Endocrinology: Hypothalamus and Pituitary Flashcards
1
Q
Location of hypothalamus
A
- Central location within the brain
- Sits in a cavity: bone = sella turcica
- Located a few cm behind the eyes
- Pituitary gland is essentially attached to hypothalamus through pituitary stalk
2
Q
Function of the hypothalamus
A
- Link between the nervous and endocrine system: receives lots of information from higher brain centres (electrical signals = nervous system) and secretes hormones (endocrine) to regulate the anterior pituitary
- Has many neural connections to other areas of the brain
- Major control centre for autonomic-mediated functions
3
Q
What does the hypothalamus regulate?
A
o Hormone production and release from pituitary; in turn influences thyroid gland (metabolism), adrenal gland (stress), gonads (reproduction)
o Contraction of uterus during labour
o Milk production and release
o Kidneys (water retention, sodium, and potassium balance
o Growth and development
o Biological rhythms
o Body temperature
o Circulation
o Food-water intake
4
Q
What are hypothalamic control centres?
A
- Hypothalamic control centres are clusters of neurons. Each cluster is identified as a nucleus, e.g., paraventricular nucleus, supraoptic nucleus
5
Q
Link between hypothalamus and pituitary
A
- Extensive neural connections exist between the hypothalamus and the rest of the brain.
- Hypothalamus is surrounded by the limbic lobe (associated with emotions)
- The pituitary is mainly controlled by the hypothalamus
- Physically connected via pituitary stalk/ infundibulum
- Many hormones released from the pituitary influence secretion from the other endocrine glands
6
Q
Development of the pituitary
A
- Anterior pituitary: up growth from oral cavity; has vascular connection with the hypothalamus
- Posterior pituitary: down growth from the brain; has neural connection with the hypothalamus
- Two glands distinct from each other, front; secretary epithelial cells, up growth from root of mouth, back: neural tissues, down growth
- As (front) moves upwards, becomes physically connected to the other portion of the gland; connections develop
7
Q
Histology of posterior pituitary
A
- Nervous tissue: axons of neurosecretory cells
- Pituicytes are a kind of glial cells: support
- Capillaries are fenestrated: no blood-brain-barrier in posterior pituitary
8
Q
Histology of anterior pituitary
A
- Chromophils (cells which take up stain; actively secreting hormones)
o Acidophils (somatotrophs ~40-50%, lactotrophs (aka mammotrophs ~10-15%)
o Basophils (corticotrophs ~15-20%, thyrotrophs ~3-5%, gonadotrophs ~10-15%) - Chromophobes (resting/ degranulated chromophils)
9
Q
Neural connections between hypothalamus and pituitary
A
- Paraventricular nucleus and supraoptic nucleus of the hypothalamus: terminal endings in the posterior pituitary
- Hypothalamus communicates with pituitary gland via neural connections involving axonal projections
- Specialised neurons in the hypothalamus produce and release specific regulatory hormones (hypothalamic releasing/ inhibiting hormones)
- These hormones travel along axons through a tract
- Axons of hypothalamic neurons terminate in the median eminence; at the base of hypothalamus, where they release their hormones into the blood vessels of the hypothalamic-pituitary portal systems
10
Q
Vascular connections between the hypothalamus and pituitary
A
- Anterior lobe of pituitary is larger, more vascular, glandular epithelial cells, anterior posterior hormones synthesised
- The hypothalamic-pituitary portal system is a complex network of blood vessels that allows direct communication between the hypothalamus and the anterior pituitary gland
- Consists of a network of capillaries in the median eminence, which receive hypothalamic hormones released by neurons
- Capillaries coalesce to form portal veins, which carry the hypothalamic hormones to a second capillary bed in the anterior pituitary gland
- In the anterior pituitary gland, the hypothalamic hormones act on specific cells, known as endocrine cells or pituitary cells, to regulate the secretion of pituitary hormones
- Anterior pituitary gland then releases its own hormones into systemic circulation, where they exert their effects on target organs throughout the body
11
Q
Posterior pituitary role
A
- An ‘extension’ of the hypothalamus
- Doesn’t synthesis hormones
- Stores hormones formed in the hypothalamic neurons
- Secretes hormones directly into the blood
- Releases 2 neurohormones: antidiuretic hormone (ADH aka vasopressin), oxytocin
12
Q
Role of anterior pituitary
A
- Short axon neurons synthesise hypophysiotropic hormones and release them into capillaries of the hypothalamic-hypophyseal portal system
- Portal vessels carry hypophysiotropic hormones to the anterior pituitary
- Endocrine cells of the anterior pituitary are controlled by hypophysiotropic hormones
- They secrete anterior pituitary hormones into systemic blood
13
Q
Another name for posterior pituitary
A
Neurohypophysis
14
Q
Another name for anterior pituitary
A
Adenohypophysis
15
Q
Hypophysiotropic hormones
A
- Top of the hormonal hierarchy
- Peptide neurohormones
- Released in very small quantities
- Two types: releasing (stimulates release) and inhibiting (suppresses release) hormones
- This is a neuroendocrine system (fast and specific)
- Part of a three hormone chain system with multiple feedback loops (short and long loop)
- Evolution has conserved use of molecules, e.g., ‘prolatin inhibiting hormone’ is dopamine
