Endocrine Principles And The Pituitary Flashcards
(62 cards)
1
Q
What do hormones do?
A
- they are the means by which cells communicate with each other
2
Q
What happens in hormonal communication?
A
- hormones released into the circulation may exert control over cells
- which are at considerable distances from the hormone secreting cell
3
Q
Why does that happen in hormonal communication?
A
- any cell in the body that expresses appropriate hormone receptors will be affected
- the effects are slower in onset, but longer sustained as hormone action continues until the circulating concentration falls due to metabolic breakdown
- this is why hormonal control is important in the regulation homeostasis over time periods from minutes to days, not seconds to seconds
4
Q
What is target cell communication?
A
- nerve cells communicate with effector cells
5
Q
What is paracrine communication?
A
- chemical factors released by cells affect the function of other cells in close proximity
6
Q
What is autocrine communication?
A
- the cell is self stimulating
7
Q
What is neuroendocrine / neurocrine secretion?
A
- nerve cell releases a neurotransmitter
- releases into the bloodstream
- to have endocrine effects
8
Q
First mechanism of action - other hormones:
A
- first messengers = peptide hormones, inside the blood vessel
- hormone receptor complex forms
- g-protein is activated
- passes through cell membrane
- activates adenylate cyclase
- ATP gets converted to cAMP
- which acts as a second messenger
- it activates kinase
- alterations in enzyme activity, opens ion channels
=TARGET CELL RESPONSE
9
Q
Second mechanism of action - thyroid hormones and steroids:
A
- steroid hormones in the blood vessel
- binds to cytoplasmic receptor
- hormone receptor complex forms
- change in gene activity
- protein synthesis
- alterations in structural proteins or enzyme activity
= TARGET CELL RESPONSE - thyroid hormones in blood vessel
- binds to mitochondrion and receptor in the cytoplasm
- increase in ATP production
- target cell response
10
Q
What do hormones do?
A
- travel via the blood stream to their specific target cell, where they act by binding to a specific membrane receptor or an intracellular one
- depending on the hormone and how membrane permeable it is
11
Q
A
12
Q
How do hormones that bind to membrane receptors act?
A
- through second messengers systems
- affecting ion channels, enzyme activity and cell function
13
Q
How do hormones acting on intracellular receptors act?
A
- may alter nuclear activity, RNA & protein formation, or increase the mitochondrial function
14
Q
What is the hypothalamus?
A
- located adjacent to the third ventricle in the forebrain
- connected by the hypophyseal stalk to the pituitary gland (hypophysis cerebri), immediately inferior to it
15
Q
How many embryologically distinct components does it have?
A
- two
16
Q
What is the anterior pituitary / adenohypophysis?
A
- classical endocrine gland containing secretory epithelial cells
- derived from an outpouching of the developing oral cavity = rathke’s pouch
17
Q
How does the anterior pituitary receive its blood supply?
A
- from a series of hypophyseal portal vessels, which link it to the hypothalamus
18
Q
What is the posterior pituitary / neurohypophysis?
A
- develops as a down growth from the brain, is continuous with the hypothalamus itself
- it is made up of adapted axons which release hormones into the blood from their terminals
- the cell bodies of the specialised neurones lie within paraventricular supraoptic nuclei of the hypothalamus
19
Q
What is the endocrine activity of the anterior pituitary regulated by?
A
- hormones secreted from the hypothalamus
- transported in the hypophyseal portal blood
20
Q
What are releasing / inhibiting hormones?
A
- factors selectively promotes or inhibits the secretion of a specific pituitary hormone
- they are generally oligopeptides, although prolactin inhibiting hormone is = dopamine, the transmitter substance
21
Q
How this works:
A
- nervous control
- hypothalamus
- anterior pituitary
- target organ
- end hormone
22
Q
What is hypothalamic secretion of pituitary regulating hormones influenced by?
A
- neurological inputs and feedback control
- the pituitary hormones and circulating products of the endocrine systems controlled by those hormones,
- can regulate hypothalamic secretion
- via feedback inhibition
23
Q
What does the posterior pituitary secrete?
A
- two peptides which are manufactured in the cell bodies of hypothalamic neurones
- these hormones are packaged in vesicles and are transported along the axons, into the posterior pituitary
- to be stored in the axon terminals
24
Q
What does appropriate sensory stimuli lead to?
A
- activation of the hypothalamic cells and the release of the hormones from the posterior pituitary into the bloodstream
25
What is neurocrine control?
- this adaptation of neurotransmission to fulfil an endocrine role
26
What does the anterior pituitary secrete?
- six peptide hormones with well defined functions
- includes hormones controlling the endocrine functions of the adrenal cortex, the thyroid and the gonads
- as well as prolactin & the growth hormone
27
When is the adrenocorticotrophic hormone (ACTH) secreted?
- in response to corticotrophin releasing hormone = CRH
- from the hypothalamus
- its action is to stimulate the release of glucocorticoids from the adrenal cortex
28
What other peptides are synthesised and secreted from the anterior pituitary, along with ACTH?
- endogenous opiate, b-endorphin, prescursors of melanocyte stimulating hormone
- roles are unclear
29
What is the thyroid stimulating hormone (TSH) secreted in response to?
- thyrotrophin releasing hormone (TRH), from the hypothalamus
- it stimulates thyroid secretion
30
What are follicle stimulating hormone (FSH) and luteinizing hormone (LH) secreted in response to?
- gonadotrophin releasing hormone (GnRH) - from the hypothalamus
- gonadotrophins stimulate the male and female gonads
31
What is prolactin secretion influenced by?
- prolactin releasing hormone (PRH)
- BUT, it is mainly controlled by = prolactin inhibiting hormone (PIH)
- which is probably dopamine
32
Stimuli which reduce PIH release from the hypothalamus do what to prolactin levels?
- raise them
- occurs during pregnancy
- allowing breasts to get ready for lactation
- resultant prolactin peaks stimulate milk production
33
What is secretion of human growth hormone (hGH) / somatotrophin controlled by?
- two antagonistic hypothalamic hormones
- growth hormone releasing hormone (GHRH)
- is more important than growth hormone inhibiting hormone (GHIH), which is somatostatin
34
What is the growth hormone?
- a major anabolic hormone which stimulates cell division and growth in bony and soft tissues around the body
35
What are the effects of the growth hormone mediated by?
- growth promoters = somatomedins
- produced by the liver in response to hGH stimulation
36
When is growth hormone important?
- during childhood & adolescence
- it has important metabolic functions throughout life
- they favour protein synthesis & promote the breakdown of fat for energy use
- has a carbohydrate sparing effect, glycogen stores increase & blood glucose levels rise
37
What does low blood glucose level stimulate?
- stimulates hypothalamic GHRH and inhibits the secretion of somatostatin from the hypothalamus & the d cells of the pancreatic islets
38
What does the resulting increase in hGH help raise?
- it leaps raise glucose concentrations back to normal
- growth hormone secretion it stimulated by trauma & stress through neural control of the hypothalamus.
39
What does the posterior lobe of the pituitary secrete?
- two short chain peptide hormones
- oxytocin
- ADH
40
What is oxytocin produced by?
- cells in the paraventricular and supraoptic nuclei of the hypothalamus
- they are reflexly activated by sensory inputs from mechanoreceptors in the breast during suckling
- oxytocin is released from the posterior pituitary in response to
41
What does oxytocin stimulate?
- the ejection of milk through contraction of the myoepithelial cells surrounding the milk ducts
- also stimulates uterine contraction during labour
42
Where is ADH produced?
- paraventricular supraoptic hypothalamic nuclei
43
What stimulates ADH?
- sensory inputs from local osmoreceptors & stretch receptors in the cardiovascular system
- stimulate these cells whenever the osmolarity of extracellular fluid rises
- or if blood volume or blood pressure falls
44
What does the resulting increase in ADH cause?
- promotes water reabsorption from the collecting ducts of the kidney
- reduces the osmolarity and expands the volume of extracellular fluids
- by promoting the production of a small volume of concentrated urine
45
What happens then?
- peripheral resistance is increased through arteriolar constriction
- which helps maintain arterial pressure
46
What is ADH’s alternative name?
Vasopressin
47
Abnormalities of pituitary function:
- deficient pituitary secretion
- those caused by excess hormone
48
What is panhypopituitarism?
- deficiencies resulting from insults to the entire gland
- due to a local tumour or surgical treatment
- can involve all the pituitary hormones
49
There may be a deficit in a single hormone…due to…
- a defect in the relevant pituitary cells or the hypothalamic cells
- that regulate their function
50
What are the main problems with deficienct secretion?
- five main problems
51
What is corticosteroid deficiency due to?
- lack of ACTH
52
What is thyroid deficiency due to?
- lack of TSH
53
What is failure of sexual function due to?
- lack of FSH/LH
54
What is dwarfism due to?
- lack of hGH in childhood
- may arise as a congenital defect, can be treated with hGH supplements
55
What is diabetes insipidus due to?
- lack of ADH
- results in an inability to concentrate urine
- patient passes a lot of dilute urine a day
- has to drink a massive volume of liquid
56
What is excess secretion?
- conditions that result from over-secretion of a single pituitary hormone
57
What is corticosteroid excess due to?
- elevated ACTH
58
What is impaired reproductive function due to?
- elevated prolactin
- hyperprolactinaemia is now recognised as causing menstrual failure and infertility
- this is because prolactin can block GnRH production by the hypothalamus
59
What is abnormal growth due to?
- due to elevated hGH
- stimulates long bone growth in children, causing giantism
- if levels are raised in adult life - there is no increase in height
- but soft tissue & body organ growth are stimulated
- this = acromegaly
60
What will a persistent excess of hGH may lead to?
- elevated blood glucose levels
= diabetes mellitus
61
What is fluid retention and low plasma osmolarity is due to?
- elevated ADH
- associated with cancer of the lung
- known as = inappropriate ADH secretion
62
Summary:
- hormones are one of a number of ways in which cells communicate with each other
- having whole body effects, which may last a relatively prolonged period
- they act on receptors, either on the cells surface, within the cytoplasm - or in the nucleus
- their secretion may be controlled by hypothalamo / pituitary / organ axis
- the pituitary gland secretes hormones which control the release of other hormones
- but also hormones which carry out their own effects
