The digestive system includes the organs that ingest food, transport food, digest the food into smaller usable components, absorb the nutrients, and expel the waste products from the body.
Small Intestine (duodenum, jejunum, ileum)
G.I. Associated Organs
Factors that influence G.I. functioning
Structures and Functions of the G.I. Tract
The G.I. Tract is a tube approximately 30 ft. (9m) extending from mouth to anus.
It is composed of four layers
Autonomic nervous system
Excitatory :Increase of peristalsis
Inhibatory : Decrease of peristalsis
Sensory information is relayed via both parasympathetic and sympathetic afferent fibers.
Enteric Nervous System
Composed of two layers
Lie between the mucosa and the circular muscle layer and the circular and longitudinal muscle layers
Neurons contribute to the coordination of the G.I. Motor and sensory activities
“ Gut Brain”
Contains numerous neurons
Ability to control movement and secretion of the G.I. Tract
G. I. Tract and the accessory organs get 25-30% of the cardiac output
Venous blood draining the GI tract organs empties in the portal vein, which then perfuses the liver
Splanchnic artery innervates the upper GI tract
Hepatic and superior mesenteric artery branches innervate the small intestine
Superior and inferior mesenteric arteries supply blood to the large intestines
Because such a large % of the cardiac output perfuses these organs, the GI tract is a major source from which blood flow can be diverted during exercise and stress.
Enzymes and hormones for digestion
Mucus to provide protection and lubrication
Covers the abdominal organs
Parietal layer lines the abdominal cavity wall
Visceral layer covers the abdominal organs
Peritoneal cavity is the potential space between the parietal and visceral layers
Two folds of the peritoneum are called the mesentery and the omentum
Attaches to the small intestine and part of the large intestine to the posterior abdominal wall
Contains blood and lymph vessels
The lesser omentum goes from the lesser curvature of the stomach to the upper duodenum to the liver
The greater omentum hangs from from the stomach over the intestines like an apron
Contains fat and lymph nodes
The mouth is the entrance of the GI tract.
The food is moved on to the stomach and other organs for digestion and absorbtion.
Intake of food
Hypothalamus “appetite center”
Directly of indirection stimulated by hypoglycemia, empty stomach, decrease of body temp
Input from higher brain centers
Appetite stimulated by taste, smell and sight
Appetite decreased by stomach distention, illness, hyperglycemia, N&V, and certain drugs
Deglutition, swallowing, mechanical component of ingestion involving the mouth, pharynx, and esophagus
Releases nutrients from food
Separation of other nutrients from food components
Takes place in the small intestine
Delivers nutrients into the blood.
Absorbing structures (microvilli) located in the small intestine transfer the nutrients into the portal blood and lymph.
Water is absorbed in colon later.
Excretes nondigestible waste
The fecal mass moves from the colon to the rectum, where it is stored and excreted.
Before the mouth
Smell and vision and hunger
Lips and oral (buccal) cavity
Hard and soft palate
What happens in the mouth?
What type of pathophysiology or conditions can cause problems while eating?
Muscleomembranous tube that may be divided into the nasopharynx, oropharynx, and the laryngealpharynx. The mucus membrane of the pharynx is continuous with the nasal cavity, mouth, auditory tubes and larynx.
Oropharynx secretes mucus
Epiglottis closes over the larynx during swallowing
Oropharynx moves the food down
Receptors in the oropharynx are stimulated by food and liquids which initiates swallowing
Hollow , muscular tubing that receives food from the pharynx and moves it to the stomach by peristaltic contractions. Located in the thoracic cavity and starts behind the trachea and the lower end of the pharynx and extends to the stomach. The upper third is composed of striated skeletal muscle and the distal two thirds is composed of smooth muscle.
Upper esophageal sphincter (criphapharyngeal) relaxes and the peristaltic wave moves the bolus into the esophagus. The muscular layers contract and propels the food in the stomach. The lower esophageal sphincter (LES) at the distal end of the esophagus remains contracted except during swallowing, belching, or vomiting.
Important barrier that prevents reflux of acidic gastric contents into the esophagus
Name That Pathophysiology
Stores food, mix food with gastric secretions and empties into the small intestine. Very little water, alcohol, electrolytes, or drugs are absorbed
Back to digestion
Mixing and propulsive movements
Controlled by the nervous system
Long smooth muscles arranged in fiber bundles that extend lengthwise along the GI tract help propel the food mass downward.
Circular contractile muscles
Smooth muscle fibers that extend around the hallow tube forming the alimentary canal.
These rhythmic contractile rings cause sweeping waves along the digestive tract pushing food forward.
This movement is called peristalsis
More defined circular muscles at strategic points form muscle sphinters that act as valves--pyloric, ileocecal, and anal—to prevent reflux and backflow and keep the food mass moving in a forward direction.
Thin embedded layer of smooth muscle produces local constrictive contractions every few centimeters.
They contact mix and chop, the food mass, effectively churning and mixing it with secretions to form a semiliquid called chyme that is ready for digestion and absorption.
HCl acid and buffer ions
Water and electrolytes
Specific enzymes attack designated chemical bonds within the structure of nutrient compounds freeing their component parts.
The major enzyme of the stomach is pepsin, which begins the breakdown of protein.
Pepsin is secreted in the form of pepsinogen and is activated by HCl acid.
Small amount of gastric lipase (tributyrase) that acts only on butter fat
Children have a gastric enzyme called renin (don’t confuse it with renal renin) that aids in the coagulation of milk. It coagulates the protein of milk from liquid to solid which slows the emptying of the stomach, ensuring a gradual passage to the small intestine.
Hydrochloric acid and buffer ions
The agents produce the pH necessary for the activity of certain enzymes
HCl acid creates the acidic environment necessary for certain enzymes to work.
A pH of 1.8-3.5 is needed for pepsin to work . A pH of 5 or above there will be little or no pepsin activity
This sticky, slippery fluid lubricates and protects the lining of the inside wall of the gastrointestional tract and eases the passage of the food mass.
Water and electrolytes
These agents provide an appropriate solution in the amounts needed to circulate the substances released in the digestive process.
Digestion and absorption
Duodenum, jejunum, and ileum
Mixes the chyme from the stomach and the digestive secretions from the pancreas and the liver from the common bile duct
Specific enzymes act on specific macronutrients to bring out their final breakdown to form the body can absorb and use.
Glands located at the entrance to the duodenum secrete large amounts of mucus to decrease the acidity of the chyme
Other mucus lubricates and protects the mucosal lining in the duodenum
Secretin: stimulates the pancreas to send alkaline pancreatic juices into the duodenum
Emulsifies the fats and facilitates digestion
The serous coat is formed by the peritoneum. The mucosa is thick, vascular, and glandular. Circular folds in the mucous and submucous layers provide greater surface for digestion and absorption.
Finger like projections in the mucous membrane. They also increase surface area for digestion and absorption.
Nutrients area absorbed in the blood stream
Water soluble vitamins (C and all B’s except B-12
Amino Acid (the end product of protein digestion)
Fat soluble vitamins (A,D,E, and K)
Fatty acids and cholestrol
Sodium, potassium, and alcohol
Absorbs fluids and electrolytes
Feces consist of water, bacteria, unabsorbed minerals, undigested food stuffs, bile pigment, and desquamated epithelial cells
Manufactures Vitamin B-12
Produce Vitamin K
Break down of amino acids and produce nitrogen
Moves and breaks down indigestible complex carbohydrates (Methane)
Largest solid organ in the body
Stores, manufactures, transforms and excretes a number of substances involved in metabolism.
Bile production and secretion
Mononuclear phagocyte system
Pear shaped sac located below the liver
Concentrates and stores bile
Bile is produced by hepatic cells and secreted into the bile ducts by hepatic cells and secreted into the biliary canaliculi of the lobes
Common Bile Duct
The hepatic duct merges with the cystic duct from the gallbladder and form the common bile duct
Back to the GB
Most bile is stored and concentrated in the gall bladder
It is released into the cystic duct and moves down the common bile duct to enter the duodeum at the ampulla of Vater
In the intestines most of the bilirubin os reduced to stercobilinogen and urobilogen by bacterial action
Too much information
Stercobilinogen accounts for the brown color of stool
Exocrine and endocrine gland
Exocrine gland: enzymes to metabolize food.
The Effects of Aging on the G.I. Tract
It’s Happening Right Now
Tooth and dentin wear down; cavities
Periodontal disease lead to tooth loss
Taste buds and sense of smell go
Esophageal smooth muscle weakens
LES becomes more incompetent
Decrease on HCL, delayed gastric emptying, and constipation
However it may be removed and the liver will compensate.