Hypothalamo-hypophyseal system Flashcards
I. What are the functions of Hypothalamo-hypophyseal system?
It is involved in the homeostatic control of the internal environment of body. It receives information about the internal and external environment and organizes the output at 3 levels:
- Neuroendocrine function: control of the pituitary gland through Hypothalamo- hypophyseal system
- Autonomic function: highest regulation center for SYM, PARA and enteric nervous system
- Emotions and drive: interconnections with limbic system, by which it generates behavior (ex: aggression)
II. Neuronal connections of hypothalamus
1. What are the 7 major Neuronal connections of hypothalamus?
- Intrahypothalamic connections
- Extrahypothalamic connections
- Retinohypothalamic tract
- Hypothalamo-hypophyseal tract
- Mammillothalamic and mammillotegmental fascicles
- 2 large tracts are the medial forebrain bundle (located at lateral hypothalamic area) and the dorsal longitudinal fascicle (Schütz)
II. Neuronal connections of hypothalamus
2. Characteristics of Intrahypothalamic connections
Intrahypothalamic connections are related to homeostasis integrating role of the hypothalamus
II. Neuronal connections of hypothalamus
3. Characteristics of Extrahypothalamic connections
Extrahypothalamic connections are reciprocal connections which has both afferent end efferent fibers
II. Neuronal connections of hypothalamus
4. Characteristics of Retinohypothalamic tract
Retinohypothalamic tract contain mostly
afferent fibers
II. Neuronal connections of hypothalamus
5. Characteristics of Mammillothalamic and mammillotegmental fascicles
Mammillothalamic and mammillotegmental fascicles contain mostly efferent fibers
II. Neuronal connections of hypothalamus
6. What are the characteristics of Hypothalamo-hypophyseal tract?
Hypothalamo-hypophyseal tract (connects hypothalamus with the neurohypophysis) is the only tract leaving the brain
II. Neuronal connections of hypothalamus
7. What are the characteristics of the medial forebrain bundle (located at lateral hypothalamic area) and the dorsal longitudinal fascicle (Schütz)?
2 large tracts are the medial forebrain bundle (located at lateral hypothalamic area) and the dorsal longitudinal fascicle (Schütz), which arises from periventricular grey matter and runs caudally within the periaqueductal grey matter toward the brainstem and spinal cord
III. Hypothalamic nuclei and areas
1. What are the 3 regions of hypothalamus?
anterior region, medial region and a posterior region
III. Hypothalamic nuclei and areas
2. Characteristics of medial region of hypothalamus
Medial region is further subdivided into a paraventricular zone, medial zone and lateral zone (containing the lateral hypothalamic area with the medial forebrain bundle)
III. Hypothalamic nuclei and areas
3. What are the characteristics of posterior region?
Posterior region consists of 2 nuclei, the posterior hypothalamic nucleus and corpus mammillare
=> Most of the anterior region nuclei, periventricular zone and the infundibular nucleus contribute to the hypothalamo-hypophyseal system
IV. Hypothalamic afferents and efferents
1. Describe Hypothalamic Afferent innervation
- Huge input from the limbic system (hippocampus - fornix, amygdala – stria terminalis and septal area - MFB)
- Retinohypothalamic tract carries information from the retina
- Somatosensory information is relayed through reticular formation and reach hypothalamus through the medial forebrain bundle
- Viscerosensory information is relayed from the brainstem (NTS) and spinal cord, either directly ascend to the hypothalamus or indirectly through reticular formation (by monoaminergic afferents)
IV. Hypothalamic afferents and efferents
1A. How does Retinohypothalamic tract participate in Afferent innervation?
- Retinohypothalamic tract carries
information from the retina
IV. Hypothalamic afferents and efferents
1B. How does Somatosensory information participate in Afferent innervation?
- Somatosensory information is relayed
through reticular formation and reach hypothalamus through the medial forebrain bundle
IV. Hypothalamic afferents and efferents
1C. How does Viscerosensory information participate in Afferent innervation?
Viscerosensory information is relayed from the brainstem (NTS) and spinal cord, either directly ascend to the hypothalamus or indirectly through reticular formation (by monoaminergic afferents)
IV. Hypothalamic afferents and efferents
2. Describe Hypothalamic Efferent innervation
Hypothalamic efferents are organized according to the 3 main targets:
1. Pituitary gland (to the neurohypophysis through HTH tract)
2. Limbic system targeted through fornix, stria terminalis + MFB (hippocampus, amygdala and septal area)
3. Autonomic centers: in spinal cord = preganglionic neurons and in brainstem = parasympathetic nuclei
Indirect connection through reticular formation Direct connection descends directly (through dorsal longitudinal fascicle)
V. The Hypothalamo-hypophyseal system
1. Definition of The Hypothalamo-hypophyseal system
It is a neuroendocrine system because the CNS influences the endocrine system through this output. Many functions are regulated by this system, containing neuroendocrine cells
V. The Hypothalamo-hypophyseal system
2. Characteristics of Pituitary gland is located ventrally to the hypothalamus
Pituitary gland is located ventrally to the hypothalamus in the hypophyseal fossa. It is connected to the hypothalamus via the infundibulum
- It is very close to the optic chiasm - enlargements/tumor of the gland will affect our vision
VI. Adenohypophysis and neurohypophysis:
1. What are the 2 main parts of Pituitary gland?
Pituitary gland is divided into 2 main parts: adenohypophysis (anterior) and neurohypophysis (posterior)
VI. Adenohypophysis and neurohypophysis:
2. What are the characteristics of neurohypophysis?
Neurohypophysis is connected to the hypothalamus via the hypothalamo- hypophyseal tract (HTH)
- It contains the median eminence, infundibular stem and the pars nervosa.
- This is a neuronal tissue that does not contain cells that produce hormones, but stores the hormones produced in the hypothalamus.
VI. Adenohypophysis and neurohypophysis:
3. What are the characteristics of adenohypophysis?
In the adenohypophysis, we have glandular tissue which produce different hormones
- This also has 3 parts: pars tuberalis (surrounds infundibular stem, together they are called infundibular stalk), pars distalis and pars intermedia (separated from pars distalis by the hypophyseal cleft)
VI. Adenohypophysis and neurohypophysis
4. Embryonic origin of Adenohypophysis and neurohypophysis
Both adeno- and neurohypophysis are ectodermal but have a different embryonic origin.
- Neurohypophysis is developed from neuroectoderm from diencephalon (newer research says telencephalon), while adenohypophysis develop from ectoderm as a small depression in the roof of the mouth (Rathke’s pouch).
- The Rathke’s pouch moves toward the neurohypophysis and form different parts of the adeno- and neurohypophysis
VII. Hypothalamo-neurohypophyseal neurosecretory system
1A. The role of Magnocellular neurons
- Magnocellular neurons of the supraoptic and paraventricular nuclei in the hypothalamus project to the neurohypophysis.
- These nuclei contain cells that produce hormones (vasopressin and oxytocin)
- Oxytocin and vasopressin are produced together with neurophysins (neurophysin 1 together with oxytocin and neurophysin 2 together with vasopressin). These are transported in the axons that run in the Hypothalamo- hypophyseal tract to the neurohypophysis
- In the neurohypophysis, oxytocin and vasopressin are stored near the terminal portion of the axon in dilated areas, containing a lot of neurosecretory granules called Herring bodies
- If there is an appropriate stimulus, vasopressin and oxytocin are cleaved from the neurohypophysis and released into the bloodstream
VII. Hypothalamo-neurohypophyseal neurosecretory system
2A. The role of parvocellular neurons
- We also have parvocellular neurons in the hypothalamus. These are in connection with the adenohypophysis, in a humoral type of connection
- Parvocellular neurons in the hypothalamus (inside tuber cinereum) send their axons toward the medial eminence and infundibulum, where these axons terminate and release hormones into the capillaries
- This tract is called (since it starts in the tuber cinereum and ends in the infundibulum/medial eminence) the tuberoinfundibular tract
- Superior + inferior hypophyseal arteries form a capillary plexus, where hormones are released and travel to the portal vessels
- Portal vessels run toward the adenohypophysis
- Hormones produced in the adenohypophysis are released into the capillaries and leave through the hypophyseal vein to the systemic circulation
- This type of circulatory is called the hypothalamo-hypophyseal portal circulation
