CH 23 part 2

Explain the digestive processes in the mouth.

Explain the digestive processes in the mouth.

• food is ingested

• mechanical digestion begins (mastication)

• propulsion is initiated by swallowing

• salivary amylase begins the chemical breakdown of starch

• the pharynx and esophagus serve as conduits to pass food from the mouth to the stomach

Describe deglutition. What are the phases?

(swallowing)

• involves the coordinated activity of the tongue, soft palate, pharynx, esophagus, and 22 separate muscle groups

• buccal phase- bolus is forced into the oropharynx

  • voluntary

• pharyngeal-esophageal phase - controlled by the medulla and lower pons-autonomic

  • all routes except into the digestive tract are sealed off

• peristalsis moves food through the pharynx to the esophagus

Describe the stomach’s regions.

Food is converted to chyme

• cardiac region - surrounds the cardiac orifice

• fundus - dome-shaped region beneath the diaphragm

• body - midportion of the stomach

• pyloric region - made up of the antrum and canal which terminates at the pylorus

  • the pylorus is continuous with the duodenum through the pyloric sphincter

Describe the stomach’s curvatures and omentums

• greater curvature - entire extent of the convex lateral surface

• lesser curvature - concave medial surface

• lesser omentum - runs from the liver to the lesser curvature

• greater omentum - drapes inferiorly from the greater curvature to the small intestine

What is the function of the oblique layer in the muscularis?

It allows the stomach to churn, mix, and pummel food physically and breaks down food into smaller fragments

What is the epithelial lining composed of?

Goblet cells that produce a coat of alkaline mucus

• the mucous surface layer traps a bicarbonate-rich fluid beneath it

What do gastric pits contain?

Gastric glands that secrete gastric juice, mucus, and gastrin

Describe glands of the stomach fundus and body.

• Gastric folds are called rugae

• gastric pits lead to gastric glands

• gastric glands of the fundus and body have a variety of secretory cells

  • mucous neck cells - secrete acid mucus

  • parietal (oxyntic) cells - secrete HCI and intrinsic factor

What is the function of chief cells?

To produce pepsinogen

• pepsinogen is activated by pepsin by

  • HCI in the stomach

  • Pepsin itself via a positive feedback mechanism

What is the function of enteroendocrine cells?

To secrete gastrin and other hormones and hormone-like products into lamina propria

How does the stomach keep from digesting itself?

The stomach is exposed to the harshest conditions in the digestive tract

• to keep from digesting itself, the stomach has a mucosal barrier

  • the barrier has a thick coat of bicarbonate-rich mucus on the stomach wall

  • epithelial cells that are joined by tight junctions

    • damaged epithelial cells are quickly replaced

  • gastric glands that have cells impermeable to HCI

How does digestion in the stomach work?

• churns food using mixing waves

• holds ingested food

• degrades this food both physically and chemically

• delivers chyme to the small intestine

• enzymatically digests protein with pepsin

• pepsinogen activated by HCL (pH 2 or less)

• peptic ulcers

Describe the small intestine. What are the subdivisions and ducts? (gross antamony)

It runs from the pyloric sphincter to the ileocecal valve (2-4m long during life). It is suspended from the posterior wall of the abdomen by the mesentery

• subdivisons

  • duodenum

  • jejunum

    • extends from the duodenum to the ileum

  • ileum

    • joins the large intestine at the ileocecal valve

• ducts

  • bile duct and pancreatic duct

    • join the duodenum at the hepatopancreatic ampulla

    • are controlled by the sphincter of Oddi (Hepatopancreatic sphincter

Describe small intestine (microscopic anatomy.

Structural modifications of the small intestine wall increases surfaces area

• pilcae circulares - deep circular folds of the mucosa and submucosa

• villi - fingerlike extensions of the mucosa

• lacteals - lymph capillaries where nutrients are absorbed

• microvilli - tiny projections of the absorptive mucosal cells’ plasma membranes

Describe the wall of small intestine

The epithelium of the mucosa is made up of absorptive cells and goblet cells

• cells of the intestinal crypts (lieberkuhn) secrete intestinal juice

• peyer’s pataches (lymphoid follicles) are found in the submucosa

• brunner’s glands in the duodenum (only) secrete alkaline mucus

What the functions of intestines?

• absorption

• digestion by intestinal juices

• segmentation

  • pendular movements

• peristalsis

Describe the liver.What are the four lobes?

The largest gland in the body. It is located in the right hypochondriac and epigastric regions.

• four lobes

  • right

  • left

  • caudate

  • quadrate

• includes falciform ligament

  • separates the right and left lobes anteriorly

  • suspends the liver from the diaphragm and anterior abdominal wall

• includes ligamentum teres (round ligament)

  • a remnant of the fetal umbilical vein

  • runs along the free edge of the falciform ligament

What is the function of the liver?

• storage, synthesis and release of various vitamins

• release of glycogen

• formation of the urea

• synthesis of the blood proteins

• detoxification of the blood

• bile production

• phagocytosis

What are some structures the liver is associated with?

• lesser omentum

  • anchors the liver to the stomach

• hepatic blood vessels

  • enter the liver at the porta hepatis

• gallbladder

  • rests in a recess on the inferior surface of the right lobe

• bile

  • leaves the liver via bile ducts; bile ducts fuse into the common hepatic duct

  • common hepatic duct fuses with the cystic duct

  • cystic duct and hepatic duct form the bile duct

Describe the microscopic anatomy of the liver.

• hexagonal-shaped liver lobules are the structural and functional units of the liver

  • composed of hepatocyte (liver cell) plates radiating outward from a central vein

• hepatocytes’ functions include

  • product of bile

  • processing blood-born nutrients

  • storage of fat-soluble vitamins

  • detoxification

• secreted bile flows between hepatocytes through bile canaliculi towards the bile ducts

• liver sinusoids - enlarged, leaky capillaries located between hepatic plates and drain into the central vein

• kupffer cells - hepatic macrophages found in the liver sinusoids

Where is blood supply stored?

• hepatic artery

• portal arteoile

• hepatic portal vein

• portal venule

• portal triad

• sinusoids

• hepatic vein

Describe the gallbladder and its functions.

Thin-walled green muscular sac on the ventral surface of the liver

• Functions

  • stores and concentrates bile by absorbing its water and ions

  • releases bile via the cystic duct, which flows into the bile duct

• mucosa folds into rugae that expands as the gallbladder fills with bile

• muscularis layer contracts and expel bile into the cystic duct

Describe the pancreas and its functions

It lies deep to the greater curvature of the stomach. The head is encircled by the duodenum and the tail abuts the spleen. Its body lies between the head and tail

• Mixed gland

• Functions

  • secretes pancreatic juices through the main pancreatic duct that fuses with the bile duct

    • accessory duct drains directly into the duodenum

• exocrine function

  • secretes pancreatic juice which breaks down all categories of foodstuff

  • acini (clusters of secretory cells) make digestive enzymes of the pancreatic juice

• endocrine function

  • release insulin and glucagon from pancreatic islets

What is the function and composition of pancreatic juice?

• composition

  • HCO3- (water solution of enzymes and electrolytes)

  • neutralizes acid chyme

  • provides optimal environment for pancreatic enzymes

• enzymes are released in inactive form and activates in the duodenum

  • Examples

    • trypsinogen is activated to trypsin

  • active enzymes secreted

    • amylase, lipases, and nucleases

    • these enzymes require ions or bile for optimal activity

Describe large intestines and its three unique features. (gross anatomy)

It frames the small intestines on three sides. It extends from the ileocecal valve to the anus (1.5 m long)

• three unique features

  • teniae coli - three bands of longitudinal smooth muscle in its muscularis

  • haustra - pocketlike sacs caused by the tone of the teniae coli

  • epiploic appendages - fat-filled pouches of visceral peritoneum

• subdivisions

  • cecum, appendix, colon, rectum, and anal canal

    • cecum lies below the ileocecal valve in the right iliac fossa and contains a wormlike vermiform appendix

• Function

  • absorbs water and eliminates waste

Describe the regions of the colon.

• regions

  • ascending colon

  • hepatic flexure

  • transverse colon

    • anchored via mesenteries called mesocolons

  • splenic flexure

  • descending colon

  • sigmoid colon

    • mesocolons

    • joins the rectum

• The anal canal (last segment of large intestine) opens to the exterior at the anus

How many valves of the rectum stop feces from being passed with gas?

Three valves

How many sphincters does the anus have?

• two

  • internal anal sphincter composed of smooth muscle

  • external sphincter composed of skeletal muscle

  • they are closed except during defecation

Describe the microscopic anatomy of the large intestine.

• colon mucosa is simple columnar epithelium except in the anal canal

• has numerous deep crypts lined with goblet cells

• anal canal mucosa is stratified squamous epithelium

What are the functions of large intestine?

• Its major function is propulsion of fecal material towards the anus

• digestion of enteric bacteria

• vitamins, water, and electrolytes are reclaimed

Describe haustral contractions in the large intestine.

• slow segmenting movement that move the contents of the colon

• haustra sequentially contracts as they are stimulated by distension

• peristalsis toward rectum

What is defecation?

Distension of rectal walls caused by feces

• stimulates contraction of the rectal walls (reflex)

• relaxes the internal anal sphincter

• voluntary signals stimulate relaxation of the external anal sphincter and defecation occurs

• diarrhea/constipation