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LSS_Abdomen > The small intestine > Flashcards

The small intestine Flashcards

1
Q

Describe the gross structure of the small intestine, including the route

A

6m long

Stomach leads on to:
- Duodenum 25cm
- Jejunum 2.5m
- Ileum 3.75m
this goes to large intestine

All have SAME basic histological organisation

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2
Q

What is the mesentery?

A

Allows folding of small intestine and supports blood supply

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3
Q

Describe digestive eptihelium and mucosa organisation

A

Lot of mucosal layers

  • provides layer of tissue for nerve plexuses and blood vessels
  • Internal mucosa are arranged in circular . folds
  • Mucosa are covered in villi
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4
Q

Describe the villi

A

Situated in small intestine
Motile with rich blood supply and lymph drainage
Good innervation
Presence of enterocytes for absorption

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5
Q

What are the types of cell in the small intestine?

A

Mucosa

  • Enterocytes
  • Goblet cells
  • Enteroendocrine cells

In the crypts

  • Paneth cells
  • Stem cells
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6
Q

What are enterocytes?

A

Tall COLUMNAR cells
Face lumen, containing microvilli

Polarised with specialisation to absorb and transport items
SHORT LIFESPAN

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7
Q

What are microvilli?

A

Attached to cytoskeleton, on apical side of villi

Surface covered with glycocalyx

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8
Q

What is the function of the glycocylax?

A

Rich carbohydrate layer, which allows for protection from digestional lumen, not stopping absorption

Traps layer of water and mucous - unstirred layer - regulates rate of absorption

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9
Q

What are goblet cells?

A

2nd most abundant

Granules containing mucus

Mucus is large glycoprotein

As you go down, more goblet cells
- becomes drier and needs lubrication

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10
Q

Enteroendocrine cells?

A

Hormone releasing cells, in the epithelial wall of the gut
- found on the tip and crypt

CHROMAFFIN CELLS

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11
Q

What are Paneth cells?

A

Only in the base of crypts

  • Has granules containing
    • antibacterial lysozyme
    • glycoproteins and zinc

Protective function - stem cells

Regulate intestinal flora

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12
Q

What are stem cells?

A

Undiff cells, can undergo differentiation

Can from any type of surface epithelium

Escalator

Have memory
- cells in the colon will form colon cells regardless of location

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13
Q

Why do epithelial cells have such a high turnover?

A

First line of defence against GI pathogens
- direct affect by toxins

Effects of agents that damage cell function diminish

Damage is short lived

If the escalator is interrupted - sever dysfunction occurs

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14
Q

How does cholera cause disease?

A

Results in prolonged chloride ion channel opening

- uncontrolled water secretion as water jus moves out

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15
Q

What are the distinguishing features of the duodenum?

A

Presence of Brunner’s glands

  • tubular mucous
  • open into crypts for alkaline secretion
  • neutralise damage of stomach acid on chyme
  • optimises pH for pancreas to act on it
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16
Q

What are the distinguishing features of the jejunum?

A

Presence of large submucosal folds
- much more pronounced - tall and thin
PLICAE CIRCULARES

17
Q

What are the distinguishing features of the ileum?

A

Lot of Peyer’s patches
- similar to large intestine - immune system link

Used to prime immune system against bacteria

Well positioned to prevent bacteria migrating back into small intestine from large

18
Q

What are the functions of small intestine motility?

A

Mix ingested food with digestive enzymes

Facilitate contact with contents of lumen and mucosa

Propel intestinal contents along tract

19
Q

How is food mixed?

A

Segmentation

  • circular muscle contraction
  • more in the duodenum than ileum
  • net movement is towards colon despite movement in both direction

Peristalsis

  • sequential muscle contraction
  • 10cm
  • more well done

Migrating motor complex - in fasting

  • smooth muscle contraction that start from stomach
  • to ensure any undugested items are sweeped all the way through
  • prevent bacteria from returning from large intestine
20
Q

What is digested in the small intestine?

A

Carbs
Proteins
Lipids

21
Q

How is food digested in the SI?

A

ALKALINE

Digestive enzymes and BILE enter duodenum from pancreatic and bile duct

MIxed in the Sphincter of Oddi

Duodenal epithelium also makes its own enzymes

22
Q

How are carbohydrates digested?

A

Begins in mouth by alpha amylase
Most in small intestine
- all types of carb

Major enzyme - pancreatic alpha amylase

  • secreted into duodenum
  • breaks starch and glycogen
  • NEEDS CL- AND ALKALINE
  • acts in lumen, by breaking into medium sized carbs
  • digestion of smaller and simple carbs happens at the brush border membrane
23
Q

How are carbs absorbed?

A

SECONDARY ACTIVE TRANSPORT - not direct ATP hydrolysis

Energy released from Na re-entering cell after being pumped out is used to pump GLUCOSE in - SGLT-2 prot

Fructose diffuses in via GLUT_2

24
Q

How are proteins digested?

A

Pepsin acts but only in acid condition

  • Inactivated by alkaline env
  • TRYPSIN from trypsinogen from pancreas
  • Converted by enterokinase ONLY in gut
  • Activates other proteases
25
Q

How are proteins absorbed?

A

Brush border peptidases break larger peptides

AAs absorbed by fac diff and secondary act trans

Di, tripeptides absorb using distinct carrier proteins

Cytoplasmic peptidases break down these dipeptides as they cross basolateral membrane - in blood its just AAs

26
Q

How are lipids digested?

A

Poor water solubility

Bile and lipase secretion

Emulsification - increase SA and allow lipase to split TGs into 2 FAs and monoglyceride

Enzymatic hydrolysis of ester linkages - LIPASE, needs colipase which is activated in gut - stop bile salt from displacing fat droplet

Solubilization of lipolytic products using bile salts

27
Q

What are the two other important lipid enzymes?

A

Phospholipase A2
- FA hydrolysis at 2 position of phospholipids - forms free FA and lyso-phospholipids

Pancreatic cholesterol esterase
- hydrolyses cholesterol esters to free cholesterol and FA

28
Q

Describe bile salt molecule

A

Amphipathic
Hydrophilic - hydroxyl and carboxyl
Hydrophobic - nucleus and methyl

Form mixed micelles - product of lipid digestion in centre, with bile salts on outside
- needed for transport to gut wall

29
Q

How are lipids absorbed?

A

Micelles present products to brush border - drops off

  • Micelle is split
    • bile salts absorbed at ileum
    • lipid absorption is complete at jejunum
    • bile salts are transported to liver to be recirculated
30
Q

following absorption, what occurs to lipids?

A

Monoglycerides and FFAs are absorbed and resynthesised
2 paths
- Monogylceride acylation
- add FAs in SER
- Phosphatidic acid pathway
- acyl coA added to phospholipid - new FA

Then, transported around body in CMs

  • 80-90pc TG
  • 8-9pc PL
  • Secreted out of basement membrane
  • Too big to go through capillaries so goes into lymph then reenters
31
Q

What separates the ileum and colon?

A

Ileocaecal sphincter

- relaxation and contraction controls movement

LSS_Abdomen (16 decks)

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