The Urinary System

Anterior view KIDNEY Produces urine URETER Transports urine toward the urinary bladder URINARY BLADDER Temporarily stores urine prior to elimination URETHRA Conducts urine to exterior Figure 26-1: An Introduction to the Urinary System

5 Functions of the Urinary System 1.Regulating blood volume and blood pressure: adjusts volume of water lost in urine, and releasing erythropoietin and renin. 2.Regulating concentrations of certain ions (sodium, potassium, etc.) in plasma: controls quantities lost in urine

5 Functions of the Urinary System 3.Helps maintain blood pH: controlling loss of hydrogen and bicarbonate ions in urine. 4. Conserving nutrients: by preventing excretion in urine 5.Assist liver: helps to detoxify poisons

Anatomy of the Kidney Veins and arteries: The Renal vein and artery are the main blood suppliers for the kidney and enter at the hilium Calyxes: Cup shaped drains for urine, multiple minor calyxes join to form a major calyx. Cortex: superficial portion of kidney

Anatomy of the Kidney Renal Capsule: layer of collagen fibers that covers the entire outer surface of the kidney Renal Pelvis: The major calyxes of the kidney combine to form the renal pelvis, which drains into the ureters. Medulla: the medulla contains 6-18 renal pyramids, which are one of the base functional structures of the kidney.

Renal Pyramid The base connects to the cortex and the tip (renal papilla) connects to a renal sinus or calyx. A Renal Lobe contains a renal pyramid, the cortex connected to it, and the adjacent renal tissues. The base functional part of a kidney is the nephron, the nephron is supplied with blood by means of the afferent arterioles.

The Nephron The basic functional unit of the kidney Chief function- filter the blood

Figure 26-6: The Functional Anatomy of a Representative Nephron and the Collecting System

The Nephron Consists of the renal tubule – Long tubular passageway AND Renal corpuscle - spherical structure -contains bowman’s capsule which contains the glomerulus ( a capillary network)

Where it Begins Blood arrives at the renal corpuscle Delivered into the glomerulus Glomerulus is where filtration occurs Distal convoluted tubule Parietal epithelium Capsular space Efferent arteriole Glomerular capillary Bowman’s capsule Juxtaglomerular cells Macula densa Juxtaglomerular apparatus Afferent arteriole Proximal convoluted tubule Visceral epithelium Capillary endothelial cell RBC Supporting cell Pores Podocyte Nucleus Lamina Capsular epithelium Capsular space Pedicels Filtration slits (a)(b) Figure 26-8: The Renal Corpuscle

Filtration Blood pressure forces water and dissolved solutes out of the glomerular capillaries into the capsular space Filtration produces a protein free solution, filtrate

The Renal Tubule Major Functions: -Reabsorbing the useful organic nutrients in the filtrate -Reabsorbing most of the water in the filtrate -Secreting any leftover waste products into the tubule

The Renal Tubule has Two Segments The proximal convoluted tubule The distal convoluted tubule Separated by the Loop of Henle

Filtration Water reabsorption Solute reabsorption Secretion Variable rate KEY Glomerulus Urine storage and elimination Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct Bowman’s capsule

The Proximal Convoluted Tubule Contain microvilli Reabsorption water, ions and other organic nutrients Release into the peritubular fluid, the interstitial fluid surrounding the renal tubule

The Distal Convoluted Tubule Secretion of wastes Some selective reabsorption under hormonal control No microvilli

The Loop of Henle Further absorption of water and both sodium and chloride ions Creates a concentration gradient in the medulla

Tubular Fluid Once the filtrate passes through the renal corpuscle and the renal tubule, it is called tubular fluid

The Collecting System Series of tubes that carry tubular fluid away from the nephron

The Collecting Duct Shared by many nephrons Responsible for final reabsorption of water Secretion of sodium, potassium, hydrogen and bicarbonate ions

The Collecting Duct Determines final osmotic concentration and volume of urine Then empties into the minor calyx

The Function of the Nephron Video bU bU

Basic Processes of Urine Formation The goal of urine production is to maintain homeostasis involving the excretion of solutes

Three Distinct Processes Filtration Reabsorption Secretion

Filtration Blood pressure: Forces water and solutes across capillary walls and into capsular space. Solute molecules: If small enough to pass through filtration membrane, they are carried by surrounding water molecules. Ex: coffee filter

Pores in endothelium Lamina densa Pedicels of podocytes Capillary lumen Glomerulus Filtration slitCapsular space (a) Small solute particles Filtrate in capsular space Plasma protein Blood Filtration pressure = 10 mm Hg Filtration slit (b) Figure 26-10: Glomerular Filtration

Reabsorption Occurs after the filtrate has left renal corpuscle (beginning of nephron). Removal of water and solutes from the filtrate and into the peritubular fluid Most reabsorbed materials are nutrients the body can use. Different from filtration: Selective process that is not based on size of solutes.

Secretion The transport of solutes from peritubular fluid to tubular fluid. Tubular fluid lowers plasma concentration of unwanted materials further after the filtration process. Happens primarily at proximal and distal convoluted tubules.

Normal kidney function can only continue if these three processes function within narrow limits

Organic Waste Products in Urine Urea – The most abundant organic waste – Generated through the breakdown of amino acids Creatinine – Generated in skeletal muscle tissue by breakdown of creatine phosphate Uric Acid – Formed through the recycling of nitrogenous bases from RNA molecules

Accessory Organs of the Urinary System

Urine Transport, Storage, and Elimination The ureters, urinary bladder, and urethra are responsible for the transport, storage, and elimination of urine.

The Ureters A pair of muscular tubes that extend from the kidneys to the urinary bladder (about 12 in. long) They extend inferiorly and medially, passing over the anterior surfaces of the psoas major muscles

The Ureters The paths of ureters in men and women are different, due to variations in the nature, size, and position of the reproductive organs In males: -The base of urinary bladder lies between the rectum and the pubic synthesis In females: - The base sits inferior to the uterus and anterior to the vagina

The Ureters The ureteral openings are slit-like rather than rounded This shape helps to prevent backflow of urine toward the ureter and kidneys when the urinary bladder contracts

Histology of the Ureters The wall of each ureter consists of 3 layers: 1.An inner mucosa 2.A middle muscular layer 3.An outer connective-tissue layer

The Urinary Bladder A hollow, muscular organ that functions as a temporary reservoir for the storage of urine Can contain as much as 1 liter of urine

The Urinary Bladder The mucosa lining the urinary bladder is thrown into folds, or rugae The triangular area bounded by openings of the ureters consists of a region called trigone - The trigone acts as a funnel that channels urine into the urethra

Middle umbilical ligament Rugae Center of trigone Prostate gland Neck Membranous urethra Internal urethral sphincter Ureteral openings Ureter Lateral umbilical ligament (c) Urinary bladder in male Prostatic urethra External urethral sphincter (in urogenital diaphragm) Figure 26-18c: Urinary Bladder – Male

Histology of the Urinary Bladder The wall of the urinary bladder contains mucosa, submucosa, and muscularis layers

The Urethra Extends from the neck of the urinary bladder to the exterior of the body In males the distance is around 7-8 in. The male urethra is subdivided in 3 portions: 1.Prostatic urethra 2.Membranous urethra 3.Spongy urethra

(a)Male External urethral orifice Urogenital diaphragm Prostate gland Rectum Peritoneum Urinary bladder Pubic symphysis External urethral sphincter Spongy urethra Urethra [see part (c)] Ureter Figure 26-18a: Urine Conduction and Storage – Male

The Urethra In females, the urethra is very short, extending around 1-2 in. from the bladder to the vestibule. Uterus (b)Female Peritoneum Urinary bladder Pubic symphysis Urethra Vestibule Vagina Rectum External urethral sphincter (in urogenital diaphragm)

Histology of the Urethra The urethral lining consists of stratified epithelium The lamina propria is thick and elastic The mucous membrane is thrown into longitudinal folds

The Effects of Aging on the Urinary System Decline in number of working nephrons: Drops by 30-40% after age 25 Reduced sensitivity: Reabsorption of water and sodium ions happens at a slower rate. Incontinence: The sphincter muscles become weaker. May cause a slow leak of urine. The Micturition reflex is compromised: diseases and age may affect urinary retention, or the ability to control urination.

Diseases of the Urinary System Nephrolithiasis- Kidney stones may form from calcium deposits or uric salts. Cystocele- Occurs in women when something like a hernia occurs and calls the bladder to sag into the vagina. Neurogenic Bladder- Muscles around the bladder that help with urine retention do not function properly. Urinary Tract Infection (UTI)- when bacteria from waste cling to the walls of the urethra and cause irritation, prominent in women but common in everyone.

Occupations Involving the Urinary System Urologist: doctors who diagnose and treat diseases involving the urinary system (i.e. kidney stones, urinary tract infections) Urology Oncologist: a doctor who diagnoses and treats cancer of the urinary system Nephrologist: a doctor who specializes in kidney care and the treatment of diseases of the kidney

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