Lecture notes
Lecture notes Contexts of Care (SHN169)
- Module
- Contexts of Care (SHN169)
- Institution
- Swansea University (SWAN)
The Endocrine System
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SHN169 – Introduction to the Endocrine SystemIntroduction to the Endocrine System
Objectives of this Session
Be able to explain what the endocrine system is, why it is needed and how it works
Appreciate differences between endocrine & exocrine glands
Explain what hormones are and what they do
Understand the ways in which we classify hormones (functionally and chemically),
and be able to provide examples of each classification
Appreciate what it means for a hormone to be water-soluble or lipid-soluble
Understand the basics of steroid and non-steroid hormone action
Name the 10 major endocrine organs/glands and understand the primary roles of
each
Appreciate the consequences which can result when an endocrine organ/gland fails
to function correctly
Understand the 3 main types of stimuli which serve to regulate the endocrine system
What is the Endocrine System?
A system of specialised organs/glands throughout the body which secrete hormones
into the blood or extracellular fluid where they act as chemical messengers
o ‘Endo’ – means internal/within.
o ‘Crine’ – means to secrete
Glands: organs which produce and secrete substances
Intracellular fluid: the fluid inside a cell
Extracellular fluid: the fluid outside a cell
Chemical messenger: a compound which transmits a message
Alongside the main 10, other organs secrete hormones as a secondary function: E.g.
Kidneys, heart, liver, stomach, skin
o Kidneys: produces erythropoietin in response to low blood oxygen levels
(hypoxia) → carried to bone marrow → stimulates stem cells → cells undergo
maturation – become red blood cells (erythrocytes)
o Heart: produces atrial natriuretic hormone → targets nephrons of kidneys →
promotes sodium (Na+ ) excretion → increased urine production & decreased
blood pressure
Why is it Needed? How does it Work?
Functioning alongside the nervous system, the endocrine system is one of the key
systems in the maintenance of homeostasis
o Homeostasis: the maintenance of relatively constant states within the body
Both the nervous and endocrine system use chemical messengers to achieve
maintenance of homeostasis
Nervous system: uses neurotransmitters
Endocrine system: uses hormones
Maintenance of homeostasis by the endocrine system is achieved through hormone
action which serves to coordinate and regulate the functions of the systems of the
body
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,SHN169 – Introduction to the Endocrine System
o Some of the numerous aspects regulated include: organ-specific functions,
growth, metabolism, sleep, mood, reproduction, water and electrolyte
balance
Hormones circulating within the blood come into contact with numerous cells
throughout the body
Not all cells however are receptive to the hormones that come into contact with
them
o Target cells: cells possessing the receptors for a specific hormone and so are
receptive to their effects
o Target organ/tissue: organ/tissue containing the target cells for a specific
hormone
o Signal transduction: process by which the chemical signal is detected by
receptor on target cell
o Some cells have receptors for hormones (endocrine system) and
neurotransmitters (nervous system)
o Neurotransmitters
Travel short distances using synapses
Effects are rapid to appear but are short-lived
o Hormones
Travel longer distances using the blood
Effects are slower to appear but are long-lasting
Glands
Organs which produce and secrete substances
Two key types:
o Endocrine glands
Secrete hormones
Released directly into the blood / extracellular fluid
They do not have ducts – referred to as ductless glands
Either glandular epithelial cells or neurosecretory cells
Neurosecretory cells
o Special, modified neurons (nerve cells)
o Secrete messenger molecules directly into bloodstream
o Secrete hormones rather than neurotransmitters
o Exocrine glands
Secrete, e.g. sweat and tears
Exo: external
Release secretions out of the body via ducts
Referred to as ducted glands
o Exocrine glands are not part of the endocrine system
o Endocrine glands are part of the endocrine system
The 10 major Endocrine Organs/Glands
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, SHN169 – Introduction to the Endocrine System
Hormones
Chemicals produced by glands or specialised cells of certain organs
Secreted into the blood or extracellular fluid where they act as chemical messengers
Hormones primarily serve to regulate the metabolic function/cellular activity of
other cells
For a hormone to have an effect the cell must possess receptors for that specific
hormone
Some common hormone effects:
o Alteration of plasma membrane permeability/electrical state
o Stimulation of protein/enzyme synthesis
o Activation/deactivation of enzymes
o Stimulation of secretions
o Stimulation of mitosis
Many endocrine functions achieve maintenance of homeostasis through hormones
with opposing effects (e.g. insulin and glucagon in control of blood sugar)
Functional classification of hormones
o Classification based on hormone function:
Tropic hormones
Target other endocrine glands
Sex hormones
Target reproductive tissues
Anabolic hormones
Bring about anabolism in their target cells
o i.e. hormones that build something up
o Chemical classification of hormones – i.e. Classification based on hormone
structure:
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