Chapter # 15

HOMEOSTASIS

Multiple choice questions.

(i) Shifts in water-solute balance are managed primarily by

(a) respiratory system (b) the urinary system

(ii) Which is the most important mechanism for water loss from the body?

(a) excretion in urine (b) sneezing

(iii) The process that normally exerts the greatest control over the water balance of an individual is

(a) sweating. (b) kidney function.

(iv) Which of the following does NOT dispose off a type of waste directly to the environment?

(a) digestive system (b) respiratory system

(v) The most toxic substances routinely found in the blood are metabolites of what type of molecules?

(a) proteins (b) carbohydrates

(vi) Which of the following is the last structure that urine passes through during its excretion from body?

(a) distal tubule (b) urethra

(vii) The process during which potassium and hydrogen ions and some toxic substances are put into urine is called

(a) tubular secretion. (b) reabsorption.

viii) Kidney health is described in terms of

(a) the number of kidney stones. (b) rate of filtration.

(ix) Why is there no glucose present in the filtrate in the distal tubule of a nephron?

(a) its molecules are too large to pass across the basement membrane

(b) it is removed by osmosis from the tubule

(d) it is actively absorb by the proximal tubule cells

(x) In case of overheating, the body temperature is regulated by:

(a) more sweating and more urination

(b) more sweating and less urination

(d) less sweating and less urination

(xi) An animal that warms itself mainly by absorbing heat from its surroundings is known as:

(a) homoiotherm (b) ectotherm

Short Questions.

Q1. Why it is necessary for a living being to maintain its internal environment at a fairly constant level?

Ans. It is necessary for a living organism to maintain its internal environment at a constant level, In order to maintain a constant chemical composition of body fluids inside to remove the toxic substances from body & to maintain normal health & body functioning, regardless of its outside environment

Q.2 How positive feedback can be harmful at times?

Ans. Positive feed back might be harmful sometimes because in certain conditions metabolic changes are too severe that normal body functioning is not possible in such cases & thus proper functioning & metabolism stops, resulting in death. For example, sometimes are so much severe that causes fever to raise to high degrees causing a high temperature level at which normal cell wear proteins stops their function & as a result of such metabolic defects death occurs.

Q.3 Describe mechanism of ultra filtration.

Ans. Formation of urine involve three key processes, ultra filtration, selective reabsorption and tubular secretion.

mechanism of ultrafiltration

i. It is filtration under pressure.

ii. The diameter of efferent arteriole is half as compared to the afferent arteriole.

iii. It results in a high blood pressure in glomerulus. About 20% of the plasma is filtered into Bowman's capsule.

iv. This filtered fluid is called glomerular filtrate.

v. This filtrate has to cross endothelium of the glomerular capillaries, basement membrane of capillaries, and endothelium of Bowman's capsule.

vi. It has chemical composition similar to that of blood plasma. It contains glucose, amino acids, vitamins, ions, nitrogenous wastes, some hormones and water.

Q.4 How regulation of blood flow to skin is meaningful to maintain body temperature?

Ans. Heat loss:

i. Heat is lost from the general body surface by a number of processes like radiation, convection, and conduction.

ii. Radiation accounts for about 50% of the total heat loss in humans.

iii. In vasodilation, certain of the arterioles beneath the epidermis dilate.

iv. Consequently, more blood flows near the body surface, losing heat through the epidermis. Evaporation is another mechanism of heat loss.

v. In humans, water loss by evaporation takes place continuously through the skin even when a person is not sweating.

vi. Activation of sweat glands enhances this process.

vii. Heat loss also occurs by evaporation from the lungs.

viii. Partial control of heat loss is possible by regulating sweating.

Q5. Why Juxtamedullary nephrons are more important in osmoregulation?

Ans. Juxtamedullary nephrons definition:

i. Juxtamedullary nephrons have their renal corpuscle close to the junction of the cortex and medulla.

ii. They have long loop of Henle which extends deep into the medulla.

iii. This type of nephron is relatively rare, and only comprise 20-30% of the nephrons in the human kidney.

iv. The greater gradient in the deep medulla make this type of nephron do more work than cortical nephrons.

v. It is these nephrons, which are responsible for the development of the osmotic gradients in the renal medulla, which are used to concentrate urine.

vi. When water is in short supply, increased water retention occurs through juxtamedullary nephrons.

Q6. How ADH controls concentration of urine?

Ans. i. When ADH body is deficient in water, hypothalamus stimulates posterior pituitary lobe to release antidiuretic hormone (ADH).

Mechanism: ADH makes collecting tubules and distal convoluted tubules of nephrons permeable to water, thus more water is absorbed, and maximum amount of water is retained in the body.

iii. The blood water content rises, which is sensed by hypothalamus, so ADH secretion slows down.

Q7. Why do marine fishes drink water unlike fresh water fishes?

Ans. Fresh water animals mostly absorb water from their surrmoundings & loss their salts into water & thus they have no need to drink water.

Whereas marine animals have excess of salts in their bodies which make their need for intake of water high.

Q8. How do some terrestrial mammals become so resistant that they are able to survive without drinking water?

Ans. Terrestrial animals:

i. In terrestrial animals evaporation of water leads to the dehydration which is the major problem faced by these animals.

ii. The successful groups of land animals are arthropods among t he invertebrates and reptiles, birds and mammals among the vertebrates.

iii. The presence of chitinous exoskeleton in arthropods and dead keratinized skin in vertebrates are adaptation to reduce water loss by their bodies.

iv. Desert mammals are very much resistant in this regard.

v. They can tolerate against strong degree of dehydration by special metabolic and behavioral adaptation.

vi. This characteristic is called anhydrobiosis.

vii. Actually, these animals feed upon seeds of desert plants in which large amount of carbohydrate is stored, during the breakdown of these compounds, water is produced as by-product that is utilized by these animals.

viii. Best example of such animals is kangaroo rat. Desert animals avoid day time heat, and emerge at night. 90% of the water that they use is metabolic water derived from cellular oxidation.

Q9. What is the benefit of Extracorporeal Shock Wave Lithotripsy (ESWL) over Per Cutaneous Nephro Lithotrypsy (PCNL).

Ans.

i. Most stones under 0.5cm can spontaneously pass from the kidney but most stones greater than 1cm cannot pass.

ii. If the stone must be removed two commonly employed methods are percutaneous nephrolithotrypsy (PCNL) and extracorporeal shock wave lithotripsy (ESWL).

iii. The type of procedure depends on the type of stone and its size.

iv. Typically, small stones can be treated with ESWL, while larger stones require PCNL.

v. ESWL uses sound waves to break the stone.

vi. A PCNL procedure is more commonly used when ESWL is not successful.

vii. First a tube is inserted into the patient's back into the kidney to create a tract.

viii. A scope is run through the tract to directly see the stone inside the kidney.

ix. Ultrasound equipment can then be inserted to break up the stone.

x. While watching the stone through the scope, the stone fragments can be grasped with special equipment and pulled through the tract out from the kidney before the advent of PCNL and ESWL, open surgical procedures were performed.

xi. This is less often necessary now, but sometimes is still performed especially for large complicated staghorn (branched) stones.

Q10. Why is the excretion of uric acid advantageous to birds and reptiles?

Ans

i. Producing uric acid instead of urea is advantageous because it is less toxic and reduces water loss and the subsequent need for water.excretion:

. .

ii. Uric acid requires a little amount of water for its excretion as complies to other waste products & thus in terrestrial invertebrates & egg laying vertebrates which both have a major water loss problem uric acid act as a metabolic waste product.

iii. It precipitates from solution inside the body & serve for formation of egg shell.

iv. After the animal hatches out of egg of the egg shell formed of uric acid left behind as waste.

Extensive Questions

Q1. Explain the working of feedback system in a living body and compare it with a non-living physical feedback system.

Ans. Mechanism of Homeostasis:

Homeostatic mechanism operates just like physical control system having three components; receptors, control center and effectors.

Receptor Sensor:

Detects changes in variable and feeds that information back to the control center (integrator).

Control center integrator:

Integrates (puts together) data from sensor and stored "set point" data.

Effecter:

Effecter is the mechanism (heating coil in this example) that has an "effect" on the variable.

i. In a common lab incubator, if temperature is decreased from set point, the thermometer (receptor) detects the change in temperature and signals the thermostat (control center), which in turn activates the heating coil (effecter).

ii. Similarly if temperature is increased from the set point again thermometer detects the change and signals the thermostat to switch off heating.

iii. Likewise, in human body thermo receptors are involved in the detection of temperature change. Hypothalamus in fore brain is a body thermostat.

iv. Stimulated once, hypothalamus acts on effectors for cooling (e.g. sweat glands) or heating (e.g. muscles) the body to reverse the change to the set point. After receiving the signal, a change occurs to correct the deviation either by depressing it with negative feedback or enhancing it with positive feedback.

Negative Feedback:

i. Negative feedback is mainly how homeostasis is maintained. This feedback results in a reversal of the direction of change.

ii. Negative feedback tends to stabilize a system, correcting deviations from the normal state.

iii. In example, negative feedback mechanism is applied to control water content in the body.

iv. When body is deficient in water, hypothalamus stimulates posterior pituitary lobe to release antidiuretic hormone (ADH).

v. ADH makes collecting tubules and distal convoluted tubules of nephrons permeable to water, thus more water is absorbed, and maximum amount of water is retained in the body.

vi. The blood water content rises, which is sensed by hypothalamus, so ADH secretion slows down.

Positive Feedback:

i. In contrast to negative feedback, positive-feedback involves a change in some variable that triggers mechanisms that amplify rather than reverse the change.

ii. During childbirth, for instance, the pressure of the baby's head against sensors near the opening of the uterus stimulates; uterine contractions, which cause greater pressure against the uterine opening, heightening the contractions which causes still greater pressure.

iii. Positive feedback brings childbirth to completion, a very different sort of process from maintaining a physiological steady state.

Q2. Describe different parts of urinary system of human with main emphasis on their role in excretion.

Ans. Urinary System of Man

Kidneys: A pair of kidneys, consists of millions of functional units, nephrons.

Blood Supply of Kidneys: The nephrons have extensive blood supply via the renal arteries, which leaves each kidney via the renal vein. The function of kidney and blood in clearing wastes is very evident from the fact that weights of kidneys account for less than 1% of the total body weight while receive 20% of blood supplied with each cardiac beat.

Pelvis: Following filtration of blood and further processing through tubular system urine is collected in a central cavity of the kidney, pelvis.

Ureter: Urine leaves the kidney through a duct ureter.

Urinary Bladder: The ureters of both the kidneys drain into urinary bladder through ureteral orifice.

Urethra: Urine leaves the body during urination, from the bladder through a tube called the urethra, which empties near the vagina in females or through the penis in males. Sphincter muscles near the junction of the urethra and the bladder control the urine in bladder.

Q3. Describe the challenges and osmoregulatory adaptations of osmoconformers and osmoregulators in marine environment.

Ans. The mechanisms involved in regulating water and electrolytes balance vary widely among the animal groups as different habitats present different challenges.

Water and solutes Relation to the Cells:

i. Animal body is composed of 70% of water.

ii. However, the quantity of water may vary from cell to cell. Water has a number of physiological properties that are of significance to the life.

iii. It is also the medium in which biochemical reactions occur.

iv. So it is very important to have a proper balance of water in the body. Osmoregulation involves the movement of water by osmosis.

v. Therefore a proper balance of solutes is also important in order to maintain water movement.

vi. Animals may be either osmoregulators or osmoconformers with respect to their osmoregulatory characteristics.

Osmoregulators:

i. Some animals like all land animals and most marine vertebrates have body fluids whose solute concentration is different from that of the external environment.

ii. Therefore they must use energy in controlling water loss or gain to keep the balance of water and solutes. Such animals are called osmoregulators.

iii. Whether an animal inhabits land, fresh water or salt water, its cells cannot survive without water.

Osmoconformers:

i. Some aquatic animals, that live in the sea have the body fluids with a solute concentration equal to that of external environment.

ii. Such animals do not undergo a net gain or loss of water because equal amounts of water move back and forth between two solutions with equal solute concentration i.e.

ii. The animal body fluids are kept isotonic. Such animals are called osmoconformers.

iii. The challenges and osmoregulatory adaptations of

osmoconformers and osmoregulators in marine environment.

Marine environment has both osmoconformers andosmoregulators, osmoregulatory adaptations of these animals are very different from each other.

2. Cartilaginous fishes such as sharks, rays and skates and some cyclostomes like Myxine (Hag fishes), have plasma that is approximately isotonic to sea water.

3. On the other hand most of the marine teleosts (bony fishes) are hypotonic tosea water. So these fishes have tendency to lose water to the environment, especially across the gill's epithelium.

4. They also have problem of excess of salts in the body due to drinking of sea water. '

5. In order to replace the water loss these fishes usually drink large amount of water unlike fresh water fishes.

6. Among the excess salts, Na+, Cl- and some amount of K+ are removed across the gill's epithelium while divalent ions like Mg++, Ca++ are excreted by the kidney.

7. Some fishes also have special salt secreting glands in the wall of rectum called rectal glands that remove salts into the digestive tract which are then eliminated from the body during egestion.

Q4. Describe the role of kidney as osmoregulatory organ.

Ans. Kidney as Osmoregulatory Organ:

Control of water level:

i. Body maintains the solute potential of blood at an approximately steady state.

ii. It is done by balancing water uptake from the diet with water lost in evaporation, sweating, egestion and urine.

iii. The solute potential is primarily achieved by the effect of antiduretic hormone.

iv. ADH is secreted by the posterior lobe of pituitary gland.

v. When body is deficient in water, hypothalamus detects a fall in blood solute potential and directs pituitary to release ADH.

vi. This hormone increases the permeability of the distal convoluted tubules and collecting ducts to water.

vii. More water is absorbed, reducing the volume of urine and making it more concentrated.

viii. When there is a high intake of water ADH release is inhibited.

ix. Less water is absorbed and a large volume of dilute urine is excreted.

Control of blood sodium level:

i. The maintenance of sodium level at a steady state is controlled by the steroid hormone aldosterone.

ii. It is secreted by adrenal cortex. Aldosterone activates sodium-potassium pumps in the distal convoluted tubules.

iii. Sodium is pumped back to blood from filtrate actively.

Q5. What is renal failure? Describe its types and causes.

Ans. Renal Failure/Kidney Failure:

Renal failure or kidney failure is a medical condition in which the normal functions of kidneys (filtration of toxins and waste products from the blood) is gradually decreased. There are two forms of kidney failure:

(a) Acute Kidney Failure:

i. Acute kidney failure occurs when kidneys suddenly become unable to filter wastes from blood.

ii. It develops rapidly over a few hours or in few days. Acute kidney failure is most common in people who are already hospitalized, particularly in critically ill people who need intensive care.

iii. Acute kidney failure can be fatal and requires intensive treatment.

iv. However, acute kidney failure may be reversible in that case, if patient otherwise in good health.

Causes:

i. Acute kidney failure can occur when something damages the kidneys like blood clots or cholesterol deposits that block blood flow in the kidneys, similarly certain chemotherapy drugs, antibiotics and toxins, such as alcohol, heavy metals and cocaine can also cause kidney failure.

(b) Chronic Renal Failure:

i. Chronic kidney failure, also called chronic kidney disease is the gradual loss of kidney function.

ii. Chronic kidney failure may not become apparent until the kidney function is significantly impaired.

iii. Chronic kidney failure can progress to end-stage renal disease (ESRD) and uremia, which is fatal without artificial filtering (dialysis) or a kidney transplant.

Causes:

i. Chronic renal failure develops gradually over time, often years to decades.

ii. The most common causes of chronic renal failure are diabetes and hypertension. Other causes include long-term daily use of anti-inflammatory drugs and other analgesic medications (pain relievers).

Q6. Explain the procedure of peritoneal and hemodialysis.

Ans. Peritoneal Dialysis:

i. Peritoneal dialysis makes use of a natural membrane in the body, the peritoneum, which encloses the abdominal cavity.

ii. In this process two catheters are surgically inserted into the abdominal cavity that serve as the portals through which dialysate (dialysis fluid) enters and leaves the cavity.

iii. The molecules of the dialysate are too large to pass through the peritoneum so the solution remains contained in the abdominal cavity.

iv. During circulation, when blood passes through the blood vessels (capillary networks) within the peritoneum, the dialysate attracts certain molecules to cross the membrane into the dialysate.

v. A second catheter carries dialysate out of the abdominal cavity.

vi. There are two stages of peritoneal dialysis, the exchange (draining the dialysate into and out of the abdominal cavity) and the dwell (the time during which the dialysate remains in the abdominal cavity).

Hemodialysis ????(page 47 topic hemodialysis)

Q7. Describe various type of kidney stones and their causes.

Ans. Urinary Stones:

Urinary stones are hard, crystalline mineral materials that stick together to form small "pebbles" within the kidney or urinary tract. They may stay in kidneys or travel out of the body through the urinary tract.

Chemical Nature of stone:or types of stones

i. The most common type of kidney stone contains calcium in combination with either oxalate or phosphate (70% of all stones).

ii. Other chemical compounds that can form stones in the urinary tract include uric acid (5-10% of all stones) and the amino acid cystine (1-3% of all stones).

iii. Kidney stones can also result from infection in the urinary tract; these are known as struvite or infection stones (15-20% of all stones).

Causes:

A number of different medical and environmental conditions can lead to an increased risk for developing kidney stones:

Hypercalcemia:

It is characterized by increased calcium level in the blood that in turn causes hypercalciuria (high calcium in the urine). These conditions may also arise in case of Hyperparathyroidism, which is the over secretion of parathormone from parathyroid gland.

In this condition, too much calcium is absorbed from food and excreted into the urine, where it may form calcium phosphate or calcium oxalate stones.

Hyperoxaluria:

It is characterized by increased oxalate level in the urine. This condition is usually associated with over use of tomato and other green leafy vegetables in the diet.

Hyperuricemia:

It is characterized by increased amount of uric acid in the blood that can lead to the formation of uric acid stones. The level of uric acid may arise in gout(genetic disorder) or due to high intake of protein in the form of meat products.

Science Technology and Society Connections

Q1. Describe the importance of kidney donation for the benefit of kidney failure patiens.

Ans. By donating kidneys one can save a life of a dying patient.

DONOR

A person, living or dead, who provides an organ is called a donor.

RECEPIENT

The person into whom the organ will be transplanted is the recipient.

RETRIEVAL

Collecting an organ from a donor is known as retrieval or procurement.

Most religious and spiritual groups either strongly endorse the act of donating organs or believe it's up to the donor to decide.

In our country strict laws are there for kidney transplant. Only first blood relative can donate kidney to a patient.

Q2. Name the important kidney transplant centers in his/her province.

Ans.

HRA Reg No	Institution	Location	Specification
50100005	KIDNEY CARE CENTRE	DIR MEDICAL TOWER HOSPITAL ROAD PESHAWAR CITY	KIDNEY CENTRE
50100010	ITTEFAQ PRIMARY HEALTH AND KIDNEY CENTRE	GULBAHAR NO 1 PESHAWAR	KIDNEY CENTRE
50100015	SHIFA KIDNEY CENTRE	444- DABGARI GARDENS, PESHAWAR	KIDNEY CENTRE
50100017	CHINA KIDNEY CENTRE	CITY MEDICAL CENTRE, HOSPITAL ROAD PESHAWAR	KIDNEY CENTRE
50100018	NEW CHINA KIDNEY CENTRE	ALI MEDICAL CENTRE HSPITAL ROAD PESHAWAR	KIDNEY CENTRE

Extra Questions

Q1. What do you know about Osmoregulation in marine animals?

Ans: Osmoregulation in marine animals:

1. Marine environment has both osmoconformers andosmoregulators, osmoregulatory adaptations of these animals are very different from each other.

2. Cartilaginous fishes such as sharks, rays and skates and some cyclostomes like Myxine (Hag fishes), have plasma that is approximately isotonic to sea water.

3. On the other hand most of the marine teleosts (bony fishes) are hypotonic tosea water. So these fishes have tendency to lose water to the environment, especially across the gill's epithelium.

4. They also have problem of excess of salts in the body due to drinking of sea water. '

5. In order to replace the water loss these fishes usually drink large amount of water unlike fresh water fishes.

6. Among the excess salts, Na+, Cl- and some amount of K+ are removed across the gill's epithelium while divalent ions like Mg++, Ca++ are excreted by the kidney.

7. Some fishes also have special salt secreting glands in the wall of rectum called rectal glands that remove salts into the digestive tract which are then eliminated from the body during egestion.

Q2. What do you know about Osmoregulation in terrestrial animal?

Ans. Osmoregulation in terrestrial animal:

1. In terrestrial animals evaporation of water leads to the dehydration which is the major problem faced by these animals.

2. The successful groups of land animals are arthropods among the invertebrates and reptiles, birds and mammals among the

vertebrates.

3. The presence of chitinous exoskeleton in arthropods and dead

keratinized skin in vertebrates are adaptation to reduce water loss by their bodies.

4. Desert mammals are very much resistant in this regard.

5. They can tolerate against strong degree of dehydration by special metabolic and behavioral adaptation.

6. This characteristic is called anhydrobiosis.

7. Actually these animals feed upon seeds of desert plants in which large amount of carbohydrate is stored, during

the breakdown of these compounds, water is produced as by-product that is utilized by these animals.

8. Best example of such animals is kangaroo rat.

9. Desert animals avoid day time heat, and emerge at night. 90% of the water that they use is metabolic water derived from cellular oxidation.

Q3. Explain the term Excretion?

Ans.

1. Metabolism of food and other chemicals in the body produces large amount of toxic by-products.

2. Water and Carbon dioxide are produced in metabolism of all, sugars, lipids and even proteins.

3. The most troublesome is the nitrogen-containing waste from the metabolism of proteins and nucleic acids.

4. Nitrogen is removed from these nutrients when they are broken down for energy or when they are converted to carbohydrates or fats.

5. The primary nitrogenous waste product is ammonia, a small and very toxic molecule.

6. Some animals excrete their ammonia directly; others first convert it to less toxic wastes such as urea or uric acid and then excrete it.

7. The form of nitrogenous waste an animal excretes depends on its habitat.

Q4. Explain the components of Renal tuble?

Ans.

The components of the renal tubule are:

Proximal convoluted tubule:

Introduction : 1. It is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle.

It is the longest part of the nephron.

(2) Lining of proximal: The proximal tubule is lined by epithelial cells having brush boarder composed of microvilli.

(3) tubule: It increases surfa ce area for reabsorption.

(function): Loop of Henle:

1) Shape: It is a long U shaped tube of the nephron.

2) Location: The loop of Henle is more prominent in juxtamedullary nephrons where it descends down to the tips of pyramids in medulla.

3) Function: It is an important part of the whole system, as it allows the kidneys to filter out salt and maintain the correct balance of water in the body.

(a) Distal convoluted tubule:

The distal convoluted tubule is the most distal portion of the nephron

(b) Collecting ducts:

1. Each distal convoluted tubule leads to a system of collecting

ducts, the first segment of which is the collecting tubule.

2. The collecting duct system begins in the renal cortex and extends deep into the medulla.

3. Finally it delivers urine to renal pelvis.

Q5. What do you know about kidney transplantation?

Ans. kidney transplantation:

1. Replacement of a diseased, damaged, or missing with a donor kidney also called a transplant.

2. Patients with end-stage renal failure are candidates for transplantation.

3. A successful transplant frees the patient from dialysis and provides the kidney's other metabolic functions.

The donor kidney must match the recipient as closely as possible in three ways.

¯ First, the donor and the recipient must have the same blood type.

¯ Second, the donor and the recipient must match Human Leukocyte Antigens (HLAs), which are proteins on the surfaces of leukocytes (white BLOOD cells), as closely as possible.

¯ Every person has six HLAs. The more HLAs that match between donor and recipient, the higher the likelihood that the recipient's body will accept the donor kidney Transplant surgeons like to see a match of three or more HLAs.

¯ Third, the donor's blood must not initiate an antibody response with the recipient's blood (called a negative cross match), which the transplant team tests by mixing samples of blood from each in a test tube.

1. The risks of transplantation surgery include bleeding during or after the operation and postoperative infection.

2. Because the transplanted kidney is lower in the abdomen than the native kidneys it lacks the protection of the rib cage and is more vulnerable to traumatic injury.

3. Most people recover fully from the surgery without complications, though there is always the risk of organ rejection can be treated with various medications.

Q6. What is thermoregulation?

Ans. Thermoregulation

1) Definition: The maintenance of body temperature by living organisms is termed as thermoregulation.

2) Effect of thermoregulation: (a) The temperature influences the metabolic activity of animals in a number of ways.

(b). The main effect is on the rate of enzyme activity and the rate of movement of atoms and molecules.

(c). This directly affects the health and growth of animals.

(d). Temperature may also affect the geographical distribution of animals through its influence on plants as primary producers in the food chain.

(e). The effect of hyperthermia on organ system of animals may be profound, and if heat stress has been severe or prolonged it may alter organ function and even kill the animals.

(3) Classification of animals: Animals are classified into two groups on the basis of maintaining their body temperature.

(a) Poikilotherms are unable to maintain their body temperature within narrow limits using physiological mechanism e.g. invertebrates, fishes, amphibians, and reptiles.

(b) Homeotherms are able to maintain a fairly constant body temperature by using physiological mechanisms e.g. birds and mammals.

Animals gain heat from two sources.

Heat sources (a) The chemical reaction of ingested nutrients

(b) The external environment, especially radiant energy from the sun.The extent to which different groups of animals are able to generate and conserve this heat is variable.

(c) Ectotherms rely on heat derived from the environment than metabolic heat to raise their body temperature e.g. reptiles, amphibians, fishes and invertebrates.

(d) Endothermic: Homeothermic animals are relatively independent of external sources of heat and rely on a high metabolic rate to generate heat which is conserved. They are described as endothermic e.g. the great white shark, flying insects, birds and polar bear.

Q 7. Explain thermoregulation in Human.

Thermoregulation in Human:

1. The ability to regulate body temperature is critical to sustain normal life.

2. Death is the ultimate result if the body temperature strays to far from the normal.

Core body temperature, the temperature of structures below the skin and subcutaneous tissue, should be maintained between 36.4 and 37.3 °C.

3. Respiratory metabolism is major source of heat energy in human.

4. Thermogenesis: This energy is mainly released by breakdown of carbohydrates and fats. The process of production in organisms is called Thermogenesis.

(a) Regulationof Thermogenesis: This process is regulated by nervous system and hormones.

Types: There are two types of thermogenesis , shivering thermogenesis and non-shivering thermogenesis.

(i) Shivering thermogenesis: Shivering thermogenesis involves repeated stimulation of voluntary muscles by motor neurons.

It produces shivering response in muscles which can increase heat production by up to five times the basal level.

(ii). Non-shivering thermogenesis Non-shivering thermogenesis is the heat production caused by the high metabolic rate.

Thyroxin, a thyroid hormone increases metabolic rate which result in heat production.

Its effects are long term.

Adrenaline produces short term increase in metabolic activity.

Q7. Describe receptors and their responses under different temperature condition in human body?

Ans.

1.Temp. control system: Human have a well-developed temperature control system involving receptors and effectors and an extremely sensitive control centre, the hypothalamus.

2.(i) Temp. control organ: Hypothalamus monitors the temperature of the blood flowing through it.

This blood is at core temperature.

ii) Also skin has hot and cold thermoreceptors.

3) Working (i) When suitably stimulated they generate nerve impulses some of which pass to the hypothalamus and others to the sensory areas of the cortex.

(ii). In most cases the activity of both skin and hypothalamus receptors combine to control body temperature.

(iii) This enables the body to make rapid and precise adjustment to maintain constant body temperature.

(4) Responses (a) at high temperature: If body temperature increases the set point in hypothalamus, a set of responses is organized by hypothalamus.

è Vasodilation to increase blood flow to the skin. It increases heat loss from the skin by radiation, convection, and conduction

è Activation of sweat glands

è Decreased metabolic activity

(b) at low temperature: Cold temperature responses regulated by hypothalamus are;

è Vasoconstriction to decrease blood flow to the skin, to reduce heat loss by radiation, convection, and conduction

è Inhibit sweating

è Inhibit panting

è Increased metabolism for shivering and release of thyroxin and adrenaline.

utmanzai

Saturday 19 July 2014

HOMEOSTASIS

mechanism of ultrafiltration

Hemodialysis ????(page 47 topic hemodialysis)

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