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Bioregulatory systems 4 > The Pancreas and Small Bowel > Flashcards

The Pancreas and Small Bowel Flashcards

1
Q

Describe the structure/layout of the pancreas and surrounding organs?

A

Liver->common Hepatic Duct->Gall bladder (attatched to the Hepatic Duct via the Cystic Duct )-> Cystic duct+ Common Hepatic Duct= Common Bile Duct -> This goes behind the Dudenom and enters the Dorsal Panceas( Now called Dorsal Pancreatic Duct/Acessory Pancreatic Duct) to meet up with the duct from the Ventral Pancreas to form the Main Pancreatic Duct-> The main Pancreatic ducts and Bile duct meet and drain together intot he Major Papilla of the Duodenom(secretes bile and other enzymes to aid digestion)

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2
Q

What is infront/behind the pancreas?

A

Infront: Stomach and then the transverse Colon

Behind: Duodenom, Kidneys

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3
Q

What are the differnt parts of the pancreas?

A

Head, neck, body and tail

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4
Q

What are some inportant landmarks on the pancreas?

A

SUPERIOR MESENTERIC VEIN:

  • enters underneath the neck of the pancreas and drains blood from the small intestine
  • The part of the pancreas behind this vein is the UNCINATE PROCESS which forms part of the Ventral Pancreas

SUPERIOR MESENTERIC ARTERY:

  • next to the vein
  • comes of the AORTA

CELIAC AXIS:

  • largest branch of the AORTA located at T12 just above the pancreas
  • 3 major arteries come from it: Common hepatic artery(to the Liver), Left Gastric Artery(to the stomach), Splenic Artery(dives in and out of the Pancreas)
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5
Q

What froms the Hepatic Portal Vein?

A

when the SUPERIOR MENSENTERIC VEIN and SPLENIC VEIN combine

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6
Q
A
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7
Q

How is the Duodenum split and why?

A

split into 4 sections (D1, D2 ,D3, D4)

-this helps us easily refer to a certain part of the pancreas

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8
Q

What are MRCPs?

A

MRIs of the pancreas

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9
Q

Which MRCP is the normal one?

A

The one on the left

-In the right MRI the ventral duct has not combined with the dorsal duct which means the dorsal duct od acting as the main pancreatic duct alone

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10
Q

What is angiography?

A
  • Putting dye into an artery/vessel to work out what happening
  • This test is used to study narrow, blocked, enlarged, or malformed arteries or veins in many parts of your body,
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11
Q

How do you define Endocrine and Exocrine?

A

Endocrine: secretion of hormones into the BLOOD STREAM to have ann effect on a distant organ

Exocrine:Secretion of hormones into a DUCT to have a local effect

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12
Q

What are the main endocrine secretions of the pancreas and their effects?

A

Insulin

Glucagon

Somatostatin-Inhibits the secretion of Insulin, Glucagon, Pancreatic juices, enzyme

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13
Q

How much of the Pancreas is endocrine vs exocrine and describe briefly the function?

A

Endocrine:

  • 2%
  • secretes hormones e.g Insulin, glucagom and somatostain from the ISLETS OF LANGERHANS

Exocrine:

  • 98%
  • secretes PANCREATIC JUICE into the Duodenum via the Main Pancreatic Duct/sphincter of Oddi/ Ampulla
  • Digestive Function
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14
Q

What are Acini?

Describe the microanatomy?

A

Sac like clusters that are attatched to ducts and surrounded by ACINAR CELLS(large with apical secretion granuales)

Acinar cells are the exocrine cells of the pancreas that secrete Pro-enzymes into the ducts via INTERCELLULAR CANALICULI, which then become activated pancreatic juice (full of enzymes) which enters duodenum to aid digestion

CENTROACINAR CELLS-makes up the duct that is in the Acinus but once the duct leaves the acinar they become normal Pancreatic duct cells(small and pale)

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15
Q

Where are the most Islets of langerhan?

A

In the tail of the pancreas-so if the tail is removed people are more likely to become diabetic

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16
Q

What is the compostion of the islets of Langerhans?

A
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17
Q

What are the 2 components of pancreatic juice?

A

From ACINAR cells: enzyme rich, viscous, low volume fluid

From the duct and CENTROACINAR cells: high volume, waery, HCO3- rich, alkaline rich

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18
Q

What does the bicarbonate in pancreatic juice do?

A

Neutralises acid CHYME from the stomach too:

  • prevent damage to the duodenal mucosa
  • raise pH to opti um range for pancreatic enzymes to work

Washes low volume eenzyme secretion out of the pancreas into the duodenom

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19
Q

What is the effect of Duodenal pH on Bicarbonate secretion?

Explain?

A

As it decrease from pH 5 to pH3 the pancreatic bicrbonate secretion increases

As it decreases from pH3 the Bicarbonate secretion plateus- this is because Bile also has bicarbonate so can help neutralise chyme AND duodenum has Brunners glands that secrete alkaline fluids

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20
Q

Explain the Bicarbonate mechanism?

A

Pancreatic HCO3- secretion:

1) CO2 + H20 ->H+ + HCO3- catalyed by CARBONIC ANHYDRASE inside pancreatic duct cell
2) Na+ runs down a gradient via PARACELLULAR (tight) JUNCTIONS and Water follow(from blood to lumen)
3) HCO3- pumped out and Cl- pumped in at lumen
4) Na+ pumped in and H+ pumped out at basolateral membrane into the bloodstream via NHE-1

(These exchanges are driven by ELECTROCHEMICAL GRADIENTS)

5) Na+/K+ ATPase pumps Na+ out (into the blood) and K+ into cell, this maintains Na+ elecrochemical gradient
6) Now you have K+ in the cell whcih is transported out via K+ channel
7) Cl- is piumped out of the cell back into the lumen via Cl- channel (Cysitc fibrosis tansmembrane conductase regulator)

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21
Q

What is the difference between bicarbonate secretionin the pancreas vs the stomach?

A

Same reaction:

H20+CO2->H+ + HC03-

In the stomach the H+ is pumped into the gastric juice and the HCO3- is pumped into the blood so Gastric venous blood is ALKALINE

In the Pancreas the H+ is pumped in to the blood and the HCO3- enters the pancreatic juice meaning the Pancreatic venous blood is ACIDIC

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22
Q
A
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23
Q

What enzymes to acinar cells make and secrete into the Pancreatic juices?

A
  • Lipases
  • Proteases
  • Amylase

synthesised and stored in zymogen (pro-enzymes) granuales

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24
Q

What is a potentiaql problem for organs that make a lot of different digestive ezymes e.g the pancreas?

How do we overcome this ?

A

-You could start to digest yourself

Solution:

  • Proteases are released as inactive pro-enzymes -this protects the ACICI and DUCTS from self-digestion
  • Pancreas also has TRYPSIN INHIBITORS incase trypsin is accidently activated when it shouldn’t be
  • Enzymes only activated in the DUODENEM
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25
Q

How are pancreatic enzymes activated?

A

-In the DUODENUM enzyme ENTEROKINASE (enteropeptidase) converts TRYPSINOGEN -> TRYPSIN

TRYPSIN then converts all the proenzymes to activated enzymes

26
Q

Why do pancreatic enzymes secretion change?

A
  • Proportion of different enzymes secreted e.g. amylase, porteases changed depending on your diet
  • Lipase require COLLIPASE to be activated and BILE SALTS fro effective action
27
Q

How do you control pancreatic juic secretion?

A

CEPHALIC PHASE:

  • Reflex reponse to SENSORY stimulation sight, taste and smell
  • Releases enzyme rich component from the acinar cells
  • Low volume and Viscous

GASTRIC PHASE:

-PHYSICAL stimulation of pancreat4ic secretion due tot he arrival of food in the stomach

INTESTINAL PHASE:

  • 70-80% of pancreatic juice secretion
  • HORMONALLY MEDIATED when gastric CHYME enters the duodenum
  • both components of pancreatic juice is stimulated
  • enzymes and HCO3- juic flow into the DUODENUM
28
Q

How are the 2 components of pancreatic juice controlled?

A

Enzyme secretion controlled in the acini by:

  • VAGUS NERVE(ACh)
  • CHOLECYSTOKININ (CKK)- secreted form duodenal i-cells which has a +ve effect on the pancrease causing enzymes to be secreted

BICARBONATE secretion controlled in DUCT and CENTROACINAR CELLS by:

-SECRETIN (cAMP) -stimulates H2O and HCO3- secretion form extalobular ducts and then the bicarbonate mechanism begins

29
Q
A
30
Q

What inhibits and stimulates the secretion of CCK?

A

Inhibits:

-TRYPSIN- hydrolyzes CCK-releasing peptide and monitor peptide, in effect turning off the additional signals to secrete CCK.

Stimulates:

-Amino acid and Fatty acids

31
Q

Briefly describe the control of HCO3- secretion in the ducts?

A

NEGATIVE FEEDBACK LOOP:

-decrease pH in the duodenum= S-cells secrete SECRETIN= Pancreas duct secretes HCO3= increases pH negatively feeback on S-cells

32
Q

Hoe can you increase bicarbonate secretion?

A

CCK alone has no effect on Bicarbonate secretion

-but if present when HCO3- has been stimulated by SECRETIN this increases HCO3- secretion greatly

33
Q

Summary of a meal?

A

1-Food mixed and digested in the stomach at pH 2

2-Chyme squirted into the duodenum

3-H+ ions in the duodneum increase SECRETIN = increase Pancreatic juice

4-Pancreatic juice is alkaline, as is bile and secretions from brunners glands

5-Peptides and fats in the duodenum cause sharp increase in CCK and vagus nerve stimulation=stimulates pancreatic enzyme release(peaks by 30 mins or until the stomach is empty)

6-CCK has combined effect with SECRETIN to increase to increase bicarbonate

34
Q

What is the simple function of the small bowel?

A

-absorb nutrients, salt and water

35
Q

What is the structure of the small Bowel?

A

Made up of the:

  • DUODENUM-25cm
  • JEJUNUM-2.5m
  • ILEUM-3.75m

Approx 6m long and 3.5cm diameter

36
Q

What is the Mesentery?

A
  • suspends small and large bowel from posterior abdominal wall which anchors them in place while allowing some movement
  • provides a conduit for blood vessels, nerves and lymphatic vessels
37
Q

Describe Epithelium of Small Bowel?

A

From inside to ouside of small intestine:

  • Lumen
  • Mucosa (plicae cirulares)
  • Submucosa
  • Circular muscle layer
  • Longitudinal muscle layer
  • Serosa
  • Plicae Circulares are folds in the mucousal membrane of the small intestine especially in the duodenum and Jejenum (feel thick compared to iliem)
  • increase the amount of surface area available for the absorption of nutrients
38
Q

What are the structure of Villi?

A

finger like projections on the eplicae circulares

  • have crypts between the villi with intestinal glands in it
  • have cells surrounding to make up the epithelium: Goblet cells, enterocytes, endocrine cell, cells of Paneth
  • Enterocytes are covered in Microvilli to form brush border
39
Q
A
40
Q

What are some features of Villi?

A

-only found in small intestine

-mobile

  • rich blood supply and lymphatic drainage
  • innervation form submucosal plexus
  • 1 cell thick epithelium dominated by enterocytes (columnar absorptive cells)
41
Q

What are some cells types of the small bowel?

A

Vili lined with:

  • enterocytes(absorptive cells)
  • scattered globlet cells(secretory)
  • enteroendocrine cells(secretory)

Crypts of Lieburkuhn epithelium includes:

  • Paneth cells(secretory)
  • stem cells
42
Q

What are features of enterocytes?

A
  • Most abundent cell in small bowel
  • Tall columnar cells with basal nucleus and microvilli
  • specialised for the absorption and transport of substances
  • Short lifespan 1-6 days
  • Absporption fromthe lumen of the bowel to the blood stream
43
Q

By hwo much do vili and microvili increase the surface area of the internal surface of the small bowel?

A

increase from 0.4m^2 to 200m^2

-at least 500 fold

44
Q

What are features of microvilli?

A
  • On top of enterocytes and make up the brush border
  • several thousand per cell
  • surface of microvili covered with Glycocalyx
45
Q

Describe function of the Glycocalyx?

A
  • rich carbohydrate layer on the apical membrane of enterocytes
  • serves as protection of enterocytes from digestive lumen yet allows for absorption
  • traps a layer of water and mucous kown as the ‘unstirred layer’-helps digestion and aids and controls absoption
46
Q

What is the function of Goblet cells?

A
  • 2nd most abundent epithelial cell type
  • have mucous containing granuales at the apical end of the cell
  • Mucous facilitates the passage of material e.g. food
  • number of goblet cell increase as you go down the small bowel from the duodneum towards the colon as things get thicker and harder to moves
47
Q

Describe Enterendocrine cells and function?

A
  • scattered among enterocytes
  • mostly found in the lower crypts
  • Hormone secreting -to help gut motility
  • referred to Chromaffin cells in old books dut to high affinty for chromium and silver salts
48
Q

Describe Paneth cells and function?

A
  • Found only in the BASES of Crypts
  • Contain large acidophilic granuales containing:
  • lysozymes(antibaxterila enzyme)
  • Glycoproteins and zinc(an essential trace metal for lots of enzymes)
  • engulf some bacteria and Protozoa and may have role in regulating intestinal flora
49
Q

Describe funtion of stem cells in the intestine?

A
  • In crypts
  • continousyl divide by mitosis
  • Migrate to the top of the villus replaceing older cells that have died by apoptosis
  • can differentiate into any cell type(pluripotent) e.g. oblet, enterocyte
50
Q

Why do enterocyes and Goblet cells have such a short life span(36 hours) compared to epithelium cells in other parts of the body?

A
  • Enterocytes are a first line of defenceagainst GI pathogens and may be directly affect by toxic substances in the diet
  • therefore effects of agents that interfere with the cell function will be diminished
  • any lesion will be short lived
  • can decrease chance of cancers forming
  • if replacement of enterocytes is interrupted e.g by radiation chemotherapy of pelvis, this damages the cells irreversibly and can cause severe intestinal dysfunction
51
Q

What are some differences between the duodenum and rest of the small bowel?

A

-Has BRUNNERS GLANDS at the base of the crypts and produce alkaline juice to neutralise acidic chyme in the stomach and provide optimum pH for the pancreatic enzymes

52
Q

Why are the Iliem and Jejunum different

A

Jejunum:

  • has thicker walls due to plicae circulares
  • Mesentry is to the upper and left of the aorta
  • supplied by LONG branches coming of the superior mesenteric artey and there a few arterial archades

Ilieum:

  • thinner walls as no plicae circulares
  • Mesentry is lower and to the right
  • Supplied by SHORTER branches of the superior mesenteric artery and has more arterial archades
53
Q

What are the 3 main functions of small bowel motility ?

A
  • To mix ingested foods with digestive secretions and enzymes
  • To facilitate contact between contents of the intestine and intesinal mucosa (where digestion and absorption takes place)
  • To propel intestinal contents along alimentary tract
54
Q

Describe the steps of Small Bowel motility?

A

1) Segmentation
2) Peristalsis
3) Migrating Motor Complex

55
Q

Describe the digestion of Carbohydrates?

A

1) begins in mouth with salivary alpha-amylase(destroyed in the stomach)
- Most digestion of carbs occur in the small intestine
2) Pancreatic alpha amylase is secreted into the duodenum in response to a meal -this continues the digetion of starch and glycogen that started with salivary amylase
3) Cl- is needed for optimum activity and and slightly neutral alkaline pH
4) Pancreatic amylase acts on starch and Glycogen in the LUMEN of duodenum to break them down into: alpha-dextrins, Maltotriose, and maltose
5) THe digestion of these substances and lactose, sucrose and trelahose continues in the MEMBRANE by specific enzymes to convert the substance into glucose or galactose
6) Glucose and Galactose are transported by SECONDARY ACTIVE TRANSPORT by carrier protein SGLT-1 on apical membrane
7) Fructose absoption by FACILITATED DIFFUSION by GLUT 5 on apical membrane
8) GLUT 2 used to facilitate exit of thes things the enter the cells at the basolateral end of the epithelium cells

56
Q
A
57
Q

How are proteins absorbed at the intesinal epithelium?

A

1) variety of PEPTIDASEs at the brush border that either break down the peptides into oligonucleotides or pure amino acids
2) Pure amino acids can be dircetly absorbed intot he cella dnthen into the interstitual fluids
3) olignonucleotides are chains of 3-4 AAs that are absorbed into the cell via H+/Oligopeptide transporter PepT1
4) these olignonucletides are then digested into Amino Acids by peptidases in the cytoplasm of the enterocytes

58
Q

Describe the digestion of lipids?

A

Happens in small bowel

1) secretion of bile, phospholipids and pancreatic lipases emulsify fat globules inot smaller molecules containing triglycerides
2) Lipase and colipase hydrolyse ester linkages and break it down into Monoglyceride and 2 fatty acids
3) Phospholipids, monoglycerides and fatty acids form micelles that can be easily absorped

59
Q

How are lipids absorped?

A

1) fatty acids(FA) and monoglycerides(MG) leave micelles and enter enterocytes
2) FAs and MGs resynthesised into triglycerides inside the cell by 2 pathways MONOGLYCERIDE ACYLATION(major) and PHOSPHATIDIC ACID PATHWAY(minor)
3) CHYLOMICRONS are synthesis containing(80-90% triglycerides, 8-9% phospholipids, 2% protein, 2% cholesterol and trace carbs). They are contained within a GOLGI APPARATUS
4) Chylomicrons secreted out of cell across basement membrane via EXOCYTOSIS
5) Chylomicrons enter LACTEAL(lymph capillary)->lymph transports them away form bowels

60
Q

What seperates the ilieum from the colon?

A

ileocaecal valve

-also prevents the backflow of bacteria into the ilieum

Bioregulatory systems 4 (11 decks)

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