Final Chapter 3

the method of expulsion of metabolic wastes excreted from the body.

1. Filtration and excretion from the blood of toxic wastes produced by the metabolic reactions of cells. 2. The maintenance of homeostasis by the balance of water and the ionic content of the blood and tissue fluid. 3. The maintenance of the normal functions of the cells and the regulation of blood content.

 Unicellular and fresh water organisms like paramecium and amoeba provide excretion by aid of contractile vacuoles.

discharge excess amount of water from cytoplasm.

There is no specialized system of excretion in plants. However, there are some organs are concerned with excretory processes, they are: stomata, lenticels, hydathodes, vacuoles, and roots. Some plants excrete organic and inorganic salt into the soil by their Plants living in calcium rich soils store nitrogenous wastes in their vacuoles in form of calcium Oxalate crystals and expelled when the leaves are shed. Plants also convert nitrogenous wastes into color pigments in their petal.

Carbon dioxide and water is excreted through lenticels and stomata.

water and salt is released from plants living in marshy environments through hydathodes in form of drops.

the method of expulsion of metabolic wastes excreted from the body.

 Waste is excreted by means of protonephridia which consist of tubules and connected flame cells.  The cilia of these flame cells are constantly in motion and elongates into tubules to excreted wastes and excess water.  The motion of the cilia of flame cells resembles flames and for this characteristic the name of flame cells is given.  Wastes and excess water are excreted by means of these ciliary movements and the water balance of the body is regulated by these flames like protonephridia.  NH3 and CO2 diffuse directly from the body.

 Pair of nephridia which function as excretory organs are located in each segment of earthworm.  A ciliary funnel shaped tip of each nephridium open to each subsequent segment.  The canals of each nephridium covered by network of capillaries.  Water, glucose, and minerals are taken up from the body fluid by cilia.  Although water and food are reabsorbed from the canals by capillaries, wastes are expelled from the nephridiopore.  Additionally, some cells of the earthworm are specialized in water absorption.  A group of these cells is located on the ventral outer surface of the intestines.  Waste is absorbed and is transferred to the body wall.  These cells involved in waste removal protect the internal organs of earthworms against ultraviolet light.  Earthworms breaking down organic materials and adding nutrients to the soil, earthworms also help loosen the soil so air can circulate.  This helps plants grow.

 In insects CO2 is excreted by means of tracheal vessels or tracheoles.  Malphigian tubules are involved in excretion of nitrogenous wastes.  One end of the malpighian tubules is blind and branches into the body cavity whereas the other end opens into last portion of digestive tract.  Metabolic wastes are carried from the body cavity to this last portion of the digestive tract by malpighian tubules and ingested water is reabsorbed from the intestine.  The nitrogenous wastes of insects are uric acid which is expelled in the feces.

are the main excretory organs of vertebrates

1. Pronephros 2. Mesonephros 3. Metanephros

 It is composed of laterally ordered nephridia.  The initial portion of a nephridium resembles a ciliary funnel.  The canals generated from the funnels of many nephridia combine with each other to form each canal which opens into the cloaca.  Each ciliary funnel connected directly to a ball of blood capillaries (glomerulus).  The wastes filtered from the glomerulus pass through the body cavity and collected by ciliary funnels and are expelled through the cloaca.  This kind of kidney is found in the embryonic stage of all vertebrates and in adult sharks.

This type of kidney differs from a pronephros kidney in that the ciliary funnels replaced with Bowman`s capsules.  Additionally, a glomerulus located in each Bowman`s capsule and waste flows directly into it from each glomerulus.  Channels drain from each Bowman`s capsule and drain into the mesonephric duct.  This type of kidney is found in the embryonic stage of reptiles, birds and mammals and in the adult form of fish and amphibian.

 This type of kidney found in adult reptiles, birds and mammals.  Metanehpros kidneys are found in pairs and located at abdomen of the body.  Each kidney contains millions of nephrons.  The first excretory channel splits into two and also known as wolf channel.  In fish and amphibian, its functions as a part of both of excretory and reproductive system.  All vertebrates excluding mammals have a single channel through which all wastes are excreted.  The same channel also forms a part of reproductive system.  In mammals however, a separate channel exists for the expulsion of waste and in reproduction.

A. Kidneys B. Urinary tract or Ureter C. Urinary bladder D. Urethra.

are two bean-shaped organs situated in the lower thoracic region of the back

1-Renal Cortex 2-Renal Medulla 3-Renal Pelvis

It is red in color and contains the Malpighian bodies, comprising the Bowman's capsule and glomerulus, which give it its rough structure.

It is located directly beneath the cortex. Urinary tracts which drain from the cortex form pyramids in this region. There are approximately (8-10) laterally arranged Malpighian pyramids. The apex of each pyramid is located in the medulla and its base is located in the cortex.

It forms the inner most portion of the kidney. Its function is the collection of urine from the Malpighian pyramids, the site of 15-20 orifices opening into the pelvis. The pelvis transmits the accumulated urine to the ureter.

nephrons

1200 nephrons

180،،، 1.5

It is a U-shaped, semi-spherical structure. The inner surface consists of squamous epithelial cells. The Bowman's capsule forms the tip of the nephron.

It is a ball of arterial capillaries located in the Bowman's capsule. Each glomerulus is formed by capillaries from a branch of the afferent renal arteriole.

It comprises a Bowman's capsule and glomerulus.

It is beneath the Malpighian body. It is formed from cuboidal epithelial cells.

extends into the loop of Henle and then into the distal convoluted tubule. The total length of these tubules that constitute a nephron in humans is approximately 5 cm.

is the primary nitrogenous waste product, but it is highly toxic. It is the excretory substance of freshwater organisms. Humans produce urea as an excretory product.

 They are muscular tubes which connect the kidneys and the back wall of the bladder.  They transport urine from kidneys to bladder.  Each ureter consists of smooth muscles and each one is (22cm) long.

 It is a sac which stores urine and it consists of smooth muscles.  In the connection point of the bladder with urethra, there are circular striated muscles.  These muscles are voluntary muscles so we can control these muscles or we can control the urination by means of these muscles.  When the bladder contracts, the urination happens.

A. glomerular filtration B. Tubular reabsorbed C. Tubular secretion

 Glomerular filtration of water, various ions, amino acids, sugar and the nitrogenous wastes. These substances pass to the Bowman's capsule from the glomerulus.

 All amino acids, glucose and some urine are reabsorbed at the proximal convoluted tubule.  Sodium, chloride and bicarbonate ions are reabsorbed and are taken up by cells by active transport.  However, 99% of water is reabsorbed passively from different regions of the tubule.

 The cells of the distal convoluted tubule excrete molecules such as penicillin, ammonia, hydrogen, potassium, pigments and excess acids.  At the end, urine is formed and excreted into the urinary bladder via the ureters.