Excretion

Define the term excretion

This is the process in which metabolic waste (Excretory products) is removed from the body cells.

Define the term egestion

This is the process in which undigested food in the alimentary canal leaves the body through the anus.

Why is excretion important in living organisms

This is because it prevents the accumulation of metallic waste which can damage cells and in turn lead to disruption of the normal balance of the internal environment.

What is the difference between the excretion and egestion?

Excretion involves the removal of metabolic waste, while egestion refers to the elimination of undigested food from the digestive tract.

What are the excretory products in plants?

1. Oxygen (A byproduct of photosynthesis)

2. Carbon dioxide

3. Water vapour

4. Nitrogenous waste/compounds

In terms of excretory products in plants, when is oxygen produced?

This is produced during the process of photosynthesis and diffuses out of the leaves through the stomata.

In terms of excretory products in plants, when is carbon dioxide produced?

This is produced during the process of respiration in the plant cells and diffuses out of the leaves through the stomata (During the night or when photosynthesis is not occurring).

In terms of excretory products in plants, when is water vapour produced?

This is produced during the process of respiration and diffuses out of the leaves through the stomata during transpiration.

In terms of excretory products in plants, when is Nitrogenous waste/compounds produced?

These are produced during the break down of proteins in plants. These insoluble substances are stored in various structures eg. Leaves, flowers, bark and seeds.

What are the excretory products in plants?

1. Nitrogenous waste/compounds (Urea, uric acid and ammonia)

2. Carbon dioxide

3. Bile salts

How are nitrogenous wastes/compounds produced in terms of excretion in animals?

These are produced from the breakdown of proteins in the cells of animal.

How is the nitrogenous compound urea formed?

This is formed in the liver of mammals from amino acids. It is nontoxic, very soluble and easily filtered by the kidneys

How is the nitrogenous compound uric acid formed?

This is produced by birds and terrestrial insects. It is less toxic than ammonia and is an ideal excretory product for organisms that produce shelled eggs.

When do humans produce uric acid?

This is produced in small quantities from the breakdown of nucleic acid and nitrogen oxide.

How is ammonia produced?

This is the main excretory product produced by aquatic animals eg. molluscs. It is very toxic, very soluble and must be diluted in a significant amount of water to be eliminated from the body

When is carbon dioxide produced?

This is produced during the process of respiration in animal cells and diffuses out of the body cells into the alveoli of the lungs. It is then expired (exhaled) through the nose

How are bile salts produced?

This is a product of haem (is a ring-shaped iron-containing molecular component of hemoglobin) in the blood. It is produced in the liver and stored in the gall bladder. It mixes with the undigested food material in the colon where it is excreted as part of the faeces.

What are the excretory organs in animals?

The kidneys (the main excretory organs), lungs, skin, liver and gills.

What are the kidneys?

These are a pair of bean shaped organs with the right kidney slightly lower than the left kidney. They located in the back of the abdominal cavity behind the intestines on both sides of the vertebral column.

What are the 3 main functions of the kidneys?

1. They excrete nitrogenous waste / compounds from the blood 

2. They maintain water salt balance in the blood (osmoregulation)

3. They maintain the acid base balance of the blood

What are the parts of the kidneys?

The renal cortex, the renal medulla, and the renal pelvis

What is the renal cortex?

This is the outer part of the kidneys which is covered by a fibrous connecting tissue forming a capsule.

Where are the glomerulus and Bowman’s Capule located?

These are located inside the renal cortex.

Where is the renal medulla located?

This is located between the renal cortex and pelvis and is composed of the tabular part of the nephron.

What are the renal pyramids and how are they formed?

These are cone-shaped structures located in the medulla (inner part) of the kidney. They are formed by blood vessels.

What is the renal pelvis?

This is the innermost part of the kidney and it is white in colour

What is the function of the renal pelvis?

This collects urine from all the collecting ducts of the nephron.

What are the ureters?

These are two thin, muscular tubes (about 25–30 cm long) located between the kidneys and urinary bladder that extend from each kidney to the urinary bladder.

What is the urinary bladder?

This is a hollow, sac-like muscular organ located below the urethra inside the pelvic cavity.

What is the function of the urinary bladder?

This stores urine temporarily until it is ready to be expelled from the body. Its walls stretch to accommodate increasing volumes of urine.

What controls the release of urine from the bladder?

The sphincter muscles control the release of urine from the bladder. The internal sphincter is involuntary and prevents leakage by staying closed until urination begins, while the external sphincter is voluntary and allows a person to control when to urinate. Together, they ensure proper urine retention and release.

Where are the sphincter muscles located?

These are located between the urethra and the urinary bladder

What is the urethra?

This is a fibromuscular thin hollow tube that connects the urinary bladder to the external opening of the body (urethral orifice). It is shorter in females and longer in males (where it also carries semen).

What is the function of the urethra?

This allows urine to pass out of the body during urination. In males, it also serves as a passage for semen during ejaculation.

What is the nephron?

This is the basic unit of structure of the kidney. It is a microscopic kidney tubule that regulates the blood composition by filtration, reabsorption and secretion of various substances. 

What are the parts of the nephron?

The Bowman’s capsule

The Proximal Convoluted Tubule (PCT)

The Loop of Henle

The Distal Convoluted Tubule (DCT)

The Collecting ducts

What is the bowman’s capsule?

This is the first part of kidney tubule and is located in the cortex. It is cup shaped and contains a mass of capillaries called the glomerulus.

What is the fluid inside the Bowman’s capsule called?

This is called filtrate and it contains water, salts, nutrients, urea

What is the function of the Bowman’s Capsule?

This collects filtrate from the glomeruli through the process of ultrafiltration

What is ultrafiltration?

This is the process by which small molecules are filtered from the blood into the nephron under high pressure, forming the initial filtrate that will eventually become urine.

What is the proximal convolution tubule (PCT)?

This is the second part of kidney tubule which is convoluted in shape and located in the cortex. It is located below the Bowman’s capsule and collects filtrate

What is the function of the proximal convoluted tubule (PCT)?

It is Involved in selective reabsorption of glucose back into the blood by the capillaries (from renal veins) that are wrapped around the nephron.

What is the loop of Henle?

This is the third part of the kidney tubule which is located in the medulla. It collects filtrate from PCT

* Amount of water reabsorbs is dependent on the length

of the structure

What is the amount of water reabsorbed dependent on?

This is dependent on the length of the loop of Henle

What is the function of the loop of Henle?

This creates a concentration gradient in the renal medulla, which enables the kidney to efficiently reabsorb water from the filtrate and produce concentrated urine.

What is the distal convoluted tubule (DCT)?

This is the fourth part of kidney tubule and is located in the cortex. It collects filtrate from Loop of Henle

What is the reabsorption of water and salts controlled by?

This is controlled by the hormone Antidiuretic Hormone (ADH)

What is the release of Antidiuretic hormone dependent on?

This is dependent on the concentration of solutes in the blood

What is the function of the Distal Convoluted Tubule (DCT)?

This is involved in the selective reabsorption of water and salts from the filtrate

What are the collecting ducts?

These are tubular structures located in the renal medulla. They Collect filtrate from Loop of Henle. Multiple nephrons connect to a single collecting duct.

What is the function of the collecting duct?

This is involved in the selective reabsorption of water and salts from filtrate

What is selective reabsorption?

is the process by which useful substances are reabsorbed from the filtrate back into the blood as it passes through the nephron in the kidney, particularly in the proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting duct.

State what happen in the PCT of a diabetic person and nondiabetic person

In a non-diabetic person, blood glucose levels are within the normal range, so when blood is filtered in the kidneys, all the glucose that enters the filtrate is reabsorbed in the proximal convoluted tubule (PCT) by active transport. As a result, no glucose is found in the urine. However, in a diabetic person, blood glucose levels are abnormally high. When this blood is filtered in the kidneys, the amount of glucose in the filtrate exceeds the reabsorption capacity of the PCT. This means that not all glucose can be reabsorbed, and the excess remains in the filtrate, eventually appearing in the urine

Explain the amount of ADH that is produced based on the concentration of solutes in the

filtrate

If the concentration of water in the filtrate is low (meaning the filtrate is concentrated and the body is dehydrated), more ADH is released, increasing the permeability of the collecting ducts so that more water is reabsorbed, resulting in concentrated urine. On the other hand, if the concentration of water in the filtrate is high (meaning the body is well hydrated), less ADH is released, so less water is reabsorbed, and the urine remains dilute.

Compare the composition of the blood in the renal artery and renal vein

The blood in the renal artery has

State what causes diuresis in the body

This is caused by factors that reduce water reabsorption in the kidneys, leading to increased urine output. These include high blood glucose (as in diabetes), low ADH levels, diuretic drugs, excessive fluid intake, and substances like caffeine and alcohol.

What is osmoregulation?

This refers to the maintenance of a constant osmotic pressure or condition of the internal

environment of the body.

How is the concentration of the blood regulated by the kidneys?

They control the amount of salts and water absorbed by the distal convoluting tubule (DCT) and collecting ducts.

What determines the amount of ADH to be produced?

The blood passes through the hypothalamus in the brain which detects the solute concentration of the blood. A message is then sent to the pituitary gland to determine the amount of antidiuretic hormone (ADH) to produce

State what is kidney failure and identify the two types of kidney failure

This is a condition in which the kidneys lose their ability to filter waste products, excess fluids, and toxins from the blood effectively. The 2 types of kidney failure are: Acute kidney failure and chronic kidney disease.

Differentiate between chronic and acute kidney failure

Acute kidney failure is characterized by the sudden and rapid loss of kidney failure often caused by severe dehydration, injury, infection, blocked urine flow, or certain medications and is typically reversible with prompt treatment while chronic kidney failure is characterized by the gradual and long-term loss of kidney function often caused by diabetes, high blood pressure, prolonged kidney infections, or inherited condition and is usually irreversible and progressive; may require dialysis or a kidney transplant

Identify two ways used to treat kidney failure

Kidney failure can be treated in two main ways. One common treatment is dialysis, a medical procedure that performs the kidneys’ function of removing waste, excess fluids, and toxins from the blood. Another treatment option is a kidney transplant, which involves surgically replacing the failed kidney with a healthy one from a donor. While a transplant can restore normal kidney function, patients must take lifelong medication to prevent their body from rejecting the new kidney.

Define the term homeostasis

This refers to all the mechanisms that are involved in the constant internal environment.

What are the importance of homeostasis?

1. It is used to establish the optimum condition of organisms

2. It is used to maintain internal conditions of organisms especially higher vertebrates in a steady and balanced state.

What are regulators (Endotherms)?

These are animals that can regulate their internal environment through control mechanisms to maintain a suitable internal temperature crucial in carrying out body functions. They are often referred to as warm-blooded animals. Examples  -  Mammals and birds.

What are non-regulators/ conformers (Ectotherms)?

These are animals that cannot regulate their own internal temperature. They adapt their behavior to the surroundings or migrate to environments with optimal temperatures. They are also referred to as cold-blooded animals. Examples  – amphibians, reptiles, insects etc.