Gastrointestinal System Flashcards
Most digestive systems function by the following means:
-movement: mixes and passes nutrients through the system and eliminates waste
-secretion: enzymes, hormones, and other substances necessary for digestion are secreted into the digestive tract
-digestion: includes the chemical breakdown of nutrients into smaller units that enter the internal environment
-absorption: the passage of nutrients through plasma membranes into the blood or lymph and then to the body
Mouth
-Digestion begins in the mouth with the chewing and mixing of nutrients with saliva
-only humans and other mammals actually chew their food
-salivary glands are stimulated and secrete saliva
-saliva contains enzymes that initiate the breakdown of starch in digestion
-once swallowed, the food moves down the pharynx, into the esophagus en route to the stomach
Stomach
the stomach is a flexible muscular sac it has three main functions:
-Mixing and storing food
-dissolving and degrading food via secretions
-controlling passage of food into the small intestine
-protein digestion begins in the stomach
-stomach acidity helps break down the food and make nutrients available for absorption
-smooth muscle moves the food by peristalsis, contracting and relaxing to move nutrients along
-smooth muscle contractions move nutrients into the small intestine where the absorption process begins
Liver (1/3)
-Largest solid organ of the body
-largest gland
-weighs about 3 pounds
-located below the diaphragm on the right side of the chest
-made up of four lobes: they are called the right, left quadrate, and caudate lobes
-the liver is secured to the diaphragm and abdominal walls by five ligaments—they are also called the falciform (that forms a membrane-like barrier between the right and left lobes), coronary, right triangular, left triangular, and round ligaments
Liver (2/3)
-Processes all of the blood that passes through the digestive system
-nutrient-rich blood is supplied to the liver via the hepatic portal vein
-the hepatic artery supplies oxygen-rich blood
-blood leaves the liver through the hepatic veins
-the liver’s functional units are called lobules (made up of layers of liver cells)
-blood enters the lobules through branches of the portal vein and hepatic artery
-the blood then flows through small channels called sinusoids
Liver (3/3)
-Responsible for performing many vital functions in the body including:
-production of bile
-production of certain blood plasma proteins
-production of cholesterol (and certain proteins needed to carry fats)
-storage of excess glucose in the form of glycogen (that can be converted back to glucose when needed)
-regulation of amino acids
-processing of hemoglobin (to store iron)
-conversion of ammonia (that is poisonous to the body) to urea (a waste product excreted in urine)
-purification of the blood (clears out drugs and other toxins)
-regulation of blood clotting
-controlling infections by boosting immune factors and removing bacteria
-the nutrients (and drugs) that pass through the liver are converted into forms that are appropriate for the body to use
Pancreas
-6-10 inches long
-located at the back of the abdomen behind the stomach
-long tapered organ
-the wider right side is called the head and the narrower left side is called the tail
-the head lies near the duodenum (the first part of the small intestine) and the tail end near the spleen
-the body of the pancreas lies between the head and tail
-the pancreas is made up of exocrine and endocrine tissues
-the exocrine tissues secretes digestive enzymes from a series of ducts that collectively form the main pancreatic duct (that runs the length of the pancreas)
-the main pancreatic duct connects to the common bile duct near the duodenum
-the endocrine tissue secretes hormones such as insulin into the bloodstream
-blood is supplied to the pancreas from the splenic artery, gastroduodenal artery, and the superior mesenteric artery
Digestive role of pancreas
-The pancreas assists in the digestion of foods by secreting enzymes to the small intestine that help break down many foods, especially fats and proteins
-the precursor to these enzymes (called zymogens) are produced by groups of exocrine cells (called acini) -they’re converted through a chemical reaction in the gut to the active enzymes (such as pancreatic lipase and amylase)
-once they enter the small intestine the pancreas also secretes large amounts of sodium bicarbonate to neutralize the stomach acid that reaches the small intestine
-the exocrine functions of the pancreas are controlled by hormones released in the stomach and small intestine (duodenum) when food is present
-the exocrine secretions of the pancreas flow into the main pancreatic duct (Wirsung’s duct) and are delivered to the duodenum through the pancreatic duct
Small intestine
-In the digestive process, most nutrients are absorbed in the small intestine
-enzymes from the pancreas, liver, and stomach are transported to the small intestine to aid digestion
-these enzymes act on fats, carbohydrates, nucleic acids, and proteins
-bile is a secretion of the liver and is particularly useful in breaking down fats
-bile is stored in the gallbladder between meals
-by the time the food reaches the lining of the small intestine, it has been reduced to small molecules
-the lining of the small intestine is covered with villi, tiny absorptive structures that greatly increase the surface area for interaction with chyme (the semi-liquid mass of partially digested food)
-epithelial cells at the surface of the villi, called microvilli, further increase the ability of the small intestine to serve as the main absorption organ of the digestive tract
Large intestine
Aka colon
-the large intestine concentrates, mixes, and stores waste material
-a little over a meter in length
-the colon ascends on the right side of the abdominal cavity, cuts across transversely to the left side and descends and attaches to the rectum, a short tube for waste disposal
-when the rectal wall is distended by waste material, the nervous system triggers an impulse in the body to expel the waste from the rectum
-a muscle sphincter at the end of the anus is stimulated to facilitate the the expelling of waste matter
-the speed at which waste moves through the colon is influenced by the volume of fiber and other undigested material present
-without adequate bulk in the diet, it takes longer to move waste along, sometimes with negative effects
