Kidneys and Fluid Homeostasis Flashcards
(28 cards)
Fluid compartments
- intracellular fluid (cytosolic): surrounding the cells but does not circulate
Extracellular fluid which consists of:
- plasma: circulates
- trans cellular fluid: outside of the normal compartments. Makes up the cerebral spinal fluid, digestive juices and mucus.
- interstitial fluid
Water balance
Osmosis
Water follows the movement of sodium ions
Water deprivation: the hypreosmolal ECF (extracellular fluid) drags water from ICF (intercellular fluid) and dehydrates the cells - intracellular dehydration
Dehydration: cellular processes less efficient, trnsport across cell membrane impaired, water involved in hydrolysis of ATP so energy metabolism impaired, can also lead to hypernatraemia - too much sodium
Causes of dehydration
- physical exercise
- dry air
- loos loss
- hypovolemic shock (not enough volume of blood)
- diarrhoea
- vomiting
- hyperthermia
- severe burns
- lacrimation (crying)
- drugs
- excess alcohol
- malnutrition
- diabetes
Hyposmolal overhydration
The water overload in the extracellular fluid is dragged into the cells in hyposmolal overhydration until osmolality balances
Cells swell and content in cell get diluted
Overhydration leads to hyponatremia - low blood sodium levels
Function of kidney
- filtration of blood
- wast excretion: toxins and nitrogenous waste
- osmoregulation
- blood composition (ions)
- blood volume
- blood pressure
- pH balance
- endocrine
- glucose homeostasis
Waste excretion
- NH3: ammonia - very corrosive and soluble. Aquatic animals okay, land mammals not. Produced when live breaks down amino acids. Trimethyl amine oxide -fishy.
- Uric acid: shelled eggs. Hardly exerts and osmotic pressure
- urea: very soluble and relatively non-toxic
Structure of kidney - microscopy
Cortex - outside
Medulla - inner part
Nephron:
- glomerulus: ball of capillaries. This is the starting point where the blood comes in.
- Bowman’s capsule: surrounds the glomerulus with all the capillaries. Together they are known as the renal corpuscle (little body)
- convoluted and straight tubes
- loop of Henle: in the medulla
Renal corpuscle
Ultrafiltration
Glomerulus: blood when it crosses the Bowman’s capsule it’s known as filtrate
Everything crosses besides enzymes and cells
Proximal tubule
Reabsorption on ions, slats, vitamins, ATP, glucose, water
Decrease in volume, so absorbs lots and pulls water with it.
Micro villi: to extend surface area
Loop of Henle
In osmotic gradient as it loops down into the medulla
Reabsorbtion of water
The longer, the more concentrated the urine that’s being produced.
Tow types of nephrons:
- Cortical nephron: sits higher up in the cortex and loop nearly dips into medulla
- juxtamedullary nephrons: closer to the medulla and loop in extends into the medulla
Descending limb: permeable to water, outside is more concentrated so water will leave.
Ascending limb: cells lining loop of Henleare not permeable to water but are permeable to ions, so some of the ions are pushed out.
Dismal tubules
Final ionic adjustment
Collections ducts
Go through osmotic gradient set up by
Go towards the bladder through the medulla - osmotic gradient, final chance to get water out of the proto-urine and back into the body.
Susceptible to hormones
Rich in sodium potassium pump - ATPase
Sodium chloride ions _ co transport
Sodium hydrogen ions - counter transport
Juxtaglomerular apparatus
Contact point between the renal corpuscle and the distal convoluted tubule
Cells are very squished together - macular densa
Granular cells secrete renin and detect sodium concentrations going past
Ultrafiltration
Will only happen if there is a pressure difference in the capillaries (glomerulus) than in the Bowman’s capsule
There should be enough pressure to force fluids through the membrane and small paws
The blood flows from the renal artery into smaller arterioles, into the capillaries in the glomerulus. So they only just before he glomerulus that they form capillaries - to maintain pressure. Goes out of the glomerulus and into a small efferent (afferent - in, efferent - outgoing) arterioles. Branches off into capillaries that go around the tubes and tubules ready to reabsorb filtrate.
Podocytes
Cells in Bowman’s capsule surround the capillaries tightly and make the transfer of fluid easy.
Starling forces: pulling pressure on the blood in the Bowman’s capsule
- hydrostatic pressure gradient
- an colloidal ‘oncoitic’ pressure gradient
Glomerular filtration rate (GFR).
Hyperosmotic urine
Collecting ducts going through the osmotic gradient set up my the loop of Henle
Collection ducts impermeable to water until ADH (vasopressin) is circulating
ADH released for the posterior pituitary in response to signals in the hypothalamus when the blood is thick
Angiotensin 2
- vasoconstrictor: will help with low blood pressure
- thirst mechanisms
- aldosterone release: for adrenal gland: affects retention of sodium, which affects the retention of water and can help mitigate against the pressure drop
- ADH: from pituitary, inserts pores into the collecting ducts - reabsorb last bits of water
RAAS (Renin-anigiotensin-aldosterone- system
- macula densa cells stimulate granular cells
- renin from the granular cells converts angiotensinogen to angiotensin 1
- ACE needed to convert angiotensin 1 to angiotensin 2
Aldosterone
- from adrenal glands
- acts in the distal convoluted tubules and collection duct epithelial cells in the nephrons
- synthesis and more opening of sodium channels in the apical membrane
- increases the activity of sodium-potassium ATPase in hasolateral me
Effect: retention of sodium and secretion of potassium. As we pull sodium in, the water will follow
ANP atrial natriuretic peptide
- released by the atria cells in the heart
- released in response to an increase in blood pressure (opposite of renin). It reduces sodium retention, therefore reduces water retention and inhibits renin release, thus decrease in aldosterone
Potassium balance
- editable cells depend on potassium concentrations gradient
- sodium reabsorptionlinked to potassium secretion (ATPase)
- aldosterone influences potassium secretion
Calcium balance
- most calcium reabsorb in the nephrons
- parathyroid PTH: in response to low calcium, stimulates calcium reabsorptionfor, the kidneys and intestine
- PTH activates carcitriol secreted by the kidneys (active form of vitamin D).
Opposing enzyme: calcitonin form thyroid
Blood pH
- measure of H+ ions
Between 7.35 and 7.45
CO2 can dissolve in water and increase pH
Can be cause by extreme diet, exercise, vomiting…
