Please feel free to chat amongst yourselves until we begin at the top of the hour. 1

Seminar Agenda Review of Course Information The Digestive System Questions & Answers 2

Review of Course Information: Projects There are 2 Projects. Each project has two parts. Project 1 is due at the end of Units 3 and 5 and Project 2 is due at the end of Units 7 and 9. Some guidelines: Use Microsoft Word Be sure to complete all parts of the assignment Use clear and concise language and proofread your work. Your work should be free of spelling and grammatical errors. 3

Unit 3-5 Project: Histology Topic Proposal: The topic should be on any of the systems covered in part 1 of this course (Histology) and be either a tissue or organ. For the tissue or organ that you selected, you should: Describe the histological characteristics of the tissue or organ. Correlate the structural characteristics of the tissue with their function. Discuss the importance of histological characteristics of the tissue or organ to the body function as a whole. 4

Unit 3-5 Project: Histology NOTE: Topic Choice, Outline and List of References are due at the end of Unit 3: 25 points Complete Paper (Part 1; Histology) due at the end of Unit 5: 50 points 5

Unit 3-5 Project: Histology Topic Proposal: Include a title page containing the title of the paper, your name and course details. Body of the project should begin on page 2. The references should start on a new page at the end of the essay. At least 3 references other than your book should be used. For information on APA reference style please go to the Kaplan Writing Center or the following websites: APA Research Style Crib Sheet: crib.html#Intext Psychology With Style: Avoid extensive quotes, unless there is absolutely no way to say it any better. Almost always you should be able to put things in your own words. Beware of plagiarism! The paper should be 4-7 pages long, including the reference page but excluding the title page. It is due no later than the end of Unit 5. 6

Any questions? 7

Digestive system 8

Digestive System Teeth Composed of Enamel, dentin, nerves and vessels Enamel 96% of hydroxyapatite crystals 4% amelogenin and enamelin proteins Extremely strong structure and more resistant to damage then bone Is derived from oral epithelium during development Dentin Inner pulp tissue containing loose connective tissue Underlies enamel and is only 70% mineralized Contains collagen instead of amelogenin Root of tooth composed of dentin and pulp Cementum surrounds the dentin on the root Resembles bone 9

Teeth 10

Teeth 11

Teeth 12

Teeth 13

Salivary Glands Three major salivary glands Parotid Submandibular Sublingual Glands are separate, identifiable organs located beneath the skin of the face that send ducts into the oral cavity. The cells that synthesize saliva form secretory units or acinus. Acinus is a small saclike dilatation, particularly one in a gland Each unit is covered by contractile myoepithelial cells that exert pressure on the acini – resulting in the secretion of saliva into the oral cavity. Intralobular ducts contain cells with simple columnar epithelium 14

Salivary Glands 15

Salivary Glands Two Types of Salivary Units exist: Serous acinus Cells have round nuclei and cytoplasms that are highly stained due to many secretory vesicles with serous proteins Secretions rich in amylase and proline-rich proteins Parotid gland is composed entirely of serous acini Von Ebner’s gland also has serous acini 16

Serous acinus 17

Salivary Glands Two Types of Salivary Units exist: Serous acinus Mocous acini Cells are more flattened, basally located nuclei, lightly stained owing to the presence of mucous proteins within secretory vesicles that fail to stain well with common histological stains Mucous glands are rich in the protein mucin Contain large number of carbohydrate molecules (highly glycosylated); Mucin is 80% carbohydrate by weight 18

Mocous acini 19

Digestive system 20

From the esophagus on… The rest of the digestive system from the esophagus onward is organized into four specific layers: Layer 1 – Mucosa A. Mucosal epithelium B. Lamina propria C. Muscularis mucosae Layer 2 – Submucosa Layer 3 – Muscularis externa Layer 4 – Adventitia or serosa 21

Esophagus Muscular tube (skeletal and smooth muscle) line with nonkeratinized stratified squamous epithelium 22

Digestive system 23

Stomach 1 - Villi 2 - submucosa 3 - muscularis propria 7 - gastric pits in the mucosa 24

Stomach Main portion of the stomach (fundus) have five epithelial cell types with distinct function Simple columnar epithelial cells (surface mucous cells) – secrete bicarbonate-rich mucus to protect the gastric tissue Mucous neck cells – secrete mucous and serve as stem cells Parietal cells – Functions to secrete a fluid rich in acid have a centrally located nucleus, brightly staining, eosinophilic cytoplasm and a distinctive round shape Have deep cytoplasmic invaginations called canaliculi that have long, flexible microvilli as well as abundance of mitochondria 25

Parietal Cells 26

Stomach (cont’d) Main portion of the stomach (fundus) have five epithelial cell types with distinct function Chief cell (at the bottom of gastric pit) Secrete enzymes such as pepsin and rennin to help digest food proteins basophilic Neuroendocrine cell Light- staining cytoplasm Produces peptide hormones including gastrin stimulate acid secretion by parietal cells 27

Stomach 28

Digestive system 29

Intestines Lined by a simple columnar epithelium, that similar to the stomach, is highly folded 30 jejunum

Small Intestines Mucosa of the small intestines posess finger-shaped epithelial projections called villi Villi serve as an expanded surface to absorb nutrients Small intestines divided into three regions: Duodenum Jejunum Ileum 31

Duodenum Short portion of small intestines Broad villi Submucosa contains mucous glands call Brunner’s gland Secrete alkaline mucus that neutralizes acid from the stomach 32

Jejunum 33 -narrow and taller villi-functions in absorption -no Brunner’s glands

Ileum Distinguishing feature of ileum is the presence of unusually prominent masses of lymphocytes, macrophages and dendritic cells in the submucosa called the Peyer’s patch Presence linked to increase in the mass of intraluminal microorganisms along the length of the gut Reflects hostile environment between the host epithelium and bacteria of the gut 34

Ileum 35

Digestive system 36

Large Intestine (Colon) Histologic feature of the large intestine are similar to small intestine except for: The mucosa of large intestine possess intestinal gland but lack villi Percentage of goblet cells within the lining of epithelium is much higher in the large intestine This is due to the absorptive ability of the intestine 9 Liters of fluid enters gut daily – only 100 ml (1%) leaves the body in stool – rest reabsorbed 37

Large Intestines 38

Hirschsprung’s disease Mature neurons are present in the gut These are derived during development from a stem cell population called neural crest cells Hirschsprung’s disease Affects 1 in 5000 newborns The neural network of the colon does not form Colonic ganglia or ganglion of the myenteric plexus do not form As a result, portions of the colon do not contract The colon becomes overfilled with material and is very painful and debilitating 39

Liver Functions as gatekeeper or filter between the gut and the rest of the body Large blood vessels convey nutrients and other molecules from the gut to the liver Here they are processed, stored or released to the body In order to do this function, it receives 1/3 of the total cardiac output – very well vacularized. Two sources of blood The gut The aorta 40

Liver Cell Types Bile Duct Simple cuboidal epithelium Associated with portal vein and hepatic artery – the three together are called portal triads Secretes bile for food digestion 41

Liver Cell Types Hepatocytes Cuboidal epithelial cells with a round, euchromatic nuclei and eosinophilic cytoplasms Each hepatocyte contains at least one surface with a groove-like indentation which function to line up to form bile canaliculi that convey bile to a bile duct The opposite surface of hepatocytes contain the endothelial cells of sinusoids Sinusoids are specialized blood vessels that lack a continuous basal lamina and have a discontinuous endothelium Can have large amounts of glycogen (depending on the meal), will stain with periodic acid-Schiff (PAS) 42

Liver Cell Types 43

Liver Cell Types 44

Hepatocyte 45

Liver cells 46

Pancreas A major gland 4% of the cells are endocrine cells and form small clusters called islets of Langerhans Endocrine glands secrete their products including hormones directly into the blood. Majority of pancreatic cells have an exocrine function and secrete into ducts Acinar cells Highly polarized. Basal portions include the nuclei and large amounts of rough endoplasmic reticulum Apical portion has large secretory granules 47

Pancreas 48 Pancreatic acinus – acinar cells with basal rER, apical zymogen granules, centroacinar cells and intercalated duct

Questions 49