MCAT Biology Lecture: Digestive System (1/2)
Summary
TLDRThis educational video script delves into the anatomy and function of the human digestive system, covering the journey of food from ingestion to absorption. It explains the roles of various organs, the process of mechanical and chemical digestion, and the importance of accessory organs and the enteric nervous system. The script also touches on the hormonal regulation of feeding behavior and the significance of the stomach and duodenum in digestion, providing a comprehensive overview for students of biology and medicine.
Takeaways
- 🍲 The digestive system's role is to break down complex foods into simpler molecules like monosaccharides, fatty acids, and amino acids for absorption and use by the body.
- 🔬 The process involves both intracellular digestion, which is part of metabolism, and extracellular digestion that occurs in the lumen of the alimentary canal.
- 📐 The alimentary canal is divided into specialized sections for different functional roles, primarily digestion and absorption, and is regulated by the enteric nervous system.
- 🦷 Ingestion begins in the oral cavity where mechanical digestion (chewing) and chemical digestion (enzymes in saliva) start to break down food.
- 🔄 Mechanical digestion involves physically breaking down food particles, while chemical digestion involves enzymatic cleavage of chemical bonds.
- 🚫 The pharynx is a shared pathway for food and air, with the epiglottis preventing food from entering the larynx during swallowing.
- 🌀 The esophagus uses peristalsis, rhythmic contractions of its muscles, to propel food towards the stomach.
- 🍽️ The stomach is a central organ for both mechanical and chemical digestion, producing enzymes and acids to break down food into chyme.
- 🧪 In the duodenum, the first part of the small intestine, enzymes and hormones are released to continue the chemical digestion process and prepare nutrients for absorption.
- 📉 Hormones such as gastrin, secretin, and cholecystokinin (CCK) play crucial roles in regulating digestion, including the release of bile and pancreatic juices.
- 🚰 Accessory organs like the salivary glands, pancreas, liver, and gallbladder provide enzymes and lubrication necessary for the digestion of food.
Q & A
What is the primary role of the digestive system?
-The primary role of the digestive system is to break down complex foods into simpler molecules such as monosaccharides, fatty acids, and amino acids, which can be absorbed and used by the body for energy, growth, development, and maintenance.
What are the two types of digestion mentioned in the script?
-The two types of digestion are intracellular digestion, which involves the oxidation of glucose and fatty acids for energy as part of metabolism, and extracellular digestion, which occurs in the lumen of the alimentary canal and involves the extraction of nutrients from food.
What is the process of mechanical digestion?
-Mechanical digestion is the physical breakdown of large food particles into smaller ones. It does not involve breaking chemical bonds and includes processes like chewing (mastication) in the mouth, which increases the surface area for enzymatic digestion.
What is the role of chemical digestion in the digestive system?
-Chemical digestion involves the enzymatic cleavage of chemical bonds in macromolecules, such as proteins, carbohydrates, and lipids, breaking them down into smaller units like peptides, monosaccharides, and fatty acids that can be absorbed by the body.
What are the main organs of the digestive system mentioned in the script?
-The main organs mentioned include the oral cavity (mouth), pharynx, esophagus, stomach, small intestine, large intestine, rectum, and accessory organs such as the salivary glands, pancreas, liver, and gallbladder.
What is the function of the enteric nervous system in the gastrointestinal system?
-The enteric nervous system, which contains about 100 million neurons, governs the function of the gastrointestinal system. It triggers peristalsis, the rhythmic contraction of the gut tube, to move material through the system and can function independently of the brain and spinal cord but is regulated by the autonomic nervous system.
How does the stomach contribute to the digestion process?
-The stomach contributes to digestion through mechanical means by churning food and chemical means by secreting substances like hydrochloric acid, pepsinogen (which becomes pepsin), mucus, intrinsic factor, and gastrin. These substances aid in protein digestion, protect the stomach lining, and regulate gastric acid secretion and motility.
What is the role of the duodenum in the digestive process?
-The duodenum is the first part of the small intestine and plays a key role in chemical digestion. It secretes enzymes like disaccharidases and peptidases that break down carbohydrates and proteins, respectively. It also releases hormones like secretin and cholecystokinin (CCK) that regulate the release of pancreatic juices and bile for further digestion.
What is the significance of the lower esophageal sphincter in the digestive process?
-The lower esophageal sphincter is a muscular ring that relaxes and opens to allow the passage of food from the esophagus into the stomach. It prevents stomach contents from flowing back into the esophagus, which would cause heartburn or other issues.
What are the main hormones involved in regulating feeding behavior and the feeling of fullness as mentioned in the script?
-The main hormones involved in feeding behavior and fullness include antidiuretic hormone and aldosterone, which promote thirst; glucagon and ghrelin, which promote hunger; and leptin and cholecystokinin, which promote the feeling of fullness.
Outlines
😀 Introduction to the Digestive System
Iman introduces the topic of the digestive system, outlining the chapter's objectives. The focus is on the anatomy of the digestive system, the roles of its organs in digestion and absorption, the accessory organs' contribution, and the processes of absorption and defecation. The script explains the transformation of complex foods into simpler molecules and the body's need for mechanical and chemical agents to break these bonds. The alimentary canal's role and the distinction between digestion and absorption are highlighted, with the latter involving the transport of nutrients to the body's tissues and cells.
😋 Role of Accessory Organs and Neurons in Digestion
The script delves into the roles of accessory organs like the salivary glands, pancreas, liver, and gallbladder in providing necessary enzymes and lubrication for digestion. It also discusses the importance of the enteric nervous system, which contains 100 million neurons responsible for peristalsis, the rhythmic contractions that move material through the digestive tract. The autonomic nervous system's influence on digestion, particularly the parasympathetic division's role in stimulating digestive activities, is also covered. Hormones that regulate feeding behavior and the significance of the oral cavity in both mechanical and chemical digestion are highlighted.
🍽️ Digestive Process from Mouth to Stomach
This paragraph describes the journey of food from the oral cavity through the pharynx and esophagus to the stomach. It details the process of chewing (mechanical digestion) and the role of saliva in moistening and initiating chemical digestion with enzymes like salivary amylase and lipase. The script explains the prevention of food entering the larynx by the epiglottis and the muscular structure of the esophagus that facilitates peristalsis. The stomach's role as a central organ in digestion, capable of both mechanical and chemical digestion, is introduced, along with its anatomical structure and the function of its various cells and glands.
🔪 Stomach's Role in Digestion and the Formation of Chyme
The stomach's function in the digestive process is explored in depth, including its capacity, structure, and the various substances it secretes to aid digestion. The role of gastric and pyloric glands in producing mucus, pepsinogen, hydrochloric acid, and intrinsic factor is detailed. The script explains how these secretions contribute to protein digestion, microbial defense, and the absorption of vitamin B12. The stomach's production of chyme, a semi-fluid mixture of partially digested food, is described as it moves into the small intestine for further nutrient absorption.
🧬 Chemical Digestion in the Duodenum and Enzyme Activation
The script focuses on the duodenum's role in chemical digestion, where enzymes and hormones are released in response to chyme from the stomach. Brush border enzymes like disaccharidases and peptidases break down carbohydrates and proteins into absorbable units. The activation of trypsinogen to trypsin by enteropeptidase is highlighted as crucial for protein digestion. Hormones like secretin and cholecystokinin (CCK) regulate the release of pancreatic juices and bile, which are essential for fat digestion and creating a feeling of fullness.
📚 Summary of Digestive System Anatomy and Digestion Process
A comprehensive summary of the digestive system's anatomy and the processes of digestion is provided. The script recaps the journey of food from ingestion in the oral cavity through mechanical and chemical digestion, the role of accessory organs, and the enteric nervous system's control of peristalsis. It also summarizes the stomach's function and the duodenum's role in chemical digestion, including enzyme and hormone release. The paragraph concludes with an invitation for questions and a teaser for the next video, which will continue the chapter.
Mindmap
Keywords
💡Digestive System
💡Ingestion
💡Mechanical Digestion
💡Chemical Digestion
💡Peristalsis
💡Stomach
💡Chyme
💡Duodenum
💡Enzymes
💡Hormones
💡Enteric Nervous System
Highlights
Introduction to the digestive system and its objectives, including anatomy, organ roles, accessory organs, and absorption and defecation.
Explanation of the complex process of converting food into simpler monosaccharides, fatty acids, and amino acids for absorption.
Differentiation between intracellular and extracellular digestion, with a focus on the alimentary canal's role in the latter.
Description of the mechanical and chemical processes involved in digestion, including the breakdown of food particles and enzymatic cleavage of chemical bonds.
The journey of food from the oral cavity through the digestive tract, highlighting the functional roles of each organ.
Role of accessory organs like salivary glands, pancreas, liver, and gallbladder in aiding digestion with enzymes and lubrication.
Importance of the enteric nervous system in controlling peristalsis and the gastrointestinal system's function.
Discussion on hormones that regulate feeding behavior and digestion, such as ghrelin, leptin, and cholecystokinin.
Mechanical digestion in the oral cavity through chewing and the role of saliva in chemical digestion.
The pharynx's function as a shared pathway for food and air, and the prevention of food entering the larynx during swallowing.
Peristalsis in the esophagus and its role in propelling food towards the stomach.
The stomach's dual role in mechanical and chemical digestion, including the production of pepsin and hydrochloric acid.
Gastrin's role in regulating hydrochloric acid secretion and stomach contractions for the mechanical breakdown of food.
Transition of chyme from the stomach to the duodenum and the duodenum's integral role in chemical digestion.
Enzyme and hormone production in the duodenum for the breakdown of disaccharides, peptides, and activation of trypsinogen.
Secretin and cholecystokinin's (CCK) role in regulating the release of pancreatic juices and bile for fat digestion and feeling of fullness.
Pancreatic juices' function in digesting carbohydrates, fats, and proteins in the duodenum.
Transcripts
hello everybody my name is Iman welcome
back to my YouTube channel today we're
going to be discussing the digestive
system in this chapter we're going to
cover the following objectives first
we'll talk about the anatomy of the
digestive system as a whole
second we will focus on the different
organs of the digestive system and talk
about their roles in ingestion and
digestion third we will briefly touch on
the accessory organs of a digestion and
then last but not least we will end the
chapter with an explanation on
absorption and defecation what a great
note to end on isn't it all right so
let's go ahead and get started with the
first objective anatomy of the digestive
system now the food we eat is complex
it's composed of meats grains vegetables
and fruits dairy products and sugars and
the role and job of the digestive system
is to take these complex foods and turn
these large macromolecules into smaller
and simpler monosaccharides fatty acids
and amino acids now in order to cleave
all of these bonds the body requires a
complex system of mechanical and
chemical agent
these compounds can then be absorbed
from the gut transported to the tissue
by the circulatory system and used by
cells and so in this chapter we will
consider the organs that make up the
digestive system as well as the
processes by which the food we eat
become the fuel we need for both energy
growth development and maintenance
so with that let's begin there are two
types of digestion that occur all right
first we have intracellular digestion
all right as a part of metabolism
involves the oxidation of glucose and
fatty acids for energy however our diets
don't consist of just pure glucose and
fatty acids rather these substances have
to be extracted from the food we eat
the processes by which these nutrients
are obtained from food occur within the
Lumen of the elementary canal and it's
known as extra cellular digestion this
is technically quote-unquote outside the
body as it is outside the cell borders
now this alimentary canal runs from the
mouth to the anus and it's sectioned off
by spinters or circular smooth muscles
around the canal that can contract to
allow compartmentalization of function
now the human digestive tract has
specialized sections with different
functional roles and the most basic
functional distinction distinction is
between digestion and absorption
now digestion involves the breakdown of
food into its constituent organic
molecules lipids into free fatty acids
and glycerol starches and other
carbohydrates into monosaccharides and
proteins into amino acids now digestion
can be subdivided into mechanical
and chemical processes mechanical
digestion is the physical breakdown of
large food particles into smaller food
particles but it does not involve
breaking chemical bonds all right
chemical digestion on the other hand is
the enzymatic cleavage of chemical bonds
such as the peptide bonds of proteins
and the glycosidic bonds of starches
all right so that's digestion that's one
basic function of the human digestive
tract the other functional role of the
digestive tract is absorption and
absorption involves the transport of
products of digestion from the digestive
tract into the circulatory system for
distribution to the body's tissues and
cells
now that we have a understanding
of that let's start talking about how
things move or progress in the digestive
system
the digestive tract begins with the oral
cavity aka the mouth
followed by the pharynx which is a
shared pathway for both food entering
the digestive system and air entering
the respiratory system from the pharynx
food enters the esophagus which
transports food to the stomach then from
the stomach food travels to the small
intestine and then the large intestine
finally waste products of digestion
enter the rectum where feces are stored
until appropriate time of release
now in addition to the actual organs of
the digestive tract the salivary glands
the pancreas the liver and the
gallbladder all help to provide the
enzymes and the lubrication necessary to
Aid the digestion of food
now believe it or not neurons also play
an important role in the
gastrointestinal system the enteric
nervous system is a collection of 100
million neurons that govern the function
of the gastrointestinal system these
neurons they're present in the walls of
the digestive tract and they trigger
this thing called peristalsis or the
rhythmic contraction of the gut tube in
order to move material through the
system and the system can function
independently of the brain and the
spinal cord although it is heavily
regulated by the autonomic nervous
system now actually the para sympathetic
division it's involved in stimulation of
digestion activities increasing
secretion from the exocrine glands and
promoting this peristalsis and then the
sympathetic division that's involved in
inhibition of these activities the fact
that so often we feel sleepy and
lethargic after eating a big meal is due
in part to our parasympathetic activity
now
that now that we have introduced the
general anatomy of the digestive system
as a whole let's start to focus on the
different organs of the digestive system
and let's talk about their role
and roles in ingestion and digestion so
to supply the body with nutrients we
must ingest or eat you know food now
several hormones are involved with the
feeding behavior and digestion digestion
begins in the mouth the oral cavity and
then it continues in the stomach and the
first part of the small intestine known
as the duodenum all right so let's talk
about every part of that process
all right we're going to talk about
every part of the process now we're
gonna focus on ingestion and digestion
all right
ingestion taking food into the body
digestion breaking down food then in the
latter half in the latter half of this
chapter specifically that last objective
will cover will focus on absorption so
moving food into cells and elimination
removing unused food
now
multiple hormones regulate feeding
behavior all right multiple hormones
regulate feeding Behavior which uh
including antidiuretic hormone and
aldosterone these promote thirst
glucagon and ghrelin which promote
hunger and leptin and Colo
cystokinin which promotes fullness now
the first part all right of us in
understanding ingestion and digestion
all right we start with the oral cavity
the oral cavity plays a role in both
mechanical
and chemical digestion of food
mechanical digestion in the mouth that's
going to involve the breaking up of
large food particles into smaller
particles by using the teeth the tongue
and the lips all right this is the
process this process is called chewing
right we know this
also called mastication all right
chewing helps to increase the surface
area to volume ratio of the food that's
going to allow for more surface area for
enzymatic digestion as it passes through
the gut tube now it also moderates the
size of the food particles that are
going to be entering the Lumen of the
alimentary canal food particles that are
too large they can create an obstructive
risk in the tract which is why this
first step is important all right
chewing your food is important now
chemical digestion begins the breakdown
of chemical bonds in the macromolecules
that make up the food all right this
relies on enzymes from the saliva
produced by the three pairs of salivary
glands saliva also AIDS mechanical
digestion by moisture moistening
moistening and lubricating food the
salivary glands like all glands of the
digestive tract are are innervated by
the parasympathetic nervous system the
presence of food in the oral cavity it
triggers a neural circuit that
ultimately leads to increased
parasympathetic stimulation of these
glands salvation Salvation can also be
triggered by signals that you know food
is near like making eye contact with a
juicy burger on the kitchen top or the
smell of your mom cooking really
delicious food in the in the kitchen
that all can be triggering signals all
right and so you start to produce saliva
in your mouth in preparation of
ingesting food and then you know once it
enters the mouth the oral cavity
digestion can begin all right
so even in preparation of ingesting food
salivation can be triggered by signals
that food is near now saliva contains
salivary amylase also known as
Thailand but that's spelled with a p in
the beginning
let's spell it out
all right and lipase now salivary
amylase this is capable of hydrolyzing
starch into smaller sugars like maltose
and dextrins while lipase catalyzes the
hydrolysis of lipids the amount of
chemical digestion that occurs in the
mouth is minimal though because the food
doesn't stay in their mouth for very
long right you don't you're not chewing
your food for like five minutes you're
chewing your food for probably a minute
minute and a half tops
our muscular tongue forms the food into
a ballis which is forced back to the
pharynx and swallowed alright so after
you're done chewing your food all right
the mechanical digestion and a little
bit of the chemical digestion that
happens to the mouth then you move it
back you swallow it and it goes the food
will make its way to the pharynx all
right so that's the next part we started
with the oral cavity now we're gonna
make it to the pharynx
the pharynx is the cavity that leads
from the mouth and posterior nasal
cavity to the esophagus the pharynx
connect not only to the esophagus but
also to the larynx which is a part of
the respiratory tract
the pharynx it can be divided into three
parts the nasopharynx
that's right behind the nasal cavity the
orphal pharynx this is at the back of
the mouth and the laryn Joe pharynx all
right and that is going to be above the
vocal cords now food is prevented from
entering the larynx during swallowing by
epiglottis which is a like a cartilage
structure that folds down to cover the
uh the laryngeal Inlet if this mechanism
Fails Like failure of this mechanism can
lead to
choking on your food all right
but we have things in place that prevent
that from happening all right so for
first the oral cavity then the food has
made it to the pharynx now from the
pharynx we make it to the esophagus the
esophagus is a muscular tube that
connects the pharynx to the stomach the
top third of the esophagus it's composed
of skeletal muscle the bottom third is
composed of smooth muscle and the middle
the middle part is kind of a mix of both
what does this mean in terms of nervous
control well while the top of the
esophagus is under somatic or voluntary
motor control the bottom and most of the
rest of the gastrointestinal tract for
that matter is under autonomic or
involuntary nervous control the rhythmic
contraction of smooth muscle that
propels food towards the stomach is
called peristalsis
all right now under normal circumstances
peristalsis proceeds down the digestive
tract however certain conditions like
exposure to chemicals or infectious
agents or physical stimulation in the
posterior pharynx and even cognitive
stimulation can lead to the reversal of
peristalsis in the process of vomiting
all right
so uh
things that certain conditions can cause
hiccups in this process of peristalsis
and that could lead to vomiting the food
that you have ingested now swallowing is
initiated in the muscles of the
oropharynx which constitutes the upper
esophageal spinster
peristalsis it squeezes pushes and then
propels the ball is towards the stomach
and as the ballis approaches the stomach
a muscular ring known as the lower
esophageal spinster all right or also
known as the cardiac spinster relaxes
and it opens to allow the passage of
food so that the food can pass through
the esophagus and make it now to the
stomach all right so again we started at
the oral cavity the mouth all right then
the food made it to the pharynx then
from the pharynx we made it to the
esophagus
and from the esophagus we make it to the
stomach now the stomach is a central
organ in the digestive process it's
capable of both mechanical and chemical
digestion it's located in the upper left
quadrant of the abdominal cavity this
muscular organ has a capacity of about
two liters and it's structured to
withstand harsh acidic environment its
location and capacity really makes it
ideal for its primary role which is the
initiation of protein digestion and the
continuation of carbohydrate and fat
digestion that began in the mouth now
the anatomical structure of the stomach
consists of four main divisions you have
the fundus the body the antrum and the
pylorus
all right so those are the four main
divisions of the stomach now the
internal lining known as the mucosa
features gastric and pyloric glands as
well as folds called rugai that increase
surface area now gastric glands are
activated by the vagus nerve part of the
parasympathetic nervous system which
itself is triggered by sensory inputs
such as this site and the smell of food
now cellular specialization within the
gastric glands facilitates its digestive
functions essentially mucous cells they
produce bicarbonate Rich mucus to
protect the stomach lining from the
acidic environment within
parietal cells they secrete hydrochloric
acid which serves multiple functions
including microbial defense protein
protein denaturation and the conversion
of pepsinogen to its active form pepsin
Chief cells they produce this pepsinogen
which is activated by the acidic
environment to become pepsin all right
and uh and this this is a unique enzyme
that's most active at low pH levels
pepsin actually Cleaves proteins into
smaller peptide fragments and that helps
initiate their digestion
so from that notably the stomach
produces six essential products all
right
it produces pepsinogen all right which
is cleave to pepsin in the stomach this
is an enzyme that partially digests
proteins it secretes mucus which
protects the mucosa
it produces hydrochloric acid which
kills microbes denatures proteins and
also converts pepsinogen into pepsin it
produces bicarbonate which also protects
the mucosa
all right it secretes water this is
dissolves and dilutes some of the
ingested material and also
it also secretes this thing called
intrinsic factor which is required for
normal absorption of vitamin B12
all right so those are the six main
products that the stomach secretes now
the pyloric glands that are located in
the antrum and the Polaris region these
they contain these cells they're called
G cells that secrete gastrin gastrin is
a peptide hormone it regulates
Hydrochloric secretion and stomach
contractions it also AIDS in the
mechanical breakdown of food and the end
product of this phase of digestion is
chime or chyme an acidic or semi-fluid
mixture that moves into the small
intestine for further nutrient
absorption and so the point here the
summary for the stomach part right
because there's a lot that's happening
in the stomach the summary is that the
stomach is a highly specialized organ
with functions that are tailored to its
acidic environment and it plays a very
very crucial role in the early stages of
digestion and it's aided by specific
cellular components that produce a
variety of enzymes and other substances
these compounds they work together to
break down food into smaller components
setting the stage up for further
digestion and absorption in the
subsequent in the in the subsequent
segments of the gastrointestinal tract
and with that note all right from the
stomach we move into the dude enough
all right
moving forward in the digestive tract
The partially dissolved food or or chime
leaves the stomach and it enters the
duodenum all right the first of three
segments of the small intestine now this
segment is integral to the chemical
digestion process all right producing
enzymes and hormones that are really
essential for the breakdown of food and
the regulation of other digestive organs
now
this one of three parts of the small
intestine despite its minor role in
absorption it really sets the stage for
nutrient uptake in the subsequent
segments of the small intestine now upon
entry into the duodenum the presence of
chime triggers the release of things
called brush border enzymes like
disaccharide disaccharide Aces and
peptides peptid aces all right as well
as hormones like secretin and cck
now disaccharide Aces including maltase
isomaltase lactase sucrase all break
down disaccharides into their
constituent monosaccharides whereas
peptide
peptidasis such as aminopeptidase and
dipeptidase they cleave peptides into
free amino acids or smaller peptides
that can then be absorbed across the
intestinal wall
now another important thing to mention
is anteropeptidase this is another
critical enzyme
that's secreted by the duodenum and it's
responsible for activating trypsinogen
to trypsin which in turn activates other
pancreas pancreatic proteases this
Cascade of enzyme activation is really
crucial for the effective breakdown of
proteins into absorbable units then
secretin and cck hormones
um are released by the duodenum they
regulate the secretion of pancreatic
juices and bile into the digestive tract
so secretin reduces gastric acid
production it increases bicarbonate
secretion from the pancreas and it also
slows gastrointestinal motility and that
allows more time for the fats to be
digested now on the other hand cck is
released in response to the presence of
amino acids
so that was secretin cck is released in
respond in response to the presence of
amino acids and fats in the chime
promoting the release of bile and
pancreatic juices now bile salts
components of bile are really essential
for the emulsification of fats it's a
necessary step for their subsequent
enzymatic digestion digestion in
addition cck
acts in the brain to promote the feeling
of fullness
now pancreatic juices stimulated by cck
they they're going to contain enzymes
that are really capable of digesting all
three main nutrient types that's
carbohydrates fats and proteins the this
bicarbonate Rich alkaline solution
neutralizes the acidic chime that comes
from the stomach and provides an optimal
environment for these enzymes to play
their role in the in in the duodenum
all right and so with that We've Ended
objective too we've covered the first
objective and we've covered the second
objective we're going to stop here all
right let's quickly summarize what we
just learned in these first two
objectives all right we talked about the
anatomy of the digestive system we
talked about intracellular digestion and
how it involves the oxidation of glucose
and fatty acids to make energy we also
talked about extracellular digestion
which occurs in the Lumen of the
elementary canal all right we talked
about two types of digestion mechanical
and chemical mechanical digestion is the
physical breakdown of large food
particles into smaller ones and chemical
digestion is the enzymatic cleavage of
chemical bonds such as the peptide bonds
of proteins or the glycosidic bonds of
starches we talked about the pathway of
the digestive tract its oral cavity then
pharynx then esophagus then stomach
followed by the small intestine and then
the large intestine and then finally the
rectum
we talked about how the accessory organs
of digestion are going to be the
salivary glands the pancreas the liver
and the gallbladder and actually the
third objective focuses focuses on these
accessory organs of digestion and then
we also mentioned that the enteric
nervous system is in the wall of the
elementary canal and it controls
peristalsis
then we moved into the second objective
where we talked about ingestion and
digestion all right we said that
multiple hormones regulate feeding
behavior all right and regulate the
feeling of fullness we talked about
um we started at the beginning in the
oral cavity that's where we start we
ingest food and then through chewing it
we start the mechanical digestion of
food while other enzymes like salivary
amylase and lipase start the chemical
digestion of food then food is formed
into a bolus and swallowed from the oral
cavity moves into the pharynx which
connects the mouth and the posterior
Naval nasal cavity to the esophagus then
we move into the esophagus where it
propels food to the stomach using
peristalsis
food enters the stomach through the
lower
esophageal spinster and then the stomach
we enter the stomach the stomach has
four parts the fundus the body the
antrum and the Polaris the stomach has a
um many important parts that contribute
to digestion we have the mucous cells
that produce bicarbonate Rich mucus to
protect the stomach we have chill cheap
cells that secrete pepsinogen a protease
activated by the acidic environment of
the stomach we have parietal cells that
secrete hydrochloric acid and intrinsic
factor which is needed for vitamin
vitamin B12 absorption we have G cells
that secrete gastrin which is a peptide
hormone that increases Hydrochloric
secretion and gastric motility all right
we covered all of those important uh
um parts of the stomach all right now
after mechanical and chemical digestion
in the food the food particles are now
called chyme or chime and the food
passes into the duodenum through pyloric
svenster
um through the pyloric's Finster now in
the duodenum this is the first part of
the small intestine it's primarily
involved in chemical digestion we have
disaccharidases and these are brush
border enzymes that break down things
like maltose isomaltose lactose and
sucrose into monosaccharides we also
have brush border peptidases including
aminopeptidase and dipeptidase then we
have enteropeptidase which activates
trypsinogen and other things like
pro-carboxy peptidases which initiates
an activation Cascade then we also have
secretin
which stimulates the release of
pancreatic juices into the digestive
tract and slows motility and then we
have cck which stimulates the bile
release from the gallbladder release of
the pancreatic juices and also plays a
role in you feeling full after you've
eaten a meal
all right so those are all the important
points from the first two objectives let
me know if you have any questions
comments concerns Down Below in the next
video we'll continue and finish up the
chapter other than that good luck happy
studying and have a beautiful beautiful
day future doctors
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