Question

Describe ( VERY brief please )  the functional anatomy of the kidneys then write a few sentences comparing bulk flow in the glomerular capillaries to other systemic capillaries. How do you solve problems with the glomerular filtration rate, renal threshold, transport maxima, and excretion rates? Why does it matter?

Answer 1

Renal capsule – tough fibrous capsule.

Perirenal fat– collection of extraperitoneal fat.

Renal fascia (also known as Gerota’s fascia or perirenal fascia) – encloses the kidneys and the suprarenal glands.

Pararenal fat – mainly located on the posterolateral aspect of the kidney.

The renal parenchyma can be divided into two main areas – the outer cortex and inner medulla. The cortex extends into the medulla, dividing it into triangular shapes – these are known as renal pyramids

The apex of a renal pyramid is called a renal papilla. Each renal papilla is associated with a structure known as the minor calyx, which collects urine from the pyramids. Several minor calices merge to form a major calyx. Urine passes through the major calices into the renal pelvis, a flattened and funnel-shaped structure. From the renal pelvis, urine drains into the ureter

The medial margin of each kidney is marked by a deep fissure, known as the renal hilum. This acts as a gateway to the kidney – normally the renal vessels and ureter enter/exit the kidney via this structure.

BULK FLOW

Unlike systemic capillaries, which receive blood from high-resistance arterioles and drain to low-resistance venules, glomerular capillaries are connected in both ends to high-resistance arterioles: the afferent arteriole, and the efferent arteriole.

Most systematic capillaries in body are Continuous capillaries that have a tight structure reducing bulk flow. While kidney glomeruli are Fenestrated capillaries that permit a larger amount of flow.

In systemic capillaries diffusion is the most widely-used mechanism, that allows the flow of small molecules across capillaries such as glucose and oxygen from the blood into the tissues and carbon dioxide from the tissue into the blood. The process depends on the difference of gradients between the interstitium and blood, with molecules moving to low-concentrated spaces from high-concentrated ones.

Bulk movement of fluid across the glomerular and peritubular capillary membranes of the renal microcirculation is driven by physical forces caused by hydraulic and colloid osmotic pressures. As blood flows from the afferent arterioles into the glomerular capillary tufts, the high hydraulic pressure predominates over the opposing Bowman's space pressure and plasma colloid osmotic pressure.

GFR

GFR= Kf × ( Hydrostatic pressure in glomerular capillaries- Hydrostatic pressure within bowman's capsule - colloidal osmotic pressure of glomerular capillaries+ colloidal osmotic pressure in bowman's capsule)

RENAL THRESHOLD

the renal threshold is the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine.

TRANSPORT MAXIMUM

transport maximum refers to the point at which increases in concentration of a substance do not result in an increase in movement of a substance across a cell membrane. In renal physiology, the concept of transport maximum is often discussed in the context of glucose and PAH.

Tm for glucose

EXCRETION RATE

The kidney's ability to perform many of its functions depends on the three fundamental functions of filtration, reabsorption, and secretion, whose sum is called renal clearance or renal excretion. That is: Urinary excretion rate = Filtration rate – Reabsorption rate + Secretion rate.