12. Intro to Endocrine system Flashcards
1
Q
What are the key features common to all control systems?
A
- stimulus
- Receptor
- Communication
- Control centre
- Effector
- Feedback
2
Q
What are the main communication pathways in the human body?
A
Nervous and endocrine system
3
Q
What is the afferent branch of the peripheral nervous system?
A
signal direction towards the brain; sensory input
4
Q
What is the efferent branch of the peripheral nervous system?
A
signal direction away from the brain; motor output
5
Q
What is paracrine signalling?
A
Hormone signal carried to adjacent cells over a short distance via interstitial fluid
6
Q
What is autocrine signalling?
A
Hormone signal acts back on the cell of origin
7
Q
What is the role of the control centre?
A
- Determines set point
- Analyses afferent input
- Determines response
8
Q
What are 2 important control centres in the brain?
A
- hypothalamus in the diencephalon
- medulla oblongata in the brain stem
9
Q
What is the hypothalamus and regions of the medulla involved in?
A
The hypothalamus is involved in the control of the endocrine system and regions of the medulla are involved in the control of ventilation and the cardiovascular system.
10
Q
What are receptors required for?
A
To detect stimuli such as changes in the environment
11
Q
What are receptors in the body usually made up of?
A
Specialised nerve endings
12
Q
Give examples of different types of receptors in the body.
A
- Chemoreceptors
- Thermoreceptors
- Proprioceptors
- Nociceptors
13
Q
What are proprioceptors?
A
Detect body position in space and movement.
Sense of awareness: where your limbs are in space
14
Q
Which nerves do receptors communicate input to the control centres with?
A
Afferent nerves
15
Q
What are effectors?
A
Agents that cause change
16
Q
Which nerves do control centres communicate input to the effectors with?
A
Efferent nerves
17
Q
What happens in negative feedback?
A
Output inhibits the function of the control centre and the effector acts to oppose the stimulus
Negative feedback gives stability to control systems and allows the set point to be controlled within fine limits.
18
Q
What is hunting behaviour?
A
In negative feedback:
tendency to overshoot the set point several times until the system returns to rest at the set point
19
Q
What happens in positive feedback?
A
Stimulus produces a response which increases its effect, rather than counteracts it i.e. the output adds on to the input
20
Q
Give examples of positive feedback.
A
Blood clotting
Ovulation - build-up of the hormone follicle stimulating hormone (FSH) causes release of an oocyte from a follicle in the ovary
21
Q
What is long loop feedback?
A
Hormone that was released from the peripheral endocrine glands inhibiting pituitary and/or hypothalamic secretion of releasing hormones.
e.g. cortisol feedbacks to pituitary and hypothalamus inhibiting release of ACTH and CRH respectively
22
Q
What is short loop feedback?
A
Generally refers to a pituitary hormone providing negative feedback to the hypothalamus
e.g. ACTH feeds back to the hypothalamus inhibiting release of CRH
23
Q
Give examples of biological rhythms.
A
- cortisol
- menstrual cycle (temperature varies)
- biological clock
24
Q
When does levels of cortisol in the blood peak and trough?
A
Peak - 7am
Trough - 7pm
25
What should be noted when taking cortisol measurements and and when should repeated measurements be taken?
Time of measurement should be noted and repeated measurements should be taken at the same time each day
26
If reduced levels of cortisol are suspected, when should measurements be taken?
7am, when levels are expected to be the highest.
27
Define homeostasis
Homeostasis is not a steady state but a dynamic
| equilibrium. Failure in homeostasis leads to disease. Homeo "same" stasis "standing"?
28
What should a sudden increase in body temperature in women be used as a marker for?
Ovulation
29
Which group of neurons in the hypothalamus are responsible for the biological clock?
Suprachiasmatic nucleus
30
What are zeitgebers? give examples.
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Environmental cues that entrain circadian cycles:
• Light
• Temperature
• Social interaction
• Exercise
• Eating/drinking pattern
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31
Which hormone is involved in setting the biological clock and where is it released from?
Melatonin, released from the pineal gland
32
What causes jet lag?
Changing of time zones results in a mismatch between environmental keys and our 'body clocks', causing 'jet lag'
33
At what levels do homeostatic mechanisms exist?
- Cell (e.g. regulation of intracellular Ca2+ concentration)
- Tissue (e.g. balance between cell proliferation and cell death (apoptosis)
- Organ (e.g. Kidney regulates water and ion concentrations in blood)
- Organism (e.g. constant body temperature)
34
What is the afferent pathway in homeostatic control systems?
Stimulus —> receptor —> control centre
35
What is the efferent pathway in homeostatic control systems?
Control centre —> effector —> change
36
What is the hypothalamic-pituitary- adrenal (HPA) axis?
- negative feedback system
- corticotropin releasing hormone (CRH) is released from the hypothalamus into the local portal circulation
- CRH binds to specific receptors on corticotropic cells of the anterior pituitary gland which stimulates the release of adrenocorticotropic hormone (ACTH) into the circulation
- ACTH is transported in the blood to the cortex of the adrenal glands where it binds to specific receptors on the cells in the zona fasciculata and stimulates the release of cortisol into the circulation —> body's response to stress
negative feedback occurs at two levels: ACTH inhibits release of CRH and cortisol inhibits release of CRH and ACTH
37
What fluctuates during the biological clock?
- temperature - drops during sleep
- cortisol - at its lowest and increases during sleep
- melatonin - increases during sleep
38
What type of receptors monitor osmolality and sodium ion concentration of blood plasma?
Osmoreceptors.
39
Which nuclei are osmoreceptors found in?
supraoptic and paraventricular nuclei of the hypothalamus
40
Cells of the supraoptic and paraventricular nuclei influence what feeling?
Thirst
41
What percentage of body weight is the total body water in men and women?
Men - 50-60%
| Women - 45-50%
42
What compartments is total body water contained in?
Intracellular fluid, extracellular fluid, blood plasma
43
What is osmotic pressure of blood plasma monitored by?
Osmoreceptors in hypothalamus
44
What is the difference between osmolarity and osmolality?
Osmolarity —> number of osmoles per litre of solution (volume)
Osmolality —> number of osmoles per kg of solution (mass)
osmoles = osmotically active particles
45
What do cells of the supraoptic and paraventricular nuclei release?
Release a hormone from the posterior pituitary gland called antidiuretic hormone (ADH)
46
What does ADH do?
Increase in the permeability of the collecting
ducts to water, thus increasing the reabsorption of water from the urine into the blood. This has the effect of making the urine more concentrated and decreasing the loss of water in the urine
47
Describe the process that occurs when there is high blood osmolality
* High blood osmolality - Body needs to conserve water
* Detected by Osmoreceptors in hypothalamus
* Posterior Pituitary secretes more ADH
* Increased reabsorption of H2O from urine into blood in collecting ducts in the kidney
* Small volume of concentrated urine
* Thirst due to osmoreceptors - Drinking reduces osmolality
48
Describe the process that occurs when there is low blood osmolality
* low blood osmolality - Body needs to excretewater
* Detected by Osmoreceptors in hypothalamus
* Posterior Pituitary secretes less ADH
* decreased reabsorption of H2O from urine into blood in collecting ducts in the kidney
* large volume of concentrated urine
49
What causes a response in target cells (of hormones)?
A change in concentration of that hormone
50
What are the chemical type classifications of hormones?
* Peptide/polypeptide hormones (largest group)
* Glycoprotein hormones
* Amino acid derivatives (amines)
* Steroid hormones
51
What are peptide/polypeptide hormones? give examples.
short or long chain(s) of amino acids.
e.g. insulin, glucagon, growth hormone, placental lactogen.
- water soluble
52
What is Endocrine signalling?
Hormone signal released into bloodstream and carried to distant target cells
53
What is Neurocrine signalling?
Hormone originates in neurone and after transport down axon releasedinto bloodstream and carried to distant target cells
54
What are glycoprotein hormones? give examples.
large protein molecules with carbohydrate side chains
e. g. luteinizing hormone (LH), follicle stimulating hormone (FSH) and thyroid stimulating hormone (TSH)
- water soluble
55
What are amino acid hormones? give examples.
small molecules synthesised from amino acids
e.g. adrenaline (a catecholamine) and the thyroid hormones - thyroxine & triiodothyronine. melatonin
- adrenal medulla hormones are water soluble
- thyroid hormones are lipid soluble
56
Define hormone
Chemical signals produced in endocrine glands or tissue that travel in bloodstream to cause an effect on other tissues.
57
What are steroid hormones? give examples.
These are all derived from cholesterol
Steroidogenic tissues convert cholesterol to different hormones
e.g. cortisol, aldosterone, testosterone & oestrogen.
- lipid soluble
58
Where do endocrine glands that produce the polypeptide hormones and catecholamines normally store their hormonal products?
Within the cells in discrete storage vesicles prior to secretion
59
Where do steroid producing tissues store their hormones?
Do not normally store hormones, but store their precursor, cholesterol, as cholesterol esters in the form of lipid droplets
60
Where does the thyroid gland store its products?
outside the cell in the form of a protein colloid
61
How are lipophilic hormones normally found in the blood?
lipophilic hormones (steroids and thyroid hormones) bind specifically or nonspecifically to proteins in the blood
62
Give an examples of a specific and non-specific binding protein for thyroid hormones.
Specific: thyroxine binding globulin (TBG)
| Non-specific: Albumin
63
What is the endocrine system?
collection of glands/ organs/ tissues that produce and release hormones (chemical signals)
64
What organs and tissues release important hormones (aside from endocrine glands)?
- heart —> ANP and BNP
- liver —> IGF1 (insulin like GF)
- stomach —> gastrin, ghrelin
- placenta —> inhibin, placental lactogen
- adipose —> leptin
- kidney —> EPO, renin, calcitriol
65
Where are the major endocrine glands located?
Hypothalamus, pineal gland, pituitary gland, thyroid gland, parathyroid gland, thymus, adrenal gland, pancreas, ovary, testis
66
What would be the expected total volume of blood in a. 70 kg man?
5 litres
67
What term is used to describe low blood sodium?
Hyponatraemia
68
What happens when plasma glucose levels rise after a meal?
- beta cells in islets of langarhans in the pancreas release insulin
- insulin stimulates glycogenesis in the liver And glucose uptake into tissues (GLUT4)
69
What happens when plasma glucose levels fall after fasting?
- alpha cells in the islets of langarhans in the pancreas release glucagon
- glucagon stimulates glycogenolysis in the liver which releases glucose back into the blood
70
What do the endocrine and nervous systems have in common?
- both neurons and endocrine cells can secrete
- both can also be depolarised
- some molecules act as both neutrotransmitter and hormone
- the mechanism of action requires interaction with specific receptors in the target cells
- both systems work in parallel to control homeostasis
71
What are the differences between the endocrine and nervous system?
- the endocrine system involves hormones as signalling molecules whereas the nervous system involves neurotransmitter and APs
- the nature of the signalling molecules in the endocrine system is chemical whereas in the nervous system it can also be electrical
- signalling molecules are carried via the bloodstream in the endocrine system but vis synapses and axons in the nervous system
- the nervous system is much faster
72
Which hormones can travel in the blood freely?
Polypeptide hormones, glycoprotein hormones and adrenaline aremrelatively hydrophilic and are transported in the bloodstream dissolved in the plasma
73
What are the roles of carrier proteins?
* Increase solubility of hormone in plasma
* Increase half-life
* Readily accessible reserve - hormones stay in their bound state until more hormone is needed and can be released from the binding protein
74
Which form of a hormone is biologically active?
Only free form is biologically active
75
What type of equilibrium is found between bound and free forms of hormone in plasma?
Dynamic equilibrium
76
What are the normal total and free concentrations of thyroid hormones in the blood?
Total = 60-160 nM
Free and therefore biological active = 15-30 pM as 75% is bound specifically to TBG and almost 25% is bound non specifically to other proteins such as albumin
77
What are the 3 main factors that determine hormone levels in the blood?
1) Rate of production
2) Rate of delivery (higher blood flow to a particular organ will deliver more hormone)
3) Rate of degradation
78
What is acromegaly?
Excess secretion of growth hormone, which, in the
| adult produces characteristic changes in the shape of the face and body and other metabolic effects
79
What are tropic hormones?
hormones that have other endocrine glands as their targets - mostly secreted by the anterior pituitary gland
80
What are trophic hormones?
stimulate growth in the target tissue
81
Where are lipophilic hormone receptors found?
cytoplasm or nucleus
82
Where are hydrophilic hormone receptors found?
cell surface
83
What is released in a cell with cell membrane receptor and how long is the response time?
Second messenger
| - seconds to minutes
84
How do G protein-coupled receptors work?
- hormone binds to the receptor e.g. adrenaline receptor
- this causes dissociation of the G protein alpha subunit
- this activates the effector protein e.g. adenylyl cyclase
- formation of second messenger e.g. cAMP
- activation of protein kinase e.g. PKA
- phosphorylation of target proteins —> cellular response
85
How do tyrosine kinase receptors work?
- hormone binds to the receptor e.g. insulin receptors
- dimerisation of receptor occurs (except insulin receptor as it is already dimerised)
- auto phosphorylation of specific tyrosines
- recruitment of adapter proteins and signalling complex
- activation of protein kinase e.g. PKB
- phosphorylation of target proteins —> cellular response
86
What are the two different types of lipid soluble hormones that bind to intracellular receptors?
Type 1 : cytoplasmic receptor binds to the lipid soluble hormone and receptor hormone complex enters the nucleus and binds to DNA
Type 2: hormone enters the nucleus and binds to pre-bound receptor on the DNA e.g. thyroid hormone
87
How do lipid soluble hormones work to express a new protein?
- hormone binds to receptor which binds/ is already bound to a specific DNA sequence called a hormone response element (HRE) in promotor region of specific genes
- affects transcription and causes a new protein to be made —> cellular response
88
What effect to intracellular receptors have and how long is the response time?
changing the rate of gene expression occurs over a longer time period (minutes-hours)
89
where are hormones inactivated?
Inactivation of hormones occurs in the liver and kidney and sometimes in target tissues
90
How are steroid hormones inactivated?
relatively small change in chemical structure that increases their water solubility enabling them to be excreted from the body in the urine or via the bile
91
How are peptide hormones inactivated?
Degraded to amino acids that are reused for protein synthesis
92
What diseases can be caused by abnormalities of the endocrine system?
Thyroid disease, diabetes, cushings disease, Addison's disease, infertility
93
What types of disorders can occur in endocrine systems?
* changes in the endocrine tissue that leads to over or under secretion of hormones or production of structurally abnormal and less effective hormones.
* The responsiveness of endocrine tissues may be altered by the presence, in the circulation, of abnormal proteins such as antibodies.
* The physiologically effective concentration of the hormone in the circulation may be reduced because of binding to circulating proteins.
* There may be changes in the responsiveness of target tissues to hormones resulting from changes to receptors and/or postreceptor events
