explain neural and endocrine control
- in order to maintain homeostasis, the endocrine system must work closely alongside the nervous system
- some glands utilize aspects of both neural and endocrine control to exert their effects within the body
explain nervous vs. endocrine control - response time
Nervous
- rapid responses (miliseconds)
Endocrine
- slow responses (min to hours)
explain nervous vs. endocrine control - duration of effects
Nervous
- brief in duration (ends when stimulus stops)
Endocrine
- long in duration (effects persist after stimulus stops)
explain nervous vs. endocrine control - number of targets
Nervous
- hard-wired to one specific target (muscle or gland)
Endocrine
- many different targets in the body (blood circulates)
explain the pituitary gland
- a very small gland located in a bony cavity at the base of the skull
- it is divided into two anatomically and functionally distinct lobes
- these 2 lobes are completely separate and do not communicate with each other
what are the 2 lobes of the pituitary gland
- posterior pituitary gland
- anterior pituitary gland
explain the posterior pituitary gland
comprised of neural-like tissues and is sometimes called the neurohypophysis
explain the anterior pituitary gland
comprised of glandular epithelial tissues and is also called the adenohypophysis
explain the relationship between the pituitary and hypothalamus
- both anterior and posterior lobes of the pituitary gland release hormones that regulate the functions of other endocrine glands or organs
- the hypothalamus controls this hormone release, but does so in a different manner for each lobe
explain how the hypothalamus stimulates hormone release in the posterior pituitary lobe
- hypothalamus is connected to the posterior pituitary by a neural pathway
- within the hypothalamus there are 2 well-defined clusters of neurons, called the supraoptic nucleus and the paraventricular nucleus
- axons from these nuclei project down the pituitary stalk and terminate on blood vessels in the posterior pituitary
explain how the hypothalamus stimulates hormone release in the anterior pituitary lobe
- hypothalamus is connected to the anterior pituitary by a unique vascular link: the hypothalamic-hypophyseal portal system
- the hypothalamus secretes hormones into this portal system and they are carried directly to the anterior pituitary where they either inhibit or promote the release of anterior pituitary hormones
explain hormones of the posterior pituitary gland
- hormones are not produced in the posterior pituitary gland itself
- hormones are synthesized in the neuron cell bodies located within the hypothalamus
- once synthesized, they are packaged into vesicles which are transported down the axons to the nerve endings in the posterior pituitary
- when an appropriate stimulus reaches the hypothalamus, these neurons transmit an action potential that causes the release of these hormone-containing vesicles into the blood
what are the hormones released from the posterior pituitary
- vasopressin
- oxytoxin
explain vasopressin released from posterior pituitary
also called antidiuretic hormone (ADH), has two major actions
1. enhancing the retention of water by the kidneys
2. causes contraction of arteriolar smooth muscle
explain oxytocin released from posterior pituitary
oxytocin has two major roles
1. stimulating contraction of uterine smooth muscle cells during childbirth
2. promoting milk ejection during breastfeeding
explain hormones of the anterior pituitary gland
- synthesizes and releases 6 hormones, all of which are peptide hormones
- within the anterior pituitary are distinct cell populations that synthesize and secrete each of the hormones
- most of the anterior pituitary hormones are tropic hormones
what are the 6 hormones released from the anterior pituitary
- GH - growth hormone (somatotropin)
- ACTH - adrenocorticotropic hormone (adrenocorticotropin)
- LH - luteinizing hormone
- TSH - thyroid-stimulating hormone (thyrotropin)
- FSH - follicle-stimulating hormone
- PRL - prolactin
explain growth hormone
the primary hormone responsible for regulating the overall body growth and is also involved in metabolism
explain adrenocorticotropic hormone
stimulates secretion of cortisol by the adrenal cortex
explain luteinizing hormone
- in females LH is responsible for ovulation and formation of the corpus luteum
- it also stimulates the secretion of estrogen and progesterone from the ovaries
- in males LH stimulates the release of testosterone from the interstitial cells of Leydig
explain thyroid-stimulating hormone
stimulates the release of thyroid hormones from the thyroid gland
explain follicle-stimulating hormone
- in females, FSH stimulates the growth and development of ovarian follicles and promotes secretion of estrogen by the ovaries
- in males, FSH is requires for sperm production
explain prolactin
- this is the only anterior pituitary hormone that is not tropic
- in females it enhances breast development and milk production
- it is present in males, but the physiological purpose is not clear
explain the hypothalamic-hypophyseal portal system - step 1
hypophysiotropic hormones (releasing hormones and inhibiting hormones) produced by neurosecretory neurons in the hypothalamus enter the hypothalamic capillaries
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