Homestasis Flashcards
What is homeostasis?
The maintenance of steady states within the body
What are the three basic features?
1) A control system with sensors which allow the monitoring of factors
2) Departure from set point = corrective mechanism put in place
3) Involvement of a negative feedback system to prevent overcorrection
What are the two types of control and what do they control?
1) Nervous control e.g. Temperature
2) Hormonal e.g. blood glucose level
What does homeostasis provide/prevent?
Provides - optimum conditions for enzyme action
Prevents - osmotic issues
Describe the two important functions of the kidney
1) Excretion - removal of the toxic waste of metabolism. e.g. Urea and Creatinine
2) Osmoregulation - control of the water potential of body fluids.
Describe the structure of the urinary system.
Blood travelling from aorta reaches Renal artery at high pressure, leaves by the Renal vein whereas the waste products and excess water pass to the ureter as urine.
What are the two main zones of the kidney? and what is its functional unit?
Cortex - Outer region
Medulla - Inner region
Functional unit - Nephron
What is the first function of the kidney?
Excretion
Describe the two processes of excretion.
1) Ultrafiltration - The filtration of plasma and substances below a certain size into the Bowman’s capsule
2) Reabsorption - Filtered useful products are REabsorbed back into the bloodstream.
What does the high hydrostatic pressure cause and how is it created?
The blood entering glomerulus has a high hydrostatic pressure because:
1) Short distance from the heart
2) Afferent > efferent
3) Coiling of the capillaries in the glomerulus restricts
blood flow thus increasing pressure.
High pressure means small molecules (glucose, amino acids, salts, urea) are forced out of capillaries into Bowman’s capsule. Larger ones are not able to be forced out.
How is ultrafiltration aided?
3 layers separate the plasma from the filtrate: Capillary ENDOthelium, basement membrane and the inner layer of the Bowman’s capsule. Two of these are v. porous:
1) The ENDOthelium of the capillaries - a single layer of squamous endothelial cells with pores between them.
2) Podocytes - extend in two planes have foot like processes which surround the capillaries but have spacious gaps called filtration slits between them.
What does the basement membrane do?
It is an extracellular matrix which acts as the effective filter.
What is glomerular filtrate?
similar to blood except with no blood cells or proteins.
What is filtration force?
Water potential in the blood plasma must be more negative than the water potential in the glomerular filtrate.
What are the two components of water potential?
Pressure potential and solute potential. The pressure potential of the blood is much greater than the back pressure created by the filtrate.
What is the solute potential?
Represented by plasma proteins as the are only plasma proteins in the blood NOT the filtrate. Filtrate is less negative. Although the difference in solute potential opposes filtration, it is INSIGNIFICANT when compared to the differences in hydrostatic pressure.
Describe reabsorption (PCT)
Useful products SELECTIVELY REABSORBED. Glucose and amino acids travel along the PCT and are selectively reabsorbed via facilitated diffusion and active transport. 70% of water then follows via osmosis. Pinocytosis of small proteins. The Cuboidal epithelial cells have a high level of metabolic activity. At the end of the PCT all glucose and amino acids will have been reabsorbed. Flow of filtrate maintains concentration gradient.
Describe reabsorption (DCT)
Depending on permeability some water may also be absorbed.
Describe the role of the Loop of Henlé.
Enable mammals to produce a hypertonic urine, significant role in water reabsorption.
Descending limb and ascending limb
Descending - Thin and permeable to water
Ascending - Thick and impermeable to water
What does the loop of Henlé do?
Ascending limb secretes Na+ and Cl- ions into the medulla. NaCl builds up in the interstitial fluid creating a v. negative solute potential. Due to negative water potential in the medulla water is drawn out of the descending limb via osmosis. Thus causing the filtrate in the descending limb to become more concentrated. Solution at the bottom becomes hypertonic to the blood.
What is the concurrent multiplier effect
Osmotic differences between Descending and Ascending limb are small but the cumulative effect of the million nephrons is large.
What is the effect of a longer loop of henle
More water can be absorbed
Kidney function 2 - Osmoregulation
The homeostatic process that controls water balance in the body. Controlled by the Antidiuretic hormone (ADH)
Where is ADH produced and stored. and how is the solute potential monitored.
Produced - HYPOTHALAMUS
Stored - POSTERIOR LOBE OF THE PITUITARY GLAND
Monitored by osmoreceptors in the hypothalamus
What happens when you sweat on a hot day/ not drinking water
- Osmoreceptors detect solute potential becomes MORE negative
- Posterior lobe of the pituitary gland releases MORE ADH into the blood
- MORE aquaporins in the DCT and collecting duct open making it become MORE permeable
- MORE water is reabsorbed
- Solute potential returns to normal, smaller volume of MORE concentrated hypertonic urine produced.
- Negative feedback prevents overcorrection
