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.• 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.