Outline: Animal Nutrition / Digestion Chapter 41

Lecture Notes: Animal Nutrition / Digestion Chapter 41

I. Nutrition

A. Major Molecular Components:

1. Proteins - Amino acids: C, H, O, N, S
2. DNA / RNA - nucleotides (base, sugar, PO₄): C, H, O, N, P
3. lipids: C, H, O, P
4. sugars: C, H, O

B. "Minor" Components (required)

1. ions: H⁺, Ca⁺⁺, Na⁺, K⁺, Cl^-, Mg⁺⁺, Fe (hemoglobin) etc. (Table 41.2)
2. vitamins: small organic molecules (Table 41.1)

complex with proteins - "coenzymes"
vitamin A: retinol, rhodopsin, vision
vitamin D: Ca⁺⁺ adsorption

C. Sources: primary producers: micro-organisms > plants

Nitrogen: bacteria > plants, (N₂ > NH₃ etc.)
Carbon: sugars from plants, photosynthesis
Oxygen: plants, O₂ is product of photosynthesis.
Phosphorous, other minerals: soil, plants

D. Essential Amino acids (human): must be eaten

1. tryptophan, methionine, valine, threonine,

phenyalanine, leucine, lycine

2. others can be synthesized from "lesser" components.
3. We live off of "primary producers".

a. animal protein: typically contains all essential amino acids
b. vegitable protein:

all essential amino acids available
typically not together in the same plant
example in book: corn and bean (Fig 41.3)

E. Essential fatty acids (human): must be eaten

a. e.g. linoleic acid, precursor to membrane phospholipids

F. Biosynthesis, metabolism: refer back to Chapter 6.

II. Ingestion, Digestion

A. Question: How do we get food inside?

Answer: We break it down to small organic molecules

in a progressive process (mouth to intestine).

B. What is "INSIDE"?

Not the alimentary canal (mouth to anus).
Inside of gut is OUTSIDE!

C. Overview: Human Digestive Pathway

1. Mouth	Mechanical breakdown, water Enzymatic (amylase)
2. Esophogus	Peristalsis, active movement valves: epiglotis, glotis
3. Stomach	Anatomy: Cardiac, Pyloric Sphinctors Gastric Juice: HCl (pH 2) disrupt extracellular matrix (see plant cell elongation, Fig. 39.5) Pepsin (protease, incomplete), pH sensitive secreted as Pepsinogen, cleaved to active form-pH "Zymogens" - proenzymes Gastric Pits: exocrine glands (scan image) Parietal Cells - secrete HCl Chief Cells - secrete Pepsinogen Mixture, Food and Juice: "Acid Chyme" Mixing: Peristalsis
4. Small Intestine	Final Hydrolysis, uptake Villi / microvilli maximize surface area, maximize absorptive surface (Fig. 41.15). Peristalsis.
4a. duodenum final breakdown	Exocrine Glands: Pancrease: Chymotrypsin/Trypsin (proteases) Bicarbonate (neutralize HCl) Liver: Bile (secreted, stored in Gall Bladder) Bile Salts: breakdown, adsorption of fats Instestinal Wall Gland Cells:
4b. jejunum absorption	absorption of molecules resulting from mechanical, enzymatic and chemical digestion. Water uptake.
4c. ilium absorption	absorption of molecules resulting from mechanical, enzymatic and chemical digestion. Water uptake.
5. Large Intestine (Colon)	Final absorption/reabsorption of water. Peristalsis. Feces: become solid as water removed. Diarrhea: surface disturbed, water resorption reduced Constipation: Peristalsis reduced (water resorption). E. coli: bacteria fauna in colon (73% fecal mass) main source Vitamin K and gas.
6. Rectum	terminus: sphincters

Liver: many roles in addition to bile production:

fat, carbohydrate storage	regulation blood glucose
synthesis blood proteins	storage iron, vitimins
conversion of ammonia >> urea	detoxification of blood

D. Hormonal Regulation of Digestion (scan image)


1. A hormone is a chemical secreted by cells in one part of

the body that is transported ... to other parts of the body,
where it affects particular target cells.

2. act over distance (in animals, hormones vs. neurotransmitters)
3. release site >>>>> target cells

all/many cells in organism exposed, only specific cells sensitive

4. all multicellular organisms
5. chemical signals that coordinate the parts of the organism

HORMONE	STIMULUS	ACTION/TARGET
Gastrin	Food in stomach	From stomach wall >> Blood Stimulates Gastric Juice Secretion
Secretin	low pH, Duodenum	from intestinal wall >> pancrease release bicarbonate
Cholecystokinin (CCK)	Food in Duodenum	from intestinal wall > Gall Bladder Contraction / Bile Release
Enterogastrone	High Fat Duodenum	from intestinal wall > stomach inhibits peristalsis slows food passage

E. Evolutionary Adaptations among vertebrates: diet dependent.

1. Teeth: consider carnivores, herbivores, snakes
2. Alimentary canal length, functional and real

- comparison between coyote and koala (Fig. 41.17)

Larger cecum, longer colon in koala permits effecient
processing of fibrous, protein-poor eucalyptus leaves.

3. Ruminants (e.g. cows):
- enlarged multichambered stomach: redigestion, bacterial activity

- quality nutrients obtained from bacteria feeding on grasses etc.

III. Specifics: pathways of molecular breakdown and absorption

A. Most enzymatic breakdown occurs in small intestine:

From: To	Mouth	Stomach	Intestine
Carbohydrates: monosaccharides	Salivary Amylase		Pancreatic Amylase Disaccharidases
Proteins: (amino acids)		Pepsin	Trypsin, Chymotrypsin Aminopeptidase Carboxypeptidase Dipeptidase
Nucleic Acids: bases, sugars, phosphates			Nuclease Nucleotidase Nucleosidase
Fats: glycerol, fatty acids, glycerides			Bile Salts Lipase

B. Anatomy of Small Intestine (fig. 41.15)


1. Surface: highly folded, huge surface area.

a. Epithelium is folded into fingers called Villi.

- Each Villus containes a lymphatic vessel called a lacteal

surrounded by blood capillaries.

- (As we will see soon, lymph vessel system empties into the

blood vascular system).

b. Microvilli on epithelial cells

- The apical membranes of epithelial cells are highly folded:

microvilli (brush boarder)
microvilli are stabilized by cytoskelaton (Actin), but differ from

cilia in having less organization (no 9+2 microtubule
arraingement, no motility).

C. Final breakdown and uptake occurs in brush border (microvilli).

Intestinal cells are joined by "tight junctions", so there is no possible movement between cells. All movement must pass through cells (through cytoplasm). This requires specific mechanisms.


Molecule	General Mode of Transport
Fructose	Diffusion into epithelial cells, through to capillaries
Glucose, Amino Acids, Peptides, Vitamins, etc.	Active transport against concentration gradients into epithelial cells Facilitated transport out of cells and diffusion into capillaries.
Fat	Movement into cells as micelles Movement out of cells as chylomicrons Movement into lacteal (lymph system).




Specific Examples:

Substance	Detailed Mode of Transport
Fat	1. Breakdown to monoglycerides & fatty acids 2. Formation into micelles 3. Diffusion into intestinal cells 4. Conversion to triglycerides 5. Formation of Chylomicrons (lipid w/ prot. coat) 6. Diffusion out of cells into Interstitial fluid 7. Diffusion into Lymph (Lacteal Capillary) 8. Finally, passage into Blood
Glucose	1. Driven by active transport of Na+ out of cells into interstial fluid. Result, intracellular [Na+] is low. 2. Co-transport of Na+ and glucose into cell from intestinal lumen (against glucose gradient but DOWN Na+ gradient). 3. Facilitated diffusion of glucose out of cell into interstitial fluid. (Poison active tranport of Na+, block glucose uptake.)

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Vocabulary

carbohydrates starch sugar lipids fatty acids phospholipids cholesterol essential amino acids vitamins enzyme cofactors DIVERSITY food vacuole lysozome intracellular digestion extracelular digestion pharynx esophogus crop gizzard ruminant cellulase   MAMMALIAN/HUMAN mouth amylase saliva

esophogus peristalsis stomach gastric juice hydrochloric acid pepsin pepsinogen (zymogen) mucus chyme pyloric sphincter small intestine duodenum jejunum ileum lumen villi / microvilli Liver Gall Bladder Pancrease   ENZYMES: Zymogens Trypsin Chymotrypsin, Aminopeptidase, Carboxypeptidase

Nucleases Bile Salts Lipases Disaccharidases dipeptidases nucleotidases nucleosidases Fat uptake micelles chylomicrons Golgi vesicles lymph large intestine colon rectum selective absorption   HORMONES gastrin secretin cholecystokinin (CCK) Enterogastrone