal cavity) Dr: Azza Zaki

Mouth Cavity • The mouth cavity is the first portion of the digestive tube. • It extends from the lips anteriorly and opens posteriorly in the oropharynx. • It is divided into: Vestibule Mouth cavity proper Dr: Azza Zaki

Vestibule • is the narrow space between the teeth and gums internally and lips and cheeks externally. • It communicates posteriorly with the mouth cavity proper by the interval behind the last molar tooth. It receives the opening of the parotid duct opposite to the upper 2nd molar tooth. Dr: Azza Zaki

Mouth Cavity Proper It is bounded: •Laterally and in front: by the teeth and gums. •Above: by the hard and soft palates. •Below: by the mucous membrane, which covers the floor of mouth. –It communicates: •Anteriorly with outside through the oral fissure. •Posteriorly with the oropharynx through the isthmus of fauces. Dr: Azza Zaki

Palate • It separates mouth cavity from nasal cavity & consists of: • The hard palate • The soft palate has a downward median projection, called "uvula". During swallowing, the uvula ascends upwards to close posterior nasal apertures. • The mouth cavity contains:

– Tongue – Teeth Dr: Azza Zaki

The Tongue

It is a highly mobile muscular organ which is formed of striated muscle fibers and covered by mucous membrane. The mucous membrane on the dorsum of the tongue is rough, and it is covered with small projections called lingual papillae. Some of the papillae contain taste buds.

Dr: Azza Zaki

Dr: Azza Zaki

Superior Surface of the Tongue Tongue papillae Filiform papillae Fungiform papillae Circumvallate papillae Sulcus terminalis: “V”-shaped sulcus: separates anterior 2/3 from posterior 1/3 of the tongue. Posterior 1/3 of tongue lies in oropharynx •Lymphatic follicles lie posterior to this sulus and called "lingual tonsils".

Dr: Azza Zaki

• Its under surface is covered by smooth mucosa which is connected to mouth floor by frenulum. • Function of the tongue: tongue • The tongue helps in deglutition, taste and speech.

Dr: Azza Zaki

Nerve Supply Of The Tongue

Dr: Azza Zaki

Nerve Supply Of The Tongue •The tongue has motor and sensory nerve supply: Motor for most of the muscles from the hypoglossal nerve. Sensory: anterior ⅔ ; by trigeminal nerve for general sensation and facial nerve for taste. posterior ⅓; by glossopharyngeal nerve for both general sensation and taste. Dr: Azza Zaki

Teeth • Deciduous (milky teeth): they are 20 teeth (4 incisors& 2 canines & 4 molars). The 1st tooth to erupt is the central incisor (6th month). • Permanent teeth: they are 32 teeth (4 incisors & 2 canines & 4 premolars & 6 molars). The 1st to erupt is the 1st molar. The last to erupt is the 3rd molar (wisdom tooth).

Dr: Azza Zaki

The Pharynx • It is a common pathway for digestive and respiratory systems. • It is musculomembranous tube that lies behind the nose, mouth and larynx. • It is about 12 cm in length and extends from the base of skull down to the 6th cervical vertebra, where it continues as oesophagus.

Dr: Azza Zaki

• It consists of three parts: – Nasopharynx: lies behind the nasal cavity and communicating freely with it through posterior nasal apertures. It communicates inferiorly with the oropharynx through the pharyngeal isthmus. It contains pharyngeal tonsil & auditory tube. – Oropharynx: lies behind the oral cavity extending from the level of soft palate to the upper end of the epiglottis. It communicates with the mouth cavity through the oropharyngeal isthmus. It contains palatine tonsil. – Laryngopharynx: lies behind the larynx communicating with it through the laryngeal inlet. It is continuous inferiorly with Dr: Azza Zakithe oesophagus

The Oesophagus It is a muscular tube about 25 cm long. It begins as the continuation of the pharynx (level of C6). It passes in the neck, then in the thorax through the mediastinum & then through the diaphragm to end in the stomach. Dr: Azza Zaki

 Most of its course is in the middle line but deviates to the left at the level of T7 vertebra where it passes in front of descending aorta till it passes through opening of the diaphragm at level of T10.  Through its course, it is related: Posteriorly  to the cervical and thoracic vertebrae, while Anteriorly  it descends behind the trachea and heart respectively Dr: Azza Zaki

The oesophagus •It has the following constrictions: Level

Distance from the incisor teeth

where it is crossed by the aortic arch

 9 inches

where it is crossed by the left bronchus

 11 inches

where it pierces the diaphragm

 16 inches Dr: Azza Zaki

The Stomach

Dr: Azza Zaki

The Stomach • It lies in the upper part of the abdominal cavity, in the epigastrium and left hypochondrium. • It is commonly Jshaped that has: – 2 orifices – 2 curvatures – 2 surfaces – 2 portions Dr: Azza Zaki

2 orifices Cardiac orifice

Pyloric orifice

It lies at junction with oesophagus.

It lies at the junction with duodenum.

It lies 1 inch to left of the midline.

It lies ½ inch to left of the midline.

It is guarded by physiological sphincter.

It is guarded by anatomical sphincter (thick circular fibers).

2 curvatures Lesser curvature

Greater curvature

It is the concave right border.

It is the convex left border.

It gives attachment to lesser omentum.

It gives attachment to greater omentum.

It shows a depression called It is 4 times longer than the Dr: Azza Zaki angular notch. lesser curvature.

–2 surfaces: •Anterior surface: it is related mainly to the left lobe of liver. •Posterior surface: related to a group of structures called "stomach bed" which include: upper part of left kidney, left supra-renal gland, spleen, body of pancreas.

Dr: Azza Zaki

2 Portions •Cardiac portion: –Fundus: is the part that lies above and to the left of the cardiac orifice. –Body: is the part between the fundus and an imaginary line between the angular notch and opposite point on the greater curvature. •Pyloric portion: –Pyloric antrum: is the dilatation following the body. –Pyloric canal: is the cylindrical part following the antrum. –Pylorus: is the opening that is surrounded by a muscular ring called pyloric sphincter. Dr: Azza Zaki

Dr: Azza Zaki

Peritoneum of the stomach • It is completely covered by peritoneum except the area on the back of the fundus. • The lesser omentum: extends from lesser curvature to the liver. • The greater omentum is attached to greater curvature then attached to the transverse colon &pancreas

Dr: Azza Zaki

Arterial Supply Short gastric Hepatic artery

Celiac artery

Left gastric artery

arteries

Right gastric artery

Gastroduodendal

Left gastroepiploic Right gastroepiploic

Dr: Azza Zaki

Splenic artery

The Small Intestine • It is 6 meters long and takes the shape of coiled loops that fill most of the abdominal cavity. • It consists of 3 divisions: • Duodenum • Jejunum • Ileum Dr: Azza Zaki

Duodenum

It is the shortest and widest part of the small intestine (about 25 cm in length).  It is “C” shaped and is formed of 4 parts. It is firmly attached to the posterior abdominal wall and not mobile. The head of pancreas lies in the “C” shaped concavity. cancer head of The bile duct and main pancreas leads to: pancreatic duct unit together and  obstructive jaundice open in the middle of the 2nd part. intestinal obstruction Dr: Azza Zaki

Jejunum and Ileum form the free part of the small intestine and are freely mobile. mobile They are attached to the posterior abdominal wall by means of mesentery. Jejunum extends from the duodenum. The ileum ends by opening into the cecum (ileocecal valve)

Jejunum

Ileum

Extent

Proximal2/5

Distal 3/5

Diameter

Larger

Smaller

Lymphatic follicles

Are few & small Are numerous & large (Payer’s patches

Mucosa

More circular folds & larger villi

Dr: Azza Zaki

Less circular folds & smaller villi

Ileum

Dr: Azza Zaki

Jejunum

Large Intestine (Colon) It is about 1.5 meters in length. It extends from the end of the ileum to the anus. It is larger in diameter than the small intestine. Dr: Azza Zaki

The large intestine has the following features: • Appendices epiploicae: are small peritoneal sacs filled with fat scattered on the wall of large intestine (except on cecum & appendix & rectum). • Taenia coli: the outer longitudinal muscle coat of large intestine is arranged in 3 longitudinal bands that begin at the base of appendix (they are absent in the appendix & rectum). • Sacculations: the length of taenia coli is shorter than the true length of large intestine  puckering of the wall. Dr: Azza Zaki

Small intestine

Large intestine

Dr: Azza Zaki

Difference between small & large intestines Small intestine Large intestine Length

About 6 meters

About 1 ½ meter

Diameter

Smaller

Larger

Appendices epiploicae

Absent

Present

Taenia coli

Absent

Present

Sacculation

Absent

Present

Mucosa

• Permanent circular folds •Villi are present •Aggregated lymph follicles

• Circular folds disappear by distension •Villi are absent •Solitary lymph node

Dr: Azza Zaki

•The large intestine is divided into the following parts: –Cecum is a blind pouch which hangs down at the junction of the ileum and the colon. The Ileocecal valve lies at its medial aspect and prevents the return of the faeces from the cecum into the small intestine. The appendix arises from the cecum about 2.5 cm below the ileocecal valve. –Ascending Colon extends from the cecum to the under surface of the liver where it turns to the left. This bend is called right colic (hepatic) flexure. Dr: Azza Zaki

Transverse Colon crosses the upper part of abdominal cavity from right to left and then curves sharply downwards under the lower end of the spleen forming the left colic (splenic) flexure. Descending Colon extends from the splenic flexure to the brim of the pelvis, where it turns towards the midline to become the sigmoid colon. Sigmoid Colon extends from the descending colon at the level of pelvic brim to the rectum. It is “S” shaped. Rectum extends from the sigmoid colon to the anal canal. It descends along the sacrum to the tip of coccyx. Its lower part shows dilatation called "ampulla of rectum". Anal Canal is the terminal portion of the large intestine. It extends from the rectum to the anus and is about 4 cm in length. In the anal canal the circular muscle fibres are thickened to form internal anal sphincter. The external anal sphincter is composed of skeletal muscle, therefore under voluntary control. Dr: Azza Zaki

Dr: Azza Zaki

Digestive Glands •Salivary Glands •Liver •Pancreas

Dr: Azza Zaki

Salivary Glands •

• •

There are three pairs of salivary glands: Parotid Submandibular

•

Sulingual

Dr: Azza Zaki

The Parotid Gland Is the largest salivary gland, which lies below & in front of the ear, between the mastoid process & ramus of the mandible. It is wedge- shaped with its base directed upwards & apex directed downwards. The parotid duct passes through the buccinator muscle & opens into the vestibule of the mouth opposite the upper second molar tooth. Its secretion is watery.

Dr: Azza Zaki

The Submandibular Gland  Lies in contact with the mandible.  Its duct opens into the floor of the mouth.  Its secretion is watery & mucous • The Sublingual gland:  It is the smallest salivary gland.  It lies under the mucous membrane of the floor of the mouth (under the tongue) it has several minute ducts, which open into the floor of the mouth.  Its secretion is mucous. Dr: Azza Zaki

Liver

• It is the largest organ of the body. • Location: • In the right hypochondrium & epigastrium. • Surfaces: • It is a wedged shaped which has: smooth convex anterior, superior, posterior & right lateral surfaces. The diaphragm separates the liver They collectively from the right pleura &lung, related to the pericardium, left pleura & lung. Dr: Azza Zaki diaphragm.

•Inferior surface: which is concave& shows impressions of these organs: •Gastric impression for the stomach •Renal impression for the right kidney •Fossa of gall bladder •Colic impression for the right colic flexure •Groove for the inferior vena cava. •Duodenal impression 7. Quadrate lobe. 8. Caudate lobe Dr: Azza Zaki 9.Porta hepatis.

Porta Hepatis

• It is the hilum of the liver • It lies between the caudate & quadrate lobes. • It gives passage to the following structures: • Hepatic ducts: ducts anterior in position • Hepatic artery: intermediate in position. • Portal vein: posterior in position

Dr: Azza Zaki

The liver has:  Two main lobes, right and left, left separated by the falciform ligament.  Two small lobes: quadrate & caudate lobes. Anatomically these 2 lobes belong to the right lobe. While physiologically, they are part of the left lobe as they are supplied by left branch of the hepatic artery.  Liver covered by peritoneum except bare area posteriorly. Dr: Azza Zaki

Blood Supply Of The Liver •

The liver has double blood supply: • Hepatic artery provides 30% • Portal vein provides 70%  The liver is drained by 2 hepatic veins which end in the inferior vena cava. Dr: Azza Zaki

Biliary System 1-Gall bladder: • It is a pear- shaped sac. • It has fundus, body and neck. • Its neck is continuous with the cystic duct. • It is located in gall bladder fossa on the inferior surface of the liver. Dr: Azza Zaki

2-Right & left hepatic ducts: • They are coming from the right & left lobes of the liver & unite to form common hepatic duct. 3-Common hepatic duct: • It is joined by the cystic duct to form common bile duct. 4-Common bile duct: • It descends behind the head of pancreas, where it joins the main pancreatic duct to open into the 2nd part of the duodenum • This opening is guarded by a valve (sphincter of oddi). Dr: Azza Zaki

Pancreas

 It is elongated gland that lies across the posterior abdominal wall at the level of 2nd lumbar vertebra.  has both endocrine & exocrine functions:  The exocrine portion: secretes pancreatic juice.  Endocrine portion: islets of langerhans( beta cells secrete insulin & alpha cells secrete glucagon)  It is not mobile as it is retro-peritoneal Dr: Azza Zaki structure.

Parts Of The Pancreas

 Head:  It is the broad right end which is enclosed within the C shaped curve of the duodenum.  It sends a downward process called uncinate process.  Neck:  It is the junction between the head and body. It is related to the portal vein (union of superior mesentric with splenic veins). veins) Dr: Azza Zaki

• • • • •

Body: Is triangular in cross section with: Anterior surface: lies behind the lesser sac Posterior surface: is related to posterior abdominal wall. Inferior surface: is related to small intestine. Tail: the left narrow end which reach to the spleen. Dr: Azza Zaki

Ducts Of The Pancreas •

Main pancreatic duct: extends through the whole length of the pancreas to unite with the common bile duct forming the hepato-pancreatic ampulla which opens in the 2nd part duodenum.

•

Accessory pancreatic duct: starts in the uncinate process & ascends in front of the main duct & opensDr: inAzza theZaki 2nd part duodenum.

Blood Supply Of The Gastroinestinal Tract • •

•      

Arterial supply: By 3 single arteries which arise from the front of the abdominal aorta: Coeliac trunk: supplies the foregut: lower part of oesophagus, stomach, upper half of the 2nd part duodenum, liver, pancreas Dr: Azza Zaki & spleen)

2- Superior mesentric artery: supplies the midgut:  Lower half of the 2nd part duodenum  Jejunum  Ileum  Caecum  Ascending colon  Right 2/3 of the transverse colon. Dr: Azza Zaki

3- Inferior mesentric artery: supplies the hindgut: Left 1/3 of transverse colon Descending colon Pelvic colon Rectum Upper half of the anal canal

Dr: Azza Zaki

Venous Drainage of GIT

Dr: Azza Zaki

Venous Drainage of GIT  By tributaries corresponding to the branches of arteries, which ultimately drained into the portal vein.  Where and how the portal vein is formed?  The portal vein is formed behind the neck of pancreas by the union of superior mesenteric vein & the splenic vein. vein The portal vein goes to the liver.  From the liver, the 2 hepatic veins drain into the inferior vena cava. Dr: Azza Zaki

Dr: Azza Zaki

References • • • • •

Clinical anatomy by systems. Snell 2007 Clinically oriented anatomy 5th ed Moore Gray’s anatomy for students. Drake Color atlas the human body. Faller 2004 Netter atlas

Dr: Azza Zaki