Hormonen (BOOK)
41.1
Hormones are secreted into the extracellular fluid, circulate in the bloodstream and communicate
regulatory messages throughout the body. Chemical signaling by hormones is the function of the
endocrine system, one of the two basic systems for communication and regulation in the animal
body. The other major system is the nervous system.
One function of endocrine signalling (hormones) is homeostasis.
Local regulators can influence cells, and can stimulate nearby target cells to perform an action.
Signalling by local regulators can either be autocrine or paracrine. In paracrine signalling target cells
lie near the secreting cells. In autocrine signalling the secreting cells themselves are target cells.
Prostaglandins are groups of local regulators with diverse and widespread functions. In the immune
system, they promote inflammation and the sensation of pain in response to injury. Drug that block
prostaglandin synthesis prevent these activities.
Synaptic signaling neurotransmitters
Neuroendocrine signaling neurohormones, which diffuse from nerve cell endings into the
bloodstream. (antidiuretic hormone kidney function, water balance and courtship behaviour)
Pheromones are chemicals that are released into the external environment.
NO functions in the body as both a local regulator and a neurotransmitter. When O2 levels in the
blood falls, epithelial cells in blood vessel walls synthesize and release NO. NO diffuses to smooth
muscle cells where it activates an enzyme that relaxes the cells vasodilation. This is also how an
erection occurs.
There are three main classes of hormones; polypeptides (hydrophilic), steroids (hydrophobic),
amines.
Response pathway
Lipid-soluble hormones exit endocrine cells by diffusing out across the membranes and coupling a
receptor inside the cell, lipid-insoluble bind to cell-surface receptors.
Lipid-insoluble:
The chain of events that converts the extracellular chemical signal to a specific intracellular response
is called signal transduction; example, stress adrenal glands secrete epinephrine (=adrenaline)
binds to G protein-coupled receptor synthesis of cyclic AMP (cAMP) as a second messenger
activation kinase A glycogen breakdown.
Lipid-soluble:
Hormones activate the receptor inside the cell. Hormone-receptor complex move into the nucleus,
where the receptor part alters transcription of particular genes by interacting with a specific DNA-
binding protein.
Hormones that are not steroids, have typically receptor in the nucleus, and not in the cytoplasm.
Although hormones bind to specific receptors, a particular hormone can vary in its effect.
, Endocrine tissues and organs
Often, endocrine cells are grouped in ductless organs called endocrine glands. Endocrine glands
secrete hormones directly into the surrounding fluid. There are several human endocrine glands;
Thyroid gland
Thyroid hormone (T3 and T4): stimulates and maintains metabolic processes
Calcitonin: lowers blood calcium levels
Parathyroid gland
Parathyroid hormone (PTH): Raises blood calcium level
Adrenal glands (a top kidneys)
o Adrenal medulla
Epinephrine and norepinephrine: raise blood glucose level; increase metabolic
activity; constrict or dilate blood vessels
o Adrenal cortex
Glucocorticoids: raise blood glucose level
Mineralocorticoids: promote retention of Na+ and excretion of K+ in kidneys
Ovaries
Estrogens: stimulate uterine lining growth; promote development and maintenance of
female secondary sex characteristics
Progesterone: promote uterine lining growth
Testes
Androgens: support sperm formation; promote development and maintenance of male
secondary sec characteristics
Hypothalamus
Hormones released from posterior pituitary
Releasing an inhibiting hormone: regulate anterior pituitary
Pituitary gland
o Posterior pituitary
Oxytocin: stimulates contraction of uterus and mammary gland cells (milk
production)
Vasopressin (= antidiuretic hormone (ADH)): promotes retention of water by kidneys;
influences social behaviour and bonding
o Anterior pituitary
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): stimulate ovaries
and testes
Thyroid-stimulating hormone (TSH): stimulates thyroid gland
Adrenocorticotropic hormone (ACTH): stimulates adrenal cortex
Prolactin: stimulates mammary gland growth and milk synthesis in mammals
Growth hormone: stimulates growth and metabolic functions
Melanocyte-stimulating hormone (MSH): affects colour of melanocytes, a type of skin
cell
Pancreas
Insulin: lowers blood glucose levels
Glucagon: raises blood glucose levels
Pineal gland
Melatonin: participates in regulation of biological rhythms
41.1
Hormones are secreted into the extracellular fluid, circulate in the bloodstream and communicate
regulatory messages throughout the body. Chemical signaling by hormones is the function of the
endocrine system, one of the two basic systems for communication and regulation in the animal
body. The other major system is the nervous system.
One function of endocrine signalling (hormones) is homeostasis.
Local regulators can influence cells, and can stimulate nearby target cells to perform an action.
Signalling by local regulators can either be autocrine or paracrine. In paracrine signalling target cells
lie near the secreting cells. In autocrine signalling the secreting cells themselves are target cells.
Prostaglandins are groups of local regulators with diverse and widespread functions. In the immune
system, they promote inflammation and the sensation of pain in response to injury. Drug that block
prostaglandin synthesis prevent these activities.
Synaptic signaling neurotransmitters
Neuroendocrine signaling neurohormones, which diffuse from nerve cell endings into the
bloodstream. (antidiuretic hormone kidney function, water balance and courtship behaviour)
Pheromones are chemicals that are released into the external environment.
NO functions in the body as both a local regulator and a neurotransmitter. When O2 levels in the
blood falls, epithelial cells in blood vessel walls synthesize and release NO. NO diffuses to smooth
muscle cells where it activates an enzyme that relaxes the cells vasodilation. This is also how an
erection occurs.
There are three main classes of hormones; polypeptides (hydrophilic), steroids (hydrophobic),
amines.
Response pathway
Lipid-soluble hormones exit endocrine cells by diffusing out across the membranes and coupling a
receptor inside the cell, lipid-insoluble bind to cell-surface receptors.
Lipid-insoluble:
The chain of events that converts the extracellular chemical signal to a specific intracellular response
is called signal transduction; example, stress adrenal glands secrete epinephrine (=adrenaline)
binds to G protein-coupled receptor synthesis of cyclic AMP (cAMP) as a second messenger
activation kinase A glycogen breakdown.
Lipid-soluble:
Hormones activate the receptor inside the cell. Hormone-receptor complex move into the nucleus,
where the receptor part alters transcription of particular genes by interacting with a specific DNA-
binding protein.
Hormones that are not steroids, have typically receptor in the nucleus, and not in the cytoplasm.
Although hormones bind to specific receptors, a particular hormone can vary in its effect.
, Endocrine tissues and organs
Often, endocrine cells are grouped in ductless organs called endocrine glands. Endocrine glands
secrete hormones directly into the surrounding fluid. There are several human endocrine glands;
Thyroid gland
Thyroid hormone (T3 and T4): stimulates and maintains metabolic processes
Calcitonin: lowers blood calcium levels
Parathyroid gland
Parathyroid hormone (PTH): Raises blood calcium level
Adrenal glands (a top kidneys)
o Adrenal medulla
Epinephrine and norepinephrine: raise blood glucose level; increase metabolic
activity; constrict or dilate blood vessels
o Adrenal cortex
Glucocorticoids: raise blood glucose level
Mineralocorticoids: promote retention of Na+ and excretion of K+ in kidneys
Ovaries
Estrogens: stimulate uterine lining growth; promote development and maintenance of
female secondary sex characteristics
Progesterone: promote uterine lining growth
Testes
Androgens: support sperm formation; promote development and maintenance of male
secondary sec characteristics
Hypothalamus
Hormones released from posterior pituitary
Releasing an inhibiting hormone: regulate anterior pituitary
Pituitary gland
o Posterior pituitary
Oxytocin: stimulates contraction of uterus and mammary gland cells (milk
production)
Vasopressin (= antidiuretic hormone (ADH)): promotes retention of water by kidneys;
influences social behaviour and bonding
o Anterior pituitary
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): stimulate ovaries
and testes
Thyroid-stimulating hormone (TSH): stimulates thyroid gland
Adrenocorticotropic hormone (ACTH): stimulates adrenal cortex
Prolactin: stimulates mammary gland growth and milk synthesis in mammals
Growth hormone: stimulates growth and metabolic functions
Melanocyte-stimulating hormone (MSH): affects colour of melanocytes, a type of skin
cell
Pancreas
Insulin: lowers blood glucose levels
Glucagon: raises blood glucose levels
Pineal gland
Melatonin: participates in regulation of biological rhythms
