Download The Digestive system - Northwest ISD Moodle

 the tube running through the body is known as the
alimentary canal, aka gastrointestinal tract.
 begins with the mouth and ends with the anus
 includes primary organs: pharynx, esophagus,
stomach, small intestine and large intestine
 includes accessory organs: salivary glands,
pancreas, liver and gallbladder. These are
connected to the GI tract by ducts
 ingestion: getting food into the body. Involves the mouth, including
the teeth, lips and tongue
 propulsion: begins after ingestion and continues all the way along
the GI tract. Propulsion is initiated by swallowing at the pharynx and
peristalsis (symmetrical contraction of muscles that moves food
along the remainder of the GI tract).
 mechanical breakdown: reduces food into smaller pieces and
increases the surface area. Examples: chewing, churning in the
stomach and further churning by muscular contraction in the small
intestine
 chemical breakdown: enzymes break large food molecules into
smaller molecules
 absorption: the movement of small food molecules from the lumen of
the small intestine into the blood
 defecation: the expulsion of food that was not absorbed. The waste
matter is called feces
 The walls of the alimentary
canal are composed
of four layers:
mucosa,
submucosa,
muscularis externa
serosa
 mucosa or mucous membrane: innermost, adjacent to the
lumen (opening)
 submucosa: below the mucosa; dense connective tissue
 muscularis externa: composed of two layers of smooth
muscle; propels food through alimentary canal by
peristalsis
 serosa: outermost layer; serous membrane that helps
minimize frinction between organs. In the abdominopelvic
region is known as the peritoneum
 the peritoneum is divided into two layers:
 parietal peritoneum: part that lines the body wall
 visceral peritoneum: part that wraps around the organs
and forms the outer layer of those organs
parietal and visceral peritoneum are held to each other by
mesentery, which helps hold the organs in their proper
place, especially the small intestine
 oral cavity: the mouth. Accomplished four of the
six key activities of digestion:
 ingestion of food
 mechanical breakdown of food (chewing)
 chemical breakdown of food (enzymes in saliva)
 propulsion of food (pushing food to pharynx for
swallowing)
The mouth has an epithelial lining of mucous membrane
(mucosa)
The lips assist with grabbing food and keeping it in the
mouth
The tongue has bumps called papillae on the surface where
taste buds are housed. Papillae also help the tongue grip
food to help manipulate food for swallowing.
Roof of mouth composed of hard palate and soft palate.
 the nasal cavity is located
above the above the
palate.
 uvula hangs down from
soft palate, preventing
food from entering the
nasal cavity when we
swallow
 teeth are used to begin the mechanical breakdown of food,
which provides greater surface area for enzymes to
chemically break down food
 the gum is called gingiva
 incisors: four teeth on top and both
 canines: on each side of incisors
 two molars
 two bicuspids arrive with permanent teeth
 third molar (wisdom teeth) may never erupt
 Anatomy of the tooth:
 crown is part that projects from jawbone
 coated with enamel
 body of tooth is made of dentin
 root is part embedded in jawbone
 neck is part between crown and root
 pulp cavity is the hollow central region containing soft
tissue, nerves and blood vessels
 root canal is a passageway for nerves and blood
vessesl to reach the pulp cavity
 periodontal ligament anchors each tooth
 three pair of salivary glands are the first accessory organs
of digestion that aid in chemical breakdown
 parotid salivary glands are the largest and lie just in front
and below the ears
 submandibular salivary glands lie are on the lower back
part of the mandible
 sublingual salivary glands are under each side of the
tongue
 Saliva is composed mostly of water but also contains
mucus, antibodies and several enzymes (salivary
amylase and lingual lipase)
Functions of saliva:
moisten and lubricate food making it easier to
taste and swallow
protect mouth against bacteria
initiate chemical breakdown of food
 Pharynx: the region that connects the mouth and the nasal
cavity to the trachea and esophagus. Composed of three
main parts:
 nasopharynx: connects the nasal cavity to the
oropharynx. Only air passes through here.
 oropharynx: lies at the back of the mouth. Food, liquids
and air pass through here.
 laryngopharynx: includes the glottis (opening to the
larynx and trachea) and extends to the top of the
esophagus.
 epiglottis: a fold of tissue on the front side of the
oropharynx and laryngopharynx. As food or liquid is
swallowed, the epiglottis contracts downward to cover the
glottis so that neither can enter the trachea.
 Esophagus: a muscular tube that connects the pharynx to
the stomach. It lies posterior to the trachea and heart and
passes through an opening in the diaphragm.
 When food enters the top of the esophagus during the act of
swallowing, a wave of peristalsis (wave of muscular
contractions) begins which pushes food downward and into
the stomach.
 Stomach: a reservoir in which food is broken down
mechanically and chemically before it enters the small
intestine. 3 regions:
 the cardia: “near the heart”, region closest to the opening of
the esophagus
 the fundus: upper end of the stomach; the body
 the pyloric region: the lower end
 empty the stomach holds 50 ml
 folds inside the wall called rugae and help increase the
stomach’s volume to two liters or more
 when food enters the stomach, it mixes with acidic gastric
juice to form chyme
 small intestine: the longest segment of the GI tract, 7-8
yards relaxed
 most chemical breakdown of food occurs in the small
intestine
 all food absorption and most water absorption occurs here
 the small intestine has three segments:
 duodenum
 jejunum
 ileum
 chemical breakdown in the small intestine:
 chyme enters the duodenum from the stomach where it mixes
with bile and pancreatic juice
 bile play a big role in emulsification, the breakdown of large
fat particles
 pancreatic juice contains several chemicals that break down
the chime and food particles
 bicarbonate: neutralizes acidic chyme
 pancreatic amylase: breaks down starches
 pancreatic lipase: breaks down lipids
 the liver and gallbladder are accessory organs
 gallbladder: stores bile and delivers it to duodenum when
needed to breakdown lipids. Can live without a gallbladder
 liver: largest organ by weight in the abdominopelvic cavity.
 specific metabolic functions of the liver include:
 maintain normal blood concentrations of glucose, lipid
and amino acids
 converts one nutrient type to another (carbohydrates to
lipids)
 synthesis and storage of glycogen
 storage of iron, lipids and fat-soluble vitamins
 absorption and inactivation of toxins, hormones,
immunoglobulins and drugs
 liver lobules: microscopically the liver is made up of a
million functional units called liver lobules.
 bile: is a water solution containing bile salts. Bile salts
combine with fat droplets in chime and emulsify (break
apart) the fats. This increases the total surface area of fats
making them easier to be broken down by lipase
 bile storage: liver makes bile all day but it’s needed only
after a meal. The gallbladder will store it and release when
needed
 Pancreas: an accessory organ behind and underneath the
stomach. It’s also part of the endocrine gland and functions
as and endocrine (secretes products into the blood) and
exocrine (secretes products into the lumen of the small
intestine) gland
 pancreatic juices: contain digestive enzymes that break
down all major classes of nutrients
 glucose regulation: pancreas secretes hormones that
regulate the concentration of glucose in the blood
 insulin: increases glucose uptake
 glucagon: promotes conversion of glycogen to glucose
 Large intestine: larger in diameter than small intestine but
only 5 feet in length
 major segments:
 cecum
 colon
 rectum
 anal canal
 the colon has four major segments:
 ascending
 transverse
 descending
 sigmoid
Once food has reached the large intestine almost all of its nutrients
have been extracted. During the 12-24 hours the residue resides in
the colon additional water, some electrolytes and water-soluble
vitamins are absorbed
 defecation begins when waste reaches the rectum. The
waste stretches the rectal wall, initiating reflex contractions
of muscles in the sigmoid colon and rectum. These
contractions push waste toward the anus, causing the
internal anal sphincter to relax.
 the external anal sphincter is skeletal muscle so is under
voluntary control