Module 7.9 Small Intestine

Question 1

The small intestine is composed of three sections:

1. the _____\_,
2. _____\_ and
3. _____\_,

which connect the stomach to the _____\_

Answer 1

The small intestine is composed of three sections:

1. the duodenum,
2. jejunum and
3. ileum,

which connect the stomach to the l_arge intestine_

Question 2

• The entrance to the small intestine is sealed by the ________ ________
• the exit from the small intestine is sealed by the ________ ________ and ________

Answer 2

• The entrance to the small intestine is sealed by the pyloric sphincter
• the exit from the small intestine is sealed by the ileocecal sphincter and valve

Question 3

The small intestine is involved in all four digestive system processes:

1. ______\_,
2. ______\_,
3. ______\_ and
4. ______\_

and is the primary site of ______\_and ______\_ in the digestive system

Answer 3

The small intestine is involved in all four digestive system processes:

1. motility,
2. secretion,
3. digestion and
4. absorption

and is the primary site of nutrient digestion and absorption in the digestive system

Question 4

Motility in the small intestine occurs through

• the processes of _______\_
• the ___________\_

Answer 4

Motility in the small intestine occurs through

• the processes of segmentation
• the migrating motility complex

Question 5

Segmentation involves _______ _____ of _________ muscle initiated by the ________cells of the ______\_

Answer 5

Segmentation involves _alternating contraction_s of circular muscle initiated by the pacemaker cells of the small intestine

Question 6

The frequency of the basic electric rhythm (BER) from the duodenum to the ileum, which allows for both and of the chyme to occur through the small intestine

Answer 6

The frequency of the basic electric rhythm (BER) decreases from the duodenum to the ileum, which allows for both mixing and propulsion of the chyme to occur through the small intestine

Question 7

Segmentation is regulated by? (3)

Answer 7

Segmentation is regulated by:

• distension of the duodenum
• the hormone gastrin
• autonomic system innervation

Question 8

Image: Segmentation in the intestine:

Neighbouring segments of intestine alternatively and in response to waves of resulting in the back and forth mixing of .

Answer 8

Image: Segmentation in the intestine:

Neighbouring segments of intestine alternatively contract and relax in response to waves of contraction resulting in the back and forth mixing of chyme.

Question 9

The migrating motility complex is a series of ___________ that move from the ____\_to the _____\_ in between meals

Answer 9

The migrating motility complex is a series of short-distance peristaltic waves that move from the duodenum to the ileum in between meals

Question 10

What is the function of the migrating motility complex?

Answer 10

The function of the migrating motility complex is to move any remaining chyme left behind during segmentation toward the large intestine

Question 11

What hormone regulates the migrating motility complex?

Answer 11

Regulation of the migrating motility complex occurs through the hormone motilin

Question 12

Motilin, the hormone that regulates the migrating motility complex. is secreted by the ______ cells of the small intestine in the absence of _____

Answer 12

Motilin, the hormone that regulates the migrating motility complex. is secreted by the endocrine cells of the small intestine in the absence of chyme

Question 13

What is the function of the ileocecal sphincter and valve? serve to regulate the emptying of the small intestine contents into the large intestine and to prevent bacterial contamination of the small intestine from the large intestine.

Answer 13

To regulate the emptying of the small intestine contents into the large intestine and to prevent bacterial contamination of the small intestine from the large intestine

Question 14

Relaxation of the ileocecal sphincter is regulated by _____\_and by ____\_ of the ____\_, which triggers a short reflex pathway.

Answer 14

Relaxation of the ileocecal sphincter is regulated by gastrin and by distension of the ileum, which triggers a short reflex pathway.

Question 15

The secretion produced by the small intestine is known as ________\_

Answer 15

The secretion produced by the small intestine is known as succus entericus

Question 16

What is succus entericus and what is its function?

Answer 16

• An aqueous salt and mucous secretion
• succus entericus functions to provide protection and lubrication for the small intestine

Question 17

Succus entericus is secreted proximally in the ______\_and is absorbed distally in the _____\_

Answer 17

Succus entericus is secreted proximally in the duodenum and is absorbed distally in the ileum

Question 18

The duodenum is also the site of entry for the secretions produced by the ____\_and ____\_.

Answer 18

The duodenum is also the site of entry for the secretions produced by the pancreas and liver.

Question 19

The apical surface of small-intestine epithelial cells contains plasma membrane enzymes, which are referred to as ____________\_.

Answer 19

The apical surface of small-intestine epithelial cells contains plasma membrane enzymes, which are referred to as brush-border enzymes.

Question 20

The brush border enzymes include

• _______
• _______
• _______

Answer 20

The brush border enzymes include

• enterokinase (which activates pancreatic trypsinogen),
• disaccharidases (which are involved in the digestion of disaccharides),
• aminopeptidases (which are involved in the digestion of peptides)

Question 21

What is the function of the brush border enzyme:

• enterokinase

Answer 21

activates pancreatic trypsinogen

Question 22

What is the function of the brush border enzyme

disaccharidases

Answer 22

involved in the digestion of disaccharides

Question 23

What is the function of the brush border enzymes

aminopeptidases

Answer 23

involved in the digestion of peptides

Question 24

Thus, the digestion that occurs in the small intestine is the result of _____________\_, as well as ______\_ and ____\_ enzymes.

Answer 24

Thus, the digestion that occurs in the small intestine is the result of brush-border enzymes, as well as pancreatic and hepatic enzymes.

Question 25

Most absorption of nutrients, water, and electrolytes is completed within the _\_\_\_\_\_\__and _\_\_\_\_\__ of the small intestine

Answer 25

Most absorption of nutrients, water, and electrolytes is completed within the _duodenum_ and _ileum_ of the small intestine

Question 26

With the exception of _\_\_\_\_\_\_\__and _\_\_\_\_\_\__, absorption is not regulated, allowing for maximum absorption

Answer 26

With the exception of _calcium (Ca2+)_ and _iron_, absorption is not regulated, allowing for maximum absorption

Question 27

The small intestine is anatomically arranged to have a _\_\_\_\_\_\_\_\_\_\__, which maximizes its absorptive capabilities

Answer 27

The small intestine is anatomically arranged to have a _large surface area_, which maximizes its absorptive capabilities

Question 28

How is the small intestine anatomically arranged to have a large surface area? (3)

Answer 28

Large surface area is the result of the presence of **circular folds**, **villi**, and **microvill**

Question 29

The small intestine contains circular folds, villi and microvilli which all serve to _**\_\_\_\_\_\_\_\_\_\_**_and maximize _\_\_\_\_\__ capability.

Answer 29

The small intestine contains circular folds, villi and microvilli which all serve to _increase surface area_ and maximize _absorptive_ capability.

Question 30

The epithelial cells of the small intestine also have _\_\_\_\_\_\_\_\_\_\_\__ specific for the absorption of key nutrients and minerals.

Answer 30

The epithelial cells of the small intestine also have _transport proteins_ specific for the absorption of key nutrients and minerals.

Question 31

Carbohydrates are absorbed as _\_\_\_\_\_\_\_\__

Answer 31

Carbohydrates are absorbed as _monosaccharides_

Question 32

Carbohydrates are absorbed as monosaccharides. This process involves transport across the **apical** surface by _\_\_\_\_\_\_\_ ______ \_\_\_\_\_\_ \_\_\_\_\_\__transport proteins and transport across the **basolateral** surface by _\_\_\_\_\_\_\_ _______ \_\_\_\_\_\_\__ proteins

Answer 32

Carbohydrates are absorbed as monosaccharides. This process involves transport across the **apical** surface by _sodium (Na+)-dependent secondary active_ transport proteins and transport across the **basolateral** surface by _facilitated diffusion carrier_ proteins

Question 33

Carbohydrate digestion and absorption across the epithelial cells of the small intestine: (1) Starch and glycogen are converted to the disaccharide maltose by _\_\_\_\_\_\_ \_\_\_\_\_\__and _\_\_\_\_\_\_ \_\_\_\_\_\__. (2) The disaccharides lactose, maltose and sucrose are converted to their respective monosaccharides by the _\_\_\_\_\_\__(lactase, maltase and sucrose) located in the _\_\_\_\_\_\_ \_\_\_\_\_\__ of the _\_\_\_\_\_\__ cells. (3) Monosaccharides are absorbed into the interior of the cell by _\_\_\_\_\_\_ ______ \_\_\_\_\_\_\_\_\_\_\_\__and move across the *basolateral* surface by _\_\_\_\_\_\_ ______ \_\_\_\_\_\_ \_\_\_\_\_\__. _\_\_\_\_\_\_ \_\_\_\_\_\__located in the *basolateral* membrane maintain the _\_\_\_\_\_ \_\_\_\_\_\__required for the *apical* membrane transport of monosaccharides.

Answer 33

Carbohydrate digestion and absorption across the epithelial cells of the small intestine: (1) Starch and glycogen are converted to the disaccharide maltose by _salivary amylase_ and _pancreatic amylase_. (2) The disaccharides lactose, maltose and sucrose are converted to their respective monosaccharides by the _disaccharidases_ (lactase, maltase and sucrose) located in the _brush borders_ of the _epithelial_ cells. (3) Monosaccharides are absorbed into the interior of the cell by _Na+-dependent secondary active transport_ and move across the *basolateral* surface by _facilitated diffusion carrier proteins_. _Na+/K+ ATPases_ located in the *basolateral* membrane maintain the _Na+ gradient_ required for the *apical* membrane transport of monosaccharides.

Question 34

**Proteins** are absorbed across the *apical* membrane as: * _\_\_\_\_ \_\_\_\__, * _\_\_\_\__ or * _\_\_\_\__ by: * _\_\_\_\_ ____ \_\_\_\___\_\_\_\_ \_\_\_\__ or * by _\_\_\_\_ ____ \_\_\_\_ \_\_\_\__.

Answer 34

**Proteins** are absorbed across the *apical* membrane as: * _amino acids_, * _dipeptides_ or * _tripeptides_ by: * _Na+-dependent secondary active_ _transport proteins_ or * by _facilitated diffusion carrier proteins_.

Question 35

**Intracellularly**, all peptides must be *catabolized* to their _\_\_\_\_\_ \_\_\_\_\__ form

Answer 35

**Intracellularly**, all peptides must be *catabolized* to their _amino acid_ form

Question 36

Transport of **amino acids** across the *basolateral* membrane occurs by _\_\_\_\_\_ _____ \_\_\_\_\_ \_\_\_\_\_._

Answer 36

Transport of **amino acids** across the *basolateral* membrane occurs by _facilitated diffusion carrier proteins._

Question 37

Protein digestion and absorption across the epithelial cells of the small intestine: (1) Dietary and endogenous proteins are converted to small peptides and amino acids by _\_\_\_\_ \_\_\_\__and _\_\_\_\_ ____ \_\_\_\__. (2) Amino acids, dipeptides and tripeptides are absorbed across the *apical* membrane by _\_\_\_\_ ____ \_\_\_\_ ____ \_\_\_\__. (3) Small peptides are catabolized to their amino acid form by _\_\_\_\__in the *brush border* of the epithelial cells or by _\_\_\_\_ \_\_\_\__. Transport of amino acids across the *basolateral* membrane occurs by facilitated diffusion carrier proteins. _\_\_\_\__located in the basolateral membrane maintain the_\_\_\_\__ required for the *apical* membrane transport of small peptides and amino acids.

Answer 37

Protein digestion and absorption across the epithelial cells of the small intestine: (1) Dietary and endogenous proteins are converted to small peptides and amino acids by _gastric pepsin_ and _pancreatic proteolytic enzymes_. (2) Amino acids, dipeptides and tripeptides are absorbed across the *apical* membrane by _Na+-dependent secondary active transport proteins_. (3) Small peptides are catabolized to their amino acid form by _aminopeptidases_ in the *brush border* of the epithelial cells or by _intracellular peptidases_. Transport of amino acids across the *basolateral* membrane occurs by facilitated diffusion carrier proteins. _Na+/K+ ATPases_ located in the basolateral membrane maintain the _Na+ gradient_ required for the *apical* membrane transport of small peptides and amino acids.

Question 38

Fats are absorbed as _\_\_\_\_\_\__and _\_\_\_\_\_\__, both of which are capable of _\_\_\_\_\_\__across the _\_\_\_\_\_\_ \_\_\_\_\_\__ of _\_\_\_\_\_\__ cells

Answer 38

Fats are absorbed as _monoglycerides_ and _fatty acids_, both of which are capable of _diffusing_ across the _plasma membrane_ of _epithelial_ cells

Question 39

**Intracellularly**, monoglycerides and fatty acids enter the _\_\_\_\_\_ ______ \_\_\_\_\_\__and reform _\_\_\_\_\_\__ which are then send to the _\_\_\_\_\__appartus for packaging into _\_\_\_\_\_\_\__

Answer 39

**Intracellularly**, monoglycerides and fatty acids enter the _smooth endoplasmic reticulum (SER)_ and reform _triglycerides_ which are then send to the _Golgi_ appartus for packaging into _chylomicrons_

Question 40

**Chylomicrons** are exocytosed across the *basolateral* membrane where they enter into the _\_\_\_\_\__ system

Answer 40

Chylomicrons are exocytosed across the *basolateral* membrane where they enter into the _lymphatic_ system

Question 41

Fat digestion and absorption across the epithelial cells of the small intestine: (1) Dietary fat is *emulsified* by _\_\_\_\_\_ \_\_\_\_\__. (2) _\_\_\_\_\_ \_\_\_\_\__ converts triglycerides into monoglycerides and free fatty acids. (3) _\_\_\_\_\__ are formed from bile salts interacting with monoglycerides and free fatty acids. (4) Monoglycerides and free fatty acids leave the micelle upon contact with the _\_\_\_\_\_ \_\_\_\_\__ of the epithelial cell. (5) Monoglycerides and free fatty acids are *resynthesized* into _\_\_\_\_\__. (6) Triglycerides aggregate and are coated with *lipoprotein* to form _\_\_\_\_\__ which are exocytosed across the *basolateral* membrane of the epithelial cell. (7) Chylomicrons enter the _\_\_\_\_\__vessels called the _\_\_\_\_\_ \_\_\_\_\__. Chylomicrons are unable to cross the _\_\_\_\_\__ membrane of blood capillaries.

Answer 41

Fat digestion and absorption across the epithelial cells of the small intestine: (1) Dietary fat is *emulsified* by _bile salts_. (2) _Pancreatic lipase_ converts triglycerides into monoglycerides and free fatty acids. (3) _Micelles_ are formed from bile salts interacting with monoglycerides and free fatty acids. (4) Monoglycerides and free fatty acids leave the micelle upon contact with the _apical surface_ of the epithelial cell. (5) Monoglycerides and free fatty acids are *resynthesized* into _triglycerides_. (6) Triglycerides aggregate and are coated with *lipoprotein* to form _chylomicrons_ which are exocytosed across the *basolateral* membrane of the epithelial cell. (7) Chylomicrons enter the _lympathic_ vessels called the _central lacteals_. Chylomicrons are unable to cross the _basement_ membrane of blood capillaries.

Question 42

The small intestine is also the site of *vitamin* absorption. _\_\_\_\_\_\_\__vitamins are transported in _\_\_\_\_\__, along with monoglycerides and fatty acids, and are _\_\_\_\_\__absorbed by _\_\_\_\_ \_\_\_\_\__

Answer 42

The small intestine is also the site of *vitamin* absorption. _Fat-soluble_ vitamins are transported in _micelles_, along with monoglycerides and fatty acids, and are _passively_ absorbed by _simple diffusion_

Question 43

**Water-soluble vitamins** require _\_\_\_\__and _\_\_\_\_\_\_ ______ \_\_\_\_\_\__ for absorption

Answer 43

**Water-soluble vitamins** require _apical_ and _basolateral_ _transport proteins_ for absorption

Question 44

Vitamin B12 is absorbed only when bound to _\_\_\_\_\_\_\_\_\_\__, which is a protein secreted by the _\_\_\_\_\_\_ \_\_\_\_\_\__ cells.

Answer 44

Vitamin B12 is absorbed only when bound to _intrinsic factor_, which is a protein secreted by the _gastric parietal_ cells.

Question 45

Unlike the absorption of nutrients and vitamins, the absorption of both _\_\_\_\__and _\_\_\_\__ is regulated

Answer 45

Unlike the absorption of nutrients and vitamins, the absorption of both _iron_ and _Ca2+_ is regulated

Question 46

Iron is _\_\_\_\_\__absorbed by the small intestine epithelial cells and can be stored in a granular form called _\_\_\_\_\__ or transported into the blood, where it binds to a plasma protein carrier called _\_\_\_\_\__

Answer 46

Iron is _actively_ absorbed by the small intestine epithelial cells and can be stored in a granular form called _ferritin_ or transported into the blood, where it binds to a plasma protein carrier called _transferrin_

Question 47

Iron absorption across the epithelial cells of the small intestine: Dietary iron that can be absorbed will be: a) moved into the _\_\_\_\_\__, where it is transported bound to the plasma protein carrier _\_\_\_\_\__, or b) stored in the epithelial cell, where it is bound to the protein _\_\_\_\_\__. Excess iron circulating in blood can also be moved into the epithelial cell for storage bound to ferritin. Iron that is not absorbed by cells and that is stored in epithelial cells being sloughed is _\_\_\_\_\__from the body in the _\_\_\_\_\__.

Answer 47

Iron absorption across the epithelial cells of the small intestine: Dietary iron that can be absorbed will be: a) moved into the _blood_, where it is transported bound to the plasma protein carrier _transferrin_, or b) stored in the epithelial cell, where it is bound to the protein _ferritin_. Excess iron circulating in blood can also be moved into the epithelial cell for storage bound to ferritin. Iron that is not absorbed by cells and that is stored in epithelial cells being sloughed is _eliminated_ from the body in the _feces_.

Question 48

Ca2+ must bind to a _\_\_\_\_\_\_\_\_\_\_\_\__ for **endocytosis** into the small intestine epithelial cell

Answer 48

Ca2+ must bind to a _brush-border calcium-binding protein_ for **endocytosis** into the small intestine epithelial cell

Question 49

Ca2+ Transport across the *basolateral* membrane occurs by a _\_\_\_\_\_\_\_\_\_\_\__

Answer 49

Ca2+ Transport across the *basolateral* membrane occurs by a _Ca2+ -ATPase._

Question 50

Ca2+ absorption is regulated by the hormones _\_\_\_\_\__hormone and _\_\_\_\__.

Answer 50

Ca2+ absorption is regulated by the hormones _parathyroid_ hormone and _calcitriol_.

Question 51

Water molecules _\_\_\_\_\_\__follow the absorption of other molecules, allowing water to be absorbed _\_\_\_\_\_\__

Answer 51

Water molecules _osmotically_ follow the absorption of other molecules, allowing water to be absorbed _passively_

Question 52

About 95% of the water present in the duodenum is absorbed by the time the chyme reaches the _\_\_\_\_ \_\_\_\_\__

Answer 52

About 95% of the water present in the duodenum is absorbed by the time the chyme reaches the _large intestine_