module 15: digestive system first half Flashcards
what is the digestive systems main function? what are the organic nutrients?
to break down organic nutrients (via digestion) so they can be absorbed into the body
organic nutrients: carbohydrates, protein, fats, water, vitamins, minerals
what happens to food in the mouth? what do salivary glands do? what is the esophagus?
in the mouth, food undergoes physical breakdown by chewing (mastication) and chemical breakdown by saliva
salivary glands produce saliva to moisten and begin digesting some food particles
the esophagus is a straight muscular tube that connects the mouth and pharynx to the stomach
what are the functions of the stomach, the liver, and the gall bladder
the stomach stores, mixes, and digests some food and delivers food to the small intestine
the liver has many functions, for digestion it produces and secretes bile
the gall bladder stores and concentrates bile
what are the functions of the pancreas, small intestine, large intestine, and rectum?
the pancreas secretes digestive enzymes, hormones, and bicarbonate
the small intestine allows digestion and absorption of most food particles
the large intestine stores and concentrates undigested material and absorbs salt and water
the rectum is the site where the defecation reflex is triggered
what do secretion and digestion mean as processes in the GI system?
secretion: the release of digestive fluids into the lumen of the GI tract, fluids include:
- water, mucus, acid, electrolytes, enzymes, bile salts, and digestive enzymes
digestion: the process where food is broken down into smaller molecules by digestive enzymes so they can be taken up by the body
what do absorption, motility, and excretion mean as processes in the GI system?
absorption: the process where small molecules are taken up by the circulatory system and distributed throughout the body
motility: the movement of food through the digestive system by the contraction of smooth muscle that lines the walls of the tract
excretion: the removal of unwanted waste products from the body after all of the wanted material is absorbed
what is a bolus? what is saliva made of? list the three salivary glands
bolus: formed when meal is broken down by chewing (mastication) and mixed with saliva
saliva consists of:
- mostly water (99.5%) with ions and proteins (0.5%)
3 salivary glands: parotid (side of jaw), submandibular (under jaw), and sublingual (under teeth)
what does saliva do to the bolus? what controls the production and secretion of saliva?
saliva lubricates the bolus and begins digesting carbohydrates because it contains the enzyme, salivary amylase
- production and secretion of saliva is under control of the autonomic nervous system (ANS)
describe the path of swallowing
- Once bolus is formed, its pushed to the back of the mouth by the tongue and the swallowing reflex will start
- Uvula of the soft palette closes over the nasopharynx
- Larynx is lifted by muscles of the neck and the epiglottis bends over the glottis, covering the larynx
- Bolus moves down the esophagus through the cardiac orifice (or lower esophageal sphincter) and into the stomach by a wave of smooth muscle called peristalsis
what are all the areas of the stomach
- Fundus (upper, dome shaped)
- Body (middle, largest area)
- Antrum (lower, can be called pyloric region/pylorus)
the pyloric sphincter, located at the distal portion regulates the emptying of the stomach into the first part of the small intestine, the duodenum
what happens when the stomach is empty?
it is thrown into folds (rugae) which increases the surface area and allows for expansion of the stomach
what does the stomach do with the bolus, is there digestion or absorption that takes place here?
the stomach liquefies, mixes, and stores each bolus of food into a mixture (called chyme) and is slowly released into the small intestine
- it regulates the amount of food entering so it can be fully digested and absorbed
some digestion takes place in the stomach
- proteins begin to be digested by the enzyme pepsin
very little absorption takes place here
- very few substances can cross stomach lining into the bloodstream
- only alcohol aspirin can cross
How is chyme mixed in the stomach? What causes this
chyme is mixed by peristaltic contraction of the stomach walls, beginning at the fundus and ending at the antrum
- contractions help move the chyme through the pyloric sphincter into the small intestine
What substances does the stomach secrete?
- mucus
- hydrochloric acid
- pepsinogen
- gastrin
- intrinsic factor
What are the functions of mucus and HCl in the stomach? Where are the cells that secrete them?
Mucus:
- secreted by cells in the body and the antrum
- protects the smooth lining of the stomach from the acidic environment produced by HCl
HCl:
- secreted by cells in the body of the stomach
- denatures (unfolds) complex protein and connective tissue
- kills bacteria
- converts the inactive enzyme pepsinogen to its active form pepsin
What are the functions of pepsinogen/pepsin, gastrin, and intrinsic factor? Where are the cells that secrete them?
Pepsinogen/pepsin (enzyme):
- secreted by cells in the body of the stomach
- inactivated enzyme pepsinogen converts to its active form pepsin by HCl, it begins to digest large protein molecules
Gastrin (hormone):
- secreted by cells in the antrum of the stomach
- stimulates secretion of HCl
Intrinsic factor:
- enhances vitamin B12 absorption
Where is the pancreas located? How are products secreted by the pancreas (the path)
lies just below the stomach and has both exocrine (digestive) and endocrine (glucose homeostasis) functions
exocrine products are secreted into a long pancreatic duct, duct merges with the common bile duct (from liver and gallbladder) just before entering the duodenum
What does the pancreas produce and secrete?
carbohydrate-digesting enzyme amylase
protein-digesting enzymes (trypsin, chymotrypsin, and proteases)
fat-digesting enzyme lipase
pancreas secretes sodium bicarbonate into the duodenum to neutralize the acid from the stomach (allows pancreatic amylase to perform its digestive function)
pancreas also produces and secretes colipase protein to bypass action of bile salts
What are the three segments of the small intestine? What leads the stomach to the small intestine? What leads the small intestine into the large intestine?
the stomach contents empty through the pyloric sphincter into the small intestine
the small intestine is divided into 3 segments:
- Duodenum (first, shortest segment)
- Jejunum (second segment)
- Ileum (longest segment)
it ends at the ileocecal sphincter where it empties into the ascending colon of the large intestine
What is the inner structure of the small intestine made of? What does this result in?
inner wall is made of folds, these contain projections called villi
- this results in a large surface area where food comes into contact
What is contained inside the villi of the inner small intestine? What cells cover the villi and what do they do?
villi contain a capillary network and lymphatic lacteal to absorb the digested material
epithelial cells which secrete digestive enzymes covers the villi
- these cells have microvilli that face at the lumen forming a brush border
What causes absorption in the small intestine? What causes digestion in the small intestine?
absorption:
- most of the digested material are absorbed into the circulatory and lymphatic system
digestion:
- digestion of chyme occurs by digestive enzymes from the pancreas and epithelial cells
- bile from the liver helps digest fat (not a digestive enzyme)
What factors enhance digestion in the small intestine? Where does most digestion and absorption take place in the small intestine?
Almost all digestion and absorption takes place in the first two segments of the small intestine: duodenum and jejunum
enhanced by large surface area created by the villi, large blood supply to the GI tract, and motility and movement of food in the intestine
What are carbohydrates made of, give some examples? What are disaccharides, give some examples? What are polysaccharides, give some examples?
carbohydrates are made up of a single building block called monosaccharides (e.g. glucose, fructose, galactose)
disaccharides are made up of two monosaccharides (maltose, lactose, sucrose)
carbohydrates made up of more than 2 units are called polysaccharides (e.g. starch, glycogen)
In what form are carbohydrates absorbed?
polysaccharides must all be broken down into monosaccharides, in this form they can be absorbed by transport systems in the walls of the small intestine
Explain carbohydrate digestion from the mouth to the stomach
- Carbohydrate digestion begins in the mouth with the salivary amylase
- salivary amylase breaks up large polysaccharides into smaller polysaccharides - Once food reaches the stomach, digestion of carbohydrates stops because of the acidic environment which denatures (breaks up) salivary amylase
Explain carbohydrate digestion in the small intestine (polysaccharide to disaccharide)
- Once food reaches the small intestine, digestion begins again because the pancreas secretes amylase into the duodenum
- Pancreas also secretes bicarbonate to neutralize the stomach acid (neutralized environment permits amylase to perform its function)
- Pancreatic amylase digests the polysaccharide starch to the disaccharide maltose
- but its needs to be a monosaccharide to be absorbed
How are disaccharides broken down to monosaccharides?
Each disaccharide needs a specific enzyme to break it down to monosaccharides
- these enzymes are located at the brush border of the microvilli on the interstitial cells
carbohydrates can now be absorbed as monosaccharides
What are the three enzymes that break down disaccharides? What are the monosaccharides each produces?
Lactase breaks down lactose to galactose and glucose
Maltase breaks down maltose to two glucose
Sucrase breaks down sucrose to glucose and fructose
Explain lactose intolerance, what causes it and what are the symptoms?
inability to digest lactose due to the inability to produce lactase:
- if lactose is not digested, it will not be absorbed and stay in the GI tract, leading to diarrhea
- if carbs are present in the large intestine, bacteria will feed on it
- leads to gas, causing cramps, bloating, diarrhea
Explain the process of carbohydrate absorption
- Intestinal epithelial cells contain Na+/K+ pumps on their basal side, establishing a concentration gradient for Na+ (high outside, low inside)
- Gradient powers the Na+/glucose co-transporter on the luminal side of the cell, transporter moves glucose into the cell as Na+ moves in, down their concentration gradient
- Once glucose is inside the cell, it will diffuse out through the basal side by facilitated diffusion
What are proteins made of? How many types of amino acids are there, number of essential/nonessential?
Proteins consist of long chains of amino acids linked together
- there are 20 different amino acids, 11 are nonessential (produced by body), 9 are essential (must come from diet)
Explain the process of protein digestion in the stomach
Digestion of proteins begins in the stomach:
- Hydrochloric acid (HCl) converts the inactive pepsinogen to the active pepsin
- HCl helps uncoil the long, twisted strands of proteins, unfolding gives the pepsin access to the long protein chains to digest them into smaller chains called polypeptides
- Polypeptides pass through the pyloric sphincter into the small intestine where they continue to be digested and absorbed
What continues protein digestion in the small intestine? Why? (3 steps)
- Pancreatic enzymes that partake in protein digestion must have a neutral pH environment to work optimally
- the chyme from the acidic stomach must be neutralized by bicarbonate (secreted by the pancreas) - Because of the neutral pH environment, the pepsin that begun digestion becomes inactivated
- Trypsin and chymotrypsin from the pancreas continue protein digestion in the small intestine
What is the class of enzymes that continues protein digestion in the small intestine? Where are they produced and secreted, where are they located?
Proteases continue digesting proteins into amino acids
- they’re produced in the pancreas and secreted into the small intestine
- some proteases are found along the brush border of the intestinal epithelial cells
What are the two classes of protease enzymes? What differentiates each of them?
Each class of protease enzymes are responsible for breaking apart amino acids located in different parts of the protein
- Endopeptidases break the bonds between amino acids in the inner part of the protein
2.. Exopeptidases break the bonds between amino acids and the ends of the protein
Explain the process of protein absorption in the small intestine
- When proteins are broken into single amino acids with a few remaining small polypeptides, absorption can occur
- intestinal epithelial cells contain Na+/k+ pumps on their basal side that establish a Na+ concentration gradient (high outside, low inside)
- Gradient powers the Na+/amino acid co transporter located on the luminal side of the cell, transporter moves amino acids into the cell as Na+ moves down its concentration gradient
- Remaining small peptides are absorbed by endocytosis
(similar to carbohydrate absorption)
Where does the large intestine begin? What are the three colons in the large intestine? What is at the end of the large intestine?
Begins at the ileocecal valve
Consists of an ascending colon, longitudinal/transverse colon, and descending colon
As well as a curved sigmoid section and the rectum that ends at the anus
- lacks the many folds and villi of the small intestine
What are the 3 functions of the large intestine?
- Water and electrolyte absorption
- Mucus secretion
- protects intestinal lining from chemical and mechanical damage
- lubricate forming feces
- some K+ and bicarbonate are secreted into the colon - Small amount of digestion (bacterial)
- occurs when undigested polysaccharides are metabolized into free fatty acids by bacteria
- bacteria produces gas (flatus)
- bacteria produces vitamin K
