Lecture 31 - Urinary system 4 (physiology) Flashcards
What is urine used for?
It is used to diagnose diseases
Composition of urine
Water approximately 1.5L 95-98% of urine is water Creatinine - comes from muscles, waste product produced by muscles from the breakdown of a compound called creatine, creatine is one of the basic muscle energy stores Urea,uric acid - urea comes from protein degradation and is actually the toxic part of the protein which is the amino part, urea is used to expel extra nitrogen from the body, uric acid comes from purines H+, NH3 Na+,K+ Drugs (antiviral, diuretics) Toxins
Composition of pathological urine
Glucose (glycosuria, diabetes) - transport system is saturated and what can’t be transported is excreted in the urine
Protein (proteinuria)
Blood (erthyrocytes, haematuria)
Haemoglobin (haemoglobinuria) - shouldn’t be there because this big protein shouldn’t be able to get through the filter
Leucocytes
Bacteria (infection)
Both of these signal infections and/or inflammation
How does normal urine look, taste or smell?
Look
Clear, light or dark amber look
Taste
Acidic (pH 5-6), NOT sweet
pH is dependent on diet - vegetarians have a pH of up to 7.2, meat eaters (high protein) have a pH of approximately 4.8
Smell
Unremarkable
How does pathologic urine look, taste or smell?
Look
Golden, brown, red, blue
Taste
Sweet - diabetes mellitus
Smell
Like fruits - ketosis (fasting), diabetes, chronic alcohol abuse
Rotten - infection (bacteria), tumour
Urine analysis
Normal values for plasma and urine
Plasma Urine
Blood Negative. Negative
Spezgravity 285-300mOsmol/L 50-1335mOsmolL
(osmolarity) Urine measurement is dependent on hydration
Glucose Postitive Negative
Protein Positive. Negative
pH 7.4 4.5-8.0
Possible disease/conditions if changed or positive in urine
Blood - haematuria, UTI, damage to filtration barrier
Spez. Gravity (approx osmolarity) - polyuria, diabetes mellitus, diabetes insipidus (concussion)
Glucose - glucosuria, diabetes mellitus
If you are peeing all of the glucose out there is not point to eating
Protein - proteinuria, glomerulonephritis, damage to filtration barrier
pH - diet dependent (athlete, vegetarian); acidosis, alkalosis, asthma, anxiety disorder
asthma, anxiety disorder - acidosis and alkalosis can be underlying causes, breathing habits change that is why
More acidic values can show acidosis
More alkaline values can show alkalosis
What are the functions of the kidney?
Summarised …
The kidney has a variety of functions - filtration, excretion, salt and water homeostasis, pH regulation, hormone synthesis
Filters blood
Hormone production (erythropoiten)
Metabolism
Gluconeogenesis
pH-regulation
Excretion of drugs, endogenous metabolites and toxins (aspirin, anti-viral drugs, urea, uric acid, herbal toxins)
Reabsorption of nutrients (amino acids, glucose)
Salt/ion homeostasis (Na+, K+, Ca2+, blood pressure
Water homeostasis (hydration, blood pressure)
Hormones and the kidney
EPO is produced by the kidney in response to low oxygen
Function - stimulates RBC production by bone marrow
Pathology - chronic renal failure, no EPO produced, no red blood cells = anaemia
Metabolism and the kidney
Kidney can convert compounds into other compounds but the liver is mostly responsible for this
Gluconeogenesis and the kidney
Kidney can if you are in fasting mode, can convert amino acids to glucose
Salt/ion homeostasis and the kidney
K+ is essential and must be maintained at appropriate levels to maintain resting membrane potential
Neurons and cardoimyocytes - action potentials, rhythm generation in pacemaker cells, contractility, signalling
The kidneys secrete K+ therefore kidney disease/failure mains hyperkalemia (death since it kills the excitation of the heart)
5g of potassium a day is the dietary need
Excretion of frugs, endogenous metabolites and toxins (aspirin, anti-viral drugs, urea, uric acid, herbal toxin) and the kidney
Lidocaine is a commonly used local anaesthetic used. Lidocaine is excreted by the kidneys after metabolisation in the liver due to its fat soluble (lipohilic) nature
Aspririn is a common painkiller and is highly hydrophilic and is excreted directly by the kidneys
Lipophilic drugs and toxins, go to liver to be metabolised into more water soluble products, go to kidney via the blood stream for excretion
Hydrophilic drugs go straight to the kidney for excretion
In the urine would be the metabolised and hydrophilic drugs and toxins (90% metabolised lidocaine and 100% aspirin)
pH regulation and the kidney
Kidney can excrete hydrogen ions in order to maintain pH
Bicarbonate is the main blood buffer - neutralising acids from metabolism to maintain a blood pH of 7.4
Bicarbonate concentration is controlled by the lungs which exhale CO2 and kidneys which reabsorb HCO3- or secrete H+
Reabsorbed more bicarbonate to bring it back up to 7.4 OR actively secrete hydrogen ions to balance out this acidity
Kidney can’t actively secrete what?
Secrete glucose - kidney is designed to take all glucose back into the system
Basic nephron processes
1- Filtration which creases a plasma like filtrate from the blood
2- Secretion which is where additional wastes are actively removed from the blood and put it into the filtrate
3- Reabsorption which removes the useful solutes from the filtrate back into the blood e.g. partial absorption - ions, complete absorption - glucose
The balance of these 3 processes determines the way a particular substance is handled in the kidneys
Filtration
Happens at the glomerulus
Many substances are filtered with a constant rate at the renal corpuscle (glomerulus) - the exception being substances bound to a protein
Big molecules such as albumin are not even filtered
More in depth
Glomerular filration rate (GFR) occurs at approximately 125mLs/min (180L/day) but only produces 1.5L of urine per day
The primary filtrate has a similar solute concentration to the plasma - filtration is not particularly selective (anything that is small enough will be filtered) - although primary filtrate has no proteins or cell
The important determinants of renal filtration (and the urine output) are renal blood flow, the filtration barrier and the driving forces
Reabsorption
Happens at the proximal tubule (bulk reabsorption), distal tulle and collecting duct (fine tuning)
Glucose is fully reabsorbed at the proximal tubule
K+ is reabsorbed or secreted in different parts of the tubule
Water is reabsorbed anywhere
Secretion
Happens at the proximal tubule
Drugs and toxins e.g. penicillin is mostly excreted by active secretion
Different substances are handled differently in different parts of the nephron
Glucose is only reabsorbed and only in the PCT
K+ is reabsorbed or secreted in different parts of the tubule (depends on diet)
Water is reabsorbed in most parts of the tube but not in the descending part of the nephron loop
Penicillin (drugs and toxins) is mostly excreted by active secretion, not filtration (only a tiny part is filtered)
Big molecules (such as albumin) are not even filtered
Roles of the different nephron parts
Glomerulus = filtration
PCT = bulk reabsorption of electrolytes (sodium and potassium), secretion of metabolites, drugs and toxins
DCT = fine tuning of electrolytes/water reabsorption
Collecting duct = fine tuning of electrolytes/water reabsorption
The renal proximal tubule facilitates
Secretion of drugs and metabolites
Summary of urine composition
The normal urine is made of mostly water, electrolytes (sodium, potassium), drugs/toxins, metabolites and acids
Summary of functions of the kidney
The kidney has a variety of functions - filtration, excretion, salt and water homeostasis, pH regulation, hormone synthesis
Summary of the nephron processes
Achieved by a variety of basic nephron processes including filtration, reabsorption and secretion
