Standardized Science Test Practice Passage 6
Timing: 7.5 minutes

Reading Passage #6

The pituitary gland has often been termed the 'Master Gland' because many of the hormones it releases effect the release of other hormones. However, the pituitary is really not the master. It is controlled by a brain region called the hypothalamus via the release of releasing factors into a special blood vessel network (hypothalamic-hypophyseal portal system) that feeds the pituicytes. These releasing factors then cause or inhibit the release of pituitary hormones which travel via the circulatory sytem to the target organ.  For example, as a woman's menstrual cycle progresses toward ovulation, the hypothalamus releases LHRH (luteinizing hormone releasing hormone) that travels via the hypophyseal portal system to the pituitary where it stimulates the production and release of LH (luteinizing hormone). LH then travels to the ovaries where it causes ovulation and the subsequent development of a progesterone secreting corpus luteum.

Anatomically and functionally the pituitary can be divided into three portions:

1) anterior pituritary (adenohypophysis)
Six peptide hormones are secreted by the adenohypophysis: Growth hormone (somatotropin, GH), corticotropin (ACTH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), Luteinizing hormone (LH), and prolactin (PRL). All except growth hormone and prolactin regulate the activities of other glands.  Somatotropin, PRL and ACTH are polypeptide hormones and LH, FSH, and TSH are glycoproteins having very similar structures.

2) intermediate lobe (pars intermedia)
In the adult human this lobe is diminished with poor vascular and neural connections such that secretion is not facilitated. Cells in the pars intermedia may secrete MSH (melanocyte stimulating hormone) which stimulates the activity of melanocytes in the skin. Melanocytes are cells containing the black pigment melanin. In humans, melanocytes are responsible for moles, freckles, and suntan.

3) posterior pituitary (neurohypophysis)
This portion of the pituitary is really an extension of the hypothalamus. Neurons with their cell bodies in the hypothalamus and their terminal protions in the neurohypophysis release two hormones. Antidiuretic hormone (ADH) and oxytocin are stored there within the terminal processes of neurons until the signal to release them is received.

 
Questions

  1. What organ controls the pituitary gland?
    1. pars intermedia
    2. master gland
    3. hypothalamus
    4. adrenal gland

  2. LHRH is a releasing factor leading to the production of which hormone?
    1. RH
    2. GH
    3. FSH
    4. LH

  3. Which of these hormones is produced by the pars intermedia?
    1. MSH
    2. PRL
    3. LH
    4. ADH

  4. Releasing factors travel through the body in this system.
    1. circulatory
    2. digestive
    3. renal
    4. hypothalamic-hypophyseal portal

  5. Which hormone is responsible for ovulation?
    1. LH
    2. FSH
    3. LHRH
    4. OVARY

  6. Cells responsible for moles, freckles, and suntan.
    1. oxytocin
    2. melanocytes
    3. neurohypophysis
    4. pituicytes

  7. Which hormone does not regulate the activities of other glands?
    1. PLR
    2. TSH
    3. FSH
    4. ACTH

  8. In adults, the pars intermedia is diminished with:
    1. few cells
    2. few releasing factors
    3. poor vascular connections
    4. melanocytes

  9. Hormones travel through the body in this system.
    1. circulatory
    2. digestive
    3. renal
    4. hypothalamic-hypophyseal portal
 
Biology Week 28

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