15 - Homeostasis Flashcards
What is homeostasis
The bodies maintenance of a dynamic equilibrium with a narrow range of conditions
How effectors and receptors respond to a stimulus
A receptor in a sense organ detects a stimulus which sends an impulse from the sensory neuron the brain (Relay Neuron), Which either processes this info into the senses for example or sends an impulse toward the motor neurone towards an effector (muscle/gland)
Difference between pos and neg feedback
A positive feedback loop amplifies a change from normal conditions, a negative feedback loop minimises the change from normal conditions.
What is a neg feedback loop
initiates a corrective mechanism whenever the internal environment deviates from its normal or acceptable level. Thermoregulation (Example) temp increase—>Corrective mechanism–>Norm Temp temp decrease–>Corrective mechanism—>Norm Temp
What is pos feedback with example
Deviation from normal conditions, amplified, leads to more deviation (rare in biology, leads to unstable + harmful conditions) Example childbirth:release of oxytocin stimulates uterine contractions which trigger release more pos feedback eg: More oxytocin is more contractions.Levs increase->pos feedback->further increase Set PointLevs decrease->pos feedback->further decrease
Why is homeostasis important (Use examples)
enzymes operate best in optimum conditions so maintenance of Ph and temp in body cells occur so enzyme linked reactions proceed efficiently .Cell Size: Water potential of blood cells will affect amount of water in tissue fluid and cells. Animal cells could desiccate or swell and burst. Independence from external environment: animals with constant internal environment maintain constant level of activity regardless of environment.
Kinesis
A movement or activity in response to a stimulus (Direction not important)
Taxies
direction of stimulus important EG: woodlouse moves away from sunlight.
Ectotherms and Endotherms
Ectotherms: Cold blooded animals that rely on the external environment to control their internal temperature. Endotherms: Warm Blooded mammals and birds, their internal core temp independant of the external environment.
How is temp change detected
Temp receptors in the skin sense changes in surface temp and temp sensors in the brain/hypothalamus detect and coordinate responses to changes in the temperature of the blood
Factors that affect an organisms core temp
Decrease: Evaporation: of water on the skin cools the skin down Convection: heating and cooling by currents of air and water, warm air/water rises and cooler air/water sinks setting a convection current. Increase: Radiation: transmission of electromagnetic waves to and from the ground/water/air.
Ectotherms behavioural responses
“To warm up/increase body temp so metabolic reactions become fast enough to be active:They bask in the sun, orientate their bodies so max SA exposed to the sun, conduction by pressing their bodies into the ground.
To COOL DOWN they: seek shade/hide in burrows, conduction by pressing their bodies against cool surfaces, minimise movement so less metabolic heat generated through respiration, orientate their bodies away from the sun.”
Ectotherm physiological responses
They need less food as a result of as less energy used to regulate temp (Food not used to generate heat eg) so can survive in habitats with difficult environments. Inactive in cold environments, greater proportion of energy used for growth.
Thermoregulation in Endotherms
use internal metabolic reactions to keep them warm (respiration). Have same behavioural mechanisms as ectotherms tho some hibernate during winter.
Physiological features in endotherms
“ways to cool down: Vasodilation: Arterioles near-surface of the skin dilate and vessels that connect arterioles with venules constrict so blood forced through capillaries near the skin and cools due to increased radiation, if skin pressed to cool surface then cools due to conduction. Sweating: sweat spreads across the skin and when it evaporates heat is lost cooling the skin below. Hair: Sits down which minimizes the layer of air and therefore insulating layer.
Warming up: Opposite of cooling down. Shivering: Involuntary contract and relaxation of muscles where the respiration used to move the muscles generate heat.”
Action Potential Mechanism
1: Neurone at resting potential, some potassium ion channels (PIC) open (Mainly those that aren’t voltage gated), sodium channels CLOSED 2: Energy of stimulus triggers opening of sodium ion channels (SIC), membrane more permeable to sodium ions so they diffuse into axon down electrochemical gradient making inside of neurone less negative 3: Change causes more SIC to open, more sodium ions diffusing into the axon, example of pos feedback 4:When PD reaches +40mv, voltage gated SICs close and voltage gated PICs open, sodium ions can no longer enter the axon but membrane more permeable to potassium ions 5:Potassium ions diffuse out of the axon down the electrochemical gradient, reducing the charge, resulting in the inside of the axon becoming more negative than the outside 6: Initially lots of potassium ions diffuse out, so axon becomes negative (compared to outside and normal resting state) Known as hyper-polarisation. Voltage-gated potassium channels close, sodium-potassium pump causes sodium ions to move out and potassium ions in, axon re-polarised and returned to resting state.
Propagation of an action potential
the initial stimulus causes change in sensory receptor triggering action potential in sensory receptor so first region of axon membrane depolarised which acts as stimulus for next region of membrane. Process continues along the length of the axon forming wave of depolarisation. Once sodium ions in axon, they’re attracted by the negative charge ahead and conc gradient to diffuse further into the axon triggering depolarisation of next section. Once action potential triggered, first region of axon membrane has been depolarised, this acts as a stimulus for depolarisation of the next region of the membrane. The process continues along the axon causing a wave of depolarisation. Localised electrical circuits are established by the influx of Na ions, causing the opening of the Na voltage gated channels a little further along the neurone.
Propagation in an unmyelinated neurone saltatory conduction
Myelin sheath acts as insulation, action potentials occur at nodes of ranvier where Na ions can pass through the protein channels. Therefore longer localised circuits arise between adjacent nodes of ranvier.Action potentials jump from node to node in a process called saltatory conduction - much faster then a wave of depolarisation along the whole length of the axon membrane.
What is excretion?
The removal of metabolic waste from the body
What are the 3 main metabolic waste products of the body?
- Carbon Dioxide 2. Bile Pigments 3. Urea
What blood vessel brings oxygenated blood to the liver?
Hepatic artery
What does the hepatic portal vein do?
Brings deoxygenated blood, rich in digested nutrients, from the small intestine to the liver
What does the hepatic vein do?
Takes deoxygenated blood away from the liver and joins the vena cava
What is a lobule?
Many vertical rows of hepatocytes arranged around a central vein
Where in the body would you find a hepatocyte?
The liver
What are sinusoids?
Capillaries which run along liver lobules
Branches of which two vessels provide blood to the sinusoids?
Hepatic artery and hepatic portal vein
What are canaliculi?
Fine ducts which carry bile from hepatocytes to the main bile duct
In which direction do canaliculi run?
The opposite direction to sinusoids
Where are sinusoids and canaliculi found in lobules?
Running in between columns of hepatocytes
What do Kupffer cells in sinusoids do ?
Phagocytose pathogens and old red blood cells
What adaptations do sinusoids have?
They are dilated and have discontinuous basement membranes, which not only allows for ready exchange of macromolecules but allows them to expand if necessary
How many different metabolic functions are linked to the liver?
500
What adaptations do hepatocytes have?
Lots of mitochondria and an enlarged Golgi apparatus, numerous microvilli in contact with sinusoids to maximise exchange
Why do sinusoids and canaliculi run in opposite directions?
To maximise exchange from hepatocytes
What are the 9 basic functions of the liver?
- Gluconeogenesis 2. Storage 3. Ornithine cycle 4. Bile synthesis 5. Production of plasma proteins 6. Detoxification of poisons 7. Synthesis of cholesterol from acetyl CoA 8. Metabolism of amino acids, fats and carbohydrates 9. Phagocytosis of old red blood cells
How is bile formed?
It is formed from haemoglobin, which is broken down after being taken from old red blood cells
Where is bile formed?
The liver
Where is bile stored?
The Gall Bladder
How is excess blood glucose stored?
Is converted to glycogen and stored in hepatocytes as granules
How are blood glucose levels increased?
The hormone glucagon (produced at alpha cells in the pancreas) causes hepatocytes to convert glycogen back into glucose, then release it into the blood
What is transamination and where does it occur?
The conversion of one amino acid into another. Occurs in the hepatocytes
What is deamination?
Where amine groups are removed from excess amino acids, forming ammonia and organic carboxylic acids
What happens to the organic carboxylic acids produced during deamination?
They can be respired to give ATP or converted to carbohydrates and stored as glycogen
Why isn’t ammonia excreted directly?
It is too toxic
What happens to ammonia produced during deamination?
It is combined with carbon dioxide in the ornithine cycle to form urea
What is the name of the cycle which produces urea from ammonia?
The Ornithine Cycle
What happens to urea after it is synthesised in the liver?
It is released into the blood, before being removed from the body as urine
Where in hepatocytes does the ornithine cycle occur?
Some in mitochondria, the rest in the cytoplasm
What are three things which are broken down from the liver during detoxification?
- Paracetamol 2. Ethanol 3. Excess insulin
Why is excess insulin broken down by the liver?
Because it can cause hypoglycemia
Why is paracetamol broken down by the liver?
Too much can cause liver and kidney failure
What is paracetamol broken down into?
Several products, which are excreted by the blood, urine and bile
What type of reaction is the conversion of ethanol to ethanal or ethanal to ethanoic acid?
Oxidation
How is ethanol broken down by the body?
It is first oxidised to ethanal, then to ethanoic acid
What is the IUPAC name for acetic acid?
Ethanoic acid
Why must excess alcohol be broken down by the liver?
It can lead to fatty liver disease or liver cirrhosis
What is fatty liver disease?
Where hepatic cell nuclei are displaced by fat-filled vesicles
What is liver cirrhosis?
An irreversible condition where hepatocytes are replaced by fibrous scar tissue
What enzyme do hepatocytes contain to break down hydrogen peroxide?
Catalase
What can ethanoic acid be used for?
In cellular respiration or to build up fatty acids
What are the two important homeostatic functions that kidneys perform?
Osmoregulation, excretion
What is the main thing that kidneys filter from the blood?
Urea and other nitrogenous waste products
What two things do kidneys help maintain in the blood?
pH and water potential
What artery provides blood to the kidneys?
Renal artery
What vein removes blood from the kidneys?
Renal vein
What part of the Vena Cava does the Renal vein drain into?
Inferior Vena Cava
What are the filtering structures within the kidneys called?
Nephrons
What tubes take urine away from the kidneys to the bladder?
The ureters
What tube takes urine from the bladder to be excreted?
Urethra
What are the three main areas of the kidney?
Cortex, Medulla, Pelvis
Which of the afferent and efferent arterioles is wider and why?
Afferent, in order to create high blood pressure within the Glomerulus
What is an adaptation of the renal cortex?
It has a very dense capillary network, in order to supply as much blood to the nephrons as possible
What gland is ADH released from?
The posterior pituitary gland
Which of the cortex and medulla is darker in colour? (in the kidneys)
Cortex
What parts of the nephron are in the medulla?
Loop of Henle and collecting duct
What parts of the nephron are in the cortex?
Bowman’s capsule, distal convoluted tubule, proximal convoluted tubule
Which part of the nephron is impermeable to water?
Ascending limb of the Loop of Henle
What is the function of the kidney pelvis?
It is a chamber where urine collects before passing into the ureters
What parts of the kidney nephron form the pyramids?
Loop of Henle and collecting duct
Where does most selective reabsorbtion of water occur in the kidney?
The proximal convoluted tubule and descending limb of the Loop of Henle
What parts of the nephron does ADH affect?
The DCT and collecting duct
How does ADH work?
It affects the permeability of the walls of the DCT and collecting duct to water, allowing more or less to leave depending on ADH concentration. It does this as ADH triggers aquaporins to be placed in their cell membranes
What is an aquaporin?
A transport or channel protein for water molecules
What is ultrafiltration?
Blood being forced out of the walls of the capillaries in the glomerulus by the high pressure, with larger parts (such as red blood cells) being retained and water and ions passing into the nephrons
What levels of mineral ions does blood leaving the nephrons have?
Ideal ion levels
What levels of urea does blood leaving the nephrons have compared to that entering it?
Much lower urea levels
Why might levels of blood glucose decrease slightly in the nephrons?
Because some is used in active transport during selective reabsorbtion
Where in the nephron does ultrafiltration occur?
Bowman’s Capsule
Where does the selective reabsorbtion of ions and glucose occur in the nephron?
The ascending limb and DCT
How are ions and glucose selectively reabsorbed in the nephron?
By active transport, and by diffusion at the very bottom of the Loop of Henle
Do the levels of amino acids change in the kidney?
No
Why is the water potential of blood in capillaries near the Loop of Henle low?
Lots of water leaves via the glomerulus
Why is it useful that the water potential of blood in the capillaries near the Loop of Henle is low?
Allows water to be reabsorbed more easily from the Loop of Henle
What two structures filter blood in the Bowman’s Capsule?
Walls of the capillaries and the basement membrane
What specialised cells act as a filter in the walls of the Bowman’s Capsule?
Podocytes
How are podocytes specialised for their function?
They have extensions called pedicels, which wrap around the capillaries and form slits to ensure that large molecules do not leave the capillaries
What is the volume of water filtered through the kidneys in a given time known as?
Glomerular filtration rate
When would urine be more concentrated?
When the body is dehydrated
Would a desert animal have a longer or shorter Loop of Henle and why?
Longer, so that they could reabsorb more water
What substances are moved from the PCT back into the blood via active transport?
Glucose, amino acids, vitamins, hormones and around 85% of sodium chloride and water
What adaptations do cells lining the PCT have?
- Covered with microvilli to increase the surface area over which substances can be reabsorbed 2. Many mitochondria to provide ATP for active transport
What cells monitor the water potential of the blood?
Osmoregulators
Where are osmoregulators found?
The hypothalamus
How can the hypothalamus affect blood water potential?
By sending nerve impulses to the posterior pituitary gland in order to stimulate it to produce more or less ADH
How is water reabsorbed from the collecting duct?
There is a high concentration of ions outside the collecting duct due to its proximity to the ascending limb of the Loop of Henle, so water can leave via facilitated diffusion through aquaporins
Why do ions leave via diffusion at the bottom of the Loop of Henle?
Water potential is very low
Why does water leave the descending limb of the Loop of Henle via osmosis?
Water potential is high due to the high amounts of ions which are reabsorbed in the PCT
Why must ions be actively transported out of the ascending limb of the Loop of Henle?
Because water potential is higher than at the bottom
What type of diffusion multiplier is used in the Loop of Henle?
A countercurrent flow system
What does the term osmoregulation mean in terms of the kidneys?
The maintenance of a stable water potential in the blood and tissue fluid
What gland produces ADH?
The hypothalamus
What type of feedback system is the one involving ADH?
Negative feedback
Does ADH act via a secondary messenger?
Yes
Does high ADH levels mean concentrated or dilute urine?
Concentrated (because more water leaves the urine in the collecting ducts)
What hormone is found in the urine of pregnant women, and used in pregnancy tests?
hCG
What are monoclonal antibodies?
Antibodies produced from a single group of genetically identical B-cells
What is an example of a use of monoclonal antibodies?
In pregnancy tests
How are monoclonal antibodies for pregnancy tests produced?
A mouse is injected with hCG so that it makes the correct antibody, with the B-cell that makes the antibody then being removed from the mouse and fused with a rapidly-dividing myeloma, creating a cell called a hybridoma which is used to create millions of cells and lots of antibodies
How is a positive signal created in a pregnancy test?
The hCG antibodies are bound to coloured beads. If hCG is present, the hormones will bind to the antibody and cause the colour of the bead to appear
What are two things other than pregnancy which urine can be used to test for?
- Anabolic steroids 2. Illegal drugs
What technique is usually used to test urine for illegal drugs or steroids?
Gas chromatography
What are 3 reasons for kidney failure?
- Kidney infections 2. Raised blood pressure 3. Genetic disorders
What are two signs of kidney failure?
- Blood in urine 2. Proteins in urine
What are the 4 main problems caused by kidney failure?
- Anaemia (in the long-term) 2. Buildup of waste products in the blood, with secondary effects- such as too much urea causing weight loss and vomiting 3. Accumulation of fluid in tissues causing swelling 4. Electrolyte imbalance, which can cause blood acidosis, water retention (through salt buildup) and brittle bones (through imbalance of calcium and phosphate ion)
What is commonly used as a measure for kidney failure?
Glomerular filtration rate- if this falls too far it indicates kidney disease
What are the two types of dialysis?
Haemodialysis and peritoneal dialysis
What are the two main treatment options for kidney failure?
Dialysis or transplant
How is dialysis fluid formulated to ensure that useful substances are not lost?
It has normal blood glucose levels to ensure that none is lost, and normal mineral ion levels so that ions can only leave via diffusion
How much urea does dialysis fluid initially contain and why?
None, so that it can leave down as steep a concentration gradient as possible
How is diffusion maximised in haemodialysis?
Via the use of a countercurrent exchange system
How does haemodialysis work?
Blood is filtered across a semipermeable membrane removing accumulated toxic waste products, solutes, excess fluid (ultrafiltration), and restoring buffering agents to the bloodstream
What are some disadvantages of haemodialysis?
- Treatment is time-consuming 2. More expensive long-term than a transplant 3. A patient can feel unwell between treatments due to toxin buildup 4. Diet of the patient must be managed very carefully
How does peritoneal dialysis work?
Dialysis fluid is inserted into the peritoneum via catheter, and substances diffuse into it across the peritoneal membranes. The fluid is then drained off.
What is an advantage of peritoneal dialysis over haemodialysis?
The patient can go about their normal lives whilst undergoing treatment
What are the main 4 problems with kidney transplant?
- Risk of rejection 2. Lack of available donor organs 3. Risk of secondary infection due to necessity of taking immunosuppressant drugs 4. New kidney only usually lasts 9-10 years
Why is only one kidney transplanted?
That’s all you need
What is a possible future solution to the lack of donor kidneys?
Growing them from embryonic stem cells
How is the risk of rejection reduced in kidney transplant?
- Antigens are matched as closely as possible to those of the patient, for example by using the kidney of a relative 2. Use of immunosuppressant drugs
