5.10 Renal System Flashcards
(38 cards)
Give some key functions of the renal system
-regulating blood volume
-regulating blood pressure
-regulating blood ionic concentration
-blood pH
-blood osmolarity
-blood glucose concentration
-excretion of waste
-production of hormones such as calcitriol and erythropoietin
What is the functional unit of the kidney
The nephron
What makes up the renal corpuscle
The glomerulus surrounded by the bowman’s capsule
Describe the glomerulus
A tangled glomerular capillary network that is surrounded by the bowman’s capsule
Describe how blood is supplied to and from the glomerulus
The afferent arteriole brings blood into the renal corpuscle and the efferent arteriole takes blood out of the renal corpuscle. The lumen of the afferent arteriole is wider than the lumen of the efferent arteriole.
The vasa recta are a group of blood vessels (forming the peritubular capillaries) that branch of from these arterioles
Describe the bowman’s capsule
A cup shaped, double walled structure that surrounds the glomerulus. It is made of 2 simple squamous epithelium layers. The inner visceral layer wraps around the endothelial cells of the glomerular capillaries. The outer parietal layer forms the outer wall of the bowman’s capsule. The space between these 2 layers is the capsular space. The proximal convoluted tubule then branches of from the bowman’s capsule.
Where does ultrafiltration of the blood take place
Through the filtration membrane in the renal corpuscle
How much blood is filtered through the renal corpuscle every day
180L of blood passes through the filtration membrane every day
Describe the 3 components of the filtration membrane that blood has to pass through.
-the endothelial cell of the glomerulus, which has small fenestration pores in it for the filtrate to pass through
-the basal lamina, which has a dense protein matrix filtering out larger molecules
-the visceral layer of the bowmans capsule with podocyte cells with projections and filtrations slits in between the projections
What is needed for the blood to pass through the filtration membrane in the bowmans capsule.
The filtration is a passive process, so it relies on high blood pressure in the glomerulus to force the filtrate through to the PCT. This high blood pressure is due to the afferent arteriole having a wider lumen diameter than the efferent arteriole. This force is known as the net filtration pressure.
How is the net filtration pressure calculated
The NFP is the net hydrostatic pressure minus the net osmotic pressure. This is calculated as the the glomerular blood hydrostatic pressure minus the capsular hydrostatic pressure and the blood colloid osmotic pressure.
What is the glomerular filtration rate
The volume of fluid filtered from the glomerular capillaries into the bowmans capsule per unit of time. The average values are between 105-125 ml/min.
How is the glomerular filtration rate controlled and affected
The glomerular filtration rate is controlled by constriction/dilation of the afferent and efferent arterioles. The GFR can be affected by changes in glomerular blood pressure, the osmotic pressure of the plasma, blood flow to the glomeruli and the permeability in the renal corpuscle
What are the 2 types of regulation mechanisms of the GFR
Intrinsic (autoregulation) regulation
Extrinsic regulation
Describe intrinsic (autoregulation) regulation mechanisms of the GFR
There are myogenic mechanisms where smooth muscle in the arteriole contracts in response to vessel stretch from increased blood pressure
There is also a tubuloglomerular feedback mechanism where macula densa cells monitor the filtrate flow. With an increased filtrate flow rate, the juxtaglomerular cells (which make up the juxtaglomerular apparatus) in the afferent arterioles will constrict and reduce blood flow into the glomerulus.
Describe the extrinsic regulation mechanisms of the GFR
In times of severe haemorrhage or dehydration, sympathetic stimulation will constrict the afferent arteriole to reduce blood flow into the glomerulus
In response to low blood pressure, juxtaglomerular cells will secrete renin causing vasoconstriction to increase blood pressure
Briefly describe the layout of the renal tubule
The renal tubule is comprised of the proximal convoluted tubule, the loop of henle and the distal convoluted tubule. The PCT and DCT are just in the renal cortex, but the loop of henle extends between the renal cortex and renal medulla. The loop of henle is made up of the descending limb, the thin ascending limb and the thick ascending limb.
Describe the structure of the collecting duct.
The collecting duct receives the filtrate from the DCT of multiple nephrons so is not part of an individual renal tubule. It is comprised of the cortical collecting duct, outer medullary collecting duct and inner medullary collecting duct.
What proportions of substances are reabsorbed in the PCT
67% of Na, Cl and K
All of the glucose and amino acids
Describe how sodium is reabsorbed into the tubular cells from the first half of the PCT
-there is a Na/H antiporter
-there are Na symporters with bicarbonate, glucose, amino acids and others
Describe how sodium is reabsorbed into the tubular cells from the second half of the PCT
In the second half of the PCT, Na is reabsorbed with Cl. There are both transcellular and paracellular routes to this.
Transcellular - Na enters via antiporters such as an Na/H
Paracellular - the Cl moves between the cells along its concentration gradient, this creates an electrical gradient which facilitates the movement of the Na through the paracellular pathways
In the PCT, how does Na leave the tubular cells into the blood stream
via Na/K - ATPase pumps
What types of substances are secreted by the PCT
Organic cations/anions, end products of metabolism, drugs and toxic chemicals. Many of these can not be filtered as they are bound to plasma proteins
How are substances secreted into the PCT
Via specific transporter proteins, either organic anion transporters (OATs) or organic cation transporters (OCTs). All the substances excreted in the PCT uses these transporters
