Digestive system

pages 65 - 79

The organs pf the digestive system are separated into what categories? (2)

• accessory digestive organs

• organs of the gastrointestinal (digestive) tract

Describe the digestive tract

• continuous muscular tube composed of skeletal muscle and smooth muscle

List the organs of the digestive tract (6)

• mouth

• pharynx

• esophagus

• stomach

• small intestine

• large intestine

List the accessory digestive organs (8)

• teeth

• tongue

• gallbladder

• digestive glands

  • liver

  • pancreas

  • salivary glands

    • parotid glands

    • submandibular glands

    • sublingual glands

True or False: food does not pass through the accessory digestive organs

True

List the functions of the digestive system (8)

• ingestion

• mastication

• propulsion

• mixing

• secretion

• digestion

• absorption

• excretion

Describe the peritoneum

• membrane that lines the walls and organs of the abdominal cavity

• two portions

  • visceral peritoneum

  • parietal peritoneum

Describe the visceral peritoneum

• covers the external surface of the organs within the abdominal cavity

Describe the parietal peritoneum

• lines the internal surface of the walls of the abdominal cavity

The space between the two layers of the peritoneum is called the…

peritoneal cavity

What is the peritoneal cavity filled with?

peritoneal fluid

Many organs of the abdominal cavity are held in place by what structures?

mesenteries

Describe mesenteries

• fused double layer of peritoneum that extends from the body wall to a digestive organ

Describe retroperitoneal organs

• organs that lie against the posterior abdominal wall (not held in place by a mesentery)

List the associated structures of the oral cavity (6)

• lips

• cheeks

• palate

• tongue

• teeth

• salivary glands

Describe the lips and cheeks

• composed mainly of muscles

  • orbicularis oris (lips)

  • buccinator (cheeks)

• involved with processes of mastication and speech

Describe the palate

• consists of two portions

  • hard palate

    • forms the roof of the mouth

    • tongue forces food against the hard palate during chewing

    • also plays a role in speech

  • soft palate

    • posterior to the hard palate

    • composed of skeletal muscle

    • closes off the nasopharynx when we swallow

Describe the tongue

• aids in

  • chewing

  • swallowing

  • speech

Describe the salivary glands

• produce and secrete saliva

• three pairs

  • parotid (one anterior to each ear)

  • submandibular (inferior to mandible)

  • sublingual (inferior to tongue)

List the functions of saliva (3)

• cleanses the mouth

• dissolves food chemicals so that they can be tasted

• contains the enzyme salivary amylase (begins breakdown of starchy foods)

Describe the pharynx

• throat

• food from the oral cavity passes through the fauces

• food then passes into the laryngopharynx

Describe the esophagus

• food passes from the laryngopharynx into the esophagus (carries food into the stomach)

• lined with stratified squamous epithelium

• no digestion “starts” in the esophagus

Describe the stomach

• food is broken down mechanically and chemically

  • three layers of smooth muscle mechanically digest the food

  • gastric glands (located in the lining of the stomach) release substances that chemically digest the food

List the major structures of the stomach (9)

• cardiac sphincter

• cardiac region

• fundus

• body

• greater curvature

• lesser curvature

• pyloric region

• pyloric sphincter

• rugae

Describe the histology of the stomach

• the internal surface of the stomach is lined with simple columnar epithelium

• the epithelium lining of the stomach contains gastric pits

  • gastric pits are the openings for the gastric glands

    • produce gastric juice

  • the highly acidic gastric juice (pH 1.5 to 3.5) contains substances that aid in chemical digestion

  • the substances that compose gastric juice are produced by the cells that form gastric glands

    • mucous cells

    • parietal cells

    • chief cells

    • endocrine cells

What is the function of simple columnar epithelium?

allows for absorption and secretion

List the cells that form the gastric glands (4)

• mucous cells

• parietal cells

• chief cells

• endocrine cells

Describe the small intestine

• digestion is completed and nearly all absorption occurs

• extends from the stomach to the large intestine

• ~20 ft long in a cadaver (shorter during life due to muscle tone)

• divided into three parts

  • duodenum

  • jejunum

  • ileum

• contains modifications that increase surface area, which allows for increased absorption

Describe the duodenum

• first portion of the small intestine

• wraps around the head of the pancreas

• lined with simple columnar epithelium

• contains glands which produce an alkaline substance that neutralizes acidic chyme

Describe the jejunum

• middle portion of the small intestine

• extends from duodenum to ileum

Describe the ileum

• last portion of the small intestine

• joins the cecum of the large intestine

Describe the modifications of the small intestine that increase surface area

• the overall length of the small intestine

• the lining of the small intestine is folded (circular folds) and has tiny fingerlike projections called villi

  • villi are lined with simple columnar epithelial cells

    • the cells contain microvilli which increase surface area

Describe the liver

• second largest organ in the body

• largest gland in the body

• located in the upper right quadrant of the abdomen

List the major structures associated with the liver (5)

• right lobe

• left lobe

• caudate lobe

• quadrate lobe

• hepatic porta

List the functions of the liver (3)

• stores glucose as glycogen

• takes waste products out of the blood

• hepatocytes of the liver produce bile

  • bile is stored in the gallbladder

List the ducts of the liver (5)

• right hepatic duct

• left hepatic duct

• common hepatic duct

• cystic duct

• common bile duct

Describe the ducts of the liver

• the right and left hepatic ducts unite to form the common hepatic duct

• common hepatic duct carries bile away from the liver

• common hepatic duct and cystic duct (from gallbladder) unite to form the common bile duct

• the common bile duct unites with the pancreatic duct to form the hepatopancreatic ampulla (ampulla of vater)

• the hepatopancreatic ampulla drains via the major duodenal papilla into the duodenum of the small intestine

Describe the pancreas

• located in the abdomen, partially behind the stomach

• is an exocrine and endocrine gland

  • substances produced by the endocrine portion of the pancreas include

    • insulin and glucagon

  • substances produced by the exocrine portion of the pancreas include

    • enzymes that aid in digestion of carbohydrates, fats, and proteins in the small intestine

    • HCO₃^- that neutralize acidic chyme in small intestine

    • exocrine pancreatic secretions exit the pancreas via the pancreatic duct

Describe the large intestine

• extends from the small intestine to the anus

List the functions of the large intestine (2)

• absorption of water

• elimination of waste products (feces)

List the divisions of the large intestine (4)

• cecum

• colon

• rectum

• anal canal

Describe the cecum of the large intestine

• first part of the large intestine

• joins with ileum of small intestine

  • forms the ileocecal junction

• the vermiform appendix is attached to the cecum

Describe the vermiform appendix

• plays a role in immunity

• can collect bacteria

Describe the colon of the large intestine

• consists of the

  • ascending colon

  • right colic (hepatic) flexure

  • transverse colon

  • left colic (splenic) flexure

  • descending colon

  • sigmoid colon

Describe the rectum of the large intestine

• portion of large intestine located between the sigmoid colon and anal canal

• stores feces

Describe the anal canal

• last 2-3 cm of the digestive tract

• extends from the rectum to the anus (external opening of anal canal)

• surrounded by internal and external anal sphincters

  • internal composed of smooth muscle

  • external composed of skeletal muscle

Describe the digestive pathway

• mouth

• fauces

• oropharynx

• laryngopharynx

• esophagus

• cardiac sphincter of stomach

• cardia region of stomach

• body of stomach

• pyloric region of stomach

• pyloric sphincter of stomach

• duodenum of small intestine

• jejunum of small intestine

• ileum of small intestine

• ileocecal valve

• cecum of large intestine

• ascending colon of large intestine

• hepatic flexure of large intestine

• transverse colon of large intestine

• splenic flexure of large intestine

• descending colon of large intestine

• sigmoid colon of large intestine

• rectum of large intestine

• anal canal

• toilet

Describe the biliary pathway

• liver - produces and excrete bile

• right and left hepatic ducts

• common hepatic duct

• cystic duct

• common bile duct

• ampulla of vater & sphincter of oddi

• major duodenal papilla

Identify the image along with the labeled structures and their functions

gastro-esophageal junction

• A: esophagus

  • lined with stratified squamous epithelium

    • protection

• B: stomach

  • lined with simple columnar epithelium

    • allows for absorption and secretion

What protects the simple columnar epithelium (lining of the
stomach) from the harsh acidic environment of the lumen of
the stomach?

Alkaline mucus made by the mucous cells

Identify the image along with the labeled structures

stomach wall

• A: gastric pits

• B: gastric glands

• C: mucous cells

  • line the stomach and gastric pits

What is the function of mucous cells?

Produce alkaline mucus to protect the stomach lining from
the acid

Identify the image along with the labeled structures and their functions

stomach wall

• A: parietal cells

  • make HCl and intrinsic factor

• B: chief cells

  • make pepsinogen (precursor to pepsin)

• C: enteroendocrine cells

  • release hormones that help with digestion

Identify the image along with the labeled structures and their functions

stomach wall

• A: parietal cells

  • make HCl and intrinsic factor

• B: chief cells

  • make pepsinogen (precursor to pepsin)

• C: enteroendocrine cells

  • release hormones that help with digestion

Identify the image along with the labeled structures and their functions

intestinal lining

• A: circular folds

  • increase surface area

  • line the small intestine

• B: villi

  • lining the circular folds of the small intestine

  • increase surface area

  • lined with simple squamous epithelium which contain microvilli

*The circular fold is the whole structure extending off of the intestinal wall and it is lined with villi

What is the function of the circular folds, villi, and microvilli?

Increase surface area for absorption

Identify the image along with the labeled structures and their functions

intestinal lining

• A: villi

  • lining the circular folds of the small intestine

  • increase surface area

  • lined with simple squamous epithelium which contain microvilli

• B: lacteals

  • absorb fats in the small intestine

• C: goblet cells

  • produce and secrete mucus

Identify the image along with the labeled structure and its function

duodenum

• A: Brunner’s gland

• secretes an alkaline substance into the lumen to neutralize the acid of the chyme from the stomach

Identify the image along with the labeled structure and its function

ileum

• A: Peyer’s patch

  • masses of lymphatic tissue that play a role in the immune system

  • contain lymphocytes and macrophages