Excretion Andosmoregulationppt09 10

7/28/2019 Excretion Andosmoregulationppt09 10

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Excretion and

Osmoregulation


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EXCRETION AND

HOMEOSTASIS

Excretion, as mention before is theremoval of metabolic wastes from thebody.

These wastes are called metabolic becausethey are made inside cells.

The term excretory products is also used tomean metabolic wastes as they are allexcreted from the body by one means oranother.


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Metabolic wastes/ excretory

products In humans and most animals the main

excretory product is Urea.

This is a nitrogen base compound whichcomes from the breakdown of excessamino acids in the liver (recall; aminoacids are the final product of digestion ofproteins and all proteins contain nitrogen).

The process which breaks down excessamino acid is called Deamination.


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Other excretory products include: carbon

dioxide which is a waste product from

respiration in cells, metabolic waterwhich isalso as a result of respiration (glucose +

oxygen carbon dioxide + water +

energy), excess salts and bile pigments.

Excess salts derive from the breakdown of

unwanted substances such as excesshormones in the blood and other substances

which go to the liver to be metabolized.


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Bile pigments come from old red blood

cells which are broken down in the liver

as well. Bile is stored in the gall bladder

and used for the digestion of fats. NBBile is the only metabolic product that is

excreted through the alimentary canal.


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TABLE SHOWING EXCETORY PRODUCTS

AND THE ORGANS THAT EXCRETE THEM

Excretory products Organs

Urea The Kidneys

Carbon dioxide, water vapour The Lungs

Metabolic water The Kidneys and the Skin

Salts The Skin and Kidneys

Bile pigments The alimentary canal


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Excretory Organs


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The Lungs:

Even though the lungs are a part of the

respiratory system, they are very

essential in excretion.

The lungs are specialized for the

diffusion of gases and Carbon dioxide is

a harmful gas that needs to get out ofthe body after respiration.


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The Lungs


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The skin Even though the skin is essential in helping to

regulate our body temperature it is quite importantin excretion.

The skin is the bodys largest organ and therefore

has a great surface area for excretion to occur.

When we sweat, we are not only cooling down thebody but getting rid of unwanted salts, water andtraces of urea.

The skin is responsible for removing wastes insweat. Sweat comes directly from the blood whichtransports useful substances as well as wastes;

even some carbon dioxide is excreted by the skin.


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The skin is made up of layers, the two mainlayers are: the epidermis which is the upperand the dermis which is the lower layer.

There is a layer of fat beneath the dermiscalled the Hypodermis.

The dermis contains most of the structures inthe skin.

For example, sweat glands, hair follicles,sebaceous/oil glands blood vessels andnerves.


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The epidermis has two sections, the upper

section is called the cornified layer, and it is

made up of dead cells and has a protective

role.

The other layer is the germinal layer withliving cells and the pigment Melanin which

gives the shin its dark colour.


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The skin is specialized for the excretion of

sweat because of its large amounts of sweat

glands which leads out through sweat pores.

Also, the many capillaries in the skin which

carries contents of the blood close to thesweat glands to be excreted.


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Fig. 2: Diagram of a human

skin


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The Kidneys:

The kidneys are the main excretory organs of the body;they excrete most of the urea, salts/ions and water fromthe body.

All these wastes together make up urine.

Humans have two kidneys which are located in the lowerback.

The left kidney is slightly above the right but they areboth embedded on either sides of the vertebral column.

Each kidney has a bean shape and is made up of threemain sections.


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The outer pale layer is called the Cortex; the

middle layer is the Medulla and the inner

stem like section which narrows to becomethe ureteris called the Pelvis.

Inside the kidneys are a series of tubuleswhich run from the Cortex to the Pelvis.

These tubules are highly coiled and arecalled Nephrons.


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Diagram of Kidney


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These small structures are responsible for

filtering the blood and removing the excretory

products.

A nephron is made up of a cup-like structure

called a Bowmans capsule.

This capsule contains a knot of capillaries

called a glomerulus; the blood is filtered heredue to the high pressure in the glomerulus.


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The Bowmans capsule is in the cortex of the

kidney and the first coiled tube which

extends from the Bowmans capsule is calledthe proximal convoluted tubule.

This tubule extends downward into theMedulla to form a loop called the loop of

Henle.


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The loop of Henle comes back up into the

cortex and forms another coil called thedistal convoluted tubule.

The coiled tubule joins the collecting ductwhich runs from the medulla to the pelvis.


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HOW IS URINE PRODUCED

FROM BLOOD

The Renal arteries carry blood with

wastes to both kidneys.

Inside the kidneys the renal artery

branches to form many afferent

arterioles which form the glomerulus in

each Bowmans capsule.


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The afferent arteriole has a larger

diameter than the efferent arteriole

which carries filtered blood away from

the glomerulus.

The fact that the afferent arteriole has a

larger diameter than the efferent this is avery high pressure in the glomerulus.


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The pressure causes the blood in the

glomerulus to be squeezed through the

capillary walls and into the Bowmans

capsule.

This is called ultra filtration or

pressurefiltration.


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Most of the constituents of blood will go

into the Bowmans capsule except for

blood cells and large protein molecules.

This filtrate is called the Glomerularfiltrate.

It is composed of water, salts, glucose,amino acids, fatty acids, glycerol and

urea.


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Fig. 3: Diagram of a human

kidney


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As the glomerular filtrate passes along the

nephron useful substances are reabsorbed.

As a matter of fact, 80% of the useful

substances are absorbed at the proximal

convoluted tubule.

This is called selective reabsorption as only

the useful substances are reabsorbed.


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This is done by active transport and

therefore requires energy.

As the remaining substances move along the

length of the nephron the next 20% of useful

substances are reabsorbed into thecapillaries that surround the nephron.

Most of the remaining water is reabsorbed inthe loop of Henle.


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While, wanted salts are reabsorbed in the

distal convoluted tubules.

When the glomerular filtrate reaches the

collecting duct it forms urine.

More water and salts are reabsorbed here.


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Urine left the collecting ducts, enter the pelvisand move to the ureter which carries urine tothe bladder where it is stored and periodicallyreleased through the urethra.

The reabsorbed constituents go into thecapillaries and then carried to the renal vein

which carries blood away from the kidneys.

Urine and sweat have very similar constituents;its the amount that varies.

Sweat is more concentrated as it contains lesswater than urine but a lot of salts.


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CONTENTS OF URINE AND

SWEATUrine Sweat

Water Water

Urea Trace of urea

Sodium chloride Sodium chloride

Other salts Other salts

Other nitrogenous

substances

Trace of bicarbonate


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Urinal System in Man


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A ureter leads from each kidney and

enters the bladder; the function of the

bladder is to store urine.

It is emptied by a tube called the

urethra, the entrance to which is

guarded by a sphincter muscle, aninvoluntary muscle.


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The urethra leads to the exterior of the

body; in females, the urethra is quite

short (about 4 cm long), and emerges

just in front of the external opening ofthe vagina (reproduction); in males, the

urethra is much longer (about 18 cm.),

leading into the penis (reproduction).


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The kidneys are the main excretory organsof the body, and nearly 2000 litres of bloodpass through them every 24 hours.

The bladder has a maximum capacity ofabout 500 cm3; when it is full, its distensionstimulates a nerve, and by a conscious

response, the bladder muscles arestimulated by urine under pressure. (SeeFig. 13).


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Function of Kidney

Urea, glucose, soluble inorganic salts,

and water (these are all small

molecules) filter through the wall of the

capillaries in the glomeruluss, thatthrough the walls of the capsule, and the

filtrate passes into the seminiferous

tubule.

Blood proteins (which are large

molecules) do not filter through.


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As the filtrate passes along the tubule,

various materials are reabsorbed and

pass back across the wall of the tubule

into the blood in the capillaries

All the glucose is reabsorbed.

A little of the urea is reabsorbed


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Sodium ions and chloride ions are

reabsorbed sufficiently to keep the blood

level of sodium chloride, exactly right.

The kidney regulates the blood level of

sodium chloride. It also regulates the

level if some other ions, such ascalcium, potassium, phosphate and

bicarbonate


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By regulating the blood level ofhydrogen ion the kidney works toprevent the blood from becoming tooacid or too alkaline.

Finally, in the collecting ducts water isreabsorbed, so that the urine as it finally

reaches the bladder is a ratherconcentrated solution of unwantedmaterials.


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Normal urine contains no glucose, no

protein, and no amino acids. It does

contain variable quantities of urea and

ions.

The amount of urine produced depends

on the amount of water which has beendrunk. An average quantity is about 1

liter to 1.5 liters per day.


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Composition of Urine

Normal urine contains 96% by weight ofwater the remaining 4% being dissolveddissolved solids.

It is a clear, amber-coloured liquid with aslightly acidic reaction.

Urea is the chief constituent of the dissolved solidsand accounts for 2%; sodium chloride accounts formore than 1%, the amount being variable


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The remainder includes phosphate,

sulphates and oxalates of potassium,

calcium and magnesium, and also 0-3% of

uric acid, a nitrogenous waste product fromproteins.


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Homeostasisis all the processes involved tomaintenance of a constant internal environment.

These include maintaining a constant blood sugarlevel, internalbodytemperature and water

balance/bloodconcentration.

The aforementioned are important as without thisregulation system the blood sugar concentrationmay increase to abnormal levels, this causes

numerous problems as seen in diabetes.


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On the other hand if the blood sugar levelfalls too low the cells will not have enough

energy to carry out their activities.

Secondly, if the internal body temperature is

too low the enzyme will be inactivated which

will reduce cellular activity, if it is too high the

enzymes will be denatured again reducing

cellular activity.


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Finally, if the blood is too concentrated with

salts it can affect the osmotic balance and

pull liquids from the cells.

This in turns will increase the blood pressure.

If it is too low the water will move into the

cells, making them too turgid and burst.


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Homeostasis is controlled by the Hypothalamusof the brain which sends messages to variousparts of the body when necessary.

Homeostasis is achieved negative feedbackand positive feedback mechanism.

Negative feedbackmechanism occurs when a

change is detected by the body and thisdetection starts a mechanism to restore thenormal condition.


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For example body temperature, water balanceand blood sugar, pH, and carbon dioxide

concentration in the body.

Positive feedback mechanism occurs lestoften in our body, it happens when the change

which stimulates the body is increased.

For example the contraction of the uterusduring birth is detected and the hormone

oxytocin is produced which increasescontraction and this cause more oxytocin to bereleased.


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Negative feedbackmechanism occurs

when a change is detected by the body and

this detection starts a mechanism to restore

the normal condition.

For example body temperature, water

balance and blood sugar, pH, and carbondioxide concentration in the body.


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Positive feedback mechanism occurs lestoften in our body, it happens when thechange which stimulates the body isincreased.

For example the contraction of the uterusduring birth is detected and the hormone

oxytocin is produced which increasescontraction and this cause more oxytocin tobe released.


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Too much Corrective mechanism

Level rise Level drops

Normal level Normal level

Level drops Level rises

Too little Corrective mechanism


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BLOOD SUGAR LEVELS

Blood sugar level is affected by a meal orseveral hours without a meal.

After a meal the blood sugar level increases.

This is detected by the islet cells of thepancreas.

Betacells in the isletofLangerhans start toproduce and secrete a hormone calledinsulin.


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Insulin in the blood causes the glucose in

the blood to be taken up by the liverand

muscles and converted to glycogen.

Some is also converted to fats and storedwhile the remainder is oxidized to produce

energy for the body.

Blood sugar level is restored.


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Glucagons cause the liver to breakdown

glycogen to glucose which is released

into the blood.

Blood sugar level is restored.

Liver

Liver


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Glycogen converted fat in liver Glycogen stored

in liver in liver

glucose glucose oxidized

Less insulin more Blood glucose less glucagons

More glucagons secreted by 90mg/100cm3

Insulin secreted bypancreas cells pancreas cells

detected by islets of Glucose detected by islets ofLangerhans in pancreas Langerhans in pancreas

Blood glucose Blood glucose

level falls Glycogen in muscles level rises

BODY TEMPERATURE


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BODY TEMPERATURE

Normal body temperature is 37C or 98.6F.Temperature is a degree of hotness orcoldness of an object.

Heat is a form of energy measured in joules.

When the internal temperature rises above

37C or 98.6F it is detected by theHypothalamus of the brain which sendselectrical impulses to the skin.


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At the skin, blood vessels dilate(vasodilatation) and have closer o thesurface, losing heat by radiation.

The sweat glands produce large amounts ofsweat which goes to the surface of the skinand evaporate.

This has a cooling effect on the body.


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Erector muscles pulls hairs flat to preventextra trapping of air over the surface of the

skin.

After all these mechanisms normal

temperature is restored.

If the body temperature falls too low then the

skin is instructed in a different way.


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Blood vessels in the skin constrict(vasoconstriction) to prevent further loss of

heat.

An involuntary muscular contraction called

shivering begins.

This produces heat for the body.


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Sweat glands become inactive and respirationincreases.

Additionally, the hairs stand erect to trap a layer

of air over the surface of the body.

This acts as an insulator like the layer of fatbeneath the skin.

Normal body temperature is usually restored.

Body temperature fall Body temperature rise


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Body temperature rise Body temperature lowered

Pituitary gland in brain

Shivering sweating

Capillaries constrict Capillaries dilate

Blood flow decreases Blood flow increases

Hair stand erect Hair lies flat

Body response

WATER BALANCE


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WATER BALANCE

The control of water balance or blood

concentration is called Osmoregulation.

If the blood is too concentrated receptors in

the hypothalamus of the brain detects it and

cause the release of a hormone called

antidiuretichormone (ADH).


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Blood dilute Blood concentrated


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Pituitary gland in brain

No thirst thirst

Less ADH in blood More ADH in blood

More water in urine Less water in urine

Less reabsorption of More reabsorption of

water into the blood water into the blood

Urine dilute Urine concentrated

Normal water potential


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Examination Questions

Read each question carefully and write

the appropriate answers.

Check your answers by reading over theresponds given

Exam type QuestionsM i t i i l bl d l l i i t t f f ti i f ll d f


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ypMaintaining normal blood sugar levels is important for proper functioning of our cells and for

ensuring our optimum energy requirements.

Figure 50 shows a schematic diagram of some of the major organs and processesassociated with maintaining normal blood sugar.

Figure 50: Schematic diagram

(a) Name organ J, which detects changes in blood glucose level. (1mk)

(b) (i) Insulin and glucagon are examples of what type of substance? (2mks)

(ii) Explain how the blood levels of the following substances change with

blood sugar concentrations. Insulin:

Glucagon: (4mks)

(c) Identify EACH of the following processes occurring in the kidney:

(i) Process H, in which sugar leaves the blood. (1mk)

(ii) Process I, in which sugar re-enters the blood. (1mk)

(d) Explain why insulin is given as an injection. (1mk)

Figure 52 shows a flow chart that represents the processes occurring indifferent structures in the kidney tubule


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different structures in the kidney tubule

Name EACH of the structures labelled A, B

and C. (3 mks)

Name TWO substances reabsorbed at B.(2 mks)

Why must the blood enter the kidney at

high pressure? (1 mk)

Suggest a possible reason for protein being

present in the urine at D. (1 mk)

(e) (i) Explain why there should

be no sugar in the urine

leaving the normal kidney.

(2mks)

(ii) State the condition associated

with the presence of sugar in

the urine. (1 mk)

3. (a) (i) Define the term 'excretion'. (2mks)


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(ii) Name TWO excretory organs, OTHER THAN

the kidneys. (2mks)

(b) (i) The kidneys regulate bloodcomposition in three ways. One way is

removing excess water. Identify TWO OTHER ways.

(2mks)

(ii) How do the kidneys assist in maintaining

blood pH? (1mk)

(c) Brian sweats profusely during a cricket

game. Explain how the sweat reaches the surface of the skin.

(3mks)

Figure 56 shows the internal structure of a human kidney


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g y

Figure 56: Internal structure of kidney

Name the parts labelled A an B. (2mks)

Describe the process of ultra-filtration and reabsorption in the nephron.

(3mks)

Define the term homeostasis. (2mks) Describe the role of the anti-diuretic hormone (ADH) in the human body.

(5mks)

Explain how the skin functions in regulating body temperature in humans.

(8mks)

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Excretion Andosmoregulationppt09 10