Anatomy of the Digestive system

An overview of the anatomy of the Digestive System.

1. ANATOMY OF THE DIGESTIVE SYSTEM Victor EKPO MSc Medical Physics, College of Medicine, University of Lagos. 2017

2. OUTLINE Introduction to the Digestive System Divisions Alimentary Canal Accessory Organs Organs Location Functions THE ROLE OF COMPUTERS IN MEDICAL PHYSICS. VICTOR EKPO. CMUL - LAGOS

3. INTRODUCTION The Digestive System is a group of organs working together to convert food into energy and basic nutrients to feed/nourish the body. ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS

4. ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS Fig: Anterior view of the Digestive System

5. Fig: Posterior view of the Digestive System

6. DIVISIONS The alimentary canal is also called the digestive tract OR gastrointestinal tract GIT (though GIT is technically stomach + intestines only). The alimentary canal is the long tube that runs from the mouth through to the anus . ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS The Digestive System consists of 2 parts: the Alimentary Canal , and their Accessory Organs .

7. ALIMENTARY CANAL The main parts of the Alimentary Canal are: * Mouth (Oral cavity) * Pharynx (Throat) * Oesophagus (also esophagus) * Stomach * Small intestine * Large intestine * Rectum and anal canal (anus).

8. ACCESSORY ORGANS The Accessory Organs include other organs (mainly glands) that aid digestion. These include: Tongue, salivary glands and tonsils (for mouth) Tubular mucous glands (for pharynx, oesophagus, large intestine) Liver , Gallbladder, and Pancreas ( for small intestine ); Epiglottis : which tips posteriorly at the pharynx to prevent food from entering the larynx/respiratory tract. Mesentery* (newly discovered organ that helps hold the intestines to the posterior abdominal cavity ).

9. ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS Digestion starts in the mouth, where food is chewed and mixed with saliva to form a bolus . The bolus produced is then swallowed down the pharynx and oesophagus via peristaltic contractions and into the stomach. In the stomach, it is mixed with gastric juice to form a semifluid substance called chyme , then moved to the duodenum (small intestine). Most of the digestion takes place in the stomach and duodenum of the small intestine. Water and some minerals are reabsorbed in the colon of the large intestine. The chyme is turned to faeces . The faeces is defecated from the anus via the rectum. DIGESTION >>>

10. LOCATION OF ORGANS Fig: Abdominopelvic Regions

11. MOUTH (ORAL CAVITY) The mouth or oral cavity is bounded by muscles and bones: Anteriorly – by the lips Posteriorly – it is continuous with the oropharynx (part of pharynx) Laterally – by the muscles of the cheeks Superiorly – by the bony hard palate and muscular soft palate Inferiorly – by the muscular tongue and the soft tissues of the floor of the mouth.

12. TONGUE The tongue is a large, muscular organ that occupies most of the oral cavity. It is attached by its base to the hyoid bone, and by thin fold of tissue called the frenulum , to the floor of the mouth. A groove called the terminal sulcus divides the tongue into two parts . Anterior: covered by papillae (contains some taste buds). Posterior: contains few small glands and a large amount of lymphoid tissue, the lingual tonsil . Fig: Dorsal surface of tongue & tonsils

13. TEETH (SKELETAL) The teeth are embedded in the mandible and maxilla bones. Movement of the m andible (lower jaw) allows chewing. The mandible is the only moveable bone in the jaw. There are 20 temporary teeth. Later, 32 permanent teeth replace the 20. There are incisors (8), canines (4), premolars (8), and molars (12). Fig: Skeletal system of the mouth

14. ANATOMY OF TEETH The teeth is composed of a crown, neck and root. The crown is covered by thin but hard enamel . The root is covered with bone-like cementum , which secures the tooth in its socket. Periodontal ligaments hold the teeth in the alveoli. Blood vessels and nerves enter the tooth through the apical foramen . The tongue and teeth are important for proper mastication of food, and also for speech. Fig: Cross section of a lower tooth

15. PHARYNX It connects to the oral cavity anteriorly, and is continuous with the oesophagus. Food passes from the oral cavity into the pharynx then to the oesophagus below it. The pharynx consists of three parts : nasopharynx , oropharynx , and the laryngopharynx. It prevents food from entering the nasal cavity (by the soft palate) and the lower respiratory tract (by the epiglottis).

16. Figs: Actions of soft palate and Epiglottis in Pharynx during swallowing EPIGLOTTIS

17. OESOPHAGUS Also called gullet or esophagus, it is an organ through which food passes from the pharynx to the stomach , aided by peristaltic contractions , of its musculature. It is about 25 cm long and 2 cm in diameter, and lies in the median plane ( mediasternum ) in the thorax, anterior to the spinal column, but posterior to the trachea.

18. CONSTRICTIONS OF THE OESOPHAGUS The oesophagus follows the curvature of the vertebral column. It also has 3 constrictions (narrowing), where adjacent structures produce impressions: Cervical Constriction ( Upper Oesophageal Sphincter ) – where Pharynx meets Oesophagus. Thoracic (Broncho-Aortic) Constriction – where it is first crossed by arch of aorta. Diaphragmatic Constriction: where it passes through the oesophageal hiatus of the diaphragm at t10, before entering the stomach .

19. OESOPHAGUS (contd.) Immediately the oesophagus has passed through the esophageal hiatus (opening ) of the diaphragm , it curves upwards before opening into the stomach . This sharp angle, as well as the sphincters at each end (e.g. cardiac sphincter), prevents the regurgitation (backflow) of gastric contents into the oesophagus . The oesophagus has thick walls consisting of the four layers/tunics common to the digestive tract: mucosa (innermost) , submucosa, muscularis , and serosa/adventitia (outermost).

20. STOMACH Fig: Anterior view of stomach and its adjacent structures

21. LOCATION OF THE STOMACH It is the enlarged hollow part of the digestive tract specialized in the accumulation of ingested food, and also acts as food blender . It is located between the oesophagus and the small intestine. It is located in the epigastric, umbilical & left hypochondriac regions of the abdominal cavity. Gastroenterology deals with the study of diseases of the stomach and intestines and their associated organs

22. PARTS OF THE STOMACH The stomach has four (4) parts: Cardiac Fundus Body Pylorus The P yloric Sphincter guards the opening between the stomach and the duodenum. When the stomach is inactive, the pyloric sphincter is relaxed and open , and when the stomach contains food, the sphincter is closed. The stomach is continuous with the oesophagus at the Cardiac Sphincter , and with the Duodenum at the Pyloric Sphincter.

23. SMALL INTESTINE The small intestine is the part of the GIT between the stomach and large intestine. The small intestine is continuous with the stomach at the Pyloric Sphincter and leads into the large intestine at the i leocaecal v alve . It is about 2.75 – 10.49 m long. For an average person, it is 3-5m. It lies in the abdominal cavity surrounded by the large intestine .

24. PARTS OF SMALL INTESTINE There are 3 parts of the Small Intestine: Duodenum : First, shortest, widest and most fixed part (0.25m long). Jejunum : This is the middle section of the small intestine (about 2.5m long) – about 2/5th Ileum : Joins the large intestine at the Ileocecal Junction (3- 3.5m long) – about 3/5th The mesentery , a double layer of peritoneum , supports and attaches the jejunum and ileum ( small intestine ) to the posterior abdominal wall.

25. PERITONEUM & MESENTERY The peritoneum ( yellow portion ) is the largest serous membrane of the body. It is a closed sac, containing a small amount of serous fluid, within the abdominal cavity. It provides attachment to organs of the GIT, and acts as a physical barrier to localize spread of infection. It invaginates the stomach, small intestine, liver, pancreas, kidney, spleen, and other pelvic organs. T he mesentery associated with the small Intestine is sometimes called the Mesentery other parts, e.g. of the colon: transverse mesocolon . Proper . There are mesenteries of

26. LIVER & GALL BLADDER The liver is an accessory digestive gland, and largest internal organ. It is involved in the: Synthesis of glucose from amino acid Breaking down of carbohydrates Synthesis of cholesterol Production of fat, through lipogenesis. Production of bile. The bile produced is stored in the gall bladder, and secreted to the small intestine during food digestion. The gallbladder is a saclike structure on the inferior surface of the liver that is about 8 cm long and 4 cm wide.

27. PANCREAS The pancreas is a pale grey gland weighing about 60g. It is about 12–15 cm long and is situated in the epigastric and left hypochondriac regions of the abdominal c avity. It consists of a broad head, a body and a narrow tail . It secrets pancreatic juice (exocrine pancreas), and insulin and glucagon (endocrine pancreas).

28. LARGE INTESTINE The Large Intestine meets the Small Intestine at the i leocaecal valve , then continues to the anal canal . It is about 1.5m long and 6.5cm wide (Small Intestine: 2.5cm). It consists of the Cecum (proximal end), Appendix, Colon (ascending, descending, sigmoid, transverse), Rectum, Anal canal (distal end) Fig: Parts of the Large Intestine

29. FUNCTIONS OF THE DIGESTIVE SYSTEM Ingestion , Mastication , Propulsion , Mixing , Secretion , Digestion , Absorption , and Elimination .

30. ORGAN FUNCTIONS Mouth Ingestion, Taste, Mastication, Digestion, Swallowing, Communication, Protection. Pharynx Swallowing, Breathing, Protection Oesophagus Propulsion, Protection. Stomach Storage, Digestion, Absorption, Mixing and Propulsion, Protection. Small Intestine Neutralization, Digestion, Absorption, Mixing and Propulsion, Excretion, Protection. Large Intestine Absorption, Storage, Mixing and Propulsion, Protection, Excretion.

31. REFERENCES Waugh A, Grant A. Ross and Wilson Anatomy and Physiology. 12th Ed., New York NY: Elsevier; 2004. Seeley RR, Stephens TD, Tate P: Anatomy and Physiology. 6th Ed., New York, NY: McGraw-Hill Companies; 2004. Moore KL, Dalley AF, Agur AM. Clinical Oriented Anatomy 6th Ed., Baltimore BA: Lippincott Williams & Wilkins; 2010. Coffey JC. The Mesentery: Structure, Function and Role in Disease. The Lancet Gastroenterology & Hepatology; 2016. Sherwood L. Fundamentals of Physiology: A Human Perspective. 3rd Ed., Florence KY: Cengage Learning. 2006.

32. THANK YOU THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS