Endocrine System Flashcards
1
Q
Define homeostasis
A
The many mechanisms in the body that seek to maintain the physical parameters within the body
2
Q
Explain the features of a control system in the body
A
- Stimulus
- Receptor - detects stimuli
- Chemoreceptors, thermoreceptors, proprioceptors (position and movement), nociceptors (pain)
- Sensors communicate through afferent pathway to the brain
- Nervous system uses action potential through nerves
- Endocrine system uses hormones
- Control center
- Determines set point, analyses afferent input and determines response
- Controlled in hypothalamus and medulla of brain stem
- Hypothalamus controls endocrine system
- Medulla controls ventilation and cardiovascular system
- Output produced by control center and communicates via efferent pathway to effectors
- Effectors - elicit change
- Eg. Sweat glands, kidney, muscles
- Negative feedback - output inhibits the function of the control centre and the effector acts to oppose the stimulus
- Response in a way to reverse the direction of change
- Positive feedback - response in a way so as to change the variable even more in the direction of the change
- Blood clotting, ovulation
3
Q
How does a biological clock work
A
- Circadian (diurnal) rhythm - set points of homeostasis changes at different times
- Eg. Menstrual cycle - women’s core body temperature increase marker for ovulation
- Eg. Cortisol levels high in the morning and gradually decrease in the day
- Biological clock located in hypothalamus in small group of neurones called suprachiasmatic nucleus
- Crossing time zones can result in mismatch in body clock and cause jet lag
- Pineal gland secretes melatonin - important in setting biological clock
4
Q
How is water in the body distributed in a 70kg male
A
- 42L (60%) is water
- 28L (66%) is intracellular and 14L (33%) is extracellular
- In the extracellular, 9L is interstitial fluid and 5L is blood plasma
5
Q
Differentiate between osmolality and osmolarity
A
- Osmolarity is number of osmoles per litre of solution
- Osmolality is number of osmoles per kg of solution
6
Q
What is normal serum osmolality
A
Serum osmolality = 275-295mOsmol/kg
7
Q
How is body water homeostasis controlled
A
- Osmoreceptors in hypothalamus monitor changes in osmolality pressure in blood plasma
- In hypertonic environment (high blood osmolality), cells lose water leading to cremation (shrinking)
- Posterior pituitary secretes more ADH which increases reabsorption of water from urine into blood
- Small volume of concentrated urine
- In hypotonic environment, body needs to excrete water
- Posterior pituitary secretes less ADH
- Decreased reabsorption of water from urine into blood in collecting ducts
- Large volume of dilute urine
8
Q
Define hormone
A
Hormones are chemical signals produced in endocrine glands or tissue travel in the bloodstream to cause an effect on other tissues
9
Q
What are the classes of hormones and gives its structure and example
A
- Peptide/polypeptide
- Largest group
- Short or large chains of amino acids - insulin, glucagon, growth hormone
- Water soluble
- Amino acid derivatives (amines)
- Synthesized from aromatic amino acids
- Adrenaline, noradrenaline, thyroid hormones all synthesized from tyrosine
- Melatonin synthesized from tryptophan
- Adrenal medulla hormones water soluble
- Thyroid hormones lipid soluble
- Synthesized from aromatic amino acids
- Glycoproteins
- Large protein molecules often made of subunits
- Carbohydrate side chain
- LH, FSH, TSH
- All water soluble
- Steroids
- All derived from cholesterol
- Steroidogenic tissues convert cholesterol to different hormones
- Cortisol, aldosterone, testosterone
- All lipid soluble
10
Q
What are mechanisms of communication through hormones
A
- Autocrine - hormone signal acts back on the cell of origin
- Paracrine - hormone signal carried to adjacent cells over a short distance via interstitial fluid
- Endocrine - hormone signal released into bloodstream and carried to distant target cells
- Neurocrine - hormone originates in neurone and transported down axon and released into bloodstream
11
Q
Through what ways are hormones transported
A
- Some hormones travel in blood in simple solution
- Peptides, adrenaline
- Some hormones are hydrophobic and require binding proteins for transport
- Increase solubility, increase half-life and make more stable
- Hormone isn’t active when bound to protein
12
Q
What factors determine hormone level in the body
A
- Rate of production - synthesis and secretion
- Rate of delivery - high blood flow to a particular organ will deliver more hormone
- Rate of degradation - hormones are metabolised and excreted from body
13
Q
What determines the effect of hormones
A
- Depends on concentration of hormone in blood stream
- For lipophilic hormones, depends on concentration of unbound or free hormones
14
Q
Describe how water soluble hormones have an effect on cells
A
- Water soluble hormones bind to cell surface receptors
- G-protein coupled receptors and tyrosine kinase
- Tyrosine kinase undergo autophosphorylation
- Dimerisation (except insulin receptor which is already dimerised)
- Recruitment of adaptor proteins and signalling complex
- Both activate protein kinase which causes phosphorylation of target proteins and cellular response
- Responses for thyroid hormone receptors slower as protein synthesis needed
15
Q
Describe how lipid soluble hormones have an effect on cells
A
- Lipid soluble hormones bind to intracellular receptors
- Can readily diffuse across plasma membrane
- Type I - cytoplasmic receptor binds hormone and receptor hormone complex enters nucleus and binds DNA
- Type II - hormone enters nucleus and binds to pre-bound receptor on DNA
- Receptor binds to specific DNA sequence called a hormone response element (HRE) in promoter region of specific genes
