The kidneys are made up by three external layers, which include the renal fascia the outermost layer , the perirenal fat capsule, and lastly, the innermost layer, the renal capsule, which then surround the space of the renal cortex.
The renal pelvis contains a hilium —the concave site in which the renal artery and vein and nerves enter the kidney and the ureter leaves the kidney. Key Terms renal medulla : The inner-most region of the kidney, arranged into pyramid-like structures, that consists of the bulk of nephron structure.
There are three major regions of the kidney: Renal cortex Renal medulla Renal pelvis The renal cortex is a space between the medulla and the outer capsule. Renal Cortex The kidneys are surrounded by a renal cortex, a layer of tissue that is also covered by renal fascia connective tissue and the renal capsule. Renal Medulla The medulla is the inner region of the parenchyma of the kidney. Renal Pelvis The renal pelvis contains the hilium. The outermost layer is a tough connective tissue layer called the renal fascia.
The second layer is called the perirenal fat capsule , which helps anchor the kidneys in place. The third and innermost layer is the renal capsule. Internally, the kidney has three regions—an outer cortex , a medulla in the middle, and the renal pelvis in the region called the hilum of the kidney.
The hilum is the concave part of the bean-shape where blood vessels and nerves enter and exit the kidney; it is also the point of exit for the ureters. The renal cortex is granular due to the presence of nephrons —the functional unit of the kidney. The medulla consists of multiple pyramidal tissue masses, called the renal pyramids. In between the pyramids are spaces called renal columns through which the blood vessels pass. The tips of the pyramids, called renal papillae, point toward the renal pelvis.
There are, on average, eight renal pyramids in each kidney. The renal pyramids along with the adjoining cortical region are called the lobes of the kidney. The renal pelvis leads to the ureter on the outside of the kidney. On the inside of the kidney, the renal pelvis branches out into two or three extensions called the major calyces , which further branch into the minor calyces.
The ureters are urine-bearing tubes that exit the kidney and empty into the urinary bladder. Figure 2. The internal structure of the kidney is shown. Because the kidney filters blood, its network of blood vessels is an important component of its structure and function.
The arteries, veins, and nerves that supply the kidney enter and exit at the renal hilum. A tough, fibrous , connective tissue renal capsule closely envelopes each kidney and provides support for the soft tissue that is inside.
In the adult, each kidney is approximately 3 cm thick, 6 cm wide, and 12 cm long. It is roughly bean-shaped with an indentation, called the hilum , on the medial side.
The hilum leads to a large cavity , called the renal sinus , within the kidney. The ureter and renal vein leave the kidney, and the renal artery enters the kidney at the hilum. The outer, reddish region, next to the capsule , is the renal cortex.
This surrounds a darker reddish-brown region called the renal medulla. The renal medulla consists of a series of renal pyramids , which appear striated because they contain straight tubular structures and blood vessels.
The fascia and, to a lesser extent, the overlying peritoneum serve to firmly anchor the kidneys to the posterior abdominal wall in a retroperitoneal position. On the superior aspect of each kidney is the adrenal gland. The adrenal cortex directly influences renal function through the production of the hormone aldosterone to stimulate sodium reabsorption.
A frontal section through the kidney reveals an outer region called the renal cortex and an inner region called the medulla Figure. The renal columns are connective tissue extensions that radiate downward from the cortex through the medulla to separate the most characteristic features of the medulla, the renal pyramids and renal papillae.
The papillae are bundles of collecting ducts that transport urine made by nephrons to the calyces of the kidney for excretion. The renal columns also serve to divide the kidney into 6—8 lobes and provide a supportive framework for vessels that enter and exit the cortex. The pyramids and renal columns taken together constitute the kidney lobes.
Renal Hilum The renal hilum is the entry and exit site for structures servicing the kidneys: vessels, nerves, lymphatics, and ureters.
The medial-facing hila are tucked into the sweeping convex outline of the cortex. Emerging from the hilum is the renal pelvis, which is formed from the major and minor calyxes in the kidney. The smooth muscle in the renal pelvis funnels urine via peristalsis into the ureter. The renal arteries form directly from the descending aorta, whereas the renal veins return cleansed blood directly to the inferior vena cava.
The artery, vein, and renal pelvis are arranged in an anterior-to-posterior order. The renal artery first divides into segmental arteries, followed by further branching to form interlobar arteries that pass through the renal columns to reach the cortex Figure. The interlobar arteries, in turn, branch into arcuate arteries, cortical radiate arteries, and then into afferent arterioles.
The afferent arterioles service about 1.
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