Important excretory organs in man's body & Structure of urinary system

From Online Sciences - January 3, 2018

The biological processes that occur in the bodies of the living organisms are carried out through the chemical reactions that leave some waste products , The living organism must get rid of these waste products as soon as they are formed , otherwise they will cause many problems and infections , this occurs through the process that is called the excretion .

Importance of excretion in animals

Excretion is the process by which the living organisms get rid of waste products that are produced from the biological processes , The excretion refers only to the materials that leave the body through the plasma membranes .

The important waste products :

There are some materials that are not considered as excretory products as :

Functions of the excretory organs in higher animals :

Excretion in man

The important excretory organs in mans body are : skin , lungs , kidneys and liver , The important waste products of human body and the organs that are responsible for their excretion .


Skin is the biggest organ in the body , as it covers the whole body and the limbs from the outside , The skin consists of two main layers which are an outer epidermis & an inner dermis , It adheres to the body by a layer of fat present under the dermis , Epidermis consists of several layers of epithelial cells .

The surface area consists of dead cells , full of a horny substance called keratin , It arises from the migration of inner layer cells of epidermis to the surface , and then die , It is worn out and continually replaced from the beneath , because it is always subjected to friction ( when wiping your face or body with a towel or rubbing your hands ) .

The inner layer makes a continuous replacement of the surface layer , Its base contains pigment cells which secrete granules called melanin that are responsible for the colour of skin , The epidermal layer of skin acts as a barrier that prevents the penetration of bacteria .

Dermis lies beneath the epidermis , consisting of connective tissues , This layer contains blood capillaries , sensory nerve endings , Lymphatics , sweat glands , sebaceous ( fat ) glands , fatty cells , hair follicles and hair muscles .

Sweat gland

The functional unit of excretion in skin , It is a coiled tube that reaches the skin surface through pores called sweat pores , Its function for extraction of sweat :


Hair is made of a hair follicle surrounded by many blood capillaries , The hair follicle is supplied with an erector muscle to move it when it contracts , At its free end , there is a sebaceous ( fat ) gland which produces an oily secretion to facilitate the exit of hair from the skin and to keep the hair soft and pliable , Sensory nerve endings respond to touch , pain , pressure and temperature .


Each vertebrate animal has two kidneys , In lower vertebrates ( as amphibians ) such as frog : the kidneys are long and thin organs which extend on the two sides of vertebral column .

In higher vertebrates ( as mammals ) : The kidneys are more firm and situated behind the peritoneum ( membrane that lines the abdominal cavity ) , a tube called the ureter runs from each kidney to the base of bladder , through which urine is collected and passed to the outside through the urethra .

Kidney in the human body


Structure of urinary system

Urine extraction

Composition of urine

Artificial kidney



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