Digestive System Lecture Notes PDF

Physiology Lecture note On Digestive system for Medical and Dental Students 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 1  Objectives Discussing about the digestive organs Main and accesso...

Physiology Lecture note On Digestive system for Medical and Dental Students 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 1  Objectives Discussing about the digestive organs Main and accessory Describing the functions of the digestive system Discussing about Food process regulation Discussing about Neuronal ✓ Digestion and absorption Intrinsic ✓ Gastrointestinal system disorders Extrinsic Hormonal Blood flow and regulation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 2  Digestive system System of main and accessory structures Main stractures (alimentary canals) Mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus Accessory structures Glands (liver, pancreas, parotid, sublingual and submandibular) Ducts Teeth, tongue Gallbladder 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 3 Digestive system … Fig 1: Structures in the Digestive System 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 4  Tissue layers of the GIT 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 5  Layers of the gastrointestinal tract ▪ Mucosa (inner layer face to the lumen) – epithelium, connective tissue ▪ Lieberkühn glands: secrete digestive enzymes, produce cells that replace surface- membrane cells shed from the tips of villi ▪ Submucosa :loose connective tissue, blood & lymphatic vessels, glands (Brunner’s glands; duodenum , alkaline fluid ), nerve plexuses ▪ Muscularis: 2 coats of smooth muscle = Fig 2: Layers of the small intestine circular(inner) & longitudinal (outer) fibers ▪ Serosa (outer):visceral peritoneum, serous cells protect underlying tissues & secrete serous fluid to 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 6 reduce friction within the abdominal cavity  Location of the gastrointestinal structures In the peritoneum It lines the abdominal cavity and organs Visceral peritoneum Covers the viscera including stomach, bowels, liver and kidneys Parietal peritoneum Covers abdominal cavity Ascites ✓ Fluid builds up between the two layers ✓ Liver disease (Hepatitis B/C virus, tumor, portal HTN, Fig 3: Layers of peritoneum and ascites cirrhosis (accumulation of fibrous tissue around hepatocytes) 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 7  Portal hypertension and ascites Hepatic portal vein: Receives the deoxygenated venous blood flow from the splanchnic bed (intestines, stomach, pancreas, and spleen) This HTN occurs when there is cirrhosis Carries nutrient-rich blood Fig 4: Hepatic portal vein and portal HTN 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 8  Consequences of cirrhosis Fig 5: Consequences of Cirrhosis 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 9  Functions of digestive system Digestion and absorption Secretion Energy production Maintain homeostasis Supplies nutrients and remove wastes Balances body fluid Defends the body HCl, lysozymes, macrophages, lymphocytes Elimination 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 10  Immune function of the GIT Intestine has lymphoid organ Gut-associated lymphoid tissue/GALT. Peyer’s patch In the mucosa and extending into the submucosa of the small intestine (ileum) Contains B-lymphocytes The major source of antibody production Microphold M cells In intestinal epithelium Phagocytes antigen and then taken by local dendritic and macrophages to be given to T cells Then immunoglobulins-secreted 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 11  Neuronal and Hormonal Control of Gastrointestinal Process 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 12  Regulation of the food processes in the GIT Absorption is not regulated ❖GIT designed to maximize absorption But other processes controlled by, Neural control system: Somatic and autonomic Intrinsic : Initiators ❖Submucosal/ Meissner's plexus ❖Constricts GI blood vessels and regulates secretions 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 13  Neural control system…. ▪ Intrinsic ….. Myenteric/Auerbach’s plexus ✓Some: accelerates movement by secreting Ach, Ser, and substance P ✓Others inhibit movement, release VIP, neurotensin, enkephalin Extrinsic : SN and PSN: modulators Hormonal control system ❖Gastrin, CCK, secretin, GIP, VIP ❖Thyroid hormones increase movement in the GIT ,but reduced by epinephrine 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 14  Neuronal regulation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 15  Intrinsic nerve regulation :Enteric nerves Initiate the food process by themselves under the control of extrinsic nerves Myenteric is between longitudinal and circular muscle layers Responses: controlled intrinsically or extrinsically Extrinsic Fig 6: Activation of nerve 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 16  Enteric nerve The smooth muscles cells also contain receptors for norepinephrine, ATP, secretin, CCk, substance p, VIP, somatostatin, and enkephalins These are also released from the enteric nerve Somatostatin : blocks the exocrine function of the stomach and the pancreas, and decreases the motility of both the stomach and the gut Catecholamine VIP: SMCs relaxation, inhibits gastric secretion and absorption from the intestinal lumen Adrenergic receptor Muscarinic receptors Ach from the nerve terminal (from PN or enteric nerve) binds on M3 Fig7: Types of enteric nerve and smooth muscle cell receptors 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 17 Myenteric/Auerbach’s plexus vs submucosal plexus Myenteric Submucosal Location In the muscular layer (b/n longitudinal and circular In submucosal layer (b/n circular muscle) muscle and mucosa) Function Increase muscle contraction, tone and velocity of Regulates secretion & local blood flow impulse conduction Released Not always excitatory (Ach), also release inhibitory ----- chemicals peptides VIP, ATP, NO 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 18  Higher center neuronal regulation of GIT processes Extrinsic nerve supply to the GIT Extrinsic nerve : the modulators Parasympathetic ▪ Cranial parasympathetic nerve fibers innervate:- ✓Salivary glands, oesophagus, stomach and its glands, pancreas, gallbladder and Brunner's gland ✓The first half of the large intestine. ▪ Sacral (2nd, 3rd, 4th ) PN innervates:- ▪ The lower part of the large intestine ▪ Sigmoidal, rectal, and anal regions well supplied with PN for defecation reflexes ▪ Parasympathetic stimulation increases digestion processes 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 19  Higher center innervation… extrinsic nerve … Sympathetic From T-5 and L-2 spinal cord segments Celiac and other mesenteric ganglia Innervate all part of the GIT and has inhibitory effects via NE GI smooth muscle cells Enteric nerves Reduces peristalsis and secretion Constricts sphincters Uses 1- for vascular constriction and 2-for GIT Muscle relaxation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 20 GIT innervation … Sympathetic innervation Parasympathetic innervation ▪ Originated in the cord b/n 5th The motor is from medulla thoracic 2nd lumbar segment oblongata (dorsal vagal complex ▪ Decreases movement ▪ Decreases secretion Celiac ganglion Superrior Mecentric ganglion Inferior Mecentric ganglion Fig 8: Sympathetic and Parasympathetic GIT Innervation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 21  Sensory ending in the GIT Sensory endings in the GIT send information to:- ✓ Enteric plexuses ✓ Vertebral ganglia of sympathetic and parasympathetic nerves ✓ Spinal cord ✓ Brainstem (via vagus) ✓ Higher brain areas These endings are affected by:_ ✓ Irritants of the gut mucosa ✓ Distention of the gut ✓ Chemicals in the gut 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 22  Sensory endings and afferent nerve of GIT Myenteric cell Mechanosensitive cells Fig 9 : Sensory endings in the GIT 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 23  Hormonal regulation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 24 Gastrointestinal hormones There are different gastrointestinal hormones Secreted from endocrine cells lining the lumen of stomach and intestine Released into the blood Not released into the lumen of the GIT 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 25  Gastrointestinal hormones Hormone Secreted from Function Stimulant Gastrin Antrum of stomach Stimulates Meal, but inhibited by GIP (G cells) - Gastric acid & pepsinogen secretion (from enteroendocrine K- cells of duodenum, facilitates secreted as - Growth of gastric mucosa insulin secretion & inhibits progastrin but - Gastric motility absorption of water & activated by Hcl - Insulin & glucagon secretion electrolytes), GIP stimulates - Reduces appetite intestine secretions Cholecystokinin I cells of duodenum ▪ Contracts the gallbladder Digestive products of fat ( and jejunum ▪ Inhibits stomach contraction & secretion fatty acids & ▪ Relaxes sphincter of oddi monoglycerides ▪ Facilitates release of pancreatic digestive enzymes ▪ Potentiates the effect of secretin 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 26  Intestinal hormones …. Secretin S cells of mucosa of ▪ Facilitates pancreatic bicarbonate Acidic juice from the the duodenum secretion stomach ▪ Reduces stomach activities GIP Mucosa of upper ▪ Reduces motor activity of the stomach fatty acids and amino small intestine an gastric emptying acids, less carbohydrate, ▪ Reduces intestine motility glucose in the blood Motilin Upper duodenum ▪ Increases gastrointestinal motility Hunger during fasting Vasoactive GIT (immune cells) ▪ Relaxation of smooth muscles GIT immune cell intestinal and hypothalamus and dilate peripheral blood activation peptide(VIP) vessels ▪  water secretion in to bile, pancreatic gland and lumen of small intestine ▪  pancreatic bicarbonate secretin and glycogenolysis ▪  stomach gastrin secretion 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 27  Gastrointestinal hormones: summary Fig 1o: Intestinal hormones and their effects 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 28 Major GIT hormones: Summary… 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 29  Gastrointestinal Reflexes 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 30  Gastrointestinal reflexes Reflex initiated by:- Enteric nerve: back to effect and secretion, peristalsis, mixing contractions controlled Prevertebral sympathetic ganglia: back to the GIT ✓ Transmit signals to along distance in the GIT such as from: ▪ Stomach to colon, colon and intestine to stomach, colon to ileum Spinal cord and brain ✓ From stomach and duodenum to brain and back to stomach via vagus ✓ From colon and rectum to s cord for defecation reflex Vagovagal reflex :both afferent and the efferent nerves are vagus Stimuli in the stomach activates afferent vagus nerve, information to brainstem and vagal efferent nerve increases stomach activities 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 31 Types of gastrointestinal reflexes Gastrocolic reflex From stomach to colon Facilities movement of feces Enterogastric reflex Small intestine to stomach Inhibitory Colonoileal reflex Colon to ileum and is inhibitor 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 32  Types of gastrointestinal reflexes … Defecation reflex Colon/rectum to spinal cord Back to colonic, rectal for abdominal contractions Chewing reflex: by medulla oblongata (MO) Local myentric reflex: Stimuli in the GIT , Stomach, activate nerve endings, and the enteric nerve innervates stomach gland for gastric juice secretion 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 33 Mechanism of chewing reflex Bolus (mouth)→Receptors and sensory impulses to MO→ Reflex inhibition of muscles of mastication→ Lower jaw drops (relax)→the drop causes lower jaw stretch spindles that leads rebound contraction of by raising the jaw→ Effect, crushing the food by contraction and relaxation processes Motor Nerve: 5th cranial motor nerve terminate on cheek muscles. 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 34  Gastrointestinal reflexes Fig 11: Pathways for Gastrointestinal Reflexes 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 35  Blood supply into GIT 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 36  Blood supply into GIT Splanchnic circulation Circulation from celiac, superior mesenteric, and inferior mesenteric arteries and is distributed to all abdominal viscera Stomach, Intestine, spleen, liver and pancreas Receives about 25% of CO (largest proportion) Important for also blood reservoir and released during stress Regulated by different factors ✓Hypoperfusion of the renal system : Increases the flow ✓Intrinsic (myogenic and metabolic) and extrinsic (autonomic and humoral) mechanisms: under normal physiological condition 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 37  Splanchnic circulation … Superior mesenteric artery from abdominal aorta supply to :- Duodenum, transverse colon and pancreas Inferior mesenteric artery from abdominal aorta supply to:- Large intestine, ascending and descending colon, and rectum 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 38  Splanchnic circulation Blood is cleared of debris and bacteria in the liver (sinusoid) Fig 12: Splanchnic circulation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 39 Arteries in the splanchnic circulation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 40  Splanchnic circulation regulation :summary Intrinsic Local metabolites and vasoactive substances Activities (meal increases flow) Local reflexes (submucosal nerve) Vasoactive substances dilate the blood vessels CCK, gastrin, secretin, Bradykinin, adenosine 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 41 Splanchnic circulation regulation : summary Extrinsic Sympathetic nerve Increases vascular resistance Catecholamine -adrenergic:- vasodilation -adrenergic:-vasoconstriction Adrenalin prefer -than -receptors Parasympathetic nerve Increases blood flow to gut 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 42  Electrical activities of GIT smooth muscle cells 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 43  Electrical activities of GIT smooth muscle cells Intestinal cell of Cajal Initiate the slow wave potential Intestinal pacemaker cells Smooth muscles Single unit with gap junction Syncytium (sharing of the same cytoplasm) Form Spike potential (AP) By slow wave potential from the intestine Cajal cells 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 44  Slow wave (graded) potential Facilitates the contraction of the tissue independent of extrinsic factors This rhythm determined by slow wave generated by pacemaker cells : intestinal cell of cajal (ICC) Is due to slow change in membrane potential by slow Na+ influx The wave transmitted to contractile cells Spike/AP formed Contraction occur 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 45  Slow wave … The intestinal cells of cajal Contact with smooth muscle cells Undergo change in membrane potential The change is periodically b/se of their unique ion channels that open and close periodically Opening brings pacemaker potential and the slow wave activity 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 46  Interstitial cells of cajal Fig 13: Gastrointestinal Cajal and smooth muscle cells 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 47  Spike potential AP that brings contraction Formed in the contractile smooth muscle cells When the RMP actually reaches more positive Caused by Ca++ influx into the smooth muscle cells The smooth muscles contain more VGCC The channels opened for long time Calcium combines with calmodulin The high the slow wave magnitude is the more the frequency of the spike By Ca++ influx but less Na+ unlike to the AP in the nerve fibers 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 48  Slow versus spike potential 4. Intestinal hormones Fig 14: Slow Wave and Spike Potentials 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 49 Factors depolarizing cells for excitation and contraction Depolarizing agents Chemicals in the diet Stretching of muscle cells Ach from enteric and parasympathetic nerve fibers Gastrointestinal hormones Parasympathetic stimulation Repolarizing agents Catecholamine Sympathetic stimulation and stress 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 50  Tonic contraction Caused by Repetitive spike potential Some hormones Ca++ influx Maintained contraction without relaxation Lower esophageal, ileocecal and internal anal sphincters 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 51  Food processes across the GIT … Gig 15: Food processes across the GITs 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 52  Digestion Mechanical digestion – Physical breakdown of food – Chewing, peristalsis and emulsification – Mixing of food without saliva by tongue – Churning (mixing) food in the stomach – Segmentation Rhythmic local constriction of GIT Food moves forward and backward 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 53  Digestion … Chemical digestion ▪ Enzymes from saliva, stomach, pancreas and intestines act on the food ▪ Reactions that break macromolecules into monomers: ▪ Polysaccharides into monosaccharides ▪ Proteins into amino acids, dipeptides and tripeptides ▪ Fats into monoglycerol and fatty acids 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 54  Factors affecting enzyme action The effect of enzymes are greatly affected by: Temperature (warm = fast, cold = slow) Concentration (more = fast, less = slow) pH (power of hydrogen) Suitable pH levels Some may also require specific metal ions to be present Coenzymes 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 55  Functional movements in the GIT Propulsive/Peristalitic movement Inherited by property of syncytial muscle Mechanism Food mass, chemicals, irritants, excite nerve endings initiates contraction of muscle 2 to 3 cm behind the distention point The reflex is initiated in the pharynx The peristalsis reflex and anal direction called law of gut 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 56  Functional movements in the GIT … Mixing movement: segmentation Peristalsis also cause mixation when forward pushing stop by closed sphincters Help in churning of food with digestive enzymes Thus intermittent constriction and obstruction used for mixation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 57  Digestion in each structure of the GIT 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 58  1. Digestion in the mouth Breaks food into smaller pieces Mechanical digestion Physical digestion to increases surface area for chemicals Chemical digestion Poor in absorption except some drugs, nitro-glycerine. To treat angina (chest pain) Secretion (saliva) 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 59  1. Mouth and saliva secretion Parasympathetic nerve stimulates the glandular cells to take Cl- Inside the cell becomes more negative Na+ inter into the cell and water follows Na+ Cl-, Na+ CHO3- K+ Na+ Cell pressure increased and open secretary border of Lumen the cells Water and electrolytes inter into the lumen Cl- Modification made in the duct Fig 16: Salivary gland acinar and ductal cells Na+ and Cl- reabsorbed and K+ and CHO3- secreted Serous cells secrete watery digestive enzymes Mucus cells secrete thick and more vicus secretion 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) Cl60  Secretions of ions in the saliva Acinar cells in the gland secrete 10 secretion The secretion moved down into the duct where modification occur In the salivary ductal cells, K+ and CHO3- secreted Na+ actively leave the cell into the interstisium with K+ exchange The 10 secretion contains ions with similar concentration to blood But saliva ion concentration vary with blood in the duct 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 61 Phases of saliva secretion ✓ Cephalic (brain) phase: Triggered by thought, smell, or sight of food ✓ Oral phase: triggered by food stimulating touch and test receptors in the mouth ✓ Gastric phase: Triggered by substances which stimulate the gastric mucosa (acids or sour taste). Stomach sends message to salivary glands 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 62 Salivary glands Intrinsic glands or bucal glands ✓ No mucose cells Secrete only serous fluid that contains alpha Minor ptyalin Secret only mucus Under the mucosal membrane of mouth, lips cheeks and tongue Lack ductule system , in front of ear Stensen’s duct Secret enzymes Extrinsic glands Major glands Ravinus duct They have ducts Fig 17: The major salivary glands Wharton’s duct 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 63 Salivary glands Extrinsic glands … Connected to the oral cavity with ducts Contain M3 receptors (target receptors for drooling treatment) The glands are Parotid (25%) : only serous/enzyme secretion Submandibular (70%) – both serous and mucus secretion Sublingual (5%) - little serous and more mucus secretion 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 64  Secretion type classification of glands Serous glands: made of serous cells, secret thin and watery saliva parotid and lingual serous glands Mucosal glands: made up of mucus cells, secret thick and viscus saliva Lingual mucus glands, (buccal glands, palatal glands) Mixed glands: submandibular and sublingual glands 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 65  Salivary gland innervation Both autonomic nerves Parasympathetic nerve (PN) ✓The gland innervates mainly by PN ✓Innervates serous cells ✓Enzyme rich saliva ✓Facilitates digestion ✓Dilates salivary blood vessels ✓Smell, taste, thought effects the PNF ✓Unpleasant food; inhibits PNF activity, thus low saliva volume SNS Viscous/mucus/thin saliva secreted 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 66 Parasympathetic and sympathetic innervation of salivary gland ThG, thoracic ganglion; ScG, superior cervical ganglion; OG, optic ganglion; SG, submandibular ganglion. Spinal cord: c, cervical vertebra; T, thoracic vertebra. cranial nerves: vii, facial nerve; iX, glossopharyngeal nerve; v, trigeminal nerve. More secretion, Enzyme rich, watery, less organic constituents saliva and dilate blood vessels supplying into the glands , mainly Ach is used using M1and M3 receptors Less secretion, thick, rich in mucus, this is b/se innervating acinar cells and constricts glandular vessels PNS innervating glands PNS innervating sublingual and submandibular originated from glands is from SSN while PNS innervating - Superior salivary nucleus parotid gland is from ISN (SSN in the pons) and SNS innervating glands is frm 1st and second inferior salivary nucleus (ISN in medulla) thoracic segment Fig 18: Salivary glands innervation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 67  Salivary nuclei At the junction of pons and medulla Activated by Tactile signals and taste stimuli in the tongue ,pharynx Hypothalamus (appetite area), Stomach and abdomens Amygdala Smooth object in the tongue Higher brain centers Sight, smell and thought 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 68 Salivary nuclei …medulla oblongata Gustatory Salivary reflex ▪ Taste-initiated secretion of saliva ▪ Information from tongue reaches to the salivary nuclei ▪ Motor commands get back to the salivary glands Fig 19: Salivary nuclei 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 69  Salivary secretion reflexes Unconditioned reflex Substance in the mouth activating sensory receptors increases saliva secretion Inborn and occurs immediately after birth Does not need previous exposure Conditioned reflex Acquired, via thinking, smelling, looking, hearing Needs previous exposure in that new neuronal circuits are developed between receptors of special sense and brain 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 70 Salivation Hyposalivation Temporal: salivation reduced temporally: Emotion, fever, dehydration Permanent: obstruction of salivary duct (sialolithiasis), absence of glands (aptyalism/xerostomia),paralysis of facial nerve (Bell’s palsy) Hypersalivation Pregnancy Tooth decay or neoplasma of mouth or tongue: continuous irritation of nerve endings in mouth Diseases of esophagus, stomach and intestine Parkinsonism and nausea 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 71 Contents of saliva Buffers Proteins (mucin, albumin) 99.4% water Antibodies 0.6% includes: Blood group components , antigens Electrolytes (Na+,Ca++, Cl—, and Enzymes HCO3—) Waste products Glycoproteins (mucins)- Glycoproteins, responsible for lubricating action 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 72  Functions of saliva ▪ Moisten, begin starch (salivary amylase) and fat digestion (lingual lipase), cleanse teeth, inhibits bacteria (containing antibodies), binds food together forming bolus ▪ Dissolving chemicals that: ✓ Stimulate taste buds ✓ Provide sensory information Initiates digestion of: ✓ Complex carbohydrates by enzyme salivary amylase (ptyalin or alpha-amylase) ✓ Lipids by enzyme lingual lipase Regulation of water balance (saliva secretion reduced during dehydration) Regulates temperature: salivation cools the body Sample sources Speech and Taste Cleansing 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 73 Tongue Tongue The tongue is made of skeletal muscle that is innervated by the hypoglossal nerves (12th cranial). On the upper surface of the tongue are small projections called papillae, many of which contain taste buds (see also Chapter 9). The sensory nerves for taste are also cranial nerves: the facial (7th) and glossopharyngeal (9th). As you know, the sense of taste is important because it makes eating enjoyable, but the tongue has other functions as well 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 74  2. Pharynx First peristalsis generated – The wave passes to the stomach But the 20 peristalsis is if the 1st failed Initiated by the myenteric nerve and partially by the vagus and glossopharyngeal Failure of vagus to the oesophagus, 20 peristalsis possible 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 75 Peristalsis and swallowing mechanism… ▪ Bolus: sensory information to medulla oblongata by ▪ Trigeminal and glossopharyngeal nerves ▪ The motor command to pharynx and upper esophagus by cranial nerve 9 and 10 ▪ During swallowing, respiratory tract closed (about for 6 sec): Respiration interruption ▪ It is the swallowing center (medulla oblongata) inhibits respiration ▪ During swallowing ✓ Epiglottis (flexible cartilage) cover and closed glottis Fig 2o: Medulla oblongata for swallowing 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 76  3. Esophagus ▪ Upper one third is skeletal and the remaining is smooth muscle ▪ Innervated by somatic motor nerve ▪ Connect with the stomach below diaphragm ▪ Inferior pharyngeal constrictor excludes air iterance ▪ Lower esophageal sphincter (LES) closes orifice to reflux but the upper prevent air iterance 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 77 Esophagus…. ▪ The esophagus below Diaphragm has the same pressure with abdominal pressure ▪ This prevent up movement of stomach contents Fundus Lower esophageal/ ▪ During expiration, abdominal contraction, and Cardiac sphincter Cardiac region pregnancy, abdominal pressure elevated that push the stomach content into esophagus Body Pyloric sphincter Pyloric region Fig 21: Lower Esophageal Sphincter 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 78  Phases of swallowing Buccal phase ✓ Tongue collects food and pushes it back into pharynx ✓ Voluntary stage Pharyngeal-phase ▪ From sensitive area in pharynx to swallowing center in the medulla ▪ Efferent to pharynx and esophagus via the 5th ,9th , 10th and 12th cranial nerve fibers Esophageal stage: upper esophageal sphincter opens; contraction of pharynx pushes the food to esophagus; food is then propelled by peristalsis to the stomach. 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 79  Common swallowing problems ▪ Inability to swallow: occurs in trauma, myasthenia gravis, poliomyelitis etc. ▪ Gastro-esophageal reflux: Occurs if the cardiac sphincter does not close. ▪ Achalasia: food accumulates in the esophagus due to incomplete relaxation of the cardiac sphincter (esophageal dilation, vomiting etc.). ▪ Aerophagia: Air swallowing with food (discomfort, belching) 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 80  4. Stomach J shape structure used to store, break up food, liquefy, propel and initiates reflex Gastro-ileac reflex; Gastro-coleic reflex Resulting in chyme formation Does not absorb significant amount of nutrients The tight junctions of the adjacent cells Absence of villi The presence of resistance mucus Absence of high osmotic gradient formation Absorbs aspirin and some lipid-soluble drugs Food reaching to the stomach, vagal reflex generated Wall tension reduced, for accommodation large food until the stomach completely filled 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 81  Functional anatomy of stomach HCl, pepsinogen and mucus secreted The pyloric region contains endocrine cells ✓ More gastrin secreted Temporary mucosal folds in the stomach, stretches out ✓ Intense contraction for mixing and open to increase stomach volume ,while these are villi in the Fig 22: Stomach small intestine pyloric sphincter 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 82  Functions of stomach Storage Mechanical function: peristalsis and segmentation Digestive function Protective function, HCI Hemopoietic function Excretory function Toxins, alkaloids and metals are excreted via gastric juice 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 83  Stomach Glands Cardiac glands: secret alkaline mucus and small amount of pepsinogen Gastric/Oxyntic glands: Main glands secreting mucus, HCl (parietal cells), pepsinogen (chief cells), mucin (mucus neck cells), and intrinsic factor (parietal cells), Mucin : carbohydrate containing proteins coating the surface of the stomach for protection and helps H.pylory colonization Pyloric glands: mucous, mucin and gastrin 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 84  Stomach defense mechanisms Prevent the stomach and duodenum from self-digestion – Mucus – Bicarbonate – Blood flow: for mucus secretion – Prostaglandins ✓ Stimulate secretion of bicarbonate and mucus ✓ Promote blood flow ✓ Suppress secretion of gastric acid 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 85 Gastric juice HCl Pepsin Rennin: enzyme, not hormone, from stomach used to digest protein milk-coagulating enzyme, coagulates the soluble milk protein helping milk to move into the intestine Not found in human, both animals Gastrolipase: weak enzyme comparing to pancreatic lipase Inactive at ph < two.five, active at Ph b/n 4 and 5 The lipid digestion product products : fatty acids and glycerol Mucus : has alkaline nature and forms mucus membrane in the inner wall of stomach Inorganic substances: Sodium, chloride, calcium, potassium 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 86  Secretion in the stomach Stomach secretes Digestive enzymes Hormones Mucus Due to The food in contact with sensory endings Activation of the enteric NS (Ach) Histamine Autonomic stimulations and hormones (gastrin) 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 87  Cells of Gastric Glands Mucus secreting cells :- exocrine cells Regenerative cells Divide rapidly to produce new cells that migrate to surface Parietal/oxyntic cells:- exocrine cells – Secrete HCl acid and intrinsic factor Chief/peptic cells :- exocrine cells and secrete ✓ Pepsinogen ✓Chymosin (break milk peptides) ✓Gastric lipase 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 88  Cells of Gastric Glands … Enteroendocrine/entrochromaffin cells in oxyntic gland and mast cells secrete histamine G cells secrete gastrin Argentaffin cells (chrommafin cells): Mostly in the fundus; serotonin. D-Cells: secrete somatostatin 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 89  Gastrin B. Secretin C. CCK D. GIP 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 90  Secretion in the stomach The pH of the secretion is 1-2 H+ is highly concentrated in the secretion 1500 calories needed for this concentration by the parietal cells HCl, pepsinogen, lipase, intrinsic factor and mucus called gastric juice 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 91  HCl secretion processes Antiportor on the apical membrane uses ATP Chloride ion pumped out to combine with H+ Bicarbonate ion exchanged with chloride ion (chloride shift) Bicarbonate ion increases blood pH Gastrin, histamine and Ach stimulate parietal cells Histamine potentates other factors (the most potential) Somatostatin, VIP and enterogasterons inhibit acid secretion 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 92  Parietal cell acid secretion process CA HO2+CO2 →H2co3 Somatostatin, VIP and enterogasterons Gastrin, histamine and Ach, spicy food, K+ Fig 23: Mechanism of acid secretion in the stomach 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 93  HCl secretion processes … Factors affecting HCl secretion H+-K+ ATPase Stomach polypeptide, Gastrin Ach from enteric and PNS Histamine (H2R ) and Somatostatin (inhibit g cell ) Intestinal factors (intestinal phase of stomach acid secretion regulation) Acid, distension, hypertonic solution, aa, FA, hormones 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 94  Factors inhibiting gastric secretion A fall in PH: As the stomach empties after a meal the pH in the stomach decreases (acidic). Consequently less gastrin and therefore less gastric juice is secreted. Gastric-inhibitory-peptide (GIP): fat empties into the duodenum, GIP is released that is transported by the blood to the stomach. CCK, VIP, secretin, somatostatin 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 95 Gastric secretion inhibitors… Gastric inhibitory peptide, GIP ✓Secreted in duodenum and jejunum by fat and glucose ✓Increase insulin secretion Vasoactive intestinal peptide, VIP, ✓Secreted from intestine ✓Inhibits stomach secretion ✓Causes peripheral vasodilation 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 96  Phases of gastric secretion 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 97  Phases of gastrointestinal control Neuronal and hormonal controls can be divided into phases The phases are based on the origin of the stimulus The phases are:- Cephalic phase Gastric phase Intestinal phase 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 98  Cephalic phase Brain cells stimulated by sensory inputs (taste, smell, thought) Increases parasympathetic out flow The signals are from cerebral cortex, appetite center of hypothalamus Via vagus efferent nerve to the stomach Contributes about 20 % of stomach activity control 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 99  Gastric phase Food substances reach in stomach, food mass/chemical in the food affects secretion & movement Secretion stimulated by Ach from vagus in the long vagal reflex Ach from local enteric nerve Histamine from gastric enteroendocrine cells Gastrin from pyloric G cells Receptors located on the parietal and chief cells Contribute to about 70 % of the control 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 100  Cephalic and gastric phases Fig 24: Cephalic and gastric phase processe 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 101  Intestinal phase Food substances reach in the small intestine, duodenum Intestinal hormones are secreted Inhibit stomach secretion (enterogastrones) Enterogastric reflex Nerve reflex also initiated Medulla oblongata (inhibit vagal output) Sensory nerve stimulation ✓ Distension ✓ Acid, fat, protein digestive products Intestinal hormone secretion ✓ Duodenal Irritation Fig 25: Intestinal phase 1/4/2025 Fig 16: Enterogastric reflex By: Abebaye A( BSc, MSc, Ph.D.) 102  Intestinal phase… Phenomena during intestinal phase of stomach activities regulation:- Vagal nerve inhibition Sympathetic nerve stimulation Gastric emptying reduced Release of NE Pyloric sphincter closed Intestinal hormonal secretion Stomach enzyme secretion inhibition 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 103  Gastric and intestinal phases Endocrine cells Fig 26: Gastric an intestinal phases 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 104  The three phases : summary Fig 27 : The three phases 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 105  Meal in the stomach and nerve regulating gastric juice secretion Meal increases the secretion (gastric/cephalic phase) More protein in the stomach increases acid secretion in to two ways ▪ Peptides stimulate the gastrin secretion ▪ Proteins in the stomach buffer H+ from the lumen : PH elevated and secretion facilitated Factors activating PSN increase gastric juice secretion Fig 28: Neuronal control of stomach secretion 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 106  Functions of HCl acid Activates pepsin and lingual lipase Facilitates secretion of pepsinogen Activates pepsinogen to pepsin conversion Liquefies and dissolves (not fat) food to form chyme Converts ingested ferrous iron (Fe 2+ ) to ferric (Fe3+ ) Destroys ingested bacteria and pathogens Stimulates hunger, important in appetite regulation Enhances motility of stomach Providing acidic medium for the action of enzymes 1/4/2025 By: Abebaye A( BSc, MSc, Ph.D.) 107  Gastric enzymes Pepsin Protein digestion Secreted as pepsinogen (inactive) HCl removes peptides and converts into pepsin (active) Work in the acidic media, PH