Digestive System

gastrointestinal tract

digests and absorbs food

accessory organs

aids digestions (teeth, tongue, gallbladder, salivary glands, liver and pancreas

ingestion

taking food into the digestive tract

propulsion

moving food along GI tract

mechanical digestion

chewing, churning, and other physical processes that increase surface area of food and prepares it for digestion by enzymes

chemical digestion

breaking down of complex food molecules into their building blocks

defecation

elimination of solid waste from the body

physiological word for chewing

mastication

chewing function

break down food into pieces small enough for enzymes to chemically digest

“baby teeth”

primary dentitions. full set = 20 dentitions

“adult teeth”

develop under the baby teeth. called permanent dentitions. full set contains 32 dentitions.

what 12 teeth do adults have that children do not

first and second premolar (bicuspids) and third molars (wisdom teeth)

tooth structure

• enamel = hardest substance in the human body which covers the crown of the tooth

• gingiva = gum tissue and this is where we find the neck of the tooth

• root = part of the tooth that is embedded in the bone

4 functions of tongue

1. Gripping and positioning food during chewing

2. Mixing food with saliva to form a bolus

3. Involved in swallowing

4. Involved in speech

tongue structure

• front 2/3 of the tongue contains papillae which increases friction to help hold the food in place and to house the taste buds

• posterior 1/3 of the tongue contains the lingual tonsils

4 functions of saliva

1. Cleansing the mouth (helping to keep it infection free) – contains lysosomes and antibodies
   called IgA

2. Dissolves food chemicals so that the taste buds can be stimulated

3. Moistens food which aids in the formation of the bolus

4. Begins the chemical digestion of carbohydrates (contains an enzyme called salivary amylase)

3 pairs of salivary glands

1. Parotid glands: in front of the ears

2. Sublingual glands: under the tongue

3. Submandibular glands: under the mandible; produce the majority of saliva (~70%)

bolus of food

food mixed with saliva and rolled into a circular shape by the tongue (easier than swallowing a “chunk” of food)

3 regions of pharynx (throat)

nasopharynx, oropharynx, and the laryngopharynx. The pharynx is a passageway for food, fluids, and air

esophagus

moves the bolus of food from the pharynx to the stomach. It is located behind the trachea

2 sphincter muscles of esophagus

superior esophageal sphincter and the inferior esophageal sphincter

how does esophagus travel

travel through the thoracic cavity and then go through an opening in the diaphragm to reach the stomach. The opening in the diaphragm is called the esophageal hiatus

2 phases of deglutition

voluntary and involuntary phases

Voluntary phase of deglutition

tongue pushes against roof of mouth, tongue muscles contract and force bolus of food into pharanyx

What does cranial nerve X control (vagus) and how?

involuntary phases of deglutition

1. stimulates uvula to block passage to nasal cavity

2. Stimulates epiglottis to block passage in laranyx

3. relaxes superior esophageal sphincter

4. ensures there is only 1 passageway open for food bolus

When does superior esophageal sphincter close and epiglottis and uvula open?

immedietely after food bolus passes through esophagus. Around same time simulation of uvula and epiglottis of vagus nerve decreases

What process moves food bolus through esophagus?

peristalis = sequential smooth muscle contraction that start at superior end of esophagus and move forward toward stomach

how long does it take solids and fluids to go through esophagus and reach stomach?

• solids = 4-8sec

• fluids = 1-2sec

when does inferior esophageal sphincter open and allow the bolus of food to enter the stomach

remains closed until food bolus reaches it (vagal stimulation)

which quadrant is most of the stomach located?

left upper quadrant. small part extends to right upper quadrant

wall of stomach

made of smooth muscle that contracts and churns to mix the bolus of food with gastric juice to form chyme.

lining of stomach

“mucosa” = contains cells that produce alkaline mucus. When stomach is empty, mucosa folds (folds are called rugae)

pH of stomach

1.5-3.5 - very acidic

chemical digestion of proteins

begins in the stomach. when proteins are exposed to acid they become denatured (lose 3-D structure and straighten into chain of amino acids). this makes it easy for enzymes to access and break peptide bonds

what do the gastric glands of the stomach contain

chief cells = produce compound called pepsinogen, later converted to pepsin (active enzyme that chemically digests proteins)

parietal cells = produce HCl in addition to denaturing proteins and converts pepsinogen into pepsin), creates hostile environment for bacteria

gastric juice

HCl and pepsin

pyloric sphincter

distal end of the stomach. controls entry of chyme into duodenum (first part of small intestine). chyme slowly reaches duodenum to give time to complete chemical digestion.

small intestine

3 regions in order

1. duodenum = absorbtion and chemical digestion

2. jejunum = absorbtion

3. ileum = absorbtion

lipid digestion

products are glycerol and fatty acids. initially absorbed into lacteals (lymphatic capillaries) and eventually end up in the blood

3 structures within small intestine

1. circular folds

2. villi = blood capillaries and lacteals found here

3. microvilli

2 types of motility and what does each accomplish?

1. mixing = back and forth movement of chyme and digestive enzymes to mix them together so that chemical digestion can occur

2. peristalsis = occurs after absorbtion is completed, so what is left is in the small intestine is waste

what 3 organs does duodenum utilize

pancreas, liver, and gallbladder. duodenum uses hormones to communicate with these organs

what is bile

alkaline substance that emulsifies lipids. bile breaks down large fat globules into smaller fat droplets which lipase can easily digest

bile production, storage, and transportation

produced by the liver, stored in the gall bladder, and transported to the duodenum when we eat lipids

3 ducts that transport bile

1. common hepatic duct = transports bile away from liver

2. cystic duct = transports bile to the gall bladder for storage and away from gall bladder for use

3. bile duct = common hepatic and cystic ducts merge to form bile duct which transports bile to duodenum for use when we eat lipids

pancreas

produces digestive enzymes and secretes them into main pancreatic duct - will transport them to duodenum

4 digestive enzymes

1. trypsin = digests proteins

2. chymotrypsin = digests proteins

3. pancreatic amylase = digests carbohydrates

4. lipase = digests lipids

4 functions of liver

1. produce bile

2. store glucose as glycogen

3. produces plasma proteins such as albumin

4. detoxifies drugs, alcohol, and toxic metabolic byproducts such as NH3

2 functions of large intestine

1. reabsorb water

2. eliminate waste

7 regions of large intestine in order

1. cecum

2. ascending colon

3. transverse colon

4. descending colon

5. sigmoid colon

6. rectum

7. anal canal

Ilececal valve

controls movement of waste from small intestine to large intestine

teniae coli

3 stripes of smooth muscle that pucker large intestine

haustra

the segments that are created when the large intestine puckers

bacterial flora

ferment indigestible carbohydrates

peritoneum

produces fluid that reduces friction as organs move

mesentery

helps hold digestive organs in place

nonpathogenic bacteria

colonize the large intestine and oral cavity. Referred to as bacterial flora and do not cause disease but produce vitamin B and K and ferment hydrates we cannot digest

2 sphincter muscles and composition

1. internal anal sphincter = smooth muscle, involuntary control

2. external anal sphincter skeletal muscle, voluntary control

serous membrane of abdominal and pelvic cavities

peritoneum - 2 tissue layers:

1. visceral = lines surface of digestive organs

2. parietal = lines cavity where organs are housed

3 serous membranes

produce fluid to lubricate and decrease friction as organs move

1. peritoneum = abdominal and pelvic cavities

2. pericardium = heart

3. pleura = lungs

mesenteries functions

double layer of peritoneum

1. primary function is to secure/hold digestive organs in place

2. pathway for nerve fibers and blood vessels

3. store visceral fat (associated w metabolic disease)