Homeostasis and Micturition: Homeostasis (“steady-state”) is a process by which animal organs and organ systems constantly respond to internal and external changes. Alterations in blood glucose or calcium levels, as well as external temperatures, could cause these changes. The term “homeostasis” refers to the body’s dynamic equilibrium. It’s dynamic because it’s constantly adapting to the changes that the body’s systems go through. Because physiological functions are controlled within precise parameters, it is balanced. Micturition, also called urination, is the process of releasing urine from the bladder. Urination is used to remove metabolic products and harmful wastes from the body that the kidneys have filtered from the blood. Let’s take a deeper look at Homeostasis and Micturition, definition, and mechanism.

Homeostasis

Homeostasis is critical for an organism’s survival. It is a self-regulatory process that maintains life by controlling internal factors. Homeostasis is a system that keeps the internal environment consistent despite changes in the external environment. Body temperature, blood pH, blood glucose levels, fluid balance, sodium, potassium, and calcium ion concentrations are all controlled by the body to maintain Homeostasis.

Regulation of Homeostasis

Fig: Regulation of Homeostasis

Three mechanisms are involved in maintaining homeostasis:

1. The control centre issues commands to the effector. It could either counteract or amplify the stimulation.
2. The receptor is a sensing component that monitors and reacts to changes in both external and internal environments.
3. The Integration Center is another name for the Control Center. It receives and interprets data from the receptor.

Homeostatic Mechanism

Fig: Homeostasis of Human Body

The purpose of Homeostasis is to keep things in balance around a specific point or value called a set point. While there will be typical variations from the setpoint, the body’s systems will normally try to return to it. A stimulus is a change in the receptor’s internal or external surroundings. The system adjusts the deviation parameter to bring it closer to the specified point. If the animal’s body becomes too hot, changes are made to cool it down. If blood glucose levels rise after a meal, changes are made to lower blood glucose levels by delivering nutrients to tissues that require them or storing them for later use.

Control of Homeostasis

A change in an animal’s environment necessitates a change in behaviour. The receptor detects a change in the environment and sends a signal to the control centre (usually the brain), which develops a response and signals it to an effector. A muscle (that contracts or relaxes) or a gland that secretes is the effector. Negative feedback loops keep homeostasis in action. Positive feedback loops push the organism further away from homeostasis, although they may be required for life to exist. The nervous and endocrine systems of mammals regulate homeostasis.

Positive Feedback Loops

Fig: Positive Feedback Loops

1. During childbirth, a positive feedback loop is activated. During childbirth, the baby’s head presses against the cervix (the bottom of the uterus, through which the baby must exit), activating brain neurons.
2. The neurons transmit a signal to the pituitary gland, which causes it to release the hormone oxytocin.
3. Oxytocin causes uterine contractions to increase, putting more pressure on the cervix.
4. This causes even more oxytocin to be released, resulting in even greater contractions.
5. Until the baby is born, there is a continuation of the positive feedback loop.

Thermoregulation

The body’s activities are influenced by its temperature. In general, as body temperature rises, so does enzyme activity. Enzyme activity doubles for every \(10^\circ \) Celsius increase in temperature, up to a point. High heat causes body proteins, including enzymes, to denature and lose their activity (around \(50^\circ {\text{C}}\) for mammals). With a few exceptions, enzyme activity decreases by \(50\% \) for every ten degrees Celsius drop in temperature until the point ofzing. Some fish can tolerate a completeze and then thaw back to normal.

Endotherms and Ectotherms

Animals can be divided into two groups:

1. Endotherms: In the face of changing environmental temperatures, maintain a steady body temperature. Endotherms are animals that regulate their body temperature through internal sources but can experience temperature extremes. Due to differences in enzyme levels of activity, these animals can maintain a level of activity at cooler temperatures that an ectotherm cannot.
2. Ectotherms: Have a body temperature that is similar to that of their surroundings and so varies with it. External temperatures are used to regulate their body temperatures.

Neural Control of Thermoregulation

1. The nervous system plays a crucial role in thermoregulation.
2. The hypothalamus of the evolved animal brain is where homeostasis and temperature regulation takes place.
3. The hypothalamus regulates body temperature by activating reflexes that produce vasodilation and perspiration when the body is too hot and vasoconstriction and shivering when the body is too cold.
4. It reacts to substances produced by the body. When phagocytic leukocytes kill bacteria, substances called endogenous pyrogens are released into the bloodstream. The hypothalamus receives these pyrogens, which reset the thermostat.
5. This causes the body’s temperature to rise, resulting in what is known as a fever. As the body’s temperature rises, iron is preserved, reducing a nutrient that bacteria require. Increased body heat boosts the activity of the animal’s enzymes and defensive cells while reducing the invading microorganisms’ enzymes and activities. Finally, the pathogen may be killed by the heat.
6. Fever, which was formerly assumed to be a side effect of infection, is now recognised as a normal defence mechanism.

Micturition

The process of expelling urine from the bladder is known as micturition. Urination is another name for it. Urination is the process of removing metabolic products and toxic wastes from the body that have been filtered from the blood by the kidneys. It’s a sophisticated process combining the sympathetic, parasympathetic, and somatic nervous systems, and the brain’s higher centres allow urinating at the right time. Other crucial aspects in this process include normal muscular tone, the lack of physical blockages, and psychological inhibition.

Anatomy & Physiology

1. The upper and lower urinary tracts are mutually dependent, with the upper tract containing the kidneys and ureters and the lower tract containing the bladder and urethra. The micturition reflex involves the lower tract.
2. The bladder is a hollow organ that serves as a reservoir for storing urine and releasing it on a regular basis.
3. The detrusor is made up of three layers of smooth muscle that line the inside of the bladder.
4. The bladder neck is an outflow into the urethra at the bottom of the bladder that is surrounded by a ring of smooth muscle known as the internal urethral sphincter and is involuntarily controlled.
5. The urethra is the channel via which urine exits the body.
6. The external urethral sphincter is formed when the pelvic floor musculature encircles the urethra and acts under conscious control.
7. Both the internal and external sphincters constrict during storage to prevent leaking.
8. The detrusor muscle is normally relaxed, allowing the bladder to expand when it fills up with urine.
9. The detrusor contracts when the bladder is full, allowing urine to exit the body through the urethra.
10. A normal adult bladder can store \(300 – 500\,{\text{mL}}\) of urine for \(2-5\) hours in a healthy adult.

Mechanism of Micturition

Fig: Micturition

1. Micturition is a complex and dispersed process that involves circuits at several levels of the brain, spinal cord, and PNS, as well as different neurotransmitters.
2. The micturition reflex is triggered when the bladder fills with pee at its most basic level. Until the bladder fills to roughly \(250\,{\rm{mL}}\) with pee, the detrusor muscle remains relaxed.
3. The detrusor muscle contracts when the bladder fills, increasing the pressure inside the bladder and triggering stretch receptors in the detrusor as well as rousing parasympathetic fibres to convey this information to the sacral neurons of the spine.
4. These fibres help in the communication of the bladder’s level of fullness. This information is combined and delivered to the brain via two different sets of neurons within the spine.
5. When the brain detects a sense of urgency, it sends command signals to the bladder, urging it to either hold on or be void.
6. If the response is to be void, parasympathetic motor neurons stimulate the detrusor muscle to contract, increasing intra-bladder pressure.
7. As a result of the increasing pressure, the internal sphincter relaxes, allowing urine to enter the bladder neck and flow into the urethra.
8. Somatic motor neurons inhibit the pudendal nerve at the same time, allowing urine to exit the body by relaxing the external sphincter.
9. Following a voluntary void, approximately 50mL of urine remains in the bladder in a healthy adult.

Stages of Micturition

There are two main stages or phases in the urinary bladder:

1. Resting (filling) stage
2. Voiding stage

1. Resting or Filling Stage

a. Urine is carried from the kidneys to the bladder via the ureters during this phase of the bladder. The ureters are narrow muscular tubes that emerge from each kidney and extend downward, where they obliquely enter the bladder.
b. The ureters’ oblique positioning in the bladder wall provides a critical purpose. There are no sphincters or muscles to protect the entry of the ureter into the urine bladder. As a result of the oblique orientation of the incision, urine cannot re-enter the ureters. At the same time, the detrusor muscle, the main muscle of the urinary bladder, relaxes, allowing the bladder to expand and accommodate more urine.

2. Voiding Stage

a. Both the urine bladder and the urethra are involved during this stage. When the bladder’s storage capacity is achieved, the detrusor muscle of the urine bladder, which had been relaxing, begins to contract.
b. The internal and external urethral sphincters are two muscles that govern the urethra. The internal sphincter is made up of smooth muscles, whereas the external sphincter is made up of skeletal muscles. During the filling stage, both of these sphincters are contracted.
c. Urine passing is controlled by the parasympathetic nervous system. Bladder afferents send signals to the pontine micturition centre and the cerebrum after ascending through the spinal cord. The sacral preganglionic neurons are excited when neurons in the pontine micturition centre fire in response to a voluntary decision to urinate.
d. Following parasympathetic stimulation of the pelvic nerve (nerve roots S2-4), acetylcholine (ACh) is released, which acts on muscarinic ACh receptors (M3 receptors) on the detrusor muscle, causing it to contract and raise intravesicular pressure. The pontine micturition centre also inhibits Onuf’s nucleus, causing relaxation by reducing sympathetic input to the internal urethral sphincter.
e. Finally, a conscious reduction in the external urethral sphincter’s voluntary contraction from the cerebral cortex allows for urethral distention and urine passage.
f. The female’s urination is facilitated by gravity, but the male’s urination is facilitated by bulbospongiosus muscular contractions down the length of the penis.

Neural Control of Micturition

1. The function of the sympathetic nerve: The detrusor muscle of the urine bladder relaxes and the internal sphincter constricts when the nerve is stimulated. As a result, it causes filling.
2. The function of the parasympathetic nerve: When this is stimulated, the detrusor muscle contracts and the internal sphincter relaxes, allowing the urine bladder to empty. As a result, the parasympathetic nerve is also known as the nerve of emptying or micturition.
3. The function of the somatic (pudendal) nerve: It maintains tonic contraction of the skeletal muscle fibres that make up the external sphincter, which keeps it constricted. The somatic (pudendal) nerve is in charge of voluntary regulation of micturition since this nerve is muted during micturition.

Summary

The process by which animal organs and organ systems constantly adjust to internal and external changes is known as Homeostasis (“steady state”). These fluctuations could be caused by changes in blood glucose or calcium levels, as well as external temperatures. The dynamic equilibrium of the body is referred to as “Homeostasis.” It’s dynamic since it’s always responding to the changes that occur in the body’s systems. It is balanced because physiological functions are controlled within exact parameters.

Homeostasis involves the receptor, the control centre, and the effector. The information received by the receptor, which includes information about the changing environment, is processed by the control centre. The effector enhances or opposes the stimulus in response to the control centre’s directives. The process of discharging urine from the bladder is known as micturition or urination. Urination is the process of removing metabolic products and toxic wastes from the body that have been filtered from the blood by the kidneys.

Frequently Asked Questions (FAQs)

Q.1. State homeostasis definition.
Ans: Homeostasis (“steady-state”) is a process by which animal organs and organ systems constantly respond to internal and external changes.

Q.2. Which body systems help to maintain homeostasis?
Ans: The neurological system and the endocrine system are both important in maintaining body homeostasis. Other organs, on the other hand, play a part in maintaining homeostasis.

Q.3. What is micturition?
Ans: The process of urine excretion from the urinary bladder is known as micturition.

Q.4. What are the main components of homeostasis?
Ans: Homeostasis involves three components- the receptor, the control centre, and the effector. The receptor receives information on the changing environment, and the control centre processes the information received by the receptor. The effector responds to the commands of the control centre by enhancing or opposing the stimulus.

Q.5. What is the storage phase and voiding phase?
Ans: The storage phase is characterised by the storage of urine by the urinary bladder. The movement is controlled by the circular sphincter muscles. The voiding phase is said to occur when the brain sends signals to begin urinating until the bladder becomes empty.

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