27-1

Human Anatomy, First Edition

McKinley & O'Loughlin

Chapter 27 : Urinary System

27-2

General Structure and Functions of the Urinary System General Concept:

Waste products accumulate in blood

Are toxic Must be removed to maintain

homeostasis Urinary System organs

remove waste products from the blood then from the body

Major homeostatic system

27-3

General Structure and Functions of the Urinary System

Organs of the Urinary System: Kidneys Ureters Urinary Bladder Urethra

Primary organs: kidneys filter waste products from the bloodstream convert the filtrate into urine.

The Urinary Tract: Includes:

ureters urinary bladder urethra

Because they transport the urine out of the body.

4

5

6

27-7

Functions of the Urinary System Removing waste products from the bloodstream. Storage of urine.

the urinary bladder is an expandable, muscular sac that can store as much as 1 liter of urine

Excretion of urine. Blood volume regulation.

the kidneys control the volume of interstitial fluid and blood under the direction of certain hormones

Regulation of erythrocyte production. as the kidneys filter the blood, they are also

indirectly measuring the oxygen level in the blood Erythropoietin (EPO): hormone produced by kidney

Released if blood oxygen levels fall Stimulates RBC production in red bone marrow

27-8

Kidneys: Gross and Sectional Anatomy Retroperitoneal

Anterior surface covered with peritoneum

Posterior surface against posterior abdominal wall

Superior pole: T-12 Inferior pole: L-3 Right kidney ~ 2cm lower than left Adrenal gland on superior pole

9

27-10

Kidneys: Gross and Sectional Anatomy

Hilum: concave medial border Renal sinus: internal space

Houses blood vessels, lymphatic vessels, nerves

Houses renal pelvis, renal calyces Also fat

27-11

Kidneys: Gross and Sectional Anatomy Surrounding tissues, from deep to

superficial: Fibrous capsule (renal capsule)

Dense irregular CT Covers outer surface

Perinephric fat (adipose capsule) Also called perirenal fat Completely surrounds kidney Cushioning and insulation

Renal fascia Dense irregular CT Anchors kidney to posterior wall and peritoneum

Paranephric fat Between renal fascia and peritoneum

12

27-13

Kidneys: Gross and Sectional Anatomy Sectioned on a coronal plane:

Renal Cortex Renal arches Renal columns

Renal Medulla Divided into renal pyramids 8 to 15 per kidney Base against cortex Apex called renal papilla

27-14

Kidneys: Gross and Sectional Anatomy Minor calyx:

Funnel shaped Receives renal papilla 8 to 15 per kidney, one per pyramid

Major calyx Fusion of minor calyces 2 to 3 per kidney

Major calyces merge to form renal pelvis Renal Lobe

Pyramid plus some cortical tissue 8 to 15 per kidney

15

16

27-17

Blood Supply to the Kidney About 20 to 25% of cardiac output

to kidneys Path:

Renal artery to segmental arteries to interlobar arteries to arcuate arteries to interlobular arteries to:

Afferent arteriole to glomerulus to efferent arteriole to peritubular capilaries and vasa recta

18

27-19

Blood Supply to the Kidney Blood plasma is filtered across the

glomerulus into the glomerular space. Once the blood plasma is filtered

blood leaves the glomerulus enters an efferent arteriole.

efferent arteriole is still carrying oxygenated blood a gas and nutrient exchange with the

kidney tissues has not yet occurred.

27-20

Blood Supply to the Kidney

The efferent arterioles branch into one of two types of capillary networks: peritubular capillaries vasa recta these capillary networks are responsible

for the actual exchange of gases and nutrients

Peritubular capillaries: primarily in cortex Vasa recta: surround the thin tubes that

project into the medulla.

27-21

Blood Supply to the Kidney Path for veins:

Interlobar veins to arcuate veins to interlobar veins to the renal vein

22

27-23

Nephrons The functional filtration unit in the kidney. Consists of the following:

Renal corpuscle Glomerulus Glomerular capsule (Bowman’s capsule)

Proximal convoluted tubule (PCT) Nephron loop (loop of Henle)

Ascending loop of Henle Descending loop of Henle

Distal convoluted tubule (DCT) collectively called the renal tubule

In both kidneys: approximately 2.5 million nephrons.

Are microscopic: measure about 5 centimeters in length.

27-24

Nephrons Cortical Nephrons

Near peripheral edge of cortex Short nephron loops Have peritubular capillaries

Juxtamedullary nephrons Near corticomedullary border Long nephron loops Have vasa recta

25

27-26

Urine Formation Three processes Filtration

Renal corpuscle: forms filtrate From blood to tubule

Reabsorption Mostly PCT Water and salt: rest of nephron From tubule to blood

Secretion From blood to tubule

27-27

Renal Corpuscle Vascular pole

Afferent and efferent arterioles Tubular pole

Connects to PCT Two structures:

Glomerulus and glomerular capsule Glomerulus

Capillary bed High pressure fenestrations

27-28

Renal Corpuscle Glomerular Capsule

Parietal layer Simple squamous epithelium

Visceral layer Podocytes

Pedicels Filtration slits

Capsular space (Bowman’s capsule): location of filtrate

Filtration membrane Fenestrations Filtration slits

29

30

27-31

Proximal Convoluted Tubule Begins at tubular pole of the renal

corpuscle. Cells: simple cuboidal epithelium

actively reabsorb from the filtrate: almost all nutrients (glucose and amino acids) electrolytes plasma proteins

Osmosis: reabsorption of 60% to 65% of the water in filtrate.

Have microvilli Solutes and water:

moved into blood plasma via the peritubular capillaries.

27-32

Nephron Loop (loop of Henle) originates at end of proximal convoluted

tubule projects toward and/or into the medulla. Each loop has two limbs.

descending limb: from cortex toward and/or into the medulla

ascending limb: returns back to the renal cortex

33

34

27-35

Distal Convoluted Tubule begins at the end of the thick ascending limb of

the nephron loop adjacent to the afferent arteriole (important

physiologically) Juxtaglomerular apparatus.

primary function: Secretion From blood plasma to filtrate. secretes ions

potassium (K+) acid (H+)

Reabsorption of water also occurs: influenced by two hormones

Aldosterone antidiuretic hormone (ADH).

27-36

Collecting Collecting Ducts Function in a well hydrated person:

transport the tubular fluid into the papillary duct and then into the minor calyx.

Function in a dehydrated person: water conservation more-concentrated urine is produced.

ADH can act on the collecting duct epithelium Cells become permeable to water Water moves from filtrate into blood plasma Involves vasa recta.

27-37

Innervation of the Kidney innervated by a mass of autonomic nervous

system fibers called the renal plexus.

The renal plexus accompanies each renal artery enters the kidney through the hilum.

27-38

Urinary Tract : Ureters long, fibromuscular tubes conduct urine from the kidneys to the urinary

bladder. average 25 centimeters in length retroperitoneal. ureters originate at the renal pelvis extend inferiorly to enter the posterolateral wall of

the base of the urinary bladder. wall is composed of three concentric tunics.

mucosa muscularis adventitia.

27-39

Urinary Tract – Urinary Bladder The urinary bladder:

expandable, muscular container serves as a reservoir for urine

positioned immediately superior and posterior to the pubic symphysis.

in females the urinary bladder is in contact with the uterus

posterosuperiorly and with the vagina posteroinferiorly. in males

it is in contact with the rectum posterosuperiorly and is immediately superior to the prostate gland.

is a retroperitoneal organ. when empty exhibits an upside-down pyramidal shape. Filling with urine distends it superiorly until it assumes

an oval shape.

27-40

Urinary Tract – Urinary Bladder Trigone

posteroinferior triangular area of the urinary bladder wall

formed by imaginary lines connect the two posterior ureteral openings and the anterior urethral opening.

The trigone remains immovable as the urinary bladder fills and evacuates.

It functions as a funnel directs urine into the urethra as the bladder wall

contracts four tunics

mucosa submucosa Muscularis: called the detrusor muscle adventitia.

Internal urethral sphincter (smooth muscle)

41

42

43

27-44

Micturition (Urination) The expulsion of urine from the bladder. Initiated by a complex sequence of events

called the micturition reflex. The bladder is supplied by both

parasympathetic and sympathetic nerve fibers of the autonomic nervous system.

27-45

Urethra Fibromuscular tube

exits the urinary bladder through the urethral opening at anteroinferior surface

conducts urine to the exterior of the body. Tunica mucosa: is a protective mucous membrane

houses clusters of mucin-producing cells called urethral glands.

Tunica muscularis: primarily smooth muscle fibers help propel urine to the outside of the body.

Two urethral sphincters: Internal urethral sphincter

restrict the release of urine until the pressure within the urinary bladder is high enough

External urethral sphincter and voluntary activities needed to release the urine are

activated.

27-46

Urethra The internal urethral sphincter

involuntary (smooth muscle) superior sphincter surrounding the neck of the

bladder, where the urethra originates. a circular thickening of the detrusor muscle controlled by the autonomic nervous system

The external urethral sphincter inferior to the internal urethral sphincter formed by skeletal muscle fibers of the urogenital

diaphragm. a voluntary sphincter controlled by the somatic nervous system this is the muscle children learn to control when they

become “toilet-trained”

27-47

Female Urethra Has a single function:

to transport urine from the urinary bladder to the vestibule, an external space immediately internal to the labia minora

3 to 5 centimeters long, and opens to the outside of the body at the external urethral orifice located in the female perineum.

48

27-49

Male Urethra Urinary and reproductive functions:

passageway for both urine and semen Approximately 18 to 20 centimeters long. Partitioned into three segments:

prostatic urethra is approximately 3 to 4 centimeters long and is the most dilatable portion of the urethra

extends through the prostate gland, immediately inferior to the male bladder, where multiple small prostatic ducts enter it

membranous urethra is the shortest and least dilatable portion extends from the inferior surface of the prostate gland through

the urogenital diaphragm spongy urethra is the longest part (15 centimeters)

encased within a cylinder of erectile tissue in the penis called the corpus spongiosum

extends to the external urethral orifice

50

27-51

Aging and the Urinary System Changes in the size and functioning of the kidneys begin

at 30. Gradual reduction in kidney size. Reduced blood flow to the kidneys. Decrease in the number of functional nephrons. Reabsorption and secretion are reduced. Diminished ability to filter and cleanse the blood. Less aldosterone or antidiuretic hormone. Ability to control blood volume and blood pressure is

reduced. Bladder decreases in size. More frequent urination. Control of the urethral sphincters—and micturition—

may be lost.

52