GI Part II Flashcards
Dr. Chad Touchberry (UMKC)
What is the purpose of the phasic portion of GI contractions?
Basically the circular muscles contract in the stomach, SI, and LI to aid in mixing the food, this is called segmented contraction
What are tonic contractions driven by, and what is there job?
Mainly by sphincters, to seperate sections of the GI tract by contracting and releasing. Tonic contraction is typically always contracted and job is seperation
What is the job of the peristaltic contractions (phasic), and where are they mostly located?
Contraction of the smooth muscle propels further and further along to propel food forward. Occurs in the esophagus, stomach, SI and LI
What principally drives SMC contraction throughout the GI system?
Driven by the basal electral rhythm (BER) generated by the SMC under control of the interstitial cells of cahal (ICC) that are the pacemakers of the GI system
What are the main phases of Chewing (mastication) & swallowing (deglutition)…?
Phase 1 Oral - Chew: (voluntary) Chewing (mastication) that breaks down the cells and increase the surface area as well as lubricate food, goal is to form a bolus. Stretch reflexes help to form rebound contractions to aid in chewing.
Phase 1 Oral - Propulsion: (voluntary) oral propulsion phase. You can’t swallow if mouth is dry. Superior constrictor muscles cause an upward movement of the soft palate to block food into the nasopharynx
Phase 2 Pharyngeal - (involuntary) food goes down esophagus and 1. Epiglottis covers the glottis shutting off respiration/protecting the airway and 2. Vocal cords are adducted to protect the airway and 3. Upper esophageal sphincter opens and allows food to enter the digestive system
Phase 3 Esophageal - (involuntary) peristalsis helps push food down to lower esophageal sphincter. Upper third of esophagus is skeletal muscle, but they are involuntary still
How is swallowing controlled?
- Vagal afferents provide sensory info about food applying pressure to walls of esophagus (Swallowing center).
- Efferent outflow to upper esophageal sphincter tells it to contract or relax by releasing or stopping Ach release
- Bottom 2/3 is smooth muscle (efferent ANS) and enteric neurons of GI cause peristalsis
- LES is under tonic contraction (from NE) and myogenic tone (diaphragm) can be relaxed through Ach. Purpose is prevent reflex (newborns don’t have a tonic sphincter until about age 2 or so)
What are the two different forms of peristalsis of the esophagus?
Primary peristalsis is controlled by the dorsal vagal complex that innervates the upper esophageal sphincter and lower esophageal sphincter through long reflexes. Vagal afferent send sensory info to DVC and vagal efferents 1. release Ach (contraction of esophagus) and 2. vagal efferent release NO/BIP to dilate downstream and relax
Secondary peristalsis the LES opens/UES closes and the enteric nervous system (short reflex) is activated by distension where interneurons (sensory ENS) are activated that cause contraction upstream of distension and relax downstream. This is not vagally innervated so a vagotomy would not inhibit this
What is a vagotomy?
The vagus nerve is cut prior to all branches that go to the GI system, this would prevent primary peristalsis
What is GERD?
GERD the LES is too relaxed and can lead to asthma. A chronic sinus infection opens and closes the UES and cause a reflex back into the esophagus.
Main thing we are worried about is Barrett’s esophagus, where the tissue is severly irritated from acid exposure leading to dysplasic (precancerous) tissue. If it is caught soon enough it can be prevented.
Treatment: Antacids/proton inhibitors and diet modifications
What is achalasia?
LES is too constricted and have very bad breath and belching, coordination of opening the UES is inhibited leading to dysphagia. People eat less or liquid diets.
Threat is megaesophagus (complete rupture)
Treatment: 1. Antispasmotic drugs (pneumatic dilator) and a stiff balloon to expand or 2. Surgical myotomy where they cut some of the LES to help
Increasing spike potential frequency
GI function would be better in a spinal cord injury patient who would lose ANS innervation and pelvic and vagus innervation. If ENS is preserved, you would have better gut function.
What is the migrating motor complex (MMC)?
Only in phase 3, M cells release motiliin that induce the phase 3 MMC. Contractions last about 5 minutes that propagate the whole GI system every 90 minutes or so.
Once we eat a meal, vagus nerve output increase contractions and inhibit motilin induced contractions
What is ghrelin?
Hunger hormone released by the stomach when it is empty, it goes to the brain and acts on the hypothalamus that increases vagus nerve activity to increase MMC.
How does stomach distension allow stretching and the ability to hold more food?
How much intragastric pressure (cmH20) is needed before someone feels full/discomfort? What is the window or pressure?
How does the stomach propel food forward through the SI?
What is the enterogastric reflex?
The duodenum of the SI is regulated by factors to slow gastric emptying through short and long reflexes as well as release of enterogastric hormones (CCK, secretin)
When you don’t have this reflex you end up with dumping syndrome causing hypertonic hypovolemia and delayed emptying
What are the rules of gastric emptying, what foods increase satiety the most?
What increases gastric emptying?
What decreases gastric emptying?
What is the function of the SI?
What is starlings law of the small intestine?
Instestino-Intestinal reflex inhibits the contraction of the small intestine that relieves thier pain before seeking medical attention
What is the BER along the SI?
How does food stuff move from the SI to LI?
What is the main function of the LI and the Bristol stool chart?
What reflexes force you to have to deficate after ingestion of food?
What are the three levels of control of the anorectal reflex to have to deficate after eating a meal?
- Rectum distends and increases enteric reflex and a more powerful extrinsic reflext through green afferant fibers.
- Pelvic efferent fibers go to descending colon and rectum to initiate contraction
3/4: S2-S4 concious cortex activates pudendal nerve to contract the external rectum to contract and deficate
What is the BER of the LI?
From liklehood to unlikelyhood:
Gastrin
Histamine
Ach
No
Yes
Yes in primary and no in secondary peristalsis
Estimated daily secretions by GI system
How are water soluble vitamins (vitamin C and B’s) absorbed?
How are fat soluble vitamins absorbed? What are the major ones?
How are most minerals absorbed?
Chloride is more absorbed
Citrate is not
What is unique about biotin and vitamin K?
How is vitamin B12 absorbed?
What will a deficiency of intrinsic factor lead too?
What are the three phases of intestinal digestion?
What is the purpose of the bile salts, lipase, and colipase in the process of absorption of FFAs?
How are lipids absorbed?
Most lipids are absorbed in the SI, what section of the small intestine absorbs the most fats?
Jejunum
What is steatorrhea?
How is cholesterol transported from the lumen? What does Ezetrol do?
What do ABCG5 and ABCG8 transporters do?
What can mutations in ABCG5 and ABCG8 lead to clinically?
Review question:
Water in the duedenum
Review question:
Induce receptor relaxation
What enzymes are involved in carbohydrate digestion?
What are the two sites of carbohydrate digestion?
What are the main functions of SGLT1, GLUT5, and GLUT 2 on the enterocyte? What maintains the Na+ gradient?
SGLT1 - transports glucose/galactose through Na+ cotransporter from lumen
GLUT5 - transports fructose only from lumen
GLUT2 - transports glucose/galactose/fructose all from the cytosol of enterocyte to the blood
Na+/K+ ATPase - maintains higher extracellular Na+ for transport to occur
How have oral rehydration solutions reduced the amount of deaths of diarrhea every year?
The more glucose you can absorb and soduim, water will follow the ions and reduce diarrhea in those individuals
Where are the majority of carbohydrates absorbed in the S. intestine?
Duodenum and Jejunum
Simple sugars are more absorbed in duodenum and fruit and more complex would be absorbed in the jejunum
How are pancreatic enzymes involved in the absorption of peptides?
- Enterokinase cleaves tripsinogen into trypsin in the lumen
- Trypsin activates the inactive downstream proteases into the active form
What are the main roles of trypsin and chymotrypsin?
Break down the larger proteins
What is the major role of elastase?
Breaks down elastin fibers which also frees AAs
What is the role of carboxypeptidase?
What are the three sites of protein digestion?
Most of the proteases exist from the pancreas that break down di and tri-peptides
What allows di and tri-peptide proteins to be more rapidly absorbed than free peptides?
A lot of drugs work by coupling to di or tri-peptide chains and are transported into blood through that cotransport.
PEPT1 relies on the Na+/K+ exchanger to maintain Na+ gradient
OATs - Organic anionic transporters use anions to move substances into the blood
OCTs - Organic cationic transporters use cations to move substances into the blood
Where are the majority of proteins absorbed in the S. intestine?
Across most of the S. Intestine and areas with most transport just have more transporters located there
Highest expression of PEPT1 is in the jejunum and illeum
What is Roux-en-Y gastric bypass surgery? What complications can occur due to this surgery?
Review table of digestion and absorption:
Overall review table:
