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Nutrition and Digestion
Organism S&F
Tony Serino, Ph.D.
Biology 201
Misericordia University
Digestion
• The reduction through mechanical and
chemical means (hydrolysis) of complex
food substances into simple monomers and
their absorption into the internal
environment.
Nutrition
Nutrition – the total process involved in acquiring and utilizing food substances
for growth, repair, maintenance and activities in living organisms
Nutritional Modes:
Herbivore –primarily plant eater
(eats producers)
Carnivore –primarily animal eater
(eats consumers)
Omnivore –eats both plant and animals
Match the animal with its mode.
Feeding
Mechanisms
• Suspension feeders –feeds by eating food particles
suspended in water (includes filter feeding)
• Substrate feeders –animals that live in or on their food
• Fluid feeders –suck nutrients from living organism
• Bulk feeders –eat relatively large chunks of food
Diet
• Are the types of foods acquired by the
organism
• Must satisfy the needs of the organism for
energy, building blocks (carbon and
nitrogen), and essential nutrients
• Essential Nutrients –are materials the
animal cannot synthesize but are required
for normal function; includes: minerals and
certain organic compounds
Essential Nutrients
• Essential Amino Acids –amino acids that cannot be synthesized by
the organism (Humans have 8 essential AA). Meat, cheese and eggs
are complete sources of these AA
• Essential Fatty Acids –FA needed by organism; found in seeds,
grains, and vegetables
• Vitamins –organic compounds used to complete protein structures
(cofactors) or coenzymes, required in small quantities
• Minerals –inorganic molecules required in very small amounts,
serve a wide variety of purposes
Deficiencies can cause malnutrition; overdose can cause toxic effects
Functions of Digestive System
• Motility(Propulsion)
– Ingestion –food enters tract
– Mastication -chewing
– Deglutition -swallowing
– Transportation through tract
(peristalsis)
– Mixing (churning, segmentation)
– Egestion (Defecation)
• Secretion
– Endocrine and Exocrine secretions
• Digestion
– mechanical and chemical breakdown
of food
• Absorption
– Passage of food particles from
external to the internal environment
Tube Movements
Peristalsis
Segmentation*
*majority of contractions of SI
Simple Digestive System:
Gastrovascular Cavities
• Seen in some flatworms and cnidarians; has only
one opening
• Used for both digestion and transportation of
nutrients to its tissues
• Sometimes referred to as an Incomplete Gut
(Complete guts have mouth and anus)
Major Organs of System
Accessory Organs
Teeth
Mouth –ingestion, mastication, mechanical dig.
Salivary glands secrete saliva –mixture of water, mucus, electrolytes, antibodies and
enzymes. Enzymes are salivary amylase (pytalin) which breaks down starches and
maltase.
Tongue –mixes food and tastes
Teeth –mechanical digestion
Teeth
Functionally allows the acquisition,
grinding and chopping of food
Specialization allows for different food
ingestion
Dental formula for adult human: (2,1,2,3)
Tooth Anatomy
Odontoblasts –secrete dentin
Ameloblasts –secrete enamel
Deglutition
(Swallowing)
Peristaltic contractions in pharynx and
esophagus transport food to stomach
Stomach
• J-shaped muscular pouch
• Receives bolus and produces chyme
• Liquefies food by mixing it with HCl
and vigorous churning
• Produces gastric juice: mucous,
water, HCl, enzymes in some
animals, some factors necessary for
vitamin absorption ( in humans, GIF
binds to vit. B12 in diet)
• Low pH stops amylase activity, but secretes
pepsinogen (pepsin) that begins break down of
proteins
• Absorbs little except imbibed water, electrolytes,
and some drugs (ie. alcohol and aspirin)
Crop and Gizzard
• Additional storage or
grinding areas associated
with the esophagus and
stomach, respectively
• Crops are specializations
of the esophagus that
temporarily store large
amounts of food; allowing
for quick intake in short
amounts of time
Gizzards –highly muscular thick walled extension of stomach used to
grind coarse food; the animal swallows small rocks that are retained in
the gizzard to grind the food into a paste
Ruminants
• Have four chambered stomach for
digestion of plant fibers
Rumen –temporary storage and largest
segment of stomach
Reticulum –this and the rumen contain large
numbers of bacteria and protists that
break down cellulose; forms the “cud”
Omasum –removes water from thoroughly
masticated cud
Abomasum –final enzymatic breakdown of
cud with stomach’s own enzymes
Ruminant eats grass with little chewing and swallows large quantities down to
the rumen. There the plant matters is mixed with mucus and enzymes produced
by bacteria in the rumen. At intervals, some of the contents pass to the reticulum
where fermentation continues. The reticulum forms boluses (cuds) that can be
regurgitated for further mastication. This may be repeated several times.
Eventually some of this well masticated mash passes to the omasum where water
reabsorption takes place before the food mass passes to the abomasum (the true
glandular portion of the stomach) where additional gastric enzymes are added to
produce chyme.
Small Intestine
• Largest amount of digestion and absorption
of gut; usually divided into 3 sections:
doudenum (neutralizes chyme and receives
secretions of liver and pancreas), jejunum
(bulk of digestion, & ileum (bulk of
absorption)
• Several structures to increase surface area:
plica, villli, length, microvilli
• Secrete or have bound enzymes that
complete digestion process
• Intestinal juice also contains mucous and
antibacterial compounds
• Absoprtion directly into capillary bed of villi
or into villus lacteal
Herbivore vs. Carnivore SI
• Herbivores have
– Longer intestine
– Large cecum houses
bacteria used in
digesting vegetation
• Carnivores have:
– Larger, more
expandable stomach
relative to body size
Large Intestine
(colon, cecum & rectum)
• Massive re-absorption of
water and electrolytes by
active absorption of Na+
• Microbe action produces
Vit. K, biotin, folic acid
and is absorbed by LI
• Responsible for egestion
(defecation reflex)
Liver
•
•
•
•
•
Metaboblizes all food groups
Storage of Fe and Cu and other metals
Storage of Vit. A, B12, D, E, K
Produces bile and most plasma proteins
Detoxifies the blood, storage of toxins
Bile Salts
Up to 95% of the
cholesterol-based bile
salts are “recycled” by
reabsorption along
the intestine.
Pancreas
• Heterocrine gland secretes pancreatic juice and hormones
• Pancreatic juice is sodium bicarbonate and digestive
enzymes including trypsin, chymotrypsin,
carboxypeptidase, lipase, etc.
• Hormones: insulin, glucagon, somatostatin
Arterial Flow to Viscera
Celiac a.
Sup. Mesenteric a.
Inf. Mesenteric a.
Hepatic Portal System
Portal vein
Superior Mesenteric v.
Splenic v.
Inferior Mesenteric v.