The Human Excretory The Human Excretory SystemSystem

Biology 2201 Unit 3 Section 4Biology 2201 Unit 3 Section 4

Excretory SystemExcretory SystemThe The kidneys kidneys regulate the amount of water, salts regulate the amount of water, salts and other substances in the blood. and other substances in the blood. The kidneys are fist-sized, bean shaped The kidneys are fist-sized, bean shaped structures that remove nitrogenous wastes structures that remove nitrogenous wastes (urine) and excess salts from the blood. (urine) and excess salts from the blood. The The ureters ureters are tubes that carry urine from the are tubes that carry urine from the pelvis of the kidneys to the urinary bladder. pelvis of the kidneys to the urinary bladder. The The urinary bladder urinary bladder temporarily stores urine temporarily stores urine until it is released from the body. until it is released from the body. The The urethra urethra is the tube that carries urine from is the tube that carries urine from the urinary bladder to the outside of the body. the urinary bladder to the outside of the body. The outer end of the urethra is controlled by a The outer end of the urethra is controlled by a circular muscle called a sphincter.circular muscle called a sphincter.

Excretory SystemExcretory System

The KidneyThe KidneyEach kidney is composed of three Each kidney is composed of three sections: sections: – the outer (renal) cortex, the (renal) medulla the outer (renal) cortex, the (renal) medulla

(middle part) and the hollow inner (renal) (middle part) and the hollow inner (renal) pelvis. pelvis.

The The cortex cortex is where the blood is filtered. is where the blood is filtered.

The The medulla medulla contains the collecting ducts which contains the collecting ducts which carry filtrate (filtered substances) to the pelvis. carry filtrate (filtered substances) to the pelvis.

The The pelvis pelvis is a hollow cavity where urine is a hollow cavity where urine accumulates and drains into the ureter.accumulates and drains into the ureter.

The Parts of the Kidney

How blood is FilteredHow blood is Filtered

The filtering units of the kidneys are the The filtering units of the kidneys are the nephronsnephrons. . There are approximately one million nephrons in There are approximately one million nephrons in each kidney. each kidney. The nephrons are located within the cortex and The nephrons are located within the cortex and medulla of each kidney. medulla of each kidney. The tubes of the nephron are surrounded by The tubes of the nephron are surrounded by cells and a network of blood vessels spreads cells and a network of blood vessels spreads throughout the tissue. Therefore, material that throughout the tissue. Therefore, material that leaves the nephron enters the surrounding cells leaves the nephron enters the surrounding cells and returns to the bloodstream by a network of and returns to the bloodstream by a network of vessels. vessels.

Parts of the NephronParts of the Nephron

Each nephron consists of the following Each nephron consists of the following parts: parts: – 1) glomerulus ; 1) glomerulus ; – 2) Bowman’s capsule ; 2) Bowman’s capsule ; – 3) proximal tubule ; 3) proximal tubule ; – 4) loop of Henle ; 4) loop of Henle ; – 5) distal tubule ; 5) distal tubule ; – 6) collecting duct.6) collecting duct.

The GlomerulusThe Glomerulus

The The glomerulus glomerulus is a mass of thin-walled is a mass of thin-walled capillaries. capillaries. The The Bowman’s capsule Bowman’s capsule is a double-walled, is a double-walled, cup-shaped structure. cup-shaped structure. The The proximal tubule proximal tubule leads from the Bowman’s leads from the Bowman’s capsule to the Loop of Henle. capsule to the Loop of Henle. The The loop of Henle loop of Henle is a long loop which extends is a long loop which extends into the medulla. into the medulla. The The distal tubule distal tubule connects the loop of Henle to connects the loop of Henle to the collecting duct.the collecting duct.~ See Figure 11.19; p. 375.~ See Figure 11.19; p. 375.

How the kidney does its job!How the kidney does its job!Kidney ActionKidney ActionBlood enters Bowman’s capsule through a tiny Blood enters Bowman’s capsule through a tiny artery — (artery — (the renal arterythe renal artery). ). The artery branches to form a The artery branches to form a glomerulusglomerulus. . Blood pressure forces some blood plasma and Blood pressure forces some blood plasma and small particles into the surrounding capsule — small particles into the surrounding capsule — (this is called the (this is called the nephric filtratenephric filtrate). ). Large particles such as blood cells and proteins Large particles such as blood cells and proteins remain in capillaries. remain in capillaries. The nephric filtrate is pushed out of the capsule The nephric filtrate is pushed out of the capsule and into the and into the proximal tubule proximal tubule . . This is where reabsorption begins. This is where reabsorption begins.

Kidney action (cont)Kidney action (cont)

Only materials needed by the body are Only materials needed by the body are returned to bloodstream — for example, returned to bloodstream — for example, 99 % of water, all glucose and amino acids 99 % of water, all glucose and amino acids and many salts are reabsorbed. and many salts are reabsorbed. Osmosis , diffusion, and active transport Osmosis , diffusion, and active transport draw water , glucose , amino acids and draw water , glucose , amino acids and ions from filtrate into surrounding cells. ions from filtrate into surrounding cells. Small villi like projections help in the active Small villi like projections help in the active transport of glucose out of the filtrate and transport of glucose out of the filtrate and speed up the reabsorption process. speed up the reabsorption process. From here, these components return to From here, these components return to the bloodstream.the bloodstream.

Kidney action (cont)Kidney action (cont)

The filtrate reaches the end of the The filtrate reaches the end of the proximal tubule and the fluid is isotonic proximal tubule and the fluid is isotonic with the surrounding cells. with the surrounding cells.

Glucose and amino acids have been Glucose and amino acids have been removed from the filtrate. removed from the filtrate.

The filtrate then moves to the The filtrate then moves to the loop of loop of Henle Henle whose primary function is to whose primary function is to remove water from the filtrate by osmosis. remove water from the filtrate by osmosis.

Kidney action (cont)Kidney action (cont)

There is in increase in sodium There is in increase in sodium concentration in the cells of the loop of concentration in the cells of the loop of Henle as we move from the area of the Henle as we move from the area of the cortex to the inner pelvis of the kidney.cortex to the inner pelvis of the kidney.

This causes water to be drawn from the This causes water to be drawn from the filtrate. filtrate.

These high levels of sodium are a result of These high levels of sodium are a result of active transport and results in increased active transport and results in increased concentration of filtrate (due to water loss).concentration of filtrate (due to water loss).

Why doesn’t water on outside go Why doesn’t water on outside go back in?back in?

The water that left the descending loop The water that left the descending loop cannot enter the ascending loop because cannot enter the ascending loop because it is impermeable to water. it is impermeable to water. As the water concentration in the filtrate As the water concentration in the filtrate decreases, the chlorine concentration decreases, the chlorine concentration increases and causes it to diffuse out of increases and causes it to diffuse out of the tubule. the tubule. This process is helped by the electrical This process is helped by the electrical attraction of chlorine to sodium. .attraction of chlorine to sodium. .

Water (cont)Water (cont)

The filtrate moves to the The filtrate moves to the distal tubule distal tubule where tubular secretion occurs. where tubular secretion occurs. Active transport is used to pull hydrogen Active transport is used to pull hydrogen ions, creatinine, drugs such as penicillin ions, creatinine, drugs such as penicillin out of the blood and into the filtrate. out of the blood and into the filtrate. Fluid from a number of nephrons moves Fluid from a number of nephrons moves from the distal tubules to a common from the distal tubules to a common collecting duct collecting duct which carries what can which carries what can now be called now be called urine urine to the to the renal pelvisrenal pelvis..

NOTENOTE

Since the kidneys control what leaves Since the kidneys control what leaves and what remains in the nephrons, they and what remains in the nephrons, they maintain the levels of water, ions and maintain the levels of water, ions and other materials nearly constant and other materials nearly constant and within the limits to maintain within the limits to maintain homeostasishomeostasis..

Function of the Kidney

The principal function of the kidney is to filter blood in order to remove cellular waste products from the body.

At any given time, 20 % of blood is in the kidneys. Humans can function with one kidney.

If one ceases to work, the other increases in size to handle the workload.

The kidney has other functions but it is usually associated with the excretion of cellular waste such as :

1) urea (a nitrogenous waste produced in the liver from the breakdown of protein. It is the main component of urine) ;

2) uric acid (usually produced from breakdown of DNA or RNA) and

3) creatinine (waste product of muscle action).

All of these compounds have nitrogen as a major component.

The kidneys are more than excretory organs.

They are one of the major homeostatic organs of the body.

They control water pH, secrete erythropoietin (a hormone that stimulates red blood cell production) and activate vitamin D production in the skin.

That is why a doctor can tell so much from a urine sample.

Disorders of the Excretory System

Our excretory system is very important in maintaining homeostasis. There are certain conditions which can affect the excretory system. We will discuss some of these common disorders.

UTI (Urinary Tract Infection)

Is a very common disorder. If the bladder has become infected, it is known as cystitis. If the urethra is infected., it is called urethritis.

UTI is more common in women than men because of differences in anatomy.

Symptoms include painful urination burning sensation), frequent urination (even if no urine present) and bloody or brown urine.

This can lead to chills, fever, nausea, vomiting and upper abdomen tenderness.

Kidney InfectionsResult when an infection reaches the kidneys and becomes known as pyelonephritis.

Common causes can be infection from elsewhere in the body or obstruction of the prostate gland (usually in older men).

For children, infection can be caused by the tube that drains urine from the kidneys and the bladder.

NOTE :

If left untreated, all UTI’s can lead to permanent kidney damage and possible kidney failure.

The general treatment is by antibiotics. A person needs to maintain good personal hygiene when eliminating wastes (liquid and solid forms) from the body.

Also, a person should drink lots of water.

Kidney StonesAre also a common kidney disorder. They form when chemicals in the urine precipitate out and form crystals. The most common crystals are from calcium oxalate, while others could be from uric acid and cystine. Kidney stones are more common in men than women and can reoccur at any time. Factors such as recurrent urinary bladder infections, insufficient water intake and consumption, low levels of physical activity, and too much Vitamin C and D intake can lead to kidney stones. One of the best ways to decrease the occurrence of stones is to drink lots of water and to change your dietary habits.

Kidney Stones (cont)Kidney Stones (cont)

Symptoms include severe back or abdomen pain, blood in the urine, nausea and vomiting. Diagnosis involves a complete medical examination, including X-rays. Treatment may vary from letting the stones pass through the urinary tract to ultrasound shock (or lithotripsy) to disintegrate the stones to a small size that can be passed through the urinary tract. Real large stones require surgery for removal.