Download small intestines

Animal Nutrition
A look at the digestive
system
What do animals need to live?

Animals make energy
using:
food
 Food
 Oxygen

Animals build bodies
using:
 Food

for raw materials
Amino acids, sugars, fats,
nucleotides
 ATP
energy for synthesis
ATP
O2
Nutritional requirements

Animals are heterotrophs
 Need
to take in food
 Why? Fulfills 3 needs …
Fuel = chemical energy for production of ATP
 Raw materials = carbon source for synthesis
 Essential nutrients = things animals cannot make


Elements (N, P, K, Fe, Na, Ca …), NAD, FAD, etc
Different ways to obtain food
filter (suspension) feeding
substrate feeding
fluid feeding
bulk feeding
Different diets; different lives

All animals eat other organisms
 Herbivores

Eat mainly plants

Giraffes, cows,
rabbits, snails
 Carnivores

Eat other animals

Sharks, hawks, spiders, snakes
 Omnivores

Eat plants & animals
Cockroaches, bears, raccoons, humans
 Humans evolved as hunters, scavengers, & gatherers

Getting & using food

Ingest


Taking in food
Digest

Mechanical digestion


Chemical digestion



Breaking down food into molecules small enough
to be absorbed into cells
Enzymes (hydrolysis)
intracellular
digestion
Absorb

Absorb across cell membrane



Breaking up food into smaller pieces
Diffusion
Active transport
Eliminate

Undigested extracellular material passes out of
digestive system
extracellular
digestion
Getting & using food

Don’t forget about enzymes

Specialized proteins that catalyze reactions
 Lower activation energy, and, therefore,
increase the rate of digestion
 Most enzymes prefer an environment of 37OC
 Generally fall into 3 main categories:
 Amylase




Proteases




Produced in salivary glands & pancreas
Digests starch into maltose & glucose, prefers pH 7
Example: salivary amylase
Produced by stomach glands
Digests proteins into amino acids; prefers pH 3
Example: pepsin
Lipase



Produced by pancreas
Digests lipids into glycerol & fatty acids; prefers pH 7
(or slightly above)
Example: pancreatic lipase
Human digestive system
Alimentary Canal
Common processes & structures

Movement & control
 Peristalsis

Push food along by rhythmic waves
of smooth muscle contraction
 Sphincters


Muscular, ring-like valves that
regulate the passage of material
between sections of digestive system
Accessory glands
 Salivary

glands, pancreas, liver & gall bladder
Secrete digestive juices (enzymes + fluid)
Swallowing (& not choking)

Epiglottis





Problem: breathing & swallowing through the same orifice
Flap of cartilage
Closes trachea (windpipe) when swallowing
Food travels down esophagus
Esophagus

Moves food to stomach by peristalsis
Ingestion

Mouth
 Mechanical digestion

Teeth

Breaking up food
 Chemical

digestion
Saliva
 Amylase
 Enzyme digests starch

Mucin
 Mucus protein (slippery)
 Protects soft lining of digestive system
 Lubricates food for easier swallowing

Buffers
 Neutralizes acid to prevent tooth decay

Anti-bacterial chemicals
 Kill bacteria that enter mouth with food
mouth
break up food
moisten food
digest starch
kill germs
Stomach

Functions
 Food storage

Can stretch to fit ~2L of food
 Disinfect

food
HCl = pH 2


Kills bacteria
Breaks apart cells
 Mechanical
digestion
 Chemical digestion

Gastric gland
Gastric juice
 Mucus, HCl, & pepsinogen
The stomach epithelium
cells must regenerate
every 3 days

Pepsin


Enzyme that breaks down protein
Secreted as pepsinogen

Activated by HCl
But the stomach is made out of protein!
What stops the stomach from digesting itself?
mucus secreted by stomach cells protects
stomach lining
mouth
break up food
moisten food
digest starch
kill germs
stomach
kills germs
store food
break up food
digest proteins
cardiac
sphincter
pyloric
sphincter
Ulcers

Used to think ulcers were
caused by stress


Tried to control with antacids
Colonized by
H. pylori
Now know bacterial infection
is cause in majority of cases



15% of infected individual develop
ulcers
Bacteria live in neutral zone
between epithelial cells and mucus
Now cure with antibiotics
Additional causes:


inflammation
of stomach
Helicobacter pylori


Coevolution of parasite & host
Excess HCl secretion
Loss of mucus barrier

Excess use of aspirin/ibuprofen
Free of
H. pylori
inflammation
of
esophagus
H. pylori
inflammatory
proteins
(CagA)
cytokines
neutrophil
cells
cell damaging
proteins
(VacA)
helper T cells
white blood
cells
Small intestine

Functions
 Major organ of digestion &
absorption
 Chemical digestion

Enzymes
 Absorption



through lining
Over 6 meters long
Huge surface area = 300m2 (~size of
tennis court)
Structure
 3 sections



Duodenum = most digestion
Jejunum = absorption of nutrients & water
Ileum = absorption of nutrients & water
Duodenum

1st section of small intestines
 Acidic
food from stomach mixes with digestive
juices from accessory glands
Pancreas
 Liver
 Gall bladder

Pancreas

Digestive enzymes
 Trypsinogen


Activated by peptidase
Becomes trypsin

Digests proteins
 Pancreatic

small intestines
amylase
Buffers
 Reduces acidity from stomach

Alkaline solution rich in bicarbonate
(HCO3-)
Pepsinogen & trypsinogen
Call called zymogens
What stops
pancreas
from digesting
itself?
Pancreas

Endocrine gland =
without ducts
Exocrine = with ducts
Exocrine & endocrine gland
 Acinar (or secretory) cells secrete digestive
enzymes into the ductile
 The ductile takes the enzymes to larger and
larger ducts until the pancreatic duct
is reached
Structure of an
exocrine gland
mouth
break up food
moisten food
digest starch
kill germs
pancreas
produces enzymes to
digest proteins & starch
stomach
kills germs
break up food
digest proteins
store food
Liver

Digestive system functions
 Produces bile


Stored in the gall bladder until needed
Breaks up fats

Acts like detergents to breakup fats
Circulatory System
Connection
bile contains colors
from old red blood
cells collected in liver =
iron in RBC rusts &
makes feces brown
Digesting lipids


Bile is produced in the liver & stored in the gall bladder
Bile salts have a hydrophobic side & a hydrophilic side



Hydrophobic attaches to lipid
Hydrophilic interacts with water
Breaks fat globules into smaller, digestible lipids
mouth
break up food
moisten food
digest starch
kill germs
liver
produces bile
- stored in gall bladder
break up fats
pancreas
produces enzymes to
digest proteins & starch
stomach
kills germs
break up food
digest proteins
store food
Digestive enzymes
Transverse section of the ileum
Perpendicular to
longitudinal muscle layer
Used for peristalsis
Control diameter
of ileum
Used for peristalsis
Absorption by small intestine

Absorption through villi & microvilli


Finger-like projections
Increases surface area for absorption
Ooooh…
Structure & Function
Absorption by small intestine
Absorption by small intestine

A villus
 Capillary
network: allows
transport of absorbed
nutrients
 Single epithelial layer:
ensures minimum distance
for diffusion
 Lacteals: absorb lipids into
lymphatic system
 Membrane proteins: enzymes that do not pass
through the digestive system


Can be reused
Can help with membrane transport



Mitochondria: provide energy for active transport
Pinocytotic vesicles: transport material in bulk
Tight junction: impermeable membrane between
cells, maintains concentration gradient
Absorption of nutrients



Lipids are absorbed via diffusion
Water-soluble molecules are absorbed via facilitated
diffusion
Glucose, amino acids, & minerals are absorbed by active
transport


Glucose uses a sodium-glucose transporter and secondary
active transport (see previous slide)
Endocytosis/pinocytosis is used for bulk transport
What is NOT absorbed?
B: bile pigments
 E: epithelial cells of the intestinal lining
 L: lignin (carb found in plants)
 C: cellulose (roughage or fiber)
 H: human microflora (bacteria)

mouth
break up food
moisten food
digest starch
kill germs
liver
produces bile
- stored in gall bladder
break up fats
pancreas
produces enzymes to
digest proteins & starch
stomach
kills germs
break up food
digest proteins
store food
small intestines
breakdown all foods
- proteins
- starch
- fats
- nucleic acids
absorb nutrients
Absorption vs Assimilation

Absorption
 The
process of
taking in
substances

Assimilation
 The
process of
using subunits
(amino acids, fatty
acids, glycerol) to
build
macromolecules,
which then become
part of the body
Large intestine (colon)

Function
 Reabsorption
of water
Use ~9 L of water every day in
digestive juices
 >90% of water is reabsorbed

No enough water
reabsorbed back into
body
 diarrhea
 Too much water
reabsorbed back into
body
 constipation

Microflora of large intestine

Living in the large intestine is a rich flora of
harmless, helpful bacteria

Over 700 species of bacteria, plus fungi & protozoa
 Escherichia
coli (E. coli)
 Bacteria produce vitamins

Vitamin K, biotin, folic acid, & other B vitamins
 Generate
gases
By-product of bacterial metabolism
 Methane, hydrogen sulfide

You’ve got
company!
Rectum

Last section of colon (large intestine)
 Eliminates
feces
Undigested materials
 B-E-L-C-H

 Does

not use peristalsis
Uses general contractions

Inner muscle layer only
 Generally
occurs 1-3 times a day
 Involves (voluntary) relaxation of anal
sphincter & increase in intra-abdominal
pressure
mouth
break up food
moisten food
digest starch
kill germs
liver
produces bile
- stored in gall bladder
break up fats
pancreas
produces enzymes to
digest proteins & carbs
stomach
kills germs
break up food
digest proteins
store food
small intestines
breakdown food
- proteins
- starch
- fats
absorb nutrients
large intestines
absorb water
Appendix



Found at the junction of the small intestine &
large intestine
About 4 inches long
Function still unknown
 Storehouse

“reboot” digestive
system after illness
 Vestigial


for good bacteria
structure
Useless remnant
from our
evolutionary past
Additional surface
area for a
cellulose-rich diet
Compare these digestive tracts- how do
they demonstrate structure fits function?
Cecum stores
food material and
bacteria capable
to digesting
cellulose
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