Digestive System Part 2 A&P Lecture PDF

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Digestive System Part 2 The Pharynx The pharynx (throat) is involved in both digestion and respiration. It receives food and air from the mouth, and air from the nasal cavities. When food enters the pharynx, involuntary muscle contractions close off the air passageways.

The Esophagus The esophagus is a hollow muscular tube that is about 25 cm long and 2 cm wide. It conveys solid food and liquids to the stomach. It begins posterior to the cricoid cartilage and ends in the stomach. It is innervated by fibers from the esophageal plexus

Passage of Food Through Esophagus The upper esophageal sphincter, which is the continuation of the inferior pharyngeal constrictor, controls the movement of food from the pharynx into the esophagus. The upper two-thirds of the esophagus consists of both smooth and skeletal. Food passes from the esophagus into the stomach at the lower esophageal sphincter, which is also known as the gastroesophageal or cardiac sphincter.

Anatomy and functions of the Esophagus

The Stomach Functions of the Stomach 1. The stomach mixes saliva, food, and gastric juice to form chyme. 2. It serves as a reservoir for food before releasing it to the small intestine. 3. It secretes gastric juice that contains HCL whose function is to kill bacteria, pepsin which begins the digestion of protein, and an intrinsic factor which aids absorption of Vitamin B12. 4. It secretes gastrin into the blood.

Gastrin It’s a group of digestive hormones secreted by the wall of the pyloric end of the stomach (the area where the stomach joins the small intestine). It is secreted by G cells in the duodenum when it is exposed to incompletely digested proteins (cleave the larger proteins into their smaller forms). It promotes increased stomach motility. It stimulates acids and enzyme production.

Anatomy of the Stomach The stomach is shaped like an expanded J ● It’s short lesser curvature forms medial surface ● It’s long greater curvature forms lateral surface

Regions of the Stomach The stomach is divided into four region that includes: ● Cardia ● Fundus ● Body ● Pylorus

Histology of the Stomach The stomach wall is composed of the same basic layers of the rest of the GI tract with certain modifications. They include: ● Mucosa ● Submucosa ● Muscularis ● Serosa

Mucosa It is composed of Simple columnar epithelial cells. The Lamina propria is composed of areolar connective tissue

Submucosa The submucosa is made up of various connective tissues, blood vessels, and nerves. Connective tissues support the tissues of the mucosa and connect it to the muscularis layer. The blood supply of the submucosa provides nutrients to the wall of the stomach connective tissue.

The Stomach Lining Gastric Pits They are shallow depressions that open onto the gastric surface. Gastric glands have 3 types of cells, and they include: 1. Mucous neck cells:They are the cells that produce mucus. 2. Parietal Cells: They produce the intrinsic factor that is needed for the absorption of Vitamin B12. 3. The chief (zymogenic) cells: They secrete pepsinogen and gastric lipase

Gastric Glands They are located in the fundus and body of stomach and they extend deep into the underlying of the lamina propria Each gastric pit communicates with several gastric glands

Types of Secretory Cells ●

Goblet cells- they secrete mucus that protects the stomach lining.

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Parietal cells- They secretes gastric acid for example hydrochloric acid (HCL)

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Chief cells- They secretes pepsinogen which is protease precursor.

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D cells- They secretes somatostatin which acts as an inhibition for acid secretion.

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G cells- They secretes gastrin which stimulates acid secretion.

Muscularis Muscularis mucosae and muscularis externa contains extra layers of smooth muscle cells in addition to circular and longitudinal layers

Serosa This is the last and outermost layer. It’s the lining that wraps around the stomach to confine it. After you chew and swallow food, it enters your stomach from the food pipe. At this point, pepsin and hydrochloric acid are releases

Digestive Hormones in the GI tract This hormones includes ● Gastrun ● Cholecystokinin (CCK) ● Secretin ● Vasoactive intestinal Peptide (VIP) ● Gastric inhibitory polypeptide (GIP) ● Moblin ● Somatostatin

Gastric Secretion

When the mucosal barrier breaks down: Ulcers The Stomach Ulcers

The Small Intestine They play a key role in the digestion and absorption of nutrients. 90% of nutrient absorption occurs in the small intestine.

The Duodenum The segment of the small intestine closest to the stomach It is about 25 cm (10 in.) long This segment of the small intestine is the “Mixing bowl” that receives chyme (Mixture of secretions and food in the stomach) from the stomach and mix it with digestive secretions from the pancreas and liver The duodenum has few plicae and also have small villi

Functions of the Duodenum ●

To receive chyme from stomach

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To neutralize acids before they can damage the absorptive surfaces of the small intestine

The Jejunum This Is the middle segment of the small intestine It is about 2.5 meters (8.2 ft) long. It Is the location of most ot the chemical digestion and nutrient absorption

The Ileum This is the final segment of the small intestine It is about 3.5 meters (11.48 ft) long, making it the longest segment of the small intestine. This is the segment that connects and joins to the large intestine.

Histology of the small intestine: Circular Folds/Plicae The small intestine is also called plicae circulares. Transverse folds are in the intestinal lining. They have permanent features that do not disappear when small intestine fills

Glands The small intestine has Goblet cells that are between the columnar epithelial cells. This cell eject or releases mucus to the intestinal surfaces

Villi It’s a series of fingerlike projections in the mucosa of small intestine. It is covered by simple columnar epithelium:–covered with microvilli

The Large Intestine The large intestine is also called the large bowel and it is about 1.5 meters long and 7.5 cm wide. It is horseshoe-shaped. It extends from the end of the ileum to the anus. It lies inferior to the stomach and liver. It frames the small intestine

Functions of the Large Intestine ●

Reabsorption of water

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Compaction of intestinal contents into feces

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Absorption of important vitamins produced by bacteria

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Storage of fecal material prior to defecation

Vitamins Produced in the Large Intestine The large intestine produces three vitamins and they include;

1. Vitamin K It is a fat-soluble vitamin that is required by the liver for synthesizing 4 clotting factors, including prothrombin.

2. Biotin It is a water-soluble vitamin that is important in glucose metabolism

3. Pantothenic acid It is a water-soluble vitamin that is required in the manufacture of steroid hormones and some neurotransmitters

Parts of the Large Intestine The large intestine is divided into three parts which includes; 1. Cecum – This is the pouch-like first portion. 2. Colon – This is the largest portion. 3. Rectum– This is the last 15 cm of the digestive tract

The Cecum This is an expanded pouch It receives material arriving from the ileum, which is a segment of the small intestine. It stores materials and begins compaction

The Appendix It is also called vermiform appendix It is a slender, hollow appendage that is about 9 cm long. It is dominated by lymphoid nodules, a lymphoid organ. It Is attached to the posteromedial surface of the cecum Mesoappendix part connects appendix to the ileum and cecum

The Colon This part has a larger diameter and thinner wall than small intestine The wall of the colon forms a series of pouches called haustra. Haustra permit expansion and elongation of colon

Colon Muscles The colon muscles have three longitudinal bands of smooth muscle called the teniae coli that run along the outer surfaces of the colon. These bands are deep to the serosa, and they are similar to the outer layer of muscularis externa. It’s muscle tone in taeniae coli creates the haustra

Serous Membrane of the Colon It contains numerous fatty appendices (also known as epiploic appendage)

The Rectum This is the last part of the colon, we have the recturm where food near the sigmoid colon enters the rectum near the sacral vertebrae. They form the last 15 cm of digestive tract. It is an expandable organ for the temporary storage of feces. The movement of fecal material into rectum triggers an urge to defecate.

The Anal Canal It is the the last portion of the rectum It contains small longitudinal folds called anal columns.

Anus It is also called anal orifice It is the exit of the anal canal

Anal Sphincters They are two type of sphinter in the anal, they include the : ● Internal anal sphincter It is a circular muscle layer of muscularis externa that has smooth muscle cells,this means it is not under voluntary control. ● External anal sphincter It encircles a distal portion of the anal canal. It is a ring of skeletal muscle fibers that is under voluntary control.

Small intestine and Associated Glandular Organs 1. Stomach- It secretes gastric juices, stomach acids and pepsin. 2. Pancreas– It produces digestive enzymes and buffers. 3. Liver– It secretes Bile that is produced in the liver. The bile contains buffers and bile salts, and it is stored in the gallbladder. The bile is discharge into small intestine

The Pancreas The pancreas is a compound tubuloalveolar gland. It lies posterior to the stomach, from the duodenum it is toward the spleen. It is bound to the posterior wall of the abdominal cavity It is wrapped in a thin, connective-tissue capsule.

Regions of the Pancreas The pancreas is divided into three regions.

1. Head This is the broad region in the loop of the duodenum.

2. Body This part is slender and it extends toward the spleen.

3. Tail This part is short and rounded

● Duct of Wirsung This is a large pancreatic duct that delivers digestive enzymes and buffers to duodenum.

Lobules of the Pancreas The pancreas lobules are separated by the connective tissue partitions (septa). It contains blood vessels and tributaries of pancreatic ducts. In each lobule, ducts branch repeatedly and end in the pancreatic acini, a blind pocket. They are lined with simple cuboidal epithelium and contain scattered pancreatic islets which is an endocrine tissue. This tissue is about 1% of pancreatic cells and is scattered around the tissue. The pancreas is formed in lobuled because of the division of connective tissue. Each lobes have ducts and pancreatic islets.

Pancreatic Enzymes 1. Pancreatic alpha-amylase It is a carbohydrase, that is it breaks down starches and it is similar to salivary amylase.

2. Pancreatic lipase It breaks down complex lipids, and releases products like, fatty acids that are easily absorbed

3. Nucleases It breaks down nucleic acids.

4. Proteolytic enzymes It breaks certain proteins apart.

Proteases break large protein complexes. Peptidases (trypsin) break small peptides into amino acids. This enzyme is 70% of all the pancreatic enzymes produced. Proteolytic enzymes are secreted as an inactive form called proenzymes. Trypsin is secreted as trypsinogen an inactive form and it get activated after reaching small intestine

Functions of the Pancreas 1. Endocrine cells It has an endocrine cell called the pancreatic islets, that secrete insulin and glucagon into the bloodstream.

2. Exocrine cells The pancreas cell is the acinar cell, this is an epithelial cell of the duct system. These cells are secreted into the duodenum like pancreatic juices.

Pancreatic Secretion The pancreatic juices secreted about 1000 ml (1 qt) per day. The juices contain water, bicarbonate, and all the pancreatic enzymes. It is controlled by hormones from duodenum. Also, the juice contain pancreatic enzymes

The Liver It is the largest visceral organ, and weighs about 1.5 kg. It lies in the right hypochondriac and epigastric regions. It extends to the left hypochondriac and umbilical regions It performs essential metabolic and synthetic functions, this makes it an important organ.

Functions of the Liver 1. Metabolic regulation 2. Hematological regulation 3. Bile production

Metabolic Regulation The liver regulates the following: ● Composition of circulating blood ●

Nutrient metabolism

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Waste product removal

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Nutrient storage

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Drug inactivation

Anatomy of the Liver The liver is wrapped in a tough fibrous capsule. It is covered by a visceral peritoneum. The liver is divided into primary lobes, a large right lobe and a much smaller left lobe. The liver is connected to the abdominal wall and diaphragm by some ligament, and they included ● Falciform ligament ● Two lateral ligament ● Coronary ligament ● Ligamentum teres hepatis It is divided into lobes, which includes ● Right lobe ● Left lobe ● Quadrate lobe ● Caudate lobe.

The Posterior Surface This part is a depression at the inferior vena cava marks division between the right lobe and the small caudate lobe.

The Falciform Ligament This is on the anterior surface. It divides the liver into a left lobe and right lobe. This ligament helps the stability of the liver and attaches the liver to the abdominal wall.

The Quadrate Lobe This is Inferior to the caudate lobe. It is located between the left lobe and the gallbladder. This lobe is important because it is close to the gallbladder.

Common Bile Duct Remember the liver produces the bile, the gallbladder stores the bile and they have some ducts that take the bile to the small intestine. The common bile duct is going to meet with the pancreatic bile and it's going to meet in a structure called the Ampulla of Vater. This duct is from the liver and gallbladder. It meets the pancreatic duct near duodenum.

Duodenal Ampulla It is also called Ampulla of Vater, which is a chamber that receives secretions from the common bile duct and the pancreatic duct. It is located halfway along the length of the duodenum

Histology of the Liver ● Hepatocytes It is a major functional cell.

● Bile canaliculi It is a small ducts between hepatocyte

● Hepatic sinusoids It is highly permeable capillaries

● Portal triad This means the three structures are together, that is, hepatic artery, hepatic vein and bile duct. .

● Bile Canaliculi The liver secretes bile fluid into a network of narrow channels called the bile canaliculi that is between opposing membranes of adjacent liver cells. It is outward, away from the central vein. It is connected with fine bile ductules which carry bile to bile ducts in the nearest portal area Basically, bile canaliculi takes the bile into the ductulus. They communicate with a close portal area to transport to the bile.

Functions of Bile ●

Emulsification- This is when bile salts break droplets apart by increasing the surface area exposed to enzymatic attack and creating tiny emulsion droplets coated with bile salts.

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They help in fat absorption.

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They neutralize gastric acid.

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They help in the secretion of bilirubin.

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They emulsion triglycerides and phospholipid.

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They prepare the triglycerides and phospholipids for the pancreatic enzymes to break them down.

The Bile Duct System They extend outward away from the central vein. It connects with the fine bile ductules which carry bile to bile ducts in the nearest portal area. From common hepatic duct to either the common bile duct, which empties into duodenal ampulla or the cystic duct, which leads to gallbladder. From the gallbladder, the cystic duct would meet the common hepatic duct that will then form the common hepatic duct that will then form the common bile duct that will end in the ampulla of the vater. And so therefore, all the secretion of bile will go to the duodenum from the ampulla of the vater.

The Right and Left Hepatic Ducts The right and left hepatic duct are going to meet with the cystic duct, and this duct will end in the duodenum. The duct also meets with the pancreatic duct. It extends from the outward, away from the central vein. Bile flows from the common hepatic duct to either the common bile duct, which empties into duodenal ampulla or the cystic duct, which leads to gallbladder.

The Common Bile Duct This duct is formed by the union of the cystic duct and the common hepatic duct. This passes within the lesser omentum toward the stomach. It penetrates wall of duodenum and meets pancreatic duct at duodenal ampulla

Metabolic Activities of the Liver ●

Carbohydrate metabolism.

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Lipid metabolism

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Amino acid metabolism

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Waste product removal known as detoxification.

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Vitamin storage

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Mineral storage

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Drug inactivation

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Synthesis of plasma membrane

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Bile acid metabolism

The Gallbladder The gallbladder is the sac that will contain the bile and is located in the fossa on the posterior surface of the liver’s right lobe. It is a pear-shaped, muscular sac It stores and concentrates bile prior to excretion into small intestine

Regions of the Gallbladder 1. Fundus 2. Body 3. Neck- It is the past that’s going to meet the cystic duct.

The Cystic Duct This extends from gallbladder. It makes a union with the common hepatic duct to forms the common bile duct

The Common Bile Duct This duct meets the pancreatic duct at duodenum before emptying into duodenal ampulla

The Duodenal Ampulla This part receives buffers and enzymes from pancreas, bile from the liver and gallbladder. This part opens into the duodenum at duodenal papilla.

Gallbladder Function It stores bile and releases it to into duodenum but only under the stimulation of hormone cholecystokinin(CCK)

The Gallbladder & Bile Modification A full gallbladder contains 40–70 ml bile. Bile composition gradually changes in gallbladder, bile salts and solutes become concentrated and water is absorbed

Gallstones Gallstones are crystals of insoluble minerals and salts. They are formed if bile is too concentrated. Small stones may be flushed through bile duct and excreted...