Alimentary Canal or Gastrointestinal Tract
muscular tube that winds from the mouth to the anus
Accessory Digestive Organs
teeth, tongue and salivary glands
gallbladder, liver and pancreas
Digestion Process
Ingestion
Propulsion
Digestion
Absorption
Defecation
Ingestion
first step of the digestive process
taking food into the mouth
Propulsion
second step of the digestive process
movement of food through the GI tract
Digestion
third step of the digestive process
mechanical and chemical processes that break down food
Absorption
fourth step of the digestive process
movement of food into blood and lymph capillaries
Defecation
fifth step of the digestive process
elimination of waste materials
Peristalsis
ripple-like wave of muscular contractions that move food along the GI tract
Segmentation
churning and mixing to help disperse material and combine it with digestive secretions
Tissue Layers of the Alimentary Canal
Mucosa
Submucosa
Muscularis
Serosa
Mucosa
innermost layer of the wall of the alimentary canal
consists of three sublayers: epithelium, lamina propria and muscularis mucosae
Epithelium
top layer of the mucosa
consisting of squamous columnar epithelium
different functions depending on the location
Lamina Propria
second layer of the mucosa
loose areolar connective tissue (blood vessels)
capillaries nourish epithelium and absorb digested nutrients
Muscularis Mucosae
bottom layer of the mucosa
thin layer of smooth muscle that produces local movements of the mucosa
Submucosa
layer of connective tissue surrounding the mucosa containing major blood and lymphatic vessels, nerves
elastic fibers enable canal to return to original shape after passage of food
Muscularis
two layers of smooth muscle surrounding the submucosa
inner circular and outer longitudinal - responsible for peristalsis
Exceptions of the Muscularis
esophagus has a mixture of smooth and skeletal muscle
stomach contains three layers of smooth muscle
Serosa
outer layer of the alimentary canal consisting of simple squamous epithelium
areolar connective tissue (blood vessels)
also called adventitia or visceral peritoneum
Teeth
humans normally have 32 permanent
incisors, canines, premolars, molars
Incisors
nipping off pieces of food (8)
front teeth
Canines
tearing and piercing (4)
after incisors
Premolars and Molars
grinding of food
20 total at the back of the mouth
Intrinsic Gland
type of salivary gland consisting of many small glands that keep oral cavity moist
Extrinsic Glands
type of salivary gland that lie external to mouth but connect through ducts
active when feeding
Pharynx
swallowed food is passed posteriorly into oropharynx and laryngopharynx
makes use of pharyngeal constrictor skeletal muscles
Voluntary Phase
first phase of swallowing
bolus pushed by tongue against hard palate and to oropharynx
Pharyngeal Phase
second phase of swallowing
soft palate and uvula close off nasopharynx
epiglottis covers laryngeal opening
Esophageal Phase
final phase of swallowing
peristalsis pushes bolus towards stomach
Esophagus
muscular tube that propels food to stomach
passes through esophageal hiatus in diaphragm
contains the four layers of the GI tract
epithelium is stratified squamous epithelium
highly folded when empty
lots of mucous glands that are triggered by food bolus
muscularis changes from skeletal to smooth as it approaches stomach
Cardiac Sphincter
prevents stomach acid from re-entering the esophagus
Stomach
temporary storage organ in which food is churned into chyme
divided into various regions
internal surface contains numerous longitudinal folds called rugae
surface of the mucosa is columnar epithelia
extending down into lamina propria are gastric glands
produce very acidic solution with digestive enzymes (gastic juice)
Protection of the Stomach from Gastric Juice
lots of mucous
epithelial cells have tight junctions
damaged cells replaced quickly
Peptic Ulcer
craterlike erosion of the mucosa in any part of the alimentary canal exposed to stomach secretions
about 98% occur in pyloric region of stomach (gastric ulcer) or first part of duodenum (duodenal ulcers)
Perforated Ulcer
stomach contents leaked into the peritoneal cavity
Small Intestine
longest part of alimentary canal
site of most enzymatic digestion and nearly all absorption
large surface area
food spends at least 12 hours here where chemical digestion takes place
3 regions
Duodenum
first section of the small intestine emerging from the stomach
25 cm in length
where bile and pancreatic secretions enter the intestine
Jejunum
middle of the small intestine
1m long
primary region for chemical digestion and nutrient absorption
Ileum
last region of the small intestine that empties into the large intestine
sphincter controls material entering into large intestine
responsible for absorption of vitamin B12 and bile salts
patches of lymph tissue
Small Intestine Histology
internally get circular folds with villi increasing the surface area of intestinal lining
each contain an arteriole, venule, capillaries and lacteal
microscopic microvilli are found on the surface of each villus
Intestinal Glands
invaginations into mucosa found between villi
secrete intestinal juice, digestive enzymes, hormones, mucous, etc.
diseases associated with these glands are colorectal caner, Crohn's diseas and cryptitis
Large Intestine
1.5m extending from the ileum to anus
frames the small intestine on three sides
consists of the cecum, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, rectosigmoid colon and rectum
Teniae Coli
three separate longitudinal bands of smooth muscle on the outside of the ascending, transverse, descending and sigmoid colons
thickenings of the muscularis
Haustra
saccules in the colon that give it its segmented appearance
series of pouches caused by the contraction of teniae coli
Appendicitis
blockage traps bacteria in lumen of appendix
begins to swell with mucous and leads to an infection
Diverticulosis
refers to presence of small pockets (diverticula) in large intestine
in some cases, spasms, cramping, diarrhea, constipation
Diverticulitis
inflamed diverticula become infected and perforate
Rectum
portion of the large intestine
no teniae coli
well developed muscularis to generate strong contractions
Anal Canal
last 3 cm of the large intestine
internal sphincter consists of smooth muscle
external sphincter consists of skeletal muscle
Hemorrhoids
stretched and inflamed veins that bulge into the lumen of the anal canal
can be caused by straining to defecate or delivering a baby
Liver
accessory organ of digestion
liver is largest gland of body
comprised of four incompletely separated lobes
falciform ligament completely divides right from left lobe
digestive function is to produce bile
Gallbladder
bile is then stored in gallbladder
dumped into duodenum via bile duct
Cirrhosis
chronic inflammation of the liver
usually the result of hepatitis or alcoholism
main cell types of liver damaged, replaced by scar tissue
only effective treatment are liver transplants with a good survival rate but few donors available
Hepatitis
inflammation of the liver
often due to viral infection
six different viruses known so far (A-F)
type A from contaminated food, water and feces
type B from blood transfusions, contaminated needles and sexually transmitted fluids
Gallstones
if there is too much cholesterol for bile to break down, it can become crystalized
cause substantial pain if they block cystic duct
Pancreas
accessory organ in digestion
produce most of enzymes that digest food in small intestine (pancreatic juice secreted through two ducts)
also lots of bicarbonate to neutralize the acid from stomach
main pancreatic duct merges with common bile duct
accessory duct enters duodenum proximally
Pancreatitis
pancreatic enzymes activated in pancreas instead of small intestine
abdominal pain, nausea, vomiting
acute lasts a few days and is normally caused by gallstones
chronic persists over many years and is often related to high consumption of alcohol
Pancreatic Cancer
dangerous to screen for, yet deadly if ignored
pancreas is very sensitive and biopsies can lead to serious complications
cancer is usually detected too late
five-year survival rate of less than 5%
emphasis on earlier detection