Chapter 47 Flashcards
Heterotrophs are divided into what three groups on the basis of their food sources?
herbivores; carnivores; omnivores
What are herbivores?
animals that eat plants exclusively
What are carnivores?
animals that eat other animals
What are omnivores?
animals that eat other animals and plants
How do single-celled organisms and sponges digest their food?
intracellularly
Describe the digestive cavity in cnidarians and planarians.
digestive cavity has only one opening that serves as both a mouth and anus
What is a gastrovascular cavity? (2)
cavity with no specialization in which every cell is exposed to all stages of food digestion; found in cnidarians and planarians
What is the minimum feature necessary for a specialized digestive system?
when the digestive tract as a separate mouth and anus
What is another name for the digestive tract?
alimentary canal
The most primitive digestive tract is found in which organism?
nematodes
Describe the digestive tract in nematodes.
a tubular gut lined by an epithelial membrane
The second most primitive digestive tract, after those in nematodes, can be found in
earthworms
Describe the digestive tract in earthworms.
digestive tract is specialized in different regions for different stages of processing food
What is absorption, in the context of food?
when the products of the chemical digestion pass through the epithelial lining of the gut into the blood
The chemical digestion of food is what type of chemical reaction?
hydrolysis reaction
What are the initial components of the vertebrate gastrointestinal tract? (2)
mouth; pharynx
What is the common passage of the oral and nasal cavities?
the pharynx
Where does the pharynx lead to?
the esophagus
What is the esophagus and what does it do? (2)
muscular tube that delivers food to the stomach; some preliminary digestion occurs here
From the stomach, where does the food go?
small intestine
What happens in the small intestine?
digestive enzymes continue digestive process
The products of digestion in the small intestine are then
absorbed across the wall of the small intestine into the bloodstream, along with water + minerals
What’s left behind after small intestine digestion then goes to
the large intestine, where some remaining water and minerals are absorbed
In vertebrates other than mammals, the large intestine waste products go into
a cavity called the cloaca, which also receives products of the urinary and reproductive system
In mammals, where are urogenital products and fecal matter separated?
in the large intestine
What are the accessory digestive organs? (3)
liver; gallbladder; pancreas
Broadly speaking, what is the liver’s role in digestion?
produces bile
What is bile?
green solution that emulsifies fat
Broadly speaking, what is the gallbladder’s role in digestion?
stores and concentrates bile
Broadly speaking, what is the pancreas’ role in digestion?
produces pancreatic juice
What is pancreatic juice?
mix of digestive enzymes and bicarbonate buffer
What is the name for the first region of the small intestine?
duodenum
Where are bile and pancreatic juice secreted into?
bile and pancreatic juice are secreted into the duodenum
What is the name for the innermost layer of the vertebrate gastrointestinal tract?
mucosa
What is the mucosa?
epithelium that lines the interior (or lumen) of the tract
What is the next major tissue layer after the mucosa?
submucosa
What is the submucosa made of?
connective tissue
What is the next major tissue layer after the submucosa?
muscularis
What is the muscularis made of?
consists of a double layer of smooth muscles
Describe the inner layer of muscles in the muscularis. (2)
circular orientation; serve to constrict the gut
Describe the outer layer of muscles in the muscularis. (2)
arranged longitudinally; work to shorten the gut
What covers the external surface of the digestive tract?
serosa
What is the serosa?
epithelial tissue layer that covers the external surface of the digestive tract
Where are nerve networks located in the digestive tract?
in the submucosa
Describe how nerve networks are arranged in the digestive tract.
intertwined in plexuses between muscle layers
How do birds make up for their lack of teeth?
gizzard
What can be found in the gizzard?
small pebbles that grind up food
How many chambers does a bird stomach have?
2 chambers
Do carnivores have a need to chew their prey?
no, because digestive enzymes can act directly on animal cells
Carnivores have what kind of teeth?
pointed teeth that lack flat grinding surface
Herbivores have what kind of teeth?
flat teeth with complex ridges suited for grinding
How many salivary glands are there in humans?
three pairs of salivary glands
How does the saliva enter the mouth?
by traveling through ducts in the mouth’s mucosal lining
Saliva contains what hydrolytic enzyme?
salivary amylase
What does salivary amylase do?
initiates breakdown of starch into maltose
What is the constant flow of saliva when the mouth is empty?
1/2 mL per minute – necessary to keep mouth moist
What triggers saliva secretion? (3)
presence of food in mouth; taste buds; olfactory neurons
What are the most potent saliva stimuli?
acidic solutions like lemon juice (increases saliva secretion 8x)
Swallowing is what kind of action?
initiated by voluntary control, continued under involuntary control
In mammals, the process of swallowing begins when
the soft palate elevates
What happens when the soft palate elevates? (3)
pushback against wall of pharynx; nasal cavity sealed off; swallowing reflex triggered
What triggers the swallowing reflex?
pushing back against the pharynx
What is the larynx?
voice box
How is food directed into the esophagus instead of the respiratory tract? (2)
motor neurons stimulate the raising of the larynx; glottis is pushed against epiglottis which blocks off trachea
What connects the pharynx and stomach?
esophagus
What is a bolus?
processed lump of food that is moved through the esophagus down to the stomach
How long is the esophagus in adult humans?
25 cm
What portions of the esophagus are devoted to voluntary and involuntary control? (2)
upper third has skeletal muscle for voluntary control; lower two-thirds has smooth muscle for involuntary control
What are peristalsis?
rhythmic, one-directional waves of muscular contractions that move food along the esophagus to the stomach
How are peristalsis useful?
enable vertebrates to swallow even if they are upside down
T/F: peristalsis are bi-directional
false, peristalsis are one-directional
What muscle controls the movement of food from the esophagus to the stomach?
sphincter
A sphincter is made of
a ring of circular smooth muscle
A sphincter opens in response to
pressure exerted by food
Contraction of a sphincter results in
food being blocked from the stomach and going back up the esophagus
Give two examples of animals that cannot regurgitate.
rodents; horses
Describe the sphincter in rodents and horses.
a true sphincter that prevents food from going back up the esophagus
Do humans have a true sphincter?
no, humans lack a true sphincter
What is the stomach?
saclike portion of the digestive tract with a highly convoluted inner surface
Why is the highly convoluted inner surface in the stomach important?
enables it to fold up when empty and expand as it fills with food
What is the volume of the human stomach when empty?
50 mL
What is the volume of the human stomach when full?
2 to 4 L
In the stomach, food being churned is mixed with
gastric juice
What is gastric juice?
an acidic secretion
What secretes gastric juice?
tubular gastric glands of the mucosa
The exocrine glands of the mucosa contain what three kinds of secretory cells?
mucus-secreting cells; parietal cells; chief cells
What do parietal cells do?
secrete HCl
What do chief cells do?
pepsinogen
Which cells secrete HCl?
parietal cells
Which cells secrete pepsinogen?
chief cells
What is pepsinogen?
inactive form of pepsin, a protease
How is pepsinogen converted into pepsin?
HCl causes pepsinogen to unfold and helps remove the 44 amino acids blocking pepsinogen’s active site
Why is it necessary for pepsinogen to first be inactive?
to prevent the chief cells from digesting themselves
What is the purpose of mucus secretions in the stomach?
prevents the interior walls from being digested
In addition to producing HCl, the parietal cells also produce
intrinsic factor
What is intrinsic factor?
polypeptide needed for the intestinal reabsorption of vitamin B12
Vitamin B12 is needed for the production of which cells?
red blood cells
People who lack sufficient intrinsic factor develop
a type of anemia called pernicious anemia
The human stomach produces about how much HCl/other gastric secretions per day?
2 L
What is the pH of the HCl solution produced daily by the stomach?
2
How many more times is gastric juice more acidic than blood?
250k more times
What does active pepsin do?
hydrolyzes food proteins into shorter polypeptides that aren’t fully digested until entering the small intestine
What is chyme?
mixture of partially digested food and gastric juice
What is the only type of molecule digested in the stomach?
only proteins are digested in the stomach; carbs and fats aren’t digested in the stomach
The acidic solution of the stomach kills
bacteria that are ingested with food
Overproduction of gastric acid can lead to
a hole through the wall of the stomach, resulting in a peptic ulcer
Peptic ulcers result from
overproduction of gastric acid
The cause of peptic ulcers is now thought to be because of
the bacterium Heliocobacter pylori
How does H. pylori survive in the face of acidic pH?
it secretes substances that buffer the pH of its surroundings
An infection by H. pylori can result in
weakened mucosal layer in the stomach, allowing acidic secretions to attack the underlying epithelium
Chyme passes through the _____ on the way from the stomach to the small intestine.
pyloric sphincter
Which molecules are absorbed through the wall of the stomach itself? (3)
water from chyme; aspirin; alcohol
Efficient digestion requires that what amounts of chyme be passed from the stomach to the small intestine at any one time?
only relatively small amounts of chyme are introduced at a time
What is the length of the small intestine in a living person?
4.5 m long
What is the length of the small intestine at autopsy when all muscles are relaxed?
6 m long
The duodenum comprises what portion of the small intestine?
the first 25 cm
The remainder of the small intestine is divided into
the jejunum and the ileum
What are the three divisions of the small intestine?
duodenum; jejunum; ileum
The duodenum receives inputs from what three organs?
acidic chyme from stomach; digestive enzymes and bicarbonate from pancreas; bile from liver and gallbladder
The digestion of food cleaved by pancreatic juice primarily occurs in
the jejunum/ileum
What are villi?
fingerlike projections that cover the epithelial wall of the small intestine
What are microvilli?
foldings of the plasma membrane that cover each villus
What is another name for the epithelial wall of the small intestine?
brush border
In addition to absorption, microvilli also participate in
digestion
Brush border enzymes include enzymes that
hydrolyze lactose and sucrose
Lactose intolerance happens because
some adult humans lose the ability to produce the brush border enzyme lactase
Which enzymes start and complete the digestive process?
start - salivary amylase; end - brush border enzymes
Pancreatic fluid is secreted into the duodenum via
the pancreatic duct
The pancreas is what kind of gland?
exocrine gland
Pancreatic fluid contains which enzymes? (4)
trypsin; chymotrypsin; pancreatic amylase; lipase
What do trypsin and chymotrypsin do?
digest proteins
What does pancreatic amylase do?
digests starch
What does lipase do?
digests fat
When secreted into the duodenum, the enzymes of pancreatic fluid are in what state?
inactive state - activated by trypsin
What digests proteins and carbohydrates?
brush border enzymes
What is the purpose of bicarbonate in pancreatic fluid?
neutralizes the HCl from the stomach and gives the chyme in the duodenum a slightly alkaline pH
What are acini?
clusters of secretory cells that produce digestive enzymes and bicarbonate
How does the pancreas function as an endocrine gland?
secretes hormones into the blood that control blood levels of glucose
Endocrine-produced hormones from the pancreas are secreted by
islets of Langerhans
What is the largest internal organ of the body?
the liver
How much does the liver weigh?
1.5 kg
Give three examples of roles the liver serves.
detoxification; protein synthesis; glycogen storage
Alcoholism leads to
cirrhosis
What is the main exocrine secretion of the liver?
bile
What is bile made of?
fluid mixture consisting of bile pigments and bile salts; mixture is delivered into duodenum during digestion of a meal
T/F: bile pigments participate in digestion.
false, bile pigments don’t participate in digestion
What are bile pigments?
waste products resulting from liver’s destruction of RBCs
How are bile pigments excreted?
with feces
What happens in jaundice?
when the excretion of bile pigments in the liver is blocked, pigments accumulate in the blood and cause a yellow staining of tissues
What role do bile salts play in digestion?
bile salts disperse large drops of fat into a fine suspension of smaller droplets, which results in a greater surface area for lipase enzymes
What structural features allow bile salts to prepare fats for enzymatic digestion?
bile salts are partially lipid-soluble and partially water-soluble
The arrival of fatty food in the duodenum stimulates what reflex?
a neural and endocrine reflex that causes the gallbladder to contract and release bile
Bile travels from the gallbladder to the duodenum via
the common bile duct
What are gallstones?
hardened precipitates of cholesterol
What forms of transport are used for amino acids and monosaccharides?
combination of active transport and facilitated diffusion
What forms of transport are used to transport glucose?
coupled transport with Na+ ions (secondary active transport)
What forms of transport are used for fructose?
facilitated diffusion
The blood carries products of digestion from the intestine to the liver via
the hepatic portal vein
What is the first organ to receive most of the products of digestion (other than fat)?
the liver
How are the products of fat digestion absorbed? (5)
fats are hydrolyzed; diffuse into epithelial cells; reassembled into triglycerides; combine with proteins to form chylomicrons; absorbed into lymphatic capillaries
What are chylomicrons?
the combination of a protein and a re-assembled triglyceride
What amount of fluid passes through the small intestine very day?
9 L
How much feces leaves the body?
50 g solid and 100 mL liquid
What is the normal fluid absorption efficiency of the human digestive tract?
99%
What is another name for the large intestine?
colon
What portion of the digestive tract does the large intestine occupy?
last meter
What are the two vestigial structures found at the junction of the small and large intestines?
cecum; appendix
T/F: digestion takes place in the large intestine
FALSE, no digestion occurs in the large intestine
What is the function of the large intestine?
to absorb water, remaining electrolytes, and products of bacterial metabolism (including vitamin K)
Describe the sphincters that control feces passage through the anus. (2)
first is composed of smooth muscle and opens involuntarily in response to pressure inside the rectum; second made of striated muscle is under voluntary control
Can animals digest cellulose?
no, they lack the enzymes necessary, but the digestive tracts can have bacteria that can digest it
Which have longer digestive tracts, herbivores or carnivores?
herbivores
How many chambers are in a ruminant’s stomach?
four
What are the four chambers in the ruminant’s stomach?
reticulum, rumen, omasum, abomasum (true stomach)
What happens in the rumen?
serves as a fermentation vat where bacteria convert cellulose into other molecules
What is rumination?
regurgitating and chewing cud
What is the purpose of rumination?
breaks tougher fiber in the diet into smaller particles
After chewing, what happens to cud?
passed into the omasum and then onto the abomasum, where it’s mixed with gastric juice and digested
Which type of animal has a simple stomach and a large cecum?
nonruminant herbivore
Which type of animal has a four-chambered stomach?
ruminant herbivore
Which type of animal has a short intestine and no cecum?
insectivore
Which type of animal has a short intestine/colon and a small cecum?
carnivore
In most mammals, where are lysozymes primarily found?
sailva and tears
How are lysozymes modified in ruminants and langurs?
they digest bacteria in the stomach
In animals like rabbits and horses, how is cellulose digested?
by microorganisms in the cecum
What is coprophagy?
eating nutrient-packed feces which allows the animal to absorb nutrients provided by microorganisms in the cecum
What synthesizes vitamin K?
intestinal bacteria
When food arrives in the stomach, proteins in the food stimulate the release of what hormone?
gastrin, a stomach hormone, that in turn stimulates the secretion of pepsinogen and HCl
What are enterogastrones?
hormones that mediate stomach/gastric inhibition
What are the three major enterogastrones?
cholecystokinin (CCK); secretin; gastric inhibitory peptide (GIP)
What is the strongest stimulus for CCK and GIP secretions?
chyme with a high fat content
Chyme with a high fat content stimulates which hormones?
CCK and GIP
Increasing chyme acidity stimulates the release of which hormone?
secretin
All three of the enterogastrones inhibit what specific function?
gastric motility (a.k.a. churning action)
What role does CCK play in addition to gastric inhibition?
stimulates increased pancreatic secretions of digestive enzymes and gallbladder contractions
What role does secretin play in addition to gastric inhibition?
stimulate the pancreas to release more bicarbonate
What was the first hormone ever discovered?
secretin
What is the source of CCK/GIP/secretin?
duodenum
CCK and GIP are stimulated by
fatty chyme in the duodenum
Secretin is stimulated by
acidic chyme in the duodenum
Which hormone is structurally similar to gastrin?
CCK
What is the source of gastrin?
pyloric portion of stomach
The liver converts ammonia into
urea
The liver converts steroid hormones into
less active and more water-soluble forms
What produces most of the proteins found in the blood plasma?
the liver
What is edema?
when fluid accumulates in the tissues
From where do the neurons in the brain get their energy?
aerobic respiration of glucose obtained from the blood plasma
What stimulates the storage of glycogen?
insulin (beta cells)
What is glycogenolysis?
breakdown of liver glycogen
What stimulates the breakdown of glycogen?
glucagon (alpha cells)
What is gluconeogenesis?
when the liver converts other molecules like amino acids/lactic acid into glucose
What is the basal metabolic rate (BMR)?
minimum rate of energy consumption under defined resting conditions
The intake of food calories is measured in
kilocalories
Food intake is under what control?
neuroendocrine control
The satiety factor is produced by
the adipose tissue
What is leptin?
a peptide hormone that controls energy sensing, food intake, and energy expenditure
Leptin is produced by
the adipose tissue
How are insulin levels affected by fasting and obesity?
fall with fasting, rise with obesity
GIP and CCK seem to function like leptin and insulin in that
they send the same kind of inhibitory signals to the brain
What does ghrelin do?
stimulates food intake and has receptors in the hypothalamus
Ghrelin levels appear to ____ before feeding
ghrelin levels appear to rise before feeding
What are the two brain neuropeptides implicated in feeding control?
neuropeptide Y (NPY) and alpha-melanocyte-stimulating hormone (a-MSH)
What does NPY do?
induces feeding activity
What does a-MSH do?
suppresses feeding activity
What stimulates the production/release of a-MSH?
leptin
What are essential nutrients?
essential nutrients an animal can’t manufacture itself
Humans require how many vitamins?
13
Humans require how many amino acids”
9
What is the function of vitamin A? (2)
used in making visual pigments; maintaining epithelial tissues
What is the source of vitamin A? (3)
green vegetables; milk products; liver
What are the deficiency symptoms of vitamin A? (2)
night blindness; flaky skin
What is the function of vitamin B1?
coenzyme in CO2 removal during cellular respiration
What is the source of vitamin B1? (3)
meats; grains; legumes
What are the deficiency symptoms of vitamin B1?
Beriberi; weakening of heart; edema
What is another name for vitamin B2?
riboflavin
What is the function of vitamin B2?
part of coenzymes FAD and FMN
What are the deficiency symptoms of vitamin B2? (2)
inflammation and breakdown of skin; eye irritation
What is another name for vitamin B3?
niacin
What is the function of vitamin B3?
part of coenzymes NAD+ and NADP+
What is the source of vitamin B3? (3)
liver; lean meats; grains
What are the deficiency symptoms of vitamin B3? (3)
pellagra; inflammation of nerves; mental disorders
What is another name for vitamin B5?
pantothenic acid
What is the function of vitamin B5?
part of coenzyme A
What are the deficiency symptoms of vitamin B3? (2)
fatigue; loss of coordination
What is another name for vitamin B6?
pyridoxine
What is the function of vitamin B6?
coenzyme in many phases of amino acid metabolism
What is the source of vitamin B6? (3)
cereals; vegetables; meats
What are the deficiency symptoms of vitamin B6? (3)
anemia; convulsions; irritability
What is another name for vitamin B12?
cyanocobalamin
What is the function of vitamin B12?
coenzyme in production of nucleic acids
What is the source of vitamin B12? (2)
red meats; dairy products
What are the deficiency symptoms of vitamin B6?
pernicious anemia
What is the function of biotin?
coenzyme in fat synthesis and amino acid metabolism
What is the source of biotin? (2)
meats; vegetables
What are the deficiency symptoms of biotin? (2)
depression, nausea
What is the function of folic acid?
coenzyme in amino acid and nucleic acid metabolism
What is the source of folic acid?
green vegetables
What are the deficiency symptoms of folic acid? (2)
anemia, diarrhea
What is the function of vitamin C? (4)
forms collagen/cementum of bone/teeth/connective tissue
What is the source of vitamin C?
fruit, green leafy vegetables
What are the deficiency symptoms of vitamin C? (2)
scurvy; breakdown of skin/blood vessels
What is another name for vitamin D?
calciferol
What is the function of vitamin D?
increases absorption of calcium and promotes bone formation
What is the source of vitamin D?
dairy products, cod liver oil
What are the deficiency symptoms of vitamin D? (2)
rickets; bone deformities
What is another name for vitamin E?
tocopherol
What is the function of vitamin E?
protects fatty acids and cell membranes from oxidation
What is the source of vitamin E? (3)
margarine; seeds; green leafy vegetables
What is the function of vitamin K?
essential to blood clotting
What is the source of vitamin K?
green leafy vegetables
What are the deficiency symptoms of vitamin K?
severe bleeding
