Biology in Focus - Chapter 33
Transcript of Biology in Focus - Chapter 33
CAMPBELL BIOLOGY IN FOCUS
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Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge
33Animal Nutrition
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Food is taken in, taken apart, and taken up in the process of animal nutrition
In general, animals fall into three categories
Herbivores eat mainly plants and algae
Carnivores eat other animals
Omnivores regularly consume animals as well as plants or algae
Most animals are also opportunistic feeders
Overview: The Need to Feed
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Figure 33.1
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Concept 33.1: An animal’s diet must supply chemical energy, organic molecules, and essential nutrients
An animal’s diet provides
Chemical energy, which is converted into ATP to power cellular processes
Organic building blocks, such as organic carbon and organic nitrogen, to synthesize a variety of organic molecules
Essential nutrients, which are required by cells and must be obtained from dietary sources
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Essential Nutrients
Essential nutrients must be obtained from an animal’s diet
There are four classes of essential nutrients
Essential amino acids
Essential fatty acids
Vitamins
Minerals
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Figure 33.2
Iron cofactor
Essentialaminoacids
NADH coenzyme(vitamin B3)
NADH
Fatty acid desaturase
γ-Linoleic acid
Phospholipids
Prostaglandins
Gly
Ile
Leu
Phe
Phe
Tyr
Glu
Linoleic acid
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In animals, fatty acids are converted into a variety of cellular components, such as membrane phospholipids, signaling molecules, and storage fats
Essential fatty acids can be synthesized by plants
Deficiencies of essential fatty acids are rare
Essential Fatty Acids and Amino Acids
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Animals require 20 amino acids and can synthesize about half from molecules in their diet
The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form
Meat, eggs, and cheese provide all the essential amino acids and are thus “complete” proteins
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Most plant proteins are incomplete in amino acid composition
Individuals who eat only plant proteins need to eat specific plant combinations to get all the essential amino acids
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Vitamins
Vitamins are organic molecules required in the diet in small amounts
Thirteen vitamins are essential for humans
Vitamins are grouped into two categories: fat-soluble and water-soluble
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Minerals
Minerals are simple inorganic nutrients, usually required in small amounts
Ingesting large amounts of some minerals can upset homeostatic balance
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Dietary Deficiencies
Malnutrition results from the long-term absence from the diet of one or more essential nutrients
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Deficiencies in Essential Nutrients
Deficiencies in essential nutrients can cause deformities, disease, and death
Animals may consume salt, minerals, shells, or stones to prevent mineral deficiencies
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Figure 33.3
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A diet with insufficient amounts of one or more amino acids is the most common type of malnutrition among humans
Individuals subsisting on simple rice diets are often deficient in vitamin A
To overcome this, scientists have engineered a strain of rice that synthesizes beta-carotene, which is converted to vitamin A in the body
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Undernutrition results when a diet does not provide enough chemical energy
An undernourished individual will
Use up stored fat and carbohydrates
Break down its own proteins
Lose muscle mass
Suffer protein deficiency of the brain
Die or suffer irreversible damage
Undernutrition
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Assessing Nutritional Needs
Genetic defects that disrupt food uptake provide information about human nutrition
For example, hemochromatosis causes iron buildup without excessive iron intake
Insights into human nutrition have come from epidemiology, the study of human health and disease in populations
Neural tube defects were found to be the result of a deficiency in folic acid in pregnant mothers
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Concept 33.2: The main stages of food processing are ingestion, digestion, absorption, and elimination
Food processing can be divided into four distinct stages
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Figure 33.4
Mechanicaldigestion
Nutrient moleculesenter body cells
Chemicaldigestion(enzymatichydrolysis)
Undigestedmaterial
EliminationAbsorptionDigestionIngestion1 2 3 4
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Ingestion is the act of eating or feeding
Strategies for extracting resources from food differ widely among animals
Video: Shark Eating a Seal
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Figure 33.5
Filter feeders Substrate feeders Fluid feeders
Bulk feeders
Caterpillar Feces
Baleen
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Figure 33.5a
Filter feeders
Baleen
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Figure 33.5b
Substrate feeders
Caterpillar Feces
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Figure 33.5c
Fluid feeders
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Figure 33.5d
Bulk feeders
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Digestion is the process of breaking food down into molecules small enough to absorb
Mechanical digestion, including chewing, increases the surface area of food
Chemical digestion splits food into small molecules that can pass through membranes
In chemical digestion, the process of enzymatic hydrolysis splits bonds in molecules with the addition of water
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Absorption is uptake of nutrients by body cells
Elimination is the passage of undigested material out of the digestive system
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Digestive Compartments
Most animals process food in specialized compartments
These compartments reduce the risk of an animal digesting its own cells and tissues
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Intracellular Digestion
In intracellular digestion, food particles are engulfed by phagocytosis
Food vacuoles, containing food, fuse with lysosomes containing hydrolytic enzymes
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Extracellular Digestion
Extracellular digestion is the breakdown of food particles outside of cells
It occurs in compartments that are continuous with the outside of the animal’s body
Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients
Video: Hydra Eating
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Figure 33.6
Mouth
Tentacles
Digestive enzymesreleased
Food particlesbroken down
Food particlesengulfed and digested
GastrodermisEpidermis
Food
1
2
3
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More complex animals have a complete digestive tract or an alimentary canal with a mouth and an anus
The alimentary canal can have specialized regions that carry out digestion and absorption in a stepwise fashion
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Figure 33.7
Crop
Gizzard
Intestine
Anus
Esophagus
Pharynx
Mouth
(a) Earthworm
EsophagusCrop
StomachGizzard
Intestine
Anus
Mouth
(c) Bird(b) Grasshopper
MouthCrop Gastric
cecae
AnusRectumEsophagus
Foregut Midgut Hindgut
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Concept 33.3: Organs specialized for sequential stages of food processing form the mammalian digestive system
The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts
Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder
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Figure 33.8
Tongue
Salivaryglands
Liver
Gall-bladder
Pancreas
SmallintestineLargeintestine
Rectum
Anus
Oral cavity
Pharynx
Esophagus
Sphincter
Sphincter
Stomach
Liver
Pancreas
Gallbladder
Duodenum ofsmall intestine
Stomach
Smallintestine
Largeintestine
RectumAnus
Salivaryglands
Esophagus
Mouth
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Figure 33.8a
Liver
Pancreas
GallbladderStomach
Smallintestine
Largeintestine
RectumAnus
SalivaryglandsEsophagus
Mouth
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Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal
Valves called sphincters regulate the movement of material between compartments
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The Oral Cavity, Pharynx, and Esophagus
The first stage of digestion is mechanical and takes place in the oral cavity
Salivary glands deliver saliva to the oral cavity through ducts
Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers
Saliva also contains mucus, a viscous mixture of water, salts, cells, and glycoproteins
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The tongue shapes food into a bolus and provides help with swallowing
The throat, or pharynx, is the junction that opens to both the esophagus and the trachea
The esophagus connects to the stomach
The trachea (windpipe) leads to the lungs
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Swallowing must be carefully choreographed to avoid choking
The esophagus conducts food from the pharynx down to the stomach through rhythmic cycles of contraction
The form of the esophagus fits its function and varies among species
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Digestion in the Stomach
The stomach stores food and secretes gastric juice, which converts a meal to a mixture of food and digestive juice called chyme
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Figure 33.9
Esophagus
Sphincter
Sphincter
Stomach
Folds ofepithelialtissue
Smallintestine
Epithelium
Production of gastricjuice
Pepsinogen andHCI secreted intolumen
HCI convertspepsinogen topepsin.
Pepsin activatesmore pepsinogen,starting a chainreaction.
Parietalcell
Pepsin(activeenzyme)
Chiefcell
Pepsinogen1
2
3
1
2
3
Gastric gland
Mucous cell
Chief cell
Parietal cell
Gastric piton the interiorsurface ofstomach
10 µ
m
HCI
H+
Cl−
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Figure 33.9a
Gastric gland
Mucous cell
Chief cell
Parietal cell
Gastric piton the interiorsurface ofstomach Epithelium
Parietalcell
Pepsin(activeenzyme)
Chiefcell
HCI
H+
Cl−
Pepsinogen
1
2
3
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Figure 33.9b-1
Production of gastricjuice
Pepsinogen andHCI secreted intolumen
Parietalcell
Chiefcell
HCI
H+
Cl−
Pepsinogen1
1
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Figure 33.9b-2
Production of gastricjuice
Pepsinogen andHCI secreted intolumen
HCI convertspepsinogen topepsin.
Parietalcell
Pepsin(activeenzyme)
Chiefcell
HCI
H+
Pepsinogen
2
1
1
2
Cl−
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Figure 33.9b-3
Production of gastricjuice
Pepsinogen andHCI secreted intolumen
HCI convertspepsinogen topepsin.
Pepsin activatesmore pepsinogen,starting a chainreaction.
Parietalcell
Pepsin(activeenzyme)
Chiefcell
HCI
H+
Pepsinogen
3
2
1
1
2
3
Cl−
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Figure 33.9c
Gastric pit on the interiorsurface of stomach
10 µ
m
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Chemical Digestion in the Stomach
Gastric juice has a low pH of about 2, which kills bacteria and denatures proteins
Gastric juice is made up of hydrochloric acid (HCl) and pepsin
Pepsin is a protease, or protein-digesting enzyme, that cleaves proteins into smaller peptides
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Figure 33.10
Fat digestion
Fat(triglycerides)
Glycerol,fatty acids,monoglycerides
Pancreaticlipase
Pancreaticnucleases
Nucleotidases
Pepsin
Pancreatic trypsinand chymotrypsin
Pancreaticcarboxypeptidase
Dipeptidases,carboxypeptidase,and aminopeptidaseDisaccharidases
Pancreatic amylases
Disaccharides
Monosaccharides Amino acids
Small peptides
Smallerpolypeptides
Small polypeptides
Nucleotides
Nucleosides
Nitrogenous bases,sugars, phosphates
Nucleosidasesandphosphatases
DNA, RNA
Nucleic aciddigestion
Protein digestion
Proteins
MaltoseSmallerpolysaccharides
Polysaccharides(starch, glycogen)
Disaccharides(sucrose,
lactose)
Carbohydrate digestionOral cavity,pharynx,esophagus
Smallintestine(enzymesfrompancreas)
Stomach
Smallintestine(enzymesfromepithelium)
Salivary amylase
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Figure 33.10a
MaltoseSmallerpolysaccharides
Polysaccharides
Carbohydrate digestion
Oral cavity, pharynx, esophagus
Salivary amylase
Disaccharides
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Figure 33.10b
Pepsin
Small polypeptides
Protein digestion
Proteins
Stomach
Carbohydrate digestion
DisaccharidesMaltoseSmallerpolysaccharides
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Figure 33.10c
Fat digestion
Fat(triglycerides)
Glycerol,fatty acids,monoglycerides
Pancreaticlipase
Pancreaticnucleases
Pancreatic trypsinand chymotrypsin
Pancreaticcarboxypeptidase
Pancreatic amylases
Disaccharides
Smallpeptides
Smallerpolypeptides
Small polypeptides
Nucleotides
DNA, RNA
Small intestine (enzymes from pancreas)
Nucleic aciddigestion
Protein digestion
Polysaccharides Disaccha-rides
Carbohydrate digestion
Aminoacids
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Figure 33.10d
NucleotidasesDipeptidases,carboxypeptidase,and aminopeptidase
Disaccharidases
Monosaccharides Amino acids
Nucleosides
Nitrogenous bases,sugars, phosphates
Nucleosidasesandphosphatases
Small intestine (enzymes from epithelium)
Nucleic aciddigestion
Protein digestionCarbohydrate digestion
Disaccharides Amino acidsSmallpeptides
Nucleotides
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Mucus protects the stomach lining from gastric juice
Also, cell division adds a new epithelial layer every three days, to replace any cells damaged by digestive juices
Gastric ulcers, lesions in the stomach lining, are caused mainly by the bacterium Helicobacter pylori
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Stomach Dynamics
Coordinated contraction and relaxation of stomach muscle churn the stomach’s contents
Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine
Stomach contents typically pass into the small intestine 2–6 hours after a meal
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Digestion in the Small Intestine
The small intestine is the longest section of the alimentary canal
It is the major organ of digestion and absorption
The first portion of the small intestine is the duodenum
Here, chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the intestinal wall
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Pancreatic Secretions
The pancreas produces proteases trypsin and chymotrypsin, which are activated in the lumen of the duodenum
Its solution is alkaline and neutralizes the acidic chyme
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Bile Production by the Liver
In the small intestine, bile aids in digestion and absorption of fats
Bile is made in the liver and stored in the gallbladder
Bile also destroys nonfunctional red blood cells
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Secretions of the Small Intestine
The epithelial lining of the duodenum produces several digestive enzymes
Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine
Most digestion occurs in the duodenum; the jejunum and ileum function mainly in absorption of nutrients and water
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Figure 33.11
Vein carryingblood to liver
Microvilli (brushborder) at apical(lumenal) surface
Villi
Lumen
Basalsurface
Lymphvessel
Capillary
Epithelialcells
(towardcapillary)
Bloodcapillaries
Epithelialcells
Largecircularfolds
Muscle layers
VilliIntestinalwall
Nutrientabsorption
Lacteal
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Figure 33.11a
Vein carryingblood to liver
Largecircularfolds
Muscle layers
VilliIntestinalwall
Nutrientabsorption
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Figure 33.11b
Microvilli (brushborder) at apical(lumenal) surface
Villi
Lumen
Basalsurface
Lymphvessel
Capillary
Epithelialcells
(towardcapillary)
Bloodcapillaries
Epithelialcells
Lacteal
Nutrientabsorption
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Absorption in the Small Intestine
The small intestine has a huge surface area, due to villi and microvilli that project into the intestinal lumen
The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption
Transport across the epithelial cells can be passive or active depending on the nutrient
Animation: Membrane Transport
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Figure 33.12
Triglyceridesare broken downto fatty acids andmonoglyceridesby lipase.
Monoglyceridesand fatty acids diffuseinto epithelial cellsand are re-formed intotriglycerides.
Triglycerides areincorporated intochylomicrons.
Chylomicrons enterlacteals and are carriedaway by lymph.
4
3
2
1
Triglycerides
Chylomicron
Lacteal
Phospholipids,cholesterol,and proteins
Triglycerides
Fatty acidsMono-
glycerides
Epithelialcell
LUMENOF SMALLINTESTINE
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Figure 33.12a
Triglyceridesare broken downto fatty acids andmonoglyceridesby lipase.
Monoglyceridesand fatty acids diffuseinto epithelial cellsand are re-formed intotriglycerides.
1
Triglycerides
Fatty acidsMono-
glycerides
Epithelialcell
LUMENOF SMALLINTESTINE
Triglycerides
2
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Figure 33.12b
Triglycerides areincorporated intochylomicrons.
Chylomicrons enterlacteals and are carriedaway by lymph.
Chylomicron
Lacteal
Phospholipids,cholesterol,and proteins
Triglycerides
3
4
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The hepatic portal vein carries nutrient-rich blood from the capillaries of the villi to the liver, then to the heart
The liver regulates nutrient distribution, interconverts many organic molecules, and detoxifies many organic molecules
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Epithelial cells absorb fatty acids and monoglycerides and recombine them into triglycerides
These fats are coated with phospholipids, cholesterol, and proteins to form water-soluble chylomicrons
Chylomicrons are transported into a lacteal, a lymphatic vessel in each villus
Lymphatic vessels deliver chylomicron-containing lymph to large veins that return blood to the heart
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Absorption in the Large Intestine
The colon of the large intestine is connected to the small intestine
The cecum aids in the fermentation of plant material and connects where the small and large intestines meet
The human cecum has an extension called the appendix, which plays a very minor role in immunity
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Figure 33.13
Ascendingportionof colon
Smallintestine
Appendix
Cecum
Junction of the small andlarge intestines
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A major function of the colon is to recover water that has entered the alimentary canal
The colon houses bacteria (e.g., Escherichia coli) that live on unabsorbed organic material; some produce vitamins
Feces, including undigested material and bacteria, become more solid as they move through the colon
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Feces are stored in the rectum until they can be eliminated through the anus
Two sphincters between the rectum and anus control bowel movements
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Concept 33.4: Evolutionary adaptations of vertebrate digestive systems correlate with diet
Digestive systems of vertebrates are variations on a common plan
However, there are intriguing adaptations, often related to diet
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Dental Adaptations
Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet
The success of mammals is due in part to their dentition, which is specialized for different diets
Nonmammalian vertebrates have less specialized teeth, though exceptions exist
For example, the teeth of poisonous snakes are modified as fangs for injecting venom
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Figure 33.14
Carnivore Herbivore
Omnivore
Incisors Canines Premolars Molars
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Mutualistic Adaptations
Many herbivores have fermentation chambers in their alimentary canals, where mutualistic microorganisms digest cellulose
Rabbits and some rodents harbor mutualistic bacteria in their large intestines and ceca
The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants, including deer, sheep, and cattle
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Figure 33.15
Rumen Reticulum
Esophagus
OmasumAbomasum
Intestine
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Stomach and Intestinal Adaptations
Many carnivores have large, expandable stomachs
Herbivores and omnivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation
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Figure 33.16
Smallintestine
Small intestine
Stomach
Cecum
Colon(largeIntestine)Carnivore
Herbivore
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Figure 33.16a
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Figure 33.16b
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Concept 33.5: Feedback circuits regulate digestion, energy allocation, and appetite
An animal’s intake of food and use of nutrients are matched to circumstance and need
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Regulation of Digestion
Each step in the digestive system is activated as needed
The enteric division of the nervous system helps to regulate the digestive process
The endocrine system also regulates digestion through the release and transport of hormones
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Figure 33.17
Food
Stomach
GastrinGastricjuices
Pancreas
Liver
Gallbladder
Stimulation
Inhibition
1
Duodenum ofsmall intestine
Bile
Chyme
HCO3−, enzymes
32
CCK
CCK
Secretinand CCK
Secretin
Gastricjuices
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Figure 33.17a
Food
Stomach
GastrinGastricjuices
Pancreas
Liver
Gallbladder
Stimulation
Inhibition
1
Duodenum ofsmall intestine
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Figure 33.17b
Bile
Chyme
HCO3−, enzymes
CCK
CCKSecretinStimulation
Inhibition
2
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Figure 33.17c
Secretinand CCK
Gastricjuices
3
Stimulation
Inhibition
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Energy Allocation
The flow and transformation of energy in an animal—its bioenergetics—determine nutritional needs
An animal’s energy use per unit of time is called its metabolic rate
Metabolic rate can be determined by monitoring an animal’s rate of heat loss, the amount of O2 consumed, or the amount of CO2 produced
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Figure 33.18-1
Organic moleculesin food
Animalbody
Externalenvironment
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Figure 33.18-2
Organic moleculesin food
Heat
Energylost infeces
Digestion andabsorption
Nutrient moleculesin body cells
Animalbody
Externalenvironment
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Figure 33.18-3
Organic moleculesin food
Heat
Energylost infeces
Energylost innitrogenouswaste
HeatCellular
respiration
Digestion andabsorption
Nutrient moleculesin body cells
Animalbody
Externalenvironment
Carbonskeletons
ATP
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Figure 33.18-4
Organic moleculesin food
Heat
Energylost infeces
Energylost innitrogenouswaste
HeatCellular
respiration
Digestion andabsorption
Nutrient moleculesin body cells
Animalbody
Externalenvironment
Carbonskeletons
ATP
Bio-synthesis
Cellularwork
Heat
Heat
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Minimum Metabolic Rate
Animals must maintain a minimum metabolic rate for basic cell functions
Basal metabolic rate, BMR, is the minimum metabolic rate of a nongrowing endotherm that is at rest, has an empty stomach, and is not experiencing stress
The metabolic rate of a fasting, nonstressed ectotherm at a particular temperature is called standard metabolic rate, SMR
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Endothermy is more energetically costly than ectothermy
For ectotherms and endotherms, activity greatly affects metabolic rate
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Regulation of Energy Storage
When an animal takes in more energy than is needed for metabolism and activity, excess energy is stored
In humans, the liver and muscle cells are used first; energy is stored as glycogen
When glycogen depots are full, additional excess energy is stored as fat in adipose cells
When fewer calories are taken in than expended, the body expends liver glycogen, muscle glycogen, and then fat, in that order
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Glucose Homeostasis
Insulin and glucagon together maintain glucose levels
Insulin levels rise after a carbohydrate-rich meal, and glucose entering the liver through the hepatic portal vein is used to synthesize glycogen
When glucose concentration is low in the hepatic portal vein, glucagon stimulates the liver to break down glycogen and release glucose into the blood
Insulin and glucagon are produced in the pancreas in beta cells and alpha cells, respectively
Animation: Homeostasis
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Figure 33.19
Transport ofglucose intobody cellsand storageof glucoseas glycogen
Breakdown ofglycogen andrelease ofglucose intoblood
Secretionof insulin bypancreas
Secretionof glucagonby pancreas
Stimulus:Blood glucose
level dropsbelow set point.
Stimulus:Blood glucose
level risesafter eating.
Homeostasis:70–110 mg glucose/100 mL blood
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Diabetes Mellitus
Diabetes mellitus is a disease caused by a deficiency of insulin or a decreased response to insulin in target tissues
Cells are unable to take up glucose to meet their metabolic needs
Fat becomes the main substrate for cellular respiration
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Type 1 diabetes is an autoimmune disorder in which the immune system destroys the pancreatic beta cells
Type 2 diabetes is characterized by a failure of target cells to respond normally to insulin
Heredity is a factor in type 2 diabetes
Excess body weight and lack of exercise increase the risk
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Regulation of Appetite and Consumption
Overnourishment causes obesity, which results from excessive intake of food energy with the excess stored as fat
Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart attacks, and strokes
Researchers have discovered several of the mechanisms that help regulate body weight
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Ghrelin, a hormone secreted by the stomach wall, triggers a feeling of hunger before meals
Insulin and PYY, a hormone secreted by the small intestine after eating, both suppress appetite
Leptin, a hormone produced by adipose (fat) tissue, also suppresses appetite and may regulate body fat levels
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Figure 33.UN01a
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Figure 33.UN01b
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Figure 33.UN02
Veins to heart
Lymphatic system
StomachLipids
Mouth
Esophagus
Small intestine
Hepatic portal vein
Liver
Absorbedwater
Absorbed food(except lipids)
Anus
RectumLargeintestine
Secretions from liver
Secretions from pancreas
Secretionsfrom gastricglands
Secretionsfrom salivaryglands