CARBOHYDRATES.docx

CARBOHYDRATES (CHO) **Lecture 1** -- Digestive System,\ ( Review ) Intestinal Villus, and\ Circulatory System **THE DIGESTIVE SYSTEM & ITS PROCESSES** The function of the digestive system is digestion and absorption. [DIGESTION] - The process of breaking down complex nutrients (foods) into si...

CARBOHYDRATES (CHO) **Lecture 1** -- Digestive System,\ ( Review ) Intestinal Villus, and\ Circulatory System **THE DIGESTIVE SYSTEM & ITS PROCESSES** The function of the digestive system is digestion and absorption. [DIGESTION] - The process of breaking down complex nutrients (foods) into simpler forms. - Purpose: EASY ABSORPTION [ABSORPTION] - The process of transferring digested nutrients from the lumen of the SI into the bloodstream - Purpose: for cellular transport/distribution and utilization [TRANSPORT] - The process of moving absorbed nutrients throughout the body through the circulatory and lymph systems The digestive system is divided into TWO major parts: 1.The gastrointestinal (GI) tract (alimentary canal) - is continuous tube with two openings, the mouth and the anus. It includes the: mouth, pharynx, esophagus, stomach, small intestine and large intestine. - Food passing through the internal cavity or lumen, of the GI tract does not technically enter the body until it is absorbed through the walls of the GI tract and passes into blood or lymphatic vessels. 2\. Accessory Organs - Include the teeth and tongue, salivary glands, liver, gallbladder, and pancreas. The treatment of food in the digestive system involves the following seven processes: **1. Ingestion** - is the process of eating. **2**. **Propulsion** - is the movement of food along the digestive tract. - The major means of propulsion is **peristalsis,** a series of alternating contractions and relaxations of smooth muscles that lines the walls of the digestive organs and that forces food to move forward. **3.** **Secretion** - Secretion of digestive enzymes and other substances liquefies, adjusts the pH of, an =d chemically breaks down food. 4\. **Mechanical** **Digestion** - is the process of physically breaking down food into smaller pieces. - This process begins with the **chewing** of food and continues with the muscular **churning** of the **stomach**. Additional churning occurs in the **small** **intestine** through muscular constriction of the intestinal wall. This process, called segmentation, is similar to peristalsis, except that the rhythmic timing of the muscle constrictions forces the food backward and forward rather than forward only. **5.** **Chemical Digestion** - is the process of chemically breaking down food into simpler molecules. The process is carried out by enzymes in the stomach and small intestines. **6.** **Absorption** - is the movement of molecules (by passive diffusion or active transport) from the digestive tract to adjacent blood and lymphatic vessels. Absorption is the entrance of the digested food into the body. **7.** **Defecation** - is the process of eliminating undigested material through the anus. Figure 1: THE HUMAN DIGESTIVE SYSTEM **Lecture 2 -** Composition,\ Classification, Function\ and Laboratory Tests of\ Carbohydrates ***[Terms]:*** **HYPERGLYCEMIA** - an increase concentration of sugar (glucose) in the blood **HYPOGLYCEMIA** - a decreased concentration of sugar (glucose) in the blood **GLYCOSURIA (GLUCOSURIA)** - presence of glucose ( sugar ) in the urine **HYPERINSULINISM** - a condition wherein there is increased secretion of insulin. **HYPOINSULINISM** - decreased secretion of insulin **INSULINOMA** - a tumor of the pancreas which results into increased secretion of insulin. - compounds composed of the: hydrogen, carbon & oxygen - **starch** (polysaccharide) in plant cells - **cellulose** ( polysaccharide ) in plant framework - **glucose** (a hexose monosaccharide) and **glycogen** ( polysaccharide ) in animals - are important sources of energy for the vital bodily functions. - In nature, carbohydrates exist most abundantly as sugars (monosaccharides and disaccharides) and starches (polymers of pentoses or hexoses) - Each contains an aldehyde ( aldose ) or ketone group ( ketose ) - A monosaccharide is a simple sugar containing 3, 4, 5 or 6 carbon atoms called *triose, tetrose, pentose and hexose* respectively. - Among the monosaccharides mentioned above, the **hexoses** (such as glucose, fructose, & galactose) and **pentose** (ribose ), are the most important from the standpoint of food and nutrition. - Carbohydrate, the major component of the human diet in many areas of the world, is an important source of body energy. - The capacity of the body to **store** carbohydrate is limited, however, and is confined to **liver** ( can store up to 10% of its wet weight ) and **muscle** ( can store up to 0.5% wet weight) - The total amount of stored carbohydrate is sufficient to fulfill the energy requirements of a person for only about **one-half day.** - All tissues can use glucose ( dextrose ), the principal and almost exclusive carbohydrate circulating in blood - Under fasting conditions, only a few tissues depend entirely for glucose as a source of energy. They are called the **glucose-dependent cells** which include the **brain** ( the most important glucose consumer ), followed by the **red blood cells**, **platelets,** **leucocytes**, **kidney medulla** and **intestinal mucosa**. - Other tissues readily oxidize fatty acids and ketones for energy purposes. - Maintenance of blood glucose, at normal levels, during fasting is partly due to the mobilization of muscle proteins into the liver, their hydrolysis into **amino acids** and the conversion of these amino acids into glucose **(gluconeogenesis)**. - Other substances capable of gluconeogenesis are **glycerol** and **lactate** - Liver gluconeogenesis therefore, is the mechanism which provides glucose to tissues that depend completely on glucose for existence during fasting. - The glucose carried in the blood to the cells is oxidized to produce the high energy molecule ATP (adenosine triphosphate) with its high-energy phosphate bonds. This ATP molecule is the main source of energy used to drive most metabolic reactions. - The most common disease entity associated with CHO metabolism is Diabetes Mellitus characterized by an insufficient level or total absence of active insulin in the blood. Insulin is a hormone secreted by the pancreas (beta cells of the Islets of Langerhans) which is needed for the facilitation of glucose transfer into the cells particularly the cells of the skeletal muscles, liver and adipose tissues. Glucose is freely permeable however to other tissues, even in the absence of insulin such as the brain, kidneys, blood cells ( rbc, wbc, platelets ) and mucosa. The brain is the first organ to suffer in case of decreased levels of blood sugar (hypoglycemia). **[Laboratory Tests]** 1. FBS ( Fasting Blood Sugar ) - requires fasting or NPO (non-per-orem) for about 6 -- 8 hours - **for the determination of hyperglycemia** - NV: \< 100 mg/dl 2. RBS  ( Random Blood Sugar ) - collected anytime of the day - used during emergency cases to determine: **insulin shock or hyperglycemic ketonic coma** - NV: \< 140 mg/dl 3. 2-HPPBS ( 2-hour Post Prandial Blood Sugar ) - monitoring of insulin response - NV : \< 140 mg/dl 4. HbA1c ( Hemoglobin A1c or Glycosylated Hemoglobin ) - it reflects the average blood glucose level over the previous 2-4 months (*due to the irreversible binding of glucose with hemoglobin*) - used to monitor patient's **compliance** on dietary and treatment plan ( *a reliable method in the monitoring of long-term glucose control* ) - performed every 3 -- 6 months ( DM patients ) \< 5.7% (normal value) 5.7% - 6.4% (prediabetes) ≥ 6.5% (diabetes) 5. OGTT / IVGTT (Oral / Intravenous Glucose Tolerance Test ) - determination of gestational diabetes mellitus during pregnancy **REVISED DIAGNOSTIC CRITERIA FOR\ GDM**\ 1. FBS = ≥ 92 mg/dl\ 2. 1 -- hour GCT = ≥ 180 mg/dl\ 3. 2-hour OGTT = ≥ 153 mg/dl\ 4. 3-hour OGTT = ≥ 140 mg/dl   [Normal Value Range for blood sugar tests] : - **At 65 -- 70 mg/dl, release of hyperglycemic hormones** - **≤ 60 mg/dl strongly suggests hypoglycemia** - **about 50 -- 55 mg / dl, symptoms of hypoglycemia may appear which include** a\. increased hunger, b\. sweating, c\. nausea and vomiting, d\. dizziness, e\. Nervousness and shaking, f\. blurring of speech and sight, and g\. mental confusion. CLASSIFICATION OF CHO **Classification:** **A. According to the Number of carbon atoms** (triose, tetrose, pentose, hexose) **B. According to the Size of the base carbon chain**: I**. Monosaccharides** - carbohydrates that cannot be hydrolyzed into simple sugars upon hydrolysis a.) **triose** ( 3C ) - formed during the metabolic breakdown of hexoses in muscle metabolism b.) **tetroses** ( 4C ) = e.g. erythrose c.) **pentoses** ( 5C ) = e.g. ribose and ribulose d.) **hexose** ( 6C ) - the most important sugar from the standpoint of nutrition and medicine Examples: **[Glucose]** ( dextrose / corn sugar / grape sugar / BLOOD SUGAR ) - found in young fruits, cereals, grains, wheat and in blood - its normal concentration in the blood is *\< 100 mg/dl* ( **70 mg/dl** as the lowest cut-off level ) - some of it are converted into glycogen (stored in the liver and skeletal muscles) or its excess is converted into fat (stored in the adipose tissue) - excretion in the urine ( glycosuria ) is associated with either DM or kidney failure or both *How to identify the cause of glucosuria? Answer: Do blood glucose test*  **[Fructose]** ( levulose ) - a product of sucrose hydrolysis the sweetest and the most soluble sugar found in honey and molasses - ***Fructosemia*** (an inherited disease due to deficiency of the enzyme ***fructose -- 1 -- phosphate aldolase*** with signs and symptoms of hypoglycemia, vomiting and severe malnutrition) **[Galactose]** - a product of lactose hydrolysis found in some glycoproteins and glycolipids in the nerve and brain tissues   - ***Galactosemia*** ( a severe inherited disease due to the inability to metabolize galactose due to the absence of the enzyme ***galactose -- 1 -- phosphate uridyl transferase*** or of ***galactokinase*** ) II\. DISACCHARIDES **Lactose** ( milk sugar ) - composed of glucose and galactose synthesized in the mammary glands - the least sweet, least fermentable of all sugars - an ideal constituent of infant milk **Maltose** ( malt sugar ) - present in germinating grains - does not occur in free state but is formed as an important transitory intermediate product of digestion of starch into glycogen and glucose - composed of two glucose units **Sucrose** ( table sugar ) - found in sugar cane, sugar beets and sugar maples - composed of fructose and glucose - considered as the standard sugar for sweetness   **III. Polysaccharides** - are very long chains ( polymers ) of monosaccharides which may be linear or branched in structure - usually tasteless - water soluble **A. Starch** ( plants ) - storage form of CHO in plants amylose = linear amylopectin = branched **B.) Glycogen** - storage form of CHO in animals ( liver and SM ) - structure is similar to amylopectin but is more highly branched - hydrolysis yields glucose, maltose and dextrin **C.) Dextrin** - gummy polysaccharide used as an adhesive on the back of stamps and mailing envelopes **D.) Dextran** - plasma volume expander ( prevents sudden drop of blood volume and thus, blood pressure ) **E.) Cellulose** - indigestible poly found in cell walls of plants which help eliminate constipated bowels **F.) Peptidoglycan** - a component of bacterial cell wall - more on Gram ( + ) organisms than the Gram (-) **G.) Heparin** - an acidic polysaccharide synthesized and stored in the mast cells of most tissues ( lungs , liver, gut ) - has an anticoagulant activity - the most expensive **H.) Inulin** - a good index for the assessment of GFR for the following reasons: a. not altered in the body b. not reabsorbed c. not secreted **C.) According to functional group:** I. aldose II\. ketose  **D. According to the stereochemistry of the** **compound**  **[Functions of CHO:]** - **fuel ( major )** - skeletal or structural functions ( PM ) - storage, nutrient and reservoir of energy, to be enlarged or depleted as the organism needs - protein sparers **Lecture 3** -- Digestion of Carbohydrates, Proteins and Lipids