Intro Flashcards
What is a circadian rhythm?
Physiological changes that occur normally as part of a 24 hour period
What are some examples of things that change in a circadian rhythm? How do they change?
Body temperature - decreases with sleep
Cortisol - increases with sleep
Melatonin - increases with sleep
What is the biological clock?
Small group of neurones in the suprachiasmatic nucleus in the brain
What are the inputs to the biological clock?
Changes in the environment to do with
- light
- temperature
- eating/drinking pattern
What is the function of the biological clock?
Responsible for putting into effect the circadian rhythm
What causes jet lag?
Mismatch of environmental inputs
and the biological clock output
What secretes melatonin?
Pineal gland
What is the function of melatonin?
Sets the biological clock
What is negative feedback?
Change away from set point causes response to reverse the direction of change
What is a classic example of negative feedback in endocrinology?
The HP axis
involves short loops, long loops and ultra short loops of negative feedback
What is positive feedback?
Change away from set point causes response to give more change in same direction
When is positive feedback used?
When a rapid change is desirable
What are some examples of positive feedback?
Blood clotting (e.g. thrombin burst)
Ovulation
Ferguson reflex - oxytocin and uterine contractions during childbirth
Which is more common - positive or negative feedback?
Negative feedback
What is responsible for detecting osmotic pressure of blood plasma?
Osmoreceptors
Where are osmoreceptors located?
Hypothalamus
What is normal blood osmolality?
275 - 295 mOsm/kg
What happens in response to osmoreceptors in the hypothalamus detecting high blood osmolality?
Posterior pituitary secretes more ADH
Increased thirst
What is the effect of increased ADH secretion?
Increased reabsorption of water from urine into blood
in collecting ducts in kidney
What effect does increased reabsoprtion of water from urine have on urine?
Smaller volume of urine produced
and urine is more concentrated
What happens in response to osmoreceptors in the hypothalamus detecting low blood osmolality?
Posterior pituitary secretes less ADH
What is the effect of decreased ADH secretion?
Decreased reabsorption of water from urine into blood
in collecting ducts in kidney
What effect does decreased reabsorption of water from urine have on urine?
Larger volume of urine produced
and urine is more dilute
What is the endocrine system?
Collection of glands throughout the body
What are hormones?
Chemical signals produced in endocrine glands
or tissues
travel through bloodstream
cause an effect on other tissues
Do only endocrine glands produce hormones?
No
other organs and tissues are release hormones
Which other organs or tissues produce hormones? What hormones?
Heart - ANP, BNP
Liver - IGF-1
Stomach - Ghrelin
Adipose - Leptin
Kidney - EPO, renin, calcitriol
What are the glands of the endocrine system?
Hypothalamus
Pituitary gland
Pineal gland
Thyroid gland
Parathyroid glands
Thymus gland
Adrenal glands
Pancreas
Ovaries
Testes
What is neurocrine secretion?
Hormone originates in neurone
transported down axon
released into bloodstream
carried to distant target cells
What are the similarities between the nervous and endocrine systems?
Neurones and endocrine cells are capable of secreting
Neurones and endocrine cells can be depolarised
Some molecules are both hormones and neurotransmitters
Mechanism of action involves interaction with specific receptors on target cells
Both control homeostasis
What do neurones secrete? What do endocrine cells secrete?
Neurones - neurotransmitters
Endocrine cells - hormones
Which system communicates faster - nervous or endocrine?
Nervous system
What is an example of a molecule that’s both a neurotransmitter and a hormone?
Dopamine = Prolactin inhibiting hormone
What are the four categories of hormones?
Peptide/polypeptide
Amino acid derivates
Glycoproteins
Steroids
What is the most common category of hormone?
Peptide/polypeptide
What are some examples of peptide/polypeptide hormones?
Insulin
Glucagon
Growth hormone
How do peptide/polypeptide hormones react to water?
Hydrophilic
water-soluble
What are amino acid derived hormones synthesised from specifically?
AROMATIC amino acids
What are some examples of amino acid derived hormones and their corresponding amino acid?
Tyrosine
- adrenaline
- noradrenaline
- thyroid hormone
Tryptophan
-melatonin
Which of the amino acid derived hormones are water-soluble?
Adrenaline
Noreadrenaline
Which of the amino acid derived hormones are lipid-soluble?
Thyroid hormone
What is the structure of glycoprotein hormones?
Large protein molecules - often subunits of them
with carbohydrate side chain
What are some examples of glycoprotein hormones?
LH - leuteinising hormone
FSH - follicle stimulating hormone
TSH - thyroid stimulating hormone
How do glycoprotein hormones react to water?
Hydrophilic
Water soluble
What are steroid hormones derived from?
Cholesterol
What are some examples of steroid hormones?
Cortisol
Aldosterone
Testosterone
How do steroid hormones react to water?
Hydrophobic
insoluble in water, lipid-soluble
Which hormones travel in the blood as part of the solution?
Peptides
Glycoprotein hormones
Some amino acid-dervied hormones
How do insoluble hormones travel in the blood?
Bound to specific carrier proteins
What are the roles of carrier proteins?
Increase solubility of hormone in blood plasma
Increase half life
Form a reserve of hormone
Is the free form or the protein-bound form of the hormone biologically active?
Free form
How are the levels of free hormone and protein-bound bound hormone controlled?
Free hormone + carrier protein = protein-bound hormone
dynamic equilibrium between the two
What are the factors determining levels of hormone in the blood? Which is the most regulated?
Rate of production
Rate of delivery - blood flow to tissue
Rate of degradation
Most regulated is rate of production
How are hormones degraded?
Metabolised and excreted from body
At what range of concentration do hormones circulate in the blood?
Picomolar
basically very low concentrations
How do hormones have effects on some cells and not others?
Target cells have specific receptors for the hormone
Non-target cells have no receptors for the hormone
so are unaffected by the hormone
Where are receptors for water-soluble hormones located?
Cell surface receptors
What are the two types of cell-surface receptors for water-soluble hormones?
GPCRs
Tyrosine kinase receptors
How do tyrosine kinase receptors work?
Ligand binds to receptor
receptor dimerises
autophosphorylation of specific tyrosines
recruitment of adapter proteins, signalling complex
activation of protein kinase…
Where are receptors for lipid-soluble hormones located?
Intracellular
- cytoplasm
- nuclear
How do lipid-soluble hormones enter the cell?
Diffuse across plasma membrane
What does a newly formed cytoplasmic receptor-hormone complex do?
Translocate into nucleus
bind to DNA
Where are nuclear receptors found?
In the nucleus
pre-bound to DNA
hormone response elements - promoter region of gene that’s regulated by the hormone
What effect does hormone binding to a nuclear receptor have?
Relieves suppression of gene transcription
that the bound receptor was responsible for
What is the result of cytoplasmic receptor-hormone complex and nuclear receptor-hormone complex?
Gene transcription
new protein produced
gives cell response
What is the nature of endocrine system signals? And nervous system signals?
Endocrine system - chemical
Nervous system - chemical and electrical
