Urinary System Flashcards
What are the dimensions of the average adult kidney?
Depth - 3cm
Length - 11cm
Width - 6cm
Weight - 150g
Describe the anatomy of the kidney
- Renal tubule lined with epithelial cells
- PCT has dense microvilli to increase SA
- Macula densa cells are chemoreceptors
- Glomerulus lines with endothelium which is adapted with fenestrations to make it porous
What are the 7 functions of the kidneys?
- Water regulation
- Maintains BP
- Gets rid of waste products
- Activates vit. D (helps body absorb Ca)
- Acid-base balance
- Maintains electrolyte balance, critical for heart rhythm
- Releases erythropoietin which causes bone marrow to make RBC
What is one of the causes of high BP?
High water levels in blood
How much of the cardiac output goes through the kidneys?
25% (1200ml)
Show the flow of blood through the renal blood vessels
- Aorta
- Renal artery
- Segmental artery
- Interlobar artery
- Arcuate artery
- Cortical radiate artery
- Afferent glomerular arteriole
- Glomerulus
- Efferent glomerular arteriole
- Peritubular capillaries and vasa recta
- Cortical radiate vein
- Arcuate vein
- Interlobar vein
- Renal vein
- Inferior vena cava
What are the nephron-associated blood vessels
- 2 capillary beds of nephron = glomerulus and peritubular/ vasa recta
- Renal plexus - provides nerve supply to kidneys and ureter
- Sympathetic vasomotor fibres - regulate blood flow by adjusting diameter of the renal arterioles
What are the functions of the glomerulus and vasa recta?
Glomerulus = filtration
Vasa recta = selective reabsorption
Describe the juxtaglomerular apparatus
- Found at the distal end of the ascending limb of the loop of Henle, lying against the afferent arteriole
- Regulates filtration and maintains systemic BP
What is glomerular filtration?
Movement of water and solutes from an area of high pressure to an area of low pressure
(Forced through capillary walls and pores of glomerulus into Bowman’s capsule)
Describe the process of glomerular filtration
- High BP in the glomerulus forces water and solutes across the filtration membrane
- Filtrate consists of water and small molecules
- Large molecules and blood cells do NOT enter the Bowman’s capsule
- The kidneys filter the body’s entire plasma volume 60 times each day
What is the filtration membrane?
Pores of glomerulus and walls of Bowman’s capsule
Name 5 small molecules in filtrate
- Glucose
- Vitamins
- Amino acids
- Waste substances
- Electrolytes
What is glomerular filtration rate?
The amount of filtrate formed by both kidneys each minute
Volume formed in adult kidneys = 120-125ml/min
What is GFR determined by?
- SA
- Filtration membrane permeability
- Net filtration pressure
What are the 2 mechanisms that control GFR?
- Intrinsic control
2. Extrinsic control
Describe intrinsic control
- Autoregulation
- Macula densa cells control degree of arteriole constriction by responding to Na levels and releasing a vasoconstricting chemical that acts on the afferent arteriole
- This system maintains a constant GFR over an arterial pressure range of 80-180mmHg
Describe extrinsic control
Norepinephrine released by sympathetic NS
Epinephrine released by adrenal medulla
This causes:
- Afferent arteriole constriction
- Inhibits filtration
- Release of renin which participates in the RAAS
What is the RAAS?
Renin Angiotensin Aldosterone System
Describe the effect of BP on arterioles
High BP = constriction of afferent arterioles and dilation of efferent arterioles
Low BP = dilation of afferent arterioles and constriction of efferent arterioles
Describe the RBC through the kidneys
- Flow through renal artery to afferent arteriole
- In glomerulus, they stay within blood and exit via efferent arteriole
- Squeeze through peritubular capillaries
- Travel through vasa recta where absorbed substances from nephron flow in via osmosis and active transport
- Peritubular capillaries in venules meet and reach renal veins where they exit kidney and flow back to heart
How much of the body does water make up?
Infant - 70%
Child - 65%
Adult - 60%
What are the 6 main functions of water?
- Universal solvent
- Transport and exchange
- Reactant
- Thermoregulation
- Lubricant
- Protection
What is the rate of water transport affected by?
- Conc. gradient
- Permeability
- SA
- Thickness of surface
- Size of particles
What is Fick’s Law?
Rate of diffusion = (SA x difference in conc.) divided by thickness of surface
Describe one possible journey of water through the kidneys
- Water is forced out of the glomerulus into the Bowman’s capsule
- 80% of water in filtrate is reabsorbed in the PCT by osmosis back into the blood
Describe the second possible journey of water through the kidneys
- Water continues down the loop of Henle
- ADH will affect reabsorption of water in the collecting duct
- Water is either reabsorbed or remains in the filtrate to exit the body in the urine
Describe the journey of urea through the kidneys
- Urea is forced out of the glomerulus into the Bowman’s capsule
- It easily passes through the nephron to the collecting duct with minimal reabsorption and exits the body in the urine
- Some urea is absorbed by diffusion until the concentrations of urea in the filtrate and blood are equal
What is urea?
A small nitrogenous waste product of metabolism
What are electrolytes?
- Salts, acids, bases and some proteins
- Solutes can be +ve (cations) or -ve (anions)
Name 5 common electrolytes and their functions
- Sodium (acts on water)
- Potassium (acts on nerves, heart and muscles)
- Calcium (acts on nerves, heart and blood clotting)
- Chloride (acts on osmotic pressure and acid-base balance)
- Phosphate (inverse relationship with calcium)
Define active transport
Movement of molecules from an area of low concentration to an area of high concentration
Describe the journey of sodium through the kidneys
- Sodium is forced through the glomerulus into the Bowman’s capsule
- 65% of sodium in filtrate is reabsorbed in proximal convoluted tubule into interstitial fluid
- Sodium diffuses from interstitial fluid into capillaries that run in opposite direction to filtrate (counter-current mechanism)
Describe the counter-current mechanism
Ascending Limb:
- Sodium is pumped out into interstitial fluid
- WP of filtrate increases, WP of interstitial fluid decreases
- Ascending limb impermeable to water
- Sodium diffuses into descending limb
Descending limb:
- Water diffuses out into interstitial fluid (which has low WP due to sodium)
- WP of filtrate in descending limb decreases
Describe the journey of aldosterone through the kidneys
- Aldosterone released by adrenal cortex as a result of the activation of the RAAS which causes reabsorption of salt at DCT/collecting duct
- This system is activated when the body experiences decrease in blood flow to kidneys so more sodium is needed in the blood to reabsorb water
- Once body is rehydrated, blood vol. increases, renin and aldosterone levels decrease
What are acid levels (H+) regulated by?
- Chemical buffers (H+ binds to buffer to prevent alteration of pH)
- Respiratory centres (eliminates H+ via carbon dioxide and water)
- Renal mechanisms (reabsorbs/ regenerates HCO3- and excretes H+ or excretes HCO3- and reabsorbs H+)
Give 3 examples of chemical buffers
- Bicarbonate
- Phosphate
- Protein
Describe the journey of hydrogen through the kidneys
- In the blood, hydrogen joins with a base and is not filtered in the glomerulus as it is too big
- The H2CO3 then breaks down due to H20 –> OH- + H+ and hydrogen ions are secreted into filtrate in exchange for sodium at the DCT
- Hydrogen ions then combine with ammonia to be secreted in urine
What is osmolarity?
The concentration of particles in a solution
Greater conc. = Greater osmotic pressure = Smaller water potential
Name the 3 types of solution based on osmolarity
High osmolarity (Low water potential) = Hypotonic Equal osmolarity (Equal water potential) = Isotonic Low osmolarity (High water potential) = Hypertonic
What is the counter-current multiplier?
Filtrate through the loop of Henle (positive feedback)
What is the counter-current exchanger?
Blood through the vasa recta
How is ADH released?
- Osmolarity of blood detected by osmoreceptors in hypothalamus
- Hypothalamus stimulates posterior pituitary gland to release ADH
Describe the process when blood has low osmolarity (high water potential)
- More ADH released
- Increased permeability of collecting duct (more aquaporins)
- More water reabsorbed
- Small volume of concentrated urine
Describe the process when blood has high osmolarity (low water potential)
- Less ADH released
- Decreased permeability of collecting duct (less aquaporins)
- Less water reabsorbed
- Large volume of dilute urine
Describe the journey of urine through the kidneys
- Peristaltic waves help convey urine to bladder for storage
- Strength and frequency of peristaltic waves adjusted according to volume of urine being produced
- Urine moves out of bladder via peristalsis and gravity
Give 3 physical characteristics of urine
- Clear and pale to deep yellow
- Ammonia odour
- pH of 6 (4.5-8.0)
What is the average length and capacity of the bladder?
Length = 12cm Capacity = 500ml
Describe the bladder
- Wall has 3 layers
- Trigone = triangular region of the bladder outlined by 3 openings
- Prostate gland is found between internal and external urethral sphincters in males
- Muscular layer of bladder = detrusor
- Folds found in empty, collapsed bladder = rugae
What is micturition?
A reflex related to urination with 2 phases:
- Storage (guarding) phase (storing urine)
- Voiding phase (releasing urine)
Describe the RAAS
- Drop in blood pressure and/or fluid volume
- Renin released from kidneys
- Renin acts on angiotensinogen to form angiotensin I
- Angiotensin-converting enzyme acts on angiotensin I to form angiotensin II
Describe the effect of angiotensin II
- Stimulates vasoconstriction of blood vessels
- Stimulates the adrenal gland to release aldosterone which stimulates reabsorption of sodium and water in the kidneys
Where are macula densa cells found?
In the juxtaglomerular apparatus
Where is the ureter located?
Run from the renal pelvis, behind the peritoneum and through the posterior wall of the bladder which prevents backflow
Where is angiotensin released from?
Liver
Where is the angiotensin-converting enzyme released from?
Lungs
