Download Digestive System part 2 accessory organs

UNIT B Chapter 9: Digestive System
Section 9.2
Accessory Organs of Digestion
The accessory digestive organs are the pancreas, liver, and
gall bladder.
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UNIT B Chapter 9: Digestive System
Hepatic
portal
system
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Section 9.2
UNIT B Chapter 9: Digestive System
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Section 9.2
Bile
•
•
•
•
Emulsifying Agent
Secreted by liver
Excess stored in gall bladder (gall)
Secretion stimulated by CCK and Secretin
Liver Function
1.
2.
3.
4.
5.
6.
7.
8.
Detoxifying blood
Making plasma proteins
Maintaining blood glucose levels
Producing bile, which contains bile salts that emulsify fat in
the small intestine
Producing urea, a nitrogenous waste product from the
breakdown of amino acids
Excrete bilirubin from old RBCs
Stores vitamins and minerals: ADEK iron and copper
Activates vitamin D
Jaundice
• Yellow discoloration of the skin
• Due to high levels of bilirubin (from old RBCs)
UNIT B Chapter 9: Digestive System
Disorders of the Liver
o Hepatitis is inflammation of the liver.
o Hepatitis A
o Hepatitis B
o Hepatitis C
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Section 9.4
UNIT B Chapter 9: Digestive System
Cirrhosis
• scarring (fibrosis) of the liver caused by
• hepatitis and chronic alcoholism
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Section 9.4
UNIT B Chapter 9: Digestive System
The Gall Bladder
Excess bile from the liver is stored
in the gall bladder
• Bile leaves the gall bladder and
proceeds to the duodenum via
the common bile duct
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Section 9.2
Gall Stones
UNIT B Chapter 9: Digestive System
Section 9.4
• Gallstones are small, hard masses that form in the gall
bladder.
o Mostly Cholesterol
o may block the common bile duct and cause jaundice
o Treatment: removal of gall bladder.
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UNIT B Chapter 9: Digestive System
The Pancreas
Exocrine function :
pancreatic juice (buffer and digestive
enzymes)
Endocrine function:
o Hormones: insulin and glucagon,
regulate blood glucose (sugar)
levels
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Section 9.2
Acinar Cells secrete Pancreatic Juice:
Water, bicarbonate
1. increases pH in the duodenum (neutralizes
gastric acid)
2. protects duodenal wall
3. activates pancreatic enzymes (inactivates pepsin
(from the stomach)
Enzymes:
trypsinogen, lipase, nucleases, and pancreatic amylase
UNIT B Chapter 9: Digestive System
Section 9.2
Islets of Langerhans secrete hormones
Insulin
• Hormone secreted when blood glucose level is high
• Stimulates the uptake of glucose by cells (liver, muscle,
adipose tissue) to lower blood glucose
Glucagon
• Hormone secreted when blood glucose level is low
• Stimulates the liver to break glycogen down into glucose to
increase blood glucose
• Stimulates adipose tissue to break fat down to glycerol and
fatty acids (to make glucose)
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UNIT B Chapter 9: Digestive System
Section 9.3
Digestive Enzymes
Digestive enzymes help break down the major components of
food: carbohydrates, proteins, nucleic acids, and fats.
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UNIT B Chapter 9: Digestive System
Section 9.3
Carbohydrate Digestion by Enzymes
The digestion of starch (a carbohydrate) begins in the mouth.
• Salivary amylase (produced by the salivary glands) digests
starch into maltose (a disaccharide)
• Pancreatic amylase (produced by the pancreas) and maltase
(produced by the small intestine) then convert maltose in the
small intestine to glucose (a monosaccharide). Glucose can be
absorbed by the small intestine.
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UNIT B Chapter 9: Digestive System
Figure 9.11 Digestion and
absorption of nutrients.
a. The breakdown of
carbohydrates, such as starch,
involves amylase enzymes.
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Section 9.3
UNIT B Chapter 9: Digestive System
Section 9.3
Carbohydrate Digestion by Enzymes
Other disaccharides, such as lactose, have their own enzyme
that digests them in the small intestine.
• Lactase is an enzyme that digests lactose, a sugar found in
milk.
o Individuals who have a lactase deficiency often have
symptoms of lactose intolerance (diarrhea, gas,
cramps) caused by the fermentation of non-digested
lactose by intestinal bacteria
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UNIT B Chapter 9: Digestive System
Section 9.3
Protein Digestion by Enzymes
The digestion of proteins begins in the stomach.
• Pepsin is an enzyme produced by gastric glands that acts on
proteins to produce peptides.
• Trypsin (produced by the pancreas) and peptidases (produced
in the small intestine) break down peptides into amino acids
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UNIT B Chapter 9: Digestive System
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Section 9.3
UNIT B Chapter 9: Digestive System
Section 9.3
Fat Digestion by Enzymes
• Lipase (produced by the pancreas) acts in the small intestine
and digests fat molecules in the fat droplets after they have
been emulsified by bile salts
• Glycerol and fatty acids enter the cells of the villi, where they
are rejoined and repackaged as lipoprotein droplets
(chylomicrons) before entering the lacteals
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UNIT B Chapter 9: Digestive System
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Section 9.3
UNIT B Chapter 9: Digestive System
Section 9.3
Regulation of Digestive Enzymes
Enzymes function best at an optimum temperature and pH
that helps maintain the proper shape to fit their substrate.
• Since the digestive system is maintained at a constant
37ºC, enzymatic activity is largely controlled by pH
o The pH of the stomach is between 1 and 2 but can
increase to around 7.4 to 7.8 when sodium bicarbonate
in pancreatic juice is released from the pancreas
o This increase in pH occurs after chyme enters the
duodenum, and allows different digestive enzymes to
be active depending on the pH
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Hormone
Released by What Part/ in
response to what?
Acts on What Part?
What does it do?
GASTRIN
upper part of stomach/in
response to protein in the
stomach
Gastric juice secreting
cells at top of stomach
Causes secretion of gastric
juices
SECRETIN
Small intestine/Acid
chyme from stomach
Pancreas
Causes pancreas to release
NaHCO3 and pancreatic
enzymes
CCK
Small intestine/Acid
chyme in stomach
Pancreas and Liver (gall
bladder)
Causes liver to secrete bile
and pancreas to secrete
pancreatic juice.
GIP
Small intestine/acid chyme Stomach
rich in fats enter duodenum
Inhibits stomach peristalsis
and acid secretion (opposes
gastrin)
Hormones that Control Digestion:
Hormone
Released by What Part/
in response to what?
upper part of stomach/in
response to protein in the
stomach
Acts on What
Part?
Gastric juice
secreting cells at
top of stomach
SECRETIN
Small intestine/Acid
chyme from stomach
Pancreas and
parietal cells of
stomach
CCK
(Cholecysto
kinin)
Small intestine/Acid
chyme in stomach
Pancreas and
Liver (gall
bladder)
GASTRIN
What does it do?
Causes secretion of
gastric juices
Also increases the
churning action of the
stomach
Is inhibited by the
presence of HCl,
Secretin, and GIP –
negative feedback loop
Causes pancreas to
release NaHCO3 and
pancreatic enzymes
Also inhibits gastric acid
secretion by the
stomach
Causes liver to secrete
bile and pancreas to
secrete pancreatic juice.
Also acts as a hunger
supressant
Specialized Cells Lining Villi
•Absorptive epithelial cell
–Contain brush border on lumen/apical side
–Brush border:
•Enzymes
•Nutrient transport molecules
•Goblet cell
–Secretes mucus