The Digestive System

and Nutrition

Simple Tube Gut

Figure 14.1

Slide 14.1Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestive System

Four Processes

• Ingestion: Taking complex organic food

molecules into the body.

• Digestion: breaking down large insoluble

molecules to simple soluble molecules.

• Absorption: the passage of digested food from

the gut into the blood for assimilation.

• Egestion: undigested material eliminated

Slide 14.3Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestive System Processes

Digestion of food

• Mammals have to produce enzymes to fully digest

carbohydrates, proteins and fats so that the

products can be absorbed in the small intestine.

• Draw a mind map summarising how all of these

substances are absorbed including names of

enzymes and products, any other secretions

needed, and where all of these substances are

produced.

Figure 14.2

Slide 14.2ACopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Gastrointestinal (GI) Tract Wall

Structure: common layers throughout the system

• Mucosa: innermost layer, nutrients pass through

• Submucosa: connective tissue, lymph and blood

vessels, nerves

• Muscularis: two or three layers of smooth

muscle, responsible for motility in GI tract

• Serosa: outermost layer, connective tissue sheath

Slide 14.2B

Gastrointestinal (GI) Tract Layers

Mouth: begins digestion

• Teeth and Tongue: skeletal muscle, moves food in

mouth and breaks it up – Mechanical Digestion

• Saliva

• Source: salivary glands

• Composition: mucus, salivary amylase,

bicarbonate, lysozyme

Slide 14.6B

The Mouth

Simple Tube Gut

• Oesophagus: connects mouth to stomach

• Structure: mix of skeletal and smooth muscle

• Mucus secreting cells: assist passage of food

• Food motility: gravity and peristalsis

Slide 14.8

Oesophagus

https://www.youtube.com/

watch?v=o18UycWRsaA

https://www.youtube.com/watch?v=Ujr0UAbyPS4

Figure 14.7

Slide 14.9ACopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Structure of the Stomach Wall

https://vimeo

.com/236442

69

Duodenum

Two important secretions:

• Bile from liver, to emusify fats and neutralise acid.

• Pancreatic enzymes (amylase, lipase and trypsin – an endopeptidase)

Duodenum structure

The Duodenum has Brunner’s Glands in the sub-mucosa which secrete and alkaline mucus:

• To Neutralise the acid (bile is also alkaline)

• To protect the gut wall.

• To provide correct pH for pancreatic enzymes.

Figure 14.9

Slide 14.10ACopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

The Wall of the Small Intestine

Villi of the small intestine

Epithelial Cell of the small intestineMonosaccharides, amino

acids, fatty acids and glycerol.

Molecules absorbed by diffusion, facilitated diffusion and active transport.

Monosaccharides and amino acids are absorbed into the blood and are taken to the liver along the hepatic portal vein.

Fatty acids and glycerol are absorbed by the lacteal and taken in the lymphatic system.

http://www.kscie

nce.co.uk/animati

ons/duodenum.ht

m

Figure 14.14

Slide 14.14B

Absorption of Fats

What happens to the absorbed food?

Monosaccharides are either used in respiration or stored as glycogen in liver and muscle cells. Excess glucose is stored as fat.

Amino acids are used to make proteins. Amino acids can be changed from one type to another in a process called transamination. Excess amino acids are deaminated (NH2 removed) and made into urea which is excreted in urine.

Fatty acids are converted to carbohydrates and used in respiration or are stored as fat.

Table 14.1

Slide 14.11

Major Digestive Enzymes

Slide 14.14C

Absorption of Nutrients

• Proteins and carbohydrates: active transport

• Lipids: broken down and reassembled

• Water: osmosis

• Vitamins and minerals: assorted means

Slide 14.10B

Small Intestine

• Functions:

• Digestion: neutralize acid from stomach, add digestive enzymes and bile, break proteins, carbohydrates and lipids to absorbable materials

• Absorption: 95% of food absorbed here

• Structure

• Regions: duodenum, jejunum, ileum

• Mucosa adaptations: villi containing blood and lacteal capillaries

Slide 14.13B.

Large Intestine: Structure and Function

• Functions: absorbs nutrients and water, and eliminates waste

• Structure:

• Cecum (blind pouch), appendix

• Colon: ascending, transverse, descending, sigmoid

• Rectum, anus

Figure 14.12

Slide 14.13A

Large Intestine

Endocrine and Nervous Systems

Regulation of Digestion

• Regulation dependent on volume and content of food

• Nervous system: stretch receptors in stomach

• Hormones:

• Gastrin: stimulates release of gastric juice

• Secretin: stimulates pancreas to secrete water and bicarbonate

• Cholecystokinin (CCK): signals pancreas to secrete digestive enzymes

Slide 14.15

Figure 14.15

Slide 14.16Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Nutrients:

Utilized or Stored Until Needed

Figure 14.16

Slide 14.17Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Food Guide Pyramid

“kaka”

Slide 14.18

Nutrition

• Carbohydrates: major energy source, simple or complex

• Lipids: cell components and energy sources, saturated or unsaturated

• Proteins: 20 amino acids

• Vitamins: fat soluble and water soluble

• Minerals: recommended daily allowance

• Fiber: some evidence decreases colon cancer

Weight Control:

Energy Consumed versus Energy Spent

• Basic Metabolic Rate (BMR) [easy formula 25 x wt. In kgs.]

• Influencing factors: gender, body composition, age, stress, food intake, genetics

• Energy balance and body weight

• Caloric content: fat = 9 Calories, Proteins and sugars = 4 Calories

• Excess intake leads to increased storage (weight)

• Physical activity: uses calories (150 calories/mile walked or jogged)

• Have to accumulate -1500 calories = one pound wt. loss

Slide 14.19

Slide 14.20

Disorders of the Digestive System

Disorders of digestive (GI) tract: lactose intolerance, diverticulosis, colon polyps, colon cancer – most common in sigmoid colon

• Disorders of accessory organs: hepatitis, gallstones

• Malnutrition: 13% of world’s population undernourished

• Eating disorders: anorexia nervosa, bulimia

• Appendicitis: low, right side pain

• Hiatal hernia: part of stomach above diaphragm –GERD- gastroesophageal reflux disease