W3 - Digestive System 2 Flashcards by Holly Tomlinson

Where does the majority of digestion take place?

Small intestine

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What is draped over the small intestine in healthy individuals?

Greater omentum

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Greater omentum

Apron-like fold of visceral peritoneum that hangs down from the stomach.

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Characteristics of the Greater omentum

Lot of fat for insulation

Rich supply of bv for heat

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What 2 anatomical specialisations serve to ⬆️ the SA of the small intestine?

Plicae circulares

Villi

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Plicae circulares in the small intestine

Circular folds in mucosal lining

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Villi

Extend into lumen of small intestines

Its capillaries enable absorption of nutrients from small intestine –> blood

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What do all blood capillaries in the absorptive areas join to form?

Hepatic portal venous system

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What is a venous portal system?

System starting in capillaries

Join to form veins

End in another group of capillaries.

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What type of glycosidic bond do maltose + sucrose have?

alpha

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What type of glycosidic bond does lactose have?

Beta

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List 3 common sugar alcohols

Xylitol

Sorbitol

Mannitol

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What are the most common oligosaccharides?

Raffinose

Stachyose

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What are the 3 main classes of polysaccharides?

Starch
Glycogen
Fibres

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What are the 2 primary lipolysis enzymes?

Lipoprotein lipase (LPL)

Hormone-sensitive lipase (HSL)

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What do LPL do with lipoproteins

Cleave FAs from chylomicron

= Chylomicron remnant

Cleaves TG from VLDL + IDL

= Forms lipoproteins IDL + LDL (containing less TG)

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De novo lipogenesis

Synthesis of FAs from ACoA

Esterification into TG’s

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What ⬆️ activity of HSL?

Glucagon

Epinephrine

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What ⬇️ activity of HSL?

Insulin

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What does HSL do in hypoglycemia?

Cleaves TGs in adipose = FA bound to albumin are released into circulation

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Why is HSL important?

For mobilising FAs so that they can be used to prod energy

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FA oxidation / beta-oxidation occurs in mitochondria but long chain FA can’t diffuse across the mit. membrane.

So how do long chain FAs enter?

FA shuttling

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What aa-derived compound shuttles long chain FAs into the mitochondria?

Carnitine

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What are the enzymes involved in FA shuttling?

CPTI

CPTII

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FA shuttling process

FA activated by the addition of a CoA --> ACoA CPTI adds carnitine --> Acyl-carnitine ^ transported into mit. matrix by translocase enzyme. In matrix, CPTII removes carnitine from activated FA (acyl-CoA) Carnitine is recycled back into cytosol to be used again.

What are the 3 major reasons for chewing food?

Mechanically ⬇️ size of particles = ⬆️ gastric emptying ⬆️ SA = ⬆️ contact area for digestive enzymes Mixes food w/ saliva + digestive enzymes.

What is the small intestine divided up into?

Duodenum Jejunum Ileum

What % of absorption takes place in the duodenum + jejunum?

~95%

What are the folds in the duodenum + jejunum called?

Kerckring folds

Function of the Kerckring folds

⬆️ SA of intestine by ~ 3 times.

What does the wall of a villus have?

Layer of epithelial cells. - Each have a brush border where absorption of nutrients occurs.

H20, H20 soluble particles + electrolyte absorption through villi

Req. transport or diffusion across luminal + contraluminal membranes of the epithelial cell into bv. Then transported to liver by hepatic portal vein.

What does each villus contain in its central part?

Lacteal

What does the lacteal in each villus do?

Transports particles that arent readily H20-soluble i.e long-chain FAs via the lymphatic vessels.

Depending on its composition, how long does food spend in the GI tract before its eliminated?

1-3 days

Define transit time

Length of time food spends in a section of the GI tract

Transit time for small intestine

~ 3-10 hrs

What does the sphincter of Oddi do?

Controls the flow of bile + pancreatic juice into the 2nd part of the duodenum.

What does bile consist of?

H20 Electrolytes Bile salts Cholesterol Lecithin Bilirubin

Through which duct is bile released?

Hepatic duct

What does the pancreas secrete to buffer the HCL acid from the stomach?

Sodium bicarbonate

To what response is pancreatic juice mainly secreted?

When there's chyme in the upper portions of the small intestine.

What moves through the ileocecal valve?

Chyme

Where does chyme move from in the ileocecal valve?

Small intestine --> large intestine

What is contraction of the ileocecal valve regulated by?

Distension of the cecum Irritating substances in the cecum Fluidity of chyme

What can restrict the emptying of the ileum?

An inflamed appendix

What does increased fluidity of the chyme increase?

Emptying from the ileum

What does parasympathetic stimulation do to the GI tract?

Stimulates motility

What is the source of the parasympathetic activity in the oesophagus, stomach, pancreas, gall bladder, small intestine + upper section of the large intestine?

Vagus nerve

Where does the lower portion of the large intestine receive parasympathetic innervation from?

Spinal nerves in sacral region

What does gastrin do?

⬆️ HCL acid + pepsinogen secretion in stomach

What does secretin do?

⬆️ H20 + bicarbonate secretion by pancreas.

How long can it take for digestion to be completed?

~ 4-6 hrs

What does saliva consist of?

99.5% H20 a-amylase Mucoid proteins Bicarbonate Electrolytes Lysosomes Lingual lipase Protein antibodies.

What do the mucoid proteins do to saliva?

⬆️ its viscosity = Helps lubricate food = easier to swallow.

Where is guanylin secreted?

Ileum + colon

What does guanylin do?

Removes NaCl + H20 from faeces.

When is the hydrolysis of all starches to maltose almost complete?

When chyme enters ileum.

What do the lingual + gastric lipase act together MAINLY on?

Short chain (C4-C6) Medium chain (C8-C10) TAG Whereas most of the long-chain (C12-C14) are digested in the small intestine.

What % is lingual lipase responsible for of triacylgylcerol digestion?

10-30%

Functions of HCL acid

Activates protease enzyme pepsin Kills pathogenic organisms ⬆️ Absorption of iron + calcium Breaks down food proteins = ⬆️ vulnerability to enzymes

Where are proteases often stored?

In inactive precursors But as soon as released into stomach or small intestine, they're activated.

Where does most vitamin absorption take place?

Jejunum Ileum - Usually by diffusion

Upper GI symptoms often reported by athletes

Heartburn Bloating Vomiting

Lower GI symptoms often reported by athletes

Urge to defecate Loose stool Diarrhoea Bleeding