Hormones and the Endocrine System (Endocrine glands respond to diverse…
Hormones and the Endocrine System
Endocrine glands respond to diverse stimuli in regulating homeostasis, development, and behavior
The pineal gland is a small mass of tissue near the center of the mammalian brain that is a primary source of the hormone melatonin, a modified amino acid
In mammals, progestins, which include progesterone, promote the
growth of the uterine lining, which supports the growth and development of an embryo.
Estrogens, the most important being estradiol, are responsible for the development and maintenance of the female reproductive system and the development of female secondary sex characteristics
When ACTH reaches the adrenal cortex via the bloodstream, it stimulates the endocrine cells to synthesize and secrete a family of steroids called corticosteroids.
The adrenal medulla produces two hormones: epinephrine (adrenaline) and norepinephrine. These hormones are members of a class of hormones, the catecholamines, amines that are synthesized from the amino acid tyrosine
If the blood Ca2+ level rises above the set point, the thyroid gland releases calcitonin, a hormone that inhibits bone resorption and enhances Ca2+ release by the kidney
When the blood Ca2+ concentration falls below the set point, the glands release parathyroid hormone (PTH)
In mammals, the parathyroid glands, a set of four small glands embedded on the surface of the thyroid, play a major role in blood Ca2+ regulation near a set point of about 10 mg/100 mL
Feedback regulation and coordination with the nervous system are common in endocrine signaling
Growth hormone (GH), which is secreted by the anterior pituitary, acts on a wide variety of target tissues with both tropic and nontropic effects.
Antidiuretic hormone (ADH), or vasopressin, also regulates both physiology and behavior.
The posterior pituitary is an extension of the hypothalamus. The anterior pituitary is an endocrine gland that synthesizes and secretes hormones.
When the blood glucose concentration falls below the set point, glucagon is released and promotes release of glucose into blood from liver glycogen, increasing blood glucose
Homeostatic control systems may rely on pairs of negatively regulated hormone pathways, each counterbalancing the other
When the blood glucose concentration exceeds the set point, insulin is released and triggers uptake of glucose from the blood into body cells, decreasing blood glucose
Unlike negative feedback, which dampens a stimulus, positive feedback reinforces a stimulus, leading to an even greater response
The response pathway for many hormones involves negative feedback, a loop in which the response reduces the initial stimulus
Hormones and other signaling molecules bind to target receptors, triggering specific response pathways
Local regulators called prostaglandins (PGs) are modified fatty acids, first discovered in prostate-gland secretions
Polypeptide local regulators include cytokines, which play a role in immune responses, and most growth factors, which stimulate cell proliferation and differentiation
The series of changes in cellular proteins that converts the extracellular chemical signal to a specific intracellular response is called signal transduction
Members of the same animal species may communicate with pheromones, chemical signals released into the external environment.
At synapses, neurons secrete molecules called neurotransmitters, which diffuse a very short distance to bind to receptors on the target cell.
Local regulators are chemical signals that act over short distances, reaching their target cells by diffusion.