W23 Urinary system (Renal) Flashcards
What does the urinary system consist of? (4)
Kidneys- renal pelvis (into which urine is drained). It is a pressure filter prdoucing urine from blood
Ureters- transport urine to the urinary bladder
Bladder- stores urine until convenient to void
Urethra- tube between the bladder and external environment. Transports urine outside of the body.
What are the main functions of the kidneys? (3)
Filtration (blood)
Reabsorption (selection)
Homeostasis
What are the substances filtered and reabsorbed by the kidneys? (6)
- Water Glomerular filtrate (180-200 l/day approx)
- Sodium Chloride (nearly all Na+ and Cl- is reabsorbed to maintain internal O.P)
- Glucose (Reabsorbed as long as plasma glucose < 200mg/100ml)
- Hydrogen ions (Normal diet generates H+ ions and kidney eliminates them)
- Urea ( End product of protein metabolism, 2/3 of that filtered is passed out in urine, the remainder is reabsorbed)
- Toxic substances ( Body metabolites drugs and drug metabolites, some of these may be actively secreted (removed)
Kidney Facts and Figures
Kidneys are ? % of body weight
How many nephrons in kidney? How long are they in length and diameter?How much plasma does the kidney process in a day?
- Kidneys are < 1% of body weight
* Yet receive about 25% of Cardiac Output
* ¼ of all ‘work’ performed by the heart is to perfuse kidneys - Functional unit is the nephron
* Approx 2.5 million
* Each approx 5 cm in length about 50 μm in diameter
* Approx 125 km tubing (not including blood vessels) - Processes 180 L plasma/day
* Only about 1.5 drops per nephron
* Of which ~ 1% ends up as urine
* About 600g of sodium reabsorbed per day
What is contained in urine? (5)
Relatively high concentrations of:
- Urea
- Uric acid
- Creatinine
- K+
- Other toxic substances
- Rest is reabsorbed
What does the gross structure of a kidney contain?
Renal cortex, renal medulla, Renal pelvis, Renal pyramid, Ureter
What is Hematuria?
What is this a sign of?
Red blood cells in urine (not normal)
Sign of damage (to barrier)
Maybe from outside or inside kidney
Outside
-Kidney stones, tumours (renal pelvis, ureter, urinary bladder, prostate, urethra)
-UTI (inflammation of urinary bladder, urethra, prostate)
-May also get WBC in urine
Inside
-Inflammation of glomeruli (eg glomeruli nephritis) – affects filtration
-Infarct – necrosis of kidney
What is the nephron?
What are the features of the nephron?
What are the 2 components?
The functional unit of the kidney (renal corpuscle and tubule)
* Each nephron has two components
* Vascular (blood)
* Tubular (filtered fluid)
Some of the nephron is in renal cortex
* outer region
* granular
Some of the nephron is in renal medulla
*inner region,
* made up of triangles (renal pyramids)
What makes up the vascular component of the nephron?
Blood travels to the Interlobular artery- afferent arteriole (aa)
Splits the glomerulus (g)
- A ball of capillaries
- Responsible for filtration
Rejoin- Efferent arteriole (ea)
- In other beds (a venule)
Splits- peritubular capillaries
- A secondary capillary bed!
- Supply renal tissue with blood
- Receives compounds reabsorbed by tubule
- Source of compounds secreted by tubule
The Nephron: Tubular component
What are they composed of?
What are the 5 components?
The Nephron: Tubular component
Composed of epithelial cells
1. Bowman’s capsule (BC)
* encloses glomerulus in cortex
* where filtration occurs
2. Proximal Convoluted Tubule (PCT)
* in cortex
* responsible for most reabsorption/secretion
3. Loop of Henle (LH)
* cortex/medulla
* responsible for osmotic gradient in medulla
4. Distal Convoluted Tubule (DCT)
* in cortex
* ‘fine-tuning’ of solute/water reabsorption
5. Collecting Tubules/Ducts (CD)
* in cortex/medulla
* “fine-tuning’ of urine concentration
What is the function of the Afferent arteriole?
Takes blood to the glomerulus
Takes blood to the glomerulus
What is Proteinuria?
Is this healthy?
Protein in urine
-Why?
CHARGE, SIZE
-Albumin slightly < 7nm (urine minute amounts)
-Some protein hormones are smaller but actively reabsorbed
V little protein found in the urine of healthy people
Question
- Haemoglobin smaller than albumin
- V little passes from the blood to filtrate – v little found infiltrate?
- Why?
What are Podocytes?
Highly specialised cells of the kidney glomerulus that help form a filtration barrier (with endothelial cells)
Podocytes are found in epithelium of BC and surround capillaries (filtration)
What are the different ways of ‘Fine-tuning’ urine osmolarity? (DCT and CD)
Hormonal mechanisms:
- Renin-angiotensin-aldosterone (RAAS) mechanisms
- Antidiuretic hormone (ADH) mechanism
- Atrial natriuretic peptide (ANP) mechanisms
- RAAS and ANP: more sensitive to changes in BP
- ADH: more sensitive to blood concentration
Low Blood Pressure
Angiotensin (RAAS)
Macula Densa cells sense low Na in filtrate in dct
JG cells also detect reduced stretch in
afferent arteriole
Renin release from kidney (from JGC)
Converts angiotensinogen (found in plasma) into angiotensin I
ACE (pulmonary capillaries) converts
angiotensin I into angiotensin II
Angiotensin II: vasoconstrictor
Increases TPR
Stimulates release of aldosterone (and thirst)
Low BP: Aldosterone
Steroid hormone / Released from adrenal cortex
Travels to DCT and CD
Bind to receptors
Stimulates Na+ reabsorption from CD into capillaries
Cl- co-transported
Water follows
Increases Blood Volume
Increases BP
ADH effect on dct and collecting duct
Anti-Diuretic Hormone (ADH)
Released from posterior pituitary
Release sensitive to…
Osmoreceptors (hypothalamus) –
sense when body fluids become concentrated
Volume stretch receptors (right atrium) (decrease)
High osmolarity or low blood pressure cause
vasopressin (ADH) release
ADH release:
Increases permeability of dct and collecting ducts to
water
Increases reabsorption in collecting ducts
Small volume concentrated urine
What is the function of Atrial Natriuretic Peptide?
Where is it released from and when?
Opposite effect (of ADH): Na+ excretion increased!
- ANP released from right atrium when blood volume increases
- Leads to increased loss/excretion of Na+
- Decreases Na+ reabsorption
- Na + remains in tubules
- Water moves towards Na +
- Increases Urine volume while reducing blood volume and BP
- Can inhibit ADH
Urine analysis:
- Would you expect cells in the urine?
- Would you expect proteins in the urine?
- Would you expect glucose in the urine?
No
Yes
No- sign of diabetes
Somatic vs Autonomic:
Voluntary or Involuntary?
Somatic- voluntary
Autonomic- Involuntary (fight or flight)
- Consists of sympathetic and parasympathetic
What are the Features and Functions of Ureters?
- Tubes that carry urine FROM each kidney TO the bladder
- Surrounded by smooth muscle which contracts
- Urine passed down ureters by peristalsis.
- 25–30 cm long & ~3-4 mm in diameter
- Pass urine by peristaltic waves (smooth muscle)
- Enter the back of the bladder
- Urine backflow - prevented by ureterovesical valves
Structure of the bladder:
What is the muscular wall made of?
- Hollow smooth muscle organ
- Bladder can be divided into two parts:
1) Body (lying above ureteral orifices)
2) Base (Consisting of trigone and bladder neck - Its muscular wall is formed of smooth muscle cells (detrusor)
- The only involuntary organ in the body under voluntary control
- All humans are incontinent at birth
- Activation of numerous neurologic reflexes are learned in early life to control the bladder
- 35+ reflexes coordinate activities of bladder smooth muscle, plus striated & smooth muscle of the urethra
Bladder filling and voiding
The filling and voiding cycle is complex and requires coordination between contractile motions of the bladder and reciprocal motions of the bladder neck.
Filling:
The detrusor is relaxed
The bladder neck is closed
Voiding
The detrusor contracts
The bladder neck opens
What occurs during the micturition reflex?
( 2 phases)
Activated when the urinary bladder
stretched= Results in micturition
Storage phase- As the bladder fills, the pressure stays low (due to highly elastic nature)
1. Voluntary signals relax the external sphincter (somatic)
2. Autonomic contraction of detrusor muscle
What are the muscarinic receptors which are part of the parasympathetic system and affect the bladder
- M2
- Cardiac
- Acts via G protein
- Inhibits Ca2+ channels & efflux K - M3
- Glandular smooth muscle
- Acts via Gq
Micturition reflex
- Activated by stretch of urinary bladder
(trigone) - Eventually Action potentials travel along
sensory nerves in pelvic nerve to sacral
region of spinal cord - Integrated at spine - AP travel Along
parasympathetic nerve to urinary
bladder
– Bladder contracts - External sphincter normally contracted
as result of somatic motor nervous
system
– Decreased AP cause Urethral sphincter to
relax - Can also be activated by irritation from
bacterial infections – in urinary bladder
– Desire to void
– Occurs when bacteria pass up along urethra
and enter and multiply within the bladder,
causing inflammation
– Usually caused by bacteria from the GI tract,
eg E.coli
– WBC and RBC in urine
What is micturition?
The voiding of urine.
Kidney facts and figures (info only)
- Kidneys are < 1% of body weight
* Yet receive about 25% of Cardiac Output
* ¼ of all ‘work’ performed by heart is to perfuse kidneys - Functional unit is the nephron
* Approx 2.5 million
* Each approx 5 cm in length about 50 μm in diameter
* Approx 125 km tubing (not including blood vessels) - Processes 180 L plasma/day
* Only about 1.5 drops per nephron
* Of which ~ 1% ends up as urine
* About 600g of sodium reabsorbed per day
What is the main function of the kidneys?
What is the name of the ball of capillaries?
What is the name of the tubular structure that surrounds this^?
Homeostasis (filtration)
Glomerulus
Bowman’s capsule
What are the names of the arterioles that take blood to and from the glomerulus?
Afferent and Efferent arterioles
What are the different components of the nephron called?
PCT, Loop of Henle, DCT, Collecting duct, Renal corpuscle?
Albumin passes into the filtrate but with Haemoglobin, but very little passes from blood to filtrate, why?
Size and Charge barrier
Haemoglobin is comprised of large proteins. It is bound to RBCs which are too large to pass through the glomerular filtration barrier.
Where is renin secreted from?
What stimuli results in the secretion of renin?
JG/ Juxtaglomerular cells
Hypotension/Low BP
What effect does the RAAS system have on Na+ (eventually)?
Reabsorption
What are the 2 branches of autonomic NS called?
Sympathetic and Parasympathetic
How many neurones are there in series?
What neurotransmitter does the first neurone of both branches secrete?
2
Acetycholine
What neurotransmitter does the second in the sympathetic NS secrete on effector organ?
Noradrenaline
Calculating how much the kidney excretes (of a compound) :
Exreted= Filtered + Secreted- Reabsorbed
Polycystic kidney disease
Fluid-filled cysts
Nephrons destroyed
Reduced renal function
= loss of functional renal mass
-Less filtration, retention of salt and water, expanded blood volume, increased BP
Renal failure leads to:
- Accumulation of the substances normally eliminated
What is GFR?
Total amount of filtrate formed per minute by the kidneys
What are the 3 layers of the filtering membrane?
- Endothelial layer (flat cells-fenestrated cytoplasm)
- Basement membrane
- Epithelial layer
Which of the following factors affect GFR?
A. Changes in Renal Blood Flow
B. Changes in glomerular filtration SA
C. Inc glucose in plasma
D. Large decrease in systolic BP (as in haemorrhage)
E. Obstruction of ureters
All except C
Renal tubules of the nephrons absorb and secrete electrolytes to maintain the body’s internal environment : Which are re -absorbed by renal tubules?
Ammonia
Chloride
Drugs/toxins
H ions
Nutrients
Potassium
Sodium
Water
Chloride, Nutrients, Nutrients, Sodium, water
Renal tubules of the nephrons absorb and secrete electrolytes to maintain the body’s internal environment : Which are secreted ?
Ammonia
Chloride
Drugs/toxins
H ions
Nutrients
Potassium
Sodium
Water
Ammonia, Drugs/toxins, H ions, Potassium
Where does most reabsorption take place? (of ions)
PCT
Which molecule is most important in the reabsorption of water
Sodium
Sodium and water retention can lead to
Hypertension
What causes the anemia that is often seen in chronic renal disease?
Lack of iron
Lack of EPOI
Lack of Vitamin B12
Anaemia- Impaired cell metabolism and feelings of coldness
Lack of EPO
Dec blood oxygen
Kidneys release EPO into the general circulation
Stimulates red blood cell production in the red bone marrow
Inc blood oxygen levels
