Anatomy & Physiology 2

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Urinary System

Back 1

- A major part of homeostasis is maintaining the composition, pH & volume of body fluids within normal limits

- Removes metabolic wastes and substances present in excess, including foreign substances like drugs & their toxic metabolites

- Consists of the following organs: kidneys, ureters, urinary bladder, urethra

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kidneys

Back 2

- Filter blood and form urine

- Reddish brown, bean- shaped organ with a smooth surface

- Tough, fibrous capsule

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Ureters

Back 3

- Transport urine from kidneys to urinary bladder

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Urinary bladder

Back 4

- Collects and stores urine

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Urethra

Back 5

- Conveys urine from urinary bladder to outside of body

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Location of the kidneys

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- Lie on either side of the vertebral column high in a depression on the posterior abdominal wall

- Retroperitoneal, behind the parietal peritoneum

- Left is 1.5 to 2 cm higher than right

- Surrounded by connective tissue (renal fascia) & masses of adipose tissue (renal fat)

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Renal Sinus

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- Hollow chamber in medial depression

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Hilum

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Entrance to renal sinus

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Renal pelvis

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- Funnel- shaped sac

- Superior end of ureter

- Collects all of the urine from the kidney, & then narrows as it leaves the kidney to become the ureter

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major calyces

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- Large tubes that merge to form renal pelvis

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minor calyces

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- Small tubes that merge to form major calyces

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Renal medulla

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- Inner region

- Composed of renal pyramids

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Renal cortex

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- Outer region of kidney

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Renal columns

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- Extensions of cortex that dip into medulla

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Renal capsule

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- Fibrous capsule around kidney

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Nephrons

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- Functional units of kidney, each of which is a site of urine production

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Renal Artery

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- Enters each kidney through the hilum, & continues to branch to the nephrons

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Nephrons

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- Each kidney contains about 1 million functional units

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Renal Corpuscle

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- Consists of a glomerulus and a glomerular capsule

- Site of blood filtration in the kidney

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Glomerulus

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- Cluster of capillaries; Filters blood, (first step in urine formation)

- Afferent arteriole -> Glomerulus -> Efferent arteriole

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Glomerular (Bowman's) Capsule

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- Receives filtrate from glomerulus

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Renal Tubule

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- Extends from glomerular capsule to collecting duct

- Filtrate proceeds from glomerular capsule -> proximal convoluted tubule -> Nephron loop, composed of a descending and an ascending limb -> Distal convoluted tubule

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Cortical Nephrons

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- Sit high in cortex, with short nephron loops

- Majority of nephrons

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Juxtamedullary nephrons

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- Sit low in cortex & have long nephron loops

- Important in regulating water balance, & urine concentration

- Small percentage of nephrons

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Juxtaglomerular Apparatus

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- A structure that regulates the secretion of renin

- The top portion of the ascending limb of the nephron loop of each nephron passes between the afferent & efferent arterioles

- The ascending limb comes in contact with the afferent arteriole, to form the juxtaglomerular appartus

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Macula densa

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- Tall, closely packed cells of the ascending limb

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Juxtaglomerular cells

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- Large vascular smooth muscle cells of the afferent arteriole

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Nephritis

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- Inflammation of the kidney

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Glomerulonephritis

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- Inflammation of the glomeruli

- Acute or chronic

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Acute Glomerulonephritis (AGN)

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- Results of abnormal immue reaction, 1-3 weeks after infection by beta- hemolytic Streptococcus

- Infection does not start in kidney

- Antigen -antibody complexes form insoluble immune complexes, which lodge in the kidneys

- Complexes deposit in and block glomeruli

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Chronic Glomerulonephritis

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- Progressive disease

- More & more nephrons are damaged, until kidneys cannot function

- Prolonged inflammation

- Fibrous tissue replaces glomerular membranes, disabling nephrons

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Urine Formation

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- The main function of the nephrons & collecting ducts is to control the composition of body fluids & remove wastes from the blood, the product being urine

- Contains: Wastes, excess water, & electrolytes

- 3 processes: Glomerular filtration, tubular re-absorption, tubular secretion

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Glomerular filtration

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- First step of urine formation

- Substances move from the blood in the glomerulus into the glomerular capsule

- Water & small dissolved molecules & ions can be filtered

- Large molecules, such as large proteins, remain in the blood because they're too large to pass through

- Glomerular capillaries are many times more permeable than other capillaries

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Fenestrae

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- Tiny openings in walls

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Gomerular filtrate

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- Formed as substances filter from glomerulus into the glomerular capsule

- Filtrate has about the same composition as tissue fluid

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Net Filtration pressure

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Force favoring filtration -- Forces opposing filtration

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Glomerular Filtration Rate (GFR)

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- Directly proportional to the net filtration pressure

- Average adult GFR = 125 mL/ min or 180 L/day

- Blood plasma is filtered about 60x/day

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Autoregulation

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- GFR remains relatively constant through this process

- Certain conditions override it, such as when GFR increases

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Renin- Angiotensin System

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- Responds to a decrease in BP

- Secretion of ADH & aldosterone, it results in conservation of Na+ & H2O & an increase in BP.

- Also keeps GFR constant

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Tubular Reabsorption

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- Movement of substances from the renal tubules into the interstitial fluid, where they then diffuse into the peritubular capillaries

- 70% occurs in the proximal concoluted tubule, which is lined with microvilli

- Different parts of the renal tubule reabsorb specific substances

- Different substances are transported back into the internal environment by different methods of transport

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Tubular Secretion

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- Movement of wastes from peritubular capillaries into renal tubules

- These substances are wastes, destined to be excreted in the urine

- Active transport mechanisms function but they work in the opposite direction as tubular reabsorption

- Secretion of subtances such as drugs & ions (k+)

Secretion of H+ ions is important in regulating the pH of body fluids

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Active Transport

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- Movement of substances against their concentration gradients; limited transport capacity due to number of carrier proteins

- Renal plasma threshold is reached when there is more transported substance in the plasma than the active transport mechanism can handle; excess spills into forming urine

- Examples: Glucose, amino acids, creatine, lactic, citric, uric, and ascorbic acid, ion

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Osmosis

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- Water reabsorption

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Endocytosis

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- Small protein reabsorption

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Urea

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- A by- product of amino acid catabolism

- The plasma concentration reflects the amount of protein in diet

- Enters the renal tubules through glomerular filtration, & undergoes both tubular reabsorption & tubular secretion

- about 80% is reabsorbed; 20% is excreted in the urine

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Uric Acid

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- A product of nucleic acid metabolism

- It enters the renal tubules through glomerular filtration

- Active transport completely reabsorbs the filtered uric acid

- About 10% of uric acid enters urine through tubular secretions & is excreted

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Urine composition

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- About 95% water

- Usually going to contain metabolic waste products: urea, uric acid, & creatine

- Likely to contain trace amounts of amino acids & varying amounts of electrolytes

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Urine volume

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- 0.6 - 2.5 L/day

- 50/60 mL of urine output/hour is normal

- Volume varies with fluid intake & environmental factors

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Renal Clearance

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- Rate at which a chemical is removed from the plasma by the kidney

- Indicates kidney efficiency, glomerular damage, progression of renal disease

- Tests: Inulin clearance test, creatinine clearance test

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Ureters

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- Tubular organs, about 25 cm long

- Each begins as renal pelvis in kidney

- Join the urinary bladder in the pelvic cavity

- Wall consists of 3 layers: Inner mucous coat (Transitional epithelium), middle muscular coat, outer fibrous coat

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Kidney Stones

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- Can be composed of uric acid, calcium oxalate, calcium phosphate, or magnesium phosphate

- Form in collecting ducts or renal pelvis of kidney

- Causes severe pain, nausea & vomiting, blood in urine

- 60% of kidney stones pass on their own; others can be shattered with lithotripsy or removed surgically

- Tendency to form these stones is inherited, specially calcium stones

- Causes: Calcium supplements, Excess vitamin D, urinary tract blockage, UTI

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Urinary bladder

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- Hollow, distensible, muscular organ located within the pelvic cavity, posterior to the pubic symphysis & inferior to the parietal peritoneum

- Storage organ for urine

- Contacts the anterior walls of the uterus & vagina in female, lies against the rectum in male

- Wall consists of 4 layers: Inner mucous coat, submucous coat, muscular coat, & outer serous coat

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Internal Urethral Sphincter

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- Surrounds the neck of the bladder

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Urethra

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- Tubular organ that conveys urine from the urinary bladder to the outside of the body

- Lined with a mucous membrane, & has a thick layer of longitudinal smooth muscle fibers

- Has many mucous glands (urethral glands)

- Female: 4 cm long, external urethral orifice is anterior to vaginal opening

- Male: 19.5 cm long, dual function for both urination & reproduction

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Micturition or Urination reflex

Back 55

- Urine leaves the urinary bladder by this