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An Introduction to Genetics and Biochemistry > Digestion 2 > Flashcards

Digestion 2 Flashcards

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1
Q

What are the key accessory organs involved in digestion after the stomach?

A

Pancreas (enzymes + bicarbonate), liver (bile production), gallbladder (bile storage/release).

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2
Q

What happens to chyme as it enters the duodenum?

A

It is acidic (pH 2–3), contains pepsin and food fragments, and is neutralized and digested by pancreatic and bile secretions.

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3
Q

What are the two major pancreatic functions?

A

Endocrine (hormones like insulin) and exocrine (digestive secretions).

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4
Q

What do acinar and duct cells secrete?

A

Acinar: inactive digestive enzymes; Duct: bicarbonate-rich fluid.

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5
Q

Why is enzyme secretion inactive (zymogens)?

A

Prevents digestion of pancreatic tissue; activated later in the duodenum.

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6
Q

Name key pancreatic enzymes and their roles.

A

Trypsinogen (proteins), amylase (carbs), lipase (fats), nucleases (nucleic acids).

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7
Q

What stimulates pancreatic secretions neurally and hormonally?

A

Neural: Parasympathetic (ACh); Hormonal: Secretin & CCK.

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8
Q

What does secretin do?

A

Stimulates duct cells to secrete bicarbonate.

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9
Q

What does CCK do?

A

Stimulates enzyme secretion and gallbladder contraction to release bile.

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10
Q

What triggers secretin and CCK release?

A

Secretin: acid in duodenum; CCK: fats & peptides in duodenum.

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11
Q

What pH is needed for pancreatic enzymes to work?

A

Around pH 7 (neutral), achieved by bicarbonate secretion.

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12
Q

How are enzymes activated in the duodenum?

A

Trypsinogen is converted to trypsin by enterokinase, which activates other enzymes.

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13
Q

What prevents duodenal damage from acid?

A

Rapid neutralization by pancreatic bicarbonate and inactivation of pepsin.

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14
Q

What is the liver’s digestive role?

A

: Produces bile, important for fat emulsification and waste excretion

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15
Q

What is the gallbladder’s function?

A

Stores and concentrates bile, releases it when stimulated by CCK.

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16
Q

Where do bile and pancreatic secretions enter the duodenum?

A

At the sphincter of Oddi (common bile duct opening).

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17
Q

Why do bile and pancreatic secretions enter the duodenum together?

A

To neutralize chyme and begin digestion immediately and efficiently.

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18
Q

What ensures secretion happens only when food is present?

A

Local sensing in the duodenum triggers hormone release; parasympathetic nerves initiate early responses.

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19
Q

What is the enzyme that helps produce bicarbonate in duct cells?

A

Carbonic anhydrase.

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20
Q

: Where are pancreatic endocrine cells found?

A

In the islets of Langerhans (produce insulin, glucagon, somatostatin).

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21
Q

Why is it important that digestive enzymes are only activated in the duodenum?

A

Prevents autodigestion of the pancreas; ensures enzymes are active only when food is present.

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21
Q

Where is enterokinase located and what does it do?

A

On the apical membrane of duodenal mucosal cells; it activates trypsinogen to trypsin.

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22
Q

What is the cascade effect initiated by enterokinase?

A

Enterokinase activates trypsin, which then activates other pancreatic enzymes.

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23
Q

How can protease inhibitors in foods (e.g. unprocessed soy) cause harm?

A

They block trypsin, causing overproduction of enzymes, which may activate in the pancreas, leading to self-digestion.

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24
What do duodenal mucosal cells sense and secrete?
They sense acid and nutrients and release secretin and CCK to stimulate pancreatic and bile secretion.
25
Why is bile necessary for fat digestion?
It emulsifies fat, allowing enzymes like lipase to function effectively.
26
What produces bile, and where is it stored?
The liver produces bile; the gallbladder stores and concentrates it.
27
What are the liver’s two main blood supplies?
Hepatic artery (oxygenated blood) and hepatic portal vein (nutrient-rich blood from GI tract).
28
What’s unique about the liver's blood flow?
It's the only organ with dual blood input (arterial + venous) for nutrient filtering and systemic supply
29
It's the only organ with dual blood input (arterial + venous) for nutrient filtering and systemic supply
They enter the hepatic portal vein and pass through the liver for processing before reaching circulation.
30
How does the liver manage carbohydrates?
Stores glucose as glycogen; can convert carbs to fat (lipogenesis).
31
What does the liver do with fats?
Repacks them into VLDL for transport; stores some fat (risk of fatty liver).
32
How does the liver handle proteins?
Can't store them directly; regulates amino acid turnover and deaminates excess for urea formation.
33
Why doesn’t protein get stored in the liver?
Excess protein is excreted as urea unless used for muscle synthesis.
34
What happens when liver stores too much fat?
Leads to fatty liver disease (alcoholic or non-alcoholic), potentially causing steatosis and liver failure.
35
: What proteins and hormones does the liver produce?
Plasma proteins, angiotensinogen (for blood pressure), and factors for clotting.
36
What detox function does the liver perform?
Uses cytochrome P450 enzymes to degrade toxins and drugs (e.g., paracetamol).
37
Why avoid grapefruit juice with some medications?
It contains bergamottin, which inhibits P450 enzymes, reducing drug breakdown and increasing toxicity.
38
What immune cells are present in the liver?
Kupffer cells (resident macrophages) patrol and destroy pathogens in the blood.
39
Why is the liver important for immune defense?
Acts as a checkpoint for all gut-derived blood, catching pathogens before systemic spread.
40
What are liver lobules and their structure?
Hexagonal units composed of hepatocytes surrounding a central vein, with blood entering from corners.
41
How is blood filtered through the liver?
Arterial and portal blood mix in sinusoids, slowly passing by hepatocytes for processing.
42
What role do hepatocytes play?
Detect, filter, and modify substances in blood; release clean plasma into circulation.
43
Why is blood flow in the liver slow?
To maximize processing time for detoxification and nutrient managemen
44
What is the basic structural unit of the liver and how is it organized?
The liver is made of hexagonal lobules with a central vein and portal triads at each vertex (artery, portal vein, bile duct). Blood flows inward to the central vein; bile flows outward to the bile duct.
45
How do blood and bile flow in the liver lobules?
Blood flows from portal triads towards the central vein; bile flows from hepatocytes outwards through canaliculi to the bile duct.
46
What is special about liver blood flow?
Blood flows slowly and tortuously through sinusoids (cavern-like spaces) to maximize processing by hepatocytes.
47
How is bile collected in the liver?
Hepatocytes secrete bile into canaliculi — tiny channels formed between adjoining cells — that drain to bile ducts.
48
What are Kupffer cells and their function?
Kupffer cells are liver-resident macrophages lining sinusoids. They destroy pathogens and possibly clear damaged hepatocytes.
49
How does bile help in fat absorption?
Bile acids emulsify fats into micelles, increasing surface area and making fats water-soluble so lipases can break them down.
50
What allows bile acids to emulsify fat?
Bile acids are amphipathic (have hydrophilic heads and hydrophobic tails), letting them surround and stabilize fat droplets
51
What waste products are excreted in bile?
Bile excretes substances like bilirubin (from haemoglobin breakdown), which gut bacteria convert to stercobilin (makes stool brown).
52
What is the unstirred layer and why are micelles important?
The unstirred layer is a water layer near the gut wall. Fat micelles can diffuse through it, enabling fat absorption.
53
What happens in the absence of bile salts?
Fat absorption becomes very inefficient — most fats are not absorbed without bile salt–mediated micelle formation.
54
What nervous system primarily regulates the release of pancreatic secretions and bile?
The parasympathetic nervous system.
55
What hormone stimulates the pancreas to release enzyme-rich secretions?
Cholecystokinin (CCK).
56
What hormone stimulates the pancreas to release bicarbonate-rich fluid?
Secretin.
57
: What triggers the release of CCK?
Presence of fats and proteins in the duodenum.
58
: Where is bile produced and where is it stored?
Produced in the liver; stored in the gallbladder.
59
Is bile continuously produced or only on demand?
Continuously produced.
60
What are two main functions of bile?
Fat emulsification and excretion of waste products (e.g. bilirubin).
61
Where does final digestion and most absorption occur?
In the small intestine.
62
What is "contact digestion"?
: Final breakdown of nutrients occurs at the brush border enzymes on enterocytes.
63
What enzyme activates trypsinogen into trypsin?
Enterokinase.
64
What structural feature increases small intestine surface area the most?
Microvilli on enterocytes (brush border).
65
What are the folds in the mucosa of the small intestine called?
Valves of Kerckring (plicae circulares).
66
What are villi?
Finger-like projections that increase surface area for absorption.
67
What are enterocytes?
Epithelial cells on villi responsible for absorption and final digestion.
68
What is the lifespan of an enterocyte?
About 2 days.
69
What protects the small intestine from self-digestion?
Mucus secreted by goblet cells.
70
hrough what vessel do nutrients (except fats) enter the liver?
: The hepatic portal vein.
71
Where do absorbed fats go before entering circulation?
nto lacteals → lymphatic system → enter bloodstream near the subclavian vein.
72
What creates the sodium gradient that drives most nutrient absorption?
Sodium-potassium ATPase.
73
Why is the blood flow design in villi important for absorption?
It maintains a low nutrient concentration in capillaries, allowing diffusion from enterocytes.
74
What muscle layers help coordinate intestinal motility?
Longitudinal and circular muscle layers.
75
What neural structures control gut motility?
Submucosal and myenteric plexuses (enteric nervous system).
76
What are the two main types of intestinal movement?
Peristalsis (propulsion) and segmentation (mixing).

An Introduction to Genetics and Biochemistry (34 decks)

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