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Alimentary System > Structure + Function: Upper GIT, Liver, Small Intestine and Large Intestine > Flashcards

Structure + Function: Upper GIT, Liver, Small Intestine and Large Intestine Flashcards

1
Q

Which structures in the Oesophagus regulate movement into and out of it?

A

Upper and Lower Oesophageal Sphincters

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2
Q

Describe the structure of the Stomach wall

A

▷Serosa: (intraperitoneal!)

▷Muscularis Externae: 3 Layers: Longitudinal (outer), Circular (middle), Oblique (inner)

▷Submucosa and Mucosa: folded (= rugae) when empty → stretch as stomach fills

▷Lumenal surface (Mucosa): surface mucus cells → gastric pits → gastric glands → mucus neck, parietal and chief cells

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3
Q

Describe the structure of the Oesphageal wall

A

▷Mucosa: Non-keratinised stratified squamous epithelium

▷Submucosa: submucosal glands -> secrete mucus into ducts

▷Muscularis Externa: upper 1/3 = skeletal muscle, lower 2/3 = smooth muscle

▷Adventitia: (retroperitoneal!)

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4
Q

What are the functions of the Stomach?

A

▷Temporary store of ingested material

▷Dissolves food particles and initiates digestive process

▷Controls delivery of contents to small intestine

▷Sterilises ingested material

▷Produces Intrinsic Factor (Vitamin B12 absorption)

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5
Q

How is chewing controlled?

A

▷Voluntary: somatic nerves -> skeletal muscles of mouth/jaw

▷Reflex: Food enters mouth -> pressure of food against gums, hard palate tongue -> increased pressure triggers mechanoreceptors -> inhibition of jaw muscles (jaw drops) -> reduced pressure -> contraction (jaw shuts) -> increased pressure -> continues…

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6
Q

What is in Saliva?

What are the functions of each?

A

▷Water -> solvent

▷Mucins -> major protein component -> mucin + water = mucus -> lubricates

▷ a-Amylase -> catalyses breakdown of polysaccharide to disaccharide

▷Electrolytes -> tonicity/pH

▷Lysozymes -> bacteriocidal -> cleaves polysaccharide component of bacterial cell wall

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7
Q

What is the reflex control mechanism of Swallowing?

A

▷Oesophageal phase: peristaltic wave sweeps along oesophagus -> propels bolus to stomach (10s)

▷LOS relaxes as bolus nears stomach -> allows entry of bolus into stomach

▷Receptive relaxation of Stomach -> via Vagal reflexes -> thin, elastic Gastric Fundus and Body relax -> Stomach volume = 50ml -> 1500ml (with no change in pressure)

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8
Q

What are the Lobes of the Liver?

A

4 Lobes:

▷Right (Biggest Lobe)

▷Left

▷Caudate

▷Quadrate

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9
Q

What is the Porta of the Liver?

A

▷Carries blood vessels (hepatic portal vein, hepatic artery), lymphatic vessels, ducts (right/left hepatic ducts, common hepatic duct) and nerves (hepatic nerve plexus) to the inferior surface of Liver

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10
Q

Which ducts lead to the Major Duodenal Papilla?

A

▷Common Hepatic duct (Liver)

▷Joined by Cystic Duct (Gallbladder)

▷Combines to form Common Bile duct

▷Common Bile duct + Pancreatic duct → Major Duodenal Papilla (Sphincter of Oddi)

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11
Q

What is located at each corner of each Hepatic Lobule?

What is located in the centre of each Hepatic Lobule?

A

▷Portal Triad: hepatic portal vein, hepatic artery, hepatic duct

▷Central vein (drains hepatic sinusoids -> hepatic veins -> IVC)

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12
Q

What is the function of the Liver hepatocytes?

A

▷Bile synthesis (-> canaliculi -> hepatic ducts)

▷Nutrient storage (glycogen, fat, vits (B12, A, D, E, K), Cu, Fe)

▷Nutrient interconversion (ie. AAs into glucose for gluconeogenesis)

▷Detoxification

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13
Q

What is the main component of Bile Pigments and what is this component made from?

A

▷Main component of Bile Pigments = Bilirubin

▷Bilirubin is made from breakdown products of Hb from old/damaged RBCs (majority broken down in the Liver)

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14
Q

Why are faeces brown and why is urine yellow?

A

▷Liver breaks down Hb in old/damaged RBCs to Bilirubin -> Bilirubin = yellow

▷Bilirubin which passes through the GIT is modified by bacterial enzymes which makes it brown -> brown faeces!

▷Bilirubin which is reabsorbed across the intestinal wall gets excreted in the urine -> yellow urine!

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15
Q

Where are Bile acids made and what are they made from?

How much is made per day?

A

▷They are synthesised in the Liver from cholesterol

▷0.5g/day -> replaces the bile salts which are lost in the faeces! (5%)

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16
Q

How increases Bile salt solubility?

How are Bile salts recycled?

A

▷Conjugation with glycine or taurine

▷Secreted Bile salts are recycled via the Enterohepatic circulation (reabsorbed at the Terminal Ileum)

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17
Q

What triggers Bile secretion?

A

Fat in the Duodenum -> release of CCK -> relaxes Sphincter of Oddi, contracts GB

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18
Q

What is the function of the Gallbladder?

A

Concentration of Bile (5-20x)

absorbs Na+ and H2O

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19
Q

What are the combined effects of Secretin and CCK?

A

▷Secretin -> Acid Neutralisation

▷CCK -> Digestion of Fats/AAs

20
Q

How does Secretin neutralise Gastric Acid?

A

Triggered by Acid in the Duodenum

▷Inhibits Gastric Acid secretion
▷Inhibits Gastric emptying 
▷Increases Duodenal HCO3- secretion
▷Increases Pancreatic HCO3- secretion
▷Increases Bile duct HCO3- secretion

Gastric Acid Neutralisation switches off Secretin release

21
Q

How does CCK enable Fat/AA digestion?

A

Triggered by Fats/AAs in the Duodenum

▷Inhibits Gastric emptying
▷Increases Pancreatic enzyme secretion
▷Gallbladder contraction
▷Relaxes Sphincter of Oddi

22
Q

What is the function of Villus and Cypt cells?

A

▷Villus cells = absorption of nutrients + H2O

▷Crypt cells (epithelial cells lining the Crypts of Lieberkuhn) = secretion of Cl- (NB. CFTR channels) and H2O

23
Q

What is the function of the Duodenum, Jejunum and Ileum?

A

▷Duodenum = Gastric acid neutralisation, Digestion, Iron absorption

▷Jejunum = Nutrient absorption (95%)

▷Ileum = NaCl and H2O absorption (chyme dehydration -> faeces!)

24
Q

What is the function of Microvilli, Villi and Circular Folds (Plicae) in the Small Intestine?

A

To enhance absorptive surface area

25
Q

What are the effects of the Parasympathetic NS on intestinal motility?

Which Nerve is involved?

A

▷Increases intestinal motility -> increased contractions

▷Vagus Nerve

26
Q

What are the effects of the Sympathetic NS on intestinal motility?

A

▷Decreases intestinal motility -> decreased contractions

27
Q

What are the effects of the Autonomic NS on BER?

A

▷No effect of ANS on BER

28
Q

What is the Law of the Intestine?

What is it mediated by?

A

▷If intestinal smooth muscle is distended (eg. by bolus of chyme): muscle on oral side of bolus contracts and muscle on anal side of bolus relaxes -> moves bolus into area of relaxation towards colon

▷Mediated solely by Neurones in Myenteric Plexus (ENS) -> ie. would occur even in an isolated small intestine!

29
Q

What is the difference between Segmentation and Peristalsis?

A

▷Segmentation = most common during meal -> rhythmic and contraction relaxation of intestinal segments -> provides thorough mixing of digestive enzymes with chyme, and brings chyme into contact with absorbing surface

▷Peristalsis = begins when segmentation stops (post-prandial) -> MMC

30
Q

What is the function of the BER?

A

Sets the frequency of the segmentation contractions

31
Q

What is responsible for generating the BER?

A

Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer (NB. gastric motility!)

32
Q

What hormone initiates the MMC and what is the MMC’s function?

A

▷Motilin

▷The MMC is the pattern of peristaltic activity travelling down the small intestine (starting in the gastric antrum) -> it aims to move undigested material into the large intestine AND limit bacterial colonisation of the small intestine
(bc then the bacteria would just accumulate over time feed on whichever food u ingest in the future!)

33
Q

What causes cessation of the MMC?

A

▷Arrival of food in the stomach -> bc it initiates Segmentation contractions so Peristalsis stops! (ergo: MMC stops)

34
Q

What is the Gastroileal Reflex?

A

▷Stimulated by the presence of food in the stomach and gastric peristalsis

▷Peristaltic contractions reaches the Ileum

▷Ileocaecal valve opens

▷Chyme enters colon

▷Distension of colon

▷Reflex contraction of Ileocaecal valve (preventing reflux of contents back into the small intestine

35
Q

What are Teniae Coli?

What are Haustra?

A

▷Three bands of longitudinal smooth muscle on the colon surface -> (longitudinal smooth muscle layer is incomplete) -> runs the entire length of the colon

▷Small, segmented pouches of bowel separated by haustral folds (folds of Mucosa) -> gives the colon its “segmented” appearances

36
Q

What type of epithelium is present in the Colon?

A

Simple Columnar Epithelium with Large, straight crypts (flat), and a large number of goblet cells (lubrication)

37
Q

What is the function of the Colon?

A

Active absorption of Na+ -> osmotic absorption of H2O

NB. no important nutrient absorption role in humans

38
Q

Why is there bacterial colonisation in the Colon?

What do intestinal bacteria ferment, and what are the products of bacterial fermentation?

A

▷Because chyme spends the longest time in the Colon than any other area of the GIT

▷Bacteria ferment cellulose from plant matter (bc they contain cellulase and humans don’t!)

▷Bacteria produce short-chain FAs, Vitamin K, and Gas (flatus)

39
Q

What is the difference between the Internal Anal Sphincter and the External Anal Sphincter?

A

▷Internal Anal Sphincter = smooth muscle (thicker muscularis mucosa than rest of GIT)

▷External Anal Sphincter = skeletal muscle

40
Q

What type of junctional epithelium is present in the Anal canal?

A

Ano-Rectal junction

▷Simple Columnar epithelium -> Stratified Squamous epithelium

41
Q

What is the Defecation Reflex?

A

▷Contraction of Rectum -> distension of rectal wall by faecal material -> stimulates mechanoreceptors in rectal wall -> stimulates urge to defecate

▷Relaxation of Internal and contraction of External Anal sphincters

▷Increased peristaltic activity in Colon (MMC) -> ­increased pressure on External Anal sphincter -> relaxes under voluntary control, causes expulsion of faeces -> Voluntary delay of defaecation - descending pathways

42
Q

What is Constipation and what causes it?

A

▷Person has difficulty emptying the colon -> fewer than 3 bowel movements/week

▷Symptoms are due to distension of the rectum

43
Q

What is Diarrhoea? What is the main cause of Diarrhoea?

A

▷Too frequent passage of faeces which are too liquid

▷Enterotoxinogenic Bacteria: ie. Vibrio Cholerae, Escherichia Coli

44
Q

What is the mechanism of action of Vibrio Cholerae for causing Cholera?

A

▷Vibrio Cholerae produces enterotoxins which maximally turn on intestinal Cl- secretion from Crypt cells -> increases H2O secretion

▷Acts by elevating intracellular secondary messengers (ie. cAMP)

▷H2O secretion swamps the absorptive capacity of the Villus cells -> profuse watery diarrhoea (25L/day)

45
Q

What is the treatment for secretory Diarrhoea and why?

A

▷Enterotoxins do not damage Villus cells -> therefore they are still able to absorb H2O from the lumen

▷Give sodium/glucose solution (ORS) -> absorbed by Villus cells and drives H2O absorption via the paracellular pathway

Alimentary System (11 decks)

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