Download Answers to WHAT DID YOU LEARN questions

CHAPTER 26
Answers to “What Did You Learn?”
1.
The GI tract includes the oral cavity, pharynx, esophagus, stomach, small
intestine, and large intestine.
2.
Secretion is the process of producing and releasing mucin or fluid products, such
as acid, bile, and digestive enzymes, in order to facilitate chemical digestion or
passage of material through the GI tract lumen. Absorption involves either the
passive movement or active transport of electrolytes, products of digestion,
vitamins, and water across the GI tract epithelium and into the GI tract blood and
lymph vessels.
3.
The components of saliva are water (primary component that moisturizes food
and cleanses mouth), ions, immunoglobulin A (a class of secreted antibodies that
inhibit bacterial growth), lysozyme (an antibacterial enzyme), mucin, and salivary
amylase (initiates chemical digestion of carbohydrates in the mouth).
4.
Permanent teeth include the incisors, canines, premolars, and molars. The
incisors are designed for slicing or cutting into food. Canines have pointed tips
for puncturing and tearing food. Premolars have flat crowns with cusps that are
used to crush and grind ingested materials. Molars have large, broad flat crowns
with distinctive cusps, and are also used for grinding and crushing.
5.
Sequential contraction of the pharyngeal constrictors decreases the diameter of the
pharynx beginning at its superior end and moving toward its inferior end, thus,
forcing swallowed material toward the esophagus.
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6.
Intraperitoneal refers to organs that are completely surrounded by visceral
peritoneum. They include the stomach, part of the duodenum of the small
intestine, the jejunum and ileum of the small intestine, the cecum, the appendix,
and transverse and sigmoid colon of the large intestine. Retroperitoneal refers to
organs that typically lie directly against the posterior abdominal wall, so only
their anterolateral portions are covered with peritoneum. Retroperitoneal organs
include most of the duodenum, the pancreas, and the ascending and descending
colon of the large intestine.
7.
The four tunics of the abdominal GI tract from the esophagus through the large
intestine and their default patterns are: (1) mucosa (typically lined with simple
columnar epithelium, an underlying areolar connective = lamina propria, and a
thin layer of smooth muscle [muscularis mucosae]), (2) submucosa (formed from
areolar or dense irregular connective tissue), (3) muscularis (typically formed
from two layers of smooth muscle [inner circular and outer longitudinal]), and (4)
an adventitia or serosa (composed of areolar connective tissue with dispersed
collagen and elastic fibers).
8.
The esophageal tunics differ from the default tunic pattern in that the mucosa has
a thick, nonkeratinized stratified squamous epithelium and the muscularis is
composed of a mixture of skeletal and smooth muscle.
9.
The three phases of swallowing are: (1) the voluntary phase, (2) pharyngeal
phase, and (3) esophageal phase. The voluntary phase occurs after the ingestion
of food. Food mixed with saliva forms a bolus that is pushed into the archway
leading into the oropharynx. The appearance of the food bolus at the oropharynx
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initiates the pharyngeal phase. The bolus passes quickly and involuntarily
through the pharynx to the esophagus. The pharyngeal phase includes elevation
of the soft palate and uvula to block the nasopharynx, the reception of the food
bolus into the oropharynx, and the movement of the larynx toward the epiglottis.
The esophageal phase (involuntary stage) moves the bolus through the esophagus
and into the stomach.
10.
The four regions of the stomach are: the cardia, fundus, body, and pylorus. The
cardia is a small, narrow, superior entryway into the stomach lumen from the
esophagus. The fundus is the dome-shaped region lateral and superior to the
esophageal connection with the stomach. Its superior surface contacts the
diaphragm. The body is the largest region of the stomach; it is inferior to the
cardiac orifice and the fundus. The pylorus is a narrow, medially directed, funnelshaped region that forms the terminal part of the stomach.
11.
The five types of epithelial cells in the stomach are: (1) surface mucous cells
(secrete mucin), (2) mucous neck cells (secrete alkaline mucin), (3) parietal cells
(secrete hydrochloric acid and intrinsic factor), (4) chief cells (secrete
pepsinogen), and (5) enteroendocrine cells (secrete gastrin).
12.
The duodenum forms the first region of the small intestine. It is mostly
retroperitoneal and is approximately 10 inches long. It is arched into a C-shape
around the head of the pancreas. The duodenum begins at the pyloric sphincter
and ends at the duodenojejunal flexure where it connects with the jejunum. The
jejunum is the middle region of the small intestine and forms approximately twofifths the length of the small intestine. The ileum is the last region of the small
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intestine and forms approximately three-fifths the length of the small intestine. It
extends from its origin at the end of the jejunum and its distal end terminates at
the ileocecal valve. The jejunum and ileum are intraperitoneal and suspended in
the abdomen by a mesentery. Internal circular folds are mucosal and submucosal
folds in all three regions of the small intestine, but are best developed in the
duodenum and jejunum. Additionally, villi are larger and more numerous in the
jejunum. Peyer's patches are much more numerous in the ileum than in the
jejunum.
13.
The ascending colon, descending colon, rectum, and anal canal are
retroperitoneal. The cecum, vermiform appendix, transverse colon, and sigmoid
colon are intraperitoneal organs.
14.
The movements and reflexes that propel material through the large intestine are
peristaltic movements (weak and sluggish), haustral churning (distension
stimulates reflex contractions), and mass movement (powerful, peristaltic-like
contractions).
15.
Portal triads are composed of at least one branch of the hepatic portal vein,
hepatic artery, and the bile duct.
16.
The gallbladder stores and concentrates the bile produced by the liver. The
gallbladder will release this concentrated bile in response to ingesting a fatty
meal.
17.
Pancreatic acini are clusters of simple cuboidal epithelial cells (called acinar cells)
that secrete pancreatic juice, which is an alkaline fluid that also contains digestive
enzymes.
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18.
A decrease in mucin secretion results in a decrease in thickness and volume of the
mucus that coats and protects the luminal lining of GI tract organs. Without this
protection, the organ lining will be subject to abrasion by a moving bolus or
chyme and damage by acid or enzymes.
19.
The liver parenchyma, gallbladder, pancreas, and biliary apparatus develop from
buds or outgrowths from the endoderm of the duodenum.
Answers to “Content Review”
1.
The oral cavity initiates the process of both mechanical and chemical digestion.
Saliva moistens the food, while the teeth break the food into smaller components.
The amylase in saliva begins the mechanical digestion of carbohydrates. The
tongue helps mix the saliva and food, and pushes the material against the palate of
the mouth, where it is transformed into a bolus. The bolus is eventually
swallowed.
2.
The general structural plan of the GI tract from the esophagus through the large
intestine is a tube composed of four concentric layers, called tunics. The tunics
from innermost to outermost are: the mucosa, submucosa, muscularis, and
adventitia (or serosa). (1) The mucosa is composed of an epithelium (an inner
superficial epithelium), a lamina propria (of areolar connective tissue), and a
muscularis mucosae (thin smooth muscle layer). (2)The submucosa is formed
from areolar or dense irregular connective tissue. (3) The muscularis typically
contains two smooth muscle layers (an inner circular and outer longitudinal). (4)
The adventitia is areolar connective tissue, while serosa also has a layer of
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peritoneum covering this connective tissue. The stomach’s mucosa is lined with
simple columnar epithelium, but no goblet cells. The mucosa also has gastric pits,
which are lined by gastric glands. The muscularis layer has three layers of
smooth muscle instead of the usual two layers.
3.
Gastric juice and pancreatic juice both assist with the chemical digestion of
ingested food. Gastric juice is produced by the gastric glands of the stomach. It
is highly acidic and contains hydrochloric acid, pepsinogen, mucin, gastrin, and
intrinsic factor (the latter assists in vitamin B12 absorption). Pancreatic juice
contrasts with gastric juice in that it is alkaline due to the high percentage of
bicarbonate. The bicarbonate acts to neutralize the acidic chyme that enters the
duodenum from the stomach. Other components of pancreatic juice include
mucin and digestive enzymes.
4.
The mucosal and submucosal tunics of the small intestine exhibit circular folds.
These help increase the surface area of the small intestine which allows more
opportunity for nutrients to be absorbed. Also, they slow down movement of the
chyme to ensure it will remain longer within the small intestine for maximal
nutrient absorption. Along these circular folds are smaller fingerlike projections
of the mucosa, called villi, which act to increase surface area for secretion and
absorption. Microvilli are apical membrane surface folds to further increase
surface area at the absorptive and secretory surface of each cell.
5.
The teniae coli are three distinct longitudinal bundles of smooth muscle in the
wall of the large intestine. They “bunch” the wall of the large intestine to help
form sacs called haustra. Movement of digested materials from one sac to the
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next is called haustral churning. It occurs after a relaxed haustrum fills with
digested/fecal material to a point where its distension stimulates reflex
contractions in the muscularis causing a churning and movement of the material
to more distal hasutra.
6.
At the periphery of hepatic lobules, there are several portal triads, composed of at
least one branch of the hepatic portal vein, the hepatic artery, and the bile duct.
The hepatic portal vein carries blood that has already passed through the capillary
beds of the GI tract, spleen, and pancreas. It brings about 75% of the blood
volume to the liver. This blood is rich in nutrients and other absorbed substances,
but relatively poor in oxygen. The hepatic artery is a branch of the celiac trunk
and it carries well-oxygenated blood to the liver. Blood from branches of these
two vessels mixes as it passes to and through the hepatic lobules and drains into
the central vein. At the center of each lobule is a central vein that drains from the
lobule. Central veins merge throughout the liver to form numerous hepatic veins
that empty into the inferior vena cava. Bile produced by hepatocytes is secreted
into bile canaliculi; it flows through these tiny channels to the portal triad where it
enters the bile ducts and eventually exits the liver. Bile emulsifies fat arriving in
the small intestine. Without this emulsification, the fat in our consumed food
could not be chemically digested.
7.
Attached to the inferior surface of the liver, the saclike organ called the
gallbladder, stores and concentrates the bile produced by the liver. Bile is a
yellow-green fluid produced by hepatocytes; its primary digestive function is to
aid in the emulsification of fat.
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8.
Ingested material (food) enters the GI tract via the oral cavity. The material is
mechanically digested by the teeth and tongue, while chemical digestion of
carbohydrates begins due to exposure to the amylase in saliva. The ingested
material is now called a bolus. When the bolus is swallowed, it leaves the oral
cavity and passes through the oropharynx, laryngopharynx, and then the
esophagus before entering the stomach, where both mechanical and chemical
ingestion of the material occurs. The material leaving the stomach is “pastelike”
and called chyme. It enters the small intestine, where mechanical and chemical
digestion will be completed. The chyme first enters the duodenum, where it will
mix with bile (from the gallbladder), pancreatic juices (digestive enzymes from
the pancreas), and bicarbonate (secreted by the wall of the small intestine). This
material travels through the jejunum and ileum, and then enters the large intestine.
Here water and ions are added. Material first enters the cecum of the large
intestine, and then travels into the ascending colon, transverse colon, descending
colon, sigmoid colon, rectum, and anal canal. Feces leaves the body through the
anus.
9. The mucin-producing cells throughout the GI tract collectively produce a
covering layer of viscous mucus. This mucus lubricates the lining and prevents
desiccation of the lining cells. Additionally, the mucus protects the epithelial
lining from abrasion or damage as a result of exposure to acid or enzymes in the
contents of the tract.
10. Most of the small intestine and the proximal part of the large intestine are formed
from a section of the embryologic gut tube called the midgut. During the fifth
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week of development, the midgut elongates and forms a primary intestinal loop.
The upper portion of the loop is called the cranial loop, while the lower part is
called the caudal loop. The cranial loop will form most of the small intestine,
while the caudal loop will form the proximal part of the large intestine. By the
sixth week, the intestinal loop grows and herniates into the umbilicus (due to
space constraints in the abdominal cavity). As it herniates, it undergoes a 90
degree counterclockwise rotation, as viewed from the front of the embryo. The
loop remains herniated until the tenth week, when the abdominal cavity has
grown spacious enough to house all of the intestines. During weeks 10–11, the
intestinal loop retracts into the body and in doing so, it rotates another 180
degrees counterclockwise. Now the cranial limb is on the left side of the body
and the caudal limb is on the right side. These limbs will attain their postnatal
position and develop into most of the small and large intestine.
11. As you make this Fantastic Voyage, you need to start with listing the structures
that you pass by as you move from the lips to small intestine (e.g., frenulum,
incisors, canines, premolars, molars, tongue, palatine tonsil, uvula, lingual tonsil,
oropharynx, laryngopharynx, epiglottis, esophagus, including superior and
inferior esophageal sphincters). Describe the parts of the stomach (cardia, fundus,
body) you pass as you head toward the pyloric sphincter (also describe the tissue
type and glands). While in the stomach, describe the changes to your pH etc. due
to the secretions of the gastric glands. Continue on through the pylorus (pyloric
antrum, canal, sphincter) and into the duodenum. Here you need to describe the
contributions from pancreas and gallbladder (via the major duodenal papilla) and
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glandular tissue of the duodenum and how they affect your structure (bile salts
from gallbladder emulsify you and other fats; lipase from pancreas begins to
hydrolyze you, etc.). Now you travel into the jejunum, where you encounter
circular folds (plicae circulares) and you get sloshed around via the process of
segmentation. In the jejunum (or ileum), you are broken down into your
component parts (glycerol and fatty acids) and are absorbed into the epithelium of
a villus in the small intestine. Here you are transported to the smooth ER and
your parts are reconstituted. Then, you and several other fat molecules are
packaged into a chylomicron and transported out of the epithelial cell into the
interstitial fluid. Your chylomicron is too large to enter the blood capillaries so
you get picked up by lacteal (through one of the valves in its wall). Next, you get
transported through various lymph vessels and lymph nodes (list the main lymph
vessels through which you are transported). Eventually, you get into the thoracic
duct, which empties you into the left subclavian vein. Now you travel to the
superior vena cava and into the right atrium. Here you pass by the sinoatrial
node, bounce off a couple of pectinate muscles, and go through the right AV
(tricuspid) valve into the right ventricle (you pass the atrioventricular node as you
get near the AV valve). Here you pass around some of the papillary muscles and
chordae tendineae and, maybe, get bounced off the interventricular septum. Upon
ventricular systole, you are pushed through the pulmonary semilunar valve into
the pulmonary trunk, then to a pulmonary artery and arteriole, and go through a
capillary in the lungs. Then, you enter a venule to a pulmonary vein and enter the
left atrium. In the left atrium, you bounce off another pectinate muscle, go past
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the fossa ovalis, and from here, you go through the left AV (bicuspid or mitral)
valve to the left ventricle. In the ventricle, you pass by several papillary muscles
and chordae tendineae and, upon ventricular systole, you get pushed through the
aortic semilunar valves into the ascending aorta (you will pass the coronary
arteries here). When you reach the aortic arch, you will pass by the
brachiocephalic trunk, left common carotid, and left subclavian arteries. Now you
go through the descending thoracic and abdominal aorta (you will pass by several
branches off the aorta as you descend the thorax and abdomen) to the common
iliac arteries, to the femoral artery, to the popliteal artery, to the anterior tibial
artery, and to the dorsal pedis artery feeding the little dermis of the foot. Here you
enter an arteriole, then a capillary, and are finally, transported out of the blood
into the tissue fluid of the dermis. The structures you list in this journey can vary
a lot from anatomy class to anatomy class so your list may be much more
extensive or less so than the above...but you made it!!
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