C14: Homeostasis Flashcards
define homeostasis
Homeostasis is themaintenanceof a constant internal body environment involving variousself-regulatory mechanismswithin the body.
examples of things regulatory mechanism control
body temperature, blood sugar levels, blood thyroxin levels, blood thyroxin levels, blood pressure and other internal conditions at stable levels.
Self-regulation in organism involve the control of biochemical processes by afeedback mechanism. what happens in a feedback mechanism
the products of the biochemical processes serve asregulatorsof the process itself.
what components do the principles of homeostasis depend on
- Receptors:these are cells or specific organs in the body that are capable of detecting a stimulus, such as a change or deviation in the external and internal environment.
- Effectors:these are tissues or organs that cause the necessary action to bring the affected condition back to a normal level after the stimulus has been received by the receptors.
describe negative feedback mechanism + eg in terms of blood-glucose
In negative feedback, the production of a certain substance inhibits the process that produces the substance, e.g. when the blood glucose level increases, the pancreas detects this change and produces the hormone insulin, which converts the excess glucose into glycogen. As the blood glucose level returns to normal, the excess insulin stops the pancreas from producing further insulin.
describe the positive feedback mechanism + eg Na+ ions
In positive feedback, the production a certain substance causes further activation of the process that produces more of the substance, e.g.during nervous transmission, the influx of Na+ ions into the membrane of the neuron, as a result of depolarization causes the membrane to become even more permeable to Na+ ions. Hence, further depolarization occurs until an action potential is generated.
5 differences between the endocrine and nervous systems
- endo: communication via chemical messengers transmitted in blood stream.
nerv: via electrochemical action potentials (impulses transmitted via neurons. - endo: hormones ‘broadcast’ all over the body but influence target cells and tissues only.
nerv: action potentials are targeted on specific cells. - endo: causes changes in metabolic activities.
nerv: causes muscles to contract or glands to secrete. - endo: has its effects over longer periods of time
nerv: produced over milliseconds - endo: long lasting
nerv: short lived and/or reversible
when does deamination happen
and what is it
and where does it happen
If more proteins are eaten than required, the excess cannot be stored. To make use of the useful potential energy of amino acids, the liver removes amino groups from them
This happens in the liver cells
describe the process of deamination (and what happens to the products)
- happens in the liver cells. together with the removal of an extra hydrogen atom.
- Theamino groupand thehydrogen atomcombine to formammoniaand, the remaining part of the amino acid formsketo acid (Keto acid may enter the Krebs cycle and be respired, or it may be converted to glucose, or may be converted to glycogen or fat for storage)
- Ammonia is a v soluble and toxic compound that can cause damage, this is prevented by immediately converting ammonia tourea, by combining w CO2, which is less soluble and less toxic.
urea is the main nitrogenous product along w …
-creatinine and uric acid
where does creatinine come from, and what happens to proportions of it
- creatine is made in the liver from certain amine acids.
- most of this is used in the muscles, in the form ofcreatine phosphate, where it acts as an energy source.
- but some of it is converted to creatinine and is excreted.
how is uric acid made?
how is it removed?
whats the advantage of such removal?
- Uric acid is made from the breakdown of purines from nucleotides, not from amino acids.
- It is not toxic and is relatively insoluble so it’s removed in the form of dry pellets or thick paste.
- This reduces water loss in animals living in dry habitats and decreases the body mass of flying animals.
kidneys are the major organ for what and what
osmoregulationandexcretionof nitrogenous waste products.
size of kidney
5cm long
basic unit of kidney:
nephron
describe structure of kidney from outer to inner in terms of the cross section
1) Fibrous Capsule: outermost layer of fibrous connective tissue covering the kidney.
2) Contains mostly the glomerulus, the Bowman’s capsule and the convoluted tubules of the nephrons. Made up of a million or so nephrons.
3) Medulla: Grouped together into renal pyramids which contain the loop of Henle and collecting ducts with a network of blood vessels. made up of many nephrons
4) Pelvis: The area where the renal pyramids project and the upper part of the ureter joins.
3 functions of the kidney
- Excretion of metabolic waste products, e.g. urea.
- Maintaining the balance of ions, e.g. Na+, Ca2+, K+, H+, Cl–, HCO3–.
- Maintaining the acid-base balance of the body, thus the pH of the urine
function of the glomerulus + structure
- blood enters from afferent, larger diameter, arteriole and leaves from the effertent, smaller diameter
- enables the blood pressure in the glomerulus to be high so that ultrafiltration can occur.
function of the bowmans capsule + structure
- made of a basement membrane and podocytes
- enables the molecules with a molecular mass of less than 68000 to pass through
function of the PCT` + structure
- numerous microvilli forming a brush border along the layer of epithelial cells lining the tubule and many mitochondria
- numerous microvilli forming a brush border along the layer of epithelial cells lining the tubule.
- helps to provide ATP energy required during the active uptake of substances in selective reabsorption from the tubule cells into the basal channels.
function of the DCT +` structure
-has brush border and numerous mitochondri
- Helps in active removal of substances (Na+and Cl–)
- Helps in absorption of K+, NH4+and certain drugs into the lumen o help maintain blood’s pH.
function of the loop of henle + structure
-consisting of a narrow descending limb with water permeable walls and a wider ascending limb with water-impermeable walls.
* Helps to operate the counter current multiplier system. * Enables water to be drawn osmotically from the D-limb to increase the concentration of glomerular filtrate. * Enables Na+and Cl–to be actively transported out of the filtrate to decrease its concentration.
function of the collecting ducts + structure
allow water to pass through the duct into the surrounding fluid of the medulla.
`describe ultrafiltration (process)
- Involves the forced removal of substances with a relative molecular mass of less than 68000 from blood into Bowman’s capsule.
- passive
- Powered by thepressure of blood. This pressure is created due to the afferent arteriole being wider than the efferent arteriole.
- This pressure is larger than the water potential of the plasma that in turnforceswater and small soluble plasmacontents out of the capillary.
- The glomerularcapillarieshave agreater number of fenestrationsin their walls than the capillaries located in other tissues; each endothelial cell has 1000s of holes in it.
- Then comes thebasement membranemade up of a network of collagen and glycoproteins. it prevents large protein molecules+blood cells from escaping the glomerulus capillaries. hence is like filter.
- Next layer is theepithelial cells (make up inner lining of Bowman’s capsule).These have many tinyfinger-like projectionswith gaps between them, and are calledpodocytes.
- in the capsule, substances are glomerular filtrate.These includeamino acids, glucose, vitamin, ions, urea, uric acid, creatinine, water and some hormones.
whats Glomerular Filtrate Rate
The rate at which the fluid filters from the blood in the glomerular capillaries into the Bowman’s capsule and has a value of 125cm3min–in humans.
what determines Glomerular Filtrate Rate
The difference between the water potential of the plasma in the glomerular capillaries and the filtrate in Bowman’s capsule
PCT is thelongest sectionof the nephron and is the site wheremost of the reabsorption(more than 80%) of the filtrate takes place.WHat are the walls made of
The walls of the tubule are made up of asingle layerofcuboidal epithelial cells.These cells are always in contact with the filtrate
`adaptations of PCT
- Microvillito increase the inner surface are of the lumen.
- Tight junctions that hold the adjacent cells togetherso that fluid cannot pass between the cells (all substances that are reabsorbed must go through the cells).
- Manymitochondriato provide energy for the Na+-K+ pump proteins in the outer membrane of the cells.
- Transporter proteinsin the membrane facing the lumen.
how are amino acids, glucose and vitamins reabsorbed in PCT. describe until movement of Na+ down its gradient
- capillaries very slow to the outer surface of the membrane have v less plasma than usual because they are coming from glomerulus after losing water ions etc
- Thebasal membranes(the ones nearest to the blood and furthest from the lumen) of the cells lining the PCTactively transport Na+ions out of the cell
- These Na+ions are then carried away in the blood hencelowering the Na+ions conc in the cell, so that they can passively diffuseinto the cell down their conc gradient, from the fluid in lumen of tubule
- Na+ions cannot diffuse freely through the membrane and can only enter through specialco-transporter proteinsin the membrane
how are amino acids, glucose and vitamins reabsorbed in PCT. describe after the movement of Na+ down its gradient
- passive movement of Na+ ions into the cell down their conc gradientprovides the energyto moveglucose molecules,even against a conc gradient.
- This movement of glucose and other solutes is an example ofsecondary active transportsince energy is used in pumping the Na+ions, not in moving these solutes.
