GI Flashcards
GI Objectives
Which GI organs are retroperitoneal?
Esophagus, some of duodenum, ascending and descending colon, pancreas (except tail end) and rectum
What are functions of the liver?
- Breaks down and builds up many biological molecules
- Stores vitamins and iron
- Destroys old blood cells
- Destroys poisons
- Produces bile
What are functions of the pancreas?
- Regulates blood glucose levels
- Bicarbonates neutralize stomach acid
- Trypsin and chymotrypsin (proteases) cleave proteins
- Carboxypeptidase cleaves proteins
- Amylase cleaves starch and glycogen
- Lipase cleaves lipids
- Nuclease cleaves nucleic acids
What are components of mucosa?
- Epithelial lining (stratified squamous, and simple columnar enteroendecrine cells. Moistoned by glandular secretions.)
- Lamina propria (areolar loose connective tissues, smooth muscle cells, lymphoid tissue, nerve endings)
- Muscularis mucosae (inner/outer layer of smooth muscle, elastic fibers)
What are components of submucosa?
Dense irregular connective tissues.
Meissner nerve plexus (secretion of digestive enzymes)
Binds to muscularis externa.
Blood & lymph vessels
Sometimes exocrine glands that secrete buffers & enzymes
What are components of muscularis externa?
Internal (circular) layer and external (longitudinal) muscle layer for peristalsis and digestion
What are components of serosa?
Loose connective tissue, adipose, simple squamous epithelium (mesothelium).
Adventitia: fibrous sheath of dense collage fibers that attaches digestive tract to adjacent structures
What are pacesetter cells?
Cells in muscularis mucosae and muscularis externa that spontaneously depolarize and set rhythmic cycles of digestion
What are 2 mechanical processes of moving digested materials?
- Peristalsis (wave like contractions to push bolus forward)
- Segmentation (churn and fragment bolus to mix contents with intestinal secretions
What local factors affect digestive functions?
pH Volume Chemical composition of intestinal contents Stretching of intestinal wall Local messengers
What are neural mechanisms that control digestive functions?
- Short reflexes (triggered by chemo/stretchreceptors, neurons in myenteric plexus)
- Long reflexes (involve interneurons and motor neurons in CNS, control large scale peristalsis. Cranial nerves IX and X or pelvic nerves in myenteric plexus)
What are characteristics of esophageal tissue?
- Mucosa has nonkeratinized, stratified squamous epithelium.
- Mucosa & submucosa adare packed into folds (expand for swallowing)
- Muscularis mucosae has irregular layer of smooth muscle
- Esophageal glands produce mucus for less friction
- Upper 3rd is skeletal muscle, middle 3rd is skeletal/smooth, lower 3rd smooth only
What are characteristics of gastric tissue?
- Simple columnar epithelium
- Rugae are folded ridges that allow stomach stretching
- Gastric pits (mucous cells) open to gastric glands (chief, parietal, G cells)
What are characteristics of small intestine tissue?
- Permanent transverse folds called circular folds (plicae circulares) for absorption
- Intestinal villi with microvilli brush border
- Each villus has capillaries originating from submucosa that carry absorbed nutrients to liver
- Lacteal lymphatic vessels absorb chylomicrons (which can’t enter capillaries)
What are characteristics of large intestine tissue?
- Larger diameter but thinner walls compared to small intestine
- Lymphoid nodules in lamina propria & submucosa
- Lacks villi
- Abundance of goblet cells (mucus)
- Intestinal glands are deeper than in small intestine
What are parietal cells?
- Most common along proximal portion of gastric gland
- Secrete intrinsic factor for B12 absorption
- Secrete H+ via ATPase & chloride in countertransport with bicarbonate (alkaline tide) to make HCl
What are Chief cells?
- Most common near base of gastric gland
2. Secrete pepsinogen, converted to pepsin by HCl. Pepsin is protein digesting enzyme
What are G cells?
- Most abundant near pylorus antorum
- Secrete gastrin, which stimulates secretion by parietal cells & chief cells. Also stimulates gastric wall contractions
What are D cells?
- Located in pylorus
2. Secrete somtatostatin, which inhibits release of gastrin
What are P/D1 cells?
Secrete Ghrelin, which increases hunger (antagonist to leptin, which decreases hunger)
What hormones does Duodenum secrete?
- Gastrin (stimulate gastric gland secretions & motility)
- Secretin (stimulates bile secretion from liver & buffers from pancreas. Reduces gastric motility & secretions)
- Gastric Inhibitory Peptide (inhibits gastric activity, stimulates insulin secretion, lipid synthesis, glucose use by skel. muscles)
- Cholecystokinin (stimulates gallbladder contraction, accelerates production & secretion of gastric enzymes, inhibit gastric activity, reduces hunger in CNS)
- Vasoactive Intestinal Peptide (stimulates secretion of intestinal glands, dilates regional capillaries, inhibits gastric acid)
- Enterocrinin (stimulates mucin production by submucosal glands)
What are Peyer’s patches?
Lymphoid tissue located in ileum that protects against bacteria from cecum
Where does B12 & bile salt absorption take place?
Ileum
What are two reflexes for defecation?
- Short reflex: Stretch receptors stimulated, neurons in myenteric plexus increase local peristalsis
- Long reflex: Parasympathetic motor neurons stimulated, increase peristaltic contractions, relax internal anal sphincter
What are the exocrine glands of pancreas?
Pancreatic acini. Simple cuboidal cells that secrete bicarbonate and phosphate buffer, stimulated to release by secretin from duodenum.
Also secrete alpha-amylase, lipase, nucleases, proteases, peptideases, which are stimulated to release by CCK & vagus nerve
What are endocrine cells of pancreas?
Alpha cells- glucagon
Beta cells- Insulin
What is anatomy of liver?
Left & right lobe divided by falciform ligament (anterior). Caudate lobe superior to quadrate lobe (posterior)
What are Kupffer cells?
Phagocytic cells in liver lining sinusoids that engulf pathogens, debris, iron, heavy metals
How are liver lobules organized?
Hexagonal shape, portal triad at each corner (branches of hepatic portal vein, hepatic artery proper, bile duct). Blood from portal vein & artery passes through lobule (hepatocytes absorb solutes & secrete proteins) on way to central vein, which becomes hepatic vein on way to inferior vena cava
What is pathway of bile through liver?
Hepatocytes secrete bile into bile canaliculi, to portal triad, to bile duct, to right & left bile duct, to common hepatic duct, to cystic duct, to gallbladder, to common bile duct, to duodenal ampulla
What is role of liver in metabolic regulation?
- Carbohydrate metabolism, stabilizes blood glucose level as determined by insulin/glucose
- Lipid reserves for maintaining triglyceride, fatty acid, cholesterol blood levels
- Removes excess amino acids from blood for synthesis of proteins, lipids or glucose
- Neutralizes ammonia to urea (ammonia from protein catabolism)
- Stores vitamins A,D,E,K,B12
- Converts iron to ferritin & storage
- Removes & breaks down certain drugs
How does liver regulate blood?
- Kupffer cells remove old RBCs from bloodstream
- Synthesis of plasma proteins
- Remove circulating hormones (E/NE, insulin, thyroid, androgens, corticosteroids, Cholecalciferol
- Removal of antibodies
- Removal/storage of toxins
- Synthesis & secretion of bile
What are functions of bile salts?
- Break lipid droplets apart in emulsification
2. Facilitate interactions between lipids and lipid-digesting enzymes from pancreas.
What is secretin?
Secreted when chime arrives in duodenum. Increases in secretion of bile by liver and buffers by pancreas. Reduces gastric motility & secretions
What is CCK?
Secreted when chime arrives in duodenum.
Relaxes hepatopancreatic sphincter/contraction of gallbladder.
Increases secretion of pancreatic enzymes.
Inhibits gastric activity, reduces hunger in CNS
What is GIP (gastric inhibitory peptide)?
Secreted when fats & carbs, especially glucose, enter small intestine. Inhibition of gastric activity, stimulation of insulin release
What is VIP (vasoactive intestinal peptide)?
Stimulates secretion of intestinal glands, dilates regional capillaries, inhibits gastric acid production.
What is Gastrin?
Secreted when exposed to large quantities of incompletely digested proteins. Increases stomach motility and secretions
What is Enterocrinin?
Released when chime enters duodenum. Stimulates mucin production by submucosal glands
What is process of swallowing?
- Tongue elevates to hard palate
- Soft palate elevates to block nasopharynx
- Epiglottis covers larynx
- Upper sphincter opens, closes after food enters.
- Lower esophageal sphincter opens when chyme enters, then closes to prevent HCl reflux.
