Urinary system - anatomy and physiology Flashcards
see paper flashcards for diagrams
How much water should a cow take in a day?
- 70-150 litres
What content/intake/output depends on what?
- age
- sex
-degree of obesity
How much water intake is normal?
- 2300 ml/day
How much water is excreted in urine?
1400 ml/day
What is a major organ involved in the urinary system?
- kidneys
What does insensible mean?
- not easily measured (e.g., like evaporative)
What are the function of the kidney?
- rid body of waste materials
- regulation of water and electrolyte balances
- regulation of arterial pressure
- regulation of acid-base balance - maintaining pH of blood
- Regulation of erythrocyte production
- gluconeogenesis (making new glucose from different stores to normal)
How do kidneys filter plasma to rid body of wate materials?
- clear unwanted substances via blood > urine
- return necessary substances to blood
What are waste products from filtering plasma?
- urea - from metabolism of amino acids
- creatinine (from muscle creatine)
- uric acid (from nucleic acids)
- end products of haemoglobin breakdown (Bilirubin)
*metabolites of various hormones
What do kidneys also eliminate from the body?
- most toxins and other foreign substances produced by the body or ingesta
- e.g., pesticides, drugs, food additives
How can the kidney’s regulate water and electrolyte balances?
- maintenance of homeostasis - excretion of water and electrolytes must match intake
- Alter sodium excretion in response to changes in sodium intake - also water, chloride, potassium and calcium
What can be used to measure kidney disfunction?
- urea and creatinine
What is hyperbilirubinemia?
- jaundice
How do kidneys regulate arterial pressure in the long-term?
- important role by excreting variable amounts of sodium and water
How do kidneys regulate arterial pressure in the short term?
- by secreting hormones and vasoactive factors (has quick arteries contract) or substances (renin)
How do the kidneys regulate acid-base balance and maintain pH of the blood?
- excretes acids
- together with lungs (carbonic acid is formed from carbonic dioxide)
How do kidneys regulate erythrocyte production?
- kidneys secrete erythropoietin which stimulates production if red blood cells
- one important stimulus for erythropoietin secretion is hypoxia
What is the kidneys function in gluconeogenesis?
- kidneys synthesis glucose from amino acids and other precursors during prolonged fasting = gluconeogenesis
- can add glucose to the blood during prolonged fasting as rapidly as liver
What is respiratory alkalosis?
- hyperventilation that increased blood pH
Why are kidneys heavily vascularised?
- due to large amounts of filtering
How much cardiac output do kidneys receive?
- 25%
How much plasma is converted into filtrate?
- 20%
What do the kidneys to to plasma and with retained cells and protein?
- they convert 20% of plasma to filtrate and the first bit is filtered out of blood
- retain cells and proteins in the circulation
How much filtrate is reabsorbed?
- all but 1% of filtrate is reabsorbed
How often is the entire circulatory volume filtered and reabsorbed?
- 30 minutes
Glomerular filtration rate and therefore kidney function is dependent on what?
- blood flow to kidneys
What is glomerular filtration rate?
- way of measuring how much filtrate is being produced
What’s included in the upper urinary tract?
- ureter
- kidney
What’s included in the lower urinary tract?
- urethra
- bladder
Where is the right kidney situated?
- right kidney is more cranial to left
Where are the adrenal glands located?
- adrenal glands cranial and medial to kidney
What is the cortex?
- outer part of kidney
- contains glomerulus and convoluted tubules
- outside - renal capsule
What is the medulla?
- inner part
- contains majority of the length of nephrons
What is the pelvis?
- centre of kidney
- collects urine - funnelled to ureter
Where is renal artery from?
- from the aorta
Where does the renal vein go?
- to inferior vena cava
What is the renal pyramid?
= triangular section of the medulla
Where is the renal calyx and what does it contain?
- at apex of pyramids
- contains renal papilla > minor calyx > major calyx > renal pelvis
Where does urine production begin?
- begins with filtration in the renal corpuscle
What is the glomerular filtrate?
- components of plasma (blood) which are filtered from the glomerulus into the bowman’s capsule
- is the volume of fluid filtered from the glomerular capillaries into the Bowmans capsule per unit time
The compositions of glomerular filtrate and urine are …
- different
When does the composition of the filtrate change?
- changes as it flows through the nephron tubule
What can kidneys not regenerate?
- cannot regenerate nephrons
- thus with age/disease nephrons decrease
What is the kidney good at coping with if its lost?
- very good at coping as an organ system with losing nephrons
Azotaemia (elevated blood urea/creatinine) doesn’t occur until what parentage loss of nephrons?
- 65-75% nephron loss
To test kidney function we used to wait till there were elevations in BUN/CRE - what test is more sensitive than this?
- symmetric dimethylarginine = SDMA
What are the four major processes of the kidney (nephron)?
- filtration of substances in the blood (afferent)
- reabsorption of substances from the renal tubules into the blood
- secretion of substances from the blood into the renal tubules (at the same time)
- excretion of waste product
Equation for excretion?
excretion = filtration - reabsorption + secretion
How do water and other small molecules cross into or out of cells?
- diffusion
- primary active
- secondary active transport
How does diffusion occur?
- passive or facilitated
- though a channel or a carrier down a energy gradient and doesn’t use ATP
How does primary active transport occur?
- pump mediated
- required ATP goes against an energy gradient - only happens one way and highly selective
How is secondary active transport mediated?
- carrier mediated
What is passive transport?
- movement of molecules within and across the cell membrane = through the concentration gradient, without using ATP
Does passive transport require carrier proteins?
- no
How fast is passive transport?
- relatively slow process
What direction does passive transport go in?
- bidirectional
Is passive transport selective?
- partly non-selective
Is passive transport affected by temperature or oxygen?
- not sensitive to temperature or oxygen content
What molecules is passive transport used for?
- oxygen
- monosaccharides
- water
- carbon dioxide
- lipids
What are the 4 categories of passive transport?
- diffusion (molecules/ions)
- osmosis (water)
- facilitated diffusion
- filtration (pressure gradient)
What is passive transport used for?
- used to maintain equilibrium either side of the cell membrane
What is active transport?
- the movement of molecules across the cell membrane, pumping molecules against the concertation gradient using ATP (energy)
Does active transport require carrier proteins?
- yes
How fast is active transport?
- rapid
What direction does active transport move in?
- unidirectional
Is active transport selective?
- highly selective
Is active transport affected by temperature and oxygen?
- affected by both - stops if no oxygen
What molecules use active transport?
- macromolecules like proteins, carbohydrate (sugars), lipids
What are the two categories of active transport?
- primary active transport
- secondary active transport
What is active transport used for?
- use to carry molecules and ions through cell membrane
Why is filtered fluid in the bowman’s space essentially protein free?
- proteins can’t fit into capsule
What is filtrate?
- concentration of soluble ions and smaller molecules in plasma
What exceptions can fit into the Bowmans capsule?
- certain low molecular weight molecules bound to plasma proteins
- such as fatty acids and calcium
What happens in the proximal convoluted tubule?
- reabsorption and secretion
How much is reabsorbed in the PCT?
What molecules are reabsorbed?
- reabsorption of 3/4 of filtered load
- including Na+, Cl-, glucose, Amino A, H2O
Sodium is transcellular and paracellular what do these mean?
- Transcellular = utilised ATPase pump, i.e., active transport
- Paracellular = diffusion, due to difference in concentrations
- massively conserved
How much water is reabsorbed in the PCT?
- approx. 65%
What two things are actively secreted unto lumen of PCT ?
- metabolites = bile salts, prostaglandins, urate
- xenobiotics = penicillin, aspirin
What is not reabsorbed in the descending limb?
- Na+ and cl+ are not reabsorbed as the region is impermeable to electrolytes
- instead become actively concentrated by water moving out
In the descending limb what happens to the concentration in the lumen?
- concentration in the lumen gets stringer as water is pulled osmotically into the surrounding medullary interstitum
What happens in the Ascending limb?
- Na+ and Cl+ passively and actively transported out of lumen i.e. reabsorbed
- Water not reabsorbed – region impermeable to water
- Result: ↑ osmotic gradient in medulla from superficial to deep
- Used to reabsorb water from collecting duct
What happens in the distal convoluted tubule?
- Small amount of Na+ actively reabsorbed here
- Cl- is co-transported with Na+
- Segment impermeable to water
- Ca2+ reabsorption occurs under the control of parathyroid hormone – important maintenance of calium
What happens in the late distal tubule and collecting ducts?
- Only 4% of Na+ actively reabsorbed here
- K+ and H+ actively secreted
- An increase in Na+ reaching this segment tends to increase K+ and H+ secretion as Na+ is reabsorbed
- Aldosterone - ↑ Na+ absorption & K+ secretion
- Water – only reabsorbed if ADH/vasopressin present i.e. largely impermeable
What is Osmolality?
- the number of milliosmoles of solute per kg solution
What is Osmolarity?
- number of milliosmoles of solute per litre solution
During osmolality how does water flow if the membrane is permeable to water?
- floes from compartment of low osmolality to one of high osmolality
What happens if plasma osmolality is too low?
- net movement of water into cells
What happens if plasma osmolality is too high?
- net movement of water out of cells
Cell function is compromised during osmolality - what happens if two much water is being moved around?
- it can be fatal
Kidneys maintain plasma osmolality within narrow limits what are these limits?
- 1% variation in plasma osmolality sufficient to trigger corrective response by the kidneys
How are the narrow limits for kidney control achieved?
- achieved by varying the amounts of water reabsorbed by the collecting ducts
What does anti-diuretic hormone (ADH) do?
- reduces diuresis ( water lost in urine)
- also known as vasopressin
What is ADH secreted by?
- secreted by posterior pituitary gland
What do ADH respond to?
- responds to increased plama osmolality
How does ADH respond to extracellular fluid osmolality being increased?
- ADH is released
- water diffused out of the distal and collecting tubules
- increase retention of water
- urine is more concentrated
How does ADH respond to a decrease in blood pressure?
- there is an increase in ADH
- blood pressure changes sensed by baroreceptors in the aortic arch and carotid sinus, which responds to stretch
What is RAAS?
- Renin Angiotensin Aldosterone System
What is renin?
- proteolytic enzyme (in kidneys) secreted by cells of afferent arteriole
How does renin respond to low sodium in the distal convoluted tubule?
- renin secreted into blood
- converts angiotensinogen (a plasma peptide, produced by the liver) -> angiotensin I which goes through the lungs and kidney -> angiotensin II has vasoactive affects
- increases blood pressure, body water and sodium content
How does blood pressure increase?
- increased by constriction of blood vessels
How is there retention of Na+ and loss of k+ from kidneys
- adrenal glands stimulate production of aldosterone leading to this affect?
Hoe does sodium retention affect the kidneys?
- increased sodium retention increases water reabsorption in the kidney to increase blood volume and blood pressure
What is involved in increased thirst and the desire for salt?
- nerves
How is osmolality of body fluids regulated?
- regulated by osmoreceptors and ADH
How are extracellular fluid volumes regulated?
- by RAAS
Osmoreceptors and ADH, and RAAS work …
- independently of each other
What is natriuresis?
= the excretion of an excessively large amount of sodium in the urine
Where is Atrial natriuretic synthesised and secreted?
- by cardiac muscle cells in the walls of the atria
What are the steps involved in Atrial natriuretic peptide and decreasing vascular resistance?
- increase in total body sodium
- increase in plasma volume
- sensed by arterial myocytes
- stimulated release if ANP
- inhibits secretion of renin, aldosterone and ADH
- vasodilation thereby decreasing vascular resistance
Acute kidney failure occurs …
- over a few days
What are the causes of acute kidney failure?
- most common = toxin ingestion
- also = nephrolithiasis (kidney stones) - block ureters
- urinary obstruction
- kidney swell
Chromic kidney failure happens over …
- over a few weeks or months
What is a cause of kidney failure?
- dental disease - bacterial build up enters the digestive system - pyelonephritis
There are no pathognomonic signs of kidney failure - what the symptoms?
- changes in drinking and urination = dehydration - can also be the cause
- lethargy, appetite, weight loss
- vomiting and or diarrhoea
- haematuria
What does decreased blood flow through the kidneys cause?
- long-term damage
What are symptoms of dehydration?
- sunken eyes = fat pad behind eye shrivels
- lethargic and inactive
- depression
- dry nose
- loss of skin elasticity
- dry gums
