Biology Excretion in humans

Very hard to remember

What is excretion?

Removal of metabolic waste products, toxic substances and substances in excess of body’s requirement

Why excrete?

So that substances do not accumulate until it is toxic and harmful to the body

Effects of excessive carbon dioxide

hypercarbia, leading to headaches, confusion, rapid breathing and premature heartbeats

Effects of mineral salts (too much and too little)

Deficiency: May lead in deficiency diseases like lack of calcium resulting into weaker bones

Excessive: Lower water potential in blood plasma, cells become dehydrated

Effects of Water ( too much and too little )

Excessive: increase water potential in water, cells might swell and burst through osmosis

Deficiency: cells may become dehydrated, and crenated.

Effects of excessive urea ( urea made be deamination of amino acids)

Abdonimal pain, nausea and vommiting

Parts of the urinary system

Kidney to ureter ( passes urine from kidney to urinary bladder) to urinary bladder (elastic muscular bag to store urine) to urethra ( urine passes from bladder to out of body ).

What are nephrons?

The basic functional unit of kidneys

Parts of the nephron

bowman’s capsule, glomerus, proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting duct

What are the 2 steps of urine formation

Ultrafiltration and selective reabsorption

How is the glomerus adapted to urine formation

1) a network of blood capillaries ( increases the surface area for filtration )

2) capillary is one-cell thick (shorten diffusion distance), partially permeable ( molecules are selective) and has pores ( allowing the selected molecules to pass through )

Urine formation

Blood plasma forced out of capillaries due to afferent arterioles thicker compared to efferent arterioles, leading the high pressure

What forms the glomerus filtrate?

Molecules like glucose, amino acids, water, urea and minerals

Molecules like platelets, blood cells and proteins remain in the capillaries)

Selective reaborption

where useful substances are reabrobed back into the blood capillaries

1) most of the water is reabsorbed by osmosis

2) ALLLLL glucose and amino acids are reabosrbed ( first by diffusion then by active transport)

3)Most mineral salts are reabsorbed

Lastly, waste materials like urea, excess water & minerals are passed out as urine

Osmoregulation

(homeostasis)

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

Osmoregulation occurs with what? (the parts)

hypothalamus that detects the change in water potential

pituitary gland that releases ADH (anti diuretic hormone) into the bloodstream and to the kidney

Why are kidneys important?

1) osmoregulators - maintain a constant water potential in the body

2) excretory organs - major role of excreting metabolic waste products

or else it would accumulate to a level that is harmful for the body

Kidney failure

2 kidneys, if one fails, the person can still lead a normal life

but if both fails, a kidney transplant or treatment with dialysis is required ( both very costly )

The dialysis machine

mimics functions of kidney

-cleaning patient’s blood from metabolic waste products

How does the dialysis machine work? (from start to back into blood)

Blood drawn from a vein from patients arm

pumped through dialysis tubing

tubing is bathed in specially controlled dialysis fluid

molecules like waste products diffuse out of tubing and into the dialysis fluid

molecules like blood cells, proteins and platelets stay in tubing

filtered blood returned back to a vein

how is the dialysis adapted to dialysis machine ( 4 adaptations )

1) same concentration of essemtial substances

2) does not contain any metabolic waste products

3) tubing are long ,narrow and coiled

4) direction of dialysis fluid is opposite direction of bloodflow