Download ch. 41 Animal Nutrition

Animal
Nutrition
AP Biology
Nutritionally Adequate Diet
• Fuel (chemical energy) for cellular
respiration
• Raw organic materials for biosynthesis
• Essential nutrients which must be obtained
in pre-made form
Homeostatic Mechanisms
• Chemical energy is obtained from the oxidation of
complex organic molecules
• Too many calories taken in, liver and muscle store
excess as glycogen; further excess stored in
adipose tissue as fat
• Too little calories taken in, glycogen is utilized
first; then fat
• Fat stores twice as much energy as carbohydrates
or proteins
Biosynthesis
• Proteins can be broken down into amino
acids that can supply the nitrogen necessary
to build other amino acids
• Fats can be synthesized from carbohydrates
• Liver is responsible for the conversions of
nutrients from one type of organic molecule
into another
Essential Nutrients
• Chemicals an animal must have but can’t
synthesize
• Essential amino acids
– Most animals can make about ½ of the 20
amino acids needed to make proteins
– Human can produce 12
Essential Nutrients
• Chemicals an animal must have but can’t
synthesize
• Essential amino acids
– Most animals can make about ½ of the 20
amino acids needed to make proteins
– Human can produce 12
– Cats are obligate carnivores—require amino
acid taurine from a meat source
• Essential fatty acids
– Humans can’t make linoleic acid; important in
making membranes
Essential Nutrients
• Vitamins—organic molecules needed in
smaller quantities than essential a.a. or f.a.
– Can serve as catalysts (coenzymes)
– Excess water soluble vitamins get excreted in
urine
– Excess fat soluble vitamins (A, D, E, and K)
are stored in body fat; can reach toxic levels
• Minerals—inorganic molecules needed in
small quantities
– Serve structural and maintenance roles (Ca2+
and Phosphorus)
– Serve as parts of enzymes (Cu) or other
molecules (Fe)
Feeding Adaptations
• Suspension-feeders—sift small particles from
the water
– Trap food on gills (clams and oysters)
– Strain food from water forced through screen-like
plates on their jaws (baleen whale)
Feeding Adaptations
• Substrate-feeders—live on or in their food
source and eat their way through their food
– Leaf miners (larvae of various insects) tunnel
through the interior of leaves
Feeding Adaptations
• Deposit-feeders—
ingests partially
decayed organic
materials along with
their substrate
– Earthworms ingest soil
and their digestive
systems extract the
organic materials
• Fluid-feeders—suck
nutrient-rich fluids
from a living host
Feeding Adaptations
• Bulk-feeders—eat relatively large pieces of
food
– Have various adaptations to kill prey or tear off
pieces of meat or vegetation
Intracellular
Digestion
• Protozoa—use
endocytosis to
form food
vacuoles around
food
– Hydrolytic
enzymes are
secreted into the
food vacuole and
digestion occurs
Extracellular Digestion
• Occurs within compartments that are
continuous, via passages, with the outside
of the body
• Animals with a simple body plan have a
gastrovascular cavity (digestive sac with
single opening)
– Cnidarians and platyhelminths
• Stings prey with
nematocysts on tentacles
• Pulls food into its mouth
and into gastrovascular
cavity
• Gastrodermal cells
secrete digestive
enzymes
• Some gastrodermal cells
have flagella
• Endocytosis of food
particles by gastrodermal
cells and food vacuoles
• Hydrolysis completed by
intracellular digestion
• Undigested materials
expelled back out the
mouth
Cnideria: Hydra
Platyheminths
Mammalian
Digestive
System
• Includes the
alimentary canal
and accessory
glands that secrete
digestive enzymes
into the canal
through ducts
Four Main Stages of Food
Processing
1. Ingestion—act of eating
2. Digestion—breaking down food into small
molecules the body can absorb
–
Enzymatic hydrolysis breaks bonds of
macromolecules
3. Absorption—uptake of small molecules
4. Elimination—undigested material passes
out of the digestive compartment
Ingestion
• Oral cavity—lined with stratified
squamous epithelium
– 32 teeth crush and tear food into smaller pieces
and increases surface area for enzyme action
Ingestion
– Salivary glands produce saliva to moisten food
and initiate carbohydrate digestion
•
•
•
•
Mucin-protects from abrasion, lubricates food
Buffers-neutralize acids
Antibacterial agents-limit bacterial flora in mouth
Salivary amylase-hydrolyzes starch and glycogen to
maltose or small polysaccharides
– Tongue (muscle)-tastes and forms food into a
bolus; pushes it into the pharynx
Ingestion
• Oral cavity—lined with stratified
squamous epithelium
– 32 teeth crush and tear food into smaller pieces
and increases surface area for enzyme action
– Salivary glands produce saliva to moisten food
and initiate carbohydrate digestion
•
•
•
•
Mucin-protects from abrasion, lubricates food
Buffers-neutralize acids
Antibacterial agents-limit bacterial flora in mouth
Salivary amylase-hydrolyzes starch and glycogen to
maltose or small polysaccharides
– Tongue (muscle)-tastes and forms food into a
bolus; pushes it into the pharynx
Ingestion
• Pharynx—intersection for both the digestive
and respiratory systems
– Thick prominent layer of elastic fibers and
several overlapping layers of skeletal muscle
• Swallowing moves the epiglottis to block
the windpipe and direct food into esophagus
Ingestion
• Esophagus—muscular tube that conducts
food from pharynx to stomach
– Distensible because of longitudinal folds along
interior of the tube (mucosa)
• Peristalsis (rhythmic smooth muscle
contractions) pushes food along the tract
– Initial entrance of bolus into esophagus is
voluntary
– The distension stimulates muscular contraction
(involuntary) to propel food toward the
stomach
Digestion
• Stomach
– Food storage
• Elastic walls with rugae, folds that
can expand to accommodate up to 2
L of food
– Churning
• Longitudinal, vertical, and diagonal
muscles contract to mix food every
20 seconds
• Converts food into a nutrient broth,
acid chyme
• Passage into small intestine
regulated by pyloric sphincter
Digestion
• Stomach
– Gastric Secretion—controlled by nerve impulses
and the hormone gastrin
• Mucous cells secrete:
– Mucin—thin mucus that protects stomach lining
– Gastrin—hormone produced by stomach and released into
bloodstream to stimulate secretion of HCl and pepsin
• Chief cells secrete:
– Pepsinogen—inactive protease that is the precursor to pepsin
– Zymogen—inactive form of a protein-digesting enzyme
• Parietal cells—secrete HCl
Digestion
• Stomach
– Protein digestion
• HCl provides acidity (pH 1-4) which:
– Kills bacteria
– Denatures proteins
– Starts the conversion of pepsinogen to pepsin; newly formed
pepsin also aids in conversion of more pepsin
• Pepsin splits peptide bonds next to some amino acids
– Does not hydrolyze protein completely
– Endopeptidase that splits peptide bonds located within the
polypeptide chain
Digestion
• Small Intestine: duodenum (.25m)
– Site of most hydrolysis of food and absorption
– Luminal surface has numerous mucosal folds, villi,
that increase
absorptive
surface area
Simple Columnar
Epithelium
Goblet cell
Digestion
• Small Intestine
– Accessory organs contribute to digestion in this
section of the tract
• Pancreas produces:
– Hydrolytic enzymes that break down all major macromolecules
– Bicarbonate buffer that neutralizes acid chyme from the stomach
• Liver produces bile that is stored in gallbladder
– No digestive enzymes
– Bile salts emulsify fats
– Contains pigments that are byproducts of destroyed erythrocytes
Digestion
• Small intestine
– Carbohydrate digestion
• Began in mouth with salivary amylase
• Begins again in duodenum
– Pancreatic amylases—starch & glycogen  maltose and
other disaccharides
• Disaccharides attach to surface of duodenal
epithelium and are hydrolyzed into monosaccharides
– Maltose hydrolyzed by maltase; sucrose by sucrase;
lactose by lactase
• Monosaccharides absorbed at the surface
Digestion
• Small intestine
– Protein digestion
• Began in stomach with pepsin
• Pancreas secretes proteases in form of zymogens
that get activated only in lumen of duodenum by
enteropeptidase
splits a.a. off
digests large
polypeptides into
shorter chains
Digestion
• Small intestine
– Nucleic acid digestion
• Nucleases hydrolyze DNA and
RNA into nucleotides
• Nucleotidases and nucleosidases
break nucleotides into nucleosides
and nitrogenous bases, sugars, and
phosphates
– Fat digestion
• Occurs only in duodenum
• Emulsification produces many
small fat droplets
• Pancreatic lipase secreted in
duodenum hydrolyzes fats into
glycerol and fatty acids
Absorption
• Small Intestine—jejunum (2.4m), ileum (3.6m)
– Brush border (microvillar surface)
is exposed to lumen of the intestine
– Nutrients are absorbed by diffusion or active
transport across the two
cell-thick epithelium and into
the capillaries or lacteals
Absorption
• Small Intestine—jejunum (2.4m), ileum (3.6m)
– Amino acids and sugars inter capillaries and are
transported by blood
– Absorbed glycerol and fatty acids are recombined in
epithelial cells and coated with
proteins (chylomicrons) which
enter lacteals
– Capillaries and veins draining
nutrients away from villi dump
into hepatic portal vessel which
leads to liver
• Organic molecules used, stored,
or converted to different forms
Elimination
• Large Intestine (Colon) (1.5m)
– Major function is to reclaim water not absorbed during
the absorption of nutrients in the small intestine
– Feces—wastes of digestive tract are moved by
peristalsis
• Intestinal bacteria live on organic material in the feces; some
producing vitamin K which is absorbed by the host
• May contain an abundance of salts
• Stored in rectum and pass through 2 sphincters (one
involuntary, one voluntary) to the anus for elimination
• Strong contractions of the colon signal need to defecate
• Too much water absorbed = constipation
• Viral or bacteria infection may lead to too little water being
absorbed = diarrhea
Evolutionary Adaptations
• Structural
adaptations often
associated with diet
– Dentition
Evolutionary Adaptations
• Structural adaptations often associated with
diet
– Poisonous snakes
• Teeth modified to inject
venom into prey
– Hollow or grooved
• Loosely hinged lower
jaw-skull articulation
Evolutionary Adaptations
• Structural adaptations often associated with
diet
– Length of Digestive Tract
• Herbivores and Omnivores have longer alimentary
canals than carnivores
– Cell walls in vegetation more difficult to digest than meat,
and nutrients less concentrated
– Longer tract allows for more time for digestion and
provides a greater surface area for absorption
• Functional length may be longer than its superficial
appearance
– Spiral valve in sharks
Evolutionary Adaptations
• Symbiotic Microorganisms
– Special fermentation chambers present in many herbivores
– Symbiotic bacteria and protozoa produce cellulase which
digests cellulose
– Microbes digest cellulose into simple
sugars and convert them into essential nutrients
– Microbes housed in
cecum (horses);
cecum and colon
(rabbits); or
specialized chamber
(reticulum) found
in
ruminants