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digestive system

organ system that processes food, extracts nutrients from it, and eliminates the residue. does this in five stages

five stages of digestion

1) ingestion 2) digestion 3) absorption 4) compaction 5) defecation


the selective intake of food


the mechanical and chemical breakdown of food into a form usable by the body


the uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and the lymph


absorbing water and consolidating the indigestible residue into feces


the elimination of feces

2 stages of digestion

mechanical and chemical

mechanical digestion

is the physical breakdown of food into smaller particles. achieved by the cutting and grinding action of the teeth and churning contractions of the stomach and small intestines.

chemical digestion

is a series of hydrolysis reactions that break down dietary macromolecules in their monomers(residues)

digestion: polysaccharides

are broken down into monosaccharides

digestion: proteins

are broken down into amino acids

digestion: fats

are broken down into monoglycerides and fatty acids

digestion: nucleic acids

are broken down into nucleotides

2 divisions of the digestive system

1) the digestive tract 2) the accessory organs

the digestive tract

is a muscular tube extending from the mouth to anus. measuring about 9m (30 ft) long in the cadaver. aka the alimentary canal.

the accessory organs

are the teeth, tongue,salivary glands, liver, gallbladder, and pancreas.

tissue layers of the digestive tract from inner to outer

MUCOSA=epithelium, lamina propria. muscularis mucosae, SUBMUCOSA, MUSCULARIS EXTERNA= inner circular layer, outer longitudinal layer, SEROSA=arelolar tissue, mesothelium

the mucosa (mucus membrane)

lining the lumen consists of an inner epithelium , a loose connective tissue layer called the LAMINA PROPRIA, and a thin layer of smooth muscle called the MUSCULARIS MUCOSAE.

the submucosa

is a thicker layer of loose connective tissue containing blood vessels, lymphatic vessels, a nerve plexus, and in some places, glands that secrete lubricating mucus into the lumen.

the muscularis externa

consists of 2 layers of muscle near the outer surface. cells of the inner layers encircle the tract while those of the outer layer run longitudinally. in some places, the circular layer is thickened to form valves (sphincters) that regulate the passage of material through the tract. the longitudinal layer is responsible for the motility that propels food and residue through the digestive tract.

the serosa

is composed of a thin layer of areolar tissue topped by a simple squamous mesothelium. it begins in the lower 3 to 4 cm of the esophagus and ends just before the rectum.

enteric nervous system

the esophagus, stomach, and intestine have a nervous network called the ________ __________ ________, which regulates digestive tract motility, secretion, and blood flow. this system is thought to have over 100 million neurons--more than the spinal cord. it can function completely independently of the CNS, although the CNS usually exerts a significant influence on its action.

the enteric nervous system is composed of 2 networks of neurons:

1) the submucosal plexus (meissner) 2) the myenteric plexus (auerbach)

the submucosal plexus (meissner)

network of neurons in the submucosa

the myenteric plexus (auerbach)

a network of neurons of the parasympathetic ganglia and nerve fiber between the 2 layers of the muscularis externa. controls peristalsis and the other contractions of the muscularis externa and the submucosae and glandular secretion of the mucosa.


connective issue sheets that stabilize the positions of the attached organs and prevent the intestines from becoming entangled. also provide passage for the blood vessels and nerves that supply the digestive tract, and contain many lymph nodes and lymphatic vessels

dorsal mesentery

the parietal peritoneum that lines the wall of the abdominal cavity, along the posterior midline(dorsal) of the body in turns inward and forms the _________ _________, a translucent 2-layered membrane extending to the digestive tract.

ventral mesentery

may hang freely in the abdominal cavity or attach to the anterior (ventral) abdominal wall or other organs

lesser omentum

a ventral mesentery, it extends from the stomach to the liver.

greater omentum

hangs from the left inferior margin (greater curvature) of the stomach and loosely covers the small intestine like an apron.

neural, hormonal, and paracrine mechanisms

the motility and secretion of the digestive tract are controlled by __________ ___________ __________.

the neutral controls:

short and long autonomic reflexes.

short (myenteric) reflexes

stretching and chemical stimulation of the digestive tract act through the myenteric nerve plexus to stimulate contractions in nearby regions of the muscularis externa, such as the peristaltic contractions of swallowing .

long (vagovagal) reflexes

act through autonomic nerve fibers that carry sensory signals from the digestive tract to the CNS and motor commands back to the digestive tract.

gastrin and secretin

hormones produced by the digestive tract.the hormones are secreted into the blood and stimulate relatively distant parts of the digestive tract

histamine and prostaglandins

paracrine secretions that stimulate digestive function. the paracrine secretions diffuse through the tissue fluids and stimulate nearby target cells

the mouth

is also known as the oral or buccal cavity.

function of the mouth

include ingestion(food intake) taste, and other sensory responses to food, chewing, chmical digestion (starch is partially digested in the mouth) swallowing, speech,and respiration.

the mouth is enclosed by:

cheeks, lips, palate, and tongue.

oral fissure

mouth's anterior opening between the lips.


mouth's posterior opening in to the throat.

the mouth is lined with:

stratifies squamous epithelium. this epithelium is keratinized in area subject to greatest food abrasion, such as the gums and hard palate, and non-keratinized in other areas, such as the floor of the mouth, soft palate, and the inside of the check and lips.

the cheeks and lips:

retain food and push it between the teeth for chewing. are essential for articulate speech, and for sucking and blowing action. their fleshiness is due to the subcutaneous fat, the buccinator muscles of the cheek , and the orbicularis oris muscle of the lips

labial frenulum

attaches each lip to the gum, between the anterior incisors.


the space between the the cheeks or lips and the teeth--the space where you insert a toothbrush when brushing your teeth.

3 areas of the lips

1) the cutaneous area 2) the red area (vermillion) 3) the labial mucosa

the cutaneous area

is colored like the rest of the face and has hair follicles and sebaceous glands, on the upper lip,this is where the mustache grows.

the red area (vermillion)

is the hairless region where the lips meet (where some apply lipstick)

the labial mucosa

is the inner surface of the lip, facing the gum and teeth.

the tongue

although muscular and bulky, is a remarkably agile and sensitive organ. it manipulates food between the teeth while it avoids being bitten, it can extract food particles from the teeth after a meal, and it is sensitive enough of feel a stray hair in a bite of food.

the tongue surface

is covered with nonkeratinized stratified squamous epithelium

lingual papillae

bumps and projections, that are the site of the taste buds.

tongue: body

the anterior 2/3 of the tongue, it occupies the oral cavity.

tongue: root

the posterior 1/3, that occupies the oropharynx.

vallate papillae

v-shaped row of papillae that marks the boundary between the body and root of the tongue

terminal sulcus

a groove behind the vallate papillae

lingual frenulum

the body of the tongue is attached to the floor of the mouth by a median fold called the _______ __________.

intrinsic muscles

the muscles of the tongue, which compose most of it's mass, contained entirely within the tongue, produce the relatively subtle tongue movements of speech.

extrinsic muscles

GENIOGLOSSUS, HYOGLOSSUS,PALATOGLOSSUS, STYLOGLOSSUS with origins elsewhere and insertions in the tongue, produce the stronger movements of food manipulation.

hard (bony) palate

is supported by the palatine processes of the maxillae and by the smaller palatine bones

soft palate

has a more spongy texture and is composed mainly of skeletal muscle and glandular tissue , but no bone.


conical medial projection of the soft palate, helps to retain food in the mouth until one is ready to swallow.


the teeth are collectively known as ______________.

function of the teeth

they serve to masticate the food, braking it into smaller pieces. this not only makes food easier to swallow, but also exposes more surface ares to the action of the digestive enzymes and thus speeds up chemical digestion.

number of teeth

adults normally have 16 teeth in the mandible and 16 in the maxilla


are chisel-like cutting teeth use to bite off a piece of food.


are more pointed and act to to puncture and shred

premolars and molars

have relatively broad surfaces adapted for crushing and grinding


each tooth is embedded in a socket called an ____________.


each tooth and socket forms a joint called a ________________.

periodontal ligament

the alveolus is lined by a , a modified periosteum whose collagen fibers penetrate into the bone on one side and into the tooth on the other.


the gum or __________ covers the alveolar bone. regions are defined by their relationship top the gingiva

the crown

is the portion above the gum.

the root

is the portion below the gum

the neck

is the point where the crown, root and gum meet.

gingival sulcus

the space between the tooth and the gum is the _____.


most of a tooth consists of hard yellowish tissue called ___________.


covers the crown and neck and CEMENTUM in the root. dentin and cementum are living conncetive tissues with cells and cell processes embedded in a calcifies matrix.


is not a tissue but a cell free secretion produced before the tooth erupts above the gum. damaged dentin and cementum can regenerate, but damaged enamel cannot--it must be artificially repaired.

pulp cavitiy

a tooth has a dilated _________ in the crown and a narrow root canal in the lower root these spaces are occupied by pulp--a mass of connective tissue, blood and lymphatic vessels and nerves.

apical foramen

these nerves and vessels enter the tooth thru a pore called the _____________. at the basal end of each root canal.


the meeting of the teeth when the mouth is closes is called _____________, and the surfaces where they meet are called the occlusal surfaces.


the occlusal surface of a premolar has 2 rounded bumps called _____, thus the premolars are also known as bicuspids. the molars have 4 or 5 _____._____ of the upper and lower premolars and molar mesh when the jaws are closed and slide over each other as the jaw make lateral chewing motions.


teeth develop beneath the gums and __________ (emerge) in predictable order.

deciduous teeth

20_______________(milk teeth or baby teeth) erupt from the ages 6-30 mo, beginning with the incisors.

permanent teeth

between 6 and 25 years of age, these are replaced by the 32 _______________.

wisdom teeth

the third molars erupt around ages 17 to 25 if at all.


over the course of human evolution, the face became flatter and the jaws shorter, leaving little room for the third molars. they often remain below the gum and become ____________ so crowed against neighboring teeth and bone that they cannot erupt.


(chewing) breaks food into pieces small enough to be swallowed and exposes more surface to the action of digestive enzymes. it is the first step in chemical digestion. ____________ requires little thought because food stimulates receptor that trigger an involuntary chewing reflex. the tongue buccinator and orbicularis muscles manipulates the food and push it between the teeth.

functions of saliva

moisten the mouth, digest a little starch and fat, cleanses the teeth, inhibits bacterial growth, dissolves molecule so they can stimulate the taste buds, and moistens food and binds particles together to aid in swallowing. it is a hypotonic solution of 97.0%-99.5 % water and solutes

solutes in the saliva

1) salivary amylase 2) lingual lipase 3) mucus 4) lysozyme 5) immunoglobulin A (IgA) 6) electrolytes

salivary amylase

solute found in saliva, an enzyme that begins starch digestion in the mouth

ligual lipase

an enzyme that is activated by stomach acid and digests fats after the food is swallowed.


bind and lubricates food mass and aids in swallowing


and enzyme that kills bacteria.

immunoglobulin A (IgA)

an antibody that inhibits bacterial growth


including sodium, potassium, chloride, phosphates and bicarbonate salts

pH of saliva


saliva begins

to digest starch before the food is swallowed and fat after it is swallowed.

2 kinds of salivary glands

intrinsic and extrinsic

intrinsic salivary glands

LINGUAL GLANDS, LABIAL GLANDS, BUCCAL GLANDS are an indefinite number of small glands dispersed amid the other oral tissues, they include the lingual glands in the tongue, labial glands on the inside of the lips, and buccal glands on the inside of the cheek

extrinsic salivary glands

PAROTID GLANDS, SUBMANDIBULAR GLANDS, SUBLINGUAL GLANDS are three pairs of larger. more discrete organs located outside the oral mucosa. that communicate with the oral cavity by way of ducts.

the parotid gland

is located just beneath the skin anterior to the earlobe. its duct passes superficially over the masseter, pierces the buccinator and opens into the mouth opposite the second upper molar tooth. MUMPS is an inflammation and swelling of the parotid gland caused by a virus.

the submandibular gland

is located halfway along the body to the mylohyoid muscle. its ducts empties into the mouth at the papilla on the side of the lingual frenulum, near the lower central incisor.

the sublingual gland

is located in the floor of the mouth. it has multiple ducts that empty into the mouth posterior to the papilla of the submandibular duct.


the extrinsic salivary glands secrete about 1.0-1.5 l of saliva per day.

salivary nuclei

food stimulates tactile, pressure, and taste receptors in the mouth, which transmit signals to a group of _________ ________ in the medulla oblongata and pons.


salivary amylase begins to digest starch as the food is chewed, while the mucus in the saliva binds food particles into a soft, slippery. easily swallowed mass called a ______. without mucus, one must drink a much larger volume of fluid to swallow food.

the pharynx

is a muscular funnel that connects the oral cavity to the esophagus, as well as connecting the nasal cavity to the larynx, thus , it is a point where the digestive and respiratory tract intersect.

pharyngeal constrictors

Superior, middle and inferior. The circular muscles that forces food downward during swallowing:

upper esophageal sphincter

made of smooth muscle at the superior end of the esophagus; relaxes so food and drink can be channeled into the esophagus, then closes once food and drink is in the esophagus, not an anatomical feature, disappears at death.


is a straight muscular tube 25-30 cm long.

esophageal hiatus

after passing downward, through the mediastinum, the esophagus penetrates the diaphragm at an opening called the ________ _______, continues another 304 cm, and meets the stomach at the level of the t7 vertebra.

cardiac orifice

where the esophagus meet the stomach. it is named this because of its proximity to the heart.

lower esophageal sphincter

a physiological sphincter that briefly slows down food before it enters the stomach . it also acts to prevent stomach contents from regurgitating into the esophagus, thus protecting the esophageal mucosa from the corrosive effect of the stomach acid.


process of swallowing, complex action involving over 22 muscles in th mouth, pharynx, and esophagus, coordinated by the swallowing center

buccal phase

The first phase in swallowing, the tongue collects food, presses it against the palate to form a bolus, and pushes it back into the oropharynx. the bolus stimulates the tactile receptors and activates the next phase

pharyngo-esophageal phase

2nd phase of swallowing is under involuntary control, 3 actions block food and drink from reentering the mouth ot entering the nasal cavity or larynx: 1) root of the tongue blocks the oral cavity 2)the soft palate rises and blocks the nasopharynx 3)the infrahyoid muscles pull back they larynx up to meet the epiglottis while the vestibular fold adduct to to close the airway


rhythmic muscular contractions that squeeze food through the esophagus into the stomach, liquid reach the stomach in 1-2 seconds, a food bolus in 4-8 seconds


large muscular sac that is located in the upper left abdominal cavity immediately inferior to the diaphragm. continues the mechanical and chemical digestion of food, internal volume of 50 ml when empty, 1.0-1.5 l after a typical meal, can expand up to 4l.


a semiliquid mass of partially digested food that passes from the stomach through the pyloric sphincter into the duodenum

lesser curvature

the smaller inside curve of the stomach between the entrance of the esophagus and the pylorus (10 cm)

greater curvature

referring to the outer and longer curve of the stomach (40 cm)

4 regions of the stomach

cardiac, fundus, body, and pylorus

cardiac region

an area of the stomach that is surrounding the cardiac orifice through which food enters the stomach from the esophagus

fundus region

a rounded portion at the top of the stomach

body region

central main portion of the stomach

pylorus region

pyloric sphincter and pyloric orifice, right before entering duodenum of small intest.

pyloric sphincter

the sphincter muscle of the pylorus that separates the stomach from the duodenum, controls the movement of chyme from the stomach to the small intestines

gastric rugae

Folds formed in the interior gastric mucosa of the stomach

gastric pits

gastric mucosa is pocked with depressions which are lined with the the same columnar epithelium as the surface. they are continually producing new epithelial cells, Channels that open into gastric glands located between the columnar cells of the mucosa

cardiac glands

gastric gland located in the cardiac region of the stomach

pyloric glands

Located between fundus and pylorus region. gastric gland

gastric glands

Glands in the gastric mucosa composed of mucous cells, chief cells, and parietal cells

mucus cells

secrete mucus that protects stomach lining from hydrochloric acid

regenerative cells

cells that divide rapidly and produce a continued supply of new cells...they are found in the base of the pit and neck of the glands

parietal cells

Cells found in gastric glands that secrete hydrochloric acid (for hydrolysis of ingested food) and gastric intrinsic factor (for absorption of vitamin B-12) and a hunger hormone called ghrelin

chief cells

A cell of the gastric glands that secretes pepsinogen (breaks down protein) and gastric lypase

enteroendocrine cells

cells that secrete hormones and paracrine messengers that regulate digestion.

gastric juice

digestive secretions of the stomach glands composed mainly of water, hydrochloric, and pepsin, stomach produces 2-3 L per day

hydrochloric acid

Substance produced by the stomach; necessary for digestion of food. pH as low as 0.8, could cause burns to the skin.

functions of stomach acid

1) activates the enzyme pepsin and lingual lipase 2) breaks up connective tissue and plant cell walls, helping to liquify food 3) converts ingested ferric ions to ferrous ions, a form of iron that can be absorbed and used for hemoglobin synthesis4) contributes to nonspecific disease resistance by destroying most ingested pathogens


Digestive enzymes are released in inactive forms, necessary to prevent the digestive enzymes from autodigesting the cells that produce them


The inactive form of pepsin that is first secreted by specialized (chief) cells located in gastric pits of the stomach, reacts with HCl to create pepsin


Breaks down proteins into amino acids


as some pepsin is formed, it coverts pepsinogen into more pepsin

gastric lipase

Secreted by glands in the stomach, this enzyme plays minor role responsible for 10-15% of fat digestion, rest take place in the sm intestine

intrinsic factor

glycoprotein secreted by parietal cells necessary for absorption of vitamin B12 in the sm intestine. w/o vit B12, hemoglobin cannot be synthesized and pernicious anemia develops

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