1. HISTOLOGY OF THE GIT (ONE) cont….
Lufukuja. G

2. GIT COMPOSITION
Lufukuja. G

3. Large intestine
Is the terminal part of the digestive tract and it consists of the caecum, vermiform appendix, colon, rectum and anal canal. The colon is divided into ascending, transverse, descending, and sigmoid parts.
Histologically the large intestine has the usual four tunics. The following are general features of the large intestine
Lufukuja. G

4. Lufukuja. G

5. Vermiform Appendix
Is the narrower diverticulum of the of the caecum arising 2.5cm below the ileocaecal valve
Tunica mucosa
Lined mostly by mucous (goblet) cells
Villi are missing
Intestinal glands are few
Lufukuja. G

6. Lufukuja. G

7. …Appendix Lamina Propria Muscularis mucosa
Extremely rich in Lymphoid tissues that are aggregated to form lymphoid (follicles) nodules
Muscularis mucosa
Is thin and it forms incomplete layer and is missing in some areas.
Lufukuja. G

8. colon The Lining epithelium
The mucosa of the large intestine does not have villi and the epithelium is lined by simple columnar, absorptive, secretory, goblet cells present in large numbers
Lamina propria:
The lamina propria contains mucosal glands
Some solitary lymphatic nodules are present in the lamina propria
Lufukuja. G

9. … colon Tunica submucosa
It has the same plan as in the other areas but has no glands
Tunica muscularis
The circular layer is continuous, but the outer longitudinal muscle layer is aggregated in the form of three bands, which are known as taenia coli except in the apendix and anal canal. Taenia coli are responsible for gathering the wall of large intestines into sacculations.
Lufukuja. G

10. Lufukuja. G

11. …colon
Tunica serosa
Is similar to small intestine, but contains short serosa process containing fats tissue known as appendices epiploicae
Lufukuja. G

12. Rectum
Is a dilated lower part of the GIT that lies between the sigmoid colon and the anal canal
Tunica mucosa
Is lined by simple columnar cells with much more goblet cells than the rest of the large intestine
Muscularis mucosa is thick, in the lower rectum, the longitudinal layer appear to shorter than the length of the rectum. This causes the mucosa to bulge into the lumen as transverse shelves called plicae transversae (Houston's valves), one on the left and two on the rigth, they help to support the feaces.
Lufukuja. G

13. Lufukuja. G

14. Rectum… Tunica muscularis
In the lower rectum, the inner circular layer thickens to form internal anal sphincter muscle.
The external anal sphincter is composed of skeletal muscle fibers surrounding the anal canal.
There are no taenia coli
Lufukuja. G

15. Ana canal Characteristic features
Anal canal is Histologically divided into proximal, middle, and distal one third. The division is based on the characteristic feature of the mucosa in these three part.
The upper folds are called anal columns or column of Morgagn.
At the lower end near the anal orifice they unite to form transverse folds called anal folds. Pockets of valves above the anal valves form the anal sinuses
Lufukuja. G

16. Lufukuja. G

17. G.Lufukuja

18. …ana canal Tunica mucosa
The upper half is lined by columnar epithelium and the lower half is lined by stratified non-keratinized squamous epithelium. However, at the cutaneous zone of anal canal (anus) the epithelial become keratinized, and beneath it are circumanal glands.
Circumanal glands consists of a group of sebaceous and apocrine sweat glands that are situated in the skin surrounding the anal orifice
Lufukuja. G

20. …ana canal Tunica submucosa Tunica muscularis
Contain mucous secreting glands, the ducts of which open in anal crypts that are situated close to the anal sinuses
It is also rich in plexus of haemorrhoidal veins
Tunica muscularis
The inner circular layer extends up to the upper one third where it thickens to form the internal anal sphincter.
Lufukuja. G

21. HISTOLOGY OF THE GIT II
(LIVER & PANCREAS)
G.Lufukuja

22. The liver
The liver is the second-largest organ of the body (the largest is the skin) and the largest gland weighing about 1.5kg
All the materials absorbed via the intestines reach the liver through the portal vein, except the complex lipids (chylomicrons), which are transported mainly by lymph vessels
It is essential to the processing metabolites, and make them ready for utilization by the body. Eliminates drugs and toxic metabolites (detoxification), Storage of some nutrients and Synthesis of cholesterol, bile salts and phospholipids & Secretion of bile
G.Lufukuja

23. Structural organization
The liver is covered by a thin connective tissue capsule (Glisson's capsule) that becomes thicker at the hilum, where the portal vein and the hepatic artery enter the organ and where the right and left hepatic ducts and lymphatics exit.
G.Lufukuja

24. G.Lufukuja

25. Histologically the liver is made up of the parenchyma (liver cells) and a stroma (connective tissue).
The Liver Lobule
The basic structural component of the liver is the liver cell, or hepatocyte. These epithelial cells are grouped in interconnected plates and constitute two-thirds of the mass of the liver.
The classic liver lobule is formed of polygonal mass of tissue with portal spaces at the periphery and a vein, called the central or centrolobular vein, in the center
Note: There are three ways of describing the structure of the liver in terms of a functional unit
The classic lobule
The portal lobule
Liver acinus
G.Lufukuja

26. In this classic lobule, the flow of blood is centripetal, from the portal areas at the periphery towards the central vein.
The flow of bile and lymph is centrifugal, from the center of the lobule towards the periphery
G.Lufukuja

27. G.Lufukuja

28. G.Lufukuja

29. …structural organization
G.Lufukuja

30. G.Lufukuja

31. Sinusoids & perisinusoidal space (space of Disse)
Between the hepatocytes and sinusoids there is a space called perisinusoidal space of Disse. It is thought that materials that come from sinusoids enter this space before they are taken by the hepatocytes. Also when the hepatocytes secrete, the materials enter this space first before entering the sinusoids.
The Space of Disse also contains Ito cells, also called hepatic stellate cells, which store fat or fat soluble vitamins (like vitamin A). A variety of insults that cause inflammation can result in Ito cells transforming to myofibroblasts, resulting in collagen production, fibrosis, and cirrhosis.
G.Lufukuja

32. Periportal space (Space of Mall)
The space of Disse is continuous at the periphery of the hepatic lobule with the space of Mall that surround the vessels and ductules in the portal area. Lymph vessels of the liver begin at the space of Mall as Cul-de-sac capillaries.
G.Lufukuja

33. Bile canaliculi
These are minute Intrahepatic bile channels that are situated between adjacent hepatocytes forming an anastomosing network which is present on almost all of the surfaces of the cells, except where the hepatocytes relate to the sinusoids.
They are not like ducts because they do not have their own wall or epithelial lining. When the liver cells secrete bile they secrete it into bile canaliculi.
Bile canaliculi drain into interlobular ductules drain into right and left hepatic ducts drain into common hepatic duct.
The common hepatic duct unites with cystic duct to for the bile duct, which opens into the duodenum.
G.Lufukuja

34. G.Lufukuja

35. Portal lobule Emphasizes the exocrine functions of the liver.
It is triangular in shape with central veins at the angles of the triangle; and a portal area at the center of the triangle
Its margins consist of imaginary lines drawn between three central veins that are close to the portal triad
One portal lobule incorporates three classical lobules. It emphasizes the flow of bile
G.Lufukuja

36. Portal lobule…
G.Lufukuja

37. Portal lobule…
G.Lufukuja

38. Liver acinus
From a metabolic perspective, the functional unit is the hepatic acinus, each of which is centered on the line connecting two portal triads and extends outwards to the two adjacent central veins.
G.Lufukuja

39. …liver acinus
The acinus is roughly divided into zones that correspond to distance from the arterial blood supply
The periportal zone I is nearest to the entering vascular supply and receives the most oxygenated blood, making it least sensitive to ischemic injury while making it very susceptible to viral hepatitis. Functionally, zone I hepatocytes are specialized for oxidative liver functions such as gluconeogenesis, β-oxidation of fatty acids and cholesterol synthesis.
G.Lufukuja

40. Zone 2 Has no sharp boundaries
But it morphologically and functionally intermediate between zones 1 and 3
G.Lufukuja

41. Centrilobular Zone III
Cells in this zone are the first to show signs of ischemic necrosis (centrilobular necrosis). They are the last to react to toxins or bile duct occlusion. cells are more important
for glycolysis, lipogenesis and cytochrome P-450-based drug detoxification, so is the first region to show fat accumulation in metabolic or drug- induced fatty livers
G.Lufukuja

42. Kupffer cells
Kupffer cells belongs to mononuclear phagocytic system and are derived from monocytes that originate from bone marrow
Kupffer cells probably phagocytize and break down damaged or senile red blood cells that have not captured by macrophages of spleen. This function increases and becomes essential after splenectomy
G.Lufukuja

43. Pancreas
G.Lufukuja

44. Pancreas
The pancreas is the main enzyme producing accessory gland of the digestive system. It has both exocrine and endocrine functions. The exocrine part of the pancreas has closely packed serous acini, similar to those of the digestive glands. It is covered by thin areola tissue that sends septae into the gland and divide it into lobules.
G.Lufukuja

45. G.Lufukuja

46. G.Lufukuja

47. Microscopic features of the exocrine pancreas
G.Lufukuja

48. Microscopic features of the exocrine pancreas
Each lobule is composed of spherical clusters of secretory exocrine cells that form the pancreatic acini or secretory endpieces. During physiological state secretion of exocrine pancreas is enhanced by cholecystokini
G.Lufukuja

49. Pancreas…
The duct system of the exocrine pancreas system begins in the acinus. These ducts are lines by simple cuboidal epithelium, but the main pancreatic duct runs from the tail to the head of the pancreas. There may be a smaller accessory pancreatic duct. They join the common bile duct to empty into the duodenum.
G.Lufukuja

50. G.Lufukuja

51. The main pancreatic
The main pancreatic duct is lined by columnar and goblet cells, it run longitudinally from the tail of the pancreas to its head and empty into the duodenal lumen at the ampulla of Varter.
G.Lufukuja

52. The endocrine tissue
The endocrine tissue of the pancreas forms islets of Langerhans of various sizes scattered throughout the exocrine tissue. Using special stains, three major cells are identified; the alpha cells, beta, delta and PP cells
G.Lufukuja

53. Alpha cells & Beta cells
Alpha cells: These occupy the central part of the islets and form 20% of the islet cells. These cells secrete glucagon hormone which increases the blood level of glucose
Beta cells: These occupy the peripheral part of the islets and constitute 75% - 80% of the islet cells. These cells secrete insulin hormone which allows utilization of glucose by the body cells, as without insulin glucose will not be utilized.
G.Lufukuja

54. Delta cells & PP cells
Delta cells :These occupy the central portion of the islets and constitute 5% of the cell population. These cells are said to secrete serotonin or pancreatic gastrin & somatostatin.
PP cells (pancreatic polypeptide producing cells): predominantly in the head of the pancreas. They secrete a pancreatic polypeptide which stimulates the chief cells of the stomach to produce more pepsinogen.
G.Lufukuja

55. LUFUKUJA G