 The overall roles of the Kidneys
 The anatomy of the Kidneys, ureters, bladder and urethra
 The Nephron
 The Micturition reflex
 The control of water, electrolytes, acid-base balance and the removal of waste
 The Juxtaglomerular apparatus and blood pressure
 Urinalysis; introduction of dipstick urine testing

ROLE OF KIDNEYS

ANATOMY OF THE KIDNEY
• Bean shaped, bilateral, retroperitoneal, on either side of the spine, between 12 th thoracic and 3 rd lumbar vertebra.
• Divided in to Adrenal, Kidney and Renal
Pelvis.
• Adrenals – situated superiorly – responsible for hormone production only not filtration.
• Renal Pelvis is passage way for blood vessels and ureter.

LOCATION, LOCATION

THE KIDNEY
• Each kidney is roughly 10 cm long and 5 cm wide, and is encased in a fibrous outer capsule called the renal capsule
• Fat- keeps the kidney in place – surrounds the renal capsule
• Renal Fascia – dense tissue that secures the kidney to the posterior wall and surrounding structures.
• The main function of the kidneys is to control blood volume and composition. They do this by filtering the blood to remove waste products, salts and water. These are secreted in the form of urine

SECTION OF KIDNEY

INTERNAL STRUCTURE
• Internally, the kidney has an outer layer of outer cortex which surrounds the inner medulla.
• The medulla consists of a number of medullary pyramids, named because of their triangular shape. These are striped in appearance because they contain microscopic coiled tubes called nephrons , the functional unit of the kidney.

THE PYRAMID

BLOOD FLOW IN THE KIDNEYS

FORMATION OF URINE
• Urine is made by the nephrons and drains into tiny collecting ducts within the medullary pyramids . The collecting ducts merge at the base of the pyramids to form the renal papilla
• From the papilla, urine drains into cuplike structures called the major and minor calyces.
• From there the urine drains into the wider open space of the renal pelvis . This acts like a funnel draining the urine out of the kidney into the ureter.

• From the glomerulus the blood pressure drops and the blood flows into arterioles which coil around the nephrons. These in turn connect to a series of small veins. These vessels reunite and ultimately form the renal vein.
• About one quarter of the total cardiac output
(or total blood flow) circulates through the kidneys. This equates to just over 1 liter of blood every minute.

THE NEPHRON
• The functional unit of the kidney is called the nephron . It comprises of a coiled renal tubule and a vascular network of peritubular capillaries. The tubule consists of different regions, each with their own important function.
• The nephron begins as a cup-like structure called the
Bowman's capsule which is where the glomerulus sits. The Bowman's capsule opens into a coiled region of tube called the proximal convoluted tubule.
• The tubule then thins and straightens out into the loop of Henle . It then coils again to form another region called the distal convoluted tubule. The distal tubule empties urine into the collecting duct

WORKING OF NEPHRON o As filtered substances flow through the nephron, they are in close proximity to the network of capillaries. These coil around the tubules and also form long loops called vasa recta which lie alongside the loop of Henle .
o This closeness between the blood stream and the renal tubule facilitates the movement of substances between the two, leading to the formation of urine

FACT
• The nephrons are responsible for filtering out of the bloodstream an estimated 43 gallons of water a day- about twice the body's entire weight in fluid - through an intricate network of tubules (little tubes)

FORMATION OF URINE

RENAL CORPUSCLE
• The Bowman's capsule and glomerulus together form the renal corpuscle . Blood enters the glomerulus via the afferent arteriole and exits in the efferent arteriole.
• The endothelium of the glomerulus contains pores, and lies adjacent to the capsule membrane, which also contains pores called filtration slits. This leaky endothelialcapsular membrane can therefore filter water and substances from the blood into the nephron.

JUXTAGLOMERULAR APPARATUS
The juxtaglomerular apparatus (JGA), located in the renal cortex, is a unique segment of the nephron where the thick ascending limb of the loop of Henle passes between the afferent and efferent arterioles of its own glomerulus.
The macula densa is the specialized area of the thick ascending limb which makes contact with the vascular elements of the JGA.
The vascular elements of the JGA contain modified smooth muscle cells of the arterioles ( granular cells ) which contain secretory granules that synthesize and secrete the enzyme renin.
A second group of JGA cells, called the lacis cells or extraglomerular mesangial cells, are not granular but also secrete renin.
It plays a major role in the renin-angiotensinaldosterone system

THE URETERS, BLADDER AND URETHRA
The Ureters are muscular tubes that link the kidney to the
Bladder.
They transport urine via peristaltic motion and gravity and enter the bladder at an oblique angle, thus preventing back-flow of
Urine.
The Bladderis a hollow muscular organ that collects and stores urine.
It has 3 layers – mucosa, sub-mucosa, and muscularis layer.
The muscularis is made of longitudinal and circular smooth muscle layer called Detrusor muscle.
The Urethra-
Extends from the bladder to the exterior.
Women – short- 4 cm
Men long – 18-20 cm

KUB

MICTURITION REFLEX
 Urine formed in each nephron drains down the collecting ducts and into the renal pelvis.
 Urine exits the kidneys via the right and left ureters , which deliver urine to the bladder by peristaltic contractions of their muscle walls, and also by gravity.
 As the bladder fills with urine, its walls expand. When it is full, the micturition reflexes are stimulated which lead to micturition, or urinating.
 Urine is expelled through a small tube called the urethra which leads to the exterior of the body.

They act as sensors to detect low levels of oxygen in the blood, then they release the hormone erythropoietin , which is the effector that travels to the bone marrow to stimulate RBC production.
This is called a negative feedback loop.
The kidneys must pay close attention to the
RBC volume in the body to ensure that oxygen levels are correct and, on the other hand, they must also pay close attention to the amount of water in the body.

Water balance is achieved in the body by ensuring that the amount of water consumed in food and drink (and generated by metabolism) equals the amount of water excreted. The consumption side is regulated by behavioral mechanisms, including thirst and salt cravings.
While almost a liter of water per day is lost through the skin, lungs, and feces , the kidneys are the major site of regulated excretion of water.
One way the kidneys can directly control the volume of bodily fluids is by the amount of water excreted in the urine. Either the kidneys can conserve water by producing urine that is concentrated, or they can rid the body of excess water by producing urine that is dilute.
Direct control of water excretion in the kidneys is exercised by vasopressin , or anti-diuretic hormone (ADH ), a hormone secreted by the hypothalamus.
ADH allows water re-absorption to occur. Without ADH, very little water is reabsorbed in the collecting ducts and dilute urine is excreted.

WATER BALANCE AND ADH
ADH secretion is influenced by several factors ( anything that stimulates ADH secretion also stimulates thirst):
1. By special receptors in the hypothalamus that are sensitive to increasing plasma osmolarity (when the plasma gets too concentrated). These stimulate ADH secretion.
2. By stretch receptors in the atria of the heart , which are activated by a larger than normal volume of blood returning to the heart from the veins. These inhibit
ADH secretion, because the body wants to rid itself of the excess fluid volume.
3. By stretch receptors in the aorta and carotid arteries , which are stimulated when blood pressure falls. These stimulate ADH secretion, because the body wants to maintain enough volume to generate the blood pressure necessary to deliver blood to the tissues.

SODIUM- KING ELECTROLYTE
The osmolarity (the amount of solute per unit volume ) of bodily fluids is also tightly regulated. Extreme variation in osmolarity causes cells to shrink or swell, damaging or destroying cellular structure and disrupting normal cellular function.
Regulation of osmolarity is achieved by balancing the intake and excretion of sodium with that of water . (Sodium is by far the major solute in extracellular fluids, so it effectively determines the osmolarity of extracellular fluids.)
An important concept is that regulation of osmolarity must be integrated with regulation of volume, because changes in water volume alone have diluting or concentrating effects on the bodily fluids. For example, when you become dehydrated you lose proportionately more water than solute (sodium), so the osmolarity of your bodily fluids increases. In this situation the body must conserve water but not sodium.

As noted, ADH plays a role in lowering osmolarity (reducing sodium concentration) by increasing water reabsorption in the kidneys, thus helping to dilute bodily fluids. To prevent osmolarity from decreasing below normal, the kidneys also have a regulated mechanism for reabsorbing sodium in the distal nephron. This mechanism is controlled by aldosterone, a steroid hormone produced by the adrenal cortex.
Aldosterone secretion is controlled two ways:
1.The adrenal cortex directly senses plasma osmolarity. When the osmolarity increases above normal, aldosterone secretion is inhibited. The lack of aldosterone causes less sodium to be reabsorbed in the distal tubule.
2. The kidneys sense low blood pressure (which results in lower filtration rates and lower flow through the tubule). This triggers a complex response to raise blood pressure and conserve volume.
Specialized cells ( juxtaglomerular cells) in the afferent and efferent arterioles produce renin , a peptide hormone that initiates a hormonal cascade that ultimately produces angiotensin II. Angiotensin II stimulates the adrenal cortex to produce aldosterone.

Low Blood pressure - Kidneys
Low Filtration rate
Juxtaglomerular cells activated
Renin produced
Angiotensin II produced
Aldosterone – Reabsorbs sodium

ACID – BASE
The process of acid-base regulation involves:
• Chemical buffering by intracellular and extracellular buffers
• Control of pCO2 by normal respiratory function
• Control of HCO3- concentration and acid excretion by the kidney
• Reclaim filtered HCO3- (therefore, avoid HCO3loss)
• Regenerate HCO3- in an amount equal to that used as buffer
• Substantial task: 180 L x 24 mmol/L = 4520 mmol bicarbonate filtered/day
• Furthermore, body must replenish bicarbonate (1 -
1.5 mmol/kg/day)
• The proximal tubule- reabsorption of bicarbonate .
The distal tubule -Bicarbonate reabsorption and regeneration

The systolic pressure is the maximum pressure in an artery at the moment when the heart is beating and pumping blood through the body.
The diastolic pressure is the lowest pressure in an artery in the moments between beats when the heart is resting.
Both the systolic and diastolic pressure measurements are important - if either one is raised, it means you have high blood pressure
Measured with a Sphygmomanometer or electronically.
Can be done with the person sitting, lying down, or slowly moving – ambulatory. Position – on arm just above the elbow at the level of the heart.
Normal BP – 120/80 +/- 10
Its goes up with age and chronic diseases and it is not fixed

URINALYSIS
Urinalysis is a physical and/or chemical examination of the urine. It consist of a battery of chemical and microscopic tests to screen for urinary tract infections, renal (kidney) disease, and diseases of other organs that result in the appearance of abnormal metabolites
(break-down products) in the urine.
The tests should be performed within 15 minutes after the urine is collected. Various tests can be conducted from the sample. Most of the screening urinalysis tests are measured by a reagent "dipstick" which contains little pads of chemicals that change color when they come in contact with the substances of interest.
There are several types of reagent strips, and it depends on the type of strip as to what tests can be performed

SIMPLE TEST

NORMAL URINE COMPOSITION
• Healthy urine is a clear aqueous solution, varying in colour from dark yellow to colourless depending on the dilution.
• The main constituents of urine are water, salts and urea.
• Urochrome is the pigment that gives urine its color.
• Urea is one of the three nitrogenous waste products.
The other two are creatinine and uric acid .
• Urine also contains various inorganic ions, including phosphate, sodium, hydrogen and chloride.
• Others include ammonia, urobilinogen and casts in minute quantities
• Lighter urine color usually indicates higher water consumption.
• Disease Indicators- disturbances in - Force, flow, frequency, control, volume, pain, colour, odour and gravels or deposits.

NORMAL URINE TEST VALUES
Water1.4 L/day
Urea1820 mg/100mL
Uric acid42 mg/100mL
Creatinine196 mg/100mL
Ammonia - 0.05 per cent
Sodium ion128 mEq/L
Potassium ion60 mEq/L
Chloride ion134 mEq/L
Bicarbonate ion14 mEq/L pH4.5 to 8.0

WHAT IS MEASURED
Gross and chemical exam
 Urine appearance and color (for example, clear, cloudy, turbid, layered; pale yellow, dark yellow, red, green, blue)
 Bilirubin - urine (a degradation product of hemoglobin)
 Glucose (sugar)
 Hemoglobin (an indication of hemolysis)
 Urine ketones (a by-product of fat metabolism and present in starvation and diabetes)
 Nitrite (an indication of urinary tract infection)
 Urine pH
 Urine protein
 Urine specific gravity (that is, how concentrated or dilute the urine is)
 Urobilinogen (a degradation product of bilirubin)
Microscopic exam:
• Bacteria and other microorganisms
(not normally present) or see urine culture (clean catch)
• Casts
• Crystals
• Fat
• Mucous
• Red blood cells (an indication of damage to the tubules)
• Renal tubular cells
• Transitional epithelial cells
• White blood cells (an indication of urinary tract infection)

http://www.nottingham.ac.uk/nursing/sonet/rlos/bioproc/kidneyanatomy/ http://www.nlm.nih.gov/medlineplus/ency/article/003579.htm
http://mcb.berkeley.edu/courses/mcb135e/kidneyfluid.html
http://sprojects.mmi.mcgill.ca/nephrology/presentation/presentation4.htm