Digestive system

The Digestive System

Organs of the Digestive System Two main groups Alimentary canal – continuous coiled hollow tube, extends from the oral entrance up to the anal exit. Accessory digestive organs, enclosed or connected to the alimentary canal.

Digestive Mucosa The Digestive Epithelium Mucosal epithelium is simple or stratified Depending on location, function, and stresses: oral cavity, pharynx, and esophagus are subjected to mechanical stress. They are lined by stratified squamous epithelium stomach, small intestine, and most of large intestine are sites for digestion and absorption. They are lined by simple columnar epithelium with mucous (goblet) cells.

Alimentary Canal It consists of the long, continuous tube that extends from the oral cavity to the anus. Along this tube, the breakdown of food or digestion occurs, absorption of nutrients and elimination of waste products also takes place. The final product of this process, a material called feces is discarded through the anal aperture.

Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine (duodenum, jejunum, ileum) Large intestine (cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum) Anus

Accessory Digestive Organs Salivary glands (Parotids, Sublingual and Submandibular) Tongue Teeth Liver and Gallbladder Pancreas

Mouth (Oral Cavity) Anatomy Lips (labia) – protect the anterior opening Cheeks – form the lateral walls Hard palate – forms the anterior roof Soft palate – forms the posterior roof Uvula – fleshy projection of the soft palate Figure 14.2a

Oral Cavity 11/15/2018 ALFONSO A. PINO. MD.

Actions of the Mouth Mastication (chewing) of food Mixing masticated food with saliva Initiation of swallowing by the tongue Allowing for the sense of taste

Salivary Glands

Salivary Secretions Salivary Glands Produce 1.0–1.5 liters of saliva each day 70% by submandibular glands 25% by parotids 5% by sublingual glands

Nasopharynx – not part of the digestive system Pharynx Anatomy Nasopharynx – not part of the digestive system Oropharynx – posterior to oral cavity Laryngopharynx – below the oropharynx and connected to the esophagus Figure 14.2a

Pharynx Function Serves as a passageway for air and food Food is propelled to the esophagus by two muscle layers Longitudinal inner layer Circular outer layer Food movement is by alternating contractions of the muscle layers (peristalsis)

Esophagus Runs from pharynx to stomach through the diaphragm; it is around 10 inches (25 cm) long Conducts food by peristalsis (slow rhythmic squeezing) Passageway for food only It connects to the stomach at the cardial region, a lower esophageal sphincter prevents the reflux of gastric acid content into the esophagus

The Esophagus

Stomach Anatomy

The Stomach

Gastric Mucosa, its secretions Simple columnar epithelium lines the interior of the stomach Mucous Cells: secrete a thick mucus to protect the gastric mucosa Parietal cells: Secrete Hydrochloric acid a potent antiseptic and the initiator of the breakdown of proteins. Also secrete Intrinsic factor for the absortion of Complex B vitamines Chief cells: Secrete a non active enzyme, Pepsinogen, once activated to Pepsin in the gastric acid medium, is one of the several digestors of proteins

Gastric Mucosa

Stomach: Functions Acts as a storage tank for food Site of food breakdown, mainly by mechanical digestion Chemical breakdown of protein begins Delivers chyme (processed food) to the small intestine

Small Intestine The body’s major digestive organ Site of nutrients absorption into the blood Muscular tube extending form the pyloric sphincter to the ileo-cecal valve Suspended from the posterior abdominal wall by the mesentery

Subdivisions of the Small Intestine Duodenum Attached to the stomach Curves around the head of the pancreas Jejunum Attaches anteriorly to the duodenum Ileum Extends from jejunum to large intestine

Small Intestine

Small Intestine: Duodenum The C shaped duodenum is just around 10 inches (25 cm.) long. It forms a “ picture frame” around the head of the pancreas It receives chyme from the stomach and is the site where most of the digestive process takes place The pancreatic duct and the bile duct open into the duodenum bringing their digestive secretions into its lumen Trypsinogen, a proenzyme secreted by the pancreas activates in the duodenum to Trypsin, the final digestor of proteins

Small Intestine: Jejunum & Ileum Jejunum: About 8 feet (2.5 m) long. The bulk of absorption of nutrients occurs in this segment of the small intestine. The presence of villi and microvilli in the jejunal mucosa increases greatly its surface of absorption Ileum: The longest segment of the small intestine, around 11.5 feet (3.5 m) long. Reabsorption of water and electrolytes occurs in the ileum. It ends opening into the proximal end of the colon, the Cecum. An sphincter (ileo-cecal valve) controls the flow of material from the ileum into the cecum

Villi of Small intestine Fingerlike projections Lined by simple columnar epithelium carpeted by microvilli Each villus contains: Absorptive cells Blood capillaries Lacteals (specialized lymphatic capillaries)

Pancreas A “fishlike” organ located in transverse orientation in the abdomen Its excretory duct, (Wirsung’s duct) runs along the full length of the organ and opens into the Duodenum, after merging with the Common Bile duct (Ductus Choledocus) An Accessory pancreatic duct (Santorini’s duct) often opens into the duodenum, usually at a proximal location from the main pancreatic duct. The exocrine cells of the pancreas (acinar and epithelial cells) secrete sodium bicarbonate and the main lipid digestive enzyme, Lipase

The Pancreas

Liver Located in the right upper abdominal quadrant, it is the most voluminous viscera in the body Consists of four lobes: Right lobe, left lobe, quadrate lobe and caudate lobe Right and left lobes are separated by the Falciform ligament. Each lobe is organized in around 100.000 lobules, each one is a secretory unit formed of thousands of hepatocytes, the productors of Bile, a catabolite of hemoglobin, whose action is the breakdown of the large lipid particles in the chyme, a process called fat emulsification.

Liver: Anterior & Inferior Views

Gallbladder A small, muscular sac, located inferior to the right hepatic lobe, its function is to store and concentrate the bile between meals, and pouring it into the duodenum for the breakdown of lipids. Contractions of the gallbladder wall occur under the stimulus of a hormone released by the duodenal mucosa (Cholecystokinin). This hormone also stimulates pancreatic secretion and relaxes the hepato-pancreatic sphincter

Bile Tree A I B D H C G E F Right & Left hepatic ducts Common hepatic duct Cystic duct Common bile duct (Ductus Choledocus) Main Pancreatic Duct (Wirsung’s duct) Duodenal Papilla (Papilla of Vater) Duodenum Accesssory pancreatic duct (Duct of Santorini) Gallbladder I B D C H G E F

Structures of the Large Intestine Around 4.9 feet (1.5 m) long, and 3 inches (7.5 cm) in diameter Colon -Cecum -Ascending -Transverse -Descending -“S-shaped” sigmoid Rectum Anus – external body opening, guarded by two sphincters; the internal anal sphincter formed of smooth muscle and thus involuntary, and the external anal sphincter, a ring of skeletal muscle and hence under voluntary control

The Large Intestine

Functions of the Large Intestine Reabsorption of water, small amounts of bile salts and some vitamins (like Vitamin K, synthesized by colonic bacteria) Eliminates indigestible food from the body as feces Does not participate in digestion of food Goblet cells produce mucus to act as a lubricant