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MCAT Biology Review 2025-26 > Chapter 9: The Digestive Sytem > Flashcards

Chapter 9: The Digestive Sytem Flashcards

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1
Q

Two types of digestion

A

Intracellular and extracellular digestion

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2
Q

Intracellular digestion

A

Intracellular digestion is part of metabolism, involves oxidation of glucose and fatty acids for energy.

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3
Q

Extracellular digestion

A

Extracellular digestion is the process by which nutrients are obtained from food and occurs within the lumen of the alimentary canal. Technically “outside” the body because the lumen interacts and communicates with the outside world.

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4
Q

Alimentary canal

A

The alimentary canal, aka the digestive tract, is the passageway of the digestive system that runs from the oral canal (mouth) to the anus (aka butthole aka Sean Colebrook)

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5
Q

Sphincters

A

Circular smooth muscle around the canal that can contract and compartmentalize the alimentary canal.

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6
Q

Digestion

A

Digestion involves the breakdown of food into its constituent organic molecules: starches and carbohydrates into monosaccharides, lipids (fats) into free fatty acids and glycerol, and proteins into amino acids.

The two kinds of digestion are mechanical and chemical.

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7
Q

Two kinds of digestion

A

Mechanical and chemical

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8
Q

Mechanical digestion

A

Mechanical digestion is the physical breakdown of large food particles into smaller particles. Does not involve breaking of chemical bonds.

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9
Q

Chemical digestion

A

Chemical digestion is the enzymatic cleavage of chemical bonds such as peptide bonds of proteins or glucosidic binds of starches.

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10
Q

Absorption

A

Absorption 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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11
Q

Path of the digestive tract

A

Oral cavity (mouth), pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus (aka Sean Colebrook).

In addition to the digestive tract itself, the salivary glands, pancreas, liver, and gallbladder help to provide the enzymes and lubrication necessary to aid in digestion.

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12
Q

Enteric nervous system

A

Enteric means of or relating to the intestines. The enteric nervous system is a collection of 100M neurons that govern the gastrointestinal system. This system can function independently of the central nervous system (however is considered part of the autonomic nervous system) but is highly regulated by the autonomic nervous system.

Parasympathetic nervous system stimulated digestion and increases secretion from exocrine glands and promotes peristalsis.

Sympathetic nervous system inhibits digestive activity.

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13
Q

What are all glands of the body innervated by (except the sweat glands)?

A

All glands of the body (except for the sweat glands) are innervated by the parasympathetic nervous system.

The sweat glands are innervated by the sympathetic nervous system.

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14
Q

Anatomy of the digestive system notes 9.1

A
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15
Q

Ingestion and Digestion 9.2 Notes

A
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16
Q

Ingestion and Digestion 9.2 Notes

A
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17
Q

Six hormones listed in the book involved in feeding behavior

A

ANTIDIURETIC HORMONE (ADH or vasopressin) secreted by the hypothalamus to the posterior pituitary, and ALDOSTERONE (renin-angiotensin II-aldosterone system, secreted by the adrenal cortex), trigger the sensation of thirst encourage fluid consumption.

GLUCAGON (secreted by the pancreas alpha cells) and GHRELIN (secreted by the stomach and pancreas) stimulate feelings of hunger.

LEPTIN (secreted by adipose tissue) and CHOLECYSTOKININ (secreted by the duodenum) stimulate feelings of satiety.

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18
Q

Three pairs of salivary glands

A

Parotid gland (just below and in front of ear)

Submandibular gland (below jaw)

Sublingual gland (floor of mouth below the tongue)

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19
Q

Two enzymes found in saliva

A

Salivary amylase (hydrolyzes starch into smaller sugars like maltose and dextrins)

Lipase (hydrolyzes lipids)

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20
Q

Pharynx

A

The pharynx leads from the mouth and posterior nasal cavity to the esophagus and larynx.

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21
Q

Three parts of the pharynx

A

Oropharynx (back of mouth) responsible for initiating swallowing, constitute the upper esophageal sphincter.

Nasopharynx (behind nasal cavity)

Laryngopharynx (above vocal cords)

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22
Q

Epiglottis

A

The epiglottis is a cartilaginous structure that folds down to cover the laryngal inlet Preventing food from entering the larynx during swallowing.

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23
Q

Esophagus and its muscle composition

A

The esophagus is a muscular tube that connects the pharynx to the stomach. The connection between the esophagus and the stomach is called the cardiac sphincter.

The top of the esophagus is composed of skeletal muscle, and therefore under somatic control.

The middle is a mix of both smooth and skeletal muscle.

The bottom is composed of smooth muscle, and therefore is completely under autonomic (involuntary) nervous control.

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24
Q

Emesis

A

Emesis is also known as vomiting. Reversal of peristalsis.

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25
Q

Upper esophageal sphincter

A

The upper esophagus sphincter is constituted by the muscles of the oropharynx aka the pharyngoesophageal sphincter.

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26
Q

Three main energy sources

A

Carbohydrates, fats, proteins

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27
Q

The stomach and its four main anatomical divisions

A

The stomach is a highly muscular organ, located in the upper left quadrant of the abdominal cavity underneath the diaphragm, That uses hydrochloric acid and enzymes to digest food.

The four main anatomical divisions of the stomach are the fundus and body, and the antrum and pylorus.

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28
Q

General anatomy of the stomach image

A
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29
Q

Rugae of the stomach

A

Rugae or folds of the lining of the stomach.

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30
Q

Gastric glands, three types, purpose, location

A

Cardiac glands: beginning of stomach, secrete mucus to protect stomach lining from self digestion. Stomach is highly acidic pH=2.

Intermediate glands: located in the central stomach, these glands produce most of the stomach’s digestive substances (HCl, mucus, pepsin) They contain three types of cells: zymogenic, parietal, and mucous neck cells.

Pyloric glands: located in the terminal portion of the stomach, these glands secrete gastrin.

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31
Q

What are the gastric glands?

A

The gastric glands respond to signals from the VAGUS NERVE of the parasympathetic nervous system, which is activated by the brain in response to site, taste, and smell of food.

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32
Q

What are the three different cell types of gastric glands?

A

The three different cell types of gastric glands are mucous cells, chief cells, and parietal cells.

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33
Q

What do the mucous cells of gastric glands do?

A

The mucous cells of gastric glands produce bicarbonate rich mucous that protects the muscular wall from the harshly acidic (pH=2) and proteolytic environment of the stomach.

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34
Q

What do the parietal cells of gastric glands do (two products)?

A

The parietal cells of gastric glands secrete hydrogen ions into the stomach as hydrochloric acid which cleaves PEPSINOGEN to PEPSIN. This is a fine example of environmental conditions favoring enzymatic reactions.

The parietal cells also secrete INTRINSIC FACTORS, a glycoprotein involved with proper absorption of vitamin B12.

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35
Q

What do chief cells of gastric glands do?

A

The chief sells secrete pepsinogen. Pepsinogen is a zymogen form of pepsin, a proteolytic enzyme.

The mighty chief pepsinogen. lol

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36
Q

Pepsin and its zymogen, and where does it come from?

A

Pepsin is a proteolytic enzyme that digest protein by cleaving peptide bonds near aromatic amino acids, resulting in short peptide fragments. Pepsin is activated by the acidic environment of the stomach meaning that it is most active at low pH.

Pepsinogen is zymogen of Pepcid. pepsinogen is released by the chief cells of intermediate gastric glands.

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37
Q

What is the the gastric intrinsic factor?

A

The gastric intrinsic factor is a glycol protein involved in the proper absorption of B12. The gastric intrinsic factor it’s released by PARIETAL CELLS.

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38
Q

What do the pyloric glands do and contain, and where are they located?

A

The pyloric glands contain G – cells (in the stomach lining) that secrete gastrin, a peptide hormone. Pyloric glands are located in the pyloric region of the stomach.

Gastrin is a hormone secreted by the pyloric glands that stimulates the secretion of HCl from parietal cells, essentially preparing the stomach for digestion.

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39
Q

What is gastrin, where does it come from, and what does it do?

A

Gastrin is a peptide hormone secreted by G – cells of the pyloric glands that induces the stomach to secrete more hydrochloric acid and signals the stomach to contract, mixing its contents.

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40
Q

What is chyme?

A

Chyme is a semi fluid mixture and is the result of solid food in the stomach mixing with acids.

41
Q

Given that the stomach is mainly an organ of digestion, few substances absorbed directly from the stomach, what are two examples?

A

Two examples of substances that absorb directly from the stomach or aspirin and alcohol.

42
Q

What are the six products secreted by the stomach?

A

The six product secreted by the stomach are:

Hydrochloric acid (kills microbes, denatures, proteins, and converts pepsinogen into pepsin)

Pepsinogen (cleaved in the stomach to pepsin; an enzyme that partially digest proteins)

Mucus (protects mucosa)

Bicarbonate (protects mucosa)

Water (dissolves and dilutes ingested material)

Intrinsic factor (required for normal absorption of vitamin B 12)

43
Q

What are the three segments of the small intestine?

A

The three segments of the small intestine are the duodenum, the jejunum, and the ilium.

44
Q

Where does the majority of chemical digestion occur in the small intestine?

A

The majority of chemical digestion occurs in the duodenum.

45
Q

Where is the majority of absorption occur in the small intestine?

A

The majority of absorption in the small intestine takes place in the jejunum and the ilium.

46
Q

What are brush border enzymes, what causes their release, and where do they come from?

A

Brush border enzymes break down nutrients into absorbable units. They can breakdown dimers and trimers of biomolecules into absorbable monomers: examples include disaccharidases (maltase, isomaltase, lactase, and sucrase) and peptidases (dipeptidases). They can break down proteins (oligopeptidases) and fats (lipases) in conjunction with bile salts.

Brush border enzymes are released by the presence of chyme in the duodenum.

47
Q

What is the pyloric sphincter?

A

The pyloric sphincter is located at the bottom of the stomach and is the entryway to the duodenum.

48
Q

What are the four disaccharidases secreted from the duodenum called and what are they (four)?

A

The enzymes released in the duodenum are known as brush border enzymes. The four types of disaccharidases are:

Maltase: digests maltose
Isomaltase: digests isomaltose
Lactase: digests lactose
Sucrase: digests sucrose solution

49
Q

What are two peptidases located in the duodenum and what do they do?

A

The two peptidases located in the duodenum are:

Aminopeptidase: Secreted by glands in the duodenum that removes the N – terminal amino acid from a peptide.

Dipeptidase: cleave the peptide bond of dipeptides to release free amino acids

50
Q

What is enteropeptidase and where is it found?

A

Enteropeptidase is an enzyme critical for the activation of trypsinogen, a pancreatic protease, to trypsin.

Enteropeptidase can also activate procarboxypeptidases A and B to the active forms.

Enteropeptidase is found in the small intestine, specifically on the brush border of the duodenal epithelial cells. ENTEROPEPTIDASE is a BRUSH BORDER ENZYME

51
Q

Trypsin

A

Trypsin is a pancreatic protease, trysinogen is activated by enteropeptidase and turns into trypsin. Trypsin is an enzyme that digests protein by breaking down long chains of amino acids into smaller pieces.

Zymogen is tripsinogen. Tripsinogen is produced in the acinar cells of the pancreas, released into the pancreatic duct, through the minor and major pancreatic papillae, into the duodenum where it is activated by ENTEROKINASE.

52
Q

What is secretin and where is it located?

A

Secretin is a peptide hormone secreted by the duodenum that causes pancreatic enzymes to be released into the duodenum. Secretin also regulates the pH of the digestive tract by reducing hydrochloric secretion from parietal cells and increasing bicarbonate secretion from the pancreas.

S-CELLS secrete SECRETIN in the DUODENUM

53
Q

What is an enterogastrone?

A

An enterogastrone, like secretin, is a peptide hormone that slows motility through the digestive tract effectively increasing time for digestive enzymes to act on chyme, especially fats.

Enterogastrone is produced in the duodenum.

CHOLECYSTOKININ is an enterogastrone.

54
Q

What is Cholecystokinin (CCK), where is it located, what activates it?

A

Cholecystokinin is a hormone that helps digest fat and protein in the small intestine and also plays a role in regulating food intake.

Cholecystokinin causes the gallbladder and pancreas to contract, which releases bile and pancreatic juice (mixture of several enzymes) to break down food.

Cholecystokinin acts in the brain to promote satiety. This makes sense because cholecystokinin is secreted in response to chyme, specifically fats and amino acids.

Cholecystokinin is released by the presence of fats and proteins in the duodenum.

CHOLECYSTOKININ is an enterogastrone.

55
Q

What is bile?

A

Bile is a complex fluid, composed of BILE SALTS, pigments, and cholesterol. Bile is an emulsifier of fats, similar to soap.

56
Q

What are bile salts and where can you find them?

A

Bile salts are derived from cholesterol. Bile salts are much like soap and detergent in that they contain a polar end and a nonpolar end and therefore emulsify fats and cholesterol into micelles.

The micelles created with bile salts and fats increases their surface area giving more opportunity for lipase to come along and chemically digest the fats. The micelles are also water soluble, fats would spontaneously separate out of solution if it weren’t for the micelles.

You can find cholecystokinin, chyme, pancreatic juice, bile, and therefor bile salts in the duodenum. Remember that cholecystokinin stimulates the release of bile and pancreatic juices.

Bile is made in the liver (from cholesterol) and stored in the gall bladder for release into the small intestine. Cholecystokinin stimulates the gall bladder to release bile.

57
Q

What is Celiac disease? Is it an allergic reaction?

A

Celiac disease is an autoimmune condition and not a true allergy. Celiac disease results from an immune reaction against gluten. The immune system will develop antibodies against gluten that will cross react with elements of the small intestine causing damage to the mucosa. Diarrhea and discomfort follows.

58
Q

What are pancreatic juices, what stimulates their secretion, and where is it found?

A

Pancreatic juices are a complex mixture of several enzymes in a bicarbonate rich alkaline solution that are secreted directly into the duodenum. Cholecystokinins promote the secretion of pancreatic juices into the duodenum.

59
Q

At what pH are pancreatic juices most active around? How does the pH increase from the stomach to the duodenum?

A

The pH for best activity of enzymes found in pancreatic juices is around 8.5, the general pH of the duodenum is around six. The increase in pH from the stomach to duodenum is mainly due to the pancreatic juices being bicarbonate rich and therefor alkaline.

SECRETIN also regulates the pH of the digestive tract by reducing HCl secretion from PARIETAL cells and increasing bicarbonate secretion from the pancreas.

60
Q

Explain the hormonal control of the exocrine pancreas (hint: two hormones and what they do)

A

Cholecystokinins are a peptide hormone that secrete in response to the presence of AA and fat in the duodenum, with parasympathetic stimulation, CCK will secrete into the pancreas and promote the secretion of bile and pancreatic juices (which are a complex mixture of several enzymes) that operate well in a more alkaline environment.

Secretin is a peptide hormone that causes pancreatic enzymes to be released into the duodenum, as well as inhibiting HCl secretions from parietal cells and increasing bicarbonate secretion from the pancreas.

61
Q

What are the accessory organs of digestion?

A

The accessory organs of digestion are the liver, pancreas, and gallbladder.

These organs originate as outgrowth of ENDODERM from the gut tube during development, remember reproduction and maturation of an embryo)

62
Q

What is the pancreas, what two rolls does it play in the body, and where is it located?

A

The pancreas is an accessory organ of digestion. The two roles/functions of the pancreas are exocrine and endocrine.

The endocrine function include the release of insulin, glucagon, and somatostatin from the islets of Langerhans scattered throughout the organ.

The exocrine function is made of ACINAR cells that produce pancreatic juices critical for digestion.

63
Q

What are acinar cells, what do they do, where are they found?

A

Acinar cells are the exocrine cells of the pancreas. They produce and secrete pancreatic juices which are bicarbonate rich alkaline secretion containing many digestive enzymes that work on all three classes of biomolecules.

Remember: all exocrine secrete their products into ducts, including acinar cells.

64
Q

What is pancreatic amylase?

A

Pancreatic amylase breaks down large polysaccharides into smaller constituents and is therefor responsible for carbohydrate digestion.

65
Q

What are pancreatic peptidases, name four kinds, and what are they activated by?

A

Pancreatic peptidases, activated by enteropeptidase, are responsible for protein digestion.

Three examples are trypsinogen, chymotrypsinogen, and carboxypeptidase A and B, and pancreatic lipase.

66
Q

How do pancreatic juices make it into the duodenum?

A

Pancreatic juices make their way into the pancreatic duct once they are secreted by acinar cells then into the duodenum through the major and minor duodenal papillae.

Papilla is small rounded protuberance on a part or organ of the body.

67
Q

What is the difference between exocrine and endocrine glands?

A

The difference between exocrine and endocrine glands is how they release their secretions. Endocrine glands secrete directly into the bloodstream where they are carried to target tissues (pituitary, thyroid, adrenal). Exocrine glands secrete into ducts which carry them into body surfaces or body cavities (mammary glands, acinar glands, salivary glands).

Interesting, the pancreas and the liver have both endocrine and exocrine functions.

68
Q

What are the functions of the liver and where is it located?

A

The liver is located in the upper right quadrant of the abdomen. The functions of the liver include:

Processing and synthesizing of nutrients (glycogenesis, glycogenolysis, storage and mobilization of fats, gluconeogenesis)

Processing of ammonia into urea for excretion

Detoxification of chemicals

Production of bile

Synthesis of albumin and clotting factors

Production of about 80% of cholesterol in body

69
Q

What is gluconeogenesis?

A

Gluconeogenesis is the production of glucose from non-carbohydrate sources, such as fats, lactate, amino acids, and pyruvate.

70
Q

What is a glycogenolysis?

A

Glycogenolysis is the process of breaking down glycogen into glucose.

71
Q

What is glycogenesis?

A

Glycogenesis is the process of converting glucose into glycogen, a molecule stored in the liver and muscles for energy.

72
Q

What are the bile ducts?

A

The bile ducts connect the liver with both the gallbladder and the small intestine.

73
Q

What is the hepatic portal vein?

A

The hepatic portal vein is where the liver receives all blood draining from the abdominal portion of the digestive tract. It is through the hepatic portal vein that nutrient rich blood can be processed by the liver before draining into the inferior vena cava. This describes in superficial detail the haptic portal system.

74
Q

What is biliruben and why is it important to know what biliruben is?

A

Biliruben is a byproduct of the breakdown of hemoglobin and is the major pigment of bile. Biliruben travels to the liver where it is conjugated (attached to a protein) and secreted as bile for excretion. Jaundice occurs when the liver is unable to process or excrete biliruben. Jaundice is indicative of liver damage, excess red blood cell destruction, or blockage of bile ducts.

75
Q

What are the major components of bile?

A

The major components of bile are:

Bile salts (emulsify fats)
Pigments (biliruben from breakdown of hemoglobin)
Cholesterol

76
Q

What is cirrhosis of the liver, and what are some processes that cause cirrhosis of the liver?

A

Cirrhosis is scarring of the liver that creates increased resistance within the hepatic portal vein, resulting in portal hypertension. This causes a back up of fluid within the portal system, resulting in swollen veins in the digestive system (especially the esophagus) which may rupture and cause life-threatening bleeding. This often manifest as hematoemesis (vomitting blood).

Cirrhosis also causes bleeding disorders because production of clotting factors is disrupted. It causes buildup of ammonia and also may cause hepatocellular carcinoma.

Causes of cirrhosis of the liver include chronic alcohol consumption, hepatitis C infection, auto immune hepatitis, and fatty liver disease.

77
Q

What is the gallbladder, where is it located, and what stimulates it?

A

The gallbladder is located between the liver and both stores and concentrates bile. Cholecystokinins trigger the gallbladder to contract and push bile out into the BILIARY TREE. The biliary tree which merges with the pancreatic duct before entering the duodenum.

78
Q

Explain stone formation in the gallbladder.

A

Cholesterol and bilirubin can form stones in the gallbladder causing painful inflammation. The stones can travel into the bile ducts and get stuck in the biliary tree. In some cases stones can get caught just before entering the duodenum (minor or major duodenal papillae), blocking the pancreatic duct causing pancreatitis.

79
Q

What is Salivary amylase, where is it produced, where does it function?

A

Produced in salivary glands, functions in mouth, hydrolyzes strarches.

80
Q

What is pancreatic amylase, where is it produced, where is its function?

A

Produced in pancreas, functions in the duodenum, hydrolyzes starch into maltose and dextrose.

81
Q

What is pepsin(ogen), where is it produced, where is its function?

A

Produce in gastric glands (chief cells), functions in the stomach, hydrolyzes specific peptide bonds, activated by HCl

82
Q

What is tripsin(ogen), where is it produced, where is its function?

A

Produced in acinar cells of pancreas, functions in the duodenum, hydrolyzes specific peptide bonds, activated by enteropeptidase.

83
Q

What is chymotripsin(ogen), where is it produced, where is its function?

A

Produced in acinar cell in the pancreas, functions in the duodenum, hydrolyzes specific peptide bonds, activated by trypsin.

84
Q

What is (pro)carboxypeptidase A and b, where is it produced, where is its function?

A

Produced in acinar cells of the pancreas, functions in the duodenum, hydrolyzes terminal peptide binds on carboxy end, activated by enteropeptidase.

85
Q

What is aminopeptidase, where is it produced, where is its function?

A

Produced in intestinal glands, functions in the duodenum, hydrolyzes terminal peptide bonds at amino ends.

Aminopeptidase is a brush border enzyme.

86
Q

What are dipeptidases, where is it produced, where is its function?

A

Produced in the intestinal glands, functions in the duodenum, hydrolyzes pairs of AA.

87
Q

What is enteropeptidase, where is it produced, where is its function?

A

Produced in intestinal glands, functions in the duodenum, main switch for activating many hydrolytic enzymes in the duodenum, converts trypsinogen to trypsin, and procarboxypeptidase A and B to carboxypeptidase A and B.

88
Q

What is enteropeptidase, where is it produced, where is its function?

A

Enteropeptidase is a brush border enzyme produced in intestinal glands, functions in the duodenum, main switch for activating many hydrolytic enzymes in the duodenum, converts trypsinogen to trypsin, and procarboxypeptidase A and B to carboxypeptidase A and B.

89
Q

What is bile, where is it produced, where is its function?

A

Produced in the liver, stored in the gallbladder, functions in the duodenum, emulsifies fats, made up of bile salts, pigments (bilirubin), and cholesterol. Bile is not an enzyme and therefor is involved in mechanical digestion of fats, specifically by producing micelles with fats.

90
Q

What is lipase, where is it produced, where is its function?

A

Produced in acinar cells of pancreas, functions in the duodenum, hydrolyzes lipids.

91
Q

Summary of the digestion of each major class of biomolecules. You could draw this.

A
92
Q

On the three sections of the small intestine, and what are their purposes?

A

The three sections of the small intestine are the duodenum, the jejunum, and the ilium.

The duodenum is primarily involved in digestion.

The jejunum and ilium Or involves in the absorption of nutrients.

93
Q

What are the two circulatory vessels in the villus, and what biomolecules are absorbed into each?

A

The two circulatory vessels in the villus are capillaries and lacteals.

The capillaries absorb water soluble nutrients, such as monosaccharides, amino acids, short chain fatty acids, water soluble vitamins, and water.

The lacteals absorb fat soluble nutrients like fats, cholesterol, and fat soluble vitamins via chylomicrons.

94
Q

What are the fat soluble vitamins?

A

The fat soluble vitamins are A, D, E, K.

95
Q

Once carbohydrates, amino acids, and short chain fatty acids diffuse from epithelial cells into the capillaries, where do they go and how did they get there?

A

Absorbed molecules go to the liver via the hepatic portal circulation.

96
Q

Once larger fats, glycerol, cholesterol, and fat soluble vitamin are packaged into chylomicrons, where do they go? How do they get there?

A

Chylomicrons enter the lymphatic system via lacteals and enter the venous circulation through the sub clavian vein via the thoracic duct in the base of the neck, ending up at the liver.

97
Q

What are the sections of the large intestine?

A

The sections of the colon are the cecum, the colon, the sigmoidal colon, and the rectum.

98
Q

What is the name for the valve located between the ilium and the cecum?

A

Iliocecal valve. Love that self descriptive stuff right there lol

99
Q

Where is the appendix, and what is it suggested to do?

A

The appendix is located on the cecum of the large intestine and once was thought to be vestigial. It is suggested that the appendix may help fight certain bacterial infections, and may also have a role in repopulating the large intestine with normal flora after episodes of diarrhea.

MCAT Biology Review 2025-26 (16 decks)

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