Unit 4: Human Urinary System — Short Questions

Urinary system of human consists of:
(a) A pair of kidneys
(b) A pair of ureters
(c) A urinary bladder
(d) A urethra

Kidneys are the main organs of urinary system. Renal arteries supply them blood with metabolic wastes (e.g., urea, extra water and salts). Kidneys filter these wastes from blood and then remove in the form of urine out of the body.

Parts of a Nephron
A nephron consists of two parts i.e., renal corpuscle and renal tubule.
1. Renal corpuscle: It is the first part of nephron and is composed of glomerulus and the Bowman's capsule.
(a) Glomerulus: The glomerulus is a network of capillaries while the.
(b) Bowman's capsule is the cup-shaped structure around the glomerulus.
2. Renal Tubule: It is a long tube attached with the Bowman's capsule. It has three parts.
(a) Proximal Convoluted Tubule: The first part is convoluted and is called the proximal convoluted tubule.
(b) Loop of Henle: The middle part is U-shaped and is called the Loop of Henle.
(c) Distal Convoluted tubule: The last part is again convoluted and is called the distal convoluted tubule.
(d) Collecting Duct
The distal convoluted tubules of many nephrons open in a single collecting duct. Many collecting ducts join together and open into the renal pelvis.

Sometimes, the filtered minerals and salts (e.g., calcium oxalate, calcium and ammonium phosphate, and uric acid etc.) gather in kidneys and make hard, crystalline deposits. Such deposits cannot pass in urine and are called kidney stones. Some stones may leave kidneys and may be trapped in ureter or urinary bladder.

Lithotripsy is a method for the removal of kidney stones. In lithotripsy, non-electric shock waves are bombarded on kidney from outside. The waves hit the stones and break them into smaller pieces, which pass out through urine.

When one or both kidneys are not able to perform their function (removing waste materials from blood and then passing them out), the condition is called kidney failure.

Treatment of Kidney Failure
(a) Dialysis
(i) Haemodialysis
(ii) Peritoneal Dialysis
(b) Kidney Transplantation

i. Excretion and Osmoregulation.
Excretion: Excretion is a process of homeostasis. In this process metabolic wastes are eliminated from the body to maintain the internal conditions at equilibrium otherwise it may harm the body.
Osmoregulation: Osmoregulation is also a process of homeostasis. Kidneys control the chemical composition of blood. They take extra and waste materials from blood and convert them to urine. It occurs in three steps.

ii. Renal cortex and renal medulla
Renal cortex: Internally the outer region of kidney is called renal cortex.
Renal medulla: Internally the inner region of kidney is called renal medulla. It is light brown in colour.

iii. Renal corpuscle and renal tubule
Renal corpuscle: It is the first part of nephron and is composed of glomerulus and the Bowman's capsule.
Renal tubule: It is a long tube attached with the Bowman's capsule. It has three parts i.e. (a) Proximal Convoluted Tubule (b) Loop of Henle (c) Distal Convoluted Tubule

iv. Pressure filtration and tubular secretion
Pressure filtration: When blood reaches glomerulus, its pressure is very high. So, many small molecules (water, salts, glucose and urea etc.) move out of glomerulus. These materials enter Bowman's capsule This step is called pressure filtration.
Tubular secretion: When useful materials are reabsorbed into blood, some of the remaining wastes present in blood capillaries to renal tubule. It is an active transport process and is called tubular secretion.

v. Haemodialysis and Peritoneal dialysis
Haemodialysis: Membrane of dialysis machine is used as dialyzer. Dialysis fluid automatically keep on circulating and replaced during the procedure.
Peritoneal Dialysis: Peritoneum in abdominal cavity is used as dialyzer. Dialysis fluid remains stagnant in peritoneal cavity during the procedure, so it has to be replaced repeatedly.
Patient has to be hospitalized and remain connected with machine during the dialysis.
It can be performed at home and the patient remain free to do routine work during the dialysis.

[Diagrams labeled with kidney structure showing: Renal Pyramid, Glomerulus, Proximal Convoluted Tubule, Distal convoluted tubule, Renal Artery, Renal Cortex, Renal Calyx, Renal Vein, Ureter, Renal Pelvis, Bowman's Capsule, Arteriole, Loop of Henle, Collecting duct]

The body cells form a variety of waste, and if these substances are allowed to accumulate, their effects are likely to be toxic. The blood and lymph carry wastes away from the tissue that produce them. Urinary system of human removes these wastes (various salts and nitrogenous waste) from the blood and transport them to outside the body

1. Kidney
It performs the following functions:

• Remove metabolic waste products i.e., urea and other nitrogenous waste from the blood.
• Regulates water content of the body fluid.
• Regulates the pH of the body fluid.
• Remove excess of water, salts, hormones and drugs.

2. Ureter: From the kidney a thin tube ureter, comes to the urinary bladder.

3. Urinary bladder: The bladder is an elastic muscular bag which stores urine.

4. Urethra: The urinary bladder has only one exit, a tube called urethra which leads out of the body

5. Pelvis of Kidney: It is the hollow chamber and it is the enlarged end or base of the ureter within the kidney.

6. Capsule of Kidney: The Bowman's capsule is a double –walled hollow cup that surrounds a tuft of blood capillaries known as glomerulus.

7. Dialysis: Dialysis is a process for removing waste and excess water from the blood.

The right kidney is 2-8 cm lower than the left kidney, because of the large liver which sits superior to it.

A ring of sphincter muscles near the junction of the urethra and the urinary bladder controls the urine in the bladder. When about 300 to 400 ml urine is collected in the bladder, we need to discharge it. In babies, this sphincter is not developed properly hence they are not able to control their urination.

During reabsorption, about 99% of the water and the most of the solutes (glucose amino acids, and salts) that enter the nephrons are returned to the blood stream as the filtrate flows along the nephron.

Urine primarily consists of water and waste products with about 95% water and 5% solids. These solid include nitrogenous wastes like urea, ammonia and creatinine. Additionally, urine carries inorganic salts and other electrolytes such as sodium, potassium and calcium.

Selective reabsorption takes place in "Renal Tubule" In this step about 99% of the glomerular filtrate is reabsorbed into the blood capillaries surrounding renal tubule.

(a) A-Glomerulus, B-Bowman's capsule.
A: The glomerulus of the nephron filters the blood and produces glomerular filtrate.
B: The Bowman's capsule collects the glomerular filtrate and passes it to next parts of the nephron.

(b) In case of shortage of water in body fluids, kidneys filter less water from glomerular capillaries and the rate of reabsorption produces small amount of concentrated urine. It increases the volume of body fluids to normal. This whole process is under hormonal control.

(i) Urinary tract infections
(ii) Kidney stones
(iii) Kidney failures

The causes of kidney stone are:
(i) Presence of high level of calcium in the blood because of other diseases.
(ii) Presence of high level of oxalate in the blood results in the formation of calcium oxalate stones.
(iii) A decrease in water intake.
(iv) Age and family history

Kidney Transplant
The kidney of a healthy person can be transplanted to diseased one. The kidney may be donated by a donor The tissue and blood chemistry of the donor should be similar to that of the patient. If the kidney is not matching 'tissue rejection' may occur and the patient's immune system destroys the donated kidney

1. Kidney Failure
If one kidney fails to function, the person can still live a normal life with another kidney. If both the kidneys fail to work, it is fatal. A general term for declined kidney function is called kidney failure. It may lead to increase in urea in blood. The rise in urea causes increase in blood pressure and anemia etc If kidney failure is not treated, death will result within a couple of weeks.

2. Treatment of Kidney Failure

• Dialysis To remove the nitrogenous wastes, the blood of the patient is treated through dialysis. Dialysis is a process for removing waste and excess water from the blood.
• Types of Dialysis There are two types of dialysis. (a) Haemodialysis (b) Peritoneal dialysis

Humans are made up of 60-70% water. There are many benefits of drinking plentiful water. Water can help us eat less, look younger and remove toxins and waste products from body. If our body lacks water then our heart has to make an extra effort and pump blood. Water can help relieve headache and back pain. It can also increase metabolic rate and improve digestive system. It can help to strengthen immune system.

In high degree renal failure transplantation is the only solution. Matching donor kidney is needed for transplant. Best donor is twin or any close relative. The average survival time of donor kidney is 10 to 15 years. A second kidney transplant is also possible.

Along with removing metabolic wastes (excretion), the kidneys play a vital role in osmoregulation, which is the regulation of water and salt balance in the body.

• Kidneys regulate the amount of water in the blood by adjusting how much water is reabsorbed from the filtrate in the nephrons.
• They also control the concentration of electrolytes such as sodium, potassium, and chloride by selective reabsorption or excretion.
• When the body has excess water, kidneys excrete dilute urine, and when water is scarce, they conserve water by producing concentrated urine.
• This process helps maintain a constant osmotic pressure and volume of body fluids, which is essential for normal cell function.

The nephron ensures that essential nutrients are not lost in urine through the process of selective reabsorption.

• When blood is filtered in the glomerulus, useful substances like glucose, amino acids, salts, and water pass into the filtrate.
• As this filtrate moves through the renal tubules, the nephron selectively reabsorbs essential nutrients back into the blood through surrounding capillaries.
• Glucose and amino acids are completely reabsorbed, while water and salts are reabsorbed according to the body's needs.
• Only waste products such as urea, excess salts, and excess water remain in the filtrate and are excreted as urine.

Some water is reabsorbed from descending limb of the loop of Henle. Large amounts of salts are reabsorbed from ascending limb of the loop of Henle.

Chronic diseases like diabetes can lead to kidney failure because they damage the small blood vessels and filtering units of the kidneys over time.

• Kidneys filter waste from the blood using tiny structures called nephrons.
• In diabetes, blood sugar levels remain high for a long time. High blood sugar damages the small blood vessels in the nephrons.
• This reduces the kidney's ability to filter blood properly.
• Proteins and useful substances may leak into the urine.
• Gradually, more nephrons stop working.
• When many nephrons are damaged, the kidneys fail to remove wastes and excess water from the body.