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HL10521 Human Physiology > Digestion and Absorption > Flashcards

Digestion and Absorption Flashcards

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1
Q

Three main macronutrients?

A

Carbohydrate, Fat, Protein

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2
Q

What must be done for humans to use macronutrients for energy production?

A

They must be broken down into their constituent parts

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3
Q

What are carbs broken down into?

A

Monosaccharides

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4
Q

What are fats broken down into?

A

Fatty acids

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5
Q

What are proteins broken down into?

A

AAs

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6
Q

What other nutrient (not macronutrient) can humans derive energy from?

A

Alcohol

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7
Q

Main processes of gastrointestinal (GI) tract?

A

Digestion, absorption, secretion, motility

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8
Q

What two main group can the gastrointestinal system tract be broken up into?

A

GI tract and accessory organs

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9
Q

Order of GI tract?

A

Mouth–> pharynx–> oesophagus–> stomach–> small intestine–> large intestine

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10
Q

What are the accessory organs?

A

Salivary glands, liver, gallbladder, exocrine pancreas

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11
Q

Main layers of GI wall (ordered lumen outwards)?

A

Mucosa, submucosa, muscularis externa, serosa

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12
Q

Why is smooth muscle needed to line the GI tract?

A

One main function of GI tract is motility, as the food needs to be passed along the lumen

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13
Q

What makes up the mucosa?

A

Epithelium, lamina propia, muscularis mucosa

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14
Q

Role of epithelium in mucosa?

A

First ones that see the food, contain endocrine and exocrine cells

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15
Q

Why does the epithelium contain endocrine cells?

A

Can secrete hormones for signalling (i.e. nutrients in intestine detected= full signal)

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16
Q

Role of lamina propia in mucosa?

A

Loose connective tissue between the epithelium and muscularis mucosa

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17
Q

What makes up the submucosa?

A

Blood and lymphatic vessels, and the submucosal plexus

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18
Q

Role of blood vessels in submucosa?

A

Transport of nutrients once it has been absorbed

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19
Q

Role of lymphatic system in submucosa?

A

fats enter it before then entering the bloodstream

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20
Q

Structure of submucosal plexus?

A

Network of neurons

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21
Q

Role of submucosal plexus?

A

Neurons are used to activate the muscles in the GI tract

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22
Q

Components of the muscularis externa?

A

Circular muscle, myenteric plexus, longitudinal muscle

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23
Q

Role of circular muscle?

A

Its contraction causes the lumen to narrow

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24
Q

Structure of myenteric plexus?

A

Networkof thin axons and neurones that is innervated from autonomic nervous system

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25
Q

What is the myenteric plexus connected to?

A

Submucosal plexus–> both contain nerves

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26
Q

Role of longitudinal muscle in muscularis externa?

A

Its contraction causes the tract to shorten

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27
Q

What can be used to change the shape of the GI tract/lumen?

A

Circular muscle and longitudinal muscle

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28
Q

What is the serosa?

A

Connective tissue that surrounds the outer surface of the tract

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29
Q

How is the GI tract kept in place?

A

Sheets of connective tissue connect the serosa to the abdominal wall

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30
Q

Where does digestion begin?

A

mouth

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31
Q

What can cause secretion of enzymes in the mouth (saliva)?

A

Thought, sight or smell of food

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32
Q

What is the cephalic phase of digestion?

A

Secretion of saliva in response to thought, sight or smell of food

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33
Q

What is produced during the cephalic phase?

A

Saliva in the mouth, gastric juices and insulin

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34
Q

How is saliva secreted?

A

Secreted into acini of salivary duct

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35
Q

What can be done to saliva once it has left the acini?

A

The conc of it can be modified by adding/removing water/ions

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36
Q

What stages of digestion occur in the mouth?

A

Mechanical breakdown of food
Mixing of food with saliva
CHO chemical digestion
Antibacterial action

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37
Q

What is in the mouth that begins the chemical digestion of CHO?

A

Salivary amylase

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38
Q

Key components of saliva?

A

Bicarbonate
Mucus
Salivary amylase
Lysozyme

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39
Q

Role of bicarbonate in saliva?

A

Neutralises acid

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40
Q

Role of mucus in saliva?

A

Lubricates and protects from abrasion

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41
Q

Role of salivary amylase in saliva?

A

Breakdown CHO

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42
Q

Role of lysozymes in saliva?

A

Destroys certain bacteria (prevents tooth decay)

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43
Q

Why does salivary amylase not do much of the total starch digestion?

A

Food usually exits the mouth soon after chewing

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44
Q

Role of pharynx?

A

Conduction of food to oesophagus from mouth

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45
Q

Role of oesophagus?

A

Conduction of food to stomach from pharynx

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46
Q

Role of epiglottis?

A

Closes so food doesn’t go down trachea

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47
Q

What is the sphincter?

A

Ring of muscle at bottom of pharynx

48
Q

Role of sphincter at bottom of pharynx?

A

prevents movement of air and stomach contents entering oesophagus

49
Q

What is peristalsis

A

Movement of food towards stomach occurs due o progressive muscular contraction

50
Q

How does peristalsis work?

A

Muscle behind food contracts while muscle in front relaxes

51
Q

What is secondary peristalsis?

A

Repetition of contraction of muscle if a large part of food does not reach the stomach

52
Q

Roles of stomach?

A

Mechanical breakdown of food
Secretion of HCl to kill bacteria
Secretion of some enzymes

53
Q

What is chyme?

A

Partially digested food mixed w/ contents of stomach

54
Q

What enzymes does the stomach secrete?

A

Pepsinogen and gastric lipase

55
Q

Role of pepsiongen?

A

becomes pepsin, and then begins protein digestion

56
Q

Role of gastric lipase?

A

Involved in fat digestion

57
Q

Roles of small intestine?

A

Chemical digestion of all nutrients
Absorption of digestive end-products, water, ions and vitamins
Secretion of hormones
Secretion of bicarbonate rich fluid

58
Q

What kind of enzymes digest chyme in the small intestine?

A

Pancreatic or brush border enzymes

59
Q

Roles of colon?

A

Absorption of ions and water
Transformation of chyme into faeces
Storage of faeces

60
Q

Role of rectum?

A

Storage of faeces

61
Q

Role of gastric pit?

A

Increase SA of stomach

62
Q

Cell types in gastric pit?

A

Mucus cells
Parietal cells
Chief cells
Enteroendocrine cells

63
Q

Role of mucus cells in gastric pit?

A

secretes mucus–> alkaline solution to protect stomach lining

64
Q

Role of parietal cells in gastric pit?

A

Secretes HCl and intrinsic factor

65
Q

Role of intrinsic factor?

A

Necessary for vitamin B12 absorption

66
Q

Role of chief cells in gastric pit?

A

Secretes pepsinogen

67
Q

How is pepsinogen activated?

A

By being in acidic conditions

68
Q

Role of enteroendocrine cells?

A

secretes gastrin

69
Q

Role of entero-chromafin-like cells (ECL)?

A

Release histamine

70
Q

Role of D cells?

A

secretes somatostatin
Important for H+ secretion

71
Q

What is potentiation?

A

action of three substances combined is greater than the sum of the individual effects

72
Q

Negative feedback of HCl secretion?

A

HCl secretion causes more somatostatin to be secreted. Somatostatin inhibiits the secretion of HCl as well as the secretion of histamine

73
Q

Role of gastrin?

A

Stimulates ECL cell

74
Q

Role of histamine in stomach?

A

Stimulates parietal cell to release HCl

75
Q

Role of ACh in stomach?

A

Stimulates parietal cell to release HCl

76
Q

Activation of pepsinogen into pepsin?

A

Chief cells secrete pepsinogen, parietal cells secrete HCl
HCl activates it to become pepsin

77
Q

Role of pepsin?

A

Breaks down large proteins into smaller peptide fragments

78
Q

How does the stomach blend food?

A

Thick muscle in antrum–> pushes food up to mix it w/ chyme
Muscle at top of stomach pushes food down

79
Q

What happens to salivary amylase in the stomach and why?

A

Denatures as pH too low

80
Q

What substances are absorbed in the stomach?

A

Alcohol and caffeine

81
Q

Role of villi and microvilli in intestine?

A

Increase SA

82
Q

What makes up the majority of the SA of the GI system?

A

Small and large intestines (mainly small)

83
Q

Roles of pancreas?

A

Secretion of pancreatic juice
Secretion of enzymes

84
Q

What enzymes does the pancreas secrete?

A

Proteases and pancreatic lipase

85
Q

Role of gall bladder?

A

Storage and concentration of bile

86
Q

Role of liver?

A

Secrete bile
Processing of absorbed nutrients

87
Q

Components of bile needed for digestion?

A

Bile salts, phospholipids and HCO3 -ion

88
Q

Components of bile that have been removed from the blood?

A

Cholesterol, bile pigments and trace metals

89
Q

Role of bile salts?

A

Emulsify fats so they can have a larger SA

90
Q

Why do bile salts emulsify fats?

A

larger SA=larger area for lipases to work on

91
Q

Why can bile salts break down fat globules?

A

They have a hydrophobic (nonpolar) side and hydrophilic (polar) sides

92
Q

What is the significance of bile salts having hydrophobic and hydrophilic regions?

A

It can bind to both fats and water

93
Q

Products of breakdown of fat globules using bile salts?

A

Micelles

94
Q

What happens to micelles after their formation?

A

They are broken down into monoglycerides and fatty acids by lipases

95
Q

Why are micelles broken down into monoglycerides and fatty acids?

A

So they can be absorbed across the intestinal lining

96
Q

Role of smooth ER in lipid absorption?

A

It reforms triglycerides out of monoglycerides and fatty acids

97
Q

Role of golgi apparatus in lipid absorption?/

A

Packages triglycerides as chylomicrons

98
Q

Difference in time taken to absorb between fats and CHOs?

A

Fats take longer to digest and absorb

99
Q

Where does protein absorption occur?

A

Lining of the intestines

100
Q

Role of brush boarder peptidases in protein absorption?

A

Breaks down small peptides into AAs

101
Q

What are AAs absorbed alongside in the intestines?

A

Na+

102
Q

Where can small peptides be broken into AAs?

A

Lumen of intestine (by brush boarder peptidases) and peptidases in the intestinal epithelial cell

103
Q

How do AAs exit the lining of the intestines?

A

Via AA transporters

104
Q

Where do AAs go after leaving the intestinal epithelial cell?

A

Interstitial fluid

105
Q

Two methods of small intestine motility?

A

Peristalsis and segmentation

106
Q

What method of motility is more common in the small intestine?

A

Segmentation

107
Q

How does segmentation work?

A

Rhythmic contraction of relaxation of longitudinal muscles

108
Q

What is the purpose of segmentation??

A

Greater mixing of material
Net flow through small intestine

109
Q

What is the gastroileal reflex response?

A

An increase in segmentation as a response to gastric emptying

110
Q

What is the migrating myoelectric complex (MMC)?

A

Moves undigested material to the large intestine
Prevents bacteria from remaining in the small intestine for too long

111
Q

Roles of large intestine?

A

Storage of material prior to defecation
Digestion of undigested material (via bacteria)
Fluid absorption, which concentrates fecal matter

112
Q

Role of ileocecal sphincter?

A

Opens to allow chyme through when ileum contacts
Closes when large intestine distends to prevent backflow

113
Q

When and why does the ileocecal sphincter open?

A

When ileum contracts, to allow chyme through

114
Q

When and why does the ileocecal sphincter close?

A

When large intestine distends, to prevent backflow

115
Q
A

HL10521 Human Physiology (13 decks)

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