Kin 110

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Kin 110

• Chapter 3
• Digestions and Absorption

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Overview of Digestion and Absorption

• Chapter 3
• Gastrointestinal tract
• Overview of Digestion (details discussed with
  each nutrient lecture)
• Mechanical
• Chemical
• Overview of Absorption (details discussed with
  each nutrient lecture)
• Circulation of nutrients
• Regulation and influences on Digestion and
  Absorption

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The Gastrointestinal Tract

• Organization
• Mouth ? anus
• Accessory organs
• Salivary glands, liver, pancreas, gallbladder
• Functions
• Ingestion
• Transport
• Secretion
• Digestion
• Absorption
• Elimination

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The Digestive Tract Wall
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• Mouth
• chews and mixes food with saliva

• Salivary Glands
• secrete enzymes mucous

• Pharynx Esophagus
• passages for food

• Stomach
• adds acid enzymes
• mixes, churns and grinds food
• regulates entry of food into small intestine

• Liver
• manufactures bile (required for fat digestion)

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• Pancreas
• secretes enzymes and buffers
• secretes hormones

• Gallbladder
• stores and releases bile

Pyloric Sphincter

• Small Intestine
• primary site of digestion and absorption

• Large Intestine
• reabsorbs water and minerals
• contains bacteria which digest some food and
  synthesize some vitamins

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Overview of Digestion

• Digestion - the mechanical and chemical breakdown
  of foods into smaller units that can be taken
  across the intestinal epithelium into the body
• Physical movement
• Peristalsis
• Waves of muscle contraction propelling food
  forward
• Segmentation
• Mixing contractions that do not propel food
  forward

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Chemical Digestion Enzymes

• Definition
• proteins that act as CATALYSTS to facilitate
  (speed up) chemical reactions
• change molecules while remaining unchanged
  themselves
• digestive enzymes break down molecules into
  smaller components via HYDROLYSIS

hydro water lysis to burst or break apart
ENZYME
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Chemical Digestion Enzymes cont.

• Examples

prefix indicates molecule the enzymes acts on
amylase sucrase lactase maltase
pepsin trypsin peptidase
lipase
digest proteins
digest carbohydrates
digests lipids
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Secretions of the Digestive Tract

• Salivary Secretions
• water, mucous, enzymes, buffers, lysozyme
• Stomach (gastric) Secretions
• hydrochloric acid, intrinsic factor, pepsinogen,
  gastric lipase, mucous, HCO3-, hormones (gastrin)
• Liver Gallbladder
• bile

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Secretions cont.

• Pancreatic Secretions
• exocrine enzymes buffers (HCO3-)
• endocrine insulin, glucagon, secretin, others
• Small Intestine
• exocrine enzymes, mucous
• endocrine paracrine CCK, motilin, others

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Absorption

• - movement of small units of food particles
  (after digestion) from the interior of the gut
  (lumen) into the blood stream or lymphatic
  system.
• - Requires particles to be broken down by
  digestion, a large surface area to interact with
  particles and in some cases specialized
  transportation mechanisms to move particles
  across cell membranes

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Large surface area facilitates absorption
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Mechanisms of Absorption

• passive (simple) diffusion
• the unassisted movement of substances in or out
  of cells down a concentration gradient

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Mechanisms of Absorption

• facilitated diffusion
• carrier proteins (transporters) in the cell
  membrane help move substances in or out of cells
  down a concentration gradient

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Mechanisms of Absorption cont.

• active transport
• the movement of molecules into or out of cells
  against a concentration gradient using a
  transport protein
• requires energy (ATP)

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Mechanisms of Absorption cont.

• endocytosis
• the uptake of material by a cell through
  indentation and pinching off of part of the
  membrane to form a vesicle

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Circulation of Nutrients

• Vascular system
• Lymphatic system

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Transport of Nutrients

• blood
• direct absorption of glucose, fructose,
  galactose, proteins, and small lipid molecules
• travels directly to the liver
• lymph
• larger lipid molecules are too large to enter the
  blood directly
• absorbed first into the lymph
• enter the blood at the inferior vena cava

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Transport of nutrients
Some nutrients travel freely in the blood (e.g.
glucose, proteins). Others are bound to protein
transporters (e.g. lipids, vitamins, and minerals)
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Regulation of GI Activity

• Nervous system
• Regulates GI activity
• Local system of nerves
• Central nervous system
• Hormonal system
• Increases or decreases GI activity

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Regulation of GI Activity cont.

• Endocrine (Hormonal) System

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Influences on Digestion Absorption

• Psychological
• taste, smell, presentation of food
• Cephalic phase (see next slide)
• Chemical
• processing of foods and food preparation,
  medications
• Bacterial
• some may cause gastris, ulcers others are
  beneficial

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Cephalic Phase Responses
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Nutrition and GI Disorders

• Constipation
• Hard, dry, infrequent stools
• Reduced by high fiber, fluid intake, exercise
• Diarrhea
• Loose, watery, frequent stools
• Symptom of diseases/infections
• Can cause dehydration
• Diverticulosis
• Pouches along colon
• High fiber diet reduces formation