Wk 3 Flashcards
Hypothalamus & The Pituitary Gland
What is the hypothalamus?
- A nervous centre regulating visceral functions
- Contains nuclei involved in basic body function
Where is the hypothalamus located?
Superior to the brain stem
What are the functions of the hypothalamus?
- Food intake
- Water intake
- Sexual behaviour
- Endocrine functions
- Autonomic nervous system
- Temperature regulation
- Sleep + wakefulness
What are the two types of hypothalamic nuceli?
- Supraoptic nuclei (magnocellular only)
- Paraventricular nuclei (magnocellular + parvocellular)
What are the two types of hypothalamus neurons that mediate endocrine function?
- Magnocellular (posterior)
- large cell body
- release pituitary hormones - Parvocellular (anterior)
- end in the median eminence
- secret hypothalamic inhibitory and releasing hormones
What is the pituitary gland?
- Lies in a bony cavity (sella turcica) located at base of brain
- Connected to median eminence of hypothalamus via pituitary stalk
What are the two major lobes of the pituitary gland?
- Anterior pituitary (left)
- Posterior pituitary (right)
What is the anterior pituitary?
- Connected to hypothalamus by hypothalamic-hypophyseal portal system
- Superior hypophyseal arteries branch out to form primary capillary plexus
- Long hypophyseal portal veins arise from primary plexus that connect to secondary plexus
- Releasing/inhibiting hormones are released at median eminence into primary capillary plexus
What are the stimulatory release factors that influence anterior pituitary hormones?
- Secretion of TSH, stimulated by thyrotropin-releasing hormone (TRH)
- Secretion of ACTH, stimulated by corticotropin-releasing hormone (CRH)
- Secretion of FSH and LH, stimulated by gonadotropin releasing hormone (GnRH)
- Secretion of GH, controlled by balance between stimulating hormone GHRH and inhibiting factor somatostatin
What is a tropic hormone?
A hormone that regulates the function of endocrine cells or glands/releases hormones. Causes growth and development of other glands/tissues.
What is the posterior pituitary?
- Connected to the hypothalamus by hypothalamic-hypophyseal tract
- Secreted neurohormones antidiuretic hormone (ADH) and oxytocin
Where are ADH and oxytocin produced?
- Posterior pituitary
- Both are peptides produced in neurons originating from paraventricular nucleus and supraoptic nucleus of the hypothalamus
- Synthesised in the neuron cell bodies
What is ADH?
- Principal hormone that controls water balance in the body
- Acts at the kidney to concentrate urine and cause water retention in body
- ADH secretion is controlled by changes in body fluid osmolarity and blood volume
- Stimulates secretion of ACTH
What are the other factors that regulate ADH?
- Reduced plasma volume
- Increased plasma osmotic pressure
- Angiotensin II
- Atrial natriuretic peptide
- Alcohol
What is ADH also known as?
Vasopressin, as it causes generalised arteriolar vasoconstriction when acting through the V1 receptors in vascular smooth muscle.
