Digestive system L 2. Lecturer Dr. Firdous M. Jaafar Department of Anatomy/Histology section

Transcription

1 Digestive system L 2 Lecturer Dr. Firdous M. Jaafar Department of Anatomy/Histology section

2 objectives 1-Describe the general structure of digestive tract: a-mucosa. b-submucosa. c-muscularis externa d-adventitia or serosa. 2-Define esophagus, and describe its structure. 3-Identify the anatomical regions of stomach, and describe their structure. a-cardia. b-fundus. c-body. d-pylorus. 4-Enumerate the types of gastric glands, and differentiate between the types of cells present in each gland.

3 General structure of digestive tract It is a hollow tube with a lumen of variable diameter and a wall made up of four main layers: mucosa, submucosa, muscularis, and serosa.

4 General structure of digestive tract 1- Mucosa: Composed of an epithelial lining; an underlying lamina propria of loose connective tissue rich in blood vessels, lymphatics, lymphocytes. There is a thin layer of smooth muscle called the muscularis mucosae usually separating mucosa from submucosa.

5 General structure of digestive tract 2- Submucosa : contains denser connective tissue with many blood and lymph vessels and the submucosal plexus of autonomic nerves. It may also contain glands and lymphoid tissue.

6 General structure of digestive tract 3- Muscularis composed of smooth muscle cells that are spirally oriented and divided into two sublayers: a- Inner circular b- Outer longitudinal In between these layers there is myenteric nerve plexus.

7 General structure of digestive tract MEDICAL APPLICATION: The abundant innervation from the autonomic nervous system that the digestive tract receives provides an anatomic explanation of the widely observed action of emotional stress on this tract,(ibs) In certain diseases, such as Hirschsprung disease (congenital megacolon) or Chagas disease (Trypanosoma cruzi infection), the plexuses in the digestive tract are severely injured and most of their neurons are destroyed. This results in disturbances of digestive tract motility, with frequent dilatations in some areas.

8 Hirschsprung disease (congenital megacolon) X Ray Barium enema

9 General structure of digestive tract 4- Serosa a thin layer of loose connective tissue, rich in blood vessels, lymphatics, and adipose tissue, with a simple squamous covering epithelium (mesothelium). In esophagus, this layer is called adventitia, with no mesothelium.

10 General structure of digestive tract

11 It is a straight muscular tube that transports food from the pharynx to the stomach. It is about 25cm long. Esophagus

12 Esophagus The wall consists of four layers: 1- mucosa: a- epithelium: stratified squamous nonkeratinized. b- lamina propria: loose connective tissue, and near stomach there is esophageal cardiac glands(mucous glands) c- Muscularis mucosae: it is thick & consists of longitudinal smooth muscle fibers.

13 Esophagus 2- The submucosa: loose CT contains the oesophageal glands(mucous glands). 3-. The muscularis externa: consists of 2 layers, of which the outer is mainly longitudinal & the inner mainly circular. Between the 2 muscle layers there is Auerbach's plexus. 4- adventitia: consists of loose connective tissue, and there is a serous layer only on the abdominal part of the oesophagus.

14 Esophagocardiac junction

15 Stomach is a mixed exocrine-endocrine organ that digests food and secretes hormones. Function: 1- continue the digestion of carbohydrates initiated in the mouth 2- add an acidic fluid to the ingested food. 3- transform it by muscular activity into a viscous mass (chyme). 4- promote the initial digestion of proteins with the enzyme pepsin. 5- produces a gastric lipase that digests triglycerides.

16 Stomach It is a dilated segment of the digestive tract. stomach can be divided into 4 divisions:- 1. Cardia 2. Fundus 3. Body both similar in structure 4. Pylorus or pyloric region. The mucosa and submucosa of the empty stomach have longitudinally directed folds known as rugae

17 Stomach

18 Stomach The wall of stomach consists of: 1- mucosa: a- epithelium: simple columnar epith. It is invaginated into lamina propria forming gastric pits. b- lamina propria: looose CT contains gastric glands.

19 The wall of stomach consists of: 1- mucosa: a- epithelium: simple columnar epith. It is invaginated into lamina propria forming gastric pits. b- lamina propria: looose CT contains gastric glands. Stomach

20 Stomach

21 Stomach Stomach is protected by: 1-The epithelium covering the surface and lining the pits is a simple columnar epithelium(surface mucous cells), the cells of which produce a protective mucus layer. 2-These cells are connected by tight junctions. 3-Rich vasculature of mucosa that provides nutrients and oxygen.

22 Stomach MEDICAL APPLICATION: Ulcer is a disruption of gastric epithelial layer caused by stress, drugs(aspirin or ethanol), some microorganisms(helicopacter Pylori), and hyperosmolality of food.

23 Gastric glands Types of gastric glands: 1- cardiac glands: lined by mucous secreting columnar cells, secrete mucous & lysozyme. 2- fundic gland: composed of: a-mucous neck cells:secrete mucous. b-peptic(chief or zymogenic) cells: found more at lower part of gland. Secrete pepsin, lipase, renin.

24 Gastric glands c- parietal(oxyntic) cells: present more at the upper half of gland, eosinophilic, secrete HCL, intrinsic factor. d- enteroendocrine(apud) cells: found at the base of gland, secrete serotonin. e- stem(undifferentiated) cell: found at the neck of gland, they have mitotic activity to replace lost cells.

25 MEDICAL APPLICATION Tumors called carcinoids, which arise from the EC cells, are responsible for the clinical symptoms caused by overproduction of serotonin. Serotonin increases gut motility, but high levels of this hormone/neurotransmitter have been related to mucosal vasoconstriction and damage.

26 Fundic gland

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28 MEDICAL APPLICATION The parietal cells secrete the HCl & gastric intrinsic factor (a glycoprotein that binds to vitamin B12 & facilitate its absorption by the intestine). In atrophic gastritis, both parietal and peptic cells are much less numerous, and the gastric juice has little or no acid or pepsin activity, and no intrinsic factor, which can lead to vitamin B12 deficiency pernicious anaemia.

29 Gastric glands 3- pyloric gland: similar to the cardiac glands, with long pit and short, coiled gland. It secrete mucous and lysozyme. It is composed of: a- mucous secreting, columnar cells. b- stem ccells. c- enteroendocrine cells; which includes: - G cells: secrete gastrin - D cells: secrete somatostatin.

30 Pyloric gland

31 Stomach c- muscularis mucosae: smooth m. arranged as an inner circular & an outer longitudinal layer, in some parts there is a third outer layer of circular fibers. 2- Submucosa:- is composed of dense connective tissue containing blood & lymph vessels & Meissner's plexus.

32 Stomach 3- muscularis externa: 3 illdefined layers of smooth m., an inner oblique, a middle circular & an outer longitudinal. Auerbach's plexus is found between the muscles. 4- serosa: a thin layer of loose connective tissue covered by mesothelium.