UNIT 12: The Digestive System Flashcards
What are the two main functions of the digestive system?
digestion and absorption
Which organs make up the digestive tract?
mouth, pharynx, esophagus, stomach, small intestine, and large intestine (and layers of smooth muscle to contract)
What are these organs lined with
mucosa
How many layers are in the GI tract?
4
What are the 4 layers?
mucosa, submucosa, muscolaris, and serosa
What is mucosa?
absorptive and secretory layer
What is the submucosa?
highly vascular layer of connective tissue
What is the muscolaris?
responsible for contractions and perstaltic movement
What is the serosa?
connective tissue continuous with the mesentery and visceral peritoneum
What are the three accessory digestive organs?
salivary glands, liver, and the pancreas
What do these accessory organs do?
they produce digestive juices that reach the digestive system through small ducts
What does the gallbladder do?
Stores the liver’s digestive juices until they are needed in the intestine.
What is digestion?
the breaking down of food substances so the body can take them up and use them to build/repair tissues, nourish cells and to provide energy
What is it called when food moves from one organ to the next?
peristalsis (looks like a wave in when travelling through the muscle)
What is the first major muscle movement in the digestive system?
swallowing (involuntary)
What is the ring-like muscle called at the junction of the stomach and esophagus?
lower esophageal sphincter (closes passage between two organs)
What happens when the sphincter relaxes?
food passes through to the stomach
How many functions does the stomach have?
3
What is one function?
storage of swallowed foods and liquids (muscles in upper part of the stomach relax in order to accept larger volumes of swallowed material)
What is another function?
mixing up the food, liquid, and digestive juice produce by the stomach
What is the last function of the stomach?
empties contents (now chyme) into the small intestine
What nutrient spends the least amount of time in the stomach?
carbs (protein stays longer but fats stays the longest)
What enzyme digests proteins
pepsin
What is the first digestive juice used in the digestive system?
saliva. Contains an a-amylase that breaks the starches down into sugars
What does the pancreas produce?
enzymes that breakdown carbs, protein and fats
Where are enzymes such as lactase, sucrase, and maltase found?
in the glands in the intestinal wall. they digest disaccharides and small glucose polymers into monosaccharides, while peptidases cleave polypeptides into individual amino acids
What digestive juice does the liver produce?
bile
What does bile acids do?
they dissolve fat into watery contents
Where are most food molecules, water and minerals absorbed?
the small intestine
What does the mucosa contain?
covered in villi (allows for foods to be absorbed)
What is villi covered in?
microvilli (allows for foods to be absorbed)
how are fatty acids, cholesterol and phospholipids taken up?
lipid micelles that are formed with bile salts by the cells of the small intestines
How many steps are carbs digested in?
2
What are the two steps?
salivary amylase and pancreatic juice
What happens to proteins in the small intestine?
trypsin, chymotripsin, carboxypeptidase, proelastase form the pancreatic juices and peptidases from the lining of the intestine complete the breakdown of proteins into amino acids
What breaks down fat molecules?
pancreatic and intestinal lipases
How is digestion controlled?
hormonal and nervous control mechanisms
What are the main hormones that control digestion?
gastrin, secretin and cholecytokinin (CCK), and gastric inhibitory peptide (GIP)
What does gastrin do?
causes the stomach to produce the acid that is necessary for pepsin to work (stimulates pepsin release)
What does secretin do?
causes the pancreas to send out a digestive juice that is rich in bicarbonate
What does the bicarbonate do?
neutralize the acidic stomach contents as they enter the small intestine
What does CCK do?
causes the pancreas to produce enzymes of pancreatic juice and stimulates contraction of the gallbladder
What hormones regulate appetite?
ghrelin and leptin
What does ghrelin do?
stimulates appetite
What does leptin do?
inhibits appetite
What doe extrinsic neural receptors do?
release acetylcholine and adrenaline
What do intrinsic neural receptors do?
speed up or delay movement of food
What are ruminants?
have a 4-chambered stomach that has the capicity to breakdown cellulose (think about cow)
What are hind-gut fermenters?
large intestines are larger than ruminant fermenters and a richer diet is requires (harder time breaking down cellulose)
