Question

Which is commonly called posterior pituitary? (a) Pars distalis (b) Pars intermedia (c) Pars nervosa (d) All of these

Short answer

(c) Pars nervosa

Step-by-step solution

Identifying the parts

First, let's identify the parts: the pituitary gland consists of two components - the anterior pituitary, known as the adenohypophysis, and the posterior pituitary, known as the neurohypophysis. The adenohypophysis comprises 'pars distalis' and 'pars intermedia'. The neurohypophysis is referred to as 'pars nervosa'.

Evaluation of Options

'Pars distalis' and 'pars intermedia' are subsections of the anterior pituitary, and thus, not the correct options. 'Pars nervosa' is the other name for the posterior pituitary - it's the correct answer. 'All of these' doesn't apply here since only one of these options is another name for posterior pituitary.

Final Answer

Upon reviewing all provided options, we conclude that 'pars nervosa' is the commonly used name for posterior pituitary.

Key concepts

Neurohypophysis

The neurohypophysis, also known as the posterior pituitary, is a key part of the pituitary gland. It plays an essential role in the body's hormone regulation system. The neurohypophysis is directly connected to the hypothalamus via the pituitary stalk, which is a bundle of nerve fibers. This close connection allows for the direct transportation of hormones produced by the hypothalamus to the pituitary.
The main function of the neurohypophysis is to store and release hormones such as vasopressin (or antidiuretic hormone, ADH) and oxytocin into the bloodstream.

• Vasopressin is crucial for regulating water balance in the body and maintaining blood pressure.
• Oxytocin is involved in childbirth and lactation, aiding uterine contractions and milk ejection during breastfeeding.

The posterior pituitary does not produce these hormones; instead, it acts as a storage site until they need to be released into the blood. Understanding the neurohypophysis helps in grasping how certain physiological processes are regulated in the body.

Pars Nervosa

The term "pars nervosa" specifically refers to the posterior lobe of the pituitary gland. It is synonymous with the neurohypophysis and is characterized by its neural origins and components.
While the anterior pituitary consists of glandular tissue, the pars nervosa is composed of nerve tissue. It's made up of non-myelinated nerve fibers that originate from the hypothalamus. These fibers transport hormones from the hypothalamus and release them into the bloodstream when triggered.

• The nerve fibers found in the pars nervosa are extensions of hypothalamic neurons called "axons."
• These axons end in small bulges known as "Herring bodies," where hormones are stored.

Besides the nerve fibers, the pars nervosa contains pituicytes, which are specialized glial cells that support the neuronal elements. Understanding the pars nervosa provides insight into the neural basis of hormone release processes of the pituitary gland.

Pituitary Gland Anatomy

The pituitary gland, often termed the "master gland," is pivotal in controlling various hormonal functions in the body. It's a small, pea-sized organ located at the base of the brain, nestled in a bony cavity known as the sella turcica.
Like a two-storey structure, the pituitary gland has two main parts:

• Anterior Pituitary (Adenohypophysis): This is the glandular portion and is responsible for producing and secreting hormones such as growth hormone, prolactin, and adrenocorticotropin.
• Posterior Pituitary (Neurohypophysis): As explained, this portion stores and releases hormones made by the hypothalamus, such as vasopressin and oxytocin.

The anterior and posterior pituitary have distinct origins, compositions, and functions. Understanding pituitary gland anatomy helps appreciate how the brain communicates with different parts of the body to regulate critical bodily functions like metabolism, growth, and reproduction. This tiny yet potent gland exemplifies how a small structure can exert vast influence over human physiology.