Chapter 41. Animal Nutrition. Dietary Categories of Animals. Herbivores eat mainly autotrophs (plants and algae) Carnivores eat other animals Omnivores regularly consume animals as well as plants or algal matter. Basic Nutritional Needs.
level rises, a gland called
the pancreas secretes insulin,
a hormone, into the blood.
Insulin enhances the transport of glucose into body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops.
Glucagon promotesthe breakdown ofglycogen in theliver and the
release of glucose
into the blood,
increasing bloodglucose level.
When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin.
below set point.
Secreted by the stomach wall, ghrelin is one of the signals that triggers feelings of hunger as mealtimes approach. In dieters who lose weight, ghrelin levels increase, which may be one reason it’s so hard to stay on a diet.
Produced by adipose (fat) tissue, leptinsuppressesappetite as its level increases. When body fat decreases, leptin levels fall, and appetite increases.
The hormone PYY,secreted by the small intestine after meals, acts as an appetite suppressant that counters the appetite stimulant ghrelin.
A rise in blood sugar level after a meal stimulates the pancreas to secrete insulinIn addition to its other functions, insulin suppressesappetite by acting on the brain.
PYYHormones and appetite
Kwashiorkor- enough calories but protein is very deficient
Beansand other legumes
Corn (maize)and other grains
LysineEssential Amino Acids
Together corn and beans would provide all 8 of the essential amino acids for humans
CropOrganization of Digestive Tube
Earthworm. The digestive tract ofan earthworm includes a muscular pharynx that sucks food in through themouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, whichcontains small bits of sand and gravel, pulverizes the food. Digestion and absorption occur in the intestine, which has a dorsal fold, the typhlosole, that increases the surface area for nutrient absorption.
Lumen of intestine
Grasshopper. A grasshopper has several digestive chambers grouped into three main regions: a foregut, with an esophagus and crop; a midgut; and a hindgut. Food is moistened and stored in the crop, but most digestion occurs in the midgut. Gastric ceca, pouches extending from the midgut, absorb nutrients.
Bird. Many birds have three separate chambers—the crop, stomach, and gizzard—where food is pulverized and churned before passing into the intestine. A bird’s crop and gizzard function very much like those of an earthworm. In most birds, chemical digestion and absorption of nutrients occur in the intestine.
A Tour of the Tube
Ascendingportion of large intestine
IIeumof small intestine
Duodenum of small intestine
A schematic diagram of the human digestive system
CecumOverview of the System
Food is pushed along the digestive tract by peristalsis … Rhythmic waves of contraction of smooth muscles in the wall of the canal
bolus to enter the
Bolus of food
Glottisdown and open
After the food
has entered the
Glottis upand closed
The larynx, the
upper part of the
moves upward and
tips the epiglottis
over the glottis,
from entering the
Waves of muscular
move the bolus down the esophagus to the stomach.
When a person is not
swallowing, the esophageal
sphincter muscle is contracted,
the epiglottis is up, and the
glottis is open, allowing air
to flow through the trachea
to the lungs.
reflex is triggered
when a bolus of
food reaches the
StomachFrom Mouth to Stomach
Folds of epithelial tissue
Interior surface of stomach.
The interior surface of the stomach wall is highly folded and dotted with pits leading into tubular gastric glands.
Pepsinogen and HCI
are secreted into the
lumen of the stomach.
pepsinogen to pepsin.
Pepsin (active enzyme)
Gastric gland. The gastric glands have three types of cells that secrete different components of the gastric juice: mucus cells, chief cells, and parietal cells.
Pepsin then activates
starting a chain
begins the chemical
digestion of proteins.
Mucus cells secrete mucus,
which lubricates and protects
the cells lining the stomach.
Chief cells secrete pepsino-
gen, an inactive form of the
digestive enzyme pepsin.
Parietal cells secrete
hydrochloric acid (HCl).Stomach structure
Duodenum of small intestineEnzymatic Action in the Small Intestine
Bile salts aid in the digestion and absorption of lipids via Emulsification
The intestinal brush border produces a variety of enzymes that contribute to digestion
Nucleic acid digestion
Fat globules (Insoluble in
water, fats aggregate as
Pancreatic trypsin and
chymotrypsin (These proteases
cleave bonds adjacent to certain
Maltose and other
Fat droplets (A coating of
bile salts prevents small drop-
lets from coalescing into
larger globules, increasing
exposure to lipase.)
Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split
off one amino acid at a time, working from opposite ends of a polypeptide.)
Amino acidsEnzymatic digestion
Enterogastrone secreted by the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the duodenum.
Gastrin from the stomach recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices.
Amino acids or fatty acids in the duodenum trigger the release of cholecystokinin (CCK), which stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder.
Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach.
InhibitionHormonal Regulation of Digestion
Vein carrying blood to hepatic portal vessel
Intestinal wallSmall Intestine…Absorption of Nutrients
The absorptive surface area of the small intestine is roughly 250 square meters - the size of a tennis court!
Large fat globules are emulsified by bile salts in the duodenum.
Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles.
up of fatty acids,
and bile salts
Fatty acids and mono-glycerides leave micelles and enter epithelial cells by diffusion.
Chylomicrons containing fattysubstances are transported out of the epithelial cells and into lacteals, where they are carried away from the intestine by lymph.
(c) OmnivoreVariations in Dentition
Pointed incisor and canines. Jagged premolars and molars
Broad ridged surfaces for grinding
Chisel shaped incisors
intestine)Stomach and Intestinal Adaptations
Snakes can “unhinge” their jaws
Many large carnivores have large very expandable stomachs
swallows a mouthful of grass, boluses
(green arrows) enter the rumen.
Reticulum. Some boluses also enter the reticulum. In both the rumen and the reticulum, symbiotic prokaryotes and protists (mainly ciliates) go to work on the cellulose-rich meal. As by-products of their
metabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud (red arrows), which further breaks down the
fibers, making them more accessible to further microbial action.
Abomasum. The cud, containing great numbers of microorganisms,
finally passes to the abomasum for digestion by the cow‘s own
enzymes (black arrows).
Omasum. The cow then reswallows
the cud (blue arrows), which moves to
the omasum, where water is removed.Ruminant Digestion