Digestion & Absorption Flashcards
Soluble Fiber
Form gels Delay gastric emptying Increase transit time Decrease nutrient absorption (enzyme activity) High binding capacity for ions, lipids
Insoluble Fiber
Decrease transit time
Increase fecal bulk (water binding capacity)
Binding capacity (lignin only)
α-Amylase
Secreted by salivary glands and pancrease
Breaks down starches (amylopectin and amylose) at α 1-4 glycosidic bonds
Lingual lipase
Secreted by salivary glands, begins fat break down
At higher concentrations in infants because they have an underdeveloped pancreas
GI tract mucosa
Epithelium- lines the lumen of GI tract (inner layer)
- Contact with food and environment
- Exocrine (digestive juices) and endocrine cells (hormones)
Lamina propria (middle layer)
- Connective tissue and blood/lymph vessels
- GALT (gut associated lymphatic tissue)
Muscularis externa (outer layer) Circular and longitudinal smooth muscle Peristalsis- progressive waves or contractions that move food (bolus) through the GI tract
Hydrochloric Acid (HCL)
Produced by parietal cells of the oxyntic glands on the stomach
Functions:
-Protein digestion
Conversion of pepsinogen to pepsin
Denaturation of proteins
-Release of nutrients from organic complexes
Micronutrients released from the organic compound such as iron from hemoglobin or magnesium from chlorophyll
-Bacteriocidal properties
Regulatory proteins
Include gastrointestinal hormones and neuropeptides released in GIT and interact with nerves going from GIT to brain
Gastrin (G-cells), acetylcholine (vagus nerve), and histamine (GI mast cells) act on parietal cells and act as secretogogues of HCL
Bile
Green-yellow fluid produced in liver and stored and concentrated in gallbladder, released into duodenum triggered by Cholecystokinin (CCK)
Alkaline pH
Bile acids- cholic acid and chenodeoxycholic acid
- Produced by hepatocytes (liver) from cholesterol
- Conjugated to glycine or taurine
- Conjugated as Na, K, or Ca salts (bile salts)
Pancreatic lipase
Hydrolyzes triglycerides
Proteases
Pepsinogen>Pepsin
- secreted by stomach
- non-active to active form due to acidic environment
Trypsinogen>Trypsin
- secreted by pancreas
- non-active to active form due to basic environment
Chymotrypsinogen>Chymotrypsin
- secreted by pancrease
- non-active to active form due to basic environment
*all are endopeptidases which cleave within the protein, resulting in peptide chains
Sucrase
Enzyme that hydrolyzes sucrose to fructose and glucose
Lactase
Enzyme that hydrolyzes lactose to galactose and glucose
Maltase
Enzyme that hydrolyzes maltose to glucose and glucose
Mechanisms for nutrient absorption
Diffusion- free movement from higher to lower concentration (down electrochemical gradient)
Facilitated diffusion- requires specific carrier, down electro-concentration gradient
Active transport- requires energy, against concentration/ electro-concentration gradient
Pinocytosis- engulfment by cell membrane
GLUT (glucose transporters)
Integral proteins- embedded in a cellular membrane in order for it to function
Each has specific combining site
Undergoes a conformational change upon binding the molecule
Can reverse this change when unbound
GLUT1 - basic supply of glucose to cells
GLUT2 – low-affinity transporter; glucose from lumen to enterocyte to blood
GLUT3 - high-affinity for brain & other glucose-dependent tissues
GLUT4 - insulin sensitive, in muscle & adipose tissues, insulin has to bind to cell membrane before GLUT4 uptakes glucose
GLUT5 - for fructose, throughout the body
