Small Intestines and Large Intestines
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Need help preparing for the Biology section of the MCAT? MedSchoolCoach expert, Ken Tao, will teach everything you need to know about Small Intestines and Large Intestines of the Digestive System. Watch this video to get all the MCAT study tips you need to do well on this section of the exam!
The human digestive system can be broken down into several segments. Two of the primary segments are the small intestine and the large intestine. Both are involved in digestion, and each plays a crucial role in nutrient absorption and the functioning of waste disposal.
Small Intestine
The small intestine can be broken down into three segments – the duodenum, the jejunum, and the ileum. The duodenum connects directly to the stomach, and the ileum is connected to the large intestine. All three segments are involved in digestion and absorption of nutrients. On the surface area of the small intestines, the small intestine can absorb large amounts of nutrients. The intestinal epithelium is folded, and the folds contain villi, which are protrusions of the epithelium. Within the villi, the individual epithelial cells contain microvilli. The purpose of the villi and microvilli is to massively increase the surface area of the small intestine in order to increase the rate of nutrient absorption.
When the pyloric sphincter relaxes, chyme is released into the duodenum. The presence of chyme in the duodenum causes the duodenum to secrete the hormones cholecystokinin, also called CCK, as well as secretin. CCK acts on the gallbladder to secrete bile, which has a vital role in emulsifying fats. Bile is a salt and is an amphipathic molecule, meaning that it has both hydrophilic and lipophilic properties. In this way, bile will aggregate towards large fat globules and can break them down into smaller fat globules, which significantly increases the rate at which fats can be broken down by the body. In the absence of bile, the body is unable to digest fat, and they are excreted in the feces. This condition is known as steatorrhea, and it can lead to fatty acid and vitamin deficiencies.
Another function of CCK is to stimulate the pancreas to release digestive enzymes. For each of the four biological macromolecules – carbohydrates, nucleic acids, proteins, and fats – there are specific digestive enzymes that break them down. Amylase breaks down carbohydrates, nuclease breaks down nucleic acids, protease breaks down proteins, and lipase breaks down fats.
Secretin, another compound released by the duodenum, stimulates the pancreas to secrete bicarbonate, which aids in digestion. Many digestive enzymes require a higher pH in order to function optimally. The chyme from the stomach, which enters into the small intestine, is at a low pH. Bicarbonate helps to increase the pH of the stomach contents in the small intestine to aid digestive enzymes. The duodenum also secretes enterokinase. Enterokinase converts trypsinogen into trypsin. Trypsinogen is one of the digestive enzymes released by the pancreas. Many of these digestive enzymes are released as zymogens or in an inactive form. Enterokinase converts trypsinogen into its active form, trypsin. Trypsin will then aid in converting other digestive enzymes into their active forms.
Large Intestine
The primary role of the large intestine is to absorb water. People with diseases that cause excess loss of fluid through the gastrointestinal tract, such as diarrhea, generally have a problem with their large intestines. Also, the large intestine stores fat for defecation and also contains healthy flora beneficial for humans. Normal flora are the gut bacteria in all human GI tracts. These bacteria are good for human health and have formed a symbiotic relationship with humans. They can produce vitamin K as well as other essential nutrients for the body. At the very end of the large intestine is the anus. The anus has both an internal and external sphincter. This anatomy is similar to the urinary sphincters in the excretory system. The internal anal sphincter is made of smooth muscle and is involuntary, and the external anal sphincter is made of skeletal muscle and is voluntary. In this way, humans do have control over defecation. A common problem in the anal region is hemorrhoids. A hemorrhoid is an inflamed vascular structure in either the external or internal anal canal. If internal, they are usually painless, and if external, they are mostly painful. Hemorrhoids are treated by increasing dietary fiber to aid digestion, medication, or surgery.
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The human digestive system can be broken down into several segments. Two of the primary segments are the small intestine and the large intestine. Both are involved in digestion, and each plays a crucial role in nutrient absorption and the functioning of waste disposal.
Small Intestine
The small intestine can be broken down into three segments – the duodenum, the jejunum, and the ileum. The duodenum connects directly to the stomach, and the ileum is connected to the large intestine. All three segments are involved in digestion and absorption of nutrients. On the surface area of the small intestines, the small intestine can absorb large amounts of nutrients. The intestinal epithelium is folded, and the folds contain villi, which are protrusions of the epithelium. Within the villi, the individual epithelial cells contain microvilli. The purpose of the villi and microvilli is to massively increase the surface area of the small intestine in order to increase the rate of nutrient absorption.
When the pyloric sphincter relaxes, chyme is released into the duodenum. The presence of chyme in the duodenum causes the duodenum to secrete the hormones cholecystokinin, also called CCK, as well as secretin. CCK acts on the gallbladder to secrete bile, which has a vital role in emulsifying fats. Bile is a salt and is an amphipathic molecule, meaning that it has both hydrophilic and lipophilic properties. In this way, bile will aggregate towards large fat globules and can break them down into smaller fat globules, which significantly increases the rate at which fats can be broken down by the body. In the absence of bile, the body is unable to digest fat, and they are excreted in the feces. This condition is known as steatorrhea, and it can lead to fatty acid and vitamin deficiencies.
Another function of CCK is to stimulate the pancreas to release digestive enzymes. For each of the four biological macromolecules – carbohydrates, nucleic acids, proteins, and fats – there are specific digestive enzymes that break them down. Amylase breaks down carbohydrates, nuclease breaks down nucleic acids, protease breaks down proteins, and lipase breaks down fats.
Secretin, another compound released by the duodenum, stimulates the pancreas to secrete bicarbonate, which aids in digestion. Many digestive enzymes require a higher pH in order to function optimally. The chyme from the stomach, which enters into the small intestine, is at a low pH. Bicarbonate helps to increase the pH of the stomach contents in the small intestine to aid digestive enzymes. The duodenum also secretes enterokinase. Enterokinase converts trypsinogen into trypsin. Trypsinogen is one of the digestive enzymes released by the pancreas. Many of these digestive enzymes are released as zymogens or in an inactive form. Enterokinase converts trypsinogen into its active form, trypsin. Trypsin will then aid in converting other digestive enzymes into their active forms.
Large Intestine
The primary role of the large intestine is to absorb water. People with diseases that cause excess loss of fluid through the gastrointestinal tract, such as diarrhea, generally have a problem with their large intestines. Also, the large intestine stores fat for defecation and also contains healthy flora beneficial for humans. Normal flora are the gut bacteria in all human GI tracts. These bacteria are good for human health and have formed a symbiotic relationship with humans. They can produce vitamin K as well as other essential nutrients for the body. At the very end of the large intestine is the anus. The anus has both an internal and external sphincter. This anatomy is similar to the urinary sphincters in the excretory system. The internal anal sphincter is made of smooth muscle and is involuntary, and the external anal sphincter is made of skeletal muscle and is voluntary. In this way, humans do have control over defecation. A common problem in the anal region is hemorrhoids. A hemorrhoid is an inflamed vascular structure in either the external or internal anal canal. If internal, they are usually painless, and if external, they are mostly painful. Hemorrhoids are treated by increasing dietary fiber to aid digestion, medication, or surgery.
MEDSCHOOLCOACH
To watch more MCAT video tutorials like this and have access to study scheduling, progress tracking, flashcard and question bank, download MCAT Prep by MedSchoolCoach
IOS Link: https://play.google.com/store/apps/de...
Apple Link: https://apps.apple.com/us/app/mcat-pr...
#medschoolcoach #MCATprep #MCATstudytools
4 سال پیش
در تاریخ 1399/06/20 منتشر شده
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