What went wrong when the king rode under the arch?

It was too low and knocked off his crown

How does the chain of blame unfold in the poem?

Each accused person blames another, ending with the king's own changes

Define glomerular filtration rate.

It is the amount of filtrate formed by the kidneys per minute, approximately 125 mL or about 180 litres per day.

What are the three main processes of urine formation?

Glomerular filtration, tubular reabsorption and tubular secretion.

Why is glomerular filtration called ultrafiltration?

Because blood is filtered so finely through three layers that almost all plasma constituents except proteins pass into the Bowman's capsule.

Distinguish between ammonotelic, ureotelic and uricotelic animals.

Ammonotelic animals excrete ammonia, ureotelic animals excrete urea, and uricotelic animals excrete uric acid, requiring progressively less water.

Give a brief account of the counter current mechanism.

The opposite flow of filtrate in the limbs of the loop of Henle and of blood in the vasa recta maintains an increasing osmolarity towards the inner medulla, which helps concentrate the urine.

Describe the role of liver, lungs and skin in excretion.

The lungs remove carbon dioxide and water, the liver excretes bile pigments, cholesterol and drugs, and the skin removes water, salts and urea through sweat and sebaceous secretions.

Explain the autoregulatory mechanism of GFR.

The juxtaglomerular apparatus releases renin when GFR falls, which through angiotensin increases glomerular blood pressure and restores GFR.

What is the significance of the juxtaglomerular apparatus?

It is a sensitive region that regulates glomerular filtration rate by releasing renin in response to a fall in glomerular blood flow or pressure.

How is kidney function regulated by hormones?

ADH promotes water reabsorption, the renin-angiotensin-aldosterone mechanism raises blood pressure and sodium reabsorption, and atrial natriuretic factor lowers blood pressure.

What is haemodialysis and why is it used?

It is a process that removes urea and other wastes from the blood of uraemic patients using an artificial kidney with a dialysing fluid, when the kidneys fail.

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Chapter 16: Excretory Products and their Elimination — Class 11 Biology

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Chapter 16: Excretory Products and their Elimination

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Mammals that excrete nitrogenous waste mainly as urea are called:

Summary

This chapter explains how animals remove nitrogenous and other wastes, focusing on the human excretory system. Ammonia, urea and uric acid are the major nitrogenous wastes; ammonotelic animals excrete ammonia, ureotelic animals such as mammals excrete urea, and uricotelic animals such as reptiles and birds excrete uric acid with minimum water loss. Excretory structures include protonephridia, nephridia, Malpighian tubules and green glands in invertebrates, and kidneys in vertebrates. The human excretory system comprises a pair of kidneys, ureters, a urinary bladder and a urethra; each kidney has about a million nephrons, the functional units, each consisting of a glomerulus enclosed in Bowman's capsule and a renal tubule (proximal convoluted tubule, loop of Henle and distal convoluted tubule) leading to a collecting duct. Urine formation involves glomerular filtration (ultrafiltration of blood, about 125 mL per minute), selective reabsorption of nearly 99 per cent of the filtrate, and tubular secretion of ions to maintain ionic and acid-base balance. A counter current mechanism between the loop of Henle and the vasa recta concentrates the urine. Kidney function is regulated by ADH, the renin-angiotensin mechanism and atrial natriuretic factor. Micturition releases urine, other organs such as lungs, liver and skin assist in excretion, and disorders include uraemia, treated by haemodialysis, and kidney stones.

Nitrogenous wastes and excretory structuresHuman excretory system and the nephronUrine formation: filtration, reabsorption, secretionConcentration of urine and counter current mechanismRegulation of kidney function and micturitionRole of other organs and excretory disorders

Key terms

Nephron

The functional unit of the kidney, consisting of a glomerulus and a renal tubule.

Glomerular filtration

The ultrafiltration of blood in the glomerulus, the first step of urine formation.

Glomerular filtration rate

The amount of filtrate formed by the kidneys per minute, about 125 mL in a healthy individual.

Reabsorption

The return of nearly 99 per cent of the filtrate to the blood by the tubular cells of the nephron.

Counter current mechanism

The arrangement of the loop of Henle and vasa recta that maintains an osmotic gradient to concentrate urine.

Micturition

The process of release of urine from the urinary bladder, controlled by the micturition reflex.

Important questions

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The functional unit of the kidney, consisting of a glomerulus and a renal tubule.

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Practice quiz · Excretory Products and their Elimination

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