Wk 3 Flashcards
Hypothalamus & The Pituitary Gland (20 cards)
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.
What occurs when ADH secretion fails?
Results in diabetes insipidus, where the formation of copious amounts of dilute urine in which the urine osmolality will be less than that of plasma.
What are the functions of oxytocin?
- Stimulating uterine contractions
- Stimulating milk ejection from lactating breast
- Important for parturition (childbirth)
- Powerful uterine response to oxytocin in labor, as uterine sensitivity to oxytocin forms later in pregnancy
What type of feedback mechanism is parturition (childbirth) reflex and milk let down reflex?
Positive feedback mechanism
What is a neuroendocrine reflex?
One part of the reflex is natural and the other part is endocrine.
What is an example of a neuroendocrine reflex?
Parturition reflex and milk let down reflex.
