2 - Endocrine Glands Flashcards
Give three examples of endocrine glands
- the thyroid/parathyroid glands
- gonads
- pancreas
What does the pancreas secrete?
Insulin
What do the gonads secrete?
Males - testosterone / Females - oestrogen and progesterone
What des the thyroid & parathyroid produce?
The thyroid produces thyroid hormones & the parathyroid produces parathyroid hormones
What are the principle endocrine glands in both females and males?
- the principle endocrine glands in males and females are the same
- we have the endocrine glands associated with the brain
- for example, the pineal gland, the hypothalamus, and pituitary glands at the base of the brain
- in the throat we have a thyroid gland and four associated parathyroid glands
What happens in the pancreas?
The pancreas secretes insulin, but also the hormone glucagon, which counteracts insulin actions on blood glucose
How are the kidneys involved?
Attached to the kidney are adrenal glands, which produce a range of steroid hormones that can regulate salt and water balance
Role of the gonads?
- the gonads are different between males and females
- in the female, there are ovaries which secrete oestrogen throughout the menstrual cycle and progesterone during pregnancy
- in males are the testes which produce testosterone
What hormones are produced by the thyroid?
- thyroxine
- calcitonin
What is the function of thyroxine and calcitonin?
Thyroxine - regulates metabolism
Calcitonin - Inhibit release of calcium from the bones
What is the function of the parathyroid hormone?
Stimulates the release of calcium from the bones
What hormones do islet cells (in the pancreas) produce?
- insulin
- glucagon
What is the function of insulin and glucagon?
Insulin - decreases blood sugar by promoting uptake of glucose by cells
Glucagon - increases blood sugar by stimulating breakdown of glycogen in the liver
What is the function of testosterone?
Regulates sperm cell production and secondary sex characteristics
What Is the function of oestrogen and progesterone?
Oestrogen - stimulates egg maturation, controls secondary sex characteristics
Progesterone - prepares the uterus to receive a fertilised egg
What hormone does the adrenal cortex produce?
Epinephrine
What is the function of epinephrine?
“fight or flight”
What hormones does the adrenal medulla produce?
- glucocorticoids
- aldosterone
- testosterone (in both sexes)
What are the functions of glucocorticoids (1), aldosterone (2), and testosterone (3)?
- part of stress response, increase blood glucose levels and decrease immune response
- regulates sodium content in the blood
- adult body form (greater muscle mass), libido
What hormone does the pineal gland produce?
Melatonin
What is the function of melatonin?
Sleep cycles, reproductive cycles in many mammals
What does the hypothalamus do?
The hypothalamus receives information from the nervous system and initiates responses through the endocrine system
What does the hypothalamus serve as?
- the hypothalamus serves as an interface between higher brain function and the production of hormones secretes into the blood
-therefore acts s a bridge between the nervous system and the endocrine system - basically there’s a collection of nerves which can receive synoptic input but can also secrete locally acting hormones
What is attached to the hypothalamus?
The pituitary gland
What is the pituitary gland composed of?
The posterior pituitary and anterior pituitary
What is the role of the posterior pituitary?
- stores and secretes hormones that are made in the hypothalamus
- these are neuroendocrine hormones
What is the role of the anterior pituitary?
- makes and releases hormones under regulation of the hypothalamus
- the hypothalamus secretes peptide hormones to regulate the activity of the anterior pituitary
Give examples of pituitary hormones
- follicle-stimulating hormone
- luteinising hormone
- thyroid-stimulating hormone
- adrenocorticotropic hormone
- melanocyte-stimulating hormone
- growth hormone
- antidiuretic hormone
- oxytocin
What is the function of follicle-stimulating hormone (1) and luteinising hormone (2)?
- stimulates egg maturation in the ovary and release of sex hormones
- stimulates maturation of egg and of the corpus lute surrounding the egg, which affects female sex hormones and the menstrual cycle
What is the function of thyroid stimulation hormone?
Stimulates the thyroid to release thyroxine
What are the functions of adrenocorticotropic hormone (1) and melanocyte-stimulating hormone (2)?
- causes the adrenal gland to release cortisol
- stimulates synthesis of skin pigments
What are the functions of growth hormone (1), antidiuretic hormone (2) and oxytocin (3)?
- stimulates growth during infancy and puberty
- signals the kidney to conserve more water
- affects childbirth, lactation, and some behaviours
How are hormones regulated?
Hormones are regulated by feedback loops
What is a negative feedback loop?
A negative feedback loops inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity
What is a positive feedback loop?
A positive feedback loop reinforces a stimulus to produce an even greater response
Give an example of a positive feedback loop
- a prime example of a positive feedback loop involved in pregnancy is oxytocin
- as the babies head moves down the birth canal, the production of oxytocin is stimulated, and the more the baby moves, the more oxytocin is produced and the more rhythmic contraction of the uterine muscles occur
- therefore there is a positive feedback enabling the baby to be born
What is the posterior pituitary involved in?
It is involved in secreting hypothalamic hormone
What is the role of neutrons in the posterior pituitary?
- neurone are sent down from the hypothalamus into the posterior pituitary
- these neurone or neuroendocrine cells secrete small peptides directly into the bloodstream across a synapse
What are the posterior pituitary neurohormones? (include the function)
- neuroendocrine has signalling, so these neurohormones include oxytocin and ADH (anti-diuretic hormone), and these are small peptides
- oxytocin interacts with receptors in the mammary glands (also involved in the contraction of uterine muscles and is involved in birth)
What are the pituitary hormone effects?
LH and FSH stimulate spermatogenesis and testosterone secretion by the testes
What are the testes hormone effects?
Testosterone and inhibin inhibit the secretion of GnRH by the hypothalamus and LH and FSH by the pituitary
What does the hypothalamus produce in the male reproductive system?
-normally the hypothalamus produces a hormone called Gonadotropin Releasing Hormone (GnRH) which is a small peptide/neuropeptide
What does the production of GnRH result in?
- GnRH interacts with receptors on gonadotroph in the anterior pituitary
- this leads to the production of LH and FSH which travel through the bloodstream (being soluble peptide hormones) & interact with receptors in the testes
What hormones are needed to sperm production?
FSH from the anterior pituitary & testosterone from the leydig cells
What are the two different types of receptors and what do they do?
- FSH receptors - found in the Sertoli cells and when they interact with these receptors, the process of spermatogenesis is promoted
- LH receptors - interact with leading cells in the tested causing increasing in intracellular activating that leads to the production of testosterone (positive feedback)
What is the negative feedback in the male reproductive system?
- there is a negative feedback effect so that too much FSH and LH is produced
- testosterone produced by the leydig cells travel through the bloodstream interacting with he nuclear receptors in the anterior pituitary nd the hypothalamus to prevent further production of GnRH and further production of FSH
How do we ensure the negative feedback in the male reproductive system is strong enough?
There is the production of another hormone from the Sertoli cells called inhibin (protein hormone)
How is the anterior pituitary and peptide hormones linked?
In the anterior pituitary there is direct synthesis and secretion of peptide hormones from the anterior pituitary cells
What is the role of the hypothalamus and peptide hormones (anterior pituitary)?
- the production of the peptide hormones is under the control of the hypothalamus
- the hypothalamus decreases neurosecretory peptides, but these enter the portal vessels, which are blood vessels that feed into the anterior pituitary
What does the anterior pituitary regulate?
- regulation of production of follicle stimulating hormone and luteinising hormone
- these are peptide hormones which regulate the action of the testes or the ovaries
What happens during menstruation?
There is a loss of the lining of the uterus
What happens day 5 of the menstrual cycle?
Another egg develops in the ovary after menses and this is stimulated by increases in oestrogen production by the ovary until we get to the midpoint of the menstrual cycle
What happens to the progesterone and oestrogen levels during the menstrual cycle?
- progesterone level is low as oestrogen is being produced
- this suppressed FSH and LH production by negative feedback
-but about day 12 to 14, about the midpoint of the menstrual cycle, we have a surge in LH and FSH production causing positive feedback on the hypothalamus and the anterior pituitary
What does early stage FSH production cause?
- this early stage FSH production surge causes ovulation (release of an egg)
- this coincides with the transformation of the follicle into the corpus luteum, and it produces progesterone instead of oestrogen
What happens when progesterone levels rise after the release of an egg?
There is a negative feedback effect on FSH and LH
What causes more progesterone production?
- the development of the corpus luteum
- as the egg is fertilised, the corpus luteum is maintained and progesterone levels level off and there is an extension of the luteal phase were the lining of the uterus is beneficial to implantation of the egg
What happens if there is no ovulation?
There is a fall in progesterone levels
