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Biomed 1 - Revision Deck > DigestiveDigestive System I > Flashcards

DigestiveDigestive System I Flashcards

1
Q

Four GI Tract layers

A
  1. Mucosa
    1. Muscosal epithelium
    2. Lamina propria
    3. Muscularis mucosa
  2. Submucosa
  3. Muscularis
  4. Serosa (peritoneum)
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2
Q

Mucosa : Epithelium

A
  • Protection for: mouth, pharynx, oesophagus, anus
  • Columnar epithelium for stomach and intestines
    • Microvilli - ⇡ surface area for absorption
    • Globlet cells - secrete mucus to lubricate food and protect against erosion
    • Enterendocrine cells - secrete hormones into blood
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3
Q

Mucosa : Lamina Propria

A
  • Connective tissue with blood and lymphatic vessels - absorption of nutrients
  • Contains MALT (mucosa associated lymphoid tissue) ⇢ collection of immune cells (lymphoctyes, macrophages)
  • in GIT - GALT
  • MALT in - tonsils, oesophagus, small intestine, appendix, large intestine
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4
Q

GALT

A
  • 70% of body’s immune cells
  • 25% of intestine mucosal mass
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5
Q

Mucosa : Muscularis Mucosa

A
  • Smooth muscle
  • Creates the villi (smooth folds) - surface area, absorption
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6
Q

Submucosa Layer

A
  • Connective tissue layer between mucosa and muscularis
  • Contains blood and lymph vessels (receive absorbed food molecules)
  • Submucosal plexus - network of neurons, ‘brain of the gut’
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7
Q

Muscularis Externa

A
  • Skeletal muscle for swallowing, defection
  • Mouth, pharynx, upper oesophagus, anal sphincter
  • Rest of GIT mostly smooth muscle (involuntary - autonomic)
    • Mixing of food with digestive juices
    • Propelling food (chyme/bolus) along digestive tract (peristalsis)
  • Between the 2 layers - nuerons - myenteric plexus
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8
Q

Peritoneum

A
  • Largest serous membrane in body
  • Has blood and lymph vessels
  • 2 layers
    • Parietal - covers wall of abdomen and pelvic cavity
    • Visceral - covers the organs
  • Peritoneal cavity - space between the 2 layers, contains lubricating serous fluid
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9
Q

Name 2 peritoneal pathologies

A
  1. Ascites - accumulation of fluid in peritoneal cavity
  2. Peritonitis - inflammation of peritoneum
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10
Q

Great Omentum

A
  • Largest fold of the peritoneum
  • Drapes over transverse colon and small intestine like apron
  • Stores fat, contains adipose tissue
  • Lymph nodes - macrophages and plasma cells
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11
Q

Lesser Omentum

A
  • Peritoneal fold
  • Suspends the stomach and duodenum from the liver
  • Pathway for blood vessels entering the liver
  • Contains hepatic portal vein
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12
Q

Enteric nervous system

A
  • Brain of the gut from oesophagus to anus
  • Independent but regulated by autonomic nervous system
  • Parasympathetic - rest and digest
    • ⇑ muscular activity (peristalsis ⇢ myenteric plexus)
    • ⇑ glandular secretions (submucosal plexus)
  • Sympathetic (fight or flight / stress)
    • ⇓ muscular activity (peristalsis ⇢ myenteric plexus)
    • ⇓ glandular secretions (submucosal plexus)
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13
Q

Myenteric plexus

A

Gut motility

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14
Q

Submucosal plexus

A

Digestive secretions

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15
Q

Portal vein vs liliac veins

A
  • Portal vein - lower oesophagus, stomach, pancreas, small and large intestine, upper rectum, spleen
  • Iliac vein - lower rectum and anal canal
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16
Q

Oral cavity

A
  • Hard palate
  • Soft palate - arch of muscle
  • Uvula - prevents food entering nasal cavity
  • Tongue - skeletal muscle
  • Papillae - cover tongue, taste buds
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17
Q

Functions of oral cavity

A
  • Mastication
  • Speech
  • Taste
  • Swallowing
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18
Q

Saliva

A
  • Produced by parotid glands, submandibular glands, sublingual glands
  • Controlled by autonomic nervous system
  • Continuous salivation - 1 - 1.5 L per day
  • Sympathetic nervous system - reduces salivation
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19
Q

Saliva - contents

A
  • Water (99.5%)
  • Mineral salts (Na, K a, Cl, bicarbonate)
  • Enzymes - salivary amylase, lysozymes
  • Mucus
  • Immunoglobulins (IgA)
  • Blood clotting factors
  • Mildly acidic (6.35-6.85 pH)
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20
Q

Saliva - functions

A
  • Digestion
  • Lubricating and dissolving food
  • Cleansing oral cavity and teeth
  • Defense - non-specific IgA
  • Taste
  • Buffer - for acidic foods
  • Waste removal - urea/uric acid
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21
Q

Oesophagus

A
  • 25 cm muscular tube attached to larynx, passes through diaphragm
  • Lined with epithelium, lubricated with mucus
  • Peristalsis (muscular contractions) - pass food to stomach
  • Epiglottis - prevent food from entering trachea
  • Lower oesophageal sphincter - seal on the stomach, prevent reflux
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22
Q

4 regions of stomach

A
  1. Cardia
  2. Fundus
  3. Body
  4. Pyloric
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23
Q

2 sphincters in stomach

A
  1. cardiac
  2. pyloric
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24
Q

Function of stomach goblet cells

A
  • Stomach secretes 2-3L of highly acidic gastric juice and mucus per day
  • Mucus produced by goblet cells acts as buffer
  • Fast turnover of eipthelial cells in stomach - replace lining every 3 days
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25
Q

Stomach - 3 types of exocrine cells

A
  1. Parietal cells
    • Intrinsic Factor (IF) - needed for Vit B12 absorption
    • Hydrochloric acid (HCl) - antimicrobial agent; assists in activating bile and pancreatic juice flow
  2. Chief cells
    1. Pepsinogen - protein and lipid digestion
    2. Gastric lipase - converts pepsinogen to active enzyme pepsin (digests protein)
  3. Goblet cells - mucus - protects against acid
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26
Q

Stomach - functions

A
  • Mixing chamber
  • Storage
  • Defence
  • Absorption (limited)
  • Digestion - mechanical and chemical
  • Satiation
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27
Q

2 stomach hormones

A
  • Ghrelin - stimulates hunger
  • Gastrin - responds to stomach distension, stimulates gastric juice secretion and gastric motility
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28
Q

Pancreas

A
  • Accessory organ of digestive system
  • Connected to duodenum via pancreatic duct
  • Exocrine function
    • Pancreatic juice ⇢ small intestine
    • Sodium bicarbonate and water
    • Protease enzymes
    • Pancreatic lipase (fats)
    • Pancreatic amylase - breaks down sugars
  • Endocrine function
    • Secrete hormones into blood
    • Insulin and glucagon
    • Somatostatin (growth-hormone inhibiting hormone)
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29
Q

Pancreatic enzymes

A
  • Pancreatic amylase - breaks down starches into sugars
  • Pancreatic lipase - lipid / fat digestion
  • Trypsin - protein digestion
  • Chymotrypsin - protein digestion
  • Ribonuclease - digest RNA
  • Deoxyribonuclease - digest DNA
30
Q

Gallbladder

A
  • Accessory digestive organ
  • Pear shaped sac 7-10 cm
  • Bile ducts from gallbladder and liver meet at common bile duct
  • Bile ducts collect bile produced by hepatocytes which pools in gallbladder
  • Bile enters small intestine via common bile duct
  • When ingest fat - gallbladder contracts to inject bile down the common bile duct into duodenum
  • Bile emulsifies fat - breaks lipids into smaller molecules - more surface area for enzymes (lipase) to work
31
Q

Bile

A
  • Composed of bile salts, cholesterol and bilirubin
  • pH 7.6 - 8.6 9mildly basic)
32
Q

Enterohepatic circulation

A

Process by which bile is absorbed and transported back to the liver from the ileum

33
Q

What produces bile?

A

Hepatocytes

34
Q

Small intestine

A
  • Food combines with stomach secretions
  • Chyme is pushed through pyloric sphincter into small intestine
  • Most digestion and absorption occurs here
  • Villi maximise surface area
  • Cells - goblet (mucous), endocrine, absorptive
35
Q

3 regions small intestine

A
  1. Duodenum - emulsification, digestion
  2. Jejunum - most absorption
  3. Vit B12 absorbed
36
Q

Villi and microvilli - purpose

A

Increase surface area for absorption

Absorbed nutrients ⇒ blood

Absorbed fatty acides ⇒ lymph

37
Q

Brush border enzymes

A
  • Attached to intestinal lining
  • Maltase, sucrase, lactase - break down sugars
  • Dipeptidase - breakdown protein into amino acids
  • Nucleosidaases and phosphatases - digest RNA and DNA
38
Q

Cholecystokinin (CCK)

A
  • Peptide hormone secreted by enteroendocrine cells in duodenum (small intestine)
  • Released in response to high fat or protein chyme entering duodenum
  • Stimulates pancreas to secrete pancreatic enzymes (digest fat, carbs, protein)
  • Increases hepatic production of bile and stimulates contraction of gallbladder
  • Mediates satiety (feeling of fullness)
39
Q

Small intestine functions

A
  • Movement - peristalsis of food
  • Digestion
  • Absorption - nutrients and water
  • Hunger / satiety
  • Immunity - Peyer’s patches, bacterial microflora
40
Q

How much of absorption occurs in small intestine?

A

90%

41
Q

Small intestine absorption

A
  • Carbs, amino acids - capillaries
    • Monosaccharides - active/passive transport
    • Amino acids - active transport
  • Fatty acids, glycerol, cholesterol and fat-soluble vitamins (A,D,E,K)
    • Emulsified by bile
    • Enter intestinal cells - simple diffusion
    • Absorbed into lacteals
    • Travel through lymphatic system and enter blood through subclavian vein
42
Q

Large Intestine

A
  • Terminal portion of GI tract
  • Where final stages of digestions, absorption, some vitamin synthesis (through bacterial activity) and stool formation occurs
  • Absorption - water, minerals, vitamins, some drugs
43
Q

Ileocaecal valve

A
  • One-way flow from small to large intestine
  • If faulty - large intestine microbes to overpopulate in the small intestine (SIBO)
44
Q

4 regions of large intestine

A
  1. Caecum - part of immune system (macrophages, lymphocytes, bacteria), appendix attached
  2. Colon - ascending, transverse, descending regions
  3. Rectum
  4. Anal canal - internal and external sphincter
45
Q

Large intestine - microbes

A
  • Most symbiotic
  • Pathogenic species - local pH, poor nutrition, antibiotics
  • Microbial fermentation - final stage of nutrient extraction
  • Bacteria ferment fibre ⇒ short-chain fatty acids (SCFAs) ⇒ support tight junctions
46
Q

Bacterial fermentation produces:

A
  • Hydrogen, CO2, methane (flatulence)
  • Fermentation of residual amino acids ⇢ hydrogen sulfide - odour
  • Toxic products ⇢ liver ⇢ excreted in urine
  • Bilirubin - decomposed pigments - colour of faeces
  • Faeces 50-60% bacteriaa
47
Q

What is needed for B12 absorption and where is it found?

A

Intrinsic Factor

Produced in parietal cells in stomach

Absorbed in terminal ileum

48
Q

Liver

A
  • 2nd largest organ (skin largest)
  • using 27% of resting metabolism
  • Filters 1.4 L of blood every minute
  • Heaviest gland in the body
49
Q

Kupffer cells

A
  • Phagocytic cells
  • Remove foreign bodies from blood
50
Q

Hepatic first pass

A
  • All blood from GIT is transported to liver via portal vein
  • Filtered/metabolised before entering systemic circulation
51
Q

Liver - functions

A
  • Cleansing blood of microbes
  • Detoxification - metabolising drugs, toxins, alcohol
  • Bile production
  • Haemoloysis (Kupffer cells)
  • Other…
52
Q

Liver - Metabolism

A
  • Carbohydrate - glucose ⇢ glycogen for storage
  • Fat - metabolises fat from storage as required
  • Protein - converts amino acids to non-essential amino acids, breaks down nucleotides to form uric acid to be excreted
53
Q

Liver Detoxification - definition

A
  • Hepatocytes convert toxins into non-toxic metabolites - excreted from the body
54
Q

Liver Detoxification - 2 classifications

A
  1. Hydrophilic - excreted in urine or bile
  2. Lipophilic - must be chemically altered into hyrdrophilic compounds
55
Q

Lipophilic to hydrophilic conversion - 2 phases

A
  1. Phase I - Bio-activation
    1. CYP450 enzymes
    2. Converts water-insoluble toxins into water soluble substances to be excreted by kidneys
    3. Converts toxins to more reactive substances to be metabolised in Phase II
  2. Phase II - Conjugation
    1. Molecules are attached to toxins to neutralise making stable (non-reactive) and water-soluble to be excreted
    2. Glutathione - key anti-oxidant in Phase II
56
Q

Abdominal quadrants

A
  1. Right hypochondrium - Epigastric region - Left Hypochondrium
  2. Right flank - Umbilical region - Left flank
  3. Right groin - Pubic region - Left groin
57
Q

Dietary Carbohhydrates

A
  1. Monosaccharides - 1 sugar unit - Glucose, Fructose, Galactose
  2. Disaccharids - 2 sugar units - Maltose, Sucrose, Lactose
  3. Polysaccharides - many sugar units - Starch, Glycogen, Cellulose
58
Q

Dietary Lipids

A
  1. Triglycerides
  2. Phospholipids
  3. Cholesterol
59
Q

Triglycerides

A
  • Predominant dietary lipid
  • Composed of glycerol and three fatty acid chains
  • Saturated or unsaturated
60
Q

Phospolipids

A
  • 2 fatty acid tails and a phospate head
  • Digested to free fatty acids and absorbed
61
Q

Cholesterol

A
  • Steroid particularly in animal foods
  • Vital for
    • cell membrane integrity
    • Vitamin D synthesis
    • Sex hormone synthesis
62
Q

Dietary lipids - functions

A
  • Energy - ATP (2nd to carbohydrates)
  • Insulation - preserve heat
  • Cell membranes
  • Hormone production
  • Protection of organs
63
Q

Saturated fatty acid

A
  • Molecule containing greatest number of hydrogen atoms
  • No double bonds
64
Q

Unsaturated fatty acids

A

One or more double bonds between carbon atoms

65
Q

Cis vs Trans Fatty Acids

A
  • CIS
    • H atoms are on the same side of the double bond
    • In nature, nearly all fats have CIS structure
    • Body can recognise and use them
  • Trans
    • H atoms are on separate sides of the double bond
    • Created in labs/industry
    • Associated with heart disease
66
Q

Proteins

A
  • Long molecules of amino acids
  • Make up 15% of total body mass
  • Amino acid chains create 3D structure of each protein which allows it to function
  • Amino acids - absorbed in small intestine
67
Q

Protein - functions

A
  • Immunity - immunoglobulin antibodies
  • Structures - muscles, collagen
  • Enzymes
  • Hormones
  • Neurotransmitters
  • Energy
68
Q

Protease enzymes

A
  • Enzymes that break down proteins
  • Proteins must be denatured first (destroy properties of a molecule)
69
Q

Protein structure

A
  • Unique 3D structure
  • ‘Lock and key’ - hormone/enzymes fit into receptor
70
Q

Enzymes

A
  • Biological catalysts
  • Speed up chemical reactions
  • Highly specific what substrate they react with
  • Lock & key structure
  • Most end in ‘ase, i.e. ’lactase’
  • Those involved in protein digestion end with -in, i.e. ‘pepsin’
  • Enzymes can perform same function many times
71
Q

Proteins are easily denatured by:

A
  • pH and temperature changes

Biomed 1 - Revision Deck (9 decks)

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