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

Goblet cell

Simple ColumnarEpithelium

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