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Animal Physiology

This presentation reviews some - but not all - of the multiple hormones in charge of regulating our body homeostasis, along with their production, properties, and relationships.
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Clara Rodríguez Fernández

on 17 January 2014

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Transcript of Animal Physiology

Melatonin
Produces
PINEAL GLAND
N-acetyl-5-methoxy-tryptamine, a tryptophan derivative
Its secretion depends on light
Retinal photosensitive ganglion cells with the photopigment melanopsin, a vitamin A-based derivative, send information about intensity and length of exposure to light
Suprachiasmatic nuclei
Responsible for
circadian cycles
Paraventricular nuclei
Via the
Sympathetic System
Superior
cervical
ganglia
The presence of light decreases NAT levels, an enzyme involved in the production of
melatonin
Functions:
- Circadian synchronization
- Reproductive cycles
- Skin colour change
Its sensibility to photoperiod allows it to control biological cycles depending on light and darkness, like sleep.

For both diurnal and nocturnal animals, light decreases melatonin levels, although its effects are different.
PITUITARY
The pituitary produces
Melanocyte-stimulating hormone
(
MSH
), which is required for producing melanin. Less light increases
melatonin
levels, reducing
MSH
levels and therefore melanin.
In long-day breeding mammals, melatonin decreases
Gonadotropin
releasing hormone levels in the hypothalamus and reduces the sensibility of the pituitary to
GnRH
, therefore inhibiting the production of
luteinizing hormone
(
LH
) and
follicle-stimulating hormone
(
FSH
).

In short-day breeding mammals the mechanism occurs the other way around.
Produces

Its melanotrope cells secrete
MSHs
, or
melanotropins
, in amphibians, reptiles, cyclostomes and most mammals.
Its size is related to the animal’s ability to change colour or the humidity of the environment.

-
Colour changes
: mainly by
alpha-MSH
. It can respond to temperature, light, rythms or emotions. They act over specialized pigmentary effector cells that accumulate pigment granules that can change their distribution under specific stimuli.
-
Pregnancy
:
MSH
is present in humans during pregnancy, without a defined origin. During birth, beta-endorphins, which are melanotropins with analgesic properties, are found in high levels, probably for fetus protection.
-
Behaviour
: melanotropins can increase excitement, motivation, attention and memory
-
Thermoregulation
: melatropins can cause hypothermia. In some reptiles whose colour depends on melanotropins these hormones determine when they absorb more heat.
-
Neuroplasticity
: melanotropic peptides can alter the synthesis of neurotransmitters, neurotransmission and excitability in the spinal cord.

GnRH
LH
FSH
HYPOTHALAMUS
TRH
TSH
The hypothalamus releases
Thyrotropin-releasing hormone
(
TRH
), which induces the pituitary to produce
Thyroid-stimulating hormone
(
TSH
), increasing thyroid gland secretion. This mechanism is regulated by a negative feedback in which thyroid hormones inhibit the release of
TRH
and
TSH
.
Thyroid gland
THYROID AND
PARATHYROID GLANDS
THYROID GLAND
Follicular cells elaborate
thyroid hormones
by using thyroglobulin, a precursor contained in the colloids.
Parafollicular or C cells secrete
calcitonin

Control of the thyroid gland
To the hypothalamus
Tyrosine derivatives that contain iodine. They act over all tissues and organs, particularly involved in metabolism regulation, growth and development.
Thyroid hormones
Produces

-
Increased metabolism
: higher body temperature and appetite. Protein synthesis, lipolysis and cholesterol excretion are stimulated.
-
Muscle
: normal growth and function of muscles and cardiac tissue.
-
Nervous system
: normal development and function of neurons, increases sympathetic system effects.
-
Reproduction
: allows normal reproductive functions in women

Calcitonin
- Bone metabolism: osteal cells posses calcitonin receptors to respond to it by inhibiting bone resorption and demineralization
- Regulates diet and appetite
- Stimulates vitamin D metabolism

Protein hormone that decreases Ca2+ levels in plasma. Its secretion is activated by elevated Ca2+ levels in blood.


Functions:
Why is calcium so important?

99% is stored in bones. The rest is strictly regulated, for its concentration has effects on:
- Blood coagulation
- Membrane potential maintenance
- Cellular replication mechanisms
- Signal transduction inside cells
- Coupling of stimulation and response (secretion or contraction)

PARATHYROID GLANDS
Four glands placed at the back side of the thyroid gland

- Main cells: more abundant, produce parathyroid hormone
- Hurtle cells: without known function, sometimes they can be a source of cancer


Increases Ca2+ in plasma and decreases phosphate levels. Its secretion is stimulated by decreased calcium levels. It can act in two different ways:
- Quick: by protein phosphorilation
- Slow: by transcription activation

Functions:
- Stimulates bone resorption, destroying osteoclasts and releasing calcium
- Increases calcium resorption in kidneys and intestines
- Induces phosphate excretion

Parathyroid hormone (PTH)
Opposite effects over calcium levels
Vitamin D3
Synthesized through liver and kidney, with an early step that requires sun light.
PTH
controls the last step, activating VitD3 production in the kidney.


Functions:
- Stimulates resorption of calcium in intestines and kidneys
- Induces mineralization and osseum remodelation
- During pregnancy, it interacts with
prolactin
Stimulates vitamin D3 production in the kidney
ADRENAL GLANDS
They consist of two parts with different origins. The adrenal medulla is of neural origin, while the adrenal cortex is derived from mesodermal cells.
Adrenal hormones
Medulla:
-
Cathecolamines
(
adrenaline
and
noradrenaline
) produce vasodilation in muscle, liver and lungs, vasoconstriction in visceral organs and increase blood sugar in response to stress

Cortex:
-
Glucocorticoids
(
cortisol
,
corticosterone
…) regulate carbohydrate metabolism


-
Mineralocorticoids
(
aldosterone
,
deoxycorticosterone
…) regulate sodium and potassium metabolism and excretion
- Cortical
androgens
and
progesterone
stimulate secondary sexual characteristics, predominantly male
Adrenal hormones
All these hormones are cholesterol derivatives. Due to their properties, they can cross the plasma membrane, and once inside the cell they interact with receptors that respond binding to DNA and regulating its expression, acting as transcription factors.

They can induce similar or opposite physiological responses in the same tissues, depending on their concentration. Their secretion is stimulated by
acetylcholine, which is released in preganglionic sympathetic neurons from the spinal cord.
Adrenalin and noradrenalin
There are different adrenergic receptors for
catecholamines
, which determine their effect on each tissue.
Adrenergic receptors
In skeletal and cardiac muscle:
There are more -receptors than -receptors
Adrenaline
induces vasodilation
In other tissues:
Adrenaline
induces vasoconstriction
There are more -receptors than -receptors
Adrenergic regulation
Continuous stimulation reduces the number of adrenergic receptors
Stimulation frequency
Involved in increasing contraction
Estrogens
Involved in facilitating relaxation
Progesterone
Facilitate regulation of the effects over the liver
Glucocorticoids
Hyperthyroidism stimulates adrenergic activity
Thyroid hormones

PANCREAS
Exocrine Pancreas
Acinar cells secrete enzymes into the pancreatic duct
Endocrine Pancreas
Alpha cells:
glucagon

secretion
Beta cells:
insulin

production
Delta cells:
somatostatin

secretion, reduces
glucagon
and
insulin
release
PP cells:
regulatory role over pancreatic enzymes production

Glucose is an essential nutrient, particularly for the brain. We consume high amounts of glucose, which can be even higher when doing physical exercise.
Both hypoglycemia and hyperglycemia have very severe consequences over the body health, like cell death or organ damage, so it is very important to regulate its concentration in blood accurately at around 5mM

Glucose homeostasis
When glucose levels are high in the blood, usually after eating,
insulin
is secreted, inducing cells to increase their glucose uptake and reducing hepatic glucose release.

When glucose levels decrease, due to exercise
or fast,
glucagon
is secreted and glucose production (from glycogen in the liver) and release are stimulated.

Alpha and beta cells are very sensitive to glucose concentration in blood
Insulin secretion
As glucose levels increase in blood, so does in beta cells, where glucose enters through specific transporters. Its oxidation produces ATP, which activates K+ channels, changing the voltage and activating Ca2+ channels, which in turn induce the release of
insulin
Preproinsulin is the first insulin precursor. When it reaches the endoplasmic reticulum, proinsulin is generated by cleaving the signal peptide. Within the endoplasmic reticulum, endopeptidases cut its C chain to derive
insulin
.
Once
insulin
is properly made and the beta cell is appropriately stimulated,
insulin
is secreted into the blood
Insulin processing
Somatostatin
Effects on gastrointestinal system:
- Inhibits endocrine (
insulin
and
glucagon
) and exocrine secretion in the pancreas
- Suppresses the release of other gastrointestinal hormones like gastrin, secretin, motilin...
- Reduces smooth muscle contractions and blood flow within the intestine

Effects on the pituitary gland

Insulin receptor
When interacting with its receptor,
insulin
generates a cascade of phosphorilation that stimulates the release of GLUT4 glucose transporters from vesicles to the plasma membrane.

These receptors are found in different numbers through different types of cells. There are two isoforms with different affinities for
insulin
.
Somatostatin regulates secretion in the pituitary
- Inhibits the release of
growth hormone
(
GH
)
- Inhibits the release of
thyroid stimulating hormone
(
TSH
)
- Inhibits the release of
prolactin
(
PLR
)

SCN
PVN
Retina
Pineal Gland
Synthesis Pathway
Melanotropins Functions:
Intermediate hypophisis
Thyroid hormones effects:
MeSH Browser, National Library of Medicine:
http://www.nlm.nih.gov/mesh/2011/mesh_browser/MBrowser.html

NovaTec Immundiagnostica GmbH:
http://www.novatec-id.com/

University of Prince Edward, Iceland:
http://home.upei.ca/

Nature:
http://www.nature.com

Scientific american:
http://blogs.scientificamerican.com/

Medical Look:
http://www.medicalook.com/

Wikipedia:
http://wikipedia.com/

Davidson College, California:
http://www.davidson.edu/academics/biology
Pictures from:
Bibliography
Knut Schmidt-Nielsen, Animal Physiology, Adaptation and Environment, 5th Edition, Cambridge University Press

MeSH Browser, National Library of Medicine:
http://www.nlm.nih.gov/mesh/2011/mesh_browser/MBrowser.html

Fu, Y. et al (2005) Intrinsically photosensitive retinal ganglion cells detect light with a vitamin A-based photopigment, melanopsin. Proc. Natl. Acad. Sci. U.S.A. 102, 10339 – 10344

Nabeel Bardeesy and Ronald A. DePinho (December 2002) Pancreatic cancer biology and genetics, Nature Reviews Cancer 2, 897-909



This presentation reviews some - but not all - of the multiple hormones in charge of regulating our body homeostasis, along with their production, properties, and relationships.

There is a scheduled order that you can follow just using the arrows, but feel free to move around with the mouse to check the relationship between different elements in the presentation.

Most arrows are blue and usually represent non-direct relationships. The black ones indicate control exertion between two elements.

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From the Pancreas
Full transcript