hypothalamus and pituitary Flashcards
what makes up the endocrine system?
the endocrine system consists of ductless glands that secrete into the blood.
what do endocrine glands secrete?
hormones
what is a hormone?
A compound that is secreted by one cell and travels through the circulatory system to affect the activities of cells in another part of the body
what processes does the endocrine system control?
processes that require durations rather than speed.
what does the endocrine system play a role in?
Important in maintaining homeostasis and other functions such as growth and reproduction
what is endocrine action?
mediators released into blood to have action at distant cells
what is paracrine action?
mediators released to have effects on neighbouring cells
what is autocrine action?
mediators released to have effects on the same cell
what are hormones?
chemical messenger secreted into blood to act on distant target cells
what are neurohormones?
hormone released by neurons.
what are some examples of neurohormones?
ADH, Oxytocin
what are autacoids or local hormones?
chemical messenger that have paracrine action
examples of autacoids?
histamine, Ecosanoids
what are neurotransmitters?
chemical messenger released from the nerve terminals at the synaptic sites in response to action potential
what do neurotransmitters do?
they act locally on the post synaptic site on adjoining target cells which may be muscle, gland or another neuron
what are neuromodulators?
Chemical messenger which act on neuron at non synaptic sites to bring changes in the nerve cell.
what are some of the major endocrine glands?
pineal hypothalamus pituitary thyroid parathyroid thymus adrenal pancreas ovary and testes
what are the 3 main categories of hormones?
peptides and protein
steroids
derivatives of amino acid tyrosine
what are some examples of peptides and protein hormones?
Pituitary hormones, insulin, glucagon, parathormone
which steroid hormones does the adrenal cortex secrete?
cortisol and aldosterone
which steroid hormones do the ovaries and the placenta secrete?
oestrogen and progesterone
which steroid hormone do the testes secrete?
testosterone
what are the examples of the derivatives of tyrosine hormones?
Thyroxine and triiodothyronine
Catecholamines: Epinephrine and norepinephrine
what are the steps in the synthesis of peptide and protein hormones?
preprohormone –> prohormone –> active hormone + scraps protein
where is preprohormone synthesised?
in the endoplasmic reticulum
what happens to the prohormone?
it is packed into secretory vesicles by the golgi complex
what happens to the active hormone?
it is stored in secretory vesicles until released
are peptide and protein hormones hydrophobic or hydrophilic?
hydrophilic
do peptide and protein hormones need plasma protein binding for transport?
no, plasma protein binding is not essential for transportation of peptide and protein hormones.
where are the receptors for peptide and protein hormones on their target cells?
on the surface, they cannot diffuse into the target cells.
how do peptide and protein hormones function?
they function by either activating send messenger system, or changing ion channel permeability
do peptide and protein hormones have a long or short duration of action?
short duration of action
what is the precursor for steroid hormones?
cholesterol
what are the steps in the synthesis of steroid hormones?
cholesterol –> pregnenolone –> to the different steroid hormones
what determines what type of steroid hormone will be synthesised?
Pregnenolone is then converted to different steroid hormones in different steroidogenic organ depending on the set of enzymes that the organ contain.
are steroid hormones hydrophobic or hydrophilic?
hydrophobic
how are steroid hormones transported in the blood?
bound to plasma proteins
where are the receptors on the target cells of steroid hormones?
the receptors are in cytoplasm or nucleus, steroid hormones can diffuse into the target cells
how do steroid hormones function?
by activating specific gene in the target cell to cause the formation of new protein
do steroid hormones have a short or long duration of action?
long duration of action
are steroid hormones stored before being secreted?
no they are released into the blood as soon as they are synthesised
are thyroxine and triiodothyronine hydrophobic or hydrophilic?
highly hydrophobic
what are the properties of thyroxine and triiodothyronine
properties are similar to steroids hormones except that special mechanism exist to store this hormone in the thyroid gland
are epinephrine and norepinephrine hydrophobic and hydrophilic?
they are small hydrophilic molecules
what are the properties of epinephrine and norepinephrine?
properties are similar to that of peptide hormones
how is the secretion of hormones regulated?
feed back loops - most common is negative feedback
what is the hypothalamus?
the part of the brain which lies below the thalamus is the main centre responsible for homeostasis
what does the hypothalamus do?
the hypothalamus receives information about the state of the body from various inputs
where does the hypothalamus receive information from?
nucleus of the solitary tract, reticular formation, retina, circumventricular organs, limbic and olfactory systems
does the hypothalamus receive information intrinsically?
yes, the hypothalamus also has some intrinsic receptors, including thermoreceptors and osmoreceptors to monitor temperature and ionic balance, respectively.
how does the hypothalamus make the required adjustments?
neural signals to the autonomic system
endocrine signals to/through the pituitary
what is the pituitary gland (hypophysis)?
A small gland, 1 cm in diameter and about 0.5 g in weight that lies in sella turcia, a bony cavity
why is the pituitary gland known as the master gland?
it controls most endocrine functions
what type of hormones are released from the pituitary gland?
most hormones released by the pituitary gland are tropic hormones
what are the 2 distinct portions of the pituitary gland?
anterior pituitary (adenohypophysis) posterior pituitary (neurohypophysis)
where does the anterior pituitary (adenohypophysis) originate from?
Rathke’s pouch, a pharyngeal epithelium.
where does the posterior pituitary (neurohypophysis) originate from?
it is actually an extension of the hypothalamus
how is secretion from the pituitary controlled?
it is controlled by the hypothalamus.
what does the posterior pituitary consist of?
the axons of 2 groups of hypothalamic secretary neurones
what does the posterior pituitary secrete?
antidiuretic hormone (ADH) and oxytocin
what produces ADH?
Neurons with cell bodies in supraoptic nuclei
what produces oxytocin?
Neurons with cell bodies in paraventricular nuclei
what hormones does the anterior pituitary secrete?
growth hormone (GH) adrenocorticotropin (ACTH) thyroid stimulating hormone/thyrotropine (TSH) Prolactin (PRL) follicle-stimulating hormone (FSH) luteinising hormone (LH)
which cell type secretes GH?
somatotropes
what cell type secretes ACTH?
corticotropes
what cell type secretes TSH?
thyrotropes
what cell type secretes LH and FSH?
Gonadotropes
what cell type secretes PLR?
lactotropes
what do the neurones within the hypothalamus secrete?
hormones that control secretion of hormones from the anterior pituitary
what are the hypothalamic hormones referred to as?
releasing hormones and inhibiting hormones
how are the hypothalamic hormones transported?
carried directly to the anterior pituitary gland via hypothalamic-hypophyseal portal veins.
how do the hypothalamic hormones function?
Specific hypothalamic hormones bind to receptors on specific anterior pituitary cells, modulating the release of the hormone they produce.
what makes up an endocrine axis?
Each endocrine axis consists of a hypothalamic factor(s), its pituitary target cell type and the ultimate target gland(s).
what are the examples of the hypothalamus pituitary axes?
Hypothalamus-Pituitary Growth Hormone Axis Hypothalamus-Pituitary Adrenal Axis Hypothalamus-Pituitary Thyroid Axis Hypothalamus-Pituitary Gonadal Axis Hypothalamus-Pituitary Prolactin Axis
