GI secretion, motility, digestion - Collins Flashcards
Peristalsis through the tract orchestrated by ____ cells.
Cajal
What two types of movement are seen in the GI tract?
Peristalsis (movement) and segmentation (mixing).
Describe the biochemical cascade that leads to contraction when Ca levels rise in a smooth muscle cell.
High Ca binds calmodulin–> calmodulin binds myosin light chain kinase–> phosphorylates myosin with ATP –> actin binds–> contraction–> repeats until Ca levels drop, then the reverse happens.
Sympathetic innervation travels through which three ganglia to reach the GI tract?
Celiac, Superior Mesenteric, Inferior Mesenteric
Parasympathetic innervation to the GI tract travels through which two nerves?
Vagus, Pelvic
To reach the lumenal cell, vagal nerve impulses will have to travel through which structures, in order (3 muscles, 2 plexi)
Longitudinal muscle–> myenteric plexus–> circular muscle–> submucosal plexus–> muscularis mucosae–> target cell
Stomach BER = 3 cycles per minute
Duodenum BER = 12 cycles per minute
Why?
Because otherwise you get a “backlog.” haha
What is the purpose of the BER? What happens when Ach is added?
The BER establishes rhythm onto the Ach stimulation, so that you get coordinated contractions that can propel contents through the tract. Otherwise you would see more chaotic movement that would be ineffectual.
Define paracrine, endocrine, and neurocrine transmission. Which cell type can do them all?
Mast cells can.
Paracrine–> direct cell/cell
Endocrine–> through the blood
Neurocrine–> nerve to cell
Describe the three steps of swallowing. Which are voluntary/involuntary?
Stage 1: Voluntary–>oral to oropharynx. Kids have to learn this
Stage 2: Involuntary–>glottis covers trachea, UES relaxes)
Stage 3: Incoluntary–>esophageal peristalsis
Failure of the LES to relax due to damage/loss of the enteric nerves of the LES wall is called _____ and can make swallowing difficult
achalasia
____ in the stomach allow increased distension WITHOUT an increase in pressure.
Rugae
This structure facilitates size-dependent movement of food into the duodenum.
Pyloric sphincter –> facilitates size-dependent movement of food into the duodenum.
Describe the muscular activity of the stomach during digestion.
Wavelike contraction of the stomach down towards the pyloric sphincter. All else gets kicked up into the fundal region. (retropulsion). At the same time you are having receptive relaxation. This cycle repeats again and again until it all gets small enough to pass through.
Carbs, fat, and protein leave the stomach in which order?
Carbohydrate is fastest. Then protein. Then fat, which is the slowest. Takes a lot of time b/c the fat isn’t soluble in water.
Describe the four steps of vomiting.
Neuronally controlled.
1) Increased salivation is important for lubrication, and also secretion of bicarbonate to protect from the gastric acid.
2) Reverse peristalsis. UES/LES must both relax
3) Contraction of abdominal muscles
4) ejection
Give two examples of neuronally-mediated “intestinal reflexes”
Gastrocecal–> food in stomach stimulates mass movement in the colon
Gastroileal–> food in stomach stimulates movement from the ileum into the colon (through the ileocecal sphincter)
EG when you eat you have to poop. Babies do this at the table, even.
What initiates MMCs? What does that even stand for? Where do they occur? How long do they last?
Migrating Motor Complexes are initiated by motilin (and possible neuronally mediated as well). They last for 90 minutes. Occur from the BODY of the stomach to the ileocecal valve.
Describe the three phases of an MMC.
Phase I–> quiescent (50%)
Phase II–> “irregular contractions” shake the rug to dislodge stuff from walls but don’t propel anything. (30%)
Phase III–>powerful contractions. Sphincters open. (20%)
What are two stimuli that control the status of the ileocecal sphincter (local signals)?
Neutral state is closed.
Opened by distension of end of ileum (local reflex)
Closed by distension of proximal colon (local reflex)
What types of movement are seen in the small intestine?
Segmentation
Peristalsis
MMC
What types of mvmt are seen in the colon?
Haustration
Mass movement
What is haustration?
Different sections of the bowel act to separate contents into discrete segments known as “haustra”. So you can poop in a reasonable amount of time. Remember the barium study–> not evenly distributed throughout the colon, but rather in several large chunks.
How often do mass movements occur in the colon?
1-3x/day
