Gastrointestinal Physiology PDF 2024

22 M.k. handout Tasneem Jarwan MOHAMMED KHATATBEH  Gastrointestinal physiology ‫ ف قررنا نعمل الشيتات بس من الهانداوت حرفيا بدون اي تغيير‬، ‫بما انه الكل بيدرس مادة الدكتور محم د خطاطبة من الهاند اوت تبعه‬ ‫ بال الكالم الزايد ههههههه بس عشان يكون واضح ضفنا جن...

22 M.k. handout Tasneem Jarwan MOHAMMED KHATATBEH  Gastrointestinal physiology ‫ ف قررنا نعمل الشيتات بس من الهانداوت حرفيا بدون اي تغيير‬، ‫بما انه الكل بيدرس مادة الدكتور محم د خطاطبة من الهاند اوت تبعه‬ ‫ بال الكالم الزايد ههههههه بس عشان يكون واضح ضفنا جنب كل فقرة من الهاند اوت‬، ‫بالمحتوى بس تغيير بالترتيب عشان نوضح المعنى‬. ♡♡♡♡ ‫ بالتوفيق ويزدووممم‬،، ‫الساليد المناسب الها من الباوربوينت تبع الدكتور‬ Introduction: Four physiological processes are taking place along the gastrointestinal (GI) tract. These include: 1. Motility. 2. Secretion. 3. Digestion. 4. Absorption. Functional structures in the gastrointestinal tract : Smooth muscle cells Interstitial cells of Cajal Secretory cells Other related structures related to the processes above : Control systems of GI functions. – Neural control: 1) Enteric nervous system. 2)Autonomic nervous system – Hormonal control: GI endocrine Blood flow to the GI. Functional structures in the gastrointestinal tract: ☆ Smooth muscle cells: 2 main layers are generally forming Gastro-intestinal tract with some variations according to organ. These layers are clearly seen In small intestine: → Longitudinal layer: outer layer of smooth muscle cells arranged longitudinally along the digestive tract. → Circular layer: extend circumferentially around the gut. Located beneath longitudinal layer. Each layer Is forming a bundle like structure. Cells In each bundle are connected together by gap junctions with permit these cells to function as syncytium. Therefore, by this organization, a group of cells Is functioning together to an effective contraction along gastro-intestinal tract. In addition to these two main layers, a third thin layer of smooth muscle cells Is also described at the junction between the mucosa and submucosa whichh is known as Muscularis mucosa. This layer is involved in the secretion from tubular glands and movements.of mucosal folds  ‫تمت اعادة صياغة بعض الفقرات‬ Characteristics of smooth muscle cells: Electrical Activity of Smooth Muscle: Smooth muscle cells are characterized by two key electrical properties: 1. Slow Waves (Basic Electrical Rhythm - BER): These are undulating changes In membrane potential. 2. Spike Potentials: These are true action potentials that appear at the peak of slow waves. ‫ بنشوف‬،‫ بالجزء األول‬.‫الصورة بتوضح كيف العضالت الملساء بتشتغل‬ ‫ وبهالحالة‬،)Spike Potentials ‫الموجات الكهربائية البطيئة (بدون‬ ‫ بنشوف إنه‬،‫ بالجزء الثاني‬.‫ قليل‬tension ‫العضلة ما بتنقبض وبيكون ال‬ ‫ الكالسيوم بيدخل‬،‫ فوق الموجات البطيئة‬spike potential ‫لما تصير ال‬ ‫ العالي في‬tension ‫ وهاد اللي بيبين ال‬،‫الخلية وبتزيد قوة االنقباض‬ ‫ هي المفتاح اللي بخلي العضلة‬spike potentials‫ يعني ال‬.‫العضلة‬.‫تشتغل وتشد‬ Calcium (Ca²+) in Smooth Muscle Contraction: The role of calcium in smooth muscle contraction is well established. The sources of Ca++ for contraction include: 1. Extracellular Fluid: Ca++ enters the cell from the interstitial fluid through activated Ca++ channels. The activation of these channels is triggered by spike potentials that occur at the peak of slow waves (true action potentials). 2. Sarcoplasmic Reticulum (SR): Ca++ is released from the SR via the formation of inositol triphosphate (IP3). IP3 is produced during signal transduction mechanisms, initiated by the activation of phospholipase C. This process occurs in response to the binding of a ligand (hormone or neurotransmitter) to its receptor. Mechanism of Contraction: Ca++ binds to calmodulin, forming a complex. → This complex activates myosin filaments, resulting in the development of attractive forces between actin and myosin, leading to smooth muscle contraction.  Gap junctions: Communication between cells Functional syncytium Chemical control of smooth muscle cells activity: Smooth muscle cells respond to a wide range of stimuli caused by neurotransmitter or hormones. This activity appears by activation of receptors on smooth muscle cells. These transmitters may induce relaxation or contraction of smooth muscle cells according to the type of transmitter, type of receptor and the transduction mechanism involved in receptor activation. Integration of Smooth Muscle Responses: The integration of responses in smooth muscle cells occurs through the binding of ligands to their receptors, resulting in tonic contraction. Variations in these tonic contractions, with increases or decreases in intensity, can be observed along the gastrointestinal (GI) smooth muscle. In addition to tonic contractions, rhythmic contractions (also referred to as phasic or rhythmic contractions) have been identified along the GI tract. In this type of contraction, a group of smooth muscle cells undergoes rhythmic cycles of contraction and relaxation, as seen in small intestinal motility. These contractile activities are primarily regulated by the electrical rhythm displayed by the smooth muscle cells of the GI tract. ____________________________________________________ Effective Activity of Smooth Muscle Cells in the GI Tract For smooth muscle cells of the GI tract to function effectively, they operate In a syncytium. This means their activity Is highly synchronized, with organized cycles of contraction and relaxation at the segmental level, promoting efficient motility of the GI.tract This synchronization is partially regulated by the enteric nervous system (ENS). Additionally, the Interstitial cells of Cajal play a crucial role In coordinating and.synchronizing this activity Interstitial Cells of Cajal (ICCs): Interstitial cells are widely spread all over the gastrointestinal tract. These cells have certain characteristics. They have large number of processes. Also, these cells communicate through these processes by gap junction with other ICCs as well as smooth muscle. In addition, these cells eliciting by themselves electrical activity as action potentials. All these have supported the theory of considering these cells as pacemaker cells of the gastro-intestinal tract  Generation of action potentials→pacemaker cells of the GI tract _________________________________________________________________________________________________ Characteristics of Interstitial Cells of Cajal (ICCs): 1. ICCs Communication: The communication between ICCs and other ICCs, as well as ICCs and smooth muscle cells, occurs through gap junctions. This communication forms the basis for the synchronization of electrical activity In smooth muscle cells, ensuring a harmonious contractile response. As a result, the smooth muscle cells function as a functional syncytium In the gastrointestinal tract. 2. ICCs Generate Slow Waves: ¤ ICCs are excitable cells capable of generating electrical activity. ¤ This activity is characterized by a sudden, periodic upstroke from a constant resting potential of about -70mV. ¤ The initiation of this activity is believed to be metabolism-dependent. ¤ These upstrokes are thought to generate slow waves in smooth muscle cells connected to ICCs or regulate the rhythm of slow waves in smooth muscle cells. 3. ICCs Receive Inputs from the ENS: ♤ In addition to communicating with smooth muscle cells, ICCs also receive inputs from the enteric nervous system (ENS). ♤ These inputs likely play a crucial role in mediating and regulating smooth muscle activity, enhancing their role in promoting coordinated contractions. ________________________________________________________________________________ Secretory cells: Secretory Cells in the Digestive System ,these cells can either exist as solitary cells lining the digestive tube or be grouped into functional structures known as glands. They are specialized for the synthesis and secretion of organic substances, such as enzymes, hormones, factors, or mucus. Some of these structures secrete only water and electrolytes, a type of secretion referred to as serous secretions. Further details about secretory cells, their functions, and their regulation will be discussed in the context of gastrointestinal secretion. _____________________________________________________________________ Enteric Nervous System (ENS): The Enteric Nervous System (ENS) is a neural network that begins at the esophagus and extends along the entire gastrointestinal (GI) tract. It consists of two main plexuses: 1. Myenteric Plexus (Auerbach’s Plexus): Located between the longitudinal and circular smooth muscle layers. Primarily controls the activity of smooth muscle cells in these layers, thereby regulating GI movements. 2. Submucosal Plexus (Meissner’s Plexus): Found in the submucosa. Primarily regulates GI secretion and local blood flow. Neural Connectivity and Sensory Input: ▪︎ Neurons within each plexus are interconnected by nerve fibers that project in oral, caudal, and circumferential directions. ▪︎ Some neural fibers connect neurons from the two plexuses. ▪︎ Sensory neurons within the ENS transmit signals from the GI epithelium to: 1)The enteric plexuses. 2)Prevertebral ganglia of the sympathetic nervous system. 4)The spinal cord. 4)The brainstem via the vagus nerve. ▪︎ These sensory neurons are stimulated by: ➔ Excessive distension of the gut. ➔ Irritation of the mucosa. ➔ The presence of specific chemical substances in the lumen. Function of Enteric Neurons: Enteric neurons regulate gastrointestinal functions by releasing various neurotransmitters that can have either inhibitory or excitatory effects on: 1-Motility. 2-Secretion. 3-Vascular blood flow. Key Neurotransmitters in the ENS: The ENS contains many neurotransmitters, including: ☆ Acetylcholine (Ach) ☆ Substance P (SP) ☆ Vasoactive Intestinal Peptide (VIP) ☆ Calcitonin Gene-Related Peptide (CGRP) ☆ Gastrin-Releasing Peptide (GRP) Additional neurotransmitters continue to be identified, highlighting the complexity of the ENS. Autonomic nervous system: Parasympathetic Nervous System: The parasympathetic nervous system is divided based on the location of neural cell bodies: 1. Cranial Division: Provides innervation through the vagus nerve to the esophagus, stomach, pancreas, small intestine, and the first half of the large intestine. 2. Sacral Division: Provides innervation through pelvic nerves to the distal half of the colon, sigmoid, rectum, and anal region. This division is particularly important in executing the defecation reflex. Effects of Parasympathetic Stimulation: 1) Increases the activity of the enteric nervous system. 2) Enhances gastrointestinal functions, including motility, secretion, and blood flow. Sympathetic Nervous System: Origin of Sympathetic Fibers: Sympathetic fibers that innervate the gastrointestinal tract originate in the spinal cord, specifically from segments T5-L2. These fibers pass through the paravertebral ganglia and synapse with a second neuron located in the celiac, superior mesenteric, or inferior mesenteric ganglia. Effects of Sympathetic Stimulation: 1) Decreases the activity of the enteric nervous system. 2) Reduces the activity of gastrointestinal smooth muscle cells. Endocrine cells and Hormones in the GI.(Enteric Endocrine System) Many hormones have been identified at the level of GI tract. Many of these have their function unidentified yet. These hormones include: ➔ Gastrin ➔ Cholecystokinin (CCK). ➔ Secretin. ➔ GIP (Gastric Inhibitory Peptide) other name is (Glucosedependent Insulino- tropic Polypeptide) Other hormones Secreted Along the Gastrointestinal Tract ,, including: ➔ Glucagon-like Peptide-1 (GLP-1) ➔ Motilin ➔ Ghrelin ➔ Amylin ➔ Enterostatin ➔ Neuropeptide Y (NPY) ➔ Pancreatic Polypeptide: Closely related to polypeptide YY and NPY Additionally, scattered endocrine cells along the GI tract release other hormones, such as: ➔ Somatostatin ➔ Neurotensin ➔ Thyrotropin-Releasing Hormone (TRH) ➔ Adrenocorticotropic Hormone (ACTH) These hormones play diverse roles in regulating various functions of the GI tract and associated systems. Blood Flow and Local activities in the GI: The blood flow to the gut is very well related to local activities. After meal the increase in absorption, secretion and motor activities is accompanied by an increase in blood flow. This increase continues during the next few hours after meal and return back over the next 2 - 4 hours. Regulation of Gastro-intestinal Blood Flow: Factors That Increase Blood Flow: 1. Release of Vasodilator Substances: ➔ After mucosal stimulation caused by meals, substances such as CCK, VIP, Gastrin, and Secretin are released. ➔ These substances also play a role in regulating smooth muscle cell activity. 2. Kinin Release: ➔ Some glands release kinins, such as kallidin and bradykinin, into the lumen and gut wall. 3. Decreased Oxygen Concentration: ➔ Low oxygen levels may increase blood flow, possibly through the release of adenosine. Role of the Enteric Nervous System (ENS): Like muscle activity, vascular flow is controlled by the ENS. Many ENS neurotransmitters, such as Substance P (SP), VIP, and CGRP, influence vascular flow by being released from ENS neurons. Role of the Autonomic Nervous System: 1. Sympathetic Stimulation: ◇ Causes vasoconstriction, leading to decreased blood flow. 2. Parasympathetic Stimulation: ◇ Increases blood flow indirectly by enhancing glandular activity, which leads to the secretion of vasodilator mediators (e.g., kinins). ◇ The parasympathetic system does not directly affect blood vessels ‫تمت كتابة هذا الشيت صدقة جارية عن روح والدة زميلنا عمرو رائد من دفعة تيجان‬ ‫️‬ ‫دعواتكم لها بالرحمة والمغفرة‬ ‫‪Thank you‬‬