Lecture 18: Introduction to GI Function and Regulation Flashcards
What are the main functions of the GI System
- Convey nutrients, water and electrolytes
- Act as barrier between external and internal environment- protection and immune function
Besides ruminants what part of the GI does fermentation take place
Large intestines
What are the 5 functions of the GI
- Motility
- Storage
- Secretion
- Digestion
- Absorption
What type of motility and secretion does the esophagus utilize
Motility: peristalsis
Secretion: mucus
What type of motility and secretion does the stomach utilize
Motility: storage and mixing
Secretion: HCl and mucous
What type of motility and secretion does the small intestine utilize
Motility: segmentation and peristalsis
Secretion: mucous, bile, pancreatic juices
What type of motility and secretion does the large intestine utilize
Motility: peristalsis, mass movements, and defecation
Secretion: mucous
Why is the storage function of the stomach important
Need to give the duodenum time to further breakdown food
What is the function of the hyolingual apparatus
Generates a negative oral cavity pressure to facilitate suckling fluids in mammals
The anatomy of large intestines reflects adaptations to feeding habits, decrease the large intestines of cows vs horses
Horses have a very large cecum in order to promote hindgut fermentation, whereas ruminants have a large small intestines as they are foregut fermenters
Describe how cleft palate occurs and how it affects GI
Cleft palate forms from failure of lateral palatine processes to form during development. Leaves a hole between oropharynx and nasopharynx so suckling of milk causes it to come out the nose
What is atresia ani/atresia coli
Defect of the formation of the rectum to the anus
What is type I atresia ani/atresia coli
Congenital anal stenosis
What is type II atresia ani/atresia coli
Imperforate anus alone
What is type III atresia ani/atresia coli
Imperforate anus combined with more cranial termination of the rectum as a blind pouch
What is type IV atresia ani/atresia coli
Discontinuity of the proximal rectum with normal anal and terminal rectal development
What causes atresia ani/atresia coli
Inadequate blood flow during embryological development can cause atrophy
What is the order of layers of the intestine from inner to outer
- Epithelium
- Lamina propria
- Muscularis mucosa
- Subumucosa
- Subumucosal plexus
- Inner circular muscle
- Myenteric plexus
- Outer longitudinal muscle
- Serosa
What type of epithelium is present in the esophagus
Multilayered stratified squamous
What type of epithelium is present in stomach, small and large intestine
Single layer columnar
What part of the intestines has just crypts
Large intestine
What part of the intestines have crypts and villi
Small intestine
What is the function of crypts and villi
Increase absorptive surface area
Why is the advantage of constant epithelial renewal in the esophagus, stomach, small and large intestine
Prevents accumulation of defects- mechanical, toxins, mutagenic
What is the risk of constant epithelial renewal in the esophagus, stomach, small and large intestines
Malignancy
Where do stem cells originate in stomach and intestines
Neck area of crypts
What do stem cells differentiate into
- Goblet cells
- Paneth cells
- Enterocytes
- Enteroendocrine cells
What are paneth cells
Immune cells that fight off bacteria, contain lysozymes
What is the intrinsic control of GI system
Enteric nervous system
What is the extrinsic control of GI system
SNS and PNS
Neurons of the ENS are located where
In between the inner circular and outer longitudinal layer of the myenteric plexus
What does the myenteric plexus innervate
Longitudinal and circular smooth muscle
What is the primary function of the myenteric plexus
Gut movement
What does the submucosal plexus innervate
Glandular epithelium, intestinal endocrine cells, and submucosal blood vessels
What is the primary function of the submucosal plexus
Intestinal secretions
What type of receptors does the gut mucosa have
Mechanoreceptors, chemoreceptors and thermoreceptors
What type of receptors does the gut wall have
Mechanoreceptors
What are the target organs of the mucosa
Glands, enteroendocrine cells
What are the target organs of the gut wall
Muscle, blood vessels
Where are neurotransmitters released from ENS neurons
Axons and axon collaterals that contain varicosities
What is the advantage of varicosities
Activate a broader area around the axon vs focused at end of axon
What is the motor function of the ENS
Innervate muscles and sphincters causing contraction and relaxation
What is the sensory function of the ENS
Detect luminal pH, temperature, pressure
What do excitatory neurons of the GI do
Increase mucosal secretions and muscle contractions
What do inhibitory neurons of the GI do
Decrease mucosal secretions and muscle relaxation
What are the excitatory neurotransmitters
ACh and substance P
What are the inhibitory neurotransmitters
NO and VIP
What are the interstitial cells of cajal
Specialized smooth muscle cells that act as pacemaker cells to control contractile, electrical rhythm of the gut
ICC have a self-generating depolarizing rhythm that controls the electrical rhythm of the gut that creates oscillations in the membrane potential. These are known as ___
Slow waves
What sympathetic nerve primarily innervates the GI
Splanchnic
How does sympathetic innervation affect motility, sphincters and secretions
Decrease motility, increase sphincter contraction and decrease secretions
What parasympathetic nerve primarily innervates the GI
Vagus
What is the effect of parasympathetic innervation of the gut on motility, sphincters and secretion
Increase motility, decrease sphincter contraction (promote relaxation) and increase secretions
Splanchnic afferent nerves carry information about ___
Gut dissension, noxious chemicals and inflammation
Are SNS efferents inhibitory or excitatory
Inhibitory
What NT does SNS use to decrease motility and glandular secretions
NE
PNS efferents are primarily inhibitory or excitatory
Excitatory
What NT does PNS use to increase gut blood flow, motility and glandular secretions
Acetylcholine
What is a vagotomy
Surgical operation to cut one or more branches of the vagus nerve to decrease rate of gastric secretion and motility
T or F: vagotomies can be performed in ruminants
False, will result in malfermentation
What cells are responsible for sensing gut content and releasing hormones and neuroactive substances
Enteroendocrine cells
What are the 5 main enteroendocrine cells of the stomach and small intestine
- Gastric
- Secretin
- CCK
- GIP
- Motilin
What cells secrete gastrin
G cells
What cells secrete CCK
I cells
What cells secrete secretin
S cells
What cells secrete motilin
M cells
What cells secrete GIP
K cells
Aldosterone stimulates the reabsorption of __ and __
Na+ and H20
What channel in the nephron does aldosterone use
ENaC
What do glucocorticoids do to Na/K ATPase
Increase activity
Aldosterone stimulates Na+ and H20 reabsorption in the colon, what other ion follows paracellularly
Cl-
