Module 5- Homeostasis

Question 1

Define homeostasis

Answer 1

Maintenance of a constant internal environment in response to internal and external changes via physiological control systems

Question 2

What do physiological control systems do in homeostasis?

Answer 2

-keep body temp, blood pH, blood glucose and blood w.p within its set limits

Question 3

What is a negative feedback loop in homeostasis?

Answer 3

When a deviation from the set limits is detected in the body by a receptor, receptors send a signal to effectors, through the nervous system, which counteract the initial change

Question 4

Describe positive feedback loops in homeostasis and give an example

Answer 4

-quite rare
-when a change from the set limits triggers a response to increase the change further
-e.g during child birth when the baby’s head presses on the cervix it causes the hormone oxytocin to be released, causing the uterus to contract which results in the release of even more oxytocin

Question 5

Why is thermoregulation important?

Answer 5

-if body temp dropped too low there would be insufficient kinetic energy for enzyme controlled reactions
-if the body temp increased too high, enzymes would denature
-either way metabolic reactions could slow to the point that cells die

Question 6

What are examples of ectotherms

Answer 6

Fish and reptiles

Question 7

How do ectotherms (both aquatic and land) mainly control their body temp

Answer 7

-By behavioural responses such as warm up against conduction of hotter surfaces,orientate themselves to have an increased surface area exposed to the sun and cool down by moving to shade or into water, minimise movements to reduce metabolic heat generated by
-rarely use physiological responses but do sometimes alter their heart rate to increase or decrease their metabolic rate
-aquatic ectotherms don’t have much need to emulate their body temp as water has a high specific heat capacity and therefore temperatures remain relatively constant
-land ectotherms have a bigger challenge as the temperature of the air fluctuates

Question 8

Compare thermoregulation in ectotherms and endotherms

Answer 8

-ectotherms are more vulnerable to changes in the environment
-endotherms can regulate their body temp within a very narrow range so is more specific
-ectotherms rely mainly on external heat sources to regulate their temperature

Question 9

How do endotherms regulate their body temperature general?

Answer 9

-through a nervous response
-peripheral thermoreceptors in the skin detect a change in the external temp and sends an impulse along a sensory neurone to the brain where the hypothalamus coordinates the impulse which triggers a response by glands in the skin and muscle

Question 10

What do endotherms do to cool down?

Answer 10

-vasodilation-the arteriolar near the surface of the skin dilate due to the contraction of muscles near the blood vessels that connect the arteriolar. More blood flows through the arterioles near the skin surface so more heat radiates from the skin surface
-sweating-as sweat evaporates from the skin surface it takes heat energy with it
-erector pili muscles-relax so hairs lie flat to improve air circulation over the skin

Question 11

What do endotherms do to warm up?

Answer 11

-vasoconstriction-arterioles near the surface of the skin constrict so very little blood flows through the capillary networks close to the surface of the skin so very little radiation takes place
-sweating-production of sweat will stop entirely
-insulation-erector pili muscles in the skin contract and stand erect to trap an insulating layer of air
-shivering-contracting and relaxing of muscles increase the rate of respiration and so more heat is produced

Question 12

When might negative feedback not be possible?

Answer 12

When the change is too dramatic

Question 13

Define excretion

Answer 13

Removal of waste products so they don’t become toxic

Question 14

What are key examples of waste products and where do they come from?

Answer 14

CO2-waste products from respiration is excreted from the lungs

Nitrogenous waste-is created from the excess amino acids in the diet which can’t be stored. Therefore excess amino acids are broken down in the liver to ammonia and then urea which is excreted from the kidneys

Question 15

Describe the structure of the liver?

Answer 15

-the liver contains a range of different enzymes that make these processes possible
-the hepatic portal vein supplies the liver with blood coming directly from the digestive system
-liver cells are called hepatocytes and have many mitochondria, large nuclei and prominent Golgi apparatus which enable a high metabolic rate
-hepatocytes also have microvilli to increase SA
-liver has a highly vascularised and lobular structure to give it an increased SA

Question 16

Describe the process that occurs in the liver?

Answer 16

-the blood delivered to the liver through the hepatic portal vein and the hepatic artery mixes in the sinusoids (spaces that are surrounded by hepatocytes)
-the blood delivered from the hepatic artery is highly oxygenated and this oxygen can mix with the blood from the hepatic portal vein.

Question 17

What are kupffer cells?

Answer 17

-Contained with the sinusoids and protect against disease
-kupffer cells are macrophages engulfing any pathogens that may have entered through the blood delivered by the hepatic portal vein which comes from the digestive system

Question 18

What do hepatocytes do?

Answer 18

-produce bile using the products from breaking down old blood
-the bile is first secreted into spaces called canaliculi and then it passes through the bile ducts to the gall bladder where its stored
-hepatocytes in response to insulin can absorb excess glucose from the blood and convert it into glycogen
-hepatocytes in response to glucagon hydrolyse glycogen back into glucose and release it into the blood

Question 19

What other functions is the liver responsible for?

Answer 19

Detoxification-the neutralisation and breakdown of unwanted chemicals such as alcohol, drugs, toxins and hormones produced from chemical reactions in the body. The liver contains enzymes to break down these into non toxic substances

Deamination of excess amino acids-excess proteins from our diet can’t be stored so are transported to the liver to be deaminated. Deamination is where the amine group is removed from the amino acids, converting it to ammonia. Ammonia is highly toxic which is why it’s converted to urea before being transported in the blood. Urea is also toxic but only in very high concentrations so is much less toxic and soluble in water

Question 20

What layers are kidneys made up of?

Answer 20

3 distinct layers- cortex, medulla, pelvis

Question 21

What is the kidney responsible for?

Answer 21

Excretion of nitrogenous waste and osmoregulation (process of controlling water potential of the blood)

Question 22

What is the cortex in the kidney and where does it carry blood from and to?

Answer 22

The dark outer layer that contains many capillary networks carrying blood from the renal arteries to the nephrons

Question 23

What does the medulla contain and what does it look like?

Answer 23

-nephrons which are structures where blood is filtered and useful substances are re absorbed into the blood
-collecting ducts
-lighter in colour

Question 24

What is the pelvis responsible for?

Answer 24

-where the urine collects before leaving the kidney and travelling to the ureter

Question 25

What occurs in the Bowman’s (renal) capsule?

Answer 25

Ultrafiltration -Everything except larger proteins, red blood cells, and most white blood cells is forced out of the blood and into the bowman’s capsule due to the high pressure caused by the difference in diameter between the afferent and efferent arterioles. The afferent arteriole is much wider than the efferent arteriole. -blood enters through the afferent arterioles and this splits into lots of smaller capillaries that make up the glomerulus -this causes a high hydrostatic pressure of the blood. Water and small molecules such as glucose and mineral ions are forced out of the capillaries and form the glomerulus filtrate -ultrafiltration removes urea from the blood but also removes a lot of water along with glucose and salt -once the fluid is forced out of the capillaries it passes through a basement membrane which acts as a sieve -the bowman’s capsule wall also has podocytes that act as an additional filter -large blood cells and proteins are too big to fit through the gaps in the capillary endothelium, so remain in the blood which leaves via the efferent arteriole

Question 26

What occurs in the proximal convoluted tubule?

Answer 26

Water, amino acids, glucose and ions are selectively reabsorbed first in the proximal convoluted tubule (PCT) -most of the glomerulus filtrate is reabsorbed back into the blood, leaving urea, excess mineral ions and water behind -due to changes in water potential caused by the transport of glucose, approx 80% of water in PCT also moves back into capillaries at this stage -the concentration of sodium ions in the PCT cell is decreased as the sodium ions are actively transported out of the PCT cells into the blood in the capillaries -due to the conc gradient, sodium ions diffuse down the gradient from the lumen of the PCT into the cells lining the PCT -this is an example of co transport as the proteins that transport the sodium ions carry glucose with it -the glucose can then diffuse from the PCT epithelial cell into the blood stream which is how all glucose is reabsorbed

Question 27

What occurs in the loop of henle?

Answer 27

-The filtrate entering the descending limb of the loop of Henle is isotonic with the blood -As it travels down the limb, water passes out of the loop into the tissue fluid by osmosis down a concentration gradient. -It then moves down a concentration gradient into the blood of the surrounding capillaries. -The descending limb is not permeable to sodium and chloride ions, and no active transport takes place here. -The fluid that reaches the hairpin bend is very concentrated and hypertonic to the blood in the capillaries. -The first section of the ascending limb of the loop of Henle is very permeable to sodium and chloride ions and they move out of the solution by diffusion down a concentration gradient. -In the second section of the ascending limb, sodium and chloride ions are actively pumped out into the medulla tissue fluid against a concentration gradient. This produces very high sodium and chloride ion concentrations in the medulla tissue. -the ascending limb of the loop of Henle is impermeable to water so water cannot follow the chloride and sodium ions down a concentration gradient. -This means the fluid left in the ascending limb becomes increasingly dilute, while the tissue fluid of the medulla develops the very high concentration of ions that is essential for the kidney to produce urine more conc than the blood -by the time the dilute fluid reaches the top of the ascending limb it is hypotonic to the blood again and enters the DCT

Question 28

What are the structures in the nephron?

Answer 28

-bowman’s capsule -proximal convoluted tubule -loop of henle -distal convoluted tubule -collecting duct

Question 29

Structure and function of loop of henle (one sentence)

Answer 29

Section of the kidney tubule that enables mammals to produce urine more concentrated than their own blood

Question 30

What occurs at the Distal convoluted tubule and collecting duct?

Answer 30

-DCT- balancing water needs of body as the permeability of the walls of the tubules varies with levels of ADH -the cells lining the DCT have many mitochondria to carry out active transport -the collecting duct passes through the concentrated tissue fluid of the renal medulla and is the main site of where the concentration and volume of the urine produced is determined

Question 31

What detects water potential of the blood? What happens if too low/high

Answer 31

Osmoreceptors in the hypothalamus detect water composition in the blood. -if water potential is too low water leaves osmoreceptors by osmosis and they shrivel. This stimulates the hypothalamus to produce more of the hormone ADH which then moves to the posterior pituitary gland to release into the bloodstream -if wp is too high water enters the osmoreceptors by osmosis which stimulates the hypothalamus to produce less ADH

Question 32

What happens when more ADH is released into the blood due to low water potential (not drinking enough)

Answer 32

-ADH will bind to complementary receptors that are only located on the target cells in the DCT and collecting duct. -when it binds it activates adenyl cyclase to make cAMP -this activates an enzyme which causes vesicles containing aquaporins to fuse with the membrane -the membrane becomes more permeable to water and more will leave to be reabsorbed back into the blood so urine will be more concentrated and in a lower volume

Question 33

What happen when less ADH is released into the blood due to high water potential?

Answer 33

-DCT and collecting duct walls become less permeable to water so less water is reabsorbed into the blood and more is lost in urine

Question 34

What can urine be used to test for?

Answer 34

-diabetes, pregnancy, anabolic steroids, drugs

Question 35

How do pregnancy tests work?

Answer 35

-Human chorionic gonadotrophin (hCG) is a hormone which is only produced in the urine during pregnancy. -In pregnancy tests, mobile antibodies specific to hCG are attached to enzymes which can change the colour of a dye. -These antibodies attach to the hCG and move along the test strip with the urine. -More monoclonal antibodies specific to hCG are fixed in a line on the test, along with the substrate for the dye enzyme. -If the hCG-antibody-enzyme complexes are formed, the enzyme changes the colour of the dye and shows a positive test line.

Question 36

How are anabolic steroids measured using urine?

Answer 36

In these tests, the ratio of testosterone to epitestosterone in the urine is measured. Increased testosterone levels relative to epitestosterone indicates anabolic steroid use, as normally these are roughly equal. This imbalance can remain in the body and be tested for between 14 and 28 days after anabolic steroids have been taken.

Question 37

Where does urine go after the collecting ducts?

Answer 37

-The collecting ducts converge in the renal pelvis to form the ureter of each kidney. -The urine passes down the ureters and into the bladder. -When the bladder is full, urine passes through the urethra and out of the body.

Question 38

What are the causes for kidney failure?

Answer 38

-infection -high blood pressure -genetic conditions -physical damage -diabetes

Question 39

What can kidney damage cause?

Answer 39

-damage to tubules, prodocytes, epithelial cells and basement membranes in bowman’s capsule which would result in large molecules diffusing out of the blood e.g proteins -this can lead to a build up of urea in the blood and an electrolyte imbalance

Question 40

What is the glomerular filtration rate?

Answer 40

-GFR indicates how well the kidneys are functioning and estimates the amount of blood passing through the kidneys per minute. -GFR decreases slightly with age but is markedly decreased if the kidneys are damaged. -measured indirectly by testing creatine levels as creatine is a breakdown product of muscles so if creatine levels in the blood increase this indicates that the kidneys aren’t filtering properly

Question 41

What is haemodialysis?

Answer 41

-Haemodialysis is a type of renal dialysis. -Sessions happen in a clinic three times weekly and last 3-4 hours. -A catheter is placed in a large vein in the groin or neck, -200 mL of blood per minute passes through the dialyser (dialysis machine) and over membranes to exchange substances into the dialysis fluid which contains no urea to maintain a steep concentration gradient so that all urea diffuses out of the blood. -patient has to maintain a careful diet to keep their blood levels as constant as possible -the dialysis fluid has normal plasma levels for glucose and mineral obs to ensure net movement of glucose out of the blood and only excess mineral ions are removed from the blood

Question 42

What is a peritoneal dialysis?

Answer 42

-Peritoneal dialysis is a type of renal dialysis. -A catheter is inserted into the abdomen. -Dialysis fluid is pumped into the peritoneal cavity. -Waste substances are removed from the blood by exchange into the dialysate across the membrane of the peritoneum. -This can be carried out overnight using an automated machine, or around four times a day with the manual exchange of waste fluid bags during which patients can carry out their daily activities -at the end dialysis fluid is drained out of the abdomen and discarded, leaving the blood in the body filtered

Question 43

What are the effects of dialysis?

Answer 43

-long term dialysis can have harmful side effects and therefore the best treatment is kidney transplant

Question 44

Kidney transplants

Answer 44

-Long waiting lists and the possibility of organ rejection following transplantation means that patients do not always survive long enough for this treatment to work. -immunosuppressant drugs will need to be taken for life to reduce the risk of patients immune system rejecting the new organ -this makes them more prone to illness -most transplanted kidneys work around 10 years