Lecture 21 Flashcards
How do cell communicate
using signalling molecules
Where are the receptors
• Cell surface • Signal transduction pathways • Second messengers • Intracellular receptors
Where are hormone produced
• Endocrine organs
What are the hormonal signalling molecules
• peptide, amine derived, steroids,
eicosanoids
What are the ways of signalling
Hormonal Electrical External Mechanical Immunological Metabolic Dissolved gases
What are external ways of signalling
• odorants, taste, light
What are immunological ways of signalling
• cytokines, chemokines
How does chemical cell
communication
• Extracellular signal binds to receptor • Signal is transduced into an activation or inactivation response through a cascade of intracellular messengers
What are the signal pathway for chemical cell communication
Multiple, hierarchical steps Amplification Activation of multiple pathways within the cell Antagonism by feedback mechani
What does the signalling molecule physiologic effect depends on
• Depends largely on the concentration of signalling
molecules in blood and extracellular fluid
• Nanomolar-Picomolar 10-9 -10-12 M
• Is also dependent on the number of receptors, their
distribution and developmental expression
• The concentration of hormones and other signalling
molecules seen by target cells is determined by three
factors:
1) Rate of production
2) Rate of delivery
3) Rate of degradation and elimination
What does feedback imply
implies a mechanism for changing rate of
production or secretion
What determine the level and duration of hormonal effects
• Lifespan in blood • Extent of binding to plasma proteins • Metabolic inactivation • Excretion • Number & sensitivity of receptors • Upregulation • Downregulation
What do cells in direct contact(adjecent) to each other signal each other
Gap
Junctions
What is the use of gap junction
Allow direct electrical and chemical communication between cells. Signals are passed through gap junctions from the cytosol of one cell to the cytosol of the next cell Quick signalling Important in propagating changes in electrical potential through tiss
How do lung cilia move in unison and heart move in unison
on
via gap junction signal
How contact is made between two cell
Contact is made between a membrane-bound signalling molecule on the surface of one cell and a complementary receptor on the surface of another cell
What does endocrine mean
If the molecule acts on
distant cells or tissues it is
What does paracrine mean
• Signal acts on neighbouring
cells
What does autocrine mean
• Signal acts on on the same
cell that released the signal
molecules
• Self-inducing
What is one thing the target cell must have in order to receive the signal
Target cell must have the
correct receptor for the
signal molecule
What are the examples of autocrine signalling
IL-1 produced by monocytes
IL-2 produced by lymphocyt
How fast does paracrine signalling degrade
The signalling molecule is rapidly taken up by cells or broken down by extracellular enzymes • Often results in a signalling concentration gradient
What is endocrine signalling
• Intercellular communication involving a molecule produced by one cell that acts on distant cells or tissues • Called hormones
Where are endocrine distributed
• Distributed in blood
What are the 4 types of hormones
- Four types of hormones
- Peptides and proteins
- Steroids
- Amines
- Eicosanoids
What are the classical hormones
- Insulin
- Adrenalin
- Thyroxine
What are the neurohormones
• Oxytocin • Antidiuretic hormone • Hypothalamic releasing and inhibiting hormones Act like classical hormones, but are released into blood from neurones
What are the main hormone producing organs in animals
- Hypothalamus
- Anterior pituitary
- Thyroid gland
- Adrenal gland
- Pancreas
- Ovaries
- Testes
What hormone does hypothalamus produce and what it hormone
(oxytocin, antidiuretic hormone via posterior pituitary & hormones that act on the anterior pituitary)
What hormone does anterior pituitary produce
( thyroid
stimulating hormone, growth
hormone)
What hormone does thyroid glad produce
(thyroid
hormones)
What hormone does adrenal gland produce
(cortisol,
adrenalin/epinephrine)
What hormone does pancreas produce
insulin
What hormone does ovaries produce
(oestrogen)
What hormone does testoesproduce
(testosterone)
How does the physiological response-driven negative feedback cycle
Endocrine gland > hormone > target organ(s) > physiological effects > circulating component (eg. blood glucose) –(negative feedback–> endocrine gland
what does pancreatic islet cells do
Increased blood glucose stimulates insulin release • Resulting decrease in blood glucose provides negative feedback
What is the function of the hypothalamus
Functionally diverse region of the brain
Located in the diencephalon below the thalamus and above the pituitary
Composed of anatomically distinct nuclei
What is the hypothalamus made of
Composed of anatomically distinct nuclei
What is pituitary gland
Complex endocrine & neuroendocrine organ
Located in the sella turcica at the base of the brain inferior to the hypothala
What are the two parts of pituitary gland
arts
• Anterior pituitary (adenohypophysis) - endocrine
• Posterior pituitary (neurohypophysis) - neuroend
What is the role of hypothalamus?
Acts as an integrating centre
• Influences physiological and
behavioural processes
essential for survival.
What is
Hypothalamus & Pituita connected together with
Connected to the pituitary via
the infundibulum (pituitary
stalk) which contains vascular
and neural connections
What is the key role of the regulating pituitary
controls anterior pituitary through inhibiting & releasing hormones These are released into the hypothalamo-hypophyseal portal system
Whereis Posterior pituitary
Collection of axons whose cell
bodies lie in the hypothalam
Made up of neural tissue
What is anterior have alot of
. Anterior pituitary
Collection of endocrine cells
What is the sequence of classical hormones to the target tissues
Hypothalamus (hypothalamic-releasing and release-inhibiting hormones (e.g. TRH) > transferred through hypothalamic-hypophysial portal vessels > anterior lobe of pituitary > releases anterior lobe hormones (e.g. TSH)
>target tissues (e.g. thyroid gland
How do neurohormones send signal to target tissue
hypothalamus > posterior lobe of pituitary (releasing posterior lobe hormones (e.g. ADH) > target tissue (e.g. kidney
Travel down axons via hypothalamohypophyseal tract Neurophysins serve as low affinity carrier proteins Stored in nerve axon terminals Nerve impulse causes release Released into a plexus of blood capillaries
What are the large neuroscretory neurons
- supraoptic nucleus
2. paraventricular nucleus
How is the hormones not diluted in the systemic circulation
• Direct vascular connection allows
delivery of regulatory hormones
directly to anterior pituitary without
dilution in the systemic circulation
Where does the Hypothalamic neurohomones target
• Secreted into a capillary bed in the lower hypothalamus • Enter hypophyseal portal veins between the hypothalamus and anterior pituitary (veins between 2 capillary beds) • Portal veins branch into a capillary bed in anterior pituitary • Pituitary endocrine cells respond to hypothalamic neurohomones and produce classical hormones that are released into the systemic circulation
What is the structure of Gonadotrophin
releasing hormone
(GnRH)
Peptide
10 aa
What is the structure of Growth hormone
releasing hormone
(GHRH)
Single chain
44 aa
What is the structure of Growth hormone
inhibiting hormone
(GHIH) or
Somatostatin (SS)
Peptide
14 aa
What is the structure of Thyrotropin
releasing hormone
(TRH)
Peptide
3 aa
What is the structure of Dopamine (DA)
Catecholamine
What is the structure of Corticotrophin
releasing hormone
[CRH]
Single chain
41 aa
what is the action of Gonadotrophin
releasing hormone
(GnRH)
Stimulates luteinizing
hormone (LH) & folliclestimulating hormone (FSH)
release by gonadotrophs
what is the action of Growth hormone
releasing hormone
(GHRH)
Stimulates GH release by
somatotrophs
what is the action of Growth hormone
inhibiting hormone
(GHIH) or
Somatostatin (SS)
Inhibits GH release by
somatotrophs
what is the action of Thyrotropin
releasing hormone
(TRH)
Stimulates TSH secretion
by thyrotrophs
what is the action of Dopamine (DA)
Inhibits prolactin (PRL)
release and secretion by
lactotrophs
what is the action of Corticotrophin
releasing hormone
[CRH]
Stimulates
adrenocorticotropic
hormone (ACTH) release
by corticotrophs.
What are the five main cell types in anterior pituitary
Thyrotrophs Corticotrophs Lactotrophs Gonadotrophs Somatotrophs
What does the anterior pituitary cell, Thyrotrophs produce
Thyroid
stimulating
hormone (TSH)
What does the anterior pituitary cell, Corticotrophs produce
Adrenocorticotropic
hormone
(ACTH)
What does the anterior pituitary cell, Lactotrophs produce
Prolactin (PRL)
What does the anterior pituitary cell, Gonadotrophs produce
Follicle stimulating hormone (FSH) Luteinising hormone (LH)
What does the anterior pituitary cell, Somatotrophs produce
Growth
hormone (GH)
What is the primary function of Thyroid
stimulating
hormone (TSH)
Stimulates release & production of thyroid
hormones
What is the primary function of Adrenocorticotropic
hormone
(ACTH)
Stimulates release & production of
glucocorticoids
What is the primary function of Prolactin (PRL)
Stimulates and sustains milk production
What is the primary function of Follicle
stimulating
hormone (FSH)
Females: stimulates egg formation (growth &
development of ovarian follicles)
Males: helps stimulate sperm formation
What is the primary function of Growth
hormone (GH)
Stimulates postnatal somatic growth &
development (IGF-I & II)
Mobilizes fat stores, stimulates protein synthesis,
inhibits insulin
What is the primary function of Luteinising hormone (LH)
Females: stimulates ovulation, corpus luteum
formation, estrogen & progesterone secretion
Males: promotes testosterone secretion, sperm release
What is endocrine axis driven negative feedback and what are they
it is a three tiered response 1. Hypothalamic releasing & inhibiting hormones • Example - thyrotropinreleasing hormone 2. Production of tropic hormones in anterior pituitary • Example – thyroid stimulating hormone 3. Production & secretion of hormones from peripheral glands • Example – T4 and T3 from the thyroid gland
