Download Comparative Vertebrate Physiology

Human Anatomy and
Physiology
Secretory functions of the
alimentary tract
Secretion from tract
Daily volume
(liters)
1.0
6 Р7
Gastric secretion
1.5
1.0 Р 3.5
Pancreatic secretion
1.0
8.0 Р 8.3
Bile
1.0
7.8
Small i ntestine secretion
2.0
7.5 Р 8.0
Large intestine secretion
0.2
7.5 Р 8.0
TOTAL
6.7
Saliva
pH
Phases of digestion



Cephalic: before food enters the
stomach
Gastric: events in the stomach
Intestinal: events in the intestine
Saliva



Parotid, submandibular, sublingual
Secretions initiated in cephalic phase by parasympathetic
influence
Composition



99.5% water, 0.5% protein and electrolytes
Protein: amylase, mucus, lysozyme
Functions




Water: softens food
Amylase: polysaccharide breakdown
Mucus: lubrication
Lysozyme: kills bacteria
Esophageal secretion

Mucus


Provides lubrication for swallowing
Transit time is about 10 seconds
Gastric secretions

1. HCl


A. Cephalic phase


By parietal cells
HCl secreted
B. Gastric phase





Breakdown proteins to peptides
More distention = more HCl release
Protein + HCl = gastrin release
Gastrin increase HCl release
Beneficial positive feedback
Gastric secretions

2. Pepsinogen - gastric phase

Stored in chief cells as zymogen granules
stomach
pepsinogen
small intestine
affect
nullified
pepsin
HCl
HCO 3
Gastric secretions

C. Intestinal phase

Inhibits gastric secretions - 3 mechanisms



Decrease parasympathetic stimulation
Local reflex action
Release of secretin, GIP and cholecystokinin
Gastric secretions

3. Mucus


Goblets cells
Functions



Prevents mechanical injury
Self digestion against pepsin
Neutralizes HCl
Inhibitors of gastric motility

1. Gastric inhibitory peptide (GIP)



Released from duodenal mucosa
Stimulus is fat and sugars in duodenum
Decreases gastric motility and secretions
Inhibitors of gastric motility

2. Secretin




Released from duodenal mucosa
Stimulus is high acidity in duodenum
Decreases gastric motility
Increases pancreas secretions
Inhibitors of gastric motility

3. Cholecystokinin




Released from duodenal mucosa
Stimulus is presence of lipid and protein
Decreases gastric motility
Increases pancreas secretions
Pancreas

Location and anatomy (acinar and duct cells)
Duct
cells
Acinar
cells
Acinar cell secretions

Proteolytic enzymes (trypsin, chymotrypsin
carboxypeptidase)


Lipase


Peptides
Fatty acids and monoglycerides
Amylase

Disaccharides: Lactose and maltose
Duct epithelial cell secretion

Bicarbonate ions

Function: neutralizes stomach acidity
Duct
cells
Acinar
cells
Hormones effecting pancreatic
secretion

1. Secretin




2. Cholecystokinin




Secreted by duodenal mucosa
In response to high [H+]
Increases bicarbonate secretion
Secreted by duodenal mucosa
In response to fat and protein
Increases total amount of enzymes secreted
3. Acetylcholine

Released from parasympathetic influence
Liver

Bile


Bile salts, bicarbonate, lecithin, water
Functions



Bile salt and water: emulsifies lipid
Lecithin: prevent reaggregration of emulsification
Bicarbonate: neutralizes gastric HCl
Hormone effecting bile release

Cholecystokinin



Released into blood by presence of fats (and
protein) in duodenum
Causes gall bladder release of bile
Causes Sphincter of Oddi to relax
Small intestine secretions

Crypts of Lieberkühn


Mucus (Brunner’s glands) and aqueous salt
Functions


Lubrication and protection
from stomach acid
Aid in enzyme breakdown
of chyme
Large intestine secretions


Crypts of Lieberkühn without
villi secretes mucus
Functions
 Protection against abrasion
 Holds feces together
 Protection against bacterial
activity