NRSG 202 - Digestive System Overview

Upper digestive tract doctor

Gastroenterologist

Lower digestive tract doctor

Proctologist

Organ pathway of digestive system

oral cavity → pharynx → esophagus → stomach → small intestines → large intestines/colon → rectum → anus

3 digestive organs outside of the digestive tract

1. Liver

2. Gallbladder

3. Pancreas

Function of digestion

break down large macromolecules into smaller molecules that can be used by our cells

6 basic processes of digestion

1. Ingestion

2. Secretion

3. Mixing and propulsion (motility)

4. Digestion

5. Absorption

6. Defecation

Ingestion

taking food into our body

4 substances secreted in digestive system

1. Water/saliva

2. Acids

3. Buffers

4. Enzymes

Mixing and propulsion (motility)

series of smooth muscle contractions and relaxations that mixes up the food with the enzymes and moves the food along the tract

Digestion

breaking food down into smaller molecules

2 types of digestion

1. Mechanical

2. Chemical

Mechanical digestion

physical digestion (tearing, mixing, etc.)

Chemical digestion

hydrolysis and enzymes break down large molecules

Absorption

nutrients are absorbed into the circulatory system → body cells

4 substances expelled from the body through defecation

1. Waste

2. Bacteria

3. Indigestibles

4. Slough cells

Enteric nervous system

extensive network of neurons that feed the digestive system

2 major plexuses of the enteric nervous system

1. Submucosal plexus

2. Myenteric plexus

Submucosal plexus

plays a role in the movement of mucosa, vasoconstriction, and innervates secretory cells of mucosal gland

Myenteric plexus

contains neural fibers from both divisions of the ANS and is responsible for gastric motility

Role of parasympathetic nervous system in digestion

increases GI secretions and motility by activating neurons in enteric nervous system

Role of sympathetic nervous system in digestion

decreases GI secretions and motility by inhibiting neurons in enteric nervous system

GI reflex pathways

made up of plexuses that regulate secretion in response to different stimuli

What is the first event of digestion that occurs in the mouth?

Ingestion

2 other names for the mouth

1. Buccal cavity

2. Vestibule

What type of gland is the salivary gland?

Exocrine

Salivary gland function

Lubricates and dissolves food

How many pairs of salivary glands are there?

3

Saliva make up

99.5% of the saliva is water and 0.5% of the saliva is salts, enzymes, dissolved gases, and organic substances

Control of salivation

Nervous system controls when and how much an individual salivates

How is saliva involved in chemical digestion?

Salivary enzymes begin to break down carbohydrates through salivary amylase

Tongue function

Tongue forms the floor of the oral cavity and plays a role in food manipulation (chewing and swallowing)

How do we taste food?

Tastebuds

Why do we need to taste our food?

evolutionary response to protect the body against poisons and unwanted substances

Where are tastebuds located?

Papillae

Teeth function

play a role in mechanical digestion through mastication, which creates a food bolus (mixture of food and saliva)

Oropharynx

portion of the pharynx where the respiratory and digestive systems merge

Oropharynx epithelium

non-keratinized stratified squamous epithelium built to deal with abrasion from food

Oropharynx function

Involved in initiating deglutition (swallowing)

Esophagus functions

• Peristalsis  - rhythmic movements of the smooth muscles that move the bolus from the mouth to the stomach

• Degluttition

2 esophageal sphincters

1. Upper esophageal sphincter

2. Lower esophageal sphincter

Lower esophageal sphincter function

ensures that food enters stomach, from stomach acids do not enter esophagu

3 stages of degluttition

1. Voluntary stage

2. Pharyngeal stage

3. Esophageal stage

Voluntary stage of deglutition

tongue assists in swallowing

Pharyngeal stage of deglutition

involuntary swallowing

Esophageal stage of deglutition

moves from the pharynx into the esophagus, conclusion of swallowing

Stomach

J-shaped organ that sits directly under the ribcage

Fundus

upper, rounded portion of the stomach that lies above the esophageal sphincter

Cardia

upper, dome-shaped portion of the stomach where it connects to the esophagus

Pyloric sphincter

separates the duodenum and stomach

Rugae

folds in the stomach that increase surface area

Mechanical digestion in the stomach

propulsion and retropulsion, stomach contracts through squeezing

Chemical digestion in the stomach

bolus is converted into chyme

2 secretory cells of the stomach

1. Parietal cells

2. Chief cells

Parietal cells of the stomach

secrete HCl into the stomach lumen

Chief cells of the stomach

secrete pepsinogen, the precursor to pepsin, into the stomach lumen (which is converted into pepsin by HCl); pepsin digests proteins

Absorption in the stomach

Very little is absorbed in the stomach, except for alcohol

Gastric emptying

slow process in which a small amount of chyme (acidic) goes through the pyloric sphincter

What occurs immediately after gastric emptying?

Substances wait on the other side of the pyloric sphincter to neutralize the chyme

Vomiting

something unwanted exists in the stomach, and reverse peristalsis occurs

Pancreas

exocrine organ not part of the digestive tract

Pancreas exocrine function

Secretes sodium bicarbonate and pancreatic juice that contains amylases, trypsin, pepsidases, lipases, and ribonucleases that break down the chyme

Sodium bicarbonate function

buffers acidic chyme so it doesn't damage small intestines

Liver and gallbladder general function

aids in lipid digestion, not part of the digestive tract

Liver and gallbladder mechanisms

Bile is secreted by the liver, and stored in and released by the gallbladder

Emulsification in the GI tract

performed by bile; large fat globules are converted into smaller fat globules

Function of small intestine

 involved in absorption and digestion

3 parts of small intestine (in order)

1. Duodenum

2. Jejunum

3. Ileum

Small intestine location

Extends from the pyloric sphincter to the iliocecal sphincter

Brush borders

villi are lined with enterocytes that have microvilli, making up brush border and increasing surface area

Brush borders function

Brush border enzymes are produced by microvilli and produce intestinal juices (chemical digestion)

Mechanical digestion in the small intestine

Segmentation and peristalsis

Segmentation

mixes the chyme with intestinal juices (no net movement)

Peristalsis in small intestines

chyme is propelled away from the stomach, towards the large intestines

Absorption in small intestines

 almost all small molecules (90%) are absorbed

2 methods of absorption in small intestine

1. Simple diffusion

2. Micelles and chylomicrons

Simple diffusion in small intestine

small molecules move across concentration gradient into the blood

Micelles and chylomicrons in small intestine

allows lipids to be taken up by lacteals (lymph vessel)

Cecum

 the place where the small intestine and large intestine meet (iliocecal junction)

4 regions of the large intestine (in order)

1. Ascending colon

2. Transverse colon (right to left)

3. Descending colon

4. Sigmoid colon (S-shape)

2 forms of mechanical digestion in the colon

1. Haustrall churning

2. Mass peristalsis

Haustrall churning

slow mixing and propulsion

Mass peristalsis

all contents are moved in a uniform fashion towards the rectum once or twice a day

Chemical digestion in the colon

Bacteria provide us with vitamins (Vitamin K) and aid in chemical digestion

3 substances that are absorbed by colon

1. Water

2. Electrolytes

3. Vitamins

What happens to the chyme after all substances are absorbed?

Becomes feces

Defecation reflex function

Eliminates feces

3 aspects of the defecation reflex

1. Mass peristalsis

2. Involuntary muscle

3. Voluntary muscle

Voluntary muscle in colon

External anal sphincter

Involuntary muscle in colon

Internal anal sphincter

Diarrhea

not enough absorption in the small intestines, which leads to excess water and fats in the stool

Constipation

feces is not able to move out of the anus due to excess absorption or improper functioning of the involuntary or voluntary muscles

Periodontal disease

inflammatory condition that affects the gums and bones that are supporting the teeth

How does periodontal disease affect digetsion?

Can make it painful to chew leading to food not being properly broken down - poor nutrient absorption

Treatment of periodontal disease

Professional cleaning, antibiotics, and possibly surgery

Prognosis of periodontal disease

If caught everly, tooth loss can be prevented. If caught late, tooth loss can occur

GERD

acid reflex (comes up from esophageal sphincter)

How does GERD affect digestion?

Causes irritation and inflammation of the esophagus

GERD treatment

Weight loss, avoid trigger foods, antacids, proton pump inhibitors, H2 blockers. New valve can be placed in surgery

GERD prognosis

Chronic condition but can be manageable with lifestyle changes and proper treatment

How do gastric ulcers affect digestion?

Impairs digestion because of perforations and bleeding in the stomach and small intestine