Animal Nutrition and Digestion

NutrientsMet

Substances in food that are essential for survival,

growth, and proper bodily function.

– They provide energy, build and repair tissue, and help maintain life

processes.

– Include proteins, carbohydrates, fats, vitamins, and

minerals.

Metabolism

The process by which your body converts the food

you eat into energy to fuel all its functions, from breathing and

digesting to moving and thinking.

– It involves all the chemical reactions in your body's cells that break down

nutrients for energy and build or repair new cells.

Lipases

Triglycerides are hydrolyzed to fatty acids and glycerol by this

Protease and peptidase

Proteins are hydrolyzed to peptides and amino acids by these

Serial action of many enzymes

Glycogen is hydrolyzed to glucose this way

Amylase and maltase

Starch is hydrolyzed to glucose by these

Dietary carbohydrate

Starch, glycogen, and

sugar is hydrolyzed to glucose.

• Glucose is absorbed into the intestinal luminal

cells.

• Glucose is transferred to other tissues.

o Glucose is stored as glycogen in muscle and liver.

o Excess glucose is used for triglyceride synthesis

(stored in body fats).

o Glucose is the primary energy source for cells that

contain few or no mitochondria.

o Glucose is the primary energy source for the brain.

Ruminant glucose synthesization

Less reliant on glucose compared to other

species, with peripheric tissues (such as muscle) utilizing

mainly VFAs and other fatty acids for energy. Glucose is not

typically absorbed from the diet, but synthesized by the

liver (gluconeogenesis) from proprionate

Dietary lipid

Dietary triglycerides are hydrolyzed to fatty acids.

• Fatty acids are reassembled into triglycerides after

absorption into the cells lining the small intestine.

• Triglycerides are packaged into chylomicrons.

• Triglycerides in chylomicrons are broken done by

hydrolysis in skeletal muscle, cardiac muscle, and

adipose tissue by lipases.

• Skeletal muscle and cardiac muscle contain abundant

mitochondria.

o Mitochondria burn fatty acids to produce ATP.

o Fatty acids are a major energy source for tissues that have

abundant mitochondria.

• Adipose tissue stores the fatty acids as triglycerides.

Dietary protein

This is hydrolyzed to amino acids.

• The presence of nitrogen in their molecule makes

amino acids unique compared to monosaccharides

and fatty acids.

• Amino acids are absorbed into the intestinal luminal

cells.

• Amino acids are transferred to other tissues.

o Amino acids are used for protein synthesis by all cells.

o Excess amino acids are used to produce energy (ATP),

some are converted into glucose.

o Excess amino acids also are used for triglyceride

synthesis (stored in body fat).

Ruminant protein

Thanks to ruminal microbes, ruminants can utilize

non-protein nitrogen (such as urea) to synthetize amino acids.

Glucose, fatty acids, and very low-density lipoproteins

Excess glucose and absorbed fatty acids are converted to

triglycerides in the liver.

• The triglycerides are packaged into very low-density

lipoproteins (VLDLs).

VLDLs

These are released into the circulation and release their

fatty acids to adipose tissue (body fat) and muscle.

o Lipases hydrolyze the triglycerides in VLDL.

o Muscle burns fatty acids for energy (if the muscle contains

abundant fatty acids).

o Adipose tissue stores fatty acids as triglycerides.

Inter-organ exchange of glucose during fasting and exercise

The liver and muscle produce glycogen from

glucose. This process is called glycogenesis.

• Liver glycogen serves as a short-term supply of

glucose.

o This temporarily maintains blood glucose levels.

o Liver glucose supplies energy for cells that cannot

burn fat for energy (the central nervous system and

red blood cells).

• Muscle glycogen serves as a short-term supply of glucose for muscle only

Inter-organ exchange of amino acids during fasting and exercise

Proteins in muscle “store” these.

• During fasting or aerobic exercise,

proteins in muscle are degraded to these.

• These are transferred to the liver

and converted to glucose.

• This is the only way that blood glucose

levels can be maintained (i.e.,

homeostasis) during fasting or long aerobic exercise

inter-organ exchange of fatty acids during fasting and exercise

Triglycerides in adipose tissue

• Adipose tissue (body fat) stores triglycerides to

supply energy.

• During fasting or aerobic exercise, triglycerides

are degraded to fatty acids, which are burned by

skeletal and cardiac muscle for energy.

• Liver converts fatty acids into ketone bodies

o Skeletal and cardiac muscle love ketone bodies.

o Ketone bodies are burned to produce energy.

• Producing ATP from fatty acids and ketone

bodies spares glucose.

Micronutrients

Vitamins and minerals largely responsible for metabolism, enzyme function, and regulation

Macronutrients

Proteins, carbs, and lipids responsible for building tissues

Cellulase

Responsible for breaking down plant cell walls (cellulose and hemicellulose), and no mammals produce this

PUFA

Polyunsaturated fatty acids, several double bonds

Eicosanoids

20-carbon lipid signaling molecules derived from polyunsaturated fatty acids that regulate inflammation, vascular tone, immune responses, and other local physiological processes.

COOH

Carboxyl group— acid on amino acids

NH2

Amine on amino acid

Intestinal luminal cells

small intestinal cells where most nutrients are absorbed

Chylomicrons

Lipoprotein packages for triglycerides to pass through bloodstream w/ highest fat : protein ratio of the lipoproteins

Triglycerides → FA pathway

Liver or chylomicrons (from enterocytes) → VLDL → TAG to cells (via lipoprotein lipase) or back to liver

HDL

“Good” cholesterol, not in excess

LDL

“Bad” cholesterol, in excess

Mucosa

absorption, secretion, direct contact

with the ingesta

Submucosa

supporting tissue (blood and

lymphatic vessels, glands, connective tissue)

Muscularis

contraction (peristaltism)

Serosa

protection, lubrification

Cephalic Phase

• Response to senses

• Parasympathetic stimulation

• Initiates gastric secretions

Gastric Phase

• Response to food in stomach

• Stimulates:

o Gastric epithelium/ Endocrine cells

▪ Produce gastrin and histamine

o Parasympathetic neurons

▪ Release of acetylcholine

Release of acetylcholine

Stimulates:

o Parietal Cells

▪ Produce HCL

▪ Produce intrinsic factor: Carrier for B12 (absorption in the ileum)

o Chief or peptic cells

▪ Pepsinogen → Pepsin (low pH)

▪ Rennin (milk digestion: nursing animals)

Amylase

Substrate: carb

Synthesis and activation: salivary glands and Pancreas; Already active

Products: disaccharides

Maltase

Substrate: maltose

Synthesis and activation: SI; already active

Products: glucose and glucose

Sucrase

Substrate: Sucrose

Synthesis and activation: SI; already active

Products: glucose and fructose

Lactase

Substrate: lactose

Synthesis and activation: SI; already active

Products: glucose and galactose

Lipase

Substrate: Lipids

Synthesis and activation: Pancreas; already active

Products: fatty acids and glycerol

Trypsinogen (active form trypsin)

Substrate: protein

Synthesis and activation: pancreas; activated by enterokinase

Products: peptides

Enterokinase

Substrate: Trypsinogen

Synthesis and activation: SI; already active

Products: Trypsin

Chymotrypsinogen (active form chymotrypsin)

Substrate: protein

Synthesis and activation: pancreas; activated by trypsin

Products: peptides

Peptidase

Substrate: Peptides

Synthesis and activation: Pancreas, activated by trypsin

Products: Amino Acids