Physiology of the Hypothalamus Pituitary Axis I&II Flashcards
What is the endocrine system?
it is a major regulatory system that coordinated life - sustaining responses and functions
what system works with the endocrine system in order to monitor and adjust physiologic activities?
the nervous system
what are neurotransmitters?
they are chemical messengers
what response does the nervous system perform?
short-term very specific responses to environment al stimuli
what does the endocrine system regulate?
longer-term ongoing metabolic processes throughout the body
what are hormones (in simple terms)?
chemical messengers (‘to excite’)
Name five pure endocrine glands:
pituitary
pineal
thyroid
parathyroid
adrenal
name 4 organs which contain endocrine cells:
pancreas
thymus
gonads
hypothalamus
what are endocrine cells?
they are glandular secretory cells that release hormones directly into the blood, lymphoid system or interstitial fluids
each hormone specificity?
each hormone is typically produced by a specific gland and has specific target organs
hormones can be divided into four classes according to their chemical structures, what are these classes?
amino acid derivatives
peptide and protein hormones
steroid hormones
fatty acid compounds
describe the chemical structure of amino acid derivative hormones?
these are derivatives of tyrosine
thyroid hormones and catecholamines
describe the chemical structure of peptide hormones:
chains of amino acids and they are the largest group of hormones
all pituitary hormones
describe the chemical structure of steroid hormones:
derived from cholesterol
reproductive organs, adrenal cortex, placenta
describe the chemical structure of fatty acid compounds, hormones:
derived from arachidonic acid
eicosanoids e.g. prostaglandins and leukotrienes
Coordinate cellular activities and affect enzymatic activity in ECF
What are diseases of endocrine glands often known as?
as hormones imbalances
treatments of diseases of endocrine glands include?
steroids
hormones
peptides and proteins
many other drugs
and treatments can often take a long time
do not confuse diseases of endocrine glands with?
with exocrinopathy (which represents a disease of the exocrine system
give examples of endocrinopathies in animals?
pituitary dwarfism
diabetes insipidus
hypo/hyperthyroidism
hypo/hypercalcaemia
hypo/hyperparathyroidism
diabetes mellitus
insulinoma
what is pituitary dwarfism?
secrete too little growth hormone in young animals
what is diabetes insipidus?
secrete too little antidiuretic hormone
what is hypo/hyperthyroidism?
secrete too little/too much thyroid hormone
what is hypo/hypercalcaemia?
circulating calcium too low/too high
what is hypo/hyperparathyroidism?
secrete too little/too much parathyroid hormone
what is diabetes mellitus?
secrete too little insulin (or insulin resistance)
what is insulinoma?
tumour secreting too much insulin
what does the hypothalamus form?
it forms the floor of a part of the brain called the diencephalon
what does the thalamus form?
forms the walls of the diencephalon
what nerve fibres does the hypothalamus have?
it has afferent and efferent nerve fibres linking to other parts of the central nervous system
what does the hypothalamus serve as a link between?
between the neuro and endocrine systems
where does the hypothalamus receive information from?
receives info from the body about internal and external environment and co-ordinates activities of various organs and tissues via endocrine and autonomic nervous systems
what is the pituitary also known as?
the hypophysis
where is the pituitary located?
in small pocket of the sphenoid bone of the skull in the base of the braincase
what is the pituitary linked to the hypothalamus by?
the infundibulum
pituitary gland consists of how many parts, and what are these parts?
3 parts
anterior lobe
intermediate lobe
posterior lobe
anterior lobe of the pituitary?
adenohypophysis - most pituitary hormones
intermediate lobe of the pituitary?
melanocyte stimulating factor
posterior lobe of the pituitary?
neurohypophysis - oxytocin and ADH
what is the posterior lobe of the pituitary?
it is an extension of the hypothalamus and is a part of the CNS
ADH and oxytocin are released from axon terminals
what are the anterior and intermediate lobes of the pituitary?
these are epithelial tissue derived from the oral cavity and contain endocrine cells
what does the pituitary control?
the endocrine system
hypothalamus and pituitary working together?
form a complex and also dominant component of the endocrine system
work together to control various different glands in the body in addition to having their own endocrine functions/hormone
what is the hypothalamic-pituitary-portal system?
release of pituitary controlled by the hypothalamus
blood brain barrier
protect from certain toxins floating around the body
blood vessels have holes in endothelium lining - these allow nutrients to leave bloodstream into extracellular fluid and bathe cells
but NO holes in blood vessels coming to brain as we can’t afford risk - tightly packed cells
protects potential leak of toxins
so active transport systems that move nutrients from blood stream into brain
what two hormones does the posterior pituitary release?
ADH and oxytocin
ADH aka?
vasopressin
ADH and oxyotcin?
both are peptide hormones that are composed of nine amino acids, seven of which are conserved
what neurons does the posterior pituitary consist of?
consists of neurosecretory neurons with the cell bodies residing within the hypothalamus in two defined nuclei and the axons of those cells residing in the posterior pituitary where the neurohormones can be relesed
what are the two defined nuclei within the cell bodies of posterior pituitary function?
supraoptic nucleus
paraventricular nucleus
ADH involved in what mechanism?
negative feedback mechanism
describe the negative feedback mechanism includingnADH?
hypothalamus detects decrease in blood volume and increase in osmolarity
makes animal thirsty and stimulates ADH producing neurons in hypothalamus
ADH released into blood which acts on the tubular cells of the collecting ducts in kidney
when ADH conc high, more aquaporins are incorporated into the luminal membranes of the tubular cells so more water absorbed from collecting ducts
blood volume increases + osmolarity decreases
animal no longer thirsty & ADH production decreases
lower ADH concentration in the blood results in fewer aquaporins and less water reabsorption - diuresis
what does ADH do?
regulation of water permeability of the renal distal tubules and collecting ducts - via insertion of aquaporin channels
what muscle does ADH cause contraction of?
of arteriolar smooth muscles
what are regulators of ADH secretion?q
extracellular osmolarity and extracellular fluid volume are primarily regulators of ADH secretion
what does water deprivation cause - ADH?
increases osmolarity of plasma and fluids bathing the brain
what does hyperosmolarity induce?
induces loss of intracellular water from osmoreceptors neurons in or near hypothalamus leading to release of ADH
what does water ingestion suppress - ADH?
supresses the firing of these osmoreceptors
ignoring water content, when is ADH also produced?
when there is a decrease in blood volume or blood pressure
what feedback mechanism is oxytocin involved in?
in positive feedback mechanism
what is oxytocin essential for?
uterine contractions during parturition contraction of myoepithelial cells in mammary alveoli for milk let-down
kitten not coming out - case 2 what do you do?
check cervix open and palpate - check animal in right orientation
secretion of hypophysiotropic hormones?
secretions regulated by one or more hypothalamic hypophysiotrophic hormones
what type of hormones are hypophysiotrophic hormones?
small peptide hormones
long loop feedback?
hormones released from the peripheral endocrine gland provides feedback to the pituitary or hypothalamus
short loop feedback?
hormones from the pituitary provides feedback to the hypothalamus
ultra-short feedback?
the hormones released by the endocrine organ directly provides feedback to the endocrine organ of origin
time period in which episodic secretions occurs over?
over the course of 24 hour period (circadian rhythms)
growth hormone is what type of hormone?
peptide hormone consisting of a single chain - 191 amino acids
growth hormone necessary for
growth
final outcome of growth is not ultimately determined growth factor - also depends on?
on genetic determination
appropriate and adequate diet
freedom from chronic disease/stressful environment
normal levels of growth-influencing hormones
growth hormone of pituitary?
most abundant hormone produced by the anterior pituitary
secretion of growth hormone?
age dependant secretion
continued secretion growth hormone beyond growth phase means?
it plays other roles as well
what is control of growth hormone secretion regulated by?
by two hypothalamic-hypophysiotrophic hormones
GHRH?
growth hormone releasing hormone
this stimulates synthesis and secretion of growth hormone
GHIH?
growth hormone inhibiting hormone
(somatostatin)
inhibits GH secretion (and other off-target effects)
what controls the secretion of GH?
growth hormone
feedback mechanisms also control secretion of GH
GH feedback onto hypothalamus to inhibit GHRH and promote GHIH - true mechanism is uncertain
intermediate lobe function? (fish and bird etc.)
similar origins to the anterior pituitary
absent in birds
regulates camo in fish, amphibians and reptiles
melanotropes?
these produce MSH (melanocyte stimulating hormone)
what does MSH scatter?
it scatters melanin granules and concentrates light reflecting particles called iridophores around the nucleus of melanocytes
increased MSH can result in?
in darker pigmentation but is not the primary cause of colour variation
MSH is structurally similar to what and what does this result in?
similar to ACTH (adrenocorticotrophic hormone) so excessive production of ACTH can also cause hyperpigmentation such as in Addison’s disease
what controls the release of pituitary hormones?
it is controlled by the hypothalamus
what does the posterior lobe of the pituitary gland contain?
the posterior lobe contains nerve fibres, glial cells and blood vessels and is part of the central nervous system
why is the posterior lobe part of the central nervous system?
as it is connected to the hypothalamus via axons
what are the anterior and intermediate lobes of the pituitary connected to the hypothalamus via?
via the hypothalamic-pituitary-portal system
describe features of the hypothalamic pituitary portal system?
it has two capillary beds in series
hypothalamic neuroendocrine cells can release neurohormones directly into the first capillary bed
neurohormones then travel through portal vessels of infundibulum to second capillary bed which surrounds the endocrine cells of the anterior and intermediate lobes
what system is the hypothalamic-pituitary-portal system similar to?
similar to hepatic portal system
what does the posterior pituitary consist of/
consists of neurosecretory neurons with the cell bodies that secrete ADH and oxytocin residing within the hypothalamus in two defined nuclei: supraoptic and paraventricular nuclei
hypothalamic-pituitary-portal system:
arterial blood coming in to feed the brain
releasing hormones are released into veins that are coming out of brain + into anterior pituitary
the blood supply for the anterior pituitary cells is coming from veins
the anterior pituitary cells are releasing their hormones into veins that go around the body and into glands
system is like veins going into veins
what is a portal system?
veins into veins
NOT RELEVANT TO THIS BUT: what is hepatic portal system?
blood going into GI tract absorbs all nutrients from GI tract
Then drains into liver and then veins leave liver and go towards the heart
So you have a venous system going into a venous system before going to heart and finding way into artery before leaving heart
where do the cells that secrete oxytocin sit in the brain?
in the supraoptic nucleus
where do the cells that secrete ADH sit in the brain?
in the paraventricular nucleus
where do the axons of the cells secreting oxytocin and ADH in the brain reside?
in the posterior pituitary where the neurohormones can be released
