Download Chapter 41 - Parkway C-2

Chapter 41 - Animal Nutrition
Introduction to Anatomy and Physiology
-Form matches function
-Natural selection acts upon variations in form that allows for
populations of organisms to be successful
-Material exchange with the internal and external environments
is dependent on the size and shape of the animal
!
-Exchange is dependent upon diffusion across a plasma
!
cell membrane
Diffusion
(a) Single cell
Simple
multicellular
organisms
possess few
membranous
layers over
which materials
must be exchanged
Complex Multicellular Organisms Cannot Freely Exchange
Materials with their Environment
External environment
Mouth
Food
CO2
O2
Bl
oo
d
0.5 cm
Respiratory
system
A microscopic view of the lung reveals
that it is much more sponge-like than
balloon-like. This construction provides
an expansive wet surface for gas
exchange with the environment (SEM).
Cells
Heart
Nutrients
Circulatory
system
10 µm
Interstitial
fluid
Digestive
system
The lining of the small
intestine, a digestive organ, is
elaborated with fingerlike
projections that expand the
surface area for nutrient
absorption (cross-section,
SEM).
50 µm
Animal
body
Excretory
system
Anus
Unabsorbed
matter (feces)
Metabolic waste
products (urine)
Inside a kidney is a mass of microscopic
tubules that exchange chemicals with
blood flowing through a web of tiny
vessels called capillaries (SEM).
Solution = Highly, folded internal membranes w/ maximal
surface area
Organizational Hierarchy in Organisms
1. Cells
All organisms are composed
of cells (Duh!)
2. Tissues
Tissues are groups of cells with
a similar structure and function
3. Organs
Different (2 or more) tissues are
used to construct organs
4. Organ Systems
5. Organisms
Various organs work together
as part of organ systems
Organ systems are required for the
maintenance of homeostasis within
an organism
Organ Systems Found in Most Animals
Through the combined actions of all of the organ systems, an
organism is capable of maintaining homeostasis (balance
between the internal and external environments)
Model for a Homeostatic Regulatory Mechanism
The control center must have a receptor, a control center,
and an effector
Negative feedback: If
Response
temperature increases (detected
No heat
produced
by receptor and processed by
Heater
control center), heater is turned off
turned
Room
off
temperature
(effector), and temperature
decreases
decreases
Set
Too
point
hot
Set point
Control center:
thermostat
Room
temperature
increases
Too
cold
Set
point
Heater
turned
on
Response
Heat
produced
Negative feedback - A response
that counteracts or works in
opposition to the stimulus
Positive feedback - A response
that reinforces the stimulus
Sweat glands secrete
sweat that evaporates,
cooling the body.
Thermostat in
hypothalamus
activates cooling
mechanisms.
Blood vessels
in skin dilate:
capillaries fill
with warm blood;
heat radiates from
skin surface.
Increased body
temperature (such
as when exercising
or in hot
surroundings)
+ΔT
-ΔT
Body temperature
decreases;
thermostat
shuts off cooling
mechanisms.
Homeostasis:
Internal body temp.
of approx.. 36–38°C
Body temperature
increases;
thermostat
shuts off warming
mechanisms.
+ΔT
-ΔT
Blood vessels in skin
constrict, diverting blood
from skin to deeper tissues
and reducing heat loss
from skin surface.
Skeletal muscles rapidly
contract, causing shivering,
which generates heat.
Decreased body
temperature
(such as when
in cold
surroundings)
Thermostat in hypothalamus
activates warming mechanisms.
Digestive System Discussion Questions
Percent remaining
A peanut butter and jelly sandwich contains a variety of
carbohydrates, fats, and proteins. Complete the graph below
to indicate the relative percentages of carbohydrate, fat, and
protein that remain in this ingested food as it progresses from
your mouth through your digestive tract. Be prepared to
explain your reasoning.
Mouth-esophagus-stomach-small intestine-large intestine-rectum
Digestive Physiology Discussion Questions
1. Saliva contains water (to moisten food), mucus (to lubricate food), salivary
amylase (to break down starch), bicarbonate (to buffer acids in food), and
antibacterial agents. Why might these last three components be necessary
when the stomach is the next destination anyway?
2. Everyone knows different parts of the tongue are especially sensitive to
different tastes. But why should we devote tongue space to bitterness?
3. In humans, the uvula hangs as a pendant from the posterior end of the soft
palate. During swallowing, it lifts upward and closes off the nasopharynx.
Why is this important?
4. Is diarrhea a defensive strategy to rid your body of pathogens or a way for
intestinal pathogens to spread to others (still occurs in less developed
countries with no sewage treatment)?
5. Would you expect carnivores to have longer or shorter intestine than
herbivores?
6. What happens if the contents of the colon pass too rapidly through the
colon? Too slowly?
Complete the concept map for the functions of the digestive
system. Do your best to fill in all of the ovals.
The main function of the digestive system is to
Break down food into
smaller molecules so
that it can be used as energy
This is accomplished by
Ingestion
Digestion
Absorption
Elimination
The Four Stages of Food Processing
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
(enzymatic hydrolysis)
Nutrient
molecules
enter body
cells
Undigested
material
Food
1 INGESTION
2 DIGESTION
3 ABSORPTION
4
ELIMINATION
Animals with simple body plans have a
gastrovascular cavity that functions in both
digestion and distribution of nutrients
Tentacles
Mouth
Food
Gastrovascular
cavity
Epidermis
Mesenchyme
Gastrodermis
Nutritive
muscular
cells
Flagella
Gland cells
Food vacuoles
Mesenchyme
Simple invertebrates such as
cnidarians and
platyhelmenthes utilize
extracellular digestion
followed by endocytosis to
absorb nutrients
More complex animals
possess a complete digestive
tract (i.e. alimentary canal)
with an opening (mouth) and
an exit (anus).
Anatomy of the Digestive System
(Alimentary Canal and Accessory Organs)
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Gallbladder
(behind liver)
Stomach
Pancreas (behind
stomach)
Large intestine
Small intestine
Rectum
Mammalian Digestive System
A long digestive tube with accessory glands that secrete
digestive juices that aid digestion
Salivary
glands
Oral cavity
Parotid gland
Sublingual gland
Esophagus
Pyloric
sphincter
Liver
Ascending
portion of
large intestine
Mouth
Pharynx
Esophagus
Submandibular gland
Stomach
Liver
Pancreas
Pancreas
Small intestine
Large intestine
Rectum
Appendix
Cecum
Gallbladder
Gallbladder
IIeum
of small
intestine
Figure 41.15
Salivary
glands
Cardiac
orifice
Tongue
Duodenum of
small intestine
Stomach
Small
intestines
Large
intestines
Rectum
Anus
A schematic diagram of
the human digestive system
Anus
Human Digestive System Overview
In the oral cavity, food is lubricated and digestion begins
– Teeth chew food into smaller particles that are exposed
to salivary amylase, initiating the breakdown of glucose
polymers
The stomach stores food and secretes gastric juice, which
converts a meal to acid chyme
-- Gastric juice is made up of hydrochloric acid and the
enzyme pepsin
The small intestine is the longest section of the alimentary
canal
- Primary organ involved in digestion and absorption
The large intestine completes the absorption of water and
compaction of feces prior to defecation
-Bacteria in the lower bowel produce vitamins
From Mouth to Stomach
4 The esophageal
sphincter relaxes,
allowing the
bolus to enter the
esophagus.
Epiglottis
up
Bolus of food
Tongue
Glottis
down
and open
Pharynx
Epiglottis
up
Glottis
Larynx
Esophageal
Epiglottis
sphincter
down
contracted
Trachea
Esophagus
To lungs
To stomach
1 When a person is not
swallowing, the esophageal
sphincter muscle is contracted,
the epiglottis is up, and the
glottis is open, allowing air
to flow through the trachea
to the lungs.
Glottis up
and closed
2 The swallowing
reflex is triggered
when a bolus of
food reaches the
pharynx.
Esophageal
sphincter
5 After the food
relaxed
Esophageal
sphincter
contracted
has entered the
esophagus, the
larynx moves
downward and
opens the
breathing
passage.
Relaxed
muscles
Contracted
muscles
3 The larynx, the
upper part of the
6 Waves of muscular
respiratory tract,
contraction
moves upward and
(peristalsis)
tips the epiglottis
move the bolus
over the glottis,
down
the esophagus
preventing food
to the stomach.
from entering the
trachea.
Relaxed
muscles
Stomach
Movement of Digested Materials
Movement through the digestive system (i.e. the alimentary
canal) is created by muscle contractions called peristalsis
Peristalsis – progressive contraction
of muscle around an organ; moves
contents in one direction
Peristalsis Animation
What is reverse peristalsis?
Journey Through the Digestive System
Food that has been chewed and swallowed travels down the
esophagus to the stomach
Esophageal sphincters or “gates” regulate the passage of
food at the beginning and end of the esophagus
Sphincters located at
the beginning of the
small intestine (i.e. pyloric
sphincter --> duodenum)
regulate the passage of
digested food from the
stomach into the rest of
the digestive system
Stomach
Primary function
To continue digestion of food particles that have passed
through the mouth, pharynx, and esophagus
The combination of partially digested food and gastric
juices produces chyme, a thick mixture of partially digested food
The digestion of protein begins in the stomach due to the action
of pepsin, a hydrolytic protease
!
-Pepsin is synthesized from an inactive precursor called
!
pepsinogen (a zymogen); HCl responsible for conversion
Anatomy of the Stomach
Esophagus
Cardiac orifice
5 µm
Stomach
Interior surface of stomach.
The interior surface of the
stomach wall is highly folded
and dotted with pits leading
into tubular gastric glands.
Gastric gland. The gastric
glands have three types of cells
that secrete different components
of the gastric juice: mucus cells,
chief cells, and parietal cells.
Pyloric
sphincter
Small
intestine
Folds of
epithelial
tissue
Epithelium
3
Pepsinogen
2
HCl
1 Pepsinogen and HCI
are secreted into the
Pepsin (active enzyme)
lumen of the stomach.
1
2 HCl converts
pepsinogen to pepsin.
Mucus cells secrete mucus,
which lubricates and protects
the cells lining the stomach.
Chief cells secrete pepsinogen, an inactive form of the
digestive enzyme pepsin.
Parietal cells secrete
hydrochloric acid (HCl).
Chief cell
Parietal cell
3 Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Stomach Wall
The inside of the stomach is lined with thick mucus
Mucus serves as an internal coating that protects the stomach
from highly acidic stomach acid
Very little, if any, absorption takes place inside of the stomach
because of the mucus
Bacteria
1 µm
Mucus
layer of
stomach
Gastric ulcers, lesions in the
lining are caused mainly by the
bacterium Helicobacter pylori
Functions of the Small Intestine
Primary Functions
1) To continue digestion with the assistance of various
enzymes from the pancreas and bile from the liver
!
2) To begin the absorption of nutrients from chyme
!
-90% of nutrient absorption takes place in the
!
small intestine
A cross-section through
the small intestine reveals
an intriguing structure…
Structure of the Small Intestine
Microvilli
(brush border)
Vein carrying blood to
hepatic portal vessel
Blood
capillaries
Epithelial
cells
Muscle layers
Villi
Epithelial cells
Large
circular
folds
Lacteal
Key
Nutrient
absorption
Intestinal wall
Villi
Lymph
vessel
Villi (s. villus) increase the surface area inside of the small
intestine helping the organ absorb nutrients from digested food
Cross-section through the Small Intestine
Increased surface area is essential for absorption in the intestine
The small intestine is organized into folds. Each fold is called a
villus.
Villi increase the surface area inside of the small intestine
Microvilli at the tip of each villus further increase the area
available for absorption
Digestive Enzymes and Their Location in
the Human Body
Site
Enzyme
Role in Digestion
Mouth
Salivary amylase
Stomach
Pepsin
Breaks down starches into
smaller polysaccharides
Breaks down proteins into small
peptides
Small intestine
(from pancreas)
Pancreatic Amylase and other
carbohydrases
Trypsin, Chymotrypsin
Pancreatic Lipase
Continues the breakdown of
polysaccharides
Continues the breakdown of
proteins
Breaks down fat into components
Emulsification of fat
Liver
Bile
Digestive System Discussion Questions
1. Although enormous quantities of various enzymes are added
to the contents of the duodenum of the small intestine, no
traces of enzymatic activity are left in the intestinal contents
when they pass into the large intestine (colon). Why? What
happens to the enzymes?
Anatomy of the Liver, Gall Bladder, Pancreas,
and Small Intestine
Liver
Gallbladder
Duodenum
Bile duct
Pancreas
Pancreatic duct
To rest of small intestine
Structure of the Liver
Liver cells synthesize and secrete bile
!
-1 liter of bile is synthesized daily!
Bile enters the small intestine
through the bile duct
Bile can also be stored in the
gall bladder
Bile is responsible for the
digestion of fats
How does bile help the small intestine to digest fats???
Pancreas
Primary Functions of the Pancreas
1) To produce a mixture of digestive enzymes that help to
neutralize the acidic chyme arriving from the stomach
!
! Important enzymes coming from the pancreas include:
! !
Lipases = Fat-digesting enzymes
! !
Carbohydrases = Carbohydrate-digesting enzymes
! !
Proteases = Protein-digesting enzymes
2) The production of insulin and glucagon
!
-Insulin and glucagon regulate the amount of glucose
!
in the blood at any time
Structure of the Pancreas
Pancreatic Enzymes
As mentioned before the pancreas secretes a mixture of
digestive enzymes as food enters the small intestine
Lipases: Responsible for digesting lipids or fats
!
Ex. Pancreatic lipase
Proteases: Responsible for digesting proteins
!
Ex. Trypsin, Chymotrypsin
Carbohydrases: Responsible for digesting carbohydrates
(i.e. sugars and starches)
!
Ex. Pancreatic amylase
Functions of the Large Intestine
Primary Functions
1) Absorption of water from digested food/chyme
2) Compaction and
storage of feces
3) Production of
essential vitamins
!
-Bacteria (E.coli) in
!
the large intestine
!
convert chemical
!
precursors into
!
vitamins (B5, K,
!
biotin)
Digestive System Discussion Questions
2. Most of the blood that leaves the digestive tract of a human
is collected into a series of veins that merge to form the
hepatic portal vein. The hepatic portal vein carries blood to
the liver. Liver capillaries drain into the hepatic vein which
carries blood to the vena cava. The vena cava transports
blood from the body to the right atrium.
Some of the products of digestion enter a different system of
transport, the lacteal system. The lacteal system bypasses
the liver and carries its contents directly to the right atrium.
Which products of digestion are carried in the blood to the
liver?
Which products of blood are carried via the lacteal system?
How does the concentration of fat leaving the small intestine
compare to the concentration in the right atrium?
Do Now - Digestive System Discussion Questions
A friend of yours has come up with a new idea for people who
don’t have time to eat. She has developed a high-powered
Blenderizer that breaks food up into very small particles. She
has tested her product on amoeba and Paramecia. Both of
these single-celled organisms can pick up these small
particles and incorporate them into food vacuoles. Your friend
is hoping to market the Blenderizer to busy people who could
“blenderize” their food and use an IV bag and tube to run the
food directly into their blood system. Your friend comes to you
for advice and possible financial support to get her idea off
the ground. What would you say to her?
Hormones Help Coordinate the Secretion of
Digestive Juices into the Alimentary Canal
Enterogastrone secreted by
the duodenum inhibits
peristalsis and acid secretion by
the stomach, thereby slowing
digestion when acid chyme rich
in fats enters the duodenum.
Liver
Enterogastrone
Gallbladder
CCK
Amino acids or fatty acids in the
duodenum trigger the release of
cholecystokinin (CCK), which
stimulates the release of digestive
enzymes from the pancreas and
bile from the gallbladder.
Gastrin
Stomach
Pancreas
Gastrin from the stomach
recirculates via the bloodstream
back to the stomach, where it
stimulates the production
of gastric juices.
Secretin
Duodenum
CCK
Key
Stimulation
Inhibition
Secreted by the duodenum,
secretin stimulates the pancreas
to release sodium bicarbonate,
which neutralizes acid chyme
from the stomach.
1. Barry is participating in a nutrition study in which he must follow a
prescribed diet and have his blood tested regularly. On one of his visits,
his test results indicate low levels of insulin, elevated levels of glucagon,
and normal levels of cortisol and growth hormone. What would you
expect his levels of blood glucose to be?
Hormone
Function
Physiological condition
Insulin
Lowers blood
glucose levels
Insulin levels increase
after large meal; decrease
during fasting or between
meals
Glucagon
Raises blood
glucose levels;
signals conversion
of stored glycogen
to glucose
Glucagon levels increase
during fasting or between
meals, decrease upon
consumption of food
Epinephrine
Increase blood
glucose levels by
signaling glycogen
breakdown
Increased metabolic activity; loss of
blood volume or reduction
in blood pressure
Homeostasis - Regulation of Glucose Levels
1 When blood glucose
level rises, a gland called
the pancreas secretes insulin,
a hormone, into the blood.
2 Insulin enhances the
transport of glucose into body
cells and stimulates the liver
and muscle cells to store
glucose as glycogen. As a
result, blood glucose level
drops.
STIMULUS:
Blood glucose
level rises
after eating.
Homeostasis:
90 mg glucose/
100 mL blood
4Glucagon promotes
the breakdown of
glycogen in the
liver and the
release of glucose
into the blood,
increasing blood
glucose level.
STIMULUS:
Blood glucose
level drops
below set point.
3 When blood glucose
level drops, the pancreas
secretes the hormone
glucagon, which opposes
the effect of insulin.
Negative Feedback - Regulation of Blood Sugar
Insulin and Glucagon Signaling
Stimulus:
Rising blood
glucose level
(After a meal)
Negative Feedback - Regulation of Blood Sugar
Insulin and Glucagon Signaling
Stimulus:
Removal
of excess
glucose
from blood
(Skipping a
meal)
Hormones Regulate Both Long-term and Short-term
Appetite by Affecting a “Satiety Center” in the Brain
Secreted by the stomach
wall, ghrelin is one of the
signals that triggers feelings
of hunger as mealtimes
approach. In dieters who lose
weight, ghrelin levels increase,
which may be one reason
it’s so hard to stay on a diet.
Produced by adipose (fat)
tissue, leptin suppresses
appetite as its level increases.
When body fat decreases,
leptin levels fall, and appetite
increases.
Ghrelin
The hormone PYY,
secreted by the small
intestine after meals,
acts as an appetite
suppressant that
counters the appetite
stimulant ghrelin.
Insulin
Leptin
PYY
A rise in blood sugar level
after a meal stimulates
the pancreas to secrete
insulin (see Figure 41.3).
In addition to its other
functions, insulin suppresses
appetite by acting on the brain.
Leptin is a Critical Satiety Hormone
Ob-/- (leptin-deficient) Wild-type
mouse
littermate