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biology topic 6 > 6.1 - digestion and absorption > Flashcards

6.1 - digestion and absorption Flashcards

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1
Q

what is the digestive system?

A
  • the system that humans use to digest food
  • where food passes from mouth to anus
  • broken from macromolecules to monomers and ions that can be absorbed
  • macromolecules are broken down through different ways but mainly through enzyme action.
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2
Q

what does the mouth do?

A
  • mechanical digestion of food by chewing, mixing with saliva and start starch digestion by enzymes
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3
Q

what does the oesophagus do?

A

moves food from the mouth to the stomach by peristalsis

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4
Q

what does the stomach do?

A
  • churning and mixing of food with secreted water and acid to kill foreign bacteria and other pathogens
  • start of protein digestion by enzymes
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5
Q

what does the small intestine do?

A
  • final stages of digestion of carbs. lipids, proteins and nucleic acids
  • neutralising of stomach acid and absorption of nutrients
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6
Q

what does the pancreas do?

A
  • synthesis and secretion of lipase, amylase and protease enzymes
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7
Q

what does the liver do?

A
  • produces bile which is used to break up or emulsify lipid droplets
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8
Q

what does the gall balder do?

A
  • it is storage and release of bile
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9
Q

what does the large intestine do?

A
  • reabsorbs water
  • further digests carbs by gut bacteria
  • forms and stores faeces
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10
Q

what and why is the structure of the small intestine?

A
  • the wall is made of circular and longitudinal muscle instead of strained muscle
  • contractions occur unconsciously or involuntarily as controlled by the enteric nervous system
  • its moderate force and some vigorous contractions move the food along the gut
  • contractions are called peristalsis
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11
Q

what happens in peristalsis?

A
  • circular muscle contracts from back to front to move food and avoid backflow
  • longitudinal muscle moves food forward
  • movement is slow
  • mixes partially digested food with enzymes to speed up the digestion process
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12
Q

what is partially digested food moving from mouth to stomach called?

A

bolus

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13
Q

what is food that has been mixed with enzymes in the stomach called?

A

chyme

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14
Q

what is the serosa of the small intestine?

A

the fibrous connective tissue that acts as a protective outer covering of small intestine

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15
Q

what is the muscle layer of small intestine?

A

the longitudinal muscle used for peristalsis and the inner circular muscle for contractions

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16
Q

what is the submucosa in the small intestine?

A

made of connective tissue and separates the muscle from the mucosa

17
Q

what is the mucosa in the small intestine?

A

has the highly folded inner layer called villi that absorbs materials from the intestinal lumen

18
Q

where are digestive enzymes secreted from?

A
  • the pancreas mainly but also the salivary gland and stomach
  • location and type of enzyme secreted depends on the specific substrate being hydrolysed (catabolic reaction)
19
Q

what does the pancreas secrete and/or synthesise?

A
  • hormones insulin and glucagon into blood from small groups of cells
  • the hormones regulate blood glucose levels
  • the rest of the pancreas synthesises and secretes digestive enzymes into the gut after food
  • this response is supported by hormones synthesised and secreted by the enteric nervous system and stomach.
20
Q

how are digestive enzymes synthesised?

A
  • by pancreatic gland cells on the rER
  • processed by the Golgi apparatus
  • secreted by exocytosis to the duct that delivers the digestive enzymes to the small intestine
    (pancreatic juice)
21
Q

what is pancreatic juice?

A
  • it contains enzymes that break down the three macromolecules ready for absorption of its monomers:
  • amylase (starch)
  • Lipase (triglycerides and phospholipids)
  • proteases (proteins and peptides)
22
Q

how do the digestive enzymes secreted by the pancreas chemically break down macromolecules into monomers?

A
  • in the small intestine
  • Amylase digests starch into maltose
  • lipase breaks down triglycerides into fatty acids and glycerol
  • phospholipase breaks down phospholipids into fatty acid, glycerol and phosphate
  • protease breaks down proteins and polypeptides into shorter peptides
23
Q

how do the enzymes that are immobilised on the plasma membrane chemically break down macromolecules into monomers?

A
  • nucleases digest DNA and RNA into nucleotides
  • maltase digests maltose into glucose and galactose
  • lactase digests lactose into glucose and fructose
  • exopeptidase digests peptides by removing one amino acid
  • dipeptidase digests dipeptides into amino acids

Cellulose from plants remains undigested and passes to the large intestine

24
Q

how is the absorption of nutrients highly efficient in the small intestine?

A
  • inner epithelial lining of the intestine is highly folded into villi that stick into the lumen.
  • they increase surface area available for absorbtion of material by diffusion or Active Transport - increase rate absorb
25
Q

what helps a villi have efficient exchange?

A
  • thin epithelial layer that absorbs materials rapidly.
  • dense network of capillaries for rapid movement of absorbed nutrients
  • microvilli on surface of epithelial cells to increase SA
  • lacteals that absorb lipids into the lymphatic system
26
Q

how do villi absorb monomers formed by digestion? and what do they absorb?

A
  • they are permeable enough to allow useful nutrients to pass through the membranes but also a barrier against harmful substances.
  • they absorb:
  • monosaccharides: glucose, fructose and galactose
  • amino acids
  • fatty acids, monoglycerides and glycerol
  • nitrogen bases from nucleotides
  • mineral ions
  • vitamin c
27
Q

nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - simple diffusion

A
  • lipids are absorbed as they are hydrophobic molecules
28
Q

nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - facilitated diffusion

A
  • hydrophilic substances like glucose, amino acids, some vitamins and minerals and fructose.
29
Q

nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - osmosis

A
  • allows water moles to diffuse across membrane in response to the movement of ions and hydrophilic monomers.
30
Q

nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - active transport

A
  • atp to pump sodium ions into the lumen from epithelial cell to maintain a concentration gradient
  • the passive re-entry of sodium ions is joined by nutrients including amino acids, glucose and mineral ions to pass from epithelial cells to capillaries
31
Q

nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - endocytosis

A
  • the bulk transport of materials
  • pinocytic vesicles are formed around fluid containing dissolved materials in the lumen by endocytosis
32
Q

digestion of starch in the small intestine.

A
  • starch is found in plants and composed of many a-glucose monomers linked together by condensation reactions
  • can’t pass through membranes it must be digested in the small intestine
  • cant be in stomach bc its too acidic for the enzymatic reactions needed
33
Q

how starch is digested.

A
  • 2 starches:
    amylose is unbranched with a-glucose linked by 1, 4 bonds
    amylopectin is branched and has 1, 6 bonds
  • amylase begins digestion, 1, 4 bonds in amylose and amylopectin are broken to form maltose and maltotriose
  • 1, 6 bonds need maltase, glucosidase and dextrinase to breakdown maltose, maltotriose and dextrins into glucose monomers
  • glucose can be absorbed by villi with sodium ions
  • then moved by facilitated diffusion into the interstitial spaces inside villus
  • then into blood where it flows via hepatic portal vein to liver where stored as glycogen
34
Q

experiment 1 - meniscus levels

A
  • bit of dialysis tubing is filled with starch solution
  • a second bit of dialysis tubing is filled with amylase solution
  • both placed in separate beakers of water
  • over time water moves into tubing via osmosis toward solute and causes meniscus to rise
35
Q

experiment 2 - maltose diffusion

A
  • a bit of dialysis tubing is filled with starch solution and put in a beaker of water
  • a second bit of dialysis tubing is filled with starch and amylase solution and put in beaker of water
  • the amylase digests starch into maltose and diffuses out to beaker

biology topic 6 (6 decks)

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