excretion in humans (chap 8) -o level pure bio

what are some metabolic waste products

• carbon dioxide

• urea

• mineral salts

• water

what is excretion

the removal of metabolic waste products, toxic substances and substances in excess of the bodies requirements, so that harmful substances will not build up in the body to cause harm

name them

1. left and right kidneys (reversed sides - same as heart)

2. ureter

3. urinary bladder

4. urethra

what is a nephron

basic functional units of the kidney

label

what is ultrafiltration

• the first stage of urgent formation

• process by which small molecules are filtered out of the blood by the glomerulus into the bowman’s capsule

how does ultrafiltration occur

• the afferent arteriole is wider than the efferent arteriole, creating a high blood pressure in the glomerulus

• blood plasma is forced out of the glomerular blood capillaries into the bowman’s capsule

• filtered blood plasma is known as the glomerular filtrate

• contains small soluble molecules such as salts, water, glucose, amino acids, and urea that is forced into the Bowman’s capsule

how is the glomerulus suited to urine formation

• the glomerulus is a network of blood capillaries that provide a large surface area for the filtration process

• the blood capillaries are one-cell thick

• blood capillaries are covered by a thin partially permeable membrane - only allows very small soluble molecules to pass through

• impermeable to blood cells, platelets and large molecules such as proteins

what is selective reabsorption

the process in which useful substances that the body needs is reabsorbed into the blood capillaries

how does selective reabsorption occur

• proximal convoluted tubule:

  • most of the water is reabsorbed by osmosis

  • all of the glucose and amino acids is reabsorbed back by active transport

  • most mineral salts are reabsorbed by diffusion and active transport

• loop of Henlé:

  • some water is reabsorbed by osmosis

  • some mineral salts are reabsorbed by active transport

• distal convoluted tubule:

  • some water is reabsorbed by osmosis

  • some mineral salts are reabsorbed by active transport

• collecting duct

  • reabsorbs some water by osmosis

what is osmoregulation

the control of water potential and solute concentration level in the blood to maintain a constant water potential in the body

why are kidneys important

1. the kidneys are excretory organs

   • they play an important role in excreting metabolic waste products

2. the kidneys are osmoregulators

   • they regulate the solute concentration and water potential in the blood to maintain a constant water potential in the blood

what are some causes of kidney failure

• high blood pressure

• diabetes

• alcohol abuse

• severe accidents

• complications from major surgeries

how does a dialysis machine work

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

2. the tubing is bathed in a specially controlled dialysis fluid. the walls of the tubing in the dialysis machine are partially permeable

3. small molecules such as urea and metabolic waste products diffuse out of the tubing into the dialysis fluid. blood cells, platelets and large molecules such as proteins remain in the tubing

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

what are the features of a dialysis machine

• dialysis fluid contains the same concentration of glucose, amino acids and mineral salts as healthy blood

  • ensures that glucose, amino acids and mineral salts do not diffuse out of the blood and into the dialysis fluid.

  • if the patients blood lacks these essential substances, these substances will diffuse into the patients blood

• dialysis fluid does not contain metabolic waste products

  • sets up a concentration gradient for waste products such as urea to diffuse into the dialysis fluid

• tubing in the machine is narrow, long and coiled

  • increases surface area-to-volume ratio which helps to speed up the rate of exchange of substances between patients blood and the dialysis fluid

• direction of blood flow is opposite to the flow of dialysis fluid

  • maintains concentration gradient for the removal of waste products

• dialysis membrane is partially permeable