Micturition and Urinary System - Class XI

A completely full urinary bladder is capable of holding approximately 500-600 ml of fluid. The urge to urinate occurs when the bladder contains about 150-200 ml of urine. The urge to urinate is stimulated by expansion of of the bladder. As the bladder walls fill with urine and expand, stretch receptors are stimulated and the micturition reflex is triggered. The micturition reflex centre is located in the spinal cord. 

The distal convoluted tubule (DCT) reacts to the amount of anti-diuretic hormone (ADH) or vasopressin in the blood. The more ADH is present in the blood, the more water is reabsorbed into it. This happens because the presence of ADH in the blood causes the cells in the DCT to become more permeable to water, therefore they allow more water to pass from the tubular fluid back into the blood. This results in more concentrated urine.

Micturition or urination is the process of expelling urine from the bladder. This act is also known as voiding of the bladder. The process of micturition is regulated by the nervous system and the muscles of the bladder and urethra. The urinary bladder can store around 350-400ml of urine before it expels it out.

The shared terminal duct of the reproductive and urinary system in the human male is urethra. In human male urethra is urinogenital duct which carry both urine and sperm. 

Urine reaches the urinary bladder from the kidney to the urinary bladder via the tube-like structure called the' ureter'. While urethra is the channel that conveys the urine from the bladder to the exterior. 

Urine is formed in the kidney. From the kidney through two tubes called ureters the urine descends into the urinary bladder. From the urinary bladder, urine is excreted to outside through urethra. So the correct path taken by urine in our body is kidneys, ureters, urinary bladder, urethra.

Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adrenal cortex to promote sodium retention by the kidneys.

During micturition, parasympathetic stimulation causes the detrusor muscle to contract and the internal urethral sphincter to relax. The external urethral sphincter (sphincter urethrae) is under somatic control and is consciously relaxed during micturition. 

Stretch receptors in the bladder wall detect fullness and trigger the micturition reflex. If these are removed, the brain does not receive the signal to void, preventing micturition.

During micturition, urine is expelled from the urinary bladder. This requires the contraction of the detrusor muscle of the bladder wall and the relaxation of both the internal urethral sphincter and the external urethral sphincter. Therefore, statements (i) and (ii) are relaxed, making option C correct.

On a humid day the water loss due to sweating will be less. If a man consumed large amounts of water or salt then the body will try to excrete out extra water and salt by increasing the urine output. In this condition the amount of ADH secretion is low and the water reabsorption in the DCT is low, making the urine hypotonic.

When the weather is hot, our body system tries to keep our body cool by evaporating the water along with unwanted things (sweating) through the skin in the form of perspiration. So, skin helps the kidney by sharing its work of cleaning the body in hot weather. In cold conditions, as sweating is much decreased, there is no perspiration and the kidney has to bear the entire burden of excretion and hence we urinate frequently.

The waste products from the blood are removed by the kidneys in the form of urine. This is done by filtering of the blood. In human adults, the normal range of urinary output is between 400 to 2000 ml daily. The amount of urine produced by the body depends on the health of the person.

Urine is a liquid created by the body in the kidneys. It is stored in the bladder and comes out of the human body through the urethra, a tube which leads from the bladder to the urethral meatus, at the tip of the penis (men) or the vulva (women). Urinating is how the body gets rid of unwanted or unneeded substances in the blood. Urine is the liquid that these substances are put in. After the blood has circulated through the body, its composition has changed, because some substances in the blood have been absorbed by the body and because the body has released other substances into the blood. 

Urine becomes hypertonic because of the loop of Henle and the collecting duct.  Salt passively diffuses out of the lower portion of the ascending limb. The upper part of ascending limb actively transports salt into the tissue of the renal medulla. Urea leaks from the lower portion of collecting duct and contributes to a high solute concentration. Water leaves descending limb of the loop of Henle, returning to the blood. Hence, urine is hypertonic to blood and isotonic to medullary plasma.

The more ADH is present in the blood, the more water is reabsorbed into it. This happens because the presence of ADH in the blood causes the cells in the last section of the DCT to become more permeable to water, therefore they allow more water to pass from the tubular fluid back into the blood. This results in more concentrated urine.

The more ADH is present in the blood, the more water is reabsorbed into it. This happens because the presence of ADH in the blood causes the cells in the DCT to become more permeable to water, therefore they allow more water to pass from the tubular fluid back into the blood. This results in more concentrated urine.

Deamination is the process by which amino acids are broken down if there is an excess of protein intake. Deamination takes place in the liver. The amino group is removed from the amino acid and converted to ammonia. Ammonia is toxic to humans, so the enzymes convert it to urea or uric acid by addition of carbon dioxide molecules, which also takes place in the liver. Urea and uric acid is excreted in urine.

As urea is the main excretory product of mammals and if the person is starving, he will have less urea in his urine.

The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys filter the blood to remove wastes and produce urine. The ureters, urinary bladder, and urethra together form the urinary tract, which acts as a plumbing system to drain urine from the kidneys, store it, and then release it during urination, respectively. Besides filtering and eliminating wastes from the body, the urinary system also maintains the homeostasis of water, ions, pH, blood pressure, calcium and RBCs.

Vitamin C is excreted in human urine because it is water soluble vitamin. 

(A) Epinephrine is related to the adrenal gland and is released during stress or emergency situation. 

• In nephrons, potassium ion, sodium chloride, calcium ion, amino acids, glucose, bicarbonate ion, and water are reabsorbed back into the bloodstream. 
• The glomerular filtrate contains a lot of water, but also important molecules like glucose, amino acids, salts, and excretory material, urea.
  
• Urine is an aqueous solution of greater than 95% water. Other constituents include urea, chloride, sodium, potassium, creatinine and other dissolved ions, and inorganic and organic compounds. Urea is a non-toxic molecule made of toxic ammonia and carbon dioxide.
  

1. Annelids have nephridia and insects have malphaghian tubules for excretion.
2. Blood enters the glomerulus via afferent arteriole and leaves via efferent arteriole.
3. During micturition, the urinary bladder contract and urethral sphincters relax to let the urine pass out from the body.

• Micturition is carried out by the parasympathetic reflexes.
• ADH hormone helps in the reabsorption of water making the urine hypertonic.
• All the large proteins, cells remain in the blood and pass into the tubule due to the presence of bowman's capsule.
• Glucose, and other important ions get reabsorbed from the PCT.
• Thus, the correct answer is 'T, F, T, T'.

Mammals, many terrestrial amphibians mainly excrete urea and are called ureotelic animals. The urea is excreted in aqueous solution in more liquified form, called urine. Urine formation involves three main processes namely, glomerular filtration, reabsorption and secretion, that takes place in different parts of the nephron.

Process of urination involves these following steps: - 

Urine is a liquid excretory product of the body excreted by the kidneys through a process called urination (or micturition) and excreted through the urethra. Urine contains urea and water. A urea is toxic it needs water to be excreted from the body.

The final passageway for urine out of the bladder is through the thin-walled urethra. This tube runs from the base of the urinary bladder to the outside of the body. In the female, it is relatively short, connecting the bladder to the external urethral sphincter. In males, it is longer. It passes through the prostate gland and travels the length of the penis before reaching the external sphincter. 

The blood is filtered by the kidney and the urine is formed. Urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. It is a hollow muscular, and distensible (or elastic) organ. Urine enters the bladder via the ureters and exits via the urethra. 

The urinary system is involved in the excretion of nitrogenous waste products such as urea, uric acid or ammonia. The excretion of nitrogenous waste from animals is important because if it is allowed to build up, it can prove toxic. The waste product is formed due to the breakdown of the amino acids.

The muscular part of the bladder wall is called the detrusor muscle. The internal and external sphincter muscles surround the bladder neck and the urethra. While the bladder is filling, the detrusor muscle is relaxed so the bladder wall can expand, and the sphincter muscles are contracted to keep the urethra closed. Sympathetic stimulation is predominant during bladder filling, and the parasympathetic causes emptying. Thus, option D is correct and other options are wrong.

The feeling of fullness sensation of urine is marked if the volume of urine increases up to 600 c.c.

Urine which is a waste product of the human system is 95% water. Remaining 5% contains urea, uric acid, creatinine,
sodium chloride, hormones, carbohydrates, fatty acids, enzymes, mucins
and pigments. While diets play a role in the excretory systems, the protein rich diet does not bring in any changes in the uric acid levels in urine.

The feeling to pass urine after a meal is often associated with the increased fluid intake from food and beverages, which increases the volume of urine produced.

The normal range for 24-hour urine volume is 800 to 2,000 milliliters per day (with a normal fluid intake of about 2 liters per day). Micturition or urination is the process of expelling urine from the bladder. This act is also known as voiding of the bladder. The excretory system in humans includes a pair of kidneys, two ureters, a urinary bladder, and a urethra. So the correct option is '1-2 liters production /day'.

The purines metabolism occur by the action of the enzymes released by the liver and intestine which help in the formation of xanthine which finally converts into uric acid as the end product.

Urination is the release of urine from the urinary bladder through the urethra to outside of the body. It is also known medically as micturition. Micturition occurs when the bladder neck and the external urinary sphincter relax and the bladder contracts, allowing for the unobstructed expulsion of urine.