Lecture note for 200 level students DIGESTIVE SYSTEM.pptx

Digestive System

1. DIGESTIVE SYSTEM BY SADIQ RABIU UMAR B.Sc. (YUMSUK), M.Sc. (BUK), MASSON AMINU DABO COLLEGE OF HEALTH SCIENCES AND TECHNOLOGY KANO STATE NIGERIA. GENERAL STUDIES UNIT 2020/2021 session   2/15/2023 1

2. Introduction Digestion is defined as the process by which food is broken down into simple chemical substances that can be absorbed and used as nutrients by the body. Most of the substances in the diet cannot be utilized as such. These substances must be broken into smaller particles, S o that they can be absorbed into blood and distributed to various parts of the body for utilization . Digestive system is responsible for these functions . Digestive process is accomplished by mechanical and enzymatic breakdown of food into simpler chemical compounds . 2/15/2023 2

3. Cont.’ All these food materials are subjected to digestive process, before being absorbed into blood and distributed to the tissues of the body . Digestive system plays the major role in the digestion and absorption of food substances . 2/15/2023 3

4. Macroscopic Structure of the GIT 2/15/2023 4

5. Functions of the Digestive System Ingestion or consumption of food substances B reaking them into small particles Transport of small particles to different areas of the digestive tract Secretion of necessary enzymes and other substances for digestion Digestion of the food particles Absorption of the digestive products (nutrients) Removal of unwanted substances from the body. 2/15/2023 5

6. Functional Anatomy of Digestive System Digestive system is made up of gastrointestinal tract (GI tract) or alimentary canal and accessory organs, which help in the process of digestion and absorption. GI tract is a tubular structure extending from the mouth up to anus, with a length of about 30 feet. It opens to the external environment on both ends. GI tract is formed by two types of organs: 1 . Primary digestive organs. 2 . Accessory digestive organs. 2/15/2023 6

7. Cont.’ 1. Primary digestive organs are the organs where actual digestion takes place. Primary digestive organs are: i . Mouth ii. Pharynx iii. Esophagus iv. Stomach v. Small intestine vi. Large intestine. 2. Accessory digestive organs are those which help primary digestive organs in the process of digestion. Accessory digestive organs are: i . Teeth ii. Tongue iii. Salivary glands iv. Exocrine part of pancreas v. Liver vi. Gallbladder. 2/15/2023 7

8. Wall of Gastrointestinal Tract In general, wall of the GI tract is formed by four layers which are from inside out: 1. Mucosa layer 2. Submucosa layer 3. Muscular layer 4. Serous or Adventitial layer. 2/15/2023 8

9. Nerve Supply to the GIT GI tract has two types of nerve supply: Intrinsic nerve supply Entrinsic nerve supply Intrinsic nerves to GI tract form the enteric nervous system that controls all the secretions and movements of GI tract . Enteric nervous system is present within the wall of GI tract from esophagus to anus. Nerve fibers of this system are interconnected and form two major networks called 1. Auerbach plexus or myenteric (between circular and longitudinal muscles layer)- contraction/movements of the GIT 2. Meissner plexus or submucosal (muscle layer and submucosa )- secretions of the GIT 2/15/2023 9

10. Extrinsic Nerve Supply to the GIT 2/15/2023 10

11. Digestive Processes The activities of the digestive system can be grouped under five main headings . 1. Ingestion . This is the taking of food into the alimentary tract , i.e. eating and drinking . 2. Propulsion . This mixes and moves the contents along the alimentary tract. 3. Digestion . This consists of: • mechanical breakdown of food by, e.g. mastication (chewing) • chemical digestion of food into small molecules by enzymes present in secretions produced by glands and accessory organs of the digestive system . 2/15/2023 11

12. Cont.’ 4. Absorption. This is the process by which digested food substances pass through the walls of some organs of the alimentary canal into the blood and lymph capillaries for circulation and use by body cells . 5. Elimination. Food substances that have been eaten but cannot be digested and absorbed are excreted from the alimentary canal as faeces by the process of defaecation . 2/15/2023 12

13. Mouth Mouth: is otherwise known as oral cavity or buccal cavity. It is formed by cheeks, lips and palate. It encloses the teeth, tongue and salivary glands. Mouth opens anteriorly to the exterior through lips and posteriorly through fauces into the pharynx . Functions of the mouth 1. Appreciation of taste of the food 2. Transfer of food (bolus) to the esophagus by swallowing 3. Role in speech 4. Social functions such as smiling and other expressions. 5. Ingestion of food materials 6. Chewing the food and mixing it with saliva 2/15/2023 13

14. Pharynx Pharynx: This is the second part of the alimentary canal. It is funnel shaped, muscular and lined with mucous membrane that is continuous with the mouth, esophagus and respiratory tract. Parts of the Pharynx: 1. Nasopharynx 2. Oropharynx 3. Laryngopharynx 2/15/2023 14

15. Esophagus Esophagus: this is a narrow muscular tube that passes down through the thorax to open into the stomach. The esophagus is about 25 cm long and about 2 cm in diameter and lies in the median plane in the thorax in front of the vertebral column behind the trachea and the heart . It is continuous with the pharynx above and just below the diaphragm it joins the stomach. Function of the esophagus : It has sphincter which opens when food is swallowed and helps to transport food from the pharynx to the stomach. 2/15/2023 15

16. Stomach Stomach: is a hollow organ situated just below the diaphragm on the left side in the abdominal cavity. Volume of empty stomach is 50mL Under normal conditions , it can expand to accommodate 1 L to 1.5L of solids and liquids. However , it is capable of expanding still further up to 4L . Parts of stomach In humans, stomach has four parts: 1. Cardiac region 2. Fundus 3. Body or corpus 4. Pyloric region. 2/15/2023 16

17. Cont.’ 2/15/2023 17

18. Functions of the stomach T emporary storage allowing time for the digestive enzymes , pepsins, to act C hemical digestion – pepsins break proteins into polypeptides Mechanical breakdown – the three smooth muscle layers enable the stomach to act as a churn, gastric juice is added and the contents are liquefied to chyme. Gastric motility and secretion are increased by parasympathetic nerve stimulation L imited absorption – water, alcohol and some lipid soluble drugs 2/15/2023 18

19. Small Intestine Small intestine: is the part of gastrointestinal (GI) tract, extending between the pyloric sphincter of stomach and ileocecal valve, which opens into large intestine . I t is longer than large intestine. Its length is about 6 meter. Important function of small intestine is absorption. Maximum absorption of digested food products takes place in small intestine. Small intestine consists of three portions : 1. Proximal part known as duodenum 2. Middle part known as jejunum 3. Distal part known as ileum Wall of the small intestine has all the four layers as in stomach 2/15/2023 19

20. Large intestine Large intestine or colon extends from ileocecal valve up to anus. It has a larger diameter than the small intestine. Parts of the large intestine: 1. Cecum with appendix 2. Ascending colon 3. Transverse colon 4. Descending colon 5. Sigmoid colon or pelvic colon 6. Rectum 7. Anal canal. 2/15/2023 20

21. Movements of the Digestive System Mastication or chewing: is the first mechanical process in the gastrointestinal (GI) tract, by which the food substances are torn or cut into small particles and crushed or ground into a soft bolus . Deglutition or swallowing: is the process by which food moves from mouth into stomach. 2/15/2023 21

22. Other movement includes Movement of the stomach Filling and emptying of the stomach Vomiting Movement of the small intestine Movement of the large intestine Defecation Evacuation of gases from gastrointestinal tract 2/15/2023 22

23. Accessory Organs of Digestive System Salivary gland: D igestive juice present in the mouth is saliva, which is secreted by the salivary glands. In humans, the saliva is secreted by three pairs of major (larger) salivary glands and some minor (small) salivary glands. Major Salivary Glands are: 1. Parotid glands 25% 2. Submaxillary glands 70% 3. Sublingual glands 5% 2/15/2023 23

24. Cont.’ Composition of saliva Saliva is the combined secretions from the salivary glands and the small mucus-secreting glands of the oral mucosa. About 1.5 litres of saliva is produced daily and it consists of: W ater M ineral salts S alivary amylase; a digestive enzyme M ucus A ntimicrobial substances; immunoglobulin and the enzyme lysozyme. 2/15/2023 24

25. Liver Liver: Liver is a dual organ having both secretory and excretory functions. It is the largest gland in the body, weighing about 1.5 kg in man. It is located in the upper and right hypochondric region of the abdominal cavity, immediately beneath diaphragm. 2/15/2023 25

26. Liver Functions of the liver: Carbohydrate metabolism Fat metabolism Protein metabolism Storage Detoxification against microbes Defence against microbes 2/15/2023 26

27. Pancreas and Biliary tract Biliary tract: This involves the route taken by bile from the liver, to the gall bladder and then to the duodenum. 2/15/2023 27 Pancreas: The pancreas is a pale grey gland weighing about 60grams . It is about 12–15cm long and is situated in the epigastric and left hypochondriac regions of the abdominal cavity. It consists of a broad head, a body and a narrow tail. It has two functions; exocrine and endocrine function

28. Disorders of the Digestive System Peptic ulceration: ulceration of the gastrointestinal mucosa is caused by disruption of the normal balance of the corrosive effect of gastric juice and the protective effect of mucus on the gastric epithelial cells. Appendicitis: this is the inflammation of the appendix cause by microbial infection mostly. Cholera: the disease is caused by vibrio cholera and is spread by contaminated water, food and hand. Symptoms include persistent diarrhea and severe dehydration. Hepatitis: this refers to inflammation of the liver and can be caused by viruses, drugs and chemicals including alcohol. 2/15/2023 28

29. Neuroanatomist /Neuroscientist/ Academictutor / Medicalreseracher /Dissector 2/15/2023 29