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Summary UNIT 9 LEARNING AIM B HOMEOSTASIS THE ROLE OF HORMONES IN OSMOREGULATIONLATEST 2021/2022
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UNIT 9 LEARNING AIM B HOMEOSTASIS THE ROLE OF HORMONES IN OSMOREGULATIONLATEST 2021/2022
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UNIT 9 LEARNING AIM B HOMEOSTASIS THE ROLE OF HORMONES INOSMOREGULATIONLATEST 2021/2022
Unit 9
Learning Aim B
Homeostasis
Homeostasis is the maintenance of a constant environment in the body. E.g. temperature, blood
pressure or any other variables within living organisms. The hormones produced by the nervous
system and the endocrine system are involved in homeostasis. In order to regulate and monitor
conditions within the body, the body uses systems of feedback. A set point is a value in which the
normal range fluctuates. For instance, the set point for normal human body temperature is around
37 ° C. A normal range is an optimally healthy and stable restricted set of values. The control centres
in the brain and other parts of the body monitor and respond to deviations from homeostasis using
negative feedback. A mechanism that reverses a deviation from the set point is negative feedback.
Negative feedback, therefore, keeps body parameters (such as blood pressure, temperature, as they
tend to fluctuate a few degrees above and below that point.) within their normal range.
Negative feedback
In negative feedback, any homeostatic process alters the direction of the stimulus. Homeostatic
mechanisms are composed of three main parts; a receptor, a control centre and an effector. A
specific sensor detects this stimulus. Examples of negative feedback include when blood pressure
increases the heart rate slows – if glucose levels are too high, the pancreas secretes insulin to
stimulate the absorption of glucose.
Positive feedback
Instead of reversing, positive feedback intensifies a change in the physiological condition of the body.
A deviation from the normal range leads to more change and the system moves away from the
normal range. Positive feedback is normal only when a definite endpoint is reached. Childbirth and
the body’s response to blood loss are two examples of positive feedback loops that are normal but
activated only when necessary. Another example of positive feedback is uterine contractions during
childbirth. During childbirth, a positive feedback loop comes into play. In childbirth, the head of the
baby presses on the cervix— the bottom of the uterus through which the baby must emerge — and
activates neurons to the brain. The neurons send a signal from the pituitary gland to release the
hormone oxytocin. Oxytocin increases uterine contractions, thereby placing pressure on the cervix.
This causes even more oxytocin to be released and makes contractions even stronger. This positive
feedback loop goes on until the birth of the baby.
Homeostasis regulates the internal environment of the human body and ensures that levels of blood
sugar, the water content in the body and temperature are balanced. Homeostasis is extremely
important for the function of the cells in the human body, cells rely on the body environment to
survive and function efficiently. It keeps the body environment under control and the conditions
inside normal in order for the cells to function effectively. If the internal environment in the body is
not right, certain processes such as osmosis will not occur. Processes such as diffusion and osmosis
depend on the body’s water and salt levels. The water and salt levels are kept constant by
homeostasis and therefore it is important that the system functions properly.
Maintenance of water levels (osmoregulation)
Osmoregulation is the process of maintaining salt and water content levels in the body and is an
example of a negative feedback mechanism. The consumption is balanced by an equal excretion of
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, fluids through urination, defecations and sweating. The body’s organs and tissues of the body are
immersed in a fluid at a constant temperature, pH, and solute level, which each contribute to
maintaining the homeostasis of the body. These solutes are held at optimal concentrations by
osmoregulation. Despite influence from external factors such as temperature, diet and weather
conditions, osmotic homeostasis is maintained.
The role of hormones in osmoregulation
Antidiuretic hormone (ADH)
Antidiuretic hormone (ADH) has a key role in osmoregulation; it informs its target organ, the kidneys
how much water to conserve when the body fluid volume, particularly of the blood, is low. ADH
controls and regulates the amount of water in the blood. It is detected by osmoreceptors in the
hypothalamus and is stored and secreted from the posterior pituitary gland. It acts by inserting
aquaporins into the collecting ducts and enables water reabsorption. More ADH means more
aquaporins are inserted, and therefore more water is reabsorbed which leads to less concentrated
urine produced. ADH also acts as a vasoconstrictor and increases blood pressure during
haemorrhaging. Whereas, if water content levels are high, osmoreceptors detect this in the
hypothalamus and the posterior pituitary gland releases less ADH into the blood. Less ADH means
the DCT and collecting ducts are less permeable and therefore less water is reabsorbed into the
blood by osmosis. In response to this, a large amount of dilute urine is produced and more water is
lost.
Atrial natriuretic peptide (ANP)
Blood pressure is reduced by the atrial natriuretic peptide (ANP) which acts as a vasodilator. In
response to high blood pressure and patients with sleep apnea, it is released by cells in the atrium of
the heart. ANP decreases both blood pressure and blood volume by binding to blood vessels and
kidneys. Additionally, ANP prevents reabsorption of sodium through the renal tubules, reducing
water reabsorption (thus acting as a diuretic) and lowering blood pressure. The ANP also inhibits the
release of renin, aldosterone and ADH, thus preventing actions of these hormones.
Renin-Angiotensin
Renin is produced by the kidney and is secreted by the juxtaglomerular complex. Renin increases
blood pressure by acting on angiotensinogen, which is produced in the liver and converts it to
angiotensin I. An enzyme called ACE then converts angiotensin I to angiotensin II. Angiotensin II has
numerous direct effects. These include arterial constriction that increases blood pressure, decreases
the rate of glomerular filtration that leads to water retention, and increases thirst.
Aldosterone
The adrenal glands located on top of the kidneys produce aldosterone. Aldosterone reabsorbs more
sodium and water and increases the blood pressure by nephron distal tubules. It sends a signal to
organs such as the kidney and colon to increase the amount of sodium the body transmits into the
bloodstream or the amount of potassium released in the urine. Aldosterone prevents sodium and
water loss; aldosterone not only manages sodium levels but also body fluid water levels.
Aldosterone, however, also stimulates potassium secretion when sodium is absorbed. In contrast, the
absence of aldosterone means that the renal tubules do not absorb any sodium and therefore it is all
excreted in the urine.
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