Digestive System Part 2 Flashcards
1
Q
How much does the liver weigh and how does it rank in size amongst body organs?
A
The liver weighs about 1.4 kg (3 lbs) and is the largest gland in the body, second in size only to the skin.
2
Q
Where is the liver located?
A
It is located below the diaphragm in the right hypochondriac region and part of the epigastric region.
3
Q
What is the function of bile and which organ produces it?
A
The liver produces bile, which is essential for the emulsification of fats.
4
Q
What is the gallbladder and where is it located?
A
A small, pear-shaped sac (7–10 cm or 3–4 inches long), located in a depression on the back of the liver, hanging from its lower front edge.
5
Q
What is the function of the gallbladder?
A
It stores bile until it is needed for digestion.
6
Q
What ducts transport bile from the liver to the duodenum?
A
The right and left hepatic ducts collect bile from the liver lobes. These merge to form the common hepatic duct, which joins the cystic duct (from the gallbladder) to form the common bile duct.
7
Q
What pancreatic duct joins the bile pathways and where do they meet?
A
The pancreatic duct, carrying pancreatic juice, meets the common bile duct at the hepatopancreatic ampulla (regulated by the sphincter).
8
Q
What role does the hepatopancreatic ampulla play?
A
It coordinates the release of bile and pancreatic juice into the duodenum, the first part of the small intestine.
9
Q
What is the joint function of bile and pancreatic juice?
A
Bile emulsifies fats, while pancreatic juice contains enzymes to digest fats, proteins, and carbohydrates, aiding efficient digestion in the small intestine.
10
Q
What regulates bile and pancreatic juice flow into the small intestine?
A
The sphincter surrounding the hepatopancreatic ampulla controls their release into the duodenum.
11
Q
What are the three major components of the liver?
A
Hepatocytes, bile canaliculi, and hepatic sinusoids.
12
Q
What are hepatocytes and how are they organized?
A
Hepatocytes are the major functional cells of the liver, organized into one-cell-thick hepatic laminae bordered by hepatic sinusoids.
13
Q
What structures are found between hepatocytes and what is their function?
A
Grooves between hepatocytes form bile canaliculi, which collect bile produced by the hepatocytes.
14
Q
What is the pathway of bile from hepatocytes to the bile duct system?
A
Bile flows from bile canaliculi → bile ductules → bile ducts → right and left hepatic ducts → common hepatic duct → common bile duct.
15
Q
What are hepatic sinusoids and what is their role?
A
Hepatic sinusoids are highly permeable blood capillaries located between rows of hepatocytes that deliver blood into the central vein.
16
Q
What happens to blood after it passes through the central vein?
A
Blood flows into hepatic veins and then into the inferior vena cava.
17
Q
What are stellate reticuloendothelial cells and what do they do?
A
Also known as Kupffer cells, these are fixed macrophages in hepatic sinusoids that help remove debris and pathogens from the blood.
18
Q
What structures make up the portal triad in the liver?
A
The bile duct, hepatic artery branch, and hepatic vein branch.
19
Q
What is the hepatic acinus, and how is it shaped?
A
The hepatic acinus is the basic unit of the liver, shaped like an oval that connects parts of two neighboring liver lobules.
20
Q
What defines the short and long axes of the hepatic acinus?
A
Short axis: Along the portal triad branches.
Long axis: Between central veins of neighboring lobules.
21
Q
What are the three zones of the hepatic acinus, and how are they organized?
A
Zone 1: Closest to the portal triad, receives the best oxygen and nutrients, regenerates first, and processes glucose.
Zone 2: Intermediate between zones 1 and 3.
Zone 3: Farthest from the portal triad, receives the least oxygen, affected first by low circulation, and prone to fat buildup.
22
Q
What are the three layers of the gallbladder wall?
A
Inner layer: Folds (rugae) of columnar epithelium for water and ion absorption.
Middle layer: Smooth muscle that contracts to release bile.
Outer layer: Covered by visceral peritoneum.
23
Q
What is the main function of the gallbladder?
A
To store and concentrate bile (up to 10 times) for the digestion of fats in the small intestine.
24
Q
What are the two sources of blood flow to the liver?
A
The hepatic artery, carrying oxygenated blood from the heart, and the hepatic portal vein, bringing deoxygenated, nutrient-rich blood from the digestive organs.
25
What happens in the hepatic sinusoids?
Oxygenated blood from the hepatic artery and deoxygenated, nutrient-rich blood from the portal vein mix in the hepatic sinusoids, which are specialized capillaries in the liver.
26
How do hepatocytes interact with the blood in the liver?
Hepatocytes absorb oxygen, nutrients, and toxins from the mixed blood in the sinusoids for metabolism, storage, synthesis, detoxification, and then release important products back into the blood.
27
Describe the blood drainage pathway from the liver.
After circulating through the hepatic sinusoids, the blood collects in the central vein of each liver lobule, then flows into larger hepatic veins, which drain into the inferior vena cava, eventually returning blood to the right atrium of the heart.
28
What is the key filtering function of the liver?
The liver acts as a filter and processor—metabolizing toxins, drugs, and other substances while ensuring that useful nutrients and products are distributed to the rest of the body.
29
Why is the liver a critical site for processing substances from the digestive system?
Since the blood from the digestive organs passes through the liver via the portal vein, it carries nutrients, toxins, drugs, and even microbes that the liver metabolizes, detoxifies, or redistributes.
30
How does the dual blood supply (hepatic artery and portal vein) benefit liver function?
The hepatic artery provides vital oxygen necessary for metabolic functions, while the portal vein delivers nutrient-rich blood, allowing hepatocytes to efficiently process and balance energy production, storage, and detoxification.
31
What is a clinical significance of the liver’s blood supply pattern?
Because blood from the digestive system, which may contain cancer cells from primary tumors, is processed by the liver, it can serve as a prime site for metastasis from cancers originating in digestive organs.
32
What is the role of the liver in bilirubin excretion?
The liver excretes bilirubin, which is derived from heme.
33
What do bile salts do, and where are they synthesized?
Bile salts, synthesized from bile acids, aid in the emulsification of fats.
34
What does the liver store?
The liver stores bile, vitamins, and nutrients (e.g., glucose and triglycerides) for later use.
## Footnote
The hepatopancreatic ampulla regulates bile release between meals.
35
How does the liver contribute to carbohydrate, lipid, and protein metabolism?
It converts and/or stores glucose, triglycerides, and other nutrients, and produces plasma proteins.
36
How does the liver process drugs and hormones?
It detoxifies alcohol, excretes drugs (e.g., penicillin, erythromycin) into bile, and alters or excretes thyroid and steroid hormones.
37
What role do Kupffer cells play in the liver?
Kupffer cells perform phagocytosis, engulfing aged red blood cells (RBCs), white blood cells (WBCs), and certain bacteria.
38
How is the liver involved in vitamin D activation?
The liver works with the skin and kidneys to activate vitamin D.
39
What is the primary function of the small intestine?
Most nutrient digestion and absorption occur in the small intestine.
40
How does the small intestine maximize surface area for digestion and absorption?
Through circular folds, intestinal villi, and microvilli.
41
How long is the small intestine in a living person?
About 5 m (16 ft).
42
Where does the small intestine start and end?
It starts at the pyloric sphincter (stomach) and ends at the ileocecal sphincter (large intestine).
43
What are the three regions of the small intestine?
Duodenum, jejunum, and ileum.
44
What is the duodenum, and how long is it?
The duodenum is the shortest part (~25 cm or 10 in), 'C-shaped,' and begins at the pyloric sphincter.
45
What happens in the jejunum?
It is the middle part (~1 m or 3 ft) where most nutrient absorption occurs.
46
What is the ileum, and how does it connect to the large intestine?
The ileum is the longest section (~2–3 m or 6–10 ft) and connects to the large intestine at the ileocecal sphincter, which regulates the flow of contents.
47
What key features make the small intestine efficient for digestion and absorption?
Its length, circular folds, villi, and microvilli provide a massive surface area for nutrient breakdown and absorption.
48
What are the two types of muscle movements in the small intestine?
Segmentation causes localized mixing of chyme with digestive juices and brings it into contact with mucosa for absorption. Peristalsis propels chyme forward through the intestine.
49
What digestive processes are completed in the small intestine?
Carbohydrates are broken down into simple sugars (glucose, fructose, galactose). Proteins are broken down into amino acids. Lipids are emulsified and digested into fatty acids and glycerol. Nucleic acids are broken down into nucleotides.
50
What percentage of nutrients and water are absorbed in the small intestine?
About 90%.
51
What structural features of the small intestine enhance absorption?
Circular folds slow down chyme movement and increase surface area. Villi are finger-like projections containing capillaries and lacteals for nutrient absorption. Microvilli form the brush border, further increasing surface area and releasing digestive enzymes.
52
What are the four layers of the small intestine, and their roles?
Mucosa contains villi and microvilli to maximize absorption. Submucosa contains glands, blood vessels, and nerves for support. Muscularis consists of smooth muscle layers enabling segmentation and peristalsis. Serosa is the outer layer that protects and anchors the intestine.
53
What is the purpose of segmentation in the small intestine?
To mix chyme with digestive juices and help it contact the intestinal walls for absorption.
54
What process propels food through the small intestine?
Peristalsis.
55
How does the small intestine differ structurally from other parts of the digestive system?
While it shares the same four layers, it is modified with structures like villi, microvilli, and circular folds to optimize digestion and absorption.
56
What are the four layers of the small intestine wall?
Mucosa, Submucosa, Muscularis, Serosa
57
What are the three sublayers of the mucosa?
Epithelium, Lamina propria, Muscularis mucosae
58
What specialized cells are found in the epithelium of the mucosa, and what are their functions?
Absorptive cells: Contain microvilli for nutrient absorption and release brush-border enzymes.
Goblet cells: Secrete mucus for lubrication and protection.
Paneth cells: Secrete lysozyme and perform phagocytosis for microbial regulation.
Enteroendocrine cells: Secrete hormones (e.g., secretin, CCK, GIP) to regulate digestion.
59
What structures are found in the lamina propria?
Blood capillaries and lacteals (lymphatic vessels) for nutrient transport.
MALT (mucosa-associated lymphatic tissue), including solitary lymphatic nodules and Peyer’s patches for immune defense.
60
What does the muscularis mucosae do?
It facilitates movement of the mucosa, improving contact between chyme and the absorptive surfaces.
61
What is the composition and function of the submucosa?
Composed of areolar connective tissue.
Contains blood vessels, lymph vessels, and the submucosal plexus, which regulates intestinal secretions and blood flow.
62
What smooth muscle layers form the muscularis, and what are their roles?
Inner circular layer: Narrows the lumen (segmentation).
Outer longitudinal layer: Shortens the intestine (peristalsis).
These layers work together to mix and propel chyme.
63
What is the role of the myenteric plexus in the muscularis?
It coordinates the muscular contractions for segmentation and peristalsis.
64
What is the serosa, and what is its role?
The serosa (visceral peritoneum) is the outermost layer that protects the small intestine and reduces friction as it moves in the abdominal cavity.
65
What structural features maximize absorption in the small intestine?
Circular folds: Slow chyme movement and increase absorption time.
Villi: Finger-like projections with capillaries and lacteals for nutrient transport.
Microvilli: Brush-border structures with enzymes to increase absorption surface area.
66
What are the brush-border enzymes, and where are they located?
They are digestive enzymes found on the microvilli of absorptive cells, aiding in the final stages of nutrient breakdown.
67
What are enteroendocrine cells, and where are they found?
Enteroendocrine cells are hormone-producing cells located in the epithelium of the small intestine.
68
What do S cells secrete, and in response to what?
S cells secrete secretin in response to acidic chyme entering the duodenum.
69
What are the functions of secretin?
Stimulates the pancreas to release bicarbonate-rich juice to neutralize stomach acid.
Slows gastric emptying.
Reduces stomach acid secretion.
70
What hormone is secreted by K cells, and when is it released?
K cells secrete glucose-dependent insulinotropic peptide (GIP) when glucose, fats, or proteins are present in the chyme.
71
What is the function of glucose-dependent insulinotropic peptide (GIP)?
It stimulates insulin secretion from the pancreas, helping the body absorb and store nutrients.
72
What hormone is secreted by CCK cells, and what triggers its release?
CCK cells secrete cholecystokinin (CCK) in response to fats and proteins in the chyme.
73
What are the functions of cholecystokinin (CCK)?
Stimulates the gallbladder to release bile for fat emulsification.
Triggers the release of pancreatic enzymes to digest proteins, fats, and carbohydrates.
Slows gastric emptying, giving the intestine more time for digestion and absorption.
74
What are circular folds?
Circular folds, or plicae circulares, are large folds of the mucosa and submucosa in the inner surface of the small intestine.
75
What is the primary function of circular folds?
Increase surface area for absorption.
## Footnote
Slow down and spiral the movement of chyme, allowing better mixing with digestive juices and nutrient absorption.
76
What are villi?
Villi are finger-like projections of the mucosa that increase surface area and absorb nutrients into the bloodstream and lymph.
77
What structures are inside each villus?
Capillaries: Absorb glucose and amino acids into the bloodstream.
## Footnote
Lacteal (lymphatic vessel): Absorbs fats and transports them into the lymph system.
78
What are microvilli?
Microvilli are tiny projections on the apical membrane of absorptive cells covering the villi, forming the 'brush border.'
79
What is the function of microvilli?
Further increase surface area for absorption.
## Footnote
Contain brush-border enzymes that finalize nutrient breakdown for absorption into the cells.
80
How do circular folds, villi, and microvilli work together?
Circular folds: Slow chyme movement for efficient digestion and absorption.
## Footnote
Villi: Absorb nutrients and transport them to the bloodstream or lymph.
## Footnote
Microvilli: Finalize food breakdown and absorb the smallest molecules into the cells.
81
What is the brush border?
A fuzzy line formed by microvilli on absorptive cells, containing enzymes that help digest food for absorption.
82
What is intestinal juice, and what does it contain?
Intestinal juice is a clear, yellow fluid containing water, mucus, and is slightly alkaline (pH 7.6) due to bicarbonate ions.
83
What is the purpose of intestinal juice?
Creates a liquid medium for chyme. Helps nutrients contact absorptive cells for easier absorption. Works with pancreatic juice to support digestion.
84
What is the brush border, and where is it located?
The brush border is the surface of microvilli on absorptive cells in the villi of the small intestine.
85
What do brush-border enzymes do?
They break down food on the surface of microvilli, right where nutrients are absorbed.
86
Which brush-border enzymes digest carbohydrates, and what are their specific functions?
α-dextrinase: Breaks down long carbohydrate chains. Maltase: Converts maltose into glucose. Sucrase: Breaks sucrose into glucose and fructose. Lactase: Breaks lactose into glucose and galactose.
87
Which brush-border enzymes digest proteins?
Aminopeptidase and Dipeptidase break proteins into amino acids.
88
Which enzymes digest nucleotides (DNA/RNA)?
Nucleosidase and Phosphatase break nucleotides into their simplest components.
89
What is the role of sloughed-off absorptive cells in digestion?
Sloughed-off cells release enzymes into the lumen, helping to further digest nutrients in the chyme.
90
What are the main roles of intestinal juice and brush-border enzymes in the small intestine?
Intestinal juice: Creates a fluid, alkaline environment for digestion. Brush-border enzymes: Finalize the breakdown of carbohydrates, proteins, and nucleic acids for absorption.
91
How does the small intestine ensure efficient digestion and absorption?
Through intestinal juice, digestion by brush-border enzymes, and additional enzyme release from sloughed-off absorptive cells. This ensures nutrients are broken down and absorbed efficiently into the bloodstream or lymph system.
92
What are the two main types of movements in the small intestine?
Segmentation and Peristalsis
93
What is segmentation, and what is its primary function?
Segmentation involves localized, mixing contractions that bring food into contact with the mucosa for absorption.
94
When does segmentation occur in the small intestine?
It occurs in portions of the small intestine distended by large volumes of chyme.
95
What is peristalsis in the small intestine?
Peristalsis involves propulsive contractions, part of the migrating motility complex, to move food forward.
96
When does peristalsis occur in the small intestine?
After most of the meal is absorbed, when the small intestine is less distended, and segmentation stops.
97
Where does the migrating motility complex begin, and how does it move?
It begins in the lower portion of the stomach and moves very slowly through the small intestine.
98
What are the main nutrients broken down in the small intestine?
Carbohydrates, Proteins, Lipids, Nucleic Acids.
99
What are carbohydrates broken into?
Simple sugars (glucose).
100
What are proteins broken into?
Amino acids.
101
What are lipids broken into?
Fatty acids and monoglycerides.
102
What are nucleic acids broken into?
Nucleotides.
103
Which enzyme begins breaking down carbohydrates, and where does this occur?
Pancreatic amylase, which starts breaking starch into smaller sugars.
104
Which brush-border enzymes complete carbohydrate digestion, and what do they do?
α-dextrinase: Breaks smaller carbohydrate chains.
Sucrase: Breaks sucrose into glucose and fructose.
Lactase: Breaks lactose into glucose and galactose.
Maltase: Breaks maltose into glucose.
105
Which pancreatic enzymes digest proteins, and what is their role?
Trypsin and chymotrypsin: Break proteins into smaller pieces.
106
Which brush-border enzymes complete protein digestion, and how do they function?
Aminopeptidase: Removes amino acids from the front end.
Carboxypeptidase: Removes amino acids from the back end.
Dipeptidase: Splits two-amino-acid chains into single amino acids.
107
What role does bile play in lipid digestion?
Bile, from the liver, emulsifies fats into tiny droplets to increase surface area for enzyme action.
108
Which enzyme breaks down lipids, and what does it produce?
Pancreatic lipase, which breaks triglycerides into fatty acids and monoglycerides.
109
Which brush-border enzymes digest nucleic acids, and what are their products?
Nucleosidases and phosphatases break DNA and RNA into:
Pentose sugars
Phosphates
Nitrogen bases
110
What are the final breakdown products of major nutrients in the small intestine?
Carbohydrates → Glucose (simple sugars).
Proteins → Amino acids.
Lipids → Fatty acids and monoglycerides.
Nucleic Acids → Pentose sugars, phosphates, and nitrogen bases.
111
How do enzymes from the pancreas and brush-border enzymes work together?
Pancreatic enzymes start digestion (breaking food into smaller pieces), while brush-border enzymes complete digestion by breaking food into absorbable forms.
112
What is the purpose of digestion?
To break food into forms that can be absorbed into the blood and lymph vessels for distribution throughout the body.
113
What are the absorbable forms of nutrients?
Monosaccharides (from carbohydrates), amino acids and peptides (from proteins), fatty acids, glycerol, and monoglycerides (from lipids).
114
How does absorption occur in the small intestine?
Through diffusion, facilitated diffusion, osmosis, and active transport.
115
How much nutrient absorption occurs in the small intestine?
About 90%, while the stomach and large intestine handle the remaining 10%.
116
How are glucose and galactose absorbed?
Mechanism: Secondary active transport coupled with sodium (Na⁺), using a sodium-glucose co-transporter at the apical surface.
## Footnote
Exit: Via facilitated diffusion into blood capillaries.
117
How is fructose absorbed?
Through facilitated diffusion across both the apical and basolateral membranes, entering blood capillaries in the villus.
118
How are individual amino acids absorbed?
Mechanisms: Active transport or secondary active transport coupled with Na⁺.
## Footnote
Exit: They diffuse into blood capillaries.
119
How are dipeptides and tripeptides absorbed?
Mechanism: Secondary active transport coupled with H⁺ ions. Intracellular process: Broken down into amino acids inside the epithelial cells.
## Footnote
Exit: Amino acids diffuse into the blood capillaries.
120
How are small short-chain fatty acids absorbed?
Via simple diffusion directly across the cell membrane, entering blood capillaries.
121
How are large short-chain fatty acids, long-chain fatty acids, and monoglycerides absorbed?
In the lumen: Form micelles with bile salts for transport to the epithelial cells. In the cells: Reassembled into triglycerides and combined with lipoproteins to form chylomicrons.
## Footnote
Exit: Chylomicrons leave the cells and enter lacteals (lymphatic vessels in the villi).
122
What are chylomicrons, and how are they transported?
Lipid-protein complexes formed in epithelial cells for transporting reassembled triglycerides. They are carried through lacteals and enter the circulatory system via the thoracic duct, draining into the left internal jugular and subclavian veins.
123
What are the key transport mechanisms for nutrient absorption?
Carbohydrates: Secondary active transport (glucose/galactose) or facilitated diffusion (fructose). Proteins: Active or secondary active transport, diffusion. Lipids: Simple diffusion, micelle formation, and chylomicron transport.
124
Where do nutrients go after absorption?
Glucose, amino acids, and small fatty acids: Enter blood capillaries. Lipids (as chylomicrons): Enter the lymphatic system through lacteals.
125
In what form are carbohydrates absorbed?
As monosaccharides.
126
What percentage of dietary carbohydrates is absorbed?
Normally, all dietary carbohydrates digested are absorbed.
127
How does fructose move across the apical membrane?
Via facilitated diffusion.
128
How do glucose and galactose move across the apical membrane?
Mechanism: Secondary active transport.
Coupling: Coupled to the active transport of sodium (Na⁺) via a symporter.
129
How do all monosaccharides exit the epithelial cell at the basolateral membrane?
They move via facilitated diffusion.
130
Where do monosaccharides go after exiting the basolateral membrane?
Into the capillaries of the villi.
131
What is the mechanism for each monosaccharide's apical and basolateral movement?
Fructose: Facilitated diffusion across both apical and basolateral membranes.
Glucose and Galactose: Secondary active transport (apical) and facilitated diffusion (basolateral).
132
Where do absorbed monosaccharides eventually end up?
In the bloodstream via the capillaries in the villi.
133
Where are most proteins absorbed in the small intestine?
Primarily in the duodenum and jejunum.
134
What percentage of proteins are digested and absorbed?
About 95–98%.
135
How are various amino acids absorbed?
Through different transporters, depending on their type.
136
How do individual amino acids enter absorptive cells?
Via active transport.
## Footnote
Some use Na⁺-dependent secondary active transport. Others use active transport by themselves.
137
How are dipeptides and tripeptides absorbed?
Through a symporter that combines them with H⁺ ions.
## Footnote
Inside the absorptive cell, they are hydrolyzed into amino acids.
138
How do amino acids exit the absorptive cells into the villus capillaries?
By diffusion.
139
What happens after amino acids are absorbed into the epithelial cells?
Dipeptides and tripeptides are broken into amino acids within the cell. Amino acids then diffuse out of the cell into the blood capillary of the villus.
140
Where do the absorbed amino acids eventually go?
Into the bloodstream, for transport to the rest of the body.
141
What mechanism is used for dipeptides and tripeptides to enter epithelial cells?
A symporter links them with H⁺ ions during transport.
142
How are most dietary lipids absorbed in the small intestine?
They are absorbed by simple diffusion as monoglycerides and fatty acids.
143
What percentage of lipids do adults absorb in the small intestine?
Adults absorb approximately 95% of lipids, while newborns absorb about 85% due to lower bile production.
144
What characterizes short-chain fatty acids?
They contain fewer than 10–12 carbon atoms. Despite being hydrophobic, their smaller size and greater water solubility allow them to directly diffuse through absorptive cells into the blood capillaries.
145
Why do long-chain fatty acids and monoglycerides require bile salts for absorption?
Because of their poor water solubility, bile salts increase their water solubility by surrounding the lipid molecules.
146
What role do bile salts play in lipid absorption?
Bile salts, due to their amphipathic nature, surround long-chain fatty acids and monoglycerides to form micelles, making these hydrophobic molecules more water-soluble.
147
What are micelles and how do they form?
Micelles are spherical structures (2–10 nm in diameter) formed by bile salts. They form because bile salts have both hydrophobic and hydrophilic regions that allow them to encapsulate lipids.
148
How do micelles function in the absorption of lipids?
They transport lipids (including fat-soluble vitamins A, D, E, K, and cholesterol) from the intestinal lumen to the brush border of absorptive cells.
149
What happens to fatty acids and monoglycerides once they enter the absorptive cells?
Inside the cells, they recombine to form triglycerides, which then aggregate with phospholipids and cholesterol and are coated with a protein to form chylomicrons.
150
What are chylomicrons, and why are they important in lipid transport?
Chylomicrons are lipid-protein complexes (approximately 80 nm in diameter) that package triglycerides for transport. They exit absorptive cells via exocytosis and enter the lacteals of the lymphatic system.
151
Once chylomicrons enter the lymphatic system, how do they reach the bloodstream?
They eventually reach the systemic circulation through the thoracic duct, which drains into the left internal jugular and left subclavian veins.
152
What additional molecules do micelles transport besides long-chain fatty acids and monoglycerides?
Micelles also transport fat-soluble vitamins (A, D, E, K) and cholesterol.
153
How are electrolytes absorbed in the gastrointestinal tract?
They are absorbed from both digestive secretions and food.
154
How is sodium (Na⁺) absorbed in the intestines?
Sodium is actively transported via Na⁺/K⁺ pumps.
155
How are chloride and bicarbonate ions absorbed?
Chloride and bicarbonate follow passively once sodium is transported.
156
What stimulates the absorption of calcium (Ca²⁺) in the intestines?
Calcitriol (the active form of vitamin D) stimulates calcium absorption.
157
Which other electrolytes are absorbed through active transport?
Iron, potassium, magnesium, and phosphate ions are absorbed via active transport.
158
How are fat-soluble vitamins (A, D, E, K) absorbed?
They are absorbed with lipids in micelles via simple diffusion.
159
How are water-soluble vitamins (B vitamins and vitamin C) absorbed?
They are absorbed via simple diffusion.
160
How is vitamin B12 absorbed in the intestines?
Vitamin B12 is absorbed in the ileum via active transport when it is bound to intrinsic factor produced in the stomach.
161
How much fluid enters the intestine daily, and what are its sources?
About 9.3 liters per day – approximately 2.3 liters from food and drink and 7 liters from digestive secretions.
162
How is water absorbed in the intestines?
The small intestine absorbs about 8.3 liters. The large intestine absorbs approximately 0.9 liters. Only about 0.1 liters are excreted in feces. Water absorption occurs via osmosis, which is tightly linked to the absorption of electrolytes and nutrients to maintain osmotic balance with the blood.
163
Can water move in and out of absorptive cells?
Yes, water movement adjusts to maintain osmotic balance with the blood through osmosis.
164
What mechanisms are involved in the absorption of nutrients and electrolytes?
Active transport: For sodium, iron, potassium, magnesium, phosphate, and vitamin B12 (with intrinsic factor). Passive transport (diffusion): For chloride, bicarbonate, fat-soluble vitamins in micelles, and water-soluble vitamins. Osmosis: Governs water absorption, maintaining balance with electrolytes and nutrients.
165
What are the main regions of the large intestine?
Cecum, Colon, Rectum, Anal canal
166
What is the mesocolon, and what is its function?
The mesocolon is a double layer of the peritoneum that attaches the large intestine to the posterior abdominal wall, helping to anchor and support it.
167
What is the anatomical connection between the large intestine and the small intestine?
The large intestine begins at the cecum, which is connected to the small intestine at the ileocecal junction.
168
What are the subdivisions of the colon?
Ascending colon, Transverse colon, Descending colon, Sigmoid colon
169
Where is the cecum located?
It is the pouch-like first segment of the large intestine, found in the lower right abdomen.
170
What structure is attached to the cecum?
The vermiform appendix, a small tube-like structure with immune-related functions.
171
What is the colon?
The colon is a long tube that joins with the cecum and is divided into four parts: the ascending, transverse, descending, and sigmoid colon.
172
What is the path and characteristic of the Ascending Colon?
It travels up the right side of the abdomen, is retroperitoneal, and ends at the right colic (hepatic) flexure near the liver.
173
How is the Transverse Colon positioned and where does it end?
It crosses the abdomen from right to left and ends at the left colic (splenic) flexure near the spleen.
174
Describe the Descending Colon.
It travels down the left side of the abdomen and is also retroperitoneal.
175
What are the characteristics of the Sigmoid Colon?
It is S-shaped, starts near the left iliac crest, moves medially, and ends at the rectum.
176
What role do haustra play in the colon?
The colon is segmented into small pouches called haustra. Through haustral churning, each segment contracts individually to mix contents and facilitate water absorption.
177
How does peristalsis function in the colon?
Peristalsis involves waves of muscle contractions that move the contents gradually through the colon.
178
What is mass peristalsis and when does it occur?
Mass peristalsis is a more powerful contraction that occurs 3-4 times a day, often triggered after eating, and it pushes large quantities of contents into the rectum.
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What functions do the beneficial bacteria in the colon serve?
They engage in protein metabolism, further process amino acids, and synthesize essential vitamins such as certain B vitamins and vitamin K.
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What substances are absorbed in the colon?
The colon absorbs remaining water, electrolytes (such as sodium and chloride), and vitamins produced by bacteria.
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How does feces form in the colon?
As water is absorbed, the indigestible substances, dead cells, waste products, and bacteria compact to form feces, which are stored in the rectum until elimination.
182
Describe the process of defecation.
Defecation is the process of expelling feces from the body through the anus and involves both involuntary and voluntary control.
183
What is the primary role of the colon in the digestive system?
The colon’s primary roles include recovering water and electrolytes, forming stool, and ensuring that waste products and bacteria are safely eliminated.
184
What are the three components of the colon's mucosa?
The mucosa consists of the epithelium, lamina propria, and muscularis mucosae.
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How does the colon’s mucosa differ from that of the small intestine?
The colon has fewer adaptations, such as villi, to increase its surface area and is primarily structured to absorb water and electrolytes rather than nutrients.
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What is the composition of the submucosa in the colon?
The submucosa is composed of areolar connective tissue that provides structural support and houses blood and lymphatic vessels.
187
What are the two muscle layers of the colon's muscularis?
The muscularis has an inner circular muscle layer and an outer longitudinal muscle layer concentrated into three distinct bands called the teniae coli.
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What role do the teniae coli play in colon function?
The teniae coli contract to produce haustra, which help mix and move the colonic contents along.
189
What is the outermost layer of the colon and its associated structures?
The outer layer is the serosa, which is the visceral peritoneum, containing small fat pouches called omental appendices.
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What is the key takeaway regarding the histology of the colon?
The colon’s histological structure is optimized for absorbing water and electrolytes, concentrating waste into feces, and facilitating movement for elimination.
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What glands are present in the mucosa of the colon?
Intestinal glands (found in the epithelium).
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What types of cells are found in the intestinal glands of the mucosa, and what are their functions?
Absorptive cells: Responsible for the absorption of water.
Goblet cells: Produce lubricating mucus to aid in stool passage.
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What structures are found in the lamina propria of the mucosa?
Lymphatic nodules
Lymphatic vessels
Blood capillaries
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What is the composition of the submucosa in the colon?
The submucosa is made up of areolar connective tissue, which provides structural support and facilitates blood and lymphatic flow.
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What is the primary role of the mucosa's absorptive cells?
To absorb water, which aids in concentrating waste into feces.
196
What is the function of the goblet cells in the colon’s mucosa?
To produce mucus, which lubricates the colon and assists in the smooth movement of fecal matter.
197
How does the lamina propria support immune function in the colon?
The lymphatic nodules provide immune protection against harmful microorganisms in the colon contents.
198
What role does gastrin play in colon motility?
Gastrin relaxes the ileocecal sphincter after a meal, facilitating the movement of chyme from the ileum into the colon.
199
What is haustral churning, and how does it function?
Haustral churning is the process where the colon’s haustra contract when distended, squeezing their contents onward. This mixing action assists in further water absorption.
200
How does peristalsis in the colon differ from earlier portions of the GI tract?
In the colon, peristalsis involves propulsive contractions that occur at a slower rate compared to the small intestine, allowing more time for water and electrolyte absorption.
201
What is mass peristalsis and when does it occur?
Mass peristalsis is a strong, coordinated contraction that begins in the transverse colon and rapidly drives contents into the rectum, often triggered as part of the gastrocolic reflex after food enters the stomach.
202
What role do bacteria play in the final stages of digestion in the colon?
Bacteria break down remaining food substances, further ferment carbohydrates and proteins into amino acids or simpler compounds, and participate in the decomposition of bilirubin, which gives feces its color.
203
Which vitamins are produced by bacterial action in the colon?
Bacterial synthesis contributes to the production of certain B vitamins and vitamin K, which are absorbed and used in normal metabolism.
204
How are bacterial products absorbed in the colon?
Bacterial products, including synthesized vitamins, are absorbed along with water and electrolytes, contributing to overall nutrient balance.
205
What are the main substances absorbed by the colon?
The colon primarily absorbs water, electrolytes (such as sodium and chloride), and some vitamins, which concentrate the intestinal contents into solid or semi-solid feces.
206
How critical is the water reabsorption in the colon?
Water reabsorption is essential for maintaining water balance. Out of 0.5–1.0 L of water entering the large intestine, nearly all is reabsorbed (only 100–200 mL remains), primarily via osmosis.
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What is the composition of feces?
Feces consist of water, inorganic salts, sloughed-off epithelial cells, bacteria, bacterial decomposition products, and any undigested portions of food.
208
How does the body detect the need to defecate?
Feces enter the rectum, causing the rectal walls to stretch. Stretch receptors in the rectal wall sense this distension and are activated.
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Where do stretch receptors in the rectum send signals?
Stretch receptors send sensory impulses to the sacral spinal cord, notifying the nervous system of the rectum filling.
210
What happens after the brain receives signals from the rectum?
The brain and spinal cord send motor impulses via parasympathetic nerves to the descending colon and sigmoid colon to push waste further, and to the rectum and anus to trigger muscle contractions.
211
How do the rectal muscles respond during defecation?
Rectal muscles contract longitudinally, shortening the rectum and increasing pressure to push feces downward.
212
What additional pressure helps expel feces during defecation?
Contractions of the abdominal muscles and diaphragm voluntarily increase rectal pressure.
213
How do the anal sphincters coordinate during defecation?
The internal anal sphincter relaxes automatically (via parasympathetic nerve control), while the external anal sphincter relaxes voluntarily, allowing control over defecation timing.
214
Why is dietary fiber essential for the defecation reflex?
Fiber adds bulk to stools, making them easier to push. It promotes a healthy colon and prevents issues like constipation that could strain the process.
215
What is the defecation reflex?
A coordinated physiological response involving sensing, signaling, muscle contractions, and regulation of internal and external sphincters to eliminate waste effectively.
216
What structural and muscular actions are central to the defecation process?
Detection: Stretch receptors sense rectal wall distension. Signaling: Parasympathetic nerves stimulate rectal muscles and anal sphincters. Expulsion: Abdominal pressure and relaxation of sphincters work together to expel feces.
217
What are the three main phases of digestion?
Cephalic phase: Prepares the digestive system for food.
Gastric phase: Breaks down food in the stomach.
Intestinal phase: Processes food in the small intestine.
218
When does the cephalic phase occur, and what triggers it?
It begins before you eat and is triggered by the sight, smell, taste, or thought of food.
219
What happens during the cephalic phase?
Nerves are activated (cerebral cortex, hypothalamus, brainstem). Gastric secretions (acid and enzymes) and motility begin. Prepares the stomach and mouth for digestion.
220
When does the gastric phase start, and what triggers it?
Begins when food enters the stomach. Triggered by stretch receptors (detect stomach expansion) and chemoreceptors (detect pH changes).
221
How does the stomach break down food during the gastric phase?
Gastric juice (acid, enzymes, and mucus) breaks down food. Muscles churn and mix food into a semi-liquid called chyme.
222
What is the role of the hormone gastrin?
Gastrin stimulates secretion of gastric juice, enhances muscle contractions for food mixing, and regulates the movement of food by tightening the lower esophageal sphincter and relaxing the pyloric sphincter to allow chyme to move to the small intestine.
223
What is the feedback mechanism in the gastric phase?
As food breaks down and pH normalizes: Signals reduce acid production. Gastric activity slows to avoid overactivity.
224
When does the intestinal phase begin, and what triggers it?
Starts as chyme enters the small intestine.
225
What neural and hormonal controls are involved in the intestinal phase?
Neural (enterogastric reflex): Slows stomach emptying to allow digestion in the intestines. Hormones: Cholecystokinin (CCK): Stimulates enzyme and bile release. Secretin: Stimulates neutralization of stomach acid.
226
What is the purpose of the intestinal phase?
Focuses on absorption of nutrients. Modulates the digestive pace for efficiency.
227
What are the primary goals of the gastric phase?
Regulate stomach acid (pH) levels. Promote stomach motility to mix food into chyme. Deliver food gradually to the small intestine.
228
How do neural and hormonal signals function in the gastric phase?
Neural signals: Stretch and chemoreceptors stimulate muscle contractions and restore low pH by promoting acid secretion. Hormonal signals (gastrin): Induce acid secretion and strengthen stomach contractions for food breakdown.
229
What ensures the gastric phase is balanced?
A feedback loop slows gastric activity as digestion progresses, avoiding excessive acid or overactivity.
230
How does the digestive system support the integumentary system?
The small intestine absorbs vitamin D, which the skin and kidneys modify to produce calcitriol. Excess dietary calories are stored as triglycerides in adipose cells in the dermis and subcutaneous layer.
231
How does the digestive system help maintain skeletal health?
The small intestine absorbs dietary calcium and phosphorus salts, which are needed to build bone extracellular matrix.
232
What is the digestive system’s role in supporting muscles?
The liver converts lactic acid (produced by muscles during exercise) into glucose.
233
How does the digestive system support the nervous system?
Gluconeogenesis in the liver provides glucose for neurons. Digestion and carbohydrate absorption contribute glucose needed for ATP production in the brain.
234
What roles does the digestive system play in the endocrine system?
The liver inactivates some hormones, ending their activity. Pancreatic cells release insulin and glucagon to regulate blood sugar. Cells in the stomach and small intestine secrete hormones to regulate the digestive process. The liver produces angiotensinogen, involved in blood pressure regulation.
235
How does the digestive system impact the cardiovascular system?
The GI tract absorbs water, which maintains blood volume and iron needed for hemoglobin synthesis. The liver synthesizes most plasma proteins and excretes bilirubin from hemoglobin breakdown in feces.
236
How does the digestive system contribute to immunity?
Gastric acidity destroys most bacteria and toxins in food. Lymphatic nodules in the GI tract’s mucosa (MALT) destroy microbes.
237
How does the digestive system assist the respiratory system?
Abdominal organ pressure against the diaphragm helps expel air quickly during forced exhalation.
238
What is the digestive system’s role in supporting the urinary system?
Water absorbed by the GI tract provides water required to produce and excrete urine.
239
How does the digestive system support reproduction?
Digestion and absorption provide nutrients, including fats, which are necessary for: Development of reproductive structures, Production of gametes (oocytes and sperm), Fetal growth and development during pregnancy.
240
What are the overall contributions of the digestive system to the body?
Breaks down dietary nutrients into forms used to produce ATP and build body tissues. Absorbs water, minerals, and vitamins essential for growth and function. Eliminates wastes as feces.
