21.8
The Pituitary Gland
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Q1: Where is the pituitary gland located in the body?
The pituitary gland is a small endocrine organ located in the sphenoid bone beneath the hypothalamus. This strategic positioning allows it to maintain close anatomical and functional connections with the hypothalamus, enabling coordinated control of hormone secretion throughout the body.
Q2: What are the two main regions of the adult pituitary gland?
The adult pituitary has two distinct anatomical and functional regions: the anterior lobe and the posterior lobe. The anterior lobe comprises the pars distalis and pars tuberalis, which contain glandular epithelial tissue that produces various hormones. The posterior lobe consists of the infundibulum and pars nervosa.
Q3: How does the hypothalamus control the anterior pituitary lobe?
The hypothalamus controls the anterior pituitary through the hypophyseal portal system, a vascular connection between the two structures. Hypothalamic hormones secreted by ventral hypothalamus cells travel through this portal system and regulate hormone secretion by anterior lobe cells, enabling integrated endocrine control.
Q4: What is the hypothalamic-hypophyseal tract and what does it do?
The hypothalamic-hypophyseal tract is a neural pathway that passes through the infundibulum, a funnel-shaped stalk connecting the hypothalamus to the posterior pituitary. This tract carries axons from the supra-optic and paraventricular nuclei, delivering ready-made hormones from hypothalamic neurosecretory cells for storage and release by the posterior pituitary.
Q5: How does the posterior pituitary differ from the anterior pituitary in structure?
The posterior pituitary maintains a neural connection with the hypothalamus via the hypothalamic-hypophyseal tract, whereas the anterior pituitary has a vascular connection through the hypophyseal portal system. The posterior lobe stores hormones produced by hypothalamic neurons, while the anterior lobe produces its own hormones in response to hypothalamic signals.
Q6: What happened to the pars intermedia during human development?
During fetal development, a third pituitary region called the pars intermedia atrophies and disappears in most individuals. However, some of its cells migrate and persist adjacent to the anterior pituitary in adults, though they no longer form a distinct functional lobe in the mature gland.
Q7: What type of tissue makes up the anterior pituitary lobe?
The anterior pituitary lobe comprises glandular epithelial tissue organized into the pars distalis and pars tuberalis. This specialized tissue produces and secretes various hormones in response to signals from the hypothalamus, making it an active endocrine organ rather than a storage site for hormones.