5.3 Homeostasis Flashcards
What is homeostasis ?
The body maintaining a dynamic equilibrium , with small fluctuations over a narrow range of conditions.
What are some factors affected by homeostasis ?
Blood pH, blood glucose concentration levels, urea concentration, temperature, water content.
What are 2 factors that are vital for homeostasis ?
Receptor and effectors as they detect and respond to change.
What is a negative feedback system ?
When a small change in one direction is detected by sensory receptors, effectors work to reverse the change. They work to reverse the initial stimulus.
What occurs in a negative feedback system when a increase is directed ?
An increase is detected, causing a reduction in levels to return back to ideal conditions.
What occurs in a negative feedback system when a decrease is directed ?
A decrease is detected, causing an increase in levels to return back to ideal conditions.
What is a positive feedback system ?
A change in conditions caused a reinforcement of the change.
Eg, blood clotting, contractions, depolarisation.
What is thermoregulation ?
Maintenance of a relatively constant core body temperature to maintain optimum enzyme activity.
What are ectotherms ?
Most animals are ectotherms and they use their surroundings to warm up their body temperature.
What are endotherms ?
Mammals and birds are endotherms. They rely on metabolic processes to warm up.
What are behavioural responses ?
Changing behaviour to control temperature of the body to warm up or cool down.
What are physiological responses ?
Body features that help to warm up or cool down the body. Eg, dark fur.
Why don’t ectotherms thermoregulate ?
They have a high heat capacity of water and many live in water.
Why do ectotherms require less food ?
They require les food due to requiring less energy to regulate temperature.
What are endotherms ?
They can regulate their body temperature within a very narrow range in a wide variety of external conditions.
How is thermoregulation regulated in endotherms ?
Endotherms use their internal exothermic metabolic activities to keep them warm.
How do endotherms cool down ?
Vasodilation occurs near surface if skin causing the arterioles to dilate. This forces blood through capillaries near the surface of the skin and heat is lost through evaporation of sweat from skin surface.
How do endotherms warm up ?
Arterioles constrict so little blood flows near surface of the skin. Sweating is decreased reducing evaporation of radiation. Shivering also occurs due to involuntary contracting of muscles. Hairs also stand up trapping air under muscles causing it to warm up.
How is the heat loss centre activated ?
Activated when blood flowing through hypothalamus increases.
How is heat gain centre activated ?
Activated when temperature of blood flowing through hypothalamus decreases.
What are the main metabolic waste products excreted in animals ?
Carbon dioxide, bile pigments and nitrogenous waste products, such as urea.
How is oxygenated blood supplied to the liver ?
Supplied by hepatic artery from the aorta.
What is the hepatic portal vein ?
Carries blood loaded with products of digestion straight from intestines to liver and this is the starting point for many metabolic activities.
What are cells in the liver called ?
Hepatocytes have large nuclei, a prominent Golgi and lots of mitochondria, indicating they are metabolically active.
What are the spaces called that are surrounded by hepatocytes ?
Sinusoids mixes blood from hepatic artery and hepatic portal vein. Mixing increases they oxygen content of the blood from hepatic portal vein.
What cells do sinusoids contain ?
Kupffer cells which act as the resident macrophages of the liver, ingesting foreign particles and helping to protect against disease.
What happens when the hepatocytes secrete bile ?
They secrete bile from the breakdown of blood into spaces called canaliculi and from these the bile drains into the bile ducts which take it into the gall bladder.
What happens when blood glucose levels rise ?
Insulin levels rise and stimulate hepatocytes to convert glucose glucose into glycogen.
What happens when blood glucose levels drop ?
Hepatocytes convert glycogen back to glucose under influence of hormone glucagon.
What is deamination ?
This is the removal of an amine group from a molecule. Removing the amino group and converting it into ammonia which is toxic to urea.
What is the ornithine cycle ?
Set of enzyme controlled reactions. Ammonia is added as well as CO2 forming citrulline and water. Ammonia is added to citrulline to form arginine and water. Finally, water is added to arginine forming ornithine and urea. Then the cycle repeats.
What carries blood to kidneys ?
The renal artery carries blood to the kidneys from the abdominal aorta.
What enzyme do hepatocytes contain ?
Contains catalase that breaks down hydrogen peroxide into oxygen and water.
What are kidneys made up of ?
Made up of millions of nephrons that act as filtering units for urea to be excreted.
What are the three main areas of the kidney ?
Cortex, medulla and the pelvis.
What is the Bowmans Capsule ?
Cup shaped structure that contains the glomerulus and capillaries. This is where ultrafiltration takes place.
What is the proximal convoluted tubule ?
The first coiled region of the tubule after the Bowmans capsule, found in the cortex of the kidney. This is where many of the substances needed by the body are reabsorbed by the blood.
What is the Loop of Henle ?
This is a long loop of tubule that creates a region with a high solute concentration in the tissue fluid deep in the kidney medulla. Descending loop is permeable to water and ascending loop is permeable to ions.
What is the distal convoluted tubule ?
The second twisted tubule where fine tuning of water takes place. The permeability of water varies in response to ADH.
What is the collecting duct ?
This is where the urine passes down through the medulla to the pelvis. More fine-tuning occurs. Walls are also sensitive to ADH.
What occurs during ultrafiltration ?
Glomerulus is supplied with blood via afferent arteriole and leaves through the efferent arteriole, causing pressure in capillaries. This forces blood out of capillaries and fluid passes through a basement membrane.
How do podocytes help ultrafiltration ?
Found in wall of Bowmans capsule that act as an additional filter. They have extensions called pedicels that wrap around capillaries (like a claw clip), causing filtration.
How does reabsorption occur ?
In proximal convoluted tubule, all glucose, amino acids and vitamins are reabsorbed back into blood via active transport.
How does loop of Henle make more concentrated urea ?
Descending limb is permeable to water so water leaves down the concentration gradient during osmosis. Ascending limb is where ions are actively pumped out of tubule and is impermeable to water.
How does the distal convoluted balance water ?
The permeability of the walls of the tubules varies with the levels of ADH. More ADH makes it more permeable to water.
What moves out of the collecting duct by diffusion ?
Water moves out of the collecting duct and it passes through the renal medulla.
What is osmoregulation ?
Osmoregulation involves controlling the water potential of the blood within very narrow boundaries.
Where is ADH produced and stored ?
It is produced by the hypothalamus and is stored in the posterior pituitary gland.
What is the role of ADH ?
ADH increases the permeability of the membrane of the collecting duct and the distal convoluted tubule.
What happens when ADH is released from the posterior pituitary gland ?
ADH binds to the receptors on the cell membrane and triggers the formation of cyclic AMP (cAMP) as a second messenger inside the cell.
What is a second messenger molecule ?
A second messenger is a molecule which relays signals received at cell surface receptors to molecules inside the cell.
What happens when cAMP is triggered in a cell ?
-Vesicles in lining of CD fuse with cell surface membranes on side of cell.
-Membranes of these vesicles contain protein based water channels (aquaporins) making it permeable to water.
-Provides a route for water to move out of the tubule cells into tissue fluid of the medulla.
What happens with ADH action when water potential rises ?
Detected by osmoreceptors in hypothalamus. This causes less ADH to be produced so less water is reabsorbed from the nephron so there are fewer aquaporins. Causes a larger volume of dilute urine to be produced.
What happens with ADH action when water potential falls ?
Detected by osmoreceptors in hypothalamus.
This causes more ADH to be produced so more water is reabsorbed from nephron as there are more aquaporins. Causes a smaller volume of concentrated urine to be produced.
What is the hormone detected in pregnancy tests ?
Human Chorionic Gonadotrophin (hCG) is the hormone produced during pregnancy.
What do pregnancy test rely on ?
They rely on monoclonal antibodies.
How are monoclonal antibodies made ?
Mouse is injected with hCG so it makes the appropriate antibody. B cells are then removed and fused with a myeloma, forming a hybridoma.
How is hCG detected in a pregnancy test on the test site ?
Urine travels along stick. If hCG is present, it will bind to the mobile monoclonal antibodies and forms a hCG antibody complex, releasing the dye.
How does the control site work in a pregnancy test ?
Here there are immobilised antibodies that bind to the mobile antibodies regardless of whether they are bound to hCG or not. The coloured line forms regardless of whether the woman is pregnant. It indicates if the test is working.
What are anabolic steroids ?
They are drugs that mimic the action of testosterone and they stimulate muscle growth. They are excreted by urine.
Why do kidneys fail ?
-Raised bp.
-Protein or blood in urine
-Loss of electrolytes
-Build up of urea
-Weakened bones
-Pain and stiffness
-Anaemia
How do you measure kidney failure ?
Measured by glomerular filtration rate (GFR). Measured by blood tests to measure the levels of creatine in the blood. If levels of creatine go up in the blood, this indicates that this is a sign of kidney failure.
What is haemodialysis ?
This involves a dialysis machine carrie out in hospital. Blood leaves and flows into a dialysis machine where it passes through the dialysis fluid and urea diffuses across the membrane into the fluid. Blood then reenters the body.
What is peritoneal dialysis ?
Makes use of the natural dialysis membranes formed by the lining of the abdomen. Usually done at home where the fluid is introduced into the abdomen. It is left so urea can diffuse out. Fluid is then drained off and discarded.
What is the best treatment for kidney failure ?
Best solution is a kidney transplant, where a single healthy kidney from donor.
What are some advantages for kidney transplants ?
Non need for regular sessions, less expensive, no dietary restriction and long term dialysis can damage the body.
What are some disadvantages for kidney transplant ?
Less readily, organs don’t last forever, risk of rejection, immunosuppressant drugs can increase chance of infection.
