chapter 34 (digestive system) Flashcards
Digestive system functions
Ingests food
Breaks food down into small molecules that can cross plasma membranes
Absorbs nutrient molecules
Eliminates indigestible remains
Digestive System
Includes all the organs, tissues, and cells involved in ingesting food and breaking it down into smaller components
Contributes to homeostasis by providing body with nutrients needed to sustain life of cells
incomplete digestive tract
has a single opening used as an entrance for food and exit for wastes
complete digestive tract
has two openings
Continuous filter feeders
Always have water moving into the mantle cavity via the incurrent siphon
Particles are deposited on gills.
Size of incurrent siphon permits entry of only small particles.
Do not need food storage area
Discontinuous feeders
Moves rapidly through water using jet propulsion
Uses tentacles to seize prey
Beaklike jaws pull pieces into the mouth with the radula
Food storage area needed
Stomach, with cecum, retains food until digestion is finished
Dentition
differs with mode of nutrition
type, number, arrangement, set of teeth.
Herbivores
Eat only plants
Incisors for clipping
Premolars and molars for grinding
Land snails and some insects are herbivores.
Koalas, which are mammals, eat only eucalyptus leaves.
Grazers, like horses, feed on grasses.
Ruminants, like cattle, goats, and sheep, have a four-chambered stomach which allows them to regurgitate solid material for complete digestion.
Carnivores
Eat only other animals
Pointed incisors and enlarged canines
Shear off pieces small enough to swallow
Spiders and sea stars are carnivores.
Dogs, lions, and dolphins are carnivores.
The lion’s pointed canine teeth are used for
killing, sharp incisors for scraping bones,
and pointed molars for slicing flesh.
Omnivores
Variety of specializations to accommodate both vegetation and meat
Clams and tube worms are invertebrate omnivores.
Humans, pigs, raccoons, and most bears are omnivores.
Dentition of the above is specialized to accommodate vegetable and meat diet.
Better ability to adapt to different food sources
Human Digestive System
Human digestive tract is complete. Part of a tube-within-a-tube body plan Begins with a mouth and ends in an anus Digestion is entirely extracellular. Is mechanical as well as chemical Digestive enzymes are secreted by The wall of the digestive tract Nearby accessory glands
Mouth
Where digestion begins
Tongue
Composed of striated muscle and an outer layer of mucous membrane
Mixes chewed food with saliva
Forms mixture into a bolus
Pharynx
Digestive and respiratory passages come together in the pharynx, then separate.
Soft palate closes off nasopharynx during swallowing
Epiglottis
Epiglottis
Covers the glottis (opening into the trachea)
Keeps food from air passages (most of the time)
Esophagus
Moves food to stomach by peristalsis
Peristalsis – Rhythmical contraction to move contents in tubular organs
Stomach
Stomach wall has deep folds (rugae)
Folds disappear as the stomach fills to an approximate volume of one liter.
Epithelial lining of the stomach has millions of gastric pits, which lead to gastric glands.
Stomach pH
about 2.0, which can kill bacteria in food
pepsin
is a hydrolytic enzyme that acts on protein to produce peptides.
Gastric glands
secrete hydrochloric acid (HCl) and pepsin
what protects the stomach wall from enzymatic action.
A layer of mucus
in the stomach When gastric acid leaks upward
the mucosal lining can be irritated.
GERD
Gastrointestinal reflux disease can cause heartburn
chyme
happens when Food mixes with gastric juices
villi
are ridges on the surface, which contain even smaller ridges called microvilli.
Contain digestive enzymes called brush-border enzymes
Greatly increase the surface area for absorption
what is in the wall of the small intestine
villi
lacteal (lymphatic capillary)
blood capillaries in the villus
large intestine has what pertaining to bacteria?
has a large population of bacteria that break down indigestible material and produce vitamins.
Pancreas
Lies deep in the abdominal cavity
what is the endocrine function of the pancreas
Secretes insulin and glucagon hormones to regulate blood glucose levels
what is the exocrine function of the pancreas
Secretes pancreatic juice and digestive enzymes
Sodium bicarbonate in pancreatic juice neutralizes acid chyme from the stomach.
Pancreatic amylase digests starch
Trypsin digests protein
Lipase digests fat
functions of the liver
Detoxification of the blood Storage of iron and some vitamins Production of plasma proteins Regulation of blood glucose levels Storage of glucose as glycogen Production of urea Removal and storage of iron and vitamins Production of bile Removal of bilirubin Regulation of blood cholesterol levels
Jaundice
yellowing of skin due to excess bilirubin
Hepatitis
inflammation of liver, most commonly caused by a virus
Cirrhosis
scarring of liver tissue, leading to reduced function
Common in alcoholics
is the liver able to regenerate in some cases?
yes
galbladder
Pear-shaped, muscular sac attached to the liver
Stores excess bile
Gallstones form when the cholesterol in bile crystallizes.
Carbohydrates
Carbohydrates are present in food in the form of sugars, starch, and fiber.
Fruits, vegetables, milk, and honey are natural sources of sugars
Monosaccharides
Glucose
Fructose
Disaccharides
Lactose (milk sugar)
Sucrose (table sugar)
After being absorbed from the digestive tract, all sugars are converted to
glucose
glucose is used for
Much of glucose is used for production of ATP by cellular respiration
plants and animals store glucose as:
Plants store glucose as starch.
Animals store glucose as glycogen.
glycogen
Starch is digested to glucose in the digestive tract and excess glucose is stored as
Fiber
Includes various indigestible carbohydrates derived from plants
Food sources rich in fiber include beans, peas, nuts, fruits, and vegetables.
Technically, fiber is not a nutrient for humans:
Cannot be digested
Soluble fiber
combines with bile acids and cholesterol in the small intestine and prevents them from being absorbed.
Insoluble fiber
adds bulk to fecal material.
This bulk stimulates movement in the large intestine, preventing constipation.
Cholesterol can be synthesized
by the body and is found in animal foods.
Lipids
Fat, oils, and cholesterol
Saturated fatty acids
(solids at room temperature) usually come from animals.
Butter, meat, whole milk, and cheeses contain saturated fats.
unsaturated fatty acids
found in plant oils
Proteins
Adequate protein formation requires 20 different types of amino acids.
Nine essential amino acids are required in the diet.
how does body fat accumulate? what are the risks?
Consumption of an excess amount of calories from any source contributes to body fat.
Increases risk of obesity and associated illnesses
what health problems are seen in obese people?
Type 2 diabetes and cardiovascular disease are often seen in people who are obese.
BMI
(BODY MASS INDEX) can be calculated by dividing weight in kilograms by height in meters squared.
Estimates indicate that about 30% of Americans are obese.
Diabetes mellitus
occurs when the hormone insulin is not functioning properly.
May occur due to insulin deficiency or insulin resistance
Excess blood glucose winds up in the urine.
High blood glucose can cause tissue damage and even death.
Type 1 diabetes can be managed by
insulin injections but type 2 is more resistant.
Leading cause of death in the US.
Cardiovascular disease
Cardiovascular disease
Arteries become blocked with plaque.
Plaque contains saturated fats and cholesterol.
Low-density lipoproteins (LDL) and high-density lipoproteins (HDL)
carry cholesterol in the blood.
HDL is “good” and LDL is “bad.”
Vitamins
Organic compounds the body is unable to produce, but are required for metabolic purposes.
The absence of a vitamin may be associated with a particular disorder.
Minerals
The body needs about 20 elements for various physiological functions.
Some individuals don’t get enough iron, calcium, magnesium, or zinc in their diets.
Many people consume too much sodium, which can contribute to hypertension.
