Digestive System

1
Mariebs Human Anatomy and Physiology Ninth
Edition Marieb w Hoehn

• Chapter 23
• Digestive System
• Lectures 9 10
• Part 4 Pancreas and Pancreatic Control

2
Pancreas
Exocrine (digestive) and endocrine (metabolic)
functions Completes digestion of proteins that
was started in the stomach
3
Blood Supply and Drainage of Pancreas
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
4
Pancreatic Juice

• pancreatic amylase splits glycogen into
  disaccharides
• pancreatic lipases break down triglycerides
• pancreatic nucleases digest nucleic acids
• bicarbonate ions make pancreatic juice
  alkaline (pH 8) and neutralize acid coming from
  stomach
• Pancreatic proteolytic enzymes?

5
Pancreatic Proteolytic Enzymes
Enteropeptidase (Enterokinase)(brush border of
sm. intestine)
Know this chart
Trypsinogen
Trypsin
Chymotrypsinogen
Chymotrypsin
Pancreas
Procarboxypeptidase
Carboxypeptidase
Proelastase
Elastase
(Proenzymes, Zymogens)
(Active enzymes)
Proteins
Dipeptides, tripeptides, amino acids
Purpose of proteolytic enzymes is continued
breakdown of proteins that began in the stomach
6
Regulation of Pancreatic Secretions

• CCK and parasympathetic NS stimulate production
  and secretion of pancreatic enzymes and zymogens
• acidic chyme stimulates release of secretin
• secretin stimulates release of watery pancreatic
  juice with bicarbonate and phosphate ( buffers
  to ? pH)

7
Regulation of Pancreas/Intestinal Digestion
Key

Stimulation
Acidic Chyme Enters Duodenum

(brush border)


Enterokinase
Cholecystokinin(CCK)
Secretin

Trypsinogen
Trypsin



Gallbladder Contraction
Relaxation of hepatopancreatic sphincter
ChymotrypsinogenProcarboxypeptidaseProelastase
TrypsinogenCarboxypeptidaseElastase
Pancreas
Bile and Pancreatic ducts
(proenzymes, zymogens)
Proteins
Bile
Lipases
HCO3-, PO43-
Nucleases(DNA, RNA)
Amylase(glycogen, starches)
(emulsification)
Di- and tripeptides
TriglyceridesCholesterolFat Soluble Vitamins
? pH to 8 (req. for enzyme action)
Nucleotides
Mono-, di-, trisaccharides
Action of brush border enzymes
Fatty acids,monoglycerides
Lacteals
Portal Vein
Amino acids
Conversion to chylomicrons
Monosaccharides
Subclavian vein
8
Review

• Stomach
• Cardiac, fundus, body, pylorus
• Mixes food and begins digestion of protein
• Limited absorption (alcohol)
• Moves food into small intestine
• Pyloric sphincter (entrance to small intestine)
• Rugae and gastric pits
• Gastric glands
• Mucous cells (goblet) secrete mucous
• Chief cells (peptic) secrete digestive enzymes,
  esp. pepsinogen
• Parietal cells (oxyntic) secrete HCl (Parietal,
  pH)
• Infants only - Gastric lipase and rennin

9
Review

• Regulation of gastric activity
• Cephalic phase (primarily neural)
• Prior to food entry into stomach
• Increased motility and production of gastric
  juice
• Gastric phase
• Neural Food entering stomach / pH rising
• Hormonal gastrin release
• Local histamine release (stimulates parietal
  cells)
• Intestinal phase
• Neural distension of duodenum (enterogastric
  reflex)
• Hormonal CCK, GIP, and secretin, gastrin
• Reduction (slowing) of gastric emptying

10
Review

• Pancreas
• Both exocrine and endocrine functions
• Main source of intestinal digestive enzymes
• Pancreatic amylase (starches)
• Pancreatic lipase (fats)
• Nucleases
• Proteolytic proenzymes / enzymes
• Regulation of pancreatic activity
• Acid chyme stimulates secretin
• Secretin stimulates watery buffering secretion
• Parasympathetic NS and CCK stimulate production
  and secretion of digestive enzymes