CH 38-2 THE PROCESS OF DIGESTION
By the end of this section you should be
able to:
Identify the organs of the digestive
system
Describe the function of the digestive
system
CH 38-2 THE PROCESS OF DIGESTION
alimentary canal – one-way tube that
passes through the body
CH 38-2 THE PROCESS OF DIGESTION
digestive system – helps convert foods
into simpler molecules that can be
absorbed and used by the cells of the
body
CH 38-2 THE PROCESS OF DIGESTION
– includes:
mouth
esophagus
 large intestine
pharynx
small intestine
stomach
CH 38-2 THE PROCESS OF DIGESTION
accessory structures: add secretions to
the digestive system
 pancreas liver  salivary
glands
CH 38-2 THE PROCESS OF DIGESTION
CH 38-2 THE MOUTH
mechanical digestion – physical
breakdown of large pieces of food into
smaller pieces
CH 38-2 THE MOUTH
chemical digestion – breakdown of
large food molecules into smaller food
molecules with digestive enzymes
CH 38-2 THE MOUTH
mouth – the organ in which digestion
begins
teeth – tear and crush food into a fine
paste until it is ready to be swallowed
– anchored to the bones of the jaw;
protected by a coating of enamel
– do much of the mechanical digestion
CH 38-2 THE MOUTH
saliva – secreted by salivary glands as
the teeth cut and grind food
– secretion is controlled by the nervous
system; can be triggered by scent
CH 38-2 THE MOUTH
three functions:
1) helps to ease the passage of food
through the digestive system by
moistening food
2) contains lysozyme – an enzyme that
fights infection by digesting the cell
walls of bacteria that enter the mouth
3) contains amylase – begins to break
the bonds in starches to produce
simpler sugars
CH 38-2 THE ESOPHAGUS
bolus – chewed clump of food that is
pushed down the throat by the tongue
and throat muscles
epiglottis – flap of tissue that covers the
trachea when swallowing to prevent
food from entering lungs
CH 38-2 THE ESOPHAGUS
esophagus – tube that connects the
throat (pharynx) to the stomach
– walls are made of ringed muscle that
squeeze food through the tube
– peristalsis – the rhythmic muscular
contractions of the smooth muscle in the
digestive system that pushes food along
CH 38-2 THE ESOPHAGUS
cardiac sphincter – also called
esophageal sphincter
– a thick ring of muscle that closes the
esophagus after food has passed into
the stomach
– prevents the contents of the stomach
from moving back into the esophagus
CH 38-2 THE ESOPHAGUS
heartburn – backflow of stomach acid
across the cardiac sphincter
– can be caused by overeating,
overdrinking, or excess caffeine
CH 38-2 THE STOMACH
stomach – large, muscular sac just
below the diaphragm in the abdomen
– three layers of smooth muscle
– churns and mixes the food that is
swallowed
CH 38-2 THE STOMACH
chemical digestion – stomach is lined
with millions of microscopic gastric
glands that release a number of
substances into the stomach
CH 38-2 THE STOMACH
gastric secretions include:
1) mucus – lubricates food and protects
the stomach lining
2) HCl – hydrochloric acid makes the
stomach contents acidic which allows
pepsin to work
CH 38-2 THE STOMACH
gastric secretions include:
3) pepsin – enzyme that begins the
digestion of protein
– works best in acidic environments
– breaks proteins into smaller
polypeptide fragments
CH 38-2 THE STOMACH
the acidic environment denatures
(“changes the shape of”) the amylase
enzyme, so carbohydrate digestion
stops in the stomach (it restarts in the
small intestine)
CH 38-2 THE STOMACH
mechanical digestion – muscular walls
of the stomach contract to churn and
mix stomach fluids and food to produce
chyme
▫ chyme – a pasty mixture of food that
results after 2 to 3 hours of churning in
the stomach
CH 38-2 THE STOMACH
pyloric valve – a ring of muscle
between the stomach and small intestine
– opens to allow chyme to flow into
the small intestine
CH 38-2 THE STOMACH
CH 38-2 THE SMALL INTESTINE
The Small Intestine
three sections:
1) duodenum
2) jejunum
3) ileum
CH 38-2 THE SMALL INTESTINE
duodenum – first of the three parts of
the small intestine
– where almost all of the digestive
enzymes enter the intestines
– chyme mixes with enzymes and
digestive fluids from the pancreas, liver,
and the lining of the duodenum
CH 38-2 THE SMALL INTESTINE
intestinal secretions
1) peptidase – breaks down dipeptides
into amino acids
2) maltase, sucrase, and lactase –
breaks down remaining disaccharide
into monosaccharides
CH 38-2 THE SMALL INTESTINE
accessory structures:
pancreas – long gland located behind
the stomach
– gland that serves three functions:
1) produces hormones that regulate
blood sugar levels
2) produces enzymes that break down
carbohydrates, proteins, lipids, and
nucleic acids
CH 38-2 THE SMALL INTESTINE
3) produces sodium bicarbonate to
neutralize HCl from stomach acid –
because pancreatic enzymes only work
in a neutral environment
CH 38-2 THE SMALL INTESTINE
liver – large, brownish organ located just
above and to the right of the stomach
– secretes bile – yellow-brown liquid
loaded with lipids and salts
– acts like a detergent - breaks fat into
smaller and smaller droplets which make it
possible for enzymes to reach more surface
area
CH 38-2 THE SMALL INTESTINE
gallbladder – pouch-like organ behind
the liver that stores bile
CH 38-2 THE SMALL INTESTINE
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
jejunum and ileum – last two sections
of the small intestine
– approximately 6 meters long
– at this point chemical digestion is
complete
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
– nutrient molecules are absorbed from
these two sections into the bloodstream
– peristalsis move the chyme along the
jejunum and ileum
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
villi – finger-like projections that
increase the surface area of the walls
of the small intestine
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
microvilli – thousands of even tinier
finger-like projections found on the
surface of the cells of the villi!
– inside each villus is a network of
capillaries and lymph vessels
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
absorption – nutrients are absorbed
into the cells of the villi lining the small
intestine
– carbohydrates and proteins are
absorbed into capillaries
– undigested fat and some fatty acids
are absorbed into lymph vessels
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
when food leaves the small intestine, it is
nutrient-free
only water, cellulose, and other
undigestible substances remain
CH 38-2 ABSORPTION IN THE SMALL
INTESTINE
appendix – small sac-like organ in small
intestine that does little to promote
digestion
– can be clogged and inflamed appendicitis
CH 38-2 THE LARGE INTESTINE
large intestine, or colon – removes
water from undigested material that is
left
– bacterial colonies produce compounds
like vitamin K
concentrated waste material passes
through the rectum and is eliminated
CH 38-2 DIGESTIVE SYSTEM DISORDERS
GERD – gastroesophageal reflux disease
– chronic heartburn in 25-35% of
people
– symptoms – heartburn, regurgitation,
difficulty swallowing
CH 38-2 DIGESTIVE SYSTEM DISORDERS
causes – defects in esophageal sphincter;
– slower than normal emptying of the
stomach;
– decreased secretion of bicarbonate by
the esophagus
– treatments – lifestyle changes;
medication to control stomach acid; surgery
CH 38-2 DIGESTIVE SYSTEM DISORDERS
peptic ulcer – hole in stomach lining
produced by the powerful acids
released into the stomach
– most are caused by Heliobacter
pylori; can be cured with antibiotics
CH 38-2 DIGESTIVE SYSTEM DISORDERS
diarrhea – irritation or infection that
interferes with the removal of water
from the large intestines
CH 38-2 DIGESTIVE SYSTEM DISORDERS
constipation – condition resulting from
the removal of too much water from the
undigested material in the large
intestine
CH 38-2 THE PROCESS OF DIGESTION
By the end of this section you should be
able to:
Identify the organs of the digestive
system
Describe the function of the digestive
system
CH 38-2 THE PROCESS OF DIGESTION
Identify the organs of the digestive
system
Mouth, pharynx, esophagus, stomach,
small intestine, and large intestine
Describe the function of the digestive
system
CH 38-2 THE PROCESS OF DIGESTION
Describe the function of the digestive
system
To convert food into simple molecules
that can be absorbed and used by the
cells of the body
CH 38-3 THE EXCRETORY SYSTEM
By the end of this section you should be
able to:
Describe the functions of the kidneys
Explain how blood is filtered
CH 38-3 FUNCTIONS OF THE EXCRETORY
SYSTEM
excretion – process by which metabolic
wastes are eliminated
– maintains homeostasis in the internal
cellular environment
– rids the body of excess salt, CO2 and
urea
– urea – toxic compound that is produced
when amino acids are used for energy
CH 38-3 THE EXCRETORY SYSTEM
organs of excretion
1) skin – excretes excess water and
salt, and a small amount of urea in
sweat
2) lungs – excrete carbon dioxide that
is produced when ATP is made
CH 38-3 THE EXCRETORY SYSTEM
3) liver – takes up amino acids from
proteins that have been broken down
– converts the amino acids into other useful
compounds
– produces nitrogen waste in the process,
which is potentially poisonous
– the liver converts this nitrogen waste
quickly to urea
– urea is removed from the bloodstream
by the kidneys
CH 38-3 THE EXCRETORY SYSTEM
4) kidneys – play an important role in
maintaining homeostasis by...
1) removing waste products from the
blood
2) maintaining blood pH
3) regulating the water content of the
blood (i.e., blood volume)
CH 38-3 THE KIDNEYS
anatomy of excretion
kidneys – located on either side of the
spinal column near the lower back
CH 38-3 THE KIDNEYS
ureter – tube that leaves each kidney
carrying urine to the urinary bladder
– maintains homeostasis in the internal
cellular environment
CH 38-3 THE KIDNEYS
urinary bladder – sac-like organ in
which urine is stored before being
excreted
CH 38-3 THE KIDNEYS
CH 38-3 THE KIDNEYS
function of kidney
1) blood enters the kidney through the
renal artery
2) kidneys remove urea, excess water
and other waste products from the
blood
CH 38-3 THE KIDNEYS
3) waste products are passed on to the
ureter
4) clean, filtered blood leaves the
kidney through the renal vein to return
to circulation
CH 38-3 THE KIDNEYS
kidney structure – 10 cm long, 6 cm in
diameter
two distinct regions:
1) renal medulla – inner part of the
kidney
2) renal cortex – outer part of the
kidney
CH 38-3 THE KIDNEYS
Kidney
Nephron
Bowman’s
capsule
Cortex
Capillaries
Glomerulus
Medulla
Renal
artery
Renal vein
Ureter
Collecting
duct
Vein
To the bladder
Artery
Loop of Henle
To the ureter
CH 38-3 THE KIDNEYS
nephrons – functional units of the
kidney; small independent processing
units
– 3 cm long, 0.03 mm wide; 1 million
per kidney!
– located in the renal cortex except for
the loop of Henle which extends into the
renal medulla
CH 38-3 THE KIDNEYS
– each nephron has one arteriole and
one venule with a network of capillaries
connecting them
– releases fluid to the collecting duct
that leads to the ureter
CH 38-3 THE KIDNEYS
▫ flow of blood through nephron – to
purify blood
1) blood enters the nephron through the
arteriole
2) impurities are filtered out and
emptied into the collecting duct
3) purified blood exits the nephron
through venule
CH 38-3 THE KIDNEYS
blood purification – requires two
processes:
1) filtration
2) reabsorption
CH 38-3 THE KIDNEYS
Filtration
Most filtration occurs in the glomerulus.
Blood pressure forces water, salt, glucose,
amino acids, and urea into Bowman’s capsule.
Proteins and blood cells are too large to
cross the membrane; they remain in the
blood. The fluid that enters the renal tubules
is called the filtrate.
Reabsorption
As the filtrate flows through the renal
tubule, most of the water and nutrients
are reabsorbed into the blood. The
concentrated fluid that remains is
called urine.
CH 38-3 THE KIDNEYS
filtration – the process of passing a
liquid or a gas through a filter to
remove waste
– takes place in the glomerulus
CH 38-3 THE KIDNEYS
glomerulus – a small network of
capillaries encased in the upper end of
the nephron by a hollow structure called
Bowman's capsule
CH 38-3 THE KIDNEYS
reabsorption – the process in which
liquid is taken back into a vessel
– most of the material removed from
the blood at Bowman's capsule is
returned to the blood
CH 38-3 THE KIDNEYS
Steps to blood purification in the
nephron:
1) the blood is under pressure and the
walls of the capillaries and Bowman's
capsule are permeable
2) fluid flows from the blood into
Bowman's capsule; this fluid is called
filtrate
CH 38-3 THE KIDNEYS
3) filtrate contains:
water
glucose amino acids
some vitaminssalts urea
filtrate does not contain: cells
plasma proteins platelets
(because they are too large to filter out)
CH 38-3 THE KIDNEYS
4) amino acids, fats and glucose are
actively pumped out of filtrate and
reabsorbed by the capillaries – water
follows by osmosis
5) filtrate (with little water or nutrients
left) drains into collecting ducts
CH 38-3 THE KIDNEYS
6) urine – the remaining filtrate; contains
urea, excess salt and water
– empties into a collecting duct
– becomes concentrated (excess water is
reabsorbed) in the loop of Henle
– loop of Henle - the section of nephron
tubule in which water is conserved and
volume of urine is minimized
CH 38-3 THE KIDNEYS
7) urine is stored in the urinary bladder
until it can be released from the body
through a tube called the urethra
CH 38-3 THE KIDNEYS
drugs in urine
– drugs are not usually reabsorbed,
they remain in the filtrate and are
eliminated in the urine
– this is why the effects of many drugs
wear off over time (e.g., antibiotics)
CH 38-3 THE KIDNEYS
– this also means that drugs become
more concentrated in the urine, so a
urine test is a quick, easy way to test for
illegal drugs
CH 38-3 THE KIDNEYS
kidney stones – calcium, magnesium,
and uric acid salts can crystallize and
form a block in the ureter
CH 38-3 THE KIDNEYS
– cause severe pain
– treated with ultrasound waves to
pulverize the stone into small fragments
that can be eliminated through the
urethra
CH 38-3 THE KIDNEYS
Control of Kidney Function
activities of the kidney are controlled
by:
1) the composition of the blood itself
2) regulatory hormones released in
response to composition of blood
CH 38-3 THE KIDNEYS
example – when you drink a glass of
water...
1) the amount of water in your blood
increases
2) the rate of water reabsorption
decreases
3) less water is returned to the blood
4) excess water is sent to the urinary
bladder to be excreted
CH 38-3 THE KIDNEYS
example – when you eat salty food...
1) the amount of salt in your blood
increases
2) the kidney allows less salt to be
reabsorbed into the blood
3) excess salt is excreted in the urine
CH 38-3 THE KIDNEYS
Homeostasis by Machine
- humans have two kidneys, but can live
with one
- if both kidneys are damaged, there
are two alternatives:
CH 38-3 THE KIDNEYS
1) kidney transplant – from a
compatible donor
CH 38-3 THE KIDNEYS
2) kidney dialysis – if no donor is
available
a) blood is removed from the body
through a tube, and is sent through a
series of tubing that acts like a nephron
b) holes in the tubing allow salt and
small molecules to pass through
CH 38-3 THE KIDNEYS
c) waste, urea, and excess salt diffuse
out of the blood into a fluid filled
chamber
d) purified blood is returned to the
body
▫ dialysis is expensive and timeconsuming (several hours, 3 times/week)
CH 38-3 THE KIDNEYS
Blood in tubing flows
through dialysis fluid
Blood pump
Used dialysis fluid
Air detector
Dialysis machine
Fresh dialysis
fluid
Compressed
air
CH 38-3 THE EXCRETORY SYSTEM
By the end of this section you should be
able to:
Describe the functions of the kidneys
Explain how blood is filtered
CH 38-3 THE EXCRETORY SYSTEM
Describe the functions of the kidneys
Remove waste products from the blood;
maintain blood pH; and regulate the
water content of the blood (blood
volume)
Explain how blood is filtered
CH 38-3 THE EXCRETORY SYSTEM
Explain how blood is filtered
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Ch 38-2 The Process of Digestion