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Also opens to the trachea (respiratory tract). During swallowing, a reflex tips the epiglottis to close the windpipe entrance.
Not swallowing Swallowing started Swallowing finished
C. The Esophagus
Is a muscular tube.
Connects the pharynx to the stomach.
Moves food down by peristalsis.
Starts digestion of proteins
D. The Stomach
Can store food for several hours.
2 major functions: digestion and defense
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. The hole was permanent and large enough that Beaumont could insert his entire forefinger into the stomach cavity.
What did he do to this poor man? Rate of Digestion of different food: Beaumont tied different types of food (protein, fat, carb) to the end of a silk string and dangled the food through the hole into the stomach. Beaumont pulled out the string 1, 2, 3 and 5 hours later. Stomach Stomach acid Fistula or tube String Food
Chemical Digestion in the Stomach
This Churns food into a thick soup called acid chyme.
The high acidity kills germs
Normally empties in 2-6 hours
The stomach contains gastric juice made of strong acid , digestive enzymes , and mucus .
Are erosions of the stomach lining.
Are often caused by a bacterium named Helicobacter pylori, NOT stress .
Nothing to do with the heart!
Discomfort or pain caused by the stomach contents traveling up from the stomach up into the gullet (lower part of your esophagus). The gullet is not made to withstand acid and is irritated and inflamed when acid from the stomach travels up into it.
Happens when you eat too much, wear tight clothes, bad posture….
E. The Small Intestine
Longest part of the alimentary canal.
Major organ for chemical digestion and absorption.
Chemical Digestion in the Small Intestine: hydrolases break down food to monomers.
Composed of 3 parts:
Duodenum (close to stomach)
Jejunum (middle part)
Receives digestive agents from several organs.
secretes bile, which helps digest fats .
Secretes juice that neutralizes stomach acids into the duodenum.
Absorption of Nutrients
It is not technically “in” the body yet .
It must be absorbed.
Although food has been ingested,
Are parts of the small intestine specialized for absorption. The jejunum and ileum The intestinal wall contains villi and microvilli , which provide a large surface area for absorption.
Removes and stores iron and vitamins A, D, E, K, and B 12
Makes plasma proteins
Regulates blood glucose, stored as glycogen
Bilirubin – hemoglobin breakdown product
Bile salts – emulsify fat
The liver has many roles
Liver produces 400-800 ml of bile each day
Stores excess bile
Water reabsorbed – thickens bile
Secreted through common bile duct into duodenum via common bile duct
Proteins that speed up specific chemical reactions
Break down carbohydrates, proteins, nucleic acids, and fats
Human Nutritional Requirements
Proper nutrition helps to maintain homeostasis.
A balanced diet provides
Fuel energy for cellular work.
to construct needed materials.
6 major classes of Nutrients
Carbohydrates and fats
Primary energy source
Growth and development
Regulate metabolism (with vitamins and minerals)
Can be energy source
Serves many important roles
Cells are 70-80% water
Vitamins and minerals
Physical activity: 30 min at least/day A lot little Amount of food and proportion for each category The more active you are the more you should eat. But the proportions should remain the same
Balancing Calories: - Enjoy your food, but eat less - Avoid oversized portions Foods to Increase: - Make half your plate fruits and veg - Make at least half your grains whole grains - Switch to fat-free or 1% fat milk Foods to reduce - Lower sodium - Drink water instead of sugary drinks
Any food made from wheat , rice , oats , cornmeal , barley or another cereal grain .
Whole grains contain the entire grain kernel -- the bran, germ, and endosperm.
Examples : whole-wheat flour, Oatmeal, brown rice
Refined grains have been milled, a process that removes the bran and germ. This is done to give grains a finer texture and improve their shelf life, but it also removes dietary fiber, iron, and many B vitamins.
Examples : white flour, white bread, white rice
OILS, FAT GROUP
Fats, oils and cholesterol
Unsaturated vs saturated lipids:
UNSATURATED = OILS
Liquid at room temperature
Found in vegetables and whole grains
SATURATED = FATS
Solid at room temperature
Animal origin (butter, meat)
Associated with cardiovascular disease
Fats That Cause Disease
Plaques form in and block arteries
Contain cholesterol and saturated fats
Not soluble in blood, ie needs carriers, which are low density lipoprotein (LDL) and high density lipoprotein (HDL)
LDL ( “bad” cholesterol) - transports cholesterol from the liver to cells
HDL- ( “good” cholesterol) - transports cholesterol away from arteries to the liver to make bile salts
Calories are a measure of the energy stored in your food . A measure of the energy you expend in daily activities . A kilocalorie is 1000 calories (The unit listed on food labels).
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.
A. Essential Amino Acids
There are 8 essential amino acids (needed to make proteins).
Different foods contain different ones.
Are organic molecules required in the diet for good health.
Vitamins are defined by their biological activity , not their structure.