digestive system, functions of the digestive system, composition of digestive system, Gastrointestinal track, acessory digestive organs, the peritoneum, lymphoid tissue in the intestines, control of digestion, neural innervation of the digestive system, hormonal regulation of digestive system, basi...
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
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