State the functions of the kidney.
- Homeostatic regulation of water and ion content of blood; regulation of osmolarity - maintenance of ion balance, regulation of extracellular fluid volume - blood pressure, regulation of pH
- Excretion of metabolic waste products e.g. urea, creatinine
- Production of hormones; renin - sodium balance, activation of vitamin D - Ca2+ balance and bone, prostaglandins and kinins - renal blood flow
Describe the structure of the kidney.
- Interior contains two layers; an outer cortex and an inner medulla
- Layers formed by the organised arrangement of tubules called nephrons
What is the nephron?
It’s the functional unit of the kidney.
Describe the structure and function of the nephron.
- Bowman’s capsule contains a network of capillaries called the glomerulus; where plasma fluid is ultra-filtrated
- Fluid then flows into the proximal tubule then into the loop of Henle
- Then into the medulla (descending limb) and then back up (ascending limb)
- The fluid then passes into the distal tubule
- Distal tubules drain into the collecting duct which pass from the cortex into the medulla
- Collection ducts drain into the renal pelvis
- Urine flows in the ureter on its way to excretion
Describe the vascular supplies to the nephron.
- Blood flows from the afferent arteriole into the glomerulus and leaves into an efferent arteriole and a second set of capillaries known as peritubular capillaries that surround the tubule
- Renal capillaries join to form venules, conducting blood out of the kidney
What is the function of the renal portal system?
- To filter fluid out of the blood and into the lumen of the nephron at the glomerulus
- Fluids are then reabsorbed from the tubule back into the blood at the peritubular capillaries
State the 4 processes of the nephron.
- Filtration
- Reabsorption
- Secretion
- Excretion
Describe filtration.
The movement of fluid from blood into the lumen of the nephron - takes place in the Bowman’s capsule
Describe reabsorption.
The movement of the filtrate from the lumen of the tubule back into the blood, through the peritubular capillaries.
Describe secretion.
Removes selected molecules from the blood and adds them to the filtrate in the tubule lumen
Describe excretion.
Anything filtered from the glomerulus is destined for excretion, unless it is reabsorbed.
What does amount of excretion equal?
amount filtered - amount reabsorbed + amount secreted
How to calculate filtration fraction?
Glomerular filtration rate/plasma flow rate
What is meant by clearance as a marker of kidney functionality?
A volume of plasma from which a substance has been removed and excreted into urine per unit time.
How can we calculate clearance?
Urine concentration x Urine flow rate / plasma concentration
What are the three filtration barriers involved in glomerular filtration?
- Capillary endothelium
- Basal lamina
- Podocytes
Describe the capillary endothelium.
- Has pores
- Pores are small enough to prevent blood cells from leaving the capillary
- On the surface are negatively charged proteins which will repulse negatively charged plasma proteins
Describe the basal lamina.
- A layer of extracellular matrix that separate the capillary endothelium from the epithelium of Bowman’s capsule
- Layer is negatively charged - excluding most plasma proteins from filtration
Describe podocytes.
- Present in Bowman’s capsule with long cytoplasmic extension called foot processes that interdigitate the basal membrane leaving narrow filtration slits.
- Proteins will be excluded from filtration according to charge and molecular weight
State the four structures involved in reabsorption.
- Proximal tubule
- Loop of Henle
- Distal tubule
- Collecting tubule
Describe the mechanism of glucose and amino acid reabsorption at proximal tubule.
- Recovery of glucose/ AA dependant on Na+/K+ pump
- Basolateral membrane
- Maintains inwardly directed electrochemical gradient for Na+
- Na+ coupled transport systems in luminal membrane enable recovery of glucose and amino acids
- ~65% of filtered Na+ is recovered from tubular fluid
- Creates osmotic gradient and allows recovery of ~65% of water
Summarise the substances reabsorbed and secreted in the proximal convoluted tubule.
Reabsorption: ~65% Na+, H2O, K+, Cl-
~100% Glucose, amino acids
~50% urea, urate
~80% HCO3
Secretion of organic anions and cations (H+) (K+)
Describe important features of the DESCENDING LIMB of the loop of Henle and why this is important in reabsorption.
- The epithelium is water permeable but impermeable to NaCl
- No active transport
The means osmolarity will increase as the descending limb progress, reaching a maximum at the loop
Describe the ascending limb of the loop of Henle.
- Water impermeable
- Thin ascending limb reabsorbs NaCl passively
- Thick ascending limb moves Na+, K+ and Cl- out of tubule fluid
- Active transport powered by Na+/K+ pump
- Osmolarity decrease as the ascending limb progress reaching a minimum at the top
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Molecular shape and bonding16
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Molecular Shape and Reactivity36
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Acid Base Theory40
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Peptides 1+221
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Chirality 1+220
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Chirality 3+422
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Functional group chemistry51
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Functional Groups 5&6 - carbonyls29
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Functional group chemistry 7&8 - amides11
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Thermodynamics 126
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Thermodynamics 223
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Thermodynamics 335
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Extent and Rate of Reaction 130
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Extent and Rate of reaction 26
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Extent and rate of reaction 312
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Extent and rate of reaction 45
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Drug Development Process 135
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Pharmaceutical quality 114
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Pharmaceutical Quality 29
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Pharmaceutical quality 317
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Renal system; physiology and function33
