chapter 16 The digestive system Flashcards
What is the function of the digestive system?
changes complex organic nutrient molecules into simple organic and inorganic molecules that can then be absorbed into the blood or lymph to be transported to cells
What are the two divisions of the digestive system?
The alimentary tube and the accessory organs
What is the alimentary tube?
extends from the mouth to the anus
consists of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine
What are the accessory organs?
Teeth, tongue, salivary glands, liver, gallbladder, and pancreas
digestion does not take place here but the organs contribute to the process
Where does digestion take place?
•oral cavity,
•stomach,
•small intestine- where most absorption of nutrients takes places
What are the two types of digestion?
Mechanical and chemical
What is Mechanical digestion?
the physical breaking up of food into smaller pieces
What is Chemical digestion?
enzymes break complex molecules into simpler chemical molecules that the body can use to
What are the three types of complex organic molecules found in food?
carbohydrates- digested into monosaccharides
proteins-digested to amino acids
fats-digested into fatty acids and glycerol
What is the function of teeth?
mechanically break down food
What are the two sets of teeth?
deciduous and permanent
What are the deciduous teeth?
they erupt through the gums about 6 months of age and the set of 20 teeth is usually complete by age 2
What are the permanent teeth?
replace the deciduous teeth
first set of molars emerge at age 6
complete set consists of 32 teeth
What is the periodontal membrane?
lines the socket and produces a bone like cement that anchors the tooth
What is the outermost layer of the crown of tooth?
Enamel- made by cells called ameloblasts
what is dentin?
within the enamel and is similar to bone
produced by cells called odontoblasts
What is the pulp cavity?
inner most portion of tooth
contains blood vessels and nerve rndings
What is the function of the tongue?
aids in keeping food between teeth and mixing it with saliva
hypoglossal nerves
sensory nerves for taste cranial nerves:facial glossopharangeal
What are papillae?
on the upper surface of the tongue many of which contains taste buds
What is the first step of swallowing?
elevation of the tongue
voluntary action
What is the digestive secretion in the oral cavity?
saliva
produced by 3 pairs salivary glands: parotid, submandibular, sublingual
cranial nerves are the facial and glossopharyngeal
takes saliva to the oral cavity
What increases saliva secretion?
presence, sight or smell of food,
parasympathetic response
What decreases saliva secretion?
stress situations- makes mouth dry
sympathetic stimulation
what does lysozyme in saliva do?
inhibit the growth of many kinds of bacteria, does not outright kill them but slows it down
What is the digestive enzyme salivary amylase?
breaks down starch molecules to shorter chains of glucose, molecules, or to maltose a disaccharide
what is the primary function of the pharynx?
swallowing
connects the oral cavity to the esophagus
no digestion takes place here
epligottis- covers thr larynx so food or liquid dont get in
What are the actions of swallowing?
•constriction of the pharynx
•cessation of breathing
•elevation if the soft palate to block the nasopharynx
•elevation of the larynx
•closure of the epiglottis and peristalsis of the esophagus
What is the esophagus?
a muscular tube that takes food from the pharynx to the stomach
no digestion takes place here
What does peristalsis of the esophagus do?
propels food in one direction and ensures that food gets to stomach
What is the lower esophageal sphincter? (cardiac sphincter)
circular smooth muscle
relaxes to permit food to enter the stomach, contracts to prevent the backup of the stomach contests
Layers of the alimentary tube
mucosa, submucosa, external muscle layer, and serosa
Mucosa
lining of the alimentary tube
made of epithelial tissue, areolar connective tissue and two thin layers of smooth muscle
secretes mucous, lubricates the passage of food, secretes digestive enzymes of the stomach and small intestine
submucosa
made of areolar connective tissue with blood vessels and lymphatic vessels
has millions of nerve fibers called the Enteric nervous system
What are the nerve networks in the submucosa called?
Meissner’s plexus- they innervate the mucosa to regulate secretions
parasympathetic increase secretions
sympathetic decreases secretions
External muscle layer
contractions of the muscle layer help break up food and mix it with digestive juices
contractions of peristalsis move food toward the anus
Auerbach’s plexus is the portion if the enteric nervous system
sympathetic-decrease contractions and peristalsis
parasympathetic- increases contractions and peristalsis
Stomach
is a sac that is a reservoir for food
when the stomach is empty the mucosa appears wrinkled or folded
what is the rugae?
folds that flatten out at the stomach is filled and permit expansion of the lining without tearing it
What are the gastric pits of the stomach?
glands of stomach and consist of several types of cells
secrete gastric juice
what do chief cells secrete?
pepsinogen- inactive form of the enzyme pepsin
it converts proteins to polypeptides
what do parietal cells secrete?
hydrochloric acid- converts pepsinogen to pepsin destroys pathogens
intrinsic factor- prevent digestion of vitamin b 12
What do mucous cells secrete?
mucous- coats the lining, prevents erosion
What is gastrin?
secreted by g cells
hormone that stimulates the secretion of greater amounts of gastric juice
What is the livers function?
production of bile
function of the hepatic duct?
takes bile out of liver
unites with cystic duct of the gallbladder to form common bile duct, while takes bile to duodenum
What do bile salts do?
emulsify fats in the small intenstine
what is production of bile stimulated by?
secretin
produced by duodenum when food enters the small intestine
function of the gall bladder?
stores bile until it is need in the small intestine
cystic duct joins the hepatic duct to form the common bile duct
Cholecystokinin- produced by the enteroendoceine cells of the duodenum-stimulates contraction of the gall bladder
biacarbonate juice of pancreas
alkaline;neutralizes the gastric juice to prevent damage
secretion of pancreatic juice is stimulated by hormones secretin and cholecystokinin
Enzyme pancreatic juice contains enzymes for 3 food types
amaylase- digest starch to maltose
trypsin-digests polypeptides to peptides
lipase-digest emulsified fats to fatty acids and glycerol
secretin
stimulates the production of bicarbonate juice by pancreas
cholecystokinin
stimulates secretion of the pancreatic enzymes
