Transcript Chapter 21: Digestive and Excretory Systems

Chapter 21:
Digestive and Excretory Systems
21.1 Nutrition
• Nutrition: The process of getting the food needed to
survive.
• Food provides energy and raw materials.
• Malnutrition: Occurs when a person does not get
enough to eat, or when the food eaten does not
provide all of the nutrients needed.
Nutrients:
• The raw materials that the body gets from food.
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Carbohydrates
Proteins
Fats
Vitamins
Minerals
Water
• All are needed by the body each day complete
metabolic jobs.
Carbohydrates:
• The main energy source for the body.
• Sugars and starches are broken down for
energy.
• Sugars: Simple carbohydrates. Make food
sweet.
– Sugar, honey.
• Starch: Complex carbohydrate.
– Bread, pasta, potatoes.
• Fiber: Complex carbohydrate from the cell
walls of plant cells.
– Not broken down by body, but keeps the digestive
system running smoothly.
– Peas, beans, fruits, vegetables, whole grains.
Protein:
• Building blocks of muscle, hair, skin, nails…
• Includes 20 amino acids.
• Essential amino acids: The nine amino acids
that the body cannot make, so needed in the
diet.
• Complete proteins: Contain all 20 amino
acids.
– Animal products.
Fats (lipids):
• Are part of the cell membrane, nerve
insulation, and hormones, are an energy
source, and store energy.
• Saturated fats: Solid at room temperature.
– Usually from animal products.
• Unsaturated fats: Liquid at room
temperature. Oils.
– Usually from plant products.
Vitamins:
• Complex organic molecules that help the body
build tissues and molecules, help regulate
body functions, and fight disease.
• Water soluble vitamins: Cannot be stored by
the body.
– Vitamin C and the B vitamins.
• Fat soluble vitamins: Can be stored in fat
tissue.
– Vitamins D, E, A, and K.
Minerals:
• Inorganic molecules that are needed for
metabolic functions.
• Make bones hard, enable nerve impulses and
muscle contraction, keep fluid balance, and
are incorporated into proteins.
• Examples: calcium, sodium, potassium, iron.
Water:
• Part of most chemical reactions in the body.
Constantly recycled in cells, but needs
replaced because some is lost through
urination, sweating, and breathing.
• Found inside and around cells.
• Largest component of blood.
• Dehydration: Occurs when water is not
replaced in the body.
Calorie:
• How energy stored in food is measured.
• 1 Calorie in heat raises 1 kilogram of water 1
degree Celsius.
• If a person consumes more Calories than are
burned through metabolism, then the excess
energy is stored as fat.
Balanced diet:
• Meals that contain all of the nutrients that the
body needs.
Previous Food Pyramid
www.mypyramid.gov
21.2 The Process of Digestion
• Digestive tract: Tube with the mouth at one
end and the anus at the other end.
• Ingestion: The process through which food
enters the digestive tract.
Digestion:
• The process of breaking down food into small
particles that can pass through cell
membranes.
• Mechanical digestion: Food is physically
chopped up. Creates more surface area for
chemical digestion.
• Chemical digestion: Chemicals break the
bonds in large molecules.
Enzymes:
• Proteins that speed up chemical reactions.
• An enzyme is not changed in the reaction.
Digestive
organs:
Mouth:
• Teeth: Chop food into smaller pieces
(mechanical digestion).
• Salivary glands: Release saliva, which contains
enzymes to start chemical digestion (breaks
down starches) and water to soften food.
• Tongue: Pushes food around mouth and
mixes it with saliva.
• Taste buds: On
top of tongue.
– Sense sweet, sour,
salty, savory
(umami), and
bitter.
Bolus:
• Small food mass that has been chewed and
mixed with saliva.
• Epiglottis: Flap of cartilage that covers
opening of trachea to prevent food from
entering the respiratory tract.
Esophagus:
• Tube that connects the pharynx to the
stomach.
• Lined with cells that secrete mucus to keep
the bolus wet.
• Smooth muscles tissue along the tube
contracts in waves (peristalsis) to push food
toward the stomach.
Stomach:
• Large muscular bag.
• Chemically digests food with acids and
enzymes (pepsin) that break down protein.
• Mechanically breaks down bolus into small
particles and mixes them with stomach
enzymes to create chyme.
• Stores food and slowly releases it into the
small intestine.
• Some cells secrete a mucus layer to protect
the stomach lining from the acid.
– If the mucus layer is damaged, acid can burn the
stomach tissue and cause an ulcer.
Stomach ulcer
Small intestine:
• The final part of digestion happens here. This
is the longest part of the digestive tract.
– 6 meters long, 2.5 centimeters wide
• Duodenum: First section of the small
intestine. Where most digestion occurs.
– Mucus protects the lining from acidic chyme
– Enzymes break down carbohydrates and proteins.
– Liver and pancreas add other enzymes and
chemicals.
– Peristalsis mixes chyme with other chemicals and
pushes the chyme along.
Liver:
• Makes bile, which breaks down fats.
• Gallbladder: Stores bile and “squirts” it into
duodenum through duct as needed.
Pancreas:
• Produces enzymes that digest proteins,
carbohydrates, fats, DNA, and RNA.
• Secretes a basic (alkaline) fluid that neutralizes
acid in the chyme.
21.3 Absorption of Food
• Absorption: The process of moving food
through the intestinal wall into the
bloodstream through diffusion and active
transport.
• Food must be filtered through the cell
membrane to get into the blood.
Small intestine:
• The only place where nutrients from food are
absorbed.
• The inner surface has folds and finger-like
projections (villi) that increase surface area,
and the cells themselves have tiny folds on
their surfaces (microvilli). In each villus is a
small artery, a small vein, capillaries, and a
lymph vessel.
How absorption works:
• Nutrients (sugars, short proteins, some
vitamins and minerals, simple fatty acids) pass
through intestinal cells and are absorbed by
capillaries.
• Fats and fat-soluble vitamins are absorbed by
the lymph vessel in villi, move through the
lymphatic system and enter the blood in the
heart to be carried to the body cells.
Nutrients in the body
• Cells break down some food molecules to
release energy.
– Molecules are converted to glucose (main energy
source), which is broken down during cellular
respiration.
• The energy is stored in ATP.
• Other nutrients are used as building blocks.
– Amino acids build proteins.
– Nucleic acids build DNA and RNA.
• Unused energy is stored in fats.
Large intestine:
• Wider and shorter than small intestine.
• Chyme here contains only indigestible
materials and water.
• Most of the water is reabsorbed.
– Prevents dehydration.
• Bacteria live in the large intestine.
– Digest cellulose (Gives off gas!)
– Secrete vitamin K, thiamine (B1), and niacin (B3)
that are absorbed by the large intestine.
21.4 What is excretion?
• Excretion: The process of waste removal.
– Solids, liquids, and gases.
Solid wastes:
• Feces: Solid material left over after digestion
and absorption of food.
– Contains water, dead bacteria, bile, salts, and
indigestible material (cellulose).
• Cellulose: Humans don’t make the enzymes
necessary to digest it.
– The fibers absorb water, which makes the feces
softer and easier to excrete.
Liquid wastes:
• Urine and sweat. Contain more than 90
percent water.
• Amino acids that are not used immediately for
building are broken down for energy.
– Nitrogen released as ammonia.
– Ammonia converted to less toxic urea.
– Kidneys filter urea out of blood.
• Urine: Contains urea, salts, pigments.
– Yellow color from the breakdown of old red blood
cells.
– Sterile in the upper urinary tract.
– Cleanses tubes.
• Sweat: Contains urea and salts.
– Excreted by glands in the skin that filter fluid
around the cells.
– Cools the body as it evaporates.
Gaseous wastes:
• Carbon dioxide.
– Carried to lungs by blood and excreted during
exhalation.
– Blood carries carbon dioxide in three ways:
• Dissolved in the plasma.
• Bound to hemoglobin.
• As bicarbonate (water plus carbon dioxide) in the
cytoplasm of red blood cells and plasma.
21.5 The Organs of Excretion
• Large intestine:
– Water and salts from chyme are reabsorbed.
– Indigestible food material is compacted into feces.
– Peristalsis moves chyme through large intestine.
• Rectum: Chamber at the end of the large
intestine that stores feces until they are
excreted.
– When the rectum is full, the person gets the urge
to defecate (push solid waste out of the body).
– Anus: The opening at the far end of the large
intestine, where feces leave the body.
Lungs:
• Excrete carbon dioxide.
– Carbon dioxide diffuses into the blood, then
diffuses from the blood to the alveoli, then is
exhaled.
Liver:
• Largest internal organ. Has 4 lobes.
• Functions:
– Makes bile (for fat dissolving)
– Breaks down hemoglobin from old red blood cells.
– Stores glucose, iron, and some vitamins.
– Removes toxins from the blood.
• Breaks down toxins, such as alcohol, into less poisonous
molecules that can be removed by the kidneys.
– Breaks down ammonia to urea.
Kidneys:
• Filter blood, remove urea and other metabolic
wastes, and make urine.
• Blood enters each kidney through arteries off
of the aorta. The arteries branch into capillary
networks that surround nephrons.
• Nephron: The functional unit of the kidney. A
long, coiled tube with a cup at one end.
Nephron:
• The cups are positioned along the outer rim of
the kidneys, and the tubes extend to center.
• The cup surrounds a ball of capillaries called a
glomerulus.
• Blood pressure pushes fluid, along with small
molecules, urea, salts, amino acids, and
glucose, through capillary walls into the
nephron.
• Reabsorption: Kidneys return the molecules
that the body needs (amino acids, glucose,
most of the water) back to the circulatory
system.
• The ends of the nephrons connect in a
collecting duct that brings urine to ureters.
• Ureter: Tube that connects kidneys to
bladder.
• Bladder: Muscular bag that stretches like a
balloon to hold urine.
• Urethra: Tube from bladder out of the body,
through which urine is excreted.
Skin:
• Contains the sweat glands.
– Two kinds:
• Most produce watery sweat, containing water, salt, and
a little urea
• The sweat glands at the base of the hairs in the armpits
and groin produce sweat that contains fatty acids and
proteins.
– Body odor is caused by bacteria breaking down the
fatty acids and proteins.