Animal Nutrition (Updated L.O.)

What is an autotroph?

An organism that produces its own organic molecules from inorganic carbon sources like CO2, using energy from sunlight or inorganic chemical reactions. These organisms serve as primary producers and form the base of most food webs.

What is a heterotroph?

An organism that obtains both energy and carbon by consuming organic molecules produced by other organisms. They cannot fix carbon, they depend directly or indirectly on autotrophs.

Why can heterotrophs not use inorganic carbon sources?

They ack the biochemical pathways required for carbon fixation, such as the Calvin cycle, and therefore cannot convert CO2 into organic molecules. As a result, they must rely on consuming organic matter for both energy and carbon.

What are the main energy-containing nutrients?

The primary energy-containing nutrients are carbohydrates, proteins, and fats, all of which contain carbon bonds that can be oxidized to produce ATP. These macromolecules also serve as building blocks for cellular structures.

Why do fats provide more energy than carbohydrates or proteins?

Contain a higher proportion of C–H bonds, which store large amounts of chemical potential energy that is released during oxidation. This is why fats yield about 9 kcal/g, compared to about 4 kcal/g for carbohydrates and proteins.

What is an essential amino acid?

An essential amino acid is one that the body cannot synthesize from simpler molecules and therefore must be obtained through the diet. Humans require nine essential amino acids to build proteins.

Why are essential amino acids required in the diet?

Humans can synthesize only 11 of the 20 standard amino acids, meaning the remaining nine must be obtained from food sources. Without these essential amino acids, protein synthesis and normal cellular function are impaired.

What are essential fatty acids?

Fatty acids that cannot be synthesized by the body and must be obtained through dietary sources such as plants or fish. They are important for membrane structure and signaling pathways.

What are vitamins?

Organic compounds required in small amounts that often function as coenzymes or precursors to coenzymes in metabolic reactions. They are essential for maintaining normal physiological processes.

What are minerals?

Inorganic nutrients that function as structural components or enzyme cofactors in the body. They also play key roles in processes such as nerve signaling, fluid balance, and bone formation.

What are electrolytes and their role?

Ions such as Na+, K+, and Cl− that help maintain osmotic balance and are critical for proper membrane potential and nerve function. They enable cells to regulate fluid movement and electrical activity.

What are the four feeding strategies?

Suspension feeding, deposit feeding, fluid feeding, and mass feeding, each adapted to specific food sources. These strategies reflect how organisms capture and process nutrients from their environment.

What is a suspension feeder?

Captures small particles or organisms from water using specialized structures like cilia or mucus. This method allows efficient feeding in aquatic environments with suspended nutrients.

What is a deposit feeder?

Ingests sediment or soil and extracts organic material from it during digestion. This strategy is common in organisms that feed on decomposing material in substrates.

What is a fluid feeder?

Consumes liquids such as nectar or blood using specialized mouthparts adapted for suction or piercing. This feeding strategy allows access to nutrient-rich fluids.

What is a mass feeder?

Ingests relatively large pieces of food and processes them mechanically and chemically. Most animals, including humans, use this feeding strategy.

How do carnivore teeth differ from herbivore teeth?

Carnivores have sharp, pointed teeth adapted for tearing flesh, while herbivores have broad, flat molars suited for grinding plant material. These structural differences reflect dietary specialization.

How are snakes adapted for feeding?

Have highly flexible skulls and loosely connected jaw bones that allow them to swallow prey much larger than their head. This adaptation eliminates the need for chewing.

What is unique about cichlid fish jaws?

They posses specialized pharyngeal jaws in addition to oral jaws, allowing them to process food more efficiently. This adaptation has enabled extensive dietary diversification and adaptive radiation.

How does the structure and function of the human digestive system compare to those of animals with different diets (e.g., cows, birds, snakes)?

• Humans: complete GI tract with specialized organs (mouth, stomach, small intestine, large intestine) that mechanically and chemically digest a mixed diet and absorb nutrients efficiently.

• Cows (herbivores): a multi-chambered stomach (rumen, reticulum, omasum, abomasum) houses symbiotic microbes that break down cellulose, allowing extraction of energy from plant material.

• Birds: the digestive system includes a crop for food storage and a muscular gizzard that grinds food mechanically, compensating for the absence of teeth.

• Snakes (carnivores), a highly flexible skull allows ingestion of large prey whole, and an elongated digestive tract enables slow, efficient digestion of large, infrequent meals.

What is an incomplete digestive tract?

Has a single opening that functions as both the mouth and anus, meaning ingestion and waste elimination occur through the same opening. This limits the ability to specialize digestive processes.

What is a complete digestive tract?

A complete digestive tract has two openings, a mouth and an anus, allowing food to move in one direction through specialized compartments. This organization improves efficiency and allows simultaneous digestion and absorption.

Why is a complete digestive system advantageous?

Allows different regions to specialize in specific digestive functions, increasing efficiency. It also enables continuous processing of food without interference between ingestion and waste elimination.

What are the four main functions of digestion?

Ingestion, digestion (mechanical and chemical), absorption, and elimination, all allowing organisms to obtain and utilize nutrients.

Where does mechanical digestion occur?

The mouth through chewing, in the stomach through churning, and in the small intestine through mixing. These processes physically break down food to increase surface area for enzymes.

Where does carbohydrate digestion begin?

Carbohydrate digestion begins in the mouth, where salivary amylase breaks down starch into smaller polysaccharides and disaccharides. This initiates chemical digestion before food reaches the stomach.

Where does protein digestion begin?

Protein digestion begins in the stomach, where the enzyme pepsin breaks proteins into smaller polypeptides in an acidic environment. This marks the start of chemical protein breakdown.

Where is most digestion completed?

In the small intestine, where enzymes from the pancreas and brush border break macromolecules into absorbable units. This is the primary site of enzymatic activity.

Where does most nutrient absorption occur?

In the small intestine, which has a large surface area due to folds, villi, and microvilli which maximize contact with digested nutrients.

What is peristalsis?

A coordinated series of smooth muscle contractions that moves food through the digestive tract. It ensures unidirectional movement from the mouth to the anus.

Step-by-step: how does peristalsis work?

• Circular muscles contract behind the bolus to increase pressure and push it forward

• Longitudinal muscles contract ahead to shorten and widen that segment

• This coordinated wave-like motion propels the bolus continuously through the digestive tract.

What is the function of HCl in the stomach?

Hydrochloric acid denatures proteins, making them easier to digest, and activates pepsinogen into pepsin. It also creates an acidic environment that helps kill ingested pathogens.

Step-by-step: how do parietal cells produce HCl?

1. Carbonic anhydrase converts CO2 and H2O into carbonic acid

2. The carbonic acid dissociates into H+ and HCO3− within parietal cells

3. The H+ ions are actively pumped into the lumen while Cl− ions diffuse in, forming HCl and lowering stomach pH

What hormone stimulates HCl release?

Gastrin. It’s a hormone that’s released in response to food or neural signals and stimulates parietal cells to secrete HCl. This enhances the stomach’s digestive activity.

Why are digestive enzymes released as inactive forms?

To prevent them from damaging the cells that produce them. They are only activated once they reach the appropriate location in the digestive tract.

Step-by-step: activation of pancreatic proteases?

1. Pancreas releases trypsinogen into the small intestine

2. In the SI, enteropeptidase converts it into active trypsin

3. Trypsin then activates additional proteases, allowing efficient protein digestion.

How is surface area increased in the small intestine?

The small intestine has folds covered with villi, which in turn are covered with microvilli, greatly increasing surface area. This structural adaptation maximizes nutrient absorption.

Why increase surface area in digestion?

Allows more contact between digested nutrients and absorptive cells, improving absorptive efficiency.

Step-by-step: carbohydrate digestion and absorption?

• CHO are first broken down by salivary and pancreatic amylase into smaller sugars

• Then further digested into monosaccharides by brush border enzymes

• These monosaccharides are absorbed via cotransport and facilitated diffusion into the bloodstream.

Step-by-step: protein digestion and absorption?

• Broken down into polypeptides by pepsin in the stomach

• Then broken down into amino acids by pancreatic and brush border enzymes in the small intestine

• These AA are absorbed through active transport into epithelial cells and then enter the bloodstream.

Step-by-step: lipid digestion and absorption?

• Emulsified by bile salts into smaller droplets

• Allows pancreatic lipase to break them into fatty acids and monoglycerides

• These FA diffuse into cells, are reassembled into triglycerides, and transported in chylomicrons.

What is the role of bile?

Contains bile salts that emulsify fats into smaller droplets, increasing their surface area for enzymatic digestion. It plays a mechanical role rather than a chemical one.

What is the role of lipase?

An enzyme that chemically breaks down triglycerides into fatty acids and monoglycerides. This allows lipids to be absorbed by intestinal cells.

Why is bile necessary for fat digestion?

Bile salts have both hydrophobic and hydrophilic regions, which allows them to surround fat droplets and keep them dispersed in water. This prevents the droplets from clumping together and increases their surface area, allowing lipase to digest fats more efficiently.

What hormone stimulates enzyme release from pancreas?

Cholecystokinin (CCK) is released in response to fats and proteins in chyme and stimulates the pancreas to release digestive enzymes. It also promotes gallbladder contraction.

What hormone stimulates bicarbonate release?

Secretin is released in response to acidic chyme entering the small intestine and stimulates the pancreas to release bicarbonate. This helps neutralize stomach acid.

Step-by-step: response to chyme in small intestine?

When chyme enters the small intestine, secretin and CCK are released in response to its acidity and nutrient content. These hormones stimulate the pancreas to release bicarbonate and enzymes and the gallbladder to release bile.

Step-by-step: high blood glucose regulation?

When blood glucose levels rise, pancreatic beta cells release insulin, which increases glucose uptake by cells and promotes glycogen storage in the liver. This lowers blood glucose back to normal levels.

Step-by-step: low blood glucose regulation?

When blood glucose levels fall, pancreatic alpha cells release glucagon, which stimulates glycogen breakdown and glucose production in the liver. This raises blood glucose back to normal levels.

What is the cause, prevalence, and treatment for Type I diabetes?

Caused by an autoimmune response that destroys insulin-producing beta cells in the pancreas, resulting in little or no insulin production. It’s much less common and is typically diagnosed in childhood or adolescence. Treatment requires lifelong insulin therapy along with careful blood glucose monitoring + diet management

What is the cause, prevalence, and treatment for Type II diabetes?

Caused by insulin resistance, where target cells do not respond properly to insulin, often reducing production over time. Its far more common and is strongly associated with obesity, lifestyle factors, and genetics. Treatment involves lifestyle changes (diet, exercise), medications to improve insulin sensitivity/secretion, and sometimes insulin

Key difference between Type I and Type II diabetes?

Type I diabetes involves a lack of insulin production, while Type II involves reduced sensitivity to insulin. Both result in impaired glucose regulation.

Why do both types cause high blood glucose?

Cells fail to take up glucose effectively, leaving excess glucose in the bloodstream, leading to chronic hyperglycemia.

How to identify a herbivore digestive system?

Herbivores typically have long digestive tracts and specialized fermentation chambers to break down cellulose. They also have flat molars adapted for grinding plant material.

How to identify a carnivore digestive system?

Carnivores have shorter digestive tracts suited for digesting protein-rich diets and sharp teeth for tearing meat. They generally lack fermentation chambers.

How to identify an omnivore digestive system?

Omnivores have intermediate digestive tract length and a mix of tooth types for processing both plant and animal material. This allows dietary flexibility.