Overview of the gastrointestinal system Flashcards
What are the factors that helps in the digestion and absorption of nutrients in the GI system?
1) Motility (Muscles are responsible for the propulsive and mixing movements from one segment to other segment in the gut)
2) Secretions (DIGESTIVE JUICES)
3) Digestion (The biochemical breakdown)
4) Absorption (small absorbable units that are transferred into the blood or the lymph)
What is meant by the motility of the GI system?
They are mixing, propulsive muscular contractions that are regulated in order to optimize the digestion and absorption
What is the alimentary canal?
1) Mouth
2) Pharynx
3) Esophagus
4) Stomach
5) Small intestine
- Duodenum
- Jejunum
- Ileum
6) Large intestine
- Cecum
- Appendix
- Colon
- Rectum
7) Anal canal
What are the glands that are associated with the GI system?
1) Salivary gland
2) Pancreas
3) Biliary system (the liver and gall bladder)
What is the function of the oral cavity, teeth and tongue?
1) Chewing
2) Moistening
- The tongue also helps inn mixing the food with the saliva, forming a bolus and pushing it backwards
What is the function of the salivary gland?
The enzymes of the saliva breaks down the carbohydrates
What is the function of the pharynx
The pharyngeal muscles propels the food in the esophagus
What is the function of the esophagus?
It transports the materials into the stomach
What is the function of the stomach?
It chemically breakdown nutrients via acids, enzymes, muscular contractions
What is the function of the pancreas?
1) Exocrine cells = secretes digestive enzymes
2) Endocrine cells = secretes hormones
What is the function of the small intestine?
1) Enzymatic digestion
2) Absorption of water, organic substrates, ions and vitamins
What is the function of the large intestine?
1) Reabsorption of the water
2) Compaction of the indigestible material to be eliminated as feces
What is the function of the gall bladder?
Stores and concentrates the bile
What is the function of the liver?
1) Secretes bile
2) Stores nutrients
What is a chyme?
It is the food that enters the stomach and gets digested
Describe the physiological anatomy of the GI wall
- Inside
1) Lumen
2) Mucosa
3) Submucosa
4) Muscularis externa (the inner and outer portions allows for the contractions to be from all directions)
- Inner circular muscle
- Outer longitudinal muscle
5) Serosa
What is the enteric nervous system?
- The nervous system of the gut formed of two parts:
1) Myenteric plexus
2) Submucosal plexus
Where is the myenteric plexus located?
between the longitudinal and circular layer
Where is the submucosal plexus located?
In the submucosa between the submucosa and the circular layer
What is the structure of the mucosa of the GIT?
1) Epithelium
2) Lamina propria
3) Muscularis mucosa
What is the function of the epithelium of the GIT?
Specialized cells in the absorption and secretion
What is the lamina propria?
A connective tissue that contains blood and lymph vessels
What is the muscularis mucosa?
Smooth muscle cells, that changes the shape and surface area of the epithelial layer
What is the submucosa made of?
1) Collagen
2) Elastin
3) Glands
4) Blood vessels
What is the function of the submucosal plexus (Meissner’s plexus)?
Secretion absorption and contraction
What is the function of the Myenteric plexus (Auerbach’s plexus)?
1) Movement of the GIT
2) Generally it is excitatory but at sphincters it is inhibitory
3) Releases VIP (vasoactive intestinal peptides)
What are the extrinsic components of the enteric nervous system?
Sympathetic (mainly postganglionic) and parasympathetic (mainly preganglionic) innervation
- The enteric nervous system can function independently or communicate extensively with the extrinsic components
What are the intrinsic components of the enteric nervous system?
1) Submucosal plexus
2) Myenteric plexus
- These can work independently, even if we cut the sympathetic and parasympathetic
What is the function of the myenteric plexus?
The myenteric plexus has a linear chain form where its stimulations leads to an increase in the:
1) Tone of the gut wall
2) Intensity of the contractions
3) The rate of rhythm of the contractions
4) The velocity of conducting the excitatory waves
What is the function of the submucosal plexus?
Controls the local intestinal secretions, absorption, and the contraction of the submucosal muscle
What are the autonomic control of the GIT?
1) Cranial division
- Vagus nerve
2) Sacral division
- Pelvic nerve
3) Parasympathetic: (long preganglionic and it increases the activity of the enteric nervous system)
4) Sympathetic
What does the cranial division innervate?
- It innervates the upper GIT (The striated muscles of the esophagus, stomach wall, small intestine and the ascending colon)
What does the sacral division innervate?
- It originates from S2, S3, & S4 segments
- It innervates the lower GIT (Muscles of the external anal canal, transverse, descending and sigmoidal colon walls)
What is the function of the sympathetic innervation?
- It inhibits the activity of the GIT
- Its fibers originates in the segments between T5 and L2
- Made of preganglionic sympathetic fibers, postganglionic sympathetic nerve will then spread to all parts of the gut
- The sympathetic nerve endings secretes nor-epinephrine which inhibits smooth muscle and it also inhibits the enteric nervous system
What is the difference between the sympathetic and parasympathetic innervations?
Sympathetic supply the whole of the gut but parasympathetic has divisions for upper parts and lower parts
Describe the structure of the smooth muscles of the GI
- Individual muscle fibers are arranged in bundles, which are electrically connected via gap junctions
- Each muscle layer acts as a syncytium
Describe the electrical activity of the GI muscles
1) Slow waves (creates low level contractions)
2) Spikes
- Contractions are strengthened by the AP
Describe the slow waves
- They are found in the resting state
- The interstitial cells of Cajal “pacemaker cells” undergo changes in membrane potential due to the unique ion channels, which opens and produce currents that might generate slow wave activity
- They have a role in producing AP/spike potential
- The frequency of the slow wave is 3 in the stomach, 12 in the duodenum and 8/9 in the ileum
What stimulates the hyperpolarization of the GI smooth muscles?
1) Norepinephrine
2) Sympathetics
What initiates the basic electrical activity?
Interstitial cells of cajal (pacemaker cells)
What are the different Basic electrical activity of the GI tract and what is its function?
- Stomach: 4/mi
- Duodenum: 12/min
- Distal ileum-8/min
- Cecum-2/min
- Sigmoid-6/min
- Its function is to coordinate the peristaltic and other motor activity, and the muscle contraction is caused by the superimposition of the spike potential over the Basic electrical rhythm
What is the spike potential?
- This is what causes the muscle to contract
- Generated by the opening of slow channels allowing the entry of sodium (for AP) and calcium (for contraction)
- If the metabolic potential is above -40 it will become a spike, if near -40 then it is a slow wave RMP
- The resting basal metabolic potential is between -50 and -60
What are the stimulates of spikes?
1) Stretch
2) Acetylcholine
3) Parasympathetics
What are the different types of GI reflexes?
1) Integrated within the enteric nervous system
2) From the gut to the sympathetic ganglia and back to the GIT
3) From the gut to the spinal cord/brain stem and back to the GIT
What are the GI reflexes that are integrated within the enteric nervous system?
- Secretion, peristalsis, mixing contractions, local inhibition
What are the reflexes from the gut to the sympathetic ganglia and back to the GIT?
1) Gastrocolic (evacuation of the colon)
2) Enterogastric (inhibition of stomach motility secretions)
3) Colonoileal (Inhibiting the emptying of the ileum into the colon)
What are the GI reflexes from the gut to the spinal cord/brain stem and back to the GIT?
1) Motor and secretory activity is controlled by the vagus
2) Pain reflex (inhibition of the entire GIT)
3) Defecation reflex (colon, rectal and abdominal contraction for defecation)
How is the GI regulates?
1) Hormones (peptides released from endocrine cells of the GIT)
2) Paracrines (peptides secreted by the GIT endocrine cells and acts locally)
3) Neurocrines (peptides synthesized in the GIT neurons and released following an action potential)
What are the hormones that are released from the endocrine cells?
1) Gastrin
2) Cholecystokinin (CCK)
3) Secretin
4) Gastric-inhibitory peptide (Glucose-dependent insulinotropic peptide)
What are the paracrines that are released by the endocrine cells?
Somatostatin
What are the neurocrines released by the GI?
1) ACh
2) Norepinephrine
3) Vasoactive intestinal polypeptide (VIP)
4) Nitric oxide (NO)
5) Gastrin-releasing peptide (GRP “bombesin”)
6) Enkephalins
7) Neuropeptide Y
8) Substance P
What stimulates the production of gastrin?
1) Protein
2) Distention
3) Nervous (vagal stimulation)
from where is the hormone gastrin produced in the body?
1) G-cells of antrum
2) Duodenum
3) Jejunum
What is the function of gastrin?
1) Increases the secretion of gastric acid
2) Increases the growth of the gastric mucosa
What stimulates the production of cholecystokinin (CCK)?
1) Fats
2) Protein
3) Acids
From where is the hormone cholecystokinin produced in the body?
1) i-cells of the duodenum
2) Jejunum
3) ileum
What is the function of cholecystokinin?
1) Increases the production of bile
2) Increases the production of pancreatic enzymes
3) Increases the contraction of the gall bladder
4) It promotes the growth of the exocrine pancreas
5) It decreases the gastric emptying
What stimulates the production of gastric inhibitory peptide (GIP)?
1) Fats
2) Proteins
3) Carbohydrates
From where is the hormone gastric inhibitory peptide produced in the body?
1) K-cells of the duodenum & Jejunum
What are the functions of the gastric inhibitory peptide?
1) Increases the release of insulin
2) Decreases gastric acid secretion
What stimulates the production of secretin?
1) Fats
2) Acids
From where is the hormone secretin produced in the body?
S-cells of the duodenum, jejunum and ileum
What is the function of secretin?
1) Increases the secretion of pepsin
2) Increases pancreatic & biliary bicarbonate secretion
3) Increases the secretion of biliary bicarbonate
4) Promotes the growth of the exocrine pancreas
5) Decreases the secretion of gastric acid
What stimulates the production of motilin?
1) Fats
2) Acids
3) Nervous stimulation
From where is the hormone motilin produced in the body?
M-cells of the duodenum and jejunum
What is the function of motilin?
It increases the gastric and intestinal motility
What are the neurotransmitters that are secreted by the enteric neurons?
1) Ach
2) NE
3) Vasoactive intestinal peptide
4) Gastrin releasing peptide
5) Enkephalins
6) Neuropeptide Y (NPY)
7) Substance P
What is the function of Ach?
- Cholinergic neuron
1) It increases the contractions of SM
2) Increases the production of saliva
3) Increases the gastric and pancreatic secretions
What is the function of Norepinephrine?
- Adrenergic neuron
1) It increases the relaxation of smooth muscle
2) Increases the secretion of saliva
What is the function of the vasoactive intestinal peptide?
- Neurons of the mucosa and SM
1) They relax the SM
2) They increase the intestinal and pancreatic secretions
What is the function of the gastrin releasing peptide?
- Neurons of the gastric mucosa
1) They increase the gastric secretions
What is the function of the enkephalins?
- Neurons of the mucosa and the SM
1) Decreases the contraction of the SM
2) Decreases the intestinal secretions
What is the function of the neuropeptide Y?
- Neurons of the mucosa and SM
1) They relax the smooth muscles
2) They decrease the intestinal secretions
What is the function of Substance P?
- Co-secreted with Ach
1) They increase the salivary secretions
2) Increases he contraction of Smooth muscles
What are the type of GI movements?
1) Propulsive movements
- Peristalsis
- Mass movement
2) Mixing movements
- Segmentation contraction
- Haustrations
What is meant by peristalsis?
- Stimulated by the distention of the gut, where a contractile ring appears around the gut and moves forward, it follows the law of the gut where a constriction ring appears behind the bolus and a relaxation will occur in front of the bolus
- An intact myenteric plexus is necessary for peristalsis
What is meant by the mixing movements?
- They vary in different parts of the gut
1) Peristalsis can cause mixing in some parts of the gut, for example when the food is blocked by a sphincter
2) Local constrictive contractions, occurs every few centimeters, lasting for 5-30 sec, acting like a chopping/shearing mechanism
What is meant by the migrating movements?
- They are waves of contraction that occurs between meals and during the fasting state at a 90 min interval
- Motilin can regulate the migrating motor complex
- Migrating motor complex occurs to prepare the gut for food
