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GI > Small intestine and pancreas 2 > Flashcards

Small intestine and pancreas 2 Flashcards

1
Q

What are the components of the small intestine?

A

Duodenum, jejunum, ileum

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2
Q

Describe the arrangement of the components of the small intestine

A
  • Duodenum from pylorus of stomach (descending then ascending portion)
  • Transition between duodenum and jejunum at duodenojejunal flexure (sits under rest of intestine)
  • Jejunum makes up most of SI
  • Ileum last part of SI
  • Ileocaecal junction very tight
  • In middle of abdomen and slightly to the right
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3
Q

What is the function of the jejunum?

A

Major site of absorption

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4
Q

Describe the duodenum

A
  • Brunner’s glands sit in submucosa
  • Compound tubular submucosal glands
  • Produce alkaliine secretion with bicarbonate
  • Protects duodenal epithelium from incoming stomach acid
  • Provide alkaline condition for intestinal enzymes to be active
  • Lubricate the intestinal wall from rough ingesta
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5
Q

Describe the ileum

A
  • Caudal to jejunum
  • Attached to caecum by ileocaecal fold
  • Contains blood vessels from caecum and colon
  • Enters ascending colon at level L1-L2 through distinct anatomic ileocaecal sphincter
  • Mostly for reabsorption of bile acids to be recycled
  • Contains Peyer’s patches
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6
Q

What is the clinical signifiance of the ileocaecal sphincter?

A
  • Is a narrowing

- Common site for obstruction

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7
Q

Where does the pancreas sit?

A

In the duodenal flexure

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8
Q

Give a basic overview of the Peyer’s patches of the ileum

A
  • GALT
  • Contain B cells and M cells
  • Take up foreign materials e.g. bacteria, viruses
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9
Q

What is the major arterial supply to the small intestine?

A
  • Caudal mesenteric and cranial mesenteric
  • Many branches
  • Mesenteric supply
  • Ileum also has antemesenteric supply from ileal branch of ileocolic artery
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10
Q

What is the major venous drainage from the small intestine

A
  • Portal vein (to liver) and cranial mesenteric
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11
Q

Describe the innervation of the small intestine

A
  • Parasympathetic pathways
  • Vagus nerve
  • General viscero-effector neurons in medulla oblongata
  • Fibres run through vagus -> dorsal vagal trunk -> coeliac and mesenteric ganglia -> along blood vesels -> gut
  • Sacral part of PSNS
  • Pelvic nerves form retroperitoneal plexus which supplies descending colon and rectum
  • Mechanical and chemo-receptors
  • Also from sympathetic ganglia (solar pelxus, caudal mesenteric ganglia)
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12
Q

Describe the blood supply to the pancreas

A
  • Coeliac and cranial mesenteric (splenic, hepatic, superior mesenteric branches)
  • Right lobe: cranial pancreatoduodenal artery (branch of hepatic)
  • Left lobe: caudal pancreatoduodenal artery (branch of cranial mesenteric)
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13
Q

Describe the venous drainage of the pancreas

A

Portal vein

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14
Q

Describe the innervation of the pancreas

A
  • Vagus - neural control
  • Sympathetic and parasympathetic control
  • PSNS: dorsal vagal trunk
  • SNS: solar plexus (splanchnic nerves)
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15
Q

Describe the microscopic structure of the small intestine

A
  • Lumen
  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa
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16
Q

Describe the lumen of the small intestine

A
  • Contains chyme

- Food, bacteria, toxins, viruses, secretions, foreign bodies

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17
Q

Describe the mucosa of the small intestine

A
  • Single epithelial layer
  • Semipermeable membrane, secretion absorption, protection
  • Mucus covered in mucin, glycocalyx and IgA
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18
Q

Describe the submucosa of the small intestine

A
  • Lamina propria
  • Structural support
  • Blood vessels
  • Lymphatics
  • Nerves
19
Q

Describe the muscularis of the small intestine

A
  • Smooth msucle circular and longitudinal) for motility
  • Mixes, stimmulated by distention, aim is to increase mucosal contact and delay passage
  • Slow aboral movement of chyme (peristalsis)
  • Interdigestive migrating motlity complex (cleaning in unfed periods)
20
Q

Describe the serosa of the small intestine

A

Strong, protective, supportive outer layer

21
Q

What happens to the rate of passage of chyme in hypermotility?

A

Delayed passage

22
Q

What happens to the rate of passage of chyme in hypomotility?

A
  • Rapid passage

- Little resistance

23
Q

What is meant by ileus?

A
  • Lack of motility leading to bacterial overgrowth
24
Q

Describe how the structure of the small intestine is related to its function

A
  • Increased surface area to increase absorption
  • Crypts produce immature enterocytes and other gut cells
  • Villus structure increases absorptive area
  • Mature enterocytes on villi absorb nutrients
  • Bigger fenestrations in the capillaries in teh villi allows passage of molecules in and out of blood
  • Villus has brush border (greater SA)
  • Goblet cells secrete mucin (pH, lubrication)
  • Stem cell zone ensures enterocytes continuously replaced at extruction zone_
  • Have enteroendocrine cells, Paneth cells, Enterocytes, Brush border
25
Q

Decribe the function of the enteroendocrine cells of the small intestine

A
  • Produce hormones
  • Scattered along epithelium
  • Respond to presence of AAs
  • Secrete CCK, acts on liver and pancreas
  • Secrete secretin, acts on pancreas
26
Q

Describe the function of the Paneth cells in the small intestine

A
  • Migrate to base of crypts
  • Produce anti-microbial defensin peptides
  • Act to keep clear of high bacterial count
27
Q

Describe the function of the enterocytes in the small intestine

A
  • Smooth endoplasmic reticulum allows intracellular transportation of nutrients
  • Pinocytosis into enterocyte allows foreign material to enter cell as vesicle
  • Fuse with enzyme packed intracellular lysosomes
  • Protective function stopping foreign materials entering the body
28
Q

Describe the function of hte brush border in the small intestine

A
  • Thick mucus layer
  • microvilli
  • Mature enterocyte brush border enzymes (integral membrane enzymes, peptidases, CHO hydrolases = lactasem maltase, sucrase)
29
Q

Describe the structure of the pancreas

A
  • 2 lobes
  • Left lies in greater omentum
  • Right embedded in duodenal flexure
  • In cat bile and pancreatic duct fused, separate in dog
  • Exocrine: acinar cells
  • Endocrine: Islets of Langerhans
30
Q

Describe the exocrine function of the pancreas

A
  • Acinar cells
  • Produce lipase, amylase, nucelases, gelatinases, proteases
  • Packaged as zymogens iin secretory vesicles in pacreas acinar cells
  • Vesicles contain trypsin inhibitor
  • Zymogens enter ducts, go to SI
  • Zymogens converted in SI lumen, massive reelase of proteases into lumen
31
Q

What is the pancreatic enzyme production and secretion stimnulated by?

A
  • Cephalic phase of digestion (autonomic neural and humoral - gastrin, synthesis of enzymes, eating)
  • Gastric phase of digestion (events in stomach, neural - gastropancreatic reflex via vagus - and humoral through gastrin)
  • Intestinal phase of digestion - events in SI, hormonally mediated e.g. CCK and secretin. Intraluminal ionised calcium stimualtes release
32
Q

Describe the control of acinar pancreas secretions

A
  • Vagus nerve (neural)
  • Gastrin from entero-endocrine cells in stomach
  • Acts on acinar cells to produce zymogens
  • CCK from enteroendocrine cells in duodenum - sense partly digested proteins and fats, acts on acinar cells to produce zymogens
33
Q

Describe the cells involved in the endocrine function of the pancreas

A
  • Islets of Langerhans
  • Alpha, beta, delta cells
  • Alpha: glucagon
  • Beta: insulin
  • Delta: somatostatin
34
Q

Describe the effect of detection of acid chyme in the duodenum on the pancreas

A
  • Duodenum entero-endocrine cells sense acidic chyme from stomach
  • Secretin release acts on pancreatic ducts
  • Epithelial cells in pancreatic ducts produce bicarbonate and water
  • Helps flush acinar enzymes into SI lumen
35
Q

Compare the 2 pathways of absoprtion in the small intestine

A
  • Paracellular and transcellular
  • Para: across tight dunctions, small molecules
  • Trans: across plasma membrane, large AAs, glucose
36
Q

Breifly outline the absorption of dietary CHO sugars in the small intestine

A
  • Amylase from pancreases processes diet starch to maltose
  • Diet also provides lactose and sucrose
  • Too big for absorption still
  • Brush border hydrolase enzymes used to produce monosaccharides maltase, lactase, sucrase)
  • Produces glucose, galactose and fructose
  • Ready to move across SI lumen membrane
37
Q

Briefly outline the absorption of glucose-galactose in the small intestine

A
  • Sodium dependent glucose transporters located in epithelium of lumen membrane
  • Sodium binds in lumen, makes transporter open to glucose/galactose
  • Glucose binds and transporterr switches to move pockets inside cell
  • Sodium and glucose enter cell
38
Q

Briefly outline the absorption of peptides in the small intestine

A
  • Diet protein digested by stomach pepsin and pancreas trypsin, chymotrypsin and carboxypeptidases
  • Results in oligopeptides (too big for absorption)
  • Brish border peptidases used
  • Producees small AA groups
  • Absorbed via sodium dependent AA transporters
39
Q

Briefly outline the absorption of lipids in the small intestine

A
  • Diet lipids digested with bile acids and pancreatic lipase
  • Fatty acids and TAGs enter GI enteroytes by simple diffusion
  • Follow FA transporter mechanism
  • Inside enterocytes lipids packaged into chylomicrons
  • Enter lymph vessels first, not blood
40
Q

What is the significance of sodium and chloride movements in the small intestine?

A
  • There is a high sodium concentration outside the cells
  • Need to keep sodium in cells at a low level
  • Wherever sodium goes, water follows
41
Q

Briefly outline water absorption in the small intestine

A
  • High osmotic pressure in lower GI lumen and cells
  • Sodium pumped into space between cells
  • Sodium diffuses into capillary bed
  • Water follows sodium into blood
42
Q

Describe chloride movement in the GI epithelium

A
  • Cl- enters from blood
  • cAMP activated
  • Cystic fibrosis transmembrane conductance receptor (CFTR) activated
  • Trasnports Cl- into lumen
  • Na+ follows Cl into lumen
  • cAMP action critical in bacterial enterotoxin action
  • Stimulate normal mechansism resulting in diarrhoea
43
Q

What is the gastrocolic reflex?

A
  • A long intestinal reflex
  • Food in stomach stimulates colonic contractions
  • Reflex medaited via afferents to CNS and efferents in parasympathetic fibres
  • Gastrocolic reflex leads to defecation soon after eating to clear way for new food
44
Q

What is the intestino-intestinal inhibitory reflex?

A
  • Loss of motility in response to sympathetic stimulation

- e.g. Acute distension due to obstruction, trauma or surgery

GI (31 decks)

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