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MEH 2023 > Intro to the endocrine system > Flashcards

Intro to the endocrine system Flashcards

1
Q

What is homeostasis?

A

The ability or tendency of a living organism, cell, or tissue to maintain a state of internal balance and dynamic equilibrium despite any changes in the conditions around it

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2
Q

Why is homeostasis important? (2)

A
  • Keeps conditions constant for enzyme action and cell functions
  • Prevents disease (as a failure in homeostasis may lead to disease)
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3
Q

What are the characteristics of a control system (4)

A

1) Stimulus (a change in the environment)
2) Receptor (detects stimuli)
3) Control centre
4) Effector (causes change)

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4
Q

Give examples of receptors that detects stimuli (4)

A
  • Chemoreceptors
  • Thermoreceptors
  • Proprioreceptors (position of body and movement)
  • Nocireceptors (pain)
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5
Q

What does the control centre do? (3)

A
  • Determines set point
  • Analyses afferent input
  • Determines response
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6
Q

Examples of effectors (3)

A

Sweat glands
Muscle
Kidney

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7
Q

What types of communication systems are there? (2)

A

Nervous system- action potentials
Endocrine system- hormones

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8
Q

What is the afferent pathway?

A

Communication pathway that links the receptor to the control centre and so conducts the action potential towards the brain (though communication could be endocrine too)

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9
Q

What is the efferent pathway?

A

Communication pathway that links the control centre to the effector and so conducts the action potential in this direction (though communication could be endocrine too)

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10
Q

What is a circadian rhythm? (2)

A
  • A natural biological process that regulates physiological functions in living organisms
  • It is a 24-hour cycle that is controlled by the internal biological clock in the brain
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11
Q

Where is the biological clock controlling circadian rhythm located?

A

in small group of neurones in suprachiasmatic nucleus of the hypothalamus

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12
Q

What keeps our biological clock in cycle? (2)

A

Zeitgebers - cues from environment such as light, temperature, social interaction, exercise, eating/drinking pattern

+ Melatonin

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13
Q

What cues from the environment keep the body on a 24 hour cycle? (5)

A
  • light
  • temperature
  • social interaction
  • exercise
  • eating/drinking pattern
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14
Q

What causes jet lag?

A

Mismatch between environmental cues and body clock when crossing time zones on a flight

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15
Q

What hormone is involved in setting biological clock?

A

Melatonin

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16
Q

Where is melatonin produced?

A

Pineal gland

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17
Q

When is cortisol high and low?

A

High: 8am - morning

Low - Midnight

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18
Q

When is melatonin high/low?

A

High during sleep

Low during the day

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19
Q

What is negative feedback? (2)

Give 2 examples

A
  • A response to a change in the body that counteracts or opposes the change
  • Most common form of feedback,

eg. the control of plasma glucose by insulin/glucagon, the control of water content by ADH

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20
Q

What is positive feedback? (2)
Give 3 examples

A
  • A given action promotes more of the same action until the stimulus is removed.
  • Rare, used when rapid change is desirable,

eg. blood clotting, ovulation, contraction of uterus

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21
Q

Examples of positive feedback

A

Blood clotting
Contraction of uterus
Ovulation

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22
Q

What is the percentage of total body water in males?

A

50-60%

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23
Q

What is the percentage of total body water in females?

A

45-50%

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24
Q

What is osmotic pressure of blood plasma monitored by?

A

Osmoreceptors in hypothalamus

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25
Q

Fluid distribution 70KG man

A
  • 42L of water
  • 2/3 intracellular (28L)
  • 1/3 extracellular (14L) - 11L interstitial, 3L plasma
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26
Q

How many litres of blood does a 70kg man

A

5 litres - 2 litres of red cells and 3 litres of blood plasma

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27
Q

Osmolarity vs osmolality

A

Osmolarity - the number of osmoles per litre of solution (volume)

Osmolality - osmoles per kg of solution (mass)

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28
Q

What is an osmole?

Give an example

A

(the amount of substance that dissociates in solution to form 1 mole of osmotically active particles) The number of osmotically active particles

eg. a 1mM (1Molar) solution of NaCl corresponds to an osmolarity of 2 as 1 from Na+ ions and one from Cl- ions as you have 2 osmotically active particles

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29
Q

Why is serum osmolality useful?

A

To investigate hyponatraemia (low Na+ in blood)
reference range is 275-295 mOsmol/kg

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30
Q

Normal blood osmolality/Normal sodium in blood

A

275-295 mOsmol/KG

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31
Q

Concentration of saline

A

0.9% NaCl

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32
Q
A
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33
Q

How does ADH control body fluids (What happens if water is low)?

A
  • High blood osmolality is detected by osmoreceptors in hypothalamus:

1)

  • There is increased thirst
  • Thus you drink more water, which reduces osmolality

2)

  • Posterior pituitary secretes more ADH
  • You get increased reabsorption of water from urine into blood in collecting ducts in the kidney
    = small volume of concentrated urine
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34
Q

What does ADH do?

A

Increases reabsorption of water from urine back into blood in kidney collecting ducts

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35
Q

How does ADH control body fluids (if water high)

A
  • Low blood osmolality detected by osmoreceptors in hypothalamus
  • Posterior pituitary secretes less ADH
  • Descreased reabsorption of water from urine into blood in collecting ducts in kidney

= large volumes of dilute urine

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36
Q

What is the normal plasma glucose level?

A

5mM (millimolar)

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37
Q

Describe what happens in the fed state (6)

A
  • Eating a meal increases plasma glucose
  • Detected by B cells in islets of langerhans in pancreas
  • Pancreas secretes insulin
  • Insulin stimulates glycogenesis in liver (storage of glucose as glycogen
  • It also stimulates glucose uptake into tissues (GLUT 4)
  • This will decline plasma glucose levels
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38
Q

What does insulin do?

A

Stimulates glycogenesis in liver

Stimulates glucose uptake via translocating GLUT4

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39
Q

Describe what happens in the fasted state (5)

A
  • Fasting decreases plasma glucose
  • Detected by Alpha cells in islets of langerhans of pancreas
  • They releases glucagon
  • Glucagon stimulates glycogenolysis (break down of glycogen to release glucose) in the liver
  • This increases plasma glucose
40
Q

What does glucagon do?

A

Stimulates glycogenolysis

41
Q

What are hormones? (2)

A
  • Chemical signals produced in endocrine glands or tissues
  • They can travel in the blood stream to cause an effect on other tissues
42
Q

What hormones does the stomach release?

A

Gastrin and Ghrelin

43
Q

What hormones does adipose tissue release?

A

Leptin

44
Q

Name the 4 mechanisms of communication via hormones

A
  • Autocrine
  • Paracrine
  • Endocrine
  • Neurocrine
45
Q

Autocrine communication

A

Hormone signal acts back on cell of origin

46
Q

Paracrine communication

A

Hormone signal is carried to adjacent cells over short distance via interstitial fluid

47
Q

Endocrine communication

A

Hormone signal is released into blood stream and carried to distant target cells

48
Q

Neurocrine communication

A
  • Hormone originates in neurone, transported down axon and released into blood stream and carried to distant target cells
49
Q

Endocrine and nervous system similarities

A 
Both secrete
Both can be depolarised
Some molecules can be neurotransmitter and hormone
Have specific receptors on target cells
Control homeostasis
50
Q

Fill this table in for the endocrine and nervous system

A
51
Q

4 different types of hormones

A
  • Glycoproteins
  • Amino acid derivatives (amines)
  • Peptide/polypeptide
  • Steroids

(GAPS)

52
Q

Describe the solubility of peptide hormones and give 3 examples

A
  • All Water soluble

(insulin, glucagon, growth hormone)

53
Q

Describe the solubility of amino acid derivatives (amines)

Give 4 examples

A
  • Adrenal medulla hormones = water soluble
  • Thyroid hormones = lipid soluble

Examples:

  • Adrenaline
  • Noradrenaline
  • Thyroid hormones
  • Melatonin
54
Q

Describe the solubility of glycoprotein hormones (4)
Give 3 examples

A
  • All water soluble
    eg LH, FSH, TSH
55
Q

Describe the solubility of steroid hormones (3)

Give 3 examples

A
  • All lipid soluble

eg cortisol, aldosterone and testosterone

56
Q

What are steroid hormones synthesised from?

A

Cholesterol

57
Q

How are hormones transported in blood? Give examples

A

Water soluble hormones can travel freely in blood ie Peptide hormones

Lipid soluble ones have to bind to carrier proteins in order to travel ie thyroid hormone

58
Q

How are thyroid hormones transported in the blood?

A

Bound to Thyroxine-binding globulin TBG

59
Q

What hormones are biologically active?

A

Free form of hormone (not bound to protein)

60
Q

Roles of carrier proteins (3)

A
  • Increase solubility of hormone in plasma
  • Increase half life
  • Readily accessible reserve
61
Q

3 main factors determining hormone levels

A

Rate of production
Rate of delivery
Rate of degradation

62
Q

Describe how the 3 main factors that determine hormone levels in blood work

A

.

63
Q

What kind of concentrations do hormones circulate the blood?

A
  • Very low concentrations (pmol/L) picomoles per litre
64
Q

How do hormones exert their effects?

A

Bind to specific receptors

65
Q

What do water soluble hormones bind to in order to exert their effects?

A

Cell surface receptors as they can’t cross the plasma membrane

66
Q

What are the 2 main classes of receptors for water soluble hormones? Give an example of each

A
  • G protein coupled receptor ie adrenaline receptor
  • Tyrosine kinase receptor ie insulin receptor
67
Q

What do lipid soluble hormones bind to in order to exert their effects?

A

Intracellular receptors (they can diffuse across the membrane)

68
Q

Describe what a Type 1 intracellular receptor does

A
  • Cytoplasmic receptor binds to hormone
  • Receptor hormone complex enter nucleus and binds to DNA
69
Q

Describe what a Type 2 intracellular receptor does

A
  • Hormone enters nucleus and binds to prebound receptor on DNA e.g. thyroid hormone
  • Binding relives repression of gene transcription
70
Q

What does the receptor bind to on DNA?

A

Hormone response element (HRE)

In promotor region of genes

71
Q

Which works faster, water soluble hormones or lipid soluble?

A

Water soluble

72
Q

Where is appetite control centre located?

A

Hypothalamus - arcuate nucleus

73
Q

What do the primary neurones in the arcuate nucleus sense? (3)

A

Primary neurones sense:
- Neuronal signals
- Nutrient signals
- Hormonal signals
From the blood

74
Q

Name the Two types of primary neurones in arcuate nucleus

A
  • Stimulatory neurones
  • Inhibitory neurones
75
Q

What do stimulatory neurones contain? What do these do?

A

Neuropeptide Y (NPY) and agouti-related peptide (AgRP)

These promote hunger

76
Q

What do inhibitory neurones contain?
What do these promote?

A

Pro-opiomelanocortin (POMC), which yields several neurotransmitters including alpha-MSH and Beta-endorphin

These promote satiety

77
Q

What do primary neurones do in order to alter feeding behaviour? (2)

A
  • Primary neurones synapse with secondary neurones
    In other regions of the hypothalamus
  • And the signals are integrated to alter feeding behaviour
78
Q

What does POMC do?

A

Yields a-MSH and B-endorphin

These promote satiety

79
Q

Name 2 Hormone signals from the gut to the hypothalamus

A

Ghrelin

Peptide tyrosine tyrosine (PYY)

80
Q

1) What is Ghrelin?

2) When is it released?

3) What does it stimulate?

A

1) A peptide hormone released from the stomach wall when empty (Ghrelin = Stomach Growling)

3)Stimulates excitatory primary neurones in arcuate nucleus so stimulates HUNGER/APPETITE

81
Q

What inhibits Ghrelin release?

A

Filling of the stomach

82
Q

1) What is PYY?
2) What cells release PYY?
3) What does PYY do?

A

1) A peptide hormone released in response to feeding

2) by cells in the ileum and colon

2) Inhibits excitatory/stimulatory primary neurones of the arcuate nucleus and and stimulates inhibitory neurones
to SUPPRESSES APPETITE

83
Q

What does PYY do when injected to mice?

A

Makes them anorexic

84
Q

What do obese humans have?

A

A blunted PYY response following food intake

85
Q

1) Where is leptin released from and to?

2) What does leptin do?

3) What is the overall effect of leptin?

A

1) Released from adipocytes into blood stream

2) Stimulates inhibitory (POMC) neurones
Inhibits stimulatory (NPY and AgRP) neurones

3) SUPRESSES APPETITE

86
Q

What does leptin to do mitochondria?

A

Induces expression of uncoupling proteins

Energy is the dissipated as heat

87
Q

What does insulin do?

A
  • Suppresses appetite - similar mechanism to leptin
  • Seems to be less important than leptin in this respect
88
Q

What does amylin do and where does it come from?

A

From beta cells in pancreas

Suppress appetite

89
Q

What is Pramlintide

A

Amylin analogue - used to treat Type 2 diabetes

90
Q

What do aMSH (from POMC) synapse at?

A

MC4 receptors - promoting satiety

91
Q

Leptin mutation discovery

A

ob/ob mice have loss of function mutation on leptin gene

92
Q

Treatment loss of leptin gene

A

Leptin injection

93
Q

What can’t you use leptin injections for?

A

Common obesity - leptin resistance instead is the problem

94
Q

What do inhibitory neurones contain?
What do these promote?

A

Pro-opiomelanocortin (POMC), which yields several neurotransmitters including alpha-MSH and Beta-endorphin

These promote satiety

95
Q

What do inhibitory neurones contain?
What do these promote?

A

Pro-opiomelanocortin (POMC), which yields several neurotransmitters including alpha-MSH and Beta-endorphin

These promote satiety

MEH 2023 (8 decks)

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