5.8. Homeostasis Flashcards
Thermoregulation receptors and effectors
Peripheral thermoreceptors in the skin, central receptors in the hypothalamus
Effectors are all body cells but main targets are: muscles, adipose tissue, liver, blood vessels, thyroid gland (thyroxine increases the level of CR in all cells) and brain
Hyperthermia regulation:
a) sweat glands activated (smooth muscles in the dermis constrict around the gland, causing the release of sweat)
b) vasodilation (hot blood flows faster and goes from vessels to skin more rapidly)
c) moving away from the heat source and moving more slowly and sleeping longer (behavioral)
Hypothermia regulation:
a) shivering of skeletal muscles (involuntary contraction and relaxation, heat produced by CR)
b) vasoconstriction (storing E inside the body)
c) brown adipose tissue and uncoupled CR – more mitochondria, no ATP produced, only heat
d) hair erection (thicker layer of insulation, not in humans, poli erector muscle activated)
e) moving faster to generate more heat (behavioral)
how does blood supply to organs depend on activity:
shunt vessels used to direct blood directly from arteriolies to venules ž
intense physical activity: increased to skeletal muscles and brain to supply more O2 and glucose for muscle contraction, mental activity heightened – reduced to the gut and kidneys, digestion and excretion suspended
wakeful rest: max to kidneys, moderate to brain and skeletal muscles, variable to digestive system
during sleep: increased in the brain (releasing toxins from the brain, regulating circadian rhythms), reduced to skeletal muscles, kidneys, variable to digestive system
excretion and osmoregulation
removal of toxic waste products of metabolism, from cells into intercellular space and from there into blood which is purified in the kidneys
control of osmotic C – the measure of solute C defined as the number of osmoles of solute per liter of solution (osmol/L) – osmol/L is the number of moles of fully dissolved solute in one liter (e.g. NaCl in water)
compare ammonia, urea and uric acid
ammonia created as a product of the deamination of excess a-a in the liver – highly toxic (amine group) so either has to be diluted in a large volume of water (like fish) or neutralized by CO2 (like humans)
when CO2 combined with amine urea is produced (fish use no energy, humans do) which is les stoxic but still soluble (in water – urine) – the most toxic nitrogenous byproduct of our metabolism
one step further for desert animals and birds which produce uric acid (in crystal form, even more E needed to produce but it’s worth it because those organisms don’t have water to spare to neutralize urea’s toxicity)
function of properly functioning kidneys:
- Volume, pH, composition of body fluids and blood pressure regulation
- Metabolic wastes removed from blood
- Rate of RBC formation controlled (disbalance in erythrocytes attributed to kidney disease)
Kidney structure:
- Renal cortex – tightly packed, outer layer of the kidneys
- Renal medulla – less tightly packed, the border between the cortex and the medulla contains a capillary network
- Renal pelvis – urine accumulates in it “drop by drop” and from there goes into the ureter
- Renal pyramids – kidney section containing structures in the cortex and in the medulla
- Renal artery – pumps blood into kidney, containing oxygenated, unpurified blood, branch of the aorta
- Renal vein – leads blood aways form the kidney, containing deoxygenated and purified blood, a branch of inferior vena cava
Renal pyramid structure:
1) Renal artery, between the cortex and the medulla, branches into
2) Afferent renal arteriole which enters the Bowman’s capsule and branches into
3) Glomerulus, a dense capillary network and a place of filtration of blood from waste products
4) The filtered blood goes away from the capsule by the narrower efferent renal arteriole (narrower to enable ultrafiltration in the glomerulus) and
5) The waste products filtered out, flow through the proximal convoluted tubule (PCT) then
6) The loop of Henle which is narrower and divided onto the descending limb and the ascending limb, then flows into
7) The distal convoluted tubule (DCT) which is, again, thicker, and finally, flows into
8) The connecting duct which connects many nephrons and which drains the urine into the renal pelvis, ureter, the bladder and the urethra.
9) All throughout the nephron there are peritubular capillaries, branches of the renal artery, which surround the tubules and ducts and flow back into the renal vein
Nephron
basic structural and functional subunit of kidneys, tubular, partly convoluted, sometimes wider, sometimes narrower hollow tube strongly associated with blood vessels – transport epithelium are the cells lining the nephron tubules
Bowman’s capsule
where renal arteriole goes into, branches into dense capillary network called glomerulus – filtration process: the capillary wall lets through sufficiently small molecules (blood cells cannot pass as well as big plasma proteins) and what is filtered through goes into the proximal tubule.
two sides of wall cells, one wall in contact with the capillary has greater space between podocytes and has little extensions towards the capillary – capillary and capsule are divided by the basement membrane (fenestras are slightly larger in kidney capillaries, glycoprotein). Podocytes wrap around the capillaries – the substances from blood do not enter the podocytes, they enter the tubule in between the cells (slits)
Peritubular arterioles:
Renal arteriole reformed and then branches back unto peritubular capillaries that completely surround the nephron tubule for reabsorption of some filtered particles (all glucose reabsorbed, as well as small a-a, Na+ ions, and most of the water). Blood is deoxygenated in the peritubular arterioles because they provide oxygen to cells in the tubules to enable them to do their function (pumping of sodium ions to enable reabsorption)
Importance of the afferent and efferent arteriole width:
Efferent arteriole is much narrower than afferent to create higher pressure in the glomerulus and increase the speed and effectiveness of filtration – outflow of blood is restricted to enable ultrafiltration in the glomerulus
Ultrafiltration enabled by (4 factors):
1) High blood pressure in glomerulus
2) Fenestrated blood capillaries
3) Basement membrane
4) Podocytes with filtration slits
PCT structure and function
one layer of cells with microvilli (brush border) on the inner side – extensions of the plasma membrane to increase SA and make reabsorption more efficient – 20% of the original filtrate V flows into the loop of Henle (180 filtrate created in one day, only 5 L of blood)
major reabsorption happens in the PCT – all glucose gets reabsorbed by Na-cotransport (Na passive, glucose active) as well as a-a, and majority of Na+, Cl- and H2O
