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HAPIB > Module 3: Digestive System > Flashcards

Module 3: Digestive System Flashcards

1
Q

What is the gastrointestinal tract?

A

Series of hollow organs

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2
Q

What organs comprise the gastrointestinal tract?

A

Mouth/oral cavity, esophagus, stomach, small intestine, large intestine, rectum, anus

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3
Q

What are accessory organs of the digestive system?

A

Organs that produce secretions, detoxify, and store substances to aid digestion

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4
Q

What accessory organs comprise the digestive system?

A

Salivary glands, liver, gallbladder, pancreas

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5
Q

Main role of digestive system?

A

Converts food into its simplest components, which are then absorbed into the bloodstream or excreted as waste

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6
Q

Five functions of digestive system?

A
  • Ingestion
  • Mechanical digestion
  • Chemical digestion
  • Absorption
  • Elimination of waste
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7
Q

Two functional divisions of digestive system organs?

A

Upper gastrointestinal tract and lower gastrointestinal tract

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8
Q

Role of upper gastrointestinal tract?

A

Food breakdown

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9
Q

Role of lower gastrointestinal tract?

A

Absorption, waste compaction and removal

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10
Q

What organs comprise the upper gastrointestinal tract?

A

Mouth/oral cavity, esophagus, stomach, small intestine (duodenum)

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11
Q

What organs comprise the lower gastrointestinal tract?

A

Small intestine (jejunum and ileum), large intestine, rectum, anus

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12
Q

Role of mouth/oral cavity

A
  • Mechanical digestion (mastication)
  • Mixing of food with saliva; salivary enzymes commence chemical digestion
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13
Q

What is mechanical digestion?

A

Crushing/shearing of ingested food

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14
Q

What is mastication?

A

Chewing, by means of movement of the jaw/tongue and grinding by teeth

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15
Q

What is chemical digestion?

A

Enzymatic breakdown of food into substances that may be absorbed

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16
Q

What is the esophagus?

A

Collapsed tubular fibromuscular organ connecting the pharynx to the stomach; runs posteriorly to trachea

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17
Q

Role of esophagus?

A

Transfers food (bolus) into stomach

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18
Q

What is bolus?

A

Rounded mass of masticated food mixed with saliva

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19
Q

Role of stomach?

A
  • Chemical digestion: bolus is mixed with gastric juices (hydrochloric acid and digestive enzymes) and converted into chyme
  • Mechanical churning also facilitates digestion
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20
Q

What is chyme?

A

Semi-fluid, pulpy, acidic mass of partially digested food mixed with gastric juices, expelled by stomach

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21
Q

Three components of small intestine?

A

Duodenum, jejunum, and ileum
(DJI)

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22
Q

Length of jejunum + ileum?

A

3-6m of small intestine

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23
Q

Length of large intestine?

A

Approximately 1.5m

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24
Q

Role of large intestine?

A
  • Chemical digestion of components not digested by small intestine
  • Reabsorption of water
  • Compacts waste (faeces) for elimination
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25
Q

Three main components of large intestine?

A

Cecum, colon, and rectum

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26
Q

Four components of colon?

A

Ascending colon
Transverse colon
Descending colon
Sigmoid colon

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27
Q

What is the cecum (structure)?

A

Expanded pouch that begins the large intestine that has an attached appendix

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28
Q

Role of rectum?

A

Store faeces prior to defecation

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29
Q

Role of salivary glands?

A

Secrete salivary amylase

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30
Q

Role of pancreas?

A

Secrete pancreatic enzymes and buffers, to break down proteins, fats, and carbohydrates

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31
Q

Roles of liver? (3)

A

Secretes bile, inactivates toxins, and stores iron/glucose/fat-soluble vitamins

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32
Q

Role of bile?

A

Emulsifies fats into fatty acids; lipid absorption and digestion

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33
Q

Role of gallbladder?

A

Stores bile

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34
Q

What are the four general major layers of the GIT?

A

Mucosa
Submucosa
Muscularis externa
Serosa/adventitia

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35
Q

What is the mucosa?

A

Innermost layer of GIT

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36
Q

Is the mucosa epithelium comprised of a single type? Why/why not

A

No; epithelial composition depends of function

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37
Q

Epithelium of mouth/esophagus mucosa?

A

Stratified squamous; protection

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38
Q

Epithelium of stomach/small intestine/large intestine mucosa (cecum and colon)?

A
  • Simple columnar; absorption
  • In small intestine, contains microvilli to increase SA for nutrient absorption
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39
Q

Epithelium of rectum/anus mucosa?

A

Stratified squamous; protection

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40
Q

Characteristic of epithelium of mucosa of GIT?

A

Contains specialised goblet cells that secrete mucus, keeping the epithelium moist, defending against pathogens/injury

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41
Q

What is the mucosa comprised of? (3)

A
  1. Epithelial mucous membrane
  2. Loose connective tissue (lamina propria)
  3. Muscularis (muscularis mucosa)
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42
Q

Why is the CT of the mucosa loose?

A

So nutrients may travel through easily

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43
Q

Characteristics of lamina propria?

A
  • Richly vascularised
  • Contain numerous immunologically competent cells (e.g. fibroblasts, macrophages, gut-associated lymphoid tissue (GALT))
  • Has sensory nerve endings
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44
Q

What is the muscularis mucosa?

A

Thin layer of smooth muscle cells

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45
Q

Role of muscularis mucosa?

A

Still under debate, but believed to alter the shape of lumen and move mucosal folds/villi

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46
Q

What is the submucosa?

A

Second-innermost layer of GIT

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47
Q

What is the submucosa comprised of?

A

Dense irregular CT, which is still relatively loose

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48
Q

Role of submucosa?

A

Provides physical support to mucosa, supplies blood/lymph vessels and nerves to GIT, and connects mucosa to underlying muscularis

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49
Q

What vessels does the submucosa contain?

A

Large blood vessels and lymphatic vessel

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50
Q

What are the submucosal glands?

A

Exocrine glands that secrete enzymes and buffers into lumen via ducts

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51
Q

What is the submucosal plexus (Meissner’s plexus)?

A

Local circuitry of sensory neurons and autonomic nerve fibres that innervate glands

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52
Q

Roles of submucosal plexus?

A

Controls glandular secretions, alters electrolyte and water transport, regulates blood flow

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53
Q

What is the muscularis externa?

A

Third-innermost layer of GIT

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54
Q

What is the muscularis externa comprised of?

A

Multiple muscle layers (organised in circular and longitudinal layers) + myenteric plexus (Auerbach plexus)

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55
Q

Is the composition of the muscle layers in the muscularis externa consistent? Why/why not?

A

No; depends on location within GIT

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56
Q

What type of muscle is the muscularis externa of esophagus?

A
  • 2 layers of muscle
  • Skeletal muscle and smooth muscle
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57
Q

What type of muscle is the muscularis externa of stomach?

A
  • 3 layers (inner oblique, middle circular, outer longitudinal)
  • Smooth muscle
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58
Q

What type of muscle is the muscularis externa of small intestine/large intestine/rectum?

A
  • 2 layers (inner circular, outer longitudinal)
  • Smooth muscle
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59
Q

Role of muscularis externa?

A

Contraction of muscle layers facilitate mechanical processing and movement of materials along GIT

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60
Q

What is the myenteric plexus (Auerbach plexus)? Location?

A

Network of sensory neurons and autonomic nerve fibres, located between circular and longitudinal muscle layers

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61
Q

Role of myenteric plexus (Auerbach plexus)?

A

Coordinates digestive muscle activity and thus motility

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62
Q

What is muscle tone?

A

Amount of tension (or resistance to movement) in muscles

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63
Q

How does the myenteric plexus carry out its function differently according to the type of neural stimulation?

A
  • Parasympathetic stimulation = increased muscle tone
  • Sympathetic stimulation = decreased muscle tone
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64
Q

What is the serosa/adventitia?

A

Outermost layer of GIT; either serosa or adventitia depending on region

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65
Q

Where is the serosa found?

A

Intraperitoneal (within peritoneal cavity) regions of GIT (i.e. most of stomach, parts of small/large intestine, and rectum)

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66
Q

Where is the adventitia found?

A

Retroperitoneal (behind peritoneal cavity) regions of GIT (i.e. oral cavity, pharynx, esophagus, parts of stomach, most of small/large intestine, and anus)

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67
Q

What is the serosa (composition and function)?

A
  • Loose CT, covered with mesothelium to lubricate outer surface of GIT and thus lower friction
  • Lubricates structures
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68
Q

What is the adventitia (composition and function)?

A
  • Dense network of collagen fibres
  • Binds/attaches structures
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69
Q

Role of mucosa?

A

Protects, secretes mucus, and mediates chemical digestion and absorption

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70
Q

What is the oral cavity lined by?

A

Oral mucosa, which is stratified squamous epithelium

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71
Q

Structures of oral cavity? (7)

A

Hard palate, soft palate, tongue, teeth, gingiva (gums), uvula, tonsils

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72
Q

Role of hard palate?

A

Bony support to oral cavity structure

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73
Q

What and where is soft palate?

A

Muscular structure, posterior to hard palate

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74
Q

What muscle is the tongue?

A

Skeletal muscle

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75
Q

Role of uvula?

A

Prevents food from entering pharynx prematurely, prior to effective mastication

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76
Q

What are the tonsils comprised of?

A

Lymphoid tissue

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77
Q

Functions of oral cavity?

A
  • Mastication, formation of bolus
  • Salivary amylase digests carbohydrates
  • Lingual lipase digests lipids (triglycerides)
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78
Q

3 major pairs of salivary glands?

A

Sublingual
Submandibular
Parotid

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79
Q

Location of sublingual salivary glands?

A

Lie on either side of tongue

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80
Q

Location of submandibular salivary glands?

A

Lie of inner surface of mandible (jaw)

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81
Q

Location of parotid salivary glands?

A

Lie just in front of ears

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82
Q

Role of sublingual salivary glands?

A

Produce mucous secretion that acts as buffer/lubricant, as well as approximately 5% of saliva entering oral cavity

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83
Q

Role of submandibular salivary glands?

A

Produce mixed serous/mucous secretion containing buffers, mucin, and salivary amylase, as well as approximately 75% of saliva entering oral cavity; secretions released under tongue

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84
Q

Role of parotid salivary glands?

A

Produce serous secretion containing abundant salivary amylase, as well as approximately 20% of saliva entering oral cavity

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85
Q

What are mumps?

A

Viral infection of parotid glands

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86
Q

How much saliva is produced daily?

A

1-1.5L

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87
Q

Composition of saliva?

A

99.4% water, and 0.6% electrolytes/buffers/antibodies/enzymes/salivary mucin

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88
Q

Functions of saliva? (4)

A

Lubrication, chemical digestion, protection, dissolving food (taste)

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89
Q

Length/width of esophagus?

A

25cm long, 2cm in diameter

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90
Q

Two sphincters of esophagus?

A

Upper esophageal sphincter and lower esophageal sphincter

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91
Q

Role of upper esophageal sphincter (UES)?

A

Prevents air entering GIT, and prevents reflux of food into airways

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92
Q

Role of lower esophageal sphincter (LES)?

A

Prevents reflux of stomach contents

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93
Q

Function of esophagus?

A

Conveys food/liquids from oral cavity into stomach, w/o absorption

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94
Q

Three phases of swallowing (deglutition)?

A
  1. Buccal phase
  2. Pharyngeal phase
  3. Esophageal phase
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95
Q

What is the buccal phase?

A
  • Voluntary
  • Contraction of tongue to push bolus up against soft palate into oropharynx
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96
Q

What is the pharyngeal phase?

A
  • Mainly voluntary
  • Tongue blocks oral cavity, epiglottis blocks larynx/trachea, UES relaxes and opens, food enters esophagus
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97
Q

What is the esophageal phase?

A
  • Mainly involuntary
  • UES contracts and closes, bolus forced through esophagus by peristalsis, LES relaxes and opens, food enters stomach and once it has, LES closes
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98
Q

What is the stomach and its role?

A

Expandable muscular organ that churns food into chyme

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99
Q

Four main regions of stomach?

A

Fundus
Cardia
Body
Pylorus

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100
Q

Where is the fundus?

A

Superior to gastroesophageal junction

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101
Q

Where is the cardia?

A

Within approximately 3cm of gastroesophageal junction

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102
Q

Role of cardia?

A

Entry point for foods/liquid into stomach, with an esophageal sphincter preventing reflux of stomach contents, and abundant mucus glands to protect from acid

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103
Q

Where is body of stomach?

A

Largest region; lies between fundus and pylorus

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104
Q

Role of body of stomach?

A

Facilitates/houses churning of ingested food

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105
Q

Where is the pylorus?

A

J-shaped curve leading to small intestine

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106
Q

Two subdivisions of pylorus?

A

Pyloric antrum
Pyloric canal

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107
Q

Role of pyloric sphincter?

A

Regulates process of chyme moving into small intestine

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108
Q

What are rugae?

A

Prominent folds/ridges of the mucosa and submucosa layers of the stomach wall, that form when stomach is empty

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109
Q

Role of rugae?

A

Facilitate expandable nature of stomach; increase SA of organ, as when stomach fills with food, rugae flatten out

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110
Q

Characteristic feature of mucosal layer of stomach?

A

Forms a series of gastric pits, each housing a number of gastric glands

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111
Q

What are gastric glands?

A

Mostly exocrine glands that open into the stomach through gastric pits in the mucosa

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112
Q

Role of gastric glands?

A

Secrete most of the acid and enzymes necessary for chemical digestion in stomach (1.5L/day) by means of specialised cells

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113
Q

Four types of cells of gastric glands?

A

Goblet cells
Parietal cells
G cells
Chief cells

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114
Q

Role of goblet cells?

A

Secrete mucus, which protects mucosal wall from acid

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115
Q

Role of parietal cells?

A

Secretes intrinsic factor which is needed for Vitamin B12 absorption by the small intestine, and HCl with kills microbes and denatures proteins

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116
Q

Role of G cells (enteroendocrine cells)?

A

Produce hormones, such as gastrin which increases stomach motility, stimulates HCl/enzyme production, and relaxes pyloric sphincter

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117
Q

Role of chief cells?

A
  • Secrete pepsinogen (inactive), which is converted to pepsin (active) by HCl, which degrades proteins
  • Secrete gastric lipase, which breaks down lipids
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118
Q

Length of small intestine?

A

3-5m

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119
Q

Length of duodenum?

A

First 20-25cm of small intestine

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120
Q

Length of jejunum?

A

1-2m

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121
Q

Length of ileum?

A

Longest segment of small intestine; 2-3m

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122
Q

Role of duodenum?

A

Receives chyme from the stomach, and digestive secretions from the
pancreas and liver; considered “mixing bowl” of small intestine

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123
Q

Structure of beginning of jejunum?

A

Marked by sharp bend at beginning

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124
Q

Role of jejunum?

A

Where majority of chemical digestion and nutrient absorption occurs

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125
Q

Role of ileum?

A

Absorption of Vitamin B12, fats (esp fatty acids and glycerol) and bile salts occurs

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126
Q

3 types of structures in the small intestine that increase SA for absorption?

A
  • Microvilli
  • Plicae circulares
  • Villi
127
Q

What are plicae circulares?

A

Deep ridges in mucosa and submucosa, that begin near proximal part of duodenum and extend to middle of ileum

128
Q

Function of plicae circulares?

A
  • Facilitate absorption
  • Shape causes chyme to move in spiral motion, slowing movement of chyme and thus increasing time available for absorption
129
Q

How much villi does the small intestine have?

A

Approximately 20-40 villi per mm2 of small intestine

130
Q

What does a capillary bed of a villus have?

A

1x arteriole
1x venule
1x lacteal

131
Q

How much microvilli does the small intestine have?

A

Approximately 200 million microvilli per mm2 of small intestine

132
Q

By what factor do structural adaptations (plicae circulares, villi, microvilli) increase the SA of the small intestinal wall?

A

600x

133
Q

Length of duodenum?

A

First 25cm of small intestine

134
Q

Role of duodenum?

A

Receives chyme from stomach, and digestive secretions from pancreas and liver; must neutralise acid. Also stimulates release of specific digestive hormones

135
Q

Characteristic features of duodenum? (3)

A
  • Few circular folds
  • Small villi
  • Submucosa contains many duodenal glands to secrete mucus
136
Q

Length of jejunum?

A

Middle 1-2m of small intestine

137
Q

Role of jejunum?

A

Where majority of nutrient absorption occurs

138
Q

Characteristic features of jejunum? (2)

A
  • Many circular folds
  • Abundant and very long villi
139
Q

Length of ileum?

A

Final 2-3m of small intestine

140
Q

Role of ileum?

A

Absorbs any final nutrients - especially Vitamin B12 and bile acids

141
Q

Characteristic features of ileum? (3)

A
  • Fewer circular folds than jejunum
  • Stumpy villi
  • Submucosa contains lymphoid nodules
142
Q

Why does the ileum’s submucosa contain lymphoid nodules?

A

To protect small intestine from bacteria colonising the large intestine

143
Q

Do the duodenum, jejunum, and ileum have distinct or indistinct boundaries?

A

Indistinct

144
Q

What are the four major hormones that regulate digestion?

A

Gastrin
Secretin
Gastric inhibitory peptide (GIP)
Cholecystokinin (CCK)

145
Q

Source of gastrin?

A

Enteroendocrine G cells in stomach (gastric glands) and duodenum

146
Q

When is gastrin released?

A

When food arrives in the stomach, and when large quantities of partially digested proteins are present in duodenum

147
Q

Functions of gastrin in the stomach?

A

Stimulates acid production by parietal cells, and muscle contractions thus increasing gastric motility

148
Q

Functions of gastrin in the duodenum?

A

Stimulates gallbladder to empty bile into duodenum, and pancreas to release pancreatic enzymes into duodenum

149
Q

Source of secretin?

A

Enteroendocrine S cells in duodenum

150
Q

When is secretin released?

A

When acidic (pH 2-4) chyme arrives in duodenum

151
Q

Functions of secretin?

A
  • Stimulates pancreas to secrete bicarbonate/buffers, liver to produce bile
  • Inhibits acid secretion from parietal cells in stomach, and gastric emptying
152
Q

Source of gastric inhibitory peptide (GIP)?

A

Enteroendocrine K cells in duodenum

153
Q

When is gastric inhibitory peptide (GIP) released?

A

When fats and carbohydrates (especially glucose) enter duodenum

154
Q

Functions of gastric inhibitory peptide (GIP)?

A
  • Stimulates pancreas to release insulin, lipid synthesis so fat accumulation, and glucose uptake by skeletal muscle
  • Inhibits lipid breakdown
  • Regulates appetite
155
Q

Source of cholecystokinin (CCK)?

A

Enteroendocrine I cells in duodenum

156
Q

When is cholecystokinin (CCK) released?

A

When fats and undigested proteins enter duodenum

157
Q

Functions of cholecystokinin (CCK)?

A
  • Promotes digestion of fat and protein
  • Stimulates pancreas to secrete pancreatic enzymes into duodenum, gallbladder to empty bile into duodenum
  • Inhibits gastric activity
  • Suppresses hunger
158
Q

What is peristalsis?

A

Moving material (bolus/chyme) along GIT (propulsion) via involuntary contraction and relaxation of longitudinal and circular muscles

159
Q

What is segmentation?

A

Mechanical mixing of chyme with digestive juices/mucosa via contractions of the circular muscles in GIT

160
Q

4 steps of peristalsis?

A
  1. Bolus arrives
  2. Circular muscles contract behind bolus
  3. Longitudinal muscles contract ahead of bolus
  4. Waves of circular muscle contractions behind bolus force it forwards
161
Q

Where does segmentation occur?

A

Mainly in small intestine, but also in large intestine

162
Q

Is segmentation stationary?

A

Yes; does not push material forwards through GIT, and occurs in localised regions

163
Q

When does segmentation cease?

A

When most of chyme has been absorbed

164
Q

Is peristalsis rhythmic or irregular?

A

Rhythmic; consistent contractions

165
Q

Is peristalsis unidirectional or multidirectional?

A

Unidirectional

166
Q

Is segmentation rhythmic or irregular?

A

Irregular; random contractions with no pattern

167
Q

Is segmentation unidirectional or multidirectional?

A

Multidirectional

168
Q

Length/width of large intestine?

A

1.5m in length, 3 inches in diameter

169
Q

Role of cecum?

A

Material from small intestine is stored and faecal compaction begins; ileocecal valve controls flow of chyme from small intestine

170
Q

What is uniquely different about the outer longitudinal muscle layer of the large intestine wall’s muscularis externa?

A

Incomplete; present in 3 separate longitudinal ribbons running down one side (teniae coli)

171
Q

What are haustra?

A

Series of pouches that are formed due to teniae coli contracting lengthwise and bunching up colon

172
Q

Frequency/length of haustral contractions?

A

Every 25 minutes; last 1 minute

173
Q

Role of haustral contractions?

A

Stimulated by presence of chyme, so push intestinal contents from one pouch to the next, facilitating mixing and water reabsorption

174
Q

How does the large intestine perform chemical digestion?

A

By means of bacteria; no digestive enzymes secreted by large intestine

175
Q

What are faeces comprised of?

A

Undigested food (cellulose), dead epithelial cells, mucus, bacteria

176
Q

Number of bowel movements?

A

Varies greatly; ranges from 2-3/day to 3-4/week

177
Q

What percent of nutrient absorption occurs in large intestine?

A

Less than 10%

178
Q

How does constipation occur?

A

Defecation is delayed, and additional water is absorbed

179
Q

How does diarrhoea occur?

A

Faeces move too quickly through large intestine and not enough water is absorbed

180
Q

How much faeces is eliminated daily?

A

200mL/day

181
Q

Humans are colonised by how many microorganisms?

A

Estimated 100 trillion microorganisms

182
Q

How much of a person’s body weight do microorganisms account for?

A

1-2kg

183
Q

What type of microorganisms colonise the human body?

A

Bacteria, fungi, viruses; most are symbiotic

184
Q

Where does the human microbiome reside?

A

Reside all over the body, but bulk live in GIT

185
Q

Where does the gut microbiota derive nutrients?

A

From host’s diet

186
Q

Correlation between gut microbiome and age?

A

Gut microbiome - whilst existent from birth - diversifies with age

187
Q

Correlation between gut microbiome diversity and health?

A

Higher microbiome diversity = indicator of good health

188
Q

Functions of gut microbiome? (5)

A
  • Facilitates chemical digestion and absorption
  • Synthesis specific vitamins (Vitamins K and B), enzymes, amino acids
  • Ferments dietary fibre and thus produces short chain fatty acids (SCFAs)
  • Affects drug metabolism
  • Aids immune system
189
Q

How does gut microbiome aid immune system?

A

Activates intestinal immune cells to secrete immunoglobulins (IgA)

190
Q

Relationship between gut microbiome and disease?

A
  • Still emerging field of research
  • Disturbance in balance of gut microorganisms = decreased microbiome diversity = increased susceptibility to disease
  • Not identified if gut microbiome alterations are the cause or effect
191
Q

What 4 conditions have changes in gut microbiota been associated with?

A
  • Inflammatory bowel disease (IBD)
  • Diabetes
  • Obesity
  • Eczema/allergies
192
Q

Size of the liver?

A

1.5kg - second largest organ and largest gland in body

193
Q

Location of liver?

A

Sits just under rib cage on right side of abdomen

194
Q

Unique characteristic of liver?

A

Capable of regeneration; may regenerate itself back to full size from as little as 51% of original liver mass

195
Q

Structure of liver?

A

Two primary lobes (left and right); vascularised and attached to abdominal wall

196
Q

What is the falciform ligament?

A

Divides liver into left and right lobes

197
Q

What is the coronary ligament?

A

Attaches superior surface of liver to diaphragm

198
Q

What is the round ligament?

A

Thickening in posterior end of falciform ligament, which connects liver to umbilicus

199
Q

What is the caudate lobe?

A

Lies between the left lobe of the liver and the inferior vena cava

200
Q

What is the quadrate lobe?

A

Sandwiched between left lobe of liver and the gallbladder

201
Q

Role of hepatic artery?

A

Brings oxygenated blood from heart to liver

202
Q

Role of hepatic portal vein?

A

Brings nutrient-rich blood from spleen and GIT to the liver

203
Q

Role of inferior vena cava?

A

Takes de-oxygenated blood away from liver back to heart

204
Q

Role of bile duct?

A

Carries bile away from liver to gallbladder and duodenum

205
Q

How many liver lobules is the liver divided into?

A

Approximately 100,000 liver lobules

206
Q

Structure of a liver lobule?

A
  • Hexagonal in shape
  • Packed with liver cells (hepatocytes)
  • Separated by interlobular septa (connective tissue)
  • Portal triad at each corner
207
Q

What 3 components are the portal triads of liver lobules comprised of?

A
  • Interlobular vein
  • Interlobular artery
  • Interlobular bile duct
208
Q

Where does blood from interlobular veins and arteries go to?

A

Liver sinusoids (large, fenestrated capillaries)

209
Q

What is at the centre of each liver lobule? Why?

A

Central vein, to take blood from sinusoids to inferior vena cava

210
Q

What percent of liver’s mass are hepatocytes?

A

80%

211
Q

Functions of hepatocytes?

A

Secretory, metabolic, and endocrine functions

212
Q

Structure of hepatocytes?

A
  • Arranged in a series of irregular plates within liver lobules
  • Tightly packed around fenestrated vessels (sinusoids), facilitating easy access to blood and therefore being able to process nutrients, toxins, and wasts in blood
213
Q

What are liver sinusoids?

A

Open, fenestrated capillaries which lack a basement membrane and contain Kupffer cells (phagocytes)

214
Q

Describe blood flow in the liver (5 steps).

A
  1. O2-rich blood (1/3) arrives from heart via hepatic artery
  2. Nutrient-rich blood (2/3) arrives from spleen and GIT via hepatic portal vein
  3. Blood combines in liver sinusoids
  4. Sinusoids all drain into central vein
  5. All central veins merge to form hepatic veins, which empty into vena cava
215
Q

Functions of liver?

A

Almost 200 known functions, including:
- Metabolism of carbohydrates, lipids, proteins
- Production of bile
- Detoxification of blood (alcohol, drugs)
- Absorption/breakdown of circulating hormones
- Storage of iron, vitamins, and glucose
- Removal of old/damaged blood cells

216
Q

Structure of gallbladder?

A

Small, pear-shaped organ that has a capacity of 50mL

217
Q

Functions of gallbladder? (2)

A
  • Stores and concentrates bile by up to 20x
  • Releases bile into duodenum when triggered by CCK

Note: does NOT make bile

218
Q

Can a person live without a gallbladder? If so, are there any side effects/consequences?

A

Yes, can have gallbladder removed by via cholecystectomy; then, bile enters duodenum directly from liver. However, may be harder to digest large amounts of fatty, greasy food

219
Q

What is bile? (structure/composition/origins)

A

Yellow-green fluid, comprising minerals, cholesterol, phospholipids, bile salts, and bile pigments, synthesised by hepatocytes in liver

220
Q

Is the production of bile a consistent process?

A

Relatively; hepatocytes constantly produce bile, but the process is increased when secretin is released due to fatty chyme entering the duodenum

221
Q

Role of bile salts?

A

Emulsify fats for absorption

222
Q

Role of bile pigments (e.g. bilirubin)?

A

Yellow in colour; intestinal bacteria breaks down bilirubin to make urobilinogen

223
Q

What is urobilinogen?

A

Brown pigment in faeces

224
Q

Function of bile?

A

Emulsifies lipids in small intestine

225
Q

Why is the function of bile important?

A

Lipids are hydrophobic, so cannot be digested in small intestine unless broken apart into smaller fragments. Bile salts and phospholipids tear large lipid globules into many tiny fragments through emulsification, thus increasing surface area available for lipases

226
Q

Location of gallbladder?

A

Sits under liver’s right lobe

227
Q

Structure of pancreas?

A

Slender, fish-shaped organ, 15cm long

228
Q

General functions of pancreas?

A

Mixture of exocrine and endocrine functions

229
Q

Exocrine functions of pancreas?

A

Cells of pancreatic acini = secrete enzymes

  • Makes digestive enzymes, which are released into duodenum and break down proteins, fats, and starches.
  • Produces pancreatic enzymes (by acinar cells)
230
Q

What do exocrine glands do?

A

Secrete their substances through ducts onto body’s surfaces

231
Q

What do endocrine glands do?

A

Secrete their substances directly into your bloodstream

232
Q

Endocrine functions of pancreas? (cells in pancreatic islets)

A

Cells in pancreatic islets = secrete hormones

  • Makes hormones via endocrine cells in pancreatic islets
  • i.e. alpha cells = glucagon, beta cells = insulin, delta cells = growth hormone-inhibiting hormone
233
Q

Role of glucagon?

A

Glycogen breakdown to form glucagon

234
Q

Role of insulin?

A

Glucose uptake by cells from bloodstream

235
Q

Role of growth hormone-inhibiting hormone?

A

Suppresses alpha and beta cells, and decreases food absorption/enzyme secretion in GIT

236
Q

Role of pancreatic duct?

A

Delivers pancreatic juice into duodenum

237
Q

3 components of pancreatic juice?

A

Water, sodium bicarbonate, digestive enzymes

238
Q

Role of sodium bicarbonate in pancreatic juice?

A

Neutralises stomach acid

239
Q

Role of alpha-amylase in pancreatic juice?

A

Breaks down certain starches (almost identical to salivary amylase)

240
Q

Role of lipase in pancreatic juice?

A

Breaks down complex lipids into fatty acids

241
Q

Role of nucleases in pancreatic juice?

A

Break down nucleic acids (RNA and DNA)

242
Q

Role of proteolytic enzymes in pancreatic juice?

A

Break down proteins into amino acids

243
Q

In what form are proteolytic enzymes existent in pancreatic juice?

A

Inactive forms; activated by enzymes in duodenum
(e.g. trypsinogen -> trypsin, chymotrypsinogen -> chymotrypsin, procarboxypeptidase -> carboxypeptidase)

244
Q

Where is pancreatic juice secreted?

A

Exocrine glands in pancreas

245
Q

Where is gastric juice secreted?

A

Secreted by gastric glands in the stomach

246
Q

Components of gastric juice?

A

Contains HCl, pepsin, intrinsic factor, mucus, and water

247
Q

Is pancreatic juice alkaline or acidic?

A

Alkaline (has sodium bicarbonate)

248
Q

Is gastric juice alkaline or acidic?

A

Acidic (has HCl)

249
Q

Main role of pancreatic juice?

A

Digest carbohydrates and fat

250
Q

Main role of gastric juice?

A

Digest proteins

251
Q

What is metabolism?

A

Sum of all chemical reactions that occur in the human body

252
Q

What is nutrition?

A

Process of providing/obtaining nutrients (often via food) for health, growth, and survival

253
Q

How are nutrients stored in the human body?

A

Simplest form: glucose, lipids, amino acids

254
Q

What are catabolic reactions?

A

Breakdown processes; involve release of energy (ATP) and heat

255
Q

What are anabolic reactions?

A

Synthesis processes; involve expenditure of energy (ATP) and heat

256
Q

What is metabolic rate? How is it measured?

A

Amount of energy used by body per day; measured as calories/day

257
Q

Formula for metabolic rate (MR)?

A

MR = BMR + energy used in physical activity + thermal effect of food

258
Q

What is basal metabolic rate (BMR)?

A

Metabolic rate when in a quiet, resting, fasting state

259
Q

Average adult metabolic rate?

A

2000 calories/day

260
Q

Average adult basal metabolic rate?

A

1200-1800 calories/day

261
Q

What is the thermic effect of food?

A

Energy required to digest, absorb, process, and transport ingested food (nutrients); peaks 2-3 hours subsequent to eating

262
Q

How does amount of muscle vs fat affect metabolic rate?

A

Muscle requires more energy to function than fat

263
Q

How does physical activity affect metabolic rate?

A

Physical activity increases amount of muscle, which thus increases metabolic rate

264
Q

How does gender affect metabolic rate?

A

On average, males have a higher metabolic rate

265
Q

How does body size affect metabolic rate?

A

Bigger people have bigger organs and thus a higher metabolic rate

266
Q

How does thyroid activity affect metabolic rate?

A

Thyroid hormones cause an increased metabolic rate

267
Q

How does environmental temperature affect metabolic rate?

A

Too hot/cold (extreme weather conditions) causes body to work harder, thus increasing metabolic rate

268
Q

How does infection/illness affect metabolic rate?

A

Energy is required to fight infection, thus increasing metabolic rate

269
Q

How do genes affect metabolic rate?

A

Metabolic rate is naturally faster/slower in some people according to their genetic predisposition

270
Q

How does age affect metabolic rate?

A

Metabolic rate decreases with age, due to there being less muscle and hormonal changes

271
Q

How does dieting affect metabolic rate?

A

Reduced calorie intake reduces metabolic rate

272
Q

What controls appetite?

A

Hypothalamus

273
Q

2 types for short-term regulators of appetite?

A

Ghrelin and peptide YY (PYY)

274
Q

1 type of long-term regulators of appetite?

A

Leptin

275
Q

Where is ghrelin secreted?

A

By empty stomach; conveys hunger to hypothalamus

276
Q

Where is ghrelin secreted?

A

By ileum/colon when food enters stomach; conveys fullness to hypothalamus

277
Q

Where is leptin secreted?

A

By adipocytes; conveys abundant fat stored to hypothalamus, decreasing appetite

278
Q

What causes obesity?

A

Unresponsiveness to leptin

279
Q

What is stockpiling of energy reserves?

A

When nutrient absorption by the GIT exceeds the body’s immediate needs

  • Excess fatty acids -> stored as triglycerides in the liver or fat
  • Excess glucose -> stored as glycogen in the liver and skeletal muscle
  • Excess amino acids -> stored as carbohydrates or fats or degraded
280
Q

What is mobilisation of energy reserves?

A

When nutrient absorption by GIT is insufficient for body’s immediate needs

  • Triglycerides -> fatty acids
  • Glycogen -> glucose
  • Contractile proteins (actin/myosin) within myofibrils -> release amino acids
281
Q

Is stockpiling anabolic or catabolic?

A

Anabolic

282
Q

Is mobilisation anabolic or catabolic?

A

Catabolic

283
Q

6 key nutrients that we consume to sustain ourselves?

A

Water, carbohydrates, lipids, proteins, minerals, vitamins

284
Q

Why are minerals a unique essential nutrient?

A

Nutrient that we cannot synthesise, and must be obtained from diet

285
Q

What is a recommended daily allowance (RDA)?

A

Estimated safe daily intake of nutrients to meet standard metabolic needs

286
Q

What are the 3 macronutrients?

A
  • Glucose (carbohydrates)
  • Fatty acids (lipids)
  • Amino acids (proteins)
287
Q

Where are carbohydrates predominantly found in?

A

Muscle, liver, blood

288
Q

Food sources of carbohydrates?

A

Plants, pasta, bread, potatoes

289
Q

Functions of carbohydrates?

A

Body’s primary source of energy; carbohydrates -> glucose -> ATP (excess glucose -> glycogen)

290
Q

RDA of carbohydrates?

A

175g/day

291
Q

Chemical structure of carbohydrates?

A

Saccharide ring of 6 carbon atoms

292
Q

What are polysaccharides?

A

Complex carbohydrates containing hundreds of carbon rings (e.g. glycogen, starch)

293
Q

What are disaccharides?

A

Contain 2 carbon rings (e.g. sucrose, lactose)

294
Q

What are monosaccharides?

A

Simplest sugars containing 1 carbon ring (e.g. glucose, fructose); only sugars absorbed in GIT

295
Q

What are lipids?

A

Insoluble organic compounds

296
Q

Role of lipids?

A

Long-term energy source (superior to carbohydrates as a stored energy source); also protection and insulation

297
Q

Most abundant form of lipid?

A

Triglycerides

298
Q

Food sources of lipids?

A

Fat and oil

299
Q

Where do saturated fatty acids originate from?

A

Animal origin

300
Q

Where do unsaturated fatty acids originate from?

A

Plant origin

301
Q

Why is it difficult to transport lipids via blood?

A

Lipids are hydrophobic, and thus do not dissolve in plasma; so, tend to stick to vessel walls

302
Q

How are lipids effectively transported despite being hydrophobic?

A

Lipoproteins surround lipids, and recognise target cells

303
Q

4 types of lipoproteins?

A
  • Chylomicrons
  • Very Low Density Lipoproteins (VLDLs)
  • Low Density Lipoproteins (LDLs)
  • High Density Lipoproteins (HDLs)
304
Q

Role of chylomicrons?

A

Transport cholesterol through lymphatic vessels to the liver

305
Q

Role of Very Low Density Lipoproteins (VLDLs)?

A

Travel through bloodstream to adipose tissue

306
Q

Role of Low Density Lipoproteins (LDLs)?

A

Known to stick to vessel walls forming plaque.

307
Q

Role of High Density Lipoproteins (HDLs)

A

Collect LDLs through the blood stream and takes them back to the liver

308
Q

Describe how carbohydrates are metabolised, absorbed and stored.

A

Complex carbohydrates are ingested.
Complex sugars are broken down into disaccharides and trisaccharides by salivary amylase.
Pancreatic enzymes in the small intestine break down the tri and disaccharides into simple sugars.
Absorbed glucose travels to the liver.

309
Q

Describe how lipids are metabolised, absorbed and stored.

A

Lipids ingested.
Triglycerides begin being broken down into diglycerides and monoglycerides by lingual lipase.
Mixing of chyme creates large lipid globules.
Lipid digestion is completed in the duodenum through bile salts and pancreatic lipase.

310
Q

Describe how proteins are metabolised, absorbed and stored.

A

Protein is ingested.
HCL denatures the proteins and pepsin breaks the peptide bonds.
Pancreatic enzymes and trypsin aid in chemical digestion and amino acid absorption.
Absorbed AAs travel to the liver.
AAs released into blood and used to synthesise plasma proteins.

311
Q

Food sources of protein?

A

Meat, dairy, eggs, nuts, etc.

312
Q

Main functions of proteins?

A

Make up tissues, constantly broken down into amino acids to produce ATP, synthesise new proteins, and convert into glucose/lipid (catabolic reactions)

313
Q

Role of parietal cells?

A

Secrete HCl

HAPIB (8 decks)

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