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WEEK 8: 8.2 Function of the digestive system Flashcards

1
Q

Why is digestive system dysfunction important?

A

Diarrhoeal diseases is the 5th leading cause of death in the world according to WHO

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2
Q

What is gastroenteritis?

A

Diarrhoea, with or without abdominal pain with vomiting and fever

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3
Q

What is the primary function of the digestive system?

A

to transfer nutrients, water and electrolytes from food into the internal environment

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4
Q

Why must food be broken down biochemically by digestion?

A

So that molecules from food can be absorbed

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5
Q

What are the accessory digestive organs of the digestive tract?

A

salivary glands, liver, gallbladder, pancreas

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6
Q

What are the main organs of the digestive tract?

A

Mouth, pharynx & Oesophagus, stomach, small intestine, large intestine

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7
Q

What is the function of the mouth?

A

Mastication (breaking food into smaller pieces)

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8
Q

What is the function of the pharynx and oesophagus?

A

swallowing and transporting food from the mouth to the stomach

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9
Q

What is the function of the stomach?

A

It begins digestion: mixing, churning and digestion (no absorption of foodstuffs apart from some substances like alcohol)

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10
Q

What is the function of the small intestine?

A

Digestion and most absorption (help from secretions from liver and pancreas)

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11
Q

What is the function of the large intestine?

A

completes the absorption of water and electrolytes, so only faeces remain

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12
Q

What is the function of salivary glands

A

secretions help in lubrication, anti-bacterial, begin digestion

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13
Q

What is the function of the pancreas?

A

It is vital for digestion, enzymes for all food categories and alkaline sol

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14
Q

What is the function of the liver and gallbladder?

A

the liver produces bile, the gallbladder stores bile

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15
Q

What is the system of the liver and gallbladder called?

A

Biliary system

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16
Q

What are the 4 layers of the GIT

A

Innermost: mucosa
Next: submucosa
Next: muscularis externa
Outermost: serosa

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17
Q

What are the 3 layers of the mucosa? briefly describe them

A
  1. Mucous membrane: protective surface barrier, epithelial tissue with exocrine, endocrine and absorptive cells
  2. Lamina propria: thin, middle layer of connective tissue containing gut-associated lymphoid tissue- defense from disease
  3. Muscularis mucosa: sparse layer of smooth muscle which upon contraction can expose different areas of surface folding
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18
Q

What is the submucosa and what does it contain?

A

thick connective tissue (gives it elasticity) and contains lymph vessels and a nerve network called the submucosal plexus

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19
Q

What is the muscularis externa and what does it contain?

A

it is a major smooth muscle coat, which has circular layers that decrease its diameter on contraction as well as longitudinal layers that decrease length on contraction. it contains the myenteric plexus (nerve bodies of the ENS)

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20
Q

What is the serosa and what does it secrete?

A

It is an outer connective tissue that secretes a serious fluid for lubrication, and is continuous with the mesentery

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21
Q

What are the 4 digestive functions?

A
  1. Motility
  2. Secretion
  3. Digestion
  4. Absorption
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22
Q

briefly describe motility

A

muscular contractions that propel and mix food, which is highly regulated by nerves

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23
Q

briefly describe secretion

A

exocrine glands secrete digestive juices. endocrine glands secrete hormones

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24
Q

briefly describe digestion

A

food (carbs, proteins, fats) is mechanically and biochemically broken down into smaller units

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25
briefly describe absorption
small units (with water and electrolytes) are transferred into the blood and lymph
26
What kind of muscle contractions allow motility in the digestive tract
smooth muscle contractions, which are involuntary
27
what is phasic smooth muscle
action potential induced bursts of contraction that plays a huge role in digestion by allowing rhythmic contractions to occur, like peristalsis
28
What is tone and what role does it play in the digestive system?
Tone refers to baseline level of continuous low-level contraction in smooth muscle, tone helps in regulating motility and allows peristalsis and segmentation to occur, as well as preventing permanent distension
29
What are the 2 types of phasic digestive motility?
Propulsive (forward) movement- peristalsis Mixing movements (segmentation)- mix in with digestive juices
30
What does the mouth and salivary glands secrete
saliva (containing amylase, mucus, lysozyme)
31
What does the pharynx and esophagus secrete
mucus
32
What does the liver and gallbladder secrete
bile
33
What does the exocrine pancreas secrete
pancreas digestive enzymes, pancreatic aqueous NaHCO3
34
What does the stomach secrete?
gastric juice (HCl, pepsin, mucus, intrinsic factor)
35
What does the small intestine secrete
succus entericus (mucus, salt) SI enzymes
36
What does the large intestine secrete
mucus
37
How does the secretion of endocrine hormones aid the digestive tract?
they help with digestive hormones as well as encourage secretion of endocrine glands
38
How is digestion accomplished at a chemical level?
Via hydrolysis, for the digestion of large molecules like proteins, fats and carbs
39
What is hydrolysis?
a chemical process where a molecule is cleaved through the addition of water molecules
40
How is absorption of carbs and proteins accomplished
by a sodium dependent symport, and then absorbed into blood
41
how is absorption of fats accomplished?
it is a passive process, it is absorbed into the lymph
42
4 factors that regulate digestive system function
autonomous smooth muscle function, intrinsic nerve plexuses, gut hormones, extrinsic nerves
43
What are the cells of the dietary tract that regulation autonomous smooth muscle function?
Non-contractile interstitial cells of cajal
44
What is the function of the cells of Cajal
they establish rhythmic slow-wave potentials that spread to smooth muscle gap junctions
45
What is the role of pacemaker cells in causing muscle contractions?
they generate slow waves of membrane potential, these waves oscillate and if they reach threshold (-30 mV), they trigger action potentials that cause muscle contractions
46
what influences whether threshold is reached?
mechanical, neural and hormonal factors
47
What is the rate of contraction set by?
pacemakers
48
What does the intensity of contractions depend on?
the number of action potentials
49
What does an increase in the number of action potentials result in?
increased cytosolic calcium concentration
50
What does increased calcium influx result in?
a contractile response
51
Explain the ion concentration gradients of K+, Na+ and Ca2+ in intestinal smooth muscle cells
K+ is high inside the cell, low outside hence moves OUTWARD Na+ and Ca2+ are high outside and low inside the cell hence move INWARD
52
What kind of resting potential occurs due to the outward flow of potassium ions?
A very negative potential inside the cell
53
During depolarisation (membrane becomes less negative), there is increased permeability to what?
Ca2+
54
During repolarization (return to resting potential) , there is increased permeability to what?
K+ (leaves the cell to make it more negative)
55
What is a syncytium
when the smooth muscle cells in the small intestine function together as a unit
56
How do electrical signals spread from cell to cell for coordinated contraction?
via gap junctions
57
How does calcium enter the smooth muscle cell?
Through voltage gated channels and receptor operated channels, as well as intracellular Ca2+ being released from the sarcoplasmic reticulum (SR)
58
Explain the steps in which smooth muscle relaxes from the release of nitric oxide (NO)
NO diffuses into cell and triggers cyclic GMP -> stimulates protein kinase G (PKG)-> activates myosin light chain phosphatase -> myosin dephosphorylated -> relaxation PKG opens K+ channels -> hyperpolarisation of membrane -> less likely for smooth muscle to contract s
59
What are the 2 major nerve networks within the DT wall?
- myenteric plexus - submucous plexus
60
where is the myenteric plexus and what is its function?
it is located between the longitudinal and circular layers of muscle it exerts control primarily over digestive tract motility (contraction/relaxation)
61
what is the function of the submucous plexus?
it plays a role in sensing the luminal environment, regulating gastrointestinal blood flow, controlling epithelial cell function
62
What are the nerve circuits that control motility in the small intestine?
1. sensory (IPAN) 2. interneurons 3. motor neurons (excitatory/inhibitory)
63
what is the main enteric excitatory neurotransmitter
Acetycholine
64
what is the main enteric inhibitory neurotransmitter?
NO
65
What are the two main divisions outside the digestive system, part of the autonomic NS
sympathetic NS parasympathetic NS
66

medicine (52 decks)

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