EXCRETION.Is the removal of waste substances
from the body, which are produced by the cells activity (metabolism) and
substances of which the body has an excess. Waste substances are usually
harmful to the living body. So the body separate, detoxicate, and remove
them. There are many chemical reactions
in the organism. All these reactions give rise to the end products, some of
which are poisonous or could affect the normal chemical reactions in the
body if they were allowed to accumulate.
i. Digested substances which
is in excess and can not be stored in the body are removed from the body
together with useless and poisonous by products of metabolism by the process
called excretion..
Fig.The structure of urinary system
i. Digested substances which
is in excess and can not be stored in the body are removed from the body
together with useless and poisonous by products of metabolism by the process
called excretion..
ii. All these reactions are
useful to the body;eg –some produce energy (respiration).
--Some build new body tissues.
--Some produce useful chemicals, ie. enzymes and hormones
iii But yet, some of these
reactions give rise to by products which are useless or even harmful to the
body. These are called excretory products and are removed from the body by
excretory organs, ie. kidney, lungs, skin, and liver
Excretory Products.
1.Carbon dioxide is useless in the body but it can also be
harmful if allowed to accumulate in large quantities, ie. forming carbonic acid
which can damage body cells.
-So carbon dioxide is an excretory
product and is removed by the lungs.
2.Water; normally it
is useful to the body but it can be harmful if allowed to accumulate to the
point that it dilutes the blood and tissue fluid. So it has to be removed as an
excretory product.
Metabolism; some of the
by-products of metabolism though useless when they are produced, they are not
excreted because they can be turned into useful materials. Example lactic acid
formed in the muscles of vertebrates during vigorous exercises.
3..Lactic acid is useless until converted back into glucose
where it is used in respiration or stored as glycogen.
The most poisonous by product
of metabolism is ammonia. It is formed during breakdown of excess
amino acid in the liver. Ammonia is very soluble and kills the cells if its
concentration rises above 1 part in 25,000. Liver converts ammonia into urea (relatively
harmless) which is released into the blood. Kidney extracts it from the blood
and excretes as a part of urine.
Other examples are hormones,
cholesterol (fats), bilirubin.
TERMS,
Defecation; is the removal from the body of indigestible
substances, ie. passage of faecal matter through anus. Faecal matter is not
true excretory product because it is not produced by metabolism.
Secretion; is the production by metabolism of useful substances
like enzymes and hormones.
Excretory Organs.
1. Kidneys:
They remove nitrogenous (urea and ammonia) compounds from the blood and
eliminate excess water and salt.
2. Liver:
excretes bile pigments derived from the decomposition of
haemoglobin and urea.
3. Lungs: Excrete
carbon dioxide and water vapour.
4. Skin: for
water, mineral salts and trace of urea excretion.
Importance of excretion;
-It is necessary because if the
wastes accumulates in the body, they will poison the body and kill the organism
-Provides a balance of chemicals in
the body for its proper functioning
URINARY SYSTEM
The urinary system is a system
concerned with production, storage and removed of urine.
-In human it is made up of the two kidneys. ureters, the bladder, the
urethra, and the sphincter muscles
|
| Fig.The structure of urinary system |
Each kidney is a solid structure lying on the body wall at the
back of the abdominal cavity
It is red-brown in colour and enclosed i the a thin membrane
There are two blood vessel connected to the kidney.Renal artery and renal vein
i.Renal artery supplies blood to the kidney
ii. Renal vein takes blood away from the kidney
Ureter is the tube which run from each kidney to the
bladder. its function is to passes urine from the kidney to bladder for
temporary storage
Th urinary bladder is a spherical muscular
sac that located within the pelvic cavity .-It store urine temporary
At the base of the urinary bladder there is a sphincter muscle that keep the
bladder from emptying until it reaches certain level
The urethra release the urine outside of the
body.The wall of urethra is composed of mucous membrane and fibrous muscles
tissueIn babies
sphincter muscle is controlled by a reflex action triggered off by
nerve endings in the stretched walls of the bladder. After about two years or
less the muscle can be controlled voluntarily
STRUCTURE OF KIDNEY
Fig.The structure of kidney
|
| Fig.The structure of kidney |
The kidney is bean-shaped with a depression near the centre of one side where there is ureter.It surrounded by fibrous connective tissue.The kidney has three distinct regions, namely the Cortex,Medulla and pelvisThe cortex is the outer The medulla is middle of layer of the kidney red in colour, it consists of loop of Henle and collecting ducts of the nephronPelvis is the region into which urine temporary accumulates before draining into the urinary bladder and it is folded to form projection called PyramidThe renal artery divides up into a great many arterioles and capillaries, each arteriole leads to glomerulus which is almost entirely surrounded by cup shaped Bowmans’s capsule. Glomeruli were discovered by Marcello Malpighi..Each kidney tubule emerges from the Bowmans’s Capsule and after a complicated series of coils and loops, it joins the wider collecting duct which collect urine from the kidney tubule (Nephron).
THE NEPHRON
Nephron is
the functional unit of the kidney.
 |
| Fig. the structure of nephron |
This is fine
inter-twined network of blood capillaries enclosed by Bowman's capsule
-It receives
blood from an afferent arterioles a branch of renal artery.
-The blood
is taken away from glomerulus by Efferent vessel towards renal vein.
2.Renal tubule
The renal
tubuleis divided into five region
i
Bownwn,scapsule.-The
expended,cup-shaped part closed end of t the glomerulus
ii.Proximal
convulated tubule
-The coiled part of the tubule next to the
Bowman's capsule-it lie in the cortex
-i I t is highly
coiled tube that extends to descending loop of Henle
iii.Loop
of Henle
-The
portionthat extends from the proximal comvulated tubule and dips into the
medulla and it bend back into the cortex to for U-shape of loop.
-Ti made up
of ascending and descending parts
iv.Distal
convulated tubule
-The coiled
part next to the open end of the tubule which joins with a collecting
duct.
v.Collecting
duct.
This is the
tube through which several other tubules empty their content.
-The
collecting ducts lead to the pelvis of he kidney
ADAPTIVE
FEATURES OF URINARY SYSTEM
The presence of numerous of
glomeruli- Increase the ultrafiltration.The different size of renal artery and renal vein..-renal vien is narrower than renal arery in order to slow down movement of blood out of glomerulus which inturn increase osmotic pressure.The epithelial nature of the Bowman;s capsule-increases the movement of filtrate into the kidney tubule.Capillaries in the kidney tubule are more coiled and provide large surface area for reabsorptionThe kidney tubules has convulated structure that increase reabsoption of important minerals back into circulatory systemThe urinary bladder has sphincter muscles that when relaxed allow movement of urine to the outside.
THE PROCESS OF URINE FORMATION
urine involves three steps, which all occur intthe nephrons of kidney. Filtration,reabsoption and secretion.
1.Filtration: Blood from the renal artery enters the glomerulus through narrow capillaries. The smaller molecules of the blood are forced under pressure out of the capillaries into the Bowmans’s capsule. Capillary membrane and capsule’s membrane act as a filter. Thus only plasma and tiny molecules like glucose, minerals, vitamins, amino acids, waste products and water pass into the capsule and large molecules such as protein blood cell retained in the blood. Thes filtated are now called the glomerulus filtrate. Glomerulus and Bowmans’s capsule are called together as the malphigian Body.
2.Reabsorption occurs as glomerulus filtrate passes out of the Bowmans’s capsule and down the kidney tubules towards the collecting ducts. All along this route, cells in the kidney tubule’s walls extract back useful substances from glomerulus filtrate so that by the time In the proximal convulated tubule all the glucose, amino acid. and some water and mineral are reabsorbed through the process of Active transport.it reaches the collecting ducts a liquid called urine has been formed. Urine contains urea and other waste excretory substances.
Content of
urine
|
%
|
Water
|
95
|
Urea
|
2
|
Uric acid
|
0.03
|
Creatinine
|
0.1
|
Salts
|
1.4
|
Ammonia
|
0.04
|
The Liver.
The liver is a large, reddish-brown in colour
owing to the large number of blood vessels it contains. It lies just below the
diaphragm. It has two lobes, and gall bladder is placed between the lobes. The
liver is the largest gland in our body. It is an enormous chemical
factory which makes and release into the body many useful
substances. As chemical factory, it needs a large supply of raw materials. The
liver obtain its supplies from blood in Hepatic Portal vein, which
brings all the digested food absorbed by the intestine.
The
liver regulates the amount of food which reaches the blood and tissue fluid. It
does this by absorbing and storing food which it receives, and then releasing
it into the circulatory system at a rate which depends upon the body’s current
needs.
Structure of
the Liver.
-Has two
lobes, and gall bladder is between the two lobes.
-Is made up
of small groups of cells called lobules. Each lobule is composed of great
number of liver cells, between which are small blood vessel and very small bile
ducts.
-The blood
vessels: Hepatic artery- brings oxygenated blood.
i.Hepatic portal vein- brings blood rich in digested food from the alimentary canal for control.
i.Hepatic portal vein- brings blood rich in digested food from the alimentary canal for control.
ii. Hepatic vein. Carries away the
deoxygenated blood.
Functions of
the Liver.
1. Regulation of blood
sugar: Excess glucose is converted into glycogen and fat under the
influence of insulin. In case of decrease of blood glucose; the stored glycogen
and fat are converted into glucose ready for respiration.
2. Deamination;
Protein is digested into amino acids. Deamination is the removal of amino group
from an amino acid, ie. changing Amino group (NH2) which would form
poisonous Amonia (NH3) into less poisonous urea to be excreted
through the kidney.
3. Detoxification; Is
the process whereby harmful (poisonous) compounds (Drugs) are
converted to less toxic compounds in the liver, which are then
excreted through urine.
4.
Manufacture of plasma protein- plasma
proteins like prothrombin and fibrinogen (for blood clotting) are manufactured
in the liver from the synthesise of amino acids.
5. Storage of minerals
and vitamins such as A, B, D,E,K,B12 for red cells in the bone
marrow.
6. Storage of blood;
it is highly vascularized, so able to hold large volume of blood.
7. Formation of
Erythrocytes in the liver of the foetus. The
liver also breaks down the old erythrocytes.
8.
Regulation of body heat.
9. Storage of iron:
iron from the haemoglobin which comes from the decomposition
(breaking) of red blood cells is stored in the liver.
10. Formation of bile;
when red blood cells break down, the green and yellow pigments are formed.
These pigments are removed from the blood by the liver and excreted in the
bile. Bile is stored in the gall bladder and is used for emulsifying fats.
The Skin.
The
skin is the largest organ of the body. Is continuous layer of tissue over the
surface of the body.
Skin
structure.
-Inner
skin called dermis.
A. Epidermis.
1. The cornified layer: the
horny layer; Is the outmost layer which consists of dead cells that form a
tough outer coat. The cells are continually worn away and replaced from
beneath. It may become very thick on the palms of the hand (when used for heavy
works) and soles of feet. It contains keratin. The
layer offers resistance from damage, bacteria, and from drying up.
2. The granular layer: contains
living cells; towards the outside it gives way gradually to the cornified layer.
3. The malphigian layer.
Contains living cells that divide actively to give rise to the upper layers of
the skin. They contain pigments called melanin which
gives colour to the skin and act as a screen against ultraviolet
radiations/rays that can cause cancer.
Dermis:
Dermis:
The
dermis is a thicker layer of connective tissue with many elastic fibres in it.
It contains sweat glands, receptor cells, blood vessels, lymphatic vessels,
adipose tissue, hair follicles and sebaceous glands.
1. Blood capillaries:
supply skin with the necessary food and oxygen and remove its excretory
products. Sweat glands and hair follicles have net work of capillaries.
-capillaries
beneath the epidermis play an important role in the temperature control.
2. Sweat glands:
they are in deeper layers of the inner skin. Sweat gland is a coiled tube of
one cell thick. It opens at the surface of the skin through sweat–pore. Sweat
gland is surrounded by network of blood capillaries from which it extracts
water containing waste substances. It absorbs excess water, mineral salts,
traces of urea and lactic acid from blood vessels. It functions when the body
temperature rises above the normal by between 0.2C to 0.5C.
3. Receptor cells: found
within the dermis are able to detect different stimuli such
as cold, heat, pressure, touch and pain.
4. Hair follicles: originate
from the epidermis. Their bases are surrounded by malphigian and
glanular layers. These are deep pit like where hair lies. Hair is made up of
dead cells containing keratin. Hair root is embedded in the follicle.
-The
erector hair (pili) muscle is attached to the hair follicle and to the
epidermis on the other end. The hair raise and lowers as muscle contracts and
relaxes respectively.
-The
granular and malpighian cells multiply and build up a hair inside
the follicle. The constant adding of the new cells to the base of the hair
causes it to grow.
5. Sebaceous gland:
it produces oily sebum which keeps the epidermis supple (not crack), makes hair
water proof, reduces tendency of skin becoming too dry after evaporation.
-Also has
antiseptic substances which protects the skin against micro organisms.
6. Sub-cutaneous fat;
is the layer beneath the dermis containing fat cells, ie. adipose tissue where
fat is stored. The fat insulate the body against heat loss. In the presence of
sunlight the layer also manufactures vitamin D.
Functions Of
The Skin.
1. Against
desiccation- prevents loss of water from the body by evaporation.
2. Protects
body against entry of micro organism and damage due to friction.
3. Excretion
of salts, excess water, traces of urea, lactic acid and carbon dioxide.
4.
Regulation of body temperature.
5. Prevention
against ultra violet rays penetrating the body through melanin
pigment.
6. Reception
of stimulus, ie. cold, heat, pain, touch and pressure.
7. Synthesis
of vitamin D.
8. Stores
fats in the adipose tissue.
COMMON COMPLICATIONS AND DISORDERS OF THE EXCRETORY SYSTEM
I.Glomerulonephritis
Is a condition where the glomerular
capillaries become inflamed and more permeable to protoein
-Proteins are excreted in the urine a
condition called proteinuria
-this result into the desease in the amount
of protein in the blood plasma. a condition called hypoproteinaemia.
-The osmotic pressure of the blood lowers
tissue fluid in the capillaries decrease and oedema occur
2. Kidney stones
-Form in the collecting ducts and pelvis of
the kidney
-They contain uric acid, calcium oxalate,
calcium phosphate or magnesium phosphate
-Stones containing calcium oxalate or
phosphate
Results in the obstruction of urine flow or
excess the certain chemicals in the blood stream
3.Cystitis
Is inflammation of the bladder caused by
infection
It caused by bacterial infection of
bladder, usually the urethra
symptoms.
- Frequent painful urination and cloudy
urine
-Fever, blood in the urine if bacterial is
passed to kidney.
Treatment.
-drinking a plenty of water that can relieve
symptom and speed up recovery
4.Kidney failure.
Is the condition where one or both kidney
cease to function
It is only treated by Dialysis or kidney transplant.
-Dialysis the patient's blood is linked
to a kidney machine
Excretion in plants.
Plants carry out metabolic processes like
respiration and photosynthesis. The main waste products are water and oxygen in
day time (photosynthesis) and carbon dioxide at night (respiration).
Plants do not need special excretory organs
because excretion is not a serious problem as it does in animals.
Why excretion is not a serious problem in
plants:
- The rate of catabolism is slow
hence waste accumulates slowly.
- Green plants can use much of
their waste products, e.g. oxygen from photosynthesis can be used for
respiration and the Carbon dioxide from respiration can be used for
photosynthesis.
- Nitrogenous compounds produced
as waste can be used by plants in the synthesis of new
Proteins. (Nitrogenous wastes are dangerous
in animals.)
Methods of excretion in plants.
- Diffusion: for
waste in gaseous form that is oxygen and carbon dioxide.
- Transpiration: water
containing by dissolved carbon dioxide and oxygen are excreted through
transpiration.
- Guttation:
excretion of water and dissolved mineral salts, (through hydathodes)
- Exudation: release
of fluids at slow rate, e.g. gums, mucilage, resins, latex, rubber, calcium
pectale and oxalates.
- Deposition: Resins,
tannins, caffeine, nicotine, quinine, morphine, khat, pyrithrin and papain are
deposited in the xylem, bark, seeds, fruits, flowers and leaves of the plants.
The depositions do not affect the metabolic activities. When these structures
(leaves, flower, fruits, seeds, and bark) aged, they drop and there by
releasing waste products.
Economic importance of plants’ Excretion.
Most of the excretory products are useful.
-These colours –are of great aesthetic value
-Used to make dyes.
- To test PH of chemical solution.
(ii) Tannins: deposited
in dead tissues that is wood and bark of acacia, conifers and mangroves.
Used in: preservative, treatment of leather;
colour of tea.
Manufacture of ink; cosmetics, e.g. henna for
nails, feet and hair
.
(iii) Latex: milky
substance from rubber tree to make rubber.
(iv) Gums: produced
by Arabic and ghath and carob, used in: -thicken food and creams.
- Manufacture of chewing gum e.g.
sapadilla gum is used.
- Agar from algae as medium to
culture micro-organisms.
- Some gums are edible.
(v) Alkaloids: produced
in many forms and stored in different organs.
(a) Quinine: from bark of
cinchona tree. Used in,
-Treatment for malaria.
- -as stimulant in drinks.
(b) Cannabis: stored in flowers,
fruit and leaves of Indian hemp(cannabis sativa)
-manufacture of drugs and painkillers.
- - induce hallucinations.
(c) Cocaine: from leaves of cacao
plants.
-As local anaesthetic.
- effect like hallucination and
convulsion
· is addictive when taken in large
amounts and leads to heart ailments.
(d)Nicotine: in leaves of tobacco
plant.
- manufacture of insecticides
- manufacture of narcotic drugs –
makes one to relax or sleep
· Tar from tobacco is poisonous- can
cause lung cancer.
(e) Caffeine: in coffee beans and
tea leaves.
-Mild stimulant and refreshes.
-Reduce fatigue that is increases mental
activity.
(f) Morphine: from poppy
plant.
-Make narcotic drugs.
- Pain killer and muscle relaxant.
(g) Papain: from papaw fruits.
-as meat tenderiser.
(h) Colchicine:
-Brings about mutation in genetic materials
thus it is useful in plant breeding.
(i) Khat (miraa/bhang):
in leaves and twigs of tree.
-Stimulant.
(j) Pyrithrim from
pyrethrum flowers.
-Used in making insecticides.
(k) Alkaloids: in Irish potatoes
when exposed to direct sunlight it turns tuber green.
- They are bitter and poisonous in
large quantity.
- Protects tubers exposed on the
ground from being fed on.