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The Digestive System

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Subdivisions of the AbdomenSubdivisions of the Abdomen

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Digestive sytem:-The organs that are involved in breaking down of food into molecules that can pass through the walls of the digestive tract and can be taken up by the cells.

Digestion process are in two stages:- mechanical digestion-Chemical digestion

-G I tract or Alimentary canal:-A continuous tube the begins at the mouth and ends at the anus.

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Digestion

• Processing of food• -2 Types of processing:

– Mechanical (physical)• Chew• Tear• Grind• Mash• Mix

– Chemical• Catabolic reactions• Enzymatic hydrolysis

– Carbohydrate– Protein– Lipid

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Digestion

• Phases– Ingestion– Movement– Digestion– Absorption– Further digestion

**chyme partially digested food(a thick, heavy,creamlike liquid).***

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Digestive System Organization

• Gastrointestinal (Gl) tract (Alimentary canal)– Tube within a tube– Direct link/path between organs– Structures

• Mouth• Oral Cavity• Pharynx• Esophagus• Stomach• Duodenum • Jejunum• Ileum• Cecum• Ascending colon• Transverse colon

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Digestive System Organization

• Descending colon• Sigmoid colon• Rectum• Anus

• Accessory structures– Not in tube path– Organs

• Teeth• Tongue• Salivary glands• Liver• Gall bladder• Pancreas

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Anatomy of the Mouth and Throat

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Human Deciduous and Permanent Teeth

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Dorsal Surface of the Tongue

Tongue…

Figure 15—2. Surface of the tongue on the region close to Figure 15—2. Surface of the tongue on the region close to its V-shaped boundary, between the anterior and posterior its V-shaped boundary, between the anterior and posterior portions. Note the lymphoid nodules (lingual tonsil), glands, portions. Note the lymphoid nodules (lingual tonsil), glands,

and papillae.and papillae.

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The Major Salivary Glands

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Deglutition (swallowing)

• Sequence:– Voluntary stage

• Push food to back of mouth

– Pharyngeal stage• Raise

– Soft palate– Larynx + hyoid– Tongue to soft palate

– Esophageal stage• Contract pharyngeal

muscles• Open esophagus• Start peristalsis

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Deglutition (swallowing)

• Control– Nerves

• Glossopharyngeal• Vagus• Accessory

– Brain stem• Deglutition center

– Medulla oblongata– Pons

– Disorders• Dysphagia• Aphagia

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Esophagus

• Surrounded by– SNS plexus– Blood vessels

• Functions– Secrete mucous– Transport food

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Peristalsis and Segmentation

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2 types of muscular action occur in the small intestines:**Segmentation and peristalsis.**

Segmentation is the muscle action that mixes chyme and digestive juices, like a cement mixer.The second action is peristalsis, moving undigested food remains toward the large intestine

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Esophagus

• Sphincters:– Upper (pharyngoesophageal sphincter)

– Lower (LES)

• Abnormalities ??

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Stomach

• Usually “J” shaped• Left side, anterior to the spleen• Mucous membrane

– G cells – make gastrin– Goblet cells – make mucous– Gastric pit – Oxyntic gland – Parietal cells – Make

HCl– Chief cells – Zymogenic cells

• Pepsin• Gastric lipase

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Anatomy of the Stomach

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Stomach• 3 muscle layers

– Oblique– Circular– Longitudinal

• Regions– Cardiac sphincter– Fundus– Antrum (pylorus)– Pyloric sphincter

• Vascular• Inner surface thrown into folds

– Rugae• Contains enzymes that work best at

pH 1-2

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Stomach

• Functions– Mix food– Reservoir– Start digestion of

• Protein• Nucleic acids

– Activates some enzymes– Destroy some bacteria– Makes intrinsic factor – B

12 absorption.

• The stomach’s activity is controlled by the PNS***

– Absorbs• Alcohol

• Water

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1.The deep folds of the stomach wall that allow for size changes of the stomach are called?a.Rugbyb.Sphincterc.Rugaed.Glottal folds2- the stomach’s activity is controlled by the _______ nervous system.

3- the final “door” of the stomach that needs to open for chyme to travel to the small intestine is located at the end of the ?a.Fundus f. ????b.Epiglottis c.Adventitiad.Serosae.Cardiac region

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Small Intestine

• Extends from pyloric sphincter ileocecal valve

• Regions– Duodenum

– Jejunum

– Ileum

• Movements– Segmentation

– Peristalsis

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The small intestines is small in diametre,not in length.Beginning from the pyloric sphincter,the small intestines is also the longest section of the alimentary canal ,with length of up to 20 feet(up to 6 metres).In small intestine, almost 80% of the absorption of usable nutrients takes place when chyme comes in contact with the mucosal walls.Simple sugars, Aa, fatty acids, vitamins and water are all absorbed here.*****Some of the remaining 20% was already absorbed in the stomach, with the rest being absorbed in the large intestines.

Any residue that cannot be utilised is sent on to the large intestine for removal from the body as fecal matter(feces).

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Small Intestine

• Histology features– Intestinal glands – Intestinal enzymes– Duodenal glands – Alkaline mucous– Paneth cells – Lysozyme– Microvilli– Lacteals– Plica circularis– Smooth muscle– Lymphatic tissue – GALT– Vascular

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Small Intestine

• Absorbs– 80% ingested water– Electrolytes– Vitamins– Minerals– Carbonates

• Active/facilitated transport

• Monosaccharides

– Proteins• Di-/tripeptides• Amino acids

– Lipids• Monoglycerides

• Fatty acids

• Micelles

• Chylomicrons

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Structure of the Villi in the Small Intestine

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The structure of the wall of the small intestine possesses circular folds called plicae circularis and finger-like protrusions into the lumen called villi.The villi which posses microscopic extensions known as microvilli. These villi are tightly packed, giving the mucosa velvety texture and appearance.The purpose of the microvilli ,villi and circular folds is to provide an incredible increase in the surface area of the small intestine.Each villus contains a network of capillaries and a lymphatic capillary called LACTEAL.Intestinal glands are located between villi.The capillaries absorb and transport sugars the result of carbohydrate digestion) and amino acids (the result of protein digestion) to the liver for further processing before they are sent throughout the body.

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Glycerol and fatty acids(obtained from the digestion of fat), are absorbed by the villi and converted into a lipoprotein that travels on to the lacteal, where it is now a white, milky substance called chyle.Chyle goes directly into the blood stream via the left subclavian vein for distribution throughout the body.

The walls of the small intestine secrete several enzymes important for the final stages of chemical digestion and two hormones that control the activity of the pancreas, gallbladder and stomach.

The pancreas is stimulated to secrete as a result of the hormone secretin that is produced by the small intestines. gall bladder activity is stimulated by the hormone cholecystokinin,which is produced by the small intestines.

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At the duodenum, additional secretions are added from the pancreas and gall bladder.The pancreas provides pancreatic juices, and the gall bladder produces bile. Bile emulsifies fat, (that is it makes fat able to disperse in water making the fat easier to breakdown.)Pancreatic juice contains enzymes and sodium bicarbonate, which neutralises the acidic chyme.The small intestine also produces digestive enzymes that are needed to complete chemical digestion.These enzymes and (mucus) are produced by exocrine cells. lactase, maltase,and sucrase are needed for the digestion of double sugars such as disaccharides that are contained in starches.Peptidases--- needed to digest portions of the protein structure called peptides.Intestinal lipase—for digestion of certain fats.

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Hormone secreting organ action Gastrin stomach stimulates release gj.Secretin duodenum stimulates release of bicarbonate and water from pancreas and bile from liver.Cck duodenum stimulates digestive enzyme release from the pancreas and bile release from the gall bladder.

*** it is important to note that the secretion of these substances is mainly due to the presence of chyme in the small intestines.****

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Small Intestine

• Secretes digestive enzymes– Peptidases

• Amino-• Di-• Tri-

– Sucrases– Maltase– Lactase– Saccharidases

• Di-• Tri-

– Lipase– Nucleases

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Small Intestine

• Control• Requires pancreatic

enzymes & bile to complete digestion

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Large Intestine

• Extends from ileocecal valve to anus• Regions

– Cecum – Appendix

– Colon• Ascending

• Transverse

• Descending

– Rectum

– Anal canal

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The large intestines is responsible for :-water reabsorption-absorption of vitamins produced by normal bacteria in the large intestines-Packaging and compacting waste products for elimination from the body.

-** because there are no villi in the large intestines, little nutient absorption occurs here.***-Approximately 1.5metres long 7.5 cm in diametre, large intestine is divided into 3 main regions; the cecum, colon, and rectum.-A pouch-shaped structure, the cecum recieves any undigested food ,such as cellulose and water from the ileum of the S.I.-The infamous appendix is attached to the cecum, about 9cm long, the appendix is a slender, hollow dead-end tube lined with lymphatic tissue.

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Because it possesses lymphatic tissue it helps to fight infection ,and also discovered to replenish the beneficial bacteria in our digestive tract.Appendicitis??Peristalsis continues in the large intestine but at a slower rate. As these slower, intermittent waves move fecal matter toward the rectum, water is removed, turning the feces from a watery soup to a semisolid mass.

Some of the water (used in digestion) and electrolytes are reabsorbed by the cecum and asc. Colon. Although this is a relatively small amount of water reabsorbed, it is crucial in maintaining the proper fluid balance in the body.As the rectum fills up with feces, a defecation reflex occurs, which causes rectal muscles to contract and anal muscles to relax.

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Defecation is controlled by a combination of voluntary and Involuntary reflexes.2 sphincters sorround the anal opening, IAS AND EAS. When feces enters the rectum the wall stretches, triggering the defecation reflex.Diarrhea ----- if fecal matter moves through the large intestines too rapidly, not enough water is adequately reabsorbed.

Constipation----- if the fecal matter remains too long in the large intestines, too much water is removed. Feces hardens.Functions of the large intestines:I bacteria aids further break down of indigestible material.II produce B- complex vitaminsIII produces most of the vitamin k****bacteria outside the intestinal wall in the blood stream, could be fatal***

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Anatomy of the Large Intestine

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Large Intestine

• Histology– No villi– No permanent circular folds– Smooth muscle

• Taenia coli

• Haustrations

– Epiploic appendages– Otherwise like rest of Gl tract

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Large Intestine

• Functions:– Mechanical digestion

• Haustral churning

• Peristalsis

– Chemical digestion – Bacterial digestion

• Ferment carbohydrates

• Protein/amino acid breakdown

– Absorbs•More water•Vitamins

– B– K

– Concentrate/eliminate wastes

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Feces Formation and Defecation

• Chyme dehydrated to form feces.

• Feces composition– Water– Inorganic salts– Epithelial cells– Bacteria– Byproducts of digestion

• Defecation– Peristalsis pushes feces

into rectum– Rectal walls stretch

• Control– Parasympathetic

– Voluntary

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Liver

• Location– R. Hypochondrium– Epigastric region

• 4 Lobes– Left – Quadrate– Caudate– Right

• Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

• Weighing approx.1.5kg(3.3 pounds).

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Liver

• Functions– Makes bile

• Detergent – emulsifies fats• Release promoted by:

– Vagus n.– CCK– Secretin

• Contains:– Water– Bile salts– Bile pigments– Electrolytes– Cholesterol– Lecithin

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Liver– Detoxifies/removes

• Drugs• Alcohol

– Stores• Glycogen• Vitamins (A, D, E, K)• Fe and other minerals• Cholesterol

– Activates vitamin D– Fetal RBC production– Phagocytosis– Metabolizes absorbed food

molecules• Carbohydrates• Proteins• Lipids

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Liver

• Dual blood supply– Hepatic portal vein

• Direct input from small intestine

– Hepatic artery.• Direct links to heart

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The liver is the largest glandular organ in the body and the largest organ in the abdomino -pelvic cavity.This organ performs many functions that are vital for survival.The hepatic portal vein (carrying blood full of the end products of digestion ) and the hepatic artery (providing oxygen rich blood).This blood flows past the hepatocytes(liver cells),which process the substances in that blood. Blood then leaves each lobule via a central vein ,which drains into the hepatic vein.The hepatic vein then drains into the IVC, returning the processed blood back to circulation.The liver plays a central role in regulating the metabolism of the body.

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Functions of the liver:-Detoxifies(removes poisons) the body of harmful substances such as certain drugs and alcohol-Creates body heat -- destroys old blood cells and recycles their usable parts while eliminating unneeded parts such as the pigment bilirubin.--forms plasma proteins,such as albumin and globulins--produces clottin factors fibrinogen and prothrombin-- creates the anticoagulant heparin--manufactures bile which is needed in the digestion of fats---stores and modifies fat for more efficient usage by the body cells.--synthesis of urea,a byproduct of protein metabolism,so it can be eliminated from the body.--stores simple sugar glucose as glycogen--stores iron and vitamins A,B12,D,E,and K--produces cholesterol.

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The gall bladder is a sac shaped organ approx. 7.5 to 10cm long.While it is storing the bile,it concentrates the bile,this makes it 6 to 10 times more concentrated than it was in the liver.

Pancreas: the exocrine portion of this gland secretes buffers and digestive enzymes through the pancreatic duct to the duodenum. These buffers are needed to neutralise the acidity of chyme in the S.I, with the buffer pH ranging from 7.5- 9.0The digestive enzymes excreted by the pancreas are:-Carbohydrases-Lipases-Proteinases and nucleases

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The Duodenum and Related Organs

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The Organs and Positions in the Abdominal Cavity

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Structures of the Alimentary Canal

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The walls of the alimentary canal:The entire alimentary canal from the esophagus to the anal canal.

Innermost layer that lines the lumen of the canal is the mucosa (mucous membrane).

The mucosa layer is composed mainly of: (i) surface epithelium (ii) connective tissue and(iii) thin smooth muscle layer sorrounding it.

The mucosa posses cells that secrete digestive enzymes to break down food and goblet that secrete mucus for lubrication.

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(2) submucosa: composed of soft connective tissue,which contains blood vessels,lymphatic tissue, similar to tonsils, called peyer’s patches and nerve endings.(3) Muscularis externa: composed of 2 layers of smooth muscle.Innermost circular layer and outer longitudinal layer.The third additional layer is the oblique smooth, but it only found in the stomach.

The outer most layer is serosa, composed of a single layer of thin flat serous fluid ,producing cells supported by connective tissue.Like other serous membranes it has two layers :(1) Parietal layer and (2) visceral layer.

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The visceral peritoneum covers the abdominal organs, and the parietal peritoneum lines the wall of the abdominal cavity. allows the friction –free movement of the digestive organs against the abdominopelvic cavity.

The esophagus differs from the rest of the alimentary canal that it possesses only a loose layer of connective tissue called the adventitia peritoneum.The stomach can hold up to 4 litres.It takes about four hours for the stomach to empty after a meal.Liquids and carbohydrates pass through fairly quickly.Proteins takes a little more time, and fats takes even longer, usually between 4 to 6 hours.Secretes gastric acid and enzymes, which mixes with food, chemical digestion.Absorb small amounts of water and substances on a limited bases,although alcohol is absorbed.

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Basic overview:

The funnel-shaped,terminal end of the stomach is called pylorus.Most of the digestive work of the stomach is performed by the pyloric region.

The orientation of the muscle in the stomach and muscular arrangement enables the stomach to churn food as it mixes it with gastric juice excreted by gastric glands from gastric pits .

With the combined efforts of muscle action and gastric juices ,both physical and chemical digestion occur in the stomach.

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Gastric juice is a general term for a combination of HCL, Pepsinogen and mucus,(1.5ml) is produced per day by the gastric glands.Gastric glands and their functions.

Digestive cells secretion type functionChief cells pepsinogen begins pro.digeParietal cells HCL activates pepsino intrinsic factor aids in B12 absMucous cells alkaline mucus protect stom lin.

Endocrine cells hormone gastrin stim.gastric gland

**the stomach’s activity is controlled by the parasympathetic nervous system ,i.e the vagus nerve .once stimulated ,the stomach ‘motility is increased and does the secretory rates of the glands.

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Three distinct phases of gastric juice production:(1)Cephalic phase:-Occurs as a result of site or smell of food.Sensory impulses stimulates the parasympathetic nervous system through the medulla oblongata, and the release of gastrin is increased.Gastrin reaches the stomach ,gastric activity is increased.(2) Gastric phase;Two-thirds of the gastric juices are secreted as the food moves to the stomach. as food gets into the stomach, the stomach distends, it sends signals back to the brain ,which fires a reply to the gastric glands to step up their work.As chyme passes into the pyloric sphincter to the first part of the small intestine, this begins the intestinal phase of gastric juice regulation.

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As the duodenum distends and senses the activity of the chyme, intestinal hormones are released that cause the gastric glands in the stomach to decrease gastric juice secretion because it is no longer needed now that the food bolus (now called chyme) has left the stomach.Once the chyme begins its movement through the duodenum and on to the rest of the small intestines,those inhibitory responses are halted so gastric juice production can continue once again when a new bolus of food enters the stomach.

***The rate of movement of chyme is very important.***If chyme passes too quickly through the stomach, the food particles may not be sufficiently mixed with gastric juices, leading to____________???Chyme that is not given time to be neutralised may lead to acidic erosion of the intestinal lining.

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(1) The finger-like projections of the wall of the small intestines is called:(a)Microvilli(b)Villi(c)Lacteals(d)Rugae(2) The duodenum releases this hormone to decrease gastric activity:(a)Cck(b)Gastrin(c)Secretin(d)Both a and c(3) This organ does most of the digestion and absorption in your digestive tract:(a)s.i(b)L.i(c)Liver

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Commonly used abdominal incisions:Any incisions or scars present? Presence of an incision may speculate what the surgeon might have done.A.Subcostal incision on the right---------------------open bladder surgery (cholecystectomy).B.Barely visible round scars around the umbilicus may suggest closed or laparoscopic cholecystectomyC.Left subcostal incision----------------to approach the spleenD.Suprapubic incisions is used to access pelvic organs----------------(C-section,hysterectomy)E.An oblique incision approximately at the meeting point of umbilical region and ® inguinal region is frequently used for appendeceptomy.F.A scar in one or both inguinal region may be indicative of previous hernia surgery.