Sistema Endócrino e Hormônios

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UNIT 4: Homeostasis 
 
Chapter 10: The Endocrine System pg. 466 
 
10.2: The Endocrine Glands pg. 473 – 482 
 
Hormones are produced by the endocrine system. These chemicals maintain 
homeostasis within the body. The endocrine system is made up of many 
glands located throughout the body. The glands produce hormones and 
secrete them into the circulatory system to be delivered to their target cells. 
Some hormones are secrete from organs, such as; the heart, liver and the 
kidneys. 
 
 
 
 
Figure 1: The major endocrine glands and cells in humans. 
 
 
 
 
 
 
 
The Vertebrate Endocrine System 
 
Hypothalamus – is the region of the brain that releases hormones to control 
the pituitary gland, which, in turn, controls other endocrine glands. 
 
Neurohormone – is a hormone produced by neurons, such as in the 
hypothalamus that controls the production of other hormones in the pituitary 
gland. 
 
Pituitary gland – is a two lobed gland within the cranial cavity that produces 
hormones that control the other endocrine glands. 
The hypothalamus gland is found at the base of the brain and is part of the 
nervous systems. The hypothalamus receives nerve impulses and produces 
special type of hormones, called a neurohormone. The hypothalamus 
coordinates actions between the brain and the endocrine system. 
Neurohormone leaves the hypothalamus and travels to the pituitary gland. 
 
The hypothalamus is also in direct contact with some sensory neurons to 
monitor changes in body chemistry and temperature. 
 
Pituitary gland is located in the cranium, below the brain, and has two lobes, 
anterior and posterior. Neurohormones from the hypothalamus travel to the 
pituitary gland via the portal vein. 
 
Two types of neurohormones secreted from the hypothalamus are releasing 
and inhibiting hormones. These hormones will affect the anterior portion of 
the pituitary gland, either stimulating or inhibiting hormones secretion. The 
hormones secreted from the pituitary gland control many other endocrine 
glands, therefore the pituitary is known as the master gland. 
 
See Table 1: Hypothalamic and Pituitary Hormones, pg. 474 
 
 
Figure 2: The hypothalamus and the pituitary gland link the endocrine system and the 
nervous system. Neurohormones produced by the hypothalamus control the anterior and 
posterior pituitary hormones, which control the endocrine glands. 
 
Anterior Pituitary Gland 
 
Anterior Pituitary Gland produces six major hormones: prolactin, growth 
hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, 
follicle-stimulating hormone, and luteinizing hormone. 
 
Prolactin (PRL) – is responsible for reproductive activities and parental care 
in vertebrates. PRL stimulates secretory cells in the mammary glands during 
late pregnancies and milk synthesis. 
 
 
Growth Hormone (GH) – stimulates cell division, protein synthesis and 
bone growth in children and adolescents. GH binds to muscles and other 
target tissues, causing them to release insulin-like growth factor (IGF), 
which directly stimulates growth. GH also controls the conversion of 
glycogen to glucose and fats to fatty acids to maintain levels in blood. GH 
also regulates the intake fatty acids and amino acids by cells and limiting the 
uptake of glucose by cells. Lack of GH can lead to dwarfism or the over 
secretion can lead to gigantism. (2.7 m) 
 
Thyroid-stimulating hormone (TSH) is responsible for stimulating the 
thyroid gland to increase in size and release thyroid hormones. 
 
Adrenocorticotropic hormone (ACTH) initiates the release of hormones 
from the adrenal cortex. 
 
Follicle stimulating hormone (FSH) affects egg development and female 
hormones in females and sperm production in males. 
 
Luteinizing hormone (LH) regulates part of the menstrual cycle in females 
and sex hormones in males. FSH and LH are known as Gonadotropins 
because they regulate the activities of the gonads (ovaries and testes) 
 
Melanocyte-stimulating hormone (MSH) and endorphins are secreted 
from the anterior pituitary gland. MSH is responsible for the secretion of 
melanin that makes your skin go darker in the sun. 
 
Endorphins (natural painkillers) act as neurotransmitters in the pathways 
that control pain, inhibiting pain perception. 
 
 
 
 
 
 
 
 
 
 
 
 
Posterior Pituitary Gland 
 
The posterior pituitary gland stores and releases two important hormones 
produced in the hypothalamus; antidiuretic hormone and oxytocin into the 
circulatory system. 
 
Antidiuretic Hormone (ADH) is responsible for the stimulating of the 
kidney cells to absorb water from the urine, to increase blood volume. 
Sensory receptors in the hypothalamus are stimulates by the high 
concentration of Na+. The kidneys are able to maintain a homeostatic 
balance of extracellular fluid in the body. Approximately 85% of the water 
that passes through the nephron is reabsorbed from the proximal convoluted 
tubule the rest is absorbed from the distal convoluted tubule only if ADH is 
present. 
 
Oxytocin stimulates the production of milk from the mammary glands and it 
also plays a key role in the stimulation of contractions during child birth. 
 
 
Thyroid and Parathyroid Hormones 
 
Thyroid gland – is an endocrine gland located in the throat that is regulated 
by the hypothalamus-pituitary system. 
 
Parathyroid hormone – is a hormone secreted by the parathyroid glands hat 
controls calcium and phosphate levels in the blood. 
 
The thyroid is located in the front of the throat, and it secretes hormones that 
have a wide range of effects. Thyroxine (T4) contains four iodine atoms, is 
responsible for increases the metabolic rate of cells and is essential for body 
growth. The thyroid is vital for growth, development, maturation, and 
metabolism is all mammals. 
 
A goiter is a condition created when the thyroid is over stimulated, the neck 
begins to swell. Iodine supplements are added to food to prevent goiters in 
many countries. 
 
 
 
Figure 6: the negative feedback control of parathyroid hormone (PTH) and calcitonin by 
the Ca2+ level in the blood. 
Adrenal Hormones 
 
The adrenal medulla secretes two adrenal hormones, epinephrine and 
norepinephrine that act as neurotransmitters. Epinephrine prepares your 
body for handling stress. 
 
The adrenal cortex secretes several hormones. Aldosterone is involved in 
osmoregulation and control of blood pressure. 
 
Pineal Gland 
 
Pineal gland – is an endocrine gland located in or on the brain of vertebrates 
that secretes the hormone melatonin to regulate biological rhythms.