INTS 11: The Hypothalamic-Pituitary Axes Flashcards

1
Q

Read and understand the learning objectives of this session

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Define endocrinology

A
  • it is the study of endocrine glands and their hormonal products
  • these are released directly into the bloodstream
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the body’s two principal communication systems?

A
  • the endocrine glands
  • the nervous system
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Define endocrine gland

A
  • a group of cells which secrete ‘messenger’ molecules (hormones) directly into the bloodstream
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Define hormone

A
  • the bioactive ‘messenger’ molecule secreted by an endocrine gland into the blood
  • i.e. not simply a metabolite or energy substrate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Define the endocrine system

A
  • the endocrine system is comprised of the endocrine glands and their hormonal products
  • it is often also used to describe the cells which respond to these hormones
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Give examples of some of the endocrine organs

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Where are endocrine cells found?

A
  • they are often grouped together in particular endocrine organs
  • e.g. thyroid gland or pituitary gland
  • some cells can also be found in other tissues that are not primarily endocrine tissues
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Discuss the properties of endocrine cells

What about protein hormone-secreting cells?

A
  • endocrine cells are highly metabolically active
  • therefore, they typically have many mitochondria
  • they have a rich blood supply to allow their secreted products to be effectively transported into the blood stream
  • often, secretory granules will be positioned in a cell adjacent to a nearby capillary
  • protein hormone-secreting cells will have a lot of RER for protein sysnthesis
  • will also contain secretory granules where protein hormones are stored
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are neurosecretory cells?

Briefly descirbe their function and morphology

A
  • a subset of endocrine cells
  • they are neurons which release hormones
  • so they will have typical neuronal morphology
  • hormones are stored in granules at the axonal terminals
  • these terminals release their contents into capillaries, allowing the hormone to enter the circulation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe this micrograph

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the three ways hormones can act?

A
  • endocrine:
  • a hormone acting on target cells at a distnace from source
  • via the bloodsteam
  • paracrine:
  • a hormone acting on nearby target cells
  • i.e. within immediate area around source
  • autocrine:
  • a hormone acting on its own immediate source
  • i.e. on the cell that released it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the three classes of hormones?

A
  • protein or peptide hormones
  • steroid hormones
  • amino acid derived hormones
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe the synthesis of protein hormones, their properties and hence their function

A
  • synthesised by the same pathways that synthesise other proteins within the cell
  • they are subsequently packaged into secretory granules where they are stored until required
  • they are typically easy to dissolve in water, so can circulate in the bloodstream without the need for binding proteins
  • they do not easily cross cell membranes and act on cell surface receptors instrad
  • the conformation of the receptors are altered when they bind a hormone
  • this stimulates intracellular signal pathways which then drive the effects of the hormone within the cell
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Describe the synthesis of steroid hormones, their properties and hence their function

A
  • synthesised from cholesterol in the mitochondria when required
  • usually not stored within the cell
  • they are hydrophobic
  • so require binding proteins to carry them through the circulation
  • due to their hydrophobicity, they can cross cell membranes relatively easily
  • then they bind to and activate intracellular or nuclear receptors
  • receptor-steroid hormone complexes can then relocate to the nucleus and influence gene transcription
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the synthesis of amino acid derived hormones, their properties and hence their function

A
  • they are a more diverse group
  • some display properties like steroid, other more like protein hormones
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe the hypothalamus

  • Location
  • Function
  • Structure
A

Location:

  • found at the base of the brain, below the thalamus

Function:

  • forms part of the limbic system: involved in processes such as learning, emotion and behaviousr
  • regulates many homeostatic processes:
  • heart rate, body temperature, metabolic rate and food intake
  • received neuronal input from a number of other brain regions, particularly the brainstem
  • hypothalamic neurons themseles signal to other brain regions to regulate behavious
  • can regulate the autonomic nervous system and the pituitary gland

Structure:

  • composed of individual nuclei and some less well define subregions which are integrated, but can regulate different physiological functions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the pituitary gland

  • Alternate name
  • Location
  • What it is
A
  • also known as the hypothysis
  • it is an endocrine organ that sits within a bony pocket underneath the hypothalamus
  • composed of anterior, intermediate and posterior lobes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Describe the structure of the pituitary gland

A
  • observe image
  • the pituitary gland is linked to the hypothalamus by a short stalk that contain nerve fibres and a specialised netowork of blood vessels, known as a portal system
20
Q

Where did the anterior and posterior lobes of the posterior pituitary gland develop from?

What are their alternative names?

What do their different developmental origins change?

A
  • Anterior lobe:
  • developed from the oral ectoderm: one of the primary germ layers in the early embryo
  • also called adenohypophysis
  • Posterior lobe:
  • develops as an extension of the hypothalamus
  • neural in origin, so called neurohypophysis
  • their different developmental origins underpins the different ways they are regulated and the different cells they contain
21
Q

What does the anterior pituitary lobe help regulate?

A
  • metabolic rate
  • stress response
  • growth
  • reproduction
22
Q

What does the posterior pituitary regulate?

A
  • water balance
  • uterine function
  • breast function
23
Q

What is neurosecretion?

A
  • the release of hormones from neurons
24
Q

What are the neurosecretory cells in the hypothalamus classed as?

A
  • parvocellular
  • magnocellular
25
Q

What are hypothalamo-pituitary axes?

Give examples

Is their any difference between posterior and anterior lobes?

A
  • how the hypothalalamus controls the pituitary glands
  • e.g. hypothalamo-pituitary-gonadal axis: regulates reproductive function
  • e.g. hypothalamo-pituitary adrenal axis: regulates stress response
  • the hypothalamus control the function of the anterior and posterior lobes of the pituitary by two different modes of neurosecretion
26
Q

Describe the posterior pituitary lobe

  • Structure: from hypothalamus to itself
  • Major hormones
A
  • cell bodies are up in the hypothalamus
  • their axons actually stretch all the way down, forming the posterior pituitary
  • the hormones made in the cell bodies are trafficked down the axon and are stored in nerve terminals in the posterior pituitary, waiting for their stimuli
  • major hormones:
  • vasopression
  • oxytocin
27
Q

Describe the anterior pituitary lobe

Structure: from hypothalamus to itself

A
  • cell bodies are in the hypothalamus and their axons extend down to the base of the hypothalamus but don’t go into the pituitary
  • this base is the median eminence, which has a capillary plexus (so good blood supply)
  • neurocrine neurons can release hypothalamic factors into this blood supply
  • there is then a portal circulation between the hypothalamus and the anterior pituitary
  • the capillary plexus spreads throughout the anterior pituitary so that anything released baths the anterior pituitary endocrine cells
28
Q

Describe parovellular neurosecretory cell bodies

  • Location
  • What hormones do they secrete?
  • Where do these hormones go?
A
  • located in the hypothalamus
  • the paraventricular nucleus
  • their relatively short axons project to the median eminence at the base of the hypothalamus
  • the neuronal terminals secrete hypothalamic hormones into the primary capillary plexus of the hypothalamo-pituitary portal circulation
  • these hormones are carried by long portal veins to the secondary capillary plexus, which supplies the anterior pituitary
  • this allows hypothalamic hormones to modulate anterior pituitary hormone release
29
Q

Describe magnocellular neurosecretory cell bodies

  • Location
  • What hormones do they secrete?
  • Where do these hormones go?
A
  • located in the hypothalamus
  • in the paraventricular and supraoptic nuclei
  • their long axons pasd through the median eminence, projecting to and forming (along with support cells) the posterior pituitary
  • these neurons secrete oxytocin and vasopression (ADH) into the general circulation in response to stimuli
30
Q

Observe the schematic diagram illustrating the hypothalamus, posterior pituitary and the cell bodies

A
  • note how hypothalamic parvocellular neurons projedt to the median eminence
  • and magnocellular neurons project to the posterior pituitary
31
Q

Observe the schematic diagram illustrating the hypothalamus, anterior pituitary and the cell bodies

A
  • hypothalamic hormones are released from parvocellular neurons at the primary capillary plexus in the median eminence
  • they are carried by the portal veins to the secondary capillary plexus where they can act on anterior pituitary cells to regulaye anterior pituitary hormone secretion
32
Q

What anterior pituitary hormones are these hypothalamic hormones responsible for?

Use diagram to help you

A
33
Q

How is homeostasis maintained in the anterior pituitary?

A
  • hormone release from the anterior pituitart is usually controlled by negative feedback
  • the products of various axes acting upon the hypothalamus and pituitary suppress their own release
34
Q

What is special about the regulation of the female hypothalamo-pituitary-ovarian axis?

A
  • it is an example of positive feedback
  • the axis is mainly controlled by negative feedback, but the luteinising hormone surge necessary for ovulation is driven by oetrogen acting at the hypothalamus and pituitary
  • this stimulates the release of more gonadotrophin releasing hormone and luteinising hormone
  • which further drives the release of more oestrogen
35
Q

What do most anterior pituitary hormones act on?

Give some examples

A
  • Most hormones from the anterior pituitary are responsible for acting on endocrine glands to stimulate the release of further hormones.
  • For example:
  • TSH stimulates the release of T3 and T4
  • ACTH stimulates the release of glucocorticoids such as cortisol
  • LH and FSH stimulate the release of testosterone or oestrogen
  • GH stimulates the release of somatomedins
36
Q

What are the two hormones released by the magnocellular neurons that terminate in the posterior pituitary?

Give their hormone type

Function

A
  • vasopressin:
  • The principal physiological action of vasopressin is to stimulate the reabsorption of water in the renal collecting ducts
  • Vasopressin thus has an anti-diuretic effect, hence its alternative name of anti-diuretic hormone (ADH)
  • Vasopressin release is stimulated when blood electrolyte concentration is high:
  • it concentrates urine in order to preserve blood electrolyte concentration within healthy limits.
  • Oxytocin:
  • acts to drive rhythmic contraction of the uterine muscles during childbirth, and contraction of myoepithelial cells in the breast to cause milk ejection during breastfeeding.
  • Oxytocin also acts on the brain, promoting, for example, maternal behaviour and social recognition.
37
Q

Give an overview of where the hormones released by the anterior and posterior pituitary act on

And what hormones

A
38
Q

Describe the function of vasopressin and dysfunction caused by the hypersecretion and hyposecretion of it

A
  • Function:
  • released in response to high blood osmolality to drive water reabsorption in the kidney
  • Hypersecretion:
  • syndrome of inappropriate antidiuretic hormone secretion (SIADH)
  • hyponatremia: low sodium concentration in the blood, due to increased blood volume
  • Hyposecretion:
  • diabetes insipidus: producing large volumes of unconcentrated urine, driving thirst and possibly dehydration
39
Q

Describe the function and dysfunction of glucocorticoids, such as cortisol, caused by the hypersecretion and hyposecretion of it

A
40
Q

Describe the function and dysfunction of the thyroid hormones, T3 and T4, caused by the hypersecretion and hyposecretion of it

A
41
Q

Describe the function and dysfunction of androgens, such as testosterone, caused by the hypersecretion and hyposecretion of it

A
42
Q

Describe the function and dysfunction of oestrogens, such as oestradiol, caused by the hypersecretion and hyposecretion of it

A
43
Q

Describe the function and dysfunction of growth hormone caused by the hypersecretion and hyposecretion of it

A
44
Q

Describe the function and dysfunction of prolactin caused by the hypersecretion and hyposecretion of it

A
45
Q

How are hormones usually measured?

A
  • Hormones occur in μM and pM concentrations and can be measured using antibodies
  • which cause a colour change when bound to the hormone etc.
  • Measuring hormones can be difficult as they are released in a pulsatile fashion so their concentrations vary greatly with time.
  • Dynamic testing involves stimulating the secretion of a hormone and conclusions can be drawn if a patient does not respond as expected.
46
Q

If you had a disease of the thyroid gland that prevented it from secreting hormones, which choice below best reflects what would happen to the levels of the various hormones involved in the hypothalamo-pituitary thyroid axis?

A