Lecture 6 - Control Of Body Fluid Volume And Osmolality Flashcards
What cells of the DCT detect levels of Na+ and Cl- in the filtrate?
Macula densa cells
What cells doe the Macula densa cells send signals to?
Granular/juxtaglomerular cells
What substance do juxtaglomerular cells produce?
Renin
What hormone do macula densa cells produce to stimulate renin release from Granular cells?
Prostaglandins
What system is stimulated when blood pressure is low?
RAAS (Renin-angiotensin-aldosterone system)
What are the 3 mechanisms by which renin is stimulated to be produced by by the granular cells?
Granular cells innervated by sympathetic system
Decreased BP means less tension in afferent arteriole wall + granular cells so renin released
Less Na+ reaches Macula densa, stimulates them to make prostaglandins which makes granular cells to make renin
What is the important substance produced in the RAAS system which helps increase BP?
Angiotensin II
How does Angiotensin II increase BP?
Directly vasoconstriction efferent arterioles
Stimulates ADH production (aquaporin translocation in CD)
Stimulates thirst
Stimulates aldosterone production (zona Glomerulosa of adrenal gland)
How does aldosterone production increase blood pressure?
More ENAC channels expressed in DCT so more Na+ reabsorbed so later down the line more water reabsorbed
How does prostaglandins affect Na+ reabsorption?
Dilates afferent arteriole
Vasodilation
Leads to renin release (RAAS)
What leads to the production of Atrial Natriuretic Peptide (ANP)?
Cardiac atrial cells detect an increase in Extracellular fluid volume
How does ANP lead to decreased Na+ reabsorption?
Inhibits Na+/K+ ATPase and closes Na+ channels in collecting duct and DCT meaning less Na+ reabsorbed so more water excreted with the Na+
How does ANP affect other factors regulating BP?
Vasodilates afferent arterioles increasing the GFR
Inhibits aldosterone secretion
Inhibits ADH release
Decrease renin release
How does hydrostatic pressure affect reabsorption of Na+ and Cl- in the PCT?
Higher the blood pressure (extra cellular fluid volume), the lower the oncotic pressure meaning less NaCl and water reabsorbed by the PCT
What happens in terms of Na+ and water reabsorption when renal artery blood pressure increases?
Less Na-H+ antiporter in PCT so less Na+ reabsorbed
Causes Pressure natriuersis and pressure diuresis
What is pressure natriuresis?
What is pressure diuresis?
Increased sodium excretion in urine due to increased renal artery pressure
Increased water excretion in urine due to increased renal artery pressure
How does the kidney respond to increased BP summary?
ANP made (cardiac atrial cells) inhibits Na/K+ ATPase reducing ENAC expression
So less Na+ reabsorbed
Inc pressure in peritubular capillaries so get pressure natriuresis and pressure diuresis
How does the kidney respond to decreased BP summary?
Prostaglandins released
RAAS system gets activated
ANGII made:
-constricts efferent arteriole
-ADH made
-thirst
-Alodsterone release which increases expression of ENAC (more Na+ reabsorbed)
What response does the kidneys have to Congestive Heart Failure?
Heart cant cope with its workload so CO falls and fails to peruse the organs like kidneys enough
Makes the kidneys think blood pressure is low leading to mechanisms which lead to increased Na+ and water reabsorption
Why is pulmonary oedema common with congestive heart failure?
Blood backs up in the left side of the heart due to CO falling
Blood therefore backs up in the Pulmonary veins leading to increased pulmonary venous pressure
So increased hydrostatic pressure in the pulmonary veins > oncotic pressure
What is the aim when treating pulmonary oedema with congestive heart failure?
Reducing the workload of the heart by reducing the fluid load of the body
What are the 4 ways pulmonary oedema can be treated in congestive heart failure?
Loop diuretics (furosemide)
ACE inhibitor (Enalapril)
Vasodilators
Nitrates
What is Hypervolemia?
Fluid overload
What usually leads to Hypervolemia?
When theres high levels of sodium leading to water retention
What often leads to Hypervolemia?
Kidney retention of Sodium and water
Excessive sodium or fluid intake
Cirrhosis
Hyperaldosteronism
What are some symptoms of Hypervolemia?
Ascites
Pleural effusion
Pulmonary oedema
What is Hypovolaemic shock?
When theres a large loss of fluids leading to a very low circulating volume of blood meaning organs not perfused properly
What are some symptoms of hypovolaemia?
Tiredness
Dizziness
Thirst
What can lead to hypovolaemia?
Haemorrhage
Sepsis
How can sepsis lead to hypovolaemia??
The widespread infection leads to widespread vasodilation
Why does vasodilation occur in hypovolaemia?
How does this affect the kidneys?
Occur in vital organs like heart, lung and brain to maintain blood supply
Leads to acute tubular necrosis in kidney
What part of the kidney is especially vulnerable to acute tubular necrosis?
Why?
PCT
Very ATP sensitive since most reabsorption occurs here
How does the body try to compensate for hypovolaemia?
Vasoconstriction
Increased strength of heart contraction (+ve inotropic response)
Increased heart rate (+ve chrontropic affect)
What condition can happen if the bodies compensatory response to hypovolaemia isn’t enough?
Vulnerable organs undergo tissue hypoxia
Acute tubular necrosis
Acute kidney injury can develop to acute tubular necrosis
What is produced when the body is trying to compensate for hypovolaemia to prevent excess vasoconstriction to ensure the blood flow through kidney is maintained to ensure suffient GFR?
Prostaglandins
How do you treat Hypovolaemic shock?
Give IV isotonic saline solution to restore extracellular volume
Why do we give isotonic saline IV in patients with hypovolaemia?
Most water stays in the Extracellular fluid compartment (interstitium and plasma) since the sodium in the saline can move very freely between the ECF compartment and Intracellular compartment
Therefore water stays in blood helping with hypovolaemia
What are some pathological changes that can be seen as a result of renal hypertension?
Arteriosclerosis of renal arteries
Hyaliniizzation of small vessels (looks glossy)
High BP can lead to Chronic Kidney Disease leading to reduced kidney size
How can renal disease lead to hypertension?
Na+ and water excretion can be impaired
Renin may be stimulated to be
Renal artery stenosis
How can renal artery stenosis lead to hypertension?
Reduced renal perfusion leads to excess RAAS activation
What type of cells detect the plasma osmolarity?
Where these cells found?
Osmoreceptors in hypothalamus
What pathways do the osmoreceptors stimulate?
ADH to reabsorb water
Thirst to take in more water
What is the supraoptic nucleus?
Neurosecretory cells in the anterior pituitary that produce hormones like ADH
What happens to ADH once its been made in the supraoptic nucelus in the anterior hypothalamus?
Transported to posterior pituitary gland
What type of hormone is ADH?
Peptide hormone
What type of change in osmolality leads to ADH release?
Osmolality increase leads to ADH release
How does ADH lead to decrease in Osmolality?
ADH binds to V2 receptor on the basal membrane of collecting duct cells
V2 = G coupled protein receptor (Gs)
Aquaporins fuse to luminal membrane
How does an increase in osmolality affect ADH secretion??
How does a decrease in osmolality affect ADH secretion?
Increase = more ADH
Decrease = less ADH
What is the relationship with BP, Osmolality values and ADH secretion?
Lower the BP the lower the Osmolality can be before ADH is released?
Higher the Bp the higher the Osmolality must be before ADH is released
When is thirst stimulated and then inhibited?
Stimulated when plasma Osmolality is increased (reduced ECF volume)
Stopped when the Osmolality returns back to its lower value
When is thirst stimulated and then inhibited?
Stimulated when plasma Osmolality is increased (reduced ECF volume)
Stopped when the Osmolality returns back to its lower value
How is ADH secretion affected in Diabetes Insipidus?
HYPOsecretion of ADH
What is the affect of having low ADH secretion on the body?
Polyuria
Thirst
Dehydration
Diluted urine
Dry mucuous membranes
How is secretion of ADH affected in SIADH (Syndrome of Inappropriate ADH secretion)?
HYPERsecretion of ADH
What are the effects of excess ADH from SIADH?
Fluid overload (oedema, ascites)
Weight gain (fluid mass)
Low urinary output
Conc urine
Hyponatremia
What is the bodies response if the plasma Osmolality is low?
Need to make Hypoosmotic urine (dilute urine)
Decrease ADH production
What is the bodies response if the plasma Osmolality is high?
Need to produce hyperosmotic urine (conc urine)
Produce ADH so water reabsorbed in CD
