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GI tract SG
GI tract Study Guide
Question | Answer |
---|---|
What is the function of the esophagus? | Protection against abrasion from food |
Describe the stomach | Thick muscular wall that churns the food and produces enzymes and mucous secretions to allow processing of food |
What is the function of the small intestine? | Absorption and further breakdown(secretions from pancreas and liver) of chime from the stomach |
What is the function of the large intestine? | Absorption of water. There is a compaction of waste material and peristalsis mediated by the muscular wall. The muscular wall is under hormonal control. |
What type are cells throughout the epithelium of the GI tract? | Enteroendocrine cells. They make many different peptides that act on the vascular system as well as the nervous system of the GI tube |
True or False: The nervous system of the GI tube has both parasympathetic and sympathetic ganglia and plexuses | True |
What layer is below the simple epithelium in the GI tract? | Lamina propria= loose connective tissue |
Describe the muscularis mucosae | Thin muscle boundary between the mucus membrane and the submucosa |
What is the muscularis externa? | The main muscle of the digestive tube organized into two layers: Outer longitudinal and inner circular |
What are the 3 layers of the stomach? | External layer longitudinal, Middle circumferential layer and oblique inner layer |
Describe the different glands | Glandular structures external to GI tube (Pancreas and Liver). Glands in the submucosa (Esophagus and duodenum). Straight tubular gland: invaginations of the epithelium: the secretory portion and the duct is the same structure. Goblet: epithelium |
Describe the esophagus | Covered with adventitia. Lumen is contorted. Esophageal glands. Mucous help food slide down. Muscularis mucosa. Lymphatics nodules in submucosa |
Describe the first, second and last 1/3 of esophagus | 1st 1/3: Voluntary control, skeletal. Middle 1/3: Mixture of smooth and skeletal. Last 1/3: Involuntary and smooth |
Describe pepsin | Secreted by the stomach and it secretes digestive enzymes. Pepsin is produced by chief cells and is in storage form, not active til it reaches a pH of 2 |
What cell produces HCl and what does HCl activate? | Parietal cells. HCl activates digestive enzymes |
What does the stomach do to prevent self digestion? | Has cells that secrete mucous |
What does the glands of the cardia and pylorus mainly produce? | Mucous and not digestively active components |
Where are the chief and parietal cells located in the stomach? | Glands of the body of stomach and the fundus |
Describe chief cells | Lots of RER and granules with pepsinogen. Stains basophilic. Large nucleus and zymogen granules |
Zymogen granules | Immature form of pepsin. Storage form of an enzyme called zymogen. Zymogen=producing enzymes. Zymogen gets secreted and activated once it reaches acid and cleavage enzymes. |
Describe parietal cells | Lots of mitochondria that pumps out protons. Stains eosinophilic. Intracellular canaliculus. Secretes HCl. Secretes intrinsic factor-B12 |
B12 in parietal cells | Peptide enters SI, acts on absorptive cells and allows vitamin B12 to be absorbed. B12 is important in blood formation. |
What is Pernicious Anemia? | Autoimmune reaction against intrinsic factor. Vitamin B12 is not absorbed successfully. |
Describe enterendocrine cells | Stain paler. Scattered throughtout glandular region. Analogous to Kulchitsky cells (Resp) Produces peptides. Secretory granules released into adjoining capillary |
Name peptides produced by enterendocrine | Somatostatin, Motilin: acts on SM, GIP: suppresses secretory of stomach, VIP: acts on capillaries, Secretin, CCK and Gastrin |
What changes from stomach to duodenum? | Encounter villi, between villi are crypts of Liberkuhn which produce mucous and digestive enzymes. Brunner's glands which are mucous secreting only in duodenum |
What does the lamina propria of the villi contain? | Blood vessels and a lymphatic vessel that is going up to the center called the lacteal |
What happens to the lipid molecules? | Broken down by lipases and rooted into the lacteal through little protein-coated structures called chymicrons |
What are enterocytes? | Absorptive cells that become engorged with nutrients. Has a microvilli border with actin. There is villin at the very tip of the microvilli that promotes absorption |
What cells are located at the base of the crypt? | Paneth cells and stem cells that supply the upper and lower regions with new cells |
What do the goblet cells contain in the SI? | Mucinogen granules that contain proteoglycans and the mucous secretion is at the apical border which help lubricate and protect epithelial surface |
What do some digestive processes in the SI break down? | Breaks down some proteins into free AA's. Each AA type has separate transportation |
What happens when the chlomicrons associate with the triglycerides? | They are exported from the cell into the extracellular space whereupon they are taken up by the lymphatic capillary |
What is the function of the Paneth cell? | Keep bacteria flora in check. Paneth cells secrete lysozymes: break down bacteria walls and defensins: impairs ability of bacteria to proliferate |
Where are the stem cells of the stomach located? | In the isthmus and neck of glands |
What can the stem cells of the stomach do? | Produce all of the specialized cells: above (glandular/sloughed off cells) or below (chief and parietal cells). Stem cells keep epithelial layer balanced |
Where are the stem cells located and what can the stem cells of the SI do? | Located almost at the base. Huge amount of sloughing off. Replenish below (Paneth cells) and above (Glandular cells/sloughed off) |
Describe the Enteric nervous system | Second brain. Submucosa: Meissner's plexus (Parasympthetic). Muscularis externa: Auerbach's plexus (Sympathetic) |
Describe the appendix | Mainly lymphoid tissue. Extension of SI and LI. Mucosa is same as LI mucosa. Does not have villi but has goblet cells. Organized into crypts and can absorb water |
Describe the Large Intestine | Smooth interior, muscularis externa has inner and outer layer that is continous and gathered into tenia. No villi. Organized into crypts (of Lieberkuhn) |
Describe the rectum | Junction between rectum has resemblance of colon and anus (stratified squamous). Abrupt change in epithelium External sphincter is skeletal under voluntary control |