Week 1 Flashcards
Hypothalamus and
pituitary overview
hypothalamus and pituitary glands (endocrine glands) are of major importance since they act as the coordinating centres of the endocrine system
Hypothalamus Function
Responsible for maintaining the body’s internal balance (homeostasis)
by stimulating or inhibiting major bodily functions such as
• the heart rate and blood pressure, body temperature, fluid and electrolyte balance
The hypothalamus is also considered the master regulator of the
endocrine system.
• Regulatory hormones secreted by the hypothalamus are transported by the hypophyseal-portal system to the anterior and posterior pituitary, prompting the release of secondary hormones that can affect various organ functions
Hypothalamus endocrine regulation
The hypothalamic hormones are referred to as releasing hormones and inhibiting hormones, reflecting their influence on pituitary hormones
Hypothalamus and
endocrine overview
Functions via three mechanisms
• Secretes regulatory hormones
• Secretes releasing hormones (RH)
• Secretes inhibiting hormones (IH)
Acts as an endocrine organ
• Releases antidiuretic hormone and oxytocin to the pituitary gland
Contains autonomic nervous system centres
• Exerts control over the suprarenal medulla
How the hypothalamus helps maintain homeostasis
the hypothalamus is responsible for creating or controlling hormones
Pituitary and endocrine system
• A pea-sized gland that is housed within a bony
structure (sella turcica) at the base of the brain.
• The sella turcica protects the pituitary but allows very
little room for expansion.
• Attached to the hypothalamus via the infundibulum
Consists of two lobes
• Adenohypophysis: anterior lobe releases nine
peptide hormones
• Neurohypophysis: posterior lobe releases two
peptide hormones
Function of the
Pituitary gland
• Controls the function of most other endocrine
glands and is therefore sometimes called the
other master gland.
• In turn, the pituitary is controlled in large part by
the hypothalamus, a region of the brain that lies
just above the pituitary.
• By detecting the levels of hormones produced by
glands under the pituitary’s control (target
glands), the hypothalamus or the pituitary can
determine how much stimulation the target
glands need.
Adenohypophysis: Anterior lobe
The anterior pituitary (or adenohypophysis) is
a lobe of the gland that regulates several
physiological processes (including stress,
growth, reproduction, and lactation).
Endocrine cells of the anterior pituitary are
controlled by regulatory hormones released
by parvocellular neurosecretory cells in the
hypothalamus.
Divided into anatomical regions known as
the pars tuberalis, pars
intermedia, and pars distalis.
Adenohypophysis: Anterior lobe hormones
Produces seven hormones.
• Growth hormone (GH)
• Thyroid-stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Beta endorphin
• Prolactin
Of the hormones of the anterior pituitary, TSH,
ACTH, FSH, and LH are collectively referred to as
tropic hormones (trope- = “turning”) because they
turn on or off the function of other endocrine
glands.
Neurohypophysis: Posterior lobe
The posterior pituitary does not produce any
hormones of its own, rather, it stores and
secretes two hormones made in the
hypothalamus:
• Oxytocin causes the uterus to contract
during childbirth and immediately after
delivery to prevent excessive bleeding.
• Vasopressin (also called antidiuretic
hormone) regulates the amount of water
excreted by the kidneys and is therefore
important in maintaining water balance in the
body.
Pituitary gland malfunction
Pituitary disorders can cause a range of symptoms.
• Challenging to diagnose.
They share these traits:
• The pituitary gland may raise or lower one or more hormones.
• A hormone imbalance can cause physical or mood changes.
• At the same time, pituitary disorders often develop slowly.
• It may take a long time until you notice symptoms.
Symptoms of pituitary disorders are like those of other diseases.
• Many people are misdiagnosed or go undiagnosed
Overproduction of pituitary hormones
Disorders that result from overproduction of
pituitary hormones include
• Acromegaly or gigantism: Growth
hormone
• Cushing disease: Adrenocorticotropic
hormone ( ACTH),
• Galactorrhea (the secretion of breast milk
by men or by women when not pregnant):
Prolactin
• Erectile dysfunction: Prolactin
• Infertility (particularly in women): Prolactin
Under production of pituitary hormones
• Disorders that result from under production of
pituitary hormones include
• Central diabetes insipidus: Vasopressin
• Hypopituitarism: Multiple hormones
Endocrine System
The nervous system and the endocrine system work together to monitor the body’s activities
• The nervous system produces short-term, very specific responses
• The endocrine system: many times it produces long-term, general responses
Endocrine system is composed of glands that secrete chemicals called hormones into the bloodstream for the control of body functions.
The role of the endocrine system is to maintain the body in balance through the release of hormones (chemical signals) directly into the bloodstream.
• Hormones transfer information and instructions from one set of cells to another.
• Many different hormones move through the bloodstream, but each type of hormone is designed to affect only certain cells.
What are hormones
Hormones are chemical substances that affect the activity of another part of the body (target site).
• Hormones serve as messengers, controlling and coordinating activities throughout the body.
• Upon reaching a target site, a hormone binds to a receptor, much like a key fits into a lock.
• Once the hormone locks into its receptor, it transmits a message that causes the target site to take a specific action.
• Hormone receptors may be within the nucleus or on the surface of the cell
Major Endocrine Glands
• Pituitary gland
• Hypothalamus
• Thyroid gland
• Thymus gland
• Suprarenal glands
• Pineal gland
• Parathyroid glands
• Pancreas
• Reproductive glands
Types of hormones
Functional
• Endocrine Hormones – Travel through the blood to act at a site distant
from the secreting cell or gland
• Paracrine Hormones – Act on cells near the secreting cell
• Autocrine Hormones – Act on the secreting cell
• Neurocrine Hormones – Secreted by neural cells
• neurotransmitters
• neurohormones
Chemical
• Protein & Polypeptide
• Amine (amino acid derived)
• Steroid
Tropic versus non tropic hormones
Non-tropic hormones are hormones
that directly stimulate target cells to
induce effects.
• For example, aldosterone acts
directly on the kidney to
promote reabsorption of sodium,
which causes an increase in
blood pressure
Tropic hormones, which act on other
endocrine glands to stimulate (or
inhibit) release of a second
hormone.
• For example, thyroid-stimulating
hormone is responsible for
stimulating the release for
thyroid hormone by acting on
the thyroid gland
Functional hormones- long distance communication
• Signal Chemicals
• Made in endocrine cells
• Transported via blood
• Receptors on target cells
Functional hormones neurocrines
Neurotransmitters are chemicals secreted by neurons that diffuse across a small gap to the target cell. neurons use electrical signals as well.
Neurohormones are chemicals released by neurons into the blood for action at distant targets
Functional hormones- Paracrine and Autocrine Hormones
• Local communication
• Signal chemicals diffuse to target
Example: Cytokines
• Autocrine–receptor on same cell
• Paracrine–neighboring cells
Chemical Hormones
• Grouped according to chemical structure.
• Steroid hormones are fat-soluble
molecules made from cholesterol.
Non- steroidal
• Protein and Amino acid derivatives,
such as epinephrine, are water-soluble
molecules derived from amino acids
(the building blocks of protein).
Water vs. Fat Soluble Hormones
Most water-soluble hormones
• Like the amino acid derivatives and peptides, can
travel freely in the blood because they “like” water.
• However, they are repelled by lipid or fatty structures
such as the membranes that surround the cell and
nucleus.
• Because of this, these hormones generally bind to
receptor sites on the outside of the cell and signal
from there.
Fat-soluble hormones
• Like the sex hormone steroids estrogens and
androgens, are fat soluble and water repellent.
• That is, they “like” lipid or fatty structures such as
those surrounding cells but are generally repelled by
watery areas.
• Steroids generally travel to their target cells attached
to a special carrier protein that “likes” water (such as,
sex steroid hormone binding globulin and serum
albumin).
• The hormones detach before passing into the cell
where they bind to receptors.
Chemical Hormones:
Protein and polypeptide Hormones: Synthesis and Release
• Products of translation
• Regulated secretion: The cell stores hormone in
secretory granules and releases them in “bursts” when
stimulated. This is the most commonly used pathway
and allows cells to secrete a large amount of hormone
over a short period of time.
• Constitutive secretion: The cell does not store
hormone but secretes it from secretory vesicles as it is
synthesized.
