topic 9 (9.1, 9.8, 9.9) Flashcards
9.1, 9.8, 9.9
9.1 [homeostasis]
Homeostasis ?
The maintenance of a state of dynamic equilibrium (stable internal environment) within the body of an organism
The 3 homeostatic mechanisms the body maintains + the importance of them ?
- pH (of Blood) – change in pH would affect enzyme activity
- Body temperature – changes in temperature affect enzyme activity
- Water potential – changes in water potential can cause cell lysis, cell shrinkage + disruption to hydrolytic metabolic reactions
What’s a Negative feedback system ?
- Away of maintaining a condition at equilibrium (eg conc of a substance)
- A process that ensures that any departure from an ideal state results in a return to the ideal state
(eg maintaining optimal body temperature - 37°C)
What’s a positive feedback system ?
- Where Effectors work to increase an effect that has triggered a response
= Amplifies the change / increase from the original condition
(eg Uterine contractions in childbirth)
Describe the negative feedback system :
1.A change in the internal environment- stimulus
2.Change is detected by receptors
3.The receptors lead to activation of a mechanism that reverses the change
4.The conditions return to the ideal and the corrective mechanism is switched off
Negative feedback system when
- Body temp drops
- Body temp rises
- Temperature drops → shivering + muscle contraction → more respiration occurs + releases heat + energy → temperature will rise back to 37°C
- Temperature rises → sweat, Vasodilation etc → evaporation from skin surface →lose heat → temperature drops back to 37°C
detected by hypothalamus
Describe the positive feedback system :
- Stimulus causes change
- Detected by receptors
- The receptors lead to activation of a mechanism that continues /enhances /amplifies this change (increase) from normal
Normal level → normal level change → receptors detect change → communication with CNS or hormonal system → effector response →target organs allow the increased level (from normal) to continue occurring
9.8
[control of heart rate in mammals]
SAN heart pacemaker controlling heart rate
SAN (pacemaker) is stimulated
→impulse is sent through the walls of the atria causing them to contract (blood is forced from the atria to the ventricles)
→impulse reaches the AVN
→ impulse travels down the bundle of his
→ impulse travels through the purkinje fibres causing walls of the ventricle to contract
→blood is forced through the arteries out the heart
What causes the SA node to speed up / slow down?
- pH levels (chemoreceptors )
→ medulla oblongata controls it - Blood pressure ( baroreceptors )
→ medulla oblongata controls it - Stress levels ( adrenal medulla - adrenaline )
What are (aortic + carotid) baroreceptors ?
- pressure receptors In wall of aorta + carotid arteries that are sensitive to blood pressure
= which can send impulses to the medulla oblongata to control blood pressure
What are (aortic + carotid) chemoreceptors ?
- pH receptors in the wall of aorta + carotid arteries that detect carbon dioxide concentration of your blood = pH of blood
- sends impulses to the medulla oblongata so that a constant blood pH can be maintained
What’s the cardiac centre ?
- Region in the medulla oblongata
- which controls the heart rate + blood pressure through hormones + nerve impulses
The medulla is connected to the SAN by two types of neurons.
- What are these 2 neurons?
- What do they secrete ?
- parasympathetic
- secrete acetylcholine = type of neurotransmitter that decreases heart rate - sympathetic
- secrete noradrenaline = type of neurotransmitter that increases heart rate
how the autonomic nervous system controls heart rate.
- Role of baroreceptors
- What happens when blood pressure is too high?
- High blood pressure detected by baroreceptors
- Impulses are sent from the baroreceptors to the medulla
= this will send the impulse down parasympathetic neurones - This causes acetylcholine to be released in the cardiac muscle
= binding to receptors on the SAN
= which reduces the rate of impulses sent from the SAN to the heart muscle
= so heart rate decreases
= decrease the blood pressure
What happens if blood pressure is too low?
- Low blood pressure is detected by baroreceptors
- Impulses are sent down sympathetic neurones by the medulla
- This causes noradrenaline to be realised in the cardiac muscle
= binding to receptors on the SAN
= which increases the rate of impulses sent from the SAN to the heart muscle
= so heart rate increases
= Increases blood pressure
how the autonomic nervous system controls heart rate.
- Role of chemoreceptors
What happens when the concentration of carbon dioxide in blood increases / pH falls ?
- CO2 conc increases = pH of blood falls
= detected by chemoreceptors - impulses sent to cardiac centre in medulla oblongata
= sent down sympathetic neurones by the medulla - This causes noradrenaline to be released in the cardiac muscle
= binding to receptors on the SAN
= SAN stimulates increase in heart rate
= increased heart rate will return the CO2 + pH of blood to normal levels
What happens when the concentration of carbon dioxide in blood decreases / pH rises ?
- CO2 conc falls = pH of blood rises
= detected by chemoreceptors - impulses sent from chemoreceptors to cardiac centre in medulla
– this will send the impulse down parasympathetic neurones - This causes acetylcholine to be released in the cardiac muscle
= binding to receptors on the SAN
= SAN stimulates decrease in heart rate = heart rate will slow to return the CO2 + pH of the blood to normal levels
cardiostimulatory centre in medulla ?
- If heart rate needs to increase
→ message sent to cardiostimulatory centre
→ Initiates action potentials which reach the heart (SAN) by sympathetic nerves
→ Increase in number of action potentials
= increase the rate + strength of heart contraction = ⬆heart rate
cardioinhibitory centre in medulla ?
- If heart rate needs to decrease
→ message sent to cardioinhibitory centre
→ Initiates action potentials which reach the heart (SAN) by parasympathetic nerves
→ Increase in number of action potentials
= decrease the rate + strength of heart contraction =⬇heart rate
role of the autonomic nervous system in causing the release of adrenaline to increase heart rate
( hormonal control by endocrine system )
- Fight/Flight or stressed = sympathetic nerve stimulates the adrenal medulla to increase release of hormone adrenaline
- Adrenaline (carried in blood) binds to receptors in target organ - including SAN
- Adrenaline stimulates cardiac centre in medulla (brain) = increasing impulses in the sympathetic neurones supplying the heart
+ has direct effect on SAN = increasing frequency of excitations = increasing heart rates
= supplying more O2 + glucose for muscles + brain for flight / fight
9.9 [osmoregulation + thermoregulation]
Thermoregulation ?
homeostatic mechanism that enables organisms to control / regulate their internal body temperature
Why does body temperature need to be regulated?
What are the 2 ways of doing this?
- to keep enzymes working close to their optimum temperature = to prevent them from denaturing
- endotherms
- ectotherms
Endotherms ?
Endotherms (mammals + birds) :
- generate their own heat to maintain a constant body temperature
- Generate heat through metabolic + physiological processes (shivering / sweating)
- contain thermoreceptors = monitor core body temp changes + communicate them to the hypothalamus which = coordinates a appropriate responses to restore optimum temp through either physiological / behavioural responses
Ectotherms ?
Ectotherms (reptiles) :
- rely on external sources of heat to regulate their body temperature
- Generate heat through behavioural changes in the environment only (eg moving to/away from shade or cool water)
How endotherms conserve heat in cold environment ?
- Vasoconstriction of blood vessels
- Raising hairs
- reduced sweat production
- Shivering
- Faster metabolic rate
- Vasoconstriction
Vasoconstriction: narrowing of blood vessels
- Arterioles constrict (become narrower)
= Blood cannot reach the capillaries near the surface of the skin - Shunt vessels dilate (widen)
= most of blood travels through this vessel (instead of capillary) - Because less blood is reaching the capillaries near surface of skin (epidermis)
= less heat radiated from skin
= heat is conserved in body
- Raising hairs
- Erector pili muscle contracts
- Hair is pulled up
- A layer of insulating air forms which keeps you warm
- Reduced sweat production
reduced sweating = cooling by evaporation reduced = less heat loss
- Shivering
Shivering
= contractions of skeletal muscles stimulated by nerve impulses sent out by the hypothalamus
= leading to an increase in temperature as heat is released
How endotherms radiate heat in warm environment :
- Vasodilation of blood vessels
- flat hairs
- Increased sweating
- Vasodilation
Vasodilation: dilating of blood vessels
- Arterioles dilate (widen)
= allow blood through - Shunt vessels constrict (narrow)
= less blood can travel through this route - More blood flow near surface of skin (epidermis)
= more heat radiated from skin
= heat is lost, reducing body temperature
- Flat hairs
- Erector pili muscle relaxes
- Hairs go down
- Layer of insulting air is lost = warmth not maintained
- Increased sweating
-Thermoreceptors in skin detect increased temp
- signals to hypothalamus via nervous system
= signals to Sweat glands
= produce sweat.
= More sweat released onto skin surface
= cooling takes place as it evaporates
sweat production decreases body temperature via evaporation from the skin surface
How endotherms can regulate temp through behaviour ?
- wear thick clothes in winter
- shelter from cold weather / sun
- swim to cool down
kangaroo rat’s adaptation to dry environment
Kangaroo rats live in very dry environments but still need to produce urine to get rid of toxic waste substances (eg urea)
Their kidneys are adapted to produce a tiny amount of very concentrated urine
EG of adaptations to extreme environments :
- hibernation - animal goes into deep sleep in winter to avoid cold weather = metabolic rate slows + body temp lowered = energy saving
- Aestivation - animals avoiding extreme hot + dry conditions by becoming completely inactive for months in dried mud / rock crevices = metabolism slows right down
[ osmoregulation ]
Be able to label a mammalian kidney diagram
use labeled diagram on google doc ‘osmoregulation’
What is osmoregulation ?
- The regulation of water content of body fluids
- The maintenance of a constant osmotic potential in the tissues of a living organism by controlling water + salt concentration
Why is osmoregulation important ?
- Because if the conc of water + solutes inside + outside of a cell is not balanced =
- water may enter the cells by osmosis
= causing the cells to swell + burst
OR
- leave the cells by osmosis
= cytoplasm becomes shrunken, concentrated + unable to function
What is deamination ?
- The removal of the amino group from excess amino acids (in ornithine cycle) in liver
- Which is then converted to ammonia and then urea, which is then excreted at kidneys
How is urea produced in the liver from excess amino acids through deamination ?
- Liver cells (hepatocytes) deaminate excess amino acids = they remove the amino group
- +convert it first into ammonia = which is very toxic
- And then into urea = which is less toxic
(by reacting with CO2 in ornithine cycle) - The urea is then excreted by kidneys by ultrafiltration to from urine (stored in bladder)
What are the 2 roles of the kidneys?
- Excretion ( removal of urea )
- Osmoregulation
- ultrafiltration
- selective reabsorption
- tubular secretion
Each kidney is made up of microscopic tubules called nephrons
- What are the 2 main types of nephrons ?
- Cortical nephrons (found in renal cortex)
- have a loop of Henle that only raches medulla
- 85% of nephrons - Juxtamedullary nephrons
- have long loops of Henle which penetrate through medulla
- efficient in producing concentrated urine
What is ultrafiltration ?
Why does it occur ?
- filtration of blood under high pressure from the glomerulus in kidney into the Bowman’s capsule
- Due to Pressure gradient (hydrostatic pressure)
- Diameter of blood vessel coming into the glomerulus (afferent arteriole) is greater than the blood vessel leaving (efferent arteriole).
What is the arteriole leading into the glomerulus called?
- Afferent arterioles
- Blood enters bowman’s capsule through wide Afferent arterioles
What is the arteriole leading out of the glomerulus called?
- Efferent arterioles
- Blood leaves bowman’s capsule through Efferent arterioles
Describe ultrafiltration :
- High blood pressure develops in the glomerular capillaries because the diameter of the blood vessel coming into the glomerulus (Afferent arterioles) is greater than that of blood vessel leaving ( Efferent arterioles)
- High pressure squeezes the blood out through the capillary wall through pores that allow only small substances to pass through
- NOT blood cells + the largest plasma proteins
- Podocyte cells of the Bowman’s capsule act as an additional filter (pedicles - small gaps)
= Glucose, amino acids, water,urea , other ions (eg sodium) will pass out of glomerulus and into bowman’s capsule
- Large proteins, RBC + WBC do not pass out of blood = so leave through Efferent arterioles
(as they’re too large to pass through the basement membrane)
What is selective reabsorption ?
Where does it occur ?
- process by which substances needed by the body are reabsorbed from the kidney tubules into the blood
- At the proximal convoluted tubule
What are the 2 regions of the Loop of Henle + describe both :
- Descending limb:
- narrow thin walls
- permeable to water - Ascending limb :
- Wider thick walls
- Impermeable to water
Describe selective reabsorption :
proximal convoluted tubule - 80% glomerular filtrate is reabsorbed
- All glucose reabsorbed back into blood through active transport - uses ATP (+ amino acids + sodium ions )
- Sodium ions are actively transported out of the proximal tubule + the chloride ions + water follow passively down concentration gradients
- urea conc rises as water reabsorbed
Descending limb:
- water reabsorbed by osmosis
- As glomerular filtrate carries on down the descending limb, the concentration of NA+ and cl- ions increases = hypertonic solution
Ascending limb:
- water permeability changes
- Na+ actively pumped out + Cl- leave
- = conc of NA+ and Cl- ions decreases = isotonic/ hypotonic solution
= Generated countercurrent multiplier
The amount of water that moves out of the collecting duct back into the body depends on …
- the permeability of the collecting duct to water
- this is strongly affected by ADH
Hypertonic solution ?
Hypotonic solution ?
Hypertonic – high solute potential
(more concentrated)
Hypotonic - Low solute potential
(less concentrated)
What is the counter-current multiplication?
- The process in the Loop of Henle where solutes are actively transported out of the ascending limb
- to create a large concentration gradient for the reabsorption of water
What causes the counter-current multiplication?
The Loop of Henle
- The flow of filtrate in the two limbs of Henle’s loop (filtrate + blood) is in opposite directions = forms a counter current
Descending Limb
- Water moves by osmosis out of the loop down the water potential gradient
Ascending Limb
- In the lower, thinner part, ions move out by diffusion (maintains water potential gradient in the descending limb)
- In the higher parts, ions move out by active transport
What is the main role of the loop of Henle ?
- to set up + maintain a salt gradient between the filtrate + blood so water is reabsorbed by osmosis
past exam Question:
Explain how the loop of Henlé is involved in the production of concentrated urine (5)
- [sodium / chloride] ions are moved out of the ascending limb by active transport (1)
- ascending limb is impermeable to water (1)
this results in a (high(er) concentration / low(er) water potential) in medulla (1) - (loop of Henle) acts as a counter-current multiplier (1)
- the collecting ducts are permeable to water (1)
- therefore water moves out (of the collecting ducts) by osmosis (1)
past exam question: [topic 4, but could link]
Explain how tissue fluid is returned to capillaries (3)
- There is more protein in plasma than tissue fluid (1)
- because plasma proteins are too large to pass out of the capillary (1)
- and oncotic pressure generated by (plasma) proteins (1)
- (so fluid moves in) as {oncotic / osmotic} pressure is greater than hydrostatic pressure (1)
What is tubular secretion ?
The process by which inorganic ions are secreted into / out of the kidney tubules as needed to maintain the osmotic balance of the blood
What is urine, what does it contain?
Pathway it takes to leave body :
- Solution of urea, mineral ions and some other metabolic wastes excreted by the kidneys
- The fluid produced by the kidney tubules
- Ureter (tube carrying urine from kidney to bladder) → Urethra (tube carrying urine from bladder to the exterior)
Reabsorption subject to need:
(negative feedback system)
- Water potential is monitored by hypothalamus
- Receptors that monitor the blood water potential are called osmoreceptors
- When water potential falls, the posterior pituitary gland is stimulated to release ADH to bring water potential back up
= negative feedback system
How is it a negative feedback system?
Water potential high = less ADH released = normal water potential restored
Water potential low = more ADH released = normal water potential restored
What is ADH and what does it do
Antidiuretic hormone - stored in pituitary gland
- ADH binds to receptor on membrane of cell
- Binding triggers release of secondary messenger
- 2° messenger triggers vesicles containing aquaporin to move towards cell surface
- Aquaporin incorporated within bilayer increases water permeability of collecting duct
- More water reabsorbed into the blood
- = smaller volume of more concentrated urine produced
Describe role of ADH + what happens when:
- Water potential high (u drink a lot of water)
= Blood becomes more dilute
- Increase in water concentration in blood
- Detected by osmoreceptors in hypothalamus
- Pituitary releases less ADH (as no impulses from hypothalamus to posterior pituitary)
- Decreases permeability of cells of collecting duct and distal convoluted tubule to water
- Less water reabsorbed and more lost in urine
- = Large volumes of dilute urine produced
= blood water potential returns to normal
Describe role of ADH + what happens when:
- Water potential low (u dehydrated)
= Blood becomes more concentrated
1. Decrease in water concentration in blood
- Detected by osmoreceptors in hypothalamus
- Sends nerve impulses to posterior pituitary
- Pituitary gland releases stored ADH
- ADH binds to complementary surface receptors on DCT and CD
- Permeability of walls of distal convoluted tubule (DCT) + collecting duct (CD) to water increases
- More reabsorption = more water returned from filtrate to blood
- Small volumes of concentrated urine produced
=blood water potential returns to normal.
What happens if you don’t produce ADH?
-You continually produce large volumes of dilute urine
- Distal convoluted tubule (DCT) + collecting duct (CD) always impermeable to water
What are the symptoms + treatment for if you don’t produce ADH?
Symptoms:
- Continual thirst
- Risk of severe dehydration
Treatment:
- Drugs to mimic ADH
- Drugs to make kidney produce more concentrated urine
How is the kidney of a kangaroo rat (Dipodomys sp) adapted for life in a dry environment?
- They have large proportion of juxtamedullary nephrons
= help ensure that large amounts of water can be reabsorbed as they are the nephrons with the longest loop of Henle - This means almost all water is reabsorbed from the Kangaroo rat’s urine, so they a produce a very small volume of very concentrated urine
- The epithelial cells of the nephrons of kangaroo rats contain high numbers of mitochondria
= provide lots of ATP for the active pumping of inorganic ions into / out of the tubules
= for efficient absorption
