Physiology Block 3 Week 13 04 GI Secretion 02

Question 1

Pancreas Secretions

Answer 1

Pancreatic secretions in response to chyme in upper small intestine with juice characteristics dependent on type of food

Common opening at sphincter of Oddi

Question 2

Pancreatic Proteins

Answer 2

Trypsin, Chymotrypsin, and Carboxypeptidase
–all secreted in inactive form

Trypsinogen –> Trypsin by enterokinase

Trypsin activates more trypsinogen, and converts chymotrypsinogen and procarboxypeptidase

Trypsin inhibitor prevents activation until secretions reach small intestines

Question 3

Protein Breakdown

Answer 3

Proteins broken down by Pepsin
Forms Proteoses, Peptones, and Polypeptides

Further degradation by Trypsin, Chymotrypsin, Carboxypeptidase, and Proelastase
Forms Polypeptides and Amino Acids

Further breakdown by Peptidases
Forms Amino Acids

Question 4

Carbohydrate Breakdown

Answer 4

Starches broken down to maltose and 3 to 9 glucose polymers

Enzymes:

• Ptyalin (saliva)
• Pancreatic amylase ** 50-80%

Question 5

Fat Breakdown

Answer 5

Majority we eat are Triglycerides

Pancreatic Lipase (fatty acids and monoglycerides)

Cholesterol esterase (Cholesterol esters)

Phospholiase (splits fatty acids from phospholipids)

Question 6

Bicarbonate Secretion

Answer 6

To neutralize acid in the upper small intestine

CO2 moves into cell from blood
Carbonic Anhydrase converts to bicarb
Bicarb actively transported out into the lumen

Question 7

Pancreatic Secretion Stimuli

Answer 7

Acetylcholine–acini

Cholecystokinin–acini
70% of total pancreatic digestive enzyme secretion

Secretin–pancreatic duct
-prosecretin converted to secretin by low pH in small intestine

Question 8

Phases of Pancreatic Secretion

Answer 8

Cephalic: 20% –mostly digestive enzymes

Gastric: 5%

Intestinal: 75%–bicarbonate rich solution

Question 9

Water vs Enzyme Secretion

HCl
Soap (Fat)
Peptone

Answer 9

HCl: mostly Water and Bicarb

Soap: equal amounts of Water and Bicarb and Enzymes

Peptones: mostly enzymes

Question 10

Pancreatic Insufficiency

Answer 10

Multiple causes including chronic alcohol use

Can affect both exocrine and endocrine functions when 90% of function is lost

Exocrine:

• weight loss: can’t break down fats
• steatorrhea: it floats

Endocrine:
-Diabetes Mellitus

Question 11

Hepatic Histology

Answer 11

Portal Triad–Portal Vein, Hepatic Artery, Bile Duct
Also Lymphatic duct (but discovered later)

Portal Vein and Hepatic Artery feed every corner of the Hepatic LOBULE and drains into central vein

Central Vein drains to the hepatic vein which drain into the IVC

Lobules drain into central vein through sinusoids

Sinusoids are fenestrated–blood can go thru the pores and come in contact with hepatocytes
Toxic stuff are cleaned and sent to central vein

Kupffer cells (surround sinusoids) act as phagocytes and remove bacteria

Substances that carry (like proteins) interact with hepatocytes too

Space of Disse–drain into lymphatic duct

Stellate Cell (within space of Disse)–makes collagen when irritated–leads to cirrhosis

Hepatocytes are arranged in plates joined by tight junctions, and their apical membranes make up the bile canaliculi
Segregated from the blood-filled sinusoids by fenestrated endothelial cells without a basement membrane, and by space of Disse
Kupffer cells reside in the sinusoidal lumen
Stellate cells are found within the space of Disse

Question 12

Biliary System

Answer 12

Bile assists in fat digestion and absorption as well as to eliminate waste products such as BILIRUBIN

Right and Left Hepatic ducts from liver drain into common hepatic duct

Cystic duct (gallbladder) connects distally with common hepatic forming common bile duct

Pancreatic duct connects with common bile duct distally

Bile secretion at 2nd part of duodenum controlled by Sphincter of Oddi

Question 13

Storage of Bile in Gallbladder

Answer 13

Mechanism for Concentration:
Absorption of Water
NaCl leads to concentration of bile salts, cholesterol, lecithin, and bilirubin

Cholesterol and lecithin are solubilized by bile salts
Volume goes from 500 ml to 50 ml

Question 14

Cholesterol Homeostasis

Answer 14

The combined fecal excretion of cholesterol and bile acids is equivalent to input of cholesterol from the DIET plus ENDOGENOUS SYNTHESIS of cholesterol

Question 15

Bile Salt Formation

Answer 15

Cholesterol broken down by hydroxyase
–Primary Bile Acids

Broken down by dehydroxylase
–Secondary Bile Acids

Conjugated with glycine
–Bile salt (NOW SOLUBLE)

Question 16

Bile Salt Function

Answer 16

Emulsification
-decreases surface area tension and breaks fat globules into smaller size particles

Forms Micelles

• soluble in chyme
• helps absorption of fat breakdown products (fatty acids, monoglycerides, cholesterol)

Question 17

Gallstone Formation

Answer 17

Majority of gallstones are cholesterol stones

Bile salts allow cholesterol to remain soluble

Fat, Forty, Fertile, Female

Causes:

1. Too much absorption of water from bile
2. Too much absorption of bile acids from bile
3. Too much cholesterol in bile
4. Epithelium inflammation

Question 18

Acute Pancreatitis

Answer 18

Causes:

• alcohol and gallstones
• medications
• elevated triglycerides
• hypercalcemia

Pt complains of severe upper abdominal pain

Blood tests show elevated lipase and amylase

Need to have pain and elevated lipase and amylase

Question 19

Biliary Atresia

Answer 19

The bile ducts inside or outside the liver do not have normal openings

With biliary atresia, bile becomes trapped, builds up, and damages the liver. The damage leads to scarring, loss of liver tissue, and cirrhosis.

Question 20

Gallbladder Contraction and Emptying

Answer 20

Vagal stimulation
–causes weak contraction of gallbladder

Secretin via blood stream
–stimulates liver ductal secretion
–produce a solution rich in NaHCO3:
helps neutralize acids and optimize pancreatic function

Cholecystokinin via blood stream (released bc fatty foods in duodenum)** (Major)

• -gallbladder contraction
• -empties in under 1 hour
• -relaxation of sphincter of Oddi

Question 21

Where are bile salts reabsorbed?

Answer 21

Enterohepatic circulation:

Bile salts reabsorbed mostly in terminal ileum–95%

Question 22

Bilirubin Metabolism

Answer 22

When RBC old or damaged, sent to spleen for breakdown
Hb released and broken down to heme
Heme converted to unconjugated bilirubin
Not water soluble, so binds albumin and sent to liver

In the liver, bilirubin CONJUGATED with glucuronic acid by glucuronyltransferase–now water soluble

Bile duct:
Large intestine flora break it down further creating urobilinogen
Broken down further to stercobilin (feces brown color) and urobilin

Systemic Circulation:
Some Urobilinogen reabsorbed and excreted in urine and oxidized to urobilin (gives yellow color)

Question 23

Direct vs Indirect Bilirubin Elevation

Answer 23

Elevated Indirect (unconjugated) Bilirubin:

• increased breakdown of RBC
• inability of bilirubin-albumin adduct to be taken up by hepatocytes (transport mech)
• inability of hepatocytes to conjugate bilirubin (enzyme deficient)

Elevated Direct Bilirubin:

• hepatocyte dysfunction
• biliary obstruction

Amount of light will determine at what total bilirubin value you are able to detect scleral icterus (yellow instead of while sclera)

Question 24

Small Intestine Secretions

Answer 24

Brunner’s Glands (duodenum):
-secrete alkaline mucus to protect mucosa

Produced in response to:

• tactile or irritating stimuli
• vagal stimulation
• SECRETIN

Inhibited by sympathetic stimulation

Question 25

Crypts of Lieberkuhn

Answer 25

Found in all parts of the Small Intestine between the villi

Secrete almost pure ECF

Goblet cells: secrete mucus
Enterocytes: secrete water and electrolytes

Question 26

Digestive enzymes on villi surface

Answer 26

Peptidase on small intestine villi surface

Break down peptides into amino acids

Question 27

Carbohydrate Digestion

Answer 27

Small intestine

Disaccharides are broken into monsaccharides by sucrase, maltase, isomaltase, and lactase

Question 28

Large Intestine Secretions

Answer 28

No villi present

Crypts of Lieberkuhn without villi
Mucus secretion:
-protects mucosa from excoriation, acid
-packing of stool
-antibacterial properties

Parasympathetic innervation through pelvic nerves (S2-S4) stimulate mucus production

Question 29

Which of the following has its major effect on the pancreatic duct epithelium?

A. Acetylcholine
B. CCK
C. Secretin
D. Amylase

Answer 29

C. Secretin

Question 30

True statements regarding bilirubin metabolism include all of the following except?

A. Under normal conditions the majority of bilirubin is derived from the breakdown of RBC
B. Bilirubin binds to albumin once within the hepatocyte
C. Stercobilin is found in feces
D. Conjugated bilirubin flows into bile canaliculi

Answer 30

B. Bilirubin binds to albumin once within the hepatocyte

Happens in the plasma and then transported to the hepatocyte

Question 31

Ascities

Answer 31

Accumulation of fluid in the peritoneal cavity

Cause:

• umbilical hernia (even an inguinal hernia)
• Caput medusae