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GI tract SG

GI tract Study Guide

QuestionAnswer
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