Kidneys & Homeostasis Flashcards
Roughly how much of our body’s weight is water?
60%
What are the constituents of the fluid component of our blood (plasma)?
- Ions
* Proteins
On average, what is the pH of human blood?
7.35-7.45
Is a solution more acidic or more alkali if it has an excess of OH- (hydroxide) ions?
Acidic
What are the organs which comprise the urinary system?
- Kidneys
- Ureters
- Bladder
- Urethra
How much urine does an average healthy adult produce per day?
Between 600 and 2300ml
What are the three regions of a kidney?
- The renal capsule
- The renal cortex
- The renal medulla
How much of the cardiac output do the kidneys receive?
Around a litre a minute / 20%
What is the renal corpuscle?
The structure in a nephron which filters the blood
What is the renal tubule?
The structure which processes the filtered urine
What are the 4 main regions of the renal tubule?
- The proximal convoluted tubule
- The distal convoluted tubule
- The loop of Henle
- The collecting duct
What is the name for the network of tubules which surrounds the renal tubule?
The peritubular capillaries
What are the three main functions of nephrons?
- Filtration
- Reabsorption
- Secretion
What is the renal capsule?
The thin outer membrane
Roughly how many nephrons does each kidney have?
One million
What is the name of the network of blood vessels which surround the renal tubule?
Peritubular capillaries
What are the main components of the nephron?
- The renal corpuscle (glomerulus and Bowman’s capsule)
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
- Peritubular capillaries
What does “afferent” mean?
“Carrying blood to”
What does “efferent” mean?
Carrying blood away from
In which part of the kidney does filtration occur?
The glomerulus
What is the ‘formula’ for urinary excretion?
Excretion =
filtration - reabsorption + secretion
What is the renal corpuscle and what does it do?
- The part of the nephron that consists of the glomerulus and surrounding Bowman’s capsule
- It is where filtration occurs
What are the main features of epithelial cells?
- They line the surface of skin, glands and cavities of the body
- Epithelium can be formed be one or many layers of epithelial cells
What is the endothelium composed of?
One layer of cells
What is the most abundant protein in the blood?
Albumin
What are the two main structures which comprise the renal corpuscle?
- Glomerular capillaries
* Bowman’s capsule
Where is glomerular filtrate formed?
The Bowman’s capsule
Where does the unfiltered blood from the glomerular capillaries flow to?
The efferent arteriole
What often causes renal dysfunction?
Inappropriate or insufficient filtration
What is the average capillary pressure in the nephron?
55 mmHg
What is the hydrostatic pressure in the Bowman’s space?
Approximately 15 mmHg
What is the oncotic pressure?
Approximately 30 mmHg
What is the effect of hyper albuminaemia?
Capillary oncotic pressure increases, which reduces glomerular filtration rates
Does glomerular blood pressure accelerate or oppose filtration?
Accelerate
Does hydrostatic pressure in the Bowman’s capsule accelerate or oppose filtration?
Oppose
Does oncotic pressure accelerate or oppose filtration?
Oppose
What does the renal corpuscle filter?
Water and small solutes
What is endothelial fenestration?
Pores in endothelial cells
How is the glomerular filtration rate calculated?
GFR = filtered plasma volume / time
What is the glomerular filtration rate in an average, healthy person?
Around 125ml per minute
What is meant by the term ‘filtered load’?
The total amount of any substance filtered through the glomerulus per unit time
Which is the part of the kidney involved in filtration?
The glomerulus
What is proteinuria?
High levels of protein in the urine
What is haematuria?
The presence of red blood cells in urine
What are the characteristics of nephrotic syndrome?
- Severe proteinuria
- Hypoalbuminaemia
- Oedema
What are the characteristics of nephritic syndrome?
- Haematuria
* Reduced urine production (oliguria)
What is oliguria?
Reduced excretion of urine
Where are most of the substances filtered by the glomerulus reabsorbed to?
The peritubular capillaries
What are the substances found in glomerular filtrate?
- Water
- Nutrients
- Ions
- Waste substances
What are the peritubular capillaries?
A network of small blood vessels which surround the renal tubule
What are ‘active processes’?
Body processes which require the use of cellular energy (ATP) due to substances being moved against their concentration gradient
What are ‘passive processes’?
Processes which do not require the use of energy as the substances are moved with the concentration gradient (ie from areas of high concentration to areas of low concentration)
Name three passive transport processes
- Osmosis
- Simple diffusion
- Facilitated diffusion
Name two active transport processes
- Active transport
* Facilitated diffusion
What is osmosis?
The diffusion of water molecules down their concentration gradient, across a semi-permeable membrane
What does the glomerulus do?
Filters your blood
What does a renal corpuscle consist of?
- A Bowman’s Capsule
* A glomerulus
What are the two routes through which water and solutes can be absorbed?
- Paracellular
* Transcellular
In the kidneys, where does sodium begin and end reabsorption?
- Begin - proximal convoluted tubule
* End - distal convoluted tubule
What type/s of transport are involved in the reabsorption of sodium in the kidneys?
- Facilitated diffusion
- Primary active transport
- Secondary active transport
What is glycosuria and when does it commonly happen?
The pathological presence of glucose in the urine
Frequently found in people with severe diabetes
What is the main waste product in plasma?
Urea
What is creatinine a waste product of?
Skeletal muscle metabolism
What is urea?
A nitrogen-containing molecule formed during the catabolism of amino acids
What is the Loop of Henle?
A u-shaped structure within the nephrons which controls water reabsorption
In the Loop of Henle, which direction does urine flow?
Opposite to the direction of blood flow
The relationship between which two things enables the nephrons to regulate water reabsorption from the Loop of Henle?
- Osmotic pressure
* Selective permeability
What are the main ions secreted in urine?
- Hydrogen
* Potassium
What is the process which enables potassium and hydrogen ions to be secreted in urine?
Active cotransport coupled to sodium reabsorption
What is the main similarity and the main difference between active transport and facilitated diffusion?
- Both are mediated by protein channels
- Facilitated diffusion is passive
- Active transport requires the use of cellular energy
Name at least three of the components of urine
- Water
- Urea
- Uric acid
- Creatinine
- Ammonia
- Sodium
- Potassium
- Chlorides
- Phosphates
- Sulfates
- Oxalates
- Some drugs
- Toxins
What type of muscle is involved in control of the internal urethral sphincter?
Smooth muscle
What type of muscle is involved in control of the external urethral sphincter?
Skeletal muscle
How is renal function measured?
By calculating the glomerular filtration rate
What is the formula for calculating the glomerular filtration rate?
GFR = filtered plasma volume / time
What does the term ‘renal clearance’ mean?
The volume of plasma from which a substance is completely removed by the kidneys per unit of time
Which substance in the body is not reabsorbed by the kidneys, and secreted in only very small amounts, and can therefore be used to measure glomerular filtration rates?
Creatinine
What is creatinine the breakdown product of?
Creatine
What is phosphocreatine?
One way muscle cells store ATP reserves
What is phosphocreatine converted to?
Creatinine (plus ATP)
What two factors affect creatinine concentration in the blood?
- Production by muscles
* Elimination by kidneys
What factors can affect blood creatinine levels?
- Gender
- Age
- Ethnicity
- Level of muscle mass
What is the formula used to calculate creatinine clearance, in order to then estimate GFR?
clearance of creatinine / ml min-1 =
amount of creatinine excreted / mg min-1 —————————————— plasma concentration of creatinine / mg ml-1
Name at least three essential functions of water in the body.
Metabolic reactions
Transport of nutrients
Controlling the body’s temperature
Eliminating metabolic wastes
On average, how much water would a 70kg person have in their body?
42 litres
Where in the body is most of the water contained?
In the cells
On average, over 24hrs, how much water is lost via the skin and lungs?
About 900ml
Through which mechanisms or body parts do we lost most of our water each day?
Skin Lungs Sweat In faeces Urine
In total, roughly how much water do we lose per day?
About 2550ml
Does dehydration affect just intracellular fluids, just extracellular fluids, or both?
Both
What is meant by the term ‘osmolarity’?
The concentration of a solution expressed as the total number of solute particles per litre
Over what percentage of body water loss will be fatal?
15-20%
How is osmolarity measured?
Either osmoles per litre or osmoles per kilogram
What is one-thousandth of an osmole called?
A milli-osmole
What are the two receptors the body has for detecting changes in water content?
- Osmoreceptors
* Vascular stretch receptors
What are the two types of vascular stretch receptor?
Bonus: where are they found / under what conditions do they activate?
- Volume receptors - found in walls of large veins and atria. Activate when there are small changes in blood volume.
- Arterial pressure receptors - Activate when there is severe blood volume loss
What is antidiuretic hormone also known as?
When is it released, and from which part of the brain?
- Vasopressin
* If osmoreceptors detect low water levels. From the hypothalamus.
What is the purpose of ADH/vasopressin?
To increase reabsorption of water
What are aquaporins? What do they do?
- A class of membrane protein
* They activate water-permeable channels in the cell membrane
Dehydration triggers what responses?
- Behavioural - thirst
* Renal - reduced water excretion
What is meant by oncotic pressure?
The pressure exerted by plasma proteins on the capillary wall
What are some of the mechanisms for ensuring adequate water balance in the body?
- Thirst, stimulating an increased intake of water
ADH - Increasing oncotic pressure reduces GFR, which reduces water excretion
What are the nephron’s functions?
- Filtration
- Secretion
- Reabsorption
How does blood pressure in the capillaries affect the GFR?
Higher pressure = higher GFR
What is meant by the term ‘myogenic’?
Originating in muscle tissue (as opposed to originating in nerve impulses)
What is the most abundant ion dissolved in plasma?
Sodium
What happens if we ingest too much sodium?
There will be an increase in plasma osmolarity which in turn will cause water retention. The increase of blood volume will ultimately increase systemic blood pressure.
What is the juxtaglomerular apparatus?
A structure in the kidney which regulates the function of each nephron
What is the macula densa?
An area of closely-packed cells which can either change resistance to blood flow in the afferent arterioles or increase renin release from the juxtaglomerular cells
What are juxtaglomerular cells?
Cells which synthesise, store and release renin
What is renin?
An enzyme which causes vasoconstriction and increases the GFR
What are extraglomerular mesangial cells?
Multi-funcitonal cells which contribute to the regulation of systemic blood pressure through the renin-angiotensin system
What is the renin-angiotensin system?
A hormone system which regulates blood pressure and fluid and electrolyte balance
What are paracrine factors?
Hormone-like signalling substances that act locally on cells within the tissue they are released into
What is the polypeptide precursor molecule which angiotensin I is cleaved from? Where is that precursor produced?
- Angiotensinogen
* The liver
Where is Angiotensin-Converting Enzyme (ACE) located?
In the inner (luminal) surface of capillary endothelial cells, especially those in the lungs
What are the two homeostatic roles of the renin-angiotensin system (RAS)?
- Counteracting a drop in blood pressure
* Counteracting an excessive reduction of the GFR
How do ACE inhibitors work?
- By blocking the conversion of angiotensin I to angiotensin II, which reduces levels of angiotensin II in the blood.
- This causes less vasoconstriction, which reduces blood pressure
What are the two macula-independent ways renin production can be stimulated?
- Nervous stimulation (noradrenalin stimulates beta-1 adrenergic receptors in juxtaglomerular cells, which increases renin production and so activates the RAS system)
- Juxtaglomerular cells are able to detect changes in blood pressure and secrete more renin
What is aldosterone?
A steroid hormone which increases sodium reabsorption from the collecting ducts
What happens if plasma sodium levels are too high?
Atrial natriuretic factor inhibits sodium reabsorption and increases GFR
What are the two mechanisms by which kidneys are able to regulate blood pH?
Hydrogen ion secretion and bicarbonate reabsorption
Production of bicarbonate via tubular metabolism
What effect does vomiting have on blood pH and why?
Increases it due to the loss of hydrogen ions from the stomach
What is the pH range within which the kidneys produce urine?
6.5 - 8
Which part of the kidney filters bicarbonate?
About what percentage of filtered bicarbonate is reabsorbed?
- The glomerulus
* About 80%
What happens to the pH of blood when bicarbonate is reabsorbed?
It increases
What is tubular metabolism?
The metabolic reactions which occur in renal tubule cells
Roughly how much fixed acid do the kidneys eliminate per day?
About 70-100 mol
What are “fixed acids”?
Give an example of one
Acids produced in the body as a result of digestion, metabolism or other physiological processes.
Lactic acid (from anaerobic glucose metabolism) Acetoacetic acid (from fat metabolism)
Can fixed acids be excreted via the respiratory system?
No
What is alkalosis?
Name some of the symptoms
- A condition which occurs if blood pH rises above 7.45
* Confusion, nausea, muscle twitching
What is acidosis?
Name some of the symptoms
- When arterial blood pH is lower than 7.35
* Confusion, headaches, fatigue, increased heart rate
What are the three hormones which modify the function of specific renal cells but which are not produced by the kidneys?
- ADH
- Angiotensin II
- Aldosterone
What type of renal cell does the hormone ADH target, and what homeostatic system does it affect?
- Tubular cells
* Water balance
What type of renal cell does the hormone Angiotensin II target, and what homeostatic system does it affect?
- Efferent arteriolar
* Blood pressure
What type of renal cell does the hormone Aldosterone target, and what homeostatic system does it affect?
- Tubular cells
* Sodium balance
What is erythropoietin?
A peptide hormone, produced by the kidneys, which stimulates red blood cell production in the bone marrow
Give two sets of circumstances in which erythropoietin (produced by the kidneys to facilitate red blood cell production) may be used.
- To treat certain types of anaemia
* By athletes, trying to enhance their performance capabilities
As well as blood detoxification, what other purposes are kidneys necessary for?
- Maintenance of water and salt pH homeostasis
- Control of blood pressure
- Regulation of hormones which control the functions of other body systems
What are the two hormones the kidneys are involved in the production and secretion of?
- ADH (antidiuretic hormone, a peptide hormone secreted in the hypothalamus)
- Vitamin D
Where is renin secreted?
The Juxtaglomerular Apparatus
Which part of the kidney is responsible for the reabsorption of amino acids?
The proximal convoluted tubule
What is the Loop of Henle’s function?
The reabsorption of water by osmosis
What occurs in the collecting ducts in the kidney?
Aldosterone-dependent sodium reabsorption
