BIOLOGY-TOPIC-EXCRETION AND OSMOREGULATION
EXCRETION AND OSMOREGULATION
Excretion is the removal of waste products of metabolism from the body. If allowed to accumulate these would prevent the maintenance of a stead state. Not that the definition states products of metabolism; This means that the waste products have been made by the body it self (cell)
-Osmoregulation is the maintenance of constant osmotic conditions in the body.
-It involves regulation of water contents and solute concentration of the body fluid particularly of sodium, potassium, chloride ions
-Body fluis include cell contents as well as fluids outside the cells such as blood plasma, tissue fluid and
Lymph.
-It is vital that the composition of these fluid should remains constant in order for the cell to work efficiently
SIGNIFICANCE OF EXCRETION AND OSMOREGULATION:
1. Removal of unwanted by products of metabolism pathways.
2. Removal of toxic waste
3. Regulation of ions concentration of the body fluid
4. Regulation of water contents of body fluid
5. Regulation of PH
EXCRETORY PRODUCTS
The major excretory products of animals are;
1. Nitrogenous compound such as urea, ammonia and uric acid.
-These comes from the break down
2. Carbondioxide from cellular respiration eg. Break down of glucose molecules results the release of
Carbon dioxide and water, but if excess water produced it referred to as the waste products
3. Bile pigments from the breakdown of haem in the liver.
EXCRETORY STRUCTURES
The following are structure used in excretion in vertebrates;
-Live
-Lungs -Skin
NITROGENOUS EXCRETORY PRODUCTS AND ENVI ROMENTS
Nitrogenous waste products are produced by the breakdown of proteins, nucleic acid, and excess amino acids.
-The first products of the breakdown of excess amino acid is ammonia.
-It is produced by the removal of the amino group from amino acid a process called DEAMINATION
Ammonia may be excreted immediately or converted into the nitrogen containing compound such as
Urea and uric acid.
Ammonia it is harmful product which required to be removed immediately or converted into less
Harmful wastes like urea and uric acid. Once the ammonia left in the body tend to destroy the cells
-The exact nature of the excretory products are determined by the availability of water to the
Organisms (That is its habitat) and the extent to which the organism control water loss.
-These correlation with habited may be summarized. Thus:
-Ammonia –aquatic (Water conservation not a problem)
-Urea -Aquatic or terrestrial
-Uric acid – Terrestrial
AMMONIA
The major sources of ammonia are the deamination of amino acids.
-Ammonia is extremely toxic and must be removed or eliminated. Being a very soluble, It can be
Eliminated from the body rapidly and safetly. If dilluted in a sufficient volume of water
Ammonia it is excreted by organisms living in water bodies eg. Fish, amphibian protozoan etc.
-Many aquatic animals excrete mainly ammonia and are called ammoniotelic
UREA
Urea, CO (NH2)2Is formed by combination of two molecules of ammonia with one of carbon dioxide
-Urea is less toxic substance formed in the liver
Co2 + 2NH3---------- C
Carbon dioxide + ammonia --------Urea +water
-Urea is less soluble; less water is need for its elimination because the tissues can tolerate higher
Concentrations of it.Urea is produced by the cyclic process known as the ornithine cycleorurea cycle
-The other aquatic and some terrestrial excrete predominantly urea are called ureotelic
URIC ACID
Uric acid is more complex molecule than urea .It is ideal excretory products of terrestrial
Organism eg birds, reptiles, insects, insects, it is removed as a solid pellet or thick paste.
The terrestrial animals excreting mainly uric acid they are called uricotelic
NEPHRON – OVERALL STRUCTURE AND BLOOD SUPPLY
The basic unit of structure and function of kidney is nephron and associated with blood supply.
-Nephron is situated in the kidney.
-Each human kidney consise of estimated one millions of nephron and each nephron has 3
Centimeters long.
-Due to the function of nephron about 125cm3 of fluid is filtered out of blood per minute. About
99
Although this varies with factor like drinking.
Each nephron is
composed of six regions namely;
1. Renal corpuscle
(Malpighian body)
-Composed of renal
capsule and glomerulus (The renal capsule is also known as the Bown man’s
Capsule)
2. Proximal convoluted tubule
3. Descending limb of the loop of hence
4. Ascending limb
of the loop of hence
5. Distal convoluted tubule
6. Collectingckict
Refers to structure of
nephron below
TYPES OF
NEPHRON
There are two types of nephron namely;
1. Cortical nephron
2. Juxtamedullary
nephron
1. CORTICAL NEPHRONE
Cortical nephronsfound in the cortex and have short loop of
hence which extends to medulla
2. JUXTAMEDULLARY NEPHRON
Juxtamedullary nephron
have they renal corpuscle close to the junction of cortex and medulla
Refers to diagram below
which show cortical and juxtamedullary nephron position in the kidney
The basic function of nephron
- Filtration
- Secretion
- Reabsorption
FILTRATION
Filtration occur in the glomerulus part of kidney
-Blood enters the glomerulus through the afferent arteriole (atterent vessel) and exist through efferent
arteriole (efferent vessel)
-The filtration in the glomerulus is under pressure which referred to as ultrafiltration
-The glomerulus is a knot of capillaries in renal capsule; the diameter of the capillaries in the
Glomerulus is much less than that of arteriole, So as the blood enters the narrow capillaries pressure
Rises.
-The water and solute molecules are squeezed out of the capillaries through that endothelium of the
Renal capsule and collected at the bowman capsule as glomerulus filtrate (GF).
-The large molecules like blood cells proteins are left behind in the blood they are large so that they
Cannot pass through the pores of endothelium in the glomerulus
-The glomerular filtrate (GF) it has chemical composition similar to that of blood plasma; It contains
Glucose, amino acids, vitamins, ions, water, urea, uric acid and some hormones
REABSORPTION
As the glomerular filtrate flows long the renal tubules, most of the filtered substances in the filtrate,
Useful to the body are selected and reabsorbed back into the blood.
-In the proximal convoluted tubule all the glucose, amino acid and some water and mineral are
Reabsorbed through the process of active transport
The proximal convoluted tubules have the following features
*The tube is long and highly coiled to provide large surface area for reabsorption
*The tube is well supplied with blood capillaries for efficient reabsorption
*The cells living the tube have numerous mitochondria which provide the necessary energy in form
Of ATP.
*The cells of the tubule have microvilli which increases the surface area for reabsorption
*The coiling of the tube slows down the speed of the flow of Glomerulus filtrate giving more time
For efficient reabsorption.
*Refer to the cross section of proximal convoluted tubule below;
THE LOOP OF HENLE
The function of loop of hence is to conserve water
-The longer the loop of hence the more concentrated the urine that can be produced, This is
Useful adaption to life on land
-Loop of hence has three distinct regions
*The descending limb – which has thin walls.
*The thin ascending limb – This is the lower half of the ascending limb has thin wall
*The thick ascending limb – This is the upper half of the ascending limb and has thick walls.
NOTE:
The descending limb is highly permeable to water and permeable to most solutes.
-It function is to allow substances to diffuse easily through its walls.
-Both parts of the ascending limb are almost totally impermeable to water.
-The cells in the think part can actively reabsorb sodium chloride, potassium and other ions from the
tubule.
TUBULAR SECREATION
The distal convoluted tubule collects wastes and other substances such as drugs from the blood for
Excretion in the urine
-From the collecting duct the urine is delivered to the renal pelvis
The urine also is composed by the following water (95%), Urea (2%), Uric acid (0.03%), Creatinine (0.1%), salts, (1.4%) ammonia (0.04%).
-The urine is collected from the pelvis by the ureter, which connects the kidney to the urinary bladder
-The urine leaves the body through the urethra.
COUNTER – CURRENT MULTIPLIER SYSTEM
Counter current multiplies system is an active process occurring in the loop of hence which responsible
For the production of concentrated.
-The counter current multiplier hypothesis of the loop of hence the outcome of this hypothesis is an
Increasing gradient of salt concentration in the medulla.
*This enables excess of water to be withdrawn by osmosis from the urine in the collecting duct
*The concentration of blood plasma is 300 units(mosmdm3) where as that of human urine is
Commonly 950 units but range from 50 – 1400 units.
-In order to be able to extract large proportional of water by osmosis and generate that
Concentration, urine the osmotic concentration in the medulla must be about 4 times that of blood
Plasma or 1200 units
*Only at such concentration is sufficient for water to be withdrawn from the filtrate as fluid passes
From the discending limb of loop of hence and collecting duct.
*As the renal fluid passes through that region water passes out of it by osmosis this lead to
Hypertonic urine produced.
Refers to diagram of counter – current multiplier of the loop of hence below;
MECHANISM OF OSMOREGULATION IN HUMAN
The body maintain solute potential of blood at an approximately stead state by balancing water
Uptakes from diet with water lost in evaporation, sweating egestion and urine. This is achieved
Primarily by the effect of the hormone called Antidiuretic Hormone (ADH)
-Diuresis is the production of large amount of dilute urine
-Antidiuresis is therefore opposition. ADH so has the effect of making urine more concentration.
-ADH is sometimes known as known as vasopressin when the blood become more concentrated(dilute potential more negative) as in a situation where too little water has been drunk, excessive sweating has occurred or large amount of salt have been eaten( osmo – receptors) in the hypothalamus defect a fall in blood solute potential.
-Osmo – receptors are special receptors which are extremely sensitive to change in blood concentration.
-They set up nerve impulses which pass to the interior pituitary gland where ADH is released. ADH travels in blood to the kidney where it increases the permeability of the distal convoluted tubule and collecting duct to water. It does this by bringing about an increase in number of water channels in the membrane living of the tubues. In the presence of ADH the increased number of water channels, allows water to move from the glome rulus filtrate into the cortex and medulla by osmosis
-Here it increase the osmotic concentration resulting in the removal of an increased volume of water
From the descending limbs
The opposite occurs when there is a high intake of water, the solute potential of the blood begans to
Get les negative. ADH release is inhibited. The wall of distal convoluted tubule and collecting duct
Becomes impermeable to water. Less water is reabsorbed as the filtrates pass through the medulla
And large volume of dilute urine is excreted
-The hypothalamus also contain a “Thirst Centre” where blood solute potential is very negative negative,
The thirst Centre stimulated the secretion of Thirst.
-Failure to release sufficient ADH lead to the condition known as Diabetes inspidus in which large
Quantities of dilute urine are produced (diuresis)
The fluid lost in the urine has to be replaced by excessive drinking.
NOTE:
Intake of Ethyl alcohol inhibits the production of ADH which lead to no reabsorption of water takes
Place hence dilute urine is produce causes dehydration and feeling of hangover
CONTROL OF BLOOD SODIUM LEVEL
The maintenance of the plasma sodium level at a stead state is controlled by steroid hormone
Aldosterone which also influence water reabsorption
Aldosterone is secreted by the cortex enter region of the adrenal glands
A decrease in blood sodium lead to a decrease in blood volume because less water enter the blood by osmosis. This returns reduces blood pressure. Aldosterone also stimulate. Sodium absorption in the gut decrease loss of sodium
-In sweat both these effect tend to rise blood sodium leves. This inturncause more water to enter the blood by osmosis raising its volume and hence its pressure.
FORMATION OF UREA IN HUMAN
Urea is the nitrogenous waste products of human and other land – living mammals
- The body is enable to store excess of amino acids taken in the diet
- NOTE:
- Those amino acids not immediately needed for protein synthesis must get rid of it.
- The process of get rid the amino acid takes place in the liver by the following;
1. Deamination
2. Detoxification
DEAMINATION
-The amino group (NH2) is removed from the amino acid and used to make ammonia (NH3)
-Amino acid is oxidized using oxygen
-Oxidizing amino acid by using oxygen result in removal of amino group
The acid group COOH can enter the kreb cycle and used as source of energy in cell respiration
The amino group is converted to ammonia (NH3) during deamination
3. DETOXIFICATION
Ammonia is converted into harmless products, urea for transport to the kidneys
Ammonia + carbon dioxide ---- urea + water
-Urea is produced by cyclic process known as ornithine cycle. Starting with ornithine in the cycle the
Overall two molecules of ammonia and one molecule of carbon dioxide era used one molecule of
Water is made (two made one used) and one molecule of urea. Ornithine is generated ready for the
Next cycle. Urea is transported in the blood plasma from the live to the kidney
ORNITHINE CYCLE
Caroline is non essential amino acid that is important intermediate in the urea cycle.
