The glands are controlled directly by stimulation from the nervous system (Endocrine System)
Endocrine system
Introduction
The endocrine system includes all of the glands of the body and the hormones produced by those glands. The glands are controlled directly by stimulation from the nervous system as well as by chemical receptors in the blood and hormones produced by other glands. By regulating the functions of organs in the body.
Function - these glands help to maintain the body's homeostasis. Cellular metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate, and digestion are among the many processes regulated by the actions of hormones.
Hypothalamus
Location - a part of the brain located superior and anterior to the brain stem and inferior to the thalamus.
Function - secretes hormones that stimulate or suppress the release of hormones in the pituitary gland, in addition to controlling water balance, sleep, temperature, appetite, and blood pressure.
It is also responsible for the direct control of the endo system through the pituitary gland. The hypothalamus contains special cells called neurosecretory cells-neurons that secrete hormones.
- Thyrotropin-releasing hormone (TRH)
- .Growth hormone-releasing hormone (GHRH)
- .Growth hormone-inhibiting hormone (GHIH)
- .Gonadotropin-releasing hormone (GnRH) Corticotropin-releasing hormone (CRH)
- .Oxytocin
Antidiuretic hormone (ADH)
All of the releasing and inhibiting hormones affect the function of the anterior pituitary gland. TRH stimulates the anterior pituitary gland to release thyroid-stimulating hormone GHRH and GHIH work to regulate the release of growth hormone GHRH stimulates growth hormone release, GHIH inhibits its release GnRH stimulates the release of follicle stimulating hormone and luteinizing hormone while CRH stimulates the release of adrenocorticotropic hormone. The last two hormones - oxytocin and antidiuretic hormone, They are produced by the by hpothalamus and transported to the posterior pituitary, where they are stored and later released.
Pituitary Gland
- .also known as the hypophysis,
- .a small pea-sized lump of tissue connected to the inferior portion of the hypothalamus of the brain.
- .Location in a small depression in the sphenoid bone called the sella turcica, 2 part - the posterior and anterior pituitary glands.
Posterior Pituitary:
It is a small extension of the hypothalamus through which the axons of some of the neurosecretory cells of the hypothalamus extend.
These neurosecretory cells create 2 hormones in the hypothalamus that are stored and released by the posterior pituitary.
1. Oxytocin - triggers uterine contractions during childbirth and the release of milk during breastfeeding.
2. Antidiuretic hormone (ADH)- prevents water loss in the body by increasing the re uptake of water in the kidneys and reducing blood flow to sweat glands.
Anterior Pituitary. The anterior pituitary gland is the true glandular part of the pituitary gland. The function of the anterior pituitary gland is controlled by the releasing and inhibiting hormones of the hypothalamus. The anterior pituitary produces 6 important hormones:
I. Thyroid stimulating hormone (TSH) - a tropic hormone responsible for the stimulation of the thyroid gland
2. Adrenocorticotropic hormone (ACTH) - stimulates the adrenal cortex, the outer part of the adrenal gland, to produce its hormones.
3 Follicle stimulating hormone (FSH) - stimulates the follicle cells of the gonads to produce gametes ova in females and sperm in males.
4. Luteinizing hormone (LH) - stimulates the gonads to produce the sex hormones estrogens in females and testosterone in males.
5. Human growth hormone (HGH) - affects many target cells throughout the body by stimulating their growth, repair, and reproduction.
6. Prolactin (PRL) - it has many effects on the body, chief of which is that it stimulates the mammary glands of the breast to produce milk.
Pineal Gland
- . A small pinecone-shaped mass of glandular tissue .
- Location - just posterior to the thalamus of the brain.
- Function - produces the hormone melatonin that helps to regulate the human sleep-wake cycle known as the circadian rhythm.
- .The activity of the pineal gland is inhibited by stimulation from the photoreceptors of the retina. This light sensitivity causes melatonin to be produced only in low light or darkness. Increased melatonin production causes humans to feel drowsy at nighttime when the pineal gland is active.
Thyroid Gland
- .A butterfly-shaped gland.
- Location - at the base of the neck and wrapped around the lateral sides of the trachea.
. The thyroid gland produces 3 major hormones :
1. Calcitonin
2. Triodothyromine (T3)
3. Thyroxine (14)
Calcitonin is released when calcium ion levels in the blood rise above a certain set point Calcitonin functions to reduce the concentration of calcium ions in the blood by aiding the absorption of calcium into the matrix of bones. The hormones T3 and T4 work together to regulate the body's metabolic rate increase levels of T1 and 14 lesd to increased cellular activity and energy usage in the body.
Parathyroid Glands
- 4 small masses of glandular tissue.
- Location on the posterior side of the thyroid gland.
- Function- produce the hormone parathyroid hormone (PTH), which is involved in calcium ion homeostasis.
- PTH is released from the parathyroid glands when calcium ion levels in the blood drop below a set point. PTH stimulates the osteoclasts to break down the calcium containing bone matrix to release free calcium ions into bloodstream. PTH also triggers the kidneys to return calcium ions filtered out of the blood back to the bloodstream so that it is conserved.
Adrenal Glands
- .A pair of roughly triangular glands
- .Location - found immediately superior to the kidneys.
- Function - The adrenal glands are each made of 2 distinct layers, each with their own unique functions: the outer adrenal cortex and inner adrenal medulla.
Adrenal cortex: The adrenal cortex produces many cortical hormones in 3 classes: glucocorticoids, mineralocorticoids, and androgens.
1. Glucocorticoids
- .breakdown of proteins and lipids to produce glucose
- . to reduce inflammation and immune response.
2. Mineralocorticoids
• help to regulate the concentration of mineral ions in the body.
3. Androgens
Testosterone is produced at low levels in the adrenal cortex to regulate the growth and activity of cells that are receptive to male hormones. In adult males, the amount of androgens produced by the testes is many times greater than the amount produced by the adrenal cortex, leading to the appearance of male secondary sex characteristics.
Adrenal medulla: The adrenal medulla produces the hormones epinephrine and norepinephrine under stimulation by the sympathetic division of the autonomic nervous system.
Function - Both of these hormones help to increase the flow of blood to the brain and muscles to improve the "fight-or-flight" response to stress. These hormones also work to merease heart ratio, breathing, and blood pressure while decreasing the flow of blood to and function of organs that are not involved in responding to emergencies.
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