Kidneys Flashcards
Where are the kidneys located?
Just behind the peritoneum - the lining of the abdominal cavity. They are partially protected by the ribs.
What part of the kidney is the attachment point of vasculature?
The indented surface of the kidneys called the hilum - the renal artery perfuses the kidney here whilst the renal vain drains the kidneys.
The nerves that innervate the kidney and the uretar also pass through the hilum.
Whats the role of the kidneys?
Regulate water concentration, inorganic ion composition, acid-base balance, and the fluid volume of the internal environment. It also excretes metabolic waste products into the urine.
Whats the journey of urine?
From the kidneys through the ureter into the bladder then excreted through the urethra.
In what way do kidneys act as endocrine glands?
They release erythropoietin, 1,25-dihydroxyvitamin D3 and renin.
Describe the structure surrounding the kidneys.
The kidney is surrounded by a protective renal capsule composed of connective tissue. This is then surrounded by the adipose capsule providing support.
The renal fascia is a layer of connective tissue encapsulating the kidneys and adrenal glands.
Describe the structure of the kidney itself.
Consists of an outer renal cortex and inner renal medulla. The connection between the tip of the medulla and the calyx (a funnel shaped structure that makes up the ureter) is called the papilla.
The hilum opens into the central cavity known as the renal sinus.
At rest the kidneys recieve 1.2L per minute. Describe the circulation of the kidneys.
Blood enters the kidney in the renal artery which splits consecutively into segmental arteries, interlobar arteries, arcuate arteries, interlobar arteries, afferent arterioles glomerular capillaries, efferent arterioles, peritubular capillaries, interlobular veins, arcuate veins, interlobular veins and renal veins then exiting the kidneys.
The kidney is composed of nephrons. What do these consist of?
An initial filtering component called the renal corpuscle and a tubule extending from this. The renal tubule is a narrow fluid filled cylinder. The renal corpuscle forms a filtrate from blood that is free of cells, larger polypeptides and proteins - this filtrate then leaves the renal corpuscle and enters the tubule.
Each nephron has 2 arterioles and 2 sets of capillaries that form a portal system.
Outline the structural features of the nephron.
The renal corpuscle (within Bowmans capsule) is the site of blood filtration. The filtrate then enters the proximal tubule then the descending limb then ascending limb of the loop of Henle then the distal tubule then the collecting duct to the bladder.
Outline the structure of the proximal tubules.
The proximal tubule consists of simple cuboidal epithelium with microvilli.
Outline the structure of the descending limb.
The thin descending limb is composed of simple squamous epithelium.
Outline the structure of the ascending limb.
The thick ascending limb is composed of simple cuboidal epithelium with no microvilli.
Outline the structure of the distal tubule.
The distal tubule consists of simple cuboidal epithelium with very few microvilli.
Describe the structure of the renal corpuscle.
The renal corpuscle is a Bowmans capsule with a glomerular capillary. The parietal layer is the outer layer of the Bowmans capsule. Blood flows into the glomerulus through the afferent arterioles. The proximal tubule exits the Bowmans capsule.
Juxtaglomerular cells surround the arterioles entering/exiting the Bowmans capsule.
The capillary endothelium, basement membrane and visceral epithelium form a filtration barrier. What are the three components of this?
1 - Basal lamina; this separates the endothelial cells from the podocytes with a thin layer of extracellular matrix.
2 - Endothelial pores; the capillaries are fenustrated but the pores are not big enough for cells to pass through.
3 - Epithelial filtration slits; there are narrow filtration slits between podocytes allowing the finest level of filtration. Podocytes are part of Bowmans capsule and surround capillaries.
Describe the process of filtration accross the membrane.
Substances in the blood are filtered through capillary pores between a single layer of endothelial cells. The filtrate then passes accross the basement membrane and through filtration slits between the foot processes (podocytes) and enters the capsule space. From here the filtrate is transported to the lumen of the proximal convoluted tubule.
The size of pores determines the level of filtration and the composition of filtrate. What are the variations in the 3 filtration barriers?
Fenestration of glomerular endothelial cells allows all components of blood plasma to pass through but prevents filtration of blood cells.
Basal lamina prevents filtration of larger proteins.
Slit membrane between podocytes prevents filtration of medium size proteins.
In health, what is the glomerular filtrate?
An ultrafiltrate of the plasma - it contains water and dissolved solutes but no cells and only trace amounts of protein.
Whats the filtration fraction?
20% amount of substance that is filtered from plasma into capsule.
What drives filtration of the glomerus?
The hydrostatic pressure of the glomerular capillaries - it is 55mmHg.
What is the hydrostatic pressure oppposed by?
Pfluid = the hydrostatic pressure of fluid in the glomerular capsule = 15mmHg.
Pi = the colloidal/oncotic pressure of the plasma proteins = 30mmHg.
The overall net filtration pressure is 10mmHg.
Whats the GFR?
Glomerular filtration rate = the volume of filtrate produced by the kidneys per minute.
In a healthy adult this is 125ml/min - this filtration fraction is 20% of total renal blood flow.
99% of the filtered volume is reabsorbed.
Despite a net filtration rate of only 10mmHg, the volume of filtrate is still high. Why is this?
The surface area of the glomerular capillaries is large.
The glomerular capillary endothelium is fenestrated.
The glomerular capillary blood pressure is high.
Changes in the diameter of the afferent and efferent arterioles alter renal blood flow and GFR. How does this happen?
Increased resistance in the afferent arteriole (increasing blood flow to other organs) will reduce the renal blood flow hence decreasing GFR. (Due to decreased capillary blood pressure).
Increased resistance in the efferent arteriole will increase the hydrostatic pressure of the glomerular capillaries hence increasing GFR.
How can you calculate the urinary excretion of a substance?
Filtration - Reabsorption + amount secreted
Discribe the journey of filtrate through the kidneys.
A substance first gets filtered out of the blood in the glomerulus, into Bowmans capsule. It then travels along the tubule where some is reabsorbed into the peritubular capillaries and some more substance gets secreted from the peritubular capillaries into the tubule. Substances in the tubule then travel to the bladder and gets eliminated through urine.
The filtrate being reabsorbed and secreted is primarily autoregulated (tuboglomerular feedback) in …
The bowmans capsule, proximal tubule and loop of Henle.
How is filtration and reabsorption controlled in the distal tubule and collecting duct?
Primarily by hormones.
What are the 6 subdivisions of renal function?
1 - Regulation of extracellular fluid volume and blood pressure.
2 - Regulation of blood osmolarity at 300mOsM - this is the number of osmotically active particles per litre of fluid.
3 - Maintenance of ion balance - sodium is the most important.
4 - Homeostatic regulation of plasma pH - this is doen through secretion/reabsorption of H+ and HCO3-.
5 - Production of hormones - synthesis of erythropoietin and production of 1,25 - dihydroxyvitamin D3.
6 - Excretion of metabolic and other wastes - creatinine, urea, urobilinogen, hormones drugs and xenobiotics.
Urobilinogen is a colorless by product of bilirubin reduction. It is formed in the intestines by bacterial action on bilirubin. About half of the urobilinogen formed is reabsorbed and taken up via the portal vein to the liver, enters circulation and is excreted by the liver.
The kidneys maintain fluid and electrolyte balance in accordance with the principle of mass balance. What does this mean?
The mass added from intake/metabolic production is equal to that lost from excretion or metabolic removal.
- Input includes substances entering through skin, lungs and intestines as well as that produced through metabolic pathways.
- Output includes substances exiting the body through kidneys, live, lungs, and skin as well as stuff metabolised to a new substance.
Whats the primary function of the kidneys?
The maintenance of fluid and electrolyte balance.
Water is 60% of the bodys weight. What can this be divided into?
40% is intracellular fluid (high potassium concentration, low sodium concentration)
20% is extracellular fluid (low potassium levels, high sodium levels) - this can be further subdivided into interstitial fluid (14%) and plasma (6%).
Define the terms isotonic, hpertonic and hypotonic in relation to osmotic equilibrium.
Isotonic = When extracellular fluid = 300mOsM, there will be no change. Hypertonic = If extracellular fluid is greater than 300mOsM there will be a net movement of water out of the cell hence the cell will shrink. Hypotonic = If extracellular fluid is less than 300mOsM there will be net movement of water into the cell and it will swell.
These changes occur because water diffuses accross the membrane in order to reach equilibrium so that extracellular = intracellular.
This osmotic equilibrium is affected by the digestion of substances in the body.
Whats the effect if you consume an isotonic substance?
There will be no effect on osmolarity but it will distribute to the extracellular fluid, raising the volume of ECF. - Adding isotonic saline to the body is a good way of increasing ECF without affecting ICF.
What happens if you ingest pure water/5%glucose solution (no penetrating solutes)?
You will increase the volume of ECF hence diluting the solutes in ECF. This will then cause water to move into ICF until equilibrium is restored. Therefore, both ICF and ECF will have lower osmolarity and both will increase in volume.
What happens if you have pure NaCl?
It will rapidly distribute to the ECF and increase the osmolarity. This increase causes water to drain out of ICF into ECF until equilibrium is restored. Therefore, both will have the same osmolarity, but ICF will have a lower volume and ECF will increase in volume.
What does regulation of salt involve?
A balance between sodium being filtered and reabsorbed (sodium does not get secreted) - this means if total body sodium decreases then so does sodium excretion because more sodium is reabsorbed.
