Chapter 22: Nutrition and Digestion At rest and at play: optimizing human physiological functioning...

Chapter 22: Nutrition and Digestion

At rest and at play: optimizing human physiological functioning

Lecture by Jennifer Lange, Chabot College

How does food become fuel and raw materials?

22.1 Why do organisms need food?

Take-home message 22.1

Animals must eat for two reasons: to acquire the energy needed for all growth and activity, and to acquire the raw materials required for life.

Animals can consume plants, animals, or both.

22.2 What’s on the menu? Organisms have a variety of diets.

Humans Are Not the Only Species that Practice Farming


All animals require food. Plants and other photosynthetic

organisms produce food through photosynthesis, and animals have one of three types of diet.

1) Carnivores consume only other animals.

2) Herbivores consume only plants. 3) Omnivores, including most humans,

consume both plants and animals.

Food energy is measured in kilocalories.

22.3 Calories count: organisms need sufficient energy.

Body weight

Energy needed each

hour Hours per

day

Animal’s caloric needs

5 grams 35 cal/gram/hr

24 hrs/day

4.2 kcal/day

=

=

Calculating the BMR of a Shrew


To function well, living organisms need sufficient energy, measured

in kilocalories. The minimal energy needed by an

individual not engaged in any activity is called its basal metabolic rate, or BMR.

Water constitutes between 6065% of body weight.

22.4 Water is an essential nutrient.

Take-home message 22-4

Water is probably the single most important component of the diet. It constitutes 6065% of the body weight of most mammals, transports nutrients and waste materials throughout the body, takes part in metabolic reactions, serves as a

solvent, lubricates many body parts, and helps regulate body temperature.

Proteins, comprised of amino acids, are the cellular workers.

22.5 Proteins in food are broken down to build proteins in the body.

Types of Proteins


Animals consume three different types of macromolecules for calories: proteins, carbohydrates, and fats.

Proteins provide raw materials for growth and for the production of enzymes.

Food sources of protein vary in amino acid composition.

Humans require 20 amino acids, and 8 of these, called essential amino acids, can only be supplied by the diet.

Sugars are the primary input for ATP production.

22.6 Carbohydrates and lipids provide bodies with energy and more.

Lipids are the primary energy storage form, but can also be used for ATP production.

Types of Lipids

Excess Calories Converted to Fat for Storage


Carbohydrates are the primary fuel on which animal bodies run.

Dietary fats function primarily as a dense source of energy that can be efficiently stored in the body.

22.7 Vitamins and minerals are necessary for good health.

Are Dietary Supplements Necessary?


Vitamins and minerals are organic and inorganic molecules in the diet.

They are used in the production and action of enzymes and other molecules involved in the processing of food and other biochemical reactions.

While vitamins and minerals are essential in small amounts, most people in the United States do not benefit from taking them as supplements.

Does eating lower calorie foods lower our daily intake of calories?

22.8 How do organisms “know” what to eat?

Lipids Provide the Most Kcal/Gramof Food


Instincts cause animals to get hungry and to seek out food when in that state.

Humans and other animals show a preference for fatty foods over carbohydrate- or protein-laden foods, a behavior reinforced by fat-laden meals stimulating the many reward centers in the brain.

These preferences probably evolved because fat has the most calories per serving.

22.9 We convert food into nutrients in four steps.


The digestive process in humans includes four distinct phases during which food is progressively chewed up, broken down, and absorbed by the body, after which the non-usable portion of the raw materials is discarded as waste.

Ingestion—Bringing Food into the Digestive Tract

22.10 Ingestion is the first step in the breakdown of food.

Ingestion—Transport to the Stomach


Ingestion is the first phase of the digestive process.

Usually lasting less than a minute, ingestion involves tearing and grinding food in preparation for passing it to the stomach.

Digestion also begins during this phase, with some starch being broken down by enzymes in saliva.

Digestion—Mechanical and Chemical Processes

In the stomach:1) Acid and

enzymes begin protein digestion.

2) Contractions and the addition of water create a liquid called chyme.

22.11 Digestion dismantles food into usable parts.

Digestion—Mechanical and Chemical Processes

In the small intestine:

1) Bile from the liver and gallbladder break apart large lipid droplets.

2) Enzymes from the pancreas accomplish most chemical digestion.

Bacterial Symbiotes Aid in Digestion

The digestive process eliminates potentially harmful substances that are ingested, including bacteria and snake venom.


Digestion—the process of dismantling large pieces of food, physically and chemically breaking them down into absorbable molecules—is the second phase of the breakdown of food in animals.

It occurs primarily in the stomach and small intestine.

The structure of the small intestine is specialized to have a large surface area for absorption.

22.12 Absorption moves nutrients from your gut to your cells.

Absorption


Absorption is the process by which energy-rich food particles are taken up from the digestive tract into the cells of the body, where they can be used for energy and building materials. It takes place primarily in the small intestine.

22.13 Elimination removes unusable material from your body.

The colon (large intestine) reabsorbs water and prepares the fecal material for passing out of the anus.

Dietary fiber (mainly cellulose) is essential to smooth passage through the colon.


The last phase of food breakdown takes place as the mostly indigestible materials leave the small intestine and enter the large intestine.

There, water and ions are absorbed before the remaining materials are defecated.

22.14 Animals have some alternative means for processing their food.

Unlike humans, other animals have evolved mechanisms for digesting cellulose.

Alternative Digestive ProcessingRuminants have multipart stomachs that house

cellulose digesting bacteria.

Alternative Digestive Processing

Koalas have a cecum, an outcropping between the small and large intestines, housing cellulose digesting bacteria.

Coprophagy—Eating Own Feces!


Most animals don’t produce enzymes that break down cellulose. In ruminant animals, complex four-part stomachs have evolved in which the animals can digest plant matter that humans cannot, in part due to the presence of symbiotic cellulose-digesting bacteria. Other animals have alternative methods of utilizing cellulose-digesting bacteria.

22.15 What Constitutes a Healthy Diet?

Balance of Food Categories Is Key

As is avoiding substances that can have negative health effects.


A balanced diet contains adequate amounts of essential nutrients and energy, but not surplus amounts, and is low in substances—including saturated fats, cholesterol, sugar, salt, and alcohol—that can have adverse health effects when consumed in greater quantities.

Why do we want to eat more than we should?

22.16 Obesity can result from too much of a good thing.


Food supplies were unpredictable for our early ancestors, leading to the evolution of strong appetites.

In the modern industrial world, such instincts have problematic consequences, leading most people to overeat and to weigh more than they would prefer and more than is healthy.

Domesticated animals have a similar problem.

Do Fad Diets Really Work?

22.17 Weight-loss diets are a losing proposition.

Weight loss can be accomplished through pills and surgery, but the safest, and most effective, method is diet monitoring and exercise.

Why Do Diets Usually Fail and Results Not Last?


Weight loss is both a simple and a complicated problem.

There is only one complete and perfect plan that guarantees success: reduced caloric intake and increased caloric expenditure.

Interventions designed to facilitate weight loss involve drugs, surgery, or behavior modification, none of which is reliably successful.

Problems regulating blood glucose levels can arise from either insulin scarcity or ineffectiveness.

22.18 Diabetes is caused by the body’s inability to regulate blood sugar effectively.

Diabetes Mellitus = Sweet UrineProblems regulating blood glucose levels can

arise from either insulin scarcity or ineffectiveness.

In both Type I and Type II diabetes, insulin injections are a treatment method.


Digesting and absorbing food leads to an increase in the amount of glucose circulating in the bloodstream. This triggers the release of insulin by the pancreas, causing the body’s cells, especially muscle cells and fat cells, to pull the glucose in for energy or storage.

Problems with regulation of blood sugar, called diabetes, affect millions of people and are caused by heredity and poor diet.

22.19 Food and infection: spicy foods are natural antibiotics.

Their prevalence in dishes is higher in environments conducive to bacterial growth.

Spices Are Natural Antibiotics

Spices with the strongest antimicrobial effects are used more frequently than those with weaker effects.


Plants produce toxic compounds that make the plant distasteful to would-be predators, either killing them outright or being so unpleasant-tasting that predators search elsewhere for a meal.

Humans seek out these toxins, using them as spices that help us fight off illness-inducing microorganisms.

Chapter 22: Nutrition and Digestion At rest and at play: optimizing human physiological functioning...

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