Lecture 9 &10 Flashcards
Hypothalmic Pituatry
What does the hypothalamus link with ?
links endocrine system and nervous system through its control of the pituatry gland (hypophesis)
When responding to various stimuli/signals what can the hypothalamus do ?
-Synthesise and releease neurohormones into circulation via posterior pituatry
-Synthesise and release hypophysiotropic hormones into the hypophyseal portal blood system to regulate hormone release from anterior pituatry
-send neural signals to regulate the release of sympathetic nervous system hormones from the adrenal medulla
2 major control of secretion-neural control of neurosecretory cells(post
What is the relationship between the hypothalamus and the pituatry gland ?
-Direct neural connection between hypothalamus & posterior pituatry gland
-Hormonal function between the hypothalamus & anterior pituatry via a dedicated portal vascular system (hypophyseal)
The embryonic development of the pituatry gland ?
pituatry gland -2 glands with 2 diff embryonic origins
-outgrowth of tissues appear from floor of brain and roof of mouth (Rathke’s pouch)
-neural ectoderm forms the neurohyphsis
-oral ectoderm forms adenohypophysis
What are the Pituatry glands 2 distinct lobe ?
-Adenopophsis (Anterior lobe)
-Neurohypophysis (Posterior lobe)
Properties of Adenohypophesis ?
-aka anterior lobe
-derived from pharyngeal ectoderm
consists of 2
1. Anterior pituatry
2. Pars tuberalis: forms pituatry stalk
accounts for 80% pituatry weight
Properties of Neurohypophysis ?
aka posterior lobe
derived from neural ectoderm
consists of 3 portions
1. Posterior pituatry
2. Medium eminence
3. Infundiblar stem/stalk
Histology ????
What are the functions of the hypothalamus ?
controls fundamental physiological activities inclusing:
-body temp
-hunger
-thirst
-sleep
Hypothalamus and pituatry is interface between endocrine and NS
recievs
Hyp…. interacts with both lobes of pituatry gland but in different ways
What are the differences between anterior and posterior pituatry ?
?????
What & where 2 neurohormones does the hypothalamus secrete ?
via posterior pituatry
oxytocin & antidiuretic (ADH)
synthesised in hypo in magnocellular neurons
transported in vesicles along axons of these neurons through ME into posterior pituatry* via infundiblum
stored in secratory granules
*consists of bundles & terminations of axons originating from the hypoth
What else does the transport of hormones from hypothalamus to the pituatry require ?
requires association with transport protein :neurophysins
-stimulation of these hypothalmic neurosecretory cells causes AP to propagte –>release of hormones directly into capillary blood network via EXOCYTOSIS (Ca2+depenedent)
-Oxytocin & ADH are nonapeptide ( 2 AA diff) which travel as free hormones on general circulation with half time -1 min
What are the functions of ADH ?
released in response to an increase in plasma osmotic pressure (osmolality) or a fall in blood volume
-Has Antidiuretic actions stimulate reabsorption of water from renal collecting ducts (cAMP dependent )
-urinary volume is decreased and urine osmolality is increased
-potent vasoconstricto
What are the functions of oxytocin ?
stimulates milk ejection response to suckling-let down
-causes contraction of mammary gland myoepthelial cells to squeeze milk towards nipple
-stimuli can cause secretion’baby cry’etc
-Uterine contractions
helps expel fetus and placenta (labour)
POSITIVE FEEDBACK
establishes maternal nehaviour
An example of positive feedback ?
Oxytocin secreted during childbirth
-increased excitability of uterus
-uterine contraction
-fetus presses on cervix
-afferent signal to hypothalamus
-oxytocin secretion by posterior pituatry–>
-birth of baby terminates positive feedback
What role does oxytocin play in men ?
- in sperm progression
- erection
- ejaculation
What is the nuclei of hypothalamus involved in ?
Hormone synthesis and excretion
1. Cortotropin-releasing hormone(paraventricular nucleus)
2. Thyrotropin-releasing hormone(PVN
3. Gonadotropin-releasing hormone POA & arcuate nucleus (AR)
Parvocellular neurons in these nuclei may release 1 or more hypophysiotr
What are the 5 principle endocrine cells ?
In the Anterior pituatry
- Somatrophs-50% secrete growth hormones aka somatropin
- Lactotrophs-15-20%:secrete prolactin (PRL)
- Gonadotrophs-10% secrete FSH,LH
- Corticotrophs:15-20% secrete ACTH & related peptides,melanoctye stimulating hormone.
- Thyrotroph-5% secrete TSH
What are the anterior pituatry hormone targets ?
- TSH –>metabolism & growth
- ACTH–>stress response ,metabolic actions
- MSH in animals– skin darkening in amphibians,reptiles and fish
- Prolactin-growth during pregenancy,many functions including reproduction,water&ion balance
- Growth hormone-
What are the functions of growth hormone ?
Acts on a variety of tissues to promote growth & development
-Anabolic :promotes protein synthesis
-Principle targets:muscles and bone
GH hypersecretion in children -gigantism(very tall-8 feet)
GH hyposecretion :pituatry dwarfism shorrt-4 feet
What are the metabolic effects of the growth hormone ?
GH increases blood glucose uptake and increase glycogenolysis
stimulas :hypoglycemia
direct effect on proteins ,fats,carbohydrates
Skeletal growth –>
What are the functions of prolactin ?
structuarally similar to GH
in females
-promotes maturity of mammary glands during pregenancy
-stimulates synthesis of milk(lactation)
-its secretion is increased by suckling
-Prolactinoma :lactating men
-Prolactin function have evolved
What is the function & anatomy of the adrenal galnd ?
located at superior pole of each kidney (suprarenal ):consist of of inner medulla & outer cortex
-2 distinct endocrine functions:secretion
-Catelcholamines(adrenaline,noradrenaline) in response to sympathetic nerve action
3 classes of steroid hormones :
glucocorticoids,mineralcorticords,sex steroids
What is the function of adrenal cortex ?
endocrine function
controlle hormonally
humans-cortisol is dominant glucocorticod rapidly relesing from cells by diffusion following synthesus mostly bound to plasma binding membrane (in blood)
endocrine system
How does the HPA axis link to Adrenal cortex ?
Cortisol is regulated by the hypothalamic -pituatry-adrenal (HPA) axis
Diurnal variaition in cortisol
Circulating glucocorticods inhibit secretions of CRH & ACTH by hypathalamus and anterior pituatry
CRH = corticotropin relaesing hormone
ACTH =adrenocorticotropin hormone
What does cortisol control ?
Control of carbohydrate and protein metabolism
counteracts stress:trauma,intense heat or cold,infection
main glucocortoid in primates & fish is cortisol .In reptiles ,amphibian
What is the stress response ?
short term
activation of both the sympathetic nervous system & HPA axis
short term response
1. glycogen broken down to glucose ; ↑ blood glucose
2. ↑ blood pressure
3. ↑ breathing rate
4. ↑ metabolic rate
5. change in blood flow patterns leading to ↑ alertness and decrease kidney & digestive activity
What is the long term stress response ?
- Retention of sodium ions & wayer by kidneys
- ↑ blood volume & blood pressure
- Proteins & afts broken down and converted to glucose leading to ↑ blood glucose
- immune sytem may be supressed
cortisol:high levels supress normal immune response to infection
A & NA
Define stress?
adverse reaction people have to excessive pressures or other types of demand placed on them
Defines stress response ?
the resonpse of an animal to a threatening/hostile or challenging situation
stressors:wounded,thermal extremes,social condititon
essential ebhaviou
What is stress repsonse associated with ?
with physiological changes ensure survival in acute crisis
healthy ,normal reaction
feedback meechanisms ensure stress response is turned off
What is chronic stress ?
stressor persists for long periods can be damaging
can lead to hypertension (↑ BP) susceptibility to infections ,supression pf reprosuctive function
Female human reproductive cycle ?
brief overview
2 linked cycles
1.Ovarian cycle :produces eggs and ovarian hormones
-involves follicle development ,ovulation ,growth ajnd eventual degeneration of the corpus luteum
2.Uterine cycle (mestrual cycle)
prepeates unterine endometrium for blastocyst implantation
involves ‘build up’ of the endometrium
in absence of implantation endometrium ‘sloughs off’ and menstruation occurs (in most mammals no bleeding)
FSH symulates follicle development ,LH surge causes ovulation
oestrogen
Hormonal control of ovarian cycle ?
Puberty:Hypothalamus ↑ GnRH release stimulates release of gonadotropins (FSH,LH) from anterior pituatry
FSH ,LH cause growth of ovarian tissue ;ovarian hormones are produced
-First 12 days oestrogen inhibits LH & FSH release
12-14 days :oestrogen exerst positive feedback-> LH surge :triggers ovulation
What does the corpus luteum function as ?
functions as an endocrine gland:produces oestrogen and progesterone
Negative feedback and the difference between short vs long ?
Endocrine cells are also under the direct/indirect negative feedback control by hormones of target glands they stimulate
long loop example :HPA axis –>cortisol can ihibit both ACTH & CRH
short loop :ACTH
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