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PCAT: BIOLOGY > Digestive System > Flashcards

Digestive System Flashcards

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1
Q

overview of what is the digestive system and what it is needed

A
  • humans are heterotrophic and unable to synthesize all own nutrients so consume food
  • food must be ingested then digested to degrade large molecules into smaller ones that can be absorbed into the bloodstream

intracellular digestion: occurs in cell in membrane bound vesicles

extracellular digestion: refers to digestive process that occurs outside of the cell within lumen or tract

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2
Q

transport of things in the small intestine

A
  • amino acids and monosaccarides pass through villi walls into capillary system
  • blood from digestive tract enters heptic portal system of the liver where it is detoxified and stripped of some nutrients
  • large fatty acids and glycerol pass into the lacteals and are reconverted into fats (fatty acids + glycerol)

*some nutreints like glucose and amino acids are actively aborbed (requiring energy) while others are passively

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3
Q

explain pathway of the digestive tract

A
  • oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus
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4
Q

what are teh accessory organs of the digestive system

A
  • salivary glands, pancreas, liver and gall bladder
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5
Q

explain the role of the oral cavity

A
  • mechanical anf chemical digetion begins
  • mechanical breaks down large food particles into smaller through mastication (also later have churning motion of stomach
  • chemical = enzymatic breakdown of macromolecules, begins in mouth with saliva

once food suff moistened and broken down its swallowed down the esophagus and is called a bolus

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6
Q

what is the purpose of saliva

A
  • lubricates the food
  • secreted in response to nervous reflex triggered by pressence of food in oral cavity
  • contains salivary amylase (ptyalin) which hydrolyses starch to maltose (a disaccharide)
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7
Q

what is the role of the esophagus

A
  • muscular tube leading from mouth to stomach
  • food is moved down via rhythmic waves of involuntary muscular contractions called peristalsis
  • esophagus closed off from stomach by contraction of the lower esophageal (cardiac) sphincter
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8
Q

explain GERD

A
  • esophagus is in the thoracic cavity which is negatively pressured relative to the environment on inhalation
  • abdominal cavity has a relative postive pressure: w/o normal defense mechanisms pressure gradients favour continual reflex of gastric materials into esophagus resuling in gastroesophageal reflex disease

*reflux can occur after spon transient lower esophageal sphincter relaxation not associated w/ swallowing

*pateitns w/ GERD usually have dec lower esophageal sphincter pressure

*resting pressure of lower esophageal sphincter range from 15-35 mmHg abovve gastric baseline

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9
Q

what is the role of the stomach

A
  • large muscular organ in upper abdomen
  • walls lined with gastric musoca: muscous membrane that contains the gastric glands
  • mucous cells in gastric pits along membrane secrete mucus to protect the stomach lining from acidic juices
  • churning of stomach and enzymatic activity produces acidic semifluid called chyme which goes into the duodemum via pyoric sphincter
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10
Q

what are the diff cell types in the stomach and what do they produce

A
  • chief cells in gastric glands synthesize pepsinogen which is converted to pepsin upon contact w/ stomahc acid to break donw proteins
  • perietal cells in gastric glands synthesize and release HCl to alter stomach pH and kill bacteria
  • also make intrinsic factor necessary for the absorption of vitamin B12
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11
Q

what are the 3 parts of the small intestine

A
  • duodenum, jejunum and ileum

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12
Q

explain strucutre of small intestine

A
  • adapted for absorption
  • very long (>6m) and coiled
  • containes villi in intestinal wall that has capillaries and lacteals (vessels of the pymphatic system)
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13
Q

where does most digestion take place, what is secreted to help there

A
  • duodenum where the secretions of the intestinal glands, pancreas, liver and gallbladder mix with acidic chyme
  • intestinal mucosa secretes lipases for fat digestion,
  • aminopeptidases for polypeptide digestion
  • disaccharides for maltose, lactose and sugrose digestion
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14
Q

lactose intolerance?

A
  • disaccharide lactase breaks down lactose (milk sugar) and is most present in infants
  • many adults lack the enzyme and are lactose intolerant
  • lactose cant be digested and is metabolized by bacteria creating discomfort
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15
Q

what is gastrin

A
  • formone of digestive system
  • produced by G cells of duodenum
  • functions to stimulate histamine and pepsinogen secretion and inc gastic blood flow
  • also stim parietal cells to produce HCl which denatures proteins and activates digestive enzymes
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16
Q

what is intrinsic factor

A

secrtion of parietal cells that facillitats the asorption of vitamin B12 across the intestinal lining

17
Q

what is cholecystokinin

A
  • produced and stores in the I cells of the duodenal and jejunal mucosa
  • involved in stimuation of pancreatic enzyme and somatostatin secretion as well as gallbladder
  • also acts as a hunger supressent

*secreted by cells in the duodenum and stimulates the release of bile into the intestine and the secretion of enzymes by the pancreas.

18
Q

what is secretin

A
  • synthesized and stored int he S cells of upper intestine
  • stimulates the secretion of bicarbonate-containing substances from the pancreas and inhibits fastric emptying and gastric acid production
19
Q

what is the role of the liver

A
  • produces bile that is stored in the gall bladder before release into SI
  • bile contains no enzymes: it emulsifies fats, breaking down large globules into small droplets
  • emulsification exposes a greater surface area to action of pancreatic lipase
  • w/o bile fats cant be digested

*liver also functions to store glycogen, convert ammonia into urea, protein synthesis, detoxification and cholesterol metabolism

20
Q

what is the role of the pancreas

A
  • produces enzymes like anylase for carbohydrat digestion, trypsin for protein digestion and lipase for fat digestion
  • chem pancreas releases chymotrypsin and enterokinase, enterokinase cleaves trupsinogen into trypsin which then activiates other zymogens
  • also secretes bicarbonate-rich juice that neutralizes the acidic chyme arriving from the stomach in duodenum

*pancreatic enzymes operate optimally at higher pH

21
Q

what is the role of the large intestine

A
  • approx 1.5m long and absorbs salts and way water not alread abosrbed by small intestine
  • rectum provides a transient storage of feces before elimination through the anus
22
Q
A

PCAT: BIOLOGY (18 decks)

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