QS Study

Pecularities of Renal Blood Flow

Renal blood flow means the total amount of blood which is transported through both kidneys per minute. This rate determines how much solute is retained or discarded, how much water is retained or discarded, and ultimately, the osmolarity of blood and the blood pressure of the body.

Fig: Pecularities of Renal Blood Flow

Pecularities of Renal Blood Flow –

  1. It is a portal system:

Type: Arterial portal system

When an artery breaks into two sets of capillaries before ending in a vein it is called portal system. The renal portal system consists of –

(i) Glomerular capillary – designed for filtration.

(ii) Peritubular capillary designed for reabsorption. (Afferent arterioles → Glomerular capillary → Efferent arterioles → Peritubular capillary).

Importance: Filtration and selective reabsorption.

  1. It is a high-pressure capillary bed (especially glomerular capillary)

Renal artery is a direct branch of abdominal aorta which is a high-pressure artery and pressure to some extent is transmitted to the renal artery. Again efferent arteriole is narrow. For both of these reasons, it is a high-pressure capillary bed.

Importance: It facilitates the filtration of blood.

  1. A high rate of blood flow

RBF is very high that is 3.54 ml/gm of kidney tissue/min.

Importance:

  • It allows proper filtration many times each day.
  • It helps in producing waste products rapidly.
  1. Selective Renal blood flow

Cortex → 95% blood flow (5m1/mg of kidney tissue/min)

Medulla → 5% blood flow

  • Outer – 2.5 ml/gm of kidney tissue /min
  • Inner – 0.6 ml /gm of kidney tissue/min).

This is because Cortex contains glomerulus. Glomerular capillaries are the main filtering bed of kidney.

Importance

  • Proper filtration of blood
  • Removal of more waste products.
  1. Autoregulation of the renal blood flow

It regulates, its own blood flow without any external stimuli relatively constantly over an arterial pressure ranged 80-170 mmHg.

Importune

It keeps Renal Blood Flow (RBF) and GFR relatively constant, despite marked changes in arterial blood pressure.

  1. Pretence of vasa recta

These are straight branches of the peritubular capillary.

Importance: Concentrated urine formation.