Homeostasis

Question 1

What is homeostasis?

Answer 1

The maintenance of a state of dynamic equilibrium through the response of the body to internal and external stimuli

Question 2

What are the two ways the heart can respond when your body demands more glucose and oxygen? (E.g. during exercise)

Answer 2

• the rate at which the heart beat can increase

* the cardiac volume can be increased by more efficient contraction of the ventricles

Question 3

What is the cardiac volume?

Answer 3

The volume of blood pumped out at each heartbeat

Question 4

What is the cardiac output and what is the equation to work it out?

Answer 4

A measure of the volume of the blood pumped by the heart beat per minute

Cardiac output (dm3 min-1) = cardiac volume (dm3) x heart rate (beats min -1)

Question 5

Where is the cardiac control centre and what does it do?

Answer 5

Its in the medulla oblongata in the brain and recieves input from a number of different receptors and controls changes to the heart rate and the cardiac volume through parasympathetic and sympathetic nerves

Question 6

What receptors send nerve impulses to the cardiac centre?

Answer 6

Chemical, stretch and pressure receptors in the lining of the blood vessels and the chambers of the heart

Question 7

How does the cardiac centre make the heart beat more quickly and the cardiac volume increase?

Answer 7

• The nerve impulses that travel doen the sympathetic nerve from the cardiac centre in the brain to the heart release noradrenaline to stimpuate the SAN. This increases the frequency of the signals from the pacemaker regiom so the heart beats more quickly.
• branches of this sympathetic nerve also pass into the ventricles so they also increase the forces of contraction

Question 8

How does the cardiac centre slow the heartbeat down?

Answer 8

Nerve impulses travelling down the parasympathetic nerves from the cardiac centre to the heart release acetylcholine, inhibiting the SAN and slowing the heart down

Question 9

What are baroreceptors?

Answer 9

Mechanoreceptors in the aorta and carotid arteries that are very sensitive to pressure changes

Question 10

What do baroreceptors do at rest?

Answer 10

Send a steady stream of signals back through sensory neurones to the cardiac centre in the brain

Question 11

Why are baroreceptors important during exercise?

Answer 11

When exercise starts the blood vessels dilate (vasodilation) in response to the hormone adrenaline which is released in anticipation of exercise and the blood pressure falls a little. This reduces the stretch on the baroreceptors and they almost stop responding, when stimulation from the baroreceptors is reduced, the cardiac control centre immedietly sends signals along the sympathetic nerve to stimulate the heart rate and increase blood pressure again by vasoconstriction. When exercise stops blood pressure in the arteries increases as the heart continues to pump harder and faster than it needs to and so the baroreceptros are stretched. They respind by sending more sensory nerve impulses to the cardiac centre that in turn sends impulses through the parasympathetic system to slow down the heart rate and cause a widening of the blood vessels. These actions lower the blood pressure again

Question 12

What are chemoreceptors?

Answer 12

Sensory nerve cells or organs that respond to chemical stimuli

Question 13

How do chemoreceptors help heart rate to increase?

Answer 13

As carbon dioxide levels go up the pH of the blood goes down and this is detected by the aortic and carotid chemoreceptors. They send impulses along sensory neurones to the cardiac control centre in the medulla and this increases the impulses travelling down the sympathetic nerve to the heart. As a result the heart rate increases giving an increased blood flow to the lungs and more CO2 is removed from the blood. As blood carbon dioxide levels fall the pH rises. The chemoreceptors respond to this by reducing the number of impulses to the cardiac centre. This reduces the number of impulses in the sympathetic nerve system to the heart and reduces the acceleration of the heart rate so that it returns to it’s intrinsic rhythm

Question 14

Why does our heart rate increase when we are stressed?

Answer 14

The synpathetic nerve stimulates the adrenal medulla to release the hormone adrenaline. It is carried around the body in the blood and binds to receptors in the target organs including the SAN. Adrenaline stimulates the cardiac centre in the brain, increasing the impulses in the sympathetic neurones supplying the heart and has a direct effect on the SAN increasing the frequency of excitation and so increasing the heart rate, supplying you with extra oxygen and glucose for the muscles and brain

Question 15

How is blood flow temporarily diverted from less important areas to provide more blood for the heart and muscles to use?

Answer 15

When many impulses travel along the sympathetic nerve to the heart to speed it up, fewer nerve impulses are sent along sympathetic nerves to many blood vessels, causing the smooth muscles lining the vessels to contract, narrowing or closing the vessels

Question 16

What is osmoregulation?

Answer 16

The maintenance of a constant osmotic potential in the tissues of a living organism by controlling water and salt concentrations

Question 17

How can the body protect the cells from osmotic damage?

Answer 17

By controlling the water potential of the blood the body can control the water potential of the tissue fluid

Question 18

What are the two organs involved in the homeostatic control of the water balance of the body and which is the main one?

Answer 18

• the kidney (main one)

* liver

Question 19

What is deamination?

Answer 19

The removal of the amino group from excess amino acids in the ornithine in the liver. The amino group is converted into ammonia and then to urea which can be excreted by the kidneys

Question 20

What is the ornithine cycle?

Answer 20

The series of enzyme-controlled reactions that convert ammonia from excess amino acids into urea in the liver

Question 21

What action of the kidneys has made it possible to conserve water?

Answer 21

Kidneys can produce urine which is hypertonic to (more concentrated than) the body fluids

Question 22

What is the structure of kidneys?

Answer 22

• they are two reddish brown organs attached to the back of the abdominal cavity
• they are surrounded by a thick layer of fat which helps protect them from mechanical damage

Question 23

How do the kidneys control the water potential of the blood that passes through them?

Answer 23

They remove the substances that would affect the water balance as well as getting rid of urea. Blood from the body is passed through the kidneys and the urea, along with excess sal5s and water is removed and forms urine

Question 23

How do the kidneys control the water potential of the blood that passes through them?

Answer 23

They remove the substances that would affect the water balance as well as getting rid of urea. Blood from the body is passed through the kidneys and the urea, along with excess sal5s and water is removed and forms urine

Question 24

What are the two roles of the kidney?

Answer 24

* excretion (the removal of urea from the body) | * osmoregulation

Question 25

What are the three main functions the kidney carries out in its osmoregulatory role?

Answer 25

* ultrafiltration * selective reabsorption * tubular secretion

Question 26

What is ultrafiltration?

Answer 26

The process by which fluid is forced out of the capillaries in the glonerulus of the kidney into the kidneyntubule through the epithelial walls of the capillary and capsule

Question 27

What is selective reabsorption?

Answer 27

The process by which substances needed by the body are reabsorbed from the kidney tubules into the blood

Question 28

What us tubular secretion?

Answer 28

The process by which inorganic ions are secreted into or out of the kidney tubules into the blood

Question 29

What are nephrons?

Answer 29

Microscopic tubules that make up most of the structure of the kidneys

Question 30

What are the two main types of nephron?

Answer 30

* cortical nephrons which are found mainly in the renal cortex. They have a loop of Henle (a U shaped tubule) that only just reaches the medulla * juxtemedullary nephrons have long loops of Henle that penetrate right through the medulla. They are particularly efficient at producing concentrated urine

Question 31

How does ultrafiltration take place?

Answer 31

High blood pressure develops in the glomerular capillaries because the diameter of the blood vessels coming into the glomerulus is greater than that of the blood vessels leaving. The high pressure squeezes the blood out through the pores in the capillary wall. Only thr blood cells and the largest plasma proteins can't get out. The cells of the Bowman's capsule next to the capilllaries act as an additional filter. The wall of the capsule is made up of special cells called podocytes. They have extensions called pedicels that wrap around the capillaries forming slits that ensure any celle, platelets or large plasma proteins that have left the capillary do not get through into the tubule itself. The filtrate that enters the capsule contains glucose, salt, urea and many other substances im the same concentrations as they are in the blood plasma

Question 32

Why does selective reabsorption take place?

Answer 32

Because although ultrafiltration removes urea from the blood it also removes a lot of water along with glucose, salt and other substances present in the plasma. Glucose is never excreted as it is needed for respiration and water and saly ect. Are also needed

Question 33

What is the proximal convoluted tube?

Answer 33

The first region of the nephron after the Bowman's capsule where over 80% of the glomeular filtrate is absorbed back into the blood

Question 34

Wwhat helps the proximal convuluted tubule with reabsorption?

Answer 34

The cells lining this tubule are covered with microvilli, which greatly increase the surface area through which substances can be absorbed. The cells also have large numbers of mitochondria indicating they are involved in an active process

Question 35

How arw the glucose, amino acids, vitamins and most hormones moved back into the blood?

Answer 35

By active transport

Question 36

How are the sodium ions and chloride ions moved into the blood?

Answer 36

The sodium ions are actively transported and the water ions follow passively down a concentration gradient

Question 37

What happens once the substances are removed from the tubule cells into the intracellular spaces?

Answer 37

They then pass by diffusion into the extensive capillary network that surround the tubules. The blood is constantly moving through the capillaries, maintaining a concentration gradient for diffusion. By the time it reaches the loop of Henle it is isotonic with the tissue fluid that surrounds the tubule

Question 38

What are the capillaries near the loops of henle called?

Answer 38

The vasa recta

Question 39

What do the loops of Henle do?

Answer 39

They create a water potential gradient between the filtrate and the medullary tissue fluid that enables water to be reabsorbed from the distal convoluted tube and collecting duct

Question 40

What is a countercurrent multiplier,

Answer 40

A system that produces a concentration gradient in a living organism using energy from cellular respiration

Question 41

What is the creation of the high concentrations of sodium and chloride ions in the tissue fluid of the medulla due to?

Answer 41

The flow of fluid in opposite directions in the adjacent limbs of the loop of Henle, combined with the different permeabilities of the different sections to water and a region of active transport

Question 42

What is the system of the loop of Henle?

Answer 42

* the descending limb: the descending limb is freely permeable to water it is not permeable to sodium and chloride ions. No active transport takes place here. The fluid entering this limb is isotonic with the blood. As it travels down the limb deeper into the medulla, the external concentration of sodium and chloride ions in the tissue fluid of the medulla and the blood in the vasa recta is higher and higher. As a result water moves of the descending limb into the tissue fluid by osmosis down a concentration gradient. It then moves into the blood of the vasa recta again down a water potential gradient. By the time the fluid reaches the hairpin bend at the bottom of the loop it is very concentrated and hypertonic to the arterial blood. * the ascending limb: the first section of the ascending limb is very permeable to sodium and chloride ions but not permeable to water. No active transport takes place in this section. Sodium and chloride ions move out of the very concentrated fluid in the loop of Henle into the tissue fluid of the medulla down concentration gradients. The second thicker section of the ascending limb is also impermeable to water but the sodium and chloride ions are actively pumped out of the tubule into the tissue fluid of the medulla and the blood of the vasa recta. This gives the tissues of the medulla the very higj sodium and chloride ion concentration that causes the water to pass out of the descending limb by osmosis. However the ascending limb is impermeable to water so water cannot follow the chloride and sodium ions out down the concentration gradient. As a result the fluid left in the ascending limb becomes less concentrated

Question 43

What is the diatal convoluted tubule?

Answer 43

The section of the nephron after the loop of Henle that leads into the collecting duct, where balancing the water needs of the body takes place

Question 44

What varies the distal convoluted tubule permeability to water?

Answer 44

Levels of antidiuretic hormone

Question 45

What is antidiuretic hormone (ADH)?

Answer 45

a hormone produced in the hypothalamus and stored in the posterior pituitary that increases the permeability of the distal convoluted thbule and the collecting duct to water

Question 46

What does the collecting duct do?

Answer 46

Takes urine from the distal convoluted tubule to be collected in the pelvis of the kidney. It is the region of the kidney where most of the water balancing needed for osmoregulation takes place

Question 47

How does the water move down the collecting duct?

Answer 47

Down a water potential gradient as it passes through the medulla, with its high levels of sodium and chloride ions and the urine becoming steadily more concentrated. Because the concentration of sodium ions in the surrounding fluid increases through the medulla towards the pyramids water may be removed from the collecting duct all the way along. This allowd for the creation of very hypertomic urine

Question 48

Where does the urine travel through your body?

Answer 48

It is collected first in the pelvis of the organ. It then passes along the ureters to the bladder, where it is stored until the bladder is sufficiently stretched to stimulate the micturition. The urine passes out of the body along a tube called the uretha

Question 49

Where else can water come from aside drinking?

Answer 49

Metabolic processes

Question 50

What are the adaptations that allow kangaroos to produce concentrated urine?

Answer 50

* a relatively large proportion of juxtamedullary neurons * relatively long loops of henle (the region that is permeable to water) * high numbers of infoldings of the cell membranes of the epithelial cells lining the tubules which give increased surface area for diffusion of inorganic ions and water, making steep concentration gradients possible * high numbers of mitochondria and mitochondria with densely arranged cristae for maximum cellular respiration are found in thr epithelial cells of the nephrons of kangaroo rats, providing the energy for the active pumping of inorganic ions into or out of the tubuled as required

Question 51

How is the osmotic potential of the blood maintained within narrow boundaries?

Answer 51

By balancing the water and salts taken in by eating and drinking water with sweating, defecating and in the urine

Question 52

What is the mechanism by which ADH increases the permeability of the walls of the distal convoluted tube and the collecting duct to water?

Answer 52

ADH binds to specific receptors on the outside of the membrane of the tubule walls, triggering reactions that lead to the formation of cAMP qe the second messenger. The cAMP sets up a series of reactions that vesicles within the cells lining the tubules to move to and fuse with the cell membrane. The vesicles contain water channels which are inserted into the membrane, making it permeable to water. Water then moves through the channels out of the tubules and into the surrounding blood capillaries by osmosis

Question 53

How can the permeability of kidney tubules be closely controlled to match the water demands of the body?

Answer 53

The amount of ADH released controls the number of channels that are inserted

Question 54

What are osmoreceptors?

Answer 54

Sensory receptors in the hypothalamus that detect a change in the concentration of inorganic ions and therefore changes in the osmotic potential of the blood

Question 55

What happens when an increasingly negative water potential in the blood is detected?

Answer 55

It is detected by osmosreceptors in the hypothalamus. They send netve impulses to the posterior pituitary which in turn releases stored ADH to the blood. The ADH is picked up by receptors in the cells of the kidney tubules. ADH increases the permeability of the distal convoluted tubule and the collecting duct to water. As a result water leaves the tubules by osmosis into the surrounding capillary network. This means more water is returned from the filtrate to the blood and a small volume concentrated urine is produced

Question 56

What happens when osmoreceptors in the hypothalamus detect the bloods water potential get less negative?

Answer 56

The release of ADH by the pituitary is inhibited. the walls of the distal convoluted tubule and the collecting duct remain impermeable to water and so little or no reabsorption takes place. Therefore the concentration of the blood is remained and large amounts of dilue urine are produced

Question 57

How does the release of ADH correspond to changes in blood pressure?

Answer 57

* A rise in blood pressure (often a sign of an increase in blood volume) will suppress the release of ADH and so increase the volume of water lost in urine and so the blood volume will decrease * a fall in blood pressure which may indicate a loss of blood volume causes an increase in the release of ADH from the pituitary and the conservation of water by the kidneys. water is returned to the blood and a small volume of concentrated urine is produced

Question 58

What is diabetes insipidus?

Answer 58

Individuals constantly produce large volumes of very dilute urine. It is caused when the individual foes not properly produce any ADH or their kidneys do not respond to ADH. Without ADH the distal convoluted tubules and collecting ducts and permenantly impermeable to water

Question 59

What are the symptoms of diabtetes insipidus?

Answer 59

The patient feels extremely thirst and has to drink large quantities of water to avoid sever dehydration

Question 60

What are the symptoms of diabtetes insipidus?

Answer 60

The patient feels extremely thirst and has to drink large quantities of water to avoid sever dehydration

Question 60

What are the symptoms of diabtetes insipidus?

Answer 60

The patient feels extremely thirst and has to drink large quantities of water to avoid sever dehydration

Question 61

How is diabetes insipidus treated?

Answer 61

Either with drugs that replace the ADH or with drugs that enable the kidneys to produce a more concentrated urine

Question 62

What is thermoregulation?

Answer 62

A homeostatic mechanism that enables organisms to control their internal body temperature within set limits

Question 63

Why do small animals transfer energy more rapdily than larger organisms?

Answer 63

Because they have a large SA:V ratio

Question 64

What are the ways an organism warms up or cools down?

Answer 64

* they warm up due to energy transferred from exothermic reactions of water * they cool down due to the evaporation of water from body surfaces * they warm up from conduction from the surroundings and cool down from conduction to the surroundings * they warm up from convection from the surroundings and cool down from convection to the surroundings * they warm up from radiation from the surroundings and cool down by radiation to the surroundings

Question 65

What are endotherms?

Answer 65

Animals that warm their bodies through metabolic processes at least in part and usually have a body temperature higher than the ambient temperature

Question 66

What are ectotherms?

Answer 66

Animals that are largely dependent on the external environment for their body temperature

Question 67

Why do endotherms need to eat more food than ectotherms?

Answer 67

Because they have a higher metabolic rate do they have to eat more food to supply their metabolic needs

Question 68

Why are there few environments where endotherms cannot survive?

Answer 68

They are adapted to conserve their body temperature when necessary and also take advantage of warmth from the environment when possible

Question 69

What are the modifications endotherms usually have that take advantage id the environment and give examples

Answer 69

Behavioural and structural modifications. E.g. when cold they may bask in the sun or have special areas of skin in order to maximise their absorption of radiation from the sun

Question 70

what is the major difference between humans and other mammals with respect to temperature regulation?

Answer 70

We can manipulate our environment to help us survive

Question 71

What is the major homeostatic organ involved in thermoregulation in most endotherms?

Answer 71

The skin

Question 72

How do the mouth and nose contribute to cooling?

Answer 72

Some cooling takes place as water evaporates from the surfaces of the mouth and nose

Question 73

How does the skin help to keep you cool (e.g. during exercise)?

Answer 73

* a rich supply of capillaries runs near to the surface of the skin. Cooling by radiation, convection and conduction to the environment takes place from the blood flowing through the skin. This cooling is controlled via the arteriovenous shunt. When you are exercising or the external temperature rises the shunts is closed which allows more blood to flow through the capillaries at the surface of the skin and vasodilation occurs. More energy is transferred to the environment by radiation * the erector pilli muscles which are attached to your hair follicles are relaxed and the body hai4w lie flat against your body minimizing any insulating air that is trapped next to the skin * the rate of sweat production from the glands increases. As more sweat is released onto the skins surfave cooling takes place as the water evaporates * subcutaneous fats act as insulation, reducing cooling. People who are very physically active have little subcuntaneous fats

Question 74

Why is it important to keep drinking water whe you are getting hot?

Answer 74

So that the tissues remain hydrated ans sweat can be produced

Question 75

What is the arteriovenous shunt?

Answer 75

A system which closes to allow blood to flow through the major capillary networks near the surface of the skin, or opens to allow blood along a shortcut between the arterioles and venules, so it does not flow through the capillaries near the surface of the skin

Question 76

What is vasodilation?

Answer 76

The widening of blood vessels by relaxation of their muscle walls, increasing blood flow

Question 77

What is vasoconstriction?

Answer 77

The narrowing of blood vessels by contraction of their muscle walls, reducing blood flow

Question 78

How does the skin help to keep us warm?

Answer 78

* the arteriovenous shunt in the blood supply to the skin opens, reducing the blood flow through the capillaries. This is vasoconstriction and it reduces energy lost from the surface of the skin * sweat production is reduced and so cooling by evaporation is reduced too. * the erector pilli muscles contract pulling the hair upright * the metabolic rate of the body speeds up, warming the body. This takes place mainly in the liver and muscles. Shivering (involuntary contractions of the skeletal muscles) also help with metabolic warming. The energy released raises the body temperature * animals living in cold areas develop thick layers of subcutaneous fat that act as an effective insulator against cooling

Question 79

What are the two types of receptors in thermoregulation?

Answer 79

* there are receptors in the brain (in the hypothalamus) which monitor the temperature of the blood * receptors in the skin detect changes in external temperature

Question 80

What does the thermoregulatory centre comprise of?

Answer 80

Temperature receptors sited in the hypothalamus in the brain that act as the thermostat of the body and fire when the temperature of the blood flowing through the hypothalamus increases or decreases

Question 81

What does the thermoregulatory centre do when the temperature of the blood flowing through the hypothalamus increases?

Answer 81

It sends out impuleses along autonomic motor nerves to effectors that increase the blood flow through the skin and increase sweating. The erector pili muscles are relaxed so that the hairs lie flat and shivering stops. The metabolic rate may be lowered

Question 82

What does the thermoregulatory centre do when the temperature of the blood flowing through the hypothalamus drops?

Answer 82

sends nerve impulses through the automatic nervous system to the skin. These cause a reduction in the blood flow through the capillaries in the skin, along with a reduction in the production of sweat and contraction of the erector pilli muscles to raise the hairs. Impulses in automatic motor neurones from the thermoregulatory centre also stimulate involuntary muscle contractions (shivering) and raise the amount of metabolic warming

Question 83

What are endothern adaptations in a cold climate?

Answer 83

* they are usually larger than their counterparts in a warm environment as this reduces their SA:V ratio and so reduces their rate of cooling * they develop thick layers of fat be eath the skin as insulation against cooling * some mammals and birds have developed countercurrent exchange systems in their limbs that allow body temperature to be conserved. The arterial blood is cooled as it flows to the extermity and the venous blood is warmed as it returns to the body * hibernation

Question 84

What do animals do before hibernation?

Answer 84

Usually dig or find a sheltered place, line it with leaves, fur or other similar materials. They also eat more than usual which results in a layer of insulating fat that prevents cooling and acts as a food store during hibernation

Question 85

What happens during hibernation?

Answer 85

The animal goes into a deep sleep and it's metabolic rate slows right down and the core body temperature is greatly lowered and then maintained at this lower level making substantial energy savings

Question 86

What is a problem with during hibernation an animal allowing their body temperature to follow that of the external environment?

Answer 86

Although is saves energy if the temperature frops too low the tissues might freeze killing the animals

Question 87

What do animals go into hibernation as a result of?

Answer 87

Both low temperatures amd a shortening of the day length

Question 88

After hibernation the metabolic rate needs to speed up really quickly. How does this happen?

Answer 88

Stores of brown fat (fat with a particularly rich blood supply) are saved during hibernation and are used up quickly to produce metabolic warming at the end of hibernation

Question 89

Why are the extermities of many animals in hot environments large and thin with a rich blood supply?

Answer 89

Because energy can be transferred to the environment quickly

Question 90

What adaptations have cammels had to make living in hot environments?

Answer 90

* they cannot cool down enough to maintain a steady internal temperature so they have evolved an ability to tolerate much larger fluctuations in the body temperature than most organisms * their major priority is to conserve water and so they don't sweat * cammels tolerate the changes in internal temperature and so this allows osmoregulation to occur successfully and also prevents damage to the cells * the low night temperature ensures the temperature does not climb too high during the day

Question 91

How is the brain cooled?

Answer 91

Due to the presence of a countercurrent exchange system

Question 92

What are four major behavioural modifications that are used by both endotherms and ectotherms in maintaining body temperature?

Answer 92

* basking: desert lizards and other animals will bask in the sun when body temperature is tending to fall. Bu orientating the body differently to the sun, or by erecting special areas of tissue that have evolved to absorb radiation from th3 sun the body temperature may be raised to a level that makes rapid activity possible * sheltering: when the core temperature is too jigj many animals shelter from the direct warmth of the sun in burrows, holes or crevices in rocks. They may also attempt extra cooling by conduction pressing the body against the cool earth * evaporation: animals can increase evaporation by panting and so exposing the moist surfaces of the mouth, by licking the body surfave or wallowing in mud or water * moving in out of the sun

Question 93

What is aestivation?

Answer 93

An extreme physiological adaptation for avoiding hot, dry conditions, similar to hibernation. The metabolic rate slows right down and the animals become completely inactive and torpid for months, burried in mud or rock crevices