27-1

The Department of Human anatomy

Urinary System

27-2

Development

The development of the kidney proceeds through a series of successive phases: the pronephros, mesonephros, and metanephros.

27-3

27-4

Pronephros It develops in the cervical region of the

embryo. During approximately day 22 of human gestation, the paired pronephron appear towards the cranial end of the intermediate mesoderm. In this region, epithelial cells arrange themselves in a series of tubules called nephrotomes and join laterally with the pronephric duct. This duct is fully contained within the embryo and thus cannot excrete filtered material outside the embryo; therefore the pronephros is considered nonfunctional in mammals.

27-5

MesonephrosThe development of the pronephric duct

proceeds in a cranial-to-caudal direction. As it elongates caudally, the pronephric duct induces nearby intermediate mesoderm in the thoracolumbar area to become epithelial tubules called mesonephric tubules. The mesonephric tubule forms a capsule around the capillary tuft, allowing for filtration of blood. This filtrate flows through the mesonephric tubule and is drained into the continuation of the pronephric duct, now called the mesonephric duct or Wolffian duct.

27-6

Metanephros During the fifth week of gestation, the

mesonephric duct develops an outpouching, the ureteric bud, near its attachment to the cloaca. This bud, also called the metanephrogenic diverticulum, grows posteriorly and towards the head of the embryo. As the cranial end of the bud extends into the intermediate mesoderm, it undergoes a series of branchings to form the collecting duct system of the kidney.

27-7

Migration After inducing the metanephric mesenchyme

the lower portions of the nephric duct will migrate caudally (downward) and connect with the bladder, thereby forming the ureters. The ureters will carry urine from the kidneys to the bladder for excretion from the fetus into the amniotic sac. As the fetus develops, the torso elongates and the kidneys rotate and migrate upwards within the abdomen which causes the length of the ureters to increase.

27-8

27-9

Development of metanephros

27-10

11

27-12

General Structure and Functions of the Urinary System

Organs of the Urinary System:- Primary organs: Kidneys filter waste products from the

bloodstream convert the filtrate into urine.

- The Urinary Tract: Ureters, Urinary Bladder, Urethra

they transport the urine out of the body.

13

14

15

27-16

Functions of the Urinary System

Removing waste product from the blood, then from the body

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

27-17

Kidneys: Gross and Sectional Anatomy Retroperitoneal

Anterior surface covered with peritoneum

Posterior surface against posterior abdominal wall

Superior pole: Th-12 Inferior pole: L-3 Right kidney ~ 2cm lower than left

18

27-19

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

superficial: Fibrous capsule (renal capsule) Perinephric fat (adipose capsule) Renal fascia Paranephric fat

20

27-21

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

27-22

Kidneys: Gross and Sectional Anatomy

Minor calyx: Funnel shaped Receives renal papilla 8 to 15 per kidney

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

23

27-24

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

flow to kidneys (1500-2000 L/day) 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

25

26

27-27

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.

27-28

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

29

27-30

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

31

Renal CorpuscleGlomerulus

• Capillary bed - rete mirabile arteriosum (wonderful network )• High pressure• fenestrations

27-32

Proximal Convoluted Tubule Begins at tubular pole of the renal

corpuscle. 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

27-33

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

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 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.

27-37

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.

38

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

27-43

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 External urethral sphincter

27-44

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”

27-45

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.

46

27-47

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

48

27-49

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.