Digestive System

A&P Exam 4

Describe anatomy of GI tract

Continuous tube from mouth to anus, has 7 sphincters of significance

Define accessory organs, give examples

Vital organs for digestion; salivary glands, liver, gallbladder, pancreas

List and describe the 7 sphincters of the GI tract

1. Upper esophageal sphincter

2. Lower esophageal sphincter

3. Pylorus sphincter

4. Sphincter of Oddi (allows entry of bile and enzymes)

5. Ileocecal (valve from small intestine to large intestine)

6. Internal anal sphincter (involuntary controlled)

7. External anal sphincter (voluntarily controlled, skeletal)

List the 4 layers of the GI wall

Mucosa, submucosa, muscularis externa, serosa

Explain components of mucosa layer

Villi - finger like projections that increase SA of epithelial layer

Crypts - contain exocrine cells that produce secretions into lumen

Lamina propria - connective tissue

Muscularis mucosa - thin layer of smooth muscle that makes flux and agitation

Explain components of submucosa layer

Blood and lymphatic vessels - allows for lots of reabsorption

Submucosal plexus - ENS innervates and influences secretion of exocrine cells

Explain components of muscularis externa layer

Circular muscle - changes diameter of GI tract wall

Myenteric plexus - communicates with submucosal plexus, engages in ENS control of circular and longitudinal smooth muscle and muscularis mucosa

Longitudinal layer - shortens and lengthens

Explain the serosa layer

Connective tissue, reduces friction between organs

How does the ENS impact the GI wall

Locally controls the myenteric plexus to control GI motility and the submucosal plexus to control secretions

How does the ANS impact the GI wall

Is an external overrider of the ENS and modulates its activity

Parasympathetic stimulates ENS activity, sympathetic inhibits ENS activity

Explain functions of digestive system

Ingesting foods, liquids, nutrients, ions

Digest large molecules into absorbable molecular forms and transport it

Absorption of nutrients from gut lumen to internal environemnt

Metabolic transformation of fuel molecules and detoxification

Excretion of metabolic end products secreted by liver (bilirubin)

Immune functions (production of antibodies)

Describe the 4 major processes of the DS

Motility - propels, mixes, and exposes contents

Digestion - breakdown both mechanically and chemically

Absorption - small intestine domination

Secretion - mucus throughout

What enxymes break down carbohydrates and what are the products

Amylase breaks down polysaccharides (starch, glycogen) → maltase breaks down maltose → glucose

Sucrase and lactase break down disaccharides (sucrose, lactose) → fructose, galactose

What enzymes break down proteins and what are the products

Pepsin, trypsin, chymotrypsin break down polypeptides → carboxypeptidase, aminopeptidase breaks down peptide fragments → amino acids

What enzymes break down triglycerides and what are the products

Lipase breaks down glycerol (3 pieces) → monoglyceride + two free fatty acids

Why is the amount of fluid so much greater than amount consumed in GI tract

Because the DS adds large volumes of fluid secretions

Where do secretions that make up the GI fluid come from?

Exocrine glands

Explain feed-forward regulation of GI tract

Sight, smell, taste of food → CNS → efferent autonomic neurons —> nerve plexus → GI glands and smooth muscle —> response

Explain short reflex regulation of GI tract

Within the Gi tract

Stimulus in GI tract → sensory receptors (chemo, osmo, mechano) → nerve plexus ENS → smooth muscle/gland →response

Explain long reflex regulation of GI tract

Stimulus → sensory neuron → CNS → efferent autonomic neurons → nerve plexus ENS → smooth gland/muscle → response

Name the GI hormones secreted by the tract that regulates the smooth muscles/glands

Gastrin, CCK, secretin, GIP (all peptides)

Explain properties of gastrin

Produced in stomach

Stimulated by amino acids, peptides in stomach, parasympathetic nerves

Inhibited by acid in stomach, somatostatin

Stimulates acid secretion, motility, ileum, and mass movement

Explain properties of CCK

Produced in small intestine

Stimulated by amino acids, fatty acids in small intestine

Stimulates insulin secretion, gallbladder

Inhibits acid secrection, motility

Relaxes sphincter of Oddi

Potentiates secretin

Explain properties of secretin

Produced in small intestine

Stimulated by acid in small intestine

Stimulates enzyme secretion, liver

Inhibits acid secretion and motility

Potentiates CCK

Explain properties of GIP

Produced in small intestine

Stimulated by glucose, fat in small intestine

Goes to pancreas → stimulates insulin into plasma

Name phases of GI control and its stimulus origins

Cephalic - head

Gastric - stomach

Intestinal - small intestine

Explain the cephalic phase of GI control

Stimulated by sight, smell, taste, chewing, emotional state

Increases secretory and contractile activity mainly by parasympathetic system
Lots of feed-forwarding

Explain the gastric phase of GI control

Stimulated by stretch, acidity, amino acids, peptides

Mediated by short and long reflexes, hormone gastrin (increases secretion and motility)

Explain the intestinal phase of GI control

Stimulated by stretch, acidity, osmolarity, digestive products

Mediated by short and long reflexes, hormones secretin, CCK, GIP

What are the phases of food as it is digested in the body

On plate/in cup → food, nutrients, liquid

in mouth/esophagus → bolus

In stomach/small intestine → chyme

In large intestine/rectum → chyme/feces

Describe first motility

Includes chewing (mastication) - grinding of food to increase surface area and mixing saliva to dissolve it and aid taste

Voluntary skeletal muscles - organizing and coordinating movements

Complex brainstem pattern - lots of contact stimuli to start patterns and maintain movement

What are the functions of the components of soliva

Water - moistens and dissolves molecules

Mucus - lubricates food, fascilitates formation of bolus for swallowing

Bicarbonate - neutralizes acids in food

Lysozyme - kills bacteria

Amylase - begins digestion of polysaccharides

Lipase - begins digestion of triglycerides

How does ANS affect secretion of saliva

Parasympathetic - lots of secretion, thin, watery

Sympathetic - little secretion, thick, viscous

Explain second motility

Swallowing (deglutition) - propels good to stomach, has two phases

Oropharyngeal phase - voluntary closing of lips and elevation of tongue (irreversible) → soft palate and uvulate elevate to block off nasal passage → larynx elevates and bolus flattens epiglottis over glottis → UES opens and smooth muscle relaxes → UES closes rapidly

Esophageal phase - peristaltic wave, propulsion

Explain the role of the esophagus

Secretes mucus to make to make GI slippery and buffers acidity to protect GI ract wall

Doesn’t digest or absorb