Introduction to Endocrinology Flashcards
look at endocrine axes
What is the definition of a hormone?
- A hormone is a chemical messenger that is secreted directly into the blood by discrete specialised cells in response to a specific stimulus and which are transported to a distant target tissue where it exerts it specific effect
What does Ernest Starling state about hormones?
- mediate cell to cell communication
- regulate physiological processes
- maintain homeostasis
There are various endocrine glands in the body - What are they responsible for?
- for hormone production
What do endocrine glands secrete?
- secrete hormones into the bloodstream
Other than endocrine glands what can also produce hormones?
- organs
- tissues
What do primary endocrine tissues do?
- tissue is solely endocrine in nature
What are examples of primary endocrine tissues?
- pituitary gland
- adrenal gland
What are secondary endocrine glands?
- tissues combine, major endocrine function with related functions
What are examples of secondary endocrine tissues?
- hypothalamus
- pancreas (insulin)
What are tertiary endocrine tissues?
- tissues has only a minor endocrine function with a major primary functions
What are examples of tertiary endocrine tissues?
- ovaries which release oestrogen and then the growth of follicles
- kidney main function is filtration but also secretes some hormones
- the heart
- the intestines
What is the function of a hormone?
- the function of a hormone is to regulate the activity of its target cells in a specific manner
How does the endocrine glands maintain hormone function?
- they receive constant rapid information about the state of systems being regulated
What does the endocrine glands receiving constant information ensure?
- ensures that the release of the hormone can be tailored to meet the requirements of the target cells
How can hormones be tailored to meet requirements of target cells?
- this is achieved by feedback mechanisms, mainly negative feedback
What do feedback systems allow for?
- the levels of hormones are tightly controlled, and homeostasis is maintained
What are the classification of hormones?
- protein and peptide hormones
- steroid hormones derived from cholesterol
- amino acids derivatives
- fatty acids derivatives
How are protein and peptide hormones synthesized?
- synthesised from amino acids
What are protein and peptide hormones like in terms of size?
- they vary in size
What is the structure of a peptide hormone?
- quite short
- consist of only single chain of few amino acids
What is the structure of a protein hormone?
- larger chains of amino acids or consists of more peptide chains
Where are protein and peptide hormones stored?
- stored in secretory vesicles until needed
- released upon a signal
What is the size of a glycoprotein hormone?
- large molecule
What are examples of glycoproteins?
- Gonadotrophins which include …
- luteinising hormone (LH)
- follicle stimulating hormone (FSH)
- thyroid stimulating hormone (TSH)
Where are gonadotrophins (glycoprotein peptide hormones) from?
- from the anterior pituitary
What is the structure of a glycoprotein peptide hormone?
- consists of two distinct peptide chains (called alpha and beta subunits) which are linked together by non-covalent bonds
What is the alpha subunit in a glycoprotein peptide hormone common to?
- LH
- FSH
- TSH
- chorionic gonadotrophin (CG)
In a glycoprotein peptide hormone what is the beta subunit responsible for?
- biological specificity
- which makes the hormone unique in function
What process do glycoprotein peptide hormones go through?
- they are glycosylated
What are steroid hormones?
- The steroids are a large class of lipids
Where are steroid hormones synthesized mainly and what is their common precursor?
- they are synthesised mainly in the adrenal cortex, testis, ovary and placenta from a common precursor which is cholesterol
Steroid hormones all have a common structure - what is this?
- consist of 3 six-membered rings and 1 five membered ring
Hormones can be derived from amino acids such as tyrosine which is a precursor for what hormones?
- adrenaline
- noradrenaline
- dopamine
- thyroid hormones = thyroxine (T4) and triiodothyronine (T3)
What are hormones derived from fatty acids called?
- eicosanoids
Hormones that have been derived from fatty acids have two major classes of messengers - what are these?
- prostaglandins (PG’s)
- leukotrienes (LTs)
What are the messengers derived from in hormone derived fatty acids?
- derived from arachidonic acid (AA)
What type of lifespan do hormone derived from fatty acids have?
- short half-life act near the site of synthesis
Where are PG’s formed?
- in most tissues of the body
The type of PG formed varies depending on what?
- on the type of down-stream enzymes present
PG’s produced in the uterus have a role in what?
- have a role in embryo implantation and in foetal membranes
- role in parturition
PG’s found in seminal vesicles promote what?
- sperm motility
How do hormones exert their effects?
- exert their effects by binding to receptors
What are the two types of hormone receptors a cell can have?
- cell-surface receptors
- intracellular receptors
What types of hormones would bind to cell-surface receptors?
- protein and peptide hormones
What type of hormone would bind to intracellular receptors and why would they bind?
- steroid hormones
- due to lipids being able to be taken into cells
What reproductive hormone is released by the hypothalamus?
- gonadotrophin-releasing hormone (GnRH)
What reproductive hormone is released by the pineal gland and what is this hormone associated with?
- melatonin
- associated with seasonality and breeding
What reproductive hormones are released by the anterior pituitary?
- LH
- FSH
- prolactin (milk secretion)
What reproductive hormone is released by the posterior pituitary and what is it important in?
- oxytocin
- important in parturition and milk let down
What reproductive hormones are released by the gonads?
- oestrogen and progesterone
- testosterone
What reproductive hormones are released by the placenta?
- oestrogens
- progesterone
- chorionic gonadotrophin
- prostaglandins (parturition)
What type of hormones are LH and FSH?
- gonadotrophins
What type of hormones are oestrogen and progesterone, and testosterone?
- steroids
What type of hormone is GnRH and what does it consist of?
- peptide hormone consisting of 10 amino acids
Where is GnRH synthesised?
- synthesised in the hypothalamus
What are GnRH derived from?
- derived from post-translation modification of precursor molecule
What type of manner are GnRH hormones secreted in?
- secreted in a pulsatile manner
What is the half-life of GnRH in a ewe?
- 7 mins
How does GnRH bind?
- binds to GnRH receptor on gonadotroph cells in anterior pituitary
How are gonadotrophins - LH and FSH secreted?
- secreted by gonadotroph cells in anterior pituitary, in response to GnRH
What type of molecules are LH and FSH?
- glycoproteins
What is the half-life of LH?
- 30 mins
What is the half-life of FSH?
- 3-4 hours
What receptors do LH and FSH bind to?
- bind to receptors in the gonads
Both LH and FSH have an effect on what?
- Will affect both testes and ovaries
What does FSH have an effect on?
- sperm production
- stimulation, growth, and maturation of follicle
What does LH effect?
- effects testes
- effects on ovulation, progesterone secretion and corpus lutetium formation
What are the gonadal steroids?
- progestins
- oestrogens
- androgens
What are the progestins?
- progesterone
- 17 alpha-hydroxyprogesterone
- 20 alpha hydroxyprogesterone
What are the oestrogens?
- oestradiol
- oestriol
- oestrone
What are the androgens?
- testosterone
- 5 alpha dihydrotestosterone
- androstenedione
- dehydroepiandrosterone
What does testosterone induce?
- induces and maintains differentiation of male somatic tissues
- induces secondary sex characteristics of males (deep voice, body hair, penile growth)
What does testosterone support?
- supports spermatogenesis (production of sperm)
What type of behaviour does testosterone influence?
- sexual
- aggressive
What does testosterone promote in the body?
- protein anabolism
- somatic growth
What does testosterone regulate the secretion of?
- regulates the secretion of gonadotrophins (negative feedback)
oestradiol stimulates the growth and activity of what?
- mammary gland
- endometrium
What does oestradiol prepare the uterus for?
- spermatozoal transport
What does oestradiol prepare the endometrium for?
- prepares endometrium for progesterone action (i.e., induce progesterone receptors)
What does oestradiol increase?
- increases vascular permeability and tissue oedema
What does oestradiol regulate the secretion of?
- regulates the secretion of gonadotrophins
What type of behaviour is oestradiol associated with in some species?
- sexual behaviour
What characteristics does oestradiol stimulate in females?
- secondary sex characteristics
What is oestradiol required for?
- normal physiological processes in the heart, muscle, bone, brain and liver
What does progesterone prepare the uterus for?
- to receive conceptus
What does progesterone do during pregnancy?
- depresses uterine activity
What effect does progesterone have on mammary glands?
- stimulates growth
- suppression on secretion of milk
What does progesterone promote the formation of?
- formation of non-penetrable cervical mucous
What effects does progesterone cause on the CNS?
- neuroprotective effects on CNS
Progesterone regulates the secretion of what?
- regulates gonadotrophin secretion through negative feedback
