Hypothalamus & Pituitary Gland

• Pituitary Gland


  located w in the sphenoid bone, the pituitary gland secretes at least 8 hormones

  its stalk, the funnel-shaped infundibulum, connects the gland to the hypothalamus superiorly

  
• Posterior Pituitary Lobe


  the posterior pituitary is composed gretly of neural tisse + nerve fibres

  releases neurohormones (hormones secreted by neurons) received ready-made from the hypothalamus

  this lobe is a hormone-storage area + not a true endocrine gland that manufactures hormones

  the posterior lobe + the infundibulum = neurohypophysis

  
• Anterior Pituitary Lobe


  the anterior pituitary is composed of glandular tissue

  it manufactures + releases a no of hormones
• Posterior Pituitary - Axon Terminals

  the posterior pituitary consists largely of axon terminals of hypothalamic neurones whose cell bodies r located in the suprapotic/paraventricular nuclei

  paraventricular neurons primarily make oxytocin

  supraoptic = ADH

  axon terminals in the posterior pituitary relsease thse hormones in response to action pots that travel down the axons of these same hypothalamic neurons
• Posterior Pituitary Hormones - Oxytocin

  stimulated by impulses from hypothalamic neurons in response to stretching of the uterine cervix during childbirth or breastfeeding

  stimulates uterine contractions + intiates labour

  initiates breastmilk ejection
• Posterior Pituitary Hormones - ADH

  stimulated by impulses from hypothalamic neurons - osmoreceptors + baroreceptors - in response to increased blood solute conc/decreased blood vol/low blood pressure

  stimulate kidney tubule cells to reabsorb water from the forming urine back into blood
• Anterior Pituitary Hormones - Growth Hormone (GH)

  stimulated by GHRH release, which is stimulated by low blood levels of GH as well as a no of secondary triggers, inc deep sleep, hypoglycemia, increases in blood levels of amino acids + exercise

  targets liver, muscle, bone, cartilage + other tissues

  stimulates release of anabolic hormone, slimulates somatic growth
• Oxytocin - Childbrith


  a strong stimulant of uterine contraction, oxytocin is released in sig higher amounts during childbirth + in nursing women

  the no of oxytocin receptors in the uterus peaks near the end of pregnancy + uterine smooth muscle becomes more + more sensitive to the hormone's stimulatory effects

  stretching of the cervix of the uterus as birth near dispatches afferent impulses to the hypothalamus

  the hypothalamus responds by synthesising oxytocin + triggering its release from the posterior pituitary
• Oxytocin - Childbirth


  oxytocin also acts as the hormonal trigger for breastmilk in women whose breasts r producing milk in response to prolactin

  suckling causes a reflex-initiated release of oxytocin, which targets specialised myopethilial cells surrounding the milk-producing glands

  these cells contract + force milk from the breast
• Anterior Pituitary -Thyroid-Stimulating Hormone (TSH)

  stimulates the thyoid gland to produce + release thyroid hormones, mainly thyroxine (T4) + triiodothyronine (T3), which regulate metabolism, energy production + development
• Anterior Pituitary - Adrenocorticotropic Hormone (ACTH)

  stimulates the adrenal cortex (outer part of the adrenal gland) to release corticosteroid hormones, particularly cortisol, which help manage stress, regulate metabolism + control inflammation
• Anterior Pituitary - Follicle-Stimulating Hormone (FSH)

  in females, it promotes the growth of ovarian follicles, which r necessary for egg development

  in males, it stimualtes sperm production
• Anterior Pituitary - Lutenising Hormone (LH)

  works closely w FSH in the reproductive system

  in females, it triggers ovulation + helps maintain the corpus luteum, which produces progesterone

  in males it stimulates the production of testosterone
• Anterior Pituitary - Prolactin

  primarily stimulates milk production in breastfeeding women

  also has roles in reproductive health + immune function in both males + females

  targets mammary glands
• Release Triggers of ADH - High Plasma Osmorality

  detected by osmorecptors in the hypothalamus when blood becomes more concentrated, like during dehydration/over consumption of electrolytes
• Release Triggers of ADH - Low Blood Volume/Pressure

  detected by baroreceptors in heart + blood vessels to conserve blood volume