ANS 230: Comparative Digestion Physiology

How are animals that ferment plant material in the stomach or specialized fore-stomach categorized?

Foregut (pre-gastric) fermenters

Into which category do animals fall if their primary microbial fermentation occurs in the cecum or colon?

Hindgut (post-gastric) fermenters

Which specific bird is identified as a unique example of a foregut fermenter?

The Hoatzin

How does the stomach structure of a Colobus monkey differ from that of most other primates like the Vervet monkey?

It consists of two distinct compartments instead of a single chamber.

What is the primary dietary benefit for Colobus monkeys having a specialized alkaline fore-stomach?

They can extract more energy from fiber and survive on a more fibrous diet.

What biological entity houses the fermentative microorganisms in herbivores?

The fermentation chamber within the gastrointestinal tract.

The cow's four-chambered stomach consists of the rumen, reticulum, omasum, and the _____.

Abomasum

Which animal is a classic example of a hindgut fermenter with a highly developed cecum and large colon?

The Horse

Approximately how many microbial cells are estimated to exist in the human microbiome?

$100$ trillion cells

Compare the number of genes in the human microbiome to the human genome.

The microbiome has over $1,000,000$ genes, while the human genome has approximately $23,000$.

Which metabolic products of microbial fermentation serve as a primary energy source for ruminants like sheep and cows?

Short Chain Fatty Acids (SCFAs) or Volatile Fatty Acids (VFAs).

Name the three primary Short Chain Fatty Acids (SCFAs) produced by gut microbes.

Acetate, Propionate, and Butyrate.

Which Short Chain Fatty Acid typically has the highest concentration and widest tissue exposure in the body?

Acetate

In which digestive region is the concentration of microbiota highest, reaching $10^{12} \sim 10^{14}$ CFU/ML?

The Colon

Why is nutrient density of the diet particularly important for carnivores?

They have relatively small stomach capacities.

How does the length of the small intestine generally compare between carnivores and herbivores?

It is generally shorter in carnivores than in herbivores.

What anatomical feature allows humans to eat both meat and tough plant material?

Having carnivore-like teeth in the front and herbivore-like teeth in the back.

Which specialized muscular organ do birds use to pulverize food in place of teeth?

The Gizzard (ventriculus)

What is the function of salivary amylase in omnivores like pigs?

Initiating the digestion of starch.

Which group of domestic animals naturally lacks salivary amylase?

Carnivores (dogs and cats).

By what muscular process does the esophagus move a food bolus toward the stomach?

Peristalsis

What are the two primary substances secreted by parietal (oxyntic) cells in the gastric glands?

$HCl$ (hydrochloric acid) and intrinsic factor.

Why is intrinsic factor essential for animal nutrition?

It is required for the absorption of Vitamin $B_{12}$.

Which gastric cells secrete pepsinogen, the inactive precursor of pepsin?

Chief cells

What are the three distinct regions of the glandular mucosa in the stomach?

Cardiac, Fundic (gastric), and Pyloric.

What is the function of the hormone Gastrin in gastric digestion?

It stimulates the secretion of gastric juices ($HCl$ and pepsinogen).

Which substance activates pepsinogen into its active form, pepsin?

$HCl$ (Hydrochloric acid).

What is the physiological role of the enzyme chymosin (rennin) in young animals?

It clots milk to prevent the immature small intestine from being overloaded.

Why is $HCl$ secretion lower ($pH$ of $3-5$) in very young animals compared to adults?

To allow for the beneficial colonization of the intestine with bacteria.

List the three segments of the small intestine in order from the stomach to the large intestine.

Duodenum, Jejunum, and Ileum.

What is the approximate number of enterocytes sloughed off into the intestinal lumen daily?

$17$ billion cells per day.

Where are most nutrients, such as fats, proteins, and carbohydrates, absorbed in the small intestine?

The proximal jejunum.

What is the primary function of the crop in the avian digestive system?

Temporary food storage.

Which organ in poultry is considered the 'true stomach' where $HCl$ and pepsin are released?

The Proventriculus

How does the large intestine of a bird differ anatomically from most mammals?

It contains two ceca instead of one and is very short.

What is the common chamber in birds where digestive, urinary, and reproductive tracts empty?

The Cloaca

Which group of carnivores has exceptionally long small intestines to meet high energy demands?

Marine mammals (dolphins and seals).

What is the function of the Margo Plicatus in the horse's stomach?

It serves as the visible border between the nonglandular and glandular mucosa.

Which Short Chain Fatty Acid is the primary precursor for Gluconeogenesis ($GNG$)?

Propionate

In the ruminant stomach, which chamber is responsible for the regurgitation of 'cud'?

The Reticulum

What is the function of the 'grit' or pebbles found in a bird's gizzard?

To help mechanically pulverize and grind hard food particles.

Which endocrine cells in the gastric glands secrete somatostatin?

D cells (Endocrine cells).

The fuzzy projections on the apical surface of intestinal epithelial cells are known as the _____.

Glycocalyx

Which digestive organ is responsible for the absorption of water and electrolytes and the formation of feces?

The Large Intestine

What is the typical $pH$ range of the small intestine contents during enzymatic digestion?

Approximately $7.0$.

What is the primary purpose of 'milk' produced in the crop of birds like pigeons and flamingos?

To nourish their young with lipid-rich epithelial cells.

What determines the variation in the structure and size of the large intestine across different species?

The importance of hindgut fermentation in that animal's diet.

Which Short Chain Fatty Acid is primarily used as an energy source for colonocytes?

Butyrate

Which organ secretes bile and pancreatic juices into the duodenum?

The Liver (bile) and the Pancreas (enzymes).

In terms of energy contribution, which animals rely more heavily on SCFAs: Pigs or Humans?

Pigs

What is the typical $pH$ of gastric juice in the stomach of an adult monogastric animal?

$2-3$

Which anatomical structure prevents stomach acid from flowing back into the esophagus in most animals?

The Lower Esophageal Sphincter.

What metabolic state in marine mammals justifies their 'exceptional' small intestine length?

High metabolic rates.

What is the term for the 'true' glandular stomach in a ruminant?

The Abomasum

Which part of the avian digestive tract is responsible for fiber fermentation?

The Ceca