Transcript Animal Nutrition Chapter 41 Animals are Heterotrophs A nutritionally balanced diet must satisfy 3 main needs: • Fuel or chemical energy • Organic raw materials for biosynthesis (food containing carbon to make carbon skeletons) • Essential.

Animal Nutrition
Chapter 41
Animals are Heterotrophs
A nutritionally
balanced diet must
satisfy 3 main needs:
•
Fuel or chemical
energy
•
Organic raw
materials for
biosynthesis (food
containing carbon
to make carbon
skeletons)
•
Essential nutrients
that the body
cannot make and
must be obtained
from food
Homeostatic Regulation of Cellular Fuel
Glucose is the main cellular fuel. Its
storage and use is closely
monitored by the animal body.
After a meal, glucose and other
monomers are absorbed into the
blood from the digestive tract.
1. If blood glucose levels rise above a
set point,
2. The pancreas release insulin, a
protein hormone into the blood
3. Insulin causes the uptake of
glucose by cells and stimulates
liver and muscle cells to store
glucose as glycogen
4. When blood glucose levels drop
below a set point, the pancreas
release glucagon that stimulate the
liver and muscle cells to
breakdown glycogen and release
glucose into the blood.
Nutritional Requirements
• Essential Fatty Acids
(certain unsaturated fatty acids like linoleic acid which is an omega-6 fatty
acid – found in sunflower oil and others)
• Essential Amino Acids
(Trp,Met,Val,Thr,Phe,Leu,Iso,Lys)
• Minerals
(Ca, P, S, Cl, Na, K, F, Mn, Mg, Fe, Cu, I, Co, Se, Cr, Mo)
• Vitamins (13 needed)
- Water-soluble
(B1, B2, B6, B12, Niacin, Folic acid, Biotin, Vitamin C, Pantothenic acid)
- Fat-soluble
(A, D, E, K)
Food Types
• Herbivores
• Carnivores
• Omnivores
Feeding Mechanisms
•Fluid-feeders
Suck nutrient-rich fluids from host
•Suspension-Feeders (Filter feeders)
Filter food from their water, so have to
be aquatic animals
•Deposit-feeders
Sift through dirt and other deposits for food
•Bulk-feeders
Eat large amounts and pieces – most
animals are bulk feeders.
•Substrate-feeders
Live on their food source and eat
through it
Food-Processing
•
•
•
•
Ingestion
Digestion
Absorption
Elimination
Where does digestion occur?
• Intracellular
Food vacuoles are helped by lysosomes to
break down food in the cytoplasm –
simplest digestive compartments
• Extracellular
Digestive organs and gastrovascular
cavities involved in digestion outside of
cells. Complex animals have the
alimentary canal or digestive tracts
Intracellular vs. Extracellular
All animals conduct both – Intracellular
and Extracellular digestion
Extracellular
• Large foods are ingested
• The digestive tract will release enzymes into its
lumen to breakdown the food into monomers
• These are absorbed by the individual cells that
line the tract
Intracellular
• Autophagy of dead organelles by lysosomes
• Phagocytosis by some cells such as
macrophages
The Mammalian Digestive System
•
•
•
•
The oral cavity, pharynx and esophagus
The stomach
The small intestine
The large intestine
The Oral Cavity
• Saliva contains an enzyme called Salivary Amylase,
that breaks down starch and glycogen into maltose
• Saliva contains a slippery glycoprotein called mucin
that protects lining of mouth from abrasions
• Saliva also contains anti-bacterial agents, buffers that
prevent tooth decay
• Teeth mechanically break food down
• Tongue tastes food and manipulates it during chewing
• Tongue shapes the chewed food into a “bolus” for
swallowing
The Pharynx
• Intersection between the esophagus and
trachea
• During swallowing, the tracheal opening is
blocked by a cartilaginous flap called epiglottis
The Esophagus
• Guides the bolus into the stomach, with the help
of involuntary smooth muscle spasms called
peristalsis
• The muscles at the top of the esophagus are
striated and so swallowing begins voluntarily
• Amylase continues to work on bolus on the way
down
The Stomach
• Located under the diaphragm, to the left of the
abdominal cavity
• Large enough to hold 2 liters of food and water –
so constant eating is not needed
• The inner epithelium secretes gastric juices –
which contains HCl, has pH of 2
• Juice also contains pepsin (secreted as pepsinogen by
chief cells in folds of stomach lining), an enzyme that
hydrolyzes proteins – works best in acidic
environments
Epithelial cells release mucous, that prevents the erosion of the
stomach lining – however, it does eventually erode and mitosis
replaces the cells
Bolus mixed with gastric juices is now a nutrient broth called Acid Chyme
Cardiac sphincter is the same as the gastro esophageal sphincter
Hiatal Hernia
• A hernia occurs when one part of the body
protrudes through a gap or opening into another
part.
• A hiatal hernia forms at the gastroesophageal
sphincter, where the esophagus joins the
stomach. Part of the stomach pushes through
this opening causing a hiatal hernia.
• A large hiatal hernia can allow food and acid to
back up into the esophagus, leading to
heartburn and chest pain.
Stomach Lining
(Goblet Cells)
(Other cells near the
pits secrete Gastrin)
(Parietal Cells)
(Chief Cells)
Helicobacter pylori
• Bacteria that cause gastric ulcers – lesions in the stomach lining
• H. pylori is a spiral-shaped gram-negative bacterium.
• it requires oxygen but at lower levels than those contained in the
atmosphere.
• With its flagella and its spiral shape, the bacterium drills into the
mucus layer of the stomach, and then can either be found
suspended in the gastric mucosa or attached to epithelial cells.
• It excretes the enzyme urease, which converts urea into ammonia
and bicarbonate. The release of ammonia is beneficial to the
bacterium since it partially neutralizes the very acidic environment of
the stomach (whose very purpose is to kill bacteria). Ammonia is,
however, toxic to the epithelial cells, and with other products of H.
pylori, including protease, catalase, and phospholipases, causes
damage to those cells
Helicobacter pylori
The Small Intestine
• Workhorse of digestion and absorption
• Longest section of alimentary canal
• First 25 cm called the duodenum where Acid
Chyme from stomach mixes with digestive juices
from pancreas, liver, gall bladder and gland
cells of the intestinal lining
• The middle section of the SI is called the
jejunum
• The last section of the SI is called the ileum
Small Intestine
• The lumen of the small intestine receives
secretions from
– the pancreas and
– Liver
– The small intestine itself
• The SI
– completes digestion of the nutrients in chyme,
– absorbs the products of digestion, and
– transports the remaining residues to the large
intestine.
The other players in SI digestion
Enzymatic Actions in the Duodenum
1. Pancreas
- Proteases called trypsinogen, chymotrypsinogen and procarboxypepsidase
are secreted into the SI lumen and then become their active forms – trypsin,
chymotrypsin and carboxypepsidase. The activation of these enzymes is
triggered by an SI enzyme called enteropeptidase.
These 3 activated enzymes help break down protein in the acid chyme.
- Pancreatic Lipase breaks down dietary fat into 1 monoglyceride and 3 fatty
acids
- Pancreatic Amylase hydrolyzes dietary starch into maltose
- Bicarbonate (HCO3- ) and Water neutralize the acidity in the acid chyme
- Two nucleases breakdown DNA and RNA.
2.
Small Intestine
- Secondary protein hydrolyzing enzymes called aminopepsidase and
dipeptidases found in the lining of the small intestine also help speed the process
of protein digestion.
Summary of Protein Digestion in SI
Aminopeptidase
Dipeptidase
Regulation of Pancreatic Secretion
• The nervous and endocrine systems regulate
release of pancreatic juice.
• Secretin from the duodenum stimulates the
release of pancreatic juice with a high
bicarbonate ion concentration but few
digestive enzymes.
• Cholecystokinin from the wall of the small
intestine stimulates the release of pancreatic
juice with abundant digestive enzymes.
Enzymatic Actions in the SI
3. Liver
- Produces bile, which is a combination of bile salts, lecithin, *bilirubin,
water and cholesterol
- Bile is stored in the gall bladder and released into the SI lumen through
the common bile duct
- Bile emulsifies dietary lipids, so that pancreatic lipase can breakdown
each triglyceride into fatty acids and glycerol.
*Bilirubin is the main bile pigment that is formed from the breakdown
of heme in red blood cells. The broken down heme travels to the liver,
where it is secreted into the bile by the liver. Bilirubin is passed in the
feces and gives it the yellow-brown color. Excess bilirubin causes
jaundice and stains skin, eyes and nails yellow.
Composition of Bile
• Bile is a yellowish-green liquid that hepatic
cells secrete; it includes water, bile salts, bile
pigments (bilirubin, biliverdin), cholesterol,
and electrolytes.
• Bile pigments are breakdown products from
red blood cells.
• Only the bile salts have a digestive function.
The gallbladder
• The gallbladder is a pear-shaped sac lying on
the interior surface of the liver.
• It is connected to the cystic duct, which joins
the hepatic duct; these two ducts merge to
form the common bile duct leading to the
duodenum.
• A sphincter muscle controls the release of
bile from the common bile duct.
Regulation of Bile Release
• Bile does not normally enter the duodenum
until cholecystokinin stimulates the
gallbladder to contract.
• The hepatopancreatic sphincter remains
contracted unless a peristaltic wave
approaches it, at which time it relaxes and a
squirt of bile enters the duodenum.
Functions of Bile Salts
• Bile salts emulsify fats into smaller
droplets, so that pancreatic lipase can
hydrolyze the triglycerides
• Aids in the absorption of fatty acids,
cholesterol, and certain vitamins
The Jejunum and Ileum
• Most of the digestion in the SI occurs in
the first section – the Duodenum
• The next sections of the SI – the Jejunum
and the Ileum, are mainly involved in the
absorption of nutrients and water
Absorption of Nutrients in the SI
• Circular folds in the epithelial tissue lining of the
intestines have finger-like projections called villi.
• Each epithelial cell of the villi has many microscopic
microvilli.
• This increases the surface area for absorption
• Capillaries and a lymphatic vessel called a lacteal
penetrate the villi – this is so that nutrients can be
absorbed across the intestinal lining, across the
capillaries, into the blood stream or lymphatic system.
Nutrients have to traverse only two layers of cells – one
layer of intestinal epithelial cells and one layer of
capillary cells
The movement of nutrients can be either active or
passive transport.
Absorption in the Small Intestine
• The small intestine is the major site of absorption within
the alimentary canal.
• There are digestive enzymes on microvilli, including
peptidases, sucrase, maltase, and lactase, and intestinal
lipase.
• Monosaccharides and amino acids resulting from
carbohydrate and protein digestion are absorbed by the
villi through active transport and enter blood capillaries.
• The intestinal villi also absorb water (by aquaporins) and
electrolytes (by active transport).
Fat Absorption
• Fatty acids are absorbed and transported differently than
the other nutrients.
1. Fats are digested into individual fatty acids in the SI
lumen by bile and lipase.
2. These fatty acids enter the cells of the SI lining via
microvilli
3. The endoplasmic reticula of the cells reconstruct the
fats (triglycerides).
4. These fats collect in clusters that become encased in
protein
5. These protein+ fat clusters are called chylomicrons.
6. Chylomicrons are carried away in lymphatic lacteals
until they eventually join the bloodstream.
Microvilli
The Lymphatic System
• Consists of organs, ducts, and nodes.
• Transports a watery clear fluid called lymph.
• This fluid distributes immune cells and other factors
throughout the body. It also interacts with the blood
circulatory system to drain fluid from cells and tissues.
• The lymphatic system contains immune cells called
lymphocytes, which protect the body against antigens
(viruses, bacteria, etc.) that invade the body.
Main functions of lymphatic system:
• to collect and return interstitial fluid, including plasma protein
to the blood,
and thus help maintain fluid balance,
• to defend the body against disease by producing
lymphocytes,
• to absorb lipids from the intestine and transport them to the
blood.
Summary of Digestion
After Absorption
• The capillaries carrying the nutrient-rich
blood join to form the hepatic portal vessel
which carries the nutrients to the liver
• The blood then goes to the heart, which
pumps the nutrient and oxygen to the rest of
the body cells
Hormones That Regulate Digestion
The hormones that control digestion are gastrin, secretin, and
cholecystokinin (CCK):
• Gastrin (Secreted by cells in stomach lining)
– causes the stomach to produce acid
– necessary for the normal growth of the lining of the stomach, small
intestine, and colon.
• Secretin (An enterogastrone secreted by cells in wall of duodenum)
– causes the pancreas to release juices with bicarbonate.
– stimulates the stomach to produce pepsin,
– stimulates the liver to produce bile.
• CCK (cholecystokinin) (An enterogastrone secreted by cells in wall of
duodenum)
– causes the pancreas to grow and to produce its digestive enzymes
– causes the gallbladder to empty stored bile into the SI.
hormones in the GI that regulate appetite:
• Ghrelin is produced in the stomach and upper
intestine in the absence of food in the digestive
system and stimulates appetite.
• Peptide YY is produced in the GI tract in
response to a meal in the system and inhibits
appetite.
Both of these hormones work on the brain to
help regulate the intake of food for energy.
Large Intestine
• The large intestine absorbs water and electrolytes and
forms and stores feces.
Parts of the Large Intestine
• The large intestine consists of the cecum
(pouch at the beginning of the large intestine),
colon (ascending, transverse, descending, and
sigmoid regions), the rectum, and the anal
canal.
• The anal canal opens to the outside as the
anus; it is guarded by an involuntary internal
anal sphincter and a voluntary external anal
sphincter muscle.
The Large Intestine
•AKA colon
•Carnivores have a small cecum ;
the appendix is a part of it
Water absorption is the main
task of LI (90% reabsorbed)
Waste (feces) is eliminated,
after being stored in the
rectum
• Large population of bacteria – most harmless, some mutualistic –
E.coli produce vitamin , others produce vitamin B, folic acid, biotin, etc.
• Some of these bacteria breakdown the undigested cellulose for food
for themselves.
• Bacteria produce gases like methane and hydrogen sulfide
• Feces contain undigested food like cellulose, bacteria, salts, bilirubin
makes it yellow!
Evolutionary Adaptations of
Digestive Systems
• Teeth – sharp incisors, canines vs. molars
• Cecum – long vs. short
• Four-chambered stomach – ruminants like
cows and sheep can regurgitate and rechew food – their stomachs contain
cellulose-digesting bacteria.
• Symbiotic bacteria – vitamin production,
cellulose digestion
Carnivores – have sharp teeth to tear flesh
Herbivores have sharp front teeth to cut vegetation and flat rear teeth
then to grind it down.
Teeth that fit the diet
Carnivores – have sharp teeth to tear flesh
Herbivores have
sharp front teeth to
cut vegetation and flat
rear teeth then to
grind it down.
Omnivore teeth
Ruminant Digestive Tract
4-Chambered Stomach
THE END