The Human Excretory The Human Excretory SystemSystem

MAJOR POINTSMAJOR POINTS

Major Points:Major Points: All cells produce waste All cells produce waste

products.products. Cells must maintain Cells must maintain

stable internal stable internal environments, called… environments, called… homeostasishomeostasis..

If cells did not get rid If cells did not get rid of waste, then as of waste, then as waste levels increase, waste levels increase, levels may become levels may become toxic, and cells may toxic, and cells may die.die.

To maintain To maintain homeostasis, homeostasis, organisms perform organisms perform EXCRETIONEXCRETION

Excretion = the removal from an Excretion = the removal from an organism organism of the toxic waste products of of the toxic waste products of metabolism.metabolism.

The waste produced by each individual cell The waste produced by each individual cell is exported into the blood. is exported into the blood.

The blood then transports waste to specific The blood then transports waste to specific organs that are specialized for waste organs that are specialized for waste removal (excretion). removal (excretion).

KidneysKidneys are the major organs involved in are the major organs involved in excretion.excretion.

You have 2 of them, bean-shaped, located You have 2 of them, bean-shaped, located in the small of your back, one behind the in the small of your back, one behind the stomach, and one behind the liver.stomach, and one behind the liver.

How does waste travel?How does waste travel?

Examples of Excretion Examples of Excretion PathwaysPathways

NHNH33 (ammonia) in (ammonia) in cells enters blood and cells enters blood and travels…travels…

To the liver to be To the liver to be converted to UREA converted to UREA (less toxic). Urea (less toxic). Urea travels…travels…

To the kidneys, then To the kidneys, then ureters that connect ureters that connect to the bladder…to the bladder…

The bladder empties The bladder empties into the urethra which into the urethra which moves waste OUT!moves waste OUT!

Another example of Another example of excretionexcretion……

COCO22 in the cells in the cells to…to…

excreted into the excreted into the blood…blood…

blood flows to blood flows to the lungs…the lungs…

and out when and out when you exhale!you exhale!

Important BeansImportant Beans

There are 3 main parts of the kidney:There are 3 main parts of the kidney:– Cortex (outermost part-- 1/3 of kidney)Cortex (outermost part-- 1/3 of kidney)– Medulla (inner 2/3 of the kidney) Medulla (inner 2/3 of the kidney) – Renal Pelvis is in the center… Funnel-shaped with Renal Pelvis is in the center… Funnel-shaped with

renal artery and renal veinrenal artery and renal vein Renal artery brings blood, wastes, and Renal artery brings blood, wastes, and

nutrients into the kidneys so kidneys can take nutrients into the kidneys so kidneys can take care of waste removal and proper absorption.care of waste removal and proper absorption.

Kidneys are made of millions of nephrons.Kidneys are made of millions of nephrons. Nephrons are the functional units of the Nephrons are the functional units of the

kidneys.kidneys.

Nephrons:Nephrons:

The functional unit The functional unit of the kidney.of the kidney.

3 Important things 3 Important things happen here:happen here:– FiltrationFiltration– Re-absorptionRe-absorption– SecretionSecretion

(Blood vessels surround nephrons)

The Three Stages:The Three Stages:#1: Filtration#1: Filtration

Materials from the blood are forced out of the Materials from the blood are forced out of the glomerulus (pack of blood capillaries) and into the glomerulus (pack of blood capillaries) and into the Bowman’s capsule (nephron) during this process.Bowman’s capsule (nephron) during this process.

High pressure also forces water, urea, glucose, High pressure also forces water, urea, glucose, vitamins, water, and salts through thin capillary walls vitamins, water, and salts through thin capillary walls of the glomerulus into the Bowman’s capsule.of the glomerulus into the Bowman’s capsule.

About 1/5About 1/5thth of the fluid portion of blood filters into the of the fluid portion of blood filters into the capsule.capsule.

The rest remains in the blood, along with big proteins The rest remains in the blood, along with big proteins and cells that are too large to fit through capillary and cells that are too large to fit through capillary walls.walls.

In a healthy kidneyIn a healthy kidney, the filtrate, the fluid entering the , the filtrate, the fluid entering the nephron, does not contain large proteins.nephron, does not contain large proteins.

#2: Reabsorption#2: Reabsorption Because filtration is non-selective, Because filtration is non-selective, it is it is

important that small molecules essential important that small molecules essential to the body be returned to blood fluid.to the body be returned to blood fluid.

The proximal tubule, the loop of Henle, The proximal tubule, the loop of Henle, and part of the distal tubule, are mainly and part of the distal tubule, are mainly responsible for this.responsible for this.

Glucose, sodium, potassium, & calcium are Glucose, sodium, potassium, & calcium are all returned to the blood (by active all returned to the blood (by active transport… we’ll learn about this soon).transport… we’ll learn about this soon).

In this region, much of the water in the In this region, much of the water in the filtrate returns to the blood (due to filtrate returns to the blood (due to osmosis…we’ll learn more about osmosis osmosis…we’ll learn more about osmosis later too).later too).

#3: Secretion#3: Secretion

As the filtrate reaches the distal As the filtrate reaches the distal tubule, some bad substances from the tubule, some bad substances from the blood enter/re-enter the filtrate by a blood enter/re-enter the filtrate by a process called secretion.process called secretion.

These substances include wastes and These substances include wastes and toxic materials… we want to get rid of toxic materials… we want to get rid of these!these!

The pH of the blood is also adjusted The pH of the blood is also adjusted here with the help of hydrogen ions here with the help of hydrogen ions that are secreted from blood to filtrate.that are secreted from blood to filtrate.

Urine FormationUrine Formation The filtrate and wastes that remain in the distal The filtrate and wastes that remain in the distal

tubule form urine.tubule form urine. Urine from several tubules flow into a collecting Urine from several tubules flow into a collecting

duct.duct. More water is reabsorbed back into the blood in More water is reabsorbed back into the blood in

this region. this region. The high salt concentration outside of the The high salt concentration outside of the

collecting duct is maintained by the loop of Henle collecting duct is maintained by the loop of Henle with active transport. Negative Cl ions are with active transport. Negative Cl ions are pumped out, and positive Na ions follow, keeping pumped out, and positive Na ions follow, keeping the salt gradient higher outside the nephron, the salt gradient higher outside the nephron, allowing water to diffuse back into the blood by allowing water to diffuse back into the blood by osmosis, keeping you more hydrated!osmosis, keeping you more hydrated!

Elimination of UrineElimination of Urine Urine from the collecting Urine from the collecting

ducts flows through the ducts flows through the renal pelvis and into a renal pelvis and into a tube called a ureter.tube called a ureter.

A ureter leads from each A ureter leads from each kidney to the urinary kidney to the urinary bladder.bladder.

Muscular contractions Muscular contractions send urine out of the send urine out of the body through the urethra.body through the urethra.

At leastAt least 500ml of urine 500ml of urine mustmust be eliminated every be eliminated every day to get rid of the day to get rid of the waste your body makes.waste your body makes.

A normal adult makes between 1.5 L to A normal adult makes between 1.5 L to 2.3 L of urine a day, depending upon2.3 L of urine a day, depending uponhydration level, and how much water hydration level, and how much water is lost through respiration and perspiration.is lost through respiration and perspiration.

MAJOR POINTSMAJOR POINTS

Kidney VersatilityKidney Versatility If you are very dehydrated, the kidney is If you are very dehydrated, the kidney is

able to secrete very concentrated urine in a able to secrete very concentrated urine in a small volume, making it possible to small volume, making it possible to discharge wastes with minimal water loss.discharge wastes with minimal water loss.

However, if you have consumed an However, if you have consumed an excessive amount of fluid, kidneys can excessive amount of fluid, kidneys can excrete a large amount of dilute urine, excrete a large amount of dilute urine, making it possible to eliminate a lot of making it possible to eliminate a lot of water, while still holding onto essential salts.water, while still holding onto essential salts.

This versatility is due to nervous and This versatility is due to nervous and hormonal control.hormonal control.

Antidiuretic Hormone (ADH)Antidiuretic Hormone (ADH)

When the body becomes dehydrated, When the body becomes dehydrated, more ADH is released from the brain more ADH is released from the brain (pituitary gland) and the kidneys reabsorb (pituitary gland) and the kidneys reabsorb more water than normal.more water than normal.

As you begin to re-hydrate, less ADH is As you begin to re-hydrate, less ADH is released, until you have plenty of water in released, until you have plenty of water in the blood fluid, and kidney reabsorb less the blood fluid, and kidney reabsorb less and less water until homeostasis is and less water until homeostasis is achieved!achieved!

Amazing little organs!!... HOMEOSTASIS!Amazing little organs!!... HOMEOSTASIS!

Blood vessels