Lecture 30 and 31 Flashcards
Fluid & Electrolyte Balance/Calcium Homeostasis
What are the most important Electrolytes in the body?
Na+, H20, K+, Ca+, H+ & HCO3-
What is the role of Na+
Cell excitability, osmolarity and ECF volume
what is the role of H20
osmolarity, blood volume and ECF volume
What is the role of Ca2+
exocytosis, muscle contractions, bone formation
what is the role of H+ AND HCO3-
pH balance and co2 transport
What are the ways water enters the body and which is the main way?
Majority from food and water, a little from metabolism
How does the body lose fluids and which is the main way?
Skin, Lungs, Feces but mostly urine (1.5L)
How much water is in the human body?
30 L Females and 42L males
how does osmolarity change in the nephron?
1) Descending loop of henle: Water is absorbed relative to the blood in the vasa recta = high osmolarity
2) Ascending loop of henle- solutes are absorbed but no water = lower osmolarity
3) Distal Tubule and Collecting Duct- water is absorbed whether is it needed or not.
4) Collecting Duct - Urine leaves with varying level of osmolarity demanding on how much was removed in previous step
What is Vasopressin?
it is a neurohormone made from the hypothalamus released in the posterior pituitary gland to cause more water to be absorbed
How is vasopressin stimulated?
- low blood pressure
- low blood volume
- high plasma osmolarity
how does vasopressin increase more water intake?
it opens more aquaporin-2 (water channels) in the apical membrane of the collecting duct of the nephron
What detects the 3 stimuli of vasopressin?
low blood pressure = carotid and aortic baroreceptors
low blood volume = atrial stretch receptors
high plasma osmolarity = hypothalamus osmoreceptors
all go to the go the the hypothalamus
What is aldosterone?
is is a steroid hormone that acts on the principle cells in the distal and collecting duct of the nephrons to absorb more Na+. It is produced and released by the adrenal cortex
what is the stimulus for Na+ reabsorption?
- angiotensin 2 which comes from low blood pressure and the renin-angiotensin system
- high K+ in plasma (not as important)
What is renin and what does it do?
it is an enzyme that turns angiotesinogen into angiotensin 1
How is angiotensinogen produced?
is it made constantly by the liver and circulates in the plasma
What are the 3 stimulus for renin production?
1) low blood pressure makes granular cells in afferent arteriole produce renin
2) low blood pressure turns sympathetic activity up which makes the granular cells make renin
3) low blood pressure makes the glomerous filtration rate go down which decreases NaCl transport across the macula dense of age distal tubule which makes the paracrine produce renin
What is angiotensin 2?
is it a hormone that affects the all the structures that can increase water absorption
How is angiotensin 2 produced?
it is produced when angiotensin converting enzyme (ACE) changes angiotensin 1 into angiotensin 2
What 5 structures does angiotensin affect?
- arterioles
- medulla oblongata
- hypothalamus
- adrenal cortex
- proximal tubule
How does angiotensin 2 affect the 5 structures?
1) vasoontricts arterioles
2) makes medulla increase sympathetic activity
3) makes hypothalamus release vasopressin and increase thirst
4) adrenal cortex to release aldosterone for Na reabsorption
5) proximal tubule to absorb more Na+
all affects increases blood pressure at the end
ph of plasma?
7.38-7.42
What are the 3 mechanisms to maintain normal pH
1) buffers - minutes
2) regulation of ventilation - hours
3) kidneys - hours-days
what things affect pH?
H+ and CO2
How does renal system compensate for pH changes?
- the proximal tubule can secrete H+ and absorb HCO3
- collecting duct can use their intercalated cells to absorb and secrete H+ and HCO3-
What are intercalated cells?
they contain high levels of carbonic anhydrase which can help in the secretion and absorption of H+ and HCO3-
What do the type A intercalated cells do?
Respond to Acidosis- secrete H+ and reabsorb HCO3
what do the type B Intercalated cells do?
responses to alkalosis - reabsorb H+ and secrete HCO3
Functions of Calcium in extracellular matrix
99% -in classified in bone and teeth
Functions of Calcium in extracellular fluid
- neurotransmitter release at synapse
- cofactor in coagulation cascade
- muscle contraction
- influences excitability of neurons
Functions of intracellular Calcium
- muscle contraction
- signal in the second messenger systems
structure of bone
- osteoblast (synthesizes bone)
- osteoclast (resorption of bone (break down))
- calcified extracellular matrix hydroxyapatite (Ca10(PO4)6(OH)2)
the three calcium homeostasis mechanisms
1) parathyroid hormone
2) Vitamin D3 (calcitriol)
3) Calcitonin
what is the parathyroid hormone
a peptide hormone which always produced but is released in plasma when Ca levels are low
sit behind the thyroid gland and increases
- resorption of Ca in bone (osteoclast)
- reabsorption of Ca in kidney
- absorption of Ca in GI tract
what is Vitamin D3 (Calcitriol)and what does it do?
uses the vitamin D sunlight and diet in combination with lung and kidney to be produced
when signalled by the PTH causes
- resorption of Ca in bone (osteoclast)
- reabsorption of Ca in kidney
- absorption of Ca in GI tract
Calcitoninand what does it do?
made in the thyroid its a peptide hormone released when Ca2+ levels are too high
- causes synthesis of Ca2+ the bone (osteoblast)
- excretion of Ca2+ in kidneys
