W3 - Digestive System 2 Flashcards
Where does the majority of digestion take place?
Small intestine
What is draped over the small intestine in healthy individuals?
Greater omentum
Greater omentum
Apron-like fold of visceral peritoneum that hangs down from the stomach.
Characteristics of the Greater omentum
Lot of fat for insulation
Rich supply of bv for heat
What 2 anatomical specialisations serve to ⬆️ the SA of the small intestine?
Plicae circulares
Villi
Plicae circulares in the small intestine
Circular folds in mucosal lining
Villi
Extend into lumen of small intestines
Its capillaries enable absorption of nutrients from small intestine –> blood
What do all blood capillaries in the absorptive areas join to form?
Hepatic portal venous system
What is a venous portal system?
System starting in capillaries
Join to form veins
End in another group of capillaries.
What type of glycosidic bond do maltose + sucrose have?
alpha
What type of glycosidic bond does lactose have?
Beta
List 3 common sugar alcohols
Xylitol
Sorbitol
Mannitol
What are the most common oligosaccharides?
Raffinose
Stachyose
What are the 3 main classes of polysaccharides?
Starch
Glycogen
Fibres
What are the 2 primary lipolysis enzymes?
Lipoprotein lipase (LPL)
Hormone-sensitive lipase (HSL)
What do LPL do with lipoproteins
Cleave FAs from chylomicron
= Chylomicron remnant
Cleaves TG from VLDL + IDL
= Forms lipoproteins IDL + LDL (containing less TG)
De novo lipogenesis
Synthesis of FAs from ACoA
+
Esterification into TG’s
What ⬆️ activity of HSL?
Glucagon
+
Epinephrine
What ⬇️ activity of HSL?
Insulin
What does HSL do in hypoglycemia?
Cleaves TGs in adipose = FA bound to albumin are released into circulation
Why is HSL important?
For mobilising FAs so that they can be used to prod energy
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
What aa-derived compound shuttles long chain FAs into the mitochondria?
Carnitine
What are the enzymes involved in FA shuttling?
CPTI
CPTII
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
