Homeostasis Flashcards
What is homeostasis?
Maintaining a constant internal environment
What does homeostasis control?
Water levels (osmoregulation) Tissue fluid O2 levels Blood sugar levels Composition of blood Temperature (thermoregulation)
Explain why the control + maintenance of internal conditions are important for an organism
Temperature = stops proteins denaturing = enzymes needed for reactions = eg. respiration
In/decrease rate of diffusion
Sugar levels = water potential = lysis of cells
Respiration
O2 levels = respiration
What is thermoregulation?
The control of internal body temperature
What is an ectotherm?
Maintain a proportion of their heat from outside sources
What is an example of an ectotherm?
Lizard + snakes
What is an endotherm?
Derive heat from source of metabolic activities inside their body
What is an example of an exotherm?
Mammals + birds
What is the hypothalamus?
Control unit for most responses
What does the hypothalamus link?
N.S to endocrine system via pituitary gland
What is the response to a decrease in temperature?
Vasoconstriction of arterioles
Shivering
Piloerection
+ metabolism
What is the response to an increase in temperature?
Vasodilation
Sweating
Pilorelaxation
- metabolism
What is a negative feedback loop?
Initiating corrective mechanisms whenever the internal environment deviates from its normal or acceptable levels
What is a positive feedback loop?
Deviation from normal conditions is amplified, leading to further deviation
What are examples of negative feedback mechanisms in the body?
Temperature control
Blood sugar levels control
Changes in heart rate
What are examples of positive feedback mechanisms in the body?
Blood clotting
Oxytocin causes more contractions
Adrenaline - HR increases till stimuli removed
Disease - increases temperature
What is osmoregulation?
The homeostasis control of water potential in the blood
What is the role of the kidney?
Control the vol of water in the body
Clean the blood
Remove any unwanted water, waste or toxins
What is the nephron?
The filtering unit of the kidney, which performs the jobs of filtering + fluid balance
What are the processes of osmoregulation?
Ultrafiltration
Selective reabsorption
Counter current multiplier
Reabsorption
Where does ultrafiltration happen?
Glomerulus
What is ultrafiltration as a result of?
Hydrostatic pressure
Which is bigger the efferent or afferent arteriole?
Afferent
What does the capillaries merge to form?
Efferent arteriole
Describe ultrafiltration
Afferent arteriole is wider than efferent
Hydrostatic pressure builds
Causes ultrafiltration through pores of membrane
What moves out for ultrafiltration?
H2O
C6H12O6
Urea
Mineral ions
What remains in for ultrafiltration?
RBCs
Proteins
What is the movement of filtrate restricted in the glomerulus by?
Capillary epithelial cells Connective tissues Epithelial cells of renal capsule Low hydrostatic pressure Low water potential of blood
What are the main adaptions of Bowman’s capsule to combat barriers of filtrate movement in glomerulus?
Podocytes (specialised cells)
Gaps in epithelial cells
What is the importance of podocytes?
Attach to capillaries to form gaps = shorter diffusion pathway
What is the importance of gaps in epithelial cells?
Easy to pass through = shorter diffusion pathway
What is selective reabsorption?
Reabsorption of certain molecules back into the blood?
How does selective reabsorption happen?
Co-transport
Where does co-transport happen in reabsorption?
Proximal convoluted tubule
Where does counter current mechanism happen in reabsorption?
Loop of Henle
Where does anti diuretic hormone happen in reabsorption?
Collecting duct
Describe co-transport
Na+ actively pumped out of cell to lumen from NaK pump
Higher conc inside lumen so lower conc inside cell
Na+ facilitatedly diffuses back in via another carrier protein
Coupled movement with glucose/amino acid
Molecule conc increases
Molecules diffuse into blood alongside some water
Describe the medulla
Inner region made up of loops of Henle, collecting ducts + blood vessels
Describe convoluted tubule
Series of loops surrounded by blood capillaries
Walls made up of epithelial cells with microvilli
Describe ureter
Tube that carries urine to the bladder
Describe glomerulus
Many branched knot of capillaries from which fluid is forced out of the blood
Describe renal vein
Returns blood to heart via vena cava
Describe cortex
Outer region made up of renal capsules (Bowman’s capsule), convoluted tubules + blood vessels
Describe Loop of Henle
Long hairpin loop extending from cortex + into medulla
Describe Bowman’s capsule
Cup shaped structure at the start of nephron, surrounding a mass of blood capillaries (glomerulus)
Describe renal artery
Supplies kidney with blood from heart via aorta
Describe collecting duct
Tube with several distal convoluted tubules from several nephrons empty
Increases width as it empties into the pelvis of the kidney
How many regions does the loop of Henle of have?
2
What are the 2 regions of the loop of Henle called?
Descending limb
Ascending limb
What does the 2 regions of the loop of Henle allow?
Allows salts to be transferred from descending to ascending limb
What is the arrangement called that is involved in the reabsorption of water?
Counter-current multiplies system
Describe the descending limb
Into the medulla
Narrow
Thin walls
Highly permeable to H2O
Describe the ascending limb
Back to cortex
Wider
Thicker
Impermeable to H2O
What happens at the descending limb?
H2O leaves via osmosis
+ enters the blood
What helps H2O to leave from the descending limb?
Low H2O potential surrounding it
What is happening at the same time in the loop of Henle, whilst the descending limb happens?
Na+ is actively transported out of the ascending limb into the interstitial region
What happens at the ascending limb?
Ascending = impermeable = H2O cannot leave
Why is there a high H2O potential in the distal convoluted tubule?
To form H2O potential gradient = H20 can move out of collecting duct + into the blood
Why can H2O move out of the collecting duct?
As its walls vary in permeability
Where does ultrafiltration happen?
Glomerulus
Where does selective reabsorption happen?
Proximal convoluted tubule
Where does the counter current multiplier happen?
Loop of Henle
Where does reabsorption into the blood happen?
Distal convoluted tubule
Collecting duct
Explain why your water levels vary
External temperature Exercise Fluid intake Salt intake Diet Drug intake Medication
Which hormone controls H2O?
ADH
Where is ADH secreted from?
Posterior pituitary gland
What does ADH do?
Increase permeability of DCT + CD
= concentrates the urine
What happens when you are dehydrated?
Decrease ψ of blood
Osmoreceptor cells in hypothalamus detect change
Cells lose water = shrivel
Stimulate neurosecretory cells in hypothalamus
Increased AP’s to posterior pituitary gland
ADH secreted into blood
Travels in blood to DCT + CD
Permeability increases
More H2O reabsorbed into blood
What when you have too much water?
Increase ψ of blood Osmoreceptors detect change Gain H2O = swell Doesn't stimulate neurosecretory cells Decreased AP's to posterior pituitary gland ADH not secreted Permeability decreases at DCT + CD Less water reabsorbed
How does ADH actually work?
Binds to complementary receptors on DCT + CD Activates enzyme phosphorylase Aquaporin fuses with membrane Increases permeability Water leaves CD Increases ψ gradient Concentrated urine
