Digestion, Absorption, and Transport

Overview 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. 1.Mechanical 2. 2.Enzymatic (chemical)

Overview 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 Anatomy

Digestive Tract  Layers of GI tract organs Serosa (outermost) Serosa (outermost) Interface between GI tract and lymph & bloodInterface between GI tract and lymph & blood Muscle Layers Muscle Layers Longitudinal musclesLongitudinal muscles Circular musclesCircular muscles Submucosal and Mucosal and layers (innermost) Submucosal and Mucosal and layers (innermost) Nerves, blood and lymph vesselsNerves, blood and lymph vessels Cells of the mucosal layer produce secretionsCells of the mucosal layer produce secretions

Mouth  Structure – teeth, tongue, salivary glands  Secretions Saliva Saliva Salivary amylase ….. Salivary amylase …..  Digestion Mechanical …. Mechanical …. Enzymatic/chemical …. Enzymatic/chemical ….  Swallow  tongue pushes food  pharynx  ……

Esophagus  Structure – 12” tube UES and LES UES and LES  Function Transports food from mouth to stomach Transports food from mouth to stomach Peristalsis and gravity aid food movement Peristalsis and gravity aid food movement  Secretions -- mucus  Digestion Mechanical (limited) Mechanical (limited) Enzymatic/chemical – starch digestion continues Enzymatic/chemical – starch digestion continues

Stomach  Structure – muscular sack that can expand extra muscle layer to aid in the mechanical digestion of food (pg 73) extra muscle layer to aid in the mechanical digestion of food (pg 73)

Stomach

Stomach Related Secretions Gastrin – hormone that stimulates stomach to release secretions Hydrochloric Acid (HCl) -- unravels proteins, kills bacteria, activates pepsinogen Pepsinogen – once activated, begins protein digestion 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 Intestine

Small Intestine (SI)   Function – The SI is where: the majority of digestion to absorbable units occurs Digestion of carbohydrates, fats, and proteins Vitamins and minerals do not need digestion Nutrients are absorbed into either capillaries or lacteals

Small Intestine

The Small Intestinal Villi

Small Intestine  Digestion - Mechanical Peristalsis pushes food through SI Peristalsis pushes food through SI Segmentation mixes chyme with digestive enzymes Segmentation mixes chyme with digestive enzymes Also breaks up food mass into smaller massesAlso breaks up food mass into smaller masses Bile emulsifies fats Bile emulsifies fats

Peristalsis & Segmentation

Muscular Action of Digestion Segmentation

SI   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 Transport   Transport pathways   Bloodstream   Water-soluble nutrients and smaller products of fat digestion   Liver   Lymphatic system   Larger fats and fat-soluble vitamins   Chylomicrons   Bypass liver at first

The 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 System

Large Intestine or Colon

 Undigested foods (fiber) enter into colon  Unabsorbed nutrients pass into colon E.g. calcium, iron, cholesterol trapped in fiber E.g. calcium, iron, cholesterol trapped in fiber

Colon  Structure 5-6’ long 5-6’ long Wider diameter than SI Wider diameter than SI No villi or microvilliNo villi or microvilli Appendix is a little pouch near beginning of colon Appendix is a little pouch near beginning of colon Colon “wraps around” SI Colon “wraps around” SI

Large Intestine or Colon