Endocrine System Flashcards
Endocrine System
Part 1
Hormones and Endocrine Glands
In the body there are 2 types of glands
1) Exocrine glands: secrete their
products into duct (e.g., sweat or
the intestines)
2) Endocrine glands: ductless and
release hormones into the blood
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
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
Response to small amount is possible due to the way the cell
‘behaves’
- This means that although a given hormone travels throughout the
body in the blood, it affects only specific target cells.
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
Hormones
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
Hormone structures and synthesis
Hormones fall into three major structural classes:
1. Amines
E.g., Thyroid hormones, Dopamine, Catecholamines (Epinephrine & Norepinephrine)
Derivatives of the amino acid tyrosine
Secreted by the adrenal medulla and the hypothalamus
2. Peptides and proteins
E.g., Insulin
The majority of hormones are polypeptides
Many peptide hormones are synthesised as large, inactive molecules that are cleaved into
active fragments.
3. Steroids
E.g., Aldosterone, Cortisol, Androgens (e.g., testosterone), Estrogens
Produced from cholesterol by the adrenal cortex and the gonads
Hormone transport, metabolism and excretion
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.
Hormone transport, metabolism and excretion
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 metabolised to more active molecules in their
target cells or organs.
Mechanisms of hormone action
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
Mechanisms of hormone action
The responsiveness of a target cell to a hormone depends on
(1) the hormone’s concentration in the blood,
(2) the abundance of the target cell’s hormone receptors, and
(3) influences exerted by other hormones.
Hormonal interactions can have three types of effects:
Permissive: action of one hormone enhances the responsiveness or activity of
another hormone
e.g., epinephrine & thyroid hormones (T3 and T4) stimulation of lipolysis
Mechanisms of hormone action
The responsiveness of a target cell to a hormone depends on
(1) the hormone’s concentration in the blood,
(2) the abundance of the target cell’s hormone receptors, and
(3) influences exerted by other hormones.
Hormonal interactions can have three types of effects:
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
Or Antagonistic: one hormone opposes the actions of another hormone
e.g., insulin & glucagon
Negative feedback systems regulate the secretion of many hormones.
Inputs that control hormone secretion
ormone secretion controlled by:
1. Plasma concentration of an ion or nutrient that the hormone regulates
2. Neural input to the endocrine cells
3. Other hormones
Inputs that control hormone secretion
- Plasma concentration of an ion or
nutrient that the hormone regulates
E.g., Insulin secretion
https://www.youtube.com/watch?v=OYH1deu7-4E&t=8s
Inputs that control hormone secretion
- Neural input to the endocrine cells
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.
Inputs that control hormone secretion
- Other hormones
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)
Endocrine disorders
The wide variety of hormones and endocrine glands determines that
disorders of the endocrine system vary considerably.
Despite varied functional consequences, all endocrine diseases can be
categorised in 1 of 4 ways.
Too little hormones (hyposecretion)
E.g., type 1 diabetes
Too much hormone (hypersecretion)
e.g., gigantism
Endocrine disorders
The wide variety of hormones and endocrine glands determines that
disorders of the endocrine system vary considerably.
Despite varied functional consequences, all endocrine diseases can be
categorised in 1 of 4 ways.
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 of hormones
Pharmacological administration of hormones for medical purposes
- Can result in supraphysiological concentrations and effects not typically observed
with at physiological concentrations.
For example: medication containing cortisol (e.g., Corticosteroids), which is
administered to suppress allergic and inflammation.
The risk of experiencing side effects depends on:
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)
