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Chapter 41. Animal Nutrition. Dietary Categories of Animals. Herbivores eat mainly autotrophs (plants and algae) Carnivores eat other animals Omnivores regularly consume animals as well as plants or algal matter. Basic Nutritional Needs.

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chapter 41

Chapter 41

Animal Nutrition

dietary categories of animals
Dietary Categories of Animals
  • Herbivores eat mainly autotrophs (plants and algae)
  • Carnivores eat other animals
  • Omnivores regularly consume animals as well as plants or algal matter
basic nutritional needs
Basic Nutritional Needs
  • Regardless of what an animal eats, an adequate diet must satisfy three nutritional needs
    • Fuel for all cellular work
    • The organic raw materials for biosynthesis
    • Essential nutrients, substances such as vitamins that the animal cannot make for itself
feeding mechanisms

Feces

SUSPENSION FEEDERS

SUBSTRATE FEEDERS

Caterpillar

Baleen

FLUID FEEDERS

BULK FEEDERS

Feeding Mechanisms

Suspension feeders shift small particles from water

Substrate feeders live in or on their food source

Bulk feeders eat largish pieces of food

Fluid feeders …well that is pretty obvious

bioenergetics basics
Bioenergetics - basics
  • Energy Budget can be viewed as the flow of food energy into and out of the animal
  • ATP is the energy currency of life
  • Nearly all of an animal’s ATP generation
    • Is based on the oxidation of energy-rich molecules: carbohydrates, proteins, and fats
glucose regulation as an example of homeostasis
Glucose Regulation as an Example of Homeostasis
  • Animals store excess calories as glycogen in the liver and muscles and as fat
  • When fewer calories are taken in than are expended … fuel is taken out of storage and oxidized
  • Glucose is a major fuel for cells
    • Its metabolism, regulated by hormone action, is an example of homeostasis
glucose metabolism

When blood glucose

level rises, a gland called

the pancreas secretes insulin,

a hormone, into the blood.

1

Insulin enhances the transport of glucose into body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops.

2

Glucagon promotesthe breakdown ofglycogen in theliver and the

release of glucose

into the blood,

increasing bloodglucose level.

4

When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin.

3

Glucose Metabolism

STIMULUS:

Blood glucose

level rises

after eating.

Homeostasis

Glucose 90mg/dl

STIMULUS:

Blood glucose

level drops

below set point.

caloric imbalance
Caloric Imbalance
  • Undernourishment
    • Occurs in animals when their diets are chronically deficient in calories
  • Overnourishment
    • Results from excessive food intake
    • Leads to the storage of excess calories as fat
    • Obesity contributes to a number of health problems, including diabetes, cardiovascular disease, and colon and breast cancer
    • Some Stats on US Obesity
      • 58 Million Overweight; 40 Million Obese; 3 Million morbidly Obese
      • Eight out of 10 over 25\'s Overweight
      • 78% of American\'s not meeting basic activity level recommendations
      • 25% completely Sedentary
      • 76% increase in Type II diabetes in adults 30-40 yrs old since 1990
hormones and appetite

Secreted by the stomach wall, ghrelin is one of the signals that triggers feelings of hunger as mealtimes approach. In dieters who lose weight, ghrelin levels increase, which may be one reason it’s so hard to stay on a diet.

Produced by adipose (fat) tissue, leptinsuppressesappetite as its level increases. When body fat decreases, leptin levels fall, and appetite increases.

Ghrelin

Insulin

Leptin

The hormone PYY,secreted by the small intestine after meals, acts as an appetite suppressant that counters the appetite stimulant ghrelin.

A rise in blood sugar level after a meal stimulates the pancreas to secrete insulinIn addition to its other functions, insulin suppressesappetite by acting on the brain.

PYY

Hormones and appetite
  • Several hormones regulate both long-term and short-term appetite by affecting a “satiety center” in the brain
role of leptin
Role of Leptin
  • Mice that inherit a defect in the gene for leptin become very obese
obesity and evolution
Obesity and Evolution
  • The problem of maintaining weight may partly stem from our evolutionary past when fat hoarding was a means of survival
what s in the diet
What’s in the Diet
  • An animal’s diet must supply
    • Fuel (energy)
    • Carbon skeletons
      • To build the complex molecules it needs to grow, maintain itself, and reproduce an animal must obtain organic precursors (carbon skeletons) from its food
    • Essential nutrients
      • Supplied in preassembled form
      • An animal that is malnourished is missing one or more essential nutrients in its diet
    • Malnutrition is much more common than undernutrition in human populations
mineral deficiencies
Mineral deficiencies
  • Herbivorous animals may suffer mineral deficiencies if they graze on plants in soil lacking key minerals
essential amino acids
Essential Amino Acids
  • Animals require 20 amino acids
    • They can synthesize about half of them from the other molecules they obtain from their diet
    • The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form
protein deficiency
Protein Deficiency
  • A diet that provides insufficient amounts of one or more essential amino acids causes a form of malnutrition called protein deficiency

Kwashiorkor- enough calories but protein is very deficient

essential amino acids1

Essential amino acids for adults

Beansand other legumes

Methionine

Valine

Threonine

Phenylalanine

Leucine

Corn (maize)and other grains

Isoleucine

Tryptophan

Lysine

Essential Amino Acids
  • Complete proteins provide all essential AAs in their proper proportions
  • Incomplete proteins do not
    • Most plant proteins are incomplete in amino acid makeup
    • So individuals who must eat only plant proteins need to eat a variety to ensure that they get all the essential amino acids

Together corn and beans would provide all 8 of the essential amino acids for humans

slide18
Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein
  • Penguins use their muscle protein as an AA source for building new proteins when their replace feathers after molting
essential fatty acids
Essential Fatty Acids
  • Animals can synthesize most of the fatty acids they need
  • The essential fatty acids are certain unsaturated fatty acids (linoleic acid in humans)
  • Deficiencies in fatty acids are rare
vitamins
Vitamins
  • Vitamins are organic molecules required in the diet in small amounts
  • 13 vitamins essential to humans have been identified
  • Vitamins are grouped into two categories
    • Fat-soluble (A, D, E, and K)
    • Water-soluble
minerals
Minerals
  • Minerals are simple inorganic nutrients usually required in small amounts
food processing
Food Processing
  • The main stages of food processing
    • Ingestion: Intake of food
    • Digestion: Process of breaking food down into molecules small enough to absorb
      • Involves enzymatic hydrolysis of polymers into their monomers
    • Absorption: The uptake of nutrients by body cells
    • Elimination: occurs as undigested material passes out of the digestive compartment
food processing1

ELIMINATION

4

ABSORPTION

2

DIGESTION

1

3

Food Processing
  • The four stages of food processing

Smallmolecules

Piecesof food

Chemical digestion(enzymatic hydrolysis)

Nutrient moleculesenter body cells

Mechanicaldigestion

Undigested material

Food

INGESTION

digestive compartments
Digestive Compartments
  • Most animals process food in specialized compartments
  • Intracellular digestion
    • Food particles are engulfed by endocytosis and digested within food vacuoles
  • Extracellular digestion
    • Is the breakdown of food particles outside cells
gastrovascular cavity

Tentacles

Mouth

Food

Gastrovascularcavity

Epidermis

Mesenchyme

Gastrodermis

Nutritivemuscularcells

Flagella

Gland cells

Food vacuoles

Mesenchyme

Gastrovascular Cavity
  • Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients

Hydra (a cnidarian)

digestive tube
Digestive Tube
  • Animals with a more complex body plan
    • Have a digestive tube with two openings, a mouth and an anus
  • This digestive tube is called a complete digestive tract or an alimentary canal
organization of digestive tube

Anus

Anus

Gastric ceca

Crop

Organization of Digestive Tube
  • The digestive tube can be organized into specialized regions that carry out digestion and nutrient absorption in a stepwise fashion

Pharynx

Esophagus

Crop

Gizzard

Intestine

Earthworm. The digestive tract ofan earthworm includes a muscular pharynx that sucks food in through themouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, whichcontains small bits of sand and gravel, pulverizes the food. Digestion and absorption occur in the intestine, which has a dorsal fold, the typhlosole, that increases the surface area for nutrient absorption.

Esophagus

Crop

Gizzard

Intestine

Pharynx

Mouth

Typhlosole

Lumen of intestine

Esophagus

Crop

Midgut

Hindgut

Grasshopper. A grasshopper has several digestive chambers grouped into three main regions: a foregut, with an esophagus and crop; a midgut; and a hindgut. Food is moistened and stored in the crop, but most digestion occurs in the midgut. Gastric ceca, pouches extending from the midgut, absorb nutrients.

Midgut

Hindgut

Foregut

Esophagus

Rectum

Mouth

Crop

Esophagus

Bird. Many birds have three separate chambers—the crop, stomach, and gizzard—where food is pulverized and churned before passing into the intestine. A bird’s crop and gizzard function very much like those of an earthworm. In most birds, chemical digestion and absorption of nutrients occur in the intestine.

Gizzard

Mouth

Intestine

Esophagus

Crop

Stomach

Gizzard

Intestine

Stomach

Anus

mammalian digestive system
Mammalian Digestive System

A Tour of the Tube

overview of the system

Salivaryglands

Cardiacorifice

Tongue

Oral cavity

Mouth

Salivaryglands

Pharynx

Parotid gland

Sublingual gland

Esophagus

Esophagus

Submandibular gland

Pyloricsphincter

Liver

Gall-bladder

Stomach

Stomach

Gall-bladder

Ascendingportion of large intestine

Small intestines

Liver

Pancreas

Pancreas

IIeumof small intestine

Large intestines

Small intestine

Duodenum of small intestine

Rectum

Anus

Large intestine

Rectum

A schematic diagram of the human digestive system

Appendix

Anus

Cecum

Overview of the System

Food is pushed along the digestive tract by peristalsis … Rhythmic waves of contraction of smooth muscles in the wall of the canal

the oral cavity pharynx and esophagus
The Oral Cavity, Pharynx, and Esophagus
  • Oral cavity
    • Food is lubricated and digestion begins
    • Teeth chew food into smaller particles that are exposed to salivary amylase, initiating the breakdown of starch
    • Tongue forms the food bolus and pushes it to the pharynx
  • Pharynx (throat)
    • The common passage way for air and ingesta
  • Esophagus
    • Conducts food from the pharynx down to the stomach by peristalsis
from mouth to stomach

The esophageal

sphincter relaxes,

allowing the

bolus to enter the

esophagus.

Epiglottisup

Bolus of food

Tongue

Glottisdown and open

Epiglottisup

Esophageal sphincterrelaxed

Pharynx

Epiglottis down

Esophageal sphinctercontracted

Esophageal sphinctercontracted

Glottis

After the food

has entered the

esophagus, the

larynx moves

downward and

opens the

breathing

passage.

Larynx

Esophagus

Trachea

To lungs

To stomach

Glottis upand closed

Contractedmuscles

Relaxedmuscles

Relaxedmuscles

The larynx, the

upper part of the

respiratory tract,

moves upward and

tips the epiglottis

over the glottis,

preventing food

from entering the

trachea.

2

1

6

4

5

3

Waves of muscular

contraction (peristalsis)

move the bolus down the esophagus to the stomach.

When a person is not

swallowing, the esophageal

sphincter muscle is contracted,

the epiglottis is up, and the

glottis is open, allowing air

to flow through the trachea

to the lungs.

The swallowing

reflex is triggered

when a bolus of

food reaches the

pharynx.

Stomach

From Mouth to Stomach
slide33
GERD
  • Gastroesophageal reflux disease (GERD)
    • Better known as heartburn
the stomach
The Stomach
  • Stomach
    • Stores food
    • Secretes gastric juice, which converts a meal to acid chyme
  • Gastric juice
    • Hydrochloric acid
    • Pepsin (enzyme)
    • Mucus (which coated the stomach lining and protects the cells from acidity
stomach structure

Stomach

Esophagus

Cardiac orifice

Folds of epithelial tissue

Pyloric sphincter

5 µm

Small intestine

2

3

1

1

3

2

Interior surface of stomach.

The interior surface of the stomach wall is highly folded and dotted with pits leading into tubular gastric glands.

Pepsinogen and HCI

are secreted into the

lumen of the stomach.

Epithelium

HCl converts

pepsinogen to pepsin.

Pepsinogen

Pepsin (active enzyme)

Gastric gland. The gastric glands have three types of cells that secrete different components of the gastric juice: mucus cells, chief cells, and parietal cells.

HCl

Pepsin then activates

more pepsinogen,

starting a chain

reaction. Pepsin

begins the chemical

digestion of proteins.

Mucus cells secrete mucus,

which lubricates and protects

the cells lining the stomach.

Chief cells secrete pepsino-

gen, an inactive form of the

digestive enzyme pepsin.

Parietal cell

Chief cell

Parietal cells secrete

hydrochloric acid (HCl).

Stomach structure

Gastric gland

  • Goblet (mucus) cells
  • Chief cells
    • pepsinogen
  • Parietal cells
    • HCl
gastric ulcers

Bacteria

Mucuslayer of stomach

1 µm

Gastric Ulcers
  • Caused mainly by the bacterium Helicobacter pylori
the small intestine
The Small Intestine
  • Small intestine
    • Longest section of the alimentary canal (six meters in humans)
    • The major organ of digestion and absorption
    • Sections
      • Duodenum
      • Jejunum
      • Ileum
enzymatic action in the small intestine

Liver

Stomach

Bile

Gall-bladder

Acid chyme

Intestinaljuice

Pancreas

Pancreatic juice

Duodenum of small intestine

Enzymatic Action in the Small Intestine
  • In the duodenum acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself
  • Pancreatic enzymes
    • Trypsin and Chymotrypsisn
    • Lipases
    • Amylase
    • Nucleases

Bile salts aid in the digestion and absorption of lipids via Emulsification

The intestinal brush border produces a variety of enzymes that contribute to digestion

enzymatic digestion

Protein digestion

Fat digestion

Nucleic acid digestion

Carbohydrate digestion

Oral cavity,

pharynx,

esophagus

Polysaccharides

(starch, glycogen)

Disaccharides

(sucrose, lactose)

Salivary amylase

Smaller polysaccharides,

maltose

Stomach

Proteins

Pepsin

Small polypeptides

Polypeptides

Lumen of

small intes-

tine

Fat globules (Insoluble in

water, fats aggregate as

globules.)

Polysaccharides

DNA, RNA

Pancreatic amylases

Pancreatic

nucleases

Pancreatic trypsin and

chymotrypsin (These proteases

cleave bonds adjacent to certain

amino acids.)

Bile salts

Maltose and other

disaccharides

Fat droplets (A coating of

bile salts prevents small drop-

lets from coalescing into

larger globules, increasing

exposure to lipase.)

Nucleotides

Smaller

polypeptides

Pancreatic carboxypeptidase

Pancreatic lipase

Amino acids

Glycerol, fatty

acids, glycerides

Small peptides

Nucleotidases

Epithelium

of small

intestine

(brush

border)

Nucleosides

Disaccharidases

Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split

off one amino acid at a time, working from opposite ends of a polypeptide.)

Nucleosidases

and

phosphatases

Monosaccharides

Nitrogenous bases,

sugars, phosphates

Amino acids

Enzymatic digestion
hormonal regulation of digestion

Enterogastrone secreted by the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the duodenum.

Liver

Entero-

gastrone

Gall-

bladder

Gastrin from the stomach recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices.

Gastrin

CCK

Stomach

Amino acids or fatty acids in the duodenum trigger the release of cholecystokinin (CCK), which stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder.

Pancreas

Secretin

Duodenum

Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach.

CCK

Key

Stimulation

Inhibition

Hormonal Regulation of Digestion
  • Hormones help coordinate the secretion of digestive juices into the alimentary canal
small intestine absorption of nutrients

Microvilli(brush border)

Vein carrying blood to hepatic portal vessel

Bloodcapillaries

Muscle layers

Epithelialcells

Epithelial cells

Largecircularfolds

Lacteal

Villi

Key

Lymph vessel

Villi

Nutrientabsorption

Intestinal wall

Small Intestine…Absorption of Nutrients
  • The small intestine has a huge surface area due to the presence of villi and microvilli

The absorptive surface area of the small intestine is roughly 250 square meters - the size of a tennis court!

absorption of nutrients
Absorption of Nutrients
  • The core of each villus
    • Contains a network of blood vessels and a small vessel of the lymphatic system called a lacteal
  • Amino acids and sugars
    • Pass through the epithelium of the small intestine and enter the bloodstream
  • After glycerol and fatty acids are absorbed by epithelial cells
    • They are recombined into fats within these cells
fat absorption

Fat globule

Large fat globules are emulsified by bile salts in the duodenum.

1

Bile salts

Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles.

2

Fat droplets

coated with

bile salts

Micelles made

up of fatty acids,

monoglycerides,

and bile salts

Fatty acids and mono-glycerides leave micelles and enter epithelial cells by diffusion.

3

Chylomicrons containing fattysubstances are transported out of the epithelial cells and into lacteals, where they are carried away from the intestine by lymph.

4

Epithelial

cells of

small

intestine

Lacteal

Fat absorption
  • These fats are then mixed with cholesterol and coated with proteins forming small molecules called chylomicrons, which are transported into lacteals
the large intestine
The Large Intestine
  • Functions
    • Recover water that has entered the alimentary canal
    • Form compact and propel the feces to the anus
  • The colon is home to a variety of bacteria including Escherichia coli
variations in dentition

Incisors

Canines

Molars

(a) Carnivore

Premolars

(b) Herbivore

(c) Omnivore

Variations in Dentition
  • Mammals have specialized dentition that best enables them to ingest their usual diet

Pointed incisor and canines. Jagged premolars and molars

Broad ridged surfaces for grinding

Reduced/absent canines

Chisel shaped incisors

Generalized/unspecialized dentition

stomach and intestinal adaptations

Small intestine

Stomach

Small intestine

Cecum

Colon(large

intestine)

Stomach and Intestinal Adaptations
  • Herbivores generally have longer alimentary canals than carnivores reflecting the longer time needed to digest vegetation

Snakes can “unhinge” their jaws

Many large carnivores have large very expandable stomachs

Carnivore

Herbivore

symbiotic adaptations
Symbiotic Adaptations
  • Many herbivorous animals have fermentation chambers where symbiotic microorganisms digest cellulose.
    • Horses, rabbits, and koalas have very large cecums housing symbionts
    • Ruminants have large populations of symbiotic prokaryotes and protozoa in their rumens and reticulums
ruminant digestion

Rumen. When the cow first chews and

swallows a mouthful of grass, boluses

(green arrows) enter the rumen.

Intestine

Reticulum. Some boluses also enter the reticulum. In both the rumen and the reticulum, symbiotic prokaryotes and protists (mainly ciliates) go to work on the cellulose-rich meal. As by-products of their

metabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud (red arrows), which further breaks down the

fibers, making them more accessible to further microbial action.

4

2

1

3

Esophagus

Abomasum. The cud, containing great numbers of microorganisms,

finally passes to the abomasum for digestion by the cow‘s own

enzymes (black arrows).

Omasum. The cow then reswallows

the cud (blue arrows), which moves to

the omasum, where water is removed.

Ruminant Digestion
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