CHAPTER 17: DIGESTIVE SYSTEM
OBJECTIVES
1.
Define the term digestion and explain its significance.
2.
Distinguish between mechanical digestion and chemical digestion.
3.
Discuss the five digestive processes that overview the many functions of the digestive
system.
4.
Distinguish between the alimentary canal and digestive accessory organs.
5.
Name two synonyms for the alimentary canal.
6.
List the organs that compose the alimentary canal and identify each on a diagram.
7.
List the digestive accessory organs and identify each on a diagram.
8.
Name the four layers that compose the wall of the alimentary canal from innermost
(lining lumen) to outermost.
9.
Compare and contrast the four layers of the alimentary canal wall (named above) in terms
of their structure, function, and any distinguishing features.
10.
Name the layer of the alimentary canal that is synonymous with visceral peritoneum.
11.
Explain the significance of mesenteries or peritoneal extensions.
12.
Describe how food is moved through the length of the alimentary canal and name the
layer responsible for these actions.
13.
Define the term digestive sphincter muscle, describe the structure of these muscles, name
the function of these muscles, and denote the major five locations of digestive sphincter
muscles.
14.
Name two synonyms for the mouth.
15.
Describe the overall structure and function of the mouth.
16.
Discuss the three portions of the palate, in terms of location and give an overall function
for the palate.
17.
Name the tissue that composes the tonsils and name the overall function of tonsils.
18.
Name the two sets of teeth we possess as humans, discuss the general structure of a tooth,
and describe the four types of teeth we possess according to their location and function.
19.
Name and locate the three sets of salivary glands in humans, name and describe the
secretions from these glands, and name the two types of cells that compose these glands.
20.
Discuss the enzyme "salivary amylase", in terms of its digestive function, location, and
secretory gland.
21.
Explain the process of deglutition.
22.
Name the function of the epiglottis.
23.
Define the term peristalsis and explain its digestive function.
24.
Define the term gastric.
25.
Describe the macroscopic structure of the stomach and locate it on a diagram or torso
model.
26.
Name the term used to describe the mucosal folds of the stomach lining and explain their
significance.
27.
Discuss the histology of the stomach wall.
28.
Name the four types of cells that compose gastric glands, name the secretion(s) that each
cell produce(s) that together compose gastric juice, and give the function of each
component of gastric juice.
29.
Define the term chyme.
30.
Name one substance that is absorbed through the gastric mucosa.
31.
Name the hormone that regulates the release of gastric juice, explain when it is released,
and the results of its action.
32.
Using anatomical terminology, describe the location of the pancreas in the abdominal
cavity.
33.
Explain how the pancreas aids in digestion by listing the components in pancreatic juice,
and naming the action of each of those components.
34.
Name the site of pancreatic enzyme action.
35.
Name the regulatory hormone responsible for the release of pancreatic juice into the
duodenum, and explain when it is activated.
36.
Using anatomical terminology, describe the location of the liver in the abdominal cavity.
37.
Name the functional unit of the liver and describe its general structure.
38.
Define the terms hepatocyte and liver sinusoids.
39.
40.
Describe the many functions of the liver.
Name the two blood vessels that supply the liver lobules with blood and track the flow of
blood into and out of the liver lobule.
41.
Name the components of a portal triad.
42.
Explain the significance and location of Kupffer's cell.
43.
Define the term emulsification and explain its role in digestion.
44.
Using anatomical terminology, describe the location of the gallbladder in the abdominal
cavity.
45.
Name the function of the gallbladder.
46.
Name the "common" route that bile travels from either the liver or gallbladder and name
the site where bile is deposited.
47.
Name the regulatory hormone that is responsible for the release of bile into the duodenum
and explain when it is activated.
48.
Name the three parts of the small intestine, and locate each on a diagram or torso model.
49.
Discuss the histology of the small intestinal wall.
50.
Name the digestive enzymes that are secreted by the mucosa of the small intestines and
explain the action of each.
51.
Identify the simplest forms of food that are absorbed through the mucosa of the small
intestine, name the transport process by which each is absorbed, and describe the fate of
each absorbed nutrient.
52.
Define the term lacteal and explain its significance.
53.
Distinguish between the duodenum and the distal small intestine (i.e. jejunum and ileum)
in terms of function.
54.
Name the four parts of the large intestine and locate each on a diagram or torso model.
55.
Name the four parts of the colon and locate each on a diagram or torso model.
56.
Identify the major digestive function of the large intestine.
57.
Explain how the movements in the large intestine differ from those throughout the rest of
the alimentary canal.
58.
Define the terms feces and defecation.
59.
Name the sphincter muscles that open to the outside and explain how their action is
controlled.
60.
List the four major organic macromolecules that we ingest, and explain how each is
broken down by various enzymes within the alimentary canal. Be sure to include enzyme
names, the location of enzyme action, and the breakdown products that result from the
enzymatic action, and explain any hormonal control of the breakdown. Finally, explain
how and where these simplest food forms are absorbed into the bloodstream or lymphatic
system.
I.
INTRODUCTION
A.
Definition:
Digestion
The process by which food substances are changed into forms that can be
absorbed through cell membranes.
B.
Digestive Processes:
1.
2.
3.
4.
5.
C.
Ingestion = taking food into the mouth.
Movement of Food = the passage of food along the gastrointestinal (GI)
tract.
Digestion = the breakdown of food by chemical and mechanical means.
Absorption = the passage of digested food from GI tract into bloodstream
(and lymph) for distribution to cells.
Defecation = the elimination of undigested material from GI tract.
Digestive Organs
See Fig 17.1, page 645.
1.
Two categories:
a.
Alimentary canal (GI Tract), which extends from mouth to anus.
o
Organs include: See Fig 17.2, page 646.
1.
2.
3.
4.
5.
6.
b.
mouth
pharynx
esophagus
stomach
small intestine
large intestine
Accessory organs release secretions into the alimentary canal that
help digest food:
o
Organs include:
1.
salivary glands
2.
liver
3.
gallbladder
4.
pancreas
II.
GENERAL CHARACTERISTICS OF THE ALIMENTARY CANAL
A.
Structure of the Wall = Four Distinct Layers
See Fig 17.3, page 647 and Table 17.1, page 646.
1.
mucosa = innermost (surrounds lumen);
a.
b.
c.
d.
composed of epithelium + CT (areolar); and small amounts of
smooth muscle
epithelium extends into lumen = villi (increases surface area);
contains many glands that secrete mucus (lubrication & protection
from harmful action of digestive enzymes);
functions:
o
o
o
2.
submucosa = beneath mucosa;
a.
b.
composed of areolar CT, blood vessels, lymph vessels, and nerves;
functions:
o
o
3.
nourishment of mucosa;
carrying absorbed nutrients away.
muscularis =2 layers of muscle
a.
b.
c.
4.
protection
secretion
absorption (of nutrients).
circular muscle layer around submucosa;
longitudinal layer around circular layer;
function: movements of food through canal (mixing & peristalsis).
serosa =outermost layer;
a.
visceral peritoneum;
b.
functions:
o
lubrication
o
free movement of canal in abdominal cavity
c.
Intestinal peritoneal extensions = mesenteries.
o
suspend the length of the intestine within abdominal cavity.
II.
GENERAL CHARACTERISTICS OF THE ALIMENTARY CANAL
B.
Movements of the tube
See Figure 17.4, page 647.
1.
Mixing: (mechanical digestion)
a.
b.
2.
Peristalsis:
a.
b.
c.
C.
accomplished by movements of longitudinal muscle layer;
propelling action;
As food passes, one section of tube relaxes (receptive relaxation),
opening next section & food moves on.
Sphincter Muscles play an important role in movements throughout the GI tract
also.
1.
2.
D.
food + digestive juices + mucus
circular muscle layer
Definition: Sphincter = a strong circular muscle which prevents
regurgitation of food.
Locations: between (regions) organs of digestive tract.
a.
esophagus and stomach
o
gastroesophageal sphincter;
b.
stomach and small intestine
o
pyloric sphincter;
c.
small and large intestine
o
ileocecal valve;
d.
large intestine to outside
o
internal anal sphincter and
o external anal sphincter.
Innervation of the Tube
1.
Autonomic Nervous System
a.
Parasympathetic – activates digestion
b.
Sympathetic – slows digestion
2.
Post-ganglionic networks
a.
Submucosal plexus = controls secretions
b.
Myenteric plexus = controls peristalsis
III.
ORGANS OF THE DIGESTIVE SYSTEM
A.
The Mouth (oral/buccal cavity):
See Fig 17.5, page 649 and Fig 17.7, page 650.
1.
adapted to receive food and start digestion by chewing & mixing with
saliva;
2.
surrounded by cheeks, lips, tongue and palate:
3.
a.
Cheeks and Lips
o
cheeks – lateral walls of mouth
o
lips = surround opening of mouth, important in monitoring
food temperature
b.
Tongue
See Figure 17.6 page 649
o
muscular (skeletal) organ on floor of mouth
o
important in mixing food (mechanical digestion) and
swallowing
o
contains many bumps called papillae, which house taste
buds
o
posterior root contains lymphatic tissue called the lingual
tonsil
c.
palate = roof of mouth
o
anterior portion = hard palate;
o
posterior portion = soft palate;
o
median extension of soft palate = uvula.
o
tonsils:
1.
Palatine tonsils = masses of lymphatic tissue lateral
to palate;
2.
Pharyngeal tonsils = adenoids; lymphatic tissue on
posterior pharynx
3.
Tonsillitis = inflammation of palatine tonsils
composed of 2 chambers:
a.
oral cavity proper = chamber that extends from teeth/gums to
pharynx;
b.
vestibule = narrow space between teeth, cheeks and lips.
III.
ORGANS OF THE DIGESTIVE SYSTEM
A.
The Mouth (oral/buccal cavity):
4.
filled with teeth:
a.
b.
c.
two sets of dentitions: See Fig 17.8, page 651 and Table 17.2, page
651.
o
deciduous teeth
1.
number 20,
2.
erupt from 6 - 32 months,
3.
lost between 6 - 12 years.
o
permanent (secondary) teeth
1.
number 32,
2.
erupt from 6 yrs - adulthood.
3.
See Fig 17.9, page 651.
function: to break food into smaller pieces. (mechanical digestion)
o
increasing surface area of food;
o
increasing effectiveness of digestive enzymes.
4 types with different functions:
See Fig 17.9, page 651.
o
incisors = front teeth;
1.
o
cuspids = canine (eye) teeth;
1.
d.
break food into bite-size pieces;
grasps and tears food;
o
bicuspids = grinding food particles;
o
molars = grinding food particles.
Tooth Structure: located in alveolar fossa of maxilla and
mandible
See Fig 17.10, page 652.
o
crown = exposed area of tooth;
o
root = area below gum (gingiva);
o
enamel =covering on crown; Ca+ salts; hardest substance in
body;
o
dentin = bulk of tooth.
III.
ORGANS OF THE DIGESTIVE SYSTEM
A.
The Mouth (oral/buccal cavity):
5.
Salivary Glands secrete saliva.
See Fig 17.11, page 654.
a.
digestive functions:
o
lubrication,
o
bind food together,
o
begin chemical digestion of carbohydrates.
1.
Enzyme = salivary amylase;
2.
break polysaccharides into disaccharides;
a.
b.
b.
c.
starch  disaccharides.
glycogen  disaccharides.
three types of salivary glands: See Figure 17.11 page 654.
o
parotid = largest; lies over masseter, mostly serous cells
o
submandibular = floor of mouth; lateral, mix of serous
and mucous cells
o
sublingual = floor of mouth, medial. Mostly mucous cells
Each salivary gland is composed of 2 types of cells:
See Fig 17.12, page 655.
o
mucous cells secretes mucus;
o
serous cells secrete watery substance containing the
enzyme salivary amylase.
III.
ORGANS OF THE DIGESTIVE SYSTEM
B.
Pharynx: See Fig 17.14, page 657.
1.
throat;
2.
3 parts
a.
nasopharynx – superior to soft palate, posterior to nasal cavity
b.
oropharynx – posterior to mouth down to epiglottis
c.
laryngopharynx – inferior to oropharynx from epiglottis to cricoid
cartilage
3.
passageway of food into esophagus (and air into larynx/trachea);
4.
Swallowing mechanism (deglutition): 3 stages
a.
Stage 1 (voluntary); Chew food & mix with saliva into bolus at
back of pharynx;
b.
Stage 2 (involuntary): Swallowing reflex triggered
o
epiglottis closes over larynx (no breathing),
o
muscles in lower pharynx relax,
o
esophagus opens & food moves in.
c.
Stage 3 (involuntary); Esophagus brings
bolus to stomach by peristalsis
C.
Esophagus: See Fig 17.15, and Fig 17.16, page 657.
1.
passageway for food from pharynx to stomach;
2.
location: mediastinum; behind trachea; goes through diaphragm at
esophageal hiatus
3.
many mucous glands;
4.
movement of food:
a.
b.
c.
d.
gravity;
peristaltic waves from esophagus
sphincter muscle (cardiac sphincter)
sphincter muscle relaxes,
food moves into stomach all at once.
meet
gastroesophageal
III.
ORGANS OF THE DIGESTIVE SYSTEM
D.
Stomach (Gastric)
1.
2.
3.
4.
5.
See Fig 17.17, page 658.
description = J-shaped, pouch-like organ;
contains extra oblique layer in muscularis
location = under diaphragm; left side;
capacity = 1 liter;
Parts of Stomach:
a.
b.
c.
d.
d.
e.
f.
cardiac region - around esophagus
fundic region - large ballooned area
body – main portion
pyloric region - near duodenum
o
The pyloric region narrows into pyloric canal.
o
The pyloric sphincter muscle lies between pylorus &
duodenum.
greater curvature
lesser curvature
body
6.
Functions
a.
mechanical digestion – churning
b.
chemical digestion of proteins – gastric juice
7.
Mucosal Structure
a.
Note the macroscopic rugae (mucosal folds) in Fig 17.17b, page
658.
b.
Microscopically, these rugae are formed by:
See Fig 17.19, page 660
o
gastric villi that project into the lumen which result in the
formation of;
o
gastric pits that are located between the gastric villi.
1.
gastric glands are located along these gastric pits ;
a.
gastric juice is secreted by these gastric
glands.
III.
ORGANS OF THE DIGESTIVE SYSTEM
D.
Stomach (Gastric)
8.
Gastric Juice:
a.
9.
See Table 17.5, page 661.
composed of:
o
mucus,

Function: lubrication, protection of mucosa from
digestion;
o
digestive enzyme pepsin,

Function: protein digestion (into peptides);
o
hydrochloric acid (HCl),

Functions:
1.
denatures proteins,
2.
kills microbes in food,
o
intrinsic factor,

Function: aids absorption of Vitamin B12. needed
for erythropoiesis
o
gastrin,
Function: regulatory hormone.
Four types of gastric cells in Gastric Glands:
See Fig 17.19, page 660
a.
b.
c.
d.
10.
See Fig 17.17, page 658.
Mucous cells secrete mucus;
Chief cells secrete pepsin;
Parietal cells secrete HCl & intrinsic factor;
G-cells secrete gastrin.
Regulation of Gastric Secretions: See Fig 17.20, page 661, and Table
17.6 page 662.
a.
Neural
o
parasympathetic – increases gastric secretion
o
sympathetic – decreases gastric secretion
b.
Hormonal
o
Gastrin – increases gastric secretion
o
Somatostatin – decrease acid secretion from parietal cells
o
Cholecystokinin – decreases gastric motility
III.
ORGANS OF THE DIGESTIVE SYSTEM
D.
Stomach (Gastric)
10.
Regulation of Gastric Secretions:
c.
3 phases of Gastric Secretion
o
Cephalic Phase (30-50% of control)

Increased parasympathetic due to sight, taste, smell,
thought of food
o
Gastric Phase (40-50% of control)

Stretch of stomach wall increases gastrin, which
increases gastric secretions

pH changes alter Gastrin release

food enters increasing pH

the reflexive increase in gastrin lowers pH

when pH lowers to 1.5 gastrin release stops

HCl released from parietal cells comes from blood

Blood pH needs to maintain 7.4

So parietal cells release bicarbonate to blood

Called the alkaline tide
o
Intestinal Phase (5% of control)

Initially releases intestinal gastrin which increases
gastric secretions

As duodenum fill a sympathetic reflex inhibits
gastrin release

Proteins and fats in duodenum stimulate
cholecystokinin release which decreases gastric
motility
11.
Gastric Absorption = Minimal (5%) some salts, water, lipid-soluble
drugs, alcohol
12.
Gastric Movements See Fig 17.21, page 662 & Fig 17.22, page 663.
a.
mixing of bolus of food + gastric juice = chyme;
b.
Peristaltic waves of stomach push chyme toward pyloric sphincter;
it relaxes; food moves into duodenum a little at a time!!!
c.
Enterogastric reflex – ensures stomach
slows down as duodenum fills
d.
Vomiting may occur to quickly remove
toxins
III.
ORGANS OF THE DIGESTIVE SYSTEM
E.
Pancreas
See Fig 17.23, page 664.
1.
Inferior to stomach – retroperitoneal
2.
Structure of the Pancreas
a.
Shrimp–like with head in concave curve of duodenum, tail
extend to the left to the spleen
b.
Few cells produce hormones (insulin and glucagon)
c.
Most cells make up pancreatic acini, which produce
pancreatic juice
3.
Secretes pancreatic juice into a pancreatic duct; pancreatic duct leads to
duodenum (small intestine);
4.
Pancreatic duct joins bile duct at the Hepatopancreatic ampulla (ampulla
of Vater) before passing through the Hepatopancreatic sphincter
(sphincter of Oddi) to enter duodenum
5.
Function of pancreatic juice:
Contains four classes of enzymes that break down:
a.
Carbohydrates (Starch and Glycogen)
o
b.
pancreatic lipase
2 fatty acids + monoglyceride;
Proteins
o
o
o
o
d.
disaccharides;
Fats/Triglycerides
o
c.
pancreatic amylase
trypsin, chymotrypsin, and carboxypeptidase
proteins
peptides;
stored and released as inactive form in zymogen granules
trypsinogen is activated to trypsin by enterokinase
trypsin then activates chymotrypsin and carboxypeptidase
Nucleic Acids
o
nucleases
nucleotides.
* Note bicarbonate ions are also released to neutralize acidic chyme entering from the
stomach
III.
ORGANS OF THE DIGESTIVE SYSTEM
E.
Pancreas
4.
See Fig 17.23, page 664.
Regulation of pancreatic secretions: See Fig 17.24, page 666.
a.
Hormones = Secretin; cholecystokinin
b.
Secretin Activation:
o
o
o
c.
F.
When duodenum fills with acidic chyme,
secretin is released from the intestinal wall
which stimulates the release of bicarbonate rich
pancreatic juice into duodenum.
Cholecystokinin Activation:
o
Once acid is neutralized
o
Proteins and fats signal cholecystokinin release from the
intestinal wall
o
Which stimulates the release of enzyme rich pancreatic
juice into the duodenum
Liver (Hepatic) See Fig 17.25-17.26, pages 667
1.
Location: below diaphragm / right side; largest internal organ
2.
Structure: 4 lobes: Fig 17.26, page 667.
a.
b.
c.
large right & small left;
quadrate and caudate lobe in posterior
each lobe is made up of:
o
Hepatic lobules = functional unit of the liver
See Fig 17.27, page 668.
1.
hexagon shaped around a central vein;
2.
contains hepatocytes which provide most functions
3.
also contains Kupffer’s cells (macrophages)
See Fig 17.28, page 668.
a.
remove and destroy:

microbes;

foreign matter.

worn platelets and erythrocytes.
III.
ORGANS OF THE DIGESTIVE SYSTEM
F.
Liver (Hepatic)
3.
Liver Functions:
a.
b.
c.
d.
e.
metabolism of monosaccharides, lipoproteins, amino acids.
storage (glycogen, Vitamin A, B12, D, iron),
filtering of blood (worn blood cells and debris),
destruction of toxic chemicals (alcohol and drugs),
production/secretion of bile.
See Table 17.7, page 670 for more specifics on liver functions.
4.
Blood Supply: See Figure 17.28, page 668.
a.
b.
c.
from 2 sources:
o
hepatic artery supplies oxygenated blood;
o
hepatic portal vein supplies deoxygenated blood filled
with:
1.
newly absorbed nutrients from small intestine,
2.
toxins from stomach, and
3.
worn blood cells from spleen.
blood enters the liver sinusoids where hepatocytes remove the
following:
o
oxygen,
o
nutrients (stored or used to make new materials),
o
poisons (detoxified),
o
worn cells and debris (phagocytosis).
Blood leaving the liver cells (deoxygenated plus liver secretions)
drains into central veins, which come together and leave the liver
as the hepatic vein.
III.
ORGANS OF THE DIGESTIVE SYSTEM
F.
Liver (Hepatic)
4.
Blood Supply:
d.
Overall scheme of Liver Blood Flow:
Hepatic Artery
(Oxygenated Blood)
from aorta)
Hepatic Portal Vein
(Deoxygenated Blood with
newly
absorbed nutrients from
Small intestine, etc.)
Liver Sinusoids
(Exchange)
Central Vein of Hepatic Lobule
Hepatic Vein
Inferior Vena Cava
5.
Composition of Bile
a.
composition:
o
bile salts (digestive function)
o
bile pigments (biliverdin and bilirubin)

breakdown products of hemoglobin
o
cholesterol
o
electrolytes
III.
ORGANS OF THE DIGESTIVE SYSTEM
G.
Gall Bladder
1.
2.
3.
4.
See Fig 17.26, page 667 and Fig 17.29, page 671.
Stores bile between meals;
Location:
underside of liver, connected via cystic duct;
Bile can flow to small intestine by either of 2 routes:
the liver or gall bladder (see below);
Bile secretion, storage, flow:
From liver:
From Gall Bladder:
Common Hepatic duct
Cystic Duct
COMMON *
BILE DUCT
Duodenum
*Hepatopancreatic Sphincter muscle usually keeps common bile duct closed.
5.
Regulation of bile release
See Fig 17.30, page 673.
a.
Hormone = CHOLECYSTOKININ (CCK);
b.
When small intestine fills with fatty chyme,
o
cholecystokinin is released into blood;
o
CCK stimulates walls of gallbladder to contract;
o
Bile passes down into cystic duct and common bile
duct;
o
Hepatopancreatic sphincter in common bile duct
opens;
c.
Functions of Bile Salts:
Emulsification of fat
molecules!
Emulsification = breaking up of fat globules into small
droplets (increases SA and increases effectiveness of
lipases).
bile is released into duodenum to emulsify fat.
Also aids in absorption of fats and fat-soluble vitamins
o
o
o
III.
ORGANS OF THE DIGESTIVE SYSTEM
G.
Small Intestine
1.
Parts of Small Intestine:
a.
b.
c.
duodenum - nearest stomach,
jejunum - mid-region,
ileum - near large intestine.
o
o
o
2.
The distal end of the ileum narrows to form the ileocecal
valve (sphincter muscle between small & large intestine).
Jejunum and ilium are attached to the posterior abdominal
wall by fold in peritoneum called mesentery
See Figure 17.33 page 674.
Functions of Small Intestine
a.
b.
c.
3.
See Fig 17.31, page 673.
Major site of chemical digestion (duodenum);
o
bile deposition
o
pancreatic juice deposition
o
small intestinal digestive enzymes
Secretions
o
mucus
o
digestive enzymes
Major site of ABSORPTION of Nutrients
o
about 90% of all;
o
through the proximal mucosa.
Mucosal Structure
See Fig 17.35 & 17.36, page 675.
a.
intestinal villi project into lumen (increasing surface area);
b.
each villus is composed of simple columnar epithelium (with
microvilli See Figure 17.37 page 676) and connective tissue with
many blood & lymph vessels (lacteals);
c.
absorbed nutrients are carried away by blood & lacteals;
d.
intestinal glands are located between villi. (increase SA more)
e.
submucosal folds called plicae circulares further increase SA
See Figure 17.38 page 676.
f.
muscularis and serosa are typical
III.
ORGANS OF THE DIGESTIVE SYSTEM
G.
Small Intestine
4.
Secretions of Small Intestine
a.
b.
mucus, from Brunner’s glands in submucosa and goblet cells
digestive enzymes:
o
peptidases
*
o
amino acids;
sucrase, maltase, lactase
*
o
peptides
disaccharides
monosaccharides;
intestinal lipases
*
TG
3 fatty acids + glycerol.
*See Table 17.9 page 677 for Summary of Major Digestive Organs
5.
Regulation of Small Intestinal Secretions
a.
Mechanical and chemical stimulation of
duodenal wall by entering chyme regulates intestinal secretions.
6.
Absorption in Small Intestine (90% of total) Fig 17.42, pg 679.
a.
Intestinal villi (and microvilli, See Fig 17.37, page 676) increase
absorptive surface area;
b.
Simplest forms of ingested food molecules are absorbed into the
intestinal mucosa:
o
monosaccharides
1.
by facilitated diffusion;
2.
carried away by submucosal blood capillary.
o
amino acids
1.
active transport;
2.
carried away by blood capillary.
o
fatty acids and monoglyceride
1.
by simple diffusion into intestinal mucosa;
2.
Once is mucosal cells, the fats are reformed into
chylomicrons (lipoproteins) by the endoplasmic
reticulum
3.
, which are absorbed by lacteals (lymphatic
capillary) and into the lymphatic system.
o
Ions and water are also absorbed
III.
ORGANS OF THE DIGESTIVE SYSTEM
G.
Small Intestine
7.
Movements through Small Intestine
a.
Mixing of chyme + intestinal juices by segmentation (mechanical
digestion)
b.
Peristaltic waves push residual chyme toward ileocecal
sphincter; it relaxes, moving food into large intestine.
c.
H.
Irritation or overdistension may cause peristaltic rush which is
rapid emptying of small intestine resulting in diarrhea.
Large Intestine
1.
Parts of Large Intestine: See Fig 17.43, page 681.
a.
b.
c.
d.
2.
Colon is divided into four (4) portions:
a.
b.
c.
d.
3.
ascending colon - from cecum to liver (right);
transverse colon - runs across top of abdomen;
descending colon - from spleen downward (left);
sigmoid colon - S-shaped portion, which becomes rectum.
Structure of the Large Intestinal Wall
a.
b.
c.
d.
e.
4.
cecum - nearest ileum of small intestine; (appendix is a blind
pouch in this region);
colon - majority of length;
rectum - distal region of colon;
anal canal - narrowing of rectum & opening to outside;
mainly same a typical See pages 645-646.
lacks villi
longitudinal muscularis layer forms 3 bands called teniae coli
pouches or haustra develop due to the tension of the teniae coli
serosa may have fatty extensions called epiploic appendages
Functions of Large Intestine:
a.
b.
c.
d.
secretion = only mucus,
absorption = water & electrolytes,
storage = feces.
intestinal flora = bacteria = digestion of substances humans can
not digest
III.
ORGANS OF THE DIGESTIVE SYSTEM
H.
Large Intestine
5.
Movements in Large Intestine:
a.
mass movements only 2-3 times a day;
b.
Peristaltic waves of large intestine move residual chyme toward
anal sphincter muscles.
6.
Control of Anal Sphincter Muscles:
a.
both voluntary & involuntary nervous control
7.
Feces:
a.
undigested & unabsorbed material;
b.
color due to bile pigments;
c.
odor due to intestinal bacteria & bacterial products formed in
digestion;
d.
75% water.
8.
Defecation = emptying of rectum.
DIGESTIVE SYSTEM SUMMARY TABLE I (keyed at the end of this outline)
NAME OF
DIGESTIVE
ORGAN
ALIMENTARY
CANAL OR
ACCESSORY?
DESCRIPTION OF
STRUCTURE
SECRETIONS
DIGESTIVE
FUNCTION
HORMONAL
CONTROL OF
SECRETIONS?
DIGESTIVE SYSTEM SUMMARY TABLE I (CONTINUED)
NAME OF
DIGESTIVE
ORGAN
ALIMENTARY
CANAL OR
ACCESSORY?
DESCRIPTION OF
STRUCTURE
SECRETIONS
DIGESTIVE
FUNCTION
HORMONAL
CONTROL OF
SECRETIONS?
DIGESTIVE SYSTEM SUMMARY TABLE I (CONTINUED)
NAME OF
DIGESTIVE
ORGAN
ALIMENTARY
CANAL OR
ACCESSORY?
DESCRIPTION OF
STRUCTURE
SECRETIONS
DIGESTIVE
FUNCTION
HORMONAL
CONTROL OF
SECRETIONS?
DIGESTIVE SYSTEM SUMMARY TABLE I (CONTINUED)
NAME OF
DIGESTIVE
ORGAN
ALIMENTARY
CANAL OR
ACCESSORY?
DESCRIPTION OF
STRUCTURE
SECRETIONS
DIGESTIVE
FUNCTION
HORMONAL
CONTROL OF
SECRETIONS?
DIGESTIVE SYSTEM SUMMARY TABLE II (Keyed at the end of this outline)
MACROMOLECULE
INGESTED
SITE OF
DIGESTION
DIGESTIVE
ENZYME(S)
ENDPRODUCT(S)
SITE AND
MODE OF
ABSORPTION
ABSORBED
INTO BLOOD
OR LYMPH
REGULATION
IV.
V.
LIFE SPAN CHANGES
A.
Mouth changes that occur with age reduce chewing ability.
1.
Enamel thins increasing sensitivity to hot and cold.
2.
Gums recede.
3.
Teeth loosen.
B.
Slowing peristalsis causes:
1.
Heartburn.
2.
Constipation.
C.
Absorption of nutrients decreases with age.
Homeostatic Disorders/Diseases:
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
Tonsillitis. See blue box on page 649.
Dental Caries. See Clinical Application 17.1, page 653.
Hiatal hernia. See blue box on page 656.
Hypertrophic pyloric stenosis. See blue box on page 659.
Gastric Ulcers and Helicobacter pylori. See blue box on page 660.
Stomach Aches. See Clinical Application 17.2, page 663.
Acute pancreatitis. See blue box on page 665.
Cystic Fibrosis. See blue box on page 665.
Hepatitis. See Clinical Application 17.3, page 670.
Gallbladder Disease. See Clinical Application 17.4, page 672.
Lactose Intolerance. See blue box on page 677.
Malabsorption. See blue box on page 679.
Appendicitis. See blue box on page 681.
Hemorrhoids. See blue box on page 682.
Disorders of the Large Intestine. See Clinical Application 17.5, pages 684-685.
VI.
Clinical Teems Related to the Digestive System See pages 686 and 688.
VII.
Innerconnections of the Digestive System See Page 687.
DIGESTIVE SYSTEM SUMMARY TABLE I:
NAME OF
DIGESTIVE
ORGAN
ORAL CAVITY
SALIVARY
GLANDS
PHARYNX
ALIMENTARY
CANAL OR
ACCESSORY?
ALIMENTARY
CANAL
ACCESSORY
ALIMENTARY
CANAL
DESCRIPTION OF
STRUCTURE
SEE OUTLINE
SEE OUTLINE
SEE OUTLINE
SECRETIONS
MUCUS
SALIVA WITH
AMYLASE
MUCUS
DIGESTIVE
FUNCTION
MECHANICAL
BREAKDOWN OF
STARCH AND
GLYCOGEN TO
DISACCHARIDES
NONE
HORMONAL
CONTROL OF
SECRETIONS?
N/A
N/A
N/A
DIGESTIVE SYSTEM SUMMARY TABLE I:
NAME OF
DIGESTIVE
ORGAN
ESOPHAGUS
STOMACH
(GASTRIC)
LIVER
ALIMENTARY
CANAL OR
ACCESSORY?
ALIMENTARY
CANAL
ALIMENTARY
CANAL
ACCESSORY
DESCRIPTION OF
STRUCTURE
SEE OUTLINE
SEE OUTLINE
SEE OUTLINE
MUCUS;
PEPSIN;
SECRETIONS
MUCUS
HYDROCHLORIC
ACID;
BILE
INTRINSIC
FACTOR;
GASTRIN
DIGESTIVE
FUNCTION
NONE
PEPSIN BREAKS
PROTEINS INTO
PEPTIDES;
EMULSIFICATION OF FATS
HCl DENATURES
THE PROTEINS
HORMONAL
CONTROL OF
SECRETIONS?
N/A
GASTRIN
SECRETED BY GCELLS
PROMOTES
RELEASE OF
GASTRIC JUICE,
ETC.
CHOLCYTOKININ (CCK)
OPENS COMMON
BILE DUCT
WHEN FATTY
CHYME FILLS
DUODENUM
DIGESTIVE SYSTEM SUMMARY TABLE I:
NAME OF
DIGESTIVE
ORGAN
GALL BLADDER
PANCREAS
SMALL
INTESTINE
ALIMENTARY
CANAL OR
ACCESSORY?
ACCESSORY
ACCESSORY
ALIMENTARY
CANAL
DESCRIPTION OF
STRUCTURE
SEE OUTLINE
SEE OUTLINE
SEE OUTLINE
AMYLASE;
PEPTIDASES;
PROTEASES
(PROTEINASES);
SUCRASE;
SECRETIONS
STORED BILE
PRODUCED IN
LIVER
MALTASE;
LIPASES;
LACTASE
NUCLEASES
DIGESTIVE
FUNCTION
HORMONAL
CONTROL OF
SECRETIONS?
EMULSIFICATION OF FATS
CCK CAUSES
CONRTACTION OF
GALLBALLDER AND
OPENS COMMON
BILE DUCT WHEN
FATTY CHYME
FILLS DUODENUM
AMYLASE:
STARCH AND
GLYCOGEN TO
DISACCHS;
PROTEASES:
PROTEINS TO
PEPTIDES;
LIPASES:
TRIGLYCERIDES
TO FATTY ACIDS
& MONOGLYCERIDES;
NUCLEASES:
NUCLEIC ACIDS
TO
NUCLEOTIDES
PEPTIDASES:
PEPTIDES TO
AMINO ACIDS;
SUCRASE,
MALTASE,
LACTASE:
DISACCHARIDES
TO MONOSACCHARIDES
SECRETIN
CAUSES
PANCREATIC
JUICE TO BE
DEPOSITED INTO
DUODENUM
N/A
DIGESTIVE SYSTEM SUMMARY TABLE I
NAME OF
DIGESTIVE
ORGAN
LARGE
INTESTINE
ALIMENTARY
CANAL OR
ACCESSORY?
ALIMENTARY
CANAL
DESCRIPTION OF
STRUCTURE
SEE OUTLINE
SECRETIONS
MUCUS
DIGESTIVE
FUNCTION
REABSORPTION
OF WATER FROM
CHYME
HORMONAL
CONTROL OF
SECRETIONS?
N/A
DIGESTIVE SYSTEM SUMMARY TABLE II
MACROMOLECULE
INGESTED
CARBOHYDRATES
PROTEINS
FATS (TRIGLYCERIDES
OR TG)
NUCLEIC
ACIDS
SITE OF
DIGESTION
1.MOUTH;
2.DUODENUM
3.DUODENUM
1.STOMACH;
2.DUODENUM
3.DUODENUM
DUODENUM
DUODENUM
DIGESTIVE
ENZYME(S)
1. SALIVARY
AMYLASE
2. PANC.
AMYLASE,
3. SUCRASE,
LACTASE,
MALTASE
1.PEPSIN;
*HCl
2.PANC.
PROTEASES;
3.
PEPTIDASES;
LIPASES
*BILE
PANCREATIC
NUCLEASES
ENDPRODUCT(S)
1 & 2.
STARCH
AND
GLYCOGEN
TO DISACCS;
HCl
DENATURES
PROTEINS;
1 & 2.
PROTEINS
TO
PEPTIDES;
3. PEPTIDES
TO AMINO
ACIDS
BILE
EMULSIFIES
TG’S;
LIPASES
BREAK TG’S
INTO FATTY
ACIDS &
MONOGLYCERIDES
NUCLEOTIDES
3. DISACCS
TO MONOSACCS
SITE AND
MODE OF
ABSORPTION
DISTAL SM.
INTESTINE;
FACILITATED
DIFFUSION
DISTAL SM.
INTESTINE;
ACTIVE
TRANSPORT
DISTAL SM.
INTESTINE;
SIMPLE
DIFFUSION
DISTAL SM.
INTESTINE
ABSORBED
INTO BLOOD
OR LYMPH
BLOOD
BLOOD
LYMPH BY
LACTEAL
BLOOD
REGULATION
SECRETIN
FOR PANC.
AMYLASE
GASTRIN
FOR PEPSIN
CCK FOR BILE;
SECRETIN FOR
PANC. LIPASES
SECRETIN
FOR PANC.
NUCLEASES
Chapter 17: Digestive System
I. Introduction
A. Digestion is the breakdown of foods into forms that cell membranes can absorb.
B. Mechanical digestion breaks large pieces of food into smaller ones without altering
their chemical composition.
C. Chemical digestion breaks down food into simpler chemicals.
D. The organs of the digestive system carry out the processes of ingestion, propulsion,
absorptions, defecation, and digestion.
E. The alimentary canal is composed of the mouth, pharynx, esophagus, stomach, small
intestine, large intestine, and anal canal.
F. The accessory organs of the digestive system are salivary glands, liver, gallbladder,
and pancreas.
II. General Characteristics of the Alimentary Canal
A. Introduction
1. The alimentary canal is a muscular tube that passes through the body’s
ventral cavity.
2. The structure of its wall, how it moves food, and its innervation are
similar throughout its length.
B. Structure of the Wall
1. The four layers of the alimentary wall are the mucosa, submucosa, muscular
layer, and serosa.
2. The mucosa is located as the inner lining and is composed of epithelial tissue,
a small amount of connective tissue, and some smooth muscle.
3. The functions of the mucosa are to secrete mucus and enzymes, and to absorb
nutrients.
4. The submucosa is located deep to the mucosa and is composed of loose
connective tissue, glands, blood vessels, lymphatic vessels, and nerves.
5. The functions of the submucosa are to nourish surrounding tissues and to carry
away absorbed substances.
6. The muscular layer is located between the submucosa and serosa and is
composed of two coats of smooth muscle tissue.
7. When the circular fibers contract, the diameter of the tube decreases.
8. When the longitudinal fibers contract, the tube shortens.
9. The serosa layer is located superficial to the muscular layer and is composed of
the visceral peritoneum.
10. The functions of the serosa are to moisten and lubricate the outside of the
organ.
C. Movements of the Tube
1. The two types of motor functions of the alimentary canal are mixing and
propelling.
2. Mixing occurs when smooth muscles in small segments of the tube contract
rhythmically.
3. Peristalsis is a wavelike motion.
4. Peristalsis occurs when a ring of contraction moves down the wall of the tube.
D. Innervation of the Tube
1. Branches of the sympathetic and parasympathetic nervous system innervate the
alimentary canal.
2. The innervation of the alimentary canal maintains muscular tone
and regulates strength, rate, and velocity of muscular contractions.
3. The submucosal plexus is important for controlling secretions by the
gastrointestinal tract.
4. The myenteric plexus is important for gastrointestinal motility.
5. The functions of parasympathetic impulses are to increase the activities of the
digestive system.
6. The functions of sympathetic impulses are decrease the activities of the
digestive system.
III. Mouth
A. Introduction
1. The functions of the mouth are to receive food and to begin digestion.
2. Mastication is chewing.
3. The mouth is surrounded by lips, cheek, tongue, and palate.
4. The oral cavity is the space between the tongue and palate.
5. The vestibule of the mouth is the space between the teeth, cheeks, and lips.
B. Cheeks and Lips
1. The cheeks form the lateral walls of the mouth and consist of skin, fat,
muscles, and an inner moist lining.
2. The lips surround the mouth opening and consist of skeletal muscles,
sensory receptors, and skin.
3. The reddish color of lips is due to the many blood vessels near their
surfaces.
C. Tongue
1. The tongue is located in the floor of the oral cavity.
2. Mucous membranes cover the tongue.
3. The frenulum of the tongue is a membranous fold that anchors the tongue to
the floor of the mouth.
4. The body of the tongue is composed of skeletal muscles.
5. Muscles of the tongue function to mix food particles and push food to the back
of the throat during swallowing.
6. Papillae of the tongue are rough projections on the surface of the tongue.
7. Functions of papillae are to provide friction and to house taste buds.
8. The root of the tongue is anchored to the hyoid bone.
9. Lingual tonsils are located on the root of the tongue.
D. Palate
1. The palate forms the roof of the oral cavity and consists of a hard part and a
soft part.
2. The hard palate is formed by the palatine processes of the maxillary bones and
palatine bones.
3. The soft palate is formed by a mucous membrane and muscles.
4. The uvula is a downward extension of the soft palate.
5. The function of the uvula is to prevent food or liquids from entering the nasal
cavity.
6. Palatine tonsils are located in the back of the mouth on either side of the
palate.
7. Pharyngeal tonsils are located on the posterior wall of the throat above the soft
palate.
E. Teeth
1. The primary teeth are the first set of teeth to develop.
2. The secondary teeth are the permanent teeth.
3. The secondary teeth consist of 32 teeth.
4. The arrangement of secondary teeth are two incisors, cuspid, two bicuspids,
and three molars (from midline to back).
5. Wisdom teeth are the third set of molars.
6. Chewing increases the surface area of food particles.
7. Incisors are specialized to bite off large pieces of food.
8. Cuspids are specialized to grasp and tear food.
9. Bicuspids and molars are specialized to grind food.
10. The crown of a tooth is the portion of the tooth above the gum line.
11. The root of a tooth is the portion of the tooth below the gum line.
12. The neck of a tooth is the area where the crown and root meet.
13. Enamel consists of calcium salts.
14. Dentin is living cellular tissue beneath enamel.
15. The root canal is located in the root of a tooth and contains blood vessels and
nerves.
16. The pulp cavity is located in the crown of the tooth and contains blood
vessels, nerves and connective tissue called pulp.
17. Cementum is bonelike material that surrounds the root.
18. A periodontal ligament is a fibrous structure that surrounds cementum and
anchors the tooth to the jaw.
IV. Salivary Glands
A. Introduction
1. Salivary glands secrete saliva.
2. The functions of saliva are to moisten food, bind food together, and begin the
chemical digestion of carbohydrates.
3. The three pairs of major salivary glands are parotid glands, submandibular
glands, and sublingual glands.
B. Salivary Secretions
1. Two cell types of salivary glands are serous and mucous.
2. Serous cells produce watery fluid that contains amylase.
3. Mucous cells produce mucus.
4. Amylase digests carbohydrates.
5. Salivary glands are innervated by both sympathetic and parasympathetic
nerves.
6. Sympathetic fibers stimulate the glands to secrete a small amount of viscous
saliva.
7. Parasympathetic fibers stimulate the glands to large amounts of watery saliva.
C. Major Salivary Glands
1. The largest of the major salivary glands is the parotid.
2. The parotid glands are located anterior and inferior to each ear.
3. A parotid duct is located within the buccinator muscle and opens into the
inside of the cheek about the level of the second molar.
4. The parotid glands secrete a water fluid rich in amylase.
5. The submandibular glands are located in the floor of the mouth on the inside
surfaces of the lower jaws.
6. The submandibular glands secrete primarily serous fluid.
7. Ducts of submandibular glands open inferior to the tongue.
8. The sublingual glands are located inferior to the tongue.
9. The sublingual glands secrete primarily mucus.
10. The ducts of sublingual glands open beneath the tongue.
V. Pharynx and Esophagus
A. Introduction
1. The pharynx is a cavity posterior to the nasal and oral cavities.
2. The pharynx and esophagus function in swallowing.
B. Structure of the Pharynx
1. The pharynx connects the nasal and oral cavities with the larynx and
esophagus.
2. The three divisions of the pharynx are the nasopharynx, oropharynx, and
laryngopharynx.
3. The nasopharynx is located behind the nasal cavity.
4. The nasopharynx provides a passageway for air.
5. The oropharynx is located behind the oral cavity.
6. The oropharynx is a passageway for food and air.
7. The laryngopharynx is located just inferior to the oropharynx.
8. The laryngopharynx is a passageway to the esophagus.
9. Constrictor muscles function to pull the pharyngeal walls inward during
swallowing.
C. Swallowing Mechanism
1. The events of the first stage of swallowing are chewing of food and the mixing
of food with saliva.
2. The events of the second stage of swallowing are pushing of food toward the
pharynx and the triggering of the swallowing reflex.
3. The events of the third stage of swallowing are movements of food through the
esophagus and to the stomach.
4. The actions of the swallowing reflex are raising of soft palate, elevation of
larynx and hyoid bone, pressing of tongue against soft palate, contraction of
pharyngeal muscles, opening of the esophagus, and movement of food into the
esophagus.
D. Esophagus
1. The esophagus is a passageway for food.
2. The esophagus propels food from the pharynx to the stomach.
3. The esophagus descends through the thoracic cavity.
4. The esophageal hiatus is an opening in the diaphragm.
5. Mucous glands are scattered throughout the submucosa of the esophagus.
6. The lower esophageal sphincter is located where the esophagus and stomach
join and functions to prevent regurgitation of food.
VII. Stomach
A. Introduction
1. The shape of the stomach is J-shaped.
2. The location of the stomach is just inferior to the diaphragm.
3. Rugae are thick folds in the lining of the stomach.
4. The functions of the stomach are to mix food with gastric juice, begin protein
digestion, to begin a small amount of absorption, and movement of food into the
small intestine.
B. Parts of the Stomach
1. The four parts of the stomach are cardiac portion, body, fundus, and plylorus.
2. The cardiac region is the region near the esophageal opening.
3. The fundic region is a pouch that extends superior to the cardiac portion.
4. The body of the stomach is the main part of the stomach.
5. The pyloric region is the narrow region that is continuous with the small
intestine.
6. The pyloric sphincter is located between the pylorus and the duodenum and
functions to control the movement of food into the small intestine.
C. Gastric Secretions
1. Gastric pits are openings of gastric glands.
2. The three cell types of gastric glands are parietal, chief, and mucous.
3. Mucous cells secrete mucus.
4. Chief cells secrete digestive enzymes.
5. Parietal cells secrete hydrochloric acid and intrinsic factor.
6. Gastric juice is a mixture of the secretions of mucous, parietal, and chief cells.
7. Pepsin is an enzyme that digests proteins.
8. The function of pepsinogen is to be converted to pepsin when needed.
9. The function of hydrochloric acid in the stomach is to convert pepsinogen into
pepsin and to destroy pathogens.
10. The coating of the stomach is important for protecting the stomach wall from
digestive enzymes and acids.
11. The function of intrinsic factor is enhance the absorption of vitamin B12.
D. Regulation of Gastric Secretions
1. Somatostatin is produced in the stomach and functions to inhibit acid
secretion.
2. Parasympathetic innervation stimulates the release of gastric juice.
3. Gastrin is produced the stomach and functions to increase the secretory activity
of gastric glands.
4. The three stages of gastric secretion are cephalic, gastric, and intestinal.
5. The events of the cephalic phase are secretion of gastric juice before food
enters the stomach.
6. The events of the gastric phase are distension of the stomach and the release of
more gastric juice.
7. The events of the intestinal phase are the movement of food into the small
intestine.
8. Cholecystokinin is produced by the small intestine and functions to inhibit
gastric secretions.
E. Gastric Absorption
1. The stomach absorbs alcohol, some drugs, salts, and a small amount of water.
2. Most nutrients are absorbed in the small intestine.
F. Mixing and Emptying Actions
1. A stomachache results from the rise of internal pressure in the stomach.
2. Chyme is food substances that have been mixed with gastric juice.
3. Peristaltic waves push chyme toward the pylorus of the stomach.
4. Stomach contractions push chyme a little at a time into the duodenum
and backwards into the stomach, mixing it further.
5. The lower esophageal sphincter prevents regurgitation of food.
6. The rate at which the stomach empties depends on the fluidity of the chyme
and its contents.
7. Liquids usually pass first through the stomach.
8. The enterogastric reflex is a reflex involving the small intestine and the
stomach. It is triggered by distension of the small intestine wall and inhibits
peristalsis in the stomach to slow down movement of food into the duodenum.
9. Vomiting results from a complex reflex that empties the stomach in the reverse
of the normal direction.
VIII. Pancreas
A. Structure of the Pancreas
1. The pancreas is located close to the duodenum posterior to the parietal
peritoneum.
2. Pancreatic acinar cells produce digestive enzymes and make up the bulk of the
pancreas.
3. Acini are clusters of acinar cells.
4. The pancreatic ducts extends the hepatopancreatic ampulla and empties into
the duodenum.
5. Hepatopancreatic ampulla is a dilated tube that receives the pancreatic duct
and hepatic duct.
6. The hepatopancreatic sphincter is the sphincter that surrounds the
hepatopancreatic ampulla.
B. Pancreatic Juice
1. Pancreatic juice contains many enzymes and bicarbonate ions.
2. The function of pancreatic amylase is to digest carbohydrates.
3. The function of pancreatic lipase is digest lipids.
4. The functions of trypsin, chymotrypsin, and carboxypeptidase are to digest
proteins.
5. Zymogen granules are granules that store pancreatic enzymes.
6. The function of trypsinogen is to be converted to trypsin.
7. The functions of nucleases are to digest nucleic acids.
C. Regulation of Pancreatic Secretion
1. Parasympathetic fibers cause the pancreas to release pancreatic juice.
2. The function of secretin is to stimulate the pancreas to release pancreatic juice
with a high concentration of bicarbonate ions.
3. The release of cholecystokinin is triggered by the presence of chyme in the
small intestine.
4. The action of cholecystokinin on the pancreas is to release pancreatic juice that
has a high concentration of digestive enzymes.
IX. Liver
A. Introduction
1. The largest internal organ is the liver.
2. The liver is located in the upper right abdominal quadrant.
B. Liver Structure
1. The two large lobes of the liver are the right and left.
2. The falciform ligament is a fold that separates the lobes of the liver and
anchors the liver to the posterior abdominal wall.
3. The two small lobes of the liver are caudate and quadrate.
4. The porta hepatis is where blood vessels and ducts enter or exit the liver.
5. The coronary ligament is a ligament that attaches the liver to the diaphragm.
6. Hepatic lobules are divisions of a liver lobe.
7. A hepatic lobule consists of many hepatic cells radiating outward from a
central vein.
8. Hepatic sinusoids are vascular channels in hepatic lobules.
9. Kupffer cells are macrophages of the liver.
10. Bile canals are canals within liver lobules that receive secretions from hepatic
cells.
11. Hepatic ducts are formed from bile canals of neighboring hepatic lobules.
C. Liver Functions
1. The liver carries on many important metabolic functions.
2. The liver plays a key role in carbohydrate metabolism by helping
maintain the normal blood glucose
concentrations.
3. The liver plays a key role in lipid metabolism by oxidizing fatty acids,
synthesizing lipoproteins, phospholipids,
and cholesterol.
4. The liver plays a key role in protein metabolism by deaminating amino
acids, forming urea, synthesizing plasma
proteins, and converting amino acids to
other forms of amino acids.
5. The liver stores glycogen, iron, and vitamins A,D, and B12.
6. Liver cells help destroy worn out red blood cells.
7. The liver removes toxic substances from the blood.
8. The liver’s role in digestion is to secrete bile.
D. Composition of Bile
1. Bile is secreted by hepatic cells.
2. Bile contains water, bile salts, bile pigments, cholesterol, and electrolytes.
3. Hepatic cells use cholesterol to make bile salts.
4. Bile pigments are products of the breakdown of hemoglobin.
5. Jaundice results from an accumulation of bile pigments in the blood stream.
E. Gallbladder
1. The gallbladder is located inferior to the liver.
2. The cystic duct is the duct of the gallbladder and opens into the common bile
duct.
3. The common bile duct is formed from the cystic duct and common hepatic
duct and opens into duodenum.
4. Gallstones form when bile is too concentrated.
F. Regulation of Bile Release
1. Cholecystokinin triggers the gallbladder to release bile.
2. Cholecystokinin is released in response to presence of lipids and proteins in
the small intestine.
G. Functions of Bile Salts
1. Functions of bile salts are to aid in the absorption of fatty acids, and certain
vitamins, and to emulsify fats.
2. Emulsification is the breaking of fat globules into smaller droplets.
3. Lack of bile salts results in poor lipid absorption and vitamin deficiencies.
X. Small Intestine
A. Introduction
1. The small intestine extends from the stomach to the large intestine.
2. The small intestine receives secretions from the pancreas, gallbladder, and
liver.
3. The functions of the small intestine are to complete digestion, absorption of
nutrients, and movement of solid wastes to the large intestine.
B. Parts of the Small Intestine
1. The three parts of the small intestine are duodenum, jejunum, and ileum.
2. The duodenum is located posterior to the parietal peritoneum just beneath the
stomach.
3. The jejunum is located in the abdominal cavity between the duodenum and
ileum.
4. The ileum is located in the abdominal cavity between the jejunum and large
intestine.
5. Mesentery is double-layered fold of peritoneum and supports the blood
vessels, nerves, and lymphatic vessels that supply the intestinal wall.
6. The greater omentum is a double fold of peritoneal membrane that drapes like
an apron from the stomach, over the transverses colon, and the small intestine.
7. The functions of the omentum are to prevent the spread of infections in the
peritoneal cavity.
C. Structure of the Small Intestinal Wall
1. The velvety appearance of the inner wall of the small intestine is due to
intestinal villi.
2. Intestinal villi are tiny projections of the mucosa of the small intestine.
3. The functions of villi are to increase the surface area of the lining of the small
intestine.
4. Each villus consists of a layer of simple columnar epithelium and a core of
connective tissue containing blood capillaries, a lacteal, and nerves.
5. A lacteal is a lymphatic capillary.
6. Microvilli increase the surface area intestinal cells.
7. Intestinal glands are between the bases of adjacent villi.
8. Plicae circulares are circular folds in the mucosa of the small intestine.
D. Secretions of the Small Intestine
1. Brunner’s glands are mucous-secreting glands and are located in the
submucosa of the proximal portion of the
duodenum.
2. Brunner’s glands secrete alkaline mucus.
3. The enzymes secreted by epithelial cells of the small intestine are
peptidase, sucrase, maltase, lactase, lipase,
and enterokinase.
4. The functions of peptidases are to digest proteins.
5. The functions of sucrase, maltase, and lactase are to digest sucrose,
maltose, and lactose.
6. The functions of intestinal lipase are to digest lipids.
E. Regulation of the Small Intestinal Secretions
1. Mechanical digestion and the presence of gastric juice in the small
intestine stimulate the duodenal mucous
glands to release large amounts of mucus.
2. Chyme stimulates the goblet cells and intestinal glands to secrete their
products.
3. Distension of the intestinal wall stimulates the parasympathetic reflex that
causes intestinal secretions.
F. Absorption in the Small Intestine
1. The most important absorbing organ is the small intestine.
2. Carbohydrate digestion begins in the mouth and is completed in the small
intestine.
3. Monosaccharides are absorbed by facilitated diffusion and active transport.
4. Protein digestion begins in the stomach and is completed in the small intestine.
5. Amino acids are absorbed by active transport.
6. Fat molecules are digested almost entirely by the small intestine.
7. Chylomicrons are lipoproteins that contain lipids and proteins.
8. Chylomicrons are carried to the blood by lymph.
9. The ions absorbed by the intestinal villi are sodium, potassium, chloride,
nitrate, and bicarbonate.
10. Water is absorbed by osmosis.
G. Movements of the Small Intestine
1. Segmentation is the major mixing movement of the small intestine.
2. Chyme moves slowly through the small intestine.
3. Parasympathetics enhance mixing and peristaltic movements and sympathetics
inhibits mixing and peristaltic movements.
4. A peristaltic rush is the rapid sweeping of chyme into the large intestine.
5. Diarrhea results from a peristaltic rush.
6. The ileocecal sphincter joins the ileum and cecum.
XI. Large Intestine
A. Introduction
1. The large intestine is located primarily in the abdominal cavity and part of the
pelvic cavity.
2. The functions of the large intestine are to form feces, eliminate solid wastes,
and to absorb remaining water and electrolytes from chyme.
B. Parts of the Large Intestine
1. The parts of the large intestine are cecum, colon, rectum, and anal canal.
2. The cecum is the initial portion of the large intestine.
3. The vermiform appendix is located off the cecum and consists of lymphatic
tissue.
4. The four parts of the colon are ascending colon, transverse colon, descending
colon, and sigmoid colon.
5. The ascending colon is located on the right side of the abdominal cavity.
6. The transverse colon is located between the ascending and descending colon.
7. The descending colon is located on the left side of the abdominal cavity.
8. The sigmoid colon is an s-shaped portion of the colon off the descending
colon.
9. The rectum is the continuation of the sigmoid colon.
10. The anal canal is the continuation of the rectum.
11. Anal columns are folds of mucous membranes in the anal canal.
12. The anus is the opening of the anal canal.
13. Two sphincters of the anus are the internal and external.
14. The internal anal sphincter is composed of smooth muscle.
15. The external anal sphincter is composed of skeletal muscle.
C. Structure of the Large Intestinal Wall
1. Teniae coli are bands of smooth muscle that extend the length of the large
intestine.
2. Haustra are pouches of the large intestinal wall created by teniae coli.
3. Epiploic appendages are collections of fat in the serosa on the outer surface of
the large intestine.
D. Functions of the Large Intestine
1. Mucus secretion into the large intestine is controlled by mechanical
stimulation and parasympathetic impulses.
2. The functions of mucus in the large intestine are to form and store feces,
eliminate feces, and absorb remaining water and electrolytes from chyme.
3. Chyme entering the large intestine contains few nutrients, nondigestible
materials, water, electrolytes, mucus, and bacteria.
4. The large intestine can absorb water and electrolytes.
5. Intestinal flora is a bacterial population that exists in the large intestine.
6. The functions of intestinal flora are to synthesize some vitamins and to
produce gas.
E. Movements of the Large Intestine
1. The movements of the large intestine are less frequent than those of the
small intestine.
2. Mass movements are produced when a large section of the intestinal wall
constricts vigorously.
3. The defecation reflex is triggered by holding a deep breath and contracting the
abdominal wall muscles.
4. The actions of the defecation reflex are to increase internal abdominal pressure
and the forcing go feces into the rectum. Peristaltic waves are triggered and anal
sphincters relax.
5. A person can inhibit defecation by contracting the external anal sphincter.
F. Feces
1. Feces are composed of materials that were not digested or absorbed, some
water, electrolytes, mucus, and bacteria.
2. The pungent odor or feces results from a variety of compounds that bacteria
produce.
XII. Life-Span Changes
A. Maintaining healthy teeth requires frequent dental checks, cleaning and plaque
removal, plus care of the gums.
B. The effects of aging on teeth include thinning of enamel, thickening of cementum,
receding of gums, and loosening of teeth.
C. Dry mouths in elderly people are usually a result of side effects of drugs.
D. Frequent heartburn may be the result of the slowing of peristalsis in the stomach.
E. Effects of aging on the small intestine include decreased efficiency in absorbing
nutrients and vitamins.
F. The effects of aging on the large intestine include thinning of the lining and decreased
mucus production that leads to constipation.
G. The effects of aging on the pancreas, liver, and gallbladder include a decline in their
secretions.