Urology

= Urology =

In Chapter 17 we learned the structure and function of the kidneys. The primary function of the kidneys is regulation of the extracellular fluid environment in the body. This is done by the formation of urine, which is modified filtrate of plasma.

The kidneys regulate: 1. The volume of blood plasma and thus contribute significantly to the regulation of blood pressure 2. The concentration of waste products in the plasma 3. The concentration of electrolytes (Na+, K+, HCO3- and other ions) in the plasma 4. The pH of plasma

[|Kidney Function] http://www.youtube.com/watch?v=4-15JUVxAm8

The human body consists of two kidneys, one on either side of the vertebral column below the diaphragm and liver. Urine is drained into a cavity know as the renal pelvis and then is channeled from each kidney via long ducts- the ureters to the urinary bladder. The Urinary bladder is a storage sac for urine. The nephron is the functional unit of the kidney responsible for the formation of urine. Each kidney contains more than one million nephons. The nephron is made up of tubules. Arterial blood enters the kidney through the renal artery, which is divided into the interlobar arteries that pass between the pyroamids through the renal columns. Arcuate arteries branch from the interlobar arteries. Arcuate arteries divide into aferent arterioles. These deliver blood into glomerulicapillary networks that produce a blood filtrate that enters the urinary tubules. The blood remaining in a glomerulus leaves through an efferent arteriole, which delivers the blood into another capillary network- the pertitubular capillaries surrounds the renal tubules. These are then drained into the the interlobular veins, arcuate veins and interlobar veins.

=Micturition Reflex=

The urinary bladder has a muscular wall know as the detrusor muscle. Numerous gap junctions interconnect its smooth muscle cells, so action potentials can spread from cell to cell. The detrusor muscle is densely innervated by parasympathetic neurons, and renal stimulation is necessary to empty the bladder. Mituriton, urination is control by two urethral sphincters.

=Nephron=

The nephron is the functional unit of the kidney responsible for the formation of urine. Each kidney contains more than a million rephrons. A nephron consists of small tubules, and is associated small blood vessels. Fluid formed by capillary filtration enters the tubules and the fluid that leaves in urine.

=Renal Blood Vessels=

Arterial blood enter the kidney through the renal artery, which is divided into interlobar arteries that pass between the pyramids through the renal columns. Arcuate arteries branch from the interlobar arteries at the boundary of the cortex and medulla. These divide into afferent arterioles, and deliver blood into the glomeruli capillary networks that produce a blood filtrate that enters the urinary tubules. The blood remaining in the glomerus leaves through an efferent arteriole, which delivers the blood into another capillary network- the peritubular capillaries surrounding the renal tubules.



http://www.medicalartlibrary.com/renal-blood-vessels.html

The glomerular (Bowman's) capsule surrounds the glomerulus. The glomerular capsule and its associated glomerulus are located in the cortex of the kidney and together constitute the renal corpuscle. The glomerular capsule contains an inner visceral layer of epithelium around the glomerular capillaries and an outer parietal layer. The space between these two layers is continuous with the lumen of the tubule and receives the glomerular filtrate. The fluid that enters the glomerular capsule passes into the lumen of the proximal convoluted tubule. The wall of the proximal convoluted tubule consists of a single layer of cuboidal cells containing millions of microvilli. This increases reabsorption. In the process of reabsorption, salt, water and other molecules needed by the body are transported from the lumen, through the tubular cells and into the surrounding peritubular capillaries. Fluid passes from the proximal convoluted tubule to the nephron loop or loop of Henle. The fluid is carried into the medulla in the descending limb of the loop and returns to the cortex in the ascending limb of the loop.

=Glomerular filtration=

The glomerular capillaries have large pores in their walls, the layer of Bowman's capsule in contact with the glomerulus has filtration slits. Water, together with dissolved solutes, can then pass from the blood plasma to the inside of the capsule and the nephron tubules. Before the fluid in blood plasma can enter the interior of the glomerular capsule, it must be filtered through three layers that could serve as selective filters. The fluid entering the glomerular capsule is referred to as filtrate. This fluid will become the urine. The first filtration barrier is the capillary fenestrae. The second is the glomerular basement membrane. The filtrate must then pass through the inner layer of the glomerular capsule, where the third filtration barrier is located. These are called podocytes,



=Reabsorption of salt and water=

The reabsorption of water from the glomerular filtrate occurs by osmosis, which results from the transport of Na+ and Cl- across the tublule wall. The proximal tubule reabsorbs most of the filtered salt and water, and most of the remainder is reabsorbed across the wall of the collecting duct under ADH stimulation. There is about 180 L of glomerular ultrafilrate are produced each day, the kidneys normally excrete only 1 to 2 L of urine a day. A volume of 400 ml of urine per day in mimimum needed to excrete the metabolic wastes produced by the body.

Next I learned active and passive transport, the countercurrent mulitplier system, the ascending limb of the Loop of Henle, countercurrent muliplication and the Vasa Recta.

=Renal Plasma Clearance=

As blood passes through the kidneys, some of the constituents of the plasma are removed and excreted in the urine. The blood is cleared of particular solutes in the process of urine formation. These solutes may be removed from the blood by filtration through the glomerular capillaries or by secretion by the tubular cells into the filtrate.

Next I learned of the role of aldosterone places in the balance in Na+/K+, sodium reabsorption, potassium secretion and about the Juxtaglomerular Apparatus. Secretion of renin into the blood thus results in the formation of angiotensin I, which is then converted to angiotensin II.

Question:

The blood is filtered through the glomerular capsule, though the nephron loop, where necessary nutrients are reabsorbed through the peritubular capillaries and smaller particles that made it passed the filter are secreted into the nephron. The remaining filtrate will be deposited into the renal pelvis, where it will exit the kidneys, through the ureters and be stored in the bladder until it is excreted from the body as urine via the urethra. The glomerular capillaries that feed the glomerular capsule start the filtering process through pores called fenestrea, which are too small to allow blood cells or platelets through, but will pass water and solutes. This solution is now passes through the glomerular basement membrane and then through the slit diaphragm, which will be excreted from the body. Substances such as albumin, which are small enough to make it through the filters, but are necessary to keep in the body are reabsorbed, often by endocytosis, into the blood from the nephron loop via the peritubular capillaries. These capillaries will also secrete ions that are present in excess in the blood, as well as medicines and potential toxins, into the nephron loop for disposal.

Electrolytes, such as potassium and bicarbonate are two examples. Potassium is controlled inversely with sodium by aldosterone. This feedback loop helps to keep the body hydrated for optimal functioning. The reabsorbtion of bicarbonate helps to maintain the acid-base balance in the body.

The number of electrolytes in the body effect the hydration of the body and the energy available to someone to perform activity.

Personal Application:

As a PTA I will be working with people who possibly have kidney or liver disease this will effect their response to exercise and will also have an effect on their amount of fluid hydration and body function. This is important to understand to determine treatment for these patients and to be cautious not to worsen their symptoms.

References: All information was taken from the text Human Physiology, Stuart Ira Fox or cited in this page.