28 Questions
What is the dual embryologic origin of the hypophysis (pituitary gland)?
Epithelial and neural
Which part of the brain forms the neural portion (neurohypophysis) of the hypophysis?
Hypothalamus
What is the name of the neural stalk that connects the neurohypophysis to the hypothalamus?
Infundibulum
Which part of the adenohypophysis (anterior pituitary) is the largest?
Pars distalis
What is the purpose of the hypothalamo-hypophyseal portal system?
To carry releasing and inhibiting hormones from the hypothalamus to the adenohypophysis
What is the function of the pituicytes in the neurohypophysis?
To provide structural support for the axons
What is the function of the superior hypophyseal arteries?
They form a primary capillary plexus in the median eminence
Where do the secretory neurons in the hypothalamus terminate?
On the capillary plexus in the median eminence
What is the purpose of the hypothalmo-hypophyseal tract?
To transport hormones from the hypothalamus to the posterior pituitary
Where are the neurons that synthesize oxytocin and antidiuretic hormone (ADH) located?
In the supraoptic and paraventricular nuclei of the hypothalamus
What is the function of the Herring bodies in the neurohypophysis?
They store the hormones synthesized by the hypothalamic neurons
How do hydrophobic steroid and thyroid hormones enter target cells?
By diffusing through the cell membranes
What is the role of transport proteins in the circulation of hydrophobic hormones?
Aid in hormone circulation but prevent diffusion into cells
Where do hydrophobic steroid and thyroid hormones primarily activate receptors in target cells?
Nucleus
What happens to hydrophobic hormones after circulating on transport proteins?
They diffuse through cell membranes to activate receptors
Why can hydrophobic steroid and thyroid hormones diffuse through cell membranes?
As they are lipid-soluble molecules
What is the mechanism of transmission for direct chemical messengers?
Direct movement through gap junctions
Which of the following is an example of a synaptic neurotransmitter?
Acetylcholine
What is the mechanism of transmission for paracrine chemical messengers?
Diffusion through extracellular fluid to nearby cells
Which of the following is an example of an autocrine chemical messenger?
Cytokine interleukin-1
What is the mechanism of transmission for endocrine chemical messengers?
Carried in the bloodstream to distant cells
Which characteristic of endocrine hormones is mentioned in the text?
They are carried in the bloodstream to target cells
What is the main function of somatotrophs?
Produce somatotropin for growth hormone
Which hormone inhibits the release of growth hormone from somatotrophs?
Somatostatin
What is the role of FSH in females?
Induces ovulation and corpus luteum formation
What does prolactin primarily stimulate?
Milk production after parturition
Which hormone is responsible for the production of testosterone in males?
Luteinizing hormone (LH)
What is the main function of corticotrophs?
Regulate adrenal cortex functions
Study Notes
Embryologic Development of Hypophysis (Pituitary Gland)
- The hypophysis (pituitary gland) has a dual embryologic origin, consisting of both epithelial and neural portions.
- The epithelial portion develops from the pharyngeal roof and Rathke's pouch.
- The pouch detaches and becomes the cellular portion, the adenohypophysis.
- The downgrowth of the brain forms the neural portion, the neurohypophysis.
- The neurohypophysis remains attached to the hypothalamus by a neural stalk, called the infundibulum.
- Neurons in the hypothalamus control the release of hormones from the adenohypophysis.
Subdivision of Hypophysis
Adenohypophysis (Anterior Pituitary)
- Pars distalis is the largest part.
- Pars intermedia is a remnant of the pouch and is rudimentary in humans.
- Pars tuberalis surrounds the neural stalk.
Neurohypophysis (Posterior Pituitary)
- Median eminence is located at the base of the hypothalamus.
- Infundibulum is the neural stalk that connects the neurohypophysis to the hypothalamus.
- Pars nervosa is the largest portion and consists of unmyelinated axons and pituicytes.
Vascular and Neural Connections of Hypophysis
- The connection between the hypothalamus of the brain and the adenohypophysis is vascular, forming the hypothalamohypophyseal portal system.
- This system carries releasing and inhibiting hormones from the ventromedial, arcuate, preoptic, and paraventricular nuclei to bind at specific receptors in cells of the pars distalis.
- Superior hypophyseal arteries form a fenestrated primary capillary plexus in the median eminence.
- Secretory neurons in the hypothalamus terminate on the capillary plexus and release hormones.
- Small venules connect to a secondary capillary plexus in the adenohypophysis, forming a portal system.
Cells and Hormones of Adenohypophysis
- There are three cell types based on stains: acidophils, basophils, and chromophobes.
- Acidophils:
- Somatotrophs secrete somatotropin (growth hormone) for cell metabolism and general body growth.
- Mammotrophs produce prolactin that stimulates mammary gland development during pregnancy and maintains milk production after parturition.
- Basophils:
- Thyrotrophs release thyroid-stimulating hormone (TSH) that stimulates the thyroid gland to produce thyroxin and triiodothyronine.
- Gonadotrophs secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
- Corticotrophs secrete adrenocorticotropic hormone (ACTH) to regulate adrenal cortex functions.
Neurohypophysis
- Does not have any secretory cells; secretory neurons are located in the hypothalamus of the brain.
- Releases two hormones from axon terminals: oxytocin and antidiuretic hormone (ADH).
Test your knowledge on how hydrophobic steroid and thyroid hormones circulate on transport proteins and activate cytoplasmic receptors in target cells.
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