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
What does the pancreas do?
1. endocrine function - insulin, glucagon, somatostatin for blood sugar level maintenance
2. exocrine function - acinar cells that produce pancreatic juices
26
What are the enzymes in pancreatic juices?
1. pancreatic amylase: breaks down large polysaccharides into small disaccharides
2. 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
3. pancreatic lipase: breaks down fats into free atty acids and glyceron
27
How are papillary juices transferred to the duodenum?
- 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
What are features of the liver?
- 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
What are the functions of the liver?
- 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
What does the gallbladder do?
- 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
What do the jejunum and ileum contain and do?
- 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
How do simple sugars and AAs get absorbed in the small intestine?
- 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
How do fats get absorbed in the small intestine?
- 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
How do vitamins get absorbed in the small intestine?
- 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
How does water get absorbed in the small intestine?
- 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
What are the three sections of the large intestine?
1. cecum: accepts fluid exiting small itntestine thru the ileocecal valve; site of attchment for appendix
2. colon: divided into ascending / transverse / descending / sigmoid colons; absorbs water and salts from undigested material; concentrates material into feces
3. rectum: storage site for feces (indigestible material, water, bacteria); eliminates it thru anus which has an internal sphincter (autonomic) and external sphincter (somatic)
37
What relationships exist with bacteria in the GI tract?
- 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)
