Hypothalamus and Pituitary

Although the endocrine system includes organs all over the body, the brain, and more specifically the hypothalamus and pituitary, is the main coordinator of the whole system. The MCAT will expect you to know general anatomy of each and which hormones are released by both.

Anatomy

On the underside of the brain there is a small protrusion that looks like a set of testicles hanging down, that is the pituitary gland. The pituitary is divided into two separate lobes the anterior and posterior. Sitting just above the pituitary is the hypothalamus (hypo meaning below so its name literally means below the thalamus).

Between the two is a thin stalk called the infundibulum that allows the hypothalamus to control the action of the pituitary by hormonal and neural mechanisms depending on which lobe is involved.

Hypothalamic-Pituitary Relationships

The hypothalamus is connected and communicates with the anterior pituitary via portal vessels that carrier hormones released from the hypothalamus to the anterior lobe there they trigger the release of hormones from the anterior lobe into the bloodstream. In contrast the hypothalamus extends the axons of it’s neurons into the posterior lobe and transports the hormones into the posterior lobe where they are stored in the axon terminals and later released.

Connection Question

What motor protein most likely moves hormones from the hypothalamus to the posterior pituitary and what structure does it “walk” along?

Answer

Kinesin and dynein are the two major motor proteins that move vesicles around the cell. Kinesin is responsible for anterograde transport, or transport outwards from the nucleus, while dyenin is responsible for retrograde transport, so from the outside of the cell towards the nucleus. Since the soma, which contains the nucleus, of the neuron sits in the hypothalamus, and the hormones are transported outwards towards the axon termial, this is an example of anterograde transport and kinesin would walk along the microtubules to move the hormones to their final destination in the posterior pituitary prior to release.

Anterior Pituitary

This means the hypothalamus and anterior pituitary require a two-hormone process. First the hypothalamus must release a hormone that travels down to the anterior pituitary triggering the release of a second hormone that will then travel to its target tissue in the body. In total the anterior pituitary releases a total of seven unique hormones: follicule-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH), prolactin (PRL), endorphins, and growth hormone (GH). The MCAT will expect you to know all of them and the hypothalamic hormone that trigger their release, which can seem really overwhelming at first.

But if you follow the inherent logic of the naming, it’s relatively easy to grasp. In most cases the hypothalamus will use a releasing hormone.

Posterior Pituitary

	Anterior Pituitary	Posterior Pituitary
Where are the hormones originally made?	Anterior pituitary	Hypothalamus
How does the hypothalamus communicate?	Neurally	Hormonally
What type of cells is each composed of?	Neuron-like cells	Endocrine cells
What hormones is each reponsble for?	FSH, LH, ACTH, TSH, PRL, Endorphins, GH	Oxytocin and Vasopressin

Content to Passage

Aging is characterized by the progressive deterioration of physiological function across multiple organ systems. The hypothalamus, and specifically the ventromedial hypothalamus (VMH), has been identified as a central regulator of systemic aging. Neuroinflammatory IKKβ/NF-κB signaling in the VMH acts as a pace-regulator of aging, in part by suppressing hypothalamic release of gonadotropin-releasing hormone (GnRH), the attenuation of which impairs neurogenesis and accelerates age-related decline.

Adapted from: Leng L, Yuan Z, Su X, Chen Z, Yang S, Chen M, et al. (2023) Hypothalamic Menin regulates systemic aging and cognitive decline. PLoS Biol

View Analysis

Aging is characterized by the progressive deterioration of physiological function across multiple organ systems. The hypothalamus, and specifically the ventromedial hypothalamus (VMH), has been identified as a central regulator of systemic aging. Neuroinflammatory IKKβ/NF-κB signaling in the VMH acts as a pace-regulator of aging, in part by suppressing hypothalamic release of gonadotropin-releasing hormone (GnRH), the attenuation of which impairs neurogenesis and accelerates age-related decline.

Tag: Aging VMH

• The mention of hypothalamus here should trigger you to think about all the things you just learned about its a broad mention in the passage and could go lots of different ways but it should prime you to think about the endocrine system
• Neuroinflammatory anytime you see inflammation you should think immune system. The MCAT has asked some subtle questions about that hinged on realizing inflammation stems from an immune response and this is easy to miss.
• gonadotropin-releasing hormone (GnRH) this is a good chance to practice breaking down the names to deduce hormone information
  • gonad: refers to reproductive and sex organs
  • tropin: this is a tropic hormone that is going to stimulate the release of another hormone
  • releasing: this definitely came from the hypothalamus “releasing” is in most hypothalamic hormone names