DIGESTIVE SYSTEM

Jhia Anjela D. Rivera1

1BS Biology, Department of Biology, College of Science, Polytechnic University of the Philippines

DIGESTIVE SYSTEM

• Consists of the digestive tract (gastrointestinal tract (GIT), alimentary canal/tract) and other associated organs

• Meals on wheels (with the aid of circulatory system)

• Digests foods into soluble form

FUNCTIONS OF DIGESTIVE SYSTEM • INGESTION – solid and liquid food intake

through the mouth • MASTICATION – chewing, grinding of

food into smaller pieces (teeth) • PROPULSION – movement of food from

one end of the digestive tract to the other

• Degluttion (swallowing) – moves liquids or a soft mass of food and liquid from the oral cavity into the esophagus

• Peristalsis – lower the food in the stomach • Mass movements

FUNCTIONS OF DIGESTIVE SYSTEM • MIXING – mixture of masticated food

with different juices/enzymes • SECRETION – added to lubricate, liquify,

buffer and digest the food • DIGESTION – break down of food into

smaller molecules that can be absorbed by the body

• ABSORPTION – movement of molecules out of the DT and into the circulation or into the lymphatic vessels (AA, FA, MS, V, M, H2O)

FUNCTIONS OF DIGESTIVE SYSTEM

• ELIMINATION – waste products excretion in the form of feces

REGIONS OF THE DIGESTIVE TRACT

ORAL CAVITY

PHARYNX

ESOPHAGUS

STOMACH

SMALL INTESTINE

LARGE INTESTINE

ANUS

PERITONEUM

• Walls and organs of the abdominal cavity are lined with serous membranes

• Visceral peritoneum – serous membrane that covers organs

• Parietal peritoneum – covers the interior surface of the wall of the abdominal cavity

• Mesenteries » These are connective tissue sheets that hold many

organs in place within the abdominal cavity » They provide a route by which vessels and nerves

can pass from the abdominal wall to the organs

PERITONEUM

• Walls and organs of the abdominal cavity are lined with serous membranes

• Visceral peritoneum – serous membrane that covers organs

• Parietal peritoneum – covers the interior surface of the wall of the abdominal cavity

• Mesenteries » These are connective tissue sheets that hold many

organs in place within the abdominal cavity » They provide a route by which vessels and nerves

can pass from the abdominal wall to the organs

PERITONEUM

• Retroperitoneal - refers to the abdominal organs that doesn’t have mesenteries

• Duodenum, pancreas, ascending and descending colon, rectum, kidneys and urinary bladder

• Mesentery proper - mesentery associated with the small intestines

• Transverse mesocolon, sigmoid mesocolon and mesoappendix

PERITONEUM

ORAL CAVITY

• Mouth • Divided into 2 regions:

• Vestibule – space between the lips • Oral cavity proper – lies medial to the teeth

ORAL CAVITY

TONGUE • Large muscular organ that almost

occupies all of the area in the oral cavity

• Holds the food in place in cooperation with the lips and cheeks during mastication

• Major sensory organ for taste and speech, plays a role in swallowing

• Frenulum – a thin fold of tissue that is attached anteriorly to the floor of the mouth

SALIVARY GLANDS

• Produce saliva (mixture of mucous and serous fluids)

• Branching ducts with clusters of alveoli at the ends of the ducts

• Three pairs of salivary glands • Parotid • Sublingual glands • Submandibular glands

SALIVARY GLANDS

• Parotid Gland • largest of the salivary glands, serous glands

located just anterior to each ear • Enter the oral cavity adjacent to the second

upper molars

• Submandibular Glands • Produce more serous than mucous secretions • Open into the oral cavity on each side of the

frenulum of the tongue

SALIVARY GLANDS

• Sublingual Glands • Smallest of the three paired salivary glands,

produce primarily mucous secretions • Lie immediately below the mucous

membrane in the floor of the oral cavity • Each has 10-12 small ducts opening onto the

floor of the oral cavity

SALIVARY GLANDS

PHARYNX

• Oropharynx and laryngopharynx transmit the food

• Epiglottis covers the opening of the larynx and keeps food and drink from entering the larynx

PHARYNX

ESOPHAGUS • Extends between the pharynx and the

stomach • about 25 cm long and lies in the

mediastinum, anterior to the vertebrae and posterior to the trachea

• passes through the esophageal hiatus (opening) of the diaphragm and ends at the stomach

• Transports food from the pharynx to the stomach

ESOPHAGUS

• Esophageal sphincter • Upper and lower ES • Regulate the movement of materials into and

out of the esophagus

ESOPHAGUS

STOMACH

• Enlarged segment of the digestive tract in the left superior part of the abdomen

• Acts as storage and mixing chamber • Located on the left superior part of

the abdomen

STOMACH

STOMACH • Most dilated part of the GIT and has a j-

like shape • Located in the epigastric, umbilical and

left hypochondrium regions of the abdomen – Divided into 4 regions

• Cardia – gastroesophageal opening • Fundus of the stomach – superior to the cardia • Body – largest part of the stomach • Pyloric part

STOMACH

• Pyloric part • Antrum – wider part of the funnel • Canal – narrow part • Orifice – opening of stomach to small

intestine • Sphincter/pylorus - thick ring of smooth

muscle, which helps regulate the movement of gastric contents into the small intestine

SMALL INTESTINE

• Longest part of the GIT • Extends from the pyloric orifice of the

stomach to the ileocecal fold • Approximately 6-7m long with a

narrowing diameter from beginning to end

• Where the greatest amount of digestion and absorption occurs

SMALL INTESTINE

• Longest part of the GIT • Extends from the pyloric orifice of the

stomach to the ileocecal fold • Approximately 6-7m long with a

narrowing diameter from beginning to end

• Where the greatest amount of digestion and absorption occurs

SMALL INTESTINE

• Consists of three parts: • Duodenum (12 inches long) • Jejunum (2.5m) • Ileum (3.5m) • Two major accessory glands, the liver and the

pancreas, are associated with the duodenum

SMALL INTESTINE

SMALL INTESTINE

• Duodenum • First part of small intestine • C-shaped, adjacent to the head of the

pancreas • 20-25cm long, above the level of umbilicus

– Divided into 4 parts: » Superior part – extends from pylori orifice of the

stomach to the neck of the gallbladder, just right to the body of L1 vertebra, clinically, it is called as duodenal cap or ampulla

SMALL INTESTINE

• Duodenum • First part of small intestine • C-shaped, adjacent to the head of the

pancreas • 20-25cm long, above the level of umbilicus

– Divided into 4 parts: » Superior part – extends from pylori orifice of the

stomach to the neck of the gallbladder, just right to the body of L1 vertebra, clinically, it is called as duodenal cap or ampulla

SMALL INTESTINE

• Duodenum » Descending part – located just to right of the

midline and extends from the neck of the gallbladder to the lower border of L3 vertebra; contains the entrance of major duodenal papilla and minor duodenal papilla

» Inferior part – longest section, crossing the IVC, aorta and vertebral column

» Ascending part – passes upward on or to the left of the aorta to approximately the upper border of L2 vertebra

SMALL INTESTINE

• Jejunum » Represents the proximal two-fifths of the small

intestine » Mostly on the left upper quadrat » Larger in diameter and has thicker wall than

ileum

• Ileum » Makes up the distal three-fifths of the small

intestine » Mostly on the right lower quadrat and opens

into the large intestine (jejunum and ileum major sites of absorption)

SMALL INTESTINE

• Ileocecal junction – site where the ileum connects to the large intestine

• Ileocecal fold – two flaps projecting into the lumen of the large intestine

• Ileocecal valve – allows the intestinal contents to move from the ileum to the large intestine, but not in the opposite direction (also a sphincter)

LARGE INTESTINE

• Extends from the distal end of the ileum to the anus

• Absorbs fluids and salts from the gut contents, thus forming feces – Consists of:

• Cecum and appendix • Colon • Rectum • Anal canal

LARGE INTESTINE

LARGE INTESTINE

• Cecum and Appendix – Cecum

• First part of the large intestine • Inferior to the ileocecal opening and in the

right iliac fossa – Appendix

• Narrow, hallow, blind-ended tube connected to the cecum

LARGE INTESTINE

• Colon – Extends superiorly from the cecum

• Consists of: – Ascending colon – Transverse colon – Descending colon – Sigmoid colon

LARGE INTESTINE

• Ascending colon – extends superiorly from the cecum and ends at the right colic flexure (hepatic flexure) near the right inferior margin of the liver

• Transverse colon – extends superiorly from the cecum and ends at the right colic flexure (hepatic flexure) near the right inferior margin of the liver

LARGE INTESTINE

• Descending colon – extends from the left colic flexure to the superior opening of the true pelvis, where it becomes the sigmoid colon

• Sigmoid colon - forms an S- shaped tube that extends into the pelvis and ends at the rectum

LARGE INTESTINE

• Rectum - straight, muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal

• Anal canal - begins at the inferior end of the rectum and ends at the anus (external GI tract opening)

• Anus – external and internal sphincter

LIVER

• largest internal organ of the body • in the right-upper quadrant of the

abdomen, tucked against the inferior surface of the diaphragm

• consists of two major lobes: left and right , and two minor lobes, caudate and quadrate

LIVER

LIVER

• Surfaces of the liver include: – Diaphragmatic surface – anterior,

superior and posterior directions (smooth and domed)

– Visceral surface – inferior directions, covered with visceral peritoneum except for fossa of the gallbladder and porta hepatis • Porta hepatis – PoE into the liver for the

hepatic arteries and the portal vein, and the exit point for the hepatic ducts

LIVER

• Lobes – Consists of two major lobes, right and left

lobes – Separated by a falciform ligament – two minor lobes: caudate and quadrate

(inferior view)

GALLBLADDER

• A pear-shaped sac lying on the visceral surface of the right lobe of the liver in a fossa between the right and quadrate lobes

• Cystic duct – Fundus of the GB – rounded end – Body of the GB – major part of the fossa – Neck of the GB – narrow part

• To store bile released by the liver

GALLBLADDER

PANCREAS • complex organ composed of both endocrine

and exocrine tissues that perform several functions

• Lies mostly posterior to the stomach and consists of: – Head of the pancreas – lies within the C-shaped

concavity of the duodenum – Uncinate process – lower part of the head – Neck of the pancreas – Body of the pancreas – elongate and extends

from the neck to the tail of the pancreas – Tail of the pancreas

PANCREAS

PANCREAS

• Pancreatic duct – begins in the tail of the pancreas

• Hepatopancreatic ampulla (Vater’s ampulla)

• Sphincter of Oddi – surround the ampulla • Accessory pancreatic duct – empties

into the duodenum just above the major duodenal papilla at the minor duodenal papilla

PANCREAS

QUIZ 1. Which of these glands does not secrete saliva into the oral cavity? • a. submandibular glands c. sublingual glands • b. pancreas d. parotid glands

2. The portion of the digestive tract in which digestion begins is the a. oral cavity. c. stomach. e. jejunum. b. esophagus. d. duodenum

QUIZ 3. Given these parts of the small intestine: 1. duodenum 2. ileum 3. Jejunum Choose the arrangement that lists the parts in the order food encounters them as it passes from the stomach through the small intestine. a. 1,2,3 c. 2,1,3 e. 3,1,2 b. 1,3,2 d. 2,3,1

QUIZ 4. Given these structures: 1. ascending colon 2. descending colon 3. sigmoid colon 4. transverse colon Choose the arrangement that lists the structures in the order that food encounters them as it passes between the small intestine and the rectum. a. 1,2,3,4 c. 2,3,1,4 e. 3,4,1,2 b. 1,4,2,3 d. 2,4,1,3

QUIZ 3. The tongue a. holds food in place during mastication. b. plays a major role in swallowing. c. helps form words during speech. d. is a major sense organ for taste. e. all of the above.