NUTRIENT DIGESTION & ABSORPTION

Transcription

1 NUTRIENT DIGESTION & ABSORPTION NUTR 2050: Nutrition for Nursing Professionals Mrs. Deborah A. Hutcheon, MS, RD, LD Lesson Objectives At the end of the lesson, the student will be able to: 1. Differentiate between digestion, absorption, & metabolism of nutrients. 2. Explain the function of each organ of the GI tract. 3. Identify which macronutrients are digested and/or absorbed at each location of the GI tract. 4. Summarize, in general terms, the key pathways for the metabolism of carbohydrate, lipid, and protein. 5. Identify key hormonal action in macronutrient metabolism. 6. Differentiate between glycolysis, glycogenesis, glycogenolysis, and gluconeogenesis. Primary Roles of the GI Tract 1. Digestion: 2. Absorption: **What is metabolism?** 1

2 Primary Organs of GI Tract Upper GI Tract: Lower GI Tract: Accessory Organs: GI Tract: Oral Cavity Organs: mouth & pharynx Function: digestive process begins Salivary Secretion: ~1 L of saliva per day. 99.5% H20 to dissolve food. Principle Enzyme: α-amylase 2nd Enzyme: lingual lipase Mucus: moisten food Other: antibacterial and antiviral compounds 2

3 Bolus: GI Tract: Esophagus Swallowing: Function: Transit from mouth to stomach (peristalsis) GI Tract: Stomach Function: partial digestion of food in an acidic environment via proteolytic & lipolytic enzymes Nutrient Absorption: alcohol & water Chyme: partially digested food Stomach Capacity Empty: Full: Stomach Emptying GI Tract: Hydrochloric Acid & Enzymes High concentration HCl- = low ph 2 Functions of HCl- Acid in Gastric Juice 1. Convert/activate pepsinogen to pepsin 2. Denature proteins (tertiary & secondary) 3. Release nutrient from organic compounds 4. Act as bactericide 3 Enzymes in Gastric Juice: 1. Pepsin: 2. α-amylase: 3. Gastric Lipase: 3

4 GI Tract: Small Intestine Function: main site for food digestion & absorption 3 Segments: duodenum, jejunum, ileum Absorptive Capacity: maximized surface area = maximize nutrient absorption (villi & microvilli) Rapid cellular turnover: Two Types of Cells GI Tract: Pancreas 1. Endocrine Cells (ductless): 2. Exocrine Cells (ancinar): Pancreatic Juice 1. Bicarbonate: 2. Electrolytes: 3. Pancreatic Digestive Enzymes Proteases: Pancreatic α-amylase: Pancreatic lipase: Digestion of Carbohydrates The end product of CHO digestion is always glucose! 4

5 GI Tract: Liver Largest single organ of the body. Main Role in Digestion: synthesis of bile GI Tract: Gallbladder Main Role: concentrate and store bile until needed in SI GI Tract: Large Intestine (Colon) Sections: ascending, transverse, descending, sigmoid. Function: final reabsorption of electrolytes and water; secretion of mucus, K+, bicarbonate. Passage of material through colon takes hours. 5

6 GI Tract: Nutrient Absorption CHO Regulatory Hormones 3 Key Hormones 1. Insulin (β-cells pancreas): 2. Glucagon (α-cells pancreas): 3. Epinephrine (adrenal medulla): *Hormonal action depends on the body s energy needs.* 6

7 *Use of CHO determined by body s energy needs* : Glycolysis Location: cytoplasm Glucose 2 pyruvates Entrance point for ALL CHO to ATP. A carbohydrate, is a carbohydrate, is a carbohydrate! 2) Glycogenesis: glucose glycogen Regulated by insulin = storage 1. Liver: major site, more important in BG homeostasis. 2. Skeletal Muscle & Adipose: majority stored in muscle. Short energy reserve: 24 hours. Holds H 2 0: glycogen loss = H 2 0 loss= fast ST wt loss 7

8 3) Glycogenolysis: glycogen glucose Regulated by glucagon (liver & adipose) & epinephrine (liver & muscle) = release Glucose enters into glycolysis 2 pyruvate (for ATP) 4) Gluconeogenesis: protein/fat glucose Main location: Liver Creation of glucose from non-cho sources. (lactate, pyruvate, glycerol, certain amino acids) When CHO intake and utilization is inadequate. Not the body s preferred, or safest, energy source. Lack of sufficient dietary CHO can lead to ketosis and protein-energy malnutrition. (Need minimum 120 g CHO/day!) Process of Protein Metabolism 1. Deamination: removal of amino group without direct transfer to another compound Produces a-keto acid + ammonia (to urea cycle) Urea Cycle: Ammonia (NH3) Urea (to kidneys) 8

9 Process of Protein Metabolism Transamination: transfer of amino group from one AA to a carbon skeleton or a-keto acid. TCA Cycle Location: mitochondria End metabolic pathway for ALL nutrients. Glucose (CHO) drives energy production. 9