1. Digestive System

2. 6 Processes of Digestion
Ingestion
Mechanical Digestion
Chewing, swallowing
Peristalsis
Segmentation
Chemical Digestion
Enzymes breaking chemical bonds
Secretion
Goblet cells secreting mucus
Organs secreting enzymes
Absorption
Nutrients pass into blood stream
Defecation
Removal of solid waste
Ingestion
Food
Mechanical
digestion
Pharynx
• Chewing (mouth)
Esophagus
• Churning (stomach)
Propulsion
• Segmentation
(small intestine)
• Swallowing
(oropharynx)
Chemical
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
digestion
Stomach
Absorption
Lymph
vessel
Small
intestine
Blood
vessel
Large
intestine
Mainly H2O
Feces
Defecation
Anus

3. Digestive System in Action
Salivary glands
Digestive System in Action
Accessory Organs to S. Intestines
stomach
Small Intestine
Blood stream
Large Intestine

4. Histology of Digestive Tract
Stratified squamous
Mouth, pharynx & esophagus
Simple Columnar
Stomach thru L.I.
Goblet cells
Villi
Microvilli

5. Mouth Main Functions Ingestion Physical digestion Chemical digestion
Tongue, teeth
Chemical digestion
Saliva and salivary glands

6. Accessory Organs of Mouth
Tongue
Taste buds
Responsible for gripping food
Mixes food with saliva
Initiates swallowing
Bolus

7. Peristalsis vs. Segmentation
From
mouth
(a) Peristalsis: Adjacent segments of
alimentary tract organs alternately contract
and relax, which moves food along the tract
distally.
(b) Segmentation: Nonadjacent segments
of alimentary tract organs alternately
contract and relax, moving the food
forward then backward. Food mixing and
slow food propulsion occurs.

8. Salivary Glands Parotid, submandibular and sublingual
Functions
Produce saliva
99% water
Contains enzyme amylase
Mucin – forms mucus
Growth Factor
Functions of Saliva
Cleanses mouth
Growth factor and lysosomes
Dissolves food for taste
Moistens food; creates bolus
Enzyme amylase begins the chemical digestion of starch A C B

9. Amylase
Starch (polysaccharide) disaccharides
maltose

10. Pharynx and Esophagus 1 Pharynx Esophagus 2 = epiglottis4
Pharynx
Back of throat
Passage way for food
Esophagus
Food chute
Stratified squamous tissue
2 = epiglottis

11. Stomach Four Primary Functions Temporary storage tank for food
Mechanically break down food
Food is converted into creamy paste called chyme
Chemical breakdown of protein begins
Production of intrinsic factor; necessary for absorbing Vitamin B12.

12. Regions of the Stomach Cardiac region Fundus Body
Upper area around cardiac sphincter
Fundus
Dome-shaped part of stomach
Body
Pylorus- inferior portion
Pyloric sphincter: controls the emptying of the stomach into the S.I.

13. Stomach Physiology Rugae Peristalsis Controlled by pacemaker cells
Becomes more forceful closer to the pyloric region

14. Gastric Wall Gastric Pit Gastric gland
Secretes mucus and enzyme pepsinogen
Parietal cells
Secrete HCl and instrinsic factor
HCl is needed to convert pepsinogen into pepsin
Kills bacteria that is ingested with food
Rennin
Chief cells – produce pepsinogen; inactive form of pepsin
Gastric Wall

15. Converting Pepsinogen to Pepsin
HCl
Mitochondria
Parietal cell
Chief cell
Enteroendocrine
cell
(c) Location of the HCl-producing parietal cells and
pepsin-secreting chief cells in a gastric gland

16. Regulation of Gastric Activity
Cephalic phase
prepares stomach to receive food
Sight, smell, taste of food
Controlled by vagus nerve and parasympathetic system
Only lasts a short time

18. 2. Gastric Phase
Stimulation of stretch receptors and chemoreceptors stimulate the release of hormone gastrin
Gastrin causes release of HCl and pepsinogen
Increase in stomach contraction intensity
Small amounts of caffeine and alcohol stimulate chemoreceptors causing an increase in gastric secretions

20. 3. Intestinal phase Begins when food starts to enter S.I.
Controls the rate of gastric emptying
Slows down gastric activities by releasing three hormones
Cholecystokinin (CCK)
Secretin
Gastric inhibitory peptide (GIP)

22. Small Intestine Digesting & Absorbing Organ Anatomy
Consists of 3 sections
Duodenum
Jejunum
Ileum
ileocecal spincter: controls flow into colon
Mesentary

24. Modifications for Absorption
Folds
Mixes chyme and slows down movement
Villi
Fingerlike projections increases surface area
Microvilli

25. Lining of Small Intestine

26. Regulation with Intestinal Hormones
Secretin: released when pH falls in duodenum (Why would this happen?)
Result: causes water and buffers to be secreted into S.I. by pancreas
Cholecystokinin (CCK): secreted when protein and lipid dense chyme arrives in S.I.
Result: increases the secretion of digestive enzymes from the pancreas and bile from the liver
Gastric Inhibitory Peptide (GIP): released when food begins to enter S.I.
Result: inhibit digestive activity in stomach; causes release of insulin from pancreas

27. Chyme enter- Bile salts and, to a lesser extent, ing duodenum
causes release of
cholecystokinin
(CCK) and
secretin from
duodenal
cells. 1
Bile salts and,
to a lesser extent,
secretin
transported via
bloodstream
stimulate liver to
produce bile
more rapidly. 4
CCK (via
bloodstream)
causes
gallbladder to
contract ; bile enters
duodenum. 5
CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream. 2
CCK induces
secretion of
enzyme-rich
pancreatic juice.
Secretin causes
HCO3–-rich 3
During
cephalic and
gastric phases,
vagal nerve
stimulation
causes weak
contractions of
gallbladder. 6

28. Organs affected by digestive hormones

29. Chemical Digestion Brush Border Enzymes
Intestinal juice is water, mucus and enzymes
Sucrase
Lactase
Maltase
Peptidases/proteases

30. Lactose Intolerance

31. Functions of Small Intestine
Segmentation: movement of food through S.I.; moves very slowly so chemical digestion can occur
Chemical Digestion:
Very few Enzymes come from S.I.
Need assistance from accessory organs
Absorption: the building blocks of food are passed into blood stream by Active Transport
Most absorption is completed b4 it reaches the ileum
Ilieum’s main function is to return bile salts to liver
Mesentary

32. Accessory Organs: Pancreas
Endocrine Gland
Produces hormones
Exocrine Gland
Produces digestive enzymes
Empties into duodenum

33. Pancreatic duct fuses with Common bile duct and enters the duodenum

34. Pancreatic Secretions
Secretes (Exocrine Gland)
Bicarbonate ions (NaHCO3-); turns acidic chyme from stomach into basic solution (ph 7-8)
Enzymes
Trypsinogen (inactive form)
Amylase
Lipase
Nucleases

35. Conversion of Trypsinogen into Trypsin
Increase in pH from bicarbonate ions and another enzymes converts trypsinogen into its active form trypsin
Trypsin is a protease and continues protein digestion

36. Digestion of Lipids
Lipase breaks down lipids into fatty acids and glycerol.
Fatty acids and glycerol can then be absorbed into the blood stream
Bile assists in this process by physically breaking down fats into smaller droplets.

37. Pancreas Secretions Endocrine Gland
Islets of Langerhans are specialized cells
Responsible for secreting 2 hormones
Glucagon
Insulin

38. Anatomy of Liver and gall bladder
Hepatic duct allows bile to leave the liver
Gall Bladder
Lies under liver; appears like a slightly inflated green balloon
Stores bile
Bile leaves the liver via the cystic duct
Cystic duct and hepatic duct join to make Common Bile Duct.

39. Functions Bile Production Only digestive process
Physically separates fats into smaller droplets; allows lipase to digest faster
(Remember fats don’t dissolve in water)
I.e. scatters fat droplets throughout solution

40. Functions of liver Metabolic Regulation
Processes all nutrients absorbed into blood
Helps regulate cholesterol levels
Forms nonessential amino acids; byproduct is ammonia (toxic)
Converts ammonia into urea (less toxic)
Stores glucose as glycogen (polysaccharide)
Stores fat soluble vitamins (A,D,E,K)
Detoxifies alcohol and drugs (both legal and illegal)
Blood leaving liver has fewer waste products than the blood that enters it.

41. Functions Continued... Assists in Regulating Blood
Produces plasma proteins
Conserves iron from old RBC’s

42. Problems with the Liver
Cirrhosis
Chronic inflammation of liver
Results from severe alcoholism or chronic sever hepatitis
Liver cells die are replaced scar tissue and fat deposits.
Hepatitis
Inflammation of liver
Caused by a virus, sewage contaminated water or feces-mouth

43. Gall Stones Cholesterol in Bile salts crystallize;
Gets stuck in duct; causes extreme pain

45. Chemical Digestion and Absorption of Proteins
Protein digestion
Enzyme(s)
and source
Site of
action
Foodstuff
Path of absorption
• Amino acids are absorbed
by cotransport with
sodium ions.
Protein
Pepsin
(stomach glands)
in presence
of HCl
Stomach
• Some dipeptides and
tripeptides are absorbed
via cotransport with H+
and hydrolyzed to amino
acids within the cells.
Large polypeptides
Pancreatic
enzymes
(trypsin, chymotrypsin,
carboxypeptidase)
Small
intestine +
Small polypeptides,
small peptides
• Amino acids leave the
epithelial cells by
facilitated diffusion, enter
the capillary blood in the
villi, and are transported
to the liver via the hepatic
portal vein.
Brush border
enzymes
(peptidases, proteases)
Small
intestine
Amino acids
(some dipeptides
and tripeptides)

46. Chemical Digestion and Absorption of Carbohydrates
Carbohydrate digestion
Enzyme(s)
and source
Site of
action
Foodstuff
Path of absorption
• Glucose and galactose
are absorbed via
cotransport with
sodium ions.
Starch and disaccharides
Salivary
amylase
Mouth
• Fructose passes via
facilitated diffusion.
Pancreatic
amylase
Small
intestine
Oligosaccharides
and disaccharides
• All monosaccharides
leave the epithelial
cells via facilitated
diffusion, enter the
capillary blood in the
villi, and are
transported to the liver
via the hepatic portal
vein.
Brush border
enzymes in
small intestine
(lactase,maltase
and sucrase)
Small
intestine
Lactose
Maltose
Sucrose
Galactose
Glucose
Fructose

47. Chemical Digestion and Absorption of Fats
Fat digestion
Enzyme(s)
and source
Site of
action
Foodstuff
Path of absorption
Unemulsified
fats
• Fatty acids and monoglycerides
enter the intestinal cells via
diffusion.
Emulsification by
the detergent
action of bile
salts ducted
in from the liver
Small
intestine
• Fatty acids and monoglycerides
are recombined to form
triglycerides and then
combined with other lipids and
proteins within the cells.
Pancreatic
lipases
Small
intestine
Monoglycerides
and fatty acids
Glycerol
and
fatty acids
• Some short-chain fatty acids
are absorbed, move into the
capillary blood in the villi by
diffusion, and are transported
to the liver via the hepatic
portal vein.

48. Chemical Digestion and Absorption of Nucleic Acids
Nucleic acid digestion
Enzyme(s)
and source
Site of
action
Foodstuff
Path of absorption
Nucleic acids
• Units enter intestinal cells
by active transport via
membrane carriers.
Pancreatic ribo-
nuclease and
deoxyribonuclease
Small
intestine
• Units are absorbed into
capillary blood in the villi
and transported to the
liver via the hepatic portal
vein.
Brush border
enzymes
(nucleosidases
and phosphatases)
Small
intestine
Pentose sugars,
N-containing bases,
phosphate ions

49. What remains in Small Intestine?
Indigestible food materials (cellulose)
Lots of bacteria
Water
Passes through ileocecal valve into Large Intestine

50. Large Intestine/Colon
Anatomy
Cecum
Appendix
Colon
Ascending
Transverse
Descending
Sigmoid
Rectum
Anal Canal

51. Microscopic Anatomy
No villi or microvilli
No cells which secrete enzymes
Many goblet cells lining the simple columnar tissue for lubrication
Rectum tissue becomes stratified squamous

52. Main functions
Absorbs water and electrolytes (Na, Cl, K)
Absorbs water soluble vitamins
Eliminates undigested food; defecation
Haustra = wall pockets (seen in picture)

53. Other Inhabitants Bacteria Responsible for fermenting undigested food
Product of these reactions is gas (H2, N2, CO2, H2S, CH4)
Assist in synthesizing vitamin B and vitamin K.