CHAPTER 11:

EXCRETION

Objectives

• Define and explain the importance ofexcretion.

• Identify the various parts of the urinary system and the function of each parts.

• Explain the function of mammalian kidney in the removal of urea and water from the body.

• Describe the process of dialysis using kidney machines.

Metabolism

• Metabolism refers to all chemical activities within the body.

• These chemical activities are called catabolic activities and anabolic activities.

• Catabolic activities refers to chemical processes which cause the breakdown of complex substances into simpler ones.

Metabolism

• Anabolic activities refers to the building up of simpler substances into more complex ones.

• Therefore,

Anabolism + Catabolism = Metabolism

Excretion in mammals – pg185Excretory products Excretory

organRemarks

Carbon dioxide Lungs Gas in expired air

Mineral salts

Nitrogenous waste products

Mainly urea Creatinine Uric acid

Kidneys

Skin

Constituents of urine

Constituents of sweat

Excretion in mammals – pg185Excretory products Excretory

organRemarks

Excess water Kidneys

Skin

Lungs

Main constituents of urine

Main constituents of sweat

Water vapour in expired air.

Bile pigments (from haemoglobin pigment)

Liver Via the intestines

What is excretion?

Excretion is the process by whichmetabolic waste products and toxicmaterials are removed from the body

ofan organism.

The urinary system

• The urinary system comprises of:

- 2 kidneys

- 2 ureters

- 1 urinary bladder

- 1 urethra

Front view of the urinary system

Left kidneyRight kidney

Left ureterRight ureter

Urethra

Bladder

Sphincter

Left kidney

Bladder

Right ureter

Right kidney

Urethra

Left ureter

Spincter

The kidneys

• Bean-shaped organs.

• Attached to the dorsal body wall, one on each side of the vertebral column.

• In man, the kidneys lies just above the waistline.

The kidneys

• Concave surface of each kidney faces the vertebral column.

• At the centre of this surface is a depression called the hilus.

• From the hilus, a narrow tube called the ureter emerges.

• Ureter convey urine from the kidney to the urinary bladder.

The kidneys

• The urinary bladder is an elastic, muscular bag where urine is collected and stored temporarily.

• At the bottom of the bladder is a sphincter muscle.

• When the bladder is full, the sphincter muscle relaxes to allow the urine to flow into the urethra and pass out of the body.

Summary

• What is excretion?

• What are the types of excretory organs present in your body?

• What is the shape of the kidney?

• Where is the kidney located?

• Name the structures which is involved in the removal of urine in the kidney.

CHAPTER 11:

EXCRETION

Re-call

• What is ‘metabolism’?

• What is the definition of ‘excretion’?

• What is the component parts of the urinary system and their functions?

Lesson objectives

• Identify the component parts of the kidney and its function.

• Identify the structure of the nephron.

• State that the formation of urine involves two processes, ultrafiltration and selective re-absorption.

Structure of the kidney

• Longitudinal section of a mammalian kidney consists of:

• An outer region called the cortex.

• A middle region called the medulla.

• An inner region leading to the ureter, called the renal pelvis.

Structure of the kidney

Structure of the kidney

• Kidneys are made up of tiny tubules called nephrons (uriniferous tubules).

• Each nephron begins in the cortex and runs down to the pelvis.

• It is in the nephron that filtering takes place and urine is formed.

Structure of a nephron

• Each nephron comprises of:

• Bowman’s capsule and glomerulus

• Proximal and distal convoluted tubules

• Loop of Henlé

• Collecting duct

CHAPTER 11:

EXCRETION

Lesson objectives

• Describe the processes (ultrafiltration and selective re-absorption) involved in urine formation.

Formation of urine

• Two main processes are involved in the formation of urine within each tubule:

• Ultrafiltration

• Selective re-absorption

Ultrafiltration

• In each glomerulus, mechanical filtration occurs. This is usually called ultrafiltration.

• Blood vessels bringing blood to each glomerulus (afferent arteriole) is quite wide, but the blood vessels taking blood away (efferent arteriole) is narrow.

• Hence, the blood pressure in the glomerulus is high.

Ultrafiltration

• Only small molecules such as water, salt, glucose and urea can go through into the tubule.

• Most protein molecules, blood cells and platelets are too big to be filtered off. They remain in the glomerular capillaries.

Selective re-absorption

• In a normal adult, about 120 cm3 of filtrate is formed in the kidney every minute.

• To prevent dehydration, a selective re-absorption of useful materials occurs.

• Wrapped around each kidney tubule are blood capillaries. They reabsorb the useful substances back to the kidney tubule.

Selective re-absorption

• Most of the water is re-absorbed by osmosis.

• Some mineral salts, all of the glucose and amino acids are re-absorbed in a healthy individual.

• The selective re-absorption process requires energy and this process is called active transport.

Selective re-absorption

• The remaining fluid continues on its way along the tubule.

• By the time the fluid reaches the collecting tubule and into the renal pelvis, it is mostly water, mineral salts and nitrogenous waste products (urea).

• This is called urine.

The normal constituents of urine

• Average composition of normal human urine (g/100 cm3) is approximately:

Water 96.0 g

Mineral salts (mainly NaCl) 1.8 g

Urea 2.0 g

Other nitrogenous substances 0.2 g

100.0 g

Summary

• Each nephron consists of a renal (Bowman’s) capsule containing the glomerulus, proximal and distal convoluted tubules, loop of Henlé and collecting duct.

• Urine formation involves two processes, namely ultrafiltration and selective re-absorption.

The normal constituents of urine

• Composition of normal urine varies considerably depending on several factors, such as diet and weather.

• Abnormal constituents of urine are found in certain disease. For example, in sugar diabetes (diabetes mellitus), the urine contains a considerable amount of glucose.

Kidneys as osmoregulators

• Water potential of the blood has to be kept relatively constant.

• Control of water content of the body is known as osmoregulation.

• The kidney, together with the hypothalamus and pituitary gland, are responsible for osmoregulation in humans.

Kidneys as osmoregulators

• The hypothalamus continuously monitors the concentration of the blood.

• The pituitary gland secretes the hormone called vasopressin or anti-diuretic hormone (ADH).

• Anti-diuretic hormone (ADH) increases water re-absorption by the kidney tubules.

CHAPTER 11:

EXCRETION

What does this picture tells you?

Lesson objectives

• State the functions of kidneys.

• Describe the process of dialysis treatment for kidney patients.

Functions of the kidneys

• Are excretory organs.

• Regulates the pH and composition of the blood plasma.

• Regulates the salt and water balance of the body fluid.

Kidney failure

Kidney failure

Kidney failure

• Sometimes, a person’s kidney may stop working properly. This might be due to an infection in the kidney.

• Prompt medical treatment have to be given and this can be done with a kidney machine.

• The process involved is called dialysis.

Kidney failure

1. In dialysis, blood is drawn from an artery in the patient’s arm and allowed to flow through the tubing in a dialysis machine.

2. The dialysis machine contains fluid consisting of water and other substances such as salt.

Kidney failure

3. As the patient’s blood passes through the dialysis machine, it is separated from the fluid by a partially permeable membrane.

4. Small molecules such as urea diffused through the membrane into the fluid.

5. Big molecules, such as proteins and blood cells, remains in the tubing.

Video clip

Kidney failure

• The filtered blood is then returned to a vein in the patient’s arm.

• Dialysis can be inconvenient and expensive for the patients.

• A better long-term solution for kidney failure is a kidney transplant. However, there are drawbacks as well.

Summary

• The urinary system consists of a pair of kidneys, ureters, urethra and urinary bladder.

• The kidney consists of a fibrous capsule, cortex, medulla and renal pelvis.

• The kidney contains numerous tubules called nephrons.

Summary

• Excretion is the removal of metabolic waste products and toxic substances from the body.

• Kidney serves as the excretory organ involved in osmoregulation, regulation of pH in blood and regulation of blood plasma composition.

Summary

• Each nephron consists of a renal (Bowman’s) capsule, the glomerulus, first (proximal) convoluted tubule, loop of Henlé and second (distal) convoluted tubule).

• Urine is formed by ultrafiltration and selective reabsorption.

• The hormone ADH regulates the amount of water reabsorbed by the kidney tubules.