Homeostasis 4. HOMEOSTASIS 4.1 Definiton and Importance Homeostasis = steady state @ internal balance. Definition: Dynamic state, an interplay between outside factors that tend to change the internal environment and internal control mechanism that oppose such changes in a living organism. The internal environment of vertebrates is called the interstitial fluid. Maintain relatively constant conditions in their internal environment even when the external environment changes. Importance: The tissues and cells require appropriate condition to function properly. Q: State the factors that might affect a complex organism’s ability to sustain life? Temperature Nutrient (glucose) Salinity (concentration of Na + & Cl - ) Waste balances Acidity (pH) Regulatory mechanism of the vertebrate are concerned with maintaining homeostasis. HMM/SCM 1424, CFS IIUM 1
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Homeostasis
4. HOMEOSTASIS
4.1 Definiton and Importance
Homeostasis = steady state @ internal balance. Definition: Dynamic state, an interplay between outside
factors that tend to change the internal environment and internal control mechanism that oppose such changes in a living organism.
The internal environment of vertebrates is called the interstitial fluid.
Maintain relatively constant conditions in their internal environment even when the external environment changes.
Importance: The tissues and cells require appropriate condition to function properly.
Q: State the factors that might affect a complex organism’s ability to sustain life? Temperature Nutrient (glucose) Salinity (concentration of Na+ & Cl -) Waste balances Acidity (pH)
Regulatory mechanism of the vertebrate are concerned with maintaining homeostasis.
4.2 Mechanism of Homeostasis These mechanisms enable regulated change. 1) Negative feedback mechanism
(Refer Figure 40.11 page 832)
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Fig 40.11: A nonliving example of negative feedback; control of room temperature
Homeostatic control mechanism in which deviation from constancy stimulates the activity of effectors that act to counteract the deviation.
An increase in some substance or activity inhibits the process leading to the increase. Known as negative feedback inhibition.
Excess Corrective mechanism Negative
feedback Set point Set point
Negative feedback
Deficiency Corrective mechanism
Diagram shows negative feedback keeps a system in stable condition. A change from usual level of a factor
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(set point) triggers a corrective mechanism which restores the factor to its usual level.
A) Thermoregulation Thermoregulation is the process by which animals
maintain an internal temperature within a tolerable change.
Each species has an optimal temperature range. E.g: Mammals (37°C), birds (40°C - 43°C)
Q: Define the term endothermic & ectothermic & how these organisms regulate their body temperature. (Refer Figure 40.12 page 834)
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Fig 40.12: The relationship in between body temperature and environmental temperature in an aquatic endotherm
and ectotherm
Endothermic : an organism that used metabolic heat to regulate their body temperature. This heat is usually used to maintain relatively stable body temperature (Independent of the environmental temperature). Being endothermic is energetically expensive. E.g: All mammals and birds.
Ectothermic: an organism that do not produce enough metabolic heat to have much effect on body temperature. Gain most of their heat from environment (Dependent of the environmental temperature). They can thermoregulate by behavioral means such as basking in the sun or seeking out shade. E.g: Most animals except birds and mammals.
Controlling body temperature in humans. (Refer Handout)
1. Regulation of skin temperature The set point is the preferred skin temperature The detectors are thermoreceptors in the skin.
Heat receptors = organ Ruffini and Cold receptors = Bulb of Krausse.
Behavioral responses act as the corrective mechanism.
2. Regulation of body core temperature (Refer Figure 40.21 page 839)
By autonomic physiological responses Optimal body core temperature is 37°C.
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The detectors are the thermoreceptors in the hypothalamus
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Fig 40.21: The thermostat function of the hypothalamus in human thermoregulation
B) Glucose regulation (Refer Figure 49.5 Raven and 56.20 Raven)
Fig 56.20 Raven : The antagonistic actions of insulin and glucagon on blood glucose.
The rise in blood glucose concentration following a meal stimulates the secretion of insulin from the islets of Langerhans in the pancreas.
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Insulin= promotes the entry of glucose in skeletal muscle and other tissue
Lowering the blood glucose and compensating for the initial rise
Glucagons stimulates the hydrolysis of liver glycogen between meals
These antagonistic effects help to maintain homeostasis of the blood glucose regulation.
Q: Determine sensor, integrating/control center and effector organ in the control of body temperature and control of glucose in human body.
Body temperature Blood glucose
Sensor Thermoreceptor in skin. Bulb of Krausse for cold stimuli and the organ Ruffini for heat stimuli.
Hypothalamus
The islets of Langerhans
Integrating/control center
Hypothalamus The islets of Langerhans
Effector organs
Refer Hand out Muscle/Liver/ Adipose tissue
C) Blood Ca ++ level regulation (Refer Figure 45.11 page )
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Fig 45.11: The roles of calcitonin and parathyroid hormone in regulating blood calcium levels in mammals
Parathyroid hormone (PTH) and calcitonin balance blood calcium.
The mammalian thyroid gland produce calcitonin and parathyroid glands produce PTH.
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If blood Ca++ falls below the set point, PTH raises the level through; Osteoclasts to decompose the mineralized matrix
of bone &release Ca++ into the blood. Stimulates reabsorption of Ca++ through the renal
tubules. Promotes the conversion of vitamin D active
hormonal form in the kidneys. The active forms act on the intestines, stimulating the uptake of Ca++ from food.
If blood Ca++ rise above the set point, calcitonin raises the level through; Exerts effects on bone and kidneys opposite those
of PTH. Stimulates Ca++ deposition in bones. Reduces Ca++ uptake in kidneys.
2) Positive feedback mechanismChange in some variable that triggers mechanisms
that amplify rather than reverse the change. Have limited function in the body because it is highly
unstable.
E.g: I) During childbirth, the opening of the uterus
II) Generation of an action potential.III) Blood clotting mechanism.
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Fig 58.7 Raven: An example of positive feedback during childbirth
4.3 Osmoregulation Regulates solute concentration and balances the gain
and loss of water. Two basic solutions to the problem of balancing water
gain with water loss.
1) Osmoconformer
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Only to marine animals is to be isoosmotic to the surroundings.
Do not compensate for changes in external osmolarity, osmoconformers often live in water that has a very stable composition and constant internal osmolarity.
2)Osmoregulator
Control its internal osmolarity because its body fluids are not isoosmotic with the outside environment.
Discharge excess water if it lives in a hypoosmotic environment or take in water to offset osmotic loss if it inhabits a hyperosmotic environment.
Osmoregulation enables animals to live in environments that are uninhabitable to osmoconformers, such as freshwater and terrestrial habitats.
Enables many marine animals to maintain internal osmolarities different from seawater.
Marine vertebrates and some marine invertebrates are osmoregulators. Marine bony fishes (e.g: cod) are hypoosmotic to
seawater and constantly lose water by osmosis and gain salt by diffusion and from the food they eat.
The fishes balance water loss by;i) Drinks seawater and actively transporting
chloride ions out through their skin and gills. Sodium ions follow passively.
ii) Kidney with small/no glomeruli
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iii) Produces very little urine.
Marine sharks and most other cartilaginous fishes (chondrichthyans) use a different osmoregulatory “strategy.”(Refer Figure 46.5(c) page 900) No continuous osmotic loss because high
concentration of urea in body fluids leads to an osmolarity slightly higher than seawater.
Water enters the shark’s body by osmosis and in food, and is removed in large volume of hypotonic urine.
Kidney with large glomeruli to reabsorbs urea.4.3.2 Freshwater animals
(Refer Figure 46.5(a) page 900)
Freshwater animals are constantly gaining water by osmosis and losing salts by diffusion. The osmolarity of their internal fluids is much higher
than their surroundings. Many freshwater animals maintain water balance by;
i) Kidney with large glomeruliii) Excreting large amounts of very dilute urine.iii) Regaining salts in food and by active uptake of
salts from their surroundings.iv) Drinks no water
Q: How does Salmon that migrate between seawater and freshwater osmoregulate?
Salmon undergo dramatic and rapid changes in osmoregulatory status: In the ocean, salmon osmoregulate as other marine
fishes do, by drinking seawater and excreting excess salt from the gills.
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When migrate to fresh water, they cease drinking, begin to produce lots of dilute urine, and their gills start taking up salt from the dilute environment.
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Fig 46.5 Solomon: Osmoregulation in fishes4.3.3 Land animals
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Most terrestrial animals have body coverings that help prevent dehydration. Waxy layers in insect exoskeletons, the shells of land
snails, and the multiple layers of dead, keratinized skin cells of most terrestrial vertebrates.
Nocturnal reduces evaporative water loss.
Most terrestrial animals lose considerable water from moist surfaces in their gas exchange organs, in urine and feces, and across the skin.
Land animals balance their water budgets by;i) Drinking and eating moist foods.ii) Used metabolic water from aerobic resp.
Some animals are adapted for minimizing water loss that they can survive in deserts without drinking.
Nitrogenous breakdown products of proteins and nucleic acids.
Some animals excrete ammonia directly, others first convert the ammonia to other compounds that are less toxic but that require energy in the form of ATP to produce.
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Fig 46.1 Solomon: Formation of nitrogenous waste
1. Ammonia Very soluble in water Tolerated at very low concentrations Need access to lots of water. Highly toxic among other nitrogenous waste. E.g: aquatic species, most bony fishes.
2. Urea Low toxicity.
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Transported & stored safely at high concentration Synthesized in the liver (NH3 + CO2) and is excreted
by the kidneys. E.g: mammals, most amphibians, sharks & some
bony fishes.
3. Uric acid Largely insoluble in water. Excreted as a semi solid paste with very little water
loss. Advantage for animals with little access to water.
More energetically expensive to be produced. Non toxic. E.g: reptiles, insects, land snails and birds.
Osmoregulatory organs in invertebrates are nephridial organs and Malphigian tubules.
Nephridial organs;
1. Protonephridia(Refer Figure 44.10 page 929)
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Fig 44.10: Protonephridia. The flame bulb system of a planarian
Flatwormshave protonephridia, a branch network of dead-end tubules.
Flame bulb with cilia that draws water and solutes from the interstitial fluid, through the flame bulb, and into the tubule system.
The urine in the tubules exits through openings called nephridiopores.
Found in rotifers, some annelids, larval molluscs, & lancelets.
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2. Metanephridia(Refer Figure 44.11 page 930)
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Fig 44.11: Metanephridia of an earthworm
Internal openings that collect body fluids from the coelom through a ciliated funnel and release the fluid to the outside through the nephridiopore.
Each segment of an annelid worm has a pair of metanephridia.
An earthworm’s metanephridia have both excretory and osmoregulatory functions.
Malpighian tubules(Refer Figure 44.12 page 930)
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Fig 44.12: Malpighian tubules of insects
Malpighian tubules of insects & other terrestrial arthropods remove nitrogenous wastes and also function in osmoregulation.
Open into the digestive system and dead-end at tips that are immersed in the hemolymph.
Insoluble uric acid, eliminated along with the feces.
Highly effective in conserving water.4.6 The urinary system of vertebrates: Kidney
(Refer Figure 44.13 (a & b) page 932)
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Fig 44.13: The mammalian excretory system Consists of the kidneys, urinary bladder, and their ducts (ureter and urethra). The main osmoregulatory & excretory organ in humans & other vertebrate.
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Compact, non-segmented organs containing numerous tubules & a dense network of capillaries associated with the tubules. Each kidney is covered by a connective tissue capsule. The outer portion of the kidney is the cortex; the inner is the medulla. The medulla is composed of 8-10 pyramids, each with a renal papilla at the apex, where the collecting ducts empty. The urine flows from a papilla to the renal pelvis. Urine exits each kidney through ureter and flows to the urinary bladder, which is a distensible, muscular sac. During urination, urine flows through the urethra. In males, the urethra also carries semen.
Q: Conduct the flow of urine.Renal pelvis ureter urinary bladder urethra
Functions of kidney
Q: List down all functions of kidney.1. Excretion of waste product2. Homeostasis of;
The functional unit of the kidney. Kidney consists of several million of nephrons. Nephron: Glomerulus, renal tubule (proximal tubule,
loop of Henle and distal tubule) and collecting duct.
Summary of blood circulation through kidney:Renal artery afferent arterioles capillaries of glomerulus efferent arterioles peritubular capillaries small vein renal vein
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Fig 44.13 (c): Nephron
Two type of nephrons; 1. Cortical nephrons
i) 80% of distributionii) almost entirely confined to the renal cortexiii) small glomeruliiv) short loops of Henle produce diluted urine
2. Juxtamedullary nephronsi) 20% of distributionii) large glomeruliiii) long loops of Henle that extend deeply into the
medulla produce concentrated urine.4.6.2 Urine formation
Accomplished by ultrafiltration, reabsorption and secretion.
(Refer Figure 46.10 page 904 - Solomon)
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Fig 46.10 Solomon: General regions of filtration, reabsorption and secretion
1. Ultrafiltration Process by which small molecules in blood are
forced out the glomerulus capillaries to the lumen of the Bowman’s capsule.
Passive process needs necessary conditions;
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a) High blood pressure(Refer Figure 46.9 (b) page 903 – Solomon)
Fig 46.9 Solomon: Nephron structure Maintain because the afferent arteriole has a
larger diameter than the efferent arteriole. Blood pressure in the glomerulus is high enough
to force substances from the blood into Bowman’s capsule.
b) The basement membrane/filtration membrane (Refer Figure 46.11 page 905 – Solomon)
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Fig 46.11 Solomon: Filtration membrane of the kidneyThe cells of the surface of the Bowman’s capsule in
contact with the glomerulus are permeable podocytes, which are separated by gaps called filtration slits.
The glomerular capillary walls and podocytes make up the filtration membrane.
Provides a filter for the selection of substances that have a relative molecular mass small enough to pass through it.
The filtration membrane is impassable to cells in the blood and most proteins.
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Q: i) Compare content of glomerular filtrate with blood components.
ii) What happen to nonfilterable blood components?
i) - The filtrate contains salt, glucose, amino acids, vitamins, nitrogenous wastes such as urea, and other small molecules.
- no RBC and plasma proteinii) Enter efferent arterioles peritubular capillaries
small vein renal vein
2. Reabsorption
The transport of molecules /useful substance out of the filtrate through the tubule wall and into the surrounding blood vessel.
Highly selective process that returns usable materials to the blood but leaves wastes & excesses of other substances to be excreted in the urine.
99% of the filtrate is reabsorbed in the renal tubules. More than 80 % of glomerular filtrate is reabsorbed
back into the blood in the proximal convoluted tubule. Q: State the adaptive structures of cells lining the proximal tubule & explain how this structure increases the reabsorption process.
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The epithelia of the renal tubules have microvilli, which increase the surface area, and abundant mitochondria to provide energy for active transport of materials.
Some materials are actively transported into the tubule cells; others follow by passive diffusion
Q: Name the materials which are actively and passively absorbed in the renal tubule?
Active transportation: glucose, amino acid, Na+
Passive diffusion: urea, water (by osmosis), Cl –
The tubular transport maximum (Tm) is the maximum rate at which a substance may be reabsorbed.
Q: Define the renal threshold.
The level above which the substance will not be reabsorbed, and is therefore excreted in the urine
3. Secretion
Transport of molecules across the membrane of blood capillaries & renal tubule into the filtrate.
Enabling the tubule to excrete molecules that are not originally present in glomerular filtrate.
Some ions & drugs are secreted into the filtrate, particularly by the cells of the distal convoluted tubule.
Controlled secretion of H+ allows regulation of blood pH.
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Aldosterone produced by the adrenal cortex, is involved in regulation of tubular secretion
4.6.3 Transport process in the Mammalian nephron
Mechanism to create an osmotic gradient between glomerular filtrate & blood for reabsorption.(Refer Figure 44.14 & 44.15 page 933 & 935)
Fig 44.14: The nephron and collecting duct; regional functions of the transport epithelium
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Fig 44.15: How the human kidney concentrates urine
1. Proximal Tubule
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Reabsorbed 2/3 NaCl and water. Active transport of Na+ out of tubule and passive
movement of Cl – (electrical attraction) and water follows by osmosis.
Filtrate isotonic to the blood plasma. Reabsorbed glucose, amino acid, K+, HCO3
-
Secrete processed drugs and poisons.
2. Loop of Henle
Water reabsorption continues in the descending limb of the loop of Henle. The wall is permeable to water but impermeable
to salt and urea. For water to move out of the tubule by osmosis,
the interstitial fluid bathing the tubule must be hyperosmotic to the filtrate.
Because the osmolarity of the interstitial fluid becomes progressively greater from the outer cortex to the inner medulla, the filtrate moving within the descending loop of Henle continues to lose water.
The wall of the ascending limb of the loop of Henle is permeable to salt, not water. As filtrate ascends the thin segment of the
ascending limb, NaCl diffuses out of the tubule into the interstitial fluid, increasing the osmolarity of the medulla.
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The active transport of NaCl from the filtrate into the interstitial fluid continues in the thick segment of the ascending limb.
By losing salt without giving up water, the filtrate more dilute as it moves up to the cortex in the ascending limb of the loop.
3. Distal tubule
Regulating the K+ and NaCl concentrations in body fluids by varying the amount of K+ that is secreted into the filtrate and the amount of NaCl reabsorbed from the filtrate.
Also contributes to pH regulation by controlled secretion of H+ and the reabsorption of HCO3
−.
4. Collecting Duct
Actively reabsorbing NaClThe degree of its permeability is under hormonal
control, the epithelium is permeable to water but not to salt (in the renal cortex) or to urea.
The filtrate becomes increasingly concentrated as it loses more water by osmosis to the hyperosmotic interstitial fluid.
In the inner medulla, the duct becomes permeable to urea.
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Because of the high urea concentration in the filtrate at this point, some urea diffuses out of the duct into the interstitial fluid.
Along with NaCl, this urea contributes to the high osmolarity of the interstitial fluid in the medulla.
Q: What are the two factors that increase the solute concentration of renal medulla?
Nacl and urea
Countercurrent multiplier System
Between the ascending & descending limbs of the loop of Henle.
The nephron can concentrate salt in the inner medulla largely because exchange between opposing flows in the descending & ascending limbs overcomes the tendency for diffusion to even out salt concentrations throughout the kidney’s interstitial fluid.
The vasa recta is also a countercurrent system, with descending & ascending vessels carrying blood in opposite directions through the kidney’s osmolarity gradient.
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As the descending vessel conveys blood toward the inner medulla, water is lost from the blood and NaCl diffuses into it.
These fluxes are reversed as blood flows back toward the cortex in the ascending vessel.
Both countercurrents maintain the steep osmotic gradient between the medulla & the cortex.
This gradient is initially created by active transport of NaCl out of the thick segment of the ascending limb of the loop of Henle into the interstitial fluid.
Mechanism countercurrent multiplier system
(Ascending & descending limbs of the loop of Henle)
Filtrate flows in opposite direction in the two limbs of the loop.
The longer the region of interactionbetween descending and ascending limb
The greater the total concentration renal medulla can be achieved
The steeper the osmotic gradient between filtrate and renal medulla
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The easier the movement of water from collecting duct renal medulla surrounding blood
vessel
4.7.4 Regulation of body fluids by hormones
The osmolarity of urine is regulated by nervous & hormonal control of water and salt reabsorption in the kidneys.
The ADH, the RAAS, and ANF regulate the kidney’s ability to control the osmolarity, salt concentration, volume, & pressure of blood.
1. Regulation by ADH(Refer Figure 44.16(a) page 937)
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Fig 44.16 (a): Hormonal control of the kidney Urine volume is regulated by antidiuretic hormone
(ADH). Osmoreceptor cells in the hypothalamus monitor the
osmolarity of the blood. If the osmoreceptor cells detect an increase in the
osmolarity of the blood, it will causes the production of ADH, and a thirst receptor causes increased fluid intake.
ADH produced by the posterior pituitary induces the epithelium of the distal tubules and collecting ducts to become more permeable to water resulting in more concentrated urine.
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Normally blood osmolarity, ADH released and water reabsorption links in a feedback loop that contributes to homeostasis.
Q: What is the effect of diuretics such as caffeine and alcohol on secretion of ADH?
Caffeine and alcohol are stimulant that suppresses ADH release, which results in increased urine production. The symptoms of a hangover are partially due to ADH suppression and the resultant dehydration.
2. Regulation by RAAS & ANF(Refer Figure 44.16(b) page 937)
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Fig 44.16 (b): Hormonal control of the kidneyA) RAAS
Juxtaglomerular apparatus (JGA) is located near the afferent arteriole secreted enzyme renin.
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When blood pressure or blood volume in the afferent arteriole drops, the enzyme renin initiates chemical reactions that convert angiotensinogen to angiotensin II.
Q: How does Angiotensin II increases blood pressure and blood volume?
i) It raises blood pressure by constricting arterioles, decreasing blood flow to many capillaries.
ii) It also stimulates the proximal tubules to reabsorb more NaCl and water. This reduces the amount of salt and water excreted and, consequently, raises blood pressure and volume.
iii) It also stimulates the adrenal glands to release aldosterone act on the distal tubules, which reabsorb Na+ and water, increasing blood volume and pressure.
Q: Summary of RAAS pathway response to low blood volume/blood pressure.
Blood volume/Blood pressure decreases:Blood volume decreases blood pressure decreases cell of juxtaglomerular apparatus secrete renin angiotensinogen angiotensin I angiotensin II constricts blood vessels and stimulate aldosterone secretion aldosterone increase sodium reabsorption blood pressure increases
B) Atrial natriuretic factor (ANF)
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Atrial natriuretic factor (ANF), opposes the RAAS. The walls of the atria release ANF in response to an
increase in blood volume and pressure. ANF inhibits the release of renin, inhibits NaCl
reabsorption by the collecting ducts & reduces aldosterone release from the adrenal glands.
Lower the blood pressure and volume.
Summary of ANF pathway:Blood volume/blood pressure increases:Blood volume increases blood pressure increases atrial of the heart stretched atrial release ANF directly inhibit sodium reabsorption and inhibit aldosterone secretion (which also inhibit sodium reabsorption) larger urine volume Blood volume decreases blood pressure decreases
4.8 Liver
The largest gland in the human body.Functions:
1. Carbohydrate metabolism Gluconeogenesis : the synthesis of glucose from
certain amino acids, lactate or glycerol Glycogenolysis : the breakdown of glycogen into
glucose Glycogenesis : the formation of glycogen from glucose
2. Protein metabolism Carry out deamination – excess amino acid are broken
down and the amine group is removed to form ammonia.
Mammal: Ammonia + CO2 urea during Ornithine cycle or urea cycle.
Also carries out transamination – amino acid can be used to synthesize other amino acid.
3. Lipid metabolism Convert excess carbohydrates to lipid when glycogen
store in the liver is full. Lipid that enter liver either broken down/modified and
then transported to other parts of body for storage. Removed excess blood cholesterol by excretion into
bile. Synthesized required cholesterol control lipid level
in the body.4. Detoxification
Removed absorbed toxic substances/make them harmless.
Toxic substances, e.g : Alcohol/nicotine broken down by chemical conversion within hepatocytes.
Foreign materials, e.g : Bacteria ingested by Kupffer cells.
5. Breakdown and formation of red blood cells Breakdown of RBC results in haem, globin & iron. In 1st trimester fetus – responsible for formation of red
blood cells.6. Bile production
Produce bile salts and form bile. Bile stored in the gall bladder.
7. Storage of minerals, vitamins and blood Minerals : copper, iron and zinc. Vitamins : A,B,C,D,E and K. Form a store of blood in its blood vessel.
8. Synthesis of plasma proteins E.g. Globulin and clotting factors – fibrinogen.
9. Breakdown of hormones Breakdown of insulin and other hormones.
10. Heat production Produce heat when body temperature falls.
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Achieved through the high metabolic activity of the liver.
4.9 Osmoregulation in Plants
Autotrophic plants can control amount of organic compound since it is synthesized according to their need.
No organs for excretion. Excretion through : Transpiration – to remove excess water Diffusion through stomata – gases (CO2 & O2) Abscission of leaf/other part of plant – to remove
inorganic ions
According to their environment and way of osmoregulation, plant can be divided into:
1. Mesophyte Terrestrial plants which are adapted to neither a
particularly dry nor particularly wet environment. Does not need adaptation features. Normal
environment. Require a continuous adequate water supply.
2. Hydrophyte Adapted to living in or on aquatic environments.
E.g: Water lily & water chestnut in ponds/lake. Grow submerged/partially submerged in water No problem of water supply Water = supportive medium Adaptations are;
Little or no lignified supporting tissue. Poorly developed xylem.
Little or no cuticle on stems and leaves. Stem & leaves have large continuous air spaces,
forming a reservoir of O2 & CO2. Also provides buoyancy to the plants tissue when submerged.
3. Halophyte Adapted to live in aquatic environment which has
greater osmotic pressure. Found in areas of high salinity. E.g: Salt marsh
grass at estuaries and saltmarshes. Adaptations are;
Mostly salt tolerant. Store water in succulent tissue. Often higher concentration of salts in their cell
than that of seawater. Thus take water from seawater by osmosis.
Extensive air spaces through the stems and roots make air available to all cells. Give buoyancy to the stem and leaves when plants are submerged at the highest tides.
4. Xerophyte Found in habitat where water is scarce/dry place.
E.g: Cacti in deserts Minimize water due to transpiration.
Summary of adaptation for xerophyte are;
Features that minimize water loss
Effect
1. Reducing transpiration
Thick cuticle to leaf and stem
Layer of hairs on the
Reduce cuticular transpiration
Traps air(moist air) and reduces the diffusion gradient
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epidermis
Massing of leaves into a rosette at ground level
Reduction in the numbers of stomata
Stomata in pits/at the bottom of the grooves
Leaves reduced to scales on a photosynthetic stem
Closure of stomata in the light
Traps moist air between leaves
Reduces the pores through which transpiration can occur
Moist air trapped outside stomata, reducing diffusion
Reduces surface area
Dark CO2 fixation(CAM)
2. Storage of water
Succulent stem and/or leaves
Water storage cells
3. Survival of desiccation
Leaf rolled up or folded when flaccid
Deep and extensive root system
Superficial root system
Reduction of area from which transpiration occur
Tapping lower water table
Absorbing overnight condensation
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“The practical life and teachings of the prophet emphasize the concept of central tendency and avoiding either extreme. Extremes of any action even if permitted, halal, are usually destructive and are not desired; the best is the equilibrium of the middle path, khair al umuur awsatuha. There must be a balance between rest and activity, release (istifragh) and retention (ihtibaas), sadness and happiness. Applications of the concept of moderation, balance, and equilibrium are found in almost all aspects of life: human behaviour, medical treatment, and use of environmental resources. The human habitat or the larger ecosystem that humans share with other living things must be maintained at a certain optimum equilibrium otherwise there will be adverse effects on life.”
MODERATION, BALANCE, AND JUST EQUILIBRIUM IN PREVENTIVE MEDICINE
