Hypothalamus-Pituitary-target Organ Axes: Feedback Control 1 Flashcards
What are the sites of control of hormone production and secretion?
Hypothalamus and Pituitary Gland
What are the hypothalamus and Pituitary glands responsible for and what do they regulate the function of?
They are responsible for somatic growth, lactation, and milk secretion.
They regulate the function of the Thyroid, Adrenal, and Reproductive Glands
Where is the hypothalamus located?
Below the thalamus and above the pituitary on either side of the third ventricle in the brain
How large is the Hypothalamus with relation to the total brain mass?
Less than 1%
What areas of the brain and spinal cord are connected to the hypothalamus?
The limbic system and autonomic brain stem areas
What are the external and internal signals that the hypothalamus receives?
External: Sensory pathways conveying info on external environment
Internal: Internal receptors conveying body temperature, Osmolarity, pressure, volume, glucose concentration, and hormone concentration.
True or False: The hypothalamus is an interface between the internal and external environment
True
What are the external responses governed by the hypothalamus?
Emotional, instinctual, appetite
External responses have connections with which part of the nervous system?
Central Nervous System CNS
Where are internal homeostasis responses produced?
ANS and endocrine system
What is the endocrine link of the hypothalamus?
It is the Hypothalamic Pituitary axis
True or False: The anterior and posterior are physiologically distinct portions that result from different sources embryonically AND are linked differently to the hypothalamus
True
Where is the pituitary gland located?
It lies in the Sella Turcica in a bone cavity at the base of the base
Compare and contrast the Anterior and Posterior Pituitary with regards to their origin and nature of cells.
Anterior pituitary: Arises from an upward and outward pouching from the epithelium of the phalanx (Rathke’s Pouch). Epitheloid nature of cells
Posterior Pituitary: Arises from a neural tissues outgrowths from the hypothalamus (extension of the hypothalamus). Glial-type cells found.
What is Rathke’s pouch
It is the part of the epithelium of the pharynx where the anterior pituitary pouches from
Briefly describe the connection of the pituitary to the hypothalamus
The posterior pituitary connects to the hypothalamus via a neutral pathway
The anterior pituitary connects via a unique vascular link
Describe the structure and function of the posterior pituitary gland
The posterior pituitary gland forms a neuroendocrine system consisting of neuro secretory neurons whose cell bodies lie in two well defined clusters located in the hypothalamus. These clusters are the Supraoptic and the paraventricular nuclei. Axons of these neurons pass through the stalk and terminate at the capillaries within the posterior pituitary. The posterior pituitary does not produce its own hormones but it is the nuclei of the neurosecretory neurons.
What are the clusters related to the posterior pituitary and where are they found?
Supraoptic and paraventricular
They are found in the hypothalamus
What does each cluster of the posterior pituitary produce?
Supraoptic produces vasopressin (ADH)
Paraventricular produces Oxytocin
Where are the hormones of the posterior pituitary produced?
Supraoptic and paraventricular nuclei of the neurosecretory neurons in the hypothalamus
What are the two hormones secreted by the posterior pituitary gland?
Vasopressin and oxytocin
Trace the path of vasopressin or ADH
Vasopressin is produced in the cell bodies of the supraoptic nuclei. They then travel down the stalk to the nerve endings in the posterior pituitary gland where they are stored. To be transported that must combine with carrier proteins called Neurophysins. When needed, it will be released to circulation (towards kidney)
How long does it take for hormones to be transported from the cell body in the hypothalamus to the posterior pituitary
Several days (slow)
True or False: The paraventricular nuclei can synthesize ADH
True, now fuck off
Okay so each nuclei can synthesize 1/6 as much of the second hormone as of its primary hormone => not exclusively produced in either nuclei
How is the hormone stored in the pituitary gland and how does it change when it is secreted?
The hormone is stored combined with neurophysins. When secreted through exocytosis, they separate immediately.
What are the carrier proteins that bind to the hormones in the Hypothalamic-posterior pituitary stalk
Neurophysins
True or False: Does the Anterior pituitary synthesize its own hormones
True
What are all the hormones that are synthesized by the anterior pituitary and state which are tropic
Growth Hormone (Somatotropin) Adrenocorticotropin Hormone (ACTH) Thyroid-stimulating Hormone (TSH) Follicle Stimulating Hormone (FSH) Leutinizing Hormone (LH, ICSH) Prolactin All tropic except prolactin
Another name for Growth hormone
Somatotropin
Define Tropic hormones
Hormones that stimulate the secretion of another hormone
What hormone(s) produced by the posterior pituitary gland are non-tropic
Oxytocin and Vasopressin
Lol
What hormone(s) produced by the anterior pituitary are non-tropic?
Prolactin
What hormone does ACTH leads to secrete?
Cortisol
What are the different cell types of the anterior pituitary and what does each produce? List them in order of most to least prevalent
Somatotropes -> GH (30-40%) Corticotropes -> ACTH (20%) Gonadotropes -> FSH and LH Lactotropes -> Prolactin Thyrotropes -> TSH Gonadotropes and Lactotropes can switch in order
How does the anterior pituitary know when to secrete hormones? Discuss the mechanism including the vascular link.
The hypothalamus releases Hypothalamic releasing and Hypothalamic inhibitory hormones (or factors). They are secreted within the hypothalamus through the vascular link in a system called the Hypothalamic Hypophyseal Portal System. It begins in the base of the hypothalamus called the Median Eminence. A group of capillaries recombine into small portal vessels and pass down the stalk. Portal vessels then branch to form most of the anterior pituitary capillaries before draining into the systemic venous system.
Does the blood first pass through the hypothalamus or the anterior pituitary? Why?
Almost all blood supplied to the anterior pituitary must first pass through the hypothalamus. This is due to the fact that blood must flow in that direction to move the hormones => immediate delivery
AND this allows the hormones to bypass general circulation.
Where does the hypothalamic hypophyseal portal start and end
Starts when the capillaries join and ends when the capillaries branch.
What are the 2 factors that regulate anterior pituitary hormone secretion?
Hypothalamic hypophysiotropic hormones
Feedback by target gland hormones
What type of hormones are the hypothalamic hypophysiotropic hormones?
(Small) Peptide hormones
True or False: A Hypothalamic Hypophysiotropic Hormone can have more than one effect AND a single pituitary hormone may be regulated by two or more hypothalamic hypophysiotropic Hormone.
Oh, and when you’re done state an example if any part (or both or none) are true
True
Example 1: PIH is identical to Dopamine; GHIH inhibits the release of GH and TSH
Example 2: Growth Hormone is regulated by GHRH and GHIH (Releasing and inhibitory).
State the effect of the following hormones on the Anterior Pituitary Gland. In the end state what the hormones I mentioned are called and another name for number 5 and another hormone that has the same role as number 6 :)
- Thyrotropin-releasing hormone (TRH)
- Corticotropin-releasing hormone (CRH)
- Gonadotropin-releasing hormone (GnRH)
- Growth hormone releasing hormone (GHRH)
- Growth hormone inhibiting hormone
- Prolactin inhibiting hormone (PIH)
- Prolactin Releasing Hormone
- Stimulates the release of TSH (thyrotropin) and Proline
- Stimulates release of ACTH (corticotripin)
- Stimulates release of FSH and LH
- Stimulates release of GH
- Inhibits release of GH and TSH
- Inhibits release of Prolactin
- Stimulates release of Prolactin
For number 5 another name is somatostatin
For number 6 Dopamine
Distinguish between Ultrashort, short, and long feedback loops. Give an example of a long feedback loop.
Ultrashort = Hypothalamic hormones inhibit their own secretion via autocrine effects
Short = Pituitary hormones inhibit the release of hypothalamic hormones
Long = Hormones from peripheral endocrine glands inhibit the release of hypothalamic and pituitary hormones
An example of a long one is cortisol.
Where do the capillaries of the anterior pituitary directly drain into
The systemic venous system
