9.1 The Digestive Tract Flashcards
How doers the digestive system contribute to homeostasis?
by ingesting food, separating it into chemical nutrients that cells can use, absorbing those nutrients, and eliminating indigestible remains
Where does digestion take place?
digestive tract
What is the digestive tract?
a tube which begins with the mouth and ends with the anus
What is the digestive system?
a type of organ system including the mouth, esophagus, stomach, intestines, and associated organs that receives food and digests it into nutrient molecules
What are the 2 things involved with digestion?
mechanical digestion and chemical digestion
What is mechanical digestion?
begins with the chewing of food in the mouth and continues with the churning and mixing of food in the stomach
What is chemical digestion?
many different enzymes break down macromolecules to small organic molecules that can be absorbed
What is the mouth bounded by?
bounded externally by the lips and cheeks
Why are lips red?
they are poorly keratinized, which allows the blood to show through
What are taste buds?
sensory receptors that occur primarily on the tongue
What happens when taste buds are activated by the presence of food?
nerve impulses travel by way of cranial nerves to the brain
What is the tongue composed of?
skeletal muscle that contracts to change the shape of the tongue
What attaches the tongue to the floor of the mouth?
a fold of mucous membrane on the underside of the tongue
What does the roof of the mouth separate?
the nasal cavity from the mouth, preventing ingested food from entering the nasal cavity
What are the 2 parts of the roof of the mouth?
anterior hard palate and posterior soft palate
What is the difference between the hard palate and the soft palate?
hard: contains several bones
soft: composed of muscle and connective tissue, ends in a finger-shaped projection called the UVULA
What is a cleft palate?
a gap left in 1/700 newborns when bones of the hard palate have not fused during fetal development
What can happen if a cleft palate is not surgically repaired?
can result in problems with feeding speech and hearing due to ear infections
Where are tonsils?
back of the mouth on either side of the tongue, and in the nasopharynx where they are called ADENOIDS
What are adenoids?
tonsils in the nasopharynx
What do tonsils contain?
lymphoid tissue that helps protect the body against infections
What is tonsilitis?
inflammation of the tonsils
What is a tonsillectomy?
a surgical procedure to remove the tonsils when tonsilitis recurs repeatedly
How many pairs of salivary glands do we have?
3
What do salivary glands do?
produce saliva to keep the mouth moist and contains enzymes that begin the process of digesting starch
Where are the salivary glands?
one pair lies on either side of the face immediately below and in front of the ears
one pair lies beneath the tongue
one pair lies beneath the floor of the mouth (ducts from these glands open under the tongue)
What are mumps?
a disease caused by a viral infection that causes the pair of salivary glands on the side of the face to swell
What is the pharynx?
a region that receives air from the nasal cavities and food from the mouth
Describe the path of food.
- from the mouth, food (bolus) passes through the pharynx and esophagus to the stomach, small intestine, and large intestine
Why does food passage and air passage cross in the pharynx?
because the trachea (windpipe) is in front of the esophagus, which takes food to the stomach
What is swallowing?
a reflex action that occurs in the pharynx in which the soft palate moves back to close off the nasopharynx and the trachea moves up under the epiglottis to cover the glottis
What is the glottis?
the opening to the larynx (voice box) and therefore the air passage
Why does food normally enter the esophagus when swallowing?
because the air passages are blocked, we do not breathe when we swallow
Why doesn’t a person breathe while swallowing?
the soft palate closes off the nasopharynx and the epiglottis covers the glottis, forcing the bolus to pass down the esophagus
What is the esophagus?
a long muscular tube that passes from the pharynx, through the thoracic cavity and diaphragm, and into the abdominal cavity, where it joins the stomach
When does the esophagus open?
it is usually collapsed, but it opens and receives the bolus when swallowing occurs
What is peristalsis?
rhythmic muscular contractions that push food along the digestive tract
Where does peristalsis begin and continue to?
begins in the esophagus and continues in all the organs of the digestive tract
What happens when peristalsis occasionally begins even though there is no food in the esophagus?
the sensation of a lump in the throat is produced
What is the esophagus’ sole purpose?
to move the food bolus from the mouth to the stomach, it does not play a role in the chemical digestion of food
What are sphincters?
muscles that encircle tubes in the body, acting as valves
Describe the relationship between tubes and sphincters.
tubes close when sphincters contract, and open when sphincters relax
What is the entrance of the esophagus to the stomach marked by?
a constriction often called a sphincter, although the muscle is not as developed as it would be in a true sphincter
What does the relaxation of the sphincter allow?
bolus to pass into the stomach
What does sphincter contraction prevent?
the acidic contents of the stomach from backing up into the esophagus
What is heartburn?
the sensation of a burning pain rising into the throat
When does heartburn occur?
when some of the stomach contents escape into the esophagus, known as ACID FLUX
How is heartburn treated?
class of drugs called proton pump inhibitors, which reduce acid production in the stomach
What is gastroesopageal reflux disease (GERD)?
a more serious form of heartburn which is frequent or persistent reflux that may lead to more serious problems such as ulcers, difficulty swallowing, or even esophageal wall by stomach acid
What is vomiting?
the forceful expulsion of stomach contents out of the body through the mouth
What can vomiting help protect?
can help protect against the ingestion of potentially harmful agents
Describe how vomiting occurs.
certain cells in the intestinal tract, as well as the brainstem, trigger the contraction of the abdominal muscles and diaphragm to propel the contents of the stomach upward through the esophagus
What is the stomach?
a thick-walled, J-shaped organ that lies on the left side of the abdominal cavity below the liver and diaphragm
it is continuous with the esophagus above and the duodenum of the small intestine below
What does the stomach do?
receives food from the esophagus, starts the digestion of proteins, and moves food into the small intestine
How big is the human stomach?
25 cm long, regardless of the amount of food it holds, but the diameter varies, depending on how full it is
What happens as the stomach expands?
deep folds in its wall, called rugae, gradually disappear and when it is full it can hold about 4 L
What lines the stomach?
columnar epithelium
What does the columnar epithelium have?
gastric pits, which lead into gastric glands
What does the term “gastric” refer to?
the stomach
What do the gastric glands do?
produce gastric juice, which contains pepsinogen, HCl, and mucus
What does pepsinogen become?
the enzyme pepsin when exposed to HCl
Why is the high acidity of the stomach beneficial?
it kills most of the bacteria and other microbes present in food
What are the three muscle layers of the stomach wall?
- longitudinal
- circular
- obliquely arranged
What does the stomach’s muscular wall do?
moves the food along, and churns it, mixing the food with gastric juice and breaking it down into smaller pieces
What does the stomach absorb?
alcohol and other liquids
What does the stomach not absorb?
most solid food substances
How long does it take for the stomach to empty?
2-6 hours
What happens when food leaves the stomach?
it is a thick, soupy liquid called chyme
Where does chyme go?
enters the small intestine in squirts by way of the pyloric sphincter, which acts like a valve, repeatedly opening and closing
Describe the anatomy of the stomach.
- stomach has a thick wall with folds that allow it to expand and fill with food
- mucosa contains gastric glands, which secrete gastric juice containing mucus and digestive enzymes
