Nutrition and Digestion

Lecture 5-2

Biology and Society: Eating Disorders

– Millions of Americans suffer from eating disorders

• Including anorexia and bulimia.

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-The causes of these diseases are unknown.-Popular culture and the media may promote unhealthy body images.

Overview of Animal Nutrition– Animals are heterotrophs, organisms that must feed on other

organisms.

HerbivoresFeed mainly on plants.

CarnivoresMainly eat animals that eat plants.

Omnivores - Ingest both plants and animals.

Dietary Categories

How do Animals Obtain FoodSuspension feeders – extract food particles

suspended in surrounding water

Substrate feeders – live in or on food source and eat their way through it

Fluid feeder – gets food by sucking nutrient-rich fluids from living host

Bulk feeders – Ingest large pieces of food

Tube worm

The Four Stages of Food Processing– Ingestion

• Is another word for eating.

– Digestion• Is the breakdown of food to small nutrient molecules.

– Absorption• Is the uptake of the small nutrient molecules by cells

lining the digestive tract.

– Elimination• Is the disposal of undigested materials from the food

we eat.

Digestion: A Closer Look– Mechanical digestion

• Begins the process.• Involves physical processes like chewing.

– Chemical digestion• Is the chemical breakdown of food by digestive

enzymes.

– Digestion• Dismantles food particles for use by the body.

Digestive Compartments– In animals, chemical digestion is contained

safely within some kind of compartment.– Food vacuoles – simplest digestive

compartment• Are intracellular organelles filled

with digestive enzymes.

– Gastrovascular cavities are

compartments with a single opening.

– Digestive tubes have two separate openings, a mouth and an anus.

Specialized organs are along the length to perform 4 main functions of food processing

A Tour of the Human Digestive System

System Map – The human digestive system consists of:

• A digestive tube, the alimentary canal• Accessory organs that secrete digestive chemicals

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– Food processing takes place along the alimentary canal.

The Mouth

– The mouth, or oral cavity,• Functions in ingestion and the preliminary steps of

digestion

Mechanical – teeth tear and grind foodChemical – amylase in saliva breaks down starch

The Pharynx

• Connects the mouth to the esophagus.• Also opens to the trachea (windpipe)

– During swallowing, a reflex tips the epiglottis to close the windpipe entrance.

The Esophagus

– The esophagus• Is a muscular tube.• Connects the pharynx to the stomach.• Moves food down by peristalsis

Peristalsis – rhythmic waves of muscular

contractions.

The Stomach– The stomach• Can store food for several hours – can store up to 2L or half gallon

-Chemical digestion – gastric juice hasmucus, enzymes, and acid

-Churns food into a thick soup called acid chyme.-Sphincter regulates transfer of chyme from stomach to small intestine

What protects the stomach lining?-Pepsin is secreted in the inactive form of pepsinogen-Mucus-Gastric juice is not secreted constantly. It is regulated by nerves-Mitosis

The Process of Science: How Does the Stomach Work?

– The accidental shooting of a man in 1822• Provided an opportunity for a doctor named William Beaumont to

learn about the stomach’s many functions.

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Stomach Ailments

– Gastric ulcers

• Are erosions of the stomach lining.

• Are often caused by a bacterium named Helicobacter pylori.

Acid Reflux (“Heart burn”) – backflow of chyme into lower end of esophagus.

The Small Intestine

– The small intestine

• Is the longest part of the alimentary canal (20ft).

• Is the major organ for chemical digestion and absorption.

• Hydrolases break down food to monomers.

.

– The duodenum – (first part of intestine)

• Receives digestive agents from several organs.

Contributing organs to digestion in small intestine are: 1 - The pancreas

Secretes juice that neutralizes stomach acids into the duodenum.

2 - The liverSecretes bile which is stored in the gall bladder. Helps digest fats.

Bile has salts that bind to fat preventing themfrom reforming large globules. Helps lipase workon them more efficiently.

Absorption of Nutrients– Although food has been ingested,

• It is not technically “in” the body yet.• It must be absorbed.

– The jejunum and ileum

• Are parts of the small intestine specialized for absorption.

– The intestinal wall

• Contains villi and

microvilli, which provide

a large surface area for

absorption (tennis court size)

The Large Intestine (and Beyond)– The large intestine or colon

• Is shorter, but wider, than the small intestine.• Makes up most of the length of the large intestine.

• Absorbs water from the alimentary canal.

• Produces feces, the waste product of food.

Cecum

– The rectum• Is the last 15 cm (6 inches) of the large intestine.• Store feces until it can be eliminated.

– The anus• Regulates opening of rectum.• Expels feces.

Human Nutritional Requirements

– Proper nutrition helps to maintain homeostasis.– A balanced diet provides

• Fuel energy for cellular work.

• Building materials to construct needed materials.

Food as Fuel– Cells• Break down food molecules in cellular respiration.• Generate many molecules of ATP.

– Calories are• A measure of the energy stored in your food.• A measure of the energy you expend in daily

activities. (1kcal = 1000 calories)

Metabolic Rate – How fast do we burn our food?– The metabolic rate of an organism is the rate of energy consumption per

day.– If we take in more than our cells can use it is stored (glycogen, fat)– MR also depends on body size, stress level, age, heredity

Food as Building Material– The cells of your body

• Assemble polymers from the monomers found in food.

– Essential nutrients

• Are substances needed by the body that it cannot make itself.

– Malnutrition results from a long term dietary deficiency of one or more of the essential nutrients.

• Protein deficiency is an example.

-Kwashiorkor is caused by inadequate protein intake.-This causes deficiency in the blood protein, manifesting inthe swelling of belly and limbs

– Undernutrition

• Is caused by inadequate intake of nutrients.

• Body begins breaking down its own molecules (including brain and muscles).

Scurvy – Lack of vitamin C

Essential Amino Acids– There are eight essential amino acids.

• Different foods contain different ones.

Vitamins– Vitamins

• Are organic molecules required in the diet for good health.

• Need less than the essential amino acids

• Function mostly as assistants to enzymes by catalyzing metabolic reactions.

Minerals– Minerals• Are inorganic substances required in the diet• Deficiency can cause health problems

(Ex. Calcium – degenerative bone disease)

Essential Fatty Acids

– Our cells make fats and other lipids by combining fatty acids with other molecules.

– Essential fatty acids are the fatty acids we cannot make from simpler molecules (omega 3 and omega 6).

– Function (to name a few):• Affects inflammation and many other cellular

functions• Affecting mood and behavior• Affecting cellular signaling)[2]

Figure 22.24

Remember, the best way to maintain a healthy weight is to eat a balanceddiet and get plenty of exercise.