Pancreas and Small bowel

Question 1

Describe the features and functions of the Endocrine part of the pancreas

Answer 1

2% of gland

Islet of langerhans

Thy secret hormones into blood: Insulin, Glucagon, Somatostatin and pancreatic peptide

They regulate blood glucose, metabolism and growth effects

Question 2

Descirbe the features and functions of the Exocrine part of the pancreas

Answer 2

98% of gland

Secrete pancreatic juice into duodenum via MPD or sphincter of Oddi or ampulla

Digestive function

Question 3

Describe the structure an features of Acinar cells (exocrine)

Answer 3

They Have ducts

they are grape like clusters of secretory units

The acinar cells secret pro-enzymes into ducts

Question 4

Descirbe the structure and functions of islets cells . What are the derived from? What is their distribution across pancreas?

Answer 4

Derived from branching duct system

lose contact with ducts to become islets

Diffrentiate into alpah and beta cells secreting into blood

There’s a greater proportion of islets in the tail of the pancreas than the head

Question 5

What are the composition of the islets cells and what do they secrete?

Describe the vasculature of islets cells

Answer 5

• Alpha cells (15-20%)- glucagon
• beta cells (60-70%)- insulin
• Delta cells (5-10%)- somatostatin

he islets are highly vascular ensuring that all endocrine calls have close access to a site for secretion

Question 6

What are the composite cells of the acini and what are their morphological features

Answer 6

Secretory acinar cells- large with apical secretion granules

Duct cells- small and pale

Just between the acinar cells and duct cell is the centroacinar cells

*Figure out which is which on picture*

Question 7

The exocrine cells makes pancreatic juries. Descirbe the composition of the pancreatic juices made by each respective acinar cells

Answer 7

Acinar cells- low volume, viscous and enzyme rich

Duct and centroacinar cells- high volume, watery and HCO3- rich

Question 8

What is fucntion of the Bicarbonate secretion made by the duct and centroacinar cells

Answer 8

120mM [H+] from stomach (plasma conc is 25mM)

It neutralises acid chyme from stomach. This prevents damage to duodenal mucosa and raises pH to optimum range for pancreatic enzymes to work

it washes low volume enzyme secretion out of pancreas into duodenum; or else it will plug out pancreatic duct

Question 9

Compare the rate of HCO3- secretion with duodenal pH

Answer 9

When duodenal pH isa less than 5, there’s a linear increases in pancreatic HCO3- secretion

if duodenal pH is less than 3, there’s not much more increase in HCO3- secretion; the graph levels out as there’s still bile made by liver (which contains HCO3-)

Question 10

Summarise the mechanism buy which HCO3- is relased from duct and centroacinar cells ?

Answer 10

CO2 enters and converted to HCO3- via carbonic anhydrase. HCO3- leaves cell via Cl-/HCO3- exchanger (AE1 ) in apical membrane; Cl- is now in cell

H+ (From CO2 reaction result ) leaves via H+/Na+ antiporter (NHE-1) EXCHANGER via basolateral membrane. Na+ now in cells

Na+ leaves via Na+/K+ ATPase pump and K+ enter cell via basolateral membrane

k+ returns to blood via K+ channel

The Cl- leaves the cell through the apical membrane via CFTR (cystic fibrosis transmembrane conductance regulator)

Question 11

Compare the outcomes of the bicarbonate reactions in the stomach parietal cell and pancreatic duct cells

Reaction : H₂O + CO₂= H₂CO₃ = H⁺ + HCO3-

Answer 11

Question 12

What enzymes are relases from acinar cells? What are they relased as

Answer 12

Lipases, proteases and amylase

they are sysntheised and stores in zymogen granules

Proteases released as inactive proenzyme; it protects the acini and ducts from autodigestion

Question 13

What does the pancreas release that inactivate trypsin? When are the enzymes activated

Answer 13

Trypsin inhibitor

enzymes only activated in duodenum

blockage of Main pancreatic duct may overload it and it could cause autodigestion

Question 14

Descirbe the process of how pancreatic enzymes are activated? What activates it

Answer 14

Duodenal mucosa secrets enterokinase/enteropeptidase. This converts trypsinogen to trypsin and trypsin converts all the other zymogen to their acitve form

Lipase requires bile salts for effective action, and also requires colipase to become its active form

Question 15

How does the pancreas adapt to diet?

Answer 15

High protein diet and low carb diets will make pancreas release more proteases and less amylase proportion

These enzymes (and bile) are essential for absorption, if inhibited it will cause malnutrition even if dietary input is OK

Question 16

Summarise the 3 phases for the control of pancreatic juice secretion

Answer 16

Cephalic pahse- reflex to smell or sight of food. Secrete only enzyme rich pancreatic juices (enzymes only - low volume)

Gastric pahse- distension in stomach activates this. Same mechanism as cephalic pahse

Intestinal phase- 70-80% of secretions. This is hormonal mediated when gastric chyme enters duodenum. BOTH enzymes and HCO3- enter duodenum

Question 17

What controls the relases of enzymes from acini cells?

Answer 17

Vagus nerve- PNS cholinergic (ACh)

Cholescystokinin (Ca2+/PLC mediated)

Question 18

What controls the secretion of pancreatic juices (bicarbonate) form duct and centroacinar cells

Answer 18

Secretin (cAMP mediated)

Question 19

Summarise how vagal and CCK stimulation control enzyme secretion in acini

Answer 19

CCK made from duodenal I cells

The diagram shows what causes release of CCK, however CCK goes and act on pancreas as a positive feedback loop

Question 20

Describe the mechanism which controls HCO3- secretion in acinar cells AND DUCTS

Answer 20

CCK mainly cause acinar fluid to be made- acinar fluid is isotonic to plasma (Na+,K+,Cl-, HCO3-)

Secretin stimulates secretion of H2O and HCO3- from cells lining extralobular ducts

SECRETIN stimulated secretion is richer in HCO3- cf acinar secretion becuase of Cl-/HCO3- exchange

Question 21

Describe the negative feedback involved in HCO3- secretion in ducts

Answer 21

Lower pH in luminal duodenum is the stimulus

Question 22

Outline the different stimulus that can affect rate of HCO3- secretion from ductal cells. Note any differences in outcome

Answer 22

Vagus nerve is similar effect to CCK

secretin has no effect on enzyme secretion

CCK and secretin stimulation GREATLY increase HCO3- secretion

Question 23

Outline the summary of a meal and how it can affect pancreatic secretions . Draw flowchart

Answer 23

Question 24

Compare the length of the components of the small bowel

Answer 24

Duodenum- 25cm

jejunum- 2.5m

ileum-3.75m

No sudden transition between them and they all have the same basic histology all organisation

Question 25

What are the functions of the mesentery?

Answer 25

Suspends small and large bowel from posterior abdominal wall; it anchors them in place whilst still allowing some movement Provides a conduit for blood vessles, nerves and lymphatic vessels

Question 26

Why is the jejunum thicker and darker than the duodenum and ileum

Answer 26

It has structures called **plicae circulares which others DON'T HAVE**

Question 27

Descirbe the small bowel digestive epithelium . Draw important ones

Answer 27

Question 28

What are the features of the villi describe the blood supply and innervation and dimension

Answer 28

Only occur in small intestine motile Hve rich blood supply and lymph drainage for absorption of digested nutrients Have good innervation from submucosal plexus Have simple epithelium: 1 cell thick and dominated by enterocytes

Question 29

What cells lines the villi?

Answer 29

Simple columnar epithelium consisting of: 1. primary enterocytes 2. scattered goblets cells 3. enteroendocrine cells

Question 30

What cells make part of the crypt of Lieburken?

Answer 30

Paneth cells Stem Cells

Question 31

What are the features of the enterocytes?

Answer 31

Most abundant cells in small bowel Tall columnar cells with micorvilli and basal nucleus specialised for absorption and transport of substances Short lifespan of 1-6 days the mcirovilli increase the surface area by 500 fold (to 200m²)

Question 32

What are the features of the Microvilli

Answer 32

Forms brush border and the surface is covered with **Glycocalyx** **GLYCOCALYX:** * rich in carbohydrate layer on apical membrane * serves as protection from digestional lumen and yet allows for absorption * traps a layer of water and mucus know as **unstirred layer: this regulates the rate of absorption from intestinal lumen**

Question 33

What are the features of Goblet cells and describe it's distribution across (down the) bowel

Answer 33

**2nd** most abundant epithelial cell type mucous containing granules accumulate at te apical end of cells causing goblet shape 'The abundance of goblet cells **decreases** in duodenum and **increases** in colon as the content in colon is much harder and hence needs mor assistance form mucus

Question 34

What are the features of Enteroendocrine cells

Answer 34

They are columnar epithelial cells that are scattered among enterocytes Most often found in lower parts of crypts Hormone secreting to influence gut motility sometimes reffed as chromaffin cells - high affinity for chromium/silver salts

Question 35

What are the features and functions of the Paneth cells

Answer 35

Found only in the bases of the crypts They also engulf some bacteria and Protozoa They have a role in regulating intesitnal flora Contain large, acidophilic granules containing: * lysozyme * glycoproteins and zinc- essential trace metal for a number of enzymes

Question 36

What are the features and functions of the stem cells

Answer 36

**They are essential in GI tract to continually replenish surcface epithelium** they continually divide by mitosis and migrate to tip of villus to replace older cells that die by apoptosis then they diffrentiate into different types of cells

Question 37

Why do enterocytes/goblet cells have a short life span compared to other cells

Answer 37

The enterocytes are constantly damaged form contents in bowel and hence die to stop it form growing cancerous.

Question 38

How can the duodenum be distinguished from other contents (parts) of the small bowels

Answer 38

Brunner's glands : these are submucosal coiled tubular mucosa glands that secrete alkaline fluid. * These neutralise acid chyme form stomach, protecting proximal small bowel * Help to optimise pH for action of pancreatic digestive enzyme They open into the base of the crypts

Question 39

How can you differentiate the jejunum from ileum

Answer 39

Jejunum- thicker walls and presence of **pilicae circulares**

Question 40

What are the functions of the small intestine motility

Answer 40

Mix ingested food with digestive secretions and enzymes Facilitate contact between contents of intestine and intestine mucosae Propel intestinal contents along intestinal tracts

Question 41

Descirbe the environment in which duodenal digestion takes place, what causes this? Where does digestion occur

Answer 41

Alkaline environment Pancreatic digestive enzymes and bile enter dueodenum via main pancreatic duct and common bile duct Duodenal epithelium produces it's own digestive enzymes; digestion occurs in lumen and in contact with membrane

Question 42

Where does digestion of carbs start and end?

Answer 42

Start in mouth via salivary amylase MOST of digestion of carbs are in small intestine simple and complex carbs(starch and pectins) can be broken down

Question 43

What is the function of pancreatic amylase and what is the condition needed for it to work?

Answer 43

Digest starch and glycogen in small bowel Needs Cl- for optimum activity and neutral/slightly alkaline pH Acts mainly in lumen (however some adsorbs to brush border)

Question 44

In what part (layer) of the duodenum does digestion of amylase products take place?

Answer 44

Amylase work in lumen but the other enzymes work in brush border

Question 45

What are the channels (channel proteins and carrier proteins) involved in digestion of carbs. Summarise

Answer 45

Absorption of glucose and galactose is by **secondary active transport**- carrier protein is SGLT-1 on apical membrane Absorption of fructose is by facilitated diffusion; carrier protein is GLUT 5 on apical membrane GLUT-2 facilitates exit into blood at basolateral memebrane N.B humans intestine can absorb 10kg of simple sugars a day

Question 46

Describe the function of trypsin

Answer 46

Activate other proteases- which then hydrolyse proteins i to single amino acids and oligopepetides

Question 47

What happens to the pepsin from the stomach once it reaches the duodenum

Answer 47

Inactivated in alkaline conditions of duodenum

Question 48

Describe the absorption of proteins in brush border of small intestine

Answer 48

Variety of **peptidases** at brush border enterocytes hydrolyse oligopeptides into AAs- this is absorbed via Na+/AA co-transporter Some enteocytes directly absorb some oligopeptide via action of H+/oligopeptide cotransporter (**PepT1**) these small peptides are digested into AAs by peptiodases in cytoplasm of enterocyte

Question 49

Descirbe the 4 stage process of digestion of lipids

Answer 49

Secretion of bile salts and pancreatic lipases Emulsification Enzymatic hydrolysis of ester linkages; colipase complex with lipase to prevent bile salts displacing lipase from fat droplet Solubilisation of lipolytic products in bile salt micelles

Question 50

Descirbe the absorption process of lipids

Answer 50

FFAs or monoglyceride leave micelles and enter enterocytes They are resynthsised into TGs via 2 pathways: * Monoglyceride acylation (major) * Phosphatidic acid pathway (minor) Then chylomicrons are synthesised in goligi apparatus Secreted across basement membrane by exocytosis Chylomicrons enter lacteal (lymphatic system); then enter blood at subclavian

Question 51

Describe the features and function of the ileocaecal valve

Answer 51

This separates the ileum from the colon it relaxes and contracts to control passage of material into colon it also prevents back flow of bacteria into ileum; colon has a lot more bacteria

Question 52

Contrast segmentation and peristalsis

Answer 52

Question 53

Label this diagram

Answer 53

Question 54

Label this diagram AND LINK it to pancreatic embryology

Answer 54

Proximal duodenum rotates clockwise and the ventral pancreatic duct buds and becomes the main pancreatic duct. The dorsal atrophies or becomes the accessory pancreatic duct. any deviation in this process will lead to dorsal pancreatic duct becoming main (Santorini) and this isn't sufficient for high flow of pancreatic juices, hence pathological

Question 55

Label this diagram

Answer 55

Question 56

Label this diagram

Answer 56