Small intestine and pancreas 2 Flashcards
1
Q
What are the components of the small intestine?
A
Duodenum, jejunum, ileum
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
3
Q
What is the function of the jejunum?
A
Major site of absorption
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
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
6
Q
What is the clinical signifiance of the ileocaecal sphincter?
A
- Is a narrowing
- Common site for obstruction
7
Q
Where does the pancreas sit?
A
In the duodenal flexure
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
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
10
Q
What is the major venous drainage from the small intestine
A
- Portal vein (to liver) and cranial mesenteric
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)
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)
13
Q
Describe the venous drainage of the pancreas
A
Portal vein
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)
15
Q
Describe the microscopic structure of the small intestine
A
- Lumen
- Mucosa
- Submucosa
- Muscularis
- Serosa
16
Q
Describe the lumen of the small intestine
A
- Contains chyme
- Food, bacteria, toxins, viruses, secretions, foreign bodies
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
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
Decribe the function of the enteroendocrine cells of the small intestine
- Produce hormones
- Scattered along epithelium
- Respond to presence of AAs
- Secrete CCK, acts on liver and pancreas
- Secrete secretin, acts on pancreas
26
Describe the function of the Paneth cells in the small intestine
- Migrate to base of crypts
- Produce anti-microbial defensin peptides
- Act to keep clear of high bacterial count
27
Describe the function of the enterocytes in the small intestine
- 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
Describe the function of hte brush border in the small intestine
- Thick mucus layer
- microvilli
- Mature enterocyte brush border enzymes (integral membrane enzymes, peptidases, CHO hydrolases = lactasem maltase, sucrase)
29
Describe the structure of the pancreas
- 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
Describe the exocrine function of the pancreas
- 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
What is the pancreatic enzyme production and secretion stimnulated by?
- 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
Describe the control of acinar pancreas secretions
- 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
Describe the cells involved in the endocrine function of the pancreas
- Islets of Langerhans
- Alpha, beta, delta cells
- Alpha: glucagon
- Beta: insulin
- Delta: somatostatin
34
Describe the effect of detection of acid chyme in the duodenum on the pancreas
- 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
Compare the 2 pathways of absoprtion in the small intestine
- Paracellular and transcellular
- Para: across tight dunctions, small molecules
- Trans: across plasma membrane, large AAs, glucose
36
Breifly outline the absorption of dietary CHO sugars in the small intestine
- 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
Briefly outline the absorption of glucose-galactose in the small intestine
- 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
Briefly outline the absorption of peptides in the small intestine
- 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
Briefly outline the absorption of lipids in the small intestine
- 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
What is the significance of sodium and chloride movements in the small intestine?
- 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
Briefly outline water absorption in the small intestine
- 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
Describe chloride movement in the GI epithelium
- 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
What is the gastrocolic reflex?
- 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
What is the intestino-intestinal inhibitory reflex?
- Loss of motility in response to sympathetic stimulation
| - e.g. Acute distension due to obstruction, trauma or surgery
