GI Physiology (topic 15)

GI Physiology (topic 15)

1. Neural and Hormonal Control

   • Nervous system
     • Extrinsic innervation
       • Sympathetic inn. : release NE , INHIBIT motor and secretory activities (ให้ blood ไปเลี้ยงส่วนอื่นเพื่อเอาตัวรอดก่อน)
       • Parasym inn. : Release Ach, vagus nerve (for most part of GI), pelvic nerve (for transverse colon, rectum, and anus), STIMULATE motor and secretory activities
     • Intrinsic innervation
       • Meissner's plexus (Submucosal plexus) : + submucosal layer, ANS control, Ach will simulate secretion (pepsinogen/gastrin/ mucus/ electrolyte)
       • Auerbach's plexus (Myenteric plexus) : lie between inner circular and outer longitudinal muscles, control GI motility
     • Minibrain (controlled by plexus)
   • Hormones
     • Gastrin
       • Location : Antrum (stm)*, Duodenum (smi)
       • Origin : secreted from G cells
       • Function : STIMULATE gastric acid (HCl) secretion , mucosal growth (mucosa)
     • Secretin
       • Location : Duodenum
       • Origin : secreted from S cells
       • Function: STIMULATE pancreatic HCO3- secretion, bile HCO3- secretion, pancreatic growth ; INHIBIT gastric acid secretion (HCl)
     • Cholecystokinin; CCK (Lipid killer)
       • Origin : Secreted from I cells
       • Location : Duodenum*, Jejunum*, Ileum
       • Functions: STIMULATE pancreatic enz and HCO3- secretion "pancreocymin", gall bladder contraction, pancreatic growth ; INHIBIT gastric emptying (ทำให้การ contract ของกล้ามเนื้อในกระเพาะช้าลง เพื่อให้มีเวลาม่ย่อยไขมันในตำแหน่งลำไส้เล็กได้มากขึ้น)
     • Gastric inhibitory peptide (GIP) or Enterogastrone or Glucose-dependent insulinotropic peptide
       • Location : Duodenum, Jejunum
       • Functions : STIMULATE insulin release (break glucose เพื่อไปส่งตับให้เปลี่ยนเป็น glucagon เพื่อป้องกันภาวะ Hyperglycemia) ; INHIBIT gastric acid secretion (HCl)
     • Motilin
       • Location : Duodenum and Jejunum
       • Property : polypeptide of 22 amino acid ; release every 90 mins
       • Function : Stimulate gastric and intestinal motility

2. Secretion

   • Salivary secretion
     • a solution containing electrolytes, produced by three main pairs of branched glands (95% of tt salivary volume) <1. parotid -cheeck 2. Submandibular <underchin> 3. Sublingual <under tongue> and 5% is from many simple glands such as glands of cheek buccal
     • Salivary secretion : about 1 litre produced/day (resting flow rate 0.5 ml/min and maximal flow rate 7 ml/min)
       • Rate varies : 1. Parotid 20% - serous (water, elect., amylase) 2. Submandibular 70% - mix (water,elect.,amylase, mucus) 3. Sublingual 5% - mucous (mucus, lingual lipase) 4. simple(buccal) 5% - mucous
     • Along salivary duct : Na+, Cl- reabsorb // K+ and HCO3- secrete
       • 1. Acinar cells : produce primary secretion that is isotonic with plasma, some salivary proteins secreted
       • 2. Duct cells : REABSORB Na+ and Cl- and SECRETE K+ and HCO3- // impermeable to water so lumen is hypotonic
     • Unconditional : nerve in mouth is stimulated, then send pai ANS, leaw reflex ma pen salivary secretion
     • Conditional : involved LEARNING. wera dai smell of food or picture food ti koey gin salivary ja secrete ork ma (Ivan Pavlov)
   • Gastric secretion
     • Oxyntic gland mucosa : ไหลเข้ากระแสเลือดแล้ววนมาใหม่ 80%
       • 1. Mucus neck cell - mucus 2. Chief cell - pepsinogen 3. Parietal or oxyntic cell - HCl, intrinsic factor 4. Surface epithelial cells - mucus
     • Pyloric gland mucosa 20%
       • secretion if mucus and pepsinogen. Endocrine secretes Gastrin
     • Stimulation of HCl secretion : 1. Parasym (Ach) 2. Gastrin by G cell 3. Histamine by ECL cell /// 1 and 2 also secrete Histamine
     • Pepsinogen secretion
   • Pancreatic secretion
     • secrete from acinar cell - low volume
     • Proenzyme : typsinogen, chymotrypsinogen, procarboxypeptidase ;;; enzyme : amylase and lipase
   • Small intestinal secretion

3. Digestion and Absorption

4. GI motility

   • Chewing (Neural Control)
     • - To reduce size of food to particles for swallowing - To mix food with salivary enz, and lubricates
   • Swallowing or Deglutition
     • - Initiate voluntary but become involuntary with 1 sec. - divided into 3 phrases 1) Oral Phase 2) Pharyngeal phase 3) Esophageal phase
   • Gastric Motility
     • Stomach : มี 4 ส่วน คือ cardiac, fundus, body, antrum, pyrorus; มี 3 ชั้น คือ outer longitudinal layer, middle circular, and inner oblique layer; innervate by both intrinsic (Myeteric plexus or Auebach's) and extrinsic nerves
     • Gastric Emptying
       • 1. Peritaltic contraction (from fundus to pyrolus) 2. contraction become more vigorrous after reaching thick antrum 3. strong antrum contraction move chyme forward 4. small portion of chyme is push through the spincter
     • Gastric mixing
       • 5. when small portion of chyme is out, spincter then close and no further emptying takes place 6. chyme is propelled and tossed back to the antrum for another mixing
   • Small intestinal motility
     • Relax length: 20 feet ; composed of three parts: Duodenum, Jejunum, and Ileum
     • Functions: absorb water, electrolyte, nutrients, drugs, and etc. ; rate of small intestinal (highest at duo ~12/min and lowest at ileum ~-8/min) อาหารบีบตัวที่ parietal แรงกว่า distal ดังนั้นอาหารเลยเคลื่อนที่ไปตามแทรกได้
     • Regulation of smi motility
       • Enteric nevous System (myenteric plexus) มีบางเซลล์ที่ generate electrical signal ทำให้เซลล์รอบข้างถูกกระตุ้น แล้วบีบตัวเป็นทอดๆ = Intrinsic smooth muscle excitability 2. Extrinsic nervous system (sym&parasym) 3. Hormones : STIMULATORS - gastrin, CCK, motilin, insulin ; INHIBITORS - secretin and glucagon
     • Types of Contraction
       • 1. Peristalsis : myogenic movement, mixing and circulate intestinal content, frequency at duodenum is greater than the distal end
       • 2. Segmental : to propel content to distal end, neurogenic movement (parasym)
   • Large intestine motility
     • Parts of large intestine : cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal
     • Types of Contraction : 1. Tone wave (myogenic), Haustral or haustrations = contraction of circular muscle forward and backward, segmented but much slower, contact with mucosa, promote absorption of water and electrolyte บีบให้อาหารสำผัสกับ epithelial to reabsorb 2. Mass peristalsis (neurogenic) = strong wave from upper end of ascending colon, resulted in emptying transverse colon, sweep ขี้into descending and rectum
     • Defaecation
       • Reflex pen tua tum hai faecae in rectum dook defaecation. 2 reflexes kue 1. reflex contraction of rectum 2. Relax anal sphincter. .
         • types of reflex : 1. Intrinsic reflex 2. parasympathetic reflex
           • Intrinsic Reflex : ผนัง rectum ขยาย (distend), initiate afferent signals ให้ myenteric plexus ถูกกระตุ้น, initiate peristalsis in colon and rectum, force faeces toward anus, internal anal sphincter relax (แต่ยังขี้ไม่ได้)
           • 2. Parasym reflex : nerve ending at rectum are stimulated, signal transmitted to spinal cord, reflex back in colon rectum and anus by parasym (pelvic nerve), intense peristalsis wave and relax the anal sphincter, then promote defaecation.
           • สุดท้ายจะมีสัญญานส่งขึ้นสมองเพื่อควบคุมให้ skeletal motor nerve ให้ relax external anal sphincter then ก็ขี้ได้แล้ว

5. The Overview

   • GI Anatomy
     • Alimentary canal
       • Oral or buccal cavity - Pharynx - Esophagus - Stomach - Small Intestine - Large Intestine
     • Accessory organs
       • Teeth - Tongue - Salivary gland - Liver - Pancreas - Gall bladder
   • Layer of GI tract wall
     • 1. Mucosa : epithelium, lamina propria and muscularis mucosae
     • 3. Muscularis : inner (thicker) circular and outer (thinner) longitudinal muscle, nerve plexus (Auerbach's plexus or Myenteric plexus --> GI motility movement)
     • 2. Submucosa : connective tissue, collagen, elastin fibrils, nerve plexus (Meissner's plexus or submucosal plexus --> stimulate gland secretion)
     • 4. Serosa or adventitia : connective tissue and squamous epithelium
   • Functions
     • 1. MOTILITY : To mix, to circulate, and to produce ขี้
     • 2. SECRETION : Exocrine secretion and endocrine secretion
     • 3. DIGESTION : small molecule and large molecule
     • 4. ABSORPTION : Passive tx, facilitated diffusion, and active tx (for valuable substance)

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