homeostasis Flashcards
1
Q
What is homeostasis?
A
The maintenance of a constant
internal environment within a living
organism
2
Q
Why are feedback systems
important?
A
Homeostasis depends on sensory receptors detecting small changes in the body, and effectors working to restore the status quo • These precise control mechanisms in the body are based on feedback systems that enable the maintenance of a relatively steady state around a narrow range of conditions
3
Q
What are negative feedback
systems?
A
They work to reverse the initial stimulus 1. A small change in one direction is detected by sensory receptors 2. Effectors work to reverse the change and restore conditions to their base level • e.g. control of blood glucose, temperature control and water balance of the body
4
Q
What are positive feedback
systems?
A
1. A change in one direction is detected by sensory receptors 2. Effectors are stimulated to reinforce that change and increase the response e.g. the blood clotting cascade • When a blood vessel is damaged, platelets stick to the damaged region and release factors that initiate clotting and attract more platelets • These platelets also add to the positive feedback cycle and it continues until a clot is formed
5
Q
What is thermoregulation?
A
The maintenance of a relatively
constant core temperature
6
Q
Define endotherms and
ectotherms
A
• Endotherms - Animals that rely on their metabolic processes to warm their bodies and maintain their core temperature • Ectotherms - Animals that use their surroundings to warm up their bodies, so their core temperature is heavily dependent on the environment
7
Q
What are the physical
processes involved in the
heating up and cooling down
of organisms?
A
• Exothermic chemical reactions • Latent heat of evaporation - objects cool down as water evaporated from a surface • Radiation - the transmission of EM waves to and from the air, water or ground • Convection - the heating and cooling by currents of air or water • Conduction - heating as a result of the collision of molecules. Air is not a good conductor of heat battleground and water are
8
Q
Describe ectotherms
A
• All invertebrate animals, fish, amphibians, and reptiles • Many ectotherms living in water don’t need to thermoregulate because the high heat capacity of water means that the temperature of the environment doesn’t change much • Ectotherms living on land face a greater challenge with thermoregulation as the temperature of the air can vary dramatically, and as a result they have develop a range of strategies that enable them to cool down or warm up
9
Q
Describe endotherms
A
• Mammals and birds • Rely on their metabolic processes warm up and they usually maintain a very stable code body temperature regardless of the environment • Have adaptions that enable them to maintain body temperature and take advantage of warmth from the environment • Survive in a wide range of environments • Metabolic rate is 5 times higher than ectotherms so they need to consume more food to meet their metabolic needs
10
Q
How is temperature regulated
in ectotherms?
A
• Behavioural responses
• Physiological responses to
warming
11
Q
What are the behavioural
responses in ectotherms?
A
Sometimes they need to warm up to reach a temperature at which their metabolic reactions happen fast enough for them to be active • Basking in the Sun, orientating their bodies so that the maximum surface area is exposed to the Sun, and even extending areas their body to increase surface area exposed to the such • Through conduction by pressing their bodies against the warm ground • Exothermic metabolic reactions e.g. muscle contraction Sometimes they need to cool down to prevent their core temperature reaching a point where enzymes begin to denature • Seek shade, hiding in cracks in rocks, or even digging burrows • Pressing their bodies against cool shady earth or stones, or move into water or mud • Orientate their does so that the minimum surface area is exposed to the Sun • Minimise movement to reduce the metabolic heat generated
12
Q
What are the physiological
responses to warming?
A
• Dark coloured skin because it absorbs more radiation than light colours • Alter their heart rate to increase or decrease the metabolic rate and sometimes to affect the warming or cooling across the body surfaces
13
Q
Advantages of being an
ectotherm
A
• Need less food than endotherms they use less energy regulating their temperatures • Therefore can survive in some very difficult habitats where food is in short supply
14
Q
How do endotherms detect
temperature changes
A
• Peripheral temperature receptors are in the skin and detect changes in the surface temperature • Temperature receptors in the hypothalamus detect the temperature of the blood deep in the body Combination of the two gives the body great sensitivity and allows it to respond not only to actual changes in the temperature of the blood, but to also pre-empt possible problems that might result from changes in the external environment
15
Q
What are behavioural
responses in thermoregulation
in endotherms?
A
Basking in the Sun and pressing themselves to warm surfaces to warm up • Wallowing in water and mud, and digging burrows to keeps warm or cool • Becoming dormant (called hibernation in cold weather, and aestivation in hot weather) • Humans wear clothes to stay warm, houses are built and then heated up or cooled down to maintain the ideal temperature
16
Q
What happens when core body
temperature increases?
A
It is important for an animal to cool down: • Vasodilation • Increased sweating • Reducing the insulating effect of hair or feathers
17
Q
Describe vasodilation
A
• Arterioles near surface of skin dilate when the temperature rises • The arteriovenous shunt vessels constrict • This forces blood through the capillary networks close to the surface of the skin • The skin flushes and cools as a result of increased radiation • If the skin is pressed against cool surfaces, the cooling results from conductions
18
Q
What is the effect of increased
sweating
A
As the core temperature starts to increase, rates of sweating also increase • Sweat spreads out across the surface of the skin • As sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface
19
Q
Reducing the insulating effect
of hair or feathers
A
1. Body temperature begins to increase 2. The erector pili muscles (the hair erector muscles) in the skin relax 3. The hair or feathers of the animal lie flat to the skin 4. This avoids trapping an insulating layer of air
20
Q
What happens when core body
temperature falls?
A
It is important for an animal to warm up: • Vasoconstriction • Decreased sweating • Raising the body hair or feathers • Shivering
21
Q
Describe vasoconstriction
A
• Arterioles near the surface of the skin constrict • The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin • The skin looks pale, and very little radiation takes place • The warm blood is kept well below the surface
22
Q
What is the effect of decreased
sweating?
A
As the core temperature falls, rates of sweating decrease and sweat production will stop entirely • Reduces cooling by the evaporation of water from the surface of the skin, although some evaporation from the lungs still continues
23
Q
Raising the body hair or
feathers
A
- Body temperature falls
- The erector pili muscles in the
skin contract, pulling the hair or
feather of the animal erect - Traps an insulating layer of air
and so reduces cooling through
the skin
24
Q
What is the effect of shivering?
A
Shivering - the rapid, involuntary contracting and relaxing of the large voluntary muscles in the body • Metabolic heat from the exothermic reactions warm up the body instead of moving it
25
Q
How is thermoregulation
controlled?
A
The heat loss centre • Activated when the temperature of the blood flowing through the hypothalamus increases • Sends impulses through autonomic motor neurones to effectors in the skin and muscles, triggering responses that act to lower the core temperature The heat gain centre • Activated when the temperature of the blood flowing through the hypothalamus decreases • Sends impulses through the autonomic nervous system to effectors in the skin and the muscles, triggering responses that act to raise the core temperature
26
Q
What are the main metabolic
waste products in mammals?
A
• Carbon dioxide - one of the waste products of cellular respiration, which is excreted from the lungs • Bile pigments - formed from the breakdown of haemoglobin from old red blood cells in the liver. Excreted in the bile from the liver into the small intestine via the gall bladder and bile duct. They colour the faeces • Nitrogenous waste products (urea) - formed by the breakdown of excess amino acids by the liver. Mammals produce urea, fish produce ammonia, birds and insects produce uric acid
27
Q
Describe the liver
A
• One of the major body organs involved in homeostasis • Reddish-brown, and is the largest internal organ of the body • Lies just below the diaphragm and is made up of several lobes • Very fast growing and damaged areas generally regenerate very quickly • Very rich blood supply
28
Q
Describe the blood supply to
the liver
A
• Oxygenated blood is supplied to the liver by the hepatic artery and removed from the liver and returned to the heart in the hepatic vein • Liver also supplied with blood by the hepatic portal vein - carries blood loaded with the products of digestion from the intestines to the liver • 75% of the blood flowing through the liver comes via the hepatic portal vein
29
Q
Describe hepatocytes
A
• Liver cells are called hepatocytes • They have a large nuclei, prominent Golgi apparatus and lots of mitochondria • Metabolically active cells
30
Q
Describe the structure of the
liver
A
• Blood from hepatic artery and hepatic portal vein is mixed in spaces called sinusoids, which are surrounded by hepatocytes • This mixing increases the oxygen content of the blood from the hepatic portal vein, supplying the hepatocytes with enough oxygen for their needs • The sinusoids contain Kupffer cells, which act as the resident macrophages of the liver, ingesting foreign particles and helping to protect against disease • Hepatocytes secrete bile from the break down of blood into spaces called canaliculi, and from these the bile drains into the bile ductules which take it to the gall bladder
31
Q
What are the functions of the
liver?
A
• Carbohydrate metabolism
• Deamination of excess amino
acids
• Detoxification
32
Q
Describe carbohydrate
metabolism
A
• When blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose to the storage carbohydrate glycogen • When blood glucose levels start to fall, the hepatocytes convert glycogen back to glucose under the influence of glucagon
33
Q
What is deamination?
A
Deamination is the removal of an amine group from a molecule • The body cannot store proteins or amino acids • And excess ingested protein would be excreted without the action of hepatocytes • Hepatocytes deaminate amino acids, and convert it first into ammonia and then to urea • Urea is excreted by the kidneys • The remainder of the amino acids can be used in cellular respiration or converted into lipids for storage
34
Q
What is transamination?
A
The conversion of one amino acid into another • Important because the diet doesn’t always contain the required balance of amino acids
35
Q
What is the ornithine cycle?
A
The set of enzyme-controlled
reactions in which the ammonia
produced in the deamination of
proteins is converted into urea
36
Q
Give an example of
detoxification that takes place
in the liver
A
The breakdown of hydrogen peroxide • Hepatocytes contain the enzyme catalase, one of the most active known enzymes, that splits the hydrogen peroxide into oxygen and water Detoxification of ethanol (the active drug in alcoholic drinks) • Hepatocytes contain the enzyme alcohol dehydrogenase that breaks down the ethanol to ethanal • Ethanal is then converted to ethanoate which may be used to build up fatty acids, or used in cellular respiration
38
Q
Describe the structure of the
kidney
A
• Cortex: The dark outer layer. This is where the filtering of the blood takes place and it has a very dense capillary network carrying blood from the renal artery to the nephrons • Medulla: Lighter in colour - contains the tubules of the nephrons that form the pyramids of the kidney and the collecting ducts • Pelvis: The central chamber where the urine collects before passing out down the ureter
40
Q
What are the main structures
of the nephron?
A
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
48
Q
What happens during
ultrafiltration?
A
1. Blood enters glomerulus through wide afferent arteriole and leaves through a narrow efferent arteriole. This causes pressure in the capillaries of the glomerulus and forces blood out through the capillary wall, like a ‘sieve’ 2. The fluid then passes through the basement membrane. Basement membrane is made up of a network of collagen fibres and other proteins that act as a second ‘sieve’ 3. Most of the plasma contents can pass through the basement membrane, but blood cells and many proteins stay in the capillary because they are too large 4. Walls of the Bowman’s capsule also involve cells called podocytes that act as an additional filter - they have extensions called pedicels that wrap around the capillaries, forming slits to make sure any cells, platelets or large plasma proteins that have passed through the basement membrane, do not enter the tubule 5. The filtrate which enters the capsule contains: glucose, salt, urea etc. 6. Volume of blood filtered through the kidneys in a given time is known as the glomerular filtration rate
64
Q
How does ADH cause an
effect?
A
Released from the pituitary gland and carried in the blood to the cells of the collecting duct where it has its effect • Doesn’t cross the membrane of the tubule cells - it binds to receptors on the cell membrane and triggers the formation of cyclic AMP (cAMP) as a second messenger inside the cell • This causes a cascade of events
66
Q
What happens with changing
ADH levels?
A
The more ADH released… • More water channels inserted into the membranes of the tubule cells • This makes it easy former water to leave the tubules by diffusion, resulting in the formation of a small amount very concentrated urine • Water is returned to the capillaries, maintaining the water potential of the blood and therefore the tissue fluid of the body When ADH levels falls… • Levels of cAMP fall, then the water channels are removed from the tubule cell membranes and enclosed in vesicles again • The collecting duct becomes impermeable to water once more, so no water can leave • Production of large amounts of very dilute urine
74
Q
What are the main stages in a
pregnancy test?
A
1. The wick is soaked in the first urine passed in the morning as it has the highest levels of hCG 2. The test contains mobile monoclonal antibodies that have small coloured beads attached to them. They will only bind to hCG, soil the woman is pregnant, the hCG in her urine binds to the mobile monoclonal antibodies and forms a hCG/ antibody complex 3. The urine carries on along the test structure until it reaches a window 4. There are mobilised monoclonal antibodies here that only bind to the hCG/antibody complex. If the woman is pregnant, a coloured line appears in the first window 5. The urine continues up through the test to a second window 6. Here there is usually a line of immobilised monoclonal antibodies that only bind to the mobile antibodies, whether these are bound to hCG or not. This coloured line forms whether the woman is pregnant or not, and indicates the test is working
87
Q
Describe haemodialysis
A
1. Blood leaves the patient’s body from an artery and flows into the dialysis machine, where it flows between partially permeable dialysis membranes 2. These membranes mimic the basement membrane of the Bowman’s capsule 3. On the other side of the membranes is the dialysis fluid which contains the normal plasma levels of glucose and mineral ions, and no urea. As a result much of the urea leaves the blood 4. The blood and dialysis fluid flow in opposite directions to maintain a countercurrent exchange system
88
Q
Describe peritoneal dialysis
A
Done inside the body - makes use of the natural dialysis membranes formed by the lining of the abdomen called the peritoneum 1. The dialysis fluid is introduced into the abdomen using a catheter 2. It is left for several hours to allow dialysis to take place across the peritoneal membranes 3. The fluid is then drained off and discarded, leaving the blood balanced again and the urea and excess mineral ions removed
89
Q
How is kidney failure treated
by transplant?
A
A single healthy kidney from a donor is placed within the body. The blood vessels are joined and the ureter of the new kidney is inserted into the bladder • The main problem is the risk of rejection • The antigens on the donor organ differ from the antigens on the cells of the recipient and the immune system is likely to recognise this • This can result in rejection and the destruction of the new kidney
