Anatomy & Physiology

The Digestive System & Body Metabolism

The Alimentary Canal (or gastrointestinal, GI, tract) is the hollow tube where digestion occurs.

The organs include: mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.

It is ~30 feet long.

Organs of the Digestive System:

http://www.google.com/imgres

Digestion is the decomposition (breakdown) of food for the body’s use.

This is both chemical and mechanical.

Mastication: chewing food.

Mouth (Oral Cavity):

Digestion begins here.

Food is broken down mechanically and chemically.

Its accessory organs:◦ Cheeks◦ Lips◦ Tongue◦ Palate◦ Teeth

http://www.blogaholics.ca/wp/uploads/illu_mouth.jpg

Swallowing occurs in 3 stages:

◦ Voluntary: food is chewed & consciously swallowed

◦ Swallowing reflex is triggered: through a variety of steps, food is moved by peristalsis to the esophagus

◦ Peristalsis: food moves through the esophagus

While swallowing, breathing does not occur.

Swallowing:

Pharynx: Esophagus:

From the stomach, food passes thru to the pharynx.

It contains 3 parts:◦ Nasopharynx (air

passageway)◦ Oropharynx (food

passageway)◦ Laryngopharynx

(passageway to the esophagus)

A tube that runs ~25cm (10”) long

Allows peristalsis to continue

Just before the esophagus meets the stomach is a circular section of smooth muscle called the cardiac sphincter (a.k.a. lower esophageal sphincter) which controls the movement of food into the stomach. Usually this sphincter is closed (until food reaches it).

◦Mucosa (mucous membrane): contains glands that secrete mucus & digestive enzymes serves as protection (underlying

tissues)

◦Submucosa

◦Muscular layer: smooth muscle and some nerves function is movement.

◦Serosa (serous layer)

The Four Layers of Tissue:

Four Layers:

http://www.web-books.com/elibrary/medicine/Physiology/Digestive/stomach.jpg

J-shaped organ that is below the cardiac sphincter of the esophagus

It can hold ~1 liter or more

It contains mucosal and submucosal layers

Mixes food with gastric juices (that contain enzymes & acids)

Stomach:

http://mywebpages.comcast.net/wnor/stomachinside.jpg

http://www.nfl.com/gamecenter?game_id=29294&displayPage=tab_gamecenter&season=2007&week=REG7

Function: Finish digestion and begin absorption of digested particles

Parts of the Small Intestine:◦Duodenum: first portion; ~25cm long◦ Jejunum: second section◦ Ileum: last section (not truly distinctive from

the jejunum)Both the jejunum and the ileum are protected by the peritoneal membrane called the mesentery

Intestinal villi are tiny projections that come from the small intestines that increase the surface area and aid in absorption.

The small intestine is the most important absorbing organ of the alimentary canal.

Small Intestine:

Small Intestine:

http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19221.jpg

http://www.google.com/imgres

Chyme moves from the small intestine into the large intestine

Much shorter than the small intestine but is larger in its diameter

“surrounds” the small intestine

absorbs water & electrolytes from chyme

the remaining material becomes feces. ◦ This is ~75% water while the remaining is

anything that was not digested or absorbed (electrolytes, mucus, intestinal cells, bacteria & bile pigments which give feces its color).

◦ Its odor comes from bacteria products.

Large Intestine:

Does not contain villi

Parts of the Large Intestine:

◦ Cecum: 1st part of the large intestine which is directly below the ileocecal sphincter. Below this is the vermiform appendix (a.k.a.

appendix). This has no known function but has been discovered to have some lymphatic tissue.

◦ Colon: has 4 portions: Ascending colon: upward Transverse colon: below the stomach; largest

section Descending colon: downward Sigmoid colon: twists into an S-shape,

becoming this; the sigmoid reaches the rectum.

◦Rectum: ends at ~5cm below the tip of the coccyx

◦Anal Canal: an opening to the external environment; feces exits the body.

The anus is guarded by 2 sphincters:

◦ The internal anal sphincter muscle: involuntary control (smooth muscle)

◦ External anal sphincter muscle: voluntary control (skeletal muscle)

Large Intestine:

http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19220.jpg

Accessory Digestive Organs

Function: masticate

Primary teeth (a.k.a. deciduous teeth) are the first set of teeth

◦ 20 teeth (10 in each jaw)

Secondary teeth (a.k.a. permanent teeth) are the second set of teeth

◦ 32 teeth (16 in each jaw)

◦ grow in at 6-25 years (3rd molars appear between 17-25)

Teeth:

http://www.cdha.ca/images/facts_baby_6.gif

http://www.tela.co.in/images/permteeth.jpg

incisors (front teeth) have sharp edges to bite off food

cuspids (eye teeth) are sharp, sometimes pointed for biting, grabbing & tearing food

biscuspids (behind cuspids) and molars (back teeth) are flat for grinding food

Classification of Teeth:

Anatomy of a Tooth:Crown (above the gum)

Root (below the gum; anchors)

Enamel (glossy white covering composed of calcium)

Dentin (bone-like substance that surrounds the tooth’s interior pulp cavity)

Pulp cavity (interior tooth composed of BVs, nerves & connective tissue)

Root canal (BVs and nerves that run the center of the pulp cavity)

http://apps.uwhealth.org/health/adam/graphics/images/en/1121.jpg

secrete saliva (contains serous fluid & mucus)

Serous fluid contains a digestive enzyme, amylase which breaks down sugars.

Mucus lubricates & coats the food

Salivary Glands:

http://cache.eb.com/eb/image?id=74321&rendTypeId=4

Endocrine AND an exocrine gland.

Produces pancreatic juice.

Pancreatic juice digests carbs, fats, nucleic acids and proteins.

Pancreas:

http://www.med.umich.edu/1libr/wha/pancreas.gif

Liver & Gallbladder:Liver: Gallbladder:

Reddish-brown 2 lobes Produces bile

(which emulsifies fat)

Connected to liver & small intestine

Stores bile

http://www.pbiv.com/images/nature/lbp/liver_diagram.gif

Ingestion: to eat

Propulsion: to move food throughout the canal (peristalsis)

Mechanical digestion: to chew, churn; physical break down

Chemical digestion: to breakdown food with enzymes

Absorption: to transport products of digestion into blood stream

Defection: to eliminate waste

Processes of Digestive Tract:

Know the location and final product of each macromolecule digestion:

..\..\..\..\A&P_files\macromolecule end product of digestion chart.docx

http://www.buzzle.com/articles/list-of-digestive-enzymes.html

Polysaccharides (mostly starch) are broken down into disaccharides and monosaccharides (sugars.)

Proteins are broken down into amino acids. Fats are broken down into glycerol and fatty

acids. Nucleic acids are broken down into nucleotides.

Digestion:

Chyme takes 3-10 hours to move through the small intestine

A peristaltic rush can occur if the small intestine is irritated.

◦This is a sweeping motion that empties the small intestine’s contents into the large intestines and continues that sweeping motion without nutrient absorption.

◦Diarrhea may result.

Movement through the Intestine & Defecation:

Movements of large intestine: both mixing and peristalsis:

Slower than the small intestine

Peristalsis occurs 2-3 times daily

Peristaltic waves produce mass movements (irritation & inflammation, such as colitis, also stimulate these mass movements)

◦Defecation reflex is the force of pushing feces out the anus

Look up online or in text! Know the following:

appendicitis, gallstones, jaundice, hepatitis, cirrhosis, heartburn, hiatal hernia, vomiting, pancreatitis, peptic ulcers, diverticulosis, diarrhea, constipation, BMR, hyperthyroidism, hypothyroidism, hypothermia, frostbite, hyperthermia, heat stroke, heat exhaustion, & appendicitis