Past Papers · SAQ
Pituitary & Hypothalamus — Hypothalamus
2023A Q16
Exam questionOutline the role of the hypothalamus.
CICMWrecks answer
Master answer
Hypothalamus
- Hypothalamus
- organ that regulates large number of autonomic/ endocrine processes
- acts as control centre
- Cells
- magnocellular neurosecretory cells in the paraventricular nucleus and the supraoptic nucleus of the hypothalamus produce neurohypophysial hormones, oxytocin and vasopressin. These hormones are released into the blood in the posterior pituitary.
- Much smaller parvocellular neurosecretory cells, neurons of the paraventricular nucleus, release corticotropin-releasing hormone and other hormones into the hypophyseal portal system, where these hormones diffuse to the anterior pituitary.
- Location
- Part of the fore brain. Considered part of the diencephalon
- Located below the thalamus and forms the floor and lower part of the lateral walls of the third ventricle
- Anteriorly extends up to the optic chiasma
- Posteriorly continuous with the tegmentum of midbrain
- Structure
- formed by gray matter conglomeration of neurons that organize in nuclei and also by white-matter substance formed by myelinated nervous fibers.
- Nuclei send and receive fibers to other parts of brain
- divided by the anterior horns of the fornix in a lateral, medial, and periventricular (median) region and by a coronal plane passing through the infundibulum in an anterior and posterior region.
- Regions
- Anterior / Prechiasmatic / Supraoptic
- located above the optic chiasm
- contains: supraoptic, preoptic and medial preoptic, the suprachiasmatic and the anterior hypothalamic nucleus, alongside with the paraventricular nucleus
- Infundibular / Tuberal
- located above tuber cinereum (between anterior and posterior)
- composed of two parts, anterior and lateral
- contains: dorsomedial, ventromedial, paraventricular, supraoptic, and arcuate nucleui
- Posterior / Mamillary
- formed by medial and lateral area
- medial area contains mamillary nuclei and posterior nucleus
- lateral area contains lateral nucleus and tuberomammillary nucleus
- Anterior / Prechiasmatic / Supraoptic
- Connections: Nervous, Endocrine, CSF, Direct to pituitary
- Blood supply
- mainly hypophyseal artery (branch of anterior cerebral artery)
- Detailed arterial supply:
- Anterior: branches of ACA and ACOM
- Tuberal: branches of PCOM and superior hypophyseal artery
- Posterior: branches of PCA
- Infundibulum: superior hypophyseal arteries from the ophthalmic branch of ICA (C6)
- drains into hypothalamohypophyseal system of veins to anterior pituitary → hypophyseal vein
Function of Hypothalamus
Autonomic nervous system activity
- CVS:
- Ant hypothalamic stimulation → ↓BP + ↓HR
- Post hypothalamic stimulation → ↑BP + ↑HR
- Thermoregulatory: integrates thermoreceptor input + controls activity of heat loss + heat gain mechanisms
- Satiety: hunger modulated by glucose, CCK, glucagon, and leptin
- Water balance:
- Osmoreceptors: control ADH release from posterior pituitary
- ATII: stimulates thirst + ADH release via subfornical organ + organum vasculosum
- Circadian rhythm
- Behaviour
- Sexual function
Endocrine/ hormonal activity
- Direct neural control of posterior pituitary gland
- Pituitary neurosecretory neurons
- Magnocellular neurons:
- consists of SON + PVN
- synthesise and secrete ADH and oxytocin
- Parvocellular neurons:
- form tuberoinfundibular tract → secrete hypophysiotropic hormones
- release controlled by Nad, dopamine, 5-HT
- Magnocellular neurons:
- Hypothalamic hormones → action in pituitary
- Anterior pituitary by hormone secretion into long portal vein
- GnRH → stimulates FSH + LH release
- CRH → stimulates ACTH release
- GHRH → stimulates GH release
- TRH → stimulates TSH release
- Somatostatin (GH inhibiting hormone) → inhibits GH, TSH, ACTH, and PRL release
- PRL releasing hormone (PRH) → stimulates PRL release
- Dopamine → inhibits PRL release
- Posterior pituitary by neuronal innervation
- ACh → stimulates release of ADH + oxytoxin
- NAd → inhibits ADH + oxytocin secretion
- Anterior pituitary by hormone secretion into long portal vein
(See next tab for detailed table of nuclei with functions, and communications of hypothalamus)
Sources: https://www.intechopen.com/chapters/63258
https://human-memory.net/hypothalamus/#Structure
JC / Kerr 2022
Nuclei and functions
| Region | Area | Nucleus | Function |
|---|---|---|---|
| Anterior (Supraoptic / prechiasmatic) | Preoptic | Preoptic nucleus | – Thermoregulation |
| Medial | Medial preoptic nucleus | – Regulates the release of gonadotropic hormones from the adenohypophysis – Contains the sexually dimorphic nucleus, which releases GnRH, differential development between sexes is based upon in utero testosterone levels – Thermoregulation | |
| Supraoptioc nucleus | – Vasopressin release – Oxytocin release | ||
| Paraventricular nucleus | – thyrotropin-releasing hormone release – corticotropin-releasing hormone release – oxytocin release – vasopressin release – somatostatin round | ||
| Anterior hypothalamic nucleus | – thermoregulation – panting – sweating – thyrotropin inhibition | ||
| Suprachiasmatic nucleus | – Circadian rhythms | ||
| Lateral | Lateral nucleus | primary source of orexin neurons that project throughout the brain and spinal cord – Mainly promotion of feeding behaviour and arousal | |
| Infundibular (Middle / tuberal) | Medial | Dorsomedial hypothalamic nuclei | – blood pressure – heart rate – GI stimulation |
| Ventromedial nucleus | – satiety – neuroendocrine control | ||
| Arcuate nucleus | – Growth hormone-releasing hormone (GHRH) – feeding – Dopamine-mediated prolactin inhibition | ||
| Lateral | Lateral nucleus | primary source of orexin neurons that project throughout the brain and spinal cord – Mainly promotion of feeding behaviour and arousal | |
| Lateral tuberal nuclei | – regulation of feeding. Its absence or destruction has been implicated in extremes of starvation such as anorexia nervosa. | ||
| Posterior (mamillary) | Medial | Mamillary nuclei (part of mamillary bodies) | – memory |
| Posterior nucleus | – Increase blood pressure – pupillary dilation – shivering – vasopressin release | ||
| Lateral | Lateral nucleus | primary source of orexin neurons that project throughout the brain and spinal cord – Mainly promotion of feeding behaviour and arousal | |
| Tuberomammillary nucleus | – arousal (wakefulness and attention) – feeding and energy balance – learning – memory – sleep |
Communications of Hypothalamus
- Nervous connections: divided into afferent and efferent fibers
- Afferent fibres: carry somatic and visceral sensations as well as from special senses
- Somatic and visceral afferents via lemniscal afferent fibers and nucleus of tractus solitarius, that reach the hypothalamus via reticular formation
- Visual afferents from the optic chiasma reach the suprachiasmatic nucleus
- Olfactory afferents are received through medial forebrain bundle
- Auditory afferents though not identified completely but are influenced by the hypothalamus
- Hippocampo-hypothalamic afferents reach via fornix to mamillary bodies
- Tegmental fibers from midbrain
- Thalamo-hypothalamic fibers from the midline and dorsomedial nuclei of the thalamus
- Amygdalo-hypothalamic fibers from the amygdaloid complex reach the hypothalamus via stria terminalis
- Efferent fibers: complex and numerous
- To brain stem and spinal cord: The hypothalamic nuclei send efferent fibers to nuclei present in the brainstem and spinal cord. In this way, they control the autonomic nervous system.
- Mammillothalamic Tract: This tract consists of fibers arising in the mamillary body and terminating in the anterior nucleus of thalamus.
- Mammillotegmental Tract: These fibers terminate in the reticular formation, present in the tegmentum of the midbrain.
- Limbic System: The nuclei in the hypothalamus also send efferent fibers to the various nuclei of the limbic system.
- Afferent fibres: carry somatic and visceral sensations as well as from special senses
- Endocrine:
- regulating factors or hormones released by hypothalamus → reach pituitary via the hypophyseal portal system of veins → cells of pituitary release hormones
- Direct:
- Cell bodies present in hypothalamus → axonal terminals in posterior pituitary gland
- Bodies synthesise oxytocin and vasopressin, stored in axonal terminals in posterior pituitary and released on demand
- CSF:
- clear metabolic waste
- distribute glucose, amino acids, lipids, and neurotransmitters
Past papers