Saliva & Gastric Secretions PDF

Block 1.2 lectures 2024-2025 lecture Highlighter key Writer Reviewer...

Block 1.2 lectures 2024-2025 lecture Highlighter key Writer Reviewer Doctor explanation Abbreviation Key information Book >> >> Maryam Alyahya Alzahraa Alshakhs 221-222-223 notes References Student explaintion Deleted Dr ShujaAnwar Kazi MBBS, M.Phil(Physiology) Department of Biomedical Sciences College of Medicine King Faisal University Al-Hassa Kingdom of Saudi Arabia [email protected]  Objectives 3 The Goals of our learning are: To understand the functions and regulation of Saliva To know about Gastric Juice in context to its: Composition, Functions, Production, Regulation To appreciate the role & regulation of GIT hormones In Gatric Juice regulation: Gastrin, Secretin, GIP, CCK  Saliva It is a mixture of secretions produced by: Daily secretion Saliva is alkaline in nature with pH 6-7, mainly produced by 3 800-1500ml glands, among them the largest is the Parotid gland There is also buccal glands that Its pH is b/w 6-7 present scattered around your mouth and all over the oral cavity many very small buccalglands  Salivary Glands Submandibular & Sublingual glands comparatively, they are smaller than the parotid — mostly producing both type of secretions ( Mucus + Serous ) — Mucus contains mucin for the lubrication which is important to protect the cells Secrete serous type of Buccal secretion Parotid Gland glands —- the largest, secreting watery contains secrete only type of saliva “Serous” mucus ptyalin —Producing the enzyme Amylaze previously reffered to as Ptyalin secrete both serous & mucus (contains mucinfor lubricating & for surface protection)secretion  Composition of Saliva Component Type Function Water (90%) Higher K (7times to Potassium concentration in the plasma 3.5-4.5 Electrolytes plasma)& HCO3, Low Hypotonic and tasteless while in the saliva its 7 times NaCL(1/7 to Plasma) higher Salivary Alpha Amylase Breaks Polysaccharides (Ptyalin) Dr said memorize the first two in addition to mucin and IgA, Lingual Lipase By Ebner’sGlands Little role in digestion others are not important Mucin Glycoprotein Lubricates food in mouth IgA Antibody Against bacteria & Antibody Viruses Lysosome Protective Antibacterial substances Prolinrich proteins Protect enamel of teeth Salivary secretion is a two-stage operation The acini in salivary glands produce the primary saliva, which is typically serous (rich in enzymes like amylase). As this primary saliva travels through the ducts, it undergoes modification Acini The primary saliva produced by the acini is similar to plasma in its composition. As it passes through the ducts, it is modified by two active processes: 1. Sodium absorption (active uptake of sodium ions). Similar in composition to plasma 2. Potassium secretion (active addition of potassium ions)to Saliva. These active processes create an ionic imbalance, which passively drives the movement of other electrolytes: Chloride ions follow sodium into the duct cells (reabsorbed). Bicarbonate ions are secreted to balance the charge, making the saliva more alkaline. In simpler terms: When two ions (sodium and chloride) are removed from the saliva, two ions (potassium and bicarbonate) are added. This adjustment ensures the saliva becomes less similar to plasma and slightly alkaline, preparing it for its roles in digestion and oral health. Salivary Duct there is excess Na+ reabsorptionover K+ secretion & this creates electrical negativity of about -70mV in salivary ducts which causes Cl- to be reabsorbed passively  REMOVES IRRITATING SUBSTANCE PROTECTION Because saliva contains the enzyme salivary DIGESTION amylaze which can digest the carbohydrates — the digestion of the carbohydrates starts from the mouth BUFFERING SINGING SPEECH  Two types of Salivary Reflexes Simple reflex When anything comes in contact with the mouth, it stimulates the (1) Simple or unconditioned reflex production of the saliva (2) Acquired or conditioned reflex Acquired reflex When you start to think about the food or see it , smell it. Unconditioned salivary reflex is triggered By (connected with memories) oral stimulation by the presence of food Conditioned salivary reflex occurs without oral stimulation thinking , seeing, smelling, hearing of pleasant food initiates salivation  Neural Innervation of the glands PONS — Glossopharyngeal nerve (cranial Mixed nerve = has a motor nerve IX) is the mixed nerve and sensation functions responsible for: Motor function: Stimulating the secretion of saliva from the parotid gland Sensory function: Providing sensation to the posterior one-third of the tongue — Facial nerve Motor function; Stimulates the submandibular and sublingual glands to produce saliva MEDULLA Sensory role: Carries taste sensation OBLONGATA from the anterior two-thirds of the tongue. & other areas of mouth (Taste) Salivary glands are controlled mainly by parasympathetic nervous system  As said before, when anything comes in contacts with the oral cavity it stimulates the production of the saliva, there are certain things that maximize the production considered as stress such as: Sour taste except the rough objects when they come in contact, such as chopping the pencil it will inhibit the saliva production  Involuntary Functionally will be divided into : sympathetic and parasympathetic Both sympathetic and parasympathetic stimulate salivary secretion The both nerves previously mentioned have an autonomic activity in autonomic we have sympathetic and Parasympathetic has the dominant role parasympatheti that work together in each gland & produces increased salivary secretion but in the same time one of them will be rich in enzymes dominant, and here the parasympathetic is the dominant Sympathetic by contrast produces smaller volume of saliva rich in mucus The glands of the stomach divided Stomach mucosa has two types into two categories depending on their location of tubular glands Oxynticglands Pyloric glands (Gastric glands) — Hydrochloric acid (pH 1) or less , is a highly strong acid that if your throw it on someone you will Secretes Hydrochloric acid burn them Mainly mucus — Pepsinogen is an inactive Pepsinogen To protect the the gastric for protection cells from HCl enzyme important for the digestion Intrinsic factor & of proteins & Gastrin — Intrinsic factor is a protein Mucus essential for the absorption of Vitamin B12 located on the inside located in antralportion surfaces of body (20%) & fundus(80%) Oxynticgland is composed of three types of cells: 1. Parietal (or oxyntic) cells secrete hydrochloric acid & intrinsic factor 2. Peptic (or chief) cells secrete large quantities of pepsinogen. 3. Mucous neck cells secrete mainly mucus. Mucous is rich in bicarbonate > prevent the acids from damaging the area — The HCl is secreted directly into the canaliculi, preventing it from coming into direct contact with the rest of the cell. “How does the cell produce HCl and — The microvilli and the cell membrane create a protect itself?” barrier from the acidic environment as you can see, these cells are follicular in shape with spaces between them called HCl the Canaliculi, lining the canaliculi are the microvilli to increase the surface area of secretion secretory HCl end Secretions comes from the canaliculi to the lumen of the stomach (where the food is digested)  2 main components needed for HCl formation: In a nutshell: 1. Water (H₂O) HCl is formed in the canaliculi by combining pH 2. Carbon Dioxide (CO₂) – sourced either from the interstitial hydrogen ions (H⁺) and chloride ions (Cl⁻). 0.8 fluid or produced metabolically inside the cell. Hydrogen ions (H⁺), derived from water dissociation, are transported into the canaliculi via the H⁺/K⁺ ATP pump. There are 2 theories about the formation of HCl, first is: This is all we are expecting you to know, no 1. Carbon Dioxide combines with water using the enzyme carbonic further anhydrase, forming carbonic acid (H₂CO₃). 2. Once it is formed, Carbonic acid dissociates into: Hydrogen ion Bicarbonate ion Second theory which is mentioned in this picture is: Carbon dioxide inside the cell reacts directly with water without forming carbonic acid. This reaction produces: Hydrogen ion (H⁺): Actively transported into the lumen of the canaliculi using the H⁺/K⁺ ATP pump (exchanging H⁺ for K⁺). Hydroxyl ion (OH⁻): Combines with CO₂ to form bicarbonate (HCO₃⁻), which is released into the interstitial space via chloride-bicarbonate exchange. When a patient comes with a gastrointeritis, stomach ulcer or bleeding in the stomach you always give medicine that inhibits the hydrogen-potassium pump Passive movement of the Cl ion that is driven by the chloride- Called proton pump inhibitor (PPI) such as: Nexium, Gastrin bicarbonate exchange, leads the ion itself to the lumen to combine with hydrogen ions forming HCl SECRETION AND ACTIVATION OF PEPSINOGEN. When pepsinogen is released from the peptic cell of the oxyntic glands of the stomach in the presence of acidic environment it tranforms from inactive to an active state (Pepsin) once the pepsin is formed its going to form other pepsinogens, so where the pepsinogen is released in an appropriate acidic environment it all become activated and further it will activate others These pepsins start the digestion of proteins  Intrinsic secreted by the parietal cells Factor Vitamin B12 is required for the production & maturation of RBCs deficiency will lead to megaloblastic anemia Essential for vitamin B12 absorption in ileum When B12 is deficient, all the folic acid accumulates inside the RBC which will lead to increase in size and become macrocytic thats why it is called megaloblastic Destruction of parietal cells in chronic gastritis develops There are 2 sources of deficiency, either the person is not eating enough B12 or due to the deficiency of ACHLORHYDRIA & PERNICIOUS ANEMIA intrinsic factor that is caused by antibodies destroying the parietal cells, in this case it becomes pernicious anemia Destroying the parietal cells will not only lead to pernicious anemia but also Achlorhydra ( abscense of HCl ) = no protein digestion  PYLORIC GLANDS Surface Mucous Cells The pyloric glands contain: Mostly mucous cells secrets large amount of thin mucus ( lubricate food movement, protection of stomach wall ) G cells secrete the hormone Gastrin Mucus is highly alkaline -at the pH- of 7- and provides a lotion/cream on the surfaces so the HCl does not come in direct contact with the cells and destroy them Produced in the stomach, enhancing the formation of the gastric juice (chyme) Further release is stimulated by more proteins  Enterochromaffin-like cells (ECL cells). The rate of formation and secretion of HClby parietal cells is directly proportional to the amount histamine secreted by the ECL cells. Enterochromaffin-like cells. ECL are stimulated : —G cells in the gastric glands release gastrin, a local hormone with a GASTRIN paracrine effect, which activates ECL cells. (ECL cells can be stimulated by Acetylcholine) –ECL cells respond by releasing histamine, which stimulates parietal ACETYLCHOLINE cells to produce hydrochloric acid (HCl). –Parietal cells are stimulated not only by histamine but also directly by acetylcholine , a neurotransmitter released by the parasympathetic nerves. Anti-Histamines block the production of HCl, which are cheaper than other drugs but has more side effects Cephalic Phase Account 3 Phases of gastric secretion 20% of Gastric secretion. 1 5 2 3 4  Gastric Phase: Once food enters the stomach it excites accounts for about 70 % of the total gastric secretion 1 3 Intestinal Phase Gastric secretion 2 1 3 4 Important to be memorized 💡: All the hormones reduce the gastric acid secretion , except (Gastrin)  team Wishes you the best