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OSSF II Exam 2: Questions With Complete Solutions
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OSSF II Exam 2: Questions With Complete Solutions
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OSSF II Exam 2: Questions With Complete SolutionsExplain the major functions of the gastrointestinal (GI) tract Right Ans -
The function of the GI tract is digestion!!
Macromolecules in food cannot be directly absorbed from the G.I. tract so they
must be degraded into monomers to be absorbed. Once absorbed, they are
synthesized back into macromolecules to be used as an energy source. This
process of breakdown and resynthesis is so that it avoids the immune system
from recognizing the ingested proteins as foreign.
There are 4 main processes of digestion (not necessarily sequentially)
1. Mechanical processing
Chewing → increase surface area of particles available for enzymatic
degradation **the chewing muscles and the external anal sphincter are the
only muscles under voluntary control in the GI tract, the rest are passive**
Alternating contraction/relaxation of stomach & small intestine → mix content
to enhance the efficiency of enzymatic degradation
2. Secretion of enzyme-containing digestive juices: Produced by epithelial cells
in the gastric & intestinal mucosa and glands/organs outside the digestive
tract (the composition and pH are adapted to the enzymes present)
--> this includes the production of endocrine factors that will also be secreted
somewhere else in the GI tract
--> Goblet cells in epithelial cells also produce mucus to protect intestinal
epithelial cells from injury and lubricate the intestinal contents
--> Water, ions, and proteins are secreted and then absorbed and recirculated
3. Enzymatic breakdown of organic nutrients: enzymes catalyze the
breakdown of polymers (carbohydrates, lipids and proteins) into monomers
by hydrolysis
--> happens in a step-wise function where different regions of GI tract secrete
different enzymes to keep breaking it down further and further
4. Absorption
--> Small molecules (monomers), water, ions, and vitamins are transported
from the digestive tract lumen to the blood or lymph capillaries
-
Describe the major anatomical structures of the digestive tract with emphasis
on differences between species Right Ans - Mammalian digestive tract
anatomy:
Digestive tract **food taken in, things are absorbed, waste is secreted**
,1. Oral cavity
2. Pharynx
3. Esophagus
4. Fermentation chamber (ruminants only - breaking down carbohydrates
from plants w/ enzymes that carnivores don't have)
5. Stomach (expandable in carnivores)
6. Small intestine
--> Duodenum
--> Jejunum
--> Ileum
7. Large intestine
--> Cecum
--> Colon (ascending, transverse, descending)
8. Rectum
Structures outside the digestive tract with secretory functions
• Salivary glands
• Pancreas
• Liver & Gallbladder
Most of the secretion occurs in the stomach and small intestine. These
secretions are from glands outside the GI tract (salivary, pancreas, liver) and
glands in the gastric mucosa and crypts of the small intestine. The primary
location of absorption is the small intestine and some in the large intestine.
Review important concepts related to cellular transport Right Ans -
Facilitated diffusion is saturable because the passive movement still requires
a channel. Na-K ATPase is the primary method of active transport in the GI
tract creating the NA gradient.
Explain the general structure of the wall of the GI tract Right Ans -
Intestinal wall structure consistent throughout most of the G.I. tract
(exception is in the oral cavity, esophagus, rectum and rumen)
From lumen ⇢⇢ outward:
1. Mucosa (have folds and extensions to increase SA for absorption)
--> Epithelial layer (single layer of columnar epithelial cells w/ tight junctions
b/w adjacent cell membranes on the lumen (apical side) forming a continuous
membrane)
,A) acts as a site for nutrient absorption and a barrier against the external
environment (toxins ingested and keep bacteria in that are part of the
digestive process)
B) High turnover rate (every 2-3 days) contributes to their protective function
(replaced before they sustain too much damage)
C) Specialized functions as they produce digestive juices, mucus and
hormones (stay in circulation or act in paracrine function) and are part of
absorption
--> Layer of connective tissue (thick) **lymphatics here pick up any bacteria
that happen to penetrate the epithelial layer**
--> Thin layer of smooth muscle (thin)
2. Submucosa
--> Collagen & elastin (CT)
--> Glands
--> Blood vessels supplying intestinal wall
--> contains submucosal plexus
3. Muscularis (important for peristalsis)
--> Circular (inner) and longitudinal (outer)
--> Intestinal motility
--> contains myenteric plexus
4. Serosa: single layer of squamous epithelial cells and secrete fluid to provide
lubrication for GI organs
**outer layer of peritoneum**
Discuss basic regulation and neural regulation basics of the GI system Right
Ans - The goal of regulation is to obtain complete absorption of ingested
organic nutrients and restore homeostasis via negative feedback mechanisms.
The G.I. functions are coordinated by neural regulation and hormonal
regulation. The relative importance of different regulator mechanisms varies
throughout the digestive tract. For example, salivary secretion is almost
exclusively through ANS, The stomach has a good mix of ANS, hormones, and
local reflexes. The pancreas is ANS and hormones. The small intestine is
mostly local reflexes with some ANS. The large intestine is mostly PNS with
some local reflexes.
Neural reflex regulation is responsible for motility and secretion. There are
sensors (for osmoloairty, pH, chemical contents, mechanical for distention of
food) in the walls of the intestinal tracts. The effectors are then the smooth
muscle cells, secretory epithelial cells and endocrine cells which produce
, either muscle contraction or secretion. Innervation to the GI tract is through
the autonomic nervous system (extrinsic) and through the enteric nervous
system (intrinsic) made of the myenteric and submucosal plexuses.
Parasympathetic fibers are carried via the vagus nerve to the upper GI tract or
the pelvic nerve to the lower GI tract. They have long preganglionic fibers that
synapse (release ACh) in the myenteric or submucosal plexus. PNS tends to be
stimulatory with increased secretion and motility resulting. The sympathetic
postganglionic fibers originate in the celiac, sup. mesenteric, inf. mesenteric
and hypogastric ganglia. They then go to the plexuses or directly to smooth
muscle, secretory cells or endocrine cells (release Norepi). SNS tends to be
inhibitory with decreased secretion and motility (except in the sphincters that
contract). Neurons of the intrinsic system synapse with each other, smooth
muscle and
Discuss the two neural reflexes in GI regulation Right Ans - The two types
of neural reflexes are the long and short reflexes. Most of the time the stimuli
is in the wall of the GI tract but there are cases where it comes from outside
the GI tract (sight/smell of food).
Short reflex arc: Adjust to local conditions, while being modulated by the ANS
--> Stretch/volume (mechanoreceptors) or Composition (chemoreceptors)
--> Can involve different segments of the G.I. tract (E.g., sensory cells in the
upper G.I. tract affecting secretion and motility in the lower G.I. tract =
"entero-enteric reflexes")
--> do not induce CNS output as signals travel through interneurons and
remain in the wall of the GI tract
--> Most effector arms are stimulatory/excitatory (pro-digestion) and use Ach
as a neurotransmitter
--> Some effector neurons release inhibitory neurotransmitters, e.g. NO, to
relax muscles (sphincters)
Long reflex arc: Central nervous system influences digestive functions
--> Afferent (sensory) arm usually originates in the G.I. tract, but they can also
originate from sensations associated with food (smell, taste, sight, sound)
--> Most of the effect is mediated through the enteric motor nerve fibers
--> Sympathetic efferent fibers also reduce the blood supply to the G.I. tract
(e.g., during exercise)
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