Chapter 6.2 Flashcards
What is the function of the digestive system?
Ingest food and break it down into smaller components
What happens to the resulting substances is digestion?
They are absorbed into the bloodstream and delivered to all the body cells by the circulatory system
What do salivary glands do?
Secrete starch digesting enzymes
What does the liver do?
Manufactures bile. It facilitates digestion of fats
What does the gallbladder do?
Stores bile until needed
What does the pancreas do?
Manufactures enzymes to digest macromolecules
Secretes bicarbonate to neutralize stomach acid that enters the small intestine
What does the mouth do?
Chews and mixes food with saliva
What does the esophagus do?
Direct food from mouth to stomach
What does the stomach do?
Adds acid, enzymes, and fluids
churns, mixes, and grinds food to a liquid mass
What does the small intestine do?
Secretes enzymes that digest macromolecules
Absorbs hydrolyzed molecule into the bloodstream
What does the large intestine do?
Absorbs water and salts; passes remaining undigested material and some water out of body
What does the rectum do?
Stores waste prior to elimination
What does the anus do?
Holds rectum closed
What organs make up the human digestive tract?
Tongue Esophagus Stomach Gallbladder Pancreas Duodenum Jejunum Ileum Large intestine Anus
What triggers the 3 pairs of salivary glands?
Smell or taste of food
Where does chemical digestion begin?
In the mouth through hydrolysis
What is the enzyme in saliva called?
Amylase
What does amylase do?
Breaks down starch in simple sugars (disaccharides)
What does the amylase do to starch?
The amylase catalyzes a hydrolysis reaction of starch
What does the tongue do as you chew?
It rolls food into a smooth lump like mass called a bolus
What is the esophagus?
A muscular portion of the digestive tract that directs food from the mouth to the stomach
How does the esophagus move food to the stomach?
Through gravity and peristalsis
What is peristalsis?
Wavelike series of muscular contractions and relaxations
What does the esophageal sphincter control?
Entry of food from the intestine to the stomach
How does the esophageal sphincter work?
It relaxes to allow the bolus to enter into the stomach
And it contracts to prevents the acidic contents of the stomach from backing up
Where is mucus produced?
Mouth
Stomach
Small and large intestines
What does mucus do in the digestive system?
Protects the cells lining the innermost portion of the digestive tract
Lubricates food as it travels through the digestive tracts
Where is acid produced?
The stomach
What does acid do?
Promotes digestion of protein
What are the 3 important functions of the stomach?
Storage, some digestion, and pushing food into the small intestine
What does the pyloric sphincter do?
Controls the exit of the stomach’s contents into the small intestine
What kinds of digestion occur in the stomach?
Physical and chemical
How does the stomach undergo physical digestion?
Peristalsis pushes food against the bottom of the stomach, churning it and breaking it into smaller pieces and mixing it with gastric juices to make chyme
What is gastric juice responsible for?
Chemical digestion in the stomach
What is gastric juices made up of?
Water, mucus, salts, hydrochloric acids, and enzymes
What is the function of stomach juices?
Provide a highly acidic environment to break down proteins in chyme and kill bacteria
Why doesn’t the stomach get digested by gastric juices?
Because it secretes little gastric juice until food is present
The cells in the stomach secrete mucus which prevent gastric juices from harming the stomach lining
The stomach produces its protein digesting enzyme called pepsin in an inactive form until hydrochloric acid is present
What happens when pepsin is activated?
It hydrolyzes proteins to yield polypeptides
What does the stomach absorb?
Some water, salts, and certain anti inflammatory medications and alcohol
What is the longest part of the digestive tract?
The small intestine
What process start physical digestion in the small intestine?
Segmentation
What happens during segmentation?
Chyme sloshes back and forth between segments of the SI that form when bands of circular muscle contract
What pushes food down the SI?
Peristalsis
What is the main function of the SI?
Complete digestion of macromolecules and absorb their component subunits
How many regions are there in the SI?
3
What is the duodenum?
The first 25 cm of the small intestine. It is U-shaped and the shortest and widest of the 3 regions
Where do villi begin in the digestive tract?
The SI
What does each villi contain?
Tiny structures called capillary networks and lymph vessels (part of the circulatory system)
What are the 3 regions of the SI?
Duodenum
Jejunum
Ileum
What does each villi contain?
Tiny structures called capillary networks and lymph vessels
What does the capillary networks and lymph vessels do in villi?
They conduct absorbed substances from the small intestine into the bloodstream and the lymphatic system
What is used to digest the macromolecules present in chyme?
The small intestine secretes enzymes from the microvilli
What is digestive assistance provided by for the small intestine?
The enzymes secreted by the pancreas, liver and gallbladder
What is known as accessory organ?
Pancreas
Liver
Gall bladder
Their role is vital but they are not physically apart of the digestive tract
What does the pancreas do?
It delivers about 1L of pancreatic fluid to the duodenum each day
What does pancreatic fluid contain?
Enzymes like
•Trypsin and chymotrypsin, which are proteases that digest proteins
•Pancreatic Amylase which is a carbohydrate that digests starch
•Lipase, which digests fat
What happens when enzymes are released into the duodenum?
Since they are released in an inactive form, they are activated by enzymes secreted by the brush border of the duodenal lining
What do pancreatic enzymes do?
Digest proteins into smaller polypeptides, polysaccharides into shorter chains of simpler sugars and fats into free fatty acids
What does pancreatic fluid contain and what is it used for?
Bicarbonate which neutralizes hydrochloric acid from the stomach and gives chyme a pH of 8
What is the largest organ in the human body?
The liver
What is the main digestive secretion made by the liver?
Bile
What is bile?
A greenish yellow fluid mixture that is made of bile pigments and bile salts
What is in bile that does not take place in digestion?
Bile pigments. They are waste products from the livers destruction of old red blood cells and are eliminated with feces
What do bile salts play a crucial role in?
The digestion of fats
What happens because fats are insoluble in the intestines?
They enter the intestines as drops within the water chyme
What is downfall of lipase in the intestines?
Because lipase is only water soluble they can only react with with fat droplets at it surface
How does bile assist lipase in accessing fats?
They work like a detergent because they are partly solvable in fats and partly soluble in water. They disperse large fat droplets into smaller droplets within chyme. Making it so there is more surface area the the lipase can act on
What happens after bile is produced in the liver?
It is sent to the gall bladder which stores it
How does the gall bladder know when to release bile?
The arrival of fat containing chyme in the duodenum stimulations the gall bladder to contract causing bile to be injected into the duodenum
Where does most of the chemical digestion occur in the SI?
Duodenum because it acts on all 4 categories of macromolecules and their components
What is enzymatic digestion of macromolecules performed by?
Carbohydrases
Lipases
Proteases
Nucleases
What do carbohydrases digest?
Carbohydrates
What do lipases digest?
Fats
What do proteases digest?
Larger polypeptides
What do nucleases digest?
Nucleic Acids
Where does the digestion of starch begin?
In the mouth with the action of salivary amylase
What happens when undigested starch reaches the stomach?
Hydrochloric Acid interrupts its digestion because salivary amylase is only active at a ph around 7
When does the digestion of starch reneging?
It starts again after being stopped in the stomach when it gets to the small intestine and pancreatic amylase completes makes it into disaccharides
What do other carbohydrases convert disaccharides into in the SI?
They hydrolyze disaccharides into monosaccharides like glucose and fructose
Through what type of transport are monosaccharides absorbed into the bloodstream?
Active transport
Where do monosaccharides go when they are absorbed into the bloodstream?
They are brought to the liver. Where monosaccharides that are not already glucose are converted into glucose
What is excess glucose converted into?
Glycogen which is stored in the liver and muscles
How and where are poly peptides produced?
Polypeptides are produced in the stomach by the action of pepsin breaking down proteins
How are polypeptides further digested after the stomach?
By 2 proteases secreted by the pancreas. They are secreted while they are inactive and then are activated by an enzyme created in the SI
What do the enzymes that break down polypeptides do?
In the SI they hydrolyze peptide bonds between specific amino acids resulting in short peptide chains
What are the subunits of proteins?
Amino acids
How are peptide chains separated into amino acids?
This is done by peptidase enzymes secreted by the pancreas and SI
What happens after proteins are broken down into amino acids?
They are absorbed through active transport into the villi and SI. They are then taken to the liver.
What happens after Amino acids are brought to the liver?
Some have their amino group removed before they are used in energy releasing reactions or converted into sugars. Some are sent throughout the body
How are proteins excreted as urine?
Amino groups brought to the liver ad combine with CO2 that lead to the formation of nitrogenous waste urea excreted in urine
Where does fat digestion occur in adults?
The duodenum of the SI
How is fat digested?
Arrival of fats in the SI secretes bile which helps to emulsify fat into smaller droplets. An then the breakdown of bonds of glycerol and fatty acids is done by lipase
What happens to cells once they are absorbed into the fats of the villi?
Fat subunits are reassembled into triglycerides and coated with proteins to make them soluble before they enter the lymph vessels. Once they enter the bloodstream their protein coat is removed and they become hydrolyzed into free fatty acids
What are nucleic acids digested by in the SI?
Enzymes called nucleases to yield nucleotides
What are the activities of the digestive tract coordinated by?
The nervous system and the endocrine system
How does the stomach know when to secrete gastrin?
When food arrives in the stomach proteins in the food stimulate secretion
What does gastrin stimulate?
The secretion of hydrochloric acid and the inactive precursor molecule of pepsin from the glands of the stomach
What does the hydrochloric acid do?
It lowers the pH of the gastric juice which stops the flow of gastrin
What does the passage of chyme to the duodenum do?
Inhibits the contractions of the stomach until the previous amount has been processed.
What is the inhibition of the contractions of guided by?
Hormones that are secreted into the bloodstream by the duodenum called secretin and CCK. This happens when chyme moves to the duodenum
What is the highest stimulus for the secretion of CCK?
Chyme with a high fat content. This enables fatty meals to remain in the stomach for longer than non-fatty meals
What is the highest stimulus for secretin?
Chyme with high acidity
What else does CCK do?
Stimulates increased pancreatic secretions of digestive enzymes and gallbladder contractions
What do gall bladder contractions do?
Inject more bile into the duodenum, which enhances the emulsifying and digestion of fats
What does secretin also do?
Stimulates the pancreas to release more bicarbonate to neutralize acidic chyme
What is the main function of the large intestine?
To concentrate and eliminate waste materials
What happens in the LI?
Water and salts are absorbed and anaerobic bacteria break down undigested foods producing vitamins b-12 and K
