Digestive System

Question 1

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

Answer 1

• 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

Question 2

transport of things in the small intestine

Answer 2

• 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

Question 3

explain pathway of the digestive tract

Answer 3

• oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus

Question 4

what are teh accessory organs of the digestive system

Answer 4

• salivary glands, pancreas, liver and gall bladder

Question 5

explain the role of the oral cavity

Answer 5

• 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

Question 6

what is the purpose of saliva

Answer 6

• 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)

Question 7

what is the role of the esophagus

Answer 7

• 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

Question 8

explain GERD

Answer 8

• 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

Question 9

what is the role of the stomach

Answer 9

• 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

Question 10

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

Answer 10

• 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

Question 11

what are the 3 parts of the small intestine

Answer 11

• duodenum, jejunum and ileum

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Question 12

explain strucutre of small intestine

Answer 12

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

Question 13

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

Answer 13

• 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

Question 14

lactose intolerance?

Answer 14

• 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

Question 15

what is gastrin

Answer 15

• 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

Question 16

what is intrinsic factor

Answer 16

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

Question 17

what is cholecystokinin

Answer 17

• 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.

Question 18

what is secretin

Answer 18

• 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

Question 19

what is the role of the liver

Answer 19

• 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

Question 20

what is the role of the pancreas

Answer 20

• 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

Question 21

what is the role of the large intestine

Answer 21

• 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

Question 22

Answer 22