GI3 Flashcards
Mixing activity in the colon is present in all species but is more pronounced in pigs and horses due to the formation of sacculations called _______
Haustra
How are amino acids absorbed in the intestinal lumen?
With sodium gradient
Secondary active transport
What are the functions of intestinal motility
Mixing of food with digestive juices (GI secretions)
Enhancing contact between intestinal wall and food
Peristalsis, propulsive movement of chyme
What are the two plexus of the enteric nervous system and where are the located?
Plexus myentericus - between longitudinal and circular muscle -> controls muscular activity
Plexus submucosus - between submucosa and circular muscle -> control mucus secretin and reabsorption
How is K+ absorbed in the small intestine?
Paracellular
What two types of neurotransmitter are secreted by enteric neurons?
Conventional (norepi and ACh)
Non-noraderenergic, non-cholinergic (NANC)
NO
VIP (vasoactive intestinal polypeptide
Substance P
What is the structure of bile acids?
Sterol ring with amino acid side chain
Amphiphatic
What is the motoric of the stomach
Tonic contraction of the fundus (gastric store)
Strong peristaltic wave in the antrum (grinder)
Passage into the grinder and the pylorus
Emptying of fluid and pre-digested particles into the duodenum. (Fluid empty faster than solid particles)
What occurs in the duodenum to breakdown lipid droplets and increase surface area
Emulsification by bile acids
What parasympathetic nerve innervates the decsending colon and the distal GI tract?
Pelvic nerve - from the sacral spinal cord
How is phosphate absorbed in the intestine?
Na+/phosphate symporter
During peristalsis, stretch in the intestinal wall is recognized by mechanoreceptors. What is the feedback neuronal feedback to the smooth muscle around the site of distention?
Proximal to distention -> excitatory motor neuron -> ACh and SP -> smooth muscle contraction
Distal to distention -> inhibitory motor neuron -> NO, ATP, VIP -> smooth muscle relaxation
____________________ of fatty acid produces AcetylCoA, NADH, FADH2
B oxidation
How is B12 absorbed in the GI tract?
B12 within a food protein
HCl and pepsin separates B12 from food protein
B12 binds to HC
Trypsin cleaves B12 from HC in duodenum
B12 combines with IF (intrinsic factor)
IF with B12 binds to receptor in ileum and is absorbed
Reflexes for pain to inhibit the GI tract, or the defecation reflex must travel to the _____________ before going back to the GI system
Spinal cord
Diarrhea is due to increased frequency for fecal volume. Fecal volume often is increased to to increased water. This increased water in the gut can result from?
Ingested water
Water secreted by glands of GI tract
Water secreted or lost through mucosal epithelium
How is Ca2+ reabsorbed in the intestine?
Calcitoriol (PTH stimulates release from the kidney)
- > increase apical Ca2+ channels
- > increase Calbindin-synthesis
- > increase Ca2+ ATPase (basolateral)
What is the migrating motoric complex?
Series of contractions occurring between meals that helps to push undigested material out of the intestine and controls bacterial population
3 phases: rest, intermittent contractions, strong peristaltic contractions
What are the extrinsic control mechanisms of the GI tracts?
Nerves- Vagus and Splanchnic nerves
Endocrine -aldosterone
What is the sequence of events of vomiting?
Antiperistaltic wave originate in duodenum
Propulsion toward stomach
Contraction of abdominal musculature increases intraabdominal pressure
Expansion of chest cavity - lower intrathoracic pressure
Relax lower esophageal sphincter
Open upper esophageal sphincter
What are important polypeptides?
Gastrin
CCK
Glucagon
ANP
What parasympathetic nerve innervates the esophagus, stomach, sm intestine, ascending colon, pancreas, gallbladder, and liver?
Vagus nerve - from medulla oblongata
Enteric neurons contain _______________ which are bulge like structures which allows it to affect a wide area
Varicosities (containing neurotransmitter )
What types of receptors detect changes int he GI and conveys these changes to the Enteric nervous system and CNS?
Mechanoreceptor- detect stretch
Chemoreceptors- nutrient, osmolarity, pH
The smooth muscles of the GI tract are connected by _________________ so they function as a syncytium
Gap junctions
What are fatty acids used for?
Energy
Structural :phospholipid and glycolipid
Hormone precursors : prostaglandin
Energy reserve :TAG in adipose tissue
After emulsification, what enzyme is required to breakdown lipids further? What does it produce?
Pancreatic lipase
Triglycerides -> free fatty acid and monoglycerides
How does the CNS regulate the enteric NS?
PSNS - ACh-> stimulators> increase secretion
SNS - NA -> inhibits ACh release
What are the three types of motor neurons from the ENS and where are they located?
Muscle motor neuron - plexus myentericus
Secretory motor neuron - plexus submucosus
Vaso motor neurons - both plexus (control blood perfusion)
What cells are the electrical pacemakers for smooth muscle cells and maintain the slow waves of the GI tract?
Interstitial cells of Cajal
Ion channels periodically open to produce current
Sympathetic nerves exit the spinal cord in the __________________ region
Thoracolumbar
What do reflexes within the gut wall control?
GI secretion, peristalsis , mixing contractions, and local inhibitory effects
Excess Acetyl CoA can be converted in the liver to ketone bodies, what are the three ketone bodies?
Acetoacetate
Acetone
3-hydroxybutyrate
Can be used in for energy in peripheral tissues-> converted back to Acetyl CoA -> Krebs cycle
How are oligopeptides reabsorbed across the intestinal wall
Oligopeptides have to be broken down by animopeptidases and oligopeptidases in the brush border to make tri- and di- peptides
Tri and di peptides are absorbed with the H+ gradient
Tertiary transport
What are slow waves of the GI tract?
Rhythmic contractions of smooth muscle, slow undulating changed in membrane potential
no action potential, does not reach threshold
Absorption of iron uses ____________ transporter at the apical membrane which cotransports Fe with _______
Ferroportin; H+
Mobilization of fats from their storage tissue requires what enzyme?
Hormone-sensitive lipase (stimulated by epi and glucagon )
During the digestive period, there are propulsive and non propulsive patterns of peristalsis in the small intestine/ What is the function of each of these patterns?
Propulsive: aboral migrating (movement of food)
Non-propulsive : small segmental contractions along intestine (mixing and distribution of nutrients)
The internal anal sphincter constriction is caused by ________________ stimulation and relaxation is caused by ____________________ stimulation
Sympathetic; parasympathetic
Reabsorption of water in the intestine is highest in the ________________ and lowest in the _______________
Jejunum; colon
De-novo synthesis of fatty acids occurs in the liver, mammary gland, and adipose cells. Describe the process
Carbohydrates and proteins –> ACoA –> malonyl CoA–> Palmitate (fully saturated fatty acid)
Stored as mono-, di- and triacylglycerols
The _________________reflex is the GI circuits of afferent and efferent fibers bringing gut stimuli to the dorsal vagal complex in the brain
Vasovagal
via vagal nerve
What is a spike potential in the GI tract
True action potential
Resting membrane potential becomes greater than -40mV
The higher the slow wave potential the more frequently there will be a spike potential -> these AP cause contractions of the smooth muscle
What are the intrinsic control mechanisms of the GI tract?
Nerves- Enteric nervous system
Endocrine- secretin, gastrin, CCK, GIP, Motilin
There are three relaxations of the stomach, what are they and what initiates them?
Receptive relaxation(vasovagal) - mechanical stimulation of pharynx
Adaptive relaxation (gastro-gastric)- food expanding stomach
Feedback relaxation (CCK)- nutrients
What stimuli can cause vomiting?
Before food intake (color, smell, emotion, appearance )
After food intake ->food particles-> visceral afferent -> vomiting center
After absorption -> particle in blood ->chemoreceptor trigger zone
What occurs to proteins in the stomach?
Partly denatured and hydrolyzed by pepsin
Proteins and polypeptides
What enzyme partially digests lipids in the stomach?
Gastric lipase
How is Mg2+ absorbed in the intestine?
Mg2+ channels
Paracellular
What are the two types of diarrhea?
Malabsorptive - does not recover all secreted water (viral/ bacterial/ protozoan destruction of villi-> less SA for absorption )
Secretory - rate of secretion is greater than absorptive capacity
(Bacteria produce enterotoxins stimulating adenylyl cyclase -> cAMP -> Cl- channel open -> H2O outflow)
How are free fatty acids and monoglycerides absorbed across the intestinal wall?
FFA, monoglycerides, and vitamins form mixed micelles
Micelles are absorbed by enterocytes
Go to ER for re-esterification (MAG+free fatty acid=TAG)
Triglycerides are surrounded by phospholipid =chylomicrons which are excocytosed into the lymphatic vessels
(Bile acids are reabsorbed at the ileum
Amino acids are important precursors to?
Serotonin (tryptophan)
Melatonin (tryptophan->serotonin)
Dopamine (tyrosine)
Histamine (histidine)
Enteric neurons are classified into what three types?
Dogiel type 1 - small cell body with short dendrites (motor)
Dogiel type 2 - large cell body with one or two long dendrites (sensory)
Dogiel type 3 - multiple shapes, motor and sensory
What is required for the breakdown of proteins and polypeptides to oligopeptides and amino acids in the small intestine?
Pepsin’s
Pancreatic polypeptides
Describe the retrosphicteric reflex
Feces accumulate in rectum -> peristaltic movement -> PSNS -> relax internal anal sphincter -> urge to deficate ->
Somatic voluntary-> pudendal nerve -> maintain contraction or relaxation of external anal sphincter
How does short chain fatty acid absorption differ from long chan?
Can be absorbed across the apical membrane directly (do not required micelle)
Do not have to be resynthesized to TAG -> directly released to portal system where they bind albumin
During swallowing of food and entering of food into the stomach the vasovagal reflex causing ______________ of the stomach.
Relaxation of the smooth muscle
What type of reflex transmits signals from one part of the GI tract to another?
Gut to preverterbral sympathetic ganglia
Eg
Gastrocolic- from stomach causing evacuation of the colon
Enterogastric - colon to sm intestine to inhibit motility
Colonoileal -colon to inhibit ileal emptying
1 palmtoyl CoA can produce ______ATP
131 (minus 2 needed) = net 129ATP
What happens to TAGs at skeletal muscle and adipose tissue
Lipoprotein lipase in capillaries converts TAG -> FFA and MAG
FFA enter muscle cells or adipocytes
Storage
Muscle makes glycerol
Adipose tissue makes TAG
What are peptides? What are important physiological peptides?
Short chains of amino acids linked by peptide bonds
Oxytocin
ADH
Bradykinin
Angiotensin II
What are pathological contractions of the intestine.
Vomiting
Diarrhea
What occurs to the remnants of chylomicrons?
Liver absorbs components in receptor-mediated endocytosis
What are the three GI reflexes essential to GI control?
Within gut wall
From gut to prevertebal sympathetic
From gut to spinal cord or brain stem
How is lipid digestion controlled?
CCK synthesized when lipids enter duodenum
-> stimulates bile acid secretion and pancreatic enzyme secretion
Secretin-> stimulates HCO3 secretion from pancreas
How is Na+ absorbed in the intestines?
Apical:
Na/H+ exchanger
Na/Glucose cotransporter
Na/Amino acid cotransporter
Basolaterally
Na/K+ ATPase
