Excretion In Humans

Question 1

What is excretion?

Answer 1

The process by which metabolic waste products and toxic waste substances that will become toxic if accumulated is removed from the body of an organism

Question 2

Why is excretion necessary/ important?

Answer 2

Living cells in the body of an organism undergoes both catabolic and anabolic reactions which produces waste products during these reactions. If the waste products accumulate, they can not only harm, but is toxic or poisonous to the body. Therefore these waste products need to be removed

Question 3

How does blood circulate at the kidney tubule?

Answer 3

Blood enters the kidney via the renal artery
The renal artery branches into many arterioles
Each arterioles further branches into a mass of blood capillaries called the glomerulus . The bowman’s capsule and the glomerulus is called the renal corpuscle or Malpighian corpuscle.
Blood leaves the glomerulus and enters the blood capillaries surrounding the kidney tubule
These blood capillaries then unite to form venues, which in turn join to form a branch of the renal vein
Blood exits the kidney via the renal vein

Question 4

What are the processes involved in urine formation?

Answer 4

Ultrafiltration

Selective reabsorption

Question 5

Where does ultrafiltration occur and what are the requirements for it to occur

Answer 5

At the renal corpuscle ( bowman’s capsule & glomerulus)

- passive process that requires high hydrostatic blood pressure and a filter

Question 6

What is reabsorbed at the proximal convoluted tubule?

Answer 6

Some mineral salts and all the glucose and amino acids is reabsorbed through the walls of the tubule into the surrounding blood capillaries through diffusion and active transport. Most water from the filtrate is reabsorbed here through osmosis

Question 7

What is reabsorbed at the loop of Henle?

Answer 7

Some water is reabsorbed through osmosis

Question 8

What is reabsorbed at the distal convoluted tubule?

Answer 8

Some water is reabsorbed through osmosis and mineral salts is reabsorbed

Question 9

What is reabsorbed at the collecting duct?

Answer 9

Some water is reabsorbed through osmosis

Question 10

What are the components of urine?

Answer 10

Excess water, excess salts and metabolic waste products such as urea, Uric acid and creatinine

Question 11

What is selective reabsorption?

Answer 11

The reabsorption of useful substances from the filtrate as the filtrate passes through the kidney tubule

Question 12

How is the high hydrostatic blood pressure at the glomerulus created and how does it aid ultrafiltration

Answer 12

The high hydrostatic blood pressure is created by the afferent arterioles that brings blood into the glomerulus being wider than the efferent arteriole that carries blood away

The high blood pressure forces most of the blood plasma out of the glomerular blood capillaries into the bowman’s capsule

Question 13

What is the filter used for ultrafiltration and how does it aid in ultrafiltration?

Answer 13

The partially permeable basement membrane that wraps around the glomerular blood capillaries acts as a filter

It only allows small molecules such as water, glucose , amino acids, mineral salts and nitrogenous waste products to pass through; these molecules form the filtrate in bowman’s capsule

While ensuring that large molecules such as plasma proteins , red blood cells and white blood cells, platelets are retained in the glomerular capillaries

Question 14

What is osmoregulation?

Answer 14

The control of water and solute concentrations in the blood to maintain constant water potential in the body

Question 15

How does water potential of blood relate to blood pressure?

Answer 15

The amount of water reabsorbed affects blood volume; kidneys play a vital role in controlling blood volume and blood pressure.
As blood water potential increases the blood pressure increases as well

Question 16

How does diuretics lower blood pressure and reduce chances of stroke?

Answer 16

Diuretics reduce production of anti-diuretic hormones to remote the production of urine, causing blood volume to decrease thus lowering the blood pressure

Question 17

Why are kidneys important

Answer 17

To excrete metabolic waste products such as urea excess water and mineral salts in the form of urine. They are osmoregulators and regulate water and solute concentrations in the blood to maintain a constant water potential in the blood

Question 18

How does a dialysis machine work?

Answer 18

The walls of the dialysis machine tubing are partially permeable, enabling small molecules like urea and other metabolic waste products to diffuse out of the blood through the tubing and into the dialysis fluid while ensuring blood cells, proteins and platelets remain in the tubing

The dialysis tubing is bathed in a specially controlled dialysis fluid

The filtered blood is then returned to a vein in the patients arm

Blood is drawn from the vein in the patients arm and is allowed to be pumped through the tubing in the dialysis machine

Blood is usually drawn from the part of the vein nearer the fist

Question 19

Which is better? A kidney transplant or dialysis

Answer 19

A real kidney would be more efficient at removing waste materials than a dialysis machine. In dialysis , each treatment takes several hours and the patient needs to be treated several times a week, thus affecting their lifestyle (SOL,QOL)