Hypothalamus and Pituitary Gland Flashcards
What is the infundibulum?
It is the stalk that conencts the hypothalamus to the pituitary gland
What type of communication exists between the pituitatary gland and the hypothalamus?
Both endocrine and neural communication (described as neuroendocrine function)
Endocrine portion: Anterior pituitary
Neural portion: Posterior pituitary
Which bone houses the pituitary gland?
The sphenoid bone
Give examples of the integrative functions of the hypothalamus
Cold
Stress
Metabolic Demand
Hydration Status
Exercise
Day/night
Menstrual Cycle
Sleep
Breastfeeding
Pregnancy
Puberty
Give examples of the integrative functions of the pituitary gland
Adrenal function
Thyroid function
Gonadal function
Lactation
Parturition (giving birth)
Growth
Water balance
Metabolism
Define trophic hormone
Trophic hormones govern the release of another hormone
What type of hormones does the hypothalamus and the anterior pituitary release?
Trophic and non-trophic hormones
What is responsible for the release of neurohormones?
The hypothalamus
Posterior pituitary (from the hypothalamus)
What type of hormones are released from the anterior pituitary?
Classic endocrine hormones
What are the two forms of the hypothalamic neurohormones?
Trophic and non-trophic
What is the travel of the trophic hormones released by the hypothalamus?
They are secreted into the capillaries and travel to the anterior pituitary.
They govern the release of anterior pituitary hormones
What is the travel of non-trophic hypothalamic neurohormones?
Produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons where thay are released into the blood)
Give examples of hypothalamic releasing hormones (trophic hormones that stimulate the release of anterior pituitary hormones)
–Thyrotrophin Releasing Hormone (TRH)
–Corticotropin Releasing Hormone (CRH)
–Growth Hormone Releasing Hormone (GHRH)
–Gonadotrophin Releasing Hormone (GnRH)
–Prolactin Releasing Hormone (PRH)
Give two examples of hypothalamic inhibiting hormones
–Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
–Dopamine aka Prolactin Inhibiting Hormone (PIH)
What type of molecules are these trophic hormones?
All are peptides apart from dopamine
Describe how the hypothalamo-hypophyseal portal system works
It is the structure that allows the passage of trophic hormones from the hypothalamus to the anterior pituitary. It is a network of tiny vessels.
Neurosecretory neurones release hormones at the median eminance
Very few neurones are needed and very small amounts of hormones are required
The distance is very short and dynamic
What is the tissue orogin for the anterior and posterior pituitary?
Anterior - Epithelial origin
Posterior - Neural tissue origin
How is the anterior and posterior pituitary connected to the hypothalamus?
Anterior - via capillary portal system
Posterior - neural connections
What hormones does the posterior pituitary release?
It releases neurohormones made in the hypothalamus
What is the adenohypophysis and neurohypophysis?
Anterior - adenohypophysis
Posterior - neurohypophysis
What makes up 2/3rds of the pituitary gland?
Anterior portion
What is the structure of the hypothalamic - hypophyseal portal system?
Two capillary beds connected in series
What controls the release of hormones from the anterior pituitary?
The hypothalamus
By trophic hormones
Either stimulate or inhibit hormone production
What type of hormones are relased from the anterior pituitary?
6 hormones are released from the anterior pituitary gland, all peptides;
5 of these are also trophic hormones
REMEMBER: Both the hypothalamus and the pituitary gland are capable of releasing both trophic and non-trophic hormones
What are the anterior pituitary hormones?
- Thyroid Stimulating Hormone (TSH) aka thyrotrophin
- Adrenocorticotrophic Hormone (ACTH) aka corticotrophin
- Follicle Stimulating Hormone (FSH)
- Luteinising Hormone (LH)
- Growth Hormone (GH)
- Prolactin
The first five are classed as trophic hormones because they control secretion of other endocrine glands and have direct or indirect effects in promoting growth
Where do endocrine cells release their hormones?
They release their hormones into the second set of capillaries for distribution to the rest of the body
What is the destination for Prolactin, GH, TSH, ACTH and gonadotrophins?
Prolactin - Mammary glands
GH - Musculoskeletal system
TSH - Thyroid gland
ACTH - Adrenal Cortex
Gonadotrophins - Ovary and testis
What is the effect of the anterior pituitary hormones?
Prolactin - Lactation (direct effect)
Thyroid stimulating hormone - Thyroid hormone release (trophic)
Adrenocorticotrophic hormone - cortisol release (trophic)
Growth hormone - causes IGF-1 release from liver (trophic) and tissue metabolism (direct)
Follicle stimulating hormone and luteinising hormone: Gonads - regulation of reproductive function (direct) and sex hormone release (trophic)
What are the three integration centres which are involved in anterior pituitary feedback control?
Hypothalamus
Anterior pituitary
Target Endocrine cell
What acts as the negative feedback signal?
The hormones themselves
Inhibits hormone secretion by integrating centres earlier in the reflex
What is the long loop feedback and the short loop feedback?
Long - loop = Feedback from endocrine target
Short - loop = Feedback from anterior pituitary to hypothalamus
Give an example of direct feedback from a physiological response (independant of pituitary control)
Parathyroid hormone
Target organ is the kidney and the bone
Increased calcium resorption in both organs
Production of calcitrol which leads to an increase in the intestinal absorption of Ca+
What are the two hormones that the posterior pituitary stores and releases?
Two neurohormones:
Vasopressing (ADH)
Oxytocin
Where are the post pituitary hormones synthesised?
In the magnocellular neurones which have thier cell bodies in specific areas of the hypothalamus
Magnocellar neurones are composed of different subsets and so either make vasopressin or oxytocin
Where do the neurones terminals end that project down the infundibulum to the posterior pituitary?
End directly on the capillaries
When thinking about vasopressin:
What is the main function?
What triggers its release?
Where is the site/mode of action?
What is the main function?
Regulates water balance
What triggers its release?
Increase in plasma osmolarity
Decrease in plasma volume/blood pressure
Where is the site/mode of action?
Kidney collecting ducts (increases water reabsorption)
Vascular smooth muscle (increases blood pressure)
When thinking about oxytocin:
What is the main function?
What triggers its release?
Where is the site/mode of action?
What is the main function?
Milk ejection and uterine contraction
What triggers its release?
Labour (baby’s head against cervix)
Suckling
Where is the site/mode of action?
Milk duct smooth muscle (contracts muscle, ejecting milk)
Uterine smooth muscle (child brith)
Summary of oxytocin and vasopressin
Give definitions of the following endocrine disorders:
Hyporesponsiveness
Hypersecretion
Hyporesponsiveness
Hyperresponsiveness
1st degree disorders
2nd degree disorders
3rd degree disorders
hyposecretion: too little hormone secreted
hypersecretion: too much hormone secreted
hyporesponsiveness: reduced response of the target cell
hyperreponsiveness: increased response of the target cell
1° disorders are those in which the defect is in the cells that secrete the hormone
2° disorders are those in which there is too little or too much trophic hormone from pituitary
3° disorders relate to hypothalamic defects
What causes hyporesponsiveness?
Alterations in receptor for hormone, disordered post-receptor events of failure of metabolic activation of hormone (where this is required for function)
Hyperresponsiveness: could be due to permissive effects e.g. Thyroid hormone ++ adrenaline mediated lipolysis.
