Chp 24-Digestive System

what is the process of consuming food?

The gastrointestinal tract allows the food to be absorbed while the accessory organs secret in order to breakdown food.

What is another name for the gastrointestinal tract? What does it consist of (mouth to anus)?

• Alimentary Canal

• Oral cavity/ mouth → pharynx → esophagus → stomach → small intestine → large intestine → anus

Examples of accessory organs in the GI tract

• Salivary glands

• liver

• gallbladder

• pancreas

Describe the process of: Ingestion

• Includes Mastication= crushing and shearing of food

  • Masseter muscles allows mouth to close

  • Controlled by CN 7 (Facial) and CN 5 (Trigeminal)

Describe the process of: Deglutition

• Includes Swallowing and Peristalsis

  • Swallowing is controlled by skeletal muscle

  • Controlled primarily By CN 10 (Vagus) along with CN 9 (Glossopharynxgeal)

What is peristalsis?

Smooth muscle contraction of alternating waves of bolus (food).

where does peristalsis occur?

Esophagus, stomach, small and large intestine

Describe the process of: Digestion

• Mechanical digestion- physical grinding of food

  • Ex. Churning (contraction of stomach muscles), Segmentation (small intestine)

• Chemical digestion- Enzymes and Hydrolysis

  • Breaks down compounds w/ water

characteristics of enzymes

1. catalyze reaction

2. lowers activation energy

3. protein

4. has specific pH and temp

5. Used more than once

6. specific/ specialized

Describe the process of: Absorption

• occurs mostly in the Jejunum (part of small intestine)

• Food is absorbed through the lumen and through epithelium lining (simple columnar). Then into the blood stream to go into body cells

Describe the process of: Defecation

• Stretch receptors in rectum

  • Internal anal sphincter is smooth muscle

  • External anal sphincter is skeletal muscle

what is the peritoneum? what is the membrane? what does the membrane do?

1. Serous membrane that lines the abdominal cavity

2. Made of mesothelium (epithelium) and areolar CT

3. Secretes watery fluid to reduce friction into peritoneal cavity

location of parietal peritoneum

Attached to wall of abdominal cavity

location of visceral peritoneum

directly on organs in abdominal cavity

Intraperitoneal

Visceral peritoneum that cover entire organ

Retroperitoneal

Not completely covered by visceral peritoneum

“SALTD SPRSS” stand for?

Intraperitoneal organs

• S- Stomach

• A- Appendix

• L- Liver

• T- Transverse colon

• D- Duodenum (1st portion)

• S- Small Intestine (jejunum + iluem)

• P- Pancreas (tail only)

• R- Rectum

• S- Spleen

• S- Sigmoid colon

“SAD PUCKER” stands for?

Retroperitonal organs

• S- Suprarenal (adrenal) gland

• A- Aorta

• D- Duodenum (2,3,4 parts)

• P- Pancreas (Head and body)

• U- Uterus

• C- Colon (descending and ascending)

• K- Kidney

• E- Esophagus

• R- Rectum (no distal 1/3rd)

How are the visceral and partiela peritoneum connected? Examples?

folds of tissue

• Greater omentum

• Less omentum

• Falciform ligament

• Mesocolon

• Mensentery proper

where is the Greater omentum located?

hangs down stomach and intestine

where is the Lesser omentum located?

Between stomach and liver.

Contains hepatic portal vein, common bile duct, and gastric arteries

where is the Mesocolon located?

connects transverse colon to back wall and covers large intestines

where is the Mesentery proper located?

covers small intestines (duodenum) and pancreas

what are the four basic layers of organs with lumens?

• Mucosa

• Submucosa

• Muscularis externa

• Serosa or adventitia

General description of Mucosa

• layer that comes in contact with food (luminal side). 3 layers

  • Epithelium- simple columnar or stratified squamous

  • Lamina propria- areolar CT w/ blood vessels

  • Muscularis mucosa- smooth muscle

what organs contain simple columnar epithelium in their mucosa

• stomach

• large intestine

• small intestine

General description of submucosa

• contains nerve plexus ( Meissner plexus)

  • regulates glands and muscularis mucosa

General description of muscularis externa

• inner circular layer

• outer longitudinal layer

• between the two layers is the Myenteric (Auerbach) plexus

  • carries impulses for smooth muscle

General description of Serosa

• Visceral peritoneum

  • contains serous membrane

General description of adventitia

• on organs located outside of peritoneal cavity

  • made up of mostly areolar connective tissue

what two body systems primarily control digestion

endocrine and nervous

what does the endocrine system do in terms of digestion

secretes hormones into blood to act on specific target organ

what nerves are involved during digestion

• intrinsic nerves (enteric NS)

• extrinsic nerves (parasympathetic and sympathetic NS)

how does the parasympathetic system affect digestion

• increases motility and secretions

• Vagus (CN 10) innervates GI organs

how does the sympathetic system affect digestion

• decreases motility and secretions

how does the enteric nervous system affect digestion

• helps control motility and secretion

• includes myenteric (auerbach plexus) and submucosal plexus

• includes sensory neurons that detect presence of certain foods (chemoreceptors) or stretch of an organ (stretch receptors)

• intramural ganglion controls peristalsis

Structures within the mouth

• labia + labial frenulum

• gingiva

• hard palate

• soft palate

• tongue

description of labia + labial frenulum

• labia=lips, keeps mouth closed

• labial frenulum connects lips to gums

description of gingiva

• stratified squamous epithelium tissue

• partially keratinized

description of hard palate

• made up by palatine and maxillary bones

• stratified squamous epithelium tissue + partially keratinized

why is the hard palate and gingiva stratified squamous epithelium tissue and partially keratinized

to protect from severe abrasion and keep mouth moist

description of soft palate

• aids in swallowing and breathing

• contains uvula that prevents food from entering the pharynx too soon

description of tongue

• deals with mechanical digestion, sensory analysis, secretion of mucus and lingual lipase, manipulation to assist chewing and swallowing

• Innervated by Hypoglossal (CN 12)

• lingual frenulum: connects body of tongue to mucosa covering floor of oral cavity

• papillae on tongue allows for taste sensation and increasing friction to help move food around

description of tonsil

contain immune cells to fight off infections

what are the 3 salivary glands

1. Parotid glands

2. Submandibular glands

3. Sublingual glands

describe the parotid gland

• long duct

• serous solution w/salivary amylase

• no mucus production

• extends from mastoid to temporal bone

describe the submandibular gland

• inner surface of mandibular

• both serous and mucus secretions

describe the sublingual glands

• short duct

• mucus rich secretions

• lubrication

• floor of mouth

how do the mucus cells appear in terms of color

appear white

how do the serous acinus appear in terms of color

appear dark

functions of saliva

• keeps oral surfaces clean

• keeps pH around 7

• prevents acid buildup

• controls bacteria

• lubricates mouth

• provides sensory information

key components of salvia

• 99.4% water

• electrolytes (Na+, Cl-, HCO3-)

• enzymes

• glycoproteins

• lysozoymes

describe amylase

begins digestion of carbohydrates through hydrolysis. made in parotid glands and optimized at a pH of 7.

describe how salivation is controlled

• controlled by autonomic NS, parasympathetic (increases secretions)

• medulla oblongata increases saliva secretions

• Facial CN innervates sublingual and submandibular glands

• Glossopharyngeal CN innervates parotid

what do teeth do? what bones have alveolar sockets for them?

• aid in mastication

• mandible and maxilla

describe the incisor teeth

• blade shaped, front of mouth, single root

• cutting/clipping

• 4 in adults

• 8 in deciduous teeth

describe the molar teeth

• large flatted crown, 4-5 rounded cusps

• crushing/grinding

• upper jaw= 3 roots

• lower jaw= 2 roots

• 6 molars in adults

• 8 molars in deciduous

describe the canine teeth

• single pointed, directly under eye

• tearing/slashing

• single root

• 2 canine in adult

• 4 canine

what type of epithelium is found in the nasopharynx? what is it a passage way for?

• pseudo stratified ciliated columnar

• air

what type of epithelium is found in the oropharynx? what is it a passage way for?

• stratified squamous

• air and food

what type of epithelium is found in the laryngopharynx? what is it a passage way for?

• stratified squamous

• food and air

what does the pharynx do?

• initiates swallowing

• palatal muscles elevate soft palate and positions pharyngeal wall. then elevates larynx bending over epiglottis. Pharyngeal constrictor muscles push bolus into esophagus

how long is the esophagus? where is it located? general function?

• 10 inches long

• Mediastinum, posterior to trachea and anterior to vertebral column

• passage way

function of upper and lower esophageal sphincters

• prevents reflux of materials from stomach

describe the histological layers of the esophagus

• mucosa= non-keratinized stratified squamous

• submucosa= areolar

• muscular= circular and longitudinal. upper 1/3 is skeletal, lower 1/3 is smooth

• adventitia= fibrous loose

what is the buccal phase of deglutition

• compress bolus against hard palate

• retraction of tongue moves bolus into oropharynx and assist in elevating soft palate, sealing off nasopharynx

• reflex response begins bolus moves down

• voluntary

what is the pharyngeal phase of deglutition

• Bolus comes into contact w/palatal arches and posterior pharyngeal wall

• epiglottis folds and directs bolus

• uvula and soft palate block nasopharynx

• mechanical stimulation sends impulse to medulla oblongata, sends bolus down

• involuntary

what is the Esophageal phase of deglutition

• Pharyngeal muscles move bolus down through esophagus entrance

• once at esophagus bolus is pushed through peristaltic waves controlled by the vagus nerves

what is peristalsis? what nerve innervates the esophagus to increase peristalsis?

• smooth muscle contractions “milk” food through digestive tract due to contraction of circular and longitudinal layers of muscularis externa

• glossopharyngeal (CN 9) and vagus (CN 10)

what is GERD (gastroesophageal reflux disease)?

Stomach acid flows back up into the esophagus and oral cavity causing heart burn and damage to the mucosal lining

what is a hiatal hernia?

When an organ (usually stomach) protrudes through the esophageal hiatus due to a tear or weakness in the diaphragm. Results in acid reflux and heartburn.

what is in the mucosa layer of the stomach?

• Simple columnar epithelium with lamina propiria w/ areolar CT and muscularis mucosa (smooth muscle)

• Has gastric pits that fold into gastric glands

• Mucus cells

• Parietal cells

• Chief cells

• G-cells

what is the purpose of chief cells

protect against acid/pH of gastric juice

describe Parietal cells

• Appear pink

• Secretes HCl that destroys bacteria, denatures proteins and activates pepsinogen

• Secretes Intrinsic factor that is needed to absorb Vit B12

describe Chief cells?

• Appear dark blue

• Makes the zymogen (proenzyme) pepsinogen

  • Released in an inactive form to protect lining of digestive tract and is activated through HCl to digest proteins

describe G-Cells

• Releases Gastrin hormone to stimulate acid secretion

• Endocrine cells in digestive lining that stimulates parietal and chief cells

what does the submucosa of the stomach contain?

• Dense irregular CT

• Rugae- folds of both mucosa and submucosa that allow for expansion

what does the muscularis externa of the stomach contain?

• 3 layers

  • Internal oblique layer (closest to submucosa)

  • Circular outer longitudinal layer

  • Inner circular layer

    • Strengthens stomach wall and assists in the mixing and churning of chyme formation

what does the serosa of the stomach contain?

• Visceral peritoneum

• squamous epithelium and loose CT

what does the hydrogen ion pump in the parietal cell membrane do? what side i sit located on? pH rage for stomach?

• increases acidity in the stomach

• luminal side

• pH 1.5-2

Reaction for HCl

H₂O + CO₂ → H₂CO₃ → HCO₃ + H⁺

• the bicarbonate goes into interstitial fluid and imports Cl- that then follows the H+

3 functions of HCl

1. kills most organisms in food

2. denatures proteins and inactivates most enzymes in food

3. helps breakdown plant cell walls and CT in meat

3 hormones that increase acid production by parietal cells

• gastrin

• acetylcholine

• histamine

cephalic phase of stomach digestion

• thinking or smelling food

• Facial (CN 7) innervates salivary glands

• Vagus (CN 10) innervates gastric gland

• under nervous control

gastric phase of stomach digestion

• Initiated by chemoreceptors and stretch receptors of stomach

• Endocrine- Gastrin promotes stomach digestion and emptying

• Nervous- Detects stretch, higher pH, stimulates mechanical churning, gastrin release. Myenteric plexus

intestinal phase of stomach digestion

• Initiated by chemoreceptors and stretch receptors in wall of duodenum

• Cholecystokinin (CCK)- made when fat enters duodenum. Gallbladder contracts, stomach shuts down, increase in pancreatic secretions

• Secretin- Made when pH of chyme is low, acts on pancreas to secrete HCO₃-

• Enterogastric reflux- Reflexive inhibition of gastric secretions initiated by arrival of chyme in small intestine

what happens during vomiting? where is the vomiting center located?

• pyloric sphincter closes and lower esophageal sphincter opens and moves up through contractions of the diaphragm and abdominal muscles. Soft palate closes nasopharynx, respiration stops, closure of glottis

• Medulla oblongata

what do the 3 major parts of the small intestines do?

• Duodenum- digestion

• Jejunum- absorption

• ileum- immunity and absorption

where does the small intestine start and end? what parts are retroperitoneal and intraperitoneal?

• Starts- Pyloric Sphincter valve

• Ends- ileocecal valve

• Duodenum is retroperitoneal, jejunum and ileum are intraperitoneal

what are microvilli? villi? plicae circularies?

• Microvilli (brush border)- folds of cell membrane

• Villi- folds of mucosa only

• Plicae circularies- folds of both mucosa and submucosa

mucosa of small intestine

• simple columnar w/ microvilli

• goblet cells- secretes mucus to protect against breakdown

• villus- in laminal propria are lacteal that transport materials that cannot enter blood ex. lipids

• brush border- contains enzymes such as maltase, sucrase, lactase, dipeptidase, aminopeptidas