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Biology 1203 Week 2
Diges2on I & II Diges2on Lab
Diges2ve anatomy lab Part 1: Locate and describe func2on of primary and accessory diges2ve organs
Explain how a hamburger is digested
Part 2: Demonstrate competency with the microscope Iden2fy major parts of microscope
as in Biol 1103 Histology of diges2ve system
DIGESTIVE SYSTEM What are the main processes that occur?
1. Describe the rela2onship between the following processes in gastrointes2nal system: inges0on, diges0on, absorp0on, defeca0on
2. Dis2nguish between extracellular diges0on and intracellular diges0on
Learning Objec2ves Anatomy & Physiology of the Diges2ve System
3. Describe the anatomy and func2ons of the: a. Buccal cavity (deglu22on) e. Pancreas
b. Esophagus f. Small intes2ne
c. Stomach g. Large intes2ne (defeca2on)
d. Liver (connec2on to gall bladder and its blood supply)
2013 Pearson Educa2on, Inc.
1. Ingestion
2. Digestion
3. Absorption
4. Defecation
Food
Pharynx Esophagus
Stomach
Lymph vessel
Small intes2ne Large intes2ne
Blood vessel
Feces
Anus
Processes in the diges2ve system 1. Inges0on
The process of taking food/liquid into the mouth
2. Diges0on Breakdown of food into
smaller pieces Mechanical: physical
breakdown (e.g., teeth) Chemical: breakdown of
molecules using enzymes 3. Absorp0on
Movement of digested products into the lumen of the GI tract, then into lympha2c and circulatory system
4. Defeca0on Elimina2on of indiges2ble
substances, wastes, bacteria, and unabsorbed substances
Extracellular Diges0on Food processing in the
diges2ve system OUTside cells by enzymes
produced by the diges2ve tract cells & glands
Plasma membrane
Phagocy0c vacuole
Diges0ve enzymes
Diges0on
Lysosome
Intracellular Diges0on Phagocy2c ac2vity of
white blood cells INside cell by enzymes of
lysosomes
Dis$nguish the 2 processes and give an example of each
DIGESTIVE SYSTEM Loca2on and general overview
1. Describe the rela2onship between the following processes in gastrointes2nal system: inges0on, diges0on, absorp0on, defeca0on
2. Dis2nguish between extracellular diges0on and intracellular diges0on
Learning Objec2ves Anatomy & Physiology of the Diges2ve System
3. 9. Describe the anatomy and func2ons of the:
a. Buccal cavity (incl. deglu22on) e. Pancreas
b. Esophagus f. Small intes2ne
c. Stomach g. Large intes2ne (defeca2on)
d. Liver (connec2on to gall bladder and its blood supply)
The Diges2ve System
Divided into two groups of organs: Gastrointes0nal (GI) tract Accessory diges0ve organs
Right lateral view of head and neck and anterior view of trunk
Tortora Figure 24.1, pg 968
Mouth (oral cavity) - contains teeth and tongue Paro$d gland
(salivary gland)
Stomach Pancreas
Large intes2ne Rectum Anal canal Anus
Esophagus Liver
Small Intes2ne Gallbladder
Diges2ve System
Layers of the GI Tract
Artery
2. SUBMUCOSA
3. MUSCULARIS: Circular muscle Longitudinal muscle
4. SEROSA: Areolar connec2ve 2ssue Epithelium
Muscularis mucosae
1. MUCOSA: Epithelium Lamina propria
Nerve
4 layers Mucosa structurally varies most
between organs protec2ve stra.ed squamous epithelium
(outer organs); simple columnar epithelium for absorp2on/secre2on (inner organs)
Tortora Figure 24.2, pg 970
BUCCAL CAVITY Anatomy and role in diges2on
Anterior view Tortora Figure 24.5, pg 975
Lips
Tongue (lifed upward)
Opening of duct of submandibular gland
Hard palate
Sof palate
Uvula
Cheek
Teeth
The Buccal Cavity
The Buccal Cavity Func2ons
Teeth: mas0ca0on to reduce par2cle size Tongue: skeletal muscle moves food around the buccal
cavity mixing it with saliva to form bolus and contains taste receptors
Saliva: secreted by salivary glands (1-1.5L/day) 99.5% water; 0.5% solutes (mucus, ions, bicarbonate, salivary amylase, lysozyme, dissolved gases)
Func2ons: Ini0al diges0on of starch in the mouth (amylase) Generally keeps mouth
moist and clean
The feel, taste, smell, sight, sound or thought of food can also promote saliva2on (cephalic phase of diges2on)
Starch Maltose
salivary amylase
... ...
Paro2d duct
Opening of paro2d duct (near second maxillary molar)
Second maxillary molar tooth
Tongue (raised in mouth)
Lingual frenulum
Sublingual ducts
Submandibular duct
Mylohyoid muscle SUBMANDIBULAR GLAND
PAROTID GLAND
Lesser sublingual duct
SUBLINGUAL GLAND
Loca2on of the major salivary glands
Tortora Figure 24.6, pg 976
ESOPHAGUS Anatomy and func2on
2013 Pearson Educa2on, Inc. Microscopic structure of the esophagus.
Mucosa (stra2ed squamous epithelium)
Submucosa (connec2ve 2ssue) Lumen Muscularis externa Circular layer Longitudinal layer
Adventitia (brous connec2ve 2ssue)
Marieb Figure 23.12a, pg 862
The esophagus Posterior to larynx
Runs from pharynx to stomach (25cm)
Upper and lower esophageal sphincters
The esophagus Transports food to the stomach through the ac2on of peristalsis (4-8s)
Upper and lower sphincters that relax during swallowing Regulate the passage of food into and out of the esophagus
No enzymes are secreted in the esophagus Salivary amylase con2nues to digest carbohydrates
Does any diges$on occur in the esophagus?
Peristal2c movement
Recall that the GI tract has 2 layers of muscle In a sec2on of the tract, circular muscles contract, squeezing the tube
At the same 2me in the sec2on inferior to the circular muscles, the longitudinal muscles contract, widening tube and shortening it
These two ac2ons proceed, sec2on by sec2on down the length of the tube
Be able to briey describe the process of peristalsis in your own words
2013 Pearson Educa2on, Inc.
Deglu22on (swallowing) Bolus of food
Tongue Pharynx Epiglojs Glojs Trachea
Buccal phase 1
Uvula Bolus EpigloUs
Esophagus
Pharyngeal phase
Esophageal phase
Esophageal phase contd
Esophageal phase contd .
Relaxed muscles Circular muscles contract Bolus of food
Longitudinal muscles contract
Gastroesophageal sphincter closed
Relaxed muscles
Circular muscles contract
Gastroesophageal sphincter opens
Upper esophageal sphincter Bolus
2
4
3
5
Stomach
Marieb Fig 23.13; pg 864
Upper esophageal sphincter
Prac2ce Ques2on 1
Gastroesophageal reux disease (GERD) What happens? Inadequate closure of the lower esophageal sphincter (LES)
Contents of the stomach move up (reux)
Why is this a problem? Low pH due to hydrochloric acid burns the unprotected esophageal wall (heartburn)
What is the cause? Alcohol, caeine, smoking
How are the symptoms controlled? Diet and medica2ons
STOMACH Anatomy and func2on
Greater curvature
Lesser curvature
Anterior view of regions of stomach
PYLORIC ANTRUM
CARDIA BODY
FUNDUS
PYLORIC CANAL
Pyloric sphincter
Duodenum
Esophagus
Lower esophageal Sphincter (LES)
PYLORUS
Tortora Figure 24.11, pg 983
Stomach Car is Fun 0l Bodies Pile
MUCOSA
SUBMUCOSA
MUSCULARIS - 3 layers
Gastric pits
SEROSA
Lumen of stomach
Three-dimensional view of layers of stomach
Tortora Figure 24.12, pg 984
Stomach layers
Gastric pit cell types and secre2ons
Gastric lipase
Gastric juice: Hydrochloric acid (HCl) Enzymes pepsinogen gastric lipase
Hormones - gastrin
Proteins Pep2des pepsin
Stomach Chemical Diges2on
pepsinogen
HCl N C
N C N C
Triglycerides (or diglycerides) Monoglycerides + Fapy Acids
gastric lipase
Triglycerides Diglycerides + Fapy Acids lingual lipase HCl
Why does the stomach not digest itself?
Pepsinogen secreted in inac0ve form of enzyme (low pH of acid ac2vates it pepsin) Mucous barrier containing bicarbonate (basic) ions to neutralize acid Rapid cell divisions replace damaged cells
Func2ons of Stomach Component Func0on
Lumen Food storage Smooth muscle Mechanical diges2on through mixing waves Gastric juice Hydrochloric acid (HCl):
oAn0bacterial oDenatures proteins oAc2vates pepsinogen oAc2vates lingual lipase
Pepsinogen: precursor of pepsin Pepsin: protein-diges2ng enzyme Gastric lipase
Endocrine glands Hormone gastrin s2mulates release of gastric juice Pyloric sphincter Regulates passage of food to duodenum Result: Chyme
Summary Diges2ve system consists of GI tract (~ 9m long tube open
to the external environment; 4 2ssue layers) and accessory organs that aid diges2on
Following inges2on: food is broken up in the oral cavity by mas2ca2on and saliva secre2on (including mucus and amylase) to produce a sof bolus of food for swallowing (deglu22on)
Deglu22on consists of 3 phases in which the bolus moves from mouth to stomach via the pharynx and esophagus
Stomach stores, churns and mixes food with (acidic) gastric secre2ons to produce liquid chyme to pass to the small intes2ne through pyloric sphincter; some protein and lipid diges0on occurs here but minimal absorp2on (water, ions, short chain FA, alcohol)
Prac2ce Ques2on 2
ACCESORY DIGESTIVE ORGANS Anatomy and func2ons of liver, gall bladder, pancreas
The small intes2ne is where the bulk of diges0on and absorp0on occur
However, we must rst cover several essen2al accessory diges2ve organs, as their role is important for the proper func2oning of the small intes2ne Liver Gall Bladder Pancreas
Accessory diges2ve organs
Falciform ligament
Diaphragm
Anterior view Tortora Figure 24.15, pg 989
Right lobe of liver
Lef hepa2c duct Right hepa2c duct
Cys2c duct
Gallbladder
Duodenum
Hepatopancrea0c ampulla (ampulla of Vater)
Common bile duct
Common hepa2c duct
Pancreas
LeZ lobe of liver
Pancrea0c duct
Liver
Pancreas Func0ons I. Diges2on (as an exocrine gland; 99% cells)
Pancrea2c juice: diges2ve enzymes and bicarbonate
II. Metabolism (as an endocrine gland; 1% cells) Glucose-regula2ng hormones: insulin and glucagon
Be able to describe these enzymes and know the site of ac$on
Diges0ve enzymes: Carbohydrates: pancrea0c amylase
(starch to maltose) Lipids: pancrea0c lipase (lipids to
triglycerides) Proteins (secreted in inac2ve form):
trypsinogen, chymotrypsinogen, procarboxypep0dase, proelastase (all digest proteins to pep2des)
Tortora Figure 24.15, pg 989
I. Diges2on i. Produc2on of bile salts
II. Metabolism i. Catabolism (breaking down of substances)
a. Hemoglobin (producing bilirubin) b. Amino acids (producing urea) c. Hormones
ii. Anabolism (synthesis of substances) a. Plasma proteins b. Glycogen
iii. Storage a. Glucose (as glycogen) b. Fat-insoluble vitamins (A, D, E, K) c. Some minerals (Cu, Fe)
III. Detoxica2on of foreign substances (alcohol, drugs)
Liver Func2ons
Oxygenated blood from hepa0c artery
Right atrium of heart
Nutrient-rich, deoxygenated blood from hepa0c portal vein
Inferior vena cava
Liver sinusoids
Hepa2c vein
Central vein
2
3
4
5
6
1
Hepa2c blood ow
Tortora Figure 24.17, pg 989
Importance of hepa2c portal system
Allows modica2on of nutrients absorbed from the diges2ve tract by the liver cells
Liver removes toxins from the blood and adds plasma proteins
Controls nutrients and substances entering the rest of the circulatory system
Gall bladder
Small pear shaped sac tucked into anterior inferior surface of liver
Stores and concentrates bile salts Bile released into the duodenum of the small intes2ne
Liver, Gall Bladder and Pancreas Connec2on with the Duodenum
Ampulla of Vater
Pancrea0c duct & duct of Santorini
Accessory Organs: Review quiz
Which organ produces bile? Which duct carries bile to the small intes2ne? Which organ plays an important role in energy metabolism?
Why does pancrea2c juice contain bicarbonate?
SMALL INTESTINE Anatomy and func2ons
Small Intes2ne Gross Anatomy
Duodenum
Jejunum
Large intestine
Ileum Rectum Jejunum
Func2ons of small intes2ne Produces intes2nal juice
Bicarbonate ions: further neutraliza2on of acidic chyme Mucus: for further lubrica2on
Most important site of chemical diges0on Comple2on of diges2on Produces diges2ve enzymes for carbohydrates and proteins (brush-
border enzymes) NB. Diges2ve enzymes from pancreas and bile (from liver) mix with
intes2nal juice in small intes2ne to aid diges2on
Absorp2on of 90% nutrients and water
Releases secre0n and cholecystokinin hormones s2mulate pancrea2c juice and bile release
Large surface area of small intes2ne enhances nutrient diges2on and absorp2on
Circular folds
Great length of small intestine
Brush border (with digestive enzymes)
Microscopic anatomy of small intes2ne
Marieb Figure 23.22, pg 876
Chemical Diges2on in the Small Intes2ne Carbohydrates
maltase sucrase lactase
Brush-border enzymes of the intes2ne
Sucrose sucrase Glucose + Fructose
Starch Maltose
pancrea$c amylase maltase
Glucose ... ...
Lactose lactase
Glucose + Galactose
Chemical Diges2on in the Small Intes2ne Lipids
Triglycerides (or diglycerides) Monoglycerides + Fapy Acids
pancrea$c lipase
Emulsica.on Fat globule
Bile salt Fat droplet coated with bile salts
Chemical Diges2on in the Small Intes2ne Proteins
Proteins Pep2des
trypsin chymotrypsin
N C
N C
carboxypep$dase aminopepdidase
dipep$dase
Amino Acids
trypsin
chymotrypsin carboxypep$dase aminopep$dase dipep$dase
endopep2dases
exopep2dases
Pancrea2c enzymes
Brush-border enzymes of the intes2ne
N C
Ac2va2on of protein diges2ve enzymes
Released from the pancreas, ac2vated in the duodenum (small intes2ne)
Trypsinogen is converted to trypsin by enterokinase (found on the intes2nal wall)
Trypsin starts to digest proteins and also converts chymotrypsinogen to chymotrypsin and procarboxypep2dase to carboxypep0dase
Absorp0on of nutrients
Most nutrients (macronutrients, minerals, vitamins) and water (90%) are absorbed in the small intes0ne
2 stages to nutrient absorp2on from GI tract enter intes0nal cells lining villi, enter either the bloodstream or the lympha0c system
Nutrients to be absorbed take the following route from the lumen of the GI tract: Plasma membrane into the intes2nal cell Plasma membrane out of the intes2nal cell
Carbohydrate Absorp2on
Glucose and galactose
Fructose
Intes2nal lumen Intes2nal cell (with microvilli)
Blood (villus capillary to hepa2c portal vein)
Carbohydrate Absorp2on
Absorp2on into intes2nal cell: Glucose, galactose, mannose: ac2ve transport (secondary)
Fructose: facilitated diusion Leaving the intes2nal cell: Glucose, galactose, mannose, fructose: facilitated diusion
Route to the liver: Bloodstream, via the hepa2c portal vein
Be able to describe the diges2on, absorp2on, and transport of carbohydrates
Lipid Absorp2on
Lipid Absorp2on Absorp2on into intes2nal cell (detach from micelles): Short chain fapy acids: simple diusion Long chain fapy acids: simple diusion
Leaving the intes2nal cell: Short chain fapy acids: simple diusion Long chain fapy acids: rebuilt into triglycerides and combine with proteins (cholesterol and phospholipids) to form chylomicrons, which leave cell by exocytosis
Route to the liver: Short chain fapy acids (& glycerol): bloodstream, via the hepa2c portal vein
Long chain fapy acids: lacteal, lympha2c system (to thoracic duct to enter systemic blood circulatory system)
Be able to describe the diges2on, absorp2on, and transport of lipids
Absorp2on of Amino Acids
Facilitated
Intes2nal lumen Intes2nal cell (with microvilli)
Blood (villus capillary to hepa2c portal vein)
Protein Absorp2on
Absorp2on into intes2nal cell: amino acids, dipep2des, tripep2des: ac2ve transport (primary and secondary)
Leaving the intes2nal cell: amino acids, dipep2des, tripep2des: facilitated diusion
Route to the liver: Bloodstream, via the hepa2c portal vein
Be able to describe the diges2on, absorp2on, and transport of proteins
Lef subclavian vein
Heart Small short-chain fapy acid
Villus (greatly enlarged)
Chylomicron
Blood capillary
Lacteal Arteriole
Amino acid
Monosaccharide Venule
Blood
Lymph Lympha2c vessel
Hepa0c portal vein Thoracic duct
Liver
Figure 24.21, pg 1002
Transport of Absorbed Nutrients
Blood Monosaccharides Amino acids
Lymph Chylomicron
Diges2on and Absorp2on Review Quiz
1. Which enzymes are required to breakdown starch into glucose?
2. Name a way in which pepsin diers from aminopep2dase?
3. How is absorp2on of amino acids and monosaccharides similar? (Clue: transport mechanisms)
4. Why arent lipids absorbed into the blood? 5. Which blood vessel carries (nutrient-rich) blood
from the small intes2ne to the liver?
10. Describe the anatomy and func2ons of the large intes2ne.
11. Describe the process of defeca2on.
Learning Objec2ves Anatomy & Physiology of the Diges2ve System
Appendix
Anterior view of large intes2ne showing major regions
Ileum
Tortora Figure 24.23, pg 1007
Rectum Cecum
Ileocecal sphincter (valve)
Transverse colon
Anal Canal Anus
The large intes2ne
Ascending colon
Descending colon
Sigmoid colon
Func2ons of large intes2ne
Absorp2on of some water, minerals and vitamins No diges2ve enzymes are secreted here Carry bacteria Digests some cellulose, protein, bilirubin Produces Vitamin K and bio2n
Forma2on of feces (stools) and defeca2on Feces = semisolid, contains water, inorganic salts, sloughed-o epithelial cells, bacteria, undigested materials, indiges2ble materials
Internal anal sphincter (involuntary)
Rectum
Anal canal
Frontal sec2on of anal canal Anal column Anus
External anal sphincter (voluntary)
Tortora Fig 24.23, pg 1007
Defeca2on
Defeca2on reex
Steps 1. Movement of the feces causes
distension of the rectal walls, which s2mulates sensory (stretch) receptors
2. In response, a spinal reex causes contrac2on of the rectal walls and opening of the internal anal sphincter
3. Voluntary signals from the cerebral cortex open the external anal sphincter and the rectum emp2es
Marieb Figure 23.31, pg 891
The Diges2ve System Summary
1. Describe the chemical diges0on of the following nutrients, specifying the source and the func$on of the principal enzymes involved:
a) Carbohydrates b) Proteins c) Lipids
Learning Objec2ves Diges2on & Absorp2on of Macromolecules
2. Specify the end-products of the diges2on of the following and explain how they are absorbed:
a) Carbohydrates b) Proteins c) Lipids
2013 Pearson Educa2on, Inc.
Foodstuff Enzyme(s) and source Site of action Path of absorption
Starch and disaccharides
Oligosaccharides and disaccharides Carbohydrate digestion
Lactose Maltose Sucrose
Galactose Glucose Fructose
Salivary amylase
Pancrea0c amylase
Brush border enzymes in small intes2ne (dextrinase, gluco- amylase, lactase, maltase, and sucrase)
Mouth
Small intes2ne
Small intes2ne
Glucose and galactose are absorbed via cotransport with sodium ions. Fructose passes via facilitated diusion. All monosaccharides leave the epithelial cells via facilitated diusion, enter the capillary blood in the villi, and are transported to the liver via the hepa2c portal vein.
Summary of Diges2on and Absorp2on Carbohydrates
Marieb Figure 23.32, pg 893
2013 Pearson Educa2on, Inc.
Protein digestion
Proteins
Large polypep2des
Small polypep2des, small pep2des
Amino acids (some dipep2des and tripep2des)
Pepsin (stomach glands) in presence of HCl
Pancrea2c enzymes (trypsin, chymotrypsin, carboxypep0dase)
Brush border enzymes (aminopep0dase, and dipep0dase)
Stomach
Small intes2ne
Small intes2ne
Amino acids are absorbed via cotransport with sodium ions. Some dipep2des and tripep2des are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells. Infrequently, transcytosis of small pep2des occurs. Amino acids leave the epithelial cells by facilitated diusion, enter the capillary blood in the villi, and are transported to the liver via the hepa2c portal vein.
Foodstuff Enzyme(s) and source Site of action Path of absorption
Summary of Diges2on and Absorp2on Proteins
Marieb Figure 23.32, pg 893
2013 Pearson Educa2on, Inc.
Fat digestion
Unemulsied triglycerides
Lingual lipase
Gastric lipase
Emulsica2on by the detergent ac2on of bile salts ducted in from the liver
Pancrea0c lipases
Monoglycerides (or diglycerides with gastric lipase) and fapy acids
Mouth
Stomach
Small intes2ne
Small intes2ne
Fapy acids and monoglycerides enter the intes2nal cells via diusion. Fapy acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells. The resul2ng chylomicrons are extruded by exocytosis. The chylomicrons enter the lacteals of the villi and are transported to the systemic circula2on via the lymph in the thoracic duct. Some short-chain fapy acids are absorbed, move into the capillary blood in the villi by diusion, and are transported to the liver via the hepa2c portal vein.
Foodstuff Enzyme(s)
and source Site of action Path of absorption
Summary of Diges2on and Absorp2on Lipids
Marieb Figure 23.32, pg 893
Diges2on Problem: Review of diges2ve enzymes Fill in the gaps
Macronutrient Diges0ve Enzyme
Source Site of ac0on Ac0on
Carbohydrate
Amylases Dissacharidases E.g. 4. __________
Saliva
3. __________ 5.___________
1.____________
Small intes2ne Small intes2ne
2._______
Dissacharide Monosaccharides
Protein
Pepsin Trypsin Chymotrypsin Carboxypep2dase Amino- and di-
pep2dases
Stomach 8. ___________ 8. ___________ Pancreas 10. __________
6.____________ Small intes2ne Small intes2ne Small intes2ne Small Intes2ne
7.___________ 7.___________ 7.___________ 9.__________ 9.__________
Lipid Bile salts Lipases
11.__________ 12. __________ Gastric Pancrea2c
Small Intes2ne Stomach Stomach Small Intes2ne
Fat (triglyceride) globules Fat droplets
13.__________ 13.__________
Diges2on Problem: Review of diges2ve enzymes Fill in the gaps
Macronutrient Diges0ve Enzyme
Source Site of ac0on Ac0on
Carbohydrate
Amylases Dissacharidases E.g. 4. maltase, lactase,
sucrase
Saliva 3. Pancreas
5. Intes$nal wall (BB)
1. Buccal cavity Small intes$ne Small intes$ne
2. Starch maltose Disaccharides monosaccharides
Protein
Pepsin Trypsin Chymotrypsin Carboxypep2dase Amino- and di-
pep2dases
Stomach 8. Pancreas 8. Pancreas Pancreas 10. Intes$nal
wall (BBE
6. Stomach Small intes$ne Small intes$ne Small intes$ne Small intes$ne
7. Protein pep$des 9. Pep$des amino acids
Lipid Bile salts Lipases
11. Liver via gall bladder
12. Tongue (lingual)
Stomach Pancreas
Small intes$ne Stomach Stomach Small Intes$ne
Triglyceride (fat) globules emulsied fat droplets
13. Triglyceride monoglyceride and faZy acids
Prac2ce Ques2on 3
3. Describe the control of the secre2on of diges2ve juices in humans in terms of:
a) Nervous control b) Hormonal control
Learning Objec2ves Diges2on & Absorp2on of Macromolecules
Phases of Diges2ve Juice Secre2on
1. Cephalic Neuronal control
2. Gastric Neuronal control Hormonal control
3. Intes2nal Neuronal control Hormonal
Control of Secre2on of Diges2ve Juices Nervous control
Sight, smell, thought or taste of food
Brain
CEPHALIC PHASE
Facial, Glossopharyngeal &
Increased gastric juice secre2on
Stomach
Increased pancrea2c juice
secre2on
Pancreas
Increased saliva
secre2on
Salivary Glands
Vagus Nerves
Control of Secre2on of Diges2ve Juices Nervous control
Distension of gastric walls / Increase in gastric pH
Neurons in the submucosal plexus of stomach
GASTRIC PHASE
Stretch receptors / Chemoreceptors
Increased HCl secre2on
Parietal Cells of Stomach
Increased gastric mo2lity -peristalsis
Smooth Muscle of Stomach
Control of Secre2on of Diges2ve Juices Hormonal control
Distension of gastric walls / Increase in gastric pH
Gastrin
GASTRIC PHASE
Stretch receptors / Chemoreceptors
Stomach
Enteroendocrine cells (G cells) of stomach
Increased gastric juice secre2on
Stomach
LES contract Pyloric sphincter- relax
Sphincters
Be able to describe the role of this hormone in the diges2ve system
Control of Secre2on of Diges2ve Juices Nervous control
Distension of duodenal walls
Sympathe2c Neurons
INTESTINAL PHASE
Stretch receptors
Increased contrac2on delays stomach contents emptying and overload
Pyloric sphincter
Control of Secre2on of Diges2ve Juices Hormonal control
Presence of chyme in the duodenum (amino acids, fapy acids, H+)
Cholecystokinin (CCK) Secre2n
Intes2nal Cells
INTESTINAL PHASE
Increased bicarbonate secre2on
Pancreas
Increased enzyme secre2on
Pancreas
Inhibits gastric juice secre2on
Stomach
Bile ejec2on
Gallbladder
Be able to describe the role of these hormones in the diges2ve system
Summary Cephalic phase (under nervous control): short-lived and
prepares mouth, stomach and small intes2ne for food
Gastric phase: increased gastric juice secre2on, mo2lity (peristalsis) of the stomach and opening of pyloric sphincter. Ini2ated by local nerves and maintained by gastrin hormone
Intes0nal phase promotes diges2on in intes2ne by slowing movement of chyme from the stomach to the small intes2ne (nervous control of pyloric sphincter) to prevent overloading. Meanwhile Secre.n and CCK increase bile, pancrea2c juice secre2on and inhibit gastric juice secre2on