Week 11 Digestive System s2 2010

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DIGESTIVE SYSTEM

Week 11



Functions:

1. Digestion

± Motility ± movement of food through the digestive tract by: Ingestion

Mastication

Degulation ± swallowing

Peristalsis

± Secretion

Exocrine ± water, HCL acid, bicarbonate

Endocrine ± hormones that regulate the digestive system



2. Absorption

± The process of digested foods transportedacross the wall of the small intestine into the

blood and lymph.



ANATOMY

Mouth

Pharynx Esophagus

Stomach

Small intestine

Large intestine Rectum

Anus



Figure 16.1



Divided into 2 main structur al areas:

Tubular gastrointestinal tract ± approximately

9m long and extends from mouth to anus

Accessory organs ± teeth, tongue, salivary

glands, liver, gallbladder, pancreas



DIGESTIVE SYSTEM ACTIVITIES

Ingestion of food into the mouth

Movement of food along the digestive tract

Mechanical preparation of food for digestion

Chemical digestion of food



Absorption of food

Absorption of digested food into the

circulatory and lymphatic system

Elimination of indigestible substances and

waste products from the body by defecation



The Or al Cavity

Functions of the Tongue ± Mechanical processing of food

± Manipulation to assist chewing and

swallowing

± Sensory analysis (taste, texture)

± Participation in speech

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings



The Or al Cavity

Salivary Glands

± Three pairs of glands ± Functions of saliva

Lubricates, cleanses oral cavity

Dissolves chemicals

Suppresses bacterial growth




The Or al Cavity

Teeth

± Participate in mastication of food

± 20 deciduous teeth (³baby teeth´)

± 32 secondary teeth (³adult teeth´)




Teeth: Structural Components and Dental

Succession

Figure 16-6(c)



The Pharynx

Functions of the Pharynx

± Common passageway for

food, drink, and air

Digestive MoviePLA Y




ESOPHAGUS

Portion of the GI tract connecting the

pharynx to the stomach.

Collapsible muscular tube.

Approximately 25cm long.







Figure 16.8a



The stomach provides for the physical

breakdown of food that must precede chemicaldigestion.

Initiate digestion of proteins (CHO continues

from mouth but fats not digested here)

Kill bacteria with the strong acidity of gastric juice

STOMACH - Functions



Functions Continued

Move food into the SI as a pasty material =

chyme. Only substances that can be absorbed and

digested in the stomach are alcohol and

aspirin



The Small Intestine

Digestion in the Small Intestine

± Most digestion and absorption occurs in the small intestine ± Digestive enzymes and buffers are released by:

Pancreas

Liver

Gall bladder

Approximately 7 metres long

Food takes 4 hours to travel through the small

intestine




Figure 16.10







The Large Intestine

Overview of the Large Intestine

± Reabsorbs water and electrolytes

± Compacts feces

± Absorbs vitamins (K, biotin, and B5) made by

bacteria

± Stores faeces before defecation

1.2 metres long

Food takes 12-18 hours to travel through






OTHER RELATED

STRUCTURES



Pancreas

Produces pancreatic juice, an exocrinesecretion containing bicarbonate andimportant digestive enzymes that is passed

into the duodenum via the pancreatic duct.

Insulin and glycogen regulator



The Liver

Functions of the Liver

± Metabolic regulation Store absorbed nutrients, vitamins

Release nutrients as needed

± Hematological regulation

Plasma protein production

Remove old RBCs

± Production of bile

Required for fat breakdown




The Liver

The Surface

Anatomy of the Liver

Figure 16-14(a)



The Liver

Figure 16-14(b)

The Surface Anatomy of the Liver



GALL BLADDER

Stores and concentrates bile

Bile contains:

± Salts, bilirubin, cholesterol and other compounds

Bile is ejected into the duodenum.



Digestion and Absorption

Processing and Absorption of Nutrients

± Two Steps in Processing M echanical

Chemical






± Carbohydrates

Starches are broken down by amylases

± Results in di- and trisaccharides

Enzymes on cell surface split them to monosaccharides

Absorbed by the walls of intestine




The Digestion and Absorption of Carbohydrates

Figure 16-18(a) (1 of 2)



Figure 16-18(a) (2 of 2)




Processing and Absorption of Fats

± Bile emulsifies fats to small droplets

± Lipase hydrolyzes triglycerides into fatty acids

and monoglycerides

± Lipids diffuse into cells of intestinal wall

± Triglycerides are reformed




The Digestion and Absorption of Lipids

Figure 16-18(b) (1 of 2)



Figure 16-18(b) (2 of 2)





± Proteins Breakdown starts in stomach

± Pepsin and HCl produce fragments

Breakdown continues in small intestine

± Pancreatic proteases produce small peptides

± Peptidases releases amino acids

Intestinal wall absorbs amino acids into the body




The Digestion and Absorption of Proteins

Figure 16-18(c) (1 of 2)



Figure 16-18(c) (2 of 2)




Water and Electrolyte Absorption

± About nine liters/day enter the digestive tract Two liters of ingested water

Seven liters of watery secretions

± Ions are absorbed by many mechanisms

Sodium, calcium, chloride, bicarbonate ± All but about 150 ml is absorbed by osmosis, as

water ³follows´ the ions





Absorption of Vitamins

± Fat-soluble vitamins combine with lipidsfor absorption

± Water -soluble vitamins diffuse across

the digestive epithelium

Exception: vitamin B12

requires intrinsic factor (from the gastric mucosa) for absorption




Aging and the Digestive System

Age-Related Changes in the Digestive

System

± Thinner, more fragile epithelium

± Reduced epithelial stem cell division

± Weaker peristaltic contraction Reduced smooth muscle tone




DIGESTIVE SYSTEMS IMPORTANCE IN

EXERCISE

Helps to digest and store fuel important for

muscle contraction Breaks down food to fuel resynthesis of ATP

( fuel used to power mitochondria)

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Week 11 Digestive System s2 2010

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