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SP MCAT Biology > Digestive System > Flashcards

Digestive System Flashcards

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1
Q

List the structures in order that occur in the digestive tract

A
  1. oral cavity (mouth)
  2. pharynx
  3. esophagus
  4. stomach
  5. small intestine
  6. large intestine
  7. rectum
  8. anus
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2
Q

Alimentary Canal

A
  • runs from mouth to anus and is sectioned off by sphincters
  • nutrients are obtained from food within the lumen of this canal and is known as extracellular digestion (“outside the body”)
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3
Q

Absorption

A

involves the transport of products of digestion from the digestive tract into the circulatory system for distribution to the body’s tissues and cells

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4
Q

Enteric Nervous System

A
  • collection of millions of neurons that help govern the function of the GI system
  • neurons are present in the walls of the digestive tract and trigger peristalsis (rhythmic contractions of the gut tube in order to move material through system)
  • can function independently of the brain and spinal cord, but is heavily regulated by the autonomic NS
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5
Q

What occurs when the parasympathetic NS stimulates the GI tract?

A
  • increases secretions from exocrine glands
  • promotes peristalsis
  • stimulates GI activities
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6
Q

What occurs when the sympathetic NS stimulates the GI tract?

A
  • decreased secretions from exocrine glands
  • inhibition of peristalsis
  • decreased blood flow to GI tract
  • slowed gut motility
  • overall inhibition of GI activities
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7
Q

What is the only gland in the body that is not innervated by the parasympathetic NS?

A

sweat glands

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8
Q

Oral Cavity

A
  • plays a role in both mechanical and chemical digestion of food
  • mastication (chewing) occurs
  • enzymes produced in the salivary glands begin breaking down chemical bonds in food macromolecules
  • salivary glands are innervated by the parasympathetic NS
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9
Q

What are the two enzymes found in the oral cavity?

A
  • salivary amylase: hydrolyzes starch into smaller sugars (maltose and dextrins)
  • salivary lipase: catalyzes the hydrolysis of lipids
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10
Q

Pharynx

A
  • cavity that leads from mouth and posterior nasal cavity to the esophagus
  • connects both the esophagus and larynx
  • food is prevented from entering the larynx during swallowing by the epiglottis
  • can be divided into 3 parts: nasopharynx (behind nasal cavity), oropharynx (back of the mouth), laryngopharynx (above vocal cords)
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11
Q

Esophagus

A
  • connects pharynx to stomach
  • top third is composed of skeletal muscle so it is under somatic (voluntary) motor control
  • bottom third is composed of smooth muscle so it is under autonomic (involuntary) control
  • middle third is composed of both muscle types
  • upper esophageal sphincter and lower esophageal sphincter (cardiac sphincter) are located here
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12
Q

Stomach

A
  • highly muscular organ that uses hydrochloric acid and enzymes to digest food
  • thick mucosa to prevent autodigestion
  • can be divided into 4 divisions: fundus, body, antrum, pylorus
  • mucosa contains gastric glands and pyloric glands
  • mainly an organ of digestion, not so much absorption
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13
Q

Gastric Glands

A
  • respond to signals from the vagus nerve of the parasympathetic NS, which activated by the brain in response to the sight, smell, and taste of food
  • contain 3 different cell types: mucous cells, chief cells, parietal cells
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14
Q

Mucous Cells

A

produce the bicarbonate-rich mucus that protects the stomach wall from the acidic (pH=2) and proteolytic environment of the stomach

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15
Q

Gastric Jucie

A

combination of secretions from chief cells and parietal cells

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16
Q

Chief Cells

A

secret pepsinogen (inactive, zymogen, form of pepsin, a proteolytic enzyme) which digests proteins

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17
Q

Parietal Cells

A
  • secrete hydrochloric acid (HCl) which has hydrogen ions that cleave pepsinogen to pepsin, decreases the pH, kills microbes, and denatures proteins
  • secrete intrinsic factor (glycoprotein involved in proper absorption of vitamin B12)
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18
Q

Pepsin

A
  • digests proteins by cleaving peptide bonds near aromatic amino acids, resulting in short peptide fragments
  • activated by the acidic stomach environment
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19
Q

G Cells

A
  • located in pyloric glands

- secrete gastrin

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20
Q

Gastrin

A
  • peptide hormone
  • induces the parietal cells in the stomach to secrete more HCl
  • signals the stomach to contract and mix its contents – increases gastric motility
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21
Q

Chyme

A

acidic, semifluid mixture that results from digestion of solid food in the stomach

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22
Q

What 2 substances can be directly absorbed from the stomach?

A
  • alcohol

- aspirin

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23
Q

What are the 6 products secreted by the stomach?

A
  1. HCl
  2. Pepsinogen
  3. Mucus
  4. Bicarbonate
  5. Water (dissolves and dilutes ingested material)
  6. Intrinsic Factor
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24
Q

Small Intestine

A
  • food leaves stomach and enters here via the pyloric sphincter
  • consists of 3 segments: duodenum, jejunum, ileum
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25
Q

Duodenum

A
  • responsible for the majority of chemical digestion
  • presence of chyme here causes the release of brush-border enzymes like disaccharidases and peptidases
  • secretes enteropeptidase (involved in activation of other digestive enzymes from the accessory organs)
  • secretes secretin and cholecystokinin (CCK) into the bloodstream
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26
Q

Brush-Border Enzymes

A
  • present on the liminal surface of cells lining the duodenum
  • break down dimers and trimers of biomolecules into absorbable monomers
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27
Q

Maltase

A
  • secreted by intestinal glands
  • functions in the duodenum
  • hydrolyzes maltose to two glucose molecules
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28
Q

Isomaltase

A
  • secreted by intestinal glands
  • functions in the duodenum
  • hydrolyzes isomaltose into two glucose molecules
29
Q

Sucrase

A
  • secreted by intestinal glands
  • functions in the duodenum
  • hydrolyzes sucrose to glucose and fructose
30
Q

Lactase

A
  • produced by intestinal glands
  • functions in the duodenum
  • hydrolyzes lactose to glucose and galactose
31
Q

Aminopeptidase

A
  • produced by intestinal glands
  • functions in the duodenum
  • hydrolyzes terminal peptide bond at amino acid
32
Q

Dipeptidases

A
  • produced by intestinal glands
  • functions in the duodenum
  • hydrolyzes pairs of amino acids
33
Q

Enteropeptidase

A
  • produced in intestinal glands
  • functions in the duodenum
  • converts trypsinogen to trypsin and procarboxypeptidases A and B to carboxypeptidases A and B
  • essentially activate zymogen forms of pancreatic peptidases
34
Q

Secretin

A
  • peptide hormone
  • causes pancreatic enzymes to be released into the duodenum
  • regulates the pH of the digestive tract by reducing HCl secretion from parietal cells and increasing bicarbonate secretion from the pancreas
  • it is an enterogastrone hormone, so it slows motility through the digestive tract
35
Q

CCK

A
  • peptide hormone
  • secreted in response to the entry of chyme into the duodenum
  • stimulates the release of both bile and pancreatic juices
  • acts in the brain to promote satiety
  • promotes the secretion of pancreatic juices into the duodenum
36
Q

Bile

A
  • produced in the liver but stored in the gallbladder
  • functions in the duodenum
  • emulsifies fat
  • complex fluid composed of bile salts, pigments, and cholesterol
37
Q

Bile Salts

A
  • derived from cholesterol
  • not enzymes so do not directly perform any chemical digestion
  • play role in mechanical digestion of fats and facilitate chemical digestion of lipids
  • have both hydrophobic and hydrophilic regions
  • in small intestine they emulsify fats and cholesterol into micelles
38
Q

Pancreatic Juices

A
  • complex mixture of several enzymes in a bicarbonate-rich alkaline solution that helps neutralize acidic chyme
  • contains enzymes that can digest all 3 types of nutrients: carbs, fats, proteins
39
Q

Accessory Organs of Digestion

A
  • organs that originate as outgrowths of endoderm from the gut tube during development
  • includes: pancreas, liver, gallbladder
40
Q

Pancreas

A
  • has both exocrine and endocrine functions
  • endocrine functions include: release of insulin, glucagon, somatostatin — peptide hormones necessary for maintenance of blood sugar levels
  • mostly made of exocrine cells called acinar cells that produce pancreatic juices
41
Q

Pancreatic Amylase

A
  • produced by acinar cells in the pancreas
  • functions in the duodenum
  • breaks down large polysaccharides into small disaccharides, making it responsible for carbohydrate digestion
42
Q

Pancreatic Lipase

A
  • produced in the pancreas by acinar cells
  • functions in the duodenum
  • hydrolyzes lipids
43
Q

Trypsin(ogen)

A
  • produced in the pancreas by acinar cells
  • functions in the duodenum
  • hydrolyzes specific peptide bonds; converts chymotrypsinogen to chymotrypsin
  • activated by enteropeptidase
44
Q

Chymotrypsin(ogen)

A
  • produced in the pancreas by acinar cells
  • functions in the duodenum
  • hydrolyzes specific peptide bonds
  • activated by trypsin
45
Q

(Pro)carboxypeptidases A and B

A
  • produced in the pancreas by acinar cells
  • functions in the duodenum
  • hydrolyze terminal peptide bond at carboxy end
  • activated by enteropeptidase
46
Q

How are pancreatic juices transferred to the duodenum?

A

via a duct system that runs along the middle of the pancreas

47
Q

What are the 5 products secreted by the pancreas?

A
  • pancreatic amylase
  • trypsinogen
  • chymotrypsinogen
  • procarboxypeptidases A and B
  • pancreatic lipase
48
Q

Liver

A
  • contains bile ducts (connect liver with the gallbladder and small intestine) that allow for bile created in the liver to travel to the gallbladder for storage or secreted in the duodenum
  • receives all blood draining from the abdomen portion of the GI tract through hepatic portal vein
  • takes up excess glucose and stores it as glycogen, and stores fat as triacylglycerols
  • can perform gluconeogenesis and glyconeogenesis
  • detoxifies endogenous compounds (those made in the body) and exogenous compounds (those brought in from the environment)
  • detoxifies and metabolizes alcohol and medications
  • synthesizes proteins like albumin and clotting factors
49
Q

Bilirubin

A
  • major pigment in bile
  • byproduct of the breakdown of hemoglobin
  • in the liver it is conjugated and secreted into bile for excretion
50
Q

Albumin

A
  • synthesized in the liver

- protein that maintains plasma oncotic pressure and serves as a carrier for many drugs and hormones

51
Q

Gallbladder

A
  • stores and concentrates bile

- stimulated by CCK to contract and push bile out into the biliary tree

52
Q

What 6 enzymes take part in carbohydrate digestion?

A
  • salivary amylase
  • pancreatic amylase
  • maltase
  • iosmaltase
  • sucrase
  • lactase
53
Q

What 7 enzymes take part in protein digestion?

A
  • pepsin
  • trypsin
  • chymotrypsin
  • carboxypeptidases A and B
  • aminopeptidase
  • dipeptidases
  • enteropeptidase
54
Q

What two products take part in lipid digestion?

A
  • bile (involved in mechanical digestion b/c not an enzyme)

- pancreatic lipase (enzyme)

55
Q

What are the 3 segments of the small intestine?

A
  • Dow Jones Industrial*
    1. duodenum
    2. jejunum
    3. ileum
56
Q

What is the main function of the jejunum and ileum?

A

absorption of nutrients

57
Q

What lines the walls of the small intestine?

A

villi (projections from the epithelia lining) that contain many microvilli

58
Q

What is located in the middle of each villus?

A

capillary bed for the absorption of water-soluble nutrients and a lacteal (lymphatic channel that takes up fats for transport into the lymphatic system)

59
Q

List the steps of absorption of carbohydrates, small fatty acids, and amino acids into the small intestine

A
  1. absorbed by secondary active transport and facilitated diffusion into the epithelial cells lining the small intestine
  2. substances move across epithelial cells into intestinal capillaries
  3. simple diffusion of these substances down their concentration gradient into the capillaries
  4. movement of absorbed molecules to the liver via hepatic portal circulation
60
Q

List the steps of absorption of larger fats, glycerol and cholesterol into the small intestine

A
  1. in small intestine the triacylglycerol is broken down via bile micelles and pancreatic lipase
  2. diffusion of fatty acids and broken down glycerol into mucosal cell
  3. reformation of parts into triacylglycerol in mucosal cell
  4. packaging of triglycerides and cholesterol into chylomicrons that enter lymphatic circulation through lacteals
  5. lacteals form the beginning of the lymphatic system through the thoracic duct
61
Q

Fat-Soluble Vitamins

A
  • dissolve directly into the chylomicrons to enter the body

- include vitamins A, D, E, K

62
Q

Water-Soluble Vitamins

A

absorbed, along with water, amino acids, and carbohydrates, across endothelial cells of the small intestine, passing directly into the plasma

63
Q

What are the two ways that water can pass into the blood?

A
  • transcellularly (across the cell membrane)

- paracellularly (squeezing between cells)

64
Q

Large Intestine

A
  • primarily involved in water absorption
  • divided into 3 major segments: cecum, colon, rectum
  • home to a large amount of bacteria (small intestine too)
  • most of the bacteria here is anaerobic
  • symbiotic relationship with gut bacteria as it produces vitamin K and biotin (vitamin B7)
65
Q

Cecum

A
  • outpocketing that accepts fluid exiting the small intestine through the ileocecal valve
  • site of attachment of the appendix
66
Q

Colon

A
  • divided into the ascending, transverse, descending and sigmoid colon
  • main function is is to absorb water and salts from undigested material left over from the small intestine, and concentrate the material into feces
67
Q

Rectum

A
  • serves as the storage site for feces

- feces consists of indigestible material, water, bacteria (E. coli and others), and certain digestive secretions

68
Q

Anus

A
  • opening through which wastes are eliminated
  • consists of two sphincters: internal (autonomic – involuntary control) and external (somatic – voluntary control) anal sphincters

SP MCAT Biology (21 decks)

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