Week 1 - Digestive System PDF

Week 1- Digestive system  Objectives By the end of this lesson you should be able to: List and describe the major processes occurring during digestive system activity Describe the tissue composition and the general functions of each of the four layers of the...

Week 1- Digestive system  Objectives By the end of this lesson you should be able to: List and describe the major processes occurring during digestive system activity Describe the tissue composition and the general functions of each of the four layers of the alimentary canal Describe the basic functions of the mouth, pharynx and oesophagus Outline the gross and microscopic anatomy of the organs of the gastro-intestinal tract and the digestive processes that occur in these locations Describe the processes of enzymatic hydrolysis (chemical digestion); classes of enzymes, the foodstuffs upon which they act and the end products of chemical digestion Briefly describe the process of nutrient absorption Read Marieb, E.N. & Hoehn, K. (2023). Chapter 23: The Digestive System,. In Human Anatomy and Physiology. (pp. 902-959). United States of America: Pearson. Digestive Processes The of food digestion involves 6 major processes : cavity (lips tongue) food 1 the. Ingestion - Involves oral , , the entry point of into the digestive System. Propulsion 2 The food - movement of through the tract by swallowing (voluntary) + peristalsis (Involuntary. Mechanical 3 The down of food digestion break into small fragments - for chemical digestion 4 Chemical The breakdown food digestion of complex molecules by -. blocks enzymes into smaller chemical building. Absorption 5 The - passage of digested end products from the digestive tract lumen into the blood or lymph via passive or active transport 6 Defecation-Elimination of from the body. indigestible substances Propulsion The propulsion of food through the digestive tract involves 2different processes swallowing voluntary act - > - - peristalsis > - involuntary act · that sees an alternate wave of muscle contraction + relaxation to push food down the tract ↓ In this the bolus is pushed down the - process , * tract by the circular muscles that contract behind the bolus - longitudinal muscles ahead of the bolus also relax to force the > - bolus ahead This process of contraction + relaxation bolus physically pushes the - down the tract Mechanical Digestion Occurs in 3 sites : major 1) The mouth-the teeth mechanically churn , grind t mix the food Saliva with 2)The stomach-food is + churned mixed with gastric juices 3)The small intestine-segmentation occurs here. · This is where the food mixes with the digestive juices which aids the process of nutrient absorption Segmentation similarly to propulsion however this - occurs process breaks the food into 'lumps' while smaller Simultaneously moving them intestine through the small Histology of the Alimentary Canal The Canal Alimentary The alimentary canal is comprised of 4 layers of tissue : major D The mucosa 2) The submucosa 3) The muscularis externa 4) The serosa The structure of each of these 4 tissues vary in - their location The sits mucosa in the inner most tissue layer > - - followed by the submucosa - the muscularis externat the serosa The forming Mucosa the outer most layer The innermost mucosa is the layer of the alimentary canal - It is composed of 3 sub layers Depithelium-(simple columnar cells) form the internal layer It is alls secretory · rich in 2) lamina propria-composed of loose tissue connective containing capillaries + lymphoid follides 3)The muscularis muscosae - a thin layer of smooth muscle that moves the mucosa The Major functions of the mucosa : D Epithelium - secrete mucus which protects the mucosa t helps food move along the canal secrete digestive which - enzymes aide in chemical digestion - Secrete hormone which control motility + secretion of digestive juices - Absorb nutrients 2)Lamina propria used capillaries are in the absorption of end products of digestion - - Lymphoid follicles present here to act to protect against infectious diseases 3) Muscularis mucosa -produces folds in the mucosa of the small intestine to increase the surface area available for absorption The submucosa - The submucosa is external to the mucosa behind the meaning it sits mucosal layer of tissue in the alimentary canal - It is composed of loose connective tissue it which allows the ability to stretch t recoil - The submucosa supplied with blood is richly vessels (for nutrient absorption) lymphatic vessels (transport of lipids) lymphoid , , tissue (immune System) + nerves (control of motility + secretion) The Muscularis Externa - The muscularis externa surrounds the submucosa tissue It is responsible for peristalsis (propulsion) - + segmentation (mechanical digestion - The tissue is composed of 2 layers of Smooth muscle · the inner circular t outer layers The Serosa - outermost layer of tissue - composed of connective tissue with a thin layer of squamous epithelium - It functions to protect the alimentary canal + anchors the alimentary tissues within the peritoneal cavity The of Organs the digestive System https://moodle.federation.edu.au/mod/book/view.php? id=7766377&chapterid=2218188 The Salivary Glands There are 3 pairs of salivary glands located in the oral cavity These include:. the sublingual gland - - the submandibular gland the parotid gland - salivary secretion is under - parasympathetic control 1-1 SL of -we produce approx.. saliva daily which is primarily composed of water (97-99%) - Saliva also contains mucin protein which acts as a lubricant , enzymes (salivary amylase , lingual lipase) which begin to help break down food , + finally antimicrobial proteins (antibodies lysozyme defensiv , , The stomach MICROSCOPIC ANATOMY OF THE STOMACH The stomach functions mechanical digester mixing food with - as a , gastric juices to liquefy+ form Chyme The stomach also disinfects food begins the chemical digestion of - , proteins , absorbs fat soluble substances (such as alcohol) + stores food the until digestion when it passes into small intestine by propulsion - The stomach mucosais is composed of columnar epithelial cells t produces an alkaline mucus -this living is spotted with gastric pits which produce mucus 37 of ↓ are connected to gastric glands that produce up to gastric juice each day - Gastric glands are composed of Chief cells (secret pepsinogen), parietal Cls (Secrete hydrochloric acid) + enteroendocrine cells (secret hormones that control gut motility + secretion It is important to remember : * - Hydrochloric acid (HC) which has a PH of 1 5-3 5.. denatures lunfolds) proteins + aides in degradation · It kills most (but not all) bacteria + activates pepsin pepsinogen is a precursor of pepsin , a protease enzyme which aides in protein digestion - the Small Intestine MICROSCOPIC ANATOMY OF THE SMALL INTESTINE - The small intestine is highly adapted for nutrient absorption Its length provides a huge surface area alone - -Circular folds ,villi+ microvilli further increase this surface area , increasing the efficiency of nutrient absorption - circular folds (plicae circulares -> are deep folds of the mucosa + submucosa + act to slow down the movement of chyme , increasing the time for nutrient absorption to Occur Villi- > are small projections of the mucosa + are - composed of epithelial cls that are absorptive + columnar t bond by tight junctions (for nutrient + electrolyte absorption) bed + The core contains a capillary a wide lymph · Capillary Dacteal) Microvilli - a small , densely packed Villi the surface , - on forming a brush boarder' · The brush boarder enzymes complete Carbohydrate , protein + nucleic acid  Along with these structures the small intestine also - , located the villi display tubular glands in the pits between These known intestinal are as crypts + they secrete - intestinal Juice (pH 7 4-.. 8) , a watery mucus that facilitates nutrient absorption - They also contain enteroendocrine cells which secrete hormones that stimulate bile t pancreatic juice secretion, lymphoid tissue for defense + stem cells that renew villus epithelium from as they migrate the crypt + up the villi It is important to remember : - 90 % of nutrient in the intestine absorption occurs small - These nutrients , as well as water , vitamins + electrolytes are absorbed across the single layer of epithelial cells + into the capillaries within the villi -water soluble nutrients are absorbed into the blood + travel via the hepatic portal vein to the liver - Lipid soluble nutrients are absorbed into the lymphatic system + enter the bloodstream at the thoracic duct THE ACCESSORY ORGANS The liver, form gall bladder + pancreas the accessory organs of the digestive system The live The liver responsible is for numerous roles : - Main function production of: bile for fat digestion Synthesis of plasma proteins (albumin clotting factor) - , - Metabolic functions: Processing of blood-bone nutrients > this includes the · - removal + storage of excess nutrients (glucose to , glycogen) breakdown of fatty acids (energy production) , use of amino glucose or fat vitamin acids to build t , mineral storage · Regulating levels of circulating nutrients this > - includes the regulation of glucose triglycerides fatty , , + acids cholesterol , drug ↓ hormone metabolism + detoxification - Heat production via chemical reactions Blood supply to the liver cual is (two sources) : 1) The hepatic artery : supplies from oxygenated blood the abdominal aorta (20 %) 2) The hepatic portal Supplies vein: nutrient rich blood from the small intestine (80 %) > - -Connective tissue divides each lobe of the liver into lobules , the functional units of the liver These hexagonal plates radiate - from the central vein with a at each portal area corner - each portal is comprised of an arteriole branch of the hepatic artery , a venule branch of the hepatic portal vein + a bile duct - Each lobe also houses sinusoids which allow hepatocytes to filler + process nutrient-rich blood , capillaries lined with Kupfer cells which remove debris , + bile canaliculi which collect + drain bile into the duct The Gall Bladder - The gall bladder is a thin walled muscular sac that stores + concentrates unused bile - Bile is secreted into the duodenre from the gall bladder or the liver Bile produced is by hepatocytes is yellow-green in colour - + The result of bilirubin by product of pigmentation is a - , a the breakdown of Bile also contains hemoglobin from recycled RBCs - bile salts + phospholipids which emulsify fats (break them down into small droplets , increasing surface area for digestive enzymes) + facilitates fat + cholesterd absorption of bile intestinal The release is triggered by - hormones secreted when Chyme enters the duodenum - It is then reabsorbed in the ilium + recycled The Pancreas The pancreas is largely - composed of exocrine tissue It produces + secretes pancreatic - Juice into ducts that deliver it to the duodenum - This pancreatic juice has a pH of 80. + is composed of : · water Electrolytes (bicarbonate to neutralize stomach acids · ions + aide enzyme activity Enzymes · digest > - Proteases - proteins - Amylases -> digest carbs - Lipases > - digest lipids > acids Nucleases > digest nucleic - - - As well as exocrine tissue , some endocrine tissue is also structurally part of the pancreas - This tissue contains islets which secrete hormones into the blood to regulate glucose levels The large Intestine MICROSCOPIC ANATOMY OF THE LARGE INTESTINE - The mucosa of the large intestine is composed of simple columnar epithelial cells It with is largely abundant crypts + large numbers of goblet - als - These act to produce that ease of faeces mucus passage I protect the intestinal wall from bacterial waste products > - - It is important that we also remember the intestine large is where chemical digestion occurs by bacteria only 500 species Approx of -. bacteria are enteric the to large intestine (some survive the + Stomach small intestine) + many of these normal flora prevent colonization by harmful bacteria , ferment undigested carbs + synthesize vitamins CHEMICAL DIGESTION Chemical digestion is catabolic process this means that it breaks - a , down larger molecules (polymers) into small units (monomers) + in the process releases energy - These smaller molecules (monomers) are then absorbed from the tract the blood lymph gastrointestinal into or - This breakdown of polymers is catalyzed by specific enzymes Digestion + Absorption of Carbohydrates -carbs make up a large portion of our dietary intake - The common carbs include : · polysaccharides - glycogen , starch + cellulose · Disaccharides esucrose , lactose t maltose · monosaccharides-> glucose , fructose + galactose https://moodle.federation.edu.au/ mod/book/view.php? id=7766377&chapterid=2218186 Digestion + Absorption of Proteins - Protein comes in many forms much of intake in the form of meats + plant - our protein is material however some protein is also present in the form of digestive - , enzymes + from breakdown of cells https://youtu.be/HL7-fYBtJ1Y? si=Vyvy5puqduU2Pm7o Digestion Absorption + of Lipids - Lipids form fat globules in aqueous solution The of majority - our dietary fats Clipids) are mostly triglycerides which are inaccessible to water-soluble enzymes - Bile salts emulsify + breakdown these lipids into smaller droplets - The pancreatic enzyme, lipase then yields free fatty acids + monoglycerides The , forming micelles with bile salts - micelles can then be passed into the intestinal mucosa Digestion + absorption of Nucleic Acids - Nucleic acids include DNA + RNA molecules - They are found in the cells from the foods we eat (plant and /or animal) These 2 nucleic acids digested in the small intestine in - are a stage process : D) Pancreatic nucleases/deoxyribonucleases break down the nucleic acids into nucleotides 2) Brush boarder enzymes break down nucleotides into their component (adenine guanine cytosine thymine) pentose bases , , , , Sugars phosphate + ions 3) Absorption occurs by active transport Summary of Nutrient Absorption 90% Approx of absorption processes in the small intestine -. occur , including most electrolytes + water The 10% the Stomach (lipid soluble substances remaining in - occurs such as alcohol) + the large intestine (water electrolytes , + some Vitamins) - Absorption occurs through mucosal epithelial cells These cells joined by tight junctions thus preventing nutrients - are , from passing between + around them