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Gastroenterology > Physiology > Flashcards

Physiology Flashcards

1
Q

Mouth and Oropharynx functions (3)

A

Chops and lubricates food
Starts carbohydrate digestion
Delivers food to oesophagus

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2
Q

Oesophagus function

A

Propels food to stomach

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3
Q

Stomach functions (3)

A

Stores/churns food
Continues carbohydrate and initiates protein digestion
Regulates chyme delivery to duodenum

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4
Q

Small intestine composition and function (2)

A

Duodenum, jejunum, ileum

Main site of digestion and absorption of nutrients

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5
Q

Large intestine composition and functions (3)

A

Caecum, appendix, colon
Reabsorbs fluids and electrolytes
Stores faecal matter before delivery to rectum

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6
Q

Rectum and Anus function

A

Regulates defecation of faces

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7
Q

Structures of hepatobilliary system (4)

A

Salivary glands
Pancreas
Gall bladder
Liver

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8
Q

Major functions of alimentary channel (4)

A

Motility (Movement) - Mostly from smooth muscle activity but skeletal muscle at mouth, pharynx,upper oesophagus, external anal sphincter
Secretion - Into lumen for digestive, protection and lubrication (In response to food, hormonal and neural signals)
Digestion - Chemical breakdown by enzymatic hydrolysis of complex foodstuff into smaller, absorbable units
Absorption - Transfer of absorbable products from GI tract to blood or lymph

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9
Q

Circular muscle contraction effects

A

Lumen becomes narrower and longer

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10
Q

Longitudinal muscle contraction effects

A

Intestine becomes shorter and fatty

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11
Q

Muscularis mucosae contraction effects

A

Changes absorptive and secretory surface area of mucosa (folding) - Mixing activity

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12
Q

Smooth muscle cells and depolarization in GI tract (2)

A

Adjacent smooth muscle cells are coupled by gap junctions - Allows slow wave of depolarization
Slow depolarization wave causes cells to depolarize and contract at the same time as a synchronous wave

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13
Q

Spontaneous activity across coupled cells is driven by

A

Pacemaker cells modulated by hormones, intrinsic and extrinsic nerves

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14
Q

Interstitial cells of Cajal (ICCs) (4)

A

Pacemaker cells located between circular and longitudinal muscle layers
Determines frequency, direction and velocity of rhythmic contractions
Form gap junctions with smooth muscle cells coupling slow waves
Some form a bridge between nerve endings and smooth muscle cells

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15
Q

Contraction in intestine occurs if (2)

A

The slow wave amplitude is sufficient to reach a threshold to trigger smooth muscle cell Ca2+ AP
Force is related to number of AP discharged - Driven by duration of slow wave above threshold

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16
Q

Frequency of slow waves in stomach

A

3/min

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17
Q

Frequency of slow waves in small intestine

A

8-12/min (Ileum)

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18
Q

Frequency of slow waves in large intestine

A

8-16/min (8 in proximal colon and 16 in sigmoid)

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19
Q

Slow wave amplitude reaches threshold depending on (3)

A

Neuronal stimuli
Hormonal stimuli
Mechanical stimuli

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20
Q

Parasympathetic autonomic innervation of GI tract

A

Preganglionic fibres releasing ACh synapse with ganglion cells (Mostly parasympathetic post-ganglionic neurones) within the enteric nervous system (ENS)

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21
Q

Parasympathetic excitatory effects (3)

A

Increased gastric, pancreatic and small intestinal secretion
Increased blood flow
Smooth muscle contraction

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22
Q

Parasympathetic inhibitory effects (2)

A

Relaxation of some sphincters

Receptive relaxation of stomach

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23
Q

Sympathetic autonomic innervation of GI tract (2)

A

Preganglionic fibres releasing ACh synapse in prevertebral ganglia
Postganglionic fibres releasing noradrenaline innervate mainly enteric neurones and other structures

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24
Q

Sympathetic excitatory influences

A

Increased splinter tone

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25
Q

Sympathetic inhibitory influnces

A

Decreased motility, secretion and blood flow

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26
Q

Enteric Nervous system (3)

A

Intrinsic to GI tissue
Reflex circuits can operate independently but can be regulated by hormones and extrinsic nerves
Coordinates muscular, secretive and absorptive activities through sensory neurones, interneurones, effector neurones

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27
Q

Myenteric (Auerbach’s) plexus function

A

Regulates motility and sphincters

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28
Q

Submucous (Meissner’s) plexus function

A

Regulates epithelium and blood vessels

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29
Q

Intrinsic reflex example

A

Local reflex (Within GI tract)

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30
Q

Extrinsic reflex examples

A

Short (Within spinal cord) and long reflex (Within spinal cord involving vagus nerve twice)

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31
Q

Local reflex example

A

Peristalsis

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32
Q

Short reflex example

A

Intestino-intestinal inhibitory reflex

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33
Q

Long reflex example

A

Gastroileal reflex (vago-vasal reflex)

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34
Q

Submucosa plexus functions (2)

A

Controls muscularis mucosae

Regulates secretion in epithelium

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35
Q

Physiological process where energy intake is matched to energy expenditure over time

A

Promotes fuel body stability

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36
Q

Importance of fat (3)

A

Energy storage
Starvation prevention
Energy buffer during prolonged illness

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37
Q

BMI calculation

A

= Weight (kg)/Height2 (m)

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38
Q

Obesity causes (2)

A

Inactivity

High consumption of fatty foods

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39
Q

Obesity consequences (8)

A 
Stroke
Alzheimer's
NAFLD Non alcohol fatty liver disease
Diabetes
Cancer
Osteoarthritis
Heart disease
Respiratory disease - Sleep apnea
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40
Q

CNS influnces energy and body weight balance by (3)

A

Behaviour - Feeding and physical activity
ANS activity - Regulates energy expenditure
Neuroendocrine system - Hormone secretion

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41
Q

Control of energy intake and body weight

locations (2)

A

Brain - Site of integration

Hypothalamus - Neural centre

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42
Q

Basic concepts of control system of energy intake (3)

A

Satiety signalling
Adiposity negative feedback signalling
Food reward

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43
Q

Satiation definition

A

Sensation of fullness generated during a meal

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44
Q

Satiety definition

A

Period of time between termination of one meal and initiation of next

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45
Q

Adiposity definition

A

State of being obese

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46
Q

Do satiation signals increase/decrease during meal to limit meal size

A

Increase

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47
Q

Satiation signal types (5)

A 
Cholecystokinin (CCK) 
Peptide YY (PYY3-36) 
Glucagon-like peptide 1 (GLP-1) 
Oxyntomodulin (OXM) 
Obestatin
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48
Q

What happens when insulin levels rise in terms of food intake and body weight

A

Inhibit food intake

Decrease body weight

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49
Q

Role of Leptin (7)

A

Food intake/energy expenditure/fat deposition
Peripheral glucose homeostasis/insulin sensitivity
Maintenance of immune system
Maintenance of reproductive system
Angiogenesis
Tumourigenesis
Bone formation

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50
Q

Food Reward mechanism

A

Consumption of sugar and fat triggers dopamine pathways

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51
Q

Obesity treatments (5)

A 
Orlistat
Contrave
Liraglutide
Bariatric surgery 
Adaptive thermogenesis
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52
Q

Orlistat (5)

A

Inhibits pancreatic lipase decreasing triglyceride absorption
Reduces fat absorption in small intestine
Side-effects include cramping, bloating, flatulence, abdominal pain and diarrhoea
Need to take vitamin supplements - Loss of fat soluble vitamins
Not effective long term and tendency of ‘rebound’ weight

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53
Q

Contrave (Mysimba) (2)

A

Dopamine re uptake inhibitor and opioid antagonist

Has cardiovascular safety issues

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54
Q

Liraglutide (Saxenda) (3)

A

Glucagon-like peptide 1 receptor agonist
Used in type 2 diabetes for weight loss via injection
Has concerns over thyroid and pancreatic cancer

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55
Q

Bariatric Surgery (2)

A

Gastric bypass surgery causing weight loss

High incidence of type 2 diabetes resolution due to decreased energy intake

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56
Q

Adaptive thermogenesis (2)

A

Cold exposure increases BAT activity

BAT dissipates fat as heat energy - Causes browing of white adipose tissue

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57
Q

Peristalsis (2)

A

Wave of relaxation followed by contraction

Moves from oral to aboral direction

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58
Q

Propulsive segment of peristalsis (2)

A

Longitudinal muscle relaxes - Release of VIP and NO from inhibitory motoneurone
Circular muscle contracts - Release of ACh and substance P from excitatory motoneurone

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59
Q

Receiving segment of peristalsis (2)

A

Longitudinal muscle contracts - Release of ACh and substance P from excitatory motoneurone
Circular muscle relaxes - Release of VIP and NO from inhibitory motoneurone

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60
Q

Segmentation characteristics (4)

A

Rhythmic contractions of circular muscle layer that mix and divide luminal contents
Occurs in small intestine (in fed state) and large intestine (hastration)
Strength is increased by parasympathetic innervation and decreased by sympathetic innervation
Initiated by small intestine pacemaker cells causing Basal Electric Rhythm which is continuous and slow

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61
Q

What is colonic mass movement

A

Powerful sweeping contraction that forces faeces into rectum – Occurs few times a day

62
Q

What is the Migrating motor complex (5)

A

Powerful slow sweeping contraction from stomach to ileocaecal valve
Occurs between meals
Clears small intestine of debris, mucus and sloughed epithelial cells between meals
Inhibited by vagal activity, feeding, gastrin and CCK
Triggered by motilin

63
Q

6 sphincters of GI tract and their function

A

Upper oesophageal sphincter - Relaxes in swallowing and closes in inspiration
Lower oesophageal sphincter - Relaxes for food entry in stomach and closes to prevent reflux to oesophagus
Pyloric sphincter - Regulates gastric emptying and prevents duodenum gastric reflux
Ileocaecal valve - Regulates flow from ileum to caecum, distension of ileum opens while proximal colon closes
Internal and external anal sphincters - Regulate defaecation reflux

64
Q

Vital part of sphincters

A

Acts as one way valve by maintaining a positive resting pressure

65
Q

Types of stomach mechanical activity (2)

A

Orad (Fundus and proximal body) - Tonic

Caudad (Distal and antrum) - Phasic

66
Q

Orad region mechanical and electrical activity (6)

A

Relaxation driven by vagus occurs during a swallow
No slow wave activity
Weak tonic contractions occurs due to thin musculature
Contents propelled to caudad region by low amplitude tonic contractions (1 min duration) – Decrease stomach size as it empties
Minimal mixing of contents allows carbohydrate partial digestion
Hormone gastrin decreases contractions and stomach emptying rate

67
Q

Caudad region mechanical and electrical activity (3)

A

Slow waves occur continuously
Phasic peristaltic contractions driven by slow waves progress from midstomach to gastroduodenal junction propelling contents towards pylorus through which a small volume of chyme flows into duodenum
Contraction velocity increases towards junction, overtaking chyme movement that rebounds against constricted distal antrum back into relaxed body of stomach – Retropulsion

68
Q

Retropulsion function (2)

A

Mixes gastric contents reducing chyme to small particles

These pass through the pylorus

69
Q

Strength of antral wave or pump is determined by (2)

A

Gastric factors

Duodenal factors

70
Q

Gastric factors (2)

A

Rate of emptying is proportional to volume of chyme

Consistency of chyme

71
Q

Distension increases motility by (3)

A

Stretch of smooth muscle
Stimulation of intrinsic nerve plexuses
Increased vagus nerve activity and gastrin release

72
Q

Duodenum must be ready to receive chyme and delays emptying through (2)

A

Neuronal response - Enterogastric reflex decreases antral activity by signals from intrinsic plexuses and ANS
Hormonal response - Enterogastestrones from duodenum inhibits stomach contraction

73
Q

Stimuli driving hormonal and neuronal response in duodenum (4)

A

Fat - Potent where it slows gastric emptying for digestion and absorption
Acid - Time is required for neutralization via bicarbonate secreted in pancreas (Optimal pH for pancreatic digestive enzymes)
Hypertonicity - Carbohydrate and protein digestion products are osmotically active drawing water into small intestine (Dangers in reduced plasma volume and circulatory disturbances)
Distension

74
Q

Parietal gland areas in the stomach (2)

A

Fundus

Body

75
Q

Pyloric gland area of the stomach

A

Antrum

76
Q

Cells and secretions of pyloric gland area (2)

A

G cells releasing Gastrin

D cells releasing Somatostatin

77
Q

Cells and secretions of parietal gland area (3)

A

Enterochromaffin like cells releasing Histamine
Chief cells releasing pepsinogen
Parietal cells releasing HCl, Intrinsic factor, Gastroferrin

78
Q

What effect does Gastrin and Somatostatin have on each other

A

They oppose each other

79
Q

Enterochromaffin like cells characteristics (2)

A

Not part of gastric gland lining

Histamine produced acts on parietal cells

80
Q

HCl functions (3)

A

Activates pepsinogen to pepsin
Denatures proteins
Kills microorganisms digested in food

81
Q

Pepsinogen and pepsin relationship (2)

A

Inactive precursor of pepsin

Pepsin formed activates pepsinogen - Autocatalytic

82
Q

Intrinsic factor and Gastroferrin function

A

Bind vitamin B12 and Fe2+ respectively, facilitating absorption

83
Q

Histamin function

A

Stimulates HCl secretion

84
Q

Somatostatin function

A

Inhibits HCl secretion

85
Q

HCl production (6)

A

Carbonic anhydrase combines CO2 with H2O to make H2CO3-
H2CO3- dissociates to H+ and HCO3-
For dissociation of H2CO3- to occur Na+ concentration must be low - Na+/K+ ATPase pumps Na+ outwards
H+/K+ ATPase pumps H+ out and K+ in from parietal cell to canaliculus (Secretory area)
HCO3- is transported into plasma by Cl-/HCO3- antiporter and transports Cl- into canaliculus via CFTR channel
K+ re enters the canaliculus by K+ channels in apical membrane

86
Q

3 secretagogues inducing acid secretions

A

ACh
Gastrin
Histamine

87
Q

H+/K+ ATPase location in resting state of parietal cells

A

Within cytoplasmic tubulovesicles

88
Q

H+/K+ ATPase location in stimulated state of parietal cells

A

Moves to apical membrane embedded in extended microvilli

89
Q

3 phases of gastric acid secretion

A

Cephalic phase - Stomach preparation to receive food
Gastric phase - When food is in stomach (Physical and chemical mechanisms)
Intestinal phase - Once chyme enters small intestine causing weak gastric section stimulation

90
Q

Cephalic phase (5)

A

Driven by CNS and vagus nerve
Vagus stimulates enteric neurones;
Releasing ACh activating parietal cells
Release of Gastrin releasing peptide, releasing Gastrin from G cells activating parietal cells
Release histamine from enterochromaffin like cells activating parietal cells
Inhibits D cells decreasing somatostatin inhibitory effect on G cell

91
Q

Gastric phase (3)

A

Stomach stretch activates reflexes causing acid secretion
Food buffers pH increase inhibits somatostatin release
Amino acids, Ca2+, caffeine and alcohol stimulate G cells

92
Q

Inhibition of gastric acid secretion in each phase (3)

A

Cephalic phase - Vagal nerve activity decreases
Gastric phase - Antral pH falls when food exits stomach causing somatostatin release and prostaglandin continually secreted reduces histamine, reducing HCl secretion
Intestinal phase - Factors reducing gastric motility reduces gastric secretion

93
Q

Gastrin functions (2)

A

Stimulates HCl secretion

Growth of gastric mucosa - Trophic effect

94
Q

Hormones of small intestine (6)

A 
Secretin
Cholecystokinin
Glucose-dependent insulinotropic peptide (GIP)
Glucagon-like peptide-1 (GLP-1) 
Motilin
Ghrelin
95
Q

Secretin characteristics (2)

A

Released from H+ and fatty acid presence

Promotes pancreatic and billiary HCO3- secretion

96
Q

Cholecystokinin (CCK) characteristics (5)

A

Released in response to monoglycerides, fatty acids, amino acids and small peptides
Inhibits gastric emptying
Promotes secretion of pancreatic enzymes
Stimulates sphincter of Oddi relaxation and contraction of gall bladder
Potentiates secretin action

97
Q

Glucose-dependent insulinotropic peptide (GIP) characteristics (3)

A

Released in response to glucose, amino acid and fatty acids
Stimulates insulin release
Inhibits gastric emptying

98
Q

Glucagon-like peptide-1 (GLP-1) characteristics (4)

A

Released from L cells of small intestine
Stimulates insulin secretion
Inhibits glucagon secretion
Decreases gastric emptying and appetite

99
Q

Motilin characteristics (2)

A

Released from M cells in fasting state

Initiates migrating motor complex

100
Q

Ghrelin characteristics (2)

A

Released from Gr cells

Stimulates appetite

101
Q

Succus entericus characteristics (3)

A

Small intestine juice
Control mechanisms -Distension, gastrin, CCK, secretion, parasympathetic and sympathetic nerve activity
Secretion is made of mucus (protection/lubrication), aqueous salt (enzymatic digestion) but no digestive enzymes

102
Q

Secretion of small intestine involves which components (3) and note

A

Na+/K+ ATPase - Moves K+ from interstitial space to enterocyte and vice versa for Na+
Na+/K+/2Cl- co-transporter - All ions travel from interstitial space to enterocyte
Cl- channel (CFTR) - Moves Cl- from enterocyte to lumen
NOTE: Na+ is osmotically active so it travels from interstitial space to lumen through crypts of Lieberkuhn

103
Q

Endocrine pancreatic secretions (2)

A

Insulin

Glucagon

104
Q

Exocrine pancreatic secretions and by what cells (2)

A

Digestive enzymes by acinar cells

Aqueous NaHCO3- solution by duct cells

105
Q

Secretion of pancreatic duct cells (7)

A

Carbonic anhydrase combines CO2 from basolateral membrane and H2O to make H2CO3 that dissociates into HCO3- and H+
Na+/Cl- cotransporter brings in HCO3- and Na+
Na+/K+ATPase pumps K+ in and Na+ out
Na+/H+ exchanger causes H+ to move out
K+/H+ATPase (proton pump) exports H+ and imports K+
Cl-/HCO3- exchanger secretes HCO3- to lumen and imports Cl- from lumen
CFTR Cl- channel moves Cl- into lumen by second messenger system mediated by secretin

106
Q

Inactive to active pancreatic enzymes (3)

A 
Trypsinogen to Trypsin
Chymotrypsinogen to Chymotrypsin
Procarboxypeptidase
A and B to Carboxypeptidase
A and B
107
Q

Control of pancreatic secretion (3)

A

Cephalic phase - Mediated by vagal stimulation
Gastric phase - Distension evokes vagovagal reflex (Parasympathetic stimulation of acinar and duct cells)
Intestinal phase

108
Q

Carbohydrate digestion key point

A

All dietary carbohydrate must be converted to monosaccharides for absorption

109
Q

Sequence of carbohydrate digestion (3)

A

Intraluminal hydrolysis => membrane digestion at brush border => Absorption (Transport process)

110
Q

Alpha amylase role (4)

A

Endoenzyme
Breaks down linear internal α-1,4 linkages but not terminal α-1,4 linkages - No glucose made
Cannot cleave α-1,6 linkages at branch points or α-1,4 linkages adjacent to branch points
Products are liner glucose oligomers - Maltose

111
Q

Oligosaccharidases properties (3)

A

Integral membrane proteins with catalytic domain
Faces GI lumen
Cleave terminal α-1,4 linkages of maltose, maltotriose and α-limit dextrins

112
Q

Lactase is broken down to

A

Glucose and galactose

113
Q

Maltase rose function

A

Degrade α-1,4 linkages in straight chain oligomers up to 9 monomers in length

114
Q

Sucrase role

A

Hydrolyses glucose to fructose

115
Q

Isomaltase role

A

Splits branching α-1,6 linkages of α-limit dextrins

116
Q

Absorption of glucose, galactose and fructose (3)

A

Occurs in duodenum and jejunum
Glucose and galactose are absorbed by secondary active transport mediated by SGLT1
Fructose by facilitated diffusion mediated by GLUT5
Exit for all monosaccharides is mediated by facilitated diffusion by GLUT2

117
Q

Mode of Operation of SGLT1 (6)

A

2Na+ binds
Affinity for glucose increases where glucose binds
Na+ and glucose translocate from extracellular to intracellular
2Na+ dissociate, affinity for glucose falls
Glucose dissociates
For ORT to work both Na+ and glucose must increase proportionally

118
Q

4 major pathways for protein digestion

A 
Luminal enzymes (protein to amino acids) => Apical membrane transporters (Amino acids in enterocyte) => Basolateral membrane transporters (Amino acid in blood)
2nd one has brush border in between luminal enzymes and apical membrane transporters converting peptides to amino acids
3rd one has intracellular hydrolysis converting peptides to amino acids in enterocytes
4th one is when peptide is transported out of enterocyte without intervening intracellular hydrolysis
119
Q

Which enzymes are endopeptidases and make oligopeptides (3)

A

Trypsin
Chymotrypsin
Elastase

120
Q

Which enzymes are exopeptidases and make single amino acids (2)

A

Carboxypeptidase A and B

121
Q

Brush border peptidases characteristics (3)

A

Numerous types due to variance in peptide bonds
Have affinity for larger oligopeptides
Can be either endopeptidases or exopeptidases - Exopeptidases are comprising aminopeptidases and carboxypeptidases

122
Q

Cytoplasmic peptidases characteristics (2)

A

Less numerous than brush border peptidases

Hydrolyses di- and tri-peptides

123
Q

Protein Absorption of amino acids (6)

A

Brush border has 7 mechanisms
5 are Na+ dependent co transporters mediating uphill movement - Secondary active transport
2 are Na+ independent mediating cationic amino acid uptake
Basolateral membrane has 5 different mechanisms
3 are Na+ independent mediating amino acid efflux
2 are Na+ dependent mediating amino acid influx

124
Q

Protein Absorption of Di-, tri-, and tetra-peptides (3)

A

Via H+ dependent mechanism at brush border
Further hydrolysed to amino acids within enterocyte
Na+-independent systems at basolateral membrane - Facilitated transport

125
Q

Scheme mechanism of amino acid absorption (3)

A

Na+ enters enterocyte from lumen and exits at interstitum
K+ moves in enterocyte from interstitum
Amino acid moves in enterocyte and interstitum by facilitated diffusion

126
Q

Scheme mechanism of oligopeptide absorption (3)

A

Na+ enters enterocyte from lumen and exits at interstitum - But has H+ moving out to lumen too
K+ moves in enterocyte from interstitum
Oligopeptide moves in enterocyte with H+ (to maintain concentration gradient) and then into interstitum by facilitated diffusion

127
Q

Emulsion droplet stabilization (3)

A

Droplets produced by mechanical disruption produces large SA to volume ratio
Increases oil-water interface digestion for lipases and esterases
Droplets are stabilized by addition of a amphiphilic coat of molecules forming a surface layer on droplet

128
Q

Lipid digestion of TAG of stomach (4)

A

By gastric lipases secreted by chief cells in response to gastrin
Has optimum pH 4
Hydrolyses TAG at 3rd position
Forms Diacylglyceral and free fatty acid

129
Q

Lipid digestion of TAG of intestine (4)

A

By pancreatic lipases secreted from acinar cells in response CCK
Full activity requires colipase cofactor, alkaline pH, Ca2+, bile salts, fatty acids
Hydrolyses TAGs at 1st and 3rd positions
Forms 2-monoacylglycerol and 2 free fatty acids

130
Q

Role of bile salts (3)

A

Emulsifies large lipid droplets
Absorbs fat soluble vitamins
Insufficiency leads too steatorrhoea

131
Q

Mechanism of bile salts (2)

A

Increases SA for pancreatic lipase but block enzyme access - So colipase binds to bile salt and lipase allowing access
Colipase is secreted as inactive procolipase - Activated by trypsin

132
Q

Where are the final products of lipid digestion stored and released from

A

Mixed Micelles

133
Q

Cylomicron formation (3)

A

Monoglycerides and free fatty acids make TAG in ER
Phospholipid synthesis and cholesterol esters makes nascent chylomicron
Nascent chylomicron the coated with Apolipoprotein ApoB-48 to make chylomicron

134
Q

Cholesterol absorption

A

Due to endocytosis in clatherin coated pits by NPC1L1 protein

135
Q

Ca2+ absorption (3)

A

By passive paracellular and active transport mechanisms
Active Ca2+ absorption is regulated by 1,25-dihydroxyvitamin D3 (calcitriol) and parathyroid hormone (increases 1,25-dihydroxyvitamin D3 synthesis)
Ca2+ channel (NOT voltage gated) and Ca2+ ATPase expression increased by 1,25-dihydroxyvitamin D3

136
Q

Dietary iron forms

A

Inorganic
Haem - Most absorbed
Ferratin - Iron store

137
Q

Iron deficiency causes

A

Microcytic anaemia

138
Q

Iron excess causes

A

Production of hydroxyl radicals and hydroxide ions in liver, pancreas and heart

139
Q

Overview mechanism of iron absorption (5)

A

Fe2+ absorbed across the apical membrane by transport process
Fe2+ conveyed to basolateral membrane via ‘molecular chaperone’
Fe2+ transported across the basolateral membrane by transport process
Fe2+ oxidized to Fe3+ and then transported to tissues
Import of haem across apical membrane followed by cytoplasmic metabolism to release Fe2+

140
Q

Reduction of Fe3+ is promoted via (4)

A

HCl
Vitamin C
Ferric reductase - Duodenal cytochrome B
Gastroferrin - Reversibly binds Fe2+ preventing formation of insoluble anion salts

141
Q

Mechanism detail of iron absorption (4)

A

Fe2+ influx is transported by Mobilferrin
Fe2+ efflux is mediated by Ferroportin 1
Some Fe2+ binds with apoferratin and is stored as ferratin
Haem entering is oxidised to release Fe2+ and Biliverdin

142
Q

Transport of iron

A

Hephaestin oxidises Fe2+ before entering blood

143
Q

Absorption of vitamin B12 (7)

A

Vitamin B12 ingested in food bound to proteins => Stomach acid releases vitamin B12 from protein => Haptocorin secreted in saliva binds vitamin B12 released in stomach => Stomach parietal cells release intrinsic factor
=> Stomach parietal cells release intrinsic factor => Vitamin B12 binds to intrinsic factor in small intestine => Vitamin B12-intrinsic factor complex absorbed in terminal ileum by endocytosis

144
Q

Fat soluble vitamin absorption (5)

A

Absorption requires adequate bile secretion and an intact intestinal mucosa
Incorporated into mixed micelles
Usually passively transported into enterocytes
Incorporated into chylomicrons or VLDLs
Distributed by intestinal lymphatics

145
Q

Water soluble vitamin absorption (5)

A

B complexes (EXCEPT B12), C, H
Either Na+ dependent or independent
Vitamin B9 - pH gradient (independent)
Vitamin C - Couples 2 Na+ inward to 1 ascorbate (dependent)
Vitamin H - Couples 2 Na+ inward to 1 biotin (dependent)

146
Q

Relation of external and internal anal sphincter (2)

A

Internal is surrounded by skeletal muscle of external anal sphincter
Teniae coli encircles rectum and anal canal

147
Q

Caecum characteristics (3)

A

Material entry permitted by gastroileal reflex in response to gastrin and CCK through one-way ileocaecal valve
Valve acts by maintaining a positive pressure, relaxation from duodenum distension, contraction to ascending colon distension
Under control by vagus nerve, sympathetic nerves, enteric neurones and hormonal signals

148
Q

Appendix properties (3)

A

Blind ended tube
Extensive lymphoid tissue connected to distal caecum via appendiceal orifice
Orifice can be obstructed by faecalith - Causes appendicitis

149
Q

Colon primary functions (5)

A

Absorption of Na+, Cl-, H2O - Condense ileocaecal material to solid stool
Absorbs short fatty acid chains - Carbohydrates not absorbed by small intestine so fermented by colonic flora first
Secretion of K+, HCO3-, mucus
Stores colonic contents
Eliminates faeces - Made of water, cellulose, bacteria, bilirubin, salts

150
Q

When rectum is full changes (2)

A

Smooth muscle in internal anal sphincter relaxes

So external anal sphincter controls defaecation

Gastroenterology (11 decks)

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