the endocrine system Flashcards
what are the 2 types of endocrine glands
Exocrine glands: secrete their
products into duct (e.g., sweat or
the intestines)
2) Endocrine glands: ductless and
release hormones into the blood
what is the endocrine system
The endocrine system is one of
the body two major communication systems:
- Consists of glands and organs that
secrete hormones
- A single gland may secret multiple
hormones
what are Hormones
Hormones are chemical
messengers carried by the blood
to target cells
hormones
Releases by glands to elicit a response
- Enhance or inhibit cellular reactions
Present at v. low concentrations
- Much lower than other similar molecules
function of hormones
Hormones help regulate:
Chemical composition and volume of internal environment (e.g., interstitial fluid)
Metabolism and energy balance
Contraction of smooth and cardiac muscle fibers
Glandular secretions
Some immune system activities
- Control growth and development
- Regulate operation of reproductive system
- Help establish circadian rhythm
how do hormones operate
Operate in synchrony with the nervous system
- Endocrine = chemical messengers
Act (relatively) more slowly Often longer lasting effects
- Nervous system = electrical conduit system
Instantaneous
Short-lived
what are the 3 structures of hormones
amines
peptide and proties
steriods
what are examples amine hormones
Thyroid hormones, Dopamine, Catecholamines (Epinephrine & Norepinephrine)
Derivatives of the amino acid tyrosine
Secreted by the adrenal medulla and the hypothalamus
what are examples of peptide hormones
The majority of hormones are polypeptides
Many peptide hormones are synthesised as large, inactive molecules that are cleaved into
active fragments.
what are examples of steroids
Aldosterone, Cortisol, Androgens (e.g., testosterone), Estrogens
Produced from cholesterol by the adrenal cortex and the gonads
how do hormones transport
Peptide and all catecholamine hormones
are water soluble and therefore circulate
dissolved in the plasma.
Some peptide hormones bind to plasma
proteins
Steroid and thyroid hormones circulate
mainly bound to plasma proteins.
how are hormones excreted
the liver and kidneys are the major organs that remove hormones from the plasma by metabolizing or excreting them.
Liver = major organ responsible for the metabolic inactivation
(otherwise called metabolism or biotransformation)
Kidneys = filter the blood, removing waste products, including
hormones and their metabolites.
Peptide hormones and catecholamines are rapidly removed from the blood
Steroid and thyroid hormones are removed more slowly Because they circulate bound to plasma proteins
After their secretion, some hormones are metabolized to more active molecules in their target cells or organs.
how do hormones work
Public transport (blood)– specific destinations (target tissues)
The presence of specific receptors for those hormones on or in the target cells necessary for response
Hormone receptors
For lipid-soluble steroid and thyroid
hormones, the majority of receptors are inside target cells affect cell function by altering gene expression
For water-soluble peptide hormones and
catecholamines, receptors are on the plasma membrane peptide hormones and catecholamines may exert both rapid (nongenomic) and slower (gene transcription) actions on the same target cell.
what determines the responsiveness of a hormone
the hormone’s concentration in the blood,
(2) the abundance of the target cell’s hormone receptors, and
(3) influences exerted by other hormones.
what are the 3 hormonal interactions
Permissive: action of one hormone enhances the responsiveness or activity of another hormone
e.g., epinephrine & thyroid hormones (T3 and T4) stimulation of lipolysis
Synergistic: the effect of two hormones acting together is greater or more
extensive than one hormone acting on its own.
e.g., follicle-stimulating hormone & estrogens
Antagonistic: one hormone opposes the actions of another hormone
e.g., insulin & glucagon
Negative feedback systems regulate the secretion of many hormones.
what controls hormone secretion
Plasma concentration of an ion or nutrient that the hormone regulates
2. Neural input to the endocrine cells
3. Other hormones
Neural input to the endocrine cells effect on secretion
The autonomic nervous system
controls hormone secretion via the
adrenal medulla and other
endocrine glands.
Neurons in the hypothalamus also
secrete hormones.
Neural input from the autonomic
nervous system controls the
secretion of many hormones.
other hormones effect of secretion
Often the secretion of a particular
hormone is directly controlled by the
blood concentration of another hormone
A hormone that stimulates the
secretion of another hormone is
often referred to as a tropic
hormone.
E.g., Thyroid-stimulating hormone
(TSH) or Follicle-stimulating
hormone (FSH)
what are endocrine disorders
he wide variety of hormones and endocrine glands determines that
disorders of the endocrine system vary considerably.
what are the 4 types of endocrine diseases
Too little hormones (hyposecretion)
E.g., type 1 diabetes
Too much hormone (hypersecretion)
E.g., gigantism
Decreases responsiveness of the target cells to hormones (hyporesponsiveness)
E.g., type 2 diabetes
Increases responsiveness of the target cells to hormone (hyperresponsiveness)
E.g., elevated heart rate due to increased circulating levels of thyroid hormone
pharmacological effects on hormones
Pharmacological administration of hormones for medical purposes
- Can result in supraphysiological concentrations and effects not typically observed
with at physiological concentrations
what impacts the risk of pharmacological
the type of steroid (oral corticosteroids more likely to cause side effects as they are acting
systemically).
the dose
the length of treatment
the age of the patient (children and older adults more susceptible)
what is the posterior pituitary gland
The posterior pituitary is really a neural extension of the hypothalamus
Hormones are synthesized in the
hypothalamus, axons pass down the
infundibulum, terminate in the
posterior pituitary and release
hormones
E.g., oxytocin and vasopressin
what does the anterior pituitary gland secret
The anterior pituitary gland secretes growth hormone (GH), thyroid-
stimulating hormone (TSH), adrenocorticotropic hormone (ACTH),
prolactin, and two gonadotropic hormones—follicle-stimulating hormone
(FSH) and luteinizing hormone (LH).
