3-NPS02_Digestion-Absorption-Metabolism.pdf

Digestion, Absorption & Metabolism Mary Winrose B. Tia, RN, MAMSN OBJECTIVES Describe processes of digestion, absorption, and metabolism Name organs in digestive system and describe their functions Name enzymes or digestive juices secreted by each organ and gland in digestive system...

Digestion, Absorption & Metabolism Mary Winrose B. Tia, RN, MAMSN OBJECTIVES Describe processes of digestion, absorption, and metabolism Name organs in digestive system and describe their functions Name enzymes or digestive juices secreted by each organ and gland in digestive system Calculate basal metabolic rate (BMR) DIGESTION Digestion is the process Breakdown of food in body whereby food is broken in preparation for down into smaller parts, absorption chemically changed, and moved through the gastrointestinal system. Mechanical digestion Food broken into smaller pieces by teeth and moved along gastrointestinal tract by peristalsis Chemical digestion Carbohydrates, proteins, and fats broken down into nutrients that tissues can absorb and use Chemical changes occur through hydrolysis Chemical digestion Enzymes act on food substances – Causing them to break down into simple compounds Enzyme can act as catalyst – Speeds up chemical reactions without itself being changed in the process Digestion in the Mouth Digestion begins in the mouth, where the food is broken into smaller pieces by the teeth and mixed with saliva Esophagus Food travels through this muscular tube  Connects mouth to stomach Peristalsis and gravity act to move bolus Cardiac sphincter opens to allow passage of bolus into stomach Stomach Temporary storage of food Kneading and mixing of food with gastric juices Regulation of slow, controlled emptying of chyme into intestine Destruction of most bacteria consumed Stomach Gastric Juices are digestive secretions of the stomach. They contain hydrochloric acid, pepsin, and mucus. In children, two additional enzymes:  Rennin  Gastric lipase DIGESTION in Small Intestine Small intestine divided into three sections: – Duodenum First section – Jejunum Middle section – Ileum Last section DIGESTION in Small Intestine Hormones released – Secretin causes pancreas to release sodium bicarbonate to neutralize acidity of chyme – Cholecystokinin triggers gallbladder to release bile Bile – Emulsifies fat after secreted into small intestine – Produced in liver – Stored in gallbladder DIGESTION in Small Intestine Enzymes found in pancreatic juice secreted into small intestine – Pancreatic proteases Splits proteins E.g., trypsin, chymotrypsin, carboxypeptidases – Pancreatic amylase Converts starches (polysaccharides) to simple sugars DIGESTION in Small Intestine Enzymes found in pancreatic juice secreted into small intestine – Pancreatic lipase Reduces fats to fatty acids and glycerol Small intestine itself produces enzymes – Lactase, maltase, and sucrase convert lactose, maltose, and sucrose to simple sugars – Peptidases reduce proteins to amino acids DIGESTION in Large Intestine Consists of cecum, colon, and rectum Major tasks of cecum: – Absorbs water and salts from undigested foods – Kneads content for enhanced absorption – Collects volatile fatty acids to be absorbed and used as sources of energy Digested food progress through colon to anal canal DIGESTION Contents travel through: 1. Ascending colon 2. Transverse colon 3. Descending colon 4. Sigmoid colon 5. Rectum 6. Anal canal ABSORPTION ABSORPTION Is the passage of nutrients into the blood or lymphatic system Nutrients must be in simplest form Ø Carbohydrates Simple sugars Ø Proteins Amino acids Ø Fats Fatty acids and glycerol Absorption in Small Intestines Where most absorption occurs Villi – Hairlike projections that increase surface area for maximum absorption – Absorb nutrients from chyme and transfer them to bloodstream Water absorbed in stomach, small intestine, and large intestine Absorption in Large Intestines Mucus protects colon from digestive juices Major tasks of large intestine: – Absorbs water – Synthesizes vitamin B and vitamin K – Collects food residue Undigested food excreted as feces METABOLISM METABOLISM Transformation of nutrients into energy within cell Occurs after digestion and absorption – Nutrients carried by blood to cells of body Aerobic metabolism combines with oxygen within each cell – Also known as oxidation METABOLISM Anaerobic metabolism fats without use of oxygen Krebs cycle – Complete oxidation of carbohydrates, proteins, and fats Anabolism – Process of using energy from oxidation to create new compounds METABOLISM Catabolism Controlled primarily by – Breakdown of compounds hormones secreted by during metabolism thyroid gland – Triiodothyronine (T3) – Thyroxine (T4) ENERGY Needed for involuntary and voluntary activity Involuntary activity – E.g., maintenance of body tissue, temperature, and growth Voluntary activity – E.g., walking, swimming, eating, reading, typing ENERGY Three groups of nutrients provide energy: – Carbohydrates – Proteins – Fats Carbohydrates should be the primary source of energy Energy Measurement Kilocalorie – Unit used to measure energy value of foods – Also known as calorie Kilojoule – 1 kilocalorie is equal to 4.184 (4.2) kilojoules, Calorie – Amount of heat needed to raise temperature of 1 kilogram (kg) of water 1 degree Celsius Energy Measurement 1 gram (g) of carbohydrate yields 4 calories 1g of protein yields 4 calories 1 g of fat yields 9 calories 1 g of alcohol yields 7 calories Energy Measurement Consider the following question: If you eat a dessert with 19 g of fat in it, how many calories from fat does it have? Energy Measurement Answer: Fat contains 9 calories per gram Dessert has 19 g of fat 9 kilocalories per gram × 19 g of fat = 171 calories Basal Metabolic Rate (BMR) Rate at which energy is needed for body maintenance Energy necessary to carry on all involuntary vital processes while body at rest Also known as resting energy expenditure (REE) Basal Metabolic Rate (BMR) Affecting factors: Greater in males than – Lean body mass females – Body size Increases during growth – Sex and fever – Age Decreases with age and – Heredity during starvation – Physical condition – Climate Calculation of BMR Harris-Benedict equation Another method used to – Used by dietitians for people estimate BMR: over age 18 – Convert body weight from – Uses height, weight, and age pounds to kg – Female BMR – Multiply kg by 24 (hours per day) 655 + (9.6 × weight in kg) + (1.8 × height in centimeters [cm]) – – Multiply answer by 0.9 for (4.7 × age) females and by 1.0 for males – Male BMR 66 + (13.7 × weight in kg) + (5 × height in cm) – (6.8 × age) Estimating BMR Consider the following questions: What is the BMR for a female weighing 110 pounds? What is the BMR for a male weighing 170 pounds? Estimating BMR 110-pound female 110 pounds ÷ 2.2 (pounds per kg) = 50 kg 50 kg × 24 hours = 1,200 calories 1,200 calories × 0.9 = 1,080 calories Estimating BMR 170-pound male 170 pounds ÷ 2.2 (pounds per kg) = 77.27 kg 77.27 kg × 24 hours = 1,854 calories 1,854 calories × 1.0 = 1,854 calories   ENERGY BALANCE This means that the number of calories consumed matches the number of calories required for one’s BMR (REE) and activity DIGESTION