Category Archives: The Digestive System

THE DIGESTIVE SYSTEM 3

Posted by on February 10, 2012 1 comment

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THE DIGESTIVE SYSTEM 3

 

 

The descending colon:

It is about 25 cm in length. It extends from the splenic flexure to end at the inlet of the pelvis where it joins the pelvic colon.

 

The pelvic colon

It is about 40 cm in length. It begins at the inlet of the pelvis and ends at the middle of the sacrum where it is connected with the rectum.

It forms a loop and it is surrounded by a peritoneal fold called pelvic mesocolon, so it is freely movable and hangs in the pelvic cavity.

 

The rectum:

It is about 12 cm in length. It begins at the middle of the sacrum and ends below the coccyx where it opens into the anal canal. In human, it is not straight as its name implies but it rather forms 3 flexures two convex to the right and one to the left.

 

The anal canal:

It is about 4 cm in length and ends below, in the perineum by the anal opening (anus). Interna) and externa! sphincters control the opening.

 

The peritoneum:.

It is a serous membrane formed of two layers; i parietal layer lining the wall of the abdomen, and a viscera Saver covering the abdominal viscera. ~

In some regions it extends as a fold formed of ‘. layers to connect the internal organs with the abdomina

wall, e.g. the mesentery and the transverse mesocolon, so that it facilitates the movement of organs of alimentary canal.

The glands associated with the alimentary canal:

1. The Salivary glands: (Fig. 27)

There are three pairs of salivary glands, which secrete the saliva into the mouth.

1.  The parotid glands: located one on each side in front and below the external ear. Each gland has a duct that opens in the vestibule of the mouth opposite the upper 2nd molar tooth.

2.  The submandibular glands: located below the body of the mandible near its angle. Their ducts open under the tongue on the sublingual papillae.

3.  The sublingual glands: located directly under the
tongue, covered by the mucous membrane of the floor of
the mouth, raising the two sublingual folds. They open by
numerous short ducts (8-20) in the floor of the mouth.

 

II. The pancreas:

The pancreas extends transversely on the posterior abdominal wall in front of the upper two lumbar vertebrae. It is 15 cm in length. Its expanded right part is called the head and it is surrounded by the duodenum. The head is followed by a constricted part called the neck, which lies in front of. the portal vein. The neck is followed by the main part called the body. .The left tapering end of the pancreas is the called the tail which rests on the spleen. The pancreas serves both exocrine and endocrine functions. It secretes the

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pancreatic juice and the hormone, insulin. The duct of the pancreas, which transmits the pancreatic juice, opens with the common bile duct in the middle of the second pan of the duodenum.

 

III. The liver:

The. liver is a large gland weighing over 1.5 kg. It is wedge shaped with its base directed to the right and its apex directed to the left.

It lies principally in the right hypochondrium but stretches across the epigastrium to reach the left hypochondrium.

It is divided into two man lobes; a large right lobe and smaller left lobe. A smaller part; the quadrate lobe, is demarcated on the inferior surface of the right lobe and another circumscribed part on its posterior surface is called the caudate lobe.

The porta hepatis is an opening on its inferior surface behind the quadrate lobe through which the right and left hepatic ducts, the hepatic artery and the portal vein pass in that order from before backwards.

 

Blood supply of the liver:

The liver has a dual blood supply:

a)  Oxygenated blood form the hepatic arterv which arises form the coaliac trunk: a branch from the aorta.

b)  Portal venous blood from the portal vein.

The blood leaves the through the hepatic veins to the inferior vana cava. The liver is the site of very many vital metabolic processes. It also secretes bile.

The biliary apparatus:(Fig. 28)

It consists of the ducts through which the bile is transported and the gall bladder, which concentrates it.

Interlobular ducts discharge their contents into the tributaries of the right and left hepatic ducts, which leave

the liver through the porta hepatis and unite to form the common hepatic duct (3cm in length).

The common hepatic duct unites with the cystic duct from the gall bladder to form the common bile duct (7.5 cm in length).

The common bile duct opens together with the

pancreatic duct in the middle of the second part of the duodenum.

The gall bladder is a pear shaped organ 7 -10 cm in length having a capacity of about 30-50″ ml. it is attached to the inferior surface of the liver to the right side of the quadrate lobe.

It consists of a fundus; which project beyond the inferior margin of the liver, a body and the neck which is the narrow part following the body and continuous with the evstic duct. The cystic duct is 3-4 cm in length. It unites with the common hepatic duct at an acute angle to form the common bile duct.

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THE DIGESTIVE SYSTEM 2

Posted by on February 10, 2012 1 comment

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THE DIGESTIVE SYSTEM 2

 

The stomach: (Fig. 26)

It is the most distensible part of the alimentary tract It transmits food from the oesophagus to the duodenum, li lies in the upper left part of the abdominal ca\iiy below the diaphragm.

It has two openings: the cardiac orifice lying ai the junction with the oesophagus and the pyloric orifice a! the junction of the stomach with the duodenum.

It has two surfaces; anterior and posterior, and r»< borders called the lesser and the greater curvatures. The

 

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lesser curvature is the concave right border while the greater curvature is the larger (4 times larger) convex left border. The stomach is divided into two portions:

a)     Cardiac portion: It includes, the cardiac orifice, the fundus (which is the part above the cardiac orifice) and the body (which follows the fundus and it is the largest part of the stomach).

b)     Pyloric portion: It includes the pyloric antrum that follow the body of the stomach, the pyloric canal which is the cylindrical part the follows the pyloric antrum and the pylorus which is the part corresponding to pyloric orifice, it contains the thick pyloric sphincter.

The position and shape of the stomach vary in different people and in the same individual depending on its content and the person’s position.

The stomach is capable of holding up to 3 liters of material in the adult. In the newborn, the stomach is about the size of the hen’s egg, and it can hold about 30 ml of fluid. The stomach functions as a reservoir for food and it secretes the digestive juice which contains hydrochloric acid and certain enzymes.

The small intestine:

The small intestine extends from the pylorus of the stomach to the ileocaecal junction where it joins the large intestine. It is about 6 meters (20 feet) long and it is divided into three parts; the duodenum, the jejunum, and the ileum. The jejunum and ileum are connected to the posterior abdominal wall by a peritoneal fold called the mesentery.

  

 

a)           The duodenum:

It is 25 cm (10 inches) long. It lies on the posterior abdominal wall behind the peritoneum. It is C-shaped and it surrounds the head of the pancreas.

The bile duct and the pancreatic duct unite and open by a common opening in the posteromedial part about the middle of the duodenum. For descriptive purposes, the duodenum consists of 4 parts: 1* part above the head of the pancreas, 2nd part on its right side, 3rd part below it, and 41h part on its left side.

b)          The jejunum:

It is called so because it contains no food after death. It comprises the upper 2/5 of the small intestine distal to the duodenum.

c)          The ileum:

It is called so because it is the most coiled part of the small intestine. It comprises the following 3/5 of the small intestine.

 

Differences between the jejunum and ileum:

1 No.

Jejunum

Ileum

1 5

Larger in diameter

Smaller in diameter

2.

The mesentrv contains small amount of fat so the blood vessels can be seen

The mesentry contains much fat obscuring its blood vessels

3.

The circular folds of the mucosa and the villi are larger and more numerous

The circular folds and villi of the mucosa are smaller and less numerous

 

Function of the small intestine:

The upper part of small intestine is mainly digestive, while its lower part is mainly absorptive.

 

The large-Intestine:

The large intestine extends from the ileocaecal junction to the anus; it is about 1.5 m long. It consists of the caecum and vermiform appendix, the ascending colon, the right colic flexure (hepatic flexure), the transverse colon, the left colic flexure (splenic flexure), the pelvic colon, the rectum and anal canal.

 

Differences between the large and small intestines:

No.

Large intestine

Small intestine

1

It has a greater calibre.

It has a lesser calibre

2.

It is 1.5 m in length

It is 6m in length

3.     The external surface

i

j contains sacs full of fat i called

! appendices epiplociae.

The external surface does not contain

appendices epiplociae.

4.

The longitudinal muscle ; layer forms 3 longitudinal | bands called taeniae col! ! which are shorter in length ! than the true length of the S large intestine so that the ! wall presents ilia titrations ! (sacculations).

The longitudinal muscle layer does not form bands 2nd the wall of the small intestine is smooth without haustrations.

  

The caecum

The caecum is present in the right iliac fossa. It is 6cm long. It is a blind pouch which- is continuous above with the ascending colon.

The ileum opens into the large intesine at the junction between the caecum and ascending colon. The vermiform appendix opens into the posteromedial aspect of the caecum about one inch (2.5cm) below the ileocaecal junction.

 

The vermiform appendix:

A very narrow worm-like tube which opens into the posteromedial aspect of the caecum about one inch (2.5 cm) below the ieocaecal junction.

Its average length is 9cm. It usually lies behind the caecum (retrocaecal) or extending into the pelvis (pelvic).

The ascending: colon: It is about 15 cm in length.

It begins at the upper end of the caecum and extends to the inferior surface of the liver, where it bends to the left to

form the right flexure (hepatic flexure) which connects it with the transverse colon.

 

The transverse colon:

It is about 50 cm in length. It extends transversely across the abdomen from the hepatic flexure to the left splenic flexure where it continues as the descending colon. A peritoneal fold called the transverse mesocolon surrounds it, so it is freely movable.

THE DIGESTIVE SYSTEM 1

Posted by on February 10, 2012 2 comments

THE DIGESTIVE SYSTEM 1

 

(Fig. 23)

The digestive system consists of the mouth, the pharynx, the oesophagus, the stomach, the small intestine and the large intestine. It also includes the associated glands as the salivan glands, the liver, and the pancreas.

The mouth:

-     The mouth is the first part of the digestive tube and it is also used in breathing. The mouth is composed of a smaller outer part called the vestibule and a larger inner part called the mouth cavity proper.

-     The vestibule is bounded externally by the cheeks and lips and internally by the teeth and gums.

-     The operture between the lips is called the oral fissure.

-     The mouth cavity proper is bounded anteriorly and on each side by the teeth and gums. Posteriorly it communicates with the oropharynx. The roof is formed b> the hard and soft palates which separate it from the nasal cavity The floor of the mouth is principally formed b> the tongue and the sublingual salivary glands, which raise a ridge of mucous membrane called the sublingual fold.

 

The LIPS:

The lips are the two muscular folds surrounding the oral fissure. /They are covered externally by the skin and internally by mucous membrane. Between the outer skin and inner mucosa is the vermilion which is the red zone to which lipstick is sometimes applied. It appears red because of the presence of capillary loops close to the surface.

 

 

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The GUMS

The gums are composed of fibrous tissue, which is covered by mucous membrane. They are attached to the margins of the alveolar processes of the upper and lower jaws and to the neck of the teeth.

 

The Tongue:

The tongue is a highly mobile muscular organ concerned with chewing, taste, swallowing, articulation (speech), and oral cleaning. It has an .upper surface, a lower surface, and two lateral borders.

 

The teeth:

The teeth are set in sockets in the alveolar processes of the jaws. There are two sets of teeth: deciduous (or milk) teeth, and permanent teeth.

Milk teeth are ten in each jaw i.e. 5 in each half of a jaw: 1 central incisor, 1 lateral incisor, 1 canine, and 2 molar teeth. They erupt during the first 2 years of life starting usually at the sixth month. They are usually shed from the sixth to the twelfth year as they are replaced by the permanent teeth.

Permanent teeth (Fig. 24) replace the milk teeth between the 6th and 18th year. Each adult jaw contains 16 permanent teeth i.e. each half of a jaw contains 8 teeth: 1 central incisor, 1 lateral incisor, 1 canine, 2 premolars and 3 molars.

N.B. incisors are the cutters. Canines are piercers. Premolars and molars are the grinders.

 

  

 

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Each tooth (Fig. 25) has a crown above the gingivae a neck embedded in the gingivae, and a root fixed in the socker of the alveolar process of the jaw by a fibrous periodontal membrane. Most of the tooth is composed of dentine which is covered b\ enamel over the crown and cementum over the root. The pulp cavity contains connective tissue, blood vessels and nerves and is continuous with the periodontal tissue through the root canal.

 

The pharynx:

See the respiratory system.

 

The oesophagus:

The oesophagus is a muscular tube about 25 cm in length. It extends from the lower end of the pharynx to the cardiac orifice of the stomach. It passes in the neck (cervical part), in the thorax (thoracic part), and in the abdomen (abdominal part). It transmits the food from the pharynx to the stomach.