Name: carbohydrates, digestion, and blood sugar
Uploaded: 2023-04-30T10:05:48.000Z
Duration: 1 min 36 s
Channel: JoVE

The commonly consumed foods, such as cereals, sugar, tubers, and milk, contain carbohydrates in three major forms, starch, lactose, and sucrose.
As soon as the food enters the mouth, salivary amylase enzymes break down the starch into smaller polymers. As the food particles travel down the digestive system into the small intestine, pancreatic amylases break it down into disaccharides, such as maltose or dextrin.
The digestive enzymes secreted by brush-border cells of the small intestine metabolize these disaccharides into glucose
Lactose, the carbohydrate found in milk, is catabolized by beta-galactosidase, an enzyme secreted by the brush-border cells, into its monomers -&#160; glucose and galactose.
Similarly, sucrose, a carbohydrate found in fruits, is hydrolyzed by the enzyme sucrase, also expressed on the brush-border cells, into its monomers -&#160; glucose, and fructose.
These monomers are then transported across the intestinal epithelium into the bloodstream and finally get absorbed by the body cells.&#160;
Once inside a cell, glycolytic pathways metabolize glucose into pyruvate, coupled with the production of energy molecules - ATP and NADH. The other two monomers, galactose, and fructose are converted to glucose-6-phosphate and then enter glycolysis.

carbohydrate metabolism

Carbohydrate Metabolism

Carbohydrates are polymers composed of molecules containing atoms of carbon, hydrogen and oxygen. One gram of carbohydrate can provide four kilo-calories of energy, which makes it the most efficient instant energy source.
Starch accounts for approximately 60% of the carbohydrates consumed by humans. Since amylase enzymes cannot function in the stomach&#39;s acidic environment, starch can only be digested in the mouth and small intestine. Simple sugars are found naturally in milk and fruits in the form of glucose, lactose, galactose and fructose. These sugars are metabolized via glycolysis and then by the citric acid cycle.
Cellulose is a carbohydrate found in plant cell walls that provides strength and stiffness to the plant. Humans cannot digest it due to the absence of cellulase, the cellulose digesting enzyme. However, these indigestible carbohydrates add fiber. Fiber adds bulk to the food that is consumed, and aids digestion by helping the partially digested food move through the intestines smoothly.
Disorders of carbohydrate metabolism
The normal range of glucose in the blood is 70-99 mg/dL. Any deviation in this level is a sign of poor metabolism and a weak regulatory system. For example, dysfunction of insulin production and secretion, as well as the target cells&#39; responsiveness to insulin, can lead to a condition termed diabetes mellitus. An increasingly common disease, diabetes mellitus has been diagnosed in more than 18 million adults and 200,000 children in the United States. It is estimated that up to 7 million more adults have the condition but have not been diagnosed. In addition, approximately 79 million people in the US are estimated to have pre-diabetes, a condition in which blood glucose levels are abnormally high, but not yet high enough to be classified as diabetes.
There are two main forms of diabetes mellitus. Type 1 diabetes is an autoimmune disease affecting the beta cells of the pancreas. These beta cells do not produce insulin; thus, synthetic insulin must be administered by injection or infusion. This form of diabetes accounts for less than five percent of all diabetes cases.
Type 2 diabetes accounts for approximately 95 percent of all cases. Lifestyle factors such as poor diet, inactivity, and the presence of pre-diabetes greatly increase a person&#39;s risk for type 2 diabetes. About 80 to 90 percent of people with type 2 diabetes are overweight or obese. In type 2 diabetes, cells become resistant to the effects of insulin. In response, the pancreas increases its insulin secretion, but over time, the beta cells become exhausted. In many cases, type 2 diabetes can be reversed by moderate weight loss, regular physical activity, and consumption of a healthy diet; however, if blood glucose levels cannot be controlled, the diabetic will eventually require insulin.
This text is adapted from <a href="https://openstax.org/books/anatomy-and-physiology/pages/17-9-the-endocrine-pancreas">Openstax, Anatomy and Physiology, Section 17.9: The Endocrine Pancreas</a>

Carbohydrates are polymers composed of molecules containing atoms of carbon, hydrogen and oxygen. One gram of carbohydrate can provide four kilo-calories ...

Education

JoVE Core

Cell Biology

Unit 1

Introduction to Metabolism

KEY TERMS AND CONCEPTS

carbohydrates, digestion, and blood sugar

Carbohydrates are an important source of energy and a key part of human nutrition. They are made of carbon, hydrogen, and oxygen. One gram of carbohydrate provides four kilo-calories of energy, so carbohydrates are the body’s most efficient instant fuel.

Starch makes up about 60% of the carbohydrates people eat. It is broken down by amylase enzymes, but amylase cannot work in the stomach’s acidic environment. That is why starch digestion happens in the mouth and the small intestine. Simple sugars also occur naturally in milk and fruits. These include glucose, lactose, galactose, and fructose.

The body uses these sugars in glycolysis, a pathway that starts sugar breakdown. The products then move into the citric acid cycle for further metabolism. Cellulose is another carbohydrate. It is found in plant cell walls and gives plants strength and stiffness. Humans cannot digest cellulose because they do not have cellulase, the enzyme that breaks it down.

Even though cellulose cannot be digested, it still matters in the diet as fiber. Fiber adds bulk to food and helps partially digested material move smoothly through the intestines. This supports digestion and helps keep food moving through the gut.

Carbohydrate metabolism also connects to blood glucose control. A normal blood glucose range is 70 to 99 mg/dL. Values outside this range can signal poor metabolism and weak regulation. Problems with insulin production or secretion, or with how target cells respond to insulin, can lead to diabetes mellitus.

Diabetes mellitus is increasingly common. It has been diagnosed in more than 18 million adults and 200,000 children in the United States. Up to 7 million more adults may have it without knowing, and about 79 million people are estimated to have pre-diabetes, where blood glucose is high but not yet in the diabetes range.

There are two main forms of diabetes mellitus. Type 1 diabetes is an autoimmune disease that affects the beta cells of the pancreas, so these cells do not produce insulin. People with this form need synthetic insulin by injection or infusion, and it makes up less than five percent of all cases. Type 2 diabetes accounts for about 95 percent of cases. It is linked to poor diet, inactivity, and pre-diabetes, and about 80 to 90 percent of people with type 2 diabetes are overweight or obese.

In type 2 diabetes, cells become resistant to insulin. The pancreas responds by making more insulin, but the beta cells can become exhausted over time. In many cases, moderate weight loss, regular physical activity, and a healthy diet can help reverse type 2 diabetes. If blood glucose still cannot be controlled, insulin may eventually be needed.

Carbohydrates, Digestion, and Blood Sugar

overview of metabolism

Metabolism in Plants, Animals, and Microbes

Metabolism is the set of chemical reactions that keep living cells working. These reactions are linked through many pathways. Together, they support the normal function of cells in plants, animals, and microbes. In plants, sunlight is the main energy source. Chlorophyll pigments in the leaves absorb this light. The plant then uses that energy for photosynthesis. During photosynthesis, water is oxidized to oxygen and carbon dioxide is reduced to glucose. Glucose then serves as a starting...

Carbohydrates are an important source of energy and a key part of human nutrition. They are made of carbon, hydrogen, and oxygen. One gram of carbohydrate provides four kilo-calories of energy, so carbohydrates are the body’s most efficient instant fuel. Starch makes up about 60% of the carbohydrates people eat. It is broken down by amylase enzymes, but amylase cannot work in the stomach’s acidic environment. That is why starch digestion happens in the mouth and the small intestine. Simple...

glycolysis: preparatory phase

Glycolysis: Energy Investment Steps

Glycolysis begins with energy investment steps in the cytoplasm of both prokaryotic and eukaryotic cells. It is the first step in cellular metabolism, which is the complete breakdown of glucose to extract energy. In heterotrophic cells, glucose enters by secondary active transport or through GLUT proteins, which are glucose transporter proteins that help glucose diffuse into the cell. The pathway starts with one six-carbon, ring-shaped glucose molecule and ends with two three-carbon molecules...

glycolysis: pay-off phase

Glycolysis: ATP and NADH Output

The pay-off phase of glycolysis turns the two three-carbon sugar molecules into ATP, NADH, and pyruvate. By this stage, the cell has already spent two ATP molecules. The remaining reactions recover that investment and add two more ATP molecules and two high-energy NADH molecules. The sixth step oxidizes glyceraldehyde 3-phosphate, a three-carbon sugar made earlier in glycolysis. High-energy electrons are transferred to NAD+, which becomes NADH. A second phosphate group is then added to form...

fates of pyruvate

Pyruvate Pathways in Fermentation

Pyruvate is a key product of glycolysis and can follow different pathways depending on oxygen availability. During glycolysis, glucose is oxidized to pyruvate, NAD+ is reduced to NADH, and two ATP are made by substrate-level phosphorylation. In aerobic organisms, pyruvate then enters the citric acid cycle, which helps produce the reduced coenzymes NADH and FADH2. These coenzymes are later oxidized in the electron transport chain to make ATP and regenerate NAD+ and FAD. When oxygen is absent,...

role of reduced coenzymes nadh and fadh&#8322;

Electron Carriers in Cellular Energy

Electron carriers help store and move energy during nutrient breakdown. Cells can save released energy by reducing these carriers or by making ATP, the cell’s main energy molecule. These mobile electron carriers bind high-energy electrons and shuttle them between compounds in metabolic pathways. The main carriers discussed here come from the B vitamin group and are nucleotide derivatives. They include nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and flavin...

overview of nitrogen metabolism

Nitrogen Cycle in Soil and Plants

Nitrogen moves through soil, plants, animals, and microbes in a cycle that keeps this macronutrient available for life. It is a major part of proteins and nucleic acids, so cells need it to build both amino acids and nucleotides. In nature, nitrogen is recycled from organic compounds and stored in several forms, including ammonia, ammonium ions, nitrate, nitrite, and nitrogen gas. Many of the key steps in this cycle are carried out only by prokaryotes. The largest nitrogen pool in terrestrial...

overview of fatty acid metabolism

Fatty Acids: Energy, Membranes, and Cholesterol

Fatty acids help cells store and use energy, and they also support important cell structures. Lipids are nonpolar and hydrophobic, so they do not mix well with water. Major lipid types include fats and oils, waxes, phospholipids, and steroids. Cells break down fatty acids by beta-oxidation. This process happens in the matrix of the mitochondria and cuts fatty acid chains into two-carbon acetyl groups. CoA picks up these groups to form acetyl CoA, which then enters the citric acid cycle. Extra...

sugars as energy storage molecules

Glucose Storage in Plants and Animals

Glucose storage in plants and animals helps cells manage energy for metabolism. Sugar is a simple carbohydrate, and cells use it because a lot of energy is stored in its bonds. Consumed carbohydrates often come from photosynthesizing organisms, especially plants. Plants make glucose during photosynthesis by using sunlight to convert carbon dioxide into sugar molecules. Because this builds a larger, energy-storing molecule, the process needs an energy input. Glucose can then be stored for later...

fats as energy storage molecules

How Triglycerides Fuel ATP Production

Triglycerides store long-term energy in fats. A triglyceride is built from glycerol and three fatty acids. When the body needs energy, these molecules are broken down first. This breakdown is called lipolysis, and it happens in the cytoplasm by hydrolysis. Lipolysis splits triglycerides into fatty acids and glycerol. The glycerol then enters glycolysis as DHAP, which connects fat breakdown to the cell’s main energy pathway. The fatty acids are then oxidized by beta-oxidation into acetyl-CoA.

regulation of metabolism

How Cells Control Metabolic Enzymes

Cells control metabolic enzymes to match changing needs and conditions. Different cells use different enzymes and energy levels, and those needs can also change within the same cell over time. Stomach cells, fat storage cells, skin cells, blood cells, and nerve cells do not all need the same metabolic activity. A digestive cell also works harder soon after a meal than it does many hours later. As cell needs change, the amount and activity of enzymes change too. Enzymes lower activation energy,...

positive and negative feedback loops

Homeostasis and Body Feedback Control

Homeostasis keeps body conditions in a steady range through feedback control. Animal organs and organ systems constantly adjust to internal and external changes. This balance is called a dynamic equilibrium because the body keeps adapting while still staying within specific ranges. The goal of homeostasis is to stay near a set point, which is the value the body tries to maintain. A change in the internal or external environment is a stimulus. A receptor detects that change and sends a signal...

key terms and concepts

Explore how carbohydrates provide energy, how starch and sugars are digested, and how blood sugar control relates to type 1 and type 2 diabetes.

Carbohydrates, Digestion, and Blood Sugar | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Carbohydrates, Digestion, and Blood Sugar

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