Regulation of Kidney Functions and Disorders of Excretory System | Biology Class 11 - NEET PDF Download

 Regulation of Kidney Function 

The regulation of kidney function is a vital process that ensures the body maintains its fluid and electrolyte balance. This regulation is primarily achieved through hormonal feedback mechanisms involving the hypothalamus, the juxtaglomerular apparatus (JGA), and, to some extent, the heart. Let's explore how these components work together to regulate kidney function.

(i) Role of Osmoreceptors

Osmoreceptors in the body play a crucial role in monitoring changes in blood volume, body fluid volume, and ionic concentration. When there is excessive fluid loss from the body, these receptors are activated. This activation stimulates the hypothalamus to release antidiuretic hormone (ADH), also known as vasopressin, from the neurohypophysis. ADH promotes water reabsorption in the later parts of the renal tubule, preventing diuresis (excessive urination).

Conversely, when there is an increase in body fluid volume, the osmoreceptors are switched off, and ADH release is suppressed, completing the feedback loop. Additionally, ADH can influence kidney function by constricting blood vessels, leading to an increase in blood pressure. This rise in blood pressure can enhance glomerular blood flow and, subsequently, the glomerular filtration rate (GFR).

(ii) Role of the Juxtaglomerular Apparatus (JGA)

The JGA plays a complex and critical role in regulating kidney function. When there is a decrease in glomerular blood flow, glomerular blood pressure, or GFR, the juxtaglomerular (JG) cells in the JGA are activated to release renin. Renin initiates a cascade that converts angiotensinogen in the blood to angiotensin I, which is further converted to angiotensin II.

Angiotensin II is a potent vasoconstrictor that increases glomerular blood pressure and, consequently, GFR. It also stimulates the adrenal cortex to release aldosterone. Aldosterone promotes the reabsorption of sodium (Na+) and water from the distal parts of the renal tubule, leading to an increase in blood pressure and GFR. This intricate process is known as the Renin-Angiotensin mechanism.

(iii) Role of Atrial Natriuretic Factor (ANF)

The heart also plays a role in regulating kidney function. When there is an increase in blood flow to the atria of the heart, Atrial Natriuretic Factor (ANF) is released. ANF promotes vasodilation, which decreases blood pressure. The ANF mechanism acts as a counterbalance to the renin-angiotensin mechanism, ensuring that blood pressure and fluid balance are maintained within optimal ranges.

 In summary, the regulation of kidney function involves a complex interplay of hormonal signals and feedback mechanisms. The hypothalamus, JGA, and heart work together to maintain fluid and electrolyte balance, adjusting kidney function as needed to respond to changes in the body's internal environment.

Micturition

•  The urine produced by the nephrons is eventually transported to the urinary bladder, where it is stored until the central nervous system (CNS) gives a voluntary signal for its release. This signaling process is triggered by the stretching of the urinary bladder as it fills with urine. 
• When the bladder stretches, the stretch receptors located on its walls send signals to the CNS. In response, the CNS transmits motor messages to initiate the contraction of the bladder's smooth muscles and the simultaneous relaxation of the urethral sphincter. This coordination leads to the release of urine.
• The act of releasing urine is known as micturition, and the neural mechanisms that cause it are referred to as the micturition reflex.
• On average, an adult human excretes about 1 to 1.5 liters of urine per day. The urine produced is a light yellow, watery fluid with a slightly acidic pH of around 6.0, and it has a characteristic odor.
• Each day, approximately 25-30 grams of urea is excreted in the urine. Various conditions can influence the characteristics of urine, and the analysis of urine is a valuable tool in the clinical diagnosis of numerous metabolic disorders and kidney malfunctions.
• For instance, the presence of glucose in urine, known as glycosuria, and the presence of ketone bodies, called ketonuria, are indicative of diabetes mellitus. 

Role of Other Organs in Excretion

• Lungs: The lungs play a significant role in excretion by removing large amounts of carbon dioxide (approximately 200 mL per minute) and substantial quantities of water daily.
• Liver: As the largest gland in the body, the liver secretes bile containing substances such as bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins, and drugs. Most of these substances are eventually excreted along with digestive wastes.
• Sweat Glands: Sweat glands in the skin eliminate certain substances through their secretions. Sweat, which is primarily a watery fluid containing sodium chloride (NaCl), small amounts of urea, and lactic acid, helps cool the body but also aids in the removal of some waste materials.
• Sebaceous Glands: Sebaceous glands secrete sebum, which contains sterols, hydrocarbons, and waxes. This secretion provides a protective oily covering for the skin while also eliminating certain substances. 
• Saliva: Interestingly, small amounts of nitrogenous wastes can also be eliminated through saliva. 

Disorders of the Excretory System

1. Uremia. When the kidneys malfunction, urea can build up in the blood, leading to a dangerous condition called uremia. This condition is harmful and can result in kidney failure. 

Hemodialysis. 
In cases of uremia, urea can be removed from the blood through a process called hemodialysis. During hemodialysis, blood is drained from a convenient artery and pumped into a dialyzing unit known as an artificial kidney. 

• Process of Hemodialysis. The procedure involves several steps: Blood drained from an artery is treated with an anticoagulant like heparin to prevent clotting. It is then pumped into a dialyzing unit containing a coiled cellophane tube surrounded by a dialysing fluid. The dialysing fluid has the same composition as blood plasma, except for nitrogenous wastes. 
• Function of the Cellophane Membrane. The cellophane membrane is porous and allows molecules to pass through based on the concentration gradient. Since nitrogenous wastes are absent in the dialysing fluid, these substances move out of the blood, effectively clearing it. 
• Returning Cleared Blood. After the blood is cleared, it is pumped back into the body through a vein. An anti-heparin is added to prevent clotting. Hemodialysis is a lifesaving procedure for thousands of uremic patients worldwide.

Kidney Transplantation
This is the most effective method for treating acute renal failure. During a kidney transplant, a functioning kidney from a donor, preferably a close relative, is transplanted into the patient. This helps reduce the risk of the kidney being rejected by the patient’s immune system. Modern clinical procedures have improved the success rate of kidney transplantation, making it a viable option for many patients with kidney failure. 

2. Renal Calculi. Also known as kidney stones, these are solid masses of crystallized salts, such as oxalates, that form within the kidney.

3. Glomerulonephritis. This condition involves the inflammation of the glomeruli in the kidneys, which can affect their filtering ability.