The Digestive System
 Digestive System
 Two groups of organs
o _________________________________________________________________________
 Digests and absorbs food
 Mouth, pharynx, esophagus, stomach, small intestine, and large intestine (ends in
the rectum and anus)
o _________________________________________________________________________
 Teeth, tongue, gallbladder
 Digestive glands
 _________________________
 _________________________
 _________________________
 Digestive Processes
 Six essential functions
o _________________________
o _________________________
 The physical movement of food
o _________________________
 The chemical breakdown of food
o _________________________
 The release of water, acids, enzymes, and buffers
o _________________________
o _________________________
 Histological Organization
 _________________________
o The inner lining of the digestive tract
o Folds to increase surface area for absorption and permit expansion after a big meal
o Secretes mucus, digestive enzymes and hormones and protects against infectious disease
 _________________________
o The second layer out from the mucosa
o Involved in controlling and coordinating contractions and regulating secretion of
digestive glands
 _________________________
o A band of smooth muscle whose contractions agitate and propel materials along the
digestive tract
 _________________________
o Outermost layer with portions suspended in mesenteries that stabilize the attached
organs and prevent tangling
 The Movement of Digestive Materials
 Pacesetter cells trigger waves of contraction resulting in rhythmic cycles of activity
o These contractions play a vital role in 2 processes: peristalsis and segmentation
 ___________________________________________________________________
 Circular muscles first contract behind the digestive contents
 Then longitudinal muscles contract shortening adjacent tract segments
 Finally a wave of contraction in circular muscles forces the materials in the
desired direction
 ___________________________________________________________________
 Results in a through mixing of the contents with intestinal secretions
 The Oral Cavity
 The mouth opens into the oral cavity (tongue, salivary glands, and teeth) which
o _________________________________________________________________________
o Mechanically processes material through the actions of the teeth, tongue, and surfaces
of the palate
o Lubricates material by mixing it with mucus and salivary secretions
o _________________________________________________________________________
 ___________________________
o Manipulates materials inside the mouth and occasionally used to bring food into the oral
cavity
 ___________________________
o There are 3 pairs of salivary glands: ___________________________________________
o At mealtimes, large quantities of saliva lubricate the mouth and dissolve chemicals that
stimulate taste buds
o Each type of salivary gland produces slightly different saliva
 ___________________________________________________________________
 __________________________________________________________________
 ___________________________
o Perform mastication (chewing) which breaks down tough connective tissues in meat and
the plant fibers in vegetable matter
o 3 parts to a tooth: ______________________________________
 Crown is covered in enamel (contains calcium phosphate)
o _______________________________ (mineralized matrix similar to bone)
o Anchored in place via cementum
o 4 types of teeth:
 ___________________________________________________________________
 ___________________________________________________________________
 ___________________________________________________________________
 The Pharynx, Esophagus, and Swallowing
 The Esophagus
o _________________________________________________________________________
o Lined with an epithelium that resists abrasion, hot/cold temperatures, and chemical
attack
Swallowing (___________________)
o A complex process that can be initiated voluntarily but proceeds automatically
o 3 phases:
 ____________________ – compression of bolus (small mass of food being
swallowed) against the hard palate
 ____________________ – bolus comes in contact with sensory receptors
initiating swallowing reflex and pushing the bolus into the esophagus
 ____________________ – bolus is pushed towards the stomach by peristaltic
contractions
 The Stomach
 4 primary functions:
o _________________________________________________________________________
o _________________________________________________________________________
o _________________________________________________________________________
o _________________________________________________________________________
 Ingested materials mix with secretions in the stomach and create chyme
 Contains rugae which are folds that increase surface area and allow for distension when food
enters the stomach
 4 regions:
o __________________ - Where the esophagus connects to the stomach
o __________________ - The bulge at the top of the stomach
o __________________ - Main portion between the fundus and pylorus
o __________________ - The end where the stomach connects to the small intestine
 2 mesenteries that hold the stomach in place: ______________________ extends below the
greater curvature and the ____________________ extends from the lesser curvature to the liver
 The Gastric Wall
 Lined with mucous cells that secrete an alkaline mucus that protects epithelial cells from acids,
enzymes, and abrasive materials
 Has gastric pits (shallow grooves) that contain gastric glands that secrete gastric juices
o 2 cells that produce the components of gastric juices
 ________________________________
 Secrete intrinsic factor and HCl
 ________________________________
 Secrete pepsinogen (inactive until mixed with HCl)
 Gastric Activity Regulation
 Regulation of gastric secretion proceeds in 3 overlapping phases:
o _____________________________________
 Initiated by the sight, smell, taste, or thought of food
 Prepares the stomach to receive food by accelerating the production of gastric
juices
o _____________________________________
 Begins with the arrival of food in the stomach
 When chyme is formed and begins to move into the small intestine

o _____________________________________
 Begins when chyme first enters the small intestine
 The rate of movement of chyme into the small intestine is highest when the
stomach is greatly distended and meals contain little protein
 The Small Intestine
 90% of nutrient absorption occurs in the small intestine
 About 20ft long and 1.6in wide
 3 segments:
o _____________ – “C”-shaped segment closest to the stomach that encloses the pancreas
 “mixing bowl” that receives chyme from the stomach, and digestive secretions
from the pancreas and liver
o _____________ – the bulk of chemical digestion and nutrient absorption occurs here
o _____________ – closest to the large intestine, ending at the ileocecal valve which the
entrance to the cecum
 Wall covered in folds (____________________________) and composed of villi
 Once chyme enters the small intestine , segmentation contractions mix it with mucous and
enzymes. As absorption occurs, weak peristaltic contractions slowly move the remaining
materials along the small intestine
o Distention of the stomach initiates the ________________________, which accelerates
glandular secretion and peristaltic activity
o The ______________ is a response to circulating levels of the hormone gastrin. The entry
of food into the stomach triggers the release of gastrin which relaxes the ileocecal valve
 The Pancreas
 The pancreas provides digestive enzymes , as well as buffers that help neutralize chyme
 An exocrine organ that produces pancreatic juices, a mix of digestive enzymes and buffers
o ___________________________________________________
o The pancreatic duct carries these secretions to the duodenum
 The pancreatic duct penetrates the duodenal wall with the common bile duct
from the liver and gallbladder
 Pancreatic enzymes do most of the digesting in the small intestine
o Classified according to their intended target: ________________ (carbs),
_______________ (lipids), ______________ (nucleic acids), and ____________ (proteins)
 The Liver
 4 unequal lobes: left and right lobes (__________________________________) and the caudate
and quadrate lobes
o Made up of about 100,000 liver lobules, the basic functional unit of the liver
 Within each lobule are liver cells (______________________)
 Blood enters the liver from the hepatic portal vein and artery then joins with the bile duct to
form the hepatic triad
 _______________________________________________________________________________
_______________________________________________________________________________
o Eventually bile leaves the liver via the common bile duct and empties into the duodenum
or cystic duct (to the gallbladder)
3 general functions:
o ____________________________________
 Blood leaving the absorptive areas of the digestive tract flows through the liver
before reaching the general circulation
 This is when hepatocytes extract absorbed nutrients/toxins and monitor/adjust
nutrient levels
o ____________________________________
 When aged or damaged RBCs, debris, and pathogens are removed from
circulation
o ____________________________________
 Dilutes and buffers chyme using bile salts (cholesterol derivatives that function in
fat emulsification and absorption)
 The Gallbladder
 ______________________________________________________________________________
 Stores and concentrates bile before it is excreted into the small intestine
o When chyme enters the small intestine bile is released by the gallbladder, travels down
the cystic duct and joins with the common hypatic duct to form the common bile duct
which enters the duodenum via the hypatopancreatic sphincter
 _______________________________________________________________________________
_______________________________________________________________________________
 The Large Intestine
 Begins at the end of the ilium and ends at the anus
 3 parts:
o _________________________________________________________________________
 Attachment site of the appendix
o _________________________________________________________________________
 Has pouches (haustra) that allow for distension and elongation
 Sectioned (in order) into the ascending colon, transverse colon, descending colon,
sigmoid colon
o _________________________________________________________________________
 Main functions include:
o _________________________________________________________________________
o Absorption of nutrients freed by bacteria
 ___________________ – reabsorbed and transported back to liver
 ___________________ – supplemental vitamins (vitamin K, biotin, and vitamin
B5) are generated by bacteria
 ___________________
 ___________________
o Storage of fecal material before defecation
 When fecal material enters the rectum it triggers the urge to deficate
