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Biology > The Digestive System > Flashcards

The Digestive System Flashcards

1
Q

What is intracellular digestion?

A

-involves oxidation of glucose and fatty acids for energy

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2
Q

What is extracellular digestion?

A

-process by which nutrients are obtained from food within alimentary canal (mouth to anus, compartmentalized by sphincters)

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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
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4
Q

What is absorption?

A

-transport of digestion products from GI tract to circulatory system for distribution

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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
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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
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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
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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)
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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
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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
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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
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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+
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13
Q

What are the 7 products the stomach secretes? What do they do, and what secretes them?

A
  1. HCl (kills microbes, denatures proteins, converts pepsinogen –> pepsin) - parietal cells of gastric glands
  2. Pepsinogen (cleaves proteins in active form) - chief cells of gastric glands
  3. Mucus (protects mucosa) - mucous cells of gastric glands
  4. Bicarbonate (protects mucosa) - mucous cells of gastric glands
  5. Water (dissolves and dilutes digested material)
  6. Intrinsic factor (required for normal absorption of Vit B12) - parietal cells of gastric glands
  7. Gastrin (induces parietal cells to secrete more HCl and signals to stomach to contract) - G-cells in pyloric glands
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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
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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
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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
  1. endocrine function - insulin, glucagon, somatostatin for blood sugar level maintenance
  2. exocrine function - acinar cells that produce pancreatic juices
26
Q

What are the enzymes in pancreatic juices?

A
  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
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
  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
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)

Biology (14 decks)

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