Download 38–2 The Process of Digestion

Biology
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38–2 The Process of
Digestion
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38–2 The Process of Digestion
Digestion
What are the organs of the digestive
system?
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38–2 The Process of Digestion
Digestion
The digestive system includes the mouth,
pharynx, esophagus, stomach, small
intestine, and large intestine.
Other structures add secretions to the
digestive system, and aid in digestion.
These include the salivary glands,
pancreas, and liver.
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38–2 The Process of Digestion
38–2 The Process of Digestion
The Digestive System
Mouth
Pharynx
Salivary
glands
Esophagus
Stomach
Liver
Pancreas
Gallbladder
Large intestine
Small intestine
Rectum
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38–2 The Process of Digestion
The Mouth
What is the function of the digestive
system?
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38–2 The Process of Digestion
The Mouth
The function of the digestive system is to
help convert foods into simpler molecules
that can be absorbed and used by the cells
of the body.
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The Mouth
The Mouth
Chewing begins mechanical digestion, which is the
physical breakdown of large pieces of food into
smaller pieces.
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38–2 The Process of Digestion
The Mouth
The teeth cut, tear, and crush food into small
fragments.
As the teeth cut and grind the food, salivary glands
secrete saliva, which moistens food and makes it
easier to chew.
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The Mouth
Saliva helps ease the passage of food through the
digestive system and also begins the process of
chemical digestion.
Saliva contains amylase, an enzyme that breaks the
chemical bonds in starches and releases sugars.
Saliva also contains lysozyme, an enzyme that fights
infection.
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38–2 The Process of Digestion
The Esophagus
The Esophagus
From the throat, the chewed food passes through
the esophagus, or food tube, into the stomach.
Food is moved along by contractions of smooth
muscle.
These contractions, known as peristalsis,
squeeze the food through the esophagus into the
stomach.
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38–2 The Process of Digestion
The Esophagus
Esophagus
Peristalsis
Bolus
Muscles
contracted
Stomach
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38–2 The Process of Digestion
The Esophagus
The cardiac sphincter closes the esophagus after
food has passed into the stomach.
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38–2 The Process of Digestion
The Stomach
The Stomach
Food from the esophagus empties into the
stomach.
The stomach continues mechanical and chemical
digestion.
Alternating contractions of three smooth muscle
layers churn food.
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38–2 The Process of Digestion
The Stomach
Chemical Digestion
The stomach lining has millions of gastric glands
that release substances into the stomach.
• Some glands produce mucus, which lubricates
and protects the stomach wall.
• Other glands produce hydrochloric acid, which
makes the stomach contents very acidic.
• Other glands produce pepsin, an enzyme that
digests protein.
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38–2 The Process of Digestion
The Stomach
Pepsin and hydrochloric acid begin protein digestion.
Pepsin breaks proteins into smaller polypeptide
fragments.
Other enzymes are denatured (broken down) by
stomach acid.
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38–2 The Process of Digestion
The Stomach
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38–2 The Process of Digestion
The Stomach
Mechanical Digestion
The stomach contracts to churn fluids and food,
gradually producing a mixture known as chyme.
After 1–2 hours, the pyloric valve between the
stomach and small intestine opens and chyme
flows into the small intestine.
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38–2 The Process of Digestion
The Small Intestine
The Small Intestine
As chyme is pushed through the pyloric valve, it
enters the duodenum.
The duodenum is the first of three parts of the
small intestine, and is where most digestive
enzymes enter the intestine.
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38–2 The Process of Digestion
The Small Intestine
Most chemical digestion and absorption of food
occurs in the small intestine.
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38–2 The Process of Digestion
The Small Intestine
Accessory Structures of Digestion
Liver
Bile duct
Gallbladder
Pancreas
Duodenum
Pancreatic
duct
To rest of small
intestine
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38–2 The Process of Digestion
The Small Intestine
Accessory Structures of Digestion
Just behind the stomach is the pancreas.
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The Small Intestine
During digestion, the pancreas:
• produces enzymes that break down
carbohydrates, proteins, lipids, and nucleic acids.
• produces sodium bicarbonate, a base that
neutralizes stomach acid so that these enzymes
can be effective.
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The Small Intestine
Assisting the pancreas is the liver, which produces
bile.
Bile dissolves and disperses droplets of fat in fatty
foods. This enables enzymes to break down smaller
fat molecules.
Bile is stored in the gallbladder.
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38–2 The Process of Digestion
Absorption in the Small
Intestine
Absorption in the Small Intestine
The small intestine is adapted for the
absorption of nutrients.
The folded surfaces of the small intestine
are covered with fingerlike projections called
villi.
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38–2 The Process of Digestion
Absorption in the Small
Intestine
The Small Intestine
Villus
Small intestine
Circular folds
Epithelial
cells
Villi
Capillaries
Lymph
vessel
Vein
Artery
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Absorption in the Small
Intestine
Cell surfaces of villi have more projections called
microvilli.
These provide an enormous surface area for the
absorption of nutrient molecules.
Slow, wavelike contractions of smooth muscles move
the chyme along this surface.
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Absorption in the Small
Intestine
Nutrient molecules are absorbed into the cells lining
the small intestine.
Most products of carbohydrate and protein digestion
are absorbed into the capillaries in the villi.
Molecules of undigested fat are absorbed by lymph
vessels.
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38–2 The Process of Digestion
The Large Intestine
The Large Intestine
When the chyme leaves the small intestine, it
enters the large intestine, or colon.
The large intestine removes water from the chyme.
Water is absorbed quickly, leaving undigested
materials behind.
Concentrated waste material passes through the
rectum and is eliminated from the body.
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Digestive System Disorders
Digestive System Disorders
Stomach acids sometimes damage the organ’s
own lining, producing a hole in the stomach wall
known as a peptic ulcer. Most peptic ulcers are
caused by the bacterium H. pylori.
Other digestive disorders include diarrhea and
constipation.
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38–2 The Process of Digestion
38–3 The
Excretory
System
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38–2 The Process of Digestion
•
Functions of
the
Excretory
Functions of the Excretory System
System
•Every cell produces metabolic wastes.
•The process by which these wastes are
eliminated is called excretion.
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•
Functions of
the
Excretory
The skin excretes excess water and salts
System
in the form of sweat.
• The lungs excrete carbon dioxide.
• The kidneys also play a major role in
excretion.
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38–2 The Process of Digestion
Functions of
the
Excretory
• The Kidneys
System
– What are the functions of the kidneys?
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– The kidneys:
Functions of
the Excretory
System
•remove waste products from the blood.
•maintain blood pH.
•regulate the water content of the blood and,
therefore, blood volume.
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The Kidneys
•The kidneys are located on either side of the
spinal column near the lower back.
•A tube, called the ureter, leaves each kidney,
carrying urine to the urinary bladder.
•The urinary bladder is a saclike organ where
urine is stored before being excreted.
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The Kidneys
• Structure of the Kidneys
Nephron
Kidney
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The Kidneys
• Blood enters the kidney through the
renal artery.
• The kidney removes urea, excess water,
and other waste products and passes
them to the ureter.
• The clean, filtered blood leaves the
kidney through the renal vein and returns
to circulation.
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The Kidneys
– Kidney Structure
•A kidney has two distinct regions:
• The inner part is called the renal medulla.
• The outer part is called the renal cortex.
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The Kidneys
Cortex
Renal
artery
Medulla
Renal vein
Ureter
To the bladder
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The Kidneys
• The functional units of the kidney are
called nephrons.
• Nephrons are located in the renal cortex,
except for their loops of Henle, which
descend into the renal medulla.
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Bowman’s capsule
The
Kidneys
Capillaries
Glomerulus
Collecting
duct
Vein
Artery
To the ureter
Loop of Henle
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The Kidneys
Capillaries
• Each nephron
has its own blood
supply:
•an arteriole
•a venule
Collecting
duct
•a network of
capillaries connecting
them
Vein
Artery
To the ureter
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The Kidneys
Capillaries
– Each nephron
releases fluids to a
collecting duct, which
leads to the ureter.
Collecting
duct
Vein
Artery
To the ureter
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38–2 The Process of Digestion
The Kidneys
– How is blood filtered?
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The Kidneys
– As blood enters a nephron through the arteriole,
impurities are filtered out and emptied into the
collecting duct.
– The purified blood exits the nephron through
the venule.
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The Kidneys
• The mechanism of blood purification
involves two distinct processes: filtration
and reabsorption.
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The Kidneys
– Filtration
•Passing a liquid or gas through a filter to remove
wastes is called filtration.
•The filtration of blood mainly takes place in the
glomerulus.
•The glomerulus is a small network of capillaries
encased in the top of the nephron by a hollow,
cup-shaped structure called Bowman's capsule.
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The Kidneys
• Fluid from the blood flows into
Bowman’s capsule.
• The materials filtered from the blood
include water, urea, glucose, salts, amino
acids, and some vitamins.
• Plasma proteins, cells, and platelets
remain in the blood because they are too
large to pass through the capillary walls.
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The Kidneys
– Reabsorption
•Most of the material removed from the blood at
Bowman's capsule makes its way back into the
blood.
•The process in which liquid is taken back into a
vessel is called reabsorption.
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The Kidneys
• Almost 99% of the water that enters
Bowman’s capsule is reabsorbed into the
blood.
• When the filtrate drains in the collecting
ducts, most water and nutrients have
been reabsorbed into the blood.
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The Kidneys
• Remaining material, called urine, is
emptied into a collecting duct.
• Urine is primarily concentrated in the
loop of Henle.
• The loop of Henle is a section of the
nephron tubule in which water is
conserved and the volume of urine
minimized.
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The Kidneys
• As the kidney works, purified blood is
returned to circulation while urine is
collected in the urinary bladder.
• Urine is stored here until it is released
from the body through a tube called the
urethra.
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38–2 The Process of Digestion
•
Control of
Kidney
Control of Kidney Function
Function
•The activity of the kidneys is mostly controlled by
the composition of the blood.
•In addition, regulatory hormones are released in
response to the composition of blood.
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•
Control of
Kidney
When you drink a liquid, it is absorbed
into the blood through theFunction
digestive
system.
• As a result, the concentration of water in
the blood increases.
• As the amount of water in the blood
increases, the rate of water reabsorption
in the kidneys decreases.
• Less water is returned to the blood, and
excess water is sent to the urinary
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•
Control of
Kidney
When the kidneys detect an increase in
Function
salt, they respond by returning
less salt
to the blood by reabsorption.
• The excess salt the kidneys retain is
excreted in urine, thus maintaining the
composition of the blood.
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38–2 The Process of Digestion
• Kidney Disorders
Kidney
Disorders
•Humans have two kidneys, but can survive with
only one.
•If both kidneys are damaged by disease or injury,
there are two options:
•
•
a kidney transplant
kidney dialysis
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38–2 The Process of Digestion
•
Kidney
Disorders
Kidney dialysis works as follows:
•Blood is removed by a tube and pumped through
special tubing that acts like nephrons.
•Tiny pores in the tubing allow salts and small
molecules to pass through.
•Wastes diffuse out of the blood into the fluid-filled
chamber, allowing purified blood to be returned to
the body.
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• Kidney Dialysis
Blood in tubing flows
Kidney
Disorders
through dialysis fluid
Blood pump
Vein
Artery
Shunt
Used dialysis fluid
Air
detector
Dialysis
machine
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Fresh
dialysis
fluid
Compressed
air
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38–2
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38–2
Food is moved through the esophagus into the
stomach by
a. air pressure.
b. muscle contractions.
c. gravity.
d. swallowing.
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38–2
A gland that has both endocrine and exocrine
functions is the
a. liver.
b. spleen.
c. pancreas.
d. gallbladder.
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38–2
The enzyme in saliva that begins the digestion
of starch is
a. amylase.
b. pepsin.
c. lysozyme.
d. peptidase.
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38–2
Stomach muscles contract to churn and mix
stomach fluids and food, producing a mixture
known as
a. chyme.
b. amylase.
c. bile.
d. acid.
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38–2
Absorption of vitamins, minerals, and digested
food molecules takes place in the
a. stomach.
b. small intestine.
c. large intestine.
d. duodenum.
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