1. Anatomy and Physiology
Marieb’s Human
Anatomy and Physiology
Ninth Edition
Marieb w Hoehn
Chapter 23
** Digestive System **
Stomach Small/Large Intestine Salivary Glands Liver
Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1]
Slides 16 – 38; 50 min [Lecture 2]
118 min (38 slides plus review of course Web sites and syllabus)

2. Overview….Where have you been?
Figures from: Marieb, Human Anatomy &Physiology, Pearson, 2013

3. Stomach Rugae flatten as stomach fills
Stomach can hold about liters of material
Gastric glands
M G cells D cells
Greater curvature
Stomach Functions: - Mixing - Reservoir - Secretion of gastric juice - Digestion, anti-bacterial action, facilitates absorption of vitamin B Secretion of gastrin, somatostatin
Range of stomach volume is about 50 ml (empty) to about 4L, or 1 gallon (very distended).
Rugae flatten as stomach fills

4. Blood Supply and Drainage of Stomach
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

5. Lining and Gastric Glands of Stomach
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

6. Gastric Secretions mucus (cardia) from goblet cells and mucous glands
protective to stomach wall
hydrochloric acid
from parietal cells
needed to convert pepsinogen to pepsin
‘p’ in parietal and ‘p’ in pH
pepsinogen
from chief cells
inactive form of pepsin
intrinsic factor
from parietal cells
required for vitamin B12 absorption
pepsin
from pepsinogen in presence of HCl
protein splitting enzyme
mucus, gastrin, somatostatin
from pyloric glands
protective to stomach wall
gastrin and somatostatin are hormones
H.Pylori is difficult to eradicate, so three medications are used simultaneously.
This is called "Triple Therapy". The best treatment at present is called OAC, taken for 7 days:
O = Omeprazole (which decreases the acid level in the stomach)
A = Amoxicillin (a penicillin antibiotic).
C = Clarithromycin (an antibiotic related to erythromycin)
OMC is used in those who are penicillin allergic, where M = Metranidazole.
INFANTS ONLY
rennin (chymosin)
gastric lipase

7. Secretion of H+ by Parietal Cells
Important functions of the stomach pH (1.5 – 2.0)
- kills microorganisms - denatures proteins - breaks down plant material and CT in meats - activates pepsin
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

8. Liver, Bile ducts, Pancreas and Small Intestine
Figures from: Marieb, Human Anatomy &Physiology, Pearson, 2013

9. Three Parts of Small Intestine
Figure from: Hole’s Human A&P, 12th edition, 2010
“Mixing bowl”; acid neutralization
Bulk of chemical digestion and nutrient absorption occurs here
The ‘bowel’ consists of the small and large intestines.
Vitamin B12 absorption
Main functions of small intestine: 1) chemical digestion 2) absorption of nutrients (90%) from chyme

10. Blood Supply and Drainage of Small Intestine
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

11. Wall of Small Intestine
Figure from: Hole’s Human A&P, 12th edition, 2010
Plicae circulares – permanent circular folds of mucosa that further increase surface area for absorption – do not flatten out with distention like rugae of stomach.
Especially prominent in lower duodenum and upper jejunum
Submucosa of duodenum contains mucus-secreting glands (Brunner’s glands) that protect the small intestine

12. Intestinal Villi & Glands
Enterocyte = Intestinal Cell
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Intestinal glands secrete an abundant watery fluid that helps absorb products of digestion. They also contain enteroendocrine cells (enterokinase, gastrin, secretin, CCK)

13. Intestinal Epithelium
Figure from: Hole’s Human A&P, 12th edition, 2010
Microvilli further increase the surface area available for absorption in the small intestine
Form a ‘brush border’ on the intestine
Digestive enzymes are embedded in the membrane of microvilli
Main function of plicae, villi, and microvilli is to increase the surface area for absorption (from about 3.6 ft2 to about 2200 ft2!)

14. Secretions of Small Intestine
peptidase – breaks down peptides into amino acids
sucrase, maltase, lactase – break down disaccharides into monosaccharides
intestinal lipase – breaks down fats into fatty acids and glycerol
enterokinase – converts trypsinogen to trypsin
gastrin/somatostatin – hormones that stimulate/inhibit acid secretion by stomach
cholecystokinin (CCK) – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, stimulates gallbladder to release bile, and relaxes hepatopancreatic sphincter (of Oddi)
secretin – stimulates pancreas to release bicarbonate ions in pancreatic juice; stimulates gall bladder to release bicarbonate-rich bile
Brush border
See Table in Marieb for a great summary of digestive enzymes

15. Movements of the Small Intestine
Movements in local segments can occur without stimulation by parasympathetic NS. However, nervous stimulation accelerates segmentation and peristalsis.
peristalsis – pushing movements
segmentation – ringlike contractions that aid in mixing and slowing peristalsis
overdistended or irritated wall triggers “peristaltic rush” resulting in diarrhea
“Long distance” movements are triggered by stomach filling: - gastroenteric reflex (↑ motility and secretion along length of small intestine) - gastroileal reflex (relaxation of ileocecal sphincter)

16. Absorption in the Small Intestine
monosaccharides and amino acids
through facilitated diffusion and active transport
absorbed into blood
electrolytes and water
through diffusion, osmosis, and active transport
absorbed into blood
vitamins
fat-soluble dissolve in dietary fats (vit A,D,E,K)
Water-soluble through diffusion, except B12 (active transport)
Vitamin K (large intestine) – with other lipids
absorbed into blood

17. Absorption of Fats in the Small Intestine
Figure from: Hole’s Human A&P, 12th edition, 2010
fatty acids and glycerol
several steps
absorbed into lymph into blood
Chylomicrons contain TG, cholesterol, and phospholipids

18. Large Intestine
The bowel includes the small and large intestines.
The main forms of Inflammatory Bowel Disease are Crohn's disease and ulcerative colitis (UC).
Accounting for far fewer cases are other forms of IBD, which are not always classified as typical IBD:
Collagenous colitis
Lymphocytic colitis
Ischaemic colitis
Diversion colitis
Behçet's disease
Indeterminate colitis
The main difference between Crohn's disease and UC is the location and nature of the inflammatory changes. Crohn's can affect any part of the gastrointestinal tract, from mouth to anus (skip lesions), although a majority of the cases start in the terminal ileum. Ulcerative colitis, in contrast, is restricted to the colon and the rectum.[4]
Pathophysiology in Crohn's disease vs. ulcerative colitis: Crohn's disease Ulcerative colitis
Autoimmune disease Widely regarded as an autoimmune disease No consensus
Cytokine response Associated with Th17[5] Vaguely associated with Th2
Microscopically, ulcerative colitis is restricted to the mucosa (epithelial lining of the gut), while Crohn's disease affects the whole bowel wall ("transmural lesions"). Finally, Crohn's disease and ulcerative colitis present with extra-intestinal manifestations (such as liver problems, arthritis, skin manifestations and eye problems) in different proportions.
Rarely, a definitive diagnosis of neither Crohn's disease nor ulcerative colitis can be made because of idiosyncrasies in the presentation. In this case, a diagnosis of indeterminate colitis may be made. Although a recognised definition, not all centres refer to this.
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 *

19. Histology of the Large Intestine
Figures from: Hole’s Human A&P, 12th edition, 2010
Walls of large intestine are much thinner than the small intestine, however, the lumen is larger
Note lack of villi and presence of numerous goblet cells (mucus)
No enzymes produced; any digestion is from previously introduced enzymes or bacteria

20. Functions of Large Intestine
little or no digestive function
absorbs water, bile salts, and electrolytes
secretes mucus (lubrication, binding, protection, pH)
conversion of bilirubin (uro- and stercobilinogen)
houses intestinal flora (~800 species of bacteria) and absorbs vitamins liberated by bacterial action (K, B5, and Biotin); produces intestinal gas (flatus)
forms and stores feces
carries out defecation
Receives about 500 ml of indigestible material per day and reduces the volume to about 150 ml of feces.

21. The Rectum, Anal Canal, and Anus
Figure from: Hole’s Human A&P, 12th edition, 2010
Temporary storage of fecal material in rectum triggers the urge to defecate
Internal anal sphincter is usually contracted but relaxes in response to distension. External sphincter must be tensed reflexively to retain feces
Rectal valves
Procto- = anus or rectum
(Keratinzed strat. squamous epithelium)

22. Movements of Large Intestine
slower and less frequent than those of small intestine
mixing movements (haustral churning every 30 min)
mass movements - usually follow meals (stimulated by distension of stomach and duodenum)
gastrocolic reflex
duodenocolic reflex
peristaltic wave from transverse colon through rest of large intestine

23. All You Need to Know???

24. Parasympathetic Defecation Reflex
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Note that this reflex opens the internal sphincter and closes the external sphincter
Need voluntary relaxation of the external sphincter for defecation

25. Feces water (75%), solids (25%) electrolytes mucus
bacteria (30% of solids) and sloughed epithelial cells
bile pigments altered by bacteria provide color (mainly urobilins and stercobilins)
odor produced by bacterial compounds (indoles and skatoles, phenols, H2S, ammonia)
indigestible materials

26. Major Organs of Digestive System
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Organs can be divided into the:
Digestive tract (primary) (alimentary canal); tube extending from mouth to anus (about 30 ft.)
Accessory organs; teeth, tongue, salivary glands, liver, gallbladder, and pancreas

27. Salivary Glands
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Parasympathetic – CN VII and IX; sympathetic via cervical sympathetic chain.

28. Secretions of Salivary Glands
Secretions are about neutral pH and continual due to basal parasympathetic stimulation, but increase after
- presence, or anticipation of, food; - parasympathetic stimulation (watery, large volume) - sympathetic stimulation (viscous, small volume)
Parotid glands
clear
primarily water, serous fluid
rich in amylase
mumps virus typically attacks here
Food in mouth stimulates the nucleus of the tractus soliarius and this stimulates the salivatory nuclei in the pons/medulla send signals to salivary glands via the facial and glossopharyngeal nerves
Submandibular glands
primarily serous fluid
some mucus, amylase
Sublingual glands
primarily mucus
most viscous

29. Liver [ Hepat(o)- ]
Round ligament is part of the falciform ligament that divides the lobes; remnant of fetal umbilical vein.
Note that the vena cava does not enter the liver; it passes by
Figure from: Martini, Anatomy & Physiology, Pearson Education, 2004

30. Arterial Supply and Venous Drainage of Liver
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

31. Hepatic Lobule
Hepatic lobules are the functional units of the liver (>100,000)
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

32. Paths of Blood and Bile in Hepatic Lobule
Figure from: Hole’s Human A&P, 12th edition, 2010
Liver’s role as an accessory organ in digestion is production of bile
Sinusoid
Hepatic portal vein → sinusoids → central vein → hepatic veins → inferior vena cava
Hepatic artery

33. Liver Functions (over 200!)
Three general categories of function
1) Metabolic regulation
Interconversion of carbohydrates, lipids, amino acids
Removal of wastes
Vitamin and mineral metabolism
Drug inactivation
Storage of fats, glycogen, iron, vit A/B12/D/E/K
2) Hematological regulation
Phagocytosis and antigen presentation; ab removal
Synthesis of plasma proteins
Removal of circulating hormones
Removal of worn-out RBCs (Kupffer cells)
Removal or storage of toxins
3) Synthesis and secretion of bile (role in digestion)
Know items in red

34. Gallbladder [Cyst(o)-]
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Main function is to store and concentrate bile between meals, and release bile under the influence of CCK

35. Composition of Bile (Chole-)
Yellowish-green liquid continually secreted by hepatocytes
water
bile salts (bile acids)
derived from cholesterol
emulsification of fats (increases surface area for digestive enzymes)
helps absorption of fatty acids, cholesterol, and fat-soluble vitamins
80% are recycled (reabsorbed and reused) – enterohepatic circulation of bile
20% excreted in feces (disposes of excess cholesterol)
bile pigments (bilirubin and biliverdin from breakdown of RBCs)
electrolytes
Gallstones most frequently occur in (5 F’s): fair, fat, female, fertile, forty.

36. Regulation of Bile Release from GB
Figure from: Hole’s Human A&P, 12th edition, 2010
fatty chyme entering duodenum stimulates the GB to release bile (via CCK)
Secretin causes the bile ducts (and pancreatic ducts) to secrete bile rich in HCO3-

37. Actions of Cholecystokinin (CCK) on Digestion
Figure adapted from: Barrett, K., Gastrointestinal Physiology, Lange, 2006
CCK
Contraction of Gallbladder
Secretion of pancreatic enzymes
Reduced emptying of stomach
Relaxation of hepatopancreatic sphincter
Protein, CHO, lipid absorption and digestion
Matching of nutrient delivery to digestive and absorptive capability

38. Pancreas Exocrine (digestive) and endocrine (metabolic) functions
Completes digestion of proteins that was started in the stomach

39. Blood Supply and Drainage of Pancreas
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

40. 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…

41. 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)
Dipeptides, tripeptides, amino acids
Proteins
Purpose of proteolytic enzymes is continued breakdown of proteins that began in the stomach

42. Regulation of Pancreatic Secretions
acidic chyme stimulates release of secretin
secretin stimulates release of watery pancreatic juice with bicarbonate and phosphate (= buffers; to  pH) CCK and parasympathetic NS stimulate production and secretion of pancreatic enzymes and zymogens
The acini of the pancreas secrete enzymes/zymogens; the ducts secrete buffers (bicarbonate, phosphates)

43. 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
Chymotrypsinogen Procarboxypeptidase Proelastase
Trypsinogen Carboxypeptidase Elastase
Pancreas
Bile and Pancreatic ducts
(proenzymes, zymogens)
Proteins
Bile
Lipases
HCO3-, PO43-
(emulsification)
Nucleases (DNA, RNA)
Amylase (glycogen, starches)
Di- and tripeptides
Triglycerides Cholesterol Fat 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
Subclavian vein
Monosaccharides

44. Life-Span Changes gums recede teeth become sensitive
teeth may loosen or fall out
heartburn more frequent
constipation more frequent
nutrient absorption decreases
accessory organs age but the effects are less noticeable