The Digestive System Flashcards
1
Q
What is intracellular digestion?
A
-involves oxidation of glucose and fatty acids for energy
2
Q
What is extracellular digestion?
A
-process by which nutrients are obtained from food within alimentary canal (mouth to anus, compartmentalized by sphincters)
3
Q
What is digestion, and what are the different types?
A
- Digestion: breakdown of food into its constituent organic molecules
- Mechanical digestion: physical breakdown of large food particles into smaller particles (no bond breaking)
- Chemical digestion: enzymatic cleavage of chemical bonds
4
Q
What is absorption?
A
-transport of digestion products from GI tract to circulatory system for distribution
5
Q
What is the path of the digestive system in the body?
A
- oral cavity to pharynx (which is for both food and air) to esophagus to stomach to small intestine to large intestine to rectum
- other structures: salivary glands, pancreas, liver, gallbladder
6
Q
What is the enteric nervous system?
A
- collection of neurons in the digestive tract walls that regulate GI system
- trigger peristalsis (rhythmic contractions of gut tube)
- can function independently of brain and spinal cord, though is heavily regulated by ANS
- peristalsis promoted by parasympathetic system, as well as increased secretions from all digestive glands
7
Q
What is the role of the oral cavity in digestion?
A
- Mastication: chewing to increase surface area to volume ratio of food for enzymatic digestion
- Chemical digestion thru saliva
- Bolus formed and swallowed
8
Q
How do salivary enzymes work?
A
- Presence of food in cavity triggers parasympathetic stimulation of the 3 salivary glands
- can also be triggered by smell or sight
- saliva has salivary amylase (hydrolyzes starch into smaller sugars) and lipase (catalyzes lipid hydrolysis)
9
Q
What is the anatomy of the pharynx?
A
- cavity from mouth and posterior nasal cavity to esophagus
- connects to esophagus and larynx
- nasopharynx (behind nasal cavity), oropharynx (back of mouth), laryngopharynx (above vocal cords)
- larynx covered by epiglottis during swallowing so food doesn’t enter it
10
Q
How does swallowing occur? What does the esophagus do? What is it made of, and how is it controlled?
A
- Oropharynx muscles (upper esophageal sphincter) initiate swallowing
- Peristalsis (rhythmic contraction of smooth muscle) to push bolus toward stomach
- Muscular ring - the lower esophageal sphincter (cardiac sphincter) relaxes to allow bolus thru at stomach
- esophagus connects pharynx to stomach
- top is skeletal muscle (somatic control), bottom is smooth muscle (autonomic), middle is mix
11
Q
Describe the anatomy of the stomach.
A
- can hold 2L
- in upper left quadrant
- 4 parts: fundus and body (top - contain gastric glands), antrum and pylorus (bottom - contain pyloric glands)
- internal curvature = lesser curvature, external = greater curvature
- lining of stomach in folds called rugae
12
Q
What do the gastric glands do? What are the 3 cell types, and what do they do?
A
- respond to signals from vagus nerve (PNS)
- 3 diff cell types: mucous, chief, parietal
- mucous cells: produce bicarb-rich mucus that protects wall from acidic environment (pH = 2)
- chief cells: secrete pepsinogen (inactive/zymogen form of pepsin, a proteolytic enzyme most active at low pH)
- parietal cells: secrete HCl - H+ will cleave pepsinogen to pepsin; secrete intrinsic factor (glycoprotein involved in proper absorption of vitamin B12)
- Gastric juice: combination of pepsinogen + H+
13
Q
What are the 7 products the stomach secretes? What do they do, and what secretes them?
A
- HCl (kills microbes, denatures proteins, converts pepsinogen –> pepsin) - parietal cells of gastric glands
- Pepsinogen (cleaves proteins in active form) - chief cells of gastric glands
- Mucus (protects mucosa) - mucous cells of gastric glands
- Bicarbonate (protects mucosa) - mucous cells of gastric glands
- Water (dissolves and dilutes digested material)
- Intrinsic factor (required for normal absorption of Vit B12) - parietal cells of gastric glands
- Gastrin (induces parietal cells to secrete more HCl and signals to stomach to contract) - G-cells in pyloric glands
14
Q
What do the pyloric glands do?
A
- contain G-cells that secrete gastrin, a peptide hormone that will induce parietal cells to secrete more HCl and stomach to contract
- leads to creation of chyme: acidic, semifluid mix with increase in SA for absorption in intestines
15
Q
What are the three segments of the small intestine?
A
- duodenum, jejunum, ileum
- duodenum does majority of chemical digestion
- jejunum and ileum do absorption
16
Q
What occurs when food enters the duodenum?
A
- food leaves stomach thru pyloric sphincter
- presence of chyme in duodenum causes release of brush-border enzymes like disaccharidases, peptidases, enteropeptidase, secretin, CCK
17
Q
What do disaccharidases do, and what are some examples? What occurs if the disaccharidase is missing? What happens if the disaccharide goes undigested?
A
- digest disaccharides
- maltase digests maltose, isomaltase - isomaltose, lactase - lactose, sucrase - sucrose
- lack of disaccharidase - bacteria in intestines hydrolyze disaccharide instead and release methane as byproduct
- undigested disaccharide can have osmotic effect, pulling water into stool and causing diarrhea
18
Q
What do peptidases do, and what are some examples? What size do proteins need to be to be absorbed?
A
- break down proteins
- aminopeptidase removes N-terminal AA from a peptide, dipeptidase cleaves peptide bonds of dipeptides
- proteins can be broken down into di- and even tripeptides and can be absorbed across intestine
19
Q
What does enteropeptidase do?
A
- activates trypsinogen, a pancreatic protease, to trypsin, which initiates an activation cascade to hydrolyze peptide bonds
- can also activate procarboxypeptidases A and B to their active form
20
Q
What does secretin do?
A
- peptide hormone that causes the release of pancreatic enzymes into duodenum
- regulates pH of GI tract by reducing HCl secretion from parietal cells and increasing bicarb secretion from pancreas
- also an enterogastrone - hormone that slows motility thru the digestive tract (more time for enzymes to act on chyme)
21
Q
What does cholecystokinin (CCK) do?
A
- secreted in response to entry of chyme in duodenum
- peptide hormone that stimulates release of bile and pancreatic juices and promotes satiety in brain
22
Q
What is bile / bile salts?
A
- Bile: bile salts, pigments, cholesterol
- Bile salts: derived from cholesterol, have hydrophilic and phobic regions so serve as a bridge between aqueous and lipid environments
- Bile salts emulsify fats and cholesterol into micelles so they can be accessible to pancreatic lipase, which is water-sol, with increased SA
- So bile gets fats into solution and increases their SA by placing them micelles
23
Q
What are pancreatic juices?
A
- mix of enzymes in bicarb-rich alkaline solution
- neutralizes acidic chyme and raises pH for digestive enzymes (which like pH of 8.5)
24
Q
What are the accessory organs of digestion, and which primary germ layer do they originate from?
A
- pancreas, liver, gallbladder
- all come from endoderm of the gut tube during development
25
Q
What does the pancreas do?
A
- endocrine function - insulin, glucagon, somatostatin for blood sugar level maintenance
- exocrine function - acinar cells that produce pancreatic juices
26
Q
What are the enzymes in pancreatic juices?
A
- pancreatic amylase: breaks down large polysaccharides into small disaccharides
- pancreatic peptidases (trypsinogen, chymotrypsinogen, carboxypeptidases A and B): released in zymogen form but once activated digest proteins
- -Enteropeptidase (from duodenum) converts trypsinogen –> trypsin –> activates all other zymogens + procarboxypeptidases A an dB - pancreatic lipase: breaks down fats into free atty acids and glyceron
27
Q
How are papillary juices transferred to the duodenum?
A
- acinar cells secrete their products into a duct system that runs along the middle of the pancreas
- the ducts empty to duodenum thru major and minor duodenal papillae
28
Q
What are features of the liver?
A
- located in upper right quadrant
- has bile ducts: connect liver with gallbladder and small intestine
- has hepatic portal vein: receives nutrient-rich blood draining from abdomen before going to inferior vena cava
29
Q
What are the functions of the liver?
A
- liver can take up excess blood sugar to form glycogen and store fats as triacylglycerols
- can also reverse this and create glucose for the body thru glycogenolysis and gluconeogenesis and mobilizing fats in lipoproteins
- detoxifies endogenous and exogenous compounds (ammonia into urea, alcohol, drugs)
- produces bile: contains bilirubin (from hemoglobin breakdown) that travels to liver, is conjugated (attached to a protein), and secreted into bile for excretion (if can’t be excreted - jaundice)
- also synthesizes certain proteins needed for body function - like albumin (maintains plasma oncotic pressure and serves as carrier for many drugs/hormones) and clotting factors
30
Q
What does the gallbladder do?
A
- stores and concentrates bile
- upon release of CCK, gallbladder pushes bile out into biliary tree
- bile duct system merges with pancreatic duct before emptying into duodenum
- common site of cholesterol or bilirubin stone formation, causing inflammation and maybe even traveling
31
Q
What do the jejunum and ileum contain and do?
A
- absorption of nutrients
- lined with villi, each of which has microvilli (increasing SA for absorption)
- middle of each villus has capillary bed for absorption of water-sol nutrients and a lacteal (lymphatic channel that takes up fats for transport in lymphatic system)
32
Q
How do simple sugars and AAs get absorbed in the small intestine?
A
- absorbed by secondary active transport and facilitated diffusion into epithelial cells lining small intestine
- then, move into intestinal capillaries
- blood is constantly passing by and carrying sugar + AA molecules away, creating a conc gradient such that blood always has a lower concentration than inside epithelial cells
- so sugars + AAs always diffuse from epithelial cells into capillaries, then to liver via hepatic portal
33
Q
How do fats get absorbed in the small intestine?
A
- short fatty acids will diffuse into intestinal capillaries (nonpolar so can easily go across cell membranes)
- larger fats move separately into intestinal cells but then reform into triglycerides
- triglycerides and cholesterol are packaged into chylomicrons, which enter lymphatic circulation thru lacteals
- lacteals converge and enter venous circulation at the thoracic duct in the base of the neck, which empties into the left subclavian vein
34
Q
How do vitamins get absorbed in the small intestine?
A
- either fat-sol or water-sol
- 4 fat-sol: A, D, E, K; water-sol are B complex, C
- fat-sol dissolve directly into chylomicrons to enter lymphatic circulation
- water-sol are taken up across endothelial cells (with sugars and AAs) and then passed into plasma
35
Q
How does water get absorbed in the small intestine?
A
- water from both intake and also secretions
- occurs by osmosis - water follows solutes
- water passes transcellulary (across cell membrane) and paracellulary (between cells) to reach blood
36
Q
What are the three sections of the large intestine?
A
- cecum: accepts fluid exiting small itntestine thru the ileocecal valve; site of attchment for appendix
- colon: divided into ascending / transverse / descending / sigmoid colons; absorbs water and salts from undigested material; concentrates material into feces
- rectum: storage site for feces (indigestible material, water, bacteria); eliminates it thru anus which has an internal sphincter (autonomic) and external sphincter (somatic)
37
Q
What relationships exist with bacteria in the GI tract?
A
- 30% of dry matter in stool is bacteria
- most are anaerobes, but cecum has many aerobic
- colon bacteria has symbiotic relationship - food for bacteria, and they make helpful byproducts (like Vit K in gut, biotin)
