Step-by-Step Guide: Understanding Renal Blood Flow and Its Importance
Renal blood circulation can be defined as the blood supply of the kidney from the body. The kidney receives blood from the body then performs the critical function of excretion. The renal blood flow is under tight regulation to achieve proper filtration and excretion of the waste. To understand renal blood circulation it is important to understand the location of the kidney. The kidney is in the dorsolumbar, retroperitoneal cavity. The nephron acts as the functional unit of the kidney. Nephron receives the incoming blood, performs its filtration, and then sends back the purified blood. This process of filtration of blood leads to the formation of the urine, excretory waste of humans. This article is focused on renal blood flow, factors affecting renal blood flow, and its regulation.
Nephron
The kidney is located in the dorsolumbar cavity of the body. The nephron can be defined as the basic functional unit. The nephron has the following vital parts: Bowman's capsule, tubule-like region, the loop of Henle. It is important to note that nephrons are terminally differentiated. To understand the peculiarities of renal circulation it is important to understand the basic anatomy of the nephron.
Bowman’s Capsule
It is a capsular cup-like structure, it has a blood vessel, the blood vessel takes blood into the bowman’s capsule, it is also known as the glomerulus. The vessel taking blood into the glomerulus is known as afferent arteriole. The vessel taking blood out from the glomerulus is known as efferent arteriole.
Tubule
Tubular shaped region evolving from Bowmans is known as the convoluted tube. The tube near Bowmans is known as the proximal convoluted tubule. The tube that originates from the far end of the nephron is called the distal convoluted tube.
Loop of Henle
Loop of Henle can be divided into ascending and descending loop of Henle. The descending segment is the thin tubular structure, the ascending segment has the anatomical segmentation into a thin and thick tubular structure.
The ascending segments that enter the medulla areas are known as DCT (distal convoluted tubule). DCT leads to a connecting tubule known as a cortical connecting tubule (CCT). Distal convoluted tubule that enters the medullary is known as MCT, medullary collecting duct. The medullary collecting duct merges with the collecting duct.
[Image will be Uploaded Soon]
Nephrons can be classified into two groups, one being cortical nephron and the other juxtamedullary nephron.
Difference Between the Types of Nephrons
Blood Vessels Involved in Renal Blood Flow
Renal blood circulation can be defined as the blood supply of the kidney and back to the body. The renal vessels involved in renal circulation can be divided into three major groups namely,
Glomerular blood vessels
Peritubular capillaries
Vasa recta
There are majorly six glomerular blood vessels involved in this renal circulation, they are as follows, renal artery, segmental artery, interlobar artery, arcuate artery, interlobular artery, and afferent artery.
It is important to note that the normal blood vessel has three layers namely, tunica interna, tunica media and, tunica externa, whereas the blood vessel responsible for the blood supply of the kidney only has tunica interna. The tunica interna layer of the blood vessels is modified to perform the special task of ultrafiltration to produce urine.
The Sequence of Blood Vessels Involved in the Blood Supply of Kidney
The flowchart here explains the sequence in which blood vessels work to facilitate renal blood supply.
Renal artery
↓
Segmental artery
↓
Interlobar artery
↓
Accurate artery
↓
Interlobular artery
↓
Afferent artery
↓
Glomerulus capillaries
↓
Efferent arteriole
↓
Peritubular capillaries or vasa recta
↓
Cortical veins
↓
Accurate veins
↓
Interlobar veins
↓
Renal vein
Renal Blood Flow
Renal blood flow is commonly known as RBF. Renal blood flow can be defined as the amount of blood received by the kidney per unit of time. In other words, it is the renal blood supply per unit time. The normal renal blood flow of the human body is RBF = 1000 mL/min. Factors affecting renal blood flow include glomerular filtration rate, colloidal osmotic pressure and, capsular hydrostatic pressure.
GFR
Glomerular filtration rate, also known as GFR, is the amount of plasma filtrate formed each minute. In simpler terms, it can be defined as the rate at which filtration occurs. Glomerular filtration can be mathematically expressed as the
GFR= Kf × NFP
Where NFP is net filtration pressure,
Kf is the filtration coefficient.
NFP
It is the net filtration pressure, it is defined on the basis of the glomerular hydrostatic pressure and colloidal osmotic pressure.
GHP or glomerular hydrostatic pressure is developed because of the change in the diameter of the afferent and efferent arteriole. The afferent arteriole generally has a large diameter when compared to the efferent arteriole.it is also denoted as PG. The osmolarity increases from afferent to efferent end because of movement of solvent out from the vessel, this leads to the comparative increase in the concentration of the plasma protein. The normal average of the glomerular hydrostatic pressure is 60 mm Hg.
COP is also known as colloidal osmotic pressure develops because of the accumulation of the plasma protein, which is denoted as the πG. It opposes filtration. The normal average value of colloidal osmotic pressure is 32mm Hg.
CHP is also known as capsular hydrostatic pressure, developed by the pressure that the bowman’s capsule exerts on the blood vessels of the glomerulus. It is denoted by PB. The normal average value of capsular hydrostatic pressure is 8mm Hg.
The net filtration in humans can be calculated by the mathematical expression which is as follows,
NFP = PG - πG + PB
NFP calculation in humans
NFP = PG - πG + PB
60 - (32 +8)
60 - 50
10 mm Hg is the net filtration pressure in humans.
Kf
It is known as the filtration coefficient. It depends on the permeability of the glomerulus and the surface area of the glomerulus. It is the function of the mesangial cell, these are specialized macrophages. This cell performs the following functions
They provide structural support to the glomerulus
They have the ability to promote and inhibit the filtration
They are the only contractile cells in the glomerulus of the nephron, the contraction and relaxation of these cells control the permeability and surface area of the glomerulus.
Factors Affecting Renal Blood Flow
Factors that affect the kidney blood flow actually affected by controlling the parameters like GFR, it can be affected by the change in glomerular hydrostatic pressure,
an increase in glomerular hydrostatic pressure leads to an increase in the GFR.
The glomerular filtration rate decreases when the colloidal osmotic pressure increases.
The glomerular filtration rate decreases with the increase in the capsular hydrostatic pressure.
FAQs on Renal Blood Circulation Simplified: Flow, Steps & Equations
1. What exactly is renal blood circulation and what is its primary importance?
Renal blood circulation refers to the process of blood flowing through the kidneys. In a healthy adult, the kidneys receive a substantial amount of blood, approximately 1100-1200 ml per minute, which is about 20-25% of the total cardiac output. Its primary importance lies in filtering waste products like urea and creatinine from the blood to form urine, regulating blood pressure, and maintaining the body's overall fluid and electrolyte balance.
2. What is the complete pathway of blood circulation through the kidney, from entry to exit?
The path of blood through the kidney is highly organized to facilitate filtration. The sequence is as follows:
- Blood enters via the Renal Artery.
- It branches into Segmental Arteries, then Interlobar Arteries, and Arcuate Arteries.
- From Arcuate Arteries, smaller Interlobular Arteries arise.
- These lead to the Afferent Arterioles, which supply blood to the glomerulus.
- Blood is filtered in the Glomerulus.
- Unfiltered blood exits the glomerulus via the Efferent Arteriole.
- This arteriole forms a capillary network called the Peritubular Capillaries (and Vasa Recta).
- Blood is then collected into the Interlobular Vein, Arcuate Vein, Interlobar Vein, and finally exits the kidney through the Renal Vein.
3. How is renal blood flow regulated within the body?
The body uses sophisticated mechanisms to keep renal blood flow and filtration constant. Regulation occurs through:
- Intrinsic Autoregulation: The kidney can manage its own blood flow. The myogenic mechanism allows the afferent arteriole to constrict or dilate in response to blood pressure changes. Tubuloglomerular feedback involves the Juxtaglomerular Apparatus (JGA) detecting filtrate composition and adjusting flow accordingly.
- Extrinsic Hormonal Control: The Renin-Angiotensin-Aldosterone System (RAAS) is a key hormonal cascade that constricts blood vessels to increase blood pressure when it drops. Hormones like ADH and ANP also play a role in regulating blood volume and pressure, which indirectly affects renal blood flow.
4. What is the difference between Renal Blood Flow (RBF) and Glomerular Filtration Rate (GFR)?
While related, RBF and GFR are distinct measurements. Renal Blood Flow (RBF) is the total volume of blood that passes through the kidneys per minute (approx. 1100-1200 ml/min). In contrast, the Glomerular Filtration Rate (GFR) is the volume of fluid filtered from the blood by the glomeruli into the Bowman's capsule per minute. The GFR is much lower, about 125 ml/min, representing only the plasma portion that gets filtered.
5. What is the specific role of the Juxtaglomerular Apparatus (JGA) in controlling renal circulation?
The Juxtaglomerular Apparatus (JGA) is a specialised structure located where the distal convoluted tubule touches the afferent arteriole. Its primary role is to act as a sensor. When it detects a drop in glomerular blood pressure, blood flow, or GFR, its juxtaglomerular cells release an enzyme called renin. Renin initiates the RAAS pathway, which ultimately helps to restore blood pressure and regulate blood flow to the glomerulus.
6. What are some key examples of physiological factors that can alter renal blood flow?
Renal blood flow is not always constant and can be altered by various physiological conditions. For example, intense exercise or stress can trigger the sympathetic nervous system, which constricts the afferent arterioles and reduces renal blood flow. Conversely, factors like hydration status and certain hormones can influence it. Severe dehydration or haemorrhage leads to a significant drop in blood volume and pressure, causing a sharp decrease in RBF as the body diverts blood to more vital organs like the brain and heart.
7. Why does the efferent arteriole have a smaller diameter than the afferent arteriole?
The smaller diameter of the efferent arteriole compared to the wider afferent arteriole is a critical structural adaptation. This difference in diameter creates resistance to blood outflow from the glomerulus. This resistance effectively 'dams up' the blood within the glomerular capillaries, significantly increasing the hydrostatic pressure inside them. This high glomerular hydrostatic pressure is the primary driving force for the efficient filtration of water and solutes from the blood into the Bowman's capsule.
