Download Nonpituitary hormones help regulate metabolism, homeostasis

Hormones and the endocrine system
1) The endocrine system and the nervous system act
individually and together in regulating an animal’s
physiology
2) Hormones and other chemical signals bind to target cell
receptors, initiating pathways that culminate in specific cell
responses
3) The hypothalamus and pituitary integrate many functions
of the vertebrate endocrine system
4) Nonpituitary hormones help regulate metabolism,
homeostasis, development, and behavior
The body’s long-lasting regulators
Concert of chemical signals – complete change of body form
e.g. metamorphosis
Hormone – from the Greek „horman“
– to excite
Elicits specific responses from target
cells only
The endocrine system and the nervous system act individually
and together in regulating an animal’s physiology
2(3) systems of internal communication - different
tasks – different signals
All hormone-secreting cells – endocrine system
Endocrine gland => messengers => extracellular fluid
The endocrine system and the nervous
system act individually and together in
regulating an animal’s physiology
Overlap between endocrine and nervous
regulation
Specialized neurons - neurosecretory cells
=> neurohormones
In insects, vertebrates
Epinephrine – in both systems –
neurotransmitter and hormone
The endocrine system and the nervous system act
individually and together in regulating an animal’s
physiology
Control pathways and feedback loops
Stimulus => receptor/sensor => control center =>
comparing incoming information to a set point =>
efferent signal => effector => response
Negative feedback – connecting response to initial
stimulus
Effector response reduces the initial stimulus
Positive feedback reinforces stimulus (release of milk)
The endocrine system and the nervous system act individually
and together in regulating an animal’s physiology - summary
Overlap between endocrine and nervous regulation
The endocrine and nervous systems often function together in maintaining
homeostasis, development, and reproduction. Endocrine glands and various
organs with primarily nonendocrine functions secrete hormones, and
specialized secretory cells derived from nervous tissue secrete
neurohormones. Both classes of hormonal signals circulate through the body
to their target tissues, functioning as long-distance regulators.
Control pathways and feedback loops
There are three major types of hormonal control pathways: endocrine,
neurohormone, and neuroendocrine. The basic components of a biological
regulatory system are present in each kind of pathway. Negative feedback
regulates many hormonal pathways involved in homeostasis.
Hormones and other chemical signals bind to target cell receptors,
initiating pathways that culminate in specific cell responses
Hormones through bloodstream
Local regulators – near secreting cells
pheromones – message to other individual by air
Three major classes – as hormones:
1) Proteins and peptides, 2) Amines from AA, 3) Steroids
(not water soluble)
Reception (binding), signal transduction, and response
Receptors in or on the target cells
Transduction – activation of enzyme, cascade of changes,
direct or indirect regulation of transcription of specific
genes
Hormones and other chemical signals bind to target
cell receptors, initiating pathways that culminate
in specific cell responses
Intracellular receptors for small hydrophobic molecules
coupled with transduction/transcription factor in
nucleus
mRNA => new protein
Different effects in different species – thyroxine
In mammals - regulates metabolism
In frogs – triggers metamorphosis of tadpoles
Hormones and other chemical signals bind to target cell receptors, initiating
pathways that culminate in specific cell responses
Particular hormone (signal) may cause diverse responses – different
receptors => different transduction => different response
e.g. epinephrine -
distribution of energy
to muscles
Local regulators – diffusion within second
Neurotransmitters
Cytokines
Growth factors (cell proliferation and differentiation)
Gas - nitric oxide NO produced in O2 insufficiency => dilates vessels => improves
blood flow
Prostaglandins (PGs) modified fatty acids
Regulation of nearby cells in various ways
e.g. excitation of uterine muscles, induction of fever and inflammation, aggregation of
platelets, sensation of pain, in respiratory system antagonists PGs E and F
Hormones and other chemical signals bind to target cell receptors, initiating
pathways that culminate in specific cell responses - summary
Cell-surface receptors for water-soluble hormones
Peptide/protein hormones and most of those derived from amino acids bind to
receptors embedded in the plasma membrane. Hormone binding triggers an
intracellular signal transduction pathway leading to specific responses in the
cytoplasm or changes in gene expression. The same hormone may have
different effects on target cells that have different receptors for the hormone,
different signal transduction pathways, or different effector proteins.
Intracellular receptors for lipid-soluble hormones
Steroid hormones, thyroid hormones, and the hormonal form of vitamin D enter target
cells and bind to specific protein receptors in the cytoplasm or nucleus. The
hormone-receptor complexes then act as transcription factors in the nucleus,
regulating transcription of specific genes.
Paracrine signaling by local regulators
Various types of chemical signals elicit responses in nearby target cells. Local
regulators include neurotransmitters, cytokines and growth factors
(proteins/peptides), nitric oxide (a gas), and prostaglandins (modified fatty acids).
The hypothalamus and pituitary
integrate many functions of the
vertebrate endocrine system
Major (20) human
glands and hormones
The hypothalamus and
pituitary integrate many
functions of the vertebrate
endocrine system
Hormone-secreting cells also in :
Heart, thymus, liver,
stomach, small intestine,
kidney, placenta
The hypothalamus and pituitary integrate many
functions of the vertebrate endocrine system
Relationship between the hypothalamus and
pituitary gland
Hypothalamus plays an integrating role in
vertebrate endocrine and nervous systems
Information from whole body and brain
through nerves
Hypothalamus then triggers the release
e.g. reproductive hormones
Hypothalamus - two sets of neurosecretory
cells
1) Posterior pituitary – neurohypophysis
Stores and secretes: ADH – excretory syst.
Oxytocin – uterine muscles, milk ejection
The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system
2) Anterior pituitary – adenohypophysis (roof of embryonic mouth)
Several hormones – other endocrine glands as their targets = tropic hormone
Neurosecretory cells => releasing and inhibiting hormones – tropic hormones for
anterior pituitary
Tropic hormones:
glycoprotein
gonadotropins
ACTH – peptide
=> Adrenal cortex
Nontropic:
PRL - great diversity
of effects
MSH – regulates
pigment cells, hunger
in mammals
Beta-endorphin – dull
the pain perception
Both: GH => IGFs
The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system - summary
Relationship between the hypothalamus and pituitary gland
The hypothalamus, a region on the underside of the brain, contains different sets of
neurosecretory cells. Some produce direct-acting hormones that are stored in and released
from the posterior pituitary. Other hypothalamic cells produce tropic hormones that are
transported by portal blood vessels to the anterior pituitary, an endocrine gland. These
tropic hormones control release of hormones from the anterior pituitary.
Posterior pituitary hormones
The two hormones released from the posterior pituitary act directly on nonendocrine tissues.
Oxytocin induces uterine contractions and milk ejection, and antidiuretic hormone (ADH)
enhances water reabsorption in the kidneys.
Anterior pituitary hormones
Both tropic and nontropic hormones are produced by the anterior pituitary. The four strictly tropic
hormones are thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH),
luteinizing hormone (LH), and adrenocorticotropic hormone (ACTH). Each acts on its target
endocrine tissue to stimulate release of hormone(s) with direct metabolic or developmental
effects. Prolactin, melanocyte-stimulating hormone (MSH), and beta-endorphin are
nontropic anterior pituitary hormones. Prolactin stimulates lactation in mammals but has
diverse effects in different vertebrates. MSH influences skin pigmentation in some
vertebrates and fat metabolism in mammals. Endorphins inhibit the perception of pain.
Growth hormone (GH) promotes growth directly and has diverse metabolic effects; it also
stimulates the production of growth factors by other tissues (a tropic effect).
Nonpituitary hormones help regulate metabolism,
homeostasis, development, and behavior
Thyroid gland (ventral surface of the
trachea) => thyroid hormones
Tri- and tetra- iodothyronine
In mammals - T4 > T3, in target cells
– T4 converted to T3
Vertebrate metabolism, development,
and maturation
Nonpituitary hormones help regulate metabolism, homeostasis, development, and
behavior
Disorders:
Deficiency => cretinism (retarded skeletal growth and mental development)
Deficiency in diet => goiter - through negative feedback on the hypothalamus
Excessive secretion => hyperthyroidism (high body temperature, high blood
pressure, sweating, weight loss, fluid accumulation behind the eyes)
Nonpituitary hormones help regulate
metabolism, homeostasis,
development, and behavior
Parathyroid hormone and calcitonin:
control of blood calcium
Blood calcium (Ca2+) level essential for all body cells
Set point - 10 mg/ 100 ml
From food or skin vitamin D => in liver
and then in kidneys stimulated by
PTH => active D
Nonpituitary hormones help regulate
metabolism, homeostasis, development,
and behavior
Insulin and glucagon: control of
blood glucose
Endocrine cells in islets of Langerhans
(1-2 % of pankreas weight)
Islet:
Alpha cells – glucagon (protein)
Beta cells – insulin (protein)
Diabetes mellitus (sugar in urine)
Type I – (insulin dependent) autoimmune
disorder against beta cells
Type II – changes in insulin receptors
(90% of people)
Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior
Adrenal hormones: Response to stress
In mammals: Adjacent to kidneys - fused endocrine and neuroendocrine gland
Fight or flight response
Catecholamines – from
AA tyrosine
Epinephrine
Norepinephrine
(sustaining blood
pressure)
Signals by sympathetic
autonomic nervous
system
Nonpituitary hormones help regulate metabolism,
homeostasis, development, and behavior
Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior - summary
Thyroid hormones
The thyroid gland produces iodine-containing hormones (T3 and T4) that stimulate metabolism
and influence development and maturation. Secretion of T3 and T4 is controlled by the
hypothalamus and pituitary in a complex neuroendocrine pathway involving two negativefeedback loops. The thyroid also secretes calcitonin, which functions in calcium
homeostasis.
Parathyroid hormone and calcitonin: control of blood calcium
Two antagonistic hormones, calcitonin and parathyroid hormone (PTH), play the major role in
calcium (Ca2+) homeostasis in mammals. Calcitonin, secreted by the thyroid, stimulates
Ca2+ deposition in bones and excretion by kidneys, thereby decreasing blood Ca2+ levels.
PTH, secreted by the parathyroid glands, has the opposite effects on bones and kidneys,
thereby increasing blood Ca2+ levels. PTH also has an indirect effect, stimulating the
kidneys to activate vitamin D, which in turn promotes intestinal uptake of Ca2+ from food.
Insulin and glucagon: control of blood glucose
Two types of endocrine cells in the pancreas secrete insulin and glucagon, antagonistic
hormones that help maintain glucose homeostasis. Insulin (from beta cells) reduces blood
glucose levels by promoting the cellular uptake of glucose, glycogen formation in the liver,
protein synthesis, and fat storage. Glucagon (from alpha cells) increases blood glucose
levels by stimulating the conversion of glycogen to glucose in the liver and the breakdown
of fat and protein to glucose. Diabetes mellitus, which is marked by elevated blood glucose
levels, may be caused by inadequate production of insulin (type I) or loss of
responsiveness to target cells to insulin (type II).
Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior –
summary
Adrenal Hormones: response to stress
Neurosecretory cells in the adrenal medulla release epinephrine and norepinephrine
in response to stress-activated impulses from the nervous system. These hormones
mediate various fight-or-flight responses. The adrenal cortex releases three functional
classes of steroid hormones. Glucocorticoids, such as cortisol, influence glucose
metabolism and the immune system; mineralocorticoids, primarily aldosterone, affect
salt and water balance. The adrenal cortex also produces small amounts of sex
hormones.
Gonadal sex hormones
The gonads – testes and ovaries – produce most of the body’s sex hormones:
androgens, estrogens, and progestins. All three types are produced in males and
females but in different proportions.
Melatonin and biorhythms
The pineal gland, located within the brain, secretes melatonin. Release of melatonin
is controlled by light/dark cycles. Its primary functions appear to be related to
biological rhythms associated with reproduction.