Digestive system
59 flashcards covering Digestive system for the MCAT Biology & Biochemistry section.
The digestive system is a network of organs and processes that break down food into usable nutrients, absorb them into the bloodstream, and eliminate waste. It includes key structures like the mouth, stomach, small intestine, and accessory organs such as the liver and pancreas. This system is vital for providing energy, supporting growth, and maintaining overall health, making it a fundamental topic in biology.
On the MCAT, the digestive system frequently appears in the Biology and Biochemistry section through multiple-choice questions that assess anatomy, physiology, and biochemical pathways, such as enzyme actions or nutrient absorption. Common traps include confusing similar processes, like mechanical versus chemical digestion, or misidentifying organ functions, so focus on integrating concepts like hormonal regulation and disorders. A solid grasp of diagrams and feedback loops will help you tackle these questions effectively.
Practice drawing the digestive tract from memory.
Terms (59)
- 01
Digestion
Digestion is the process of breaking down food into smaller molecules that can be absorbed and used by the body, involving both mechanical and chemical actions in the gastrointestinal tract.
- 02
Mechanical digestion
Mechanical digestion refers to the physical breakdown of food into smaller pieces through actions like chewing and churning, which increases the surface area for chemical digestion.
- 03
Chemical digestion
Chemical digestion is the enzymatic breakdown of food molecules into their absorbable components, such as proteins into amino acids, using acids and enzymes in various organs.
- 04
Ingestion
Ingestion is the process of taking food into the body through the mouth, where it begins the digestive journey.
- 05
Mastication
Mastication is the act of chewing food in the mouth, which mechanically breaks it down and mixes it with saliva to form a bolus.
- 06
Saliva
Saliva is a watery fluid secreted by salivary glands that contains enzymes like amylase to begin carbohydrate digestion and lubricates food for swallowing.
- 07
Salivary amylase
Salivary amylase is an enzyme in saliva that breaks down starch into maltose in the mouth, initiating carbohydrate digestion.
- 08
Pharynx
The pharynx is a muscular tube that serves as a passageway for food from the mouth to the esophagus and prevents it from entering the trachea.
- 09
Esophagus
The esophagus is a muscular tube connecting the pharynx to the stomach, using peristaltic waves to propel food downward.
- 10
Peristalsis
Peristalsis is a series of wave-like muscle contractions that move food through the digestive tract, from the esophagus to the intestines.
- 11
Lower esophageal sphincter
The lower esophageal sphincter is a ring of muscle at the junction of the esophagus and stomach that prevents stomach acid from refluxing back up.
- 12
Stomach
The stomach is a J-shaped organ that stores food, mixes it with gastric juices, and begins protein digestion through mechanical churning and chemical action.
- 13
Chyme
Chyme is the semi-liquid mixture of partially digested food and gastric juices that exits the stomach and enters the small intestine.
- 14
Gastric juice
Gastric juice is a mixture of hydrochloric acid, enzymes like pepsin, and mucus secreted by the stomach lining to break down proteins and kill bacteria.
- 15
Pepsin
Pepsin is a stomach enzyme activated from pepsinogen that breaks down proteins into smaller peptides in the acidic environment of the stomach.
- 16
Hydrochloric acid
Hydrochloric acid is secreted by the stomach parietal cells to create an acidic pH that denatures proteins and activates enzymes like pepsin.
- 17
Small intestine
The small intestine is the primary site for nutrient absorption, where most chemical digestion occurs through enzymes from the pancreas and intestinal lining.
- 18
Duodenum
The duodenum is the first section of the small intestine where bile and pancreatic juices mix with chyme to continue digestion of carbohydrates, proteins, and fats.
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Jejunum
The jejunum is the middle section of the small intestine primarily responsible for the absorption of nutrients like sugars, amino acids, and fatty acids.
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Ileum
The ileum is the final section of the small intestine that absorbs bile salts, vitamin B12, and any remaining nutrients before material passes to the large intestine.
- 21
Villi
Villi are finger-like projections in the small intestine lining that increase surface area for nutrient absorption into the bloodstream.
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Microvilli
Microvilli are tiny folds on the surface of intestinal cells that further amplify the absorption area for nutrients in the small intestine.
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Absorption
Absorption is the process by which digested nutrients pass through the intestinal wall into the bloodstream or lymph for distribution to the body.
- 24
Liver
The liver produces bile for fat emulsification, processes absorbed nutrients, and detoxifies substances, playing a key role in digestion and metabolism.
- 25
Bile
Bile is a fluid produced by the liver and stored in the gallbladder that emulsifies fats in the small intestine, aiding in their digestion and absorption.
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Gallbladder
The gallbladder stores and concentrates bile from the liver, releasing it into the small intestine when fats are present to facilitate digestion.
- 27
Pancreas
The pancreas secretes digestive enzymes and bicarbonate into the small intestine to break down carbohydrates, proteins, fats, and neutralize acidic chyme.
- 28
Pancreatic amylase
Pancreatic amylase is an enzyme from the pancreas that breaks down starches into disaccharides in the small intestine.
- 29
Trypsin
Trypsin is a pancreatic enzyme that breaks down proteins into smaller peptides in the small intestine, activated from trypsinogen.
- 30
Lipase
Lipase is an enzyme that breaks down fats into fatty acids and glycerol, primarily in the small intestine with the help of bile.
- 31
Large intestine
The large intestine absorbs water and electrolytes from indigestible material, forming feces and housing beneficial bacteria.
- 32
Colon
The colon is the main part of the large intestine that reabsorbs water and salts, compacting waste into feces.
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Rectum
The rectum is the final straight portion of the large intestine that stores feces until they are expelled during defecation.
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Defecation
Defecation is the expulsion of feces from the body through the anus, controlled by reflex and voluntary muscle actions.
- 35
Gastrin
Gastrin is a hormone secreted by the stomach that stimulates the release of gastric juice and increases gastric motility in response to food.
- 36
Secretin
Secretin is a hormone released by the duodenum in response to acidic chyme, stimulating the pancreas to secrete bicarbonate to neutralize pH.
- 37
Cholecystokinin
Cholecystokinin is a hormone from the small intestine that stimulates the release of bile from the gallbladder and pancreatic enzymes for digestion.
- 38
Enteric nervous system
The enteric nervous system is a network of nerves in the gastrointestinal tract that controls digestive processes independently of the central nervous system.
- 39
Vagus nerve
The vagus nerve provides parasympathetic stimulation to the digestive organs, enhancing secretion and motility during digestion.
- 40
pH in digestion
pH varies in the digestive system, being acidic in the stomach to activate pepsin and alkaline in the small intestine to optimize enzyme function and protect the mucosa.
- 41
Carbohydrate digestion
Carbohydrate digestion begins in the mouth with amylase and continues in the small intestine with enzymes breaking down complex carbs into simple sugars for absorption.
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Protein digestion
Protein digestion starts in the stomach with pepsin and is completed in the small intestine by enzymes like trypsin, resulting in amino acids for absorption.
- 43
Lipid digestion
Lipid digestion occurs mainly in the small intestine, where bile emulsifies fats and lipase breaks them down into fatty acids and monoglycerides.
- 44
Nucleic acid digestion
Nucleic acid digestion in the small intestine breaks down DNA and RNA into nucleotides using enzymes from the pancreas and intestinal juices.
- 45
Water absorption
Water absorption primarily occurs in the large intestine, where it is reabsorbed from the remaining intestinal contents to form solid feces.
- 46
Electrolyte absorption
Electrolyte absorption happens mainly in the small and large intestines, where ions like sodium and chloride are taken up to maintain fluid balance.
- 47
Enzyme specificity
Enzyme specificity means each digestive enzyme acts on particular substrates, such as amylase on starches, ensuring efficient breakdown without unnecessary reactions.
- 48
Feedback mechanisms
Feedback mechanisms in digestion, like hormonal signals, regulate enzyme secretion and motility to match the presence and type of food ingested.
- 49
Gut microbiota role
Gut microbiota aid digestion by fermenting undigested carbohydrates, producing vitamins, and competing with harmful bacteria in the large intestine.
- 50
Emulsification
Emulsification is the process where bile breaks large fat globules into smaller droplets in the small intestine, increasing the surface area for lipase action.
- 51
Denaturation
Denaturation is the unfolding of proteins by stomach acid, making them more accessible to digestive enzymes like pepsin.
- 52
pH optima for enzymes
Each digestive enzyme has an optimal pH for activity, such as pepsin at low pH in the stomach and pancreatic enzymes at neutral pH in the intestine.
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Common trap: Small vs. large intestine
A common error is confusing the small intestine's role in nutrient absorption with the large intestine's focus on water reabsorption and waste compaction.
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Peristaltic regulation
Peristaltic regulation involves neural and hormonal controls that adjust the speed and strength of contractions based on the digestive tract's contents.
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Bicarbonate secretion
Bicarbonate secretion by the pancreas neutralizes acidic chyme entering the small intestine, protecting the intestinal lining and enabling enzyme function.
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Micelle formation
Micelle formation in the small intestine involves bile salts surrounding digested fats, facilitating their absorption into intestinal cells.
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Lacteal absorption
Lacteal absorption refers to the uptake of fats and fat-soluble vitamins into the lymphatic system via the lacteals in the small intestine villi.
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Gastric inhibitory peptide
Gastric inhibitory peptide is a hormone that slows gastric emptying and stimulates insulin release in response to glucose in the intestine.
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Appendix function
The appendix, though not essential for digestion, contains lymphoid tissue that supports immune function and may aid in gut microbiota recovery.