Anatomy and physiology of the kidneys and measurement of kidney

2. Review of the literature

2.1 Anatomy and physiology of the kidneys and measurement of kidney

2.1.1 Anatomy and physiology of the kidneys

The kidney is a bean shaped, bilateral retroperitoneal organ. It is constructed of renal cortex, underlying renal pyramids, urine collection system, and vasculature. It is enclosed in a fibrous capsule surrounded by perinephric fat. Blood supply is carried by the renal artery emerging from the aorta just below the superior mesenteric artery. The renal vein leads blood into the inferior vena cava. On the left side, the renal vein passes under the superior mesenteric artery. On the left side, the gonadal vein merges with the renal vein. Urine secreted from the kidney is led to the urinary bladder through the calyxes, the renal pelvis, and the ureter. The ureter, renal vein, and renal artery pass the kidney through the renal hilum on the medial side of the kidney.

Lymphatic fluid from the kidney drains into the lumbar lymph nodes. (Figure 1) (Drake et al., 2010)

The kidney is composed of approximately 1 million nephrons, which is the basic unit of a kidney. A nephron consists of the afferent arteriole, efferent arteriole, glomerulus, proximal tubule, the loop of Henle, the distal tubule and a collection duct that leads urine into the renal papilla leading to the calyxes. The afferent arteriole brings blood to the glomerulus and the efferent arteriole leads blood out from the glomerulus. The glomerulus and its capillary structures are supported by mesangial cells. There is

some kidney related issues concerning joint replacement operations. Not enough is known of the patient characteristics of those joint replacement patients who have chronic kidney disease. Acute kidney injury (AKI) after joint replacement is a rare but potentially preventable adverse event with some unaddressed risk factors. Some of its risk factors are still uncharted. After TJA, short-term mortality risk after joint

replacement remains elevated for approximately 90 days, while the most common reasons for mortality are ischemic heart disease, cerebrovascular events, and pulmonary embolism (Berstock, J. R. et al., 2014; Berstock, J. R. et al., 2018). After this period, mortality is no longer affected by the operation itself. Information on short- and long-term mortality of patients undergoing operations aiming to improve quality of life is important when preoperatively evaluating the risks and benefits of the operation, but also the cost effectiveness of the operation. Many comorbidities are known to affect short- and long-term mortality after joint replacement, but the role of different CKD stages in postoperative mortality is yet to be established.

The present study ascertains the unknown issues in the relationship between renal function and the outcomes of joint replacement operations, and addresses recognition of CKD in these patients. This includes investigating the risk factors for AKI,

reporting the patient groups with high prevalence of CKD, studying the performance of SCr as a predictor of CKD and analyzing mortality and implant survival in different CKD stages.

2. Review of the literature

2.1 Anatomy and physiology of the kidneys and measurement of kidney function

2.1.1 Anatomy and physiology of the kidneys

Lymphatic fluid from the kidney drains into the lumbar lymph nodes. (Figure 1) (Drake et al., 2010)

autoregulation that adjusts the constriction in the afferent and efferent arterioles, thereby maintaining the ideal pressure on the glomerulus. The aim of the

autoregulation is to keep the glomerular filtration rate (GFR) stable in different arterial pressure conditions. Autoregulation works when mean arterial pressure exceeds 70mmHg. Between the afferent and efferent arteriole, lies the macula densa, which senses the chemical changes in tubular fluid and regulates constriction of the afferent arteriole, thereby keeping the glomerular perfusion stable. There are also other factors influencing capillary blood flow such as sympathetic activity, angiotensin, natriuretic peptide and nitric oxide. When the circulating blood volume is decreased, angiotensin constricts the efferent arteriole three times more than the afferent arteriole, resulting in stable GFR as the hydrostatic pressure increases inside Bowman´s capsule. In these situations, prostaglandins decrease constriction of the afferent arteriole and prevent excessive constriction that would result in a decrease in GFR. By this mechanism, non-steroidal anti-inflammatory drugs (NSAID´s), decreasing the number of prostaglandins, can impair glomerular blood flow and decrease GFR. Besides NSAIDs, use of diuretics and angiotensin receptor blockers also affectglomerular perfusion (Fournier et al., 2014; Lee et al., 2007). The efferent arteriole proceeds to the lower parts of the kidney and forms a network of capillaries around the tubule structures. In the glomerulus, water and small soluble molecules are filtrated through the glomerular capillaries to the Bowman’s capsule. This glomerular filtrate is

processed into urine in the tubules. GFR is the indicator of kidney function. Besides the glomerular blood flow, characteristics of the glomerular capillaries, underlying the basal membrane and visceral part of Bowman’s capsule also affect filtration. The tubules reabsorb most of the useful filtrated substances such as water, glucose, and sodium back into the circulation. The tubules also secrete smaller sized, water soluble organic products and pharmacological agents in to the filtrate. The tubules also take care of electrolyte balance, acid and base balance. From the tubules, urine is secreted into the collection duct that leads eventually to the calyxes. The osmolality of the urine is regulated by antidiuretic hormone (ADH). When ADH is present, the collector

ducts become more permeable to the water and therefore water is reabsorbed making the urine hyperosmotic. Besides their secretion and reabsorption function, the kidneys have a remarkable role in erythropoiesis, the secretion of renin, and bone mineral regulation. (Boron, Walter F., and Emile L. Boulpaep., 2016; Wein et al., 2016)

Figure 1. Anatomy of the kidneys (modified from Gray’s Anatomy for Students) (Drake et al., 2010)

2.1.2 Measurement of kidney function

As mentioned earlier, GFR is the indicator of kidney function. Determining GFR, however, is time consuming and impractical as it entails continuous infusion of medical substances and simultaneous urine collection (Soveri et al., 2014). Therefore, more practical methods have been developed to estimate the true GFR. In clinical practice, various equations have been provided to make an estimated GFR (eGFR)

autoregulation that adjusts the constriction in the afferent and efferent arterioles, thereby maintaining the ideal pressure on the glomerulus. The aim of the

Figure 1. Anatomy of the kidneys (modified from Gray’s Anatomy for Students) (Drake et al., 2010)

2.1.2 Measurement of kidney function

In document Chronic Kidney Disease in Patients Undergoing Hip or Knee Joint Replacement (sivua 20-24)