DIGESTIVE SYSTEM
The digestive system consists of
the following parts:
1. Mouth Cavity & Salivary glands
Contents of the mouth:
Tongue-teeth-openings of the salivary glands.
A.The Tongue
- It is a muscular organ covered by mucous membrane.
- It consists of 3 parts: tip, root and body.
Functions of the tongue:
1. Chewing.
2. Speech.
3. Taste.
4. Swallowing.
B. Teeth
Two types:
I. Milk (deciduous) teeth: Temporary teeth present in the children, 20 in number
10 above and 10 below.
II. Permenant teeth: They are 32 teeth, 16 above and 16 below, arranged in each
half of jaw as follows: 2 incisors, canine, 2 premolars, 3 molars.
1- Mouth cavity and salivary
glands.
2- Pharynx.
3- Oesophagus.
4- Stomach.
5- Small intestine.
6- Large intestine.
7- Liver and biliary system
8- Pancreas.
1. Mouth Cavity & Salivary glands
Contents of the mouth:
Tongue-teeth-openings of the salivary glands.
A.The Tongue
- It is a muscular organ covered by mucous membrane.
- It consists of 3 parts: tip, root and body.
Functions of the tongue:
1. Chewing.
2. Speech.
3. Taste.
4. Swallowing.
B. Teeth
Two types:
I. Milk (deciduous) teeth: Temporary teeth present in the children, 20 in number
10 above and 10 below.
II. Permenant teeth: They are 32 teeth, 16 above and 16 below, arranged in each
half of jaw as follows: 2 incisors, canine, 2 premolars, 3 molars.
C. Salivary Glands:
1- Parotid gland: It is the largest salivary gland, wedge-shaped, lies below the external
auditory meatus. It has nearly a horizontal duct which pierces the cheek to open in
the vestibule of the mouth opposite the upper 2nd molar tooth.
2- Submandibular gland: It is about 1/2 the parotid size, lies deep to and below
the mandible. Its duct opens in the floor of the mouth in the sublingual papilla on
either side of the frenulum of tongue.
3- Sublingual gland: It is the smallest salivary gland, lies under the mucous
membrane of the floor of the mouth called sublingual fold. It has 12-15 small
ducts which open in the sublingual fold and few of them open into the duct of
submandibular gland.
2. Pharynx
Funnel-shaped muscular tube about 5 inches long, lies behind the nasal cavity, oral
cavity and larynx. It lies infront of the upper 6 cervical vertebrae and is divided into 3
parts:
1. Nasopharynx: It lies behind the nasal cavity, above the soft palate and acts as
a passage for air only. Its upper part contains the nasopharyngeal tonsil while
the lower part shows the opening of the pharyngotympanic (Eustachian) tube.
2. Oropharynx: It lies behind the oral (mouth) cavity, below the soft palate and
acts as a passage for food and air. Its lateral wall contains the palatine tonsil.
3. Laryngopharynx: It lies behind the larynx and acts as a passage for food only.
3. Oesophagus
Length: It is a muscular tube 25 cm long
Beginning: it begins in the neck as continuation of the pharynx.
Course and end: It descends for a short course in the neck, then it enters the
thoracic cavity, then it passes through the diaphragm to enter the abdomen where
it ends in the cardiac end of the stomach.
Parts: the oesohagus has 3 parts; short cervical part, long thoracic part and very
short abdominal part.
4. Stomach
It is the most dilated part of the digestive tract.
Position: It lies in the upper part of the abdominal cavity behind the left lobe of
liver and anterior wall of abdomen. It lies infront of the left kidney, pancreas and
spleen.
5. Small intestine
It has 3 parts:
A- Duodenum: The shortest and widest part of the small intestine. It is C-shaped
tube, 25 cm in length with its concave part directed to the left side and is
occupied by the head of the pancreas.
B- Jejunum.
C- Ileum.
6. Large Intestine
Parts:
1- Caecum: It lies in the lower right part of the abdominal cavity. It has lower blind
end and it is continuous with ascending colon. The lower end of the ileum and the
appendix open into it.
2- Vermiform appendix: It is variable in length and in position and it opens into
the caecum below the opening of the ileum.
3- Ascending colon. 4- Right colic flexure. 5- Transverse colon.
6- Left colic flexure. 7- Descending colon. 8- Sigmoid (pelvic) colon.
9- Rectum. 10- Anal canal which opens below by the anus.
Liver
Site, size, shape: Large wedge-shaped organ about 1.5 Kg in weight lies in the
upper right part of the abdominal cavity below the diaphragm.
Structure: It consists of large right lobe and small left lobe. It also shows special
fossa for gall bladder.
Porta hepatis: it is the hilum of the liver through which the hepatic artery and
portal vein enter and the common hepatic duct leaves the liver.
Gall bladder: A piriform sac that lies in special fossa in the lower surface of the
right lobe of the liver. It stores and concentrates the bile which is secreted from liver.
The bile leaves the gall bladder through the cystic duct which unites with the
common hepatic duct of liver to form the bile duct.
Biliary System
1- Liver secretes the bile through the right and left hepatic ducts which unite
together forming the common hepatic duct.
2- Gall bladder receives the bile and evacuates it through the cystic duct.
3- The common hepatic duct unites with the cystic duct to form the bile duct.
4- The bile duct unites with the pancreatic duct to form the hepatopancreatic duct
which opens into the middle of the posteromedial surface of the second part of
the duodenum.
Pancreas
Soft lobulated gland, 12-15 cm long lies transversely on the posterior wall of the
abdomen. It extends from the duodenum on the right side to the spleen on the
left side behind the stomach on the surface of the left kidney.
It consists of 4 parts: head, neck, body, tail.
Function:
1. Endocrine function: It secretes 2 hormones which regulate the level of the
blood glucose, they are:
a- Insulin hormone: lowers the blood glucose level.
b- Glucagon hormone: Elevates the blood glucose level.
2. Exocrine function: secretes pancreatic enzymes in the pancreatic juice
which helps the digestion of food.
The pancreatic juice is secreted through the pancreatic duct which unites with
the bile duct and open together into the duodenum.