Biology sem1- chap9

8/7/2019 Biology sem1- chap9

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OBJECTIVES Explain the significance of maintaining a

constant internal environment

Explain control of body temperature in

animal

Discuss some of the adaptations of plants

to environment



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HOMEOSTASIS

(homeo=sameness;-stasis=standing still)

The condition in which the body¶s internalenvironment remains relatively constant,within physiological limits

Homeostasis is a dynamic condition²inresponse to changing condition, the body¶sequilibrium point can change over a narrowrange that is compatible with maintaining life



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Important aspect of homeostasis is to maintaining the volume

and composition of body fluids

Intracellular fluids ± the fluid within cells

Extracellular fluids ± the fluid outside body cells

Interstitial fluid

± theextracellular fluids that fills the narrow spaces between cellsof tissues

Plasma ± extracellular fluids within blood vessels



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Process to maintaining the dynamic equilibrium in the body include

the :

Excretion

Osmotic balance

Important factors to maintain dynamic equilibrium:

Substances dissolved in water: ± Oxygen and carbon dioxide

± Nutrients (proteins, fatty acids, glucose level)

± Ions pH

Temperature

Osmotic pressure



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The waste products:

Carbon dioxide Bile pigments (biliverdin and bilirubin)

Water from the cell respiration

Urea



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Physiological control Body can regulate its internal environment through the feedback

systems

Feedback system ± a cycle of events in which the status of body condition is continuallymonitored, evaluated, changed, remonitored, re-evaluated and so on.

Each monitored variable, such as body temperature, blood pressure, blood glucose level is termed a controlled condition

Any disruption that changes a controlled condition is called a stimulus



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3 basic components make up a feedback system

1. R eceptor

body structure that monitors changes in a controlled condition and sendsinput in the form of nerve impulses or chemical signals to a control center.

2. Control centre set the range of values within which a controlled condition should be

maintained, evaluates the input it receives from receptors and generatesoutput commands when they are needed.

Output from the control center can occur in several forms: nerve impulses,

hormones , or

other chemical signals



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3. Effector

body structure that receives output from the control

centre and produces a response or effect that changesthe controlled condition.

As a control system operates, the effector

response feed back and influences the magnitudeof the stimulus by either depressing it (negative

feedback) or enhancing it (positive feedback)



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N egative feedback

Homeostatic mechanism that stops or reduces theintensity of the original stimulus and consequentlycauses a change in a variable that is opposite in directionto the initial change (The output is used to reduce input)

Positive feedback a feedback mechanism in which the response enhances

the original stimulus (The output is used to enhance theinput)

Example : The secretion of oxytocin duringchildbirth



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Homeostatic regulation

i. Every changes in the physical or chemical factors

of the internal environment ± detected by receptor

ii. Receptor send information about the changes to a

control systemiii. Action signals are transmitted through nerve

impulses or hormone to the target organ

± Trigger the correction mechanism to return the physical

or chemical factors to normal condition



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iv. Any increase in the value of a physical or

chemical factor in the internal environment will

trigger a correction mechanism to reduce thatvalue

Conversely, a reduction in the value of the

physical or chemical factor will trigger a

mechanism to increase the amount of that factor.



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If the control centre or correction

mechanism is disrupted, the change

occurring in the factor cannot be reversed

± The value of the factor continuing to rise or fall

± This is called positive feedback



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Schematic representation of homeostatic process

Normal condition

Receptor Control centre Effector Correction

mechanism

Normal

condition

restored

Receptor Control centre Effector Correction

mechanism

Factor value increase accelerated

Factor value decrease accelerated

increase

decrease

Positive feedback

Positive feedback

Transmission

of nerve

impulse or

secretion of

hormone

Negative feedback

Negative feedback

decrease

increase

Transmission

of nerve or

secretion of hormone



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Negative feedback in

control of blood

glucose level



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Control of blood sugar level

Regulated by the activities of several organs,

particularly the pancreas and liver

Any changes in blood sugar level

± Detected by pancreas

Endocrine gland

± Secrete insulin and glucagon

Beta cells of the islets

of Langerhans

Alpha cells of the islets of

Langerhans



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Schematic representation of blood sugar level regulation

Normal sugar level

Beta cell of the

islets of

Langerhans tosecrete insulin

Liver stimulated to convert

i. Glucose to CO2 + H2O

ii. Glucose to glycogen

iii. Glucose to fat

Blood sugar level falls

Normal sugar level

Alpha cells of

the islets of Langerhans

stimulated to

secrete

glucagon

Liver stimulated to convert

i. Glycogen to glucose

ii. Reduce glucose

oxidation

Blood sugar

level rises

Blood sugar

level rises

Blood sugar

level falls

Negative feedback

Negative feedback

decrease

increase



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An organism exchanges heat with its environment by

four physical processes

1. C onduction ± The direct transfer of thermal motion (heat) between molecules of the

environment and a body surface

2. C onvection ± The transfer of heat by the movement of air or liquid past a body surface

3. Radiation ± The emission of electromagnetic waves produced by all objects warmer than the

absolute zero

4. E vaporation ± The loss of heat from a liquid¶s surface that is losing some molecule as gas



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Body temperature regulation in humans and other mammals

Thermoreceptor

in skin

Body temperature

Hypothalamus, the

thermoregulatory centre in brain

Blood

capilaries

Erector

muscles

Sweat

gland

Skeletal

muscles

Adrenal

gland

Thyroid

gland

Vasodilation or

vasocontraction

Erection or

no erection

Sweating or

no sweating

Shivering or

no shivering

Adrenaline

level increases

or decreases

Thyroxine

level increases

or decreases

E fferent nerve

Afferent nerve Afferent nerve

Temperature regulation through physical action Temperature regulation

through metabolic action



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Schematic representation of body temperature regulation in mammals

Normal bodytemperature

Thermoregulatory

centre(hypothalamus) in

brain

Correction mechanism

Vasodilation

Sweating

Non-erection of hair

Drop in metabolic rate

Normal bodytemperature

Afferent

nerve

Thermoregulatory

centre

(hypothalamus) in

brain

Correction mechanism

Vasocontriction

No sweating

Hair erection

Increase in metabolic

rate

Temperature

rises

Temperature

falls

Efferentnerve

Temperature

falls

Temperature

rises

Efferent

nerve

Afferent

nerve



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LIVER



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Liver structure

Largest visceral organ inthe body

Metabolic centre in the body

Processed and stored food Received blood

± Hepatic artery

Oxygenated blood from the

dorsal aorta ± Hepatic portal vein

Nutrient rich blood fromsmall intestine

Sent blood to heart

± Hepatic vein



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Liver cell ± hepatocyte

Liver is made up of

many cylindrical lobes

Interlobular blood

vessel

± Branches of the hepatic

artery and hepatic

artery and hepatic

portal vein

± Connect to periphery

of each lobes



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Canalikuli

± Bile duct branches into

a network of finevessels

± Pass between cells of

lobes

Sinusoid ± Capillaries which form

from hepatic arteriole

and hepatic portal

venule

± Flow to central vein



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Kupffer cell

± Specialized ameboid

cell

± Attach to the inner wall

of sinusoid

± Phagocytosing old red

blood cells and patogens

Bile duct

± Carry bile to gall

bladder



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Functions of liver

1. Carbohydrate metabolism

Regulates blood sugar level

± Glycogenesis

Convert excess sugar to glycogen

± Glycogenolysis

Broken down the glycogen

± Cori cycle

Convert lactate into glucose



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2. Lipid metabolism

± Breaks down fat

± Transport of lipid

Produces globulin to transport fat

Stored in the form of adipose tissues



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3. Protein metabolism

Regulates protein and amino acid ± Deamination

Produced non-nitrogenous and nitrogenous parts

Non-nitrogenous part - convert into glucose in liver and stored as glycogen or broken down to release heat

Nitrogenous part ± enter ornithine cycle

± Ornithine cycle To convert ammonia (toxic) into urea (less toxic)



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4. Processing drugs and hormones

the liver can detoxify substances such as alcohol or excrete drugssuch as penicillin, erythromycin and sulfonamides into bile

5. Excretion of bilirubin

bilirubin derived from the heme of aged red blood cells, isabsorbed by the liver from the blood and secreted into bile

6. Synthesis of bile salts

bile salts are used in the small intestine for the emulsification andabsorption of lipids, cholesterol, phospholipids and lipoproteins

7. Storage

in addition to glycogen, the liver is a prime storage site for certainvitamins (A, cobalamin, D, E and K) and minerals (iron andcopper) which are released from the liver when needed elsewherein the body



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8. Phagocytosis

Kupffer¶s cells phagocytize aged red blood cells

and white blood cells and some bacteria

9. Activation of vitamin D

the skin, liver and kidneys participate in

synthesizing the active form of vitamin D



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R ole of the liver in (the

control) blood glucoselevel, fatty acids and

protein



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Carbohydrate Metabolism

Regulation of blood sugar level



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Carbohydrate Blood glucose Glucose-6-phosphate

(Tissue and liver)

Glucose-1-phosphate

Glycogen

(Liver)

Glycogen

(Muscle)

Pyruvate

aerobicanaerobic

Lactate + energy CO2 + H2O + energy

Amino acid Glycerol, fatty acid

digestion insulin

glycogenesis

glycogenolysisGluconeogenesis

Carbohydrate Metabolism



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Cori Cycle shows glycogen and lactate

movement between the liver and muscle



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Fats (lipid) metabolism

Fats in the liver can be modified for respiration and can be stored in the body

cells

Hepatocytes synthesize the cholesterolwhen the level is decreased. It also canexcreted cholesterol into bile when the levelof the cholesterol is increased



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Protein Metabolism

Protein being recycled are first broken down into amino

acids. Hepatocytes convert amino acids to fatty acid, ketone

bodies, glucose or oxidize them to carbon dioxide andwater

There are two ways of protein metabolism ± Deamination

a conversion consists of removing the amino group from the aminoacids and converting it to ammonia

± Transamination

the transfer of an amino group from an amino acid to pyruvic acid or toan acid in the Krebs cycle-can synthesized nonessential amino acids

Ornithine Cycle shows the formation of urea



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Metabolism of excess amino acid

Excess amino acid

Keto acid + NH3

Glucose

Glycogen Fats

Krebs

cycle

Ornithine

cycle

deamination

H2O + CO2 urea

CO2

Production of organic base

Nucleotide synthesis

Nucleic acid synthesis



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Ornithine cycle (urea cycle)

citruline

arginosuccinate

arginine

ornithine

H2O

urea

Carbamoyl phosphate

Pi

aspartate

NH3

ATP

AMP + PPi

fumarate

Deamination of amino acid

NH3 + CO2 + H2O

2 ATP

2 ADP + Pi



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That¶s all for today



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K idney



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Objectives Kidney structure and nephron

Urine formation involving ultrafiltration and

reabsorption Urine concentration by counter current

multiplier mechanism

Water regulation by ADH

Osmoregulation of mineral ions by aldosterone

pH regulation of the tissue fluid



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Introduction

yKidney

± main function in homeostasis

± urine formatian ; eliminate the nitrogen by products of protein metabolism and maintain

water balance



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Urinary system

Kidney ± pair of bean-shaped organ (about 10 cm long in human), located in

the region of the lower back

Ureter ± urine exits the kidney through this duct



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Urinary bladder

± ureter of both kidneys carries the urine to a urinary bladder

Urethra

± during urination, urine leaves the body through this and sphincter muscles near

the junction of the uretra and the bladder control urination



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Structure of kidney

andnephron



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Structure of kidney

renal pelvis

± within the kidney , the mouthof the ureter flares open toform a funnel-likestructure.and has cup-shapedextensions that receive urinefrom the renal tissue

± This tissue is divided into :-

renal cortex

± outer region

renal medulla

± inner region

nephron

± microscopic excretory tubules

± Each kidney composed of roughly 1 million nephrons



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Structure of nephron Bowman¶s capsule

± a hollow, cup shaped ( diameter b

200Qm) in the cortex of the kidney.

Glomerulus

± the cupped wall region and bloodvessel

± blood ±filtering unit

Proximal convoluted tubule

± close to the capsule , highly coiled anddiameter b60Qm

± Located in the cortex of the kidney.

Loop of Henle

± hair-pin shaped and have descendinglimb & ascending limb

± Located in the medulla of the kidney.



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Distal convoluted tubule ± located in the cortex of thekidney.

Collecting duct ± end of kidney and located in

the medulla of the kidney ± Several nephrons feed into

the same collecting duct

± The collecting ducts alleventually drain into the pelvis of the kidney, from

where the urine flows intothe ureter.



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Nephron and blood

circulation



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Nephron and blood circulation

Renal artery

± blood enters the kidney bythe renal artery which branches into afferentarteriole.

Afferent arteriole ± brings blood towards each

Bowman¶s capsule,dividing to form a network of capillaries calledglomerulus in the hollow of the capsule.

Efferent arteriole

± blood leaves the Bowman¶scapsule (capillaries) in anefferent arteriole, which isnarrower than the afferentarteriole

The efferent arteriole



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The efferent arterioledivided to form second setof capillaries whichsurround the proximal and

distal convoluted tubulesand the loops of Henle inthe medulla

The capillaries of the vasarecta (peritubular capillaries) run parallel tothe loops of Henle and thecollecting duct in themedulla.

Blood leaves the kidneythrough the renal vein

Renal arteryÄ afferent arterioleÄ glomerulusÄefferent arterioleÄ vasa rectaÄ renal vein



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Urine Formation

U i F ti



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Urine Formation

1) Ultrafiltration in

Bowman¶s capsule

Ultrafiltration of the blood

± it filters out molecules which

are much smaller than red

blood cell and plasma

proteins

± occurs as blood pressure

forces water ,urea, salts, and

other small solutes from the blood in the glomerulus into

the lumen of Bowman¶s

capsule.

Factors contribute to ultrafiltration process:-



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Factors contribute to ultrafiltration process:

i. The hydrostatic blood pressure in the glomerulus is higher than inother capillaries.

due to the high resistance to outflow presented by the efferent arteriole, which issmaller in diameter than the afferent arteriole

ii. Large amount of glomerulus filtrate large surface area for filtration provided by the highly coiled glomerulus capillaries



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iii. High permeability of the glomerulus The wall of Bowman¶s capsule in contact with capillaries consists of

specialized epithelial cell called podocytes. These cells have numerous

cytoplasmic extension called foot processes that cover most of the

capillaries.

Foot processes of adjacent podocytes are separated by narrow gaps called

filtration slits.



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The perforated walls of the

capillaries and the podocytes form

a filtration membrane that permitsfluid and small solutes dissolved in

the plasma, such as glucose, amino

acids, sodium, potassium,chloride,

bicarbonate, other salts, and urea,

topass through and become part of

the filtrate.

This filtrate membrane holds back

blood cells, platelets, and most of

the plasma protein.



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2) R eabsorption (proximalconvoluted tubule, loop of

Henle, distal convolutedtubule)

As the glomerular filtrates flowthrough the nephron, varioussubstances move out of it. Thenthey cross the cells that make upthe nephron¶s wall into the blood inthe capillaries running alongsidethe nephron.

Most reabsorption takes places asthe fluid flows through the proximal convoluted tubule.



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Capillaries reabsorb usefulmolecules such as glucose,amino acids, vitamins, most of the water, sodium andchloride ions.

The kidney tubules are beingadapted to increase thereabsorption efficiency by thefollowing factors.

a. The proximal and distaltubule are long and winding.Therefore both the surfacearea , and the time availablefor reabsorption are increased.

a. The tubules have walls whichare only one cell thick.Diffusion is efficient onlyover very small distances.



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c. The cells of the proximal and distal convulated tubules have a brush border of microvilli which increase the surface area in contact with the fluid, and thereforeincrease the rate at which substances can be absorbed from it.

d. The bases of the proximal tubule cells are irregular in shape where they are adjacentto a blood capillary and there are numerous intercellular spaces. The cells areideally adapted for the diffusion of absorbed substances into the capillary network that surround the tubule.

They also contain numerous mitochondria which are the sites of aerobic respiration. The energy is required for active uptake when substances are moved across cells such as sodium ions and glucose.



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Urine concentration by counter current multiplier mechanism



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Definition:

µcountercurrent¶

± fluids past each other inopposite directions.

± fluid flow down(descending limb) and up(ascending limb) of theloop.

µmultiplier¶

± fluid flow down thedescending limb, highconcentration of NaCl andmost hypertonic round the

hairpin ± fluid flow up the ascending

limb, less concentrated of NaCl; hypotonic

Urine concentration located in loop of Henle



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The function of the loop

of Henle ± to conserve water.

± the longer the loop of Henle, the more concentrated theurine that can be produced.

± loop of Henle create a water potential gradient betweenthe renal filtrate and the peritubular (medullary)fluid which bathes the loop;create a very highconcentration of salts in the

tissue fluid in the medullaof the kidney.

Urine concentration located in loop of Henle.



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This mechanism based of:-

i. The descending limb thin walls.

high permeable to water and permeable to most

ions/solutes.

its function is to allow

substances to diffuse

easily through its wall andwater would follow

by osmosis.

ii Th di li b



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ii. The ascending limb

the thin ascending limb

o this is the lower half of theascending limb and has

o thin wall like the descendinglimb.

o impermeable to water but

permeable to ions

the thick ascending limb

o this is the upper half of theascending limb and has thick

walls.o impermeable to water but

permeable to ions.

o actively reabsorb sodium andchloride from the tubule to

blood




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There is a gradient of

NaCl across the medulla

The filtrate which enters

the loop of Henle is

isotonic with the

peritubular fluid

Only the thin part of thedescending limb is freely

permeable to water.



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The sodium and chloride ions

are actively pumped out of the

thick ascending limbs , into

the tissue fluid outside.

As the two limb are so close toone another, this produce a

high concentration of sodium

and chloride ions around the

descending limb.



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When the fluid flows down thedescending limb, it is surrounded bytissue fluid with a high

concentration of ions and therefore alow water potential.

This causes water in the descendinglimb drawn out by osmosis.

The water moves straight into thecapillaries (vasa recta) surroundingthe loop of Henle.

At the same time, sodium and

chloride ions diffuse into the fluid inthe tubule, down their concentrationgradient.



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The effect is cumulative and

therefore the filtrate at the bottom of the descending limb and as it beginsto turn the hairpin, it has lost a lot of water and gained a lot of sodiumand chloride ions ( moreconcentrated than at either end).

As the fluid flows up the ascendinglimb, it continues to lose sodiumand chloride ions, and therefore become less concentrated.

The filtrate entering the distal tubuleis hypotonic to the peritubular fluid.



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Function of complex of blood capillaries runsalongside the loop of Henle:

± supply oxygen and nutrients so that cells in the walls of the loop can produce the large amount of ATP for active transport.

± take away much of the salt and water from the tissuefluid in the medulla, helping to maintain the gradients

built up by the loop.

H d hi h i h l



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How does this mechanism help to

conserve water?

The final part of each nephron, the collecting duct,also passes through the medulla of the kidney.

As the fluid flow through the collecting ducts,water can be drawn out of them, by osmosis, intothe concentrated tissue fluid in the medulla.

The more concentrated the tissue fluid, the morewater can be drawn out, and the moreconcentrated the urine can be.



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Concepts

The kidney play central role in the regulation of the water content of the body or osmoregulation.

The water content of the blood is monitored by

osmoreceptor cells in the hypothalamus and these

cells produce antidiuretic hormone, ADH.

Summarize



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Su e

Source Target tissue Actions Factors that

StimulateR elease

Produced in

hypothalamus;

released by

posterior

pituitary gland

Distal

convoluted

tubule and

collecting ducts

Increases

permeability of

the collecting

ducts to water,

increasing

reabsorption and

decreasing water

excretion

Low fluid intake

decreases blood

volume and

increases

osmotic pressure

of blood;

receptors in

hypothalamus

stimulate posterior

pituitary




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g y

Low intake of water

Water content of the blood is lower than normal, the body begins todehydrate, causing the blood volumeto decrease.

The concentration of salts dissolved

in the blood becomes greater

Osmotic pressure increase.

Osmoreceptor in hypothalamus aresensitive to this osmotic change andstimulate the posterior lobe of the pituitary to release more ADH

ADHmakes the collecting duct wall

more permeable to water



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High intake of water

Water content of the blood is higher than normal, the body fluids begin todilute, causing the blood volume to increase.

Concentration of salts dissolved in the blood becomes less

Osmotic pressure decrease.

Osmoreceptor in hypothalamus are sensitive to this osmotic change and

stimulate the posterior lobe of the pituitary to release less ADH

ADH makes the collecting duct wall less permeable to water

Less osmotic uptake of water is allowed (less water reabsorption)

Large volumes of diluted urine are produced

This water loss reduces the solute concentration of the blood



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The maintenance of the plasma sodium level iscontrolled by aldosterone.

Secreted by the cortex

region of the adrenalgland.

Aldosterone stimulates the

distal tubule to increasesodium reabsorption andthereby maintains the balance of salt and water inthe body fluids.




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When blood sodium level decrease

A decrease in blood sodium leadsto a decrease in blood volume because less water enters the blood by osmosis.

Reduces blood pressure.

This decrease in pressure andvolume stimulates a group of secretory cells, the juxtaglomerular complex, situated between the

distal convoluted tubule and theafferent arteriole, to release anenzyme called renin.

Renin passes into the blood here



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Renin passes into the blood whereit acts on its substrate, a proteincalled angiotensinogen,converting it to angiotensin.

The arrival of angiotensin at theadrenal glands causes aldosteroneto be secreted into the blood.

Therefore, increase the rate of reabsorption of sodium ions fromthe distal convoluted tubules.

Thus, fewer sodium ions are lostin the urine, and more are retainedin the blood.

Thus causes more water to enter the blood by osmosis, raising itsvolume and hence its pressure.



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pH regulation

of

the tissue fluid



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Carbon dioxide reacts with water to produce carbonic

acid:

CO2 + H2O H2CO3

Carbonic acid dissociates to produce hydrogen ionsand hydrogencarbonate ions:

H2CO3

H+ + HCO3

-

pH regulation of the tissue fluid



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p g

The kidney help to regulate pH by altering the rate at which they excrete

hydrogen ions.

Hydrogen ions are continually secreted into the fluid as it passes along thenephron.

The rate at which they are secreted depends on the pH of the blood.

An equivalent number of hydrogen ions must therefore be excreted in urine tomaintain acid-base balance.

In addition, the kidneys assist the lungs by eliminating CO2 that enters the renaltubules during filtration or that diffuses into the tubular fluid as it travels toward

the renal pelvis.

Hydrogen ions are secreted into the tubular fluid along the proximal convoluted tubule,the distal convoluted tubule, and the collecting duct.



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If the blood fluid pH is low (acidosis - developed

when the normal plasma buffer mechanisms are

stressed),

± more hydrogen ions are secreted into the tubules or the

collecting duct from the blood.

± more hydrogen ions are lost from the body in the urine.

± Addition of that is removal of CO2, activity of buffers

in the tubular fluid and reabsorption of NaHCO3

± A fall in pH also stimulates the kidney cells to produce

the base ion ammonium (NH4

+) which combines with

acids brought to the kidney and then excreted asammonium salts.

If blood pH is high (alkalosis)



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If blood pH is high (alkalosis),

± then fewer hydrogen ions are secreted into the

nephron; ± they remain in the body rather than passed out in the

urine.

± The collecting system transports HCO3

- into tubular

fluid while releasingHCl into peritubular fluid.

± The concentration of HCO3

- in plasma decreases,

promoting the dissociation of H2CO3

and the release

of hydrogen ions. ± The additional H+ generated at the kidneys help return

the pH to normal levels.



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Water

concentration in

plant

Objectives



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Objectives

i. The role of stomata in water loss throughtranspiration

ii. Significance of transpiration

iii. Plant adaptation to the habitats

± Xerophytes

± Hydrophytes ± Mesophytes

± Halophytes



BerpenyakitTidak berpenyakit

Pengumuman Jabatan Pertanian

Bagaimana hendak mengenali penyakit Lembu Gila.



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The role of stomata in

water loss throughtranspiration



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The role of stomata in water loss through

transpirationSignificance of transpiration

Loss of water from plants¶surface is called transpiration

Water normally leaves the plant as water vapour.

The change from the liquid state to the vapour state

requires the addition of energy which is provided by thesun, and it is this energy that maintains the flow of water throughout the entire plant.

T i i f h b i f



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Transpiration occurs from the stomata by evaporation of water from cells and diffusion of the water vapour throughstomata, the pores found in the epidermis of leaves andgreen stems.

About 90% of the water is lost through transpiration.

Water in the plant is in direct contact with water in soil andwith water vapour in the air around the plant.

Water movement from higher water potential to the lower water potential is called potential gradient.

The gradient is maintained by solar energy and evaporationof water from the surface of the plant (transpiration)

Water is essential for plant metabolism, but is continuously beingl t t th t h th h th t t



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lost to the atmosphere through the stomata.

Photosynthesis requires a supply of CO2

entering the stomatafrom the atmosphere.

Therefore, plants need to minimize the loss of water to theatmosphere and the need to allow the diffusion of CO2.

Closing the stomata can control water loss.

However, the opening of stomata at times helps CO2 to enter anddissolves in the water on the walls of the intercellular spaces

below the stomata, before entering the plant¶s cells.

A plant must responds both to the need to conserve water and therequirement of CO2



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Plant adaptation to the habitats

Xerophytes

Hydrophytes

Mesophytes

Halophytes

The rate of transpiration depends on whether

conditions like humidity and the time of the day.



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Xerophytes

Plants which grow in dry habitats and subjected todrought.

Example : cactus

Adaptations to reduce water loss

It has a very long, shallow, spread-out root system.

It has a swollen , succulent stems or leaves.

It has specialized leaves that may be hairy, rolled or reduced to spikes or reduced leaf size.

It has a round shape, giving it a low surface area tovolume ratio.

Adaptations to reduce water loss



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It has a very long, shallow, spread-out root system.

It has a swollen , succulent stems or leaves.

It has specialized leaves that may be hairy, rolled or reduced to spikes or reduced leaf size.

It has a round shape, giving it a low surface area to volume ratio.

The stomata are sunken into pits and surrounded by hairs.

It has hairs over its surface which trap moisture.

It has thick layers of epidermis and heavily waxed on the cuticle of the leaves.

It has crassulacean acid metabolism (CAM) mechanism of photosynthesis; their stomatastay closed during the heat of the day and open during the cooler, more humid night.

Some spesies survive in the seed or spore stage and germinate, grow, flower and seed in ashort time following rainfall.



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Hydrophytes

plant that lives either in very wet soil or

completely or partially submerged in

water Examples : pondweed

( El odea sp), waterlily ( Nymphaea sp).

Adaptation to survive in very wet condition;



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Adaptation to survive in very wet condition;

It has absence or reduction of a root systems

It has specialized leaves (ribbonlike leaves) that may be either floatingor finely divided, with little or no cuticle

It has a few xylem tissues

It has many air holes/air chambers in the stem (for O2 and CO2storage which supply oxygen to the roots and enable them to float)

Epidermis :

to absorb nutrients from the water, not for protection (absorpingnutrients and water through their leaves)

contained chlorophyll

No stoma ± if there is, it will be at the upper part of a leaf



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Mesophytes

Plants growing under conditions in which

there is normally an adequate water supply

The majority of angiosperm plant spesies

are mesophytes, and they faced with the

problem of water loss by evaporation fromall aerial parts



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Adaptation to reduce water loss

Presence of cuticleProtected stomata whose diameters can be

regulated

Variable leaf shape

Abscission (leaf fall)

Ecological distribution based upon tolerance to

dehydration

It has stoma closed when it is very hot (daytime ±afternoon)



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Halophytes

Plants which live in an environment where there is plenty of water,but they have difficulty obtaining it because it is salty

Conditions like this are found in estuaries and salt marshes

Plants adapted to live in salty conditions

Salinity changes according to environment

Examples : S partina sp(cord grass) and mangroves

Adaptations to water conservation :



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It has root cells with very low water potentials (high transpiration ability ; thereforecell water potential are lower than habitat water potential).

It has hydatode at the side of the leaves or special salt glands at the margins to excreteexcessive salt by active transport onto the leaf surface.

It has roots submerged in salt water/ knee root ± above the surface of the salty muds(mangrove)

It has an extensive systems of rhizomes for propagation.

It has adventititous root for anchorage and uptake of water as well as ions.

It has root systems that are able to tolerate high salinities. Many spesies haveextensive roots which are able to store water when it is freely available.

It is capable of storing water in its succulent tissues.

It has respiratory roots/pneumatophores which are dotted with lenticels, (small vent-like openings) that take in air and channel it to the parts of the root that are buried beneath the mud (mangrove).



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Biology sem1- chap9

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