L2 Introduction to GI Physiology Flashcards
where does the alimentary canal pass though?
pharynx, oesophagus, stomach, small and large intestines
how long is the GI tract?
8 or 9 metres:
pharynx, oesophagus and stomach = 1m
small bowel = 6m
large bowel = 1.5m
what are the functions of the GI tract?
Ingestion Mechanical Processing Digestion Secretion Absorption Excretion
what is ingestion?
Occurs when materials enter digestive tract via the mouth
what is mechanical processing?
Crushing and shearing, wetting and softening
Makes materials easier to propel along digestive tract
what is digestion?
The chemical breakdown of food into small organic fragments for absorption by digestive epithelium
what is secretion?
Is the release of water, acids, enzymes, buffers, and salts
By epithelium of digestive tract
By glandular organs
what is absorption?
Movement of organic substrates, electrolytes, vitamins, and water across digestive epithelium into interstitial fluid of digestive tract
what is excretion?
Removal of indigestible material, and waste products from body fluids
what can barretts oesophagus lead to ?
dysplasia, which can lead to metaplasia and then cancer
what are the functions of the peritoneum?
lines the abdominal cavity (parietal peritoneum)
covers organs (visceral peritoneum)
Forms mesenteries, which suspend the organs, support them, and keep them from tangling
Secretes peritoneal fluid, which provides lubrication, and permits organs to move against each other without friction.
which organs are retroperitoneal?
kidney, pancreas and part of duodenum
what are the functions of the mesenteries?
Mesenteries suspend the organs, and stop the loops of gut getting tangled around each other.
Also carry blood vessels, nerves, and lymphatics.
Fat pads cushion and protect organs.
what are the 3 main blood supplies to the GI tract?
coeliac artery, superior mesenteric artery and inferior mesenteric artery
which vein does blood from the GI tract mainly drain into?
hepatic portal vein which carries absorbed nutrients to the liver for processing
what are the major layers of the GI tract in order?
from innermost to outermost:
- mucosa
- submucosa
- muscularis externa
- serosa
what is the difference between epithelia and glands?
epithelia - Layers of cells covering internal or external surfaces
glands - structures that produce secretions
are epithelial cells polarised or not? how can you tell?
yes - photomicrograph can show protein detected at one pole of the cell
what are the different types of cell junctions?
occluding junctions such as tight junctions
cell-cell anchoring junctions such as adherens junction and desmosomes
channel-forming junctions such as gap junctions
cell-matrix anchoring junction such as hemidesmosomes (and actin-linked cell-matrix adhesion)
what is a tight junction and where is it found in relation to the cell?
seals gap between epithelial cell and is found most apically
what is a adheren junction and where is it found in relation to the cell?
connects actin filament bundle in one cell with that in the next cell and is found apically
what is a desmosome and where is it found in relation to the cell?
connects intermediate filaments in one cell to those in next cell. is found in middle of apical and basal sides
what is a gap junction and where is it found in relation to the cell?
allows passage of small water-soluble molecules from cell to cell. found basally (but not attached to basal layer)
what is a hemidesmosome?
anchors intermediate filaments in a cell to extracellular matrix
what is the difference between absorption and secretion?
Movement from the external compartment (the lumen of the renal tubule or gut) to the internal compartment (the blood) is called absorption. Good examples of this are glucose absorption in the gut and renal tubule
Movement from the internal compartment to the external compartment is called secretion. Good examples of this are protons (H+) and potassium in the renal tubule and HCO3- which is secreted by the pancreas.
what is the difference between transcellular and paracellular absorption/secretion?
trancellular = through the cell - two barriers (apical and basolateral membranes) must be traversed
paracellular = netween the cells (not through)
what is passive transport?
Non coupled - solute moves down its electrochemical gradient.
Can occur via pores or channels e.g. diffusion of ions, H2O
Transporters – facilitate diffusion of small non electrolytes
can be transcellular or paracellular
what is primary and secondar active transport?
Primary
Energy to drive transport comes directly from ATP
Substrate moves against an electrochemical gradient
Secondary
Energy to drive active transport comes from electrochemical gradient for one substrate (set up by primary active transport)
Second substrate moves against its electrochemical gradient
is only transcellular
what will drive net fluid movement?
net solute movement will tend to drive net fluid movement.
where does the main sensory and motor control of the GI activity come from?
parasympathetic nerves - The vagus controls foregut and midgut derivatives, while pelvic splanchnic nerves supply hindgut components.
promotes digestive processes
which nervous system inhibits hut activity?
sympathetic nervous system
depresses digestive activity
how does autonomic nervous sytem act on GI?
via enteric nervous system
what is the enteric nervous system?
most activity of muscle in gut wall is locally regulated and controlled, by a set of nerves lying between the muscle laters, and underneath the submucosa. This “enteric nervous system” can control the normal gut motility essentially autonomously, although parasympathetic and sympathetic nerves allow some degree of central control.
Myenteric & submucosal plexi
Communication within & between plexi
Processes extend to target cells
Modulated by input from ANS
what are slow waves and what do they do?
periodic shifts (depolarisations) in the resting membrane potential of the cells. This makes it easier for a small signal to initiate a contraction and/or an action potential.
In practice, what this means is that neural and hormonal signals will initiate activity only during a slow wave: thus the slow waves give an underlying structure to the activity of the smooth muscle.
what are the features of slow waves?
Regular oscillations in resting membrane potential
3 - 12 min-1
Set timing- contraction may occur
Pacemaker (ICC) cells
what are interstitial cells of cajal?
mediators of slow waves - connections with each other and smooth muscel cells
