Biology · Class 11 Science

Ch 15Excretion and Osmoregulation — Class 11 Biology, concept-first.

Every living cell constantly runs a huge set of chemical reactions collectively called metabolism — the breaking-down (catabolic) reactions and the building-up (anabolic) reactions that keep the organism alive.

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Modes Of Nitrogenous Excretion

Ammonotelism, ureotelism and uricotelism based on excreted nitrogen form.

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15.1

Excretion and Excretory Products

15.1.1

Modes of Nitrogenous Excretion

Ammonia is the direct, unmodified product of deamination, and it is also the most toxic of the three nitrogenous waste forms an animal can excrete.

15.1.2

Osmoregulation, Osmoconformers and Osmoregulators

Excretory organs do far more than simply remove waste — they are central to homeostasis, the maintenance of a stable internal environment, because the composition of the blood (and so of every tissue)…

15.1.3

Excretory Structures Across the Animal Kingdom

Before the vertebrate kidney evolved, the animal kingdom experimented with several very different excretory arrangements, and simpler organisms still rely on them today.

15.2

Excretory System in Human Being: Gross Anatomy

In humans, the excretory system is built around a pair of bean-shaped kidneys, positioned one on either side of the vertebral column, spanning roughly from the 12th thoracic vertebra to the 3rd lumbar…

15.2.1

Internal Structure of the Kidney

Each kidney is wrapped in three protective tissue layers. The outermost, the renal fascia, is a thin sheet of fibrous connective tissue that anchors the kidney to the abdominal wall and to nearby tiss…

15.2.2

Nephron: Structure and Regions

The nephron is the structural and functional unit of the kidney — each kidney has close to a million of them.

15.2.3

Juxtaglomerular Apparatus and Renal Blood Supply

Where the very start of the DCT of a nephron loops back and touches the afferent arteriole of that same nephron, two specialised cell populations meet to form the juxtaglomerular apparatus (JGA).

15.3

Urine Formation

Urine formation happens in three successive steps: ultrafiltration (glomerular filtration), selective reabsorption, and tubular secretion (augmentation).

15.4

Concentration of Urine: The Countercurrent Mechanism

Under conditions such as low water intake or heavy sweating, the human kidney can concentrate urine to almost four times the osmolarity of blood — up to about 1200 mOsm/L, against blood's normal 300 m…

15.5

Composition and Hormonal Regulation of Urine

Normal human urine is a pale-yellow, transparent liquid, its colour coming from the pigment urochrome; its exact composition varies with the food and fluid a person has consumed.

15.6

Role of Skin and Lungs in Excretion

Excretion is not the kidney's job alone; two other organs make a real, if smaller, contribution.

15.7

Disorders and Diseases of the Excretory System

The excretory system is subject to a number of well-recognised disorders, each traceable to a specific point of failure in filtration, reabsorption, or the tubes and organs that store and carry urine.

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