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ObjectivesObjectives

To begin unit on excretory system.

I.D. elements of the gross anatomy.

- Kidney

- Bladder

- Sphincters

Introduce the nephron and its general function.

Learn some interesting facts about the excretory system.

Functions of the Functions of the Excretory SystemExcretory System�The kidneys excrete nitrogenous wastes, such as

urea, uric acid, creatinine and ammonium.

�The kidneys maintain blood volume by regulating water excreted.

�Monitor blood composition and blood pH by regulating electrolyte excretion.

�Kidneys secrete the enzyme renin, which helps maintain blood pressure.

�The kidneys secrete erythropoietin, which stimulates RBC production.

�Gluconeogenesis during prolonged fasting.

Figure 25.1

Esophagus (cut)Inferior vena cava

Adrenal gland

Hepatic veins (cut)

Renal artery

Renal hilum

Renal vein

Iliac crest

Kidney

Ureter

Urinary

bladder

Urethra

Aorta

Rectum (cut)

Uterus (part

of female

reproductive

system)

Amazing FactsAmazing Facts

About 1100-1200 liters of blood pass through the capillaries in our kidneys every day.

The kidneys filter nearly 200 liters of fluid from the bloodstream every day!

Our kidneys extract about 180 L (45 gallons) of fluid/filtrate.

The kidneys refine the filtrate, and in a typical day we excrete only about 1.5 L of urine.

Figure 25.2a

Body wall

• Perirenal

fat capsule

Renal

artery

Renal

vein

Inferior vena cava

Aorta

• Fibrous

capsule

• Renal fasciaanteriorposterior

Supportivetissue layers

Body of

vertebra L2

PeritoneumPeritoneal cavity

(organs removed)

Anterior

Posterior(a)

Position said to be

Retroperitoneal

Figure 25.3

Renal cortex

Renal medulla

Major calyx

Renal pelvis

Ureter

Minor calyx

Renal column

Renal pyramid

in renal medulla

Fibrous capsule

Renal

hilum

(a) Photograph of right kidney, frontal section (b) Diagrammatic view

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Blood and Nerve SupplyBlood and Nerve Supply

� Renal arteries deliver ~ 1/4 (1200 ml) of cardiac output to the kidneys each minute.

� Most of the blood directed towards cortex, where urine production occurs.

� Nerve supply is via sympathetic fibers from the renal plexus.

Function of the NephronFunction of the Nephron

The functional unit of the kidney.

Primary role is to filter the blood.

Produces concentrated urine.

More than 1 million nephrons are packed into each kidney!

Location of the NephronLocation of the Nephron

o Found in the renal cortex.

o Cortical nephronsaccount for 85% in human kidney.

o Portions of the nephron

extend into the renal

medulla.

Primary parts of NephronPrimary parts of Nephron

1. Glomerulus: a tuft of capillaries

2. Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus

Figure 25.5

Urinary BladderUrinary Bladder

> Muscular sac for temporary storage of urine

> Retroperitoneal, on pelvic floor posterior to pubic symphysis

◦ Males—prostate gland surrounds the neck inferiorly

◦ Females—anterior to the vagina and uterus

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Urinary BladderUrinary Bladder

� Muscular sac for temporary storage of urine

� Retroperitoneal, on pelvic floor posterior to pubic symphysis

◦ Males—prostate gland surrounds the neck inferiorly

◦ Females—anterior to the vagina and uterus

SphinctersSphincters

I. Internal urethral sphincter

� Involuntary (smooth muscle) at bladder-urethra junction

� Contracts to open

II. External urethral sphincter

� Voluntary (skeletal) muscle surrounding the urethra as it passes through the pelvic floor