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Physiology Flashcards

1
Q

What nervous system is stimulatory to the enteric NS and what is inhibitory?

A

Sympathetic is inhibitory, and PNS is stimulatory

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2
Q

How does the sympathetic NS and the PNS have effects on the GI system?

A

SNS has effects on blood vessels, secretory cells and the enteric NS

PNS has only effects on the enteric NS

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3
Q

Three main salivary glands?

A

Sub-maxillary gland

Parotid

Sub-lingual

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4
Q

Main composition of saliva?

A

Enzymes: amylase, lipase, lysosymes

Inorganic: Ca++, Phosphate, K+, Cl-, Na+

Organic: Urea, citrate, AA’s, Steroid hormones

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5
Q

Functions of saliva?

A

Moistens food

Digests food

Buffer action

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6
Q

What are the effects of the SNS and PNS on salivary glands?

A

SNS causes vasoconstriction, and less secretion

PNS causes vasodilatation and more secretion

When both are activated the PNS overrides the action of the SNS

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7
Q

Two phases of saliva secretion?

A

Cephalic phase triggered by sight/smell of food

Reflex phase triggered by chewing

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8
Q

Actions of the two oesophageal sphincters?

A

UOS - prevents air swallowing

LOS - prevents acid reflux

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9
Q

Phases of swallowing?

A
  1. Close nasal opening
  2. Displace larynx superiorly and anteriorly
  3. Close epiglottis
  4. Relax UOS
  5. Contract pharynx
  6. UOS contracts
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10
Q

Phases of gastric acid secretion?

A

Cephalic phase - sight/smell of food

Gastric phase - presence of food in stomach causes gastrin secretion

intestinal phase - food in the duodenum first stimulates motility + acid secretion then inhibits it.

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11
Q

Three parts of the stomach?

A

Fundus (superior)

Body

Antrum (inferior)

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12
Q

What cells release H+ into the stomach lumen?

A

Parietal cells

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13
Q

What two compounds stimulate the release of H+ into the stomach lumen?

A

Histamine and gastrin

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14
Q

What things can induce vomiting?

A

Blood-borne stimuli affecting the CTZ

Intestinal blockage

Smells/tastes/sights affecting the VC in reticular formation

Labyrinthian system affecting the VC

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15
Q

Stages of vomiting?

A

Retching - rhythmic contractions of the diaphragm and abdominal muscles against a closed glottis

Stomach tone in fundus and peristaltic activity is decreased

Duodenal and proxial jejunal tone is increased, duodenal contents reflux back into stomach

Strong contractions LOS opens, mouth opens

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16
Q

Consequences of vomiting?

A 
Metabolic alkalosis
Hypovolaemia
Hypokalaemia
Hyponatraemia
Mallory Weiss tear
Fatigue
Teeth damage
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17
Q

What is trypsinogen converted to and by what?

A

To trypsin by enteropeptidase

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18
Q

What three enzymes of pancreatic secretion are converted to their active forms by trypsin?

A

Chymotrypsinogen to Chymotrypsin

ProcarboxypeptidaseA,B to carboxypeptidase A,B

Proelastase to Elastase

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19
Q

Enzymes in pancreatic secretions?

A

Trypsin, Chymotrypsin, carboxypeptidase A,B, Elastase

Amylase, Lipase, Nuclease, Kallikrein

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20
Q

What four things control pancreatic secretion?

A

Secretin: Na+ and H2O secretion

CCK and gastrin: Stimulates enzyme secretion

Vagus nerve activity: increased enzyme and H2O and Na+ secretion

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21
Q

When is secretin released, where and it’s effects?

A

Cells in lieberkuhn crypts release it in low pH

Stimulates Na+ and H2O release in pancreas

Inhibits stomach acid secretion

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22
Q

When is CCK released and it’s effects?

A

Stimulus is food in duodenum/jejunum

Stimulates gall bladder contraction

Stimulates pancreatic enzyme secretion

Some gastrin-like activity

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23
Q

Phases of pancreatic secretion?

A

Cephalic phase by vagus

Gastrin phase by the distension of the stomach

Intestinal - secretin, CCK and vagus stimulates

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24
Q

Components of bile?

A

Bile acids

Phospholipids

Cholesterol

Bile pigments

Protein

Inorganic ions: Na+, K+ e.t.c.

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25
Q

How is bilirubin formed?

A

From the breakdown of haemoglobin

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26
Q

What is free bilirubin?

A

Unconjugated bilirubin, usually travels bound to plasma proteins

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27
Q

What happens to free bilirubin once it is taken up by the liver?

A

It is conjugated and then secreted into the bile through the bile duct

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28
Q

What can cause dark urine? Why?

A

Biliary obstruction: conjugated bilirubin will pass into the blood and then go to the urine

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29
Q

Process that conjugated bilirubin follows as it is converted to stercobilin?

A

Conjugated bilirubin is converted by bacteria to urobilinogen

Urobilinogen to urobilin

Urobilin to Stercobilinogen

Stercobilinogen to Stercobilin (brown colour in faeces)

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30
Q

What are the three signs of excessive haemolysis, relating to bilirubin? Why?

A

Jaundice (free and conjugated bilirubin in plasma)

Yellow urine (Urobilin in plasma)

Dark faeces (more stercobilin in the gut)

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31
Q

What are the three signs of Biliary obstruction, relating to bilirubin? Causes?

A

Jaundice (excessive plasma bilirubin in skin)

Dark Urine (excessive conjugated bilirubin in urine)

Pale faeces (bile pigments do not reach lower gut)

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32
Q

What are the three signs of liver failure in relation to bilirubin? Causes?

A

Jaundice (excessive free bilirubin in skin)

Pale urine (conjugated bilirubin not in plasma)

Pale faeces (stercobilinnot formed in gut)

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33
Q

Three things that stones can be made of?

A

Cholesterol

pigment

Mineral (Ca2+)

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34
Q

How does bile reach the duodenum?

A

Between meals the sphincter at the base of the bile duct is contracted to divert bile into the gall bladder

Food in the duodenum causes CCK to be released which causes the gall bladder to contract

The sphincter opens and bile passes into the duodenum as food passes through

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35
Q

What is the function of bile acids?

A

Promote choleresis (bile flow)

Stimulate phospholipid secretion

Help solubilise cholesterol in the bile duct and gall bladder

Emulsify lipids in the jejunum

Aid absorption of fat soluble vitamins A, D, E and K

Stimulate colonic motility

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36
Q

Why do bile acids not reach the colon?

A

Reabsorbed in terminal ileum

37
Q

What are the two proteins that bind B12 in the human body, how do they function together to absorb B12 into the body?

A

R protein and Intrinsic Factor

R protein saturates B12 with a higher affinity than IF

In the stomach most B12 is bound to R protein, in the jejunum R protein is digested and B12 moves to IF instead

When bound to IF it binds to a cell surface receptor which is then internalised and B12 moves to the ECF

38
Q

What does reduced B12 absorption cause?

What is it called when its due only to lack of intrinsic factor?

A

Anaemia

Pernicious anaemia

39
Q

Why does a continuous bleed of only a few ml a day so easily lead to anaemia?

A

Only a small amount of iron is absorbed daily, and only a small amount of red cells with new iron are produced, most is recycled, so therefore a loss of more red cells than are made will cause anaemia

40
Q

How is iron taken into the body?

A

DMT (Divalent metal transporter) uptakes iron into epithelial cells

In epithelial cells some iron binds to ferritin and some passes into blood and transported bound to transferrin

The ferritin iron stays in the cell and is not used

EPO decreases the production of ferritin and therefore increases the amount of iron in the bloodstream

41
Q

How is Vitamin D made into calcitriol?

A

Vit D made in the skin under UV light

Hydroxylated at position 25 in the Liver

Hydroxylated at position 1 in the kidneys

42
Q

Major action of calcitriol?

A

Promote Gi absorption of calcium

43
Q

How is Copper taken into the body?

A

Taken up into epithelial cells by the DMT transporter

Then transported from epithelial cells to the ECF by an ATPase

Travels bound to plasma proteins and amino acids

Taken into cells by amino acids, then the excess secreted by menkes ATPase

44
Q

What is Menke’s disease and Wilsons disease?

A

Menke’s disease - Low activity of Menke’s ATPase

Wilsons disease - inability to excrete copper into the bile

45
Q

How long does the chyme take to transverse the small intestine?

A

3-5hrs

46
Q

What is an MMC or migrating myoelectric complex?

A

A burst of intense activity in the intestine, repeated every 90mins or so in the fasting state to clear debris

47
Q

What initiates an MMC?

A

The hormone motilin

48
Q

What is somatostatin, two examples of what causes it’s release?

A

Inhibits gastrin secretion

Excess acid and CCK causes D cells to release it

49
Q

Why is the amount of chyme that enters the duodenum through the pylorus regulated?

A

Because the chyme has a high osmotic activity and even more so when it is further broken down, if not regulated there would be fluid expansion from the epithelium, possibly causing syncope

50
Q

What is in the ‘intestinal juice’?

A

Duodenal (from Brunner’s glands):

  • Mucus
  • Pepsinogen II
  • EGF
  • Bicarbonate

Intestinal glands

  • Mucus
  • Enteropeptidase
  • Bicarbonate
51
Q

What are the main protein digesting enzymes?

A

Pepsin, trypsin, chymotrypsin, carboxypeptidases, elastase

52
Q

What converts pepsinogen to pepsin?

A

H+ and also pepsin itself

53
Q

How efficient is fat absorption in the body?

A

Very, 95% absorbed.

54
Q

What does lipase do to triglycerides? What happens to the products of this?

A

Turns them into a monoglyceride and two free fatty acids

These are taken up in micelles and then taken into epithelium, reconstituted to triglycerides and then transported in chylomicrons

55
Q

What are the 4 fat-soluble vitamins, how are they transported into the body?

A

Vit A, D, E and K

Transported into the body via micelles

56
Q

What is the total uptake of water from the GI system?

A

11 Litres

57
Q

Differences in water absorption in duodenum, jejunum, ileum and colon?

A

The duodenum is very permeable and there tends to be a osmotic flow into the lumen

The jejunum has a rapid absorption of sodium, cholride, bicarbonate, sugars and amino acids

The ileum has a smaller surface area than the jejunum and transport is not as rapid

The colon powerfully reabsorbs sodium chloride and water, whilst potassium is actively secreted and bicarb is in exchange for chloride

58
Q

What does each of these do to absorption and secretion in the intestine.

  1. Stimulation of the sympathetic nervous system
  2. Stimulation of the Parasympathetic nervous system
  3. Aldosterone and Angiotensin II
  4. Histamine
A
  1. Sympathetic NS: Decreases secretion and increases absorption
  2. PNS: Increases secretion, decreases absorption
  3. Promote absorption
  4. Increase secretion and decrease absorption
59
Q

Main role of all the sodium that is absorbed in the GI tract?

A

Used to absorb the products of digestion and carbohydrates

60
Q

Three main reasons for diarrhoea?

A

Increased rate of transit: e.g. IBS or laxatives

Failure to absorb e.g. Familial chloride diarrhoea, Damaged mucosa

Increased secretion e.g. ‘Pancreatic Cholera’, Cholera Disordered prostaglandin metabolism

61
Q

How does cholera produce diarrhoea?

A

Cholera recognises ganglioside Gm1 (a glycolipid)

catalyses the transfer of ADP to the α subunit, adenylyl cyclase is constantly stimulated, causing constant secretion

62
Q

Innate defence mechanisms of the GI system to infection?

A

Mucus forms physical barrier

Trefoil factors - aid barrier repair and wound healing

Defensins (antimicrobial proteins)

63
Q

What cells synthesise defensins?

A

Paneth cells

64
Q

What is the immunological lining of the gut called?

A

Gut associated lymphoid tissue (GALT)

65
Q

What is the Waldeyer ring?

A

Tonsils and adenoids which form a ring at the entrance to the gut and airways

66
Q

What are Peyers patches?

A

Patches in the small intestine that contain 30-40 lymphoid follicles

67
Q

What are microfold cells (M cells)?

A

They are cells in the gut that are in the epithelial barrier over peyers patches, they transfer particles from the gut to antigen presenting cells at the basal layer

68
Q

What is pocketing in M cells?

A

When a ‘pocket’ forms in the M cell to allow antigens to be presented to T memory cells, B cells and APC

69
Q

What infectious organisms exploit M cells?

A

Salmonella, Cholera and polio

70
Q

What is the antibody of the mucosal immune system, what are the two forms?

A

IgA - IgA1 and IgA2

71
Q

Where/how is IgA made

A

Made in plasma cells of gut lamina propria

Transported across epithelial cells

Released into gut lumen, where it binds to mucus

72
Q

What are intra-epithelial lymphocytes?

A

Unconventional T cells that were concentrated in the gut

73
Q

Functions of the large intestine?

A

Absorption of salt and water

Secretion of potassium and bicarbonate

Manufacture of some vitamins by some bacteria

74
Q

Is the ileo-caecal valve normally open or closed? Why?

A

Closed - don’t want colon contents e.g. bacteria refluxing into the ileum

75
Q

What causes the ileo-caecal valve to open?

A

Material in ileum induces peristalsis, producing the gastro-ileal reflex

76
Q

What happens in the proximal and distal colon?

A

Proximal is where water and salt absorption mostly occurs

Distal is where thick paste is moved anally by short range peristalsis

77
Q

What is the gastro colonic reflex

A

Colonic movements: Acts by vagus and pelvic innervation, with gastrin and CCK playing a role, about 30 mind after a meal

78
Q

Two types of colon movements?

A

Colono-colono reflexes

Gastro-colonic reflex

79
Q

What hormone controls ion movements in the colon?

A

Aldosterone

80
Q

Mechanism for ion movements in the colon?

A

Tight junctions have a very low permeability, causing a very high PD across the colon

81
Q

How is the urge to defaecate produced?

A

Mass movements of distal colon fill the rectum

Distension of rectum:

Reduces internal anal sphincter tone

Increases external anal sphincter tone

82
Q

How is continence usually maintained?

A

The rectum is usually fairly empty

The angle of the sigmoid colon in unfavourable

Puborectal muscle is contracted

Tone of anal sphincters is high (usually)

83
Q

How do dietary fibres speed transit?

A

Provide bulk to distend the gut tube

84
Q

What hormone controls Na+ absorption in the colon?

What enhances Na+ absorption?

A

Aldosterone

Short chain fatty acids

85
Q

Where in the Gi tract is most of the water absorbed?

A

The colon

86
Q

Metabolic functions of bacteria in the colon?

A

Hydrolyse urea (salvage nitrogen)

Salvage short chain fatty acids

Synthesise Vit K

87
Q

What do the colonic bacteria use for energy? Where do they get it from?

A

CHO

Dietary residue and endogenous losses

88
Q

Whats NSP?

A

Non-starch polysaccharide, and example of CHO used by colonic bacteria

GI (11 decks)

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