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The posterior pituitary gland(PPG): Stores and releases oxytocin and ADH produced by the hypothalamus. has a distinct histological structure. It is characterized by specialized neural tissue. This tissue stains much lighter than the tissues of the anteriorThe front of the body or toward the front when standing in the anatomical position. pituitary glands.
Histology
The posterior pituitary glandEndocrine gland at the brain’s base controlling many hormones. is a mass of neural tissue. It is one of the 4 types of tissue in the human body. As with all nervous tissue, neuroglia are present, as seen by their darkly-stained nucleiClusters of neurons in the CNS responsible for processing information.. Pituicytes are modified axon terminals of nerve fibers originating from the hypothalamusA small but vital brain region controlling hormones, temperature, and autonomic functions.. Using the traditional H&E stain, these structures are poorly visualized. However, the nuclei of neuroglial cellsThe basic structural and functional units of life. called pituicytes take a dark stain.
Axons of the paraventricular and supraoptic nuclei originate in the hypothalamus. They travel through the infundibulumThe stalk connecting the hypothalamus to the pituitary gland.. They terminate in the posterior pituitary gland. Their axon terminals contain vesicles filled with hormones synthesized in the hypothalamus, but stored in the posterior pituitary gland. The nerve terminals release these hormones into the systemic circulation. This happens in response to a neural trigger that is an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission. from the hypothalamus.
Antidiuretic Hormone (ADH)
The antidiuretic hormoneADH A hormone that increases water reabsorption in the kidneys to concentrate urine and reduce water (ADH) is synthesized by the supraoptic nucleusThe control center of the cell that contains DNA and directs cellular activities. of the hypothalamus. It is stored in the modified axon terminals of the posterior pituitary gland. Osmoreceptors in the hypothalamus detect high osmolarityA measure of solute concentration in fluid; affects fluid movement between compartments. (saltiness) of the blood plasmaThe liquid component of blood.. In response, the hypothalamus sends an action potential to the posterior pituitary gland. This action releases ADH. ADH targets cells in the kidney increasing reabsorptionThe process of fluid moving back into capillaries from surrounding tissues due to colloid osmotic p or conservation of waterThe universal solvent essential for life.. This causes concentrated urineThe liquid waste excreted by the kidneys..
Oxytocin (OXT)
Oxytocin is synthesized in the paraventricular nucleus of the hypothalamus. It is stored in the modified axon terminals in the posterior pituitary gland. The hypothalamus sends an action potential to the posterior pituitary gland. This action causes oxytocin(OXT): Stimulates uterine contractions and milk ejection. to be released from the modified axon terminals. Oxytocin acts on smooth muscle cells in the uterine wall, causing rhythmic contractions that help to facilitate labor and delivery. Oxytocin also plays a critical role in milk ejection (letdown) during breastfeeding
Figure 1: Slide227 Pituitary gland, monkey, Masson trichrome, 40X
Figure 2: Slide 226 Pituitary gland, human, H&E, 40X
Figure 3: Slide 227XC-HE Pituitary gland, monkey, cross section, H&E, 40X
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.
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List of terms
- posterior pituitary gland
- anterior
- pituitary gland
- nuclei
- hypothalamus
- cells
- infundibulum
- action potential
- antidiuretic hormone
- nucleus
- osmolarity
- plasma
- reabsorption
- water
- urine
- oxytocin