Cheryl has taught veterinary and medical student for over 20 years and has a DVM and PhD degree in reproductive biology.
Pituitary Gland and Hypothalamus
The pituitary gland has two separate embryological origins. The anterior pituitary gland is derived from an upward extension of oral ectoderm, whereas the posterior pituitary gland is derived from a downward extension of neuroectoderm. The hypothalamus produces hormones and other factors that regulate production of hormones by the anterior pituitary gland. Hypothalamic hormones travel down axons of neurons to reach the posterior pituitary gland where they are stored and released from.
Posterior Pituitary Gland
The posterior pituitary gland is comprised of two regions:
- Pars nervosa
The infundibulum region is further divided into:
- Median eminence
- Stem or stalk, a region that connects the median eminence to the pars nervosa region
The median eminence stores hypothalamic releasing and inhibiting factors that affects cells within the pars distalis of the anterior pituitary gland. Example hormones that are produced in the hypothalamus and then travel down the axons to the median eminence include:
- Gonadotropin releasing hormone (GnRH): stimulates folliculotrophs and luteotrophs to produce FSH and LH, respectively
- Cortisol releasing factor: stimulates corticotrophs to produce adrenocorticotropic hormone (ACTH)
- Thyroid releasing hormone: stimulates thyrotrophs to produce thyroid stimulating hormone (TSH)
- Growth hormone releasing hormone: stimulates somatotrophs to produce growth hormone (GH)
Within the median eminence, these hormones are stored as Herring bodies. These hormones reach the pars distalis region of the anterior pituitary gland via the hypothalamic-hypophyseal (pituitary gland)-portal system. Within the median eminence, these hormones are released into primary capillaries. They will then enter portal venules in the pars tuberalis region of the anterior pituitary gland. They will then enter secondary capillaries located in the par distalis where they are released to stimulate cells within this region.
Note: While the median eminence stores and releases hypothalamic hormones, it does not produce any hormones.
Pars nervosa is part of the posterior pituitary gland. Similar to the median eminence, it stores and releases hypothalamic hormones. Hypothalamic hormones stored and released from the pars nervosa include:
- Vasopressin (anti-diuretic hormone, ADH): stimulates water reabsorption by the collecting duct of the kidney.
- Oxytocin: stimulates uterine and mammary gland contraction at the time of birth. Contraction of the mammary gland results in 'milk let down'. This hormone also regulates maternal and paternal care.
Both vasopressin and oxytocin are nine amino acids in length, and thus, they have a short half-life in the bloodstream.
Support cells in the median eminence and pars nervosa are called pituicytes, but they do not produce any hormones.
Anterior Pituitary Gland
The anterior pituitary gland is derived from oral ectoderm. There are divisions to the anterior pituitary gland:
- Pars tuberalis
- Pars distalis
- Pars intermedia
The pars tuberalis contains the portal veins/venules that connect the primary capillary bed in the median eminence to the secondary capillary bed in the pars distalis. Thus, this region is involved in the hypothalamic-hypophyseal portal system. No hormones though are produced from this region.
The pars distalis produces most of the hormones for the anterior pituitary gland. The cells within this region are separated into two types:
- Chromophiles: that stain either with acidic (acidophils) or basic (basophils) dye.
- Chromophobes: that do not stain with either acidic or basic dye, such cells may have previously been chromophiles but released their granules (degranulated).
Acidophils include two types of cells:
- Somatotrophs produce growth hormone (GH, somatotropin) that stimulates somatomedin (insulin-like growth factor)from the liver, which results in muscle proliferation and lengthens the long bone if the growth plate is still evident. GH is inhibited by somatostatin that is produced from various organs, including the stomach and pancreas. Growth hormone releasing hormone from the hypothalamus stimulates GH production.
- Lactotrophs produce prolactin that stimulates milk secretion. It is inhibited by dopamine from various regions in brain.
Basophils include four types of cells:
Folliculotrophs and luteotrophs are also called gonadotrophs as they stimulate gonadal processes in the female and male. Folliculotrophs produce follicle stimulating hormone (FSH) in response to GnRH from the hypothalamus. FSH stimulates ovarian folliculogenesis (ovarian follicle development) in females and spermatogenesis (spermatozoa development) in males. Luteotrophs produce luteinizing hormone (LH) that stimulates thecal cells in the ovary and Leydig (interstitial cells) in the testis to produce testosterone. A surge of LH in females lead to ovulation, release of the egg and surrounding cells.
Corticotrophs produce adrenocorticotropin (ACTH) in response to cortisol releasing factor (CRF) from the hypothalamus. It stimulates the zona fasciculata and zona reticularis of the adrenal cortex region to produce glucocorticoids, inhibit inflammation, and sex steroid hormones, stimulate male and female reproduction.
Thyrotrophs produce thyroid stimulating hormone (TSH) in response to thyroid releasing hormone (TRH) from the hypothalamus. TSH stimulates the production of thyroxine (T3 and T4) by the thyroid gland. Thyroxine regulates energy metabolism and heart rate.
The hypophyseal cavity is between the pars distalis and pars intermedia. The pars intermedia of the anterior pituitary gland resides next to the pars nervosa of the posterior pituitary gland. The main hormone produced by the pars intermedia is melanocyte stimulating hormone (MSH) that stimulates melanization of skin.
This lesson discussed the embryological origins of the anterior pituitary gland (oral ectoderm) and posterior pituitary gland (neuroectoderm). Hormones produced by the hypothalamus and pituitary gland were discussed. Only the anterior pituitary gland produces hormones. The median eminence and pars nervosa of the posterior pituitary gland store hypothalamic hormones as Herring bodies and then release such hormones when stimulated. Hypothalamic hormones stored and released from the median eminence include: Gonadotropin releasing hormone, cortisol releasing factor, thyroid releasing hormone, and growth hormone releasing hormone: stimulates somatotrophs to produce growth hormone (GH). Hypothalamic hormones stored and released from the pars nervosa are: Vasopressin (anti-diuretic hormone, ADH) and oxytocin.
The three regions of the anterior pituitary gland are:
- Pars tuberalis: contain portal veins/venules of the hypothalamic-hypophyseal portal system
- Pars distalis: produce most of the pituitary gland hormones
- Pars intermedia: produces melanocyte stimulating hormone (MSH)
Cells in the pars distalis include:
- chromophils: acidophils and basophils
- chromophobes: degranulated acidophils and basophils
To unlock this lesson you must be a Study.com Member.
Create your account
Register to view this lesson
Unlock Your Education
See for yourself why 30 million people use Study.com
Become a Study.com member and start learning now.Become a Member
Already a member? Log InBack