Transcript Digestion in Animals – part 2

Digestion in Animals – part 2
Phylum Chordata
• Dorsal, hollow nerve cord
• Notochord
Class Osteichthyes –
bony skeleton fish
Class Amphibia – smooth, slimy
skin, must return to the water to
reproduce
Class Reptilia – scaly skin;
lay eggs on land
Class Aves – Birds – feathers;
fly (most); lay eggs with hard shells
on land
Class Mammalia – feed young with
milk from mammary glands; hair
Mammalia – Monotremes –
Egg-laying Mammals
Mammalia – Marsupials – pouched
mammals
Mammalia – Placental Mammals –
young develop in placenta before
birth
VI. The Human Digestive System
Consists of muscular tube extending from
mouth to anus, and associated organs
(e.g., salivary glands, gall bladder, liver,
pancreas).
B. Overview—Food is ingested, digested, nutrients absorbed,
waste expelled; different types of foods (proteins, fats)
acted upon in different parts of system.
1. Ingestion—entry of food through mouth
2. Mechanical processing—physical manipulation of solid
food by teeth, mixing by tongue
3. Digestion—chemical breakdown of food into small
molecules
4. Secretion—release of water, acids, enzymes, buffers
from lining of tract and accessory organs, aid in
digestion
5. Absorption—movement of small organic molecules,
electrolytes, vitamins, water, across epithelium into
capillaries and lymphatic vessels
6. Excretion—elimination of waste after compaction
VII. Components of the Digestive System
Digestive (or alimentary or
gastrointestinal) tract begins in oral
cavity, ends in rectum and anus.
VII. Components of the Digestive
System
Oral cavity—Food tasted,
chewed, partially
digested here.
Salivary glands—produce almost half a
gallon (1.5 L) of saliva each day; saliva is
99 percent water, also ions, buffers, waste
products, antibodies, & digestive enzymes.
Teeth break down connective animal tissues and
plant fibers in food.
Pharynx and esophagus
1. Pharynx, or throat, transmits solid
food, liquids, air; muscular
contractions in pharyngeal muscles
initiate swallowing.
2. After swallowing from throat, food
moves through all other structures
by the process of peristalsis
3. Esophagus is muscular tube, about
0.8 in. diameter; begins in pharynx,
ends in stomach.
E. Stomach—Dimensions vary; can be narrow tube
when empty or expanded into a sac that can hold
almost 0.5 gallon; accordion-like folds in muscle
wall (rugae) allow expansion.
Functions include:
a) Temporary storage of ingested food
b) Mixing of ingested food
c) Digestion of
proteins through
acids and enzymes
c) Absorption of
some substances
(e.g., alcohol)
Digestion by gastric juices
a)Epithelium secretes gastric juices
containing HCl and pepsin from glands
in gastric pits; HCl reduces pH to level
suitable for protein-degrading activity of
pepsin.
b) Epithelium also secretes mucous,
which coats inner lining of stomach and
protects it from corrosive action of
gastric juices.
Small intestine is almost 10 ft long, 1.6
to 1 inch wide; about 80 percent of
absorption occurs here; has three
regions:
1. Duodenum—closest to stomach;
connects with it through pyloric
sphincter; receives chyme from
stomach, secretions from pancreas
and liver.
2. Jejunum—about 3 ft long; most
chemical digestion and absorption
of nutrients and water occurs here.
3. Ileum—about 6 ft long; connects
with large intestine through
sphincter muscle.
Pancreas extends laterally from
duodenum; about 6 in. long; functions:
1. secretes, digestive enzymes lipases, carbohydrases, proteases)
and buffers.
2. produce s
a) Insulin—causes cells to take up
sugars from bloodstream.
b) Glucagon—releases glucose
from storage in skeletal
muscles, liver.
Liver and gallbladder
1. Liver is largest organ in body (not
counting skin); has two lobes;
Functions of the liver:
a) Regulating body metabolism; extracts
nutrients absorbed into bloodstream;
monitors and adjusts levels of key nutrients
in blood.
b) Removes and destroys some toxins
(e.g., alcohol).
c) Serves as large reservoir of blood;
phagocytes here constantly remove cell
debris, pathogens, damaged RBCs.
d) Produces bile, which aids in digestion of
fats.
2. Gallbladder is muscular sac that stores bile
produced by liver; bile produced in liver may flow
directly into small intestine through common
hepatic duct (as during mealtimes), or may back
up through cystic duct to be stored in gallbladder.
Large intestine: is about 5 ft long
1. Functions—holds and compacts undigested
material; absorbs water and vitamins
produced by intestinal bacteria.
2. Structure—has three main regions:
a) Cecum—expanded chamber, receives chyme
from small intestine through ileocecal valve;
vermiform appendix is slender, hollow
extension containing lymphatic tissue.
b) Colon—longest portion; has characteristic
series of muscular pouches; water is
reabsorbed here; bacterial activity may
produce hydrogen sulfide (produces odor of
feces), flatus (gas) due to bacterial action on
undigested plant polysaccharides.
c) Rectum—chamber at end of tract; usually
empty, except when peristaltic contractions
force feces into it from colon; triggers
defecation reflex, excretion through opening,
the anus.
VIII.Different Digestive Processes for
Different Foods and Nutrients
A. Large organic molecules broken down to
simple building blocks prior to absorption;
digestive enzymes split bonds between
basic units through hydrolysis.
1. Carbohydrates
a) Digestion begins in mouth; salivary
amylases break complex carbohydrates
down to 2–3 carbon sugars.
b) In duodenum, pancreatic amylases
digest 2–3 carbon sugars to singlecarbon sugars; these pass into
interstitial fluid of microvilli, enter
intestinal capillaries, then are carried to
liver via hepatic portal vein.
2. Proteins
a) Digestion begins in stomach; low pH,
activity of pepsin split proteins into small
fragments.
b) In duodenum, pancreatic proteases break
protein fragments into amino acids; amino
acids absorbed by microvilli, carried to liver.
3. Lipids (mostly triglycerides)
a) Emulsified by bile to form small droplets
suitable for enzyme action.
b) Pancreatic lipases break lipids into fatty
acids.
c) Fatty acids enter intestinal cells, bind to
lipid-transport proteins, then enter lymphatic
vessels that underlie microvilli and eventually
enter venous circulation.
B. Water and vitamins
1. Water: in addition to 2 L to 2.5 L of
water that enters as food and drink,
secretions of tract contribute 6–7 L
more; most of it is reabsorbed, only
about 150 mL leaves in fecal waste.
2. Vitamins are organic compounds,
needed in small quantities
a) Fat-soluble vitamins (A, D, E, K)
are stored in body; excessive
intake leads to toxic effects,
liver damage.
b) Water-soluble vitamins (C, B) not
readily toxic; excess excreted.
The
End