Chapter 18 GI Tract Flashcards
(200 cards)
1
Q
Path of ingesta
A
1) oral cavity
2) Pharynx
3) Upper pharyngoesophageal sphincter
4) Esophagus
5) Lower gastroesophageal sphincter
6) Stomach (cardia, fundus, body, antrum, pylorus)
7) Pyloric Sphincter
8) Small Intestine (duodenum, jejunum, ileum)
9) Illeocecal valve
10) Large intestine (cecum, colon, rectum)
11) Anus
12) Internal and External Anal Sphincters
2
Q
6 Sphincters/Valves in GI tract
A
1) Upper pharyngoesophageal sphincter
2) Lower gastroesophageal sphincter
3) Pyloric sphincter
4) Illeocecal valve
5) Internal anal sphincter
6) External anal sphincter
3
Q
Accessory GI organs
A
1) Teeth
2) Salivary glands
3) Tongue
4) Liver
5) Gallbladder
6) Pancreas
4
Q
4 Layers of Digestive Tract
-include sublayers of mucosa and muscularis
-include plexus’
A
1) Mucosa
-epithelium
-lamina propria
-muscularis mucosa
2) Submucosa
-submucosal plexus
3) Muscularis
-circular muscle
-myenteric plexus
-longitudinal muscle
4) Serosa
5
Q
Activities of the Digestive System
A
1) Motility- Mastification, deglutition, peristalsis, segmentation, haustration, and defecation
2) Secretion
3) Digestion
4) Absorption
5) Storage
6) Elimination
7) Regulation
6
Q
Digestion breaks down non-absorbable ________ including (name them) into absorbable ___________ building blocks.
Includes ________ into monomers aided by specific enzymes
A
Polymers —> Monomers
Polymers: carbohydrates, lipids, proteins
-Hydrolysis
7
Q
Digestion obtains basic organic molecules to make ________, build _______, and serve as ________ and _______.
A
-Make ATP
-Build tissues
-Cofactors & Coenzymes
8
Q
Mastification
A
Chewing
-Mixes food with saliva
9
Q
Components that make up saliva
A
1) Salivary Amylase
2) Mucus
3) Growth factors
10
Q
3 Pairs of Salivary Glands
A
1) Paratoid
2) Submandibular
3) Sublingual
11
Q
3 Pairs of Salivary Glands
A
1) Paratoid
2) Submandibular
3) Sublingual
12
Q
3 Stages of Deglutition
A
1) Oral stage voluntary
2) Pharyngeal stage involuntary
3) Esophageal stage involuntary
13
Q
Oral stage voluntary
A
Bolus moves from oral cavity to pharynx (back of throat) by the tongue.
This is voluntary.
14
Q
Esophaegeal stage voluntary
A
bolus moves from pharynx through upper esophageal sphincter and into the esophagus.
-Soft palate covers nasopharynx
-Epiglottis covers vocal folds (larynx)
-Vocal folds close
-Upper esophageal sphincter relaxes
15
Q
Esophageal State involuntary
A
bolus moves down esophagus through peristalsis, through lower esophageal sphincter, and into the stomach.
16
Q
Muscular Arrangement of the Esophagus
A
Upper third contains skeletal muscle and it transitions into smooth muscle
17
Q
In stage 3 of deglutition, the lower esophageal sphincter _____ to allow bolus to pass.
A
Relax
18
Q
Why does lower esophageal sphincter close?
A
to prevent regurgitation of stomach contents including stomach acids.
When this fails to close properly, someone can have gastroesophageal reflux disease (GERD) also known as heart burn
19
Q
Gastroesophageal Reflux Disease (GERD)
A
-heart burn
-caused by weakened or relaxed lower esophageal sphincter
-stomach acid or bile flows back into the esophagus, causing irritation and inflammation
Treatments: Medications such as proton pump inhibitors (PPIs) and H2 blockers can also be prescribed to reduce acid production and relieve symptoms.
20
Q
Esophageal peristalsis
Describe Peristaltic Wave
A
Series of localized reflexes in response to distention of wall by bolus
Coordinated, wave-like muscular contractions
- Circular smooth muscle contracts on proximal side and relaxes on distal side of bolus
- Followed by longitudinal contraction (shortening) of smooth muscle
After food passes into the stomach, the lower esophageal sphincter constricts
21
Q
Circular smooth muscle contracts on ______ side and relaxes on ________ side of bolus.
A
proximal; distal
22
Q
If a disease only damaged the myenteric plexus and not the submucosal plexus, which process would be impaired?
A
Peristalsis
23
Q
If a disease only damaged the submucosal plexus and not the myenteric plexus, which process would be impaired?
A
glandular secretion, blood flow, and nutrient absorption
-impair Secretion from mucosal glands
-impair vasodilation of capillaries in the submucosa
-damage to the submucosal plexus may indirectly impair water absorption by enterocytes by affecting the secretion of substances required for efficient absorption of water and other nutrients, but it is not the primary process that regulates water absorption.
24
Q
What is the role of salivary amylase?
A
begins starch digestion
25
What are different components of stomach, in order from proximal to distal
1. Cardia
2. Fundus
3. Body
4. Antrum
5. Pylorus
26
Deeper in the mucosa of the stomach contains _______ lined with ________ that secrete different substances.
gastric pits lined with gastric glands
27
Functions of the Stomach
1. Stores food-- the rugae allows for expansion
2. Churns food to mix with gastric secretions
3. Initiates digestion of proteins
4. Kills bacteria
5. Moves food (chyme) into small intestine
28
3 muscle layers of the stomach
1. Inner oblique
2. Circular
3. Outer Longitudinal
29
Describe motility in gastric mixing in the stomach
weak peristaltic constricting waves from the fundus to the antrum
This mixing combines the food with gastric secretions to make chyme.
During the mixing process, the pyloric sphincter (to small intestine) is closed
30
Describe motility in gastric emptying of the stomach
aka chyme from stomach --> pyloric sphincter --> duodenum of small intestine
Strong peristaltic waves starting in antrum to pylorus
Pyloric sphincter relaxes to allow chyme to enter the duodenum
A full duodenum exerts pressure that closed pyloric sphincter
31
Exocrine
-excreted into ______
excreted into lumen that is technically outside of the body
32
Paracrine
-excreted into _______
-travels to ______
interstitial fluid and travels to adjacent cells to bind receptors
33
Endocrine
-excreted into _______
-enters _______
-travels to ______
excreted into interstitial fluid, enters blood stream, and travels to tissues throughout the body.
Eventually returns to the same tissue through the blood stream
34
Mucosa of the stomach contains numerous _______________.
_________ line the pits and secrete exocrine molecules and water (gastric juice) into _______, and endocrine and paracrine signaling molecules into __________ of mucosa.
Gastric pits
Gastric glands line pits
exocrine = lumen
endocrine + paracrine = interstitial space
35
Goblet cells secrete
Mucus and Bicarbonate
36
Parietal cells secrete
HCl and Intrinsic factor (IF)
37
Intrinsic factor is secreted by _______ cells. It is a polypeptide that promotes absorption of _________ in the ________.
This helps prevent which disease?
IF secreted by parietal cells.
Promotes absorption of vitamin B12 in the ileum.
Pernicious anemia
38
Chief Cells secrete
Pepsinogen
(inactive form of pepsin. Becomes active when mixes with HCl from parietal cells.)
39
Enterochromaffin Cells (EC) secrete _____.
Function:
Exocrine/Endocrine/Paracrine??
serotonin
Aids in motility-- binds to receptors on smooth muscle cells that line gut wall
Stimulates smooth muscle contraction --> promotes peristalsis --> propels food through GI tract
PARACRINE
40
Serotonin is screted by ______ cells and aids in ________. This is a ________ signaling molecule as it is secreted into _______ and acts on ______.
Enterochromaffin cells; motility
Paracrine; secreted into interstitial space and acts locally on nearby cells.
41
Enterochromaffin-Like cells (ECL) secrete __________.
Function?
Exocrine/Endocrine/Paracrine??
Histamine
Increase gastric acid secretion (histimine binds to H2 receptors on parietal cells).
Paracrine
42
G cells secrete __________.
Function?
Exocrine/Endocrine/Paracrine??
Gastrin into bloodstream
Stimulates gastric acid production + secretion by binding to G receptor on parietal cell. Also carried to ECL cells (produce histamine --> stimulates secretion of gastric acid from parietal cells)
ENDOCRINE
43
D cells secrete ________.
Function?
Exocrine/Endocrine/Paracrine??
Somatostatin
Inhibits secretion of GI hormones.
Decreases gastric acid (HCl) secretion.
PARACRINE AND ENDOCRINE
44
Ghrelin cells secrete __________.
Function?
Exocrine/Endocrine/Paracrine??
Ghrelin
Stimulate hunger
Endocrine
45
3 Phases of Gastric Activities elicited by eating
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
46
How is gastric motility and secretory activity affected by 1st phase of gastric activity: Cephalic phase
This phase begins before food enters stomach. It is stimulated by the sight, smell, and taste of food.
Increases vagal tone (inc activity of the vagus nerve, which is a major nerve of the parasympathetic nervous system--This can cause the release of acetylcholine, a neurotransmitter that stimulates digestive processes, such as gastric acid secretion, enzyme secretion, and gastric motility. Promote the relaxation of the lower esophageal sphincter, which can aid in the passage of food from the esophagus to the stomach. Additionally, vagal stimulation can increase blood flow to the digestive organs, promoting nutrient uptake and waste elimination.)
Activates Gastrin (stimulates parietal cells to secrete HCl)
Activates Histamine (stimulates and binds to parietal cells to produce more HCl)
Increase secretions
47
How is gastric motility and secretory activity affected by 2nd phase of gastric activity: gastric phase
Food in the stomach causes physical distention of stomach and the presence of chemical nature of chyme (amino acids) stimulates secretions.
This leads to positive feedback to where an increase in secretion of HCl and pepsinogen leads to an increase in gastric secretion.
48
Explain positive feedback in the gastric phase
the stimulus is the presence of food in the stomach, which triggers the release of gastric juices. The response is the release of hydrochloric acid and pepsinogen by the gastric glands, which help to break down the food and prepare it for digestion.
The release of hydrochloric acid and pepsinogen in turn stimulates the release of more gastric juices from the gastric glands. This amplifies the initial response and further enhances the breakdown of the food. The positive feedback loop continues until the stomach is emptied of its contents or until other mechanisms, such as negative feedback, intervene to bring the response back to baseline levels.
food in stomach --> release of gastric juices --> release of HCl and pepsinogen --> release of more gastric juices ---> amplifies digestion and further breaksdown food ---> continues until stomach empties contents into small intestine
49
Intestinal phase of gastric activity: how is gastric motility and secretory activity affected?
In this phase the chyme exits the stomach and enters the small intestine.
Gastric activity is inhibited!!
50
What activates cephalic phase, gastric phase, and intestinal phase?
Impact on motility + secretion
Cephalic: sight, smell, taste of food
-inc vagal tone
-activation of gastrin + histamine
-inc secretions
Gastric: food in stomach
-distention of stomach walls
-presence of chyme (chemical= amino acids)
-increased secretions
Intestinal: chyme enters small intestine
-gastric activity is inhibited
51
How do acetylcholine, gastrin, and histamine affect HCl secretion?
they all stimulate HCl secretion by parietal cells in the stomach
52
Which receptor on parietal cells’ basal membrane does acetylcholine bind to?
muscarinic receptors (M3)
53
Which receptor on parietal cells’ basal membrane does gastrin bind to?
cholecystokinin (CCK) B receptors
54
Which receptor on parietal cells’ basal membrane does histimine bind to?
H2 receptors
55
Which aspects of the nervous system provide input by releasing acetylcholine onto parietal cells?
Enteric and parasympathetic nervous system
56
All of these receptors and proton pumps on Parietal cells of stomach are targeted by antagonists or inhibitors to provide relief from heartburn and peptic ulcers.
What ways do peptic ulcers arise and how do the drugs used to treat it function?
Cause:
1) Gastrin-secreting tumor
2) Helicobacter pylori (H.pylori)
3) NSAIDs (aspirin, ibuprofen, etc) inhibit paracrine secretion of PGE2 and PGI2
57
Gastrinomas are neoplasms ("tumors") that secrete gastrin. A patient that develops a gastrinoma will have excess levels of what in the stomach?
Hydrochloric acid
58
What are peptic ulcers?
erosions of mucosa of stomach or duodenum
Both HCl and pepsin can damage lining and produce a peptic ulcer
59
Causes of peptic ulcers?
1) Gastrin-secreting tumor
2) Helicobacter pylori (H.pylori)
3) NSAIDs (aspirin, ibuprofen, etc) inhibit paracrine secretion of PGE2 and PGI2
60
Treatment for peptic ulcers?
Antibiotics may be useful in treating ulcers, why?
1. Proton pump inhibitors
-omeprazole (prilosec)
2. Histimine receptor (H2) blockers can treat gastrititis
-famotidine (pepcid)
-ranitidine (xantac)
H. pylori is an infection that allows bacterium to damage protective mucus layer of stomach and small intestine and lets acid damage lining and cause ulcers. Antibiotics kill bacteria.
61
What are the functions of HCl?
Provide acidic gastric environment
1) denatures ingested proteins
2) activates pepsinogen to pepsin (pH=2)
3) Kills bacteria
62
Digestion in the stomach
1) Proteins denatured (acidic environment from presence of HCl) and partially digested by pepsin. Makes them more digestible aka breaks them down.
2) Carbohydrate digestion by salivary amylase is soon inactivated by acidity
63
Absorption in the stomach
is MINIMAL!!!
-alcohol (ethanol) -- main absorption site is small intestine
-aspirin and salicylates -- unionizes at gastric pH
64
In Gastric acid (HCl) production by parietal cells:
What occurs in cytosol?
What occurs at apical membrane (boarding gastric lumen)
65
In Gastric acid (HCl) production by parietal cells:
What occurs in cytosol?
What occurs at apical membrane (bordering gastric lumen)?
What occurs at basolateral membrane (into bloodstream)?
In cytosol: (catalyzed by carbonic anhydrase)
CO2 + H2O --> H+ + HCO3-
At apical membrane:
-H+ enters gastric lumen via active transport: H+/K + ATPase (proton pump) **note that H+ is higher in conc in lumen (3x10^6 times more in lumen) so it needs active transport to move against concentration gradient
-Cl- enters gastric lumen via facillitated diffusion (Facilitated diffusion is a passive transport mechanism that involves the movement of molecules or ions across a membrane down their concentration gradient, without the use of energy.) ***** move into the gastric lumen through chloride channels present on the apical membrane of the parietal cells.
Basolateral Membrane:
Secondary active transport moves HCO3- out along conc gradrient, coupled with moving Cl- into lumen against conc gradient
66
Concentration of Cl- is ______ in the parietal cells than it is in the lumen.
higher in cell
67
Cl- enters parietal cells on the _________ membrane via ______ and exits out of the ___________ membrane via.
Enters basolateral membrane via secondary active transport (against conc gradient-- coupled w/ moving HCO3- out)
Exits apical membrane into lumen via facilitated diffusion along its concentration gradient from high in cell to low in lumen.
68
What is the source of H+ in the hydrochloric acid in the stomach lumen?
It comes from bicarbonate in the parietal cells.
It is actively transported across apical membrane of parietal cells.
69
What are some of the protective mechanisms that keep the stomach from digesting itself?
Physical and Chemical Barriers?
Structural and Cellular Barriers?
Alkaline Mucus containing HCO3- forms a barrier against actions of pepsin and acid.
Structural and Cellular Barriers:
1) Tight junctions between adjacent epithelial cells
2) Rapid rate of cell division (entire epithelium replaced in 3 days)
3) Prostaglandins E2 (PGE2) and I1 (PGI2)-- they inhibit the release of gastric acid, increase mucus secretions, and increase mucosal blood flow
70
Each cycle of hydrochloric acid production by gastric parietal cells results in the following net effect on chloride? Bicarbonate? H+? K+?
1 Cl- from interstitial compartment to gastric lumen.
1 H+ from intracellular compartment to gastric lumen.
1 HCO3- from intracellular compartment to interstitial compartment.
1 K+ from gastric lumen to intracellular compartment.
71
What are the 3 segments of the small intestine in order?
1. Duodenum
2. Jejunum
3. Ileum
72
Where do bile and pancreatic ducts empty?
duodenum of small intestine
73
Describe the progressive anatomy of the mucosa from folds to villi to microvilli.
Folds (plicae circulares) --> villi --> microvilli (brush border)
Plicae Circulares: large, permanent folds of the mucosa and submucosa that are visible to the naked eye.
Villi: circular folds contain smaller finger-like projections called villi
Microvilli: Villi are covered in even smaller hair-like structures called microvilli.
**greatly increases the surface area of the small intestine, allowing for efficient absorption of nutrients.
74
Where are intestinal crypts located?
What occurs here?
Base of villi
Mitosis in intestinal crypts replaces the epithelial cells at the tips of villi when they are exfoliated.
75
Epithelial cells (enterocytes) are interspersed with ________.
Goblet cells
76
Epithelial cells at the tips of villi are exfoliated and replaced by mitosis in ________.
intestinal crypts
77
Lamina Propria contains?
Lymphocytes, capillaries, and central lacteal
78
What are the main substances absorbed from the duodenum and jejunum vs. ileum?
Duodenum & Jejunum-- absorbs carbohydrates, amino acids, lipids, iron, Ca2+, and H2O
Ileum-- absorbs bile salts, vitamin B12, electrolytes, and H2O.
79
Complete digestion and absorption of carbohydrates, proteins, and fats occurs in __________.
small intestine
80
Digestion in the small intestion requires both ______ and ______ enzymes.
Pancreatic and Brush Border Enzymes
81
Brush Border enzymes of microvilli are ______ to the cell membrane. They are not _______.
Attached and not secreted
82
Which type of nutrients is enzymatically cleaved by brush border enzymes?
Which is NOT enzymatically cleaved?
carbohydrates and proteins are enzymatically cleaved by brush border enzymes in the small intestine
--enzymes such as sucrase, lactase, and maltase break down carbohydrates into simple sugars such as glucose, fructose, and galactose
--enzymes such as peptidases and aminopeptidases break down proteins into amino acids.
lipids are broken down by pancreatic lipase and bile salts.
-----On the other hand, lipids (fats) are not enzymatically cleaved by brush border enzymes. Instead, they are broken down by pancreatic lipase, which is secreted by the pancreas and released into the small intestine along with bile salts. Bile salts emulsify the lipids, breaking them into smaller droplets, which increases the surface area for pancreatic lipase to work on.
83
What is the difference between brush border enzymes vs. secreted enzymes? What types of molecules are digested in the SI?
-Brush border enzymes are produced by the epithelial cells lining the microvilli of the small intestine, where they are anchored.
-They act on molecules that have already been partially digested by other enzymes such as salivary and pancreatic enzymes.
-Brush border enzymes complete the digestion of carbohydrates and proteins by breaking them down into their smaller components, which can then be absorbed by the small intestine.
-In contrast, secreted enzymes are produced by the salivary glands, stomach, pancreas, and liver.
-These enzymes are released into the digestive tract and act on large molecules such as carbohydrates, proteins, and lipids to break them down into smaller molecules that can be absorbed by the body.
-SI digests and absorbs a variety of molecules, including carbohydrates, proteins, lipids, vitamins, and minerals.
84
Which processes contribute to water levels in the lumen of the GI tract vs. in which segments is water absorbed into the body?
Is there a net gain or loss of water from the GI tract into the body? Which GI tract segments primarily contribute to water absorption?
Diet: food and drink
Digestive Secretions: Saliva
Gastric Secretions
Bile from liver
Pancreatic juice
Small intestinal Secretions
Colonic mucous secretions
Water is primarily absorbed into the body from the small intestine (7800 mL) and colon (1250 mL).
Net gain of water from GI tract into the body. The GI tract absorbs most of the ingested water, and only a small amount is excreted in the feces (150 mL)
The small intestine absorbs the majority of the ingested water along with nutrients, while the colon absorbs any remaining water and electrolytes. The large intestine's main function is to form and store feces, so it primarily reabsorbs water to maintain proper fecal consistency.
85
__________ intestine absorbs all but ~2 L of ingested H2O, and H2O from GI secretions.
Small
86
The small intestine absorbs electrolytes, Na+ and Cl- through _______________.
Na+ is cotransported with ________.
Na+, K+ ATPase pump moves Na+ ______ of enterocytes and _______ interstitial fluid.
Water follows Na+ by _______.
facilitated diffusion
Glucose
Na+ out of enterocytes and into interstitial fluid
Osmosis
87
Large intestine absorbs Na+ via __________. H2O follows by ________.
Roughly _______ mL H2O remains in feces daily.
facilitated diffusion; osmosis; 100+ mL
88
Two major types of motility patterns derived from contractions in the small intestine:
1) Peristalsis- movement of chyme through small intestine; slow and weak movement - avg 1 cm/min
2) Segmentation- major contractile activity of the small intestine 2-3x/min; strong contraction of circular smooth muscle to mix chyme
89
Motility in small intestine:
______ is slow and weak movement of chyme through small intestine. Average ______ cm/min
________ is the major contractile activity of small intestine and occurs ______x/min. Strong contraction of __________ muscle to mix chyme.
Peristalsis: slow, weak movement of chyme; 1 cm/min
Segmentation: strong, 2-3x/min; contraction of circular smooth muscle to mix chyme.
90
Name 4 endocrine regulatory hormones that enterocytes secrete to regulate the activity of the intestines.
1) Secretin
2) Cholecystokinin (CCK)
3) Gastric inhibitory peptide or Glucose-dependent insulinotropic peptide (GIP)
4) Motilin
91
What is the stimulus that causes enterocytes in the intestines to secrete secretin?
This stimulates ____ and _____ secretion in ________ juice.
Inhibits _______ secretion.
Drop in pH
Stimulates HCO3- and H2O in pancreatic juice.
Inhibits gastic secretion
92
What is the stimulus that causes enterocytes in the intestines to secrete Cholecystokinin (CCK) a.k.a pancreazymin?
Stimulates contraction of _________; thus secretion of ______.
Stimulates enzymatic and _____ secretion in pancreatic juice.
Stimulus: partially digested fats and proteins
Stimulates:
-Contraction of gallbladder -> secrete bile
-Enzymatic and HCO3- secretion in pancreatic juice.
93
What is the stimulus that causes enterocytes in the intestines to secrete Gastric inhibitory peptide or glucose-dependent insulinotropic peptide (GIP)?
Stimulates ________ secretion from endocrine ______.
Inhibits gastric ______ and _____ secretion that slows emptying.
Stimulus: proteins, fats, carbohydrates
Stimulates: insulin secretion from endocrine pancreas
Inhibits gastric motility and HCl secretion to slow emptying-- allows for more time for the digestive enzymes and nutrients in the chyme (the partially digested food) to be absorbed in the small intestine.
94
Motilin is released from ____ cells during ______ and this stimulates ______.
M cells; fasting; motility
(Motilin is a hormone that is produced by special cells in the small intestine called M-cells, which are located in the upper part of the small intestine known as the duodenum. Motilin plays an important role in regulating gastrointestinal motility by stimulating the contraction of the smooth muscle in the upper gastrointestinal tract.)
*This can be particularly important during the fasting state when the stomach and small intestine are empty and need to be cleared of any residual material.
95
Paracrine regulation of Intestinal activity:
Filling of intestines leads to an increase in intestinal pressure. This increases the secretion of _______ from the ____ cells in intestinal mucosa. This leads to an increase in _______.
Filling --> inc intestinal pressure --> EC cells secrete serotonin --> inc muscle contractions
96
Which muscles of SI are involved in peristalsis and which are involved in segmentation?
The circular and longitudinal muscles of the muscularis layer are involved in peristalsis, while only the circular muscles are involved in segmentation.
97
What processes do the SI endocrine hormones secretin, cholecystokinin, and GIP modulate? What does the paracrine signaling molecule serotonin do?
Secretin: response to acidity in chyme entering SI
-Inc secretion of bicarbonate rich fluids from pancreas to neutralize acid before it enters SI
-Dec gastric acid secretion
-Dec gastric motility
**overall neutralize acidic chyme and slow emptying for more efficient absorption and digestion in SI
Cholecystokinin: response to protein and fat in chyme
-inc digestive enzymes
-inc bicarbonate rich fluids from pancreas
-inc contraction of gallbladder -> inc secretion of bile into SI
-Dec gastric emptying
-Dec gastric acid secretion
***slow emptying for more efficient digestion and absorption
GIP: response to glucose and fatty acids in chyme
-inc insulin
-dec gastric acid
-dec motility
***overall regulate blood glucose levels, and slow emptying of stomach to have more efficient digestion and absorption in SI
98
What are the segments of the large intestine, in order.
1. Cecum
2. Ascending colon
3. Transverse colon
4. Descending colon
5. Sigmoid colon
6. Rectum
7. Anal canal
8. Anus
99
How are haustrations vs. propulsive movements in the LI related to segmentation vs. peristalsis in the SI?
Haustrations: slow, segmenting contractions of the circular smooth muscles in the colon that divide the colon into sac-like pouches called haustra. These contractions help to mix the contents of the colon and promote the absorption of water and electrolytes.
Segmentation movements: in the small intestine- contraction of circular smooth muscles in a rhythmic pattern that creates segment-like divisions of the intestine, helping to mix and expose the chyme to the absorptive surface.
Propulsive movements in the LI: involve the coordinated contraction of the circular and longitudinal smooth muscles to move the contents of the colon towards the rectum for elimination.
These movements are similar to the peristaltic movements that occur in the small intestine, which involve the sequential contraction and relaxation of the circular and longitudinal smooth muscles to move the chyme along the length of the intestine towards the ileocecal valve.
Haustrations: Segmentation
Propulsive movements: Peristalsis
100
What molecules are primarily absorbed by the colon? What remains?
Water, electrolytes, vitamins B and K (produced by microbial), short-chain fatty acids...
Remains: Undigested food particles, dead bacteria, and waste material, are formed into feces and eliminated from the body through the anus during defecation.
101
What are some beneficial products of metabolism by LI microbiota?
1. Vitamin K
2. Vitamin B
3. Short-chain fatty acids
102
>____ different different species of microbes live in large intestine.
>400
103
Microbes make _________ and some _______ (riboflavin, thiamin, biotin, pantothenic acid, folic acid)
vitamin K and some B vitamins
104
Microbes make _______________ from cellulose.
short-chain fatty acids (FA)
105
Short-chain fatty acids produced by Microbes from cellulose in large intestine are used for ________ by large intestine ________ cells.
FAs help absorb ____, _____, _____, _____, _______
energy by epithelial cells
Na+, Ca2+, HCO3-, Mg2+, and Fe2+
106
Disruption of normal microflora leads to _____________ disease.
Irritable bowel disease
107
An estimated ______% of volume of stool is bacteria.
30%
108
Defecation Reflux:
Waste material passes to rectum ---> _______ of rectum by fecal material ---> signals sent to ______ region of the spinal cord --> induction of defecation reflex ---> __________ relaxation of internal anal sphincter and _________ relaxation of external anal sphincter
This is aided by contractions of _______ and ______ muscles which push feces from rectum.
--> defecation!!!
distention; signals sent to sacral region of spinal cord
involuntary relaxation of internal anal sphincter
voluntary relaxation of external anal sphincter
Aided by contractions of abdominal and pelvic muscles
109
What is the largest internal organ?
Liver
110
The liver has amazing regenerative abilities because active hepatocytes undergo _______.
mitosis
111
5 functions of liver
1) detoxification of blood
2) Carbohydrate metabolism
3) Lipid metabolism
4) Protein synthesis
5) Secretion of bile
112
The liver is perhaps the most underappreciated organ in basic physiology courses. What are the many jobs of the liver, in general and specifically?
1) Detoxification: The liver is responsible for detoxifying harmful substances, such as drugs, alcohol, and environmental toxins.
2) Metabolism: The liver is involved in the metabolism of carbohydrates, fats, and proteins, and helps to regulate blood glucose levels.
3) Synthesis: The liver synthesizes important proteins, such as albumin, clotting factors, and lipoproteins.
4) Storage: The liver stores glycogen, vitamins, and minerals, such as iron and copper.
5) Regulation of blood glucose levels: The liver plays an important role in regulating blood glucose levels by storing glucose as glycogen and releasing it into the bloodstream when needed.
113
___________ brings oxygenated blood to liver. It branches off ____.
Hepatic artery brings oxygenated blood to liver. Branches of aorta.
114
Hepatic portal system brings ________ and ______ blood from ______ to _______.
nutrients and deoxygenated blood from abdominal organs to the liver.
115
______________ is the venous return for the abdominal organs.
Hepatic portal system
The portal system is responsible for carrying blood from the abdominal organs, including the stomach, intestines, pancreas, and spleen, to the liver. The portal vein is the main vessel of the portal system, and it receives blood from the capillary beds of the abdominal organ
116
Which organ system does not drain into hepatic portal system?
The renal system (kidneys) does not drain into the hepatic portal system. Instead, the kidneys drain directly into the systemic circulation through the renal veins, which merge with the inferior vena cava. The renal veins carry blood that has been filtered and processed by the kidneys, including waste products such as urea and excess water and electrolytes. This blood is then returned to the heart and distributed throughout the body.
117
Multiple ______________ take _______ blood from liver to inferior vena cava.
hepatic veins; deoxygenated
118
The liver is organized to _________.
filter the blood
119
Where does hepatic artery originate from and where does it go?
Aorta --> liver lobules
120
Where does hepatic portal system originate from and where does it go?
Mesenteric vein and splenic vein (from digestive organs) ---> liver lobules
121
Where does hepatic veins originate from and where does it go?
Liver lobules --> inferior vena cava
122
Which have relatively oxygenated vs. deoxygenated blood?
-Hepatic Artery
-Hepatic Portal System
-Hepatic veins
-Hepatic Artery: oxygenated
-Hepatic Portal System: deoxygenated
-Hepatic veins: deoxygenated
123
What carries nutrients from the GI tract to the liver?
Hepatic portal system
124
Where are the 2 capillary beds on either side of the hepatic portal system?
1st Capillary bed: stomach and intestine walls
2nd Capillary bed: Liver lobules
125
What is the anatomy of hepatic lobules?
Hepatic lobules have hexagonal shape with 6 corners. On each corner there is a portal triad: hepatic artery, hepatic portal vein, and bile duct.
Portal triad feeds into sinusoids that are capillary-like structures lined with endothelial cells. Sinusoids run to center of lobule to central vein that feeds into the hepatic vein. In between each sinusoid is cords or plates of hepatocytes.
126
How do hepatic arteries, portal veins, sinusoids, central veins, and bile ductules fit into hepatic lobule?
The liver is composed of functional units called hepatic lobules. These lobules are roughly hexagonal in shape and are composed of plates of hepatocytes (liver cells) arranged around a central vein.
The hepatic artery and portal vein are two major vessels that supply blood to the liver. The hepatic artery brings oxygenated blood from the heart, while the portal vein brings nutrient-rich blood from the gastrointestinal tract.
The sinusoids are specialized capillaries that lie between the plates of hepatocytes. They receive blood from both the hepatic artery and portal vein and are lined with specialized cells called Kupffer cells, which play a role in filtering and phagocytosing foreign substances.
Bile ductules are small ducts that collect bile produced by hepatocytes.
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Portal Triads
Portal triads are structures that contain branches of the hepatic artery, portal vein, and bile ductules. These structures are located at the corners of the hepatic lobules and provide the blood supply and drainage of bile from the liver.
128
What happens to oxygen levels as blood travels through the sinusoids?
As blood travels through the sinusoids, oxygen levels decrease as oxygen is taken up by hepatocytes for metabolic processes.
129
What happens in the sinusoids?
Blood percolates through endothelium-lined sinusoids between cords or plates of hepatocytes.
130
What is the path from bile canaliculi to the gall bladder?
The path from bile canaliculi to the gallbladder involves the merging of bile ductules to form larger bile ducts:
- Bile canaliculi are small channels between hepatocytes that transport bile produced by the hepatocytes to the bile ductules.
-Bile ductules are small ducts that collect bile produced by hepatocytes.
-These ductules merge to form larger bile ducts
-Which eventually merge with the common hepatic duct and then the cystic duct to form the common bile duct.
-The common bile duct then transports bile to the gallbladder or the duodenum.
131
Perimeter of each lobule is defined by ________ at the corners
portal triads
132
Oxygen-rich blood from hepatic ____ and nutrient-rich blood from hepatic ______ mix and flow through _______ toward the central vein in the center of each lobule.
Oxygen-rich blood from hepatic artery; nutrient rich blood from hepatic portal vein mix and flow through sinusoids toward central vein, located at center of each lobule.
133
Fenestrated endothelium
Hepatocytes directly exposed to blood
134
Bile canaliculi collects waste products and flows in opposite direction to ___________ in portal triads which delivers it to the _____________.
Bile canaliculi --> bile ductules --> portal triad --> gallbladder
135
Bile is stored in the _________ until signaled to release.
Gallbladder
136
What is the primary signal that tells gallbladder to release stored bile? Is it endocrine or nervous system signal?
Cholecystokinin is an endocrine (hormonal) signal that tells gallbladder to contract and release bile.
137
What is the nervous system signal for bile release from the gallbladder?
Parasympathetic and enteric nervous system release neurotransmitter Acetylcholine (ACh).
ACh stimulates the contraction of the gallbladder causing it to release bile.
138
What are the endocrine and nervous system signals for bile release from the gall bladder?
The main hormonal signal is the hormone cholecystokinin (CCK), which is released by the small intestine in response to the presence of fatty acids and amino acids in the lumen of the duodenum. CCK stimulates the contraction of the gallbladder and relaxation of the sphincter of Oddi, which allows bile to flow from the gallbladder into the duodenum.
neurotransmitters, such as acetylcholine, can stimulate the contraction of the gallbladder.
139
How does enterohepatic recirculation of bile work?
95% of the bile from the ileum of the small intestine is reabsorbed and taken back to the liver via the portal vein. Once in the liver, the hepatocytes can reuse them in the production of new bile. Hepatocytes secrete bile acids into the bile canalli --> bile ductules --> common bile duct --> gallbladder.
Gallbladder stores the bile until signaled by presence of fat in intestine, CCK. Releases it into SI. This recirculates again and again...
140
What are the most important components of bile, and what are their functions?
1) Bile acids and bile salts
2) Bile pigment -- bilirubin
3) Electrolytes, cholesterol, HCO3-, and water
141
Bile pigment is the breakdown of waste products of hemoglobin.
Explain how this turns into conjugated bilirubin.
Aged red blood cells (RBCs) are broken down by macrophages, which are mainly found in the spleen and bone marrow. During this process, hemoglobin is released from the RBCs and broken down into heme and globin. The heme is then converted into biliverdin, which is further converted into unconjugated bilirubin.
Unconjugated bilirubin is not water-soluble and cannot be excreted in urine. Instead, it is transported in the blood to the liver, where it is conjugated with glucuronic acid to form water-soluble bilirubin diglucuronide. Conjugated bilirubin is then excreted in bile and released into the small intestine to aid in the digestion and absorption of dietary fats.
142
What is the precurser for bile acids and bile salts?
Cholesterol
143
Bile salts and bile acids aid in digestion of ______.
Fat
144
What clinical condition results from biliary elevated bilirubin levels?
Jaundice or icterus
145
Endocrine Pancreas includes __________.
This secretes what 3 hormones?
Islets of Langerhans: insulin, glucagon, and somatostatin
146
What are pancreatic acini and how do pancreatic exocrine secretions reach the duodenum? What are the endocrine and neural signals for secretion?
Pancreatic acini are clusters of cells in the pancreas that produce and secrete digestive enzymes and other components of pancreatic juice
Pancreatic exocrine signals go through the pancreatic duct, which joins with the common bile duct from the liver and gallbladder before emptying into the duodenum.
Secretin, Cholecystokinin, and parasympathetic and enteric nervous system (ACh)
147
What are the main components of pancreatic juice?
1. H2O
2. HCO3-
3. Digestive enzymes (trypsinogen)
148
Complete digestion of food requires action of both __________ and _______ enzyme.
Pancreatic + brush border enzyme
149
Zymogens
Inactive precursor of most pancreatic enzymes
150
Most pancreatic enzymes are produced as inactive precursors called _________.
Zymogens
151
Trypsin when activated by _________ in the small intestin triggers activation of other pancreatic enzymes
enterokinase
152
________ (when activated with enterokinase in the small intestine) triggers the activation of other pancreatic enzymes
Trypsin
153
_______________ inhibits activation of trypsin in the pancreas. What would happen if it did not?
Pancreatic trypsin inhibitor; start digesting pancreas from inside
Trypsin is an enzyme that breaks down proteins into smaller peptides and amino acids, and is important for the digestion and absorption of dietary proteins. However, if trypsin is not properly regulated, it can lead to damage of the pancreas and surrounding tissues
154
Three pancreatic enzymes
1) Trypsin-- internal peptide bonds
2) Lipase-- removes FAs from glycerol
3) Amylase -- starch digestion
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What do trypsin, lipase, and amylase contribute to digestion?
1) Trypsin is a protease enzyme that breaks down proteins into smaller peptides and amino acids. It is produced in the pancreas as an inactive precursor called trypsinogen, which is activated by another enzyme called enterokinase that is produced in the small intestine. Once activated, trypsin can break down dietary proteins into smaller peptides and amino acids.
2) Lipase is an enzyme that breaks down fats and oils into smaller fatty acids and glycerol. It is produced by the pancreas and secreted into the small intestine along with bile from the liver and gallbladder. Lipase works by breaking down the large lipid molecules in food into smaller droplets, which can then be emulsified and more easily digested and absorbed.
3) Amylase is an enzyme that breaks down carbohydrates into smaller sugars such as glucose and fructose. It is produced by the pancreas and also by the salivary glands in the mouth. Amylase works by breaking down the complex carbohydrates in food such as starch and glycogen into smaller sugars that can be absorbed into the bloodstream.
156
What are zymogens and how do the intestinal brush border enzymes contribute to functionality of many pancreatic enzymes?
Zymogens are inactive precursor forms of enzymes that are produced and stored in the pancreas until they are needed for digestion.
The intestinal brush border enzymes, also known as the microvillar enzymes, are enzymes that are located on the surface of the intestinal cells in the small intestine. These enzymes are responsible for the final breakdown and absorption of nutrients from food.
intestinal brush border enzymes come in - they can help to cleave the intermediate forms of some pancreatic enzymes, such as trypsinogen, into their active forms.
In addition to their role in activating zymogens, the intestinal brush border enzymes also help to break down certain carbohydrates and proteins that are not fully digested by the pancreatic enzymes
157
Neural regulation of GI activities occurs _______ and lasts _______. Whereas, Hormonal regulation occurs _________ and lasts _________.
Neural: faster, shorter
Hormonal: slower, longer
158
Neural regulation of GI tract can be broken down into _________ and _________ components.
Extrinsic and intrinsic components
159
Extrinsic nervous system includes what two divisions?
1. Parasympathetic division
2. Sympathetic division
160
Neural regulation of GI tract:
The parasympathetic division of the extrinsic nervous system is generally ____________.
The sympathetic division of the extrinsic nervous system is generally ___________.
Parasympathetic --> stimulatory
Sympathetic --> inhibitory
161
How do the extrinsic components of neural regulation of the GI tract contribute to GI function?
Extrinsic neural regulation refers to the influence of the autonomic nervous system on the GI tract, which is controlled by the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system is generally associated with the "fight or flight" response, and tends to inhibit GI activity, while the parasympathetic nervous system is associated with the "rest and digest" response, and tends to stimulate GI activity.
162
The parasympathetic division is generally stimulatory and is mediated by ________ and _________ nerves.
Vagus and sacral
Vagus nerve innervates abdominal cavity: esophagus, stomach, small intestine and proximal colon. Activation of the parasympathetic nervous system promotes digestive processes such as the secretion of digestive enzymes and the contraction of smooth muscles in the digestive tract, which helps to move food through the digestive system. It also stimulates the release of bile from the gallbladder and pancreatic juice from the pancreas, which aids in the digestion of fats and carbohydrates.
Sacral nerves provide parasympathetic innervation to the distal colon and rectum.
163
The sympathetic division is generally inhibitory: inhibits _________ and ______, stimulates contraction of ____________.
Inhibits peristalsis and secretion; stimulates contraction of sphincters (this slows down digestion).
164
The intrinsic division associated with neural regulation of GI tract activities includes:
1) Enteric Nervous system (enteric or visceral brain)
2) Submucosal and Myenteric Plexi-- where extrinsic and intrinsic nervous system meet.
165
Is the enteric nervous system (ENS) part of the autonomic or somatic nervous system?
The ENS is part of the autonomic nervous system and is responsible for regulating local GI function.
166
Let’s take the perspective of the myenteric and submucosal plexi being the ENS. How do these two parts interact?
The myenteric and submucosal plexuses are the two main components of the enteric nervous system (ENS). The myenteric plexus is located between the longitudinal and circular muscle layers of the muscularis externa, while the submucosal plexus is located in the submucosal layer of the gut wall.
The myenteric plexus is responsible for regulating gut motility, while the submucosal plexus is responsible for regulating the secretion of fluid and electrolytes into the gut lumen.
The myenteric and submucosal plexuses are interconnected and can communicate with each other to coordinate gut function. For example, the myenteric plexus can stimulate the submucosal plexus to increase secretion of fluid and electrolytes in response to the presence of food in the gut. Similarly, the submucosal plexus can stimulate the myenteric plexus to increase gut motility in response to the need to move food through the gut more quickly.
167
Let’s take the perspective of the myenteric and submucosal plexi being the ENS. How do these two parts interact? How do sensory afferent and autonomic neurons interact with the ENS? Compare and contrast the locations and primary functions of the myenteric plexus vs. submucosal plexus.
The myenteric plexus receives input from sensory afferent neurons that detect stretch, tension, and chemical changes in the gut wall. It also receives input from autonomic neurons, including parasympathetic neurons that stimulate gut motility and sympathetic neurons that inhibit it. The myenteric plexus then sends output to the circular and longitudinal muscle layers to coordinate gut contractions.
The submucosal plexus receives input from sensory afferent neurons that detect chemical changes in the gut lumen. It also receives input from autonomic neurons, including parasympathetic neurons that stimulate secretion and blood flow and sympathetic neurons that inhibit them. The submucosal plexus then sends output to the secretory cells and blood vessels in the submucosa to regulate secretion and blood flow.
168
Myenteric or Auerbach's plexus innervates _____ muscle of muscular layer from _________ through entire GI tract.
It increases what 4 things?
Innervates smooth muscle from esophagus --> entire GI tract
1) increases tone (tonic)
2) increases intensity of contractions (phasic)
3) Increases the rate of contractions (phasic)
4) Increases conduction rate of excitatory waves
The myenteric plexus can increase the tone (tonic) of the smooth muscle, which helps to maintain a constant level of contraction in the gut wall. It can also increase the intensity and rate of contractions (phasic), which helps to move food and waste materials through the gut. In addition, the myenteric plexus can increase the conduction rate of excitatory waves, which helps to coordinate contractions along the length of the gut.
169
Submucosal or Meissner's plexus is found in the ___ and _____. It innervates the _____ layer.
It controls local secretion, local absorption, and local contraction of ______________.
SI and LI; innervates mucosal layer
Muscularis mucosa
170
Slow waves are not ______. They are generated by _________________, which are a specialized ________ cells. They are characterized by slow, rhythmic, low intensity gradually bringing smooth muscle to ______.
Slow waves are not action potentials.
Generated by interstitial cells of Cajal. They are specialized pacemaker cells.
Slowly bring smooth muscle to threshold.
171
How are slow waves and spike potentials related? Which signals result in depolarization vs. hyperpolarization? What types of neurotransmitters are released by the initial acetylcholine signal proximal vs. distal to a bolus of food, and how does each type affect smooth muscle?
Slow waves and spike potentials are both types of electrical activity that occur in smooth muscle cells of the gastrointestinal (GI) tract.
When the slow wave reaches threshold, it triggers the opening of voltage-gated calcium channels in the smooth muscle cells, which leads to a rapid influx of calcium ions into the cells. This influx of calcium ions then triggers the release of neurotransmitters, such as acetylcholine (ACh), from the enteric neurons that innervate the smooth muscle cells. The ACh released proximal to a bolus of food causes smooth muscle contraction, while the ACh released distal to a bolus of food causes relaxation of the smooth muscle.
172
Spike potentials are ________.
They arise when slow waves reach approximately ____mV.
They last _____ than neuronal AP.
Stretch and parasympathetic nervous system trigger ___________.
Sympathetic nervous system (norepinephrine, sympathetics) triggers __________.
Action potentials
-40 mV
Last longer than neuronal AP
Stretch + Parasympathetic NS --> depolarization
Sympathetic NS --> hyperpolarization
Spike potentials are rapid depolarizations of the smooth muscle cells that result in contraction of the muscle.
173
What types of neurotransmitters are released by the initial acetylcholine signal proximal vs. distal to a bolus of food, and how does each type affect smooth muscle?
Proximal to bolus: Ach, Substance P
Affect: Smooth muscle contraction behind bolus
Distal to bolus: NO, VIP, and ATP
Affect: smooth muscle relaxes in front of bolus
nitric oxide (NO) and vasoactive intestinal peptide (VIP),
174
Presence of bolus induces contraction and relaxation _________ in the same muscle bundles.
simulataneously
175
Stretch from bolus triggers ________. There is also a potential role for chemoreceptors.
Afferent ______ neurons -> _________ interneurons in ENS --> ACh triggers release of ______ and _____ proximal to bolus to stimulate smooth muscle ______ behind bolus AND ACh triggers release of ____, ____, ____ distal to bolus to stimulate smooth muscle ______ in front of bolus.
Stretch triggers mechanoreceptors.
Afferent sensory neurons --> cholenergic interneurons in ENS --> ACH triggers release of ACh and Substance P proximal to bolus to cause contraction --> ACH triggers release of NO, VIP, and ATP distal to bolus to cause relaxation .
176
Several fast-acting, short reflexes within the GI tract are mediated by _____.
ENS
177
Short reflexes within GI tract are mediated by ________.
Long reflexes involved communication through ______ to mediate _____ function.
Short: ENS
Long: need CNS to mediate ENS
178
Gastroileal reflex
1. Inc gastric activity
2. Inc motility of ileum
3. Inc movement of chyme through ileocecal sphincter
179
Illeogastric reflex
Inc in distention of ileum --> decrease in gastric motility
180
Intestino-intestinal reflex
Inc in distention of one GI segment --> relaxation throughout the rest of the intestine
181
GI Hormones tend to target _______ and ______.
Paracrine mediators (histamine, serotonin) tend to target ______ and _______.
Hormones: epithelial cells, smooth muscle
Paracrine: epithelial cells, neurons
182
Digestion and Absorption of Carbohydrates:
What enzyme begins starch digestion?
What enzyme digests starch into oligosaccharides?
What enzymes hydrolyze oligosaccharides into monosaccharides?
Salivary amylase begins starch digestion.
Pancreatic amylase digests starch --> oligosaccharides
Brush border enzymes hydrolyze oligosaccharides --> monosaccharides
183
What form of carbohydrates can be absorbed?
only monosaccharides can be absorbed
These include: glucose, galactose, and fructose
184
How does glucose cross the apical vs. basal sides of enterocytes in the journey to access the blood stream?
Glucose enters apical side of enterocytes from intestinal lumen via secondary active transport, co-transporting glucose with Na+.
Glucose exits enterocytes on basal side into interstitial fluid via GLUT2-- facilitated transport.
Absorbed monosachharides goes to blood via portal vessel to the liver.
185
Lactose intolerance is due to a ________ insufficiency.
lactase
186
Digestion of proteins begins in the ______.
Stomach
187
What enzyme begins protein digestion in the stomach?
Pepsin converts protein into polypeptides
188
Protein Digestion:
Begins in stomach when ____ digest proteins to form polypeptides.
In duodenum and jejunum:
1. ___________ cleave peptide bonds in the interior of the polypeptide. (ex: ________, ________)
2. ___________ cleave peptide bonds from the ends of the polypeptide. (ex: ________, _________)
In the enterocytes: Di- and tripeptides --> ________
Stomach: pepsin
1. Endopeptidases
-trypsin
-chymotrypsin
2. Exopeptidases
-carboxypeptidases
-aminopeptidases (brush border enzyme)
Enterocytes:
di- and tripeptides --> amino acids
189
What forms of proteins can be absorbed?
Free amino acids, Di-peptides, and Tri-peptides
190
Free amino acids enter enterocytes via _________ transport.
They are ____-transported with ____.
Amino acids exit enterocytes and enter interstitial fluid via ____________.
Secondary active transport
Co-transported with Na+
Exit via facilitated diffusion
191
Di-Peptides and Tri-peptides are absorbed by enterocytes via ________ transport using a ________ to transport them into the cytoplasm.
Secondary active transport using H+ gradient.
192
What happens when di- and tripeptides enter enterocytes?
They get hydrolyzed into amino acids
193
The arrival of lipids in the duodenum leads to increased secretion of _____.
bile
194
Two functions of bile salts
1. Emulsification- forms smaller fat molecules from big fat droplets. This increases the surface eareas for lipid-lipase contact.
2. Micelle formation- transports digested fat in micelles and moves to brush border for absorption.
195
Pancreatic lipase + colipase converts ________ to _________ + __________.
triglycerides --> fatty acids + monoglycerides
196
Pancreatic phospholipase digests _____ into ________.
phospholipids into fatty acids
197
What are the primary components of micelles?
1. Bile salts
2. Free fatty acids
3. monoglycerides
4. Phospholipids
5. Cholesterol
198
Micelles allow diffusion of constituents through ________ water layer on enterocytes ---> absorption through _____ membranes of epithelium.
unstirred water layer.
Apical membranes
199
Once the components of micelles (bile salts, free fatty acids, monoglycerides ,phospholipids, and cholesterol) cross the apical membrane and enter the enterocytes, they are resynthesized into ______ and ________.
These reformed components combine with _______ to form ________.
Resynthesized triglycerides and phospholipids. Combine with apolipoprotein to form chylomicrons.
200
Chylomicrons secrete into ___________ which enter larger _________ vessels that travel through the _______ duct and mix with venous blood at ______ and ultimately enter blood circulation.
Chylomicrons --> central lacteals --> larger lymphatic vessels --> pass through thoracic duct --> mix with venous blood at vena cava --> blood circulation
