Week 7 - The Urinary System/pH And Homeostasis Flashcards
How does the kidney maintain homeostasis?
- regulating blood electrolytes by secreting excessive ions into urine
- regulates blood pH by excreting/conserving H+ or bicarbonate ions
- regulating blood volume by conserving or eliminating water
- regulating blood pressure (by regulating blood volume)
- maintaining blood osmolarity by secreting excessive Na+ into urine
- excreting waste products: ammonia, urea, creatinine
- producing hormones (EPO, calcitriol, and produced the enzyme renin which leads to the production of angiotensin and aldosterone
- regulating blood glucose
What are nephrons?
More than a million microscopic functional units that make up the bulk of each kidney
What are the 2 main regions of the nephrons?
- renal corpuscle
- renal tubule
What is formed when fluid is filtered out of the blood of the nephrons?
Forms Filtrate
What are the two parts of the Renal Corpuscle?
- The Glomerulus (a mass of capillaries) - The Glomerular (Bowman’s capsule)
Where does nutrients enter the Renal Corpuscle?
Fed by the Afferent Arteriole
Where do nutrients drain in the Renal Corpuscle?
Excited into the efferent arteriole
What is the blood pathway through the nephron IN ORDER
- renal artery
- afferent arterioles
- glomerulus
- efferent arterioles
- peritubular capillaries
- renal veins
What are the 3 steps to urine formation?
- Glomerular Filtration
- Tubular Reabsorption
- Tubular Secretion
What is Glomerular Filtration?
Water and small dissolved solutes move from the blood into the glomerular capsule
What does Glomerular Filtration need to be effective?
A constant blood pressure to force the fluids and solutes across the membranes into the Glomerular capsule
What type of the bodies nutrients are too large to filter into the Glomerular capsule?
Blood cells, plasma proteins, platelets. They remain in the blood
Where does Glomerular filtrate travel?
Into the renal tubules
What are the 3 waste products?
- creatinine (a waste product of muscle metabolism, excreted vis Glomerular filtration)
- urea (limited reabsorption in from the convoluted tubule)
- some electrolytes (Na+, K+)
What happens is there is a reduction in Glomerular filtration?
A rise in creatinine levels in the blood
The is the Glomerular filtration rate?
The amount of filtrate for are by both kidneys per minute
What is Tubular Reabsorption?
The process of returning important substances from the filtrate back into the blood
How does tubular Reabsorption occur?
- Passive transport (proximal convoluted tubule is ‘leaky’ and allies substances (Na+) to pass through into the capillaries)
• water flows by osmosis - Active transport (sodium/potassium pump)
• All cells have a decrease in Na+ in the cytosol
What has the greatest level of Reabsorption?
The proximal convoluted tubule
What is completely Reabsorbed?
- glucose
- amino acids
What is largely reabsorbed?
- water (99%)
- Na+, Cl-, Ca2+, H+, HCO3-
Wherever Na+ goes, water will follow
What is reabsorbed somewhat?
- Ca2+
- Mg2+
What is reabsorbed very little
- urea
- Unic acid
What happens as solutes are reabsorbed?
Water is reabsorbed via osmosis
Where does tubular reabsorption occur?
Mainly in the proximal convoluted tubule
Where does the filtrate move?
Through the tubule (loop of Henle & distal convoluted tubule) “finned tuned”
What is tubular secretion?
Process of removing waste materials from the blood to the filtrate
How does secretion occur in the proximal convoluted tubule, distal convoluted tubule and collecting ducts?
Active transport
The process of tubular secretion controls…
Controls pH
- hydrogen ions (H+) are secreted to raise the pH (less acid) in the body
- bicarbonate (HCO3-) is conserved (also raises the blood pH)
- potassium is also secretes - depending on the body’s needs (K+)
What is the renal threshold?
Measurement of the kidneys ability to reabsorb a particular substance from the filtrate
What happens is the threshold of a substance is exceeded?
Then the substance cannot be reabsorbed from the filtrate and is excreted in the urine
What is normally found in urine?
- water
- ions (Na+, K+, Ca2+)
- dead cells (epithelial cells)
- hormones (HCG)
What are 4 normal findings in urine?
- colour should be yellow or amber
- should be transparent when fresh
- the volume should be 1-2L/24hrs
- the pH should range between 4.6-8.0
What are 4 abnormal findings in urine?
- blood present (present with trauma, infection, during menstruation)
- glucose present (people with diabetes)
- leukocytes present (with infection)
- ketones present (diabetes, starvation, low levels of carbohydrates)
What are the three ways urine moves from he kidney to the bladder?
- Peristaltic contractions
- Hydrostatic pressure
- Gravity
What systems affect urine production?
- cardiac (blood flow and blood pressure)
- endocrine (hormone release for high and low blood volume)
- nervous (sympathetic nervous system response)
What are the 4 ways in which the renal system contributes to the homeostasis of the cardiovascular system?
- Kidneys filter the blood and dispose of nitrogenous wastes, maintain fluid, electrolyte, and acid base balance in the blood
- kidneys produce renin which initiates the RAAS pathway when blood pressure is lowered
- kidneys control blood volume and blood pressure by regulation of Na+ and water balance
- kidneys produce erythropoietin which stimulates the production of red blood cells
What hormones do the kidneys produce?
- Erythropoietin
- Calcitriol
- renin
What does erythropoietin do?
- plays an important role in production of RBC
- released in response to hypoxaemia
- stimulates red bone marrow to produce red blood cells
What does calcitriol do?
- active form of VitD
- helps promote absorption of calcium in food
- helps regulate bone formation
What does renin do?
Released from cells in afferent arterioles when blood pressure drops
What are the 2 hormones that respond to decreased blood volume and result in less urine production to increase blood volume and BP?
- Aldosterone
2. Antidiuretic hormone (ADH)
What does Aldosterone do to help decrease blood volume?
- released from adrenal cortex (on top of kidneys)
- works on nephrons to increase tubular reabsorption of Na+ and therefore water by osmosis
- urine production decreases
What does antidiuretic hormone (ADH) do to help decrease blood volume?
- increases water permeability in nephrons to reabsorb more water into blood
- urine production decreases
- produced in hypothalamus, stored and released by pituitary gland
What is the hormone that responds to increase blood volume and results in more irons production to reduce blood volume and BP?
- Atria Natriuretic Peptide (ANP)
What does atrial natriuretic peptide do to help increase blood volume?
- increases Na+ secretion and therefore water
- urine production is increased
- released from atria in the heart
What are 3 age related changes to the urinary system?
- due to decreased mobility and dehydration, elderly may be more susceptible to:
• a cute and chronic kidney inflammation
• kidney stones - due to decreased thirst sensation, elderly may have increased susceptibility to dehydration
- potential for functional incontinence
• drinking less to avoid using the bathroom, risking the chance of incontinence
pH measured at 7 is considered..
Neutral
pH below 7.35 is considered..
Acidic
pH about 7.45 is considered…
Alkaline
What is the normal pH of extracellular fluid?
7.35-7.45
Why is a pH below 7.35 dangerous
Because H+ alterations can:
- disrupt the stability of cell membranes
- alter the structure of proteins
- change the activity of important enzymes
What are the 3 mechanisms to control systemic pH?
- buffer systems in the blood respond immediately (HCO3-)
- respiratory system systems involving exhalation of C02, takes minutes to respond
- renal response systems involving kidney excretion of H+ take hours to respond (24hrs)
What is involved in the regulation of acid-base balance?
- the body’s protein buffer systems
- the lungs
- the kidneys
What happens if there is excess C02?
The blood becomes more acidic
What happens when carbon dioxide levels rise?
More carbonic acid forms, additional hydrogen ions and bicarbonate are released and the pH goes down
What happens when Pco2 falls? (Partial pressure of carbon dioxide)
The reaction runs in reverse, and carbon acid dissociates into carbon dioxide and water
- this removes H+ ions from solution and increases the pH
What is more common, Acidosis or Alkalosis?
Acidosis
Why is a shift in pH from neutral to acidic bad?
There is a major adverse impact on the nervous and the cardiovascular system
(Individual may become comatose)
(Cardiac contractions become weak and irregular)
(Signs and symptoms of heart failure may develop)
What does a buffer system do?
Minimise marked changes in the pH of a solution
What are the 3 main buffer systems?
- proteins
- carbonic acid - bicarbonate
- phosphates
When are buffers effective?
Only if there is a way to excrete the excess acid or base - primarily accomplished by the lungs or the kidney
What is expired in the air with every breath we take?
C02 and H20
What happens if we change the rate or depth of our breathing?
It can adjust pH
How does the renal system regulate pH?
Maintains pH by controlling secretion and reabsorption of H+ and HCO3-
How does the renal system regulate the Acidosis pH?
- more H+ secretes into filtrate (excreted in urine)
- more HCO3- reabsorbed (into blood)
How does the renal system regulate the alkalosis pH?
- Less H+ secreted info filtrate (excreted in urine)
- Leas HCO3- reabsorbed (into blood)
What are some consequences of acidosis?
- main effect is depression of synaptic transmission
- clinical signs::
• weakness
• fatigue
• headaches
• confusion
• vital signs change - pH less that 6.8 cause coma and death
What is Respiratory Acidosis?
If the pH drops due to respiratory dysfunction
What happens in respiratory acidosis?
- rate of C02 production exceeds rate of elimination
- if C02 accumulates reaction is driven to the RIGHT
- results in increased H+
What is the response to respiratory acidosis?
- rise in PCO2 detected by chemoreceptors
- pons and medulla react by sending motor signals to respiratory muscles
- Respiratory rate and depth increase to ‘blow-off’ C02
What is respiratory alkalosis?
If the pH rises due to hyperventilation
What happens in respiratory alkalosis?
- rate of C02 elimination exceeds rate of production
- if C02 drops, the reaction is driven to the LEFT
- results in decreased H+
What is the response to respiratory alkalosis?
- drop in PC02 detected by chemoreceptors
- pons and medulla react by inhibiting motor signals to respiratory muscles
- Respiratory rate and depth decrease to conserve C02
What is Metabolic acidosis?
If the pH drops due to a non-respiratory cause
- acids accumulate in the blood due to cellular metabolism
What happens in metabolic acidosis?
- Anaerobic cellular respiration produces lactic acid
- large scale fat metabolism produces ketones
- excess alcohol metabolism produces acetic acid
What is the response to metabolic acidosis?
- Buffer system
• acts quickly
• HC03- binds excess H+ to increase
pH - respiratory system
• acts quickly
• “blows-off” excess C02 to increase pH - Renal system
• acts slowly
• eliminates H+ from the body to increase pH
What is metabolic alkalosis?
If pH rises due to a non-respiratory cause
- occurs when non-respiratory acids are lost
What happens in metabolic alkalosis?
- can happen with loss of stomach acids (hydrochloric acid) with severe vomiting or loss of gastric contents through nasogastric drainage
- use of diuretics causing excessive loss of H+
What is the response to the metabolic alkalosis?
- buffer system
• acts quickly
• HC03- releases H+ to decrease pH
- respiratory system
• acts quickly
• reduces Respiratory rate and depth to
conserve C02 to decrease pH
- Renal system
• acts slowly
• reabsorbs H+ from the tubule into blood to
decrease pHWhat are the consequences of alkalosis?
- main effect is nervous system over-excitability
- clinical signs::
• cardiac arrhythmias
• confusion
• convulsions
• hyperreflexia
• vital signs changes - pH greater than 7.65 can cause coma and death
