Animal Nutrition

Key Concepts• Why eat? Eat what?• Design of digestive systems• Processing steps and their hormonal

control• Challenge of herbivory

• herbivores • carnivores • omnivores • detritivores• frugivores

Animals are heterotrophs,obtain nutrition from other organisms

What do animals get from food? 1. Energy from chemical bonds 2. C skeletons (ex. acetyl, some amino acids)

3. Minerals - macro- and micronutrients

4. Vitamins

Extracting these substances is an engineering ‘problem’

Different diets need different processing machinery

• Carnivores large canines, slashing premolars

• Herbivores sharp incisors and molar grinding surfaces

• Omnivores relatively unspecialized teeth, to do a little of everything

• vegetarian mosquito larvahas brushy mouthparts to produce currents

• carnivorous mosquito larva has sorry brushes and large nasty jaws

• vegetarian mosquito larvahas brushy mouthparts to produce currents

• carnivorous mosquito larva has weak brushes and large nasty jaws

gut=long tube

• continuous space with outside of organism

• extracellulardigestion

• specialization of different regions

Specialized sections

• esophagus• stomach• small intestine• large intestine

Tissue layers are similar along its length AND in

different animals

From the inside out -

• mucosa • submucosa • muscle layers

Storage?Humans In other animals, can be used for food storage.

Esophagus

Honeypot ants –enormous storage

capacity

• Extra muscle • Preliminary

digestion of protein• Some absorption of

small molecules

Stomach

Gastric glands contain 3 types of secretory cells

• mucus • hydrochloric

acid • pepsinogen

• Mucus protects cell surfaces

• Hydrochloric aciddissolves extracellular matrix, kills most bacteria, low pH (2)

• Pepsinogen?

Pepsinogen is an inactive form of a protein-digesting enzyme, pepsin

zymogens

Zymogen activation - they are activated when their catalytic action is

appropriatetrypsinogen trypsin

How is pesinogenactivated?

• By low pH • Pepsin works well

at low pH

Pepsinogen is an inactive form of a protein-digesting enzyme, pepsin

The sequence of digestion along the long tube is coordinated by hormones

foodhormone secretioninitiates digestion

product inhibits

Gastric mucosal cells secrete a hormone, gastrin, in response to food in the stomach

food

gastrin secretioninto bloodstream

stomach secretes gastric juices including HCl

low pH (very acid)

Each hormone can stimulate more than one response

food

gastrin secretion

stomach secretes gastric juices

low pH (very acid)

increase stomach movement

moves mix into small intestine

Most digestion and absorption takes place small intestine

LIVER

PANCREAS

The duodenumis a receiving center.

It receives material from the stomach, the liver, and the pancreas.

Structure of the intestine

• large circular folds

• villi• muscle layers

Villi

• microvilli• capillaries• lymph duct

(lacteal)

Surface area of small intestine• Tube 3 cm x 6 meters, SA ~0.6 m2

• Circular folds add ~ 3x• Villi add ~ 10x• Microvilli add ~ 20x

600 x

TOTAL SURFACE AREA = 360 m2

What is this S.A. for?

Increased surface area for absorption -general feature of animal digestive systems

• Liver bile which emulsifies fats

• Pancreasenzymes to digest carbos, proteinsand fats

agents of digestion

The products of both protein and carbohydrate digestion are water soluble

Amino Acids

ProteinCarbohydrate

Monosaccharides

This means

• they CANNOT passively cross cell membranes (lipid bilayer),

• but they CAN dissolve in the blood

Actively transported

Once they reach the blood they are carried in solution.

Fat and the products of fat digestion are NOT water soluble

This means•they CANNOT dissolve in the intestine

or in blood, but•they CAN passively cross cell

membranes

1. bile salts stabilize small fat droplets 2. lipase cuts fats into fatty acids and

monoglycerides3. bile salts are recycled

Digestion of fats

1. Fatty acids are lipid soluble. They can pass through cell membrane

2. In the intestinal cell, fatty acids are repackaged into chylomicrons

3. Chylomicrons are transported out of cell into lymph system

Transport of fat across wall

Control of digestion in the SMALL INTESTINE by hormones

food delivered from stomach

hormone secretioninitiates nutrient-specific digestion

Examples from the small intestine: 1. Cholecystokinin

2. Secretin

mix enters the small intestine

fats and proteins low pH

cholecystokinin (CKK) released by intestinal cells

secretin released by intestinal cells

muscle movement

1. gall bladder releases bile salts

2. pancreas secretes digestive enzymes

pancreas secretes bicarbonate which neutralizes acid

chyme enters the small intestine

fats and proteins low pH

cholecystokinin (CKK)released by intestinal cells

secretin released by intestinal cells

1. gall bladder contracts to release bile salts

2. pancreas secretes digestive enzymes

pancreas secretes bicarbonate

muscle movement

NEXT ...

the large intestine, where water and ions are reabsorbed

*

If evolution is so clever, why do we have appendices?

vestigial cecum

Remember that...

Different diets require different processing machinery

These requirements are ALSO reflected in the ‘design’ of the digestive system

Cellulose: most animals cannot digest

(without help from other kingdoms)

Plants have tough cell walls.

It isn’t easy being an herbivore

1. Longer guts for longer processing time

2. Help from bacteria and protiststhat have CELLULASE or other useful enzymes

3. Chew well

What to do, gutwise?

Carnivore Vegetarian

Ruminant herbivores• Cattle• Sheep • Goats• Deer• Giraffes • Antelope

and their relatives, the camels and llamas

Ruminant herbivores

• multiple stomach compartments• bacterial fermentation aiding

digestion• cud-chewing

and their relatives, the camels and llamas, have

Ruminants have 4

stomach compartments

1. rumen2. reticulum3. omasum4. abomasum

Other cellulose eaters with symbionts