The Excretory System

Functions of the Urinary System

Filtration of the blood– Occurs in the glomerulus of the kidney

nephron– Contributes to homeostasis by removing

toxins or waste

Unit 1 - Objective 1

Urinary System

Renal arteryKidney

Ureter

Urinary Bladder

Renal Vein

For sphincters, see next slide

Functions of the Urinary System

Reabsorption of vital nutrients, ions and water– Occurs in most parts of the kidney

nephron– Contributes to homeostasis by

conserving important materials

Unit 1 - Objective 1

Urinary System

Internal urethral sphincterExternal Urethral Sphincter

Male Sphincters Female Sphincters

Functions of the Urinary System

Secretion of excess materials– Assists filtration in removing material

from the blood– Contributes to homeostasis by

preventing a build-up of certain materials in the body such as drugs, waste,etc.

Unit 1 - Objective 1

Functions of the Urinary System

Activation of Vitamin D– Vitamin D made in the skin is converted to

Vitamin D3 by the kidney– Active Vitamin D (D3) assists homeostasis

by increasing calcium absorption from the digestive tract

Functions of Kidney Structures

The Renal Artery– Transports oxygenated blood from the

heart and aorta to the kidney for filtration

Functions of Kidney Structures

Renal Vein– Transports filtered and deoxygenated

blood from the kidney to the posterior vena cava and then the heart

Unit 1 - Objective 1

Functions of Kidney Structures

Nephron– The physiological unit of the kidney used

for filtration of blood and reabsorption and secretion of materials

Functions of Kidney Structures

Capsule– The outer membrane that encloses,

supports and protects the kidney

Functions of Kidney Structures

Cortex– The outer layer of the kidney that contains

most of the nephron; main site for filtration, reabsorption and secretion

Unit 1 - Objective 1

Functions of Kidney Structures

Medulla– inner core of the kidney that contains the

pyramids, columns, papillae, calyces, pelvis and parts of the nephron not located in the cortex; used for salt, water and urea absorption

Unit 1 - Objective 1

Functions of Kidney Structures

Ureter– Transports urine from the renal pelvis to

the bladder

Functions of Kidney Structures

Renal Pyramids– Triangular shaped units in the medulla that

house the loops of Henle and collecting ducts of the nephron; site for the counter-current system that concentrates salt and conserves water and urea

Diagram of Kidney Nephron

Efferent arteriole

Afferent arteriole

Bowman’s capsule

Collecting duct

Proximal convoluted tubuleGlomerulus

Peritubular capillaries

Vasa recta

Decending limb of loop of Henle

Ascending limb of loop of Henle

Distal convoluted tubule

Functions of Nephron Structures

Glomerulus– The site for blood filtration– operates as a nonspecific filter; in that, it will

remove both useful and non-useful material

– the product of the glomerulus is called filtrate

Functions of Nephron Structures

Bowman’s Capsule– A sac that encloses Bowman’s Capsule and

transfers filtrate from the glomerulus to the Proximal Convoluted Tubule (PCT)

Unit 1 - Objective 1

Functions of Nephron Structures

– The primary site for secretion (elimination) of drugs, waste and hydrogen ions

– Saves water for the body

Site of Filtration

Glomerulus– the Glomerulus is the site of filtration– the filtration mechanism is sieve-like and

consists of fenestrated glomerular capillaries, podocytes and a basement membrane that allows free passage of water and solutes smaller than plasma proteins

The Juxtaglomerular Apparatus

Used in maintaining blood pressure

Disorders of the Urinary System

Renal Calculi (kidney stones)– caused by the crystallization of calcium,

magnesium or uric acid salts that precipitate in the renal pelvis.

– If the calculi become large and travel down the ureter, they can cause excruciating pain

Disorders of the Urinary System

Cystitis– typically caused by bacteria from the anal

region, but, can also be caused by sexually transmitted diseases and various chemical agents

– can lead to inflammation, fever, increased urgency and frequency of urination and pain

Disorders of the Urinary System

Glomerulonephritis ( Bright’s Disease)– caused by inflammation of the glomeruli due

to an abnormal immune response (autoimmune, streptococcal antibody complexes).

– Inflammation of the glomeruli leads to faulty filtration (passage of blood cells and proteins) and possible kidney failure.

Unit 1 - Objective 1

Disorders of the Urinary System

Incontinence– caused by loss of the ability to control

voluntary micturition (releasing urine from the bladder) due to age, emotional disorders pregnancy, damage to the nervous system, stress, excessive laughing and coughing

– leads to wetting of clothing, discomfort and embarrassment

Dialysis Therapy

Dialysis is a process that artificially removes metabolic wastes from the blood in order to compensate for kidney (renal) failure. Kidney failure results in the rapid accumulation of nitrogen waste (urea, etc.) which leads to azotemia. Uremia and ion disturbances can also occur. This condition can cause acidosis, labored breathing, convulsions, coma and death.

Dialysis Therapy

The most common form of dialysis is hemodialysis which uses a machine to transfer patient’s blood through a semipermeable tube that is permeable only to selected

substances.

Dialysis Therapy

Some key aspects of hemodialysis are:

- blood is typically transferred from an arm artery

- after dialysis, blood is typically returned to an arm vein

- to prevent clotting, blood is typically heparinized

- dialysis sessions occur about three times a week

- each dialysis session can last four to eight hours!

- long term dialysis can lead to thrombosis (fixed blood clots),

infection and death of tissue around a shunt (the blood access

site in the arm)

Source:

Modified from Robert F. Allen