GI Map Checklist
Human Anatomy | Human Physiology
50 pts | Single Page
Rubric
Anatomy 10 pts
Histology + Micro 10 pts
Neural 5 pts
Function 5 pts
Visual + Effort 15 pts
Accuracy 5 pts
How to Build Your GI Map -- Read This First
▼ Collapse
🎨 This is a Visual, Not a List
Your GI Map is a single-page illustrated diagram -- not an outline, not a study guide written in bullet points, and not a paragraph essay. If your final product looks like a table or a numbered list, start over. The goal is a hand-drawn or digitally designed map that traces the digestive tract from mouth to anus with annotated structures, zoom-in boxes, and brief labels. Think of it as a page out of a medical atlas that you made yourself.
You are not being graded on artistic ability. Stick figures, rough sketches, and imperfect circles are completely fine. What matters is that you drew something -- a real visual representation -- not that it looks beautiful.
📷 What "Visual" Actually Means
Every region of the GI tract should be drawn as a shape on the page -- even a simple oval or tube. From that shape, you pull out and annotate. Here are the three visual tools you should be using:
🔍 Zoom-In Boxes
Draw a small box or circle that zooms in on a specific region. For example: draw the stomach shape, then draw a small magnified box off to the side showing the gastric gland with labeled parietal, chief, G, and D cells. Connect it to the main diagram with a line or bracket. This is how you show histology without cluttering your main diagram.
▣ Cross-Sectional Boxes
At least one region should include a small cross-section diagram showing the four histological layers -- mucosa, submucosa, muscularis externa, and serosa/adventitia -- as concentric rings or layered bands. The small intestine cross-section is a great choice: you can show villi pointing inward, label the layers, and mark where Meissner\'s and Auerbach\'s plexuses sit between the muscle layers.
→ Arrows and Brief Captions
Every label on your map should be a short phrase of 1-5 words, connected by an arrow to the structure it describes. Captions can be slightly longer (one sentence max) but should be written as annotations, not prose. Example: "Parietal cell -- HCl + intrinsic factor" is a good caption. A paragraph explaining the parietal cell is not.
✅ Use This Checklist the Right Way
The checklist in this tool is organized by region and category -- anatomy, histology, cells, secretions, neural, and function. Work through each region on your actual map first, then come back and check off what you included. Do not write out every checklist item as text on your map -- that defeats the purpose. Each item on this list should correspond to a label, a zoom-in box, a symbol, or an arrow on your drawing.
A good gut check: if you can fold your map and all the information is still readable as prose without the drawing, you have not made a map. You have made a document. Go back and draw.
💡 Practical Layout Tips
●Start by sketching the full GI tract as a flow from top to bottom or in a winding path -- mouth at the top, anus at the bottom. Leave margins and blank space around each organ for your annotations.
●Place accessory organs (liver, gallbladder, pancreas, salivary glands) off to the side with arrows connecting their ducts to the correct GI region.
●Use color to differentiate regions or categories -- for example, one color for histology labels, another for secretions, another for neural structures. A simple legend in the corner is enough.
●Reserve at least one corner or side margin for your cross-section or zoom-in histology boxes. These do not need to be large -- a 2-inch box is sufficient if it is clearly labeled.
●For neural integration, mark Meissner\'s and Auerbach\'s plexuses directly on your cross-section diagram between the correct muscle layers -- do not just list them as text. Show their location.
●For the physiology panel (A&P course): feedback loops should be drawn as small circles or loops with arrows marked "+" (stimulates) and "-" (inhibits). A loop that is one inch in diameter and clearly labeled is more valuable than a paragraph of text.
●Scan or photograph your finished map at high resolution before submitting. Make sure all labels are legible in the digital version.
Bottom line: The rubric rewards completeness and accuracy -- not beauty. A clean, clearly labeled sketch that includes all required structures, histological layers, cell types, and functional annotations will score well. A gorgeous digital illustration that is missing parietal cells or the myenteric plexus will not. Draw first. Label accurately. Keep text short.
Category:
Anatomy
Histology
Cells
Secretions
Neural
Function
Oral Cavity
Mouth - beginning of the GI tract
0%
Anatomy
- ✓Lips, cheeks, hard palate, soft palate, uvula
- ✓Tongue (intrinsic + extrinsic muscles) + lingual frenulum
- ✓Teeth: incisors, canines, premolars, molars
- ✓Palatine tonsils, lingual tonsils (Waldeyer\'s ring)
Histology
- ✓Stratified squamous epithelium (non-keratinized most surfaces; keratinized = gingiva, hard palate)
- ✓Taste buds on fungiform, circumvallate, and foliate papillae
Cells Secretions
- ✓Serous cells - watery enzyme-rich saliva; Mucous cells - mucin for lubrication
- ✓Salivary amylase (starch digestion), lingual lipase, lysozyme, IgA, bicarbonate
Function
- ✓Mastication + bolus formation; chemical digestion begins (starch); taste, speech, pH buffering
Salivary Glands
Accessory | Parotid, Submandibular, Sublingual
0%
Anatomy
- ✓Parotid - Stensen\'s duct (upper 2nd molar); CN IX. Submandibular - Wharton\'s duct; CN VII. Sublingual - ducts of Rivinus; CN VII
Histology
- ✓Parotid = purely serous; Submandibular = mixed (mostly serous); Sublingual = mostly mucous
- ✓Striated ducts modify ion content; myoepithelial cells surround acini (expel saliva)
Cells
- ✓Serous acinar cells - amylase, lysozyme, IgA; Mucous acinar cells - mucin glycoproteins
Pharynx
Nasopharynx, Oropharynx, Laryngopharynx
0%
Anatomy
- ✓Three regions: nasopharynx, oropharynx, laryngopharynx
- ✓Pharyngeal constrictors (superior, middle, inferior) coordinate swallowing
Histology
- ✓Nasopharynx = pseudostratified ciliated columnar; Oro/laryngopharynx = stratified squamous
Function
- ✓Deglutition: voluntary oral phase, involuntary pharyngeal + esophageal phases; epiglottis deflects to protect airway
Esophagus
UES and LES | Cervical, Thoracic, Abdominal
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Anatomy
- ✓UES (skeletal, prevents air entry); LES/cardiac sphincter (smooth, prevents GERD)
- ✓Three anatomical narrowings: cricopharyngeal, aortic arch, diaphragmatic hiatus
Histology
- ✓Stratified squamous non-keratinized epithelium (mucosa)
- ✓Muscularis: upper 1/3 skeletal, middle mixed, lower 1/3 smooth; adventitia (not serosa) in thorax
- ✓Esophageal mucous glands in submucosa for lubrication
Neural
- ✓Meissner\'s plexus (submucosal) + Auerbach\'s plexus (myenteric) present throughout; vagus CN X controls peristalsis
Function
- ✓Peristalsis transports bolus to stomach; no digestion or absorption
Stomach
Cardia, Fundus, Body, Pylorus
0%
Anatomy
- ✓Four regions: cardia, fundus, body (corpus), pylorus; greater and lesser curvature
- ✓Pyloric sphincter - controls chyme release into duodenum; angular incisure at body/pylorus junction
Histology
- ✓Rugae - longitudinal folds of mucosa/submucosa; expand to accommodate food
- ✓Simple columnar epithelium; gastric pits leading to gastric glands
- ✓Muscularis externa: THREE layers - oblique (inner), circular (middle), longitudinal (outer)Unique to stomach - enables churning and retropulsion
- ✓Serosa (visceral peritoneum) covers entire stomach
Cells Secretions
- ✓Parietal cells (oxyntic) - HCl + intrinsic factor | Fundus/body glandsHCl activates pepsinogen; intrinsic factor required for B12 absorption (ileum)
- ✓Chief cells (zymogenic) - pepsinogen + gastric lipase | Fundus/body glands
- ✓G cells - gastrin | Pyloric antrum; D cells - somatostatin; ECL cells - histamine (stimulates HCl)
- ✓Mucous neck cells + surface mucous cells - protective mucus layer against HCl
Neural
- ✓Meissner\'s plexus - glandular secretion; Auerbach\'s plexus - peristalsis and churning
Function
- ✓Mechanical churning + chemical protein digestion; bolus converted to chyme
- ✓Limited absorption: alcohol, aspirin, lipid-soluble drugs; cephalic/gastric/intestinal secretion phases
Small Intestine
Duodenum, Jejunum, Ileum | ~6-7 meters
0%
Anatomy
- ✓Duodenum (~25 cm): C-shaped, retroperitoneal; ampulla of Vater + sphincter of Oddi (bile + pancreatic juice entry)
- ✓Jejunum (~2.5 m): prominent plicae circulares, thick walls, many villi
- ✓Ileum (~3.5 m): Peyer\'s patches; ileocecal valve connects to large intestine
Histology
- ✓Plicae circulares (valves of Kerckring): permanent circular folds; +3x surface area
- ✓Villi: finger-like projections with lacteal (lymphatic) core; +10x surface area
- ✓Microvilli (brush border): apical enterocyte surface; +20x SA; brush border enzymes embedded
- ✓Crypts of Lieberkuhn: intestinal glands; stem cells, Paneth cells at base
- ✓Brunner\'s glands (duodenum only): submucosal; alkaline mucus neutralizes chyme
- ✓Peyer\'s patches (ileum): submucosal lymphoid aggregates - immune surveillance
Cells Secretions
- ✓Enterocytes: brush border enzymes (maltase, sucrase, lactase, aminopeptidases); nutrient absorption
- ✓Goblet cells (mucus); Paneth cells (defensins, lysozyme - antimicrobial, crypt base)
- ✓S cells - secretin (acid chyme trigger); I cells - CCK (fat/protein trigger); K cells - GIP (glucose/fat trigger)
- ✓M cells (Peyer\'s patches): transcytose antigens to underlying lymphocytes
Neural
- ✓Meissner\'s plexus: secretion + blood flow; Auerbach\'s: peristalsis + segmentation
Function
- ✓Duodenum: neutralizes chyme; bile + enzymes arrive; major digestion begins
- ✓Jejunum: primary absorption of carbs, proteins, fats, most vitamins and minerals
- ✓Ileum: B12 (intrinsic factor complex), bile salts (enterohepatic circulation), fat-soluble vitamins A/D/E/K
Large Intestine
Cecum, Colon (4 parts), Rectum, Anal Canal
0%
Anatomy
- ✓Cecum + appendix (vermiform - lymphoid tissue)
- ✓Colon: ascending, transverse (hepatic/splenic flexures), descending, sigmoid
- ✓Rectum + anal canal; internal sphincter (smooth, involuntary) + external (skeletal, voluntary)
- ✓Haustra (sacculations), teniae coli (3 longitudinal muscle bands), epiploic appendages
Histology
- ✓NO villi; flat mucosal surface with deep crypts of Lieberkuhn; abundant goblet cells
- ✓Anal canal: stratified squamous below pectinate (dentate) line; columnar above
Cells Secretions
- ✓Goblet cells: mucus for lubrication; Colonocytes: absorb water and electrolytes (Na+, Cl-, K+)
- ✓Gut microbiome: ferments fiber; produces vitamins K + B12; short-chain fatty acids
Neural
- ✓Auerbach\'s plexus: mass movements; defecation reflex: parasympathetic (pelvic splanchnic); voluntary ext. sphincter
Function
- ✓Water and electrolyte absorption; fecal compaction and storage; microbial fermentation; vitamin synthesis
Liver
Accessory | Largest gland in the body
0%
Anatomy
- ✓Right, left, caudate, quadrate lobes; falciform ligament; ligamentum teres
- ✓Porta hepatis: portal vein + hepatic artery + bile ducts; common hepatic duct + cystic duct = CBD --> ampulla of Vater
- ✓Dual blood supply: portal vein (75%, nutrient-rich) + hepatic artery (25%, oxygenated)
Histology
- ✓Classic hepatic lobule: hexagonal; portal triads at corners, central vein in center
- ✓Sinusoids (fenestrated endothelium); Space of Disse between sinusoids and hepatocytes
Cells Secretions
- ✓Hepatocytes: bile, albumin, clotting factors, glucose, urea, lipoproteins
- ✓Kupffer cells: macrophages in sinusoids (phagocytose bacteria, worn RBCs)
- ✓Stellate/Ito cells (Space of Disse): vitamin A storage; become fibroblasts in cirrhosis
- ✓Bile composition: bile salts (emulsify fats), bilirubin, cholesterol, phospholipids, bicarbonate
Function
- ✓Bile production; carbohydrate/lipid/protein metabolism; detoxification; storage (glycogen, vitamins, iron); synthesis of plasma proteins and clotting factors
Gallbladder
Accessory | Bile storage and concentration
0%
Anatomy
- ✓Fundus, body, neck; cystic duct (valves of Heister) joins common hepatic duct; lies in gallbladder fossa
Histology
- ✓Simple columnar epithelium with microvilli (absorbs water to concentrate bile up to 10x)
- ✓No submucosa or muscularis mucosae; Rokitansky-Aschoff sinuses (mucosal outpouchings)
Function
- ✓Stores and concentrates bile; releases into CBD when CCK is secreted (fat in duodenum)
Pancreas
Accessory | Exocrine + Endocrine
0%
Anatomy
- ✓Head (duodenal C-loop), neck, body, tail (spleen); mostly retroperitoneal
- ✓Duct of Wirsung (main) + Santorini (accessory); join CBD at ampulla of Vater
Histology
- ✓Exocrine (~95%): serous acini of acinar cells; centroacinar cells lining duct lumen
- ✓Endocrine (~5%): islets of Langerhans scattered among acini
Cells Secretions
- ✓Acinar cells: amylase, lipase, trypsinogen, chymotrypsinogen, elastase, phospholipase A2 | Stimulated by CCK
- ✓Centroacinar cells: bicarbonate-rich fluid | Stimulated by secretin
- ✓Alpha cells - glucagon; Beta cells - insulin (most numerous); Delta cells - somatostatin; PP cells - pancreatic polypeptide
Function
- ✓Exocrine: neutralizes acid chyme (bicarbonate); digests all macronutrients (enzymes)
- ✓Endocrine: insulin/glucagon regulate blood glucose; somatostatin modulates both
Neural Integration
Enteric Nervous System - the "Second Brain"
0%
Neural
- ✓Meissner\'s plexus (submucosal): between mucosa and inner circular muscleControls: glandular secretion, mucosal blood flow, sensory detection of luminal contents
- ✓Auerbach\'s plexus (myenteric): between inner circular and outer longitudinal muscleControls: peristalsis, segmentation, GI smooth muscle tone (motility)
- ✓ENS: ~500 million neurons; functions independently of CNS
- ✓Parasympathetic (vagus CN X / pelvic splanchnic): stimulates motility and secretion
- ✓Sympathetic (celiac, sup/inf mesenteric ganglia): inhibits motility; vasoconstriction
- ✓Peristalsis reflex: stretch detected, circular muscle contracts behind bolus, relaxes ahead (law of the intestine)
Drawing Reminders: Single page, front side only. Use arrows and brief captions - avoid paragraphs. Color-code your regions. Label the 4 histological layers (mucosa, submucosa, muscularis externa, serosa/adventitia) on at least one cross-section. Show both plexus locations between the muscle layers. Optional: add mnemonics or brief clinical correlations.
Rubric | 50 pts Total
Anatomical Accuracy
10 pts
Histology + Microanatomy
10 pts
Neural Components
5 pts
Functional Annotations
5 pts
Visual Organization
10 pts
Accuracy + Effort
10 pts
How to use this panel: Each card is a hormone, enzyme cascade, or regulatory loop. Check it off as you add it to your map. For each one, your map should show the ON stimulus, the EFFECT, and the OFF signal. A tiny labeled loop is enough -- no paragraphs needed.
Chips:
ON triggers release
EFFECT what it does
OFF what stops it
LINK draw this
Gastric Secretion Phases
Cephalic, Gastric, Intestinal
0%
- ✓Cephalic PhaseONSight, smell, taste, or thought of food; mediated entirely by vagus nerve (CN X) before food arrivesEFFECTStimulates gastric glands (HCl, pepsinogen, mucus); ACh from vagus also stimulates G cells to release gastrinOFFRemoval of sensory stimulus; rising acid pH; somatostatin from D cellsLINKWhy hunger and anticipation cause "stomach growling" -- entirely neural, no food required
- ✓Gastric PhaseONStomach distension (stretch receptors); peptides and amino acids; rising pH as food buffers acidEFFECTLocal myenteric reflexes + vagovagal reflexes stimulate G cells (gastrin) and ECL cells (histamine) -- massive HCl and pepsinogen amplificationOFFpH falls below 3: somatostatin (D cells) inhibits G cells; secretin from duodenum inhibits gastrin once chyme exitsLINKGastrin also increases LES tone and stimulates motility -- one hormone, multiple coordinated effects
- ✓Intestinal PhaseONAcid chyme entering duodenum; fats and proteins; osmolarity and distension of duodenal wallEFFECTReleases secretin (neutralize acid) and CCK (digest fats/proteins); enterogastric reflex slows gastric emptyingOFFRising duodenal pH removes secretin stimulus; fat digestion removes CCK stimulus; gastric emptying slows automaticallyLINKIntestinal phase is INHIBITORY to the stomach -- protects the duodenum from acid chyme overload
Key GI Hormones
Gastrin, Secretin, CCK, GIP, Motilin, Somatostatin
0%
- ✓Gastrin -- G cells, pyloric antrumONPeptides/amino acids in stomach; vagal ACh (cephalic phase); stomach distension; rising pH (food buffers acid)EFFECTStimulates parietal cells (HCl); chief cells (pepsinogen); increases LES tone; promotes motility; stimulates ECL cells (histamine)OFFpH < 3 directly inhibits G cells; somatostatin (D cells); secretin from duodenum
- ✓Secretin -- S cells, duodenumONAcid chyme in duodenum (pH < 4.5); fatty acids in duodenumEFFECTPancreatic centroacinar cells secrete bicarbonate (neutralizes acid); inhibits gastric acid; inhibits gastrin; stimulates bile flow from liverOFFRising duodenal pH removes the acid stimulus -- self-resolving negative feedbackLINKDraw the acid-bicarbonate seesaw: parietal cell HCl --> duodenum pH drops --> secretin --> pancreatic HCO3- --> pH rises --> secretin stops
- ✓CCK (Cholecystokinin) -- I cells, duodenum/jejunumONFats (fatty acids, monoglycerides) and proteins (peptides, amino acids) in duodenumEFFECTGallbladder contraction (bile release); pancreatic acinar enzymes; relaxes sphincter of Oddi; inhibits gastric emptying; satiety signal to hypothalamusOFFDigestion of fats/proteins removes duodenal stimulus; trypsin cleaves CCK-releasing factorLINKCCK coordinates THREE organs simultaneously: stomach (slow), gallbladder (contract), pancreas (release enzymes). Draw all three arrows from one I cell.
- ✓GIP (Glucose-dependent Insulinotropic Peptide) -- K cells, duodenum/jejunumONGlucose and fats in the duodenum (after a mixed meal)EFFECTInhibits gastric acid and motility; stimulates insulin from pancreatic beta cells (incretin effect)OFFFalling blood glucose; glucose absorption removes duodenal stimulusLINKIncretin effect: oral glucose causes more insulin release than IV glucose because the gut signals the pancreas in advance
- ✓Motilin -- M cells, duodenum/jejunumONFasting state; released cyclically every 90-120 minutes between mealsEFFECTInitiates migrating motor complex (MMC): powerful peristaltic waves sweep residue from stomach through SI -- "intestinal housekeeper"OFFFood intake; secretin and CCK released after eating suppress the MMCLINKBorborygmi (stomach growling when hungry) = motilin-driven MMC. Erythromycin is a motilin agonist used for gastroparesis.
- ✓Somatostatin -- D cells (stomach, pancreas, intestine)ONLow gastric pH; high blood glucose; fat/protein in gut -- generally "too much" of any GI stimulusEFFECTInhibits virtually everything: gastrin, secretin, CCK, GIP, insulin, glucagon, HCl, pancreatic enzymes, GI motility. The master brake of the GI system.OFFRemoval of stimulus; vagal stimulation can suppress D cell activityLINKSomatostatin acts PARACRINE (on neighboring cells, not through blood). D cells are positioned beside G cells, parietal cells, and beta cells to provide local inhibition. Draw short local arrows.
Enzyme Activation Cascades
Proenzymes, activation sequences, brush border digestion
0%
- ✓Pepsinogen -- Pepsin cascade (stomach)ONChief cells release pepsinogen (inactive); HCl drops luminal pH below 2EFFECTLow pH cleaves pepsinogen --> pepsin; pepsin then autocatalytically activates more pepsinogen; cleaves peptide bonds in proteinsOFFpH rises above 5: pepsin irreversibly inactivated; bicarbonate in duodenum immediately deactivates pepsin when chyme arrivesLINKDraw the autocatalytic loop with a note: "self-amplifying but pH-dependent." Why proenzymes? Premature activation would digest the cell that made them.
- ✓Trypsinogen -- Trypsin cascade (duodenum)ONPancreas secretes trypsinogen; enteropeptidase (enterokinase) on duodenal brush border cleaves it to trypsinEFFECTTrypsin activates itself (autocatalysis) AND activates chymotrypsinogen, proelastase, procarboxypeptidases, phospholipase A2. Trypsin = "master activator" of all pancreatic proenzymes.OFFPancreatic secretory trypsin inhibitor (PSTI) prevents premature activation inside the gland; no enteropeptidase outside the duodenumLINKDraw the cascade tree: enterokinase --> trypsin --> everything else. In pancreatitis: premature intrapancreatic activation --> autodigestion.
- ✓Brush Border Enzyme Digestion (small intestine)ONSubstrate contacts enterocyte apical membrane (physical contact required -- these enzymes are NOT secreted into the lumen)EFFECTMaltase: maltose --> 2 glucose. Sucrase: sucrose --> glucose + fructose. Lactase: lactose --> glucose + galactose. Aminopeptidases: complete protein digestion at cell surface.OFFNo substrate = no activity; enzyme expression can be reduced (lactase decline in adults = lactose intolerance)LINKFinal digestion happens AT the cell surface, not in the lumen. Draw a tiny enterocyte with enzymes sticking out of the brush border, products entering the cell.
Bile and Fat Digestion Loop
Emulsification, micelles, enterohepatic circulation
0%
- ✓Bile Release and EmulsificationONFat in duodenum --> I cells release CCK; vagal stimulation also promotes gallbladder contractionEFFECTGallbladder contracts + sphincter of Oddi relaxes; bile salts emulsify fat globules into tiny droplets; dramatically increases surface area for pancreatic lipaseOFFFat digestion and absorption removes CCK stimulus; gallbladder relaxes
- ✓Micelle Formation and Fat AbsorptionONPancreatic lipase cleaves triglycerides --> monoglycerides + fatty acids; bile salts aggregate around productsEFFECTMicelles ferry lipids to enterocyte brush border; lipids diffuse across membrane; reassembled into triglycerides inside cell; packaged into chylomicrons; secreted into lacteals (lymph, not portal blood)OFFShort/medium-chain FAs bypass lacteals and go directly to portal blood
- ✓Enterohepatic Circulation of Bile SaltsONBile salts reach terminal ileum after participating in fat digestionEFFECT~95% of bile salts actively reabsorbed in terminal ileum; enter portal blood; returned to liver; re-secreted into bile -- recycled 2-3x per mealOFF~5% lost in feces; liver synthesizes new bile salts from cholesterol to replace lossesLINKDraw the full loop: liver --> bile duct --> duodenum --> jejunum (micelles) --> ileum (reabsorbed) --> portal vein --> liver. Ileal disease (Crohn\'s) breaks this loop --> fat malabsorption.
Neural Regulation of GI Function
ENS reflexes, ANS control, motility patterns
0%
- ✓Peristalsis Reflex -- Law of the IntestineONDistension of the gut wall activates intrinsic primary afferent neurons (IPANs)EFFECTAscending excitation (ACh): circular muscle contracts BEHIND the bolus. Descending inhibition (VIP, NO): circular muscle relaxes AHEAD of bolus. Net = propulsion.LINKDraw two arrows at any gut segment: "+" ACh behind, "-" VIP/NO ahead. Label: ascending excitation / descending inhibition.
- ✓Segmentation vs. PeristalsisONSegmentation: pacemaker cells in circular muscle; dominant in SI during active digestion. Peristalsis: dominant in esophagus always; SI between meals (MMC).EFFECTSegmentation MIXES chyme with juices and maximizes contact time with absorptive surface (no net movement). Peristalsis PROPELS bolus forward.LINKParasympathetic favors both; Sympathetic inhibits both. Draw the ANS balance beam: "rest and digest" vs. "fight or flight."
- ✓Gastroileal and Gastrocolic ReflexesONFood entering the stomach (distension and chemical stimulation)EFFECTGastroileal reflex: relaxes ileocecal valve (chyme from ileum --> cecum). Gastrocolic reflex: mass movements in large intestine -- why eating causes urge to defecate.LINKDraw a long reflex arc: stomach --> ileocecal valve and stomach --> colon. Mediated by vagus + ENS reflexes + gastrin/serotonin.
Blood Glucose -- GI-Pancreas Axis
Insulin, glucagon, incretin effect, seesaw feedback
0%
- ✓Insulin Secretion -- Beta cellsONRising blood glucose (ATP closes K+ channel, depolarization, Ca2+ entry); GIP and GLP-1 incretins from gut; vagal ACh; amino acidsEFFECTGLUT4 translocated to surface in muscle and adipose (glucose uptake); glycogen synthesis; fat storage; protein synthesis; inhibits gluconeogenesis and lipolysisOFFFalling blood glucose; somatostatin (D cells); sympathetic stimulation suppresses insulinLINKIncretin loop: food in duodenum --> GIP/GLP-1 --> beta cells release insulin BEFORE glucose even peaks in blood. The gut anticipates the glucose load.
- ✓Glucagon Secretion -- Alpha cellsONFalling blood glucose; amino acids (protein-only meal); sympathetic stimulation; cortisolEFFECTGlycogenolysis: liver glycogen --> glucose. Gluconeogenesis: liver makes new glucose. Lipolysis: fat breakdown. Net: raises blood glucose.OFFRising blood glucose; insulin (beta cells inhibit alpha cells paracrine); somatostatinLINKDraw the insulin-glucagon seesaw. High glucose --> insulin up, glucagon down. Low glucose --> glucagon up, insulin down. Somatostatin sits at the fulcrum inhibiting both.
Feedback Loop Drawing Guide
How to draw ON/OFF loops on your GI map
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- ✓Acid-Bicarbonate Feedback LoopMAP ITParietal cell --> HCl --> duodenum pH drops --> S cells release secretin --> pancreas secretes HCO3- --> pH rises --> secretin stops. Draw as a closed circle with + and - arrows.
- ✓Gastrin Negative Feedback LoopMAP ITG cell --(gastrin)--> parietal cell --(HCl, pH drops)--> D cell --(somatostatin)--> inhibits G cell. A tiny 3-cell loop with +/- arrows is all you need.
- ✓CCK Three-Target Integration MapMAP ITI cell --> CCK --> [1] gallbladder contracts + [2] pancreatic enzymes released + [3] gastric emptying slows. One source, three arrows, three targets.
- ✓Enterohepatic Circulation CircuitMAP ITLiver makes bile salts --> gallbladder stores --> duodenum (bile released) --> jejunum (micelles, fat absorption) --> ileum (95% reabsorbed) --> portal vein --> liver. Draw as a full loop with arrows.
- ✓Insulin-Glucagon SeesawMAP ITDraw a balance beam. Left: HIGH glucose --> insulin up, glucagon down. Right: LOW glucose --> glucagon up, insulin down. Somatostatin sits above the fulcrum, inhibiting both simultaneously.
Physiology Map Tips: Tiny labeled arrows are enough -- no paragraphs needed. A small circle with "+" and "-" communicates a feedback loop perfectly. Use a different ink color for physiology annotations so they stand out from anatomy labels. These loops are what your A&P course will expand on -- this panel gives you the scaffolding now.
