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38–1 Food and Nutrition
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Food and Energy
Food and Energy
You need to eat food to obtain energy.
The energy in food is measured in Calories (capital C). One Calorie is equal to calories.
One calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius.
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Food and Energy
Caloric needs vary for each person.
An average-sized female teenager needs about Calories a day.
An average-sized male teenager needs about Calories a day.
If you exercise regularly, your energy needs may be higher.
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Nutrients
Nutrients
Nutrients are substances in food that supply the energy and raw materials your body uses for growth, repair, and maintenance.
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Nutrients
The nutrients that the body needs are:
water
carbohydrates
fats
proteins
vitamins
minerals
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Nutrients
Water 
Why is water such an important nutrient?
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Nutrients
Every cell in the human body needs water because many of the body's processes take place in water.
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Nutrients
Water makes up blood, lymph, and other bodily fluids.
Water is lost during sweating, when it evaporates to cool the body.
Water vapor is also lost from the body with every breath you exhale and in urine.
Humans need to drink at least one liter of water each day.
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Nutrients
Carbohydrates 
Carbohydrates are the main source of energy for the body.
There are two types of carbohydrates:
simple
complex
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Nutrients
Simple carbohydrates are found in fruits, honey, and sugar cane.
Simple carbohydrates do not need to be digested or broken down.
Complex carbohydrates, or starches, are found in grains, potatoes, and vegetables.
Complex carbohydrates need to be broken down before they can be used by the body.
Many foods contain the complex carbohydrate cellulose, or fiber.
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Nutrients
Fiber is needed in your diet.
Bulk supplied by fiber helps muscles keep food and wastes moving through your digestive and excretory systems.
Whole-grain breads and many fruits and vegetables have fiber.
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Nutrients
Fats  
Fats, or lipids, are an important part of a healthy diet.
Fats are formed from fatty acids and glycerol.
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Nutrients
Fats are needed:
to produce cell membranes, myelin sheaths around neurons, and certain hormones.
to help the body absorb fat-soluble vitamins.
to protect body organs and insulate the body.
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Nutrients
Fats are classified as saturated or unsaturated.
When there are only single bonds between carbon atoms in the fatty acids, the fat is saturated.
Most saturated fats are solids at room temperature—including butter and other animal fats.
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Nutrients
Unsaturated fats have at least one double bond in a fatty acid chain.
Unsaturated fats are usually liquids at room temperature.
Because many vegetable oils contain more than one double bond, they are called polyunsaturated.
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Nutrients
Proteins 
Proteins supply raw materials for growth and repair of structures such as skin and muscle.
They have regulatory and transport functions.
Proteins are polymers of amino acids.
The body can synthesize only 12 of the 20 amino acids used to make proteins.
The other 8 amino acids are called essential amino acids; they must come from food.
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Nutrients
Animal products, including meat, fish, eggs, and milk, contain all 8 essential amino acids.
Foods derived from plants, such as grains and beans, do not.
Therefore, people who don’t eat animal products must eat a combination of plant foods to obtain all of the essential amino acids.
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Nutrients
Vitamins 
Vitamins are organic molecules that help regulate body processes, often working with enzymes.
Most vitamins must be obtained from food.
A diet lacking certain vitamins can have serious, even fatal, consequences.
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Nutrients
There are two types of vitamins:
fat-soluble
water-soluble
The fat-soluble vitamins A, D, E, and K can be stored in the fatty tissues of the body.
The body can build up stores of these vitamins for future use.
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Nutrients
Fat-Soluble Vitamins
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Nutrients
The water-soluble vitamins dissolve in water and cannot be stored in the body.
Eating a diet containing a variety of foods will supply the daily vitamin needs of nearly everyone.
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Nutrients
Water-Soluble Vitamins
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Nutrients
Water-Soluble Vitamins
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Nutrients
Minerals 
Inorganic nutrients that the body needs, usually in small amounts, are called minerals.
By eating a variety of foods, you can meet your daily requirement of minerals.
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Nutrients
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Nutrients
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38–1
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38–1
Which nutrient is found in fruits, sugars, and whole-grain breads?
protein
fat
carbohydrates
vitamins
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38–1
Organic molecules that help regulate body processes and often work with enzymes are
fats.
minerals.
vitamins.
amino acids.
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38–1
Which two vitamins can be made by the body?
vitamins a and B
vitamins C and D
vitamins A and K
vitamins D and K
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38–1
The most important nutrient is
fat
water
vitamins
protein.
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38–1
The foods that should make up the largest part of your diet are
fats and sweets.
meat, poultry, and fish
milk, yogurt, and cheese.
breads, cereals, rice, and pasta.
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Biology
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36. 38–2 The Process of Digestion
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Digestion
What are the organs of the digestive system?
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Digestion
The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
Other structures add secretions to the digestive system, and aid in digestion. These include the salivary glands, pancreas, and liver.
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39. 38–2 The Process of Digestion
The Digestive System
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Stomach
Pancreas
Gallbladder
Large intestine
Small intestine
Rectum
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The Mouth
What is the function of the digestive system?
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The Mouth
The function of the digestive system is to help convert foods into simpler molecules that can be absorbed and used by the cells of the body.
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The Mouth
The Mouth
Chewing begins mechanical digestion, which is the physical breakdown of large pieces of food into smaller pieces.
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The Mouth
The teeth cut, tear, and crush food into small fragments.
As the teeth cut and grind the food, salivary glands secrete saliva, which moistens food and makes it easier to chew.
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The Mouth
Saliva helps ease the passage of food through the digestive system and also begins the process of chemical digestion.
Saliva contains amylase, an enzyme that breaks the chemical bonds in starches and releases sugars.
Saliva also contains lysozyme, an enzyme that fights infection.
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The Esophagus
The Esophagus
From the throat, the chewed food passes through the esophagus, or food tube, into the stomach.
Food is moved along by contractions of smooth muscle.
These contractions, known as peristalsis, squeeze the food through the esophagus into the stomach.
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The Esophagus
Esophagus
Bolus
Muscles contracted
Peristalsis
Stomach
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The Esophagus
The cardiac sphincter closes the esophagus after food has passed into the stomach.
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The Stomach
The Stomach
Food from the esophagus empties into the stomach.
The stomach continues mechanical and chemical digestion.
Alternating contractions of three smooth muscle layers churn food.
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The Stomach
Chemical Digestion
The stomach lining has millions of gastric glands that release substances into the stomach.
Some glands produce mucus, which lubricates and protects the stomach wall.
Other glands produce hydrochloric acid, which makes the stomach contents very acidic.
Other glands produce pepsin, an enzyme that digests protein.
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The Stomach
Pepsin and hydrochloric acid begin protein digestion.
Pepsin breaks proteins into smaller polypeptide fragments.
Other enzymes are denatured (broken down) by stomach acid.
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The Stomach
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The Stomach
Mechanical Digestion 
The stomach contracts to churn fluids and food, gradually producing a mixture known as chyme.
After 1–2 hours, the pyloric valve between the stomach and small intestine opens and chyme flows into the small intestine.
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The Small Intestine
The Small Intestine
As chyme is pushed through the pyloric valve, it enters the duodenum.
The duodenum is the first of three parts of the small intestine, and is where most digestive enzymes enter the intestine.
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The Small Intestine
Most chemical digestion and absorption of food occurs in the small intestine.
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The Small Intestine
Accessory Structures of Digestion
Liver
Bile duct
Pancreas
Gallbladder
Pancreatic duct
Duodenum
To rest of small intestine
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The Small Intestine
Accessory Structures of Digestion
Just behind the stomach is the pancreas.
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The Small Intestine
During digestion, the pancreas:
produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids.
produces sodium bicarbonate, a base that neutralizes stomach acid so that these enzymes can be effective.
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The Small Intestine
Assisting the pancreas is the liver, which produces bile.
Bile dissolves and disperses droplets of fat in fatty foods. This enables enzymes to break down smaller fat molecules.
Bile is stored in the gallbladder.
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59. Absorption in the Small Intestine
The small intestine is adapted for the absorption of nutrients.
The folded surfaces of the small intestine are covered with fingerlike projections called villi.
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60. Absorption in the Small Intestine
Villus
Small intestine
Circular folds
Epithelial cells
Villi
Capillaries
Lymph vessel
Vein
Artery
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61. Absorption in the Small Intestine
Cell surfaces of villi have more projections called microvilli.
These provide an enormous surface area for the absorption of nutrient molecules.
Slow, wavelike contractions of smooth muscles move the chyme along this surface.
Minerals are sometimes called trace elements because they are needed by the body in such small amounts.
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62. Absorption in the Small Intestine
Nutrient molecules are absorbed into the cells lining the small intestine.
Most products of carbohydrate and protein digestion are absorbed into the capillaries in the villi.
Molecules of undigested fat are absorbed by lymph vessels.
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The Large Intestine
The Large Intestine
When the chyme leaves the small intestine, it enters the large intestine, or colon.
The large intestine removes water from the chyme.
Water is absorbed quickly, leaving undigested materials behind.
Concentrated waste material passes through the rectum and is eliminated from the body.
Minerals are sometimes called trace elements because they are needed by the body in such small amounts. 
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64. Digestive System Disorders
Stomach acids sometimes damage the organ’s own lining, producing a hole in the stomach wall known as a peptic ulcer. Most peptic ulcers are caused by the bacterium H. pylori.
Other digestive disorders include diarrhea and constipation.
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38–3 The Excretory System
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66. Functions of the Excretory System
Every cell produces metabolic wastes.
The process by which these wastes are eliminated is called excretion
- Skin excretes excess water and salts in the form of sweat.
- Lungs excrete carbon dioxide
- Kidneys also play a major role in excretion.
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67. Functions of the Excretory System
The Kidneys What are the functions of the kidneys?
remove waste products from the blood.
maintain blood pH.
regulate the water content of blood - therefore, blood volume
Photo Credit: © Fred Hossler/Visuals Unlimited
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The Kidneys
The Kidneys
- located on either side of the spinal column
- Ureter carries urine to the urinary bladder
- Urinary bladder is where urine is stored
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The Kidneys
Structure of the Kidneys
Kidney
Nephron
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The Kidneys
Kidney Structure 
A kidney has two distinct regions:
The inner part is called the renal medulla.
The outer part is called the renal cortex.
Blood enters the kidney through the renal artery
The kidney removes urea, excess water, and other waste products and passes them to the ureter
The clean, filtered blood leaves the kidney through the renal vein and returns to circulation
The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Because the pancreas and most of the gallbladder are behind other organs, their locations are indicated by dotted lines.
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The Kidneys
Cortex
Medulla
Renal artery
Renal vein
Ureter
To the bladder
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The Kidneys
Nephrons: - functional units of the kidney - located in the renal cortex
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The Kidneys
Capillaries
Bowman’s capsule
Glomerulus
Collecting duct
Vein
Artery
To the ureter
Loop of Henle
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The Kidneys
Capillaries
Each nephron has its own blood supply:
an arteriole (artery)
a venule (vein)
a network of capillaries connecting them
Collecting duct
Vein
Artery
To the ureter
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The Kidneys
How is Blood filtered? As blood enters a nephron, impurities are filtered out and emptied into the collecting duct The purified blood exits the nephron through the venule (vein) The mechanism of blood purification involves two distinct processes: filtration and reabsorption
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The Kidneys
Filtration 
- Passing a liquid or gas through a filter to remove wastes
- mainly takes place in the glomerulus
The glomerulus is a small network of capillaries encased in the top of the nephron by a hollow, cup-shaped structure called Bowman's capsule.
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The Kidneys
Reabsorption 
Most of the material removed from the blood at Bowman's capsule makes its way back into the blood.
The process in which liquid is taken back into a vessel is called reabsorption
Almost 99% of the water that enters Bowman’s capsule is reabsorbed into the blood.
Muscles in the walls of the esophagus contract in waves. Each wave pushes the chewed clump of food, or bolus, in front of it. Eventually, the bolus is pushed into the stomach.
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The Kidneys
As the kidney works, purified blood is returned to circulation while urine is collected in the urinary bladder.
Urine is stored here until it is released from the body through a tube called the urethra.
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79. Control of Kidney Function
The activity of the kidneys is mostly controlled by the composition of the blood.
In addition, regulatory hormones are released in response to the composition of blood.
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80. Control of Kidney Function
For Example:
When you drink a liquid, it is absorbed into the blood - As a result, the concentration of water in the blood increases - As the amount of water in the blood increases the rate of water reabsorption in the kidneys decreases
Therefore: Less water is returned to the blood, and excess water is sent to the urinary bladder to be excreted as urine
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81. Homeostasis by Machine
Humans have two kidneys, but can survive with only one.
If both kidneys are damaged by disease or injury, there are two options:
a kidney transplant
kidney dialysis
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82. Homeostasis by Machine
Kidney dialysis works as follows:
Blood is removed by a tube and pumped through special tubing that acts like nephrons
Tiny pores in the tubing allow salts and small molecules to pass through
Wastes diffuse out of the blood into the fluid- filled chamber, allowing purified blood to be returned to the body
Digestive enzymes break down foods and make nutrients available to the body.
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83. Homeostasis by Machine
Blood in tubing flows through dialysis fluid
Kidney Dialysis
Blood pump
Vein
Artery
Shunt
Used dialysis fluid
Dialysis machine
Fresh dialysis fluid
Compressed air
Air detector
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38–3
A dialysis machine performs the function of which structure in the excretory system?
nephron
ureter
urethra
glomerulus
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38–3
In the human body, the kidneys play an important role in
producing digestive enzymes.
circulating the blood.
destroying old red blood cells.
maintaining homeostasis.
Accessory structures, including the liver and pancreas, add secretions to the digestive system. The pancreas secretes enzymes that help break down carbohydrates, proteins, and fats.
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38–3
In the nephron, most filtration occurs in the
renal tubule.
capillaries.
glomerulus.
loop of Henle.
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38–3
Urine leaves the body through the
loop of Henle.
glomerulus.
urethra.
bladder.
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38–3
Materials filtered out of the blood include all of the following EXCEPT:
water.
urea.
amino acids.
plasma proteins.
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