The Digestive SystemTuesday, January 12th, 2010

What makes up our Body Systems?• Specialized cells come together to form tissues

Muscle TissueNervous Tissue

Connective Tissue Epithelial Tissue

What makes up our Body Systems?

Ex. stomach, heart, skin

Ex. Respiratory, Circulatory, Immune, Nervous Systems

The Digestive System

What role does the Digestive System play in our bodies?

- Converts the food we eat into energy our bodies can use

- Involves the breakdown of food, absorption of nutrients into our bloodstream, and elimination of unused materials

Nutrients• Any substance consumed by an animal that is

needed for survival, growth, development, tissue repair, or reproduction

• Used to make ATP, act as building blocks, or as cofactors (chemical compounds attached to proteins)

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Nutrients

Regardless of what an animal eats, an adequate diet must satisfy three nutritional needs– Fuel for all cellular work– The organic raw materials for biosynthesis– Essential nutrients, substances such as vitamins that

the animal cannot make for itself

Think About It

• What are the categories of organic nutrients we require and why do we require each?

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Animals require…• 5 categories of organic nutrients:– Carbohydrates (quick energy & cell receptors)– Proteins (enzymes, cell structure, membrane

support, muscles, skin, hair, nails)– Lipids (stored energy, cell membrane, protectant)– Nucleic Acids (DNA, RNA)– Vitamins (health & strength, act as coenzymes)

• Inorganic nutrients:– Minerals ex. Ca2+, K+, Fe3+ (health & strength, act as

cofactors)

Note:• Water is not a nutrient, but is necessary for:– maintaining cell functions– transporting nutrients & wastes – chemical reactions (breakdown of CHO, fats,

proteins)– cooling body through sweat– lubrication (joints, mouth)

• Body requires 3 – 5 litres of water each day

Food Groups & Recommended Servings1. Grain Products (6-7 servings)2. Vegetables & Fruits (7-8 servings)3. Milk Products (3-4 servings)4. Meat & Alternatives (2-3 servings)** Oils & Fats (2-3 Tbsp)

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What is one Food Guide Serving?

Canada’s Food Guide:

http://www.hc-sc.gc.ca/fn-an/food-guide-aliment/index-eng.php

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Think About It

• List the digestive organs and accessory organs of the digestive system.

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Organs in the Digestive System

IIeumof small intestine Duodenum of

small intestine

Appendix

Cecum

Ascendingportion of large intestine

Anus

Small intestine

Large intestine

Rectum

Liver

Gall-bladder

Tongue

Oral cavityPharynx

Esophagus

Stomach

Pyloricsphincter

Cardiacorifice

Mouth

Esophagus

Salivaryglands

Stomach

Liver

Pancreas

Gall-bladder

Large intestines

Small intestines

Rectum

Anus

Parotid glandSublingual gland

Submandibular gland

Salivaryglands

A schematic diagram of the human digestive system

Pancreas

Sooo…

• How do the nutrients get into our blood to be distributed throughout the body?

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• Food is mechanically and chemically broken down into these molecules during digestion, after which they can be taken up by body cells through the separate process of absorption.

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Think About It

• What does physical digestion mean?• What does chemical digestion mean?

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Principles of digestion and absorption

• Digestion requires enzymes capable of hydrolyzing bonds

• Products of digestion must be absorbed across plasma membranes

• Minerals, vitamins and monomers do not require digestion

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Mechanical Breakdown in the

Mouth

• Chewing involves teeth & the skeletal muscles of jaws, lip, cheeks and tongue and is controlled by cranial nerves.

What are the functions of chewing?

The functions of chewing are to

1)reduce the size of food in order to be swallowed & to increase the surface area for enzymes to act

2) move the food around mouth to stimulate taste and touch receptors and promote secretions of saliva

Chemical Breakdown in the Mouth• Why is the production of saliva important for

health?

Saliva

• You produce 1-2L of saliva per day secreted at rate of 4 ml/minute

• Saliva contains water, mucus, salivary amylase, and bicarbonate ions

HCO3-

Salivary amylase

• The functions of saliva are to:

1) moisten/soften and lubricate the food

2) neutralize acid produced by bacteria using HCO3

- ions in saliva (helps prevent tooth decay)

3) convert starch to maltose with salivary amylase enzyme (*enzymes are specific*)

The Role of Saliva

• How is the release of saliva controlled?

The Role of Saliva

• When food is sensed (smell, touch, thought):

Messages are sent to the salivary center in the medulla and nerve impulses are sent back to the salivary glands causing the release of saliva

The process of swallowing and peristalsis

• Once chewed, food is called a bolus

• Swallowing occurs when bolus exits mouth into esophagus (through pharynx)

• Swallowing begins as a voluntary action

• Action continues by involuntary peristalsis of esophagus

** NO absorption has occurred up to this point** Carbohydrate digestion BEGAN in mouth

Pharynx• The oral & nasal cavities connect to both trachea &

esophagus via the pharynx

• How is food prevented from going down your air passages?

• Why is it impossible to breathe and swallow at the same time?

Swallowing1. SOFT PALATE MOVES BACK to cover openings to

nose (nasopharyngeal openings)

2. TRACHEA (WINDPIPE) MOVES UP under a flap of tissue called the epiglottis, blocking its opening

3. The GLOTTIS (opening to the LARYNX / “voicebox”) is closed when the trachea moves up feel you Adam’s Apple (part of larynx) when you swallow

4. Food then has one route to go down the ESOPHAGUS.

• Why is it not a good idea to talk & eat at the same time?

• Epiglottis does not fully cover trachea & food goes down the “wrong way” can be coughed back up

• Soft palate doesn’t fully cover opening to nasal cavity and food gets into nasal cavity

Esophagus• Muscular tube ~25cm long

extending from pharynx to stomach

• Made of several types of tissue:

Inner surface lined with mucus membranes. This layer is attached by connective tissue to a layer of smooth muscle containing both circular and longitudinal muscle.

EsophagusFood moves down esophagus through

PERISTALSIS (rhythmical muscle contractions) takes about 9sec for food to move from pharnyx to stomach

Pressure differences caused by waves of muscle contractions allow contents to move in one direction towards stomach

Normal pressure usually prevents stomach contents from entering esophagus, but when does creates heartburn (stomach acid irritation)

• Can we swallow upside down?

• Yes – because the muscles around the esophagus are strong enough to push food up to your stomach(However, it is not recommended you try this!)

Digestion Overview

• http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072956208&alaid=ala_996421&showSelfStudyTree=true