Summary The Digestive System

The Digestive System
COMPONENTS OF THE DIGESTIVE
SYSTEM
Functions of the Digestive System
 Ingestion and mastication
 Secretion (water, acid, buffer,
enzymes into lumen)
 Propulsion and mixing
 Digestion
 Mechanical
 Chemical
 Absorption (passing into blood and
lymph)
 Defecation (elimination of forces)  Visceral
Composition  Covers organs
 Parietal
The digestive system is composed of two  Covers interior surface of body
groups of organs wall
 Mesenteries
 Gastrointestinal (GI) track
 Two layers of peritoneum
 Mouth
 Routes by which vessels and
 Pharynx
nerves pass from body wall to
 Oesophagus
organs
 Stomach
 Omentum
 Small intestine (duodenum,
 Folds of visceral peritoneum
ileum, jejunum)
 Greater – hangs from stomach
 Large intestine
 Lesser – covers liver
 Colon
 Rectum Lymphoid Tissue in the Intestines
 Anal canal
 Acessory digestive organs  Digestive tract is an important
 Teeth component of body’s immune system
 Tongue  Largest mass of lymphoid tissues in
 Salivary glands body
 Tonsils  Mucosa – associated lymphoid tissue
 Liver in body
 Gallbladder  Stores immune cells
 Pancreas  Includes
 Tonsils
The Peritoneum  Adenoids
 Peyer’s patches
 Serous membrane forming the lining of
 Large aggregates in
the abdominal cavity
appendix
 It covers most of the intra-abdominal
 Large intestine
organs
 Small aggregates in
oesophagus

,CONTROL OF DIGESTION  Ghrelin
 Binds to receptor in the
Neural innervation of the digestive
arcuate nucleus (where
system
are specific neurons –
Enteric nervous system NPY-n)
 Result in the feeling of
 10 million neurons – nervous system hunger
 Sensory, motor, interneurons  Secretions
 Neurons extending from oesophagus  Helps regulate the pH
to anus environment in the
 2 plexuses (branching network of duodenum
axon)  Inhibits gastric acid
 Myenteric – GI tract motility, secretion
reflexes  Promotes bicarbonate
 Submucosal – secretion production by pancreatic
Autonomic nervous system cells
 GIP
 Initiate reflexes because of sight, smell  In the mucosa of the
or taste of food small intestine
 Mainly parasympathetic simulation  Released mediated by
 Increases secretion the presence of glucose
 Activity by stimulating ENS or fatty acids in the
 Sympathetic stimulation decreases duodenum
activity by inhibiting ENS  Results in the release of
 Decreased muscle contraction insulin by the pancreas
 Decreased secretions and inhabitation of
 Decreased blood flow to gastric mobility and acid
digestive tract secretion
Hormonal Regulation of Digestive  Motilin
System  Increase motility of
several portions of gut
Chemical regulations  Stimulates the release of
 Endocrine hormones local juices
 Paracrine signals  Stimulated by the
 E.g. histamine help local presence of acid and fat
reflexes in ENS control in duodenum
conditions of digestive tract (pH  Gastric
levels)  Stimulus the parietal
 Hormonal signals cells of the stomach
 Leptin  Results in the increased
 Adipose tissue increases of acid production
energy sources  Promotes gastric motility
producing leptin  Triggered by the
 Leptin binds to receptor presence of peptides in
in the arcuate nucleus the stomach
(where are specific  Pancreatic polypeptide
neurons – POM-C)  Regulates the release of
 Result in the feeling of pancreatic secretions
satiety (exocrine and endocrine)

,  Complex action discerns Thick connective tissue binding
the need for enhancing mucosa to muscularis
or inhibiting local actions  Blood, lymphatic vessels
 Amylin  Parasympathetic submucosal
 Plays a role in glycemic plexus
regulation by slowing  Muscularis
gastric emptying and  Voluntarily skeletal muscle
promoting satiety found in:
 Prevent extreme spikes  Mouth
in plasma glucose  Pharynx
 GLP1 and GLP2  Upper 1/3 of oesophagus
 Increase intestinal blood  Anal sphincter
flow  Involuntary smooth muscle
 Increase the activity and  2 to 3 layers
expression of epithelial  Arranged in inner circular, outer
brush – border digestive longitudinal fibres
enzymes and nutrients  Myenteric plexus between
transports muscle layers
 Increase the intestinal  Control movement
digestive and absorptive  Control secretion
capacity (glucagonlike  Serosa
peptide)  Outermost covering of organs
 Oxyntomodulin suspended in abdominopelvic
 Function unknown cavity
 Binds GLP1 and is  Connective tissue also
reproduced by the gastric called visceral
oxyntic cells (parietal peritoneum
cells)  Oesophagus lacks serosa
 PYY 3-36  Has adventitia (blends
 Increase intestinal blood with connective tissue
flow and the activity and surrounding structure)
expression of epithelial
brush
 Currently under
investigation
 Cholecystokinin
 Triggers the
concentration of the gall
bladder sphincter
 Response to the
presence of fatty food in
UPPER GI TRACT
the duodenum
Phases of Digestion
BASIC LAYERS OF THE GI TRACT
 Cephalic
The Four Basic Layers
 Smell, sight, thought, initial
 Mucosa taste of food activates neural
 Lining of lumen centers in cerebral cortex,
 Mucous epithelium hypothalamus, brain stem
 Lamina propria  Prepares moth and stomach for
 Muscularies mucosae food to be eaten
 Submucosa  Gastric