Download Nutrition and Digestion

Nutrition and Digestion
Functions of the Digestive System
1. To break down the foods the body ingests into a form that the body cells can
use
2. Transfers nutrients in this form out of the digestive tract and into the blood
circulation
So food to usable nutrients
Polymers to monomers
Polysaccharides to monosaccharides
Proteins to amino acids
Fats (triglycerides) to monoglycerides and fatty acids
Functions
3. To retain the waste that remains after nutrients from the food have been
transferred
4. To eliminate this waste from the body
The Digestive System
The digestive tract is essentially a long muscular tube with two openings mouth and anus
It receives input along its length from accessory organs and glands
There is mechanical digestion, breaking large chunks of food into smaller
pieces, providing greater exposure of the molecules to enzymes
There is chemical digestion, hydrolysis reactions that break macromolecules
using water
These reactions are catalyzed by enzymes
How can all of this chemical digestion occur without the body digesting its own
macromolecules?
Compartmentalization
Compartments
The simplest type of digestion occurs within a cellular organelle
As a cell engulfs food by phagocytosis, a food vacuole forms, which then fuses
with a lysosome containing enzymes to form a digestive compartment
As the food is digested, small food molecules pass into the cytoplasm
Compartments
Sponges are the only animals that digest food solely within their cells
Most animals use a digestive compartment to process food
Compartments
Simpler animals, including cnidarians (such as hydras and jellies) and
flatworms, have a gastrovascular cavity, a digestive compartment with a
single opening that functions as both the
entrance for food (like a mouth) and
the exit for undigested wastes
Compartments
The vast majority of animals have a digestive tube with two separate openings,
a mouth and an anus
Such a tube is called an alimentary canal, or digestive tract
Food moves through specialized regions that digest and absorb nutrients in a
stepwise fashion
This adaptation allows for much more efficient food processing
Human Digestive System
Mouth
Food is chewed (mechanical breakdown)
Complex carbohydrate digestion begins
Saliva secreted from the salivary glands contains salivary amylase
The tongue mixes the chewed food with saliva forming a bolus
Pharynx
The pharynx
connects the mouth to the esophagus and
opens to the trachea, or windpipe, which leads to the lungs
During swallowing, a reflex
moves the opening of the trachea upward and
tips a door-like flap called the epiglottis to close the entrance to the
trachea
Esophagus
Peristalsis moves the bolus through the esophagus and into the stomach
Stomach
The bolus moves past the cardiac sphincter into the stomach
The stomach is highly elastic and convoluted, capable of expanding to
accommodate the amount of food consumed
Storage of food material
“Time-release ” transfer into the small intestine
Secretions include mucus, HCl, enzymes (pepsin), and hormones (gastrin)
This mixture is now called chyme
Small intestine
Accessory organs aid the digestion that occurs in the small intestine
The pancreas produces enzymes for the digestion of carbohydrates, fats,
proteins, and nucleic acids and buffer to neutralize the chyme
The liver produces bile that is stored in the gallbladder - important for the
emulsification of fats
Emulsifiers (bile) break up large globs of fat into smaller droplets
This increases the number of fat molecules available to be digested
Small intestine
The chyme is stored in the stomach where there is continued digestion
Small amounts move past the pyloric sphincter into the small intestine
The small intestine is the site of the completion of digestion
The typical meal takes 3-6 hours to move out of the stomach ~4 tablespoons at
a time
Completed digestion leaves monomers from those original polymers
Absorption
Monosaccharides and amino acids cross the intestinal lining into the
circulatory system for distribution
Fatty acids move into the lymphatic system
The intestinal lining is covered with villi and microvilli to increase the surface
area facilitating absorption
Large intestine (colon)
Material that is not absorbed from the small intestine is moved into the large
intestine
It is the site of concentration and storage of feces
Undigested and unabsorbed material, water , and bacteria
Water is reclaimed leading to concentration of feces
Also absorbs vitamins produced by our resident bacteria
Rectum and anus
Material that collects in the colon eventually moves into the rectum
The nervous system controls the sphincter muscle at the anus to retain/expel
the fecal material
Bulk, roughage, or fiber is fibrous material that makes the feces more bulky
leading to a regular need to expel
Human Nutrition
A nutrient must do at least one of the following:
Provides energy
Acts as a structural building block for the body
Regulates a process in the body
There are 6 categories of nutrients
Water, minerals, vitamins, carbohydrates, proteins, lipids
Calories
All of the calories that we take in during the day come from proteins,
carbohydrates, or lipids
A calorie is the amount of energy required to raise the temperature of 1 gram
(ml) of water by 1°C
A nutritional calorie (Calorie) is the amount required to raise 1000 grams (1
liter) by 1°C
Metabolic Rate
The rate at which your body consumes energy is called your metabolic rate
A person’s metabolic rate consists of
the basal metabolic rate (BMR), the amount of energy it takes to maintain
body functions, and
any additional energy consumption above that base rate
The more active you are, the greater your actual metabolic rate and the greater
the number of calories your body uses per day
Any excess Calories that we consume during the day gets stored
Mainly as fat, very little as glycogen
Each gram of fat stores and yields 9 Calories
Each gram of carbohydrate and protein stores and yields 4 Calories
Proteins
Our digestive system breaks proteins from food down to individual amino
acids
Although we have the ability to make 12 of the amino acids from scratch, there
are 8 that we cannot make - essential amino acids
Most proteins from animal products are complete, containing all 8
essential amino acids
Most proteins derived from plant products are not
Carbohydrates
Can be divided into simple sugars (mono- and disaccharides) and complex
carbohydrates consisting of digestible (starch) and indigestible (fiber)
Nutritionists recommend a diet that is
Low in simple sugars added to processed foods
High in complex carbohydrates from fresh fruits, vegetables, and wholegrain foods
Simple sugars represent “empty” Calories without vitamins and minerals
They can result in a surge of glucose in the bloodstream
Complex carbohydrates require more digestion resulting in a slow and steady
supply of glucose
Water
For most people under most circumstances, thirst is an accurate guide to
ensure we take in enough water to stay sufficiently hydrated
Vitamins
Vitamins are needed by the body to facilitate chemical reactions
People who eat a balanced diet should be able to obtain enough of all needed
nutrients in their food
Minerals
Minerals are needed by the body to either help form bodily structures or to
facilitate chemical reactions
Lipids
Excellent source of energy but also play many roles in the body
The form for much of our dietary lipids is the triglyceride
The amount of saturation of those fatty acids is key
Trans fats and saturated fats increase the risk of cardiovascular disease
Polyunsaturated and monounsaturated fats are neutral
Unsaturated fats rich in omega-3 fatty acids are protective
A Healthy Diet
Diets can be judged as healthy to the extent that they contain a high proportion
of healthy foods
Food pyramids are a useful visual guide to the intake of different foods
Nutritional Disorders
Dietary problems can have severe health consequences
Obesity
Obesity
is a too-high body mass index (BMI),
is the nutritional disorder of greatest concern,
increases the risk of heart attack, diabetes, cancer, and several other
diseases