Download Digestive System

Digestive System
Digestion – a process that involves physically and chemically altering the composition of food
into smaller units of nutrition.
Digestive Functions include:

Ingestion – the act of bringing food into the digestive tract (alimentary tract or GI tract)

Mechanical Digestion – the mechanical breakdown of large food molecules

Motility- movement of food through the digestive tract through wave like contractions called
peristalsis.

Chemical Digestion – the release of chemicals into the digestive tract to catalyze digestion

Absorption– Movement of nutrient molecules from the digestive tract mucosa to the blood and
lymph

Elimination – movement of waste or undigested food out of the body. This act is called
defecation.
Mechanical Digestion
Mastication or the act of chewing physically breaks down large chunks of food. The teeth
are necessary for this to occur. Salivary glands assist the breakdown by secreting enzymes that
catalyze the digestion. Mastication leads to the formation of a bolus or a ball of food
Deglutition or the act of swallowing occurs through the placement of the bolus to the
stomach by the tongue. This triggers wave-like contractions or peristalsis of the oropharynx and
esophagus.
Teeth – two sets form during development
1. Primary teeth – deciduous teeth
a. Appear from 6 months to 2-4 years of age
b. There are 20; 10 in each jaw
c. Are lost between 6 & 13 years of age
2. Secondary teeth – permanent teeth
a. Appear from 6 years on and up to 17-25 years of age
i. The 3rd set of molars, wisdom teeth, can show up from 17-15 years of age
b. 32 teach in all
c. Push out the primary teeth
Structure of teeth – 2 main portions
1. Crown
a. Enamel – covers the crown; Calcium salts; does not get replaced
b. Dentin – like bone, but harder; surrounds the pulp cavity (which has the blood
vessels, nerves, and pulp or connective tissue)
2. Root
a. Root canal
b. Cementum – encloses the root
c. Periodontal ligament – surrounds the cementum
Muscles of Mastication- Skeletal muscles also play an important role in mechanical digestion.
1. Tongue (body of it)
2. Temporalis
2. Masseter
3. Medial & Lateral pterygoid
4. Suprahyoid muscles
5. Infrahyoid muscles
Muscles of Deglutition
1. Tongue
a. Genioglossus – protrudes tongue
b. Hyoglossus – depresses tongue
2. Phaynyx – oropharnyx; 2nd part of the pharynx
3. Esophagus – from pharynx to the stomach
Once swallowed, food passes through the Gastroesophageal or esophageal sphincter which divides
the respiratory system (upper esophageal sphincter- UES) from the digestive system (lower
esophageal sphincter- LES).
Chemical digestion
 Connection to the parasympathetic nervous system – secretion is increased with pleasant
smells and stopped with unpleasant smells
 Salivary glands secrete saliva
o Serous cells – amylase splits starch and glycogen molecules into disaccharides
o Mucus cells – mucous binds food particles and lubricates during swallowing
Stomach
The stomach has three divisions.
1. Fundus – upper left
2. Body
3. Pylorus – lower portion
Functions:
1. Food storage
2. Disinfect food
a. Destroys pathogenic bacteria
b. HCl – pH of 2
3. Chemical digestion
a. Limited amount of absorption for certain drugs, water, alcohol, short-chain fatty acids
b. Pepsinogen released to mix with HCl to break down proteins
Food moves out of the stomach through the pyloric sphincter in to the small intestine.
Small Intestine
The small intestine is divided into three major portions:
1. Duodenum – pyloric end of stomach attaches; 10 inches or 25 cm
2. Jejunum – 2.5 m or 8 feet; turns forward and downward
3. Ileum – 3.5 m or 12 feet
Functions:
1. digestion & absorption
2. chemical digestion
•
digestive enzymes
3. absorption through lining
•
over 6 meters!
•
small intestine has huge surface area = 300m2 (~size of tennis court)
**Once food moves through the small intestine, it enters the large intestine.
Large Intestine

The large intestine is also referred to as the colon. The Large intestine consists of 4 major
divisions:
1. Cecum
a. Vermiform appendix – projecting downward from large intestine’ narrow tube with a
closed end; no known digestive function; contains lymphatic tissue
2. Colon
a. Ascending colon
b. Transverse colon – longest and most movable part
c. Descending colon – downward
d. Sigmoid colon – S-shaped curve
3. Rectum – lies next to the sacrum and follows curvature; elimination
4. Anal canal – last 2.5-4.0cm of large intestine
a. Anus – canal that opens to the outside with two sphincter muscles
i. Internal anal sphincter muscle – smooth muscle under involuntary control
ii. External anal sphincter muscle – skeletal muscle under voluntary control
The major function of the colon is absorbing water and electrolytes of undigested food.
Accessory Organs
1. Liver
The function of the liver is to detoxify and filter the blood, assist in carbohydrate,
lipid, and protein metabolism and produces urea.
2. Gall Bladder
Stores bile, reabsorbs water to concentrate bile, and releases bile.
3. Pancreas
The pancreas is both an endocrine and exocrine gland. One of the endocrine
functions is to secrete insulin directly into the bloodstream. The exocrine function is to
secrete digestive chemicals through many islets through ducts to the GI tract.
Gastrointestinal Disturbances

Constipation – decreased motility of the colon, resulting in difficulty in defecation

Diarrhea – elimination of liquid feces, accompanied by abdominal cramps; Rotavirus in infants
can cause this issue.

Emesis – vomiting

Anorexia – chronic loss of appetite

Nausea – unpleasant feeling that often lead to vomiting

Gastroenteritis - Gastritis – stomach inflammation; enteritis – intestinal inflammation

Heartburn - an irritation of the esophagus that is caused by stomach acid refluxing back into
the esophagus from the stomach because the LES is not closing properly

Gas or Flatulence - the state of having excessive stomach or intestinal gas; can result in
uncomfortable feelings of bloating, as well as increased belching (burping) or passing of gas
from the rectum; Most people produce about 1-3 pints of gas a day, and pass gas about 14
times a day; The primary components of gas, flatus, are five odorless gases: nitrogen,
hydrogen, carbon dioxide, methane, and oxygen; odor comes from sulfur containing
compounds and certain spices or foods

Lactose intolerance – do not produce sufficient lactase to adequately digest lactose or milk
sugar; causes bloating, intestinal cramps and diarrhea. Can take pills for it now or infants drink
a soy formula.
Pathologies

Appendicitis – the appendix becomes inflamed and infected. Surgery required to prevent
rupturing. If it ruptures, the contents of the large intestine may enter the abdominal cavity and
cause serious infection called peritonitis. Can lead to death if untreated or not treated soon
enough.

Hemorrhoids – dilated veins that result from direct irritation or from increases in venous
pressure; inflamed and enlarged, cause pain, itching and sometimes bleeding; often from
pregnancy or constipation and the straining associated with it; literally a pain in the rear

Celiac Disease – mal-absorption in the small intestine is the reaction to gluten found in wheat
and rye. Microvilli are damaged and villi can be destroyed preventing the absorption of
nutrients; Symptoms are diarrhea, weight loss, weakness, vitamin deficiencies, anemia, bone
demineralization. Must follow a gluten-free diet.

Hiatal Hernia – a portion of the stomach is pushed through the hiatus (opening) of the
diaphragm, often weakening or expanding the cardiac sphincter at the inferior end of the
esophagus.

Gastroesophageal reflux disease (GERD) – backward flow of stomach acid into the
esophagus; causes burning and pressure behind the sternum; occur often but can be helped
with diet changes and some medications.

Gall stones – solid clumps of cholesterol that form in the gallbladder in 1 in 10 Americans.
Some produce pain and can require surgery. Sometimes removal of the gallbladder can be
necessary.

Gastric Ulcers – craterlike wound or sore in the stomach or duodenum. Causes burning pain
can result in hemorrhage, inflammation, scarring, or other serious health complications. Dr.
Barry Marshall and Dr. J. Robin Warren were awarded the Nobel Prize in Physiology or
Medicine in 2005 for discovering that infection with a spiral shaped bacteria, Helicobacter
pylori, and not excessive acid secretion was the primary cause of most ulcers.

Crohn’s Disease/Inflammatory Bowel Syndrome – inflammatory condition; autoimmune
colitis affects the small intestine; may need a change in diet, avoiding some foods, and drug
therapy

Hepatitis – inflammation of the liver; starts out with flu symptom, then proceeds to rash,
abdomen pain, dark and foamy urine and pale feces, skin and eyes turn yellow (jaundice);
medical attention necessary to prevent kidney failure and 5% can develop liver cancer; since it
is a virus – antibiotics will not help.
o Hep A – spreads by contact with food or objects contaminated with virus-containing
feces; can happen in daycares through diaper changes; usually short and mild course
o Hep B – spreads by contact with virus-containing body fluids such as blood, saliva, or
semen. (transfusions, needles {think tattoos}, and sexual activity)
o Hep C – causes ½ of all known cases; transmitted through blood by sharing razors,
needles, mom to fetus, use of blood products; many suffer chronic symptoms; need
interferon therapy.

Cirrhosis – degenerative liver condition; can be caused by hepatitis, chronic alcohol abuse,
malnutrition, or infection; damaged tissue is replaced with fibrous scar tissue and it will cont
function properly.

Acute Pancreatitis – results from a blockage in the release of pancreatic juice. Trypsin builds
up.

Colon Cancer – colorectal cancer; screen with stool samples and fiber optic colonoscopy;
procedure will sometimes remove the suspicious tissue, polyps, or a portion of the colon. Many
need screening after the age of 50. If you have a family history, do it after 30 or 40.
Surgeries for Weight Loss – Bariatric surgeries (per Mayo Clinic)

Roux-en-Y (roo-en-y) - most common method of gastric bypass; not reversible; surgeon cuts
across the top of your stomach, sealing it off from the rest of your stomach; resulting pouch is
about the size of a walnut and can hold only about an ounce of food (normally holds 3 pints of
food) ; cuts the small intestine and sews part of it directly onto the pouch; Food bypasses most
of your stomach and the first section of your small intestine; enters directly into the middle part
of your small intestine.

Biliopancreatic diversion with duodenal switch - complex, multipart procedure, about 80
percent of the stomach is removed; the pyloric valve remains, along with a limited portion of
the small intestine that normally connects to the duodenum. This surgery both limits how much
you can eat and reduces the absorption of nutrients; Effective but more risks!

Laparoscopic adjustable gastric banding (LAGB) - the surgeon positions an inflatable band
around the uppermost part of the stomach; when inflated, it acts like a belt; separates the
stomach into two parts; small upper pouch limits the amount of food you can eat; can be
adjusted so that it restricts more or less food; may need adjustment often

Vertical banded gastroplasty - also called stomach stapling, divides the stomach into two
parts, restricting how much food you can eat; not as popular and less long term success

Sleeve gastrectomy - called a vertical sleeve gastrectomy; the structure of your stomach is
changed to be shaped like a tube, which restricts the amount of calories your body absorbs.