digestion and absorption

Question 1

what are the 4 stages of food processing

Answer 1

ingestion, digestion, absorption and elimination

Question 2

what is ingestion

Answer 2

the act of eating or feeding

Question 3

what are the 4 feeding mechanisms

Answer 3

filter feeding
bulk feeding
fluid feeding
substrate feeding

Question 4

what are the layers of the gut

Answer 4

serosa, muscularis externa, submucosa, mucosa

Question 5

what makes the serosa

Answer 5

connective tissue, longitudinal smooth muscle

Question 6

what makes the muscularis externa

Answer 6

myenteric plexus, circular smooth muscle

Question 7

what makes the submucosa

Answer 7

submucosa plexus, loose connective tissue with collagen and elastin fibres

Question 8

what makes the mucosa

Answer 8

muscularis mucosa, lamina propria, epithelium

Question 9

what does amylase breakdown in the mouth

Answer 9

starch

Question 10

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

Answer 10

bolus

Question 11

what receives the bolus of food

Answer 11

the pharnyx

Question 12

what 2 passageways does the pharynx lead to

Answer 12

the trachea and the oesophagus

Question 13

swallowing is carefully controlled to prevent food entering what

Answer 13

the trachea

Question 14

how is food pushed along in the oesophagus

Answer 14

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

Question 15

what is the sphincter

Answer 15

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

Question 16

what are the 2 roles of the stomach in digestion

Answer 16

storage

process food into a liquid suspension

Question 17

what is the digestive fluid called that the stomach excretes

Answer 17

gastric juice - it mixes with food through the churning action

Question 18

what is the mixture of ingested food and gastric juice called

Answer 18

chyme

Question 19

How does the HCl of the gastric juice help liquefy food

Answer 19

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

Question 20

how does the gastric juice help break down proteins

Answer 20

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.

Question 21

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

Answer 21

parietal cells

chief cells

Question 22

how do parietal cells produce HCL

Answer 22

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

Question 23

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

Answer 23

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

Question 24

Do HCl and pepsin form in the gastric glands

Answer 24

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

Question 25

how does pepsin activate pepsin

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

parietal chief mucous

Question 28

what about the stomach enhances breakdown of food by gastric juices

Answer 28

muscular activity - series of muscular contraction and relaxation

Question 29

how does churning facilitate chemical digestion

Answer 29

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

Question 30

what moves the contents of the stomach into the small intestine

Answer 30

peristaltic contractions

Question 31

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

Answer 31

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

Question 32

what is heartburn

Answer 32

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

Question 33

most enzymatic hydrolysis of macromolecules form food occurs where

Answer 33

the small intestine

Question 34

does the small of small intestine mean length or diameter

Answer 34

diameter

Question 35

what forms the first 25cm of the small intestine

Answer 35

the duodenum

Question 36

what happens in the duodenum

Answer 36

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

Question 37

what is triggered when chyme arrives in the duodenum

Answer 37

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

Question 38

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

Answer 38

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

Question 39

name some enzymes that the pancreas releases into the small intestine

Answer 39

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

Question 40

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

Answer 40

others are bound to the surface of epithelial cells

Question 41

why are fats difficult to digest

Answer 41

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

Question 42

what is fat digestion stimulated by

Answer 42

bile salts

Question 43

what do bile salts act as

Answer 43

emulsifiers that break apart fat and lipid globules

Question 44

which organ secretes bile

Answer 44

the liver

Question 45

bile salts are a major component of what

Answer 45

bile

Question 46

where is bile stored and concentrated

Answer 46

the gallbladder

Question 47

as well ass digestion what else does bile production contribute to

Answer 47

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

Question 48

where do the contents of the duodenum got to

Answer 48

jejunum and ileum (by peristalsis)

Question 49

what are the 3 parts of the small intestine

Answer 49

duodenum jejunum ileum

Question 50

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

Answer 50

the jejunum and the ileum linings

Question 51

what are the projections on the small intestine lining called

Answer 51

villi

Question 52

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

Answer 52

microvilli

Question 53

where do the microvilli face

Answer 53

the intestinal lumen

Question 54

what is the brush border

Answer 54

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

Question 55

why is the increased surface area due to the villi beneficial

Answer 55

it allows for increased rate of nutrient absorption

Question 56

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

Answer 56

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

Question 57

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

Answer 57

amino acids, small peptides, vitamins and most glucose molecules

Question 58

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

Answer 58

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

Question 59

where does the blood travel from the liver

Answer 59

the heart then to other tissues and organs

Question 60

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

Answer 60

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

Question 61

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

Answer 61

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

Question 62

fatty acids and monoglycerides are absorbed by what

Answer 62

intestinal epithelial cells

Question 63

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

Answer 63

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

Question 64

once they exit the small intestine where do the chylomicrons go

Answer 64

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

Question 65

which organ system is the lacteal part of

Answer 65

the lymphatic system

Question 66

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

Answer 66

lymph

Question 67

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

Answer 67

the heart

Question 68

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

Answer 68

water and ions

Question 69

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

Answer 69

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

Question 70

Which organ does the alimentary canal end with

Answer 70

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

Question 71

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

Answer 71

T shaped

Question 72

where does the colon lead to

Answer 72

the rectum and the anus

Question 73

why is the cecum important

Answer 73

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

Question 74

do humans have a small cecum compared to other mammals

Answer 74

yes

Question 75

the appendix is a finger shaped extension of what

Answer 75

the cecum

Question 76

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

Answer 76

water recovery

Question 77

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

Answer 77

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

Question 78

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

Answer 78

diarrhoea

Question 79

what occurs when the feces moves along the colon too slowly

Answer 79

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

Question 80

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

Answer 80

it helps move food along the alimentary canal

Question 81

what contributes to one third of the dry weight of feces

Answer 81

bacteria living on unabsorbed organic material in the colon

Question 82

by products of colon bacteria digestion are what

Answer 82

gases - methane and hydrogen sulphide

Question 83

gases and ingested air are expelled through the anus as what

Answer 83

flatulence - farts

Question 84

what is another name for parietal cells

Answer 84

oxyntic cells

Question 85

what type of cells produce saliva

Answer 85

acini cells

Question 86

how are the actions of the stomach in digestion regulated

Answer 86

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

Question 87

g cells stimulate the release of what

Answer 87

gastrin