THE HUMAN DIGESTIVE SYSTEM Flashcards
1
Q
why is food digested? (2)
A
- insoluble/too big to cross membrane and be absorbed into blood
- polymers must be broken into monomers to be rebuilt into useful molecules
2
Q
gut (4)
A
- where digestion occurs
- long hollow muscular tube
- movement in one direction by peristalsis
- several sections of unique mechanical/chemical digestion and absorption
3
Q
functions of the gut (4)
A
- ingestion, taking food in
- digestion, break down of molecules by mechanical/chemical digestion
- absorption, passage of useful molecules into gut wall into blood
- egestion - elimination of waste not made by the body
4
Q
types of digestion (2)
A
- mechanical - chewing/crushing
- chemical - secreted enzymes
5
Q
function of parts table 223
A
function half
6
Q
structure of the gut wall (4)
A
- serosa - tough connective tissue, reduces friction
- muscle - two layers (circular/longitudinal), make waves of contractions (peristalsis) to push food along
- submucosa - connective tissue w/ blood/lymph vessels, remove ab
7
Q
unlabelled gut
A
label lumen, serosa, longitudinal muscle, circular muscle, epithelium,
8
Q
what must the gut wall do before absorption
A
- break down macromolecules into smaller molecules
9
Q
how are carbohydrates digested? (4)
A
- digested from polysaccarides to disaccarides to monosaccarides
- amylase hydrolyses starch into maltose
- maltase digests maltose into glucose
- sucrase digests sucrose, lactase digests lactose`
10
Q
how are proteins digested? (4)
A
- they are very large molecules so digested into polypeptides, into dipeptides, into amino acid
- protein digesting enzymes = protease, peptidase
- endopeptidases hydrolyse peptide bonds in the protein
- exopeptidases hydrolyse peptide bonds at the end of the polypeptides
11
Q
how are fats digested?
A
- into fatty acids and monoglycerides by lipase
12
Q
buccal cavity (3)
A
- where mechanical digestion begins (the mouth)
- food is mixed with saliva and chewed by the teeth
- increases foods surface area for enzymes to access
13
Q
what is in saliva? (3)
A
- amylase
- HCO3- and CO3^2- so the pH is akaline for amylase
- mucus to lubricate the food’s passage down the oesophagus
14
Q
oesophagus
A
- carries food from the mouth to the stomach
15
Q
the stomach (3)
A
- food is digested in the stomach
- kept there by contraction of two sphincters/rings of muscle
- stomach wall muscles contract rhythmically and mix food with gastric juice secreted by the glands in the wall
16
Q
what does gastric juice contain?
A
- peptidases, secreted by zymogen/chief cells at the base of the gastric pit
- hydrochloric acid, secreted by oxyntic cells to lower the pH for enzymes
- mucus, secreted by goblet cells, at the top of the gastric pit, forms a lining to protect the stomach wall from enzymes and lubricate food
17
Q
how are peptidases secreted?
A
- as inactive pepsinogen from the zymogen cells and activated by H+ to pepsin, an endopeptidase
18
Q
gastric pit picture p225
A
labels: gastric pit, goblet cells, submucosa, immature goblet cells, zymogen cells, oxyntic cells
19
Q
what are the regions of the small intenstine (2)
A
- the duodenum
- the ileum
20
Q
how is partially-digested food allowed into the duodenum?
A
- relaxation of pyloric sphincter muscle at the base of the stomach, allowing food through in small doses
21
Q
bile (3)
A
- made in the liver
- stored in the gallbladder
- passed into the duodenum by the bile duct
22
Q
what is in bile? (3)
A
- no enzymes
- amphipathic bile salts, emulsify lipids in food by lowering surface tension and increasing surface area by breaking globules into smaller globules
- is alkaline and neutralises acid from stomach, makes pH suitable for small intestine
23
Q
amphipathic
A
- contain both hydrophilic and hydrophobic parts
24
Q
pancreatic juice (2)
A
- secreted by islet cells (exocrine glands in the pancreas)
- enters duodenum through pancreatic duct
25
what is in pancreatic juice?
- enzymes
| - sodium hydrogen carbonate
26
enzymes in pancreatic juice? (4)
- endopeptidases, to hydrolyse protein to peptides
- amylase, to digest any remaining starch to maltose
- lipase, lipids to fatty acids and monoglycerides
- trypsinogen, inactive enzyme converted into protease trypsin by enterokinase (duodenal enzyme)
27
purpose of sodium hydrogen carbonate in pancreatic juice? (3)
- raises pH
- neutralises acid from the stomach
- providing pH for pancreatic enzymes
28
what happens to food coming from the stomach? (2)
- lubricated by mucus
| - neutralised by alkaline secretions from cells at the base of the crypts of Lieberkühn, called Brunner's glands
29
enzymes associated with villi (3)
- endo/exopeptidases secreted by cells at villus tips to digest polypeptides
- enzymes on epithelial cell membranes that digest dipeptides into amino acids
- carbohydrases digest disaccarides and they are absorbed into epithelial cells of the villi
30
how is the ileum well-adapted (4)
- very long with folded lining
- villi on the surface of the folds
- microvilli on the epithelial cells
- all produce large SA for absorption
31
how does absorption occur? (2)
- by diffusion, facilitated diffusion and active transport
| - epithelial cells have many mitochondria for ATP
32
how are amino acids absorbed? (3)
- absorbed into epithelial cells by active transport
- pass into capillaries by facilitated diffusion
- water-soluble and dissolve in plasma
33
how is glucose absorbed? (4)
- passes into epithelial cells w/ glucose by co-transport
- move into capillaries, sodium by active transport, glucose by facilitated diffusion
- dissolve in plasma
- diffusion/facilitated diffusion are slow so active transport is used for some to prevent it being lost in faeces
34
how are fatty acids / monoglycerides absorbed? (2)
- diffuse into epithelial cells into lacteals, ending lymph capilaries in villi
- lacteals transport fat-soluble molecules through lymphatic system to left subclavian vein near heart
35
how are minerals absorbed? (2)
- into the blood by diffusion/facilitated diffusion/active transport
- dissolve in plasma
36
how are vitamins absorbed? (2)
- B/C water soluble and absorbed into blood
| - A,D,E fat soluble absorbed into lacteals
37
how is water absorbed? (2)
- absorbed into epithelial cells in ileum
| - into capillaries via osmosis
38
what happens to lipids after absorption (2)
- used in membranes and to make hormones
| - excess is stored
39
where do glucose and amino acids go after absorption?
- taken to the liver by the hepatic portal vein
40
what happens to glucose in the liver? (2)
- taken to body cells and respired for energy or stored as glycogen in liver/muscle cells
- excess stored as fat
41
what happens to amino acids in the liver? (3)
- taken to body cells for protein synthesis
- excess not stored so liver deanimates and converts amine groups to urea and carried in blood, excreted at kidney
- remains of amino acid conversed into carbohydrate for storage or conversion to fat
42
what is the large intestine made up of? (4)
- the caecum
- the appendix
- the colon
- the rectum
43
what passes into the colon? (4)
- undigested food
- mucus
- bacteria
- dead cells
44
how does the colon work? (6)
- less villi with a major role in water absorption
- vitamin K and folic acid secreted by mutualistic microorganisms living there
- minerals absorbed from colon
- as material passes along, water absorbed
- reaches the rectum semi-solid
- passes along rectum and egested as faeces in defecation
