THE DIGESTIVE SYSTEM

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Food for Energy and Growth

The food animals eat provides both a source of energy and essential molecules that the animal body is not able to manufacture for itself

an optimal diet contains more carbohydrates than fats and also a significant amount of protein

Figure 31.1 The pyramid of nutrition

Food for Energy and Growth Carbohydrates are obtained primarily

from cereals, grains, and breads on the average, carbohydrates contain 4.1

calories per gram the body uses carbohydrates for energy

Dietary fats are obtained from oils, margarine, and butter and are abundant in fried foods, meats, and processed snack foods fats contain 9.3 calories per gram the body uses fats to construct cell membranes,

to insulate nervous tissue, and to provide energy

Food for Energy and Growth

Proteins can be obtained from many foods, including poultry, fish, meat, and grains proteins have 4.1 calories per gram proteins are used for energy and as

building materials for cell structures, enzymes, hemoglobin, hormones, and muscle and bone tissue

Animation: Energy for Activity

Food for Energy and Growth

In wealthy countries, being significantly overweight is common this is due to habitual overeating and high-

fat diets, in which fats constitute over 35% of the total caloric intake

the standard measure of appropriate body weight is the body mass index (BMI), estimated as your body weight in kg, divided by your height in meters squared

Figure 31.3 Are you overweight?

66% of Americans are overweight with a BMI of 25 or more

Animation: Body Mass Index

Food for Energy and Growth

One essential characteristic of food is its fiber content fiber is the part of plant food that cannot be

digested by humans diets that are low in fiber result in a slower

passage of food through the colon low fiber is thought to be associated with

incidences of colon cancer

Food for Energy and Growth

Over the course of evolution, many animals have lost their ability to manufacture certain substances they need many vertebrates are unable to

manufacture one or more of the 20 amino acids used to make proteins humans are unable to synthesize eight amino

acids, which must be obtained from proteins in food

these are called essential amino acids

Food for Energy and Growth

In addition to supplying energy, food must also supply essential minerals, such as calcium and phosphorous some minerals are required in very small

amounts and are called trace elements

Essential organic substances that are used in trace amounts are called vitamins many vitamins are required cofactors for

enzymes

Digestion13

Processing of food Types

Mechanical (physical) Chew Tear Grind Mash Mix

Chemical Catabolic reactions Enzymatic hydrolysis

Carbohydrate Protein Lipid

Types of Digestive Systems

Heterotrophs are divided into three groups on the basis of their food sources herbivores eat plants exclusively carnivores are meat eaters omnivores eat both plants and animals

Single-celled organisms, as well as sponges, digest their food intracellularly

All other animals digest their food extracellularly, within a digestive cavity

Digestion15

Phases Ingestion Movement Digestion Absorption Further digestion

Digestive System Organization

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Gastrointestinal (Gl) tract (Alimentary canal) Tube within a tube Direct link/path between organs Structures

Mouth Oral Cavity Pharynx Esophagus Stomach Duedenum Jejenum kIleum Cecum Ascending colon Transverse colon

Digestive System Organization

Descending colon Sigmoid colon Rectum Anus

Accessory structures Not in tube path Organs

Teeth Tongue Salivary glands Liver Gall bladder Pancreas

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The Mouth and Teeth

Many vertebrates have teeth, and chewing (mastication) breaks up food into small particles and mixes it with fluid secretions mammals have heterodont dentition, teeth of

different specialized types the general pattern of dentition is modified in different

mammals depending on their diet in carnivorous mammals, the canines are prominent, and

other teeth are more bladelike and sharp in herbivorous mammals, incisors are well-developed for

snipping, canines are reduced or absent, and molars are large and flat, with complex ridges well suited to grinding

The Mouth and Teeth

Humans are omnivores and human teeth are specialized for eating both plant and animal material humans are carnivores in the front of the

mouth and herbivores in the back children have only 20 teeth but these are

lost during childhood and replaced by 32 adult teeth

Figure 31.9 Human teeth

The tooth is a living organ.

Anatomy of the Mouth and Throat

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Human Deciduous and Permanent Teeth

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Dorsal Surface of the Tongue

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The Major Salivary Glands24

Deglutition (swallowing)

Sequence Voluntary stage

Push food to back of mouth

Pharyngeal stage Raise

Soft palate Larynx + hyoid Tongue to soft palate

Esophageal stage Contract pharyngeal

muscles Open esophagus Start peristalsis

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Deglutition (swallowing)

Control Nerves

Glossopharyngeal Vagus Accessory

Brain stem Deglutition center

Medulla oblongata Pons

Disorders Dysphagia Aphagia

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The Esophagus and Stomach

The esophagus is a muscular tube that connects the pharynx to the stomach the upper third is enveloped in skeletal

muscle for voluntary control of swallowing the lower two-thirds is surrounded by

involuntary smooth muscle rhythmic waves of contractions, called

peristalsis, propel food towards the stomach

Esophagus28

Usually collapsed (closed) 3 constrictions

Aortic arch Left primary bronchus Diaphragm

Surrounded by SNS plexus Blood vessels

Functions Secrete mucous Transport food

Peristalsis and Segmentation

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Esophagus30

Sphincters Upper Lower

Abnormalities Achalasia Atresia Hernia Barret’s esophagus Esophageal varices

The Esophagus and Stomach

The movement of food from the esophagus into the stomach is controlled by a ring of circular smooth muscle, called a sphincter contraction of the sphincter prevents food in the

stomach from moving back into the esophagus in humans, stomach contents can be brought

back out during vomiting the relaxing of the sphincter may lead to acid

reflux, which is when stomach acid moves into the esophagus this produces a burning sensation known as heartburn

The Esophagus and Stomach

The stomach is a saclike portion of the digestive tract the stomach contains an extra layer of

smooth muscle for churning food gastric juice is released by gastric glands

in the lining of the stomach parietal cells secrete hydrochloric acid (HCl) chief cells secrete pepsinogen

pepsinogen requires a low pH to be activated into pepsin, a protease that begins the digestion of proteins

Stomach33

Usually “J” shaped Left side, anterior to the spleen Mucous membrane

G cells – make gastrin Goblet cells – make mucous Gastric pit – Oxyntic gland – Parietal cells –

Make HCl Chief cells – Zymogenic cells

Pepsin Gastric lipase

Anatomy of the Stomach34

Stomach

3 muscle layers Oblique Circular Longitudinal

Regions Cardiac sphincter Fundus Antrum (pylorus) Pyloric sphincter

Vascular Inner surface thrown

into folds – Rugae Contains enzymes that

work best at pH 1-2

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Stomach

Functions Mix food Reservoir Start digestion of

Protein Nucleic acids Fats

Activates some enzymes

Destroy some bacteria Makes intrinsic factor –

B 12 absorption Destroys some bacteria

Absorbs Alcohol Water Lipophilic acid B 12

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The Small and Large Intestines

The small intestine is the true digestive vat of the body only relatively small portions of chyme are

introduced into the small intestine at one time this allows time for acid to be neutralized and

enzymes to act in the small intestine, carbohydrates,

protein, and lipids are broken down and absorbed into the bloodstream

Small Intestine

Absorbs 80% ingested water Electrolytes Vitamins Minerals Carbonates

Active/facilitated transport

Monosaccharides Proteins

Di-/tripeptides Amino acids

Lipids Monoglycerides Fatty acids Micelles Chylomicrons

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1.6 The Small and Large Intestines While some enzymes necessary for

digestion are secreted by the cells of the intestinal wall, most are made in the pancreas the pancreas is an exocrine gland,

meaning it secretes through ducts the pancreas sends it products via a duct

that empties into the first part of the small intestine, the duodenum

The Small and Large Intestines

Much of the food energy the vertebrate body harvests is obtained from fats fat digestion involves bile salts that are

secreted into the duodenum by the liver bile salts act like detergents and combine

with drops of fat to form microscopic droplets this process is known as emulsification this increases the surface area for the enzyme

lipase to work on in order to breakdown the fat

Small Intestine

Secretes digestive enzymes Peptidases

Amino- Di- Tri-

Sucrases Maltase Lactase Saccharidases

Di- Tri-

Lipase Nucleases

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Small Intestine

Control Requires

pancreatic enzymes & bile to complete digestion

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Large Intestine43

Extends from ileocecal valve to anus Regions

Cecum – Appendix Colon

Ascending Transverse Descending

Rectum Anal canal

Anatomy of the Large Intestine

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Large Intestine45

Histology No villi No permanent circular folds Smooth muscle

Taeniae coli Haustra

Epiploic appendages Otherwise like rest of Gl tract

Large Intestine46

Functions Mechanical digestion

Haustral churning Peristalsis Reflexes

Gastroileal Gastrocolic

Chemical digestion – Bacterial digestion Ferment carbohydrates Protein/amino acid

breakdown

– Absorbs•More water•Vitamins

– B– K

– Concentrate/eliminate wastes

Feces Formation and Defecation Chyme dehydrated to

form feces Feces composition

Water Inorganic salts Epithelial cells Bacteria Byproducts of digestion

Defecation Peristalsis pushes feces

into rectum Rectal walls stretch

Control Parasympathetic Voluntary

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Liver48

Location R. Hypochondrium Epigastric region

4 Lobes Left Quadrate Caudate Right

Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

Liver

Functions Makes bile

Detergent – emulsifies fats

Release promoted by: Vagus n. CCK Secretin

Contains Water Bile salts Bile pigments Electrolytes Cholesterol Lecithin

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Liver

Detoxifies/removes Drugs Alcohol

Stores Gycolgen Vitamins (A, D, E, K) Fe and other minerals Cholesterol

Activates vitamin D Fetal RBC production Phagocytosis Metabolizes absorbed

food molecules Carbohydrates Proteins Lipids

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Liver

Dual blood supply Hepatic portal

vein Direct input from

small intestine Hepatic

artery/vein Direct links to

heart

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Animation: Impact of Alcohol

Vitmins53

• organic compounds that the body uses for metabolic purposes but is unable to produce in adequate quantity

Nutrient RDA Potential toxic effects Main function Best food sourcesVitamin A Men: 3,000 IU

Women: 2,300 IULiver toxicity, dry rough skin and

cracked lips, irritability, headache, birth defects

Healthy immune barriers and epithelial tissue, growth,

reproduction, bone and red blood cell formation, vision

Foods high in beta carotene, fortified

foods, liver

Beta carotene (as mixed

carotenoids)

N.D. Possibly increased lung cancer in smokers, harmless orange skin

colour

Antioxidant, source of vitamin A, immune booster, possible cancer

prevention, vision

Orange, yellow, red and green vegetables

and fruitsVitamin D 9-50 years: 200 IU

51-70 years: 400 IU> 70 years: 600 IU

osteoporosis: 1,000 IU

Heart/liver/kidney toxicity, hypercalcemia (excess calcium in

the blood)

Calcium metabolism, bone mineralization, possible cancer

prevention

Fortified milk, fatty fish

Vitamin E 22 IU Possible increase in heart disease, excess bleeding

Antioxidant, anticoagulant, protection from heart disease,

possible cancer prevention

Wheat germ, vegetable oils, nuts

Vitamin K M: 120 mcgW: 90 mcg

Interaction with blood thinners Bone mineralization, blood clotting

Green leafy vegetables

Vitamin C M: 90 mgW: 75 mg

smokers add 35 mg

Pro-oxidant, excess iron absorption, diarrhea

Antioxidant, immunity, antiviral in test-tubes, cancer prevention,

increases iron absorption

Fruits and vegetables, especially peppers and

citrus fruits

Thiamine (B1) M: 1.2 mgW: 0.9 mg

Very high doses may promote tumour growth

Energy metabolism, mood, nervous system

Whole grains, brown rice, fortified foods,

legumes, pork, oysters

Riboflavin (B2) M: 1.3 mgW: 1.1 mg

N.D. Energy metabolism, antioxidant, possible migraine prevention

Dairy products, leafy greens, oysters

Niacin (nicotinic acid)

M: 16 mgW: 14 mg

Itching, skin flushing,Liver toxicity, insulin resistance

Energy metabolism, lowers LDL cholesterol and triglycerides,

raises HDL cholesterol

Poultry, red meat, fish, legumes, peanut

butter, nutsVitamin B6 M: 1.3-1.7 mg

W: 1.3-1.5 mgNerve damage (neuropathy) Protein metabolism, immunity,

neurotransmitter synthesis (e.g. serotonin and dopamine), treats peripheral neuropathy and PMS

Meat, fish, poultry, eggs, potatoes, fortified cereals,

peanuts, soybeansFolate 0.4 mg High dose can mask B12 deficiency

leading to nerve damageCell division, prevents neural tube defects and perhaps other birth defects, lowers homocysteine,

possible cancer prevention

Leafy greens, legumes, oranges, broccoli,

cauliflower

Vitamin B12 (cobalamin)

2.4 mcg Rare cases of eye damage Cell division, amino acid metabolism, nervous system,

mental function

Fish, shellfish, meat, fortified soy and rice milk, fermented soy

products

Minerals

Major and trace minerals Major minerals are essentials of

cells and body fluids and are structural components of tissues

Trace minerals are for support for larger molecules to function

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Minerals (table 8.5 in book)56

Calcium 1,000-1,200 mgCalcium deposits in soft

tissuesBone mineralization, muscle contraction

Dairy products, fortified soy and

rice milk, fish bones

MagnesiumM: 400 mgW: 320 mg

Diarrhea, decreased calcium absorption

Bone mineralization, active in more than 300 chemical reactions in the

body

Whole grains, nuts, green vegetables,

legumes

IronM: 8 mg

W: 18 mgIron overload disorders,

heart disease, liver cirrhosis

Makes hemoglobin which carries oxygen, makes

energy in the mitochondria

Meat, legumes, tofu, leafy greens, breakfast cereals

ZincM: 11 mgW: 8 mg

Immune suppression, nausea, metallic taste,

copper deficiency

Growth, immunity, wound healing, taste, sperm

production, antioxidant, prostate health

Oysters, meat, poultry, fish

Selenium 55 mcgBrittle hair and nails,

irritability, garlic breath, fatigue, nausea

Antioxidant, immunity, possible cancer

prevention, viral infections

Whole grains from selenium-rich soils, poultry, meat, dairy

Class homework

Keeping a food diary for 1 full week (7 days) Track all food and beverage consumption Use websites to track calories

Fitwatch.com Use measuring cups/spoons If you work-out; track your calorie outtake Also want 1 pg of what you learned over the

week Due via email in table format by NOV 18th

Worth: 50 points

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Example: 58DATE: 10/16 Food Items: Calories

Breakfast: 1 egg sandwich (egg, bread, cheese, and ketchup)1 apple

27050

Snack: Hand full of almonds 150

Lunch: 2-Mc Donalds hamburgers with no cheese & NO PICKLEDiet coke

4000

Snack: Green tea with splendaAnimal crackers (20 of them)

0250

Dinner: Chicken breast (med size) with sweet potato, butter, and corn 2 cups of milk Glass of green tea sweetened with splendaPiece of pumpkin pie with cool whip

630

2000580

Activity: Walked the dogs around the neighborhood for 30 mins -250

Other notes: Had no energy when I got up this morning but by the afternoon I was feeling pretty good.

Total: 2530-250=2280