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PinkMonkey Online Study Guide-Biology

19.3 Skin and Lungs as Accessory Excretory Organs

In addition to the urinary system, the skin, lungs and liver of vertebrates are accessory excretory organs.

(1) Skin: Human skin possesses glands for secreting two fluids on its surface, namely sweat from the sweat glands and sebum from sebaceous glands. (Fig. 19.7). Sweat is a watery fluid containing in solution primarily contains sodium-chloride, lactic acid, urea, amino acids and glucose. It helps in excreting mainly water and sodium chloride, and a small amount of urea and lactic acid.

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Figure 19.7 Vertical Section of the Skin

Sebum is a wax-like secretion which helps to excrete some lipids such as waxes, sterols, other hydrocarbons and fatty acids on the skin.

(B) Lungs: Lungs which are the main respiratory organs of vertebrates, help to eliminate the entire volume of carbon dioxide produced in the body, as well as some moisture, during expiration. The lungs maintain the blood-gas homeostasis through elimination of carbon dioxide. When lungs fail to eliminate enough carbon dioxide, the kidneys attempt to compensate. They change some of the carbon dioxide into sodium bicarbonate, which becomes part of the blood buffer system.


(1) Excretion is the removal of nitrogenous waste products from the body. (2) Animals are classified as ammoniotelic, ureotylic, uricotylic and guanotelic according to the predominant excretory product excreted. (3) Kidneys are the most important excretory organs of mammals. Through filtration, reabsorption and active transport, waste is remove, but kidneys conserve substances useful to the organisms. (4) In general, kidneys regulate the intake and the outflow of water and salts in the blood and help to maintain homeostasis. (5) Regulation of kidney function is achieved by certain hormones such as antidiuretic hormone, aldosterone and angiotensin. (6) Skin and lungs also act as accessory excretory organs.



Table of Contents

19.0 - Introduction
19.1 - Ammonotelism, Ureotelism and Uricotelism
19.2 - Excretory System of Man
19.3 - Skin and Lungs as Accessory Excretory Organs

Chapter 20


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