MCAT Biology Lecture: Digestive System (1/2)

Summary

This 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

00:00

😀 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.

05:01

😋 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.

10:02

🍽️ 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.

15:04

🔪 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.

20:04

🧬 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.

25:05

📚 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.

Keywords

💡Digestive System

The digestive system is a series of organs responsible for breaking down food into nutrients that can be absorbed by the body. In the video, it is the central theme, with the anatomy and function of the system being discussed in detail, including its role in both mechanical and chemical digestion.

💡Ingestion

Ingestion refers to the process of taking food into the body. It is the first step in digestion and is mentioned in the script as the starting point for the body's ability to derive nutrients from food, highlighting its importance in the overall digestive process.

💡Mechanical Digestion

Mechanical digestion is the physical breakdown of food into smaller pieces, primarily through the action of chewing in the mouth. The script describes how this process increases the surface area of food particles, facilitating enzymatic digestion later in the gastrointestinal tract.

💡Chemical Digestion

Chemical digestion involves the enzymatic breakdown of food into its constituent molecules. The script explains how this process occurs in the mouth with enzymes like salivary amylase and continues in the stomach and small intestine with various other enzymes.

💡Peristalsis

Peristalsis is the rhythmic contraction of the muscles in the gastrointestinal tract that moves food along the digestive system. The script describes peristalsis as a key mechanism for the progression of food from the mouth to the stomach and beyond.

💡Stomach

The stomach is a muscular organ that plays a central role in the digestive process, particularly in the digestion of proteins. The script details the stomach's structure and function, including the production of hydrochloric acid and pepsinogen, which are essential for breaking down food.

💡Chyme

Chyme is the semi-liquid mixture of partly digested food and stomach acids. The script mentions chyme as the product of stomach digestion that moves into the small intestine for further nutrient breakdown and absorption.

💡Duodenum

The duodenum is the first part of the small intestine and is crucial for chemical digestion. The script discusses its role in activating pancreatic enzymes and the release of hormones like secretin and cholecystokinin, which regulate digestion.

💡Enzymes

Enzymes are biological catalysts that speed up chemical reactions, including the breakdown of food molecules. The script provides examples of various digestive enzymes, such as pepsin, amylase, and lipase, and explains their specific roles in digestion.

💡Hormones

Hormones are chemical messengers that regulate various physiological processes, including digestion. The script mentions hormones like gastrin, secretin, and cholecystokinin, which are involved in the regulation of stomach acid, pancreatic juice secretion, and feelings of fullness.

💡Enteric Nervous System

The enteric nervous system is a network of neurons that governs the function of the gastrointestinal system. The script explains its role in triggering peristalsis and its ability to function independently of the brain and spinal cord, yet being regulated by the autonomic 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