Download OLD NOTES – FOR REFERENCE ONLY! Chapter 41 – Animal

OLD NOTES – FOR REFERENCE ONLY!
Chapter 41 – Animal Nutrition
I.
Nutritional Requirements
a. Glucose regulation = form of homeostasis
i. Pancreas secretes:
1. Insulin  stimulates liver to store glucose; decreases blood
glucose; secreted after eating a lot
2. Glucagon  stimulates liver to break down glycogen; increases
blood glucose
b. Undernourishment vs. Overnourishment
c. Feedback mechanism of appetite
i. Leptin  hormone produced by adipose cells
1. high leptin levels = depress appetite and increase energy
consuming activities
2. low leptin levels = increase appetite
d. Essential Nutrients  must be obtained in food, body cannot make
i. 4 classes:
1. amino acids  animals can make about ½; others come from diet
2. fatty acids  can make MOST from carbon skeletons, but some
exceptions (ex. Linoleic acid)
3. vitamins
4. minerals  inorganic; ex. Calcium and phosphorus
II.
Food Types and Feeding Mechanisms
a. Opportunistic feeders; Heterotrophs = herbivores, carnivores, omnivores
b. Four major mechanisms for food ingestion:
i. Suspension Feeders  sift small particles; ex. Clams, oysters, baleen
whales
ii. Substrate Feeders  live in or on food source; ex. Maggots
1. Deposit feeders – type of substrate feeder, salvage partially
decayed organic materials consumed with soil; ex. Earthworm
iii. Fluid Feeder  suck nutrient-rich fluids from living host; ex. Mosquito
and leech
iv. Bulk Feeder  eat large amounts at a time; ex. Python
III.
Food Processing
a. Four Main stages of food Processing
i. Ingestion  act of eating; organisms need to break down the
macromolecules in order to use them
ii. Digestion  process of breaking down food
iii. Absorption  cells absorb molecules (such as amino acids)
iv. Elimination  undigested material passes out of digestive compartment
IV.
b. Digestion occurs in specialized compartments (contains enzymes, no selfdigestion)
i. Intracellular Digestion (food vacuoles) vs. Extracellular Digestion
ii. Gastrovascular Cavities
1. single opening compartment
2. simple animals (cnidarians, hydra)
3. function in both digestion and distribution of nutrients
iii. Complete Digestive Tract (Alimentary Canal)
1. two openings – mouth and anus
2. most animals have this
3. set of tubes that can be divided into specialized regions
a. Ex. Mouth  Pharynx  Esophagus  Crop  Gizzard
 Stomach  Intestine
Mammalian Digestive System
a. Consists of alimentary canal and accessory glands (salivary glands, pancreas,
liver, gallbladder)
b. Peristalsis  smooth muscle contractions that push food through digestive tract
c. Beginning of Food Processing:
i. Oral Cavity
1. grinds food; releases saliva
2. Salivary Amylase  enzyme in saliva that breaks down
carbohydrates
ii. Pharynx
1. opens to both esophagus and trachea (windpipe)
2. Swallowing = epiglottis (flap) blocks trachea opening (glottis)
3. Fig 41.14 pg. 861
iii. Esophagus
1. moves food from pharynx down to stomach
d. Food Storage and Preliminary Digestion
i. Stomach = elastic
ii. Stomach secretes gastric juice (a digestive fluid)
1. pH of 2 (acidic!)
2. contains Pepsin  enzyme (hydrolysis of proteins)
a. Pepsin secreted in inactive form – Pepsinogen
b. Once food enters stomach, HCl is also secreted, binds with
pepsinogen and activates the pepsin  POSITIVE
FEEDBACK
c. Fig 41.15 pg. 862
iii. Stomach has mucus lining to protect against self-digestion
iv. Pyloric Sphincter  opening from stomach to small intestine
e. Small Intestine
i. Major Function = digestion and absorption
ii. Longest part of alimentary canal
iii. Three parts:
1. Duodenum  first 25 cm, breaks down food
a. The acid chyme from the stomach mixes with the digestive
juices from the accessory glands here
i. Pancreas  makes bicarbonate to act as a buffer
ii. Liver  produces bile that can help digest fats
iii. Gall Bladder  stores the bile until its needed
2. Jejunum  role in absorption of nutrients and water
3. Ileum  role in absorption of nutrients and water
iv. Carbohydrate Digestion
1. Polysaccharides  Disaccharides  Monosaccharides (glucose!)
2. Maltase  enzyme that breaks disaccharides into glucose
3. Begins with salivary amylase in oral cavity; finishes with
pancreatic amylase
4. Monomers absorbed into the blood
v. Protein Digestion
1. Begins with Pepsin in stomach; eventually broken down into
amino acids
2. Relevant enzymes:
a. Trypsin and Chymotrypsin  target peptide bonds and
break large proteins
b. Carboxypeptidase  takes off one amino acid at a time
starting at carboxyl group
c. Aminopeptidase  takes off one amino acid at a time
beginning at the amino end
d. All these enzymes are secreted by the pancreas in an
inactive form; the enzyme enteropeptidase must be secreted
to activate them
vi. Nucleic Acid Digestion
1. Nucleases  enzymes that break down DNA and RNA into
nucleotides
vii. Fat Digestion
1. Reach small intestine undigested
2. Emulsification  process where bile salts keep fat from coalescing
a. Therefore, the fat droplets stay small and the enzyme lipase
can hydrolyze them
***** Fig 41.17 pg. 864 – All Enzymes Necessary in Human Digestion*****
viii. Absorption of Nutrients
1. Small Intestine has a very large surface area
2. Fingerlike projections = Villi, which contain microvilli, which
increase the rate of absorption
3. Lacteal  small vessels of the lymph system (contain lymph) that
go through the villi; nutrients diffuse into here
4. Capillaries and veins that drain nutrients away from villi empty
into the hepatic portal vessel, which drains to the liver (first chance
at nutrients!)
a. Function of liver = helps regulate blood/glucose levels
5. HIGH energy cost to digest food
f. Hormones help regulate digestion
i. Make sure digestive juices are only present when needed
ii. Gastrin  hormone secreted by stomach wall when food arrives;
stimulates production of gastric juices
iii. Enterogastrones  secreted by duodenum, stimulates secretion of
hormone secretin (which signals the pancreas to release bicarbonate
buffer)
1. Cholecystokinin (CCK)  causes gallbladder to contract and
release bile; triggers release of pancreatic enzymes
g. Large Intestine (colon)
i. Major Function = reclaiming water
ii. Cecum  one small part of large intestine, contains fingerlike extensions
(appendix = dispensable)
iii. Lined with bacteria
iv. Rectum  terminal portion of colon; stores feces until eliminated;
sphincter muscles
V.
Adaptations of Vertebrate Digestive System
a. Dentition  structural differences in teeth based on diet
b. Length of alimentary canal correlated with diet
c. Digestive systems include symbiotic bacteria (help with cellulose digestion)
d. Ruminant (deer, cattle, sheep) Digestion:
i. Stomach = 4 chambers; digest these symbiotic organisms that are rapidly
reproducing in the digestive tract