Chapter 24 - The Digestive System - Part 2 Flashcards
the pharynx is a passageway between the __ and the ____
between the oral cavity and the esophagus
the pharynx is a passageway for both __ and ___
food/liquid and air
Food normally passes through the ___pharynx and ____pharynx on the way to the esophagus
oropharynx and laryngeal pharynx
the pharynx is a ___ shaped tube lined with a ___ membrane
funnel shaped tube lined with a mucous membrane
the muscles or the pharynx work together with the muscles of which 2 other structures to start swallowing??
the muscles of the oral cavity and the esophagus
Describe the structure and function of the pharynx
the pharynx is an anatomical space that receives a food bolus or liquids and passes them to the esophagus as part of the swallowing process
The esophagus is a hollow, muscular tube that conveys food and liquids to…..
the stomach
the esophagus lies ___ to the trachea and connects the ___ to the ____
POSTERIOR to the trachea and connects the pharynx to the stomach
what is another word for swallowing
Deglutition
is swallowing voluntary or involuntary? explain
swallowing is initiated voluntarily but proceeds automatically once it begins
Name the structure connecting the pharynx to the stomach
the esophagus
Compared to the other segments of the digestive tract, what is unusual about the muscularis externa of the esophagus?
- it contains skeletal muscle cells along most of the length of the esophagus
-it is surrounded by adventitia rather than a serosa
What is occuring when the soft palate and larynx elevate and the glottis closes?
swallowing (deglutition) is occurring
what is the term for the hollow interior of an organ
the lumen
What prevents air from entering the esophagus and prevents backflow of materials from the stomach?
resting muscle tone in the circular muscle layer of the esophagus
The wall of the esophagus has __ layers
3
Name the 3 layers of the wall of the esophagus
Mucosa
Submucosa
Muscular Layer
What anchors the esophagus to the body wall?
adventitia
What are the 4 phases of swallowing?
-buccal phase
-pharyngeal phase
-esophageal phase
-bolus enters stomach
describe the buccal phase
the bolus is compressed against the hard palate. tongue is retracted which forces the bolus into the oropharynx
Describe the pharyngeal phase
bolus comes into contact with posterior pharyngeal wall. Larynx elevates. Folding of the epiglottis directs the bolus past the closed glottis. The uvula and soft palate block passage to the nasopharynx
Describe the esophageal phase
the contraction of the pharyngeal muscles forces the muscles through the entrance of the esophagus. Bolus is pushed towards stomach through peristalsis
The esophagus goes through what?
the diaphragm
Name the 4 major functions of the stomach
-temporary storage of ingested food
-mechanical breakdown of ingested food
-disruption of chemical bonds in food (through the action of acids and enzymes)
-production of “intrinsic factor”
What is “intrinsic factor”?
a GLYCOPROTEIN needed for the absorption of vitamin b12
What is chyme and where is it produced?
produced in the stomach
ingested substances combined with the secretions of the glands of the stomach. HIGHLY ACIDIC
What is the shape of the stomach?
an expanded “J” with a short lesser curvature and a long greater curvature
The stomach can be divided into 4 regions?
-the cardia
-the fundus
-the body
-the pylorus
what is the smallest part of the stomach?
the cardia
what is the smallest part of the stomach?
the cardia
Which part of the stomach has many mucous glands whose secretions coat the connection with the esophagus and help protect that tube from the acids and enzymes of the stomach?
the cardia
what is the largest region of the stomach?
the body
Which region of the stomach acts as a “mixing tank” for ingested foods and secretions produced by the stomach?
the body
which region of the stomach forms the sharp portion of the “j”
the pylorus
what regulates the release of chyme into the duodenum?
the pyloric sphincter
what kind of epithelium lines all the portions of the stomach?
simple columnar epithelium
what glands secrete gastric juice and in which regions of the stomach are these glands located?
gastric glands secrete gastric juice
gastric glands are found in the FUNDUS and BODY of the stomach
GASTRIC GLANDS are dominated by 2 types of secretory cells:
parietal cells
chief cells
which cells secrete intrinsic factor?
parietal cells
besides gastric juices and intrinsic factor, what else do parietal cells secrete?
hydrochloric acid
Why is hydrochloric acid NOT produced in the cytoplasm?
HCl is such a strong acid that it would erode a secretory vessel and destroy the cell
How is HCl produced since it cannot be produced in the cytoplasm?
CO2 + H2O becomes carbonic acid (H2CO3) which then dissociates into H+ + HCO3-
the bicarbonate ions are ejected into the interstitial fluid and chloride ions are transported in
the chloride ions diffuse across the cell and exit through open chloride channels into the LUMEN of the gastric gland where it combines with the H ions that are actively transported also into the lumen of the gastric glands
the secretions of parietal cells keep the pH of the stomach at ___-____
1.5-2
What are 4 reasons for the pH of the stomach being so low?
-the acidity of gastric juices kills any microorganisms ingested with food
-the acidity denatures proteins and inactivates most of the enzymes in food
-the acidity helps break down plant cell walls and the connective tissues in meat
-an acidic environment is essential for the activation and function of PEPSIN, a protein-digesting enzyme secreted by chief cells
What is pepsin and what secretes it?
a protein digesting enzyme secreted by chief cells
Where are chief cells most abundant in a gastric gland?
at the base
What 2 enzymes are produced by the stomachs of newborn infants and are important in the digestion of milk?
rennine (aka chymosin)
gastric lipase
Glands in the pylorus primarily produce…
a mucous secretion (rather than enzymes or acid)
gastrin is produced by…..
G cells
What does Gastrin stimulate?
stimulates secretion by both parietal and chief cells as well as contractions of the gastric wall
besides G cells, the pyloric glands also contain ___ cells which release ___
D cells which release somatostatin
What is somatostatin?
a hormone that inhibits the release of gastrin
Name the 4 major regions of the stomach
cardia
fundus
body
pylorus
Discuss the significance of the low pH in the stomach
this creates an acidic environment that kills most microbes ingested with food, denatures proteins and inactivates most enzymes in food, helps break down plant cell walls and meat connective tissue, and activates pepsin
How does a large meal affect the pH of blood leaving the stomach?
Big meals (especially with a high protein content) stimulate INCREASED STOMACH ACID SECRETION. When gastric glands are secreting, bicarbonate ions enter the blood stream to increase the blood pH. This vascular phenomenon is known as the alkaline tide
When a person suffers from chronic gastric ulcers, the branches of the vagus nerves that serve the stomach are sometimes cut in an attempt to provide relief. Why might this be an effective treatment?
The vagus nerves contain parasympathetic motor fibers that can stimulate gastric secretions, even if food is not present in the stomach (the cephalic phase of gastric digestion)
Cutting the branches of the vagus nerves that supply the stomach would prevent this type of secretion from occurring and thereby reduce the likelihood of ulcer formation
What structure allows for expansion of the gastric lumen
ruggae - prominent folds in mucosa of empty stomach
Are nutrients absorbed in the stomach?
NO
Give 4 reasons why nutrients are not absorbed in the stomach
-the epithelial cells are covered by a blanket of alkaline mucus and are not directly exposed to chyme
-the epithelial cells lack the specialized transport mechanisms of cells that line the small intestine
-the gastric lining is relatively impermeable to water
-digestion has not been completed by the time chyme leaves the stomach
Most of the important digestive and absorptive steps of digestion take place where?
in the small intestine
The liver secretes ___ which is stored in the ____ for discharge into the _____
the liver secretes BILE which is stored in the GALLBLADDER for discharge into the SMALL INTESTINE
What does bile contain which makes it important for digestion?
buffers, and bile salts which facilitate the digestion and absorption of lipids
What organ produces digestive enzymes as well as buffers that help neutralize chyme?
the pancreas
99% of nutrient absorption takes place in the small intestine. Where does that other 1% occur?
in the large intestine
the small intestine has 3 segments:
the duodenum (closest to stomach)
the jejunum
the ileum
Which segment of the small intestine is a “mixing bowl” that receives chyme from the stomach and digestive secretions from the pancreas and liver?
the duodenum
The bulk of chemical digestion and nutrient absorption occurs in what segment of the small intestine?
the jejunum
what is the name of the sphincter that controls the flow of material from the ileum into the “cecum” of the large intestine?
the ileocecal valve
the small intestine fills much of what cavity?
the peritoneal cavity
the small intestine is stabilized in the peritoneal cavity by…..
mesentary proper
the pancreas is a ___ that lies ___ to the stomach
gland that lies posterior to the stomach
the pancreas produces ___ which buffers stomach acid
sodium bicarbonate
where does the pancreas empty its contents?
into the duodenum
What does the small intestine contain which increases its surface area greatly for absorption?
villi with microvilli covering it
in addition to capillaries and nerve endings, what else does each villus contain in the small intestine?
a lymphatic capillary called a lacteal
what is the function of a lacteal?
they transport materials that cannot enter blood capillaries (absorbed fatty acids are assembled into protein-lipid packages that are too large to diffuse into the bloodstream) CHLYOMICRONS
What is the function of intestinal juice?
it moistens chyme, helps buffer acids, and keeps digestive enzymes and products of digestion in solution
most intestinal juice arrives by _____
osmosis
name the 3 regions of the pancreas
the head
the body
the tail
describe the surface of the pancreas
lumpy, lobular texture
the pancreas is primarily an ___ organ
exocrine (produces digestive enzymes and buffers)
what delivers the secretions of the pancreas to the duodenum?
the large pancreatic duct
the pancreas is what type of gland (structurally)
compound tubuloalveolar gland
the pancreas has 2 distinct functions: 1 __ and the other ___
1 endocrine and the other exocrine
what is the endocrine function of the pancreas
secrete insulin and glucagon into the bloodstream to control blood sugar
the exocrine cells of the pancreas secrete….
pancreatic juice into the small intestine
name 4 pancreatic enzymes
-pancreatic alpha amylase
-pancreatic lipase
-nucleases (break down RNA or DNA)
-proteolytic enzymes (proteases, peptidases)
____ enzymes account for about 70% of the total pancreatic enzyme production
proteolytic
proteolytic enzymes are secreted as ___ ___ and dont become activated until…
secreted as inactive proenzymes and dont become activated until they reach the small intestine
What is the largest visceral organ?
the liver
liver cells are called…
hepatocytes
what are the basic functional units of the liver?
liver lobules
adjacent lobule are separated by….
an interlobular septum
the liver secretes a fluid called bile into a network of narrow channels (called _____) between the opening membranes of adjacent liver cells
bile caniliculi
name 3 general categories of functions of the liver
- metabolic regulation
- Hematological regulation
- Bile production
liver cells extract ___ or ___ from blood before it reaches systemic circulation through the hepatic veins
nutrients or toxins
the liver can metabolize which 3 things:
carbohydrates
lipids
amino acids
the liver neutralizes ammonia by converting it to ____
urea
the liver strips off amino groups when converting amino acids to lipids or carbohydrates, or when breaking down amino acids to get energy. What is this process called?
deamination
____-soluble vitamins are absorbed from the blood and stored in the liver
fat-soluble
A, D, E, K, B12
Give an example to show that a function of the liver is “mineral storage”
the liver converts iron reserves to ferritin and stores this protein-iron complex
the liver participates in ____ inactivation
drug inactivation
the liver receives ____% of cardiac output
25%
one of the biggest functions of bile is….
emulsification
