EXCRETORY SYSTEM

What is Excretion?

The process of ridding the body of waste in order to maintain homeostasis.

Excretory System

How does the excretory system maintain homeostasis?

–It regulates heat, water, salt, acid-base concentrations and metabolite concentrations

ORGANS OF EXCRETION

Skin and associated glands: – sweat is removed by skin as a waste

product trying to Remove heat and salts

Lungs: Removes carbon dioxide

Liver: – get rid of unneeded wastes in the body. It changes toxic

ammonia, which is a poisonous gas , to urea, a harmless fluid.

Kidneys; removes nitrogenous waste (urea)

What is the Function of the Human Excretory System?

Maintain proper water balance in the body and to also remove liquid waste (urine)Kidneys filter approximately200L of blood or filtrate everydayRemove approximately 1-2 L of fluid everyday

Parts of the human excretory System

KidneysUretersUrinary bladderurethra

Urinary System

Kidneys

Kidneys: – filter blood to produce urine.. Maintain

water balance and rid body of nitrogenous waste (urine) created by the liver

The kidney is a lima bean shaped structure found on both sides of the spinal column in the lower back

The Kidney

KIDNEY PARTS Kidney has three distinct regionsCortex: – the outer part– Function: filter blood

Medulla:– the middle part made up of collecting ducts– Function: collect filtrate (filtered materials from the

blood) and carries it to the renal pelvisPelvis: – the inner cavity where urine collects. It is connected to

the ureters– Function: Filtrate (now called urine) drains from the

pelvis into the ureters for removal

MAJOR FUNCTIONSOF KIDNEYS

1. Filters blood of:  Urea – formed in the liver from the

breakdown of ammonia Creatinine – formed in the muscles Uric Acid – formed as a result of the

breakdown of nucleic acids (DNA and RNA)

2. Controls the balance of water in our bodies3. Regulates pH of the blood4. Regulates the concentration of dissolved ions in the blood

5. Secretes a hormone that causes a production of red blood cells

6. Activates Vitamin D production in the skin

Parts of Excretory system cont’d

Urinary Bladder: – hollow muscular pouch located in the pelvis – Function: hold urine until it is released from the body. A

typical bladder is able to hold up to about 500ml of urine.

Urethra: – hollow tube leading from the bladder to the outside of the human

body– function: carries urine from the bladder to the outside of the body.

Ureters: – hollow tubes connecting the renal pelvis to the urinary bladder– Function: carry urine from the kidney to the urinary bladder

IMPORTANT BLOOD VESSELS

Renal Artery: carries contaminated blood into the kidney.

Renal Vein: carries purified blood from the kidney and returns it back into circulation by way of the inferior vena cava.

NEPHRONS

Tiny filtering units called nephrons fill the cortex and medulla of the kidney.Basic functional unit of kidney responsible for filtering the blood and maintaining proper water balanceExtends from renal cortex (glomerulus/ Bowman's capsule) into the renal medulla (loop of Henle)Each kidney contains 1 to 1.25 million nephrons.

Parts of the NephronRenal artery: – this is the artery that carries blood TO the kidney to be filtered

Renal vein:– this is the vein that carries blood FROM the kidney AFTER it has been filtered

Glomerulus;– A tight ball of blood capillaries located in the Bowman's capsule of Nephron. – Blood pressure created here causes material to be filtered from the blood

Bowman's capsule: – A cup shaped structure that receives filtrate from the Glomerulus

Proximal tubule: – tube connected to the Bowman's capsule. – Filtrate enters the proximal tube from the Bowman's capsule.– Reabsorption of Amino Acids and Glucose occurs here

Loop of henle:– long u shaped tube that extends into the renal medulla.

Responsible for maintain salt balance by reabsorption or releasing salt in the filtrarte

Distal tubule;– tube extending from the loop of henle. – It also reabsorbs materials from the filtrarte . Tubular secretions

occurs here. Materials such as creatinine and drugs are added to the filtrate

Collecting tubule: – tube that extends from the distal tubule to the renal pelvis. This

portion of the nephron is mainly responsible for reabsorption of water

Nephron Function (4 stages)

1. Filtration:

Blood travels from the renal artery, to an arteriole and then into the glomerulus, a mass of capillaries surrounded by the Bowman’s capsule.

Blood pressure forces some plasma of the blood, containing both waste and useful material, into the Bowman’s capsule. This material is called the nephric filtrate.

The filtrate contains such things as: water, urea, uric acid, salt, glucose, amino acids, ions and vitamins.

1. FiltrationFiltration – Hydrostatic pressure (blood pressure) forces water and dissolved substances out of the glomerular blood into Bowman’s capsule.H2O, glucose, amino acids, electrolytes, wastesAverages 125 ml/min for both kidneys Æ180 liters/dayThe vast majority of the filtrate must be taken back

2. Re-absorption:

From the Bowman’s capsule the filtrate is pushed into the proximal tubule. The process of re-absorption, of useful materials within the filtrate, into the capillary network that surrounds the nephron than begins.

Reabsorption occurs by osmosis, diffusion, and active transport

Reabsorbed materials include water, glucose, amino acids, ions and vitamins

When the filtrate reaches the end of the distal tubule the solution is isotonic (the filtrate and the surrounding cells have the same concentration of water and solutes).

The filtrate then moves down the descending loop of Henle; as the loop descends further into the inner medulla, sodium concentrations in the surrounding tissue increase which draws water out of the filtrate (by osmosis).

At the bottom of the loop sodium ions in the filtrate are at high concentration and therefore diffuse out of the tubule.

Positive sodium ions are followed by negative chloride ionsWater cannot reenter the ascending loop because this loop is impermeable to water

H2O - osmosisNaCl - active transportGlucose, amino acids - active co-transport

3. Secretion

Occurs in the distal tubule

Involves active transport of substances from the capillaries into the tubule

Substances include hydrogen ions, creatinine and drugs

4. Elimination

The fluid than enters the collecting duct as urine. It passes through the pelvis into the ureter.

Most of the water, ions and useful nutrients (glucose, amino acids) have been reabsorbed.

Path of filtrate through nephron:

Bowman’s capsule - proximal tubule - loop of Henle - distal tubule - collecting duct

Control of Water Balance

When water levels are too low:

1) The hypothalamus stimulates the pituitary gland to secrete a hormone called anti-diuretic hormone (ADH) or Vasopressin. ADH travels through blood to kidneys.

2) ADH increases the permeability of the tubules and collecting ducts

3) More water is reabsorbed into the blood so the urine is more concentrated

When water levels are too high:

1)Hypothalamus doesn’t stimulate ADH secretion

2)Little water is reabsorbed into the blood so the urine is more dilute.

Other

Aldosterone: affects distal tubule and collecting tubule to reabsorb sodium ionsANP( atrial natruuretic peptide: increase glomerulus filtration rate by dilating the arterioles and inhibits the collecting ducts from reabsorbing sodum.

Excretory System Disoders

These are problems associated with the kidneys, bladder , or uretersWe will examine the following disorders:– 1. Urinary tract Infections

• Cystitus• Ureyhritis• Pyelonephritis

– 2. Kidney stones– 3. Kidney Failure

Urinary Tract Infections UTI’s

These are Bacterial Infections of the kidneys, bladder or UrethraThere are 3 types of UTI’s– 1. Cystitis- infection of the bladder– 2. Urethritis- infection of the urethra (tube leading

from the bladder to the outside of the body)– 3. Pyelonephritis- infection of the kidney

Causes of UTI’s

Bacteria from the anus (femalesBlocked prostate (men)Bacterial infection from other areas of the bodyNote: UTI’s are more common in females than males

Symptoms of UTI’s

Painful urinationBurning sensationBloody or brown urineChills, fever, nausea

Danger and Treatments

Danger of UTI’s– Permanent damage to the kidneys and possible

kidney failure.

Treatments of UTI’s– antibiotics

2. Kidney Stones

What are Kidney Stones?– These are hard crystals of calcium oxalate or uric

acid that foem in the kidney bladder or ureter/urethra– Kidney stones form when materials in the urine

solidify– Kidney stones are more common in men than

women

Causes of Kidney Stones?

Urinary tract infectionsNot drinking enough waterToo much vitamin C and D

Symptoms of Kidney Stones

Severe pain in abdomen and backBlood in urineNauseavomiting

Treatments of Kidney Stones

Change dietDrink lots of waterUltrasound( breaks them up so they can pass) called lithotripsySurgery (open)Incision through the back (nephrolithotomyInsertion of thin telescopic instrument into urinary tract( ureteroscopsy)

Kidney Failure

When the kidneys are not working correctly, waste products and excess fluid can build up and the levels of sodium, potassium, phosphate and calcium are not regulated correctly.

symptoms of kidney disease, which can include high blood pressure, excessive tiredness, fluid retention and possibly lower back pain.

CausesKidney damage can occur for a number of reasons diabetes, high blood pressure, infections and a group of diseases that affect the glomerulus. The kidneys also need an adequate supply of blood, so if there is something wrong with the blood vessels to the kidney, such as a narrowing, this will prevent the kidneys from working efficiently.

Treatments

dialysis – cleans and filters your blood using a machine to temporarily

rid your body of harmful wastes, extra salt, and extra water. Hemodialysis helps control blood pressure and helps your body keep the proper balance of important chemicals such as potassium, sodium, calcium, and bicarbonate.

– Dialysis can replace part of the function of your kidneys. Diet, medications, and fluid limits are often needed as well. Your diet, fluids, and the number of medications you need will depend on which treatment you choose.

Kidney transplantation – surgically places a healthy kidney from another

person into your body. The donated kidney does enough of the work that your two failed kidneys used to do to keep you healthy and symptom free.