Overview of GI Physiology Flashcards
name the layers of the go tract from inside out
Mucosa muscular mucosa internal submucosal plexus (meissner plexus) submucosa external submucosal plexus circular muscle layer myenteric plexus longitudinal muscle serosa
where does blood from the gut, spleen and pancreas flow to the liver via
the portal vein
blood filtered by the liver sinuses leaves via the
hepatic vein and drains into the vena cava
what does the blood filtering process by the liver sinuses allow
the removal of bacteria/particulate matter that might enter the blood from the GI tract and prevents direct transport of potentially harmful agents into the body
what are villi
small arteriole and venule that interconnect with a system of multiple looping capillaries (countercurrent system)
increase in blood flow to the villus is most likely cause by
- vasodilators released from GI mucosa (CCK, VIP, Gastrin)
- vasodilators released from GI glands (bradykinin)
- decreased o2 concentration in the gut wall due to increased metabolism
- subsequent adenosine release
what differs in the oesophagus and distal rectum anatomy in the composition of the GI tract
they lack serosa and mesentery
where is the submucosal plexus found
small and large intestine - between the circular smooth muscle layer and the mucosa (innervating glandular epithelium, endocrine glands and blood vessels - controls GI secretion
where is the myenteric plexus found
throughout the GIT - between the circular and longitudinal muscle (innervating both layer)
what are the four functions of motility
- propel ingested food along the entire length of the GIT
- mixing and grinding of the contents of the GIT
- Aid absorption of nutrients and water
- Clear the stomach and intestines of luminal contents
fed state
- peristalsis and mixing movements
- functions 1-3
inter digestive state - between meals
- also known as the migrating motor complexes (MMCs)
- responsible for clearing the stomach and intestines of luminal contents
role of the parasympathetic neurones in the ENS
branches of the vagus, pelvic and splanchic nerves
- innervate neurones in the myenteric plexus
- main function is to stimulate GI motility and secretion
role of the sympathetic neurones in the ENS
these originate from the celiac, superior and inferior mesenteric and hypogastric plexuses
- terminate on the enteric nerves, the smooth muscles and the mucosa
- main function is to inhibit GIT motility and secretion
tell me about smooth muscle
- muscle fibres connected bu gap junctions and focal adhesions (adherens junctions)
- actin and myosin filaments aligned diagonally along long axis of the cells
- filaments anchored at dense bodies (alpha - actinin - rich) scattered throughout sarcoplasm
- contractile arrays anchored to sarcolemma by dense plaques
electrical activity in the GI smooth muscle is initiated where
interstitial cells of cajal
what are the two types of electrical activity
- slow waves
- spike potentials
role of slow waves
to excite the appearance of spike potentials
the higher the slow wave potential
greater frequency of spike potentials, therefore the stronger the contraction of the smooth muscle
how can baseline membrane potential vary
- depolarisation leads to increased excitability
- hyper-polarisation leads to decreased excitability
what ions are involved in electrical activity in smooth muscle
due to the opening of calcium ion channels leading to the influx of ca2+ into the cells, and is then terminated by K+ efflux
peristalsis
the stretch initiates the circular muscles behind (oral end) it to contract (ascending excitatory reflex) and the circular muscles in front (anal end) of it to reflex (descending inhibitory reflex)
segmentation - large intestine
- contractions of circular muscle layer at short intervals along GIT
- contractions start as n 1 opposite
- contractions then move forward to now contract in original relaxed area (2 opposite)
migrating motor complexes
- between meals or when fasting
- function to clear stomach and small intestine debris and bacteria
happens in 4 stages
what are the phases of MMC
- Phase I (45-60 mins) - quiescent period
with slow waves
– Phase II (30-35 mins) - action potential activity on slow waves but sporadic contractions of circular muscle
– Phase III (2-12 mins) - action potential activity on slow waves but regular contractions of circular muscle
– Phase IV – period in which action potential activity and contraction reduce and merge into phase I
Peristalsis
