Digestion, Absorption, Digestion, Absorption, and Transportand Transport

Overview Digestive SystemOverview Digestive System

Functions: Digestion, Absorption, Elimination

Digestion – process of breaking down foods to release nutrients

• Goal is to break nutrients into absorbable units

2 types of digestions: 1. Mechanical

2. Enzymatic (chemical)

Overview Digestive SystemOverview Digestive System

Absorption – movement of nutrients out of GI tract into blood or lymph Water soluble nutrients Fat soluble nutrients

Excretion – elimination of undigested foods (feces)

GI Tract GI Tract AnatomyAnatomy

Digestive TractDigestive Tract

Layers of GI tract organsLayers of GI tract organs Serosa (outermost)Serosa (outermost)

• Interface between GI tract and lymph & blood Interface between GI tract and lymph & blood Muscle LayersMuscle Layers

• Longitudinal musclesLongitudinal muscles• Circular musclesCircular muscles

Submucosal and Mucosal and layers Submucosal and Mucosal and layers (innermost)(innermost)• Nerves, blood and lymph vessels Nerves, blood and lymph vessels • Cells of the mucosal layer produce secretionsCells of the mucosal layer produce secretions

MouthMouth

Structure – Structure – teeth, tongue, salivary glandsteeth, tongue, salivary glands SecretionsSecretions

SalivaSaliva Salivary amylase …..Salivary amylase …..

Digestion Digestion Mechanical ….Mechanical …. Enzymatic/chemical ….Enzymatic/chemical ….

Swallow Swallow tongue pushes food tongue pushes food pharynx pharynx …… ……

EsophagusEsophagus

Structure – 12” tubeStructure – 12” tube UES and LESUES and LES

FunctionFunction Transports food from mouth to stomachTransports food from mouth to stomach Peristalsis and gravity aid food movement Peristalsis and gravity aid food movement

Secretions -- mucusSecretions -- mucus Digestion Digestion

Mechanical (limited)Mechanical (limited) Enzymatic/chemical – starch digestion continuesEnzymatic/chemical – starch digestion continues

StomachStomach Structure – Structure –

muscular sack muscular sack that can expandthat can expand extra muscle extra muscle

layer to aid in layer to aid in the mechanical the mechanical digestion of digestion of food (pg 73)food (pg 73)

StomachStomach

Stomach Related SecretionsStomach Related Secretions

1. Gastrin – hormone that stimulates stomach to release secretions

2. Hydrochloric Acid (HCl) -- unravels proteins, kills bacteria, activates pepsinogen

3. Pepsinogen – once activated, begins protein digestion

4. Mucus – secreted by goblet cells, protects stomach, moistens food

Stomach - - Digestion

Mechanical• Stomach muscles grind food into a paste called

chyme

Enzymatic/chemical• Proteins uncoiled• Protein digestion to polypeptides begins• Starch digestion stops

Small IntestineSmall Intestine

Small Intestine (SI)Small Intestine (SI)

Function – The SI is where:1. the majority of digestion to absorbable units

occurs• Digestion of carbohydrates, fats, and proteins • Vitamins and minerals do not need digestion

2. Nutrients are absorbed into either capillaries or lacteals

Small IntestineSmall Intestine

The Small Intestinal VilliThe Small Intestinal Villi

The Small Intestinal VilliThe Small Intestinal Villi

Small IntestineSmall Intestine

Digestion - MechanicalDigestion - Mechanical Peristalsis pushes food through SIPeristalsis pushes food through SI Segmentation mixes chyme with digestive Segmentation mixes chyme with digestive

enzymes enzymes • Also breaks up food mass into smaller massesAlso breaks up food mass into smaller masses

Bile emulsifies fatsBile emulsifies fats

Peristalsis & SegmentationPeristalsis & Segmentation

Muscular Action Muscular Action of Digestionof Digestion

SegmentationSegmentation

SISI

Absorbed into lacteals (lymph) Digested fats Fat soluble vitamins Cholesterol

Nutrients travel through lymph system to chest area where lymph and blood join

Nutrients enter blood and travel to liver

Preparing Nutrients for Preparing Nutrients for TransportTransport

Transport pathways Bloodstream

Water-soluble nutrients and smaller products of fat digestion

Liver Lymphatic system

Larger fats and fat-soluble vitaminsChylomicronsBypass liver at first

The Vascular SystemThe Vascular System

Closed system of vessels Heart pump

Blood Delivers oxygen and nutrients Removes carbon dioxide and wastes Blood flow

Special routing for digestive system Liver

The Vascular SystemThe Vascular System

Large Intestine or ColonLarge Intestine or Colon

Large Intestine or ColonLarge Intestine or Colon

Undigested foods (fiber) enter into colonUndigested foods (fiber) enter into colon Unabsorbed nutrients pass into colonUnabsorbed nutrients pass into colon

E.g. calcium, iron, cholesterol trapped in fiberE.g. calcium, iron, cholesterol trapped in fiber

ColonColon

StructureStructure 5-6’ long5-6’ long Wider diameter than SIWider diameter than SI

• No villi or microvilliNo villi or microvilli Appendix is a little pouch near beginning of Appendix is a little pouch near beginning of

colon colon Colon “wraps around” SIColon “wraps around” SI

Large Intestine or ColonLarge Intestine or Colon