The Hypothalamus and Pituitary Gland

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hypothalamus

region of the brain that links the nervous and endocrine system by sensing internal and external conditions of the body and releasing regulatory hormones that control pituitary function and maintain homeostasis

infundibulum

a stalk of nervous tissue (primarily axons) attaching the pituitary gland to the hypothalamus; pituitary stalk

pituitary gland

glandular structure associated with the hypothalamus which releases hormones; also called hypophysis

adenohypophysis

the glandular portion of the pituitary gland; aka Anterior Pituitary or Pars Distalis

neurohypophysis

the neural portion of the pituitary gland; aka Posterior Pituitary or Pars Nervosa

tropic hormones

hormones from the anterior pituitary that stimulate the secretion of other hormones in the body; also called trophic hormones

hypothalamohypophysial portal system

a unique vascular connection joining the capillary network of the hypothalamus to the glandular portion of the pituitary gland

hypothalamus

a glandular structure below the thalamus of the brain

almost all hormonal secretions from the pituitary gland are controlled by the ____________

hypothalamus

the hypothalamus senses external and internal stimuli and then communicates with the rest of the body via the ___________ _________

pituitary gland

what stimuli does the hypothalamus sense?

• pain

• fear

• excitement

• odors

• circulating hormones

the hypothalamus consists of neurosecretory neurons with axons extending distally towards the pituitary gland. Give the detailed description of the way these axons extend into it.

• to the proximal infundibulum associated with the anterior pituitary

• to the distal infundibulum associated with the posterior pituitary

what does the hypothalamus produce?

neurohormones

what are the two classifications of neurohormones?

• protein/peptide hormones

• amine hormones

• inhibiting hormones

• releasing hormones

list the peptide/protein neurohormones produced by the hypothalamus

• thyrotropin-releasing hormone (TRH)

• gonadotropin-releasing hormone (GnRH)

• growth hormone-inhibiting hormone (somatostatin, GHIH)

• growth hormone-releasing hormone (GHRH)

• corticotropin-releasing hormone (CRH)

• prolactin-releasing factor (PRF)

list the amine neurohormone produced by the hypothalamus

prolactin-inhibiting hormone (dopamine, PIH)

list the hypothalamic inhibiting neurohormones

• growth hormone-inhibiting hormone (Somatostatin, GHIH)

• Prolactin-inhibiting hormone (Dopamine, PIH)

list the hypothalamic releasing neurohormones

• thyrotropin-releasing hormone (TRH)

• gonadotropin-releasing hormone (GnRH)

• growth hormone-releasing hormone (GHRH)

• corticotropin-releasing hormone (CRH)

• prolactin-releasing factor (PRF)

hypothalamic neurohormones can cause the anterior pituitary to release _________ __________ , which stimulate distant endocrine glands to increase production of their own hormones which act of distant target cells

tropic hormones

hypothalamic neurohormones can cause the _________ __________ to release non-tropic hormones directly on target cells in the body

posterior pituitary

the hypothalamus communicates with the pituitary gland in 2 different ways. explain them.

• direct neural connection between the hypothalamus and the posterior pituitary

• vascular portal system connecting the hypothalamus and anterior pituitary

what is the vascular portal system connecting the hypothalamus with the anterior pituitary?

Hypothalamohypophysial Portal System

another name for the pituitary gland…

Hypophysis

function of the hypophysis

an organ within the head below the brain and controls chemical messaging that affects many crucial organs and body functions

morphology of the hypophysis

• anterior pituitary more externally located

• posterior pituitary more internally located

list all terminology regarding the pituitary gland

Pituitary Gland (Hypophysis)

• Anterior Pituitary (Adenohypophysis)

• Posterior Pituitary (Neurohypophysis)

list the sections of the hypophysis

strictly endocrine

• pars distalis

• pars intermedia

  • a tissue section that separates the posterior pituitary from the anterior lobe. it marks the boundary between the two pituitary lobes.

• pars tuberalis

  • wraps around the pituitary stalk

strictly neuroendocrine (neurohormones)

• pars nervosa (associated with posterior pituitary)

hormones secreted by posterior pituitary:

• anti-diuretic hormone (ADH, Vasopressin)

• oxytocin

how are the hormones made and secreted by the posterior pituitary?

synthesized in the neuron cell bodies within the hypothalamus and carried by the neuron axons to the posterior lobe where they are released

what is the most important hormone for the control of water balance in the body?

anti-diuretic hormone (ADH, Vasopressin)

the anti-diuretic hormone is produced in response to…

• increased blood osmolality (too concentrated; not enough water)

  • ex: dehydration

• hypotension (severe decreased BP)

what are the effects that the anti-diuretic hormone has on the body?

• water retention by kidneys

• vascular constriction to increase BP

function of oxytocin

induces smooth muscle contractions in the mammary glands and uterus

effects of oxytocin on the body:

• milk let-down reflex

  • contraction of alveoli in the mammary gland

• uterine contractions

  • contractions of the myometrium of the uterus

list the hormones secreted by the anterior pituitary (Adenohypophysis, Pars Distalis)

• corticotropin (Adrenocorticotropic hormone, ACTH)

• thyroid-stimulating hormone (TSH, thyrotropin)

• follicle stimulating hormone (FSH)

• luteinizing hormone (LH)

• growth hormone (GH, somatotropin)

• prolactin (PRL)

what hormones are considered tropic hormones?

• ACTH

• TSH

• GH

• FSH

• LH

they stimulate other endocrine glands to produce their hormones

why is Prolactin not a tropic hormone?

it acts directly on the mammary tissue to produce milk