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BIO125 Physiology > Week 4 The digestive system II > Flashcards

Week 4 The digestive system II Flashcards

1
Q

What does digestion depend on?

A

Secretions from:

  • Multicellular glands
  • Single secretory cells scattered throughout GIT
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2
Q

Where do digestive secretions take place?

A

Mouth
Stomach
Pancreas
Liver

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3
Q

What glands exist in the oral cavity?

A

• Salivary glands

– typical mammal has multiple pairs of extrinsic salivary glands

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4
Q

What glands does a dog have in its oral cavity?

A 
Dog
– Parotid glands (anterior to ear)
– Orbital glands (near eye)
– Mandibular glands (near lower jaw)
– Sublingual glands (beneath tongue)
x2 cell types
• mucus secreting
• serous secreting
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5
Q

What is saliva made of?

A

Saliva – 99.5% H2O, 0.5% electrolytes & protein

– important salivary proteins = amylase, mucus, lysozyme

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6
Q

How much is salivary secretion in humans?

A

1-2L in humans

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7
Q

How is salivary secretion controlled?

A

Parasympathetic system:

  • simple reflex
  • conditioned reflex
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8
Q

What is the simple reflex in the parasympathetic system?

A

– food in mouth
– chemoreceptors & pressure receptors activated (buccal cavity)
– stimulus → impulses → salivary centre → impulses (extrinsic
autonomic nerves) → salivary glands → secretion

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9
Q

What is the conditioned reflex in the parasympathetic system?

A

Conditioned reflex – learned response (Ivan Pavlov)
– salivation occurs without oral stimulation
– thinking/seeing/smelling food → salivation
– mediated via cerebral cortex

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10
Q

Who coined the term conditioned reflex?

A

Ivan Pavlov (learned response-conditioned reflex)

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11
Q

Under what conditions is salivary secretion inhibited?

A 
Dehydrated animals
– Initiate sympathetic response
– Blood flow to salivary glands restricted = Prevents secretion
• Humans – stressful situations
– Dry mouth
– Same sympathetic response
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12
Q

Describe the inside of the stomach

A 
Sphincters x2
• Surface = columnar
epithelium with tight
junctions
• Luminal surface – gastric pits
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13
Q

What are gastric pits?

A

Gastric pits are cavities in the mucosa that include:
-mucousneck cells
-chief cells
-parietal cells
-enteroendocrine cells
and are responsible for the production of gastric fluid

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14
Q

What are the types of secretory cells?

A

• x4 cell types
1. Mucous neck cells (secrete acid mucous)
– protective
2. Parietal cells (secrete acid)
– primarily HCl
1. Chief cells (secrete digestive enzymes)
– Pepsinogen (protease) - digests protein
2. Enteroendocrine cells (secrete hormones)
– E.g. gastrin, excitatory – promotes digestive activity (secretion)

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15
Q

Which vertebrates do NOT have acidic stomachs?

A 
• Platypus
– Reasons unclear
• Gastric brooding frog
– Swallows fertilised eggs
– Young produce prostaglandin E2
– Inhibits acid secretion
– Frogs hop up oesophasgus & out through mouth
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16
Q

How is gastric secretion regulated?

A

Complex regulation – neural and hormonal control
• Presence of food
• Anticipation of food
• Gastrin = key
– Stimulates Enterochromaffin-like cells
» secrete histamine – stimulates HCl secretion
– Stimulates Chief cells

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17
Q

What is the pancreas?

A

Organ with exocrine &endocrine roles,

  • duct cells & acinar cells = exocrine portion of pancreas
  • islets of lagerhans = endocrine portion of pancreas
18
Q

What does the exocrine portion of the pancreas do?

A

secrete through ducts
(exo = external, crine = secretion)
secretory product = pancreatic juice – function relates to GIT

19
Q

What does the endocrine portion of the pancreas do?

A 
lack ducts (endo = internal)
release secretory products into blood
key secretory products = insulin & glucagon – function relates to GIT
20
Q

What do duct cells and acinar cells secrete?

A 
Duct cells:
-secrete aqueous NaHCO(3)-  solution
Acinar cells:
-secrete digestive enzymes
(enzymes leave through zymogen granules)
21
Q

What is the secretory product of the exocrine portion of the pancreas?

A

-pancreatic juice – function relates to GIT-
Pancreatic juice:
Bicarbonate, Pancreatic amylase, Pancreatic lipases, Proteases,Nucleases
Acinar cells
• produce small volume of primary secretion & digestive enzymes
• digests chyme
Duct cells
• produce bicarbonate-rich fluid
• neutralises chyme

22
Q

How is pancreatic juice secretion regulated?

A

-acid in duodenal lumen leads to
-the release of secretin and VIP (vasoactive intestinal peptide) from duodenal mucosa which in turn
-stimulates pancreatic duct cells and
-increases pancreatic HCO(3)- secretion which neutralizes the acid
AND
-digestive products in duodenal lumen lead to
-the release of CCK (cholecystokinin) from duodenal mucosa which
-stimulates pancreatic acinar cells and
-increase pancreatic enzyme secretion that digest the products in the lumen.

23
Q

How is glucose regulated?

A

In the Endocrine portion of pancreas = key secretory products = insulin & glucagon – function relates to GIT and to glucose regulation
• Islets of Langerhans contain pancreatic β cells & pancreatic α cells
Alpha cells secrete Glucagon (when Low blood glucose)
Beta cells secrete Insulin (when High blood glucose)
Act as a team to maintain blood glucose between set points (5 mmol)

24
Q

What happens after digestion?

A

Molecules are transported across plasma membrane in different ways

25
Q

How are polar molecules transported?

A

Polar molecules e.g. monosaccharides, amino acids
‒ Cannot penetrate plasma membrane
‒ Require specific protein transporter
‒ Type of transporter depends on transmembrane gradient
1. Favorable concentration gradient (high – low)
‒ Facilitated diffusion e.g. glucose transported by GLUT proteins
2. Against concentration gradient (low – high)
‒ Active transport e.g. amino acids use secondary transport

26
Q

How are other molecules transported?

A

Vesicular
• Cells engulf regions of plasma membrane to form vesicles
1. Nutrients in solution = pinocytosis
2. Nutrients are particulate = phagocytosis
1 +2= endocytosis
• Cells can also expel nutrients by exocytosis
• E.g. pathways are important for complex lipids

27
Q

How are carbohydrates digested?

A

dietary carbohydrates → monosaccharides
– digestion begins in the mouth with salivary amylase
-then in the small intestine pancreatic amylase as well as sucrase lactase and maltase break dissacharides down into monosacharides

28
Q

How is glucose and galactose absorbed?

A 
Through:
Na+ glucose-transporter
• aka SGLT-1 (symporter)
• secondary active transport
GLUT-2
• facilitated diffusion (passive)
29
Q

How is fructose absorbed?

A 
Through:
GLUT-5
• facilitated diffusion (passive)
GLUT-2
• facilitated diffusion (passive)
30
Q

How are proteins digested?

A 
Digestion
proteins → AA
• digestion begins in the stomach
Gastric pepsin
and in the small intestine:
Pancreatic proteolytic enzymes
Aminopeptidases
Intracellular peptidases
31
Q

How are proteins absorbed?

A 
• Amino acids (transport similar to glucose)
– apical membrane
• Na+ co-transporters (symporter)
• secondary active transport
– basolateral membrane
• facilitated diffusion (passive)
32
Q

How are lipids digested?

A 
lipids are hydrophobic > challenge
chemical & physical transformations before digested & absorbed
Bile is key
• synthesized in liver
• stored in gall bladder
• secreted into small intestine
-detergent action
• aids digestion by pancreatic lipase
• lipid → monoglycerides & free fatty acids
• participates in formation of micelles
• aids absorption
33
Q

What is bile and bile salts?

A

• BILE
-bile salts
-cholesterol
-lecithin
-bilirubin
= aqueous alkaline fluid
Bile salts
– lipid-soluble part & water-soluble part
– adsorb on surface of fat droplets
– mixing movement of SI > break up fat droplets
– water soluble surface prevents re-coalescing

34
Q

What do bile salts and lecithin do?

A

formation of micelles – water soluble
– core = hydrophobic (monoglycerides & free fatty acids)
– shell = hydrophilic
micelles transport H20 insoluble substances → enterocytes

35
Q

How are lipids absorbed?

A 
-apical membrane
• passive diffusion
enterocyte
• TGs re-synthesised
• chylomicrons
-basolateral membrane
• exocytosis
• enter lymphatic vessels
36
Q

Hows the GIT controlled?

A

Neural & hormonal control

• Overlapping regulatory pathways > very complex

37
Q

What are the layers of GIT wall?

A 
Muscularis externa:
-Smooth muscle layer
• inner circular layer (↓ diameter)
• outer longitudinal layer (↓ length)
• nerve plexus - myenteric plexus 
Then:
-submucosa
Layer of connective tissue
• blood & lymph vessels
• nerve plexus - submucosal plexus
• plexus = network of nerves
38
Q

How is GIT motility determined?

A

Determined by contractile activity of circular smooth muscle
• Tonic contraction controls diameter of lumen
• Regulated by intrinsic/local pathways
• muscle cells (myogenic)
• neurotransmitters released from motor nerves (neurogenic)
-Myenteric plexus – motility & enzyme secretion
-Submucosal plexus – GIT blood flow & ion/water transport
-Enteric Nervous System (ENS) – works to regulate gut function

39
Q

How do suites of neurotransmitters & hormones control gut motility?

A

-Neural control (CNS and ENS)
receptors (chemoreceptors & mechanoreceptors)
→ hypothalamus & spinal cord
→ parasympathetic / sympathetic neurons send impulses back
-Parasympathetic
Acetylcholine
↑ motility
-Sympathetic
Norepinephrine, somatostatin & neuropeptide Y
↓ motility

40
Q

What does the myenteric plexus do?

A

myenteric plexus integrates information → smooth muscle

41
Q

What role does timing play in GIT motility?

A

• Timing is key
– Optimal time for digestion & assimilation
↑ motility > ↑ rate of passage through GIT > ↓ absorption
BUT
↓ motility > animal carries around indigestible material
e.g. fruit-eating birds vs nectar eating birds

42
Q

Do Fruit-eating birds have a faster passage rate of contents through the GIT
compared to nectar-eating birds?

A

False , nectar eating birds have a faster passage rate of contents as they do not carry around indigestible material.

BIO125 Physiology (17 decks)

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