The hypothalamus
- The hypothalamus is a major control centre for homeostasis
- It constantly measures the condition of the body and regulates
functions using both nerves and hormones
- It is responsible for control of
- Emotional response
- Temperature regulation
- Appetite
- Water balance
- Hormonal control is exerted through the anterior and posterior
pituitary
- It controls both lobes of the pituitary gland
- Anterior pituitary is formed in the embryo from Rathke's pouch
- Posterior pituitary is a projection from the hypothalamus
- The anterior pituitary is controlled by endocrine mechanisms
- The posterior pituitary is connected directly to hypothalamus by
nerves
The anterior pituitary gland
- The hypothalamus controls the anterior pituitary through a series of
releasing hormones
- Releasing hormones travel in a portal system to the pituitary gland
- They either stimulate of inhibit the release of anterior pituitary
hormones
- The anterior pituitary produces 6 major hormones
- ACTH - acts on the adrenal cortex
- TSH - acts on the thyroid
- LH / FSH act on the ovaries and testes
- Prolactin - acts on the breast
- Growth hormones - has diverse actions
- The anterior pituitary is controlled by negative feed back loops
Adrenocorticotrophic hormones
- CRH is produced in hypothalamus
- Stimulates release of ACTH from anterior pituitary
- ACTH stimulates adrenal cortex to release several hormones
- Glucocorticoids
- Androgens
- Mineralocorticoids
- Raised levels of glucocorticoids reduce ACTH release
- ACTH levels are increased in fever, stress, hypoglycaemia
Thyroid stimulating hormone
- TRH is produced in hypothalamus
- Stimulates release of TSH from anterior pituitary
- TSH stimulates thyroid hormone production
- Raised levels of thyroid hormones inhibits release of TRH and TSH
- TRH levels increased in exercise and as part of stress response
Gonadotrophins
- GnRH is produced by the hypothalamus
- Stimulates release of LH and FSH from anterior pituitary
- FSH stimulates sperm and egg production
- LH causes ovarian follicle maturation and ovulation
- LH causes release of gonadal hormones (testosterone and oestrogen)
- Rising levels of gonadal hormones inhibits GnRH, LH and FSH
Growth hormones
- GHRH is produced by the hypothalamus
- Stimulates release of GH by anterior pituitary
- Growth hormone is non-trophic and has direct action on non-endocrine
cells
- It is an important anabolic hormones
- Stimulates many cells to grow and divide
- Stimulates bone and skeletal muscle growth
- Increases protein production by liver and muscle
- Stimulates gluconeogenesis
- Converts glucose to glycogen stores
The posterior pituitary gland
- Nerves go directly from two nucleii in the hypothalamus (supraoptic
& paraventricular) to the posterior pituitary
- Posterior pituitary hormones are made in the cell bodies of the
nerves
- Hormones travel down the nerve axons by axoplasmic transport to the
pituitary
- Hormones released from the pituitary as needed by neurosecretion
- The posterior pituitary releases two hormones
- ADH - acts on collecting duct of the kidney to increase water
retention
- Oxytocin stimulates uterus to contract during childbirth
- Also causes vasoconstriction & raises blood pressure
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