Case uitwerking Homeostasis and Organ Systems (BBS1002)
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Course
Homeostasis and Organ Systems (BBS1002)
Institution
Maastricht University (UM)
This concise academic document explores how key body systems—nervous, respiratory, cardiovascular, gastrointestinal (GI), and urinary—work together to maintain homeostasis. It covers the nervous system's role in rapid regulation, the respiratory system's gas exchange, the cardiovascular system'...
,Case 1: Big tension
1. Overview of the nervous system
The central nervous system contains over 100 billion neurons. Signals enter these
neurons through synapses, located in the neuron dendrites or on the cell body. The
signal travels through the neuron and leaves via the axon. This axon can have
separate branches to other parts of the nervous system. A signal travels from
dendrite, to cell body to axon.
The nervous system is divided into two main parts: the Central Nervous System
(CNS), which includes the brain and spinal cord, and the Peripheral Nervous System
(PNS), which connects the CNS to the limbs and organs. Within the PNS, 12 cranial
nerves (originating from the brain) and 31 spinal nerves (emerging from the spinal
cord) play key roles in transmitting signals between the
CNS and the rest of the body.
Sensory: Most activities of the nervous system are
initiated by sensory experiences that excite sensory
receptors. These sensory experiences can either cause
immediate reactions from the brain, or memories of the
experiences can be stored in the brain for minutes, weeks
or years and determine bodily reactions at some time. The
sensory system has a somatic portion, which transmits
sensory information from the receptors of the entire body
surface and from some deep structures. This information
enters the central nervous system through peripheral
nerves and is conducted immediately to multiple sensory
areas in the spinal cord at all levels; the reticular substance
of the medulla, pons, and mesencephalon of the brain; the
cerebellum; the thalamus; and areas of the cerebral cortex.
Motor: The most important eventual role of the nervous
system is to control the various bodily activities. This task
is achieved by controlling contraction of appropriate
skeletal muscles throughout the body, contraction of smooth muscle in the internal
organs, and secretion of active chemical substances by both exocrine and endocrine
glands in many parts of the body. These activities are called motor functions of the
nervous system, and the muscles and glands are called effectors because they are
the actual anatomical structures that perform the functions dictated by the nerve
signals. To control skeletal muscle contraction, there is the skeletal motor nerve axis.
To control smooth muscle, glands and other internal bodily systems, there is the
autonomic nervous system.
1. Anatomical organisation of autonomic nervous system
The autonomic nervous system is activated mainly by centres located in the spinal
cord, brain stem, and hypothalamus. The hypothalamus acts as the primary control
centre, integrating signals and managing homeostasis by adjusting ANS activity.
The brainstem contains centres that control specific functions like heart rate, blood
pressure, and respiratory rhythm. For instance, the medullary cardiovascular centre
manages blood vessel constriction and heart rate through sympathetic and
parasympathetic pathways
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,The autonomic signals are transmitted to the various organs of the body through two
major subdivisions called the sympathetic nervous system and the parasympathetic
nervous system.
Ganglia: Ganglia (singular: ganglion) are clusters of neuron cell bodies located
outside the central nervous system (CNS) that act as relay stations for nerve signals.
In this context, a relay station refers to a point where nerve signals are passed, or
"relayed," from one neuron to another. In ganglia, this typically
means that a signal from a preganglionic neuron (the neuron
coming from the central nervous system) reaches the ganglion
and is then transferred to a postganglionic neuron (the neuron
that will carry the signal to the target organ or tissue).
Sympathetic
- Structure and pathways: Sympathetic nerve fibres
originate in the spinal cord between segments T1 and
L2. They exit the spinal cord through spinal nerves and
reach the sympathetic chain, a series of interconnected
ganglia running parallel to the spine. From here, fibres
can either synapse immediately or travel up or down the
chain to other ganglia. Some fibres bypass the chain
entirely and reach prevertebral ganglia (e.g., celiac and
hypogastric ganglia) closer to target organs.
- Preganglionic and Postganglionic Neurons:
Sympathetic pathways consist of two neurons in
sequence. The preganglionic neurons originate in the
spinal cord and release acetylcholine (ACh) at
synapses within ganglia. The postganglionic neurons,
extending from ganglia to target organs, typically
release norepinephrine, exerting a stimulatory effect on
target tissues, such as increasing heart rate and dilating
bronchioles.
Parasympathetic:
- Structure and Pathways: The parasympathetic nervous
system has fibres that exit the CNS through cranial
nerves (especially III, VII, IX, and X) and sacral spinal
(lateral horn) nerves (S2-S4). Origin of the nucleus in
the brain. Unlike the sympathetic system,
parasympathetic ganglia are located close to or within
the walls of target organs, resulting in shorter
postganglionic fibres. This proximity allows for more
specific and localised control, as the PNS typically
promotes a “rest and digest” state, slowing heart rate,
stimulating digestion, and promoting relaxation.
- Preganglionic and Postganglionic Neurons: In the PNS,
both preganglionic and postganglionic neurons release
acetylcholine, which binds to muscarinic receptors on
target tissues to produce calming effects, such as
reducing cardiac output and increasing gastrointestinal
activity.
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, 2. Function of the autonomic nervous system
The function of the Autonomic Nervous System (ANS) is to regulate involuntary body
functions, ensuring the maintenance of homeostasis (balance in internal conditions)
and enabling rapid responses to external stimuli. The ANS controls vital processes
like blood pressure, heart rate, digestion, respiration, and glandular secretion, often
without conscious awareness.
● Maintaining Cardiovascular Stability:
○ The ANS manages arterial pressure through both the sympathetic and
parasympathetic systems, with the sympathetic system increasing blood
pressure during activities or stress by constricting blood vessels and
stimulating heart rate. In contrast, the parasympathetic system lowers heart
rate to help the body relax.
○ These functions are controlled through complex reflexes like the baroreceptor
reflex, which adjusts blood pressure almost instantaneously by detecting
changes in the stretch of blood vessels and modulating autonomic output
accordingly.
● Controlling Gastrointestinal and Excretory Functions:
○ The ANS is essential for digestive motility and secretion. The
parasympathetic system promotes digestion by increasing peristalsis and
relaxing digestive sphincters, thus supporting movement and absorption in
the gastrointestinal (GI) tract.
○ Urination and defecation are also under autonomic control, coordinated
through reflexes that allow the bladder and rectum to empty once they reach
a certain fullness. The sacral parasympathetic pathways facilitate these
actions.
● Regulating Body Temperature and Sweating:
○ The sympathetic system plays a primary role in body temperature regulation
by controlling sweat gland activity and adjusting blood flow to the skin. During
overheating, sympathetic activation causes sweating and vasodilation of skin
blood vessels to release heat. This system also responds to cold by reducing
blood flow to the skin to conserve heat
● Responding to Stress and Emergencies:
○ Known as the "fight-or-flight" response, the sympathetic nervous system
prepares the body for action in stress or danger by increasing heart rate,
dilating airways, and mobilising energy stores. This coordinated response
enables the body to react swiftly and effectively to immediate threats.
○ In these situations, the adrenal medulla releases epinephrine (adrenaline),
which reinforces sympathetic effects, enhancing the body’s capacity for
intense physical activity by boosting cardiovascular and metabolic functions
● Managing Glandular Secretion:
○ Both divisions of the ANS regulate the secretion of glands throughout the
body. The parasympathetic system enhances secretion in glands related to
digestion (e.g., salivary and gastric glands), while the sympathetic system
regulates secretion in sweat and adrenal glands. The balance between these
two systems determines the volume and type of secretions released
- Integration with the CNS and Reflex Actions: The ANS is governed by the
hypothalamus, brainstem, and spinal cord, which receive sensory input and modulate
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