Function of the small and large intestine

Question 1

why are muscle contractions of the small intestine important?

Answer 1

to mix the content
ensure luminal content contracts with the epithelial cells
transport chyme along the tract

Question 2

what are the two types of contractions of the small intestine in the digestive phase?

Answer 2

segmentation (mixing contractions)
peristalsis (propulsive contractions)

Question 3

what are type of contractions are mixing movements?

Answer 3

non-propulsive

Question 4

during propulsive movements, what muscles are contracting and what muscles are relaxing?

Answer 4

the longitudinal muscle relax and the circular muscle contract WHICH makes the small intestine squeeze together
the longitudinal muscle contracts and circular muscle relaxes which allows chyme to move through the small intestine as the small intestine increases in diameter

Question 5

what type of contraction are the segmentation contractions?

Answer 5

mixing movements
non-propulsive

Question 6

contracted ?

Answer 6

now distended

Question 7

which muscle, longitudinal/circular is closest to the lumen?

Answer 7

circular muscle and the longitudinal is on the outside

Question 8

MMC?

Answer 8

migrating motility complex?

Question 9

MMC - Intergidestive
Propulsive movements consists of?

Answer 9

This process sweeps the intestines clean between meals
Between periods of peristaltic contractions
Also gets rid of bacteria and sloughed off epithelial cells
Meal consumption interrupts the MMC

Question 10

what are the pacemaker cells?

Answer 10

intersticial cells of Cajal = ICC

Question 11

what type of muscle cells are the pacemaker cells?

Answer 11

modified smooth muscle cells

Question 12

in the pacemaker cells, describe the membrane potential?

Answer 12

there are spontaneous oscillations in membrane potential

Question 13

where are pacemaker cells present?

Answer 13

throughout the smooth muscle portions of the GI tract

Question 14

what are pacemaker cells responsible for?

Answer 14

the slow waves of smooth muscle, whether it is contracting or not

Question 15

how do pacemaker cells control muscle contractions?

Answer 15

they can only occur at the same or a lesser frequency than the slow waves

Question 16

what stimulates the smooth muscle cells after a meal?

Answer 16

after a meal, the smooth muscle cells are stimulated by acetylcholin released by nerve impulses and by gastrin

Question 17

number of pacemaker cells (ICC) throughout small intestine?

Answer 17

numerous throughout

Question 18

what does each area of ICC do?

Answer 18

controls a small area of the intestine

Question 19

where is the frequency of slow waves the highest?

Answer 19

in the proximal small intestine

Question 20

slow waves are not enough to cause? what does there need to be?

Answer 20

not enough to cause contractions on their own
there needs to be sufficient membrane depolarisation to cause action potentials

Question 21

11

Question 22

13 and 12

Question 23

digestion of chyme in non-ruminants?

Answer 23

digestion of chyme has not proceeded far when it leaves the stomach

Question 24

where does most digestion and absorption occur?

Answer 24

in the small intestine
carbs and protein digestive in small intestine
if not broken down in SI then they are moved to LI for microbial digestion

Question 25

what are the three structures of the SI that increase surface area?

Answer 25

folds in the inner surface of the small intestine (mucosa) the mucosa is covered in villi villi have microvilli

Question 26

what does the enterocyte structure consist of?

Answer 26

apical membrane: contact w/ intestinal lumen tight junctions (loose) : connect adjacent enterocytes Basolateral membrane: extracellular space (EC fluid)

Question 27

describe the transfer of nutrients from thelumen of the digestive tract to blood or lymph capillaries?

Answer 27

from lumen across the apical membrane into the enterocyte :organis aciorss or between enterocytes (tight nunctions): water and ions from extracellular fluid (lateral space) into blood of lymph: water and ions

Question 28

endocytosis mechanism and when released on the other side?

Answer 28

`exocytosis mechanism

Question 29

luminal phase of digestion occurs where?

Answer 29

inside lumen of SI

Question 30

what produces amylase?

Answer 30

pancreas

Question 31

anti-peristaltic movements?

Answer 31

moving the contents backwards in the intestine (large)`

Question 32

how many types of contractions in caecum?

Answer 32

2

Question 33

how many types of contractions in the colon?

Answer 33

4 types of contractions

Question 34

ICC?

Answer 34

intersticial cells of Cajal

Question 35

slow waves of the pacemaker cells are not enough to what?

Answer 35

cause contractions on their own

Question 36

what does there need to be in order to cause action potentials?

Answer 36

there needs to be sufficient membrane depolarisation to cause action potentials

Question 37

what releases peptides and neurotransmitters in the vicinity of the smooth muscle cells - thus affecting the membrane potential?

Answer 37

the ENS (enteric nervous system) the enteric endocrine and paracrine cells

Question 38

what happens to the smooth muscles when the membrane potential is depolarised?

Answer 38

the action potentials will fire and the smooth muscle contracts

Question 39

what increases contraction strength of the smooth muscle of the GI tract?

Answer 39

the increased activity in parasympathetic vagal fibres

Question 40

what leads to a decrease in contraction strength of the smooth muscle within the GI tract?

Answer 40

increased sympathetic activity

Question 41

what contractions does the enteric nervous system primarily regulate?

Answer 41

the strength of peristaltic and segmentation contractions is primarily regulated by the enteric nervous system

Question 42

when chyme enters the intestine, what happens?

Answer 42

the pacemaker cells (ICC) are activated (depolarisation)

Question 43

where does most digestion and absorption occur?

Answer 43

in the small intestine

Question 44

where are carbs and proteins digested?

Answer 44

in the small intestine

Question 45

if the carbs and proteins are not broken down in the small intestine, what happens to them?

Answer 45

then they are moved to the large intestine for microbial digestion

Question 46

what does the enterocyte structure consist of?

Answer 46

apical membrane tight junctions (loose) basolateral membrane

Question 47

Describe the location of the apical membrane?

Answer 47

it is in contact with the intestinal lumen

Question 48

what do tight junctions do?

Answer 48

they connect adjacent enterocytes

Question 49

where is the basolateral membrane found?

Answer 49

in the extracellular space

Question 50

describe the ORGANIC transfer of nutrients from the lumen of the digestive tract to the blood or lymph capillaries?

Answer 50

from lumen across apical membrane into the enterocyte

Question 51

describe the transfer of nutrients (water and ions) from the lumen of the digestive tract to the blood or lymph capillaries?

Answer 51

across or between enterocytes (tight junctions)

Question 52

describe the transfer of nutrients (water and ions) from the lumen of the digestive tract to the blood or lymph capillaries in the extracellular fluid?

Answer 52

from extracellular fluid (lateral space) into blood or lymph

Question 53

what is transcellular absorption?

Answer 53

organic nutrients are transported from intestinal lumen to the interstitial fluid by going across the enterocytes

Question 54

what is paracellular absorption?

Answer 54

where inorganic ions and water can diffuse through tight junctions connecting enterocytes

Question 55

what are the two mechanisms of absorption?

Answer 55

transcellular absorption and paracellular absorption

Question 56

what types of transport are involved within the transcellular absorption?

Answer 56

simple diffusion - passive transport (ions) carrier proteins (facilitated diffusion) - passive transport endocytosis/exocytosis - active transport

Question 57

describe why we need to use diffusion as a way of transport for transcellular absorption?

Answer 57

cell membranes act as a barrier only water-soluble and lipid-soluble non-polar substances can permeate water diffuses rapidly due to aquaporins

Question 58

why do we need carrier proteins as a way of transport for transcellular absorption?

Answer 58

water-soluble nutrients that are too large to diffuse through channels go through protein pumps

Question 59

why do we need to use endo/exocytosis for transcellular absorption?

Answer 59

large molecules need this way of transport and vesicles form around nutrients to transport it across the cell

Question 60

what nutrients does the small intestine absorb?

Answer 60

monosaccharides amino acids lipids vitamins Ca2+ Fe2+

Question 61

what does the ileum absorb?

Answer 61

bile salts and vitamin B12

Question 62

what does the large intestine absorb?

Answer 62

volatile fatty acids (VFAs)

Question 63

what do both the large and small intestine absorb?

Answer 63

water and salt (NaCl)

Question 64

phases of the chemical digestion?

Answer 64

luminal and membranous phase

Question 65

chemical digestion is...

Answer 65

catalysed by enzymes

Question 66

where are the enzymes that are catalysing the chemical digestion found?

Answer 66

in the lumen of the salivary gland, gastric gland and pancreas (luminal phase) and in the membrane surface of the epithelium (membranous phase)

Question 67

where are the digestive enzymes coming from?

Answer 67

from salivary, gastric and pancreatic glands

Question 68

where are the digestive enzymes in the membranous phase synthesised?

Answer 68

synthesised in the enterocytes and attached to apical membrane

Question 69

what does the production of amylase result in?

Answer 69

results in disaccharides, trisaccharides and oligosaccharides

Question 70

what produces amylase and in all species and what produces amylase in some species?

Answer 70

ALL = pancrease SOME = salivary gland

Question 71

what enzyme catalyses luminal phase digestion?

Answer 71

amylase

Question 72

what enzyme catalyses membranous-phase digestion?

Answer 72

substrate specific enzymes

Question 73

what are the enzymes that catalyse the membranous-phase digestion synthesised by?

Answer 73

synthesised by enterocytes which are exposed at apical membrane

Question 74

what do the substrate specific enzymes used in membranous-phase digestion result in?

Answer 74

formation of monosaccharides maltose > glucose sucrose > glu + fruc lactose > glu + galac

Question 75

what is glucose absorption linked to?

Answer 75

sodium absorption

Question 76

what pump is involved in carbohydrates absorption?

Answer 76

the Na-K-ATPase pump

Question 77

what happens to monosaccharides following absorption?

Answer 77

they are transported via the portal vein to the liver where they are stored as glycogen

Question 78

start at slide 25!!!!!!!!