Urinary System

URINARY SYSTEM The urinary system consists of the following organs: 1. two kidneys – which remove substances from the blood, form urine and help regulate various metabolic processes 2. urinary bladder – which serves as urine reservoir 3. two ureters – which transport urine away from the kidneys 4. single urethra – which carries urine from the bladder to the outside of the body This system which other organs, regulates the volume and composition of the interstitial fluid within a narrow range of values. The kidneys are the major excretory organs of the body. The skin, liver, lungs and intestines eliminate waste products but if the kidneys fail to function, other excretory organs cannot adequately compensate. KIDNEYS -

Two-bean shaped organs, each about the size of tightly clenched fist It occupies the hypochondrial region Located in the posterior (back) part of the abdomen, flanking the vertebra column and approximately between the 12th thoracic and 3rd lumbar vertebrae Each kidney is about 11-12cm. long; 5-6 cm wide; and 3 cm thick and weighs about 130 g. Composed of a dark or reddish-brown color due to high degree of vascularity (presence of blood vessels) Right kidney is lower than the left (LK is positioned up to an inch higher than the RK) Structure : Lateral surface of the kidney is covex but it’s medial side is deeply concave.

FUNCTIONS OF THE KIDNEYS 1. To remove waste products from the blood and excrete them to the outside 2. To regulate the fluids, electrolytes, blood pressure and pH within the . •

The main functions of the lower urinary tract are the storage and elimination of formed urine.

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COMPONENTS: cortex, medulla, renal pelvis and nephron

Cortex - outer layer of kidney: contains glomeruli, proximal tubule of nephron a and distal tubules of nephron

Medulla - inner layer of kidney: contain loops and henle and collecting tubules Renal Pelvis - collects urine calices Nephron - the unit of structure of the kidney, responsible for the actual, purification and filtration of the blood. There are about two million in each one consists of renal corpuscle and renal tubule which carry out the functions of the nephron. Renal Corpuscle – consist of glomerulus, a tangled cluster of blood capillaries which is surrounded by a thin-walled saclike structure called Bowman’s capsule. Function: Filtration of water and dissolved substances GLOMERULUS from the plasma Bowman’s capsule – is an expansion at the closed end of a renal tubule Function: Receives the glomerular filtrate Renal Tubules = consist of the following: 1. Proximal convoluted tubule - which makes up the bulk of the renal cortex, absorb/s glucose. Functions: Reabsorption of glucose, amino acids, lactic acid, ascorbic acid, phosphase ions, calcium ions and sodium ions by active transport. Reabsorption of water by osmosis Active secretion of substances such as penicillin, histamine, creatinine and hydrogen ions. 2. Descending limb of the loop of Henle - the thin segment of the loop is lined with squamous cells without brush border of the microvilli. 3. Ascending limb of loop of Henle – the thick segment of the loop has thicker walls than the descending limb. 4. Distal convoluted tubule – secrete/s hydrogen ions Frunction: Reabsorption of sodium ions by active transport Reabsorption of wate by osmosis Active secretion of hydrogen ions Passive secretion of potassium ions by electrochemical attraction 5. Collecting tubules - the distal tubes empty their contents here. It is totally permeable to urea and the tubules unite with each other in the medulla and the final convergence leads to the formation of the papillary duct.

- It absorb/s water - Sodium, water and glucose substances are reabsorbed by the tubules and returned to the blood. Hilus - the slit-like opening in the middle of the concave medial border of the kidney. Nerves and blood vessels pass through the hilus into the renal sinus within. Renal pyramids - are conical segments within the internal medulla of the kidney. Composed of 8-18 cone-shaped subdivisions. They contain the secreting apparatus and tubules and also known as “malphighia pyramids”. Renal columns of Bertin - are lines of the kidney matrix which support the cortex of the kidney. Composed of lines of blood vessels and urinary tubes along a fibrous, cortical material. Papillae (plural for papillar) - are small conical projections along the inner wall of the renal sinus. They feature small opening through which urine passes, entering the calyses. Calyces (plural for calyx) - are the recesses in the internal medulla of the kidney which enclose the pyramids. They are used to subdivide the sections of the kidney anatomically, which distinction being made between major calyces and minor calyces. Renal capsules - the membranous covering of the kidney. It directly covers the renal cortex which forms the outer stratum of the kidney. Cortex – is the outer section which cover the internal medulla. It is visible near the outer edge of the cross sectioned kidney. It is composed of blood vessels and urine tubes an supported with fibrous matrix. Renal Artery - One quarter of the total blood output comes from the heart to kidneys along the renal artery. Note: Patients with end stage renal disease are sometimes treated with kidney transplant. In this process, a kidney from a living donor whose tissues are antigenically similar to those of the recipient is placed in the depression on the medial surface of the right or left ilium(iliac fossa) The renal artery and vien of the donor kidney are connected to the receipient’s iliac artery and vein respectively, and the ureter of the kidney is attached to the dome of recipient’s urinary bladder.

Physiology of Urine Formation: -

The urine has the following characteristics:

COLOR

AMBER

pH or REACTION

ACID ON MIXED DIET ALKALINE ON A VEGETABLE DIET

SPECIFIC GRAVITY

1.010 – 1.020

QUANTITY

ABOUT I LITER/DAY or 1,000 mL

INORGANIC SUBSTANCES

GRAMS PER HOUR

SODIUM

6

CHLORIDE

7

CALCIUM

0.2

POTASSIUM

2

PHOSPHATES

1.7

SULFATE

1.8

ORGANIC SUBSTANCES UREA

20-30

URIC ACID

0.6

CREATININE AMMONIA

1.2 0.5-0.9

THREE MAIN PROCESSES BY WHICH URINE IS FORMED A.

Glomerular Filtration

It is the fluid that filters through the glomerulus into the Bowman’s capsule. It occurs in the same manner that fluid filters out of any high pressure capillary in the body. However, the anatomical structure of the arterioles favors high blood pressure in the glomerulus and in effect favors the filtration of the blood. Another factor which affects the GF, is the hydrostatic pressure of the fluid in the Bowman’s capsule. The greater the capsular pressure, the less will be the glomerular rate, normal: (100-150ml/min for males; 105-132 ml/min for females) The plasma colloid osmotic pressure also is another factor- the greater the plasma colloid pressure, the lesser the glomerular filtration rate. Other factors affecting glomerular infiltration 1. 2. 3. 4. 5.

renal blood flow afferent arteriolar constriction arterial pressure efferent arteriolar constriction sympathetic stimulation

B. Tubular Reabsorption The substances reabsorbed are sodium, postassium, bicarbonate, chloride, glucose, amino acids, Vit. C and water. The processes affecting reabsorption are diffusion, osmosis and active transport. 1.

Absorption capabilities of Tubules, a. Proximal tubules - about 65% of all reabsorption occurs in these tubules because of the presence of extensive brush border and basal invaginations of tubular cells b. Thin segment of loop of Henle - has no brush border but has an extensive pore system. This segment is adapted for simple diffusion and substances.

URETHRA - convey/s urine from the urinary bladder to the outside - the short length of the female urethra predisposes the females to urinary tract infections - the male urethra serves both the excretory and reproductive functions. It is also made up of prostatic portion, membranous portion and spongy portion.

CLINICAL TERMS RELATED TO URINARY SYSTEMS: ACETONURIA

- presence of acetone in the urine

ALBUMINURIA

- presence of albumin in the urine

ANURIA

- absence of urine output due to failure of kidney function or a urine output less than 240 ml in 24 hrs.

DEHYDRATION DIURESIS

- excessive removal of water in the body - increase in urine output

ENURESIS

- bedwetting

GLYCOSURIA

- presence of glucose in the urine

NEPHRECTOMY

- surgical removal of a kidney

NEPHROLITHIASIS

- presence of a stone/s in the kidney

OLIGURIA

- urine output of 250-500 ml in 24 hours

PYURIA

- presence of pus in the urine

POLYURIA

- daily increase in urine output

SPECIFIC GRAVITY

- ratio of the weight of urine in that of an equal volume of water; it is an expression of the concentration of the urine

EXCRETORY SYSTEM/URINARY SYSTEM/UROGENITAL SYSTEM Urinary elimination depends on effective functioning of 4 urinary tract organs: KIDNEYS, URETERS, BLADDER, URETHRA 1. Kidneys - filter from the blood any products for which the body ha no use. Each kidney has (1) renal artery that originates from the abdominal aorta and enters the kidney at the hilum. The renal vein exits through the hilum and joins the inferior vena cava. It is estimated that, in the average adult, 1200 ml of blood passes through the kidneys every minutes. This represents about 21% of the cardiac output (5600 ml per minutes). The body’s total blood supply circulates through the kidneys approximinately 12 times per hours. From this blood, the nephron, the functional unit of the kidney, forms a fluid called glomerular filtrate (about 180 liters daily or 25 ml per minute). This volume-time ratio is referred to as the glomerular filtration rate (GFR). The glomerulus is a tuft or a collection of blood vessels surrounded by Bowman’s capsule. The pore of the glomerulus are large enough for water and some solutes to pass through but are to small for large molecules, such as protein and formed elements in the blood, to filter through. The glomerular filtrate is chemically almost the same as plasma but has only minute quantities of protein (0.03%) compares to the amount found in plasma (7%), Proteinuria (presence of protein in the urine) is a sign of glomerular injury. Glomerular filtrate consists of water, electrolytes, creatinine, glucose, urea, amino acids, uric acid, bicarbonate and other electrolytes. After the filtrate enters the Bowman’s capsule, it passes into the tubular system, where about 99% of it is reabsorbed into the bloodstream. The remaining 1% forms the urine to be excreted from the body. Thus, the function of the nephron is to return the majority of the glomerular filtrate to the circulation. The kidneys therefore are the most important organs in regulating body fluid balance. 2. Ureters - Once the urine is formed in the kidneys, it enters the ureters via collecting ducts and then passes on to the bladder. The ureters are from 25 to 30 cm. (10 to 12 in) long in the adult and about 1.25 cm. (0.5 in) in diameter. The upper end of each ureter is funnel-shaped as it enters the kidney, forming what is referred to as the renal pelvis. The lower ends of the ureters enter the bladder at the posterior corners of the floor of the bladder. At this junction between the ureter and the bladder, there is a flaplike fold of mucous membrane that acts as a valve to prevent reflux (blackflow) of urine up the ureters to the kidneys.

3. Bladder - The urinary bladder is hollow, muscular organ that serve as a reservoir of urine and as the organ of excretion. When empty, it lies behind the symphysis pubis. In the male, the bladder lies in front of the rectum and above the prostate gland; in female, it lies in front of the uterus and vagina. The wall of the bladder is made up of (4) layer (a) mucosa and lamina propria (b) a submucous connective tissue layer; (c) a muscular layer consisting of (3) layers of smooth muscle fibers some of which extend lengthwise, some obliquely, and some more or less circularly and are called the detrusor muscle; and (d) and outer serous layer. The base of the bladder is called the trigone. It is triangular area marked by the ureter openings at the posterior corners forming the base and the opening of the urethra at the anterior inferior corner forming the apex. Urine exits from the bladder through the urethra. The amount of urine normally stored in the bladder varies among individuals and with age. . For an adult, the desire to void is normally experienced when the bladder contains between 250 to 450 ml. of urine. Normal output of urine for an adult is about 1500 ml/day. The bladder is capable of considerable distention because of rugae (folds) in the mucous membrane lining and because of the elasticity of its walls. When full, the dome of the bladder may extend above the symphysis pubis, in extreme situations it may extend as high as the umbilicus. 4. Urethra - The urethra extends from the bladder to the urinary meatus (opening or passage) and is the exit passageway for the urine. It is lined with mucous membrane. In the adult male, the urethra functions as a passageway for reproduction fluid (semen) as well as urine. In the adult female, the urethra lies directly behind the symphysis pubis, anterior to the vagina, and is about 3.7 cm (1.5 in) in length. The urethra serves only as passageway for the elimination of urine. The urinary meatus is located between the labia minora, in front of the vagina and below the clitoris in the male, it is located at the distal end of the penis. The male urethra is about 20 cm (8in) long. In both the males and females, the urethra has a mucous membrane lining that is continuous with the bladder and the ureters. Thus an infection of the urethra can readily extend through the urinary tract to the kidneys. Women are particularly prone to UTI because of the shortness of their urethras.

URINATION Micturition, voiding and urination - all refer to the process of emptying the bladder. Urine collects in the bladder until pressure stimulates sensory nerve ending in the bladder wall called stretch receptors. This occurs in adults, when bladder contain between 250 ml and 450 ml of urine/ in children 50 to 200 ml stimulates these nerves. Once excited, the stretch receptors transmit impulses to the spinal cord, specifically to the voiding reflex center located at the level of the 2nd to 4th sacral vertebrae. Some impulses continue up to the spinal cord to the voiding control center in the cerebral cortex. If the time is appropriate to void, the brain then sends impulses through the spinal cord to the motor neurons in the sacral area, causing stimulation of the parasympathetic nerves. As a result, urine can be released from the bladder , but it is still impeded by the external urinary sphincter. If the time and place are appropriate for urination. The conscious portion of the brain relaxes the external urethral sphincter muscle, and urination takes place. If the time and place are inappropriate, the micturition reflex usually subsides until the bladder become more filled and the reflex is stimulated again. The sympathetic nervous system also innervates the bladder causing it to relax. Voluntary control of urination is possible only if the nerves supplying the bladder and urethra, the neural tracts of the cord and brain, and the motor arca of the cerebrum are all intact. The individual must be able to sense that the bladder is full. Injury to any of these parts of the nervous system – for example – cerebral hemorrhage or spinal cord injury – results in intermittent involuntary emptying of the bladder. Elderly people whose cognition is impaired may not be aware of bladder fullness. 1. Urinary incontinence - involuntary micturition 2. Automatic bladder - situation when there is damage to the spinal cord above the sacral vertebrae the micturition reflex may remain intact and urination may occur reflexively. 3. Retention - condition when a person is unable to void even though the bladder contains an excessive amount of urine. 4. Urinary suppression - a more serious complication characterized by the inability to void because the kidneys are not secreting any urine and therefore the bladder is empty.

5. Polyuria or diuresis - production of abnormally large amounts of urine by the kidneys such as 2500 ml/day due to (a) excessive fluid intake (b) ingestion of substances containing caffeine and alcohol (c) diabetes mellitus (d) hormone imbalances (ex. Deficiency of antidiuretic hormone (ADH) or (c) chronic kidney disease. 6. Oliguria - voiding scant amounts of urine, such as less than 500 ml. in 24 hrs. 7. Anuria - adult’s voiding less than 100 ml/day. 8. Nocturia or nycturia - increased frequency at night that is not a result of an increase in fluid intake. 9. Cystitis - acutely inflamed bladder characterized by frequency w/o an increase in fluid intake. 10. Dysuria - voiding that is either painful or difficult. 11. Enuresis - repeated involuntary urination in children beyond the age when voluntary bladder control is normally acquired, usually 4 or 5 yrs. Of age. FREQUENCY - voiding at frequent intervals that is more often than usual; number of times a person gets out of bed to void. The terms complete kidney shutdown, renal failure and urinary suppression have the same meaning. CATHETERIZATION – introduction of a tube – known as catheter – through the urethra into the bladder to remove urine.