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Unit 8 > Digestion and Absorption 1 Lecture > Flashcards

Digestion and Absorption 1 Lecture Flashcards

1
Q

What types of molecules can not cross cell membranes so are not involved in metabolic processes?

A

Large molecules
Hydrophilic molecules

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2
Q

What is meant by digestion?

A

Breaking large molecules down into smaller molecules

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3
Q

What is meant by absorption?

A

When small molecules pass through cell membranes into the blood or lymph capillaries

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4
Q

What are the two different models of enzyme action?

A

1 Lock and Key model - active site is complimentary to the substrate
2. Induced fit model - Active site undergoes geographical adaptation to match the substrate as it binds

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5
Q

What is meant by cleavage?

A

The splitting of a large or complex molecule into smaller/simpler molecules normally be enzymes

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6
Q

What are the digestion products of….
A protein
B. Fats
C. Carbohydrates

A

A. Amino acids
B. Fatty acids and glycerol
C. Monosaccharides

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7
Q

What are the key three functions of the mouth in mechanical digestion?

A

Mastication
1. reduces the size of ingested particles
2. mixes food with salvia, expoes to enzymes and lubraicaion
3. Increases the surface area of ingested particles

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8
Q

What is the role of the mouth in chemical digestion?

A

Contains alpha-amylase to digest starch
Contains lingual lipase to hydrolyses lipids
Has a pH of 6.2 to 7.6 to eliminate acid from food, drink and bacteria

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9
Q

What is the role of alpha amylase?

A

Cleaves internal alpha 1,4 glycosidic bonds present in starch molecules
Produces maltose, maltotriose and alpha limit dextrins

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10
Q

Explain the role of lipases

A

Hydrolyse three ester bonds in lipid to create one glycerol and 3 fatty acid molecules

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11
Q

What is the key idea of hydrolysis?

A

Uses a water molecule to break a chemical bond

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12
Q

What is the key role of the oesophagus in digestion?

A

Rapid movement of food from mouth to stomach by peristalsis
The upper and lower oesophageal sphincters control the movement of food into and out of the oesophagus

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13
Q

Describe the muscle movements in peristalsis.

A

Circular muscle infront of bolus relaxes
Circular muscle behind bolus contracts
Longitudinal muscle infront of and ontop of bolus contracts
Longitudinal muscle behind bolus relaxes

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14
Q

How much gastric juice does the stomach produce in a day?

A

2L of gastric juice a day

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15
Q

How much food can the stomach hold?

A

2 to 4 litres

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16
Q

What is the stomach ph?
How does this aid digestion?

A

Ph of 1 - 3.5
Break down food by hydrolysis
Activates enzymes
Denatures proteins
Kills bacteria

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17
Q

How does the stomach protect itself from stomach acid?

A

Mucus lines the walls of the stomach and protects from damage
Also has a thin layer of bicarbonate
This prevents self digestion

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18
Q

What is the role of intrinsic factor?

A

Produced in the stomach
Is a glycoprotein needed for intestinal absorption of vitamin B12.

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19
Q

What is gastric juice made of?

A

Water
Hydrogen ions
proteases
Intrinsic factor

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20
Q

What is the role of vitamin B12?

A

Red blood cell maturation
Neurological development

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21
Q

What is the role of acetylcholine in stomach acid secretion?

A

Released by the parasympathetic nervous system
Binds to M3 receptors on parietal cells
Activates phospholipase C - catalyses the formation of IP3
IP3 causes the release of intracellular calcium ions and activates calmodulin kinase
This phosphorylate a variety of porteins leading to H+ secretion

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22
Q

What is the role of gastrin in stomach acid secretion?

A

Released as a hormone into the blood by G-cells
Binds to CCK2 receptors on parietal cells
Activates phospholipase C - catalyses the formation of IP3
IP3 causes the release of intracellular calcium ions and activates calmodulin kinase
This phosphorylate a variety of porteins leading to H+ secretion

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23
Q

What is the role of ECL cells in stomach acid secretion?

A

Activated by gastrin binding to CCK-2 receptors
Release histamine

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24
Q

What is the role of histamine in stomach acid secretion?

A

Histamine binds to H2 receptors on parietal cells
Activates adenylate cyclase
Forms cAMP
cAMP activates protein kinase A
This phosphorylates a variety of protein leading to H+ secretion

25
Q

What are the cellular mechanism involved in the secretion of HCL?

A

Water in the cytoplasm dissociates into OH- and H+
H+ is activly transported out the apical membrane by a H+ K+ ATPase ( in exchange for K+)
OH- reacts with CO2 which has diffused into the cell, this is catalysed by carbonic anhydrase to HCO3-
Cl- is exhanged across the basolateral membrane for HCO3- by facillitated diffusion
Cl- is transported across the apical membrane by faciliatated diffusion.

26
Q

What is the role of carbonic anhydrase?

A

Catalyses the formation of HCO3- from water and CO2

27
Q

Describe the mechanism of protein digestion in the stomach

A

Protein increases the pH of the stomach
This triggers gastrin release from G cells
Gastrin activates ECL cells to secrete histamine
Histamine and gastrin stimulate parietal cells to secrete HCL
Gastrin also stimulates chief cells to release pepsinogen
Pepsinogen in convertes to pepsin by HCl, pepsin then cleaves protein.

28
Q

What is the negative feedback mechanism that regulate protein digestion in the stomach?

A

Decreased pH causes D-cells to release somatostatin
Somatostatin inhibits G-cells, reducing the release of gastrin.

29
Q

What cell type is primarily responsible for the digestion of fats in the stomach?

A

Chief cells producing gastric lipase

30
Q

What stimulates fat digestion in the stomach?

A

Neurohormonal stimuli
Gastrin and cholinergic mechanisms

31
Q

What inhibits fat digestion in the stomach?

A

CCK - cholecystokinin
GLP-1 Glucagon-like peptide-1

32
Q

What is the role of the stomach in the digestion of carbohydrates?

A

Salivary amylase inactivates - hence little chemical digestion occurs
Mechanical breakdwon from chruning of stomach
Peristalsic contractions mix into a more uniform micture of chyme

33
Q

What is meant by retropulsion and propulsion in relation to peristalsis in the stomach?

A

Retropulsion - forced backwards towards the cardiac
Propulsion - forced forwards towards the pylorus

34
Q

What is the role of the stomach in mechanical digestion?

A

Mixes food with gastric juices
This softens the food to make chyme
Propulsion and retropulsion of food
Break food down into smaller pieces

35
Q

What is the role of the stomach in gastric emptying?

A

Hold food for 4 to 6 hours
Absorbs some non-polar substances but very little
Pylorus acts as a filter to the duodenum
Gastric emptying is when peristaltic contractions increase in strength causing liquid chyme to pass through the pyloric sphincter into the duodenum

36
Q

Suggest why carbohydrates empty the fasts out of the stomach.
Why is this significant?

A

Undergoe very little digestion in the stomach
Same calorie value but not as full

37
Q

What section of the small intestine do the common bile duct and pancreatic duct join with?

A

The duodenum

38
Q

What are the four main cell types in the small intestine?

A

Absorptive cells
Goblet cells
Enteroendocrine cells
Paneth cells

39
Q

What is the role of enterocytes in the small intestine?

A

Also known as absoprtive cells
- complete digestion in the brush border
- absorb minerals into serosal side (ions, water, sugars, peptides and lipids)

40
Q

What is the role of goblet cells in the small intestine?

A

Secrete mucus to the lumenal side
Acts as a protective barrier

41
Q

What is the role of enteroendocrine cells in the small intestine?

A

Release signalling molcules (CCK and motilin) to regulate and coordinate the activites of the digestive system

42
Q

What process does CCK signalling aid?

A

Inhibits Gastric emptying

43
Q

What process does motilin aid?

A

Peristalsis

44
Q

What is the role of paneth cells in the small intestine?

A

Release bacteriotaxic peptides and growth factors
Part of the innate immune system - defence against microbes in the gut

45
Q

What is the role of the duodenum in gastric emptying?

A

Provides negative feedback regulation to inhibit gastric emptying
Intestinal receptors are activated by pressure of chyme
CCK - increases distenstibility of proximal stomach
Acid - inhibits motility and emptying
Secretin and gastric inhibitory peptide will also delay gastric emptying

46
Q

Give an overview of the role of the small intestine in the chemical digestion of carbohydrates?

A

Secretin and CCK stimulate pancreatic amylase release
Starch digested into maltose, maltotriose and alpha -limit dextrins
Oligosaccharides and disaccharides are digested and the brush borded by cell membrane bound enzymes

47
Q

What are some examples of brush border enzymes and what do they do?

A

Lactase - hydrolyses lactose to glucose and galactose
Sucrase - hydrolyses sucrose to glucose and fructose
Maltase - hydrolyses maltose into glucose and glucose
Isomaltase - hydrolyses alpha 1,6 bonds of limit dextrins

48
Q

What is the role of the small intestine in the digestion of fats?

A

Lipase action hydrolyses to fatty acids and glycerides
Bile - emulsifies to form micells increasing the surface area
Micells transport to brush border where fatty acids and monoglycerides can diffuse across

49
Q

What is the role of the small intestine in the digestion of protein?

A

Contains proteases such a trypsin and chymotrypsin
And brush border peptidases to hydrolyse to dipeptides and amino acids for absoprtion

50
Q

What is the role of the small intestine in mechanical digestion?

A

Segmentation and peristalsis to mix chyme with secretion

51
Q

What features of the small intestine help increase the surface area to aid absorption?

A

Folded into
-plicae circulares
- villi
-microvilli

52
Q

How are monosaccharides absorbed across the intestineal wall?

A

SGLT1 co-transports glucose/galactose into lumen alongside Na+
This is a form of secondary active transport where a low concentration of Na+ in the cytoplasm is established by the sodium potassium pump
Glucose and galactose then cross the basolateral membrane by facillitated difussion by GLUT2 receptors
Fructose facilitated diffusion into cell by GLUT5 then facilitated diffusion out of basolateral membrane by GLUT2 receptors

53
Q

What is the main role of the large intestine in digestion?

A

Has no digestive enzymes
Reclaims water and electrolytes
Will store then eliminate waste by the anus (aided by peristalsis)
Can hold food for 36 hours

54
Q

What are non-digestable carbohydrates?

A

Typically plant in origin
Include fibres, some starch, cellulose, hemicellulose, lactulose, sorbitol and sucrulose

55
Q

How are non-digestible carbohydrates digested?

A

Bacterial flora aids digestion
By anaerobic fermentation
This results in vitamin K production and flatus (due to methane and hydrogen production)

56
Q

What is the role of vitamin K?

A

Produced by bacteria in the large intesine then abosrbed
Important substance for clotting.

57
Q

What are the different types and properties of dietary fibres?

A

Soluble - slow transit time through colon, includes pectins from fruit/veg, hemicellulose from cereal
Insoluble - draws water into stool, this softens and increases faecal weight, speed up transit time and movement consistency e.g cellulose from plants.

58
Q

What are the key ways to maintain a healthy large intestine?

A

Eat plenty fibre to help bacteria
Avoid using uneccesary antibiotics to preserve microbial flora
Drink plenty water to prevent constipation.

59
Q

Label the different salivary glands

A

Parotid
Sublingual
Submandibular

Unit 8 (22 decks)

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