1. Phases of Gastric Secretion

2. Stomach Histology Rugae: Folds in stomach when empty
Gastric pits: Openings for gastric glands
Contain cells
Surface mucous: Mucus
Mucous neck: Mucus
Parietal: Hydrochloric acid and intrinsic factor
Chief: Pepsinogen
Endocrine: Regulatory hormones

5. Hydrochloric Acid Production

6. Movements in Stomach

8. Small Intestine Site of greatest amount of digestion and absorption
Divisions
Duodenum
Jejunum
Ileum: Peyer’s patches or lymph nodules
Modifications
Circular folds or plicae circulares, villi, lacteal, microvilli
Cells of mucosa
Absorptive, goblet, granular, endocrine

9. Movement in small intestine:
Mixing: Segmental contraction that occurs in small intestine
Secretion: Lubricate, liquefy, digest
Digestion: Mechanical and chemical
Absorption: Movement from tract into circulation or lymph
Elimination: Waste products removed from body

10. Small Intestine Secretions
Mucus
Protects against digestive enzymes and stomach acids
Digestive enzymes
Disaccharidases: Break down disaccharides to monosaccharides
Peptidases: Hydrolyze peptide bonds
Nucleases: Break down nucleic acids
Duodenal glands
Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa

11. Duodenum and Pancreas

13. Duodenum Anatomy and Histology

14. Liver Lobes Ducts Major: Left and right Minor: Caudate and quadrate
Common hepatic
Cystic
From gallbladder
Common bile
Joins pancreatic duct at hepatopancreatic ampulla

17. Blood and Bile Flow

18. Duct System

19. Gallbladder Bile is stored and concentrated
Stimulated by cholecystokinin and vagal stimulation
Dumps into small intestine
Production of gallstones possible
Drastic dieting with rapid weight loss

20. Pancreas Anatomy Secretions Endocrine Pancreatic juice (exocrine)
Pancreatic islets produce insulin and glucagon
Exocrine
Acini produce digestive enzymes
Regions: Head, body, tail
Secretions
Pancreatic juice (exocrine)
Trypsin
Chymotrypsin
Carboxypeptidase
Pancreatic amylase
Pancreatic lipases
Enzymes that reduce DNA and ribonucleic acid

21. Bicarbonate Ion Production

22. Gastric hormones:

23. Liver Histology
portal
triad
Figure 24.20a, b

24. 3. Architecture of the Hepatic Parenchyma
The hepatic lobule is the structural unit of the liver.
Portal vein
Bile duct
Sinusoids
Central vein
Liver cells (Hepatocytes)
Portal area
Hepatic artery

25. …each day around 600 ml of bile is produced…
Bile acid
Phospholipids
Cholesterol
Bilirubin
Waste products
Electrolytes
Mucin

26. Functions of the Liver Bile production Storage
Salts emulsify fats, contain pigments as bilirubin
Storage
Glycogen, fat, vitamins, copper and iron; huge blood reservoir of blood (storage); very high lymph flow
Nutrient interconversion – Metabolic functions (see next slide)
Detoxification
Hepatocytes remove ammonia and convert to urea; metabolizes drugs, hormones; has the Cytochrome P-450 enzyme system.
Phagocytosis – Cleans the blood
Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria
Synthesis
Albumins, fibrinogen, globulins, heparin, clotting factors
The liver is the largest gland in the body and performs an astonishingly large number of tasks that impact all body systems. One consequence of this complexity is that hepatic disease has widespread effects on virtually all other organ systems. At the risk of losing sight of the forest by focusing on the trees, I will only briefly mention the vasculare and metabolic functions of the liver. It is a storage of cabohydrate, lipid copper and iron as well as it is able to interconvert nutrients. It detoxificate the bloocd by removing ammonia and converting it to ureal. The vascular functions include formation of lymph and it is part of phagocytic system. The Kupfeer cells phagocytize old blood cells and the liver also syntezise important components of the wound healing.
But we have focused on the very first one, the secretory and excretory functions of the liver, because it is the only one that directly affects digestion - the bile production which plays a critical role in the digestion and absorption of dietary lipids. However, the understanding the vascular and metabolic functions of the liver is critical to appreciating the gland as a whole.

27. Liver’s Role in Metabolism
Carbohydrate Metabolism
Storage of large amounts of glycogen
Conversion of galactose and fructose to glucose
Gluconeogenesis
Formation of many chemical compounds from intermediate products of carbohydrate metabolism
Fat Metabolism
Beta-oxidation of fatty acids to supply energy to for other functions in the body
Synthesis of cholesterol, phospholipids, and most lipoproteins (and their receptors)
Synthesis of fats from proteins and carbohydrates

28. Liver’s Role in Metabolism (cont’d)
Protein Metabolism
Deamination of amino acids
Formation of urea for removal of ammonia from the body fluids
Formation of plasma proteins
Interconversion of the various amino acids and synthesis of other compounds from amino acids

29. Exocrine Pancreas – Enzymes
Trypsinogen
Chymotrysinogen
Carboxypeptidases
Pro-elastase
Phospholipase
pancreatic lipase
Pancreatic amylase
Pancreatic juice is composed of two secretory products critical to proper digestion: digestive enzymes and bicarbonate. The enzymes are synthesized and secreted from the exocrine ascinar cells, whereas bicarbonate is secreted from the epithelial cells lining small pancreatic ducts.
Digestive Enzymes
The pancreas secretes a magnificent battery of enzymes that collectively have the capacity to reduce virtually all digestible macromolecules into forms that are capable of, or nearly capable of being absorbed. Three major groups of enzymes are critical to efficient digestion:
Proteases
Digestion of proteins is initiated by pepsin in the stomach, but the bulk of protein digestion is due to the pancreatic proteases. Several proteases are synthesized in the pancreas and secreted into the lumen of the small intestine. The two major pancreatic proteases are trypsin and chymotrypsin, which are synthesized and packaged into secretory vesicles as an the inactive proenzymes trypsinogen and chymotrypsinogen.
As you might anticipate, proteases are rather dangerous enzymes to have in cells, and packaging of an inactive precursor is a way for the cells to safely handle these enzymes. The secretory vesicles also contain a trypsin inhibitor which serves as an additional safeguard should some of the trypsinogen be activated to trypsin; following exocytosis this inhibitor is diluted out and becomes ineffective - the pin is out of the grenade.
Once trypsinogen and chymotrypsinogen are released into the lumen of the small intestine, they must be converted into their active forms in order to digest proteins. Trypsinogen is activated by the enzyme enterokinase, which is embedded in the intestinal mucosa.
Once trypsin is formed it activates chymotrypsinogen, as well as additional molecules of trypsinogen. The net result is a rather explosive appearance of active protease once the pancreatic secretions reach the small intestine.
Trypsin and chymotrypsin digest proteins into peptides and peptides into smaller peptides, but they cannot digest proteins and peptides to single amino acids. Some of the other proteases from the pancreas, for instance carboxypeptidase, have that ability, but the final digestion of peptides into amino acids is largely the effect of peptidases in small intestinal epithelial cells. More on this later.
Pancreatic Lipase
The major form of dietary fat is triglyceride, or neutral lipid. A triglyceride molecule cannot be directly absorbed across the intestinal mucosa. Rather, it must first be digested into a 2-monoglyceride and two free fatty acids. The enzyme that performs this hydrolysis is pancreatic lipase, which is delivered into the lumen of the gut as a constituent of pancreatic juice.
Sufficient quantities of bile salts must also be present in the lumen of the intestine in order for lipase to efficiently digest dietary triglyceride and for the resulting fatty acids and monoglyceride to be absorbed. This means that normal digestion and absorption of dietary fat is critically dependent on secretions from both the pancreas and liver.
Pancreatic lipase has recently been in the limelight as a target for management of obesity. The drug orlistat (Xenical) is a pancreatic lipase inhibitor that interferes with digestion of triglyceride and thereby reduces absorption of dietary fat. Clinical trials support the contention that inhibiting lipase can lead to significant reductions in body weight in some patients.
Amylase
The major dietary carbohydrate for many species is starch, a storage form of glucose in plants. Amylase is the enzyme that hydrolyses starch to maltose (a glucose-glucose disaccharide), as well as the trisaccharide maltotriose and small branchpoints fragments called limit dextrins. The major source of amylase in all species is pancreatic secretions, although amylase is also present in saliva of some animals, including humans.
Other Pancreatic Enzymes
In addition to the proteases, lipase and amylase, the pancreas produces a host of other digestive enzymes, including ribonuclease, deoxyribonuclease, gelatinase and elastase.
Bicarbonate and Water
Epithelial cells in pancreatic ducts are the source of the bicarbonate and water secreted by the pancreas. The mechanism underlying bicarbonate secretion is essentially the same as for acid secretion parietal cells and is dependent on the enzyme carbonic anhydrase. In pancreatic duct cells, the bicarbonate is secreted into the lumen of the duct and hence into pancreatic juice.

30. Bicarbonate Ion Production

37. Lipoproteins Types Chylomicrons VLDL LDL HDL Enter lymph
Transports cholesterol to cells
HDL
Transports cholesterol from cells to liver

39. Water and Ions: Water Ions
Can move in either direction across wall of small intestine depending on osmotic gradients
Ions
Sodium, potassium, calcium, magnesium, phosphate are actively transported

40. Large Intestine: Extends from ileocecal junction to anus
Consists of cecum, colon, rectum, anal canal
Movements sluggish (18-24 hours)

41. Large Intestine Cecum Colon Rectum Anal canal
Blind sac, vermiform appendix attached
Colon
Ascending, transverse, descending, sigmoid
Rectum
Straight muscular tube
Anal canal
Internal anal sphincter (smooth muscle)
External anal sphincter (skeletal muscle)
Hemorrhoids: Vein enlargement or inflammation

42. Secretions of Large Intestine
Mucus provides protection
Parasympathetic stimulation increases rate of goblet cell secretion
Pumps
Exchange of bicarbonate ions for chloride ions
Exchange of sodium ions for hydrogen ions
Bacterial actions produce gases called flatus

43. Histology of Large Intestine

44. Movement in Large Intestine
Mass movements
Common after meals
Local reflexes in enteric plexus
Gastrocolic: Initiated by stomach
Duodenocolic: Initiated by duodenum
Defecation reflex
Distension of the rectal wall by feces
Defecation
Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration

45. Reflexes in Colon and Rectum:

46. Digestion, Absorption, Transport
Breakdown of food molecules for absorption into circulation
Mechanical: Breaks large food particles to small
Chemical: Breaking of covalent bonds by digestive enzymes
Absorption and transport
Molecules are moved out of digestive tract and into circulation for distribution throughout body

47. Effects of Aging Death of myenteric plexus neurons
Atrophy of sphincter muscles
Incontinence
Decrease in mucus layer, connective tissue, muscles and secretions
Increased susceptibility to infections and toxic agents
Ulcerations and cancers