Unit 9: Human Regulation and reproduction
Learning aim B: understand the homeostatic mechanisms used by the human body.
Criteria covered:
B. D2: analyse the impact of homeostatic dysfunction on the human body.
B. M2: Explain the role of hormones in homeostatic mechanisms.
B. P2: Describe h...
Homeostatic control of body system
Homeostasis- The constant maintenance of a constant internal environment within an organism.
One’s body needs to sustain its internal condition at certain levels to function. Homeostasis is called the preservation
of internal conditions such as pH, temperature, and salt concentration in a stable equilibrium.
Homeostasis is also known as a process of self-regulation by which an organism seeks to preserve equilibrium when
adapting to the optimal environment for its survival.
For example: homeostatic helps maintain optimal conditions for enzyme action and all cell functions, which then
helps metabolic reactions to occur at appropriate rates. What will happen if homeostatic dysfunctions for the
enzymes? As metabolic reactions involve enzymes, change in temperature such as increased body temperature will
denature enzymes preventing the enzymes from conducting metabolic reactions effectively. What will happen if fault
occurs in metabolic reaction? This will cause the organism to either have adequate or inadequate number of vital
substances required to remain healthy.
This helps us understand the significance of homeostasis’s role in an organism.
Feedback and control
Homeostasis calls for a high degree of monitoring and control; to detect internal and external changes and respond
stimuli, hormones and nervous system communicate to bring about changes that brings symptoms back to the correct
level.
How is does hormones and nervous system helps homeostatic? The endocrine and nervous system are crucial for
homeostasis.
Endocrine transmits information through hormones which travels through the blood.
Endocrine glands pass secretion directly into the blood stream rather than flowing a long
duct. Slower messages are sent through hormones which allows more than one tissue,
organ, or organ system to be targeted as it is carried around the body. Whereas Exocrine
glands contain ducts that transport secretion from the glands to its surface.
(Figure 1: the endocrine system)
The nervous system uses nerve cells which transfers information as electrical impulses.
Rapid messages are sent by the nervous system unlike endocrine.
(Figure 2: the nervous system)
These feedback mechanisms are used to track and control conditions within the organisms.
There are two main feedbacks called negative feedback and positive feedback:
Negative feedback
, The mechanism that reverses the change in internal conditions is called negative
feedback; reverses change inside the organism through the effectors restoring the
change back to the optimum.
(Figure 2.1)
Mechanism of negative feedback
The optimal point for the organism is tracked by the receptors.
They send signals to a co-ordinator (hormones or nervous system) when the receptors sense some changes
away from the optimum.
The co-ordinator (hormones or nervous system) then determines which response is sufficient and sends
signals to the effectors to carry it out.
Effectors bring about a transition that allows the internal regulatory changes to their optimal conditions.
How does co-ordinated response work?
Signals are obtained from several diverse sources by co-ordinators, these need to be evaluated before producing a
response to function effectively. For example, signals can come from several various receptors that covers diverse
types of stimuli and all this must be evaluated before sending the affecting signals.
For example, there are temperature receptors in both the skin (e.g., Arms) and in the hypothalamus (found deep
within the brain). As we exercise, we sweat, which lowers the skin temperature if the co-ordinator just. used skin
information, it will. work to boost the body temperature when we exercise, but instead the co-ordinator uses
hypothalamic as well as skin information to make an effective appropriate response.
(Figure 3: negative feedback in a central heating system)
An example of negative feedback
The hypothalamus in the brain regulates body temperature. The reaction is that the body starts to sweat to try to reduce
the temperature down to the correct amount if the hypothalamus senses that the body is too hot. Sweating will stop
until the body temperature is back to the correct amount. Conversely, if the hypothalamus senses that the body is too
cold, the reaction is that the body starts shivering to attempt to lift the temperature up to the correct amount. The
shivering will stop until the body temperature is up to the correct amount.
Positive feedback
Contrary to the negative feedback, positive feedback is the opposite: every change away from the sixed point is
increased. A significant, unstable changes within the organism is caused by this mechanism. It is typically harmful,
but there are instances when for example, its useful for action potential in neurons: nerve cells need to be able to
, transmit electrical impulses for communication along their axon length, they rely on
positive feedback to function, influx of sodium ions triggers depolarisation during
action potentials, which results in the opening of more voltage-gated sodium
channels, resulting in even more depolarisation.
(Figure 3.1: positive feedback)
(Figure 4: positive feedback during labour)
An example of positive feedback loop
When the head of the foetus pushes up against the cervix in childbirth, it activates the nerves that tell the brain to
activate the pituitary gland, which then releases oxytocin. Oxytocin triggers the contraction of the uterus. This brings
the foetus ever closer to the cervix, leading to the development of more oxytocin before birth happens and the baby
leaves the womb. Breastfeeding is also a positive feedback loop; the pituitary gland of the mother releases more of the
hormone prolactin as the baby suckles, which allows more milk to be produced.
Role of hormones and glands
Endocrine glands- glands that release hormones directly into the blood are endocrine.
(Figure 5: 12 endocrine glands in both female and male body)
What is the importance of these three areas in the function of glands?
,Thermoregulation- This is regulated to maintain the temperature, which is normally 37 ° C, at which the enzymes of
the body function best.
Glucose regulation- This is regulated to provide a steady supply of glucose to cells for respiration. It is regulated by
glucose release and storage, which is controlled by insulin in turn.
Water balance- To protect cells, this is regulated by preventing too much water from entering or leaving them. Water
content is regulated by the loss of water from:
Lungs - as we breathe out.
Skin - by sweating.
Body - in the urine produced by the kidneys.
There are major endocrine glands, but I will go into detail with only 3 endocrine glands:
Pituitary endocrine gland
Pituitary gland is found within the base of the brain.
They secrete 5 types of hormones into the bloodstream:
- Growth hormone
- Prolactin hormone
- antidiuretic hormone
- Thyroid stimulating hormone
- Adrenocorticotropic hormone
which functions in controlling many other glands such as thyroid.
(Figure 6)
Thyroid endocrine gland
Thyroid gland is found underneath the larynx in the neck.
They secrete 1 type of hormone into the bloodstream:
- Thyroxine hormone
which functions in the regulation of the metabolic rate.
(Figure 7)
Pan
c reas; an
exocrine and endocrine gland
Pancreas is found in the abdomen.
Exocrine’s function in pancreas:
secretes alkaline mucus which functions to
neutralise stomach contents as they enter the
duodenum.
,Endocrine’s function in pancreas:
secretes insulin and glucagon which functions in blood and glucose’s regulation.
(Figure 8)
The pancreas acts both in an endocrine and exocrine gland. The Islets of Langerhans have an endocrine function that
includes secreting insulin directly into the blood from beta cells and glucagon from alpha cells. The pancreas' exocrine
function includes the secretion through the pancreatic tract of digestive enzymes such as amylase, trypsin, and lipase
to the duodenum. The alpha and beta cells contain several ribosomes and rough endoplasmic reticulum to produce
protein hormones effectively. They also contain many Golgi that are involved in packaging the hormones into
vesicles, then secreting the hormones from secretory vesicles through exocytosis. They contain many mitochondria to
produce Adenosine triphosphate, as the cells are continually active.
Thermoregulation
(Figure 9: 2 negative feedback loops when it gets too cold and too warm)
An ectotherm is an organism that, with the assistance of an external source, controls its body temperature. Ectotherms
are unable to increase their respiration rate to increase the internal output of heat so they cannot rely on internal energy
sources. Therefore, by sharing heat with their environment, for example by exposing their body to sun, orienting it to
either minimise or increase sun exposure, hiding away from sun or increasing breathing for heat loss by water
evaporation, they regulate their body temperature.
Endotherms are willing, regardless of the external temperature, to maintain a steady body temperature. These involve
thermoreceptors that detect changes in core body temperature and transmit them to the hypothalamus, which in turn
directs appropriate responses through either physiological or behavioural responses to restore the optimum
temperature. Actions taken by endotherms to regulate body temperature by heat gain or loss of heat include:
Shivering- skeletal muscle contractions triggered by nerve impulses sent out by the hypothalamus contribute
to temperature rise as heat is released.
Sweat glands- development of sweat to reduce body temperature by evaporation.
Arterioles- dilate to accelerate the loss of heat as blood flows closer to the surface. It reduces blood flow and
therefore minimises heat loss.
Hairs on the skin lie flat- elevated to provide insulation and reduce heat loss to decrease insulation and
increase heat loss.
, The role of skin in the thermoregulation
(Figure 10: the human skin showing the structures involved in thermoregulation)
Skin capillaries are involved in controlling heat as well as delivering nutrients and oxygen to the arteriole of the skin
that carry blood to the capillaries of the skin containing muscle in their walls. The muscles in the arterial walls relax as
the temperature of the skin increases. This induces the dilation of the arteriole, which allows more blood to flow to the
skin surface capillaries. It is called VASODILATION. Heat is then lost to the environment.
Consequence to human health that may result from dysfunction of the homeostatic mechanism
Impact of an imbalance in thermoregulation - Hypothermia
As the temperature of the skin decreases, the arterial muscles contract. It flows less blood to the capillaries.
Restricting the supply of blood and reducing cardiac oxygen. It is more difficult for the heart to pump to circulate
blood into the constricted blood vessels. Blood pressure and heart rate rise consequently. If blood pressure gets too
high, the blood vessels, the heart, and other organs, such as the brain, kidneys, and eyes, are put under extra strain.
The risk of a variety of severe and potentially life-threatening health problems such as heart failure and heart attacks
may be increased by constant high blood pressure.
To stop blood entering the capillary Emergency medical treatment for hypothermia
network, blood is diverted along a shunt may involve either of the following measures to
vessel and less heat is transmitted to the raise the body temperature, depending on the
environment. seriousness of hypothermia
In addition to that, each follicle of hair Passive rewarming.
in the skin is linked to the muscle of the It is enough to cover them with hot
erector. The muscle contracts and pulls blankets for those with moderate
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