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Physiology Flashcards

1
Q

What is ptyline?

A
  • Amylase

- Carbohydrate digestion

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2
Q

What is pepsin?

A
  • Begins to digest proteins

- Cuts off chains

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3
Q

What does intrinsic factor help absorb?

A
  • Vitamin B12
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4
Q

Name 4 proteases made in the pancrease?

A
  • Trypsin
  • Chymotrypsin
  • Carboxypeptidase
  • Elastase
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5
Q

Name brush border proteases

A
  • Aminopeptidase

- Dipeptidase

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6
Q

Most important lipase in TG digestion

A

Pancreatic lipase

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7
Q

Name 2 nucleases in pancreatic juice

A
  • Ribonuclease

- Deoxyribonuclease

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8
Q

Name 2 nucleases in the brush border

A
  • Nucleosidases

- Phosphatases

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9
Q

Describe enteric SM and action

A
  • Phasic pacemaker
  • Continual slow intrinsic electrical activity
  • Subtle increase in tension
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10
Q

What is BER?

A
  • Basal electrical rhythm
  • 2 types –> slow waves and spikes
  • Largely controlled by vagus nerve (parasympathetics)
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11
Q

What is MMC?

A

Migrating motor complex

  • Interdigestive housekeeping
  • Makes sure nothing is left in tube
  • 90-120 minutes
  • Stops with feeding
  • Requires extrinsic nervous system
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12
Q

What is peristalsis?

A
  • Gut wall reflex
  • Initiates retrograde circular contraction
  • Moves anterograde
  • Occurrence is independent of extrinsic innervation
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13
Q

2 things that cause contraction (peristalsis)?

A
  • Substance P

- ACh

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14
Q

3 things that cause relaxation (peristalsis)?

A
  • NO
  • VIP
  • ATP
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15
Q

What is released when there is distension in the gut? (bolus detected by stretch receptors)

A
  • 5-HT
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16
Q

What happens to the slow wave rhythm along the length of the intestines?

A
  • Slow wave rhythm DECREASES (12/min in duodenum, 8/min in the ileum)
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17
Q

Why is migration through the colon slow?

A
  • Allow time for Na absorption - therefore time for water absorption
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18
Q

What is the ileocaecal valve?

A
  • Restricts reflux bug movement

- Opens/closes with changes in colon/ileum pressures

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19
Q

Approximately how long does food remain in the caecum/transit time?

A

4 hours

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20
Q

In general, internal sphincters are _____?

A

involuntary

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21
Q

Involuntary sphincters are controlled by what two things?

A
  • Myogenic tone

- Relative pressures

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22
Q

Name the 2 nerve plexuses in the ENS

A
  • Submucosal plexus (Meissner’s)

- Myenteric plexus (Auerbach’s)

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23
Q

Describe the submucosal plexus (ENS)

A
  • Meissner’s
  • Between the mucosa and circular muscle later
  • Controls local secretion and blood flow
  • Chemical digestion
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24
Q

Describe the myenteric plexus (ENS)

A
  • Auerbach’s
  • Between the circular and longitudinal muscle layers
  • GI tract motility
  • Mainly coordinates longitudinal muscle movement
  • Mechanical digestion
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25
Q

What ANS stimulates the ENS? (increases secretions and activity)

A

Parasympathetic

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26
Q

What ANS inhibits the ENS? (decreases secretions and activity)

A

Sympathetic

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27
Q

What is the gastrocolic reflex?

A

Stomach –> colon evaculation

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28
Q

What is the enterogastric reflex?

A

Colon –> SI (inhibit stomach motility and secretion)

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29
Q

What is the colonoileal reflex?

A

Colon –> ileum (inhibit ilieal emptying)

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30
Q

Describe secretin

A
  • Duodenal S cells
  • Secreted in response to acid
  • Mildly inhibits GIT motility
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31
Q

Describe CCK

A
  • Duodenal and jejunum I cells
  • Secreted in response to FA and sugar
  • Moderate inhibitor of GIT motility
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32
Q

Describe motilin

A
  • Duodenal and jejunum M cells
  • Secreted in response to high pH
  • Initiates MMC
  • Suppressed by feeding
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33
Q

Name the 4 phases of digestion

A
  • Interdigestive phase
  • Cephalic phase
  • Gastric phase
  • Intestinal phase
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34
Q

Describe the cephalic phase

A
  • Largely neural control
  • Smell/sight etc - activates neural centres
  • Vagus = stimulatory
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35
Q

Describe the gastric phase

A
  • Neural and hormonal control

- Food enters stomach - promotes gastric secretions and motility (vaso-vagal reflex)

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36
Q

Describe the intestinal phase

A
  • Largely hormonal
  • Begins when food enters SI
  • Stimulates flow of bile and pancreatic juices
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37
Q

Name the 3 types of exocrine glands in the stomach mucosa and what they secrete

A
  • Mucous necks cells = mucous
  • Parietal cells = IF and HCl
  • Chief cells = pepsinogen and gastric lipase
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38
Q

Name the 3 types of endocrine cells and what they secrete

A
  • G cells = gastrin

- D cells = somatostatin

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39
Q

What is the volume of the stomach when empty and when full?

A
  • 150mL

- 1500mL

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40
Q

Gastric emptying based on food type

A

CHO > protein > fay

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41
Q

Name 3 things that inhibit gastric emptying

A
  • CCK
  • Secretin
  • GIP
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42
Q

Name things (not substances) that decrease gastric emptying

  • ANS
  • Acidity
  • Fat/AA
  • Tonicity
A
  • Increased SNS
  • Decreased PNS
  • Increased acidity
  • Increased fat
  • Increased AA
  • Hypertonicity
  • Distension
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43
Q

What do ECL cells do?

A
  • Secrete histamine
  • Secrete in response to ACH and gastrin
  • Stimulate gastric acid secretion
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44
Q

Where in the stomach is the oxyntic (acid producing) gland area?

A
  • Body and fundus
  • Proximal 80%
  • Secretes HCl, pepsinogen, IF, mucus
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45
Q

What proton pump drives acid transport?

A
  • H+/K+ ATPase proton pump
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46
Q

Where are acid producing proton pumps found?

A
  • Canalicular membrane of secreting cells
  • Vesicles of quiescent cells (endocytosed when not active)
  • Inhibited by PPI
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47
Q

3 roles of gastrin

A
  • Stimulate acid release from parietal cells
  • Stimulate histamine release from ECL cells
  • Stimulate pepsinogen release from cheif cells
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48
Q

What two cells does somatostatin inhibit? (released by D cells)

A
  • G cells

- Parietal cells

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49
Q

What things stimulate pepsinogen secretion?

A
  • ACh (vagus)
  • Histamine (ECL)
  • Gastrin (G cells)
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50
Q

What is the gastric lumen protective barrier?

A

A mucous layer containing bicarbonate for protection (secreted by surface epithelium)

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51
Q

What is the transcellular route?

A
  • Across apical and basolateral membrane (need at least one active transporter)
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52
Q

What is the paracellular route?

A
  • Through the intercellular space - passive
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53
Q

What is the dominant cation in the cell?

A
  • Potassium
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54
Q

What is the dominant cation outside the cell?

A
  • Sodium
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55
Q

What is the ion movement in the sodium/potassium pump?

A
  • 3 sodium out, 2 potassium in
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56
Q

Name a type of indirect active transport

A
  • Sodium glucose symporter (process driving by high extracellular sodium concentration)
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57
Q

What is most of the water absorbed in the GIT?

A
  • Small intestines (small quantities in the stomach and colon)
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58
Q

Where are most of the electrolytes and mineral absorbed in the GIT?

A
  • Small intestines - can be active or passive
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59
Q

4 mechanisms of Sodium absorption

A
  • Passive diffusion (distal colon)
  • Na-glucose or Na-AA cotransport (jejunum and ileum)
  • Na-H exchange (duodenum and jejunum)
  • Parallel Na-H and Cl-HCO3 exchange (ileum and proximal colon)
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60
Q

3 mechanisms of Chloride absoprtion

A
  • Passive diffusion (Jejunum, ileum and distal colon)
  • Cl-HCO3 exchange (ileum, proximal colon and distal colon)
  • Parallel Na-H and Cl-HCO3 exchange
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61
Q

Chloride secretion - 4 types of channels

A
  • CaCC (Ca activated Cl channels)
  • VRAC (volume regulated anion channels)
  • LGAC (ligand gated anion channels)
  • CFTR (CF transmembrane conductance regulator)
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62
Q

Opening of CFTR

A
  • cAMP activated PKA
  • Phosphorylates R-domain
  • Cl moves down its concentration gradient
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63
Q

Closing of CFTR

A
  • PPases dephosphorylates R-domain

- Channel closes

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64
Q

2 mechanisms of potassium absorption

A
  • Passive diffusion (jejunum and ileum)

- Active K-H exchange (distal colon)

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65
Q

2 mechanisms of potassium secretion

A
  • Passive secretion

- Apical K channel powered by basal Na-K pump

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66
Q

Bioavailability depends on 4 factors

A
  • pH
  • Redox state of the metal
  • Dietary complexes which diminish absorption
  • Dietary complexes which enhance solubility
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67
Q

Complexes that INCREASE absorption

A
  • Ascorbate
  • Glutathione
  • Lactate
  • Pyruvate
  • Cysteine
  • Histidine
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68
Q

Complexes that DECREASE absoprtion

A
  • Phytates (cereals)
  • Tannates (tannin in tea)
  • Oxalates (rhubarb, parsley)
  • Carbonates
  • Competition by other minerals
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69
Q

1g of Ca ingested - how much is usually absorbed?

A
  • 0.5g
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70
Q

2 mechanisms by which calcium is absorbed

A
  • Active transcellular route (duodenum)

- Paracellular diffusion (SI)

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71
Q

2 forms of dietary iron

A
  • Haem (meat, blood, muscle)

- Non-haem (vegetables, ferric or ferrous)

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72
Q

What % of ingested iron is actually absorbed?

A

10%

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73
Q

Role of HEPCIDIN

A
  • Closes ferroportin

- Traps iron in cell

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74
Q

What is ferritin?

A
  • Intracellular store of iron
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75
Q

What is transferrin?

A

Transport iron in blood

76
Q

What does Mg absorption efficiency depend on?

A
  • Mg concentration in diet and within the cell
77
Q

How does Mg enter the enterocyte?

A
  • TRPM6 (transient receptor protein 6)

- Cation channel protein

78
Q

Name the 4 fat soluble vitamins

A
  • A
  • D
  • E
  • K
79
Q

What % of a diet should proteins make up?

A

15-20% kJ

80
Q

What % of a diet should fat make up?

A

<30% kJ

81
Q

What % of a diet should CHOs make up?

A

50-55% kJ

82
Q

3 types of fat (forms)

A
  • Triglycerides
  • Cholesterol
  • Phospholipids
83
Q

What is the glycocalyx?

A
  • Enzyme trap

- Brush border enzymes on apical surface

84
Q

Name the 3 monosaccharrides

A
  • Glucose
  • Galactose
  • Fructose
85
Q

Name the 2 starches

A
  • Amylopectin (90%)

- Amylose (10%)

86
Q

What are starches broken down by?

A
  • Alpha-amylases (saliva and pancreatic juice)
87
Q

Name the 2 transporters involved in the absorption of monosaccharides

A
  • SGLT1 (sodium glucose con-transporter 1)

- GLUT5 (facilitated glucose fructose transporter)

88
Q

What needs to be present for glucose to be absorbed?

A
  • Na transport
89
Q

What 2 monosaccharides make up sucrose?

A
  • Glucose

- Fructose

90
Q

What 2 monosaccharides make up lactose?

A
  • Glucose

- Galactose

91
Q

What phenomenon occurs due to the inability to breakdown lactose in the gut?

A
  • Osmotic drag

- Diarrhoea and bloating

92
Q

What is glucoamylase/maltase?

A
  • Removes glucose monomers for transport
93
Q

What is sucrase-isomaltase?

A
  • 2 enzymes

- Splits sucrose, maltose and maltotriose

94
Q

Where does protein absorption occur?

A

Small intestine (digestion in stomach and SI)

95
Q

Where is pepsin found?

A

Stomach - digests 10-15% of dietary protein

96
Q

Where are pancreatic proteases found?

A

Small intestine - convert 70% of luminal protein to oligopeptides and 30% to AA

97
Q

What is PepT1?

A
  • Permits the uptake of di- and tri- peptides
  • Helps break these down further in the enterocyte
  • Requires a hydrogen ion gradient to work
98
Q

Name 3 phospholipids

A
  • Lecithin
  • Cephalin
  • Sphingomyelins
99
Q

What is cholesterol synthesised from?

A

Acetyl-CoA

100
Q

What is a chylomicron?

A
  • Lipoprotein complex that carries lipids from SI through circulation
101
Q

What apolipoproteins are found on mature chylomicrons, and what donates them?

A
  • Apo-C2
  • Apo-E
  • HDL donates these
102
Q

Main functions of the liver

A
  • Filtration and storage of blood
  • Metabolism
  • Bile formation
  • Store iron and vitamins
  • Form blood proteins
  • Inactivate various substances
  • Immunity (Kupffer)
103
Q

Approximate weight of an adult liver

A

1.5 k g(approx 2.5% of body weight)

104
Q

What % of cardiac output does the liver receive at rest?

A

25%

105
Q

What is abundant in hepatocytes?

A

SER and RER

106
Q

Approximately how much blood does the liver hold?

A

450 mL (10%) - can hold up to 1500 mL

107
Q

What are Kupffer cells?

A
  • Liver macrophages
  • Remove 99% of GIT bacteria and endotoxin via endocytosis
  • Involved in iron metabolism
108
Q

T/F? There are vasodilating fibres in portal vein smooth muscle

A

False (only NA controled vasoconstriction)

- All dilation is under local control

109
Q

What is arteriodilation regulated by?

A
  • Adenosine (dilator) clearance

Decrease flow rate = increase adenosine = dilate = increase flow rate

110
Q

What is countercurrent flow?

A
  • Efficient extraction for extensive biochemical modification
111
Q

Pressure in portal vein

A

10 mmHg

112
Q

Pressure in hepatic vein

A

5 mmHg

113
Q

Pressure in hepatic artery

A

90 mmHg

114
Q

Liver is a _____ ____ buffer

A

Blood glucose

115
Q

Glycogenesis is?

A

Glucose to glycogen (storage)

116
Q

Glycogenolysis is?

A

Glycogen to G-1-P to G-6-P to glucose

117
Q

What is gluconeogenesis?

A

Glucose generated from fat and some amino acids - via pyruvate

118
Q

The liver is the primary site for ____?

A

Beta-oxidation - breakdown of FA to acetyl CoA

119
Q

Name of cholesterol synthesis pathway

A

Mevalonate pathway

120
Q

Deamination pathway

A

AA to keto acid to ATP and ammonia

121
Q

What is transamination?

A

Breakdown of AA no longer needed

- Interconversion of non-essential AA

122
Q

5 plasma proteins synthesised by the liver

A
  • Acute-phase protein (CRP, complement, coagulation factors)
  • Albumin
  • Hormone-binding proteins
  • Angiotensinogen
  • Transferring
123
Q

Why is ammonia dangerous to the body?

A
  • Neurotoxic - can freely cross BBB
124
Q

Liver metabolises blood-borne hormones - name 5

A
  • Insulin
  • Glucagon
  • All steroids
  • Vitamin A
  • Vitamin D
125
Q

Vitamin A is stored in the liver for how long?

A

5-10 months

126
Q

Vitamin B12 is stored in the liver for how long?

A

1 year

127
Q

Vitamin D is stored in the liver for how long?

A

2-4 months

128
Q

Ferroxidase catalyses what conversion?

A

Fe2+ to Fe3+ - safe storage

129
Q

Ferroductase catalyses what conversion?

A

Fe3+ to Fe2+ - soluble release

130
Q

Iron is bound to what globular protein in liver?

A

Ferritin

131
Q

What does hepicidin do?

A
  • Released by the liver when plasma iron levels are elevated

- Switches off ferroportin (IREG1) channels in the intestines, liver and spleen

132
Q

What makes bile hypertonic?

A

Active secretion across canalicular membrane

133
Q

What enters the biliary system via active secretion?

A
  • Bile acids, phosphatidylcholine, BG, BG2, cholesterol, xenobiotics, dragged things passively
134
Q

What enters the biliary system by diffusion?

A
  • Water
  • Glucose
  • Ca
  • Glutathione
  • AA
  • Urea
    (Leaky tight junctions)
135
Q

What is secreted into the bile ducts as protection?

A
  • Mucous
  • HCO3-
  • IgA
136
Q

What is bile acid/salt synthesised from?

A
  • Cholesterol
137
Q

Where are primary bile acids synthesised?

A

Hepatocytes - secreted into bile canaliculi

138
Q

What conjugates with bile acids once secreted into bile canaliculi?

A

Glycine or taurine

139
Q

What converts primary bile acids to secondary bile acids?

A

Bacteria in the intestinal lumen

140
Q

How big is the total bile acids pool?

A

3g

141
Q

What % of bile acids in reabsorbed in the terminal ileum and returned to the liver?

A

90-95%

142
Q

What % of the total bile pool does the liver synthesise each day?

A

5-10%

143
Q

Name the 2 enzymes that convert haem to bilirubin?

A
  • Haem oxygenase (haem to biliverdin)

- Biliverdin reductase

144
Q

Where does haemoglobin pahgocytoses occur? (split into globin and haem)

A

RES

145
Q

Where does albumin-bound-bilirubin enter?

A

Space of Disse adjacent to the basolateral membrane

146
Q

How does albumin-bound bilirubin enter the hepatocytes?

A

Organic anion transporting polypeptide (OATP)

147
Q

What causes the conjugation between bilirubin and glucuronic acid?

A

Glucuronyl transferase (UDP-G) on the SER

148
Q

Product of bilirubin and glucuronic acid conjugation

A

Bilirubin di-glucunoride (BG2)

149
Q

How is BG2 pumped into canaliculus?

A

Via multidrug resisance protein 2 (MRP-2)

150
Q

Bugs convert bilirubin (di)-glucunoride into…?

A

Urobilinogens

151
Q

2 broad causes of jaundice

A
  • Haemolytic

- Hepatic

152
Q

What is jaundice of the neonate?

A

Newborn infants have poorly developed bilirubin conjugation enzymes (premature infants more affected)

153
Q

What damage does unconjugated bilirubin cause in jaundice of the neonate?

A
  • Kernicterus - often lethal
154
Q

Nerve that runs near the pancreatic acinus (and what it releases)

A

Vagus nerve - acetylcholine

155
Q

Describe duct cells

A
  • Produce and secrete alkaline fluid
  • Flatter cells
  • Surround intercalated duct
156
Q

Describe acinar cells

A
  • Exocrine
  • Produce and secrete enzymes
  • Grape-like
  • Zymogen granules
  • RER
157
Q

pH of alkaline secretions from the pancrease

A

pH = 8

158
Q

Mixture released by duct cells lining the pancreatic ducts

A
  • HCO3-
  • Na
  • K
  • Water
159
Q

Why is the pancreas not digested itself by the enzymes?

A
  • Proteases synthesised in inactive form

- Trypsinogen converted to trypsin by enterokinase

160
Q

Where is enterokinase found?

A
  • Small intestines - tethered to brush border (not free)
161
Q

Role of trypsin

A
  • Activate other proteases

chymotrypsinogen, procarboxypeptidase

162
Q

What is the trypsin inhibitor produced by?

A

Acinar cells

163
Q

What is acute pancreatitis?

A
  • Pancreas digests itself within hours
164
Q

Inactive proteases are constantly synthesised and stored as _____?

A

Zymogen granules (secretory vesicles)

165
Q

4 things that regulate pancreatic secretions

A
  • ACh from vagus (stimulate HCO3- and enzyme release)
  • Secretin from duodenal S cells (HCO3- production)
  • CCK from gut mucosal I cells (enzyme production and secretion)
  • Somatostatin from intestinal D cells (inhibitory - duct and acinar cells)
166
Q

Nerve that runs near the pancreatic acinus (and what it releases)

A

Vagus nerve - acetylcholine

167
Q

What molecule regulates GB contraction and sphincter of Oddi relaxation?

A
  • CCK
168
Q

Describe acinar cells

A
  • Exocrine
  • Produce and secrete enzymes
  • Grape-like
  • Zymogen granules
  • RER
169
Q

pH of alkaline secretions from the pancrease

A

pH = 8

170
Q

Mixture released by duct cells lining the pancreatic ducts

A
  • HCO3-
  • Na
  • K
  • Water
171
Q

Why is the pancreas not digested itself by the enzymes?

A
  • Proteases synthesised in inactive form

- Trypsinogen converted to trypsin by enterokinase

172
Q

Where is enterokinase found?

A
  • Small intestines - tethered to brush border (not free)
173
Q

What 2 things in the duodenum trigger CCK release?

A
  • Fatty acids

- Amino acids

174
Q

What is the trypsin inhibitor produced by?

A

Acinar cells

175
Q

What is acute pancreatitis?

A
  • Pancreas digests itself within hours
176
Q

Inactive proteases are constantly synthesised and stored as _____?

A

Zymogen granules (secretory vesicles)

177
Q

4 things that regulate pancreatic secretions

A
  • ACh from vagus (stimulate HCO3- and enzyme release)
  • Secretin from duodenal S cells (HCO3- production)
  • CCK from gut mucosal I cells (enzyme production and secretion)
  • Somatostatin from intestinal D cells (inhibitory - duct and acinar cells)
178
Q

3 phases of pancreatic secretion

A
  • Cephalic - 10-20% of secretions
  • Gastric - 5-10% of secretions
  • Intestinal - 80% secretions
179
Q

What molecule regulates GB contraction and sphincter of Oddi relaxation?

A
  • CCK
180
Q

Composition of bile

A
  • 85% water
  • 10% bile salts
  • 3% mucus
  • 0.7% inorganic salts
181
Q

How much bile does the gall bladder hold?

A

-<60mL (but can hold up to 450mL - on day worth of bile)

182
Q

What happens to liver bile when it goes to the gall bladder?

A
  • Becomes acidic (7.4-6.9)
183
Q

Process of gallstone formation

A

Cholithithiasis

184
Q

4 causes of gallstones

A
  • Too much absorption of water from bile
  • Too much absorption of bile acids from bile
  • Too much cholesterol in bile
  • Inflammation of epithelium
185
Q

Substance that causes GB contraction

A

ACh

186
Q

2 substances that cause Sphincter of Oddi relaxation

A
  • NO

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