Homeostasis 6: Homeostasis 6:

The Excretory SystemThe Excretory System

The Excretory System Overview

The Excretory System Overview

• Excretion is the process of separating wastes from body fluids, then eliminating the wastes from the body (also called the urinary system)

• Four functions: • Excretion of metabolic wastes such as nitrogenous wastes

(ammonia, urea, uric acid).• Maintain the water-salt balance. Through controlling the

salts in the blood, the kidneys can also control the amount of water and therefore the blood pressure.

• Maintain the acid-base balance: kidneys regulate the pH of the blood at 7.4 by excreting H+ ions and reabsorbing bicarbonate (HCO3-) ions

• Secretion of hormones: help the endocrine system by secreting calcitriol (active form of vitamin D that helps calcium absorption) and erythropoietin (stimulates production of red blood cells).

• Excretion is the process of separating wastes from body fluids, then eliminating the wastes from the body (also called the urinary system)

• Four functions: • Excretion of metabolic wastes such as nitrogenous wastes

(ammonia, urea, uric acid).• Maintain the water-salt balance. Through controlling the

salts in the blood, the kidneys can also control the amount of water and therefore the blood pressure.

• Maintain the acid-base balance: kidneys regulate the pH of the blood at 7.4 by excreting H+ ions and reabsorbing bicarbonate (HCO3-) ions

• Secretion of hormones: help the endocrine system by secreting calcitriol (active form of vitamin D that helps calcium absorption) and erythropoietin (stimulates production of red blood cells).

The Organs of the Excretory System

The Organs of the Excretory System

• Kidneys: fist-sized in lower back. Most people have two, but can live with only one. Produce the urine.

• Ureters: kidneys release urine into these two muscular, 28 cm long tubes where urine travels via peristaltic actions

• Urinary bladder: muscular area controlled by two sphincters (one is involuntary controlled, the other is voluntarily controlled) that holds the urine.

• Urethra: tube that allows urine to exit the body. In males it joins with the ductus deferens, in females the reproductive and urinary tract have separate openings.

• Kidneys: fist-sized in lower back. Most people have two, but can live with only one. Produce the urine.

• Ureters: kidneys release urine into these two muscular, 28 cm long tubes where urine travels via peristaltic actions

• Urinary bladder: muscular area controlled by two sphincters (one is involuntary controlled, the other is voluntarily controlled) that holds the urine.

• Urethra: tube that allows urine to exit the body. In males it joins with the ductus deferens, in females the reproductive and urinary tract have separate openings.

KidneysKidneys• Bean-shaped and reddish brown in colour.• Concave side of each kidney has a

depression where a renal artery enters and a renal vein and a ureter exit the kidney.

• Has 3 regions: • Renal cortex: outer layer• Renal medulla: inner layer• Renal pelvis: central cavity that is continuous

with the ureters

• In the renal cortex and medulla are more than a million nephrons with its own network of blood vessels that filter substances from the blood.

• Bean-shaped and reddish brown in colour.• Concave side of each kidney has a

depression where a renal artery enters and a renal vein and a ureter exit the kidney.

• Has 3 regions: • Renal cortex: outer layer• Renal medulla: inner layer• Renal pelvis: central cavity that is continuous

with the ureters

• In the renal cortex and medulla are more than a million nephrons with its own network of blood vessels that filter substances from the blood.

Nephron PictureNephron Picture

The Nephron has Three Main Regions:

The Nephron has Three Main Regions:

• A Filter: The filtration structure at the top of each nephron is a cap-like formation calle the Bowman’s Capsule. In each capsule, the renal artery enters and splits into a fine network of capillaries called a glomerulus, which acts as a filtration device. Proteins and other large molecules, red blood cells cannot pass through and must remain in the blood. Water, small molecules, ions and urea pass through the walls and continue further into the nephron. The fluid that is filtered is called the filtrate.

• A Filter: The filtration structure at the top of each nephron is a cap-like formation calle the Bowman’s Capsule. In each capsule, the renal artery enters and splits into a fine network of capillaries called a glomerulus, which acts as a filtration device. Proteins and other large molecules, red blood cells cannot pass through and must remain in the blood. Water, small molecules, ions and urea pass through the walls and continue further into the nephron. The fluid that is filtered is called the filtrate.

• A Tubule: the Bowman’s Capsule is connected to a small, long, narrow tubule that is twisted back on itself to form a loop. This loop acts as a reabsorption device for substances that are useful to the body such as glucose and ions and it has 3 sections: • Proximal tubule• The loop of Henle• Distal tubule

• A Tubule: the Bowman’s Capsule is connected to a small, long, narrow tubule that is twisted back on itself to form a loop. This loop acts as a reabsorption device for substances that are useful to the body such as glucose and ions and it has 3 sections: • Proximal tubule• The loop of Henle• Distal tubule

• A Duct: the tubule empties into a larger channel called a collecting duct. It functions as a water-conservation device, reclaiming water from the filtrate passing through it so that very little water is lost from the body. The filtrate that is left is now called urine. The water and solutes that were reabsorbed are returned to the body through the renal vein.

• A Duct: the tubule empties into a larger channel called a collecting duct. It functions as a water-conservation device, reclaiming water from the filtrate passing through it so that very little water is lost from the body. The filtrate that is left is now called urine. The water and solutes that were reabsorbed are returned to the body through the renal vein.

Practice: Practice:

• Page 448 #1, 4, 6, 7.• Page 448 #1, 4, 6, 7.

Urine FormationUrine Formation

How Urine FormsHow Urine Forms

• Glomerular filtration: moves water and solutes from blood into the nephron

• Tubular reabsorption: removes useful substances (sodium) from filtrate and returns back into blood for reuse

• Tubular secretion: moves additional wastes and excess substances from blood into the filtrate

• Water reabsorption: removes water from filtrate and returns it to the blood for reuse.

• Glomerular filtration: moves water and solutes from blood into the nephron

• Tubular reabsorption: removes useful substances (sodium) from filtrate and returns back into blood for reuse

• Tubular secretion: moves additional wastes and excess substances from blood into the filtrate

• Water reabsorption: removes water from filtrate and returns it to the blood for reuse.

Glomerular FiltrationGlomerular Filtration• Some water and dissolved substances from blood

are forced into the Bowman’s capsule from the glomerulus.

• This process happens at millions of nephrons at one time

• Capillaries of the glomerulus have many pores in their tissue walls that allow for water and most other dissolved molecules (not RBCs nor proteins) to pass through.

• Blood pressure at the glomerulus is much higher, which provides the forces for filtration.

• Every day 1600L-2000L of blood pass through the kidneys, making 180L of filtrate

• Some water and dissolved substances from blood are forced into the Bowman’s capsule from the glomerulus.

• This process happens at millions of nephrons at one time

• Capillaries of the glomerulus have many pores in their tissue walls that allow for water and most other dissolved molecules (not RBCs nor proteins) to pass through.

• Blood pressure at the glomerulus is much higher, which provides the forces for filtration.

• Every day 1600L-2000L of blood pass through the kidneys, making 180L of filtrate

Tubular Reabsorption: Proximal Tubule

Tubular Reabsorption: Proximal Tubule

• About 65% of the filtrate that passes through the length of the proximal tubule will be reabsorbed.

• Involves both active and passive transport.• Cells of the proximal tubule contain many

mitochondria to drive the active transport of sodium ions, glucose and other solutes back into the blood.

• Negatively charged ions tag along passively, attracted to the positive charges.

• Water follows by osmosis

• About 65% of the filtrate that passes through the length of the proximal tubule will be reabsorbed.

• Involves both active and passive transport.• Cells of the proximal tubule contain many

mitochondria to drive the active transport of sodium ions, glucose and other solutes back into the blood.

• Negatively charged ions tag along passively, attracted to the positive charges.

• Water follows by osmosis

Proximal Reabsorption:

Loop of Henle

Proximal Reabsorption:

Loop of Henle• As the Loop of Henle dips into the medulla region, it is

increasingly salty so water moves via osmosis into the capillaries. The permeability of the descending loop is such that water can move, but solutes are only slightly able to move.

• By the end of the descending loop of Henle, the concentration of Na+ inside the tubule is at a maximum.

• The permeability of the nephron tubule changes as it ascends. It is now impermeable to water and slightly permeable to solutes so Na+ can diffuse into the blood.

• As the Loop of Henle dips into the medulla region, it is increasingly salty so water moves via osmosis into the capillaries. The permeability of the descending loop is such that water can move, but solutes are only slightly able to move.

• By the end of the descending loop of Henle, the concentration of Na+ inside the tubule is at a maximum.

• The permeability of the nephron tubule changes as it ascends. It is now impermeable to water and slightly permeable to solutes so Na+ can diffuse into the blood.

• At the thick-walled part of the ascending loop of Henle, Na+ are actively transported into the blood.

• By now, 2/3rds of the Na+ and water from the filtrate have been reabsorbed.

• At the thick-walled part of the ascending loop of Henle, Na+ are actively transported into the blood.

• By now, 2/3rds of the Na+ and water from the filtrate have been reabsorbed.

Tubular Reabsorption: Distal Tubule

Tubular Reabsorption: Distal Tubule

• Active reabsorption of Na+ from the filtrate depends on the needs of the body.

• Passive reabsorption of negative ions occurs by attraction.

• Active reabsorption of Na+ from the filtrate depends on the needs of the body.

• Passive reabsorption of negative ions occurs by attraction.

Tubular SecretionTubular Secretion

• Hydrogen ions are actively secreted into the distal tubule to help maintain pH balance.

• Potassium is also secreted into the distal tubule

• Other substances that are not normally a part of the body, such as penicillin and other medications, are secreted from the blood into the distal tubule.

• Hydrogen ions are actively secreted into the distal tubule to help maintain pH balance.

• Potassium is also secreted into the distal tubule

• Other substances that are not normally a part of the body, such as penicillin and other medications, are secreted from the blood into the distal tubule.

Water Reabsorption: Water Reabsorption:

• Filtrate entering the collecting duct stil has a lot of water.

• Passive reabsorption of water happens due to the fact that the collecting duct dips deep into the medulla where the area is very salty.

• Hormones can help control reabsorption and secretion.

• Filtrate is now only 1% the original filtrate volume and is now called urine.

• Filtrate entering the collecting duct stil has a lot of water.

• Passive reabsorption of water happens due to the fact that the collecting duct dips deep into the medulla where the area is very salty.

• Hormones can help control reabsorption and secretion.

• Filtrate is now only 1% the original filtrate volume and is now called urine.

Practice: Practice:

• Page: 455 # 1-4, 7, 9-11.• Page: 455 # 1-4, 7, 9-11.

Other Functions of the Excretory System

Other Functions of the Excretory System

• Regulating Water-Salt Balance through reabsorption of water: • Force generated as water moves by osmosis is called

osmotic pressure.• Osmoreceptors are cells that are sensitive to osmotic

pressure and many are located in the hypothalamus.• When blood becomes too concentrated, osmoreceptors in

the hypothalamus send impulses to the pituitary to release ADH (antidiuretic hormone), which travels to the kidneys, where it increases the permeability of the distal tubule and collecting duct.

• Ethanol and caffeine are diuretics, so they increase the volume of urine by inhibiting the release of ADH.

• Regulating Water-Salt Balance through reabsorption of water: • Force generated as water moves by osmosis is called

osmotic pressure.• Osmoreceptors are cells that are sensitive to osmotic

pressure and many are located in the hypothalamus.• When blood becomes too concentrated, osmoreceptors in

the hypothalamus send impulses to the pituitary to release ADH (antidiuretic hormone), which travels to the kidneys, where it increases the permeability of the distal tubule and collecting duct.

• Ethanol and caffeine are diuretics, so they increase the volume of urine by inhibiting the release of ADH.

• Regulating Water-Salt Balance through reabsorption of salts: • Hormones regulate the reabsorption of sodium at the

distal tubule• Aldoesterone, secreted by the adrenal cortex,

stimulates the excretion of potassium ions and the reabsorption of sodium ions.

• When the blood volume is too low to promote glomerular filtration, the kidneys release renin, which triggers the release of the aldosterone, which increases the reabsorption of Na+, followed passively by water and Cl-.

• Regulating Water-Salt Balance through reabsorption of salts: • Hormones regulate the reabsorption of sodium at the

distal tubule• Aldoesterone, secreted by the adrenal cortex,

stimulates the excretion of potassium ions and the reabsorption of sodium ions.

• When the blood volume is too low to promote glomerular filtration, the kidneys release renin, which triggers the release of the aldosterone, which increases the reabsorption of Na+, followed passively by water and Cl-.

Maintaining Blood pHMaintaining Blood pH

• The acid-base buffers in the blood as well as the respiratory system can help regulate the minor blood pH changes.

• The kidneys regulate more drastic changes, but they work a bit slower.

• They usually are excreting extra H+ ions and reabsorbing HCO3- ions

• The acid-base buffers in the blood as well as the respiratory system can help regulate the minor blood pH changes.

• The kidneys regulate more drastic changes, but they work a bit slower.

• They usually are excreting extra H+ ions and reabsorbing HCO3- ions

Releasing HormonesReleasing Hormones

• If the oxygen-carrying capacity of the blood is reduced, the kidneys release erythropoietin which stimulates the production of red blood cells in bone marrow.

• When calcium levels in the blood fall, the parathyroid gland releases the parathyroid hormone, which signals to the kidneys to release calcitriol, which promotes calcium absorption from the digestive tract.

• If the oxygen-carrying capacity of the blood is reduced, the kidneys release erythropoietin which stimulates the production of red blood cells in bone marrow.

• When calcium levels in the blood fall, the parathyroid gland releases the parathyroid hormone, which signals to the kidneys to release calcitriol, which promotes calcium absorption from the digestive tract.

Disorders of the Excretory SystemDisorders of the

Excretory System• Urinary tract infections (viral or bacterial)

which cause a painful burning during urination and a need to urinate more often.

• Kidney Stones: development of crystalline formations due to excess calcium in the urine caused by low activity levels, recurrent urinary tract infections and insufficient water consumption.

• Urinary tract infections (viral or bacterial) which cause a painful burning during urination and a need to urinate more often.

• Kidney Stones: development of crystalline formations due to excess calcium in the urine caused by low activity levels, recurrent urinary tract infections and insufficient water consumption.

• Renal Insufficiency: damage to nephrons from infection, high blood pressure, diabetes mellitus, polycystic kidney disease (genetic), trauma, poisoning, atherosclerosis.• A person can survive with as little as 1/3 of

a kidney, if 75% or more of the nephrons are destroyed, however, we can no longer maintain homeostasis.

• Hemodialysis or peritoneal dialysis• Kidney transplant

• Renal Insufficiency: damage to nephrons from infection, high blood pressure, diabetes mellitus, polycystic kidney disease (genetic), trauma, poisoning, atherosclerosis.• A person can survive with as little as 1/3 of

a kidney, if 75% or more of the nephrons are destroyed, however, we can no longer maintain homeostasis.

• Hemodialysis or peritoneal dialysis• Kidney transplant

Practice:Practice:

• Page 465 #2, 4, 7, 8.• Page 465 #2, 4, 7, 8.