L2 Introduction to GI Physiology

Question 1

where does the alimentary canal pass though?

Answer 1

pharynx, oesophagus, stomach, small and large intestines

Question 2

how long is the GI tract?

Answer 2

8 or 9 metres:

pharynx, oesophagus and stomach = 1m
small bowel = 6m
large bowel = 1.5m

Question 3

what are the functions of the GI tract?

Answer 3

Ingestion
Mechanical Processing
Digestion
Secretion
Absorption
Excretion

Question 4

what is ingestion?

Answer 4

Occurs when materials enter digestive tract via the mouth

Question 5

what is mechanical processing?

Answer 5

Crushing and shearing, wetting and softening

Makes materials easier to propel along digestive tract

Question 6

what is digestion?

Answer 6

The chemical breakdown of food into small organic fragments for absorption by digestive epithelium

Question 7

what is secretion?

Answer 7

Is the release of water, acids, enzymes, buffers, and salts
By epithelium of digestive tract
By glandular organs

Question 8

what is absorption?

Answer 8

Movement of organic substrates, electrolytes, vitamins, and water across digestive epithelium into interstitial fluid of digestive tract

Question 9

what is excretion?

Answer 9

Removal of indigestible material, and waste products from body fluids

Question 10

what can barretts oesophagus lead to ?

Answer 10

dysplasia, which can lead to metaplasia and then cancer

Question 11

what are the functions of the peritoneum?

Answer 11

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.

Question 12

which organs are retroperitoneal?

Answer 12

kidney, pancreas and part of duodenum

Question 13

what are the functions of the mesenteries?

Answer 13

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.

Question 14

what are the 3 main blood supplies to the GI tract?

Answer 14

coeliac artery, superior mesenteric artery and inferior mesenteric artery

Question 15

which vein does blood from the GI tract mainly drain into?

Answer 15

hepatic portal vein which carries absorbed nutrients to the liver for processing

Question 16

what are the major layers of the GI tract in order?

Answer 16

from innermost to outermost:

• mucosa
• submucosa
• muscularis externa
• serosa

Question 17

what is the difference between epithelia and glands?

Answer 17

epithelia - Layers of cells covering internal or external surfaces

glands - structures that produce secretions

Question 18

are epithelial cells polarised or not? how can you tell?

Answer 18

yes - photomicrograph can show protein detected at one pole of the cell

Question 19

what are the different types of cell junctions?

Answer 19

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)

Question 20

what is a tight junction and where is it found in relation to the cell?

Answer 20

seals gap between epithelial cell and is found most apically

Question 21

what is a adheren junction and where is it found in relation to the cell?

Answer 21

connects actin filament bundle in one cell with that in the next cell and is found apically

Question 22

what is a desmosome and where is it found in relation to the cell?

Answer 22

connects intermediate filaments in one cell to those in next cell. is found in middle of apical and basal sides

Question 23

what is a gap junction and where is it found in relation to the cell?

Answer 23

allows passage of small water-soluble molecules from cell to cell. found basally (but not attached to basal layer)

Question 24

what is a hemidesmosome?

Answer 24

anchors intermediate filaments in a cell to extracellular matrix

Question 25

what is the difference between absorption and secretion?

Answer 25

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.

Question 26

what is the difference between transcellular and paracellular absorption/secretion?

Answer 26

trancellular = through the cell - two barriers (apical and basolateral membranes) must be traversed

paracellular = netween the cells (not through)

Question 27

what is passive transport?

Answer 27

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

Question 28

what is primary and secondar active transport?

Answer 28

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

Question 29

what will drive net fluid movement?

Answer 29

net solute movement will tend to drive net fluid movement.

Question 30

where does the main sensory and motor control of the GI activity come from?

Answer 30

parasympathetic nerves - The vagus controls foregut and midgut derivatives, while pelvic splanchnic nerves supply hindgut components.

promotes digestive processes

Question 31

which nervous system inhibits hut activity?

Answer 31

sympathetic nervous system

depresses digestive activity

Question 32

how does autonomic nervous sytem act on GI?

Answer 32

via enteric nervous system

Question 33

what is the enteric nervous system?

Answer 33

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

Question 34

what are slow waves and what do they do?

Answer 34

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.

Question 35

what are the features of slow waves?

Answer 35

Regular oscillations in resting membrane potential
3 - 12 min-1
Set timing- contraction may occur
Pacemaker (ICC) cells

Question 36

what are interstitial cells of cajal?

Answer 36

mediators of slow waves - connections with each other and smooth muscel cells