Lecture 31 - Urinary system 4 (physiology)

Question 1

What is urine used for?

Answer 1

It is used to diagnose diseases

Question 2

Composition of urine

Answer 2

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

Question 3

Composition of pathological urine

Answer 3

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

Question 4

How does normal urine look, taste or smell?

Answer 4

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

Question 5

How does pathologic urine look, taste or smell?

Answer 5

Look
Golden, brown, red, blue

Taste
Sweet - diabetes mellitus

Smell
Like fruits - ketosis (fasting), diabetes, chronic alcohol abuse
Rotten - infection (bacteria), tumour

Question 6

Urine analysis

Answer 6

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

Question 7

Possible disease/conditions if changed or positive in urine

Answer 7

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

Question 8

What are the functions of the kidney?

Answer 8

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)

Question 9

Hormones and the kidney

Answer 9

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

Question 10

Metabolism and the kidney

Answer 10

Kidney can convert compounds into other compounds but the liver is mostly responsible for this

Question 11

Gluconeogenesis and the kidney

Answer 11

Kidney can if you are in fasting mode, can convert amino acids to glucose

Question 12

Salt/ion homeostasis and the kidney

Answer 12

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

Question 13

Excretion of frugs, endogenous metabolites and toxins (aspirin, anti-viral drugs, urea, uric acid, herbal toxin) and the kidney

Answer 13

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)

Question 14

pH regulation and the kidney

Answer 14

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

Question 15

Kidney can’t actively secrete what?

Answer 15

Secrete glucose - kidney is designed to take all glucose back into the system

Question 16

Basic nephron processes

Answer 16

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

Question 17

Filtration

Answer 17

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

Question 18

Reabsorption

Answer 18

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

Question 19

Secretion

Answer 19

Happens at the proximal tubule

Drugs and toxins e.g. penicillin is mostly excreted by active secretion

Question 20

Different substances are handled differently in different parts of the nephron

Answer 20

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

Question 21

Roles of the different nephron parts

Answer 21

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

Question 22

The renal proximal tubule facilitates

Answer 22

Secretion of drugs and metabolites

Question 23

Summary of urine composition

Answer 23

The normal urine is made of mostly water, electrolytes (sodium, potassium), drugs/toxins, metabolites and acids

Question 24

Summary of functions of the kidney

Answer 24

The kidney has a variety of functions - filtration, excretion, salt and water homeostasis, pH regulation, hormone synthesis

Question 25

Summary of the nephron processes

Answer 25

Achieved by a variety of basic nephron processes including filtration, reabsorption and secretion