chapter 45 lecture

8/13/2019 Chapter 45 Lecture

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Nutrition, Digestion &

AbsorptionChapter 43

Nutrition

Nutrient

◦ Any organic or

inorganic substance

taken in that is

required for:

Survival

Growth

Development

Tissue repair

Reproduction

Nutrition

◦ The process of

consuming and

using food and

nutrients

Ingestion

Digestion

Absorption

Elimination

Nutrition

Any nutritionally adequate dietsatisfies two primary purposes:

◦ 1) fuel (chemical energy)

◦ 2) raw organic materials (biosynthesis)

Homeostatic mechanismsmanage these resources.

Nutrient Requirements

Organic

◦ Carbohydrates

◦ Protein

Lipids◦ Vitamins

Inorganic

◦ Minerals

◦ Water

Essential nutrients

Certain compounds cannot besynthesized from any ingested orstored precursor molecule

Must be obtained in diet

4 groups◦ Essential amino acids

◦ Essential fatty acids

◦ Vitamins

◦ Minerals

Essential Amino Acids

8 Required

◦ Tryptophan, methionine, valine, threonine,

phenylalanine, leucine, isoleucine, lysine

Carnivores and omnivores readily

obtain all 8 in meat

Most plants do not contain every

essential amino acid in sufficient

quantity

Essential Fatty Acids

Needed for membrane structure

Unsaturated fatty acids found primarily

in plants

Strict carnivores obtain them from fish

or adipose tissue of birds and

mammals

Essential Vitamins

Organic nutrients that serve ascoenzymes◦ Water-soluble vitamins

vitamin C – not stored

◦ Fat-soluble vitamins vitamin A – stored in adipose tissue

Not all animals require the same vitamins◦ Only primates and guinea pigs can’t synthesize

vitamin C

Vitamin C – Citric AcidVitamin A – Ascorbic

Cofactor

◦ a non-protein

chemical compound

that is bound to a

protein and is

required for the

protein's biological

activity

◦ organic or inorganic

Coenzymes

◦ A cofactor that is

loosely bound

Essential Minerals

Inorganic ions that serve as building

materials and cofactors

◦ Ca, P, S, K, Cl, Fe, Mg, Zn, I, Na

Many required in only trace amounts

◦ Less than 1 mg/day

Some can be stored

◦ Iodine or calcium

Animals are Heterotrophs

Herbivores

◦ Plant material only

Carnivores

◦ Animal flesh and fluids

Omnivores

◦ Both plant and animal material

Feeding Strategies

Suspension-feeders◦ baleen whale, bivalves, lancelet, tunicate

Substrate-feeders / grazers

◦ chiton, earthworm

Bulk-feeders

◦ Most carnivores, herbivores and

omnivores◦ python, lion, bear

Fluid-feeders

◦ mosquito, leech

Ingestion

Digestion

Chemical and mechanical breakdownof organic molecules into units small

enough for the body to absorb.

◦ Intracellular◦ Extracellular

Intracellular

◦ Unicellularorganisms

◦ Sponges

Extracellular – Gastrovascular

Cavity

Cnidarians

Flatworms

Tentacle

Gastrovascular

cavity

Extracellular – Complete Digestive

Alimentary Canal with specialized

regions

Extracellular Digestion

Hydrolysis

Absorption

Passive Diffusion

Facilitated Diffusion

Active Transport

Summary

Alimentary Canal

Divided into Functional Regions

Specialized for:

◦ Fragmentation

◦ Storage

◦ Grinding

◦ Chemical digestion – hydrolysis

◦ Absorption

Vertebrate Digestive Tract

Pharynx

Esophagus

Stomach◦ crop and gizzard

Small intestine

Large intestine

◦ (cloaca) Rectum

Accessory Organs

◦ Produces bile

Gall bladder

◦ Stores bile Pancreas

◦ Produces gastric

enzymes

Layers of the Gastrointestinal

Tract Mucosa

◦ Epithelial

Submucosa

◦ Connective tissue

◦ Nerves Muscularis

◦ Smooth muscle

Circular

Longitudinal Serosa

◦ Connective tissue

The tongue mixes foodwith saliva.◦ moistens and lubricates

◦ secretions controlled by

nervous system Taste-sensitive neurons inthe mouth send impulsesto the brain, whichresponds by stimulatingthe salivary glands.

◦ Antimicrobial

compounds◦ kills ingested bacteria

Initiation of chemicaldigestion polysaccharides

Vertebrate Teeth

Carnivorous mammalshave pointed teeth thatlack flat grindingsurfaces.

Herbivores must

pulverize cellulose ofcell walls of planttissue beforedigestion.◦ have large, flat teeth

suited to grinding Humans are

essentially carnivoresin the front, andherbivores in the back.

Pharynx and Esophagus

Swallowing centerstimulatessuccessive waves ofcontraction that

moves food alongesophagus tostomach. peristalsis

◦ Food entry is

controlled by ring ofsmooth muscle.sphincter

Storage organ

Dilation of lower

esophagus

Little or nodigestion

Birds that eat

primarily grains

and seeds havelarger crops than

birds that eat

insects and worms29

Mouth:

Has no teeth and cannot grind food

Two parts of

the stomach—

Proventriculus:

Secretes acid

and enzymes

Gizzard:

Contains tiny pebbles

that help pulverize food

Intestine:

Digests and

absorbs food

Esophagus:

Moves food to

the crop by

peristalsis

A dilation of

the esophagus

that stores and

softens food

Cloaca:

Receives undigested

material for excretion

Stomach

Rugae◦ Surface is highly convoluted, enabling it to fold

when empty and expand as it fills with food.

Secretory systems

◦ Exocrine glands contain two cell types: parietal cells - secrete hydrochloric acid

chief cells - secrete pepsinogen

Stomach

◦ Human stomach

produces about 2

liters of HCl and

other gastric juiceseveryday.

helps denature food

proteins

◦ leaves the stomach

through the pylorics hincter.

Digestive Tract of a Ruminant

Multichambered

◦ Forestomach (3)

Microbes

◦ True stomach

Extremely long

small intestines

Others◦ Cecum

Pouch at beginning of

large intestine

Variation Based on Diet

Small Intestine

Epithelial wall covered with villi

◦ covered by microvilli (brush border)

greatly increase surface area

Accessory Organs

Absorption

Glucose and amino acids enter thebloodstream via the hepatic portal

Fat enters the lymphatic system.◦ Vessel called a lacteal

Absorption

intestine

Protein Carbohydrate

Bile salts Emulsification

droplets

Free fatty

acids,

monoglycerides

Resynthesis

of triglycerides Triglycerides

+ protein cover

Chylomicron

Fat globules

(triglycerides)

saccharides Amino

Blood capillary (a) (b)

Lymphatic capillary

Epithelial

cell of

intestinal

villus

Large Intestine

Concentratesundigested

material

undigested material,primarily bacterial

fragments and

cellulose,

compacted and

stored

First Section

◦ cecum and

appendix,

Large Intestine

Middle Section

◦ Colon

Ascending

Transverse

Descending

Final Section

◦ Sigmoid colon

◦ Rectum

◦ Anus

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