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Digestive System Physiology > Pancreas and Liver > Flashcards

Pancreas and Liver Flashcards

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1
Q

The pancreas contains 2 types of tissue. What are these, and what are they involved in?

A

EXOCRINE tissue
ENDOCRINE tissue

Both involved in metabolism of nutrients, BUT:

  • have different functions
  • under different regulation
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2
Q

What type of cells make up exocrine tissue?

A

DUCT CELLS

ACINAR CELLS

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3
Q

What type of cells make up endocrine tissue?

A

ISLETS OF LANGERHANS

release glucagon [a cells] and insulin [b cells]

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4
Q

What is released from DUCT cells?

A

AQUEOUS ALKALINE SOLUTION
(sodium bicarb. rich)

–largest component of pancreatic juice

–neutralises chyme!
.secrete aqueous NaHCO3- [into lumen]
.absorb H+ [into blood]

(Acid-Base balance of body not altered by digestion)

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5
Q

What is released from ACINAR cells?

A

PANCREATIC ENZYMES

  • Proteolytic enzymes
  • Pancreatic Amylase
  • Pancreatic Lipase
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6
Q

What is the function of proteolytic enzymes?

A

PROTEIN digestion

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7
Q

What is the function of pancreatic amylase?

A

CARB. digestion

  • hydrolyses polysaccharides into disaccharides (maltose)
  • can be secreted in ACTIVE from as secretory cells don’t contain polysaccharides
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8
Q

What is the function of pancreatic lipase?

A

FAT digestion

  • hydrolyses triglycerides into monoglycerides & free fatty acids
  • secreted in ACTIVE from as triglycerides are not the structural component of pancreatic cells
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9
Q

What are the 3 main pancreatic proteases?

What happens when these enzymes are released into the duodenum?

A
  1. Trypsinogen
  2. Chymotrypsinogen
  3. Procarboxypeptidase

Trysinogen —(*Enterokinase)—> Trypsin
*expressed on epithelial cells

Chymotrysinogen —(Trypsin)—> Chymotrypsin
Procarboxypeptidase —(Trypsin)—> Carboxypeptidase

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10
Q

What protective mechanisms are in place to ensure the cells of the pancreas & duodenum (S.I.) aren’t digested by these proteolytic enzymes?

A
  • 3 main pancreatic enzymes are all stored in INACTIVE form
  • Trysinogen —(*Enterokinase)—> Trypsin
  • Pancreas produces TRYPSIN INHIBITOR
  • Duodenum secretes mucus
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11
Q

What is pancreatic insufficiency?

A

Pancreas not able to secrete sufficient enzumes

THUS, digestion of food incomplete/not possible

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12
Q

What is the main outcome of pancreatic insufficiency?

A

STEATORRHEA

=excess fat in faeces (~70%)

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13
Q

How are exocrine secretions regulated?

A

BY HORMONES

  • secretion
  • CCK
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14
Q

What happens when ACIDIC chyme is released into the duodenum?

A

SECRETIN release from enteroendocrine cells of duodenal wall (duod. mucosa) –>

Pancreatic DUCT cells –>

Increase secretion of aqueous NaHCO3 solution into duodenal lumen

THUS, this NEUTRALISES the acidic chyme

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15
Q

What happens when FAT & PROTEIN-RICH chyme is released into the duodenum lumen?

A

CCK release from enteroendocrine cells of duodenal wall (duod. mucosa) –>

Pancreatic ACINAR cells –>

Increase secretion of pancreatic digestive enzymes into duodenal lumen

THUS, this DIGESTS the fat & protein in chyme

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16
Q

SECRETIN

Study These Flashcards
A

Secretion of ENZYME-rich pancreatic juice

17
Q

CCK

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A

Secretion of BICARB.-rich pancreatic juice

18
Q

What is the pancreas innervated by?

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A

Predominant stimulation is during intestinal phase!

Small amount of stim. in response to VAGAL (cephalic phase) & GASTRIN (gastric phase)

-causes a limited release of pancreatic juice

19
Q

What is the major DIGESTIVE role of the Liver?

Study These Flashcards
A

SECRETION OF BILE SALTS

20
Q

Discuss blood flow to and from the liver.

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A

Liver RECEIVES blood from 2 sources:

  1. arterial blood from AORTA (via hepatic artery)
  2. venous blood from DIGESTIVE TRACT (via hepatic PORTAL vein

Blood flow FROM liver:
-via hepatic vein
(leads to INFERIOR VENA CAVA)

21
Q

Discuss blood flow in a single liver lobule

Study These Flashcards
A

Blood flows from periphery –>
Sinusoids (lined by Kupffer cells) –>
Central vein
[central veins converge to become hepatic vein!]

22
Q

Discuss the bile secretion pathway in the liver

Study These Flashcards
A

Bile secreted from hepatocytes –>
Bile canaliculus –>
Peripheral bile duct
[bile ducts converge to become the common bile duct]

23
Q

What are the components of bile?

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A

-Bile salts
(derivatives of cholesterol)

-Cholesterol

-Lecithin
(phospholipid)

-Bilirubin
(waste product from old RBCs)

-Aq. alkaline fluid
(from duct cells)

24
Q

What is the function of the GALLBLADDER?

Study These Flashcards
A

STORAGE OF BILE BETWEEN MEALS
(as the liver secretes bile continuously)

CONCENTRATES BILE (5-10x)
-actively transports salt (Na+) out, THUS H20 follows!)

–Holds 50mL of concentrated bile (so can accommodate larger volumes from the liver)

25
How does bile travel to the duodenum?
Ducts from LIVER - merge to form COMMON HEPATIC DUCT Gallbladder - CYSTIC DUCT --CYSTIC DUCT & COMMON HEPATIC DUCT merge to form BILE DUCT & sphincter
26
How do bile salts facilitate fat digestion & absorption?
1. EMULSIFICATION [digestion] | 2. MICELLES [absorption]
27
How do bile salts facilitate emulsification?
Triglycerides are INSOLUBLE in H20 THUS, aggregate in aq. S.I. Bile salt molecules absorb on the surface of lipid droplets THUS, provides a larger surface area on which the enzyme pancreatic lipase can act to digest the fats into fatty acids and glycerol.
28
What is the structure of a bile salt molecule?
LIPID-SOLUBLE PORTION (derived from non-polar cholesterol) NEGATIVELY CHARGED H20-SOLUBLE PORTION (polar hydroxyl & carboxyl groups all located on 1 side) ( (-) charge causes electrical repulsion between lipid droplets) THUS, bile salt molecules absorb on the surface of lipid droplets
29
How do bile salts facilitate micelles?
- The formation of micelles facilitates FAT ABSORPTION - 3-10nm - Bile salts & lecithin aggregate in small clusters, with fat soluble parts forming a hydroPHOBIC core -Are H20-soluble thanks to hydroPHILIC shell (But are able to dissolve lipid soluble molecules in the core. e.g. monoglycerides, FFA, vitamins & cholesterol)
30
Discuss cholesterol's ability to dissolve in the core of a micelle
The amount of cholesterol that can be carried depends on relative amount of bile salts & lecithin ``` If cholesterol secretion is out of proportion --> MICROCRYSTALS FORM (cholesterol gallstones) ```
31
What is a form of treatment for cholesterol gallstones?
Ingestion of bile salts --> THUS, increases bile salt pool --> THUS, dissolves cholesterol!
32
What is enterohepatic circulation?
BILE SALT RECYCLING Following their role in fat digestion + absorption, most bile salts are reabsorbed by active transport in the terminal ileum! (approx. twice) -they are returned via the HEPATIC PORTAL SYSTEM to liver, the re-secreted
33
What is bile secretion regulated by?
CHOLERETICS | =substances that increase bile secretion
34
What are the types of choleretics that regulate bile secretion?
--CHEMICAL BILE SALTS stimulates their own secretion when returned to liver during meal digestion --HORMONAL SECRETIN stimulates an aq. NaHCO3 bile secretion to neutralise chyme --NEURAL VAGAL stimulation of liver to increase bile flow during cephalic phase plays minor role
35
What is Bilirubin?
-2nd major component of bile! (not involved in digestion, instead a waste product excreted in bile) -Derived from degradation of HEME (iron-containing) part of haemoglobin in RBCs --bilirubin is a yellow pigment, makes bile yellow --in intestines, bilirubin is modified by bact. enzymes (makes faeces brown) --some modified bilirubin is reabsorbed & can be excreted in urine (unmodified can't pass kidneys) [makes urine yellow] --patients w. jaundice have a yellow colour as bilirubin accumulates in body (haemolytic, hepatic, obstructive)
36
What is hepatitis?
Inflammatory disease of liver!
37
What are the causes of hepatitis?
MULTIPLE CAUSES: - viral - obesity - toxic agents
38
What are the outcomes of hepatitis?
Repeated or prolonged inflammation (most commonly associated w. alcoholism leads to CIRRHOSIS!) -Active liver tissue is reduced (replaced by CT!) & eventually leads to liver failure

Digestive System Physiology (6 decks)

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