9.2 Accessory Organs of Digestion Flashcards
What are the 4 accessory digestive organs?
pancreas, liver, gall bladder, salivary glands
Where is the pancreas?
lies deep in the abdominal cavity, resting on the posterior abdominal wall
What is the pancreas?
an elongated and somewhat flattened organ that has both endocrine and exocrine functions
What happens in the exocrine function of the pancreas?
most pancreatic cells produce pancreatic juice, which contains sodium bicarbonate to help neutralize the stomach acid, and digestive enzymes for all types of food
What does the pancreas do as an endocrine gland?
secretes insulin and glucagon
What is glucagon?
hormone that help keep the blood glucose level within normal limits?
What are the pancreatic islets?
clusters of at least 3 typed of endocrine cells: alpha, beta, delta
What do alpha cells do?
produce glucagon
What do beta cells do?
produce insulin
What do delta cells do?
produce somatostatin
What are insulin and glucagon important for?
regulating the blood glucose level
When is insulin secreted?
when the blood glucose level is high, which usually occurs just after eating
What does insulin stimulate?
the uptake of glucose occurs just after eating, especially liver cells, muscle cells, and adipose tissue cells
What is glucose stored as in liver and muscle cells?
glycogen
What does the breakdown of glucose in the muscle cells do?
supplies energy for protein metabolism
What does the breakdown of glucose in fat cells do?
supplies glycerol for the formation of fat
Where does glucagon come from?
secreted from the pancreas, usually before eating, when the blood glucose level is low
What are the major target tissues of glucagon?
liver and adipose (fat) tissue
What does glucagon stimulate?
stimulates the liver to break down glycogen to glucose
What is also used as energy sources by the liver?
fat and protein, thus sparing glucose
What do adipose tissue cells do?
break down fat to glycerol and fatty acids, then the liver takes these up and uses them as substrates for glucose formation
What lowers the blood glucose level?
insulin
What raises the blood glucose level?
glucagon
What is somatostatin?
a growth hormone inhibiting hormone
What is somatostatin produced by?
pancreas, cells in the stomach, and small intestine
What are somatostatin’s main effects?
to inhibit the release of growth hormone, as well as to suppress the release of various hormones produced by the digestive system, including insulin and glucagon
What is the overall effect of somatostatin on the digestive tract?
to generally decrease the absorption of nutrients
What is the liver?
largest gland in the body
Where is the liver?
lies mainly in the upper right section of the abdominal cavity, under the diaphragm
What does the liver contain?
~100,000 lobules that serve as its structural and functional units
What are the 3 structures located between the lobules?
bile duct, branch of hepatic artery, branch of hepatic portal vein
What does the bile duct do?
takes bile away from the liver
What does the hepatic artery do?
brings oxygen-rich blood to the liver
What does the hepatic portal vein do?
transports nutrients from the intestines
What does each lobule have?
a central vein that enters a hepatic vein
How does the liver act as the gatekeeper to blood?
as blood from hepatic portal vein passes through the liver, it removes poisonous substances and detoxifies them
What does the liver also remove and store?
iron and vitamins A, D, E, K, and B12
What does the liver do?
makes many of the plasma proteins and helps regulate the quantity of cholesterol in the blood
What does the liver maintain the blood glucose level at?
50-80 mg, or 100 mL, even though a person eats intermittently
What happens when insulin is present?
any excess glucose in the blood is removed and stored by the liver (and muscles) as glycogen
What does glycogen do between meals?
glycogen is broken down to glucose, which enters the hepatic veins, and in this way the blood glucose level remains relatively constant
What does the liver do if the supply of glycogen is depleted?
converts glycerol (from fats) and amino acids to glucose molecules
What does the conversion of amino acids to glucose do?
necessitates deamination, which involves the removal of amino groups
What does the the liver do by a complex metabolic pathway?
combines ammonia with carbon dioxide to form urea
What is urea?
the usual nitrogenous waste product from amino acid breakdown in humans
Describe the regulation of high blood glucose level.
- when the blood glucose level is high, (after eating) pancreas secretes insulin
- insulin promotes storage of glucose as glycogen and synthesis of proteins and fats (as opposed to their use as energy sources)
- liver stores glucose from blood as glycogen
- muscle cells store glycogen and build protein
- adipose tissue uses glucose from blood to form fat
- therefore, insulin lowers the blood glucose level to normal
Describe the regulation of low blood glucose level.
- when blood glucose level is low, (before eating) pancreas secretes glucagon
- glucagon acts opposite to insulin
- liver breaks down glycogen to glucose, glucose enters blood
- adipose tissue breaks down fat
- therefore, glucagon raises the blood glucose level to normal
What does the liver produce?
bile
Where is bile?
stored in the gall bladder
What colour is bile and why?
yellowish-green because it contains the bile pigments bilirubin which is derived from the breakdown of hemoglobin (red pigment in RBC)
What does bile contain?
bile salts
Where does bile salt come from?
derived from cholesterol
What do bile salts do?
emulsify fat in the small intestine
What happens when fat is emulsified?
it breaks up into droplets, providing a much larger surface area that can be acted upon by a pancreatic lipase
What are the 7 functions of the liver?
- detoxifies blood by removing and metabolizing poisonous substances
- stores iron and vitamins A, D, E, K, and B12
- makes many plasma proteins (ie. albumins and fibrinogen) from amino acids
- stores glucose as glycogen after a meal, and breaks down glycerol to glucose to maintain the glucose concentration of blood between eating periods
- produces urea after breaking down amino acids
- removes bilrubin (a breakdown product of hemoglobin) from the blood and excretes it in bile (a liver product)
- helps regulate blood cholesterol level, converting some to bile salts
Describe the hepatic portal system.
- small intestine absorbs products of digestion
- nutrient molecules travel in hepatic portal vein to liver
- liver monitors blood content
- blood enters general circulation by way of hepatic veins, which empty into the inferior vena cava
What is the gall bladder?
a pear-shaped, muscular sac attached to the surface of the liver
How much bile does the liver produce?
~400-800 mL everyday, and any excess is stored in the gall bladder
Why is water reabsorbed by the gall bladder?
so that bile becomes a thick, mucus-like material
Where does bile go when needed?
leaves the gall bladder and proceeds to the duodenum via the common bile duct
