5.2 Carbohydrates: Digestion and Absorption


– WELCOME TO SECTION 2 OF
CARBOHYDRATES ON DIGESTION AND ABSORPTION. WE’RE GOING TO START BY TAKING A LOOK AT WHAT HAPPENS
WHEN WE EAT CERTAIN TYPES OF CARBOHYDRATES. WE’LL START WITH MY
EXAMPLE OF A BAGEL. AND I’M CHOOSING A BAGEL BECAUSE
BAGELS HAVE A LOT OF STARCH, THEY’RE HIGHLY REFINED,
AND THEY’RE MOSTLY STARCH, SO THEY DO BREAK DOWN
VERY QUICKLY. WE THINK ABOUT THE STARCH, AND HOW WITH A STRING OF
SUGAR UNITS OR GLUCOSE UNITS. NOW STARCH DIGESTION
ACTUALLY STARTS IN THE MOUTH. AND YOU CAN TEST
THIS YOURSELF BY TAKING I MEAN LIKE A
HIGHLY REFINED BAGEL, WHITE BAGEL OR SOMETHING
AS SIMPLE AS A SALTINE THAT’S MOSTLY STARCH AND PUT IT
INTO YOUR MOUTH AND JUST CHEW. INSTEAD OF SWALLOWING
RIGHT AWAY, JUST CONTINUE TO CHEW. IT WILL BECOME A LITTLE
BIT LIKE A PASTE, BUT YOU’LL EXPERIENCE A SENSE, A TASTE SENSATION WHICH
GOES FROM MORE OF A BLAND STARCHINESS TO A LITTLE BIT
OF A SUGAR OR SWEET TASTE. AND THAT IS THE
INITIAL PHASES OF THE STARCH DIGESTION HAPPENING. NOW WHAT’S BECOME OF THAT PASTE,
YOU KNOW, GO DOWN THE ESOPHAGUS TO THE
STOMACH THERE IS REALLY LITTLE TO KNOW CARBOHYDRATE DIGESTION
HAPPENING IN THE STOMACH. THE MAIN DIGESTION HAPPENS
WITHIN THE INTESTINES. SO WITHIN THE INTESTINES, THE STARCH IS THEN BROKEN DOWN
INTO A STRING OF GLUCOSE CHAINS. REMEMBER THESE ARE JUST
INDIVIDUAL GLUCOSE HERE, AND THEN INTO MALTOSE. MALTOSE IS A DISACCHARIDE. ONCE IT GOES INTO
MALTOSE IT WILL THEN BE BROKEN DOWN
INTO GLUCOSE. SO THIS IS OUR
SINGLE SUGAR UNIT. NOW WHAT ABOUT IF WE TOOK A
PIECE OF CANDY AND THE REASON I’M MENTIONING CANDY IS BECAUSE
CANDY IS MADE OF SUCROSE. SO WE DON’T HAVE STARCH,
WHAT WE HAVE IS OUR GLUCOSE AND FRUCTOSE LINKED TOGETHER
AS OUR DISACCHARIDE SUCROSE. SO AGAIN WE MIGHT HAVE SOME
DIGESTIONS START IN THE MOUTH, BUT MOST OF THESE
DIGESTIONS IS GOING TO TAKE PLACE IN THE
SMALL INTESTINE. REMEMBER DIGESTION
IS THE BREAKDOWN OF FOOD INTO ITS
INDIVIDUAL NUTRIENTS. ONCE IT ENTERS THE INTESTINES, IT CAN EASILY BE BROKEN DOWN
INTO GLUCOSE AND FRUCTOSE, THE TWO MONOSACCHARIDES
OR INDIVIDUAL SUGAR UNITS. LET’S TAKE A LOOK AT MILK, AND REMEMBER THE MAIN
CARBOHYDRATE IN MILK IS LACTOSE. SO WE HAVE OUR
DISACCHARIDE LACTOSE WITH GLUCOSE AND GALACTOSE. SO WHEN THESE ENTER INTO
THE INTESTINES, IT’S GOING TO BECOME
THE MONOSACCHARIDES, GLUCOSE AND GALACTOSE, SO LACTOSE BREAKING DOWN INTO
THE INDIVIDUAL SUGAR UNITS. SO THESE HAVE ALL BROKEN DOWN
INTO THEIR INDIVIDUAL, MONOSACCHARIDES INDIVIDUAL SUGAR
UNITS WITHIN THE INTESTINE. SO THIS REPRESENTS THE
INTESTINES OVER HERE. AND THESE ARE THE
INTESTINAL CELLS AND THIS REPRESENTS
THE BLOOD STREAM. SO AS EACH OF THESE THE GLUCOSE
AND FRUCTOSE AND GALACTOSE, THE MONOSACCHARIDES HAVE,
THEY’VE ALREADY BEEN BROKEN DOWN FROM THE CARBOHYDRATE FOODS
THAT THEY HAVE COME FROM. THEY THEN CROSS THROUGH THE INTESTINAL CELLS
INTO THE BLOODSTREAM. AND NOW THEY CAN GO
THROUGHOUT THE BLOODSTREAM. SO WITHIN THE BLOODSTREAM,
I DO WANT TO POINT OUT THAT MOST OF THE CELLS IN THE
BODY CAN USE GLUCOSE AND SO CELLS CAN PICK UP GLUCOSE AND
IMMEDIATELY USE THAT FOR ENERGY. THAT’S WHAT, WHY
CELLS WANT GLUCOSE, IS THEY WANT THAT
FORM OF ENERGY. BUT THE GALACTOSE AND THE FRUCTOSE HAVE TO
GO TO THE LIVER. SO FOR THE MOST PART THESE ARE, THEY GO TO THE LIVER,
THE LIVER IS, ONE OF THE, THE LIVER DOES A LOT OF THINGS
BUT FOR OUR DISCUSSION HERE, THE LIVER IS REALLY
GOING TO GO THROUGH THE METABOLISM OF CARBOHYDRATES. THIS IS WHERE THE CARBOHYDRATES
ARE METABOLIZED AND AS FAR AS FRUCTOSE AND GALACTOSE,
THEY ARE CONVERTED TO GLUCOSE. THEY ALSO CAN’T HAVE OTHER
EFFECTS OR BE STORED AS, CONVERTED AND THEN
STORED AS FAT, BUT FOR THE MOST PART WHAT
I WANT YOU TO UNDERSTAND IS THAT CELLS CAN USE
GLUCOSE FOR ENERGY. IT DOESN’T HAVE TO GO THE LIVER,
BUT IF THE GLUCOSE, FRUCTOSE AND LACTOSE
GO TO THE LIVER, THEY CAN BE
CONVERTED TO GLUCOSE. IN A WAY EVERYTHING
ENDS UP AS GLUCOSE.  

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