The Concept of Excretion

Other excretory products include chemicals from medicines, toxic substances, and circulating

• Carbon dioxide:This is a by-product of respiration of both plants and animals. It is excreted

through the pores of the stomata in plants (Some of the carbon dioxide produced by respiration is used in photosynthesis). In man, carbon dioxide is eliminated from the body by lungs.

• Water:The concentration of water in cells must be kept within narrow limits. Too litle oF too

much water can have a negative effect on the osmotic condition in and around the cell Therefore, it has to be regulated, Plant cells are protected from bursting by theit cell walls Animals do not have cell walls, and will burst if they have too much water. Exeess water is lost from the surface of gaseous exchange in both plants and animals, In mammals, water is also lost through sweat and through osmoregulation controlled by the kidneys

• Urea:This is a compound produced im mammals from the breakdown of excess amino acids

Amino acids cannot be stored because their accumulation is toxic, They are therefore converted into a less toxic substance. This process occurs in the liver and is called de-amination Ammonia is converted to urea by the liver. Urea is transported by blood to the kidneys where they are excreted. The kidneys are also used to remove uric acid, water, excess salts, excess hormones and bile pigments

• Calcium oxalate:This is a waste material produced by plants and is stored as an insoluble

crystalline structure in the cells. Calcium oxalate is stored in aging leaves, stems and roots, flowers or fruits

• Oxygen:Through the process of photosynthesis, oxygen is produced as a by-product. Some of

the oxygen is used for respiration, and the remainder is excreted through the stomata of the leaves.in plants, some waste substances are stored m parts of the plant that are dead. Examples of this are the tannin in the bark of trees such as mangroves and the dyes in the heartwood of tees such as logwood. The purpose of the storage of waste material ranges from protection to @ decreased tisk of being consumed

Exeretion in Human

The main excretory system in humans is the urinary system. The skin also acts as an organ of exeretion by removing water and small amounts of urea and salts (as sweat), The urinary system includes 2 pair of bean-shaped kidneys located in the back of the abdominal cavity

Exeretory Organs in Human Being

excretory product Organ Mode of excretion

Carbon dioxide Lungs Exhalation

Kidneys Urine

Lirea and excess mineral salts

Skin Sweat

Excess water Kidneys Unne

There are special organs concerned with removal of excretory products from the body. Such organs are called excretory organs. The excretory organs in an animals body are the kidney, the skin the lungs and the liver. ‘The following table shows the excretory organs and the products they exerete The table below summarizes excretory products in humans and the organs concerned with excretion of the product and the mode of excretion

Skin Sweat

Waste Advantages Disadvantages Habitat Excreted by

ue pigments (rom oreaxuown or naem )gi@o1ny Lever acces Toxic in concentrated Marine and fresh water Produced with litle Ammonia solution Excretion take Water invertebrates, bony fishes, energy place in lot of water amphibians Less toxic. than Fe : Requires more energy to Land, Adult amphibians, turtles, ren ammonia. Less water is produce it Sea ‘mammals and bony fishes needed to excrete it ' ¥ Reptiles, birds, insects,

Very little water is used Requires considerable Uric Acid Land gastropods (snails and] for its exeretion ‘energy to produce it slugs) Relatively non toxic Arid JGuanine Less water is used to More energy is needed Scorpions, Spiders habitat excrete it A comparison between different excretory products can be made. Following is the comparison between different types of excretory products: The excretory organs in humans beings may conventionally be put into two groups namely,

primary and accessory organs: Primary exeretory organs

• Kidneys:Kidneys are bean-shaped organs of a reddish brown colour that are found in the sides of

the vertebral column. Onee the body has extracted wastes from food, it sends the wastes to the kidneys, The kidneys filter the wastes, including urea, salt and excess water, which are flushed out of the body as urine

• Skin:The skin performs its excretory fimetion vin the sweat glands. These are coiled tubules

surrounded by blood capillaries. These glands produce sweat that contains mineral salts, excess oils, water, and traces of urea and lactic acid from the surrounding blood vessels which are then excreted out of the body through sweat pores. The tubules extend into sweat duets which open on the surface of the skin as pores. Sweating also helps to cool the body during evaporation

• Lungs:The lungs are very important excretory organs as they expel carbon dioxide from the

body via exhalation. The lungs use cells known as alveoli to remove the carbon dioxide from our blood, Otherwise, the carbon dioxide would accumulate and have a detrimental effect to our body.

Accessory excretory organs

• Liver: Although considered a secondary or accessory excretory organ, the liver plays a vital part

in keeping the body clean, Amino acids are the end-product of proteins. Excess amino acids cannot be stored inthe body. ‘They are taken from the gut into the liver by the hepatic portal vein The liver converts them into useful carbohydrates (stored in the form of glycogen) and ammonia.

Ammonia is very poisonous and must be removed fiom the body. ‘The liver converts ammonia into a harmless compound called urea. Urea dissolves in the blood and is transported into the kidney via the hepatic vein where it 18 removed as component of urine.Harmful poisons and chemicals that are either produced in the body or consumed are broken down and detoxified by the liver.

• Gall bladder:AMtough the gallbladder does not have a highly significant role play in the

excretory system, it does have a function that assists the overall process, Bile, a liquid produced by the liver to break down waste, is first stored in the gall bladder. When needed, it 1s discharged into the small intestine whose role is to break down fats, ethanol and other acidic wastes

• Urinary bladder: The waste fluid that is created in the liver and collected in the kidney is

transferred into the urinary bladder where it is temporatily stored until the individual urinates The urinary bladder provides a short term solution for storing urine in the body until it is ultimately discharged

• Ureters:The ureters tubes of smooth muscle fibre transfer liquid waste from the kidneys into the

urinary bladder. The urine is moved with penstaltie movements which force the urine away from the kidneys. The ureters also have ureterovesical valves which ensure the waste Mud does not travel back into the kidney

• Urethra: Tho urethra runs through the penis in males, and serves es « carrier of semen as well as

urine for their ultimate discharge out of the body. The urethra tube is shorter in females and is just above the vaginal opening

• Large intestine:¥ood particles are absorbed into the blood stream via the small intestine, The

undigested substances are transferred to the large intestine which essentially serves as storage organ for the excretory produets. The descending, ascending and transverse colons also facilitate the ubsorption of leover vitamins, water and salt, The distal stright section (known as the rectum) is used forthe storage of waste products (faeces) before they are excreted from the body via the anal canal with the help of internal and external sphincters.

The Urinary System and its Adaptive Features The urinary system is a system concemed with production, storage and removal of urine. In humans, itis made up of the two kidneys, ureters, blood vessels that join them, urinary bladder and urethra Adrenal ghind z= vere, ~~ Renal artery cee,. agers Medulla — es Cortex” \ — per se a

Y— Urethra

Structure of the kidney

Space inside the kidney which collects the urine and leads it to the ureter. The ureter passes urine ental. returned tothe circulatory system fiom the kidneys via the renal vein. Blood entering the kidneys ff a \S4 ee Ol fe GN mentee Sages }\\ \ > // \\\ rr noe The nephron nephron is differentiated into the proximal convoluted tubule. loop of Henle and the distal surrounds the dense network of blood capillaries called the glomerulus.

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homers (capitaren) MN (FS S o WUE fA ge + ] rt There is a branch of the renal artcry;the afferent arteriole, entering the small cup-like space of Emerging from this network, the capillaries re-unite to form a small arteriole, known length of the tubules, absorbing various substances. These capillaries eventually reunite to drain into the renal vein, The efferent arteriole is smaller than the afferent arteriole. This difference in

diameter helps to raise the glomerular pressure and aids in ultra filtration Some animals do not have a well developed kidney: they may have structures called nephridia Animals such as earthworms that are simple tube-like structures have nephridia that have the same role as the more complex nephrons in the kidneys.

The Process of Urine Formation

The blood from the afferent arteriole, which enters the Bowman's capsule, is rich in mutrients such as glucose, fatty acids, amino acids, vitamins, proteins, urea and excess salts. A nephron is the structural and functional unit ofa kidney which is concemed with excretion and haemostasis.

The three (3) distinet stages of urine formation are: (1) glomerular filtration, (2) tubular reabsorption and secretion, and (3) water conservation

• Glomerular filtration:Filtrtion occurs in the glomerulus (plural; glomeruli). Because the

lumen of the afferent arteriole is significantly smaller than the efferent arteriole there is a large amount of pressure in the glomerulus. This pressure forces forces plasma, the liqud portion of the blood, through the capillary walls in the glomerulus. The plasma contains water, glucose, amino acids, urea, salts, uric acid, vitamins, and hormones, Red blood cells and proteins are retained in the blood capillaries because they are too large to pass through the wall. This process

is called ultrafiltration and the fluid which passes ito the Bowman’s capsule is known as the glomerular filtrate The glomerular filtrate collects in the capsule and enters the renal tubule at the proximal convoluted tubule which is coiled to imerease the surface are for reabsorption of substances

• Reabsorption and secretion: The efferent arteriole branches into capillaries which surround the

proximal convoluted tubule. Thete, glucose, amino acids, vitamins, hormones and about 80% of sodium chloride and water are reabsorbed into the blood capillaries. Only the substances that are useful to the body are reabsorbed. This is referred to as selective reabsorption. Normally 100% of glucose is reabsorbed. Blood cells are not reabsorbed due to their large molecular size Reabsorption involves both diffusion and active transport (against concentration gradient), which

urine. Tubular secretion is the passage of certain substances out of the capillaries directly into the osmosis. The tubule is also highly coiled to increase the surface area for reabsorption. ‘The ge sages Sion a. oe Mg y ~“\ j~

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Adaptations of the urinary system to its functions

• The urinary system has a large afferent arteriole, and narrow efferent arteriole, which allows

build up of pressure, thus facilitating ultra-filtration 2 The glomerulus capillaries are highly coiled and semi permeable, eausing a build up of pressure inthe glomerulus hence ultrafiltration,

• The glomerular cspillaries are semi permeable (tubule also semi permeable) to allow selective

movement of materials in and out of the nephron (selective reabsorption)

• The tuboles? epithelium is thin (I cell thick) to reduce diffusion distance for faster passage and

henee reabsorption of materials; and they are and leakier than normal capillaries

• tis connected to a collecting duct, which channels the filtrate (urine) out of the nephron to the

ureter to allow for continous functioning of the nephron.

• The proximal convoluted tubule and the distal convoluted tubule are coiled so as to increase the

nephrons’s length and hence more surface area for efficient reabsorption to take place

• The Bowman's capsule is cup-shaped to provide maximum surface area for filtration

8, The tubule is supplied with a network of blood capillaries for maximum reabsorption

• The nephrons are numerous in number for efficient excretion of waste products

Complications and Disorders ofthe Exeretory System

Disease Cause(s) Symptoms __Effeets Prevention/treatment

Damage to the kidney due to accident or complications during surgery Low blood volume due to Oedema excessive (swelling of the bleeding legs, ankles, . i Bone damage, Poor intake of feet, face or ~ Avoid potassium-nich] ids hands due to OT PAS: rage tke citrus fits, abnormal heart Medication, for excess fluids) bananas, instant coffee Kidney (renal) failure ~ rhythm, loss of

example, High levels of peanuts and chocolate

failure of the kidney to memory, pain in diuretics ("water urea in blood May roguire a kidney function adequately duc the back or side ; pills!) may cause leading to apa ho partial or entire and if not treate a excessive water vomiting, Medications e.g struction of ephons a

Obstruction of loss, blood ia sin Bests involves both renal artery, urine or Dialysis i kidneys 7 causing blocking difficulty im of blood flow to urinating the kidneys Loss of appetite Kidney stones Chronic diseases that gradually cause the kidneys © stop finetioning Dehydration from loss of body fluid (for

example,

Vomiting, diathoea, sweating, fever) Prostate cancer may block the wrethra and prevent the bladder fiom emptying Lack of vitamins Extreme pain Inadequate intake and difficulty Taking a balanced dict of water in urination that is low in. protein, Ceriain types of Pain in the low May lead to nirogen and sodium rugs back and/or kidney failure Drinking plenty of Decrease in urine side, groin, or Toxicity due to water Volume and/or an abdomen urine staying in Avoid beverages that}

kidney somes excess of stone- Blood in the the body for a contain caffeine like forming urine due to longtime coffe, substances in the damage of the Severeback pain Surgical treatment to} urine inside walls of Surgery and. remove the stones Dehydration the kidney, medications are May require kidney from reduced ureter or expensive transplant fluid intake or urethra Medications strenuous Nausea and (painkillers)

exercise vomiting

Obstruction 10 Chills and fevee the flow of urine Infection inthe unary tract Frequent or intense urge 10 thous title comes out Drinking lot of fis when you do ® Maintaining tile Pain during hygiene Complete urination Pain or ?

Medications ae Cleanse genital rey pressure in the expensive before sex Bacterial back or lower Urinary tract infections Pain and Urinate after ‘sex. to infection in the abdomen (ars) nuisance due to flush away any bacteria urinary tract Cloudy, dark > Y urge 10 urinate that may have entered bloody, oF sequently your urethra strange:

• Keep genital area dry

smelling urine by wearing cotton] Feeling tired or underwear and loose] shaky Sitting clothes Fever oF chills @ sign the infection may have reached your kidneys) Liver cirrhosis: & Alcohol and viral Loss of weight Severe cirthosis Avoiding excess condition in which liver hepatitis Band Poor appetite is fal consumption of aleahiol eclls dogencrate and ate Attack by Abdominal Easy bruising, Avoiding fatty foods replaced by sear tissue, bacterial and pain yellowing of the Low sal intake

Jeausing the liver to viruses Blood stained skin Euting varied, easily shrink, ‘harden, become Parasites such-as vomit (Goundice) itching digestible food fibrous and fail’ to liver flukes and -and fatigue. Plenty of rest function normally schistosomia Ocdema, ascites’ Medical treatment Obstruction of (accumulation of Liver transplant in ease the gall Bladder fluid inthe of severe cirthosis Exposure 0 abdominal chemical poisons cavity), and Tiver

such as siliea and cancer ashesiog is a viral disease-virus is Hygienic processing of transmitted food Nausea through body Proper disposal of fluids such rene May lead t0 i ids such as lay Tead to Tver sewage saliva, blood and failure Treatment of water Hepatitis inflammation discomfon _ a semen fot treated Proper handing of ot the liver Jaundice * fe There are five early may lead to blood Dark brown main types of death Screening blood before}

wine and hepatitis: A,B, uransfusion whitish faeces © D, and E – Using sterilized needles plus types X and and syringes G Not yet very Blood in urine. Expenses. on Stop smoking clear but a Frequent medication Avoid exposure to

Bladder Cancer ”

number of'_urinary tract Pain – reduces industrial chemicals reasons uch “ag infections, the qualily of Eat healthy foods, smoking painful life, choose low-fit, low, radiation, wrination and cholesterol diet cha parasitic urge to urinate includes plenty of fruits infection, without actual and vegetables exposure to flow. Avoid dehydration by] chemicals Weight or increasing your uid (carcinogens) appetite loss imiake, —_partieularly

may cause the Abdominal or water, Water dilutes disease back pain, cancer-causing persistent chemicals raisod temperature or Common Complications and Disorders of the Exeretory System A large number of medical conditions of varying intensity are associated with the excretory system, Ifthese are not addressed immediately, they may even prove to be fatal and claim one's life. We need to be well acquainted with the most commonly occurring diseases oF excretory

system along with their description, symptoms and effective treatment measures. The table below shows some of the common complications and disorders of the exeretory system, their

causes, symptoms, effects and preventive measures

The Causes, Symptoms, Effects and Control Measures of Common Complications and Disorders of the Exeretory System

Disorders ofthe Excretory System

Exeretion in Plants

Iypes of Exeretory Products Eliminated by Plants Exeretion oceurs in plants and animals as they both have waste products to be removed from their bodies. Compared to animals, plants do not have a well-developed excretory system to throw out nitrogenous waste materials. This is because of the differences in their physiology.

Therefore, plants use different strategies for excretion Plants eliminate some waste through diffusion, During the day, excess oxygen gas produced by photosynthesis is released through the stomata Carbon dioxide produced by respiration is normally used up during photosynthesis At night, however, as photosynthesis slows down, carbon dioxide is not used up as fist as it is produced, and it is released as a waste product

Plants also produce oxygen as a by-product of photosynthesis, The oxygen that is not used for respication is also excreted through the stomata, Excess waler evaporates mostly from stomata and also from the outer surface of the stem, fruits, ete., throughout the day. This process of getting rid of excess water is called transpiration, Many plants store organic waste products in their permanent tissues that have dead cells, e.., in

heartwood, Plants also store waste within their leaves or barks. These wastes are periodically removed as the leaves and barks fall off Some of the waste products are stored in special cells or cellular vacuoles, Various waste products such as tannins, essential oils, gums, resins, etc., are produced during catabolic processes, Tea leaves contain tannin. Tannins are found also inthe barks of trees The leaves of many plants, like Eucalyptus, lemon, ete., contain essential oils. The coating of

oranges and lemons and the petals of flowers like rose and jasmine also contain oils. Some plant wastes are stored as a thick, white fluid. You may have seen white Muid ooze out when you pluck « papaya ora fig or other plants. ‘This white fuid is called latex.

Gums are a group of sticky. water- soluble wastes found in the common gum tree. Resins are another group of wastes found commonly in the stems of conifers (es . pine, fir), Alkaloids are a group of toxic waste products, But some of these are useful to us. Quinine and morphine are medicines derived fiom alkaloids stored in Cinchona bark and opium poppy Rowers respectively. Caffeine found in coffee seeds and nicotine in tobacen Teayes is also

alkaloids, Plants also eliminate waste by the accumulation of waste in the vacuoles of the aging leave cells. These leaves will eventually dic and fall off, removing waste in the process. ‘This process is called abseission.

Organic acids, which might prove harmful to plants, often combine with excess cations and precipitate out as insoluble erystals that can be safely stored in plant ells. Calcium oxalate crystals aceurmulate in some tubers like yam.

Aquatic plants lose most of their metabolic wastes by direct diffusion into the water surrounding them. Terrestrial plants excrete some waste into the soil around them. In plants, breakdown of substances is much slower than in animals. Plants do not have specialized exeretory organs for the removal of metabolic wastes Plants do not need a specialized exeretory system like in animals because of the following 4 ‘The rate of producing waste products in plants is much lower

b. Most exeretary products fiom plants are removed by diffusion through the stomata or lentivels Lenticels are areas in woody stems where the cells are loosely packed allowing gaseous exchange and removal of waste products © The major excretory products of plants are carhon dioxide, oxygen and water. These products are recycled. For example, the oxygen released as a by product during photosynthesis, is used in respication by animals and plants The carbon dioxide released during respiration is used for

photosynthesis by the plants, Water is released into the atmosphere where st enters the water cycle,

• Plants produice less poisonous substances compared to the nitrogenous wastes produced by

animals © Plants have large vacuoles which store waste substances often accumulating at concentrations that lead to crystal formation in form of oil droplets or granules, {Plants can also store the waste products in organs that are destined (o fall or die off So they can be excreted via abscission. Other waste material such as resins, saps and latexes are forced out from the interior of some plants by hydrostatic pressure inside the plant

The Importance of Common Exctetory Products of Plants Have you ever noticed sticky, milky or oily substances being oozed from the bark of wees? These are excretory products and may be resins, gums, latex and or other excretory products, These products may be poisonous. However, many have found use in everyday life of humans, such as latex which is used to produce gloves and clothing. The table below shows functions of

some plant waste products ditt (waste) Plant source Use and effects

Treatment/tanning of hides and skins into leather, ie. it

Dead tissues of plants combines with animal proteins to form a complex Tannins such as acacia, conifers, compound which is not easily broken down by animal coffe and mangroves, proteases Iti used in the manufacture of inks and dyes, Alkaloids. Are nitrogenous excretory products in plants and occur in various forms- Common alkaloids include ) Cafieine and -Coflee fiuits and tea -Mild stimulants to increase mental activity and reduce

sophilinet leaves fatigue -A drug for the treatment of malaria.-An additive in drinks P)Quinine = Bark of cinchona tree to act asa stimulant, AA very expensive drug for local anaesthetics ) Cocaine = Leaves of coca plant A painkiller and also gives. great _mental and physical strength.

Note: Overdose may lead to hallucinations, anxiety and even death Manufacture of drugs such as painkillers Results in relation, talkativeness, and greater appreciation Fruits, lowers and leaves paneer of sound and colour ) Cannabis of cannabis sativa (bhang Decreased performance in concentration, intellectual and oor marijuana) manual asks Overdose effects are similar to that of eocaine , Manufacture of drugs like morphine and codeine both of

“Opium poppy which are effective painkillers, musele relaxant, cough Priatesmorphingy “Pum POPP) a . suppressants, and anti-dianthoeal Manufacture of insecticides and narcotic dnugs (drugs that stimulate sleep or stimulate a feeling of relaxation and ) Nicotine “Tobacco leaves ‘mask the sensation of pain) A common cause of respiratory and cardiae diseases, due to tar from its smoke -Epicarp of pawpaw fruits }) Papain pes oF -Has proteolytic activity hence used as a meat tenderizer

(especially aw). Interferes with the process of eell division resulting into }) Colchicine Roots ofthe crocus plant, mutations; and thus useful in plant breeding itis also carcinogensc (cancer-causing) ) Pyrethrins “Flowers of pyrethrum Making of insecticides ) Khat (mira) Leaves and twigs of the -Used as @ stimulant hirungi) “Khat” plat ‘ Rubber tree Manufacture of shoe soles, tyres, ete alex Sapodita Manufacture of chewing gum

Most are edible and thus used fo thicken foods and creams Different plants such as Gum from sapodille is used to make chewing gum. Gums Arabic ghath and carob, Agar extract (a gum) from algae is used as @ growth acacia tre, ete. ‘medium to culture microorganisms.

Is also used to make cough medicine Petals and leaves of Extracted for making dyes. Amihocyanins various plants, and are Used in making PH indicators, mostly red, blue or purple. Digitalis soxal Manufacture of drugs used for treatment of heart diseases ycosides such as digitoxin Certain tree stems like the Remnin -Manufacture of varnish anel gum casuarina tree oll Manufacture of perfume and ointment for insect bites.

certain trees