1. Nutrition and Digestion
Chapter 34

2. Nutrients
Nutrients - substances obtained from the environment that organisms need for growth and survival
Six major categories
Carbohydrates
Lipids
Proteins
Minerals
Vitamins
Water

3. Energy Most energy is provided by carbohydrates and fats
Cells rely on a supply of energy to maintain their activities
Nutrients that supply energy are lipids, carbohydrates, and proteins
Broken down by digestion to their subunits, which are used during cellular respiration
Energy from these subunits is released and is captured in ATP

4. Energy is measured in calories
A calorie - the amount of energy required to raise 1 gram of water 1 degree Celsius
Food calorie content is measured in units of 1,000 calories (kcal) known as Calories
The average human burns 70 Calories per hour at rest, and up to 20 Calories per minute during exercise
People differ in metabolic rate - the speed at which cellular reactions that release energy will occur
Exercise significantly boosts Caloric requirements

5. Carbohydrates A source of quick energy
Include glucose, sucrose, and polysaccharides, long chains of sugar molecules
Cellulose, starch, and glycogen are polysaccharides composed of glucose chains
Cellulose - structural component of plant cell walls
Starch -storage material of plants
Glycogen - used by animals for short-term energy storage

6. Fats and Oils The most concentrated energy source
Contain over 2X as many Calories per unit weight as do carbohydrates or proteins
When an animal’s diet provides more energy than it expends, most of the excess carbohydrates and fats are stored as body fat
Fat is hydrophobic, neither attracts nor dissolves in water
Stored fat does not accumulate water and so more energy can be stored per unit of weight from fats than from other molecules
Fat deposits also provide insulation for animals living in cold environments - seals, whales, walruses

7. Fat Provides Insulation

8. Body Mass Index (BMI) a common tool for estimating a healthy weight
A BMI between 18.5 and 24.9 is healthy
The U.S. Centers for Disease Control and Prevention estimate that about 33% of all U.S. adults are overweight (BMI between 25 and 29.9) and an addition 33% are obese (BMI of 30 or more)

9. Essential Nutrients Provide raw materials
Our cells can synthesize most of the molecules our bodies require, but they cannot synthesize certain raw materials, called essential nutrients, which must be supplied in the diet
Essential Nutrients for humans include certain fatty acids, amino acids, a variety of minerals, vitamins, and water

10. Essential Fatty Acids
Certain fatty acids are essential in the human diet
Fats and oils provide a source of energy and essential fatty acids
Essential fatty acids serve as raw materials used to synthesize molecules in a wide range of physiological activities
They help us absorb fat-soluble vitamins, are important in cell division, fetal development, and immune response
Sources of essential fatty acids are fish oils, canola oil, soybean oil, flaxseed, walnuts

11. Amino Acids Building blocks of protein
Protein from food is broken down into its amino acid subunits, which can be used to synthesize new proteins
Protein functions in the body - act as enzymes, receptors on cell membranes, oxygen transport molecules, structural proteins, antibodies, muscle proteins
Humans are unable to synthesize of the 20 amino acids needed
Must be obtained in the diet, are called essential amino acids
Protein-rich foods - meat, milk, eggs, corn, beans, soybeans

12. Kwashiorkor is Caused by Protein Deficiency
Symptoms:
Changes in skin pigment
Decreased muscle mass
Diarrhea
Failure to gain weight and grow
Fatigue
Hair changes

13. Minerals
Minerals - elements that play a role in animal nutrition and can only be obtained in diet or drinking water
Calcium, magnesium, and phosphorus are components of bone and teeth
Sodium, calcium, and potassium - needed for muscle contraction and nerve impulses
Iron - hemoglobin in the blood
Iodine - hormones produced by the thyroid gland
Animals also require trace amounts of zinc, magnesium, copper, and chromium

15. Vitamins Play a role in metabolism
Vitamins - organic molecules that animals require in small amounts for normal cell function, growth, and development
Vitamins are required for the proper functioning of enzymes that control metabolic reactions in the body
Vitamins are essential nutrients that the body cannot synthesize and must be obtained in the diet
They are grouped into two categories: water soluble or fat soluble

16. Water Soluble Vitamins - B, C

17. Water-soluble vitamins
Vitamin C and the nine compounds that make up B-vitamin complex
Because these substances dissolve in the watery blood plasma and are filtered out by the kidneys, they are not stored in appreciable amounts
Most act as coenzymes -work in conjunction with enzymes to promote chemical reactions
Each vitamin participates in several metabolic processes so the deficiency of one vitamin can have wide-ranging effects
For example, folic acid is required to synthesize thymine, a nucleotide; folic acid deficiency impairs cell division
Important for pregnant women to get enough folic acid to supply a rapidly growing fetus
Folic acid deficiency leads to a reduction in red blood cells and anemia

18. Fat Soluble Vitamins - ADEK

19. Pellagra Is Caused by Niacin Deficiency

20. Fat-soluble Vitamins
Can be stored in body fat and accumulates over time
Vitamin A is used to synthesize the light-capturing molecule in the retina of the eye
Vitamin D is required for bone formation
Deficiency can lead to bone deformities such as rickets
Rickets Photos
Vitamin E is an antioxidant, neutralizing free radicals that form in the body
Vitamin K helps to regulate blood clotting

21. Water The human body is about 60% water
A person can survive longer without food than without water
All metabolic reactions occur in solution, and water participates directly in hydrolysis reactions that break down proteins, carbohydrates, fats
Water is the principal component of saliva, blood, lymph, extracellular fluid, and cytoplasmic fluid
By sweating, people use evaporation of water to prevent overheating
Urine, mostly water, is necessary to eliminate cellular waste products

22. Digestion
Digestion - the process that physically and chemically breaks down food, accomplished by digestive systems
Takes in food and digests complex molecules into simpler molecules that can be used by the body
Material that cannot be absorbed is expelled

23. Digestive Systems Perform 5 Tasks
Ingestion: Food is brought into the digestive tract through an opening, usually a mouth
Mechanical digestion: Food is physically broken down into smaller pieces that have a greater surface area, allowing digestive enzymes to attack them more efficiently
Chemical digestion: Digestive chemicals and enzymes break down large food molecules into smaller subunits
Absorption: The small subunits are transported out of the digestive tract through cells lining the digestive tract to the blood for use by body cells
Elimination: Indigestible materials are expelled from body

24. How do sponges digest?
Sedentary filter-feeders that lack a digestive chamber
Rely on intracellular digestion, occurs in individual cells
Digestion takes place in collar cells lining water-filled sponge chambers
Sponges are permanently attached to rocks, circulating seawater and food particles through pores in their bodies
Collar cells engulf food particles in the water and ingest them using phagocytosis, forming a food vacuole
The food vacuole fuses with a lysozome, a packet of digestive enzymes within the cell that breaks down the food into smaller molecules
Smaller food molecules are absorbed into the cell cytoplasm
Indigestible material is expelled from the cell and sponge through a large opening in the body wall

25. Intracellular Digestion in a Sponge
Water, uneaten food,
and wastes are expelled
through the large opening
at one end of the sponge 6
Waste products are
expelled by exocytosis 5
H2O
H2O
(a) Tube sponges
The food
vacuole merges
with a lysosome 4
collar cell
H2O Carrying
food particles
enters the pores 1
collar
H2O
H2O
Food particles
are filtered from the
water by the collar 2
lysosome
with
digestive
enzymes
Food enters the
collar cell by phagocytosis,
forming a food vacuole 3
food vacuole
(b) A simple sponge
(c) Collar cell

26. Extracellular Digestion
The simplest digestive system is a chamber with one opening
All other types of animals evolved a chamber within the body in which chunks of food are broken down by enzymes outside the cells, a process called extracellular digestion
A sac with one opening is the simplest digestive system, and is found in the cnidarians such as sea anemones, Hydra, and sea jellies

27. Gastrovascular Cavity
Gastrovascular cavity - a single opening at one end that acts as both a mouth and an anus
Food is captured by stinging tentacles that bring food to the mouth and into the gastrovascular cavity
Gland cells lining the gastrovascular cavity release enzymes and digest the prey
Nutritive cells lining the cavity then absorb the nutrients, and food particles are engulfed by phagocytosis
Further digestion occurs within the vacuoles in the nutritive cells and undigested wastes are expelled through the mouth

28. Digestion in a Sac prey (a) Hydra with prey Tentacles with
stinging cells capture
the prey and carry
it into the mouth 1
mouth
Gland cells secrete
digestive enzymes into
the gastrovascular
cavity and begin
extracellular digestion 2
prey
Nutritive cells engulf
food particles and
complete digestion
within food vacuoles 3
gastrovascular
cavity
(b) Food processing in Hydra

29. Tubular Digestive Systems
Most animals have tubular digestive systems with specialized compartments
Most invertebrate animals—mollusks, arthropods, echinoderms, earthworms, and all vertebrates—have digestive systems that are one-way tubes that begin with a mouth and end with an anus
Specialized regions within the tube physically grind up the food and enzymatically break it down, absorbing the nutrients, and expelling the wastes through the anus

30. Earthworm
As it burrows the worm ingests soil through the esophagus, a muscular tube leading from the mouth to the crop, an expandable sac where food is stored
The food is released into the gizzard, where sand grains and muscular contractions grind it into smaller particles
In the intestine, enzymes breaks down food particles, producing small molecules that are absorbed into the worm’s body
Undigested organic matter is expelled through the anus

31. A Tubular Digestive System4 1 3 2

32. Vertebrate Digestion Specializations
Different animals have radically different diets
Carnivores -wolves, cats, seals, and predatory birds - eat other animals
Herbivores - eat only plants - seed-eating birds, deer, camels, cows, many rodents such as mice
Omnivores - humans, bears, and raccoons - eat both animals and plants

33. Teeth
The teeth of omnivores, carnivores, and herbivores are adapted to their diet
Incisors for biting
Canines for tearing
Premolars for grinding
Molars for crushing and chewing

34. Omnivores, like humans, have flat incisors for shearing food, small canines, and large premolars and molars for crushing and grinding
Carnivores have enlarged canines for stabbing and tearing flesh, and molars and premolars with sharp edges for shearing through tendon and bone
Herbivores have reduced canines but large incisors for snipping plants, and big, flattened premolars and molars for grinding plant material

35. Teeth Have Evolved to Suit Different Diets

36. Birds Bird’s stomachs grind food
Birds lack teeth and swallow their food whole
The food passes through a muscular esophagus and enters the crop, which stores and moistens the food
The food enters the stomach, the first chamber secretes protein-digesting enzymes, and the second chamber (a thick- walled, muscular chamber) grinds the food
The food enters the gizzard and ground further
Pulverized food particles are released to the small intestine, where they are further digested and nutrients absorbed

37. Bird Digestive Adaptations
Crop:
Stores and
moistens food
Stomach chamber #1:
Secretes protein-digesting enzymes
and begins protein digestion
Stomach chamber #2 (gizzard):
Crushes and grinds food
large intestine
esophagus
liver
anus
small
intestine

38. Ruminant Specialized stomachs allow ruminants to digest cellulose
Ruminant herbivores are able to break down cellulose and extract nutrients from tough plant matter
These animals have elaborate digestive systems that house microorganisms able to break down cellulose
Ruminants have multiple stomach chambers that contribute to the digestion of plant cellulose
The first chamber is the rumen, which houses microorganisms that use enzymes to break down and ferment cellulose and other carbohydrates
The plant material enters the reticulum, where it is formed into a cud that is regurgitated, chewed, and swallowed back into the rumen
The partially digested plant material enters the omasum where water, salts, and some small organic molecules are absorbed
Plant material is then passed to the abomasum, where acid and protein- digesting enzymes begin protein digestion
Most of the products of digestion are absorbed through the wall of the small intestine

41. Small Intestine Small intestine length is correlated with diet
Because cellulose is difficult to digest, herbivore intestines are long, to allow more time for nutrient absorption
Carnivore intestines are relatively short because proteins are easy to digest
In frogs the herbivorous tadpole has a long small intestine, but the carnivorous frog intestine shortens to one-third its tadpole length

42. Human Digestive System
The human digestive system, which is adapted for processing a wide variety of foods, provides a good example of the mammalian digestive system

43. The Human Digestive Tract
Salivary glands: Secrete
lubricating fluid and
starch-digesting enzymes
Pharynx: Shared digestive
and respiratory passage
Oral cavity, tongue,
teeth:
Epiglottis: Directs food
down the esophagus
Stomach: Breaks down
food and begins protein
digestion
Esophagus: Transports
food to the stomach
Liver: Secretes bile (also
has many non-digestive
functions)
Gallbladder: Stores
bile from the liver
Small intestine:
Food is digested
and absorbed
Pancreas: Secretes pH
buffers and several
digestive enzymes
Rectum: Stores
Large intestine: Absorbs
vitamins, minerals, and
water; houses bacteria;
produces feces

44. Animation: Overview of the Digestive System

45. Mechanical and Chemical Digestion
Chewing begins the mechanical breakdown of food
Three pairs of salivary glands produce saliva to begin chemical digestion
The functions of saliva include:
Saliva contains amylase - breaks starch into sugars
It contains bacteria-killing enzymes and antibodies to guard against infection
It lubricates food to ease swallowing
It dissolves some molecules, acids and sugars, exposing them to taste buds on tongue, which helps to identify the type and quality of food

47. How Do Humans Digest Food?
The tongue pushes food into the pharynx
The epiglottis folds over the larynx (leads to the trachea and the lungs) keeps swallowed food from entering the trachea
The esophagus conducts food to the stomach, mechanical and chemical digestion
Swallowing forces food into a muscular tube - esophagus
Muscles surrounding the esophagus produce waves of muscular contraction, called peristalsis, which propel food to the stomach and though the rest of the digestive tract

48. The Challenge of Swallowing
tongue 1
roof of mouth
The
tongue forces
food into the
esophagus
food
The tongue
manipulates
food while
chewing
pharynx
epiglottis
The larynx moves
up and the epiglottis
folds over the larynx 2
epiglottis
esophagus
food
The epiglottis is
elevated to allow air
to flow through the
pharynx into the larynx
larynx
esophagus
Food enters
the esophagus 3
larynx
(a) Before swallowing
(b) During swallowing

49. Stomach
Food enters the stomach, expandable muscular sac
Food is held in the stomach by two rings of circular muscles, called sphincter muscles
The sphincter at the top, the lower esophageal sphincter, keeps food and acid from sloshing up into the esophagus
A second sphincter, the pyloric sphincter, separates the lower portion of the stomach from the upper small intestine, regulating the passage of food into the small intestine

50. The Stomach lower esophageal sphincter muscle layers pyloric sphincter
lining
outer
membrane
small intestine

51. Four Functions of the Stomach
It stores food and gradually releases it into the small intestine at a rate that allows the small intestine to completely digest the food and absorb the nutrients
It produces a variety of churning contractions for the mechanical breakdown of food
It begins protein breakdown using secretions from gastric glands, clusters of specialized epithelial cells that line the stomach
It secretes the digestion-regulating hormone gastrin

52. Gastric Gland Secretions
Hydrochloric acid, pepsinogen, and mucus
Hydrochloric acid (HCl) gives the stomach an acidic pH of 1 – 3 which destroys many microbes swallowed along with food
Pepsinogen is the inactive form of pepsin, a type of protease—a protein-digesting enzyme
The stomach’s acidity converts inactive pepsinogen into pepsin, its active form
Mucus coats the stomach and as a barrier to self-digestion
Food in the stomach is converted to chyme, a mixture of partially digested food and stomach secretions
Peristaltic waves move the chyme toward the small intestine

53. Small Intestine Most chemical digestion occurs in the small intestine
The small intestine - a long, narrow tube that receives food from the stomach
The main functions are to chemically digest food into small molecules and to absorb these molecules into the body
Most fat and carbohydrate digestion occurs in the small intestine, and protein digestion started in the stomach is completed here

54. Digestive Secretions also come from…
After the stomach releases chyme into the small intestine, chemical digestion is accomplished with the aid of enzymes and other digestive secretions from three sources:
The liver
The pancreas
The cells of the small intestine

55. Liver and Gallbladder
The liver and gallbladder provide bile which helps break down fats
Functions of the liver
It stores fats and carbohydrates
It regulates blood glucose levels
It synthesizes blood proteins
It stores iron and certain vitamins
It converts ammonia into urea
It detoxifies harmful substances
It produces a liquid called bile, which is stored in the gallbladder
The bile is released through the bile duct and empties into the first segment of the small intestine, the duodenum

56. Digestive Secretions into the Small Intestine
Liver: Produces bile, which is
stored in the gallbladder
Gallbladder: Stores
and releases bile into
the small intestine via
the bile duct
Stomach: Releases
acidic chyme into
the small intestine
Pancreas: Produces sodium
bicarbonate and digestive
enzymes, and releases them
into the small intestine via
the pancreatic duct
Cells in small intestine
lining: Produce enzymes
that complete carbohydrate
and protein digestion
bile duct
duodenum
pancreatic
duct

57. Bile A mixture made of bile salts, water, other salts, cholesterol
Bile salts emulsify large fat globs into microscopic particles
Lipid-digesting enzymes from the pancreas, called lipases, are able to attack the fat molecules due to the increased surface area for digestion produced by emulsification

58. Pancreas Supplies several digestive secretions to the small intestine
Lies between the stomach and small intestine
Two types of cells
One type produces hormones that regulate blood sugar concentration
The other secretes pancreatic juice, a digestive secretion that is released into the small intestine through the pancreatic duct
Pancreatic juice contains:
Water
Sodium bicarbonate, which neutralizes the acidic chyme
Digestive enzymes
Amylase breaks down carbohydrates
Lipases break down lipids
Proteases break down proteins and peptides

59. Microvilli in Small Intestine
The digestive process is completed by cells of the intestinal wall
Small intestinal cells have microscopic projections or microvilli that increase the surface area for absorption and release enzymes that complete the digestion process
Some enzymes complete the breakdown of peptides to amino acids
Other enzymes break disaccharides into monosaccharides
Additional enzymes digest lipids
Most absorption occurs in the small intestine
The intestinal lining provides a large surface area for absorption
The small intestine has numerous folds with fingerlike projections, called villi, on its surface to increase absorptive surface area
Each villus cell has many microvilli that increase surface area even more

60. The Structure of the Small Intestine
fold of the
intestinal
lining
capillaries
microvilli
villi
lacteal
arteriole
intestinal
gland
lymph
vessel
venule
(a) Small intestine
(b) A fold of the
intestinal lining
(c) A villus
(d) Cells of a villus

61. Movement in the Small Intestine
Unsynchronized contractions of the circular muscles of the small intestine, called segmentation movements, slosh the chyme back and forth, bringing nutrients into contact with the enormous surface area of the small intestine
After absorption is complete, peristaltic waves conduct the leftovers into the large intestine

62. Movement out of the Small Intestine
Nutrients are transported through the intestinal wall in several ways
Each intestinal villus contains capillaries and lymph vessels, called lacteals, that are responsible for the collection of absorbed nutrients that pass across the intestinal cells
Nutrients are absorbed into intestinal cells by diffusion or active transport, and then diffuses from the cell to the bloodstream
Water is absorbed by osmosis
Fats are absorbed into the lacteals as chylomicrons, which then enter lymphatic capillaries that lead to the bloodstream

63. Large Intestine
Water is absorbed and feces are formed in the large intestine
The large intestine is about 5 feet long and 2.5 inches wide; most is called the colon, the last 6 inches is the rectum
A mix of water, undigested nutrients, fiber enter the large intestine
The remaining semisolid material is called feces
The feces is transported by peristaltic contractions to the rectum, which expands and stimulates defecation
The large intestine contains bacteria that consume unabsorbed nutrients and synthesize vitamins such as vitamin B12, thiamin, riboflavin, and vitamin K
The large intestine absorbs vitamins, water, and salts

64. Animation: The Digestion of Food

65. Control of Digestion Controlled by the nervous system and hormones
Food triggers nervous system responses
The nervous system responds to sensory input, such as sight, smell, taste, and even thought of food
Signals from the brain act on the salivary glands and other parts of the digestive system, preparing it to digest and absorb food
Hormones help regulate digestive activity
Hormones secreted by the digestive system enter the bloodstream and circulate through the body, acting on receptors within the digestive tract
Like most hormones, they are regulated by negative feedback

66. Examples of Hormonal Control
For example, the amino acids and peptides in chime stimulate cells in the stomach lining to release gastrin into the bloodstream
Gastrin stimulates further acid secretion in the stomach, which promotes protein digestion
When the pH of the stomach reaches a high level of acidity, this inhibits gastrin secretion, which in turn inhibits further acid production

67. Negative Feedback Controls Stomach Acidity
chyme
stimulates
gastrin secretion
inhibits
stimulates
acid secretion

68. Two additional hormones are released by cells of the duodenum in response to the acidity and nutrients in chyme, particularly peptides and fats
Secretin slows stomach acid production and inhibits stomach contractions
Cholecystokinin stimulates the pancreas to release enzymes and the gallbladder to release bile \
These hormones help regulate the chemical environment within the small intestine, and the rate at which chyme enters, promoting optimal digestion and absorption of nutrients