Endocrinology Session 3 Flashcards
What is the function of the pituitary gland and the hypothalamus?*
Link between endocrine and nervous system
Where does the pituitary gland sit?
Sella turcica
What processes are modulated by the complex?
- Growth
- Reproduction
- Adrenal gland function
- Water homeostasis
- Milk secretion and lactation
- Thyroid gland function
- Puberty
Why is the posterior pituitary not a true gland?
It secretes hormones that are produced by the hypothalamus
Where does the anterior pituitary gland arise from?
- Oral ectoderm (Rathke’s pouch)
- Primitive gut tissue
What does the posterior pituitary gland arise from?
Neuroectoderm (primitive brain tissue)
How is the posterior pituitary gland physically connected to the hypothalamus?*
Through infundibulum
What nuclei secrete oxytocin and antidiuretic hormone in the posterior pituitary?
Supraoptic and paraventricular hypothalamic nuclei
How does the neurocrine function of the posterior pituitary occur?
- Hormones from nuclei transported down axons to posterior pituitary
- Stored and released from PP into general circulation to act on distant targets
Where are the hormones synthesised in hypothalamus stored?
- Stored in median eminence
- Released into blood supply called the HYPOPHYSEAL PORTAL SYSTEM (connection of two capillary beds) and into anterior pituitary
What is the function of the hormones released by the anterior pituitary?*
Stimulation/inhibition of target endocrine cells in anterior pituitary gland
What are the functions of anterior pituitary hormones?
- Acting on neighbouring cells (autocrine/paracrine)
- Acting on distant targets (neurocrine)
What are the functions of the hormones secreted into the hypophyseal portal system?
Acting on endocrine cells within anterior pituitary
What is the function of ADH/vasopressin?
Regulation of body water volume and how much water is reabsorbed back into the body via the kidney
What is the function of oxytocin?
- Regulating uterine contractions during childbirth
- Milk letdown during breastfeeding
What are the tropic (hormones that are affecting the synthesis and release of another hormone) hormones in the hypothalamus?
TRH (thyrotropin releasing hormone) - stimulate thyroid gland
PIH (prolactin release-inhibiting hormone) - dopamine
CRH (corticotropin release hormone) - ACTH and cortisol synthesis
GnRH (gonadotropin release hormone) - FSH and LH
GHRH (growth hormone releasing hormone)
GHIH (growth hormone inhibiting hormone)
What is the difference between tropic and trophic hormones?
Tropic: stimulate/inhibit release of other hormones
Trophic: hormones affecting growth
What is TSH?
AP gland:
Thyroid stimulating hormone
(secretion of thyroid hormone)
What is ACTH?
AP gland:
Adrenocorticotropic hormone
(secretion from adrenal cortex)
What is LH?
AP gland:
Luteinising hormone
(ovulation/sex hormone secretion)
What is FSH?
AP gland:
Follicle stimulating hormone
(egg/sperm development)
What is PRL?
AP gland:
Prolactin
(mammary gland development, milk secretion)
What is GH?
AP gland:
Growth hormone
(Growth and energy metabolism)
What is the relationship between the hormones and the glands?**
Slide 12
How are the pathways of hormonal production regulated?**
Negative feedback (short/long loops)
What stimulates the hypothalamus to produce CRH and then ACTH?*
Stress (pain, hypoglycaemia, low BP) produces CRH and acts on the anterior pituitary (via hypophyseal portal system) which produces ACTH, and which then stimulates adrenal cortex to produce cortisol.
What controls growth?
- Genetics
- Environment
- Nutrition
- GROWTH HORMONE
What is necrosis?
Cell death by damage
What is atrophy?
Decrease in cell size/number
What is apoptosis?
Programmed cell death
What is hypertrophy?
Increase in cell size
What is hyperplasia?
Increase in cell number
Where is growth hormone produced and what stimulates its production?
- Anterior pituitary
- Stimulated by hypothalamic GHRH
- Inhibited by hypothalamic somatostatin
How are growth-promoting effects triggered?
Via insulin-like growth factors (somatomedins)
Which cells produce IGFs and why?
Cells of liver and skeletal muscle produce and secrete IGF in response to growth hormone secreted from the anterior pituitary
Is GH an active hormone?
No - it has a signal peptide that must be cleaved before proper folding
What is the function of GH?*
Stimulating bone growth
- Length & width before epiphyseal closure
- Width after epiphyseal closure (maintain bone mass)
What are the direct and indirect effects of GH?
- Direct: GH receptors
- Indirect: Producing IGFs
- Local tissue growth (muscle)
What is the function of IGF?
Bone and cartilage growth stimulation
What do GH and IGFs do in adults?
Maintain muscle and bone mass
Promoting healing and tissue repair
Modulating metabolism and body composition
How is GH secretion controlled?
Via hypothalamus
- GHRH: + GH secretion
- Somatostatin: - GH secretion
How does sleep affect GH secretion?*
- Deep sleep = a lot of GH
- REM = less GH secretion
(Why uninterrupted sleep important in children)
How do stress and exercise affect GH secretion?
Stress = GH secretion Exercise = GH secretion
How do glucose and FAs affect GH secretion?
- Low glucose/FA = Increase
- High glucose/FA = Decrease
How do fasting and obesity affect GH secretion?
- Fasting: + Secretion
- Obesity: - Secretion
How is GH secretion regulated?*
Short loop and long loop negative feedback
What mediates long loop feedback and how?*
- IGFs
- Inhibit release of GHRH
- Stimulate somatostatin release, which therefore inhibits GH release from anterior pituitary
What mediates short loop feedback?
GH itself via stimulating somatostatin release
What does growth hormone deficiency cause in children and what are the defining features?*
Pituitary dwarfism
- Proportionate
- Hormone can be absent or deficient
- Respond to GH
- Height below 3rd percentile
- Slow growth
- Delayed sexual development
What are the causes of pituitary dwarfism?
Damage to skull due to a traumatic injury which then causes damage to pituitary gland and release of GH
What is acromegaly and what causes it?*
Large extremities (hands/feet/jaw) caused by excess growth hormone
Caused by a pituitary adenoma developing in adulthood and causing widening
What is gigantism and what causes it?*
Prolonged bone growth before epiphyseal plate fusion due to excess GH
Caused by pituitary adenoma in childhood
How does GH exert effects on cells?*
- GH receptors activate Janus kinases (JAKs, tyrosine kinase receptors)
- GH binding causes receptor dimerisation
- Causes change in conformation and activates receptor
- Autophosphorylation of own residues
- Activates transcription of IGF and signalling pathways
What are the differences between IGF1 and IGF2?
IGF1: adults
IGF2: foetal growth
How are IGFs modulated?
Binding proteins (modulate bioavailability)
What do IGFs modulate?
- Hypertrophy
- Hyperplasia
- Protein synthesis +
- Lipolysis +
What are IGF actions?
- Autocrine/paracrine (skeletal muscle)
- Endocrine (liver)
Discuss the insulin like growth factor receptors. ***
SLIDE 25
- Hybrid receptors (1/2 insulin 1/2 IGF1 receptors, etc)
- Mitogenic and metabolic effects
What is the action of insulin?
Somatic growth + IGF interaction
What is the action of thyroid hormones?
CNS development and GH secretion
What is the action of androgens?
Pubertal growth, increase in muscle mass, closure of epiphyseal plates
What is the action of oestrogen?
Decrease of somatic growth and closure of epiphyseal plates
What is the action of glucocorticoids?
Inhibition of somatic growth
