Anatomy Exam 3

List the GI Tract organs in order

1. oral cavity

2. pharynx

3. esophagus

4. stomach

5. small intestine

6. large intestine

7. anal canal

List the accessory digestive organs in order

1. teeth

2. tongue

3. salivary glands

4. liver (gland)

5. gallbladder

6. pancreas (gland)

6 general functions of the digestive system

• ingestion

• motility

• secretion

• digestion

• absorption

• elimination

list the tunics of the GI tract from innermost to outermost

1. mucosa

2. submucosa

3. muscularis

4. serosa or adventitia

describe the 3 layers of the mucosa

(mucosa is inner-most layer of GI tract)

1. epithelium

   1. in contact with contents of lumen

   2. simple columnar epithelium

      1. except for esophagus (nonkeratinized, stratified squamous)

2. lamina propria

   1. areolar connective tissue

   2. substances moved through simple columnar are absorbed into blood or lymphatic capillaries in lamina propria

   3. houses MALT

3. muscularis mucosae

   1. directly adjacent to submucosa

   2. composed of thin layer of smooth muscle

   3. contractions facilitate release of secretions from mucosa to lumen and increase absorption

describe the 2 main components of the submucosa

(submucosa is second inner-most layer of GI tract)

1. submucosal nerve plexus (Meissner plexus)

   1. fine branches of nerves extending into mucosa

   2. the autonomic motor neurons within this plexus innervate smooth muscle and glands of mucosa and submucosa

2. mucosa-associated lymphoid tissue (MALT)

   1. called GALT in GI tract

   2. in small intestine, organized as larger aggregates of lymphoid nodules called Peyer patches

   3. protects from harmful agents by preventing ingested microbes from crossing GI tract wall into body

   4. also in lamina propria of mucosa

3. COMPOSED OF AREOLAR AND DENSE IRREGULAR CONNECTIVE TISSUE, MANY BLOOD VESSELS, LYMPH VESSELS, NERVES, GLANDS

describe the 3 layers of the muscularis

(muscularis is third most inner layer of GI tract)

1. composed of smooth muscle

   1. inner circular layer of circumferentially oriented smooth muscle cells

      1. contractions constrict lumen

   2. outer longitudinal layer of lengthwise smooth muscle cells

      1. contractions shorten lumen

2. myenteric nerve plexus (Auerbach plexus)

   1. fine branches of nerves and associated autonomic ganglia located between the two layers of smooth muscle

   2. motor neurons in this plexus control contractions of muscularis

3. FUNCTION IS MOTILITY

muscularis contractions: mixing vs propulsion

mixing:

• backward and forward motion

• blends secretions with ingested material in GI tract

• does NOT result in direction movement of contents

• includes mixing waves by stomach and segmentation by small intestine

propulsion:

• directional movement of materials through GI tract

• occurs by peristalsis (contraction that moves like waves)

• results in one-way movement of lumen contents from esophagus to anus

adventitia vs serosa

outermost tunic of GI tract

• adventitia:

  • composed of areolar connective tissue with dispersed collagen and elastic fibers

• serosa:

  • adventitia plus outer covering of serous membrane called visceral peritoneum

  • only intraperitoneal digestive organs have a serosa as their outermost tunic

• EXCEPTIONS:

  • esophagus has nonkeratinized stratified squamous epithelium in its mucosa to protect its lining

  • stomach has 3 layers of smooth muscle in muscularis to help with swallowing

enteric nervous system (ENS)

• array of sensory and motor neurons that extend from the esophagus to anus

• neurons form both submucosal nerve plexus and myenteric nerve plexus in GI tract wall

• innervates smooth muscle and glands of GI tract and mediates the coordinated reflexes for mixing and propulsion

autonomic nervous system (ANS)

• parasympathetic and sympathetic divisions of ANS innervate wall of GI tract

• parasympathetic and sympathetic axons synapse with smooth muscle and glands of GI tract wall and with neurons in ENS

• parasympathetic innervation promotes GI tract activity

  • stimulates motility and release of secretions, relaxes GI tract sphincters

• sympathetic innervation opposes GI tract activity:

  • inhibits GI tract motility and release of secretions, contracts GI tract sphincters, vasoconstricts blood vessels in GI tract wall

short reflex

local nerve reflex

• only involves ENS (enteric)

• sensory input from stretch or chemoreceptors is relayed to neurons in ENS

  • smooth muscle contraction and gland secretion of GI tract wall is altered

• function in small segments to changes in stimuli

long reflex

nerve reflex involving sensory input relayed to CNS (integration center)

• autonomic motor output is relayed to alter smooth muscle contraction and gland secretion of GI tract wall

  • often also relayed to other structures like accessory digestive organs

• results in coordinated smooth muscle contractions and secretory activity

name the 2 primary stomach digestive hormones

• gastrin

  • stimulated by bolus in stomach

  • targets stomach

  • stimulates stomach motility and release of gastric secretions from parietal cells and chief cells

• somatostatin

  • stimulated by increased stomach acidity

  • targets GI tract and pancreas

  • inhibits gastrin, inhibits release of acidic secretions by parietal cells, inhibits acinar cells in releasing pancreatic juice

name the 4 primary small intestine digestive hormones

• cholecystokinin (CCK)

  • stimulated by chyme entering duodenum

  • targets stomach, gallbladder, pancreas, hepatopancreatic sphincter, ileocecal valve

  • inhibits stomach motility and gastric secretions

    • stimulates release of bile

    • stimulates release of pancreatic juice

    • causes relaxation

• secretin

  • stimulated by chyme entering duodenum

  • targets stomach, liver, pancreas

  • inhibits stomach motility and gastric secretions, stimulates secretion of HCO3

• glucose-dependent insulinotropic peptide (GIP)

  • stimulated by increase in glucose in small intestine

  • targets pancreas

  • primarily regulates release of insulin from beta cells

• motilin

  • stimulated by increased amounts released later in intestinal phase

  • targets small intestine

  • regulates migrating motility complex to move lumen contents from small to large intestine

name the primary liver digestive hormone

hepcidin

• stimulated by increased iron content in chyme

• targets small intestine

• inhibits absorption of iron

describe the peritoneum and its layers

• peritoneum

  • serous membrane associated with the abdominopelvic cavity

• parietal peritoneum

  • lines the inner surface of abdominal wall

• visceral peritoneum

  • covers the surface of internal organs within the abdominopelvic cavity

• peritoneal cavity

  • between parietal and visceral peritoneum

  • potential space containing serous fluid (produced by both layers)

    • lubricates both surfaces, allows organs to move freely

list the intraperitoneal organs

1. stomach

2. most of small intestine

3. parts of large intestine (cecum, vermiform appendix, transverse and sigmoid colon)

4. most of liver

these are completely surrounded by visceral peritoneum and have serosa as outermost layer (not adventitia)

list the retroperitoneal organs

1. pancreas

2. esophagus (abdominal portion)

3. most of duodenum (small intestine)

4. parts of large intestine (ascending and descending colon)

5. rectum

these lie outside the parietal peritoneum directly against the posterior abdominal wall

• only anterolateral portions are covered with parietal peritoneum

• not completely enveloped by visceral peritoneum

• outermost layer is adventitia (not serosa)

mesentery

double layer of peritoneum that attaches to the inner abdominal wall

• supports, suspends, stabilizes the intraperitoneal GI tract organs

• blood vessels, lymph vessels, nerves are sandwiched between 2 layers of a mesentery

• contains multiple tissues, considered as an organ by some

list the upper GI tract organs and their functions (5)

• oral cavity and salivary glands

  • mechanical digestion (mastication) begins in oral cavity

  • saliva is released from salivary glands in response to presence of food in oral cavity

  • saliva mixes with food to form bolus

  • salivary amylase in saliva initiates chemical digestion of starch

• pharynx

  • bolus is moved into pharynx during swallowing

  • mucus secreted in saliva and superior part of pharynx provides lubrication to facilitate swallowing

• esophagus

  • bolus is transported from pharynx through esophagus into stomach

  • mucus secretion by esophagus lubricates passage of bolus

• stomach

  • bolus is mixed with gastric secretions as muscularis in stomach wall contracts

  • secretions are released into stomach lumen by epithelial cells of stomach mucosa

    • secretions include HCl, digestive enzymes, mucin

  • mixing continues, acidic semifluid (chyme) is formed

describe the histology of the oral cavity

• stratified squamous epithelial lining of oral cavity

  • protects against abrasive activities associated with chewing

• nonkeratinized type of epithelium lines most of oral cavity

• keratinized type lines lips, portions of tongue, small region of hard palate

intrinsic salivary glands vs extrinsic salivary glands

intrinsic:

• located within oral cavity

• unicellular exocrine glands

• continuously release small amounts of secretions independent of presence of food

• saliva contains lingual lipase

  • enzyme is activated by low pH of stomach

  • begins digestion of triglycerides

• extrinsic:

  • located outside oral cavity

  • multicellular exocrine glands

  • produces most saliva

name and describe the 3 pairs of extrinsic salivary glands

• parotid salivary glands

  • largest

  • located anterior and inferior to the ear, partially overlying the masseter

  • produce about 25-30% of saliva, transported through parotid duct to oral cavity

  • EX mumps is an infection of parotid glands by virus

• submandibular salivary glands

  • both inferior to floor of oral cavity and medial to body of mandible

  • produce most saliva (60-70%)

  • submandibular duct opens from each gland through a papilla in the floor of oral cavity on either side of lingual frenulum

• sublingual salivary glands

  • inferior to the tongue, medial and anterior to submandibular salivary glands

  • each gland extends multiple tiny sublingual ducts that open onto inferior surface of oral cavity, posterior to submandibular duct papilla

  • only produce 3-5% of saliva

mucous cells vs serous cells

two types of secretory cells housed in large salivary glands that produce components of saliva

• mucous cells

  • secrete mucin

    • forms mucus upon hydration

• serous cells

  • secrete watery fluid containing electrolytes and salivary amylase

• parotid glands primarily produce serous secretions

• submandibular and sublingual glands produce both mucus and serous secretions

list the 6 functions of saliva

1. moistens ingested food as it forms into bolus

2. initiates chemical breakdown of starch in oral cavity because of salivary amylase

3. initiates chemical breakdown of triglycerides in stomach due to lingual lipase secreted by intrinsic salivary glands

4. acts as watery medium where food molecules are dissolved so taste receptors may be stimulated

5. cleanses oral cavity structures

6. helps inhibit bacterial growth in oral cavity

   1. contains antibacterial substances like lysozyme and IgA antibodies

what regulates salivation

salivary nuclei within the pons

• basal level of salivation in response to parasympathetic stimulation

• input to salivary nuclei is received from chemoreceptors and stretch receptors in upper GI tract

• spoiled foods cause bacterial toxins in stomach to stimulate receptors that initiate sensory input to salivary nuclei

• higher brain centers send input to salivary nuclei in response to thought, smell, or sight of food

• sympathetic stimulation occurs during exercise or when one is excited or anxious

  • results in more viscous saliva by decreasing water content of saliva

    • sympathetic stimulation constricts blood vessels of salivary gland, decreases fluid added to saliva

anatomy of the pharynx

• funnel-shaped, muscular passageway for both air and food

• superior, middle, and inferior pharyngeal constrictors

  • pairs of skeletal muscle composing the wall of the pharynx

• oropharynx and laryngopharynx are lined with nonkeratinized stratified squamous epithelium

  • provides protection against abrasion associated with swallowing ingested materials

anatomy of the esophagus

• tubular passageway for ingested food and drink

• typically collapsed, expands when ingested materials are swallowed

• begins at cricoid cartilage in larynx

• directly anterior to vertebral bodies, posterior to trachea until passes through opening in diaphragm (esophageal hiatus)

• last 1.5 cm of esophagus is in abdominal cavity, connects with stomach