Summary thus far in the duodenum Stimulants bulk

Summary – thus far in the duodenum • Stimulants – bulk and chemicals and nutrients • Receptors –mechano- and chemo-receptors & enteroendocrine cells • Signals to the stomach regulate its function – (secretion and muscle contraction) & then make it stop • Signals to the pancreas, liver, and gallbladder to release chemicals to promote digestion • Structural changes - increases surface area to improve absorption. 1

Objectives • Compare peristalsis and segmentation. • Describe the structure and function of the interstitial cells of Cajal. • Describe and compare the mechanisms employed for the absorption of fats, carbohydrates and proteins. • Describe the design and function of the large intestine. • Explain the importance of osmosis and the formation of a desiccated mass. • Describe the short and long reflex loops involved in the elimination of solids.

Intestine: Absorption and Elimination • • • Why do you eat? Where does the food go? Can you turn potato chips into muscle? What is the hepatic portal system? How efficient is the GI system? What is left after absorption? 3

Readings – Digestive 5 • Mc. Kinley, O’Loughlin, and Bidle, Anatomy and Physiology An integrative Approach, p 10151061. • Large intestine 1045 -1057 • Review Membrane transport mechanisms 106 -115 4

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What happens to chyme (bread+) in the Small intestine • Pancreas releases digestive enzymes • Liver – makes bile for lipid absorption • Digestion FULL SPEED • Absorption of building blocks through enterocytes • Water (re)absorption • Undigested material remains and is eliminated Digestion and absorption are important here 6

Intestinal plicae and villi W E I EV R plica villi plica d o o g a s i h Is t the r o f c i t a schem ne? i t s e t n i l l sma 7

Fig 24. 4 Peristalsis, segmentation, and… • Peristalsis – process that moves chyme forward – in 1 direction • Segmentation – irregular contractions forcing chyme in both directions NO NET PROGRESS – Passes nutrients back and forth to optimize absorption • Interstitial cells of Cajal – motor neurons in the myenteric plexus – Intrinsic control – Slow, constant contractions 8

Segmental contractions - mixing contraction and mixing - No net forward movement 9

videos • Peristalsis in duodenum #1 -62 • Segmentation in jejunum #1 -70 10

Fig 24. 4 w e i v Re Peristalsis, segmentation, and… • Peristalsis – process that moves chyme forward – in 1 direction • Segmentation – irregular contractions forcing chyme in both directions NO NET PROGRESS – Passes nutrients back and forth to optimize absorption • Interstitial cells of Cajal – motor neurons in the myenteric plexus – Intrinsic control – Slow, constant contractions LUMEN 11

Smooth muscle design and function • Smooth muscle acts like a syncytium • = a gap junction • If one smooth muscle contracts, the signal is transferred to the next cell, and the next, etc. via gap junctions • Smooth muscle in the gut maintains a tone and if properly excited will contract. 12

Interstitial cells of Cajal They form networks in the muscular layers of the alimentary tract, with their location in the GIT being organ and species specific. ICC originate slow wave intestinal pacemaker activity and mediate input from the enteric nervous system. 13

Interstitial Cells of Cajal (ICC) are the Pacemakers of the Gut ICC are like the pacemaker cells in the heart (SA and AV nodes) – they establish a base rhythm for the smooth muscle cells in the gut called a slow wave.

Absorption of nutrients Lumen of intestine ts r nutrients t u e n i digestion Enterocytes (absorptive cells) To vena cava Lamina propria: CT with blood vessels or Lacteals To liver 15

Lumen of small intestine Cell of duodenum (enterocyte) Pancreatic secretions (inactive enzymes) trypsinogen Enteropeptidase activates trypsin • • Chymotrypsinogen • Chymotrypsin s e Procarboxypeptidase • Carboxypeptidase m y z s n n e e e g Pro(co)lipase • (Co)lipase v i o t c m A y z prophospholipase • Phospholipase nutrients 16

Hepatic Portal System • Portal system = a blood vessel connecting 2 capillary beds • Drains lg. and sm. intestine and stomach, etc. into the liver capillaries (sinusoids). Nutrients obtained from the intestines go directly to the liver for storage, synthesis or elimination or reuse. 17

w e i ev R Fig 3 -15 Membrane Functions GI lumen enterocyte 18

Fat digestion and absorption Large lipid droplets Bile salts from liver Triglycerides cholesterol Lumen of intestine emulsion Lipase & colipase micelles cholesterol Monoglycerides and free FA Enterocyte cytoplasm Chylomicrons (TG, chol & prot. ) Into Lacteals 19

1. Bile salts from liver coat droplets. 2. Pancreatic lipase and colipase breakdown fats and monoglycerides and fatty acids stored in micelles. 3. Monoglycerides and fatty acids move out of micelles and enter cells by diffusion. 4. Cholesterol is transported into cells by a membrane transporter. 5. Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons. 6. Chylomicrons are released into the lymphatic system. 20

Intestinal Villus: blood vessels and lacteals 21

Complex carbohydrates Fig 2 -12 • Only monosaccharides can pass through plasma membranes • Sugars used as fuel by cells to make ATP • Extra sugars stored as glycogen in muscle and liver 22

Fig 2 -11 Di and monosaccharides Disaccharidases in the glycocalyx of microvilli create monosaccharides Lactose intolerance occurs when a disaccharidase is missing and lactose (glucosegalactose) can not be divided into 2 sugars. 23

Glucose absorbed via secondary active transport (symporter) Lumen of intestine Na+ (High conc. ) Lactose intolerance Glucose or galactose Intestinal cell (enterocyte) ter r o p s n a r t co Na+ Facilitated transporter K+ Capillary to portal system 24

Glucose transport: Symporter & active transport 2 o Fig 3 -20 GI lumen (High conc. ) • Glucose and Na+ go thru the same channel • If Na+ concentration gets high inside the cell, the transport stops. • The Na+-K+ ATPase pumps Na+ out of the cell and keeps Na+ concentration low • Cotransport of Na+ and glucose continues when the ATPase 25 pump works

Glucose transport – by facilitated transport -from cytoplasm into lamina propria cytoplasm High conc. Lamina propria • Glucose moves from a high concentration to a low concentration • To maintain the low glucose concentration, glucose undergoes facilitated transport out of the basal membrane of the cell. 26

Protein absorption protein Lumen of intestine peptidases peptide peptidases Amino acids cotransport with Na+ di & tripeptides cotransport with H+ H+ Na+ Enterocyte cytoplasm with Cotransporters H+ Na+ To the liver 27

Peptide/amino acid transport H+ • H+/peptide and Na+/aa cotransporters (symporters) Na+ enterocyte H+ H+ Na+ K+ • H+/peptide and Na+/aa cotransporters (antitransporters) Na+ and H+ concentration inside the cell must be kept low. 28

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Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Transverse colon Ascending colon Descending colon Large Intestine Cecum Vermiform appendix Rectum Sigmoid colon Anal canal Transverse mesocolon Omental appendices Haustrum Teniae coli Descending abdominal aorta Ascending colon Descending colon Ileocecal valve Cecum Vermiform appendix Rectum Ileum Sigmoid mesocolon Anal canal (a) Large intestine, anterior view

Large Intestine • Sigmoidoscopy • Colonoscopy Transverse mesocolon Haustrum – diverticula – cancer Ileocecal valve Cecum Vermiform appendix Rectum Ileum Sigmoid mesocolon Anal canal 31

Large Intestine • Receives chyme from ileum • Smooth surface (NO VILLI) • Crypts of Leiberkuhn – Glands with Goblet cells – Absorptive cells • Forms feces – Desiccated, solid mass 32

Cells of Large Intestine • Smooth surface with no plicae and no villi • Glands present • Mostly goblet cells • Secrete mucous to lubricate surface and protect from shear forces 33

Water movement in the GI system • 9000 ml into the GI system • Final release = 150 ml • Remaining fluid is recaptured by reabsorption thru epithelial cells in the small and large intestine • Principles of Osmosis are important here 34

Water addition in the colon 2 Cl. Cl- Na+ Colon epithelial cell Lumen of • Cl- and Na+ (with gradient) into the cell. • Cl- (with gradient) into the lumen • Na+/K+ ATPase pump removes Na+ from cell Na+ COLON K+ Na+ H 2 O • Na+ follows Cl- to balance charge • H 2 O follows solutes Basic principle: water will follow the solutes. 35

Water movement in the colon • Principles of osmosis are important • If ions go into the lumen, water will follow and the stool is soft = diarrhea • If the ions go into the lamina propria (interstitial fluid), water will follow and the stool is dehydrated, hardened and compacted. – When nutrients are absorbed. Water follows the building blocks into the lamina propria. 36

Examine the rectal-anal junction This is most easily done with the slide. Examine the change in the epithelium and the differences in the tissues below the epithelium. junction 37

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Anal sphincters Fig. 26. 22 b Rectum Rectal valve Levator ani muscle Anal canal Rectal veins Internal anal sphincter Smooth muscle (involuntary) Anus External anal sphincter Skeletal muscle (voluntary) Anal columns (b) Anal canal Anal sinuses

Elimination of wastes • Short reflex feedback loop – Distention of rectum and stimulation of stretch receptors – Stimulation of myenteric plexus in sigmoid colon and rectum – Increased local peristalsis • Long reflex feedback loop – Stimulation of parasympathetic neurons in spinal cord – Increased peristalsis in large intestine • Relaxation of both anal sphincters allows defecation to occur 39

Fig 24. 25 Elimination of Wastes • Short reflex loop #1 -3 • Long reflex loop • Relaxation of internal and then external sphincter 40

6. Colonic phase - summary Stimuli Mechanical – rectal distension (possibly chemical via presence of free fatty acids in the lumen) Pathways Extrinsic and intrinsic neural pathways. Skeletal muscle controlled by CNS Effects Absorption of water and small ions Inhibition of secretion and motor activity in small intestine Propulsive motor patterns to enhance motility 41

Summary: Absorption and Waste Elimination • Small intestine – Digestion of lipids, carbohydrates, and proteins – Absorption of carbohydrates and proteins into the portal system – Absorption of lipids into lacteals (lymphatic system) – Mechanisms: Diffusion, facilitated diffusion, 10 and 20 active transport, co- & anti-porters • Large intestine – Structure and function: goblet cells – Importance of osmosis and water movement – Elimination of wastes 42

Why do you eat? 43

• Videos – Aboral • Baby • Rocket sled – Oral • #1 – 79 vomiting • Hail to colo-rectal surgeon 44