DIGESTIVE SYSTEM
- The digestive system provides the body with nutrients for
maintenance of life
- The various organs in this system work together in the process
of:
1. Ingestion – where in food from outside the body enters the
alimentary tract through the mouth
2. Digestion – which could be mechanical (physical breakdown
of food into smaller pieces) or chemical (enzymatic action)
3. Absorption of digested materials
* Chewing lubricates the food by mixing it with saliva. It decreases the size of
the food particles to facilitate swallowing and begin the digestive process.
2. Teeth
Deciduous teeth (6 months – 2 years)
= 20
Central incisor
Lateral incisor
Canine (cuspid)
First molar
Second molar
Permanent teeth (6-12 years)
= 32
Central incisor
Lateral incisor
Canine
First premolar (bicupid)
Second premolar (bicuspid)
First molar
Second molar
4. Elimination of undigested materials
Third molar (wisdom tooth)
SUBDIVISION
A. Alimentary Canal
1. mouth
2. pharynx
3. esophagus
4. stomach
5. small intestine
6. large intestine
7. rectum
8. anal canal
B. Accessory digestive organs
1. salivary glands
2. liver and gall bladder
3. pancreas
II. PHARYNX
- common passage for food, fluid and air
- continuous with the esophagus
- muscles of the wall initiate wavelike contractions
which propel food to the esophagus
Has three parts:
a. Nasopharynx – located behind the nasal cavity
A. ORGANS OF THE GASTROINTESTINAL TRACT
I. MOUTH/ ORAL CAVITY – subdivided into the:
a. Vestibule – space between the lips and cheeks externally and
teeth internally
b. Oral cavity proper – space enclosed by the teeth
Structures inside the oral cavity proper:
1. Tongue – dorsal surface divided into anterior 2/3 and
posterior 1/3 by the sulcus terminalis
- papillae found in this surface
a. Filiform – most numerous, with pointed ends
b. Fungiform – larger, rounded, with some taste buds
c. Vallate – around 8-12, located anterior to the sulcus terminalis
- contains the greatest amount of taste buds
d. Foliate
b.
Oopharynx – from the soft palate to the epiglottis
(behind oral cavity)
c.
Laryngopharynx – from the epiglottis to the base of
the larynx (behind larynx)
Events during swallowing:
1. Nasopharynx closes, at the same time, breathing is
inhibited
2.
Laryngeal muscles contract to close the epiglottis and
elevate the larynx
3.
Peristalsis sweeps in the pharynx to propel the food
with the simultaneous opening of the upper
esophageal sphincter
- The swallowing reflex is coordinated in the medulla
III. ESOPHAGUS
- conducts food from the pharynx to the stomach by peristalsis
- with three constrictions
1. At the beginning (caused by cricopharyngeus muscle)
- known as the Upper Esophageal Sphincter (UES), an anatomic
sphincter
2. At the level of the left main stem bronchus
3. At the lower end (as it passes to through the diaphragm)
- known as the lower esophageal sphincter (LES), only a
physiologic sphincter
-where final digestion of food and where absorption takes
place
Three structural modifications increase absorptive area
1. Microvilli - minute projections of the surface plasma
membrane of the cells in the lining epithelium
2. Villi – fingerlike projection of the mucosa that gives a
velvety appearance and texture
3.
Pilicae Circulares/valves of Kerkring – deep folds of
mucosa and submucosa
The duodenum is further subdivided into:
a. superior/first part
- the first inch is called “duodenal bulb”
b. descending/second part
- contains the greater and lesser duodenal papillae into which
the common bile duct and the pancreatic ducts empty their
secretions
c. horizontal/ third part
d. ascending/fourth part – ends in the duodeno-jejunal
junction
IV. STOMACH
- physical breakdown food into smaller pieces
• Suspensory ligament of Treitz - band of fibrous muscular
tissue which extends from the duodenojejunal angle into
the right crus of the diaphragm
• Peyer’s patch – large collection of lymphoid tissue found
in the ileum
- temporary storage of food
- found on the upper left side of the abdominal cavity
Has the following parts:
1. Cardiac region – area surrounding the point of entry of food
in the stomach.
2. Fundus – the expanded region lateral to the cardiac region
3. Body
4. Pylorus – terminal part, continuous with the small intestine
through the pyloric sphincter
5. Lesser curvature – concave medial border
6. Greater notch – sharp angle between the esophagus and
fundus
7. Angular notch – sharp angle found on the lesser curvature
VI. LARGE INTESTINE
- has the following parts:
1. cecum
2. appendix
3. ascending colon
4. right colic flexure
5. transverse colon
6. left colic flexure
7. Descending colon
V. SMALL INTESTINE
- has three parts
a. duodenum
b. jejunum
c. ileum
8. Sigmoid colon
9. Rectum
10. Anal canal
a. common hepatic duct
b. hepatic artery
c. Portal vein
•
The large intestine functions to compact and propel
the fecal matter towards the anal canal and eliminate
it in the anus. Also, absorption of the remaining water
and some electrolytes in the undigested food also
occurs.
•
The bacterial flora in the large intestine provides the
body with vitamin K
B. ACCESSORY ORGANS OF DIGESTION:
I. Salivary Glands
III. Gallbladder
PARTS
1. Fundus
2. Body
3. Infundibulum (Hartmann’s pouch)
4. Neck
- layers of the wall
1. mucosa
2. muscular layer
3. fibrous layer
- Spiral valve of Heister – produced by the mucosal duplication of the first
part of the cystic duct.
- Extrahepatic biliary system – right and left hepatic ducts join to form the
common hepatic duct which further joins the cystic duct from the
gallbladder to form the common bile duct. The common bile duct opens
into the duodenum with the pancreatic duct.
- Ampulla of vater – a reservoir formed within the wall of the second part of
the duodenum formed by the junction of the common bile duct and
main pancreatic duct.
- Duodenal papilla – elevation in the duodenal mucosa into which ampulla of
vater opens
II. Liver
- peritoneal attachments
1. Falciform ligament
- attaches the liver to the superior abdominal wall
- ligamentum teres hepatis is found on its free edge
- divides the liver classically into right and left lobes
2. Coronary ligament
- upper and lower layers enclose the “bare area”
- forms the right triangular ligament
3. Left triangular ligament
- attaches the left lobe to the diaphragm
Parts seen in the visceral or inferior surface of the liver
1. fissure for ligamentum teres (from umbilical vein) and
ligamentum venosum ( from ductus venosus )
2. gallbladder fossa and sulcus of the inferior vena cava (imaginary
line passing here divides the liver functionally into right and left
lobes)
3. porta hepatis – contains the portal triad
Spinchter of oddi – smooth muscle surrounding the opening of
ampulla of vater in second part of duodenum
IV. Pancreas
Parts
1. Head – surrounded by the duodenum
2. Neck and body – found at the back of the stomach
3. Tail – related to the spleen
Ducts
1. main pancreatic duct of Wirsung
2. accessory duct of Santorini – opens into the duodenum in the
minor papilla, 2cm above the major duodenal papilla
Digestion and Absorption of Foodstuff
1. Mouth – digestion of carbohydrates by salivary amylase (starch
→ oligosaccharides)
- no protein or fat digestion taking place here
2. Stomach – pepsin in the presence of HCl (protein changed to
shorter polypeptide) no carbohydrates or fat digestion
3. Small intestine
a. Carbohydrates – pancreatic amylase ( starch → dissacharides)
- brush border enzymes (dissacharides → monosaccharides)
b. Protein – pancreatic enzymes (protein to shorter polypeptide)
- brush border enzymes (dipeptides → amino acids)
c. Lipids – pancreatic lipase (triglycerides → monoglycerides and
free fatty acids)
- needs emulsification by bile from liver.