animal nutrition - university of arizona animal nutrition key concepts • why eat? eat what? •...
TRANSCRIPT
1
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
2
• 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
3
• Extra muscle • Preliminary
digestion of protein• Some absorption of
small molecules
StomachGastric 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
4
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
5
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
6
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
7
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
8
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 herbivore1. 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