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digestion and absorption Flashcards

1
Q

what are the 4 stages of food processing

A

ingestion, digestion, absorption and elimination

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2
Q

what is ingestion

A

the act of eating or feeding

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3
Q

what are the 4 feeding mechanisms

A

filter feeding
bulk feeding
fluid feeding
substrate feeding

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4
Q

what are the layers of the gut

A

serosa, muscularis externa, submucosa, mucosa

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5
Q

what makes the serosa

A

connective tissue, longitudinal smooth muscle

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6
Q

what makes the muscularis externa

A

myenteric plexus, circular smooth muscle

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7
Q

what makes the submucosa

A

submucosa plexus, loose connective tissue with collagen and elastin fibres

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8
Q

what makes the mucosa

A

muscularis mucosa, lamina propria, epithelium

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9
Q

what does amylase breakdown in the mouth

A

starch

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10
Q

the tongue and the saliva manipulate food until it forms what shape

A

bolus

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11
Q

what receives the bolus of food

A

the pharnyx

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12
Q

what 2 passageways does the pharynx lead to

A

the trachea and the oesophagus

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13
Q

swallowing is carefully controlled to prevent food entering what

A

the trachea

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14
Q

how is food pushed along in the oesophagus

A

by peristalsis - muscular contraction - alternating waves of smooth muscle contraction

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15
Q

what is the sphincter

A

found at the end of the oesophagus and is a ring like valve of muscle that regulates passage of food into the stomach

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16
Q

what are the 2 roles of the stomach in digestion

A

storage

process food into a liquid suspension

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17
Q

what is the digestive fluid called that the stomach excretes

A

gastric juice - it mixes with food through the churning action

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18
Q

what is the mixture of ingested food and gastric juice called

A

chyme

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19
Q

How does the HCl of the gastric juice help liquefy food

A

it disrupts the extracellular matrix that binds cells together in meat and plants

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20
Q

how does the gastric juice help break down proteins

A

the low pH of the juice unfolds the proteins so that their peptide bonds become exposed.
the peptide bonds are then attacked by protease/pepsin, cleaving the proteins into smaller polypeptides.

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21
Q

which cells in the gastric glands produce the components of gastric juice

A

parietal cells

chief cells

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22
Q

how do parietal cells produce HCL

A

they use an ATP driven pump to expel hydrogen ions into the lumen.
They also diffuse chlorine ions into the lumen via their specific membrane channels
Thus HCL is only formed in the stomach

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23
Q

How do chief cells result in pepsin being released into the stomach

A

The chief cells release an inactive form of pepsin into the stomach called pepsinogen.
The HCl produced by the parietal cells converts pepsinogen into pepsin by clipping the molecule to expose the active site

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24
Q

Do HCl and pepsin form in the gastric glands

A

No - their components are released into the stomach from the glands and then they are transformed

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25
Q

how does pepsin activate pepsin

A

HCl activates some pepsin from pepsinogen then pepsin can also activate the pepsinogen with the same clipping action as HCl to form the active site

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26
Q

why don’t HCl and pepsin eat through the lining of the stomach

A

mucous is secreted by cells in the gastric glands to protect against self digestion

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27
Q

what are the 3 different types of cell kin the gastric glands

A

parietal
chief
mucous

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28
Q

what about the stomach enhances breakdown of food by gastric juices

A

muscular activity - series of muscular contraction and relaxation

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29
Q

how does churning facilitate chemical digestion

A

it mixes the food, bringing it all into contact with the gastric juices that are secreted by the lining of the stomach

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30
Q

what moves the contents of the stomach into the small intestine

A

peristaltic contractions

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31
Q

What does the sphincter, located at the stomach opening to the small intestine do

A

It allows only one squirt of chime into the small intestine at a time

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32
Q

what is heartburn

A

sometimes the sphincter at the top of the stomach allows some chime into the lower oesophagus which causes a burning sensation

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33
Q

most enzymatic hydrolysis of macromolecules form food occurs where

A

the small intestine

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34
Q

does the small of small intestine mean length or diameter

A

diameter

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35
Q

what forms the first 25cm of the small intestine

A

the duodenum

36
Q

what happens in the duodenum

A

chyme mixes with digestive juices from the pancreas, liver, gallbladder and gland cells from the intestinal wall

37
Q

what is triggered when chyme arrives in the duodenum

A

the production of the hormone secretin, which stimulates the pancreas to release bicarbonate

38
Q

what does bicarbonate, released by the pancreas do to the chime from the stomach in the duodenum

A

the bicarbonate neutralises the chime and secretes numerous digestive enzymes into the small intestine

39
Q

name some enzymes that the pancreas releases into the small intestine

A

trypsin and chymotrypsin that are produced in inactive forms. they become activated in the lumen of the duodenum in a similar way to pepsinogen in the stomach

40
Q

some of the enzymes secreted by the epithelial lining if the duodenum are secreted into the lumen. where do the rest get secreted to

A

others are bound to the surface of epithelial cells

41
Q

why are fats difficult to digest

A

the are insoluble in water so form large globules that cannot be attacked efficiently by the digestive enzymes

42
Q

what is fat digestion stimulated by

A

bile salts

43
Q

what do bile salts act as

A

emulsifiers that break apart fat and lipid globules

44
Q

which organ secretes bile

A

the liver

45
Q

bile salts are a major component of what

A

bile

46
Q

where is bile stored and concentrated

A

the gallbladder

47
Q

as well ass digestion what else does bile production contribute to

A

the destruction of red blood cells that are no longer fully functional

48
Q

where do the contents of the duodenum got to

A

jejunum and ileum (by peristalsis)

49
Q

what are the 3 parts of the small intestine

A

duodenum
jejunum
ileum

50
Q

in what part of the small intestine does nutrient absorption occur in

A

the jejunum and the ileum linings

51
Q

what are the projections on the small intestine lining called

A

villi

52
Q

what are the microscopic projections in each epithelial cell within each villi

A

microvilli

53
Q

where do the microvilli face

A

the intestinal lumen

54
Q

what is the brush border

A

the side by side microvilli give the intestinal epithelium a brush like appearance hence the name

55
Q

why is the increased surface area due to the villi beneficial

A

it allows for increased rate of nutrient absorption

56
Q

is transport across the epithelial cells of the intestine passive or active

A

both - it depends on the nutrient
e.g. fructose moves by facilitated diffusion down its concentration gradient from the lumen of the small intestine into the epithelial cells. from there it exits the basal surface and is absorbed into blood vessels or capillaries at the core of each villus

57
Q

which nutrients get pumped against their concentration gradient into the epithelial cells of the tissues

A

amino acids, small peptides, vitamins and most glucose molecules

58
Q

the capillaries and veins that carry nutrient rich blood away from the villi converge into what

A

the hepatic portal vein - a blood vessel that leads directly to the liver

59
Q

where does the blood travel from the liver

A

the heart then to other tissues and organs

60
Q

why might blood leaving the liver have a very different nutrient balance compared to the blood that entered it

A

it converts many organic nutrients into different forms for use elsewhere
the arrangement allows the liver to remove any toxic substances before they can circulate broadly

61
Q

what is the product of hydrolysis of fat by lipase in the small intestine

A

fatty acids and a monoglyceride (glycerol joined to a fatty acid)

62
Q

fatty acids and monoglycerides are absorbed by what

A

intestinal epithelial cells

63
Q

what happens when the fatty acids and monoglycerides are absorbed by the epithelial cells of the intestine

A

they reform to make triglycerides again. they then become coated in phospholipids, cholesterol and proteins, forming globules called chylomicrons

64
Q

once they exit the small intestine where do the chylomicrons go

A

the lacteal - a vessel at the core of each villus - part of the lymphatic system

65
Q

which organ system is the lacteal part of

A

the lymphatic system

66
Q

what is the clear fluid contained within the network of vessels of the lymphatic system

A

lymph

67
Q

lymph containing the chylomicrons passes into the larger vessels of the lymphatic system and eventually into larger veins that return the blood directly to what

A

the heart

68
Q

in addition to absorbing nutrients the small intestine recovers two things - what are they

A

water and ions

69
Q

water is reabsorbed into the small intestine by what method of transport

A

osmosis - when sodium and other ions are pumped out of the lumen

70
Q

Which organ does the alimentary canal end with

A

the large intestine - which includes the colon, cecum and rectum

71
Q

what shape is the junction that joins the small intestine to the large intestine

A

T shaped

72
Q

where does the colon lead to

A

the rectum and the anus

73
Q

why is the cecum important

A

for fermenting ingested material - especially in mammals that eat a large amount of plant material

74
Q

do humans have a small cecum compared to other mammals

A

yes

75
Q

the appendix is a finger shaped extension of what

A

the cecum

76
Q

which process does the colon complete that began in the small intestine

A

water recovery

77
Q

once the water has been recovered from the colon what is left over

A

feces - the waste of the digestive system, that become increasingly solid as they get moved along the colon by peristalsis

78
Q

if the lining of the colon is irritated, less water may be reabsorbed resulting in what

A

diarrhoea

79
Q

what occurs when the feces moves along the colon too slowly

A

constipation - too much water reabsorbed and the feces becomes too compact

80
Q

the undigested material in feces includes cellulose - why is this beneficial

A

it helps move food along the alimentary canal

81
Q

what contributes to one third of the dry weight of feces

A

bacteria living on unabsorbed organic material in the colon

82
Q

by products of colon bacteria digestion are what

A

gases - methane and hydrogen sulphide

83
Q

gases and ingested air are expelled through the anus as what

A

flatulence - farts

84
Q

what is another name for parietal cells

A

oxyntic cells

85
Q

what type of cells produce saliva

A

acini cells

86
Q

how are the actions of the stomach in digestion regulated

A

by the endocrine cells that produce histamine and serotonin hormones to promote digestion and somatostatin hormone to inhibit digestion

87
Q

g cells stimulate the release of what

A

gastrin

A (17 decks)

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