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Physiological concepts > Wk7 - secretion > Flashcards

Wk7 - secretion Flashcards

1
Q

In terms of cellular mechanisms of secretion, what ion(s) is the following organ capable of secreting:
Kidney.
(note: answers are those relevant to this course).

A
  1. Hydrogen ions

2. Potassium ions

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2
Q

In terms of cellular mechanisms of secretion, what ion(s) is the following organ capable of secreting:
Stomach.
(note: answers are those relevant to this course).

A

Hydrogen ions from parietal cells only.

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3
Q

What is the main purpose of kidney tubule secretion? Is this an active or passive process?

A

Secretion of substances from peritubular capillaries/ ECF back into the filtrate is a way to rid the body of unwanted substances, as they will subsequently pass out of the body in the urine.

Transepithelial transport mechanisms for kidney tubule secretion involve BOTH passive and active mechanisms.

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4
Q

What is the main purpose of hydrogen ion secretion in the kidney? When would the kidney be secreting more hydrogen ions then usual?

A

The main purpose of hydrogen ion secretion is acid base balance. The kidney will be less hydrogen ions when the blood is too alkaline (not acidic enough), in order to conserve the blood H+.

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5
Q

What parts of the nephron undergo hydrogen ion secretion?

A
  • PCT
  • DCT
  • CD
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6
Q

Where are potassium ions reabsorbed, and secreted in the nephron? Is this an active or passive process?

A

K+ ions are actively reabsorbed in the PCT, and actively secreted in the DCT + CD.

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7
Q

Normally, what percentage of K+ ions which enter the filtrate are excreted in the urine?

A

All of the potassium which is filtered in the glomerulus is actively reabsorbed. However, under normal conditions, 10-15% of that which was reabsorbed is then actively secreted back into the filtrate. The extent to which this occurs is based upon the bodies potassium balance at the time.

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8
Q

The secretion of K+ is coupled with the (secretion/ reabsorbtion) of what ion? Through what channel does this occur?

A

Na reabsorption. This occurs through a cation exchanger known as the NaK pump!

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9
Q

What factors alter the rate of potassium secretion?

A
  1. Acidosis: high [H+] causes decreased K+ secretion. This is because H+ and K+ compete in terms of secretion, and when a person is acidotic H+ secretion takes priority.
  2. Aldosterone: aldosterone stimulates K+ secretion.
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10
Q

Explain the relationship between the adrenal cortex and levels of K+.

A

High [K+] stimulates the adrenal cortex to release aldosterone.
High [aldosterone] stimulates the secretion of K+ into the tubules of the nephron.

Thus, a negative feedback cycle exists; where the end result (lowered K+) negates the stimulus (high K+).

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11
Q

List the 4 types of mucosal cells of the stomach.

A
  1. Chief (zymogenic) cells
  2. Parietal (oxyntic) cells
  3. Mucous neck cells
  4. Entero-endocrine cells
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12
Q

For the following mucosal cell of the stomach, state what it secretes:
Chief cell.

A

Chief cells release pepsinogen.

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13
Q

For the following mucosal cell of the stomach, state what it secretes:
Parietal cells.

A

Parietal cells release HCl and intrinsic factor.

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14
Q

For the following mucosal cell of the stomach, state what it secretes:
Mucous neck cells.

A

Mucous neck cells secrete mucous.

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15
Q

For the following mucosal cell of the stomach, state what it secretes:
Entero-endocrine cells.

A

Entero-endocrine cells release gastrin.

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16
Q

What is the name for the collective fluid released from the gastric glands.

A

Gastric juice.

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17
Q

Explain how chief and parietal cells functions are interdependent.

A

Chief cells secrete pepsinogen, whereas parietal cells secrete HCl (as well as intrinsic factor, although that is besides the point). Pepsinogen is inactive unless in an acidic environment, which is why the HCl from the parietal cells is imperative. The acidic environment converts pepsinogen into its active proteolytic form pepsin, so that it is able to break down proteins.

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18
Q

What occurs to parietal cells upon stimulation for them to secrete? (brief answer)

A

Parietal cells undergo a morphological change post stimulus to secrete.

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19
Q

What does the ionic composition of gastric secretion depends upon?

A

The ionic composition of gastric secretion depends upon the rate of secretion.

In times of high gastric secretion (ie. when lots of food is present), there is an increased secretion of H+, and thus high [H+] in the gastric juice.

In times of low gastric secretion, there is a decreased secretion of H+ and an increased secretion of Na+, resulting in a low [H+] but a high [Na+] within the gastric juice.

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20
Q

What are the 2 structural features of interest regarding parietal cells? What’re the functions of these features?

A
  1. Secretory canaliculi - region packed full of villi, and lined with microvilli. Occurs throughout the cytoplasm, connected by a common outlet to cells luminal surface. Function to increase the surface area of the parietal cell, increasing its efficiency of secretion.
  2. Tubulovesicular system (TV) - an extensive network of tubules and vesicles.
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21
Q

What occurs to parietal cells upon stimulation for them to secrete? (extended

A
  1. Increased SA - the tubulovesicular (TV) system fuses with the plasma membrane of the secretory canaliculi, bringing about a huge increase in surface area.
  2. Increased HCl pumping sites - within the TV system is the HCl secretory apparatus. By fusing with the secretory canaliculi, there is an increase in the amount of HCl pumping sites available.
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22
Q

At max rates of H+ secretion, parietal cells can pump out H+ against how steep of a gradient?
Express this in terms of the pH of the parietal cell, compared to the pH of the lumen.

A

10^6:1.
pH parietal cell = 7.0
pH gastric lumen = 1.0

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23
Q

The following question regards parietal cells:

How does chloride secretion occur?

A

a. ) Energy is used to pump H+ into the gastric lumen against its concentration gradient, and this sets up the electrical gradient for Cl- anions to follow. Thus, Cl- passively moves down an electrical gradient due to the large amount of H+ in the gastric lumen.
b. ) Chloride molecule influx occurs in parallel with carbonic acid efflux. As so much Cl- is within the cell (due to so much HCO3- having to leave, which is a product of how much H+ secretion there is), there is an elecrochemical gradient for Cl- to flow out of the cell and into the gastric lumen. It does so through an electrogenic channel.

(note: A & B are both likely to be true, but primarily reason is A)

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24
Q

From where is H+ derived, for secretion from parietal cells? Explain the path taken by molecules subsequently. (extended answer)

A

H+ is derived from the dissociation of water, into OH- and H+. H+ is then secreted from the parietal cell with a cation exchanger (active, bringing K+ into the cell, H, K-activated ATPase or primary protein pump).

The OH- then combines with CO2, with aid of carbonic anhydrase, to form carbonic acid. Carbonic acid then exits the parietal cell into the interstitial fluid, in exchange for a Cl- molecule (anion exchanger). Carbonic acid moves down its electrochemical gradient and so this is a passive process.

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25
Q

From where can CO2 be sourced in any general cell?

A
  1. CO2 derived from metabolic reactions occurring within the cell.
  2. CO2 from blood/ plasma.
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26
Q

What is the protein responsible for the secretion of H+ in parietal cells called?

A

The primary proton pump.

H+, K+ activated ATPase.

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27
Q

What is an essential condition required for the primary proton pump to work?

A

The stomach must have a ready supply of K+.

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28
Q

Explain what is meant by the following general term(s):

Alkaline tide.

A

In times of high levels of digestion, the stomach produces H+ in excess. This means there is an equally large increase in the amount of HCO3- which leaves the parietal cell in the blood. This wave of alkaline substance is thus referred to as an ‘alkaline tide’.

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29
Q

Briefly detail the 3 phases for gastric secretion & motility.

A
  1. Cephalic phase (excitatory) - sight/ smell/ thought of food stimulates CC and hypothalamus, parasympathetic stimulation.
  2. Gastric phase (excitatory & continuing) - stretch receptors pick up distention of stomach & chemoreceptors pick up increased pH of gastric juice.
  3. Intestinal phase (inhibitory) - duodenum stretch receptors pick up distention and regulate how much chyme can pass into rest of small intestine. This is done in effort to regulate the work load of the main “business end” of the GIT; the small intestine.
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30
Q

The following question regards control of gastric secretion at the cellular level:
What hormones are responsible for binding to receptors on parietal cells, inducing an increase of HCl secretion?
Do these hormones bind on the same, or different receptors?

A

ACh, gastrin and histamine all bind to separate receptors on the parietal cell, to bring about an increase of HCl secretion.

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31
Q

The following question regards control of gastric secretion at the cellular level:
From where does ACh arise?

A

ACh comes from the parasympathetic nerves innervating the gut.

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32
Q

The following question regards control of gastric secretion at the cellular level:
From where does gastrin arise?

A

Gastrin comes from the G cells in the mucosa of the duodenum and the gastric antrum. Gastrin then reaches parietal cells through the bloodstream.

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33
Q

The following question regards control of gastric secretion at the cellular level:
From where does histamine arise?

A

Histamine originates from mast cells within the gastric mucosa, and diffuses to the parietal cells.

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34
Q

The following question regards control of gastric secretion at the cellular level:
How is it that gastrin, ACh and histamine cause an increase in the level of HCl secretion? (basic answer)

A

Histamine, ACh and gastrin all induce the fusion of the TV system with the apical membrane, which increases the amount of H+ pumping sites available.

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35
Q

The following question regards control of gastric secretion at the cellular level:
How do ACh and gastrin bring about an increase in the level of HCl secretion? (detailed answer)

A
  1. ACh and gastrin bind to their respective receptors.
  2. This opens calcium channels, increasing intracellular [Ca+2].
  3. Increased Ca+2 increased HCl secretion.

(note: exact mechanism by which increased Ca+2 or increased cAMP enchances HCl secretion unknown)

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36
Q

The following question regards control of gastric secretion at the cellular level:
How does histamine bring about an increase in the level of HCl secretion? (detailed answer)

A
  1. Histamine binds to H2 receptors.
  2. This activates adenyl cyclase.
  3. Adenyl cyclase increases [cAMP].
  4. Increased cAMP increases HCl secretion.

(note: exact mechanism by which increased Ca+2 or increased cAMP enchances HCl secretion unknown)

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37
Q

The following question regards control of gastric secretion at the cellular level:
What drugs are able to block the effect of gastrin/ histamine/ ACh?

A
  1. Cimetidine

2. Ranitidine.

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38
Q

What are histamine H1 receptors involved with (as oppose to H2 receptors, which activate adenyl cyclase)?

A

Histamine H1 receptors are involved in the immune response.

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39
Q

The following question regards control of gastric secretion at the cellular level:
Compare the potency of the 3 chemicals which control gastric secretion, at the cellular level.

A

Histamine - most potent.
ACh - potent.
Gastrin - less potent.

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40
Q

The following question regards control of gastric secretion at the cellular level:
Do the effects of each chemical augment eachother, or act against?

A

Effects of histamine, ACh and gastrin augment (enhance, stack on top of) eachother.

41
Q

The following question regards control of gastric secretion at the tissue level:
When is stomach HCl secretion at basal rate? How does basal rate of HCl secretion vary throughout the day (“vary diurnally”)?

A

HCl secretion will be at basal rate when the stomach has been empty for several hours. Basal rate of HCl secretion varies throughout the day; highest in the evening and lowest in the morning.

42
Q

During a meal, rate of HCl secretion increases significantly. Briefly, what mechanisms acheive this?

A

HCl secretion is increased through vagal and hormonal stimulation of parietal cells.

43
Q

Other then vagal/ hormonal stimualtion, how else may gastric secretion be enhanced?

A

Gastric secretion is also effected by..

  • caffeine
  • calcium
  • alcohol
44
Q

Briefly, what regulates sweating?

A

The autonomic nervous division of the nervous system.

45
Q

Sweat glands are innervated by different types of nerve fibres, depending on there type. Expand on this.

A

Eccrine sweat glands - cholinergic innervation, in order to reduce core body temperature.

Apocrine sweat glands - adrenergic innervation, sweat in times of excitement/ anticipation.

46
Q

The following question relates to eccrine sweat glands:

Explain their structure.

A

Eccrine sweat glands are simple, coiled tubular glands. Their structure can be broken down into 2 parts:

  1. A deep, subdermal coiled portion which produces (and secretes) sweat.
  2. A duct portion which passes the secretion to the skin surface.
47
Q

The following question relates to eccrine sweat glands:

Explain the contents of their primary secretion.

A

Eccrine primary secretion is (normally) isotonic to blood. However, by the time this secretion reaches the surface of the skin, it becomes hypotonic.

48
Q

The following question relates to eccrine sweat glands:

Where are they found?

A

Eccrine glands are found all over the body, most numerous in areas of thick skin & axillae.

49
Q

The following question relates to eccrine sweat glands:

Do these glands respond to emotional stress/ gustatory stimulus?

A

YES - eccrine sweat glands also respond to emotional/ gustatory stimulus.

50
Q

t/f: the subdermal portion of an eccrine sweat gland produces and secretes sweat, which is then unchanged as it passes through the duct and to toward the surface.

A

FALSE - the duct modifies the primary secretion of the subdermal portion.

51
Q

Describe the composition of the primary secretion from eccrine sweat glands. Include in your answer the concentrations of Na+ and Cl-.

A

Primary secretion (eccrine) is similar composition to blood plasma, except without the proteins.
[Na+] = 142 mMol/ L
[Cl-] = 104 mMol/ L.

52
Q

How is it the amount of sweat secreted is changed?

A

By the variable amount of reabsorption which occurs in the duct of the sweat gland.

53
Q

Explain the composition, including what constituents are/ aren’t reabsorbed, upon slight stimulation of eccrine sweat glands.

A
  • almost all Na and Cl reabsorbed
  • 5 mMol/ L
  • as the osmotic pressure (of sweat) falls, more water is reabsorbed
  • other constituents are therefor concentrated, such as lactic acid, urea, K+
54
Q

Explain the composition, including what constituents are/ aren’t reabsorbed, upon strong stimulation of eccrine sweat glands.

A
  • approximately 50% of Na and Cl reabsorbed
  • 60 mMol/ L
  • for an unacclimatised person this can represent a large loss of Na and Cl
  • water reabsorption limited so other constituents at low concentration (lactic acid, urea, K+)
55
Q

How much saliva do humans produce per day?

A

approximately 1L

56
Q

Which salivary gland is largest? What is the composition of this large, salivary gland?

A

The paortid salivary glands are the largest, and they secrete serous fluid only.

57
Q

What is the composition of the other 2 salivary glands (not parotid)?

A

The submandibular and sublingual salivary glands are both serous and mucous producing.

58
Q

Explain the relevance of the following term, in regards to salivary glands:
Acini.

A

Salivary glands have a typical acinar gland structure; composed of flasks and ducts.
Acini are clusters of cells.

59
Q

Briefly contrast the composition of serous fluid and mucous? What types of cells produce these substances?

A

Serous cells - produce serous fluid, which is watery.

Mucous cells - produce mucous, which is viscous.

60
Q

How is salivary secretion controlled? (extended answer)

A

Salivary secretion is controlled by the ANS. Both divisions (PNS + SNS) stimulate secretion, although PNS is stronger and longer lasting.
PNS - stimulates a serous saliva.
SNS - stimulates a mucous saliva.

61
Q

What is the general composition of saliva? (individual components)

A

Saliva is 99.5% water and 0.5% solutes. Solutes include…

  • salts
  • lysozyme
  • amylase
  • lipase
  • IgA
62
Q

Explain some general functions of saliva. (6)

A
  1. Lubricates food for swallowing
  2. Dissolves food for tasting
  3. Buffers acidic foods (via bicarbonate)
  4. Chemical digestion (via amylase + lipase)
  5. Destroy bacteria (via lysozyme)
  6. Protects mouth from infection (via rinsing action).
63
Q

In terms of per gram of tissue, what is the maximum rate of secretion of saliva?

A
  1. 0 ml/ min/ gram of tissue.

note: this is a HUGE volume of secretion!

64
Q

How does the tonicity of saliva compare to that of blood plasma?

A

Saliva is always hypotonic to blood plasma; that is, it has less dissolved solutes.

65
Q

What is the (relative) pH of primary salivary secretion? How may this change?

A

The pH of primary salivary secretion depends upon the activity (or inactivity) of the salivary glands.
During resting - pH is slightly acidic.
During high activity (active secretion) - pH of saliva becomes basic, due to an increased [HCO3-].

66
Q

Detail the two stage model for secretion of saliva. (note: cellular mechanisms for transport of substances not included)

A
  1. Acini produce an isotonic primary secretion:
    - The serous acinar cells contain zymogen granules, which contain salivary amylase (which is added to the primary secretion).
    - contains a concentration of Na, K, HCO3- and Cl- similar to that of blood plasma.
  2. Excretory duct cells modify the primary secretion:
    - This includes the reabsorption of Na+ and Cl-.
    - The secretion of (that is, entered into the saliva) K+ and HCO3-.
67
Q

Why is it that during times of active secretion, primary salivary secretion becomes more basic?

A

Due to increased [HCO3-].

68
Q

The following questions regards ionic movements in acinar cells (of salivary glands):
How is K+ and Cl- brought into the acinar cell, from the ECF?

A

An Na-K-2Cl cotransport mechanism brings K+ and Cl- into the acinar cell, across the basolateral membrane (from ECF). This is primary active transport.

69
Q

The following questions regards ionic movements in acinar cells (of salivary glands):
How is Na+ secreted from the acinar cell?

A

Na+ is secreted via a paracellular transport mechanisms only. Na+ moves through these “leaky tight junctions” due to the electrical gradient established by Cl- (which has moved through the apical membrane).

(note: this means the only Na+ entering the acinar cell is that involved in the Na-K-Cl cotransport mechanism, and therefor it is only there temporarily).

70
Q

The following questions regards ionic movements in acinar cells (of salivary glands):
How do acinar cells secrete chloride?

A

Cl- enters the acinar cell past the basolateral membrane via the Na-K-Cl cotransport mechanism. Due to this, it is in high concentration within the acinar cell, and then passes the apical membrane moving down its concentration gradient.

71
Q

The following questions regards ionic movements in acinar cells (of salivary glands):
How is HCO3- secreted from the acinar cell?

A

HCO3- is secreted via an electrogenic ion channel in the apical membrane.

72
Q

The following questions regards ionic movements in duct cells (of salivary glands):
How is Na+ reabsorbed into the duct cell?

A

Na reabsorbed through antiport with K+, thus this is also the mechanism for K+ secretion.
(note: this is the NaK pump)

73
Q

The following questions regards ionic movements in duct cells (of salivary glands):
How is HCO3- secreted from the duct cell, into the saliva?

A

HCO3- is secreted through antiport with Cl-, thus this is also the mechanism for Cl- reabsorption.

74
Q

t/f: loose junctions between duct cells allow movement of water and solutes.

A

FALSE.

Tight junctions exist between duct cells, which are impermeable to water and solutes.

75
Q

As saliva flows through ducts, how does its tonicity change?

A

The saliva becomes more hypotonic the further down the duct.

76
Q

How does flow rate alter the tonicity of saliva

A

However, the faster the flow rate, the closer saliva becomes to isotonicity with blood plasma. That is, the faster the flow rate, the less hypotonic the saliva is; as there is less time for Na+ and Cl+ to be reabsorbed.

77
Q

How much does a human pancreas weigh? (relative)

A

A human pancrease weighs less then 100 g.

78
Q

Approximately, how much pancreatic juice does the pancrease produce per day?

A

The pancreas produces ~1000ml of pancreatic juice per day.

79
Q

Is the pancrease an exocrine, or an endocrine gland?

A

Trick question - the pancrease is BOTH and endocrine and exocrine gland.
However, in terms of digestion it is the exocrine component which is relevant.

80
Q

Break down the basic constituents of pancreatic juice. (hint: pancreatic juice can be broken down into 2 main components)

A
  1. Aqueous component - high [HCO3-]; for neutralisation of acidic chyme.
  2. Enzyme component - digest carbs, proteins and fat
81
Q

Briefly, what controls pancreatic secretion?

A

Acid/ chyme in the duodenum elicits neural/ hormonal control mechanisms for pancreatic secretion.

82
Q

Briefly expand on the hormonal control of pancreatic secretion. (2)

A
  1. Hormone cholecystokinin is released from the duodenal mucosa; this stimulates the release of pancreatic juice which is rich in enzymes.
  2. Hormone secretin is released from duodenal mucosa; this stimulates release of pancreatic juice rich in HCO3-.
83
Q

Microscopically, pancrease tissue resembles what other tissue type?

A

Salivary gland tissue.

84
Q

What nerve innervates the acinar and islet cells of the pancreas?

A

The vagus nerve innervates both the acinar and islet cells of the pancreas.

85
Q

What nerves innervate pancreatic blood vessels?

A

Postganglionic sympathetic nerves innervate the pancreatic blood vessels.

86
Q

Explain the effect(s) of neural stimulation on the pancreas.

A

PNS -> stimulates pancreatic secretion.

SNS -> inhibits pancreatic secretion.

87
Q

Specifically, what enzymes do the acinar cells of the pancrease produce (with regard to digestion)?

A
  • Proteases (inactive form)
  • α-amylase
  • lipases
88
Q

Why is it that the acinar cells of the pancrease release proteases in their inactive form? What substance prevents the premature activation of these proteolytic enzymes?

A

Proteases must be in their inactive form in the pancrease/ pancreatic ducts, as otherwise they will begin to breakdown the surrounding tissue. This would mean essentially eating away at your own pancreas.

The substance responsible for this is the trypsin inhibitor.

89
Q

What produces the aqueous component of pancreatic juice?

A

The aqueous component of pancreatic juice is initially produced by the acinar cells, and modified by the duct cells. This is in a similar fashion to the salivary gland.

90
Q

How does flow rate influence the tonicity of pancreatic secretion?

A

It doesn’t!
Pancreatic juice is almost isotonic to blood plasma at all flow rates.
(note: this is only true for the most part. [HCO3-] varies with pancrease secretion rate to some extent)

91
Q

Expand on the composition of Na, K, Cl and HCO3 in pancreatic juice.

A

[Na] and [K] in pancreatic juice are similar to that of blood plasma. [Cl] varies reciprocally with [HCO3-], which is dependant on secretin and pancreatic juice secretion rates.

[HCO3] varies between 60-120mMol/ L.

92
Q

Specifically, what is the range of concentration of HCO3- in pancreatic juice? What does this depend upon?

A

[HCO3-] in pancreatic juice varies between 60-120 mMol/ L.

93
Q

t/f: the aqueous and enzyme components of pancreatic secretion are controlled separately.

A

true.

94
Q

The composition of pancreatic juice varies between <1% and 10% protein content. Why is this?

A

Because the aqueous and enzyme components of pancreatic secretion are controlled separately.

95
Q

Pancreatic secretion is primarily controlled by neural and hormonal mechanisms. However, pancreatic secretion is affected by one other phenomena. What is this?

A

Pancreatic secretion is also affected by mechanisms involved with the regulation of gastric juice secretion.

96
Q

Pancreatic secretion is also affected by mechanisms involved with the regulation of gastric juice secretion. How is this true for the cephalic phase of gastric secretion? (2)

A
  1. Pancreatic juice is also produced in response to vagal stimulation.
  2. Gastrin released from the stomach mucosa increases the rate of pancreatic juice secretion.
97
Q

Pancreatic secretion is also affected by mechanisms involved with the regulation of gastric juice secretion. How is this true for the gastric phase of gastric secretion? (1)

A

Further release of gastrin during the gastric phase enhances rate of pancreatic secretion.

98
Q

Pancreatic secretion is also affected by mechanisms involved with the regulation of gastric juice secretion. How is this true for the intestinal phase of gastric secretion? (2)

A
  1. Acid in duodenum/ jejunum induces release of large volumes of aqueous PJ. This is due to the action of secretin, as secretin is stimulated by acidic pH’s (<4.5).
  2. Presence of AA, FA’s and peptides increase the amount of cholecystokinin, which stimulates release of PJ which is more rich in enzymes.

Physiological concepts (12 decks)

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