1. Anatomy & Physiology of the Digestive System

2. Learning objectives
Identify the organs of the digestive system and their major functions
Outline the mechanisms that regulate digestion
Describe the anatomy of the organs and accessory organs of the digestive system
Discuss the functions of the major structures and regions of the digestive system and discuss the regulation of their activities

3. Learning objectives (continued)
Explain the significance of the large intestine in the absorption of nutrients
Describe the events involved in the digestion of organic and inorganic nutrients
Summarize the effects of the aging process on the digestive system

4. The Digestive system:
The alimentary canal or gastrointestinal (GIT) tract digests and absorbs food and drugs
Alimentary canal – mouth, pharynx, esophagus, stomach, small intestine, and large intestine
Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreas

5. Functions of the Digestive system
Ingestion: The act of eating
Mechanical digestion: tearing, chewing and the churning effects of peristalsis
Peristalsis: the rhythmic contractions of our digestive organs that propel the food
Chemical digestion: Release of enzymes along the digestive tract which chemically change the complex polymers into basic monomers required by the body

6. Secretion: Various fluids are secreted to protect the linning of the GI tract
Absorption: The monomers and the water need to be transported to the body from the GI tract via the blood stream, but they first need to be absorbed into the blood
Storage and toxin processing: The blood containing the nutrients pass through the liver, which stores some sugar (glycogen), and breaks down toxic chemicals
Excretion and egestion: Release of waste products (faeces) via the anus

7. Structures of the Digestive System

8. The components of the Digestive System

9. Layers of the GI Tract 1. Mucosal layer 2. Submucosal layer
3. Muscularis layer
4. Serosa layer

10. Mucosa :
The innermost layer, mucous membrane
Outside the mucosa is the lumen, where all the mechanical
and chemical digestion (extracellular) occurs.
Produces enzymes that are released by exocytosis
Food nutrients do not enter the body until it is absorbed by the mucosa
Consists of epithelial tissue and is avascular
It secretes the enzymes for digestion and provides chemical protection from those enzymes

11. Submucosa:
Consists of connective tissue
Contains blood vessels and lymphatics
Food absorbed from the mucosa enter the submucosa and eventually carried away by the blood vessels.
Many glands of the mucosa extend into this layer

12. Muscularis externaL
Peristalsis (movement of food along the GI tract is accomplished in this layer
Consists of two separate layers of smooth muscle
a longitudinal layer
Transverse or circular layer
Peristalsis achieved by alternating contractions of the two layers

13. The Serosa(ADVENTITIA):
Outermost layer
A combination of connective tissue and an outermost epithelial layer
Releases a simple tear-like secretion to lubricate the organs of the GI tract

14. Nerve supply to the Digestive System
In the layers of the connective tissues of the submucosa and the serosa are a number of nerves.
The nerves are of three types:
Sensory
Sympathetic
parasympathetic

15. Other supplies to the Digestive system
There are simple connections from each of the layers of connective tissue to other body systems
Capillaries connect the organs to the cardiovascular system
Hormones from the endocrine system also run to other parts of the body through the capillaries
Drainage and uptake of lipids are accomplished through vessels of the lymphatic system.

16. Peritoneum Peritoneum visceral layer covers organs
parietal layer lines the walls of body cavity
Peritoneal cavity
potential space containing a bit of serous fluid

17. Parts of the Peritoneum
Mesentery
Mesocolon
Lesser omentum
Greater omentum

18. Omentum: double layered extension or fold
of peritoneum that passes from the stomach
and proximal part of the duodenum to
adjacent organs in the abdominal
Cavity or to the abdominal wall.
The lesser omentum: connects the lesser
curvature to the stomach and proximal part of
the duodenum to the undersurface of the liver.

19. Greater Omentum: prominent fold that hangs
down like an apron from the greater curvature
of the stomach and proximal part of the
duodenum
It covers the coils of the small intestines and
is folded back on itself to be attached to the
transverse colon and its mesentery.

20. Functions:
Preventing the visceral peritoneum from
adhering to the parietal peritoneum
Wrapping itself around inflamed organs
such as the appendix to wall it off
Cushioning the abdominal wall against
injury.
Insulating against loss of body heat.

21. Greater Omentum, Mesentery & Mesocolon

22. mesocolon: a broad fold of
the peritoneum which connects the trans
colon to the posterior wall of the
abdomen.
Mesentery:

23. Lesser Omentum

24. Peritonitis
Acute inflammation of the peritoneum
Cause:
contamination by infectious microbes during surgery or from rupture of abdominal organs

25. Salivary Glands Parotid below your ear.
Submandibular is under lower edge of mandible
Sublingual is deep to the tongue in floor of mouth
All have ducts that empty into the oral cavity

26. Composition and Functions of Saliva
Wet food for easier swallowing
Dissolves food for tasting
Bicarbonate ions buffer acidic foods
-bulemia---vomiting hurts the enamel on your teeth
Chemical digestion of starch begins with enzyme (salivary amylase)
Enzyme (lysozyme) ---helps destroy bacteria
Protects mouth from infection with its rinsing action

27. Salivary Gland Cellular Structure
Cells in acini (clusters)
Serous cells secrete a watery fluid
Mucous cells (pale staining) secrete a slimy, mucus secretion

28. Salivation
Increase salivation
sight, smell, memory of food, tongue stimulation---rock in mouth
cerebral cortex signals the salivatory nuclei in brainstem
Parasympathetic stimulation
Stop salivation
dry mouth when you are afraid
sympathetic nerves

29. Mumps
Myxovirus that attacks the parotid gland
Symptoms
inflammation and enlargement of the parotid
Fever & sour throat
swelling on one or both sides
Sterility rarely possible in males with testicular involvement Vaccine available since 1967

30. Digestion in the Mouth
Mechanical digestion (mastication or chewing)
breaks into pieces
mixes with saliva so it forms a bolus
Chemical digestion
amylase
begins starch digestion at pH of 6.5 or 7.0 found in mouth
when bolus & enzyme hit the pH 2.5 gastric juices hydrolysis ceases
lingual lipase
secreted by glands in tongue
begins breakdown of triglycerides into fatty acids and glycerol

31. Funnel-shaped tube continuous with the esophagus
Pharynx
Funnel-shaped tube continuous with the esophagus
Skeletal muscle lined by mucous membrane
Deglutition or swallowing is facilitated by saliva and mucus
starts when bolus is pushed into the oropharynx
sensory nerves send signals to deglutition center in brainstem
soft palate is lifted to close nasopharynx
larynx is lifted as epiglottis is bent to cover glottis

32. Esophagus Collapsed muscular tube In front of vertebrae
Posterior to trachea
Posterior to the heart
Pierces the diaphragm

33. Histology of the esophagus
Mucosa = stratified squamous
Submucosa = large mucous glands
Muscularis = upper 1/3 is skeletal, middle is mixed, lower 1/3 is smooth
upper & lower esophageal sphincters are prominent circular muscle
Adventitia = connective tissue blending with surrounding connective tissue

34. Physiology of the Esophagus - Swallowing
Voluntary phase---tongue pushes food to back of oral cavity
Involuntary phase----pharyngeal stage
breathing stops & airways are closed
soft palate & uvula are lifted to close off nasopharynx
vocal cords close
epiglottis is bent over airway as larynx is lifted and closed

35. Swallowing
Upper sphincter relaxes when larynx is lifted
Peristalsis pushes food down
circular fibers behind bolus
longitudinal fibers in front of bolus shorten the distance of travel
Travel time is 4-8 seconds for solids and 1 sec for liquids
Lower sphincter relaxes as food approaches

36. Gastroesophageal Reflex Disease
If lower sphincter fails to open
distension of esophagus feels like chest pain or heart attack
If lower esophageal sphincter fails to close
stomach acids enter esophagus & cause heartburn (GERD)
for a weak sphincter---don't eat a large meal and lay down in front of TV
smoking and alcohol make the sphincter relax worsening the situation
Control the symptoms by avoiding
take Tagamet or Pepcid 60 minutes before eating
coffee, chocolate, tomatoes, fatty foods, onions & mint

37. Anatomy of Stomach
Size when empty
large sausage
stretches due to rugae
Parts of stomach
cardia
fundus---air in x-ray
body
pylorus---starts to narrow as it approaches pyloric sphincter
Empties as small squirts of chyme leave the stomach through the pyloric valve

38. Pylorospasm and Pyloric Stenosis
Abnormalities of the pyloric sphincter in infants
Pylorospasm
muscle fibers of sphincter fail to relax trapping food in the stomach
vomiting occurs to relieve pressure
Pyloric stenosis
narrowing of sphincter indicated by projectile vomiting
must be corrected surgically

39. Mucosa & Gastric Glands
Hydrochloric acid converts pepsinogen from chief cell to pepsin
Intrinsic factor
absorption of vitamin B12 for RBC production
Gastrin hormone (G cell)
release more gastric juice
increase gastric motility
relax pyloric sphincter
constrict esophageal sphincter preventing entry

40. Physiology--Mechanical Digestion
Gentle mixing waves
every 15 to 25 seconds
mixes bolus with gastric juice to turn it into chyme (a thin liquid)
More vigorous waves
travel from body of stomach to pyloric region
Intense waves near the pylorus
open it and squirt out 1-2 teaspoonsful with each wave

41. Physiology--Chemical Digestion
Protein digestion begins
HCl denatures (unfolds) protein molecules
HCl transforms pepsinogen into pepsin that breaks peptide bonds between certain amino acids
Fat digestion continues
gastric lipase splits the triglycerides in milk fat
most effective at pH 5 to 6 (infant stomach)
HCl kills microbes in food
Mucous cells protect stomach walls from being digested with thick layer of mucous

42. Vomiting (emesis)
Forceful expulsion of contents of stomach & duodenum through the mouth
Cause
irritation or distension of stomach
unpleasant sights, general anesthesia, dizziness & certain drugs
Sensory input from medulla cause stomach contraction & complete sphincter relaxation
Contents of stomach squeezed between abdominal muscles and diaphragm and forced through open mouth
Serious because loss of acidic gastric juice can lead to alkalosis

43. Anatomy of the Pancreas
5" long by 1" thick
Head close to curve in C-shaped duodenum
Main duct joins common bile duct from liver
Opens 4" below pyloric sphincter

44. Composition and Functions of Pancreatic Juice
pH of 7.1 to 8.2
Contains water, enzymes & sodium bicarbonate
Digestive enzymes
pancreatic amylase, pancreatic lipase, proteases
most of the enzymes are activated by trypsin produced inside pancreas
ribonuclease----to digest nucleic acids
-procarboxypeptidase

45. Pancreatitis
Pancreatitis---inflammation of the pancreas
Acute pancreatitis---associated with heavy alcohol intake or biliary tract obstruction
results as patient secretes trypsin in the pancreas & starts to digest himself

46. Regulation of Pancreatic Secretions
Secretin
acidity in intestine causes increased sodium bicarbonate release
GIP
fatty acids & sugar causes increased insulin release
CCK
fats and proteins cause increased digestive enzyme release

47. Anatomy of the Liver and Gallbladder
weighs 3 lbs.
below diaphragm
right lobe larger
gallbladder on right lobe

48. Hepatocytes arranged in lobules
Histology of the Liver
Hepatocytes arranged in lobules
Sinusoids in between hepatocytes are blood-filled spaces
Kupffer cells phagocytize microbes & foreign matter

49. Pathway of Bile Secretion

50. Bile Production Bile is secreted by the liver
yellow-green in color & pH 7.6 to 8.6
Components
water & cholesterol
bile salts = Na & K salts of bile acids
bile pigments (bilirubin) from hemoglobin molecule
globin = a reuseable protein
heme = broken down into iron and bilirubin

51. Regulation of Bile Secretion

52. Liver functions-cabohydrate metabolism
Turn proteins into glucose
Turn triglycerides into glucose
Turn excess glucose into glycogen & store in the liver
Turn glycogen back into glucose as needed

53. Liver function-lipid metabolism
Synthesize cholesterol
Synthesize lipoproteins----HDL and LDL(used to transport fatty acids in bloodstream)
Stores some fat
Breaks down some fatty acids

54. Liver function-protein metabolism
Deamination = removes NH2 (amine group) from amino acids so can use what is left as energy source
Converts resulting toxic ammonia (NH3) into urea for excretion by the kidney
Synthesizes plasma proteins utilized in the clotting mechanism and immune system
Convert one amino acid into another

55. Other Liver Functions
Releases bile salts that help digestion by emulsification
Stores fat soluble vitamins-----A, B12, D, E, K
Stores iron and copper
Phagocytizes worn out blood cells & bacteria
Activates vitamin D (the skin can also do this with 1 hr of sunlight a week)
Detoxifies the blood by removing or altering drugs & hormones(thyroid & estrogen)
Removes the waste product--bilirubin

56. Anatomy of the Small Intestine
20 feet long----1 inch in diameter
Large surface area for majority of absorption
3 parts
duodenum---10 inches
jejunum---8 feet
ileum---12 feet
ends at ileocecal valve

57. Histology of Small Intestine

58. Functions of Microvilli
Absorption and digestion
Digestive enzymes found at cell surface on microvilli
Digestion occurs at cell surfaces
Significant cell division within intestinal glands produces new cells that move up
Once out of the way---rupturing and releasing their digestive enzymes & proteins

59. Cells of Intestinal Glands
Absorptive cell
Goblet cell
Enteroendocrine
secretin
cholecystokinin
gastric inhibitory peptide
Paneth cells
secretes lysozyme

60. Mechanical Digestion in the Small Intestine
Weak peristalsis in comparison to the stomach---chyme remains for 3 to 5 hours
Segmentation---local mixing of chyme with intestinal juices--- back & forth movement

61. Digestion of Carbohydrates
Mouth---salivary amylase
Esophagus & stomach---nothing happens
Duodenum----pancreatic amylase
other enzymes (maltase, sucrase & lactase) act on disaccharides
produces monosaccharides--fructose, glucose & galactose
lactose intolerance (no enzyme; bacteria ferment sugar)--gas & diarrhea

62. Digestion of Proteins Stomach HCl denatures or unfolds proteins
pepsin turns proteins into peptides
Pancreas
digestive enzymes---split peptide bonds between different amino acids
other enzymes-----aminopeptidase or dipeptidase------split off amino acid at amino end of molecule or split dipeptide

63. Digestion of Lipids Mouth----lingual lipase Small intestine
emulsification by bile
pancreatic lipase---splits into fatty acids & monoglyceride

64. Digestion of Nucleic Acids
Pancreatic juice contains 2 nucleases
ribonuclease which digests RNA
deoxyribonuclease which digests DNA
Nucleotides produced are further digested by nucleosidase and phosphatase.
pentose, phosphate & nitrogenous bases
Absorbed by active transport

65. Regulation of Secretion & Motility
Enteric reflexes that respond to presence of chyme
increase intestinal motility
VIP (vasoactive intestinal polypeptide) stimulates the production of intestinal juice
segmentation depends on distention which sends impulses to the enteric plexus & CNS
distention produces more vigorous peristalsis
10 cm per second
Sympathetic impulses decrease motility

66. Absorption in Small Intestine

67. Where will the absorbed nutrients go?

68. Absorption of Monosaccharides
Absorption into epithelial cell
glucose & galactose---- (active transport)
fructose-----facilitated diffusion
Movement out of epithelial cell into bloodstream
by facilitated diffusion

69. Absorption of Amino Acids & Dipeptides
Absorption into epithelial cell
active transport with Na+ or H+ ions.
Movement out of epithelial cell into blood
diffusion

70. Absorption of Lipids
Small fatty acids enter cells & then blood by simple diffusion
Larger lipids exist only within micelles (bile salts coating)
Lipids enter cells by simple diffusion leaving bile salts behind in gut
Bile salts reabsorbed into blood & reformed into bile in the liver
Fat-soluble vitamins within micelles enter cells by simple diffusion

71. Absorption of Lipids (2)
Inside epithelial cells fats are rebuilt and coated with protein to form chylomicrons
Chylomicrons leave intestinal cells by exocytosis into a lacteal
travel in lymphatic system to reach veins near the heart
removed from the blood by the liver and fat tissue

72. Absorption of Electrolytes
Sources of electrolytes
GI secretions & ingested foods and liquids
Enter epithelial cells by diffusion & secondary active transport
sodium & potassium move = Na+/K+ pumps (active transport)
chloride, iodide and nitrate = passively follow
iron, magnesium & phosphate ions = active transport
Intestinal Ca2+ absorption requires vitamin D & parathyroid hormone

73. Absorption of Vitamins
Fat-soluble vitamins
travel in micelles & are absorbed by simple diffusion
Water-soluble vitamins
absorbed by diffusion
B12 combines with intrinsic factor before it is transported into the cells

74. Absorption of Water 9 liters of fluid dumped into GI tract each day
Small intestine reabsorbs 8 liters
Large intestine reabsorbs 90% of the last liter
Absorption is by osmosis through cell walls into vascular capillaries inside villi

75. Anatomy of Large Intestine
5 feet long by 2½ inches in diameter
Ascending & descending colon
Cecum & appendix
Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx
Anal canal = last 1 inch of GI tract
internal sphincter----smooth muscle & involuntary
external sphincter----skeletal muscle & voluntary control

76. Appendicitis
Inflammation of the appendix due to blockage of the lumen by chyme, foreign body, carcinoma, stenosis
Symptoms
fever, elevated WBC count, high neutrophil count
pain, anorexia, nausea and vomiting
pain localizes in right lower quadrant
Infection may progress, perforation within 24 to 36 hours
Emergency surgery required

77. Mechanical Digestion in Large Intestine
Smooth muscle = mechanical digestion
Peristaltic waves (3 to 12 contractions/minute)
churning----relaxed pouches are filled from below by muscular contractions (elevator)
gastroilial reflex = when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room
gastrocolic reflex = when stomach fills, a strong peristaltic wave moves contents of transverse colon into rectum

78. Chemical Digestion in Large Intestine
No enzymes are secreted only mucous
Bacteria ferment
undigested carbohydrates into carbon dioxide & methane gas
undigested proteins into simpler substances (indoles)----odor
turn bilirubin into simpler substances that produce color
Bacteria produce vitamin K and B in colon

79. Absorption & Feces Formation in the Large Intestine
Some electrolytes---Na+ and Cl-
After 3 to 10 hours, 90% of H2O has been removed from chyme
Feces are semisolid by time reaches transverse colon
Feces = dead epithelial cells, undigested food such as cellulose, bacteria (live & dead)

80. Defecation Gastrocolic reflex moves feces into rectum
Stretch receptors signal sacral spinal cord
Parasympathetic nerves contract muscles of rectum & relax internal anal sphincter
External sphincter is voluntarily controlled

81. Diarrhea = chyme passes too quickly through intestine
Defecation Problems
Diarrhea = chyme passes too quickly through intestine
H2O not reabsorbed
Constipation--decreased intestinal motility
too much water is reabsorbed
remedy = fiber, exercise and water

82. Aging and the Digestive System
Changes that occur
decreased secretory mechanisms
decreased motility
loss of strength & tone of muscular tissue
changes in neurosensory feedback
diminished response to pain & internal stimuli
Symptoms
sores, loss of taste, peridontal disease, difficulty swallowing, hernia, gastritis, ulcers, malabsorption, jaundice, cirrhosis, pancreatitis, hemorrhoids and constipation
Cancer of the colon or rectum is common

83. GOOD LUCK !