Structure of The Kidney

Objectives1) Define the term excretion and explain the

importance of removing waste material from the body

2) Describe the process which forms urea from amino acids

3) Describe the general structure of the kidney, the nephron, and associated blood vessels

Excretion • What waste material do we produce?– CO2 released through lungs– Feces released through digestive tract – Urine released through kidneys

• All are poisonous materials (toxins)• Where do they come from?– CO2 cellular respiration– Feces material not absorbed by body– Urine forms from urea; produced by

the liver from excess amino acids

It All Starts In The Liver• After absorption, food

molecules are assimilated• Assimilation to become a

useful part of a cell or organ• Roles of the Liver1) Glycogen is made from excess

blood glucose2) Amino acids used to make

proteins3) Fatty acids/glycerols are made

into fat4) Form cholesterol from fat5) Excess amino acids

deaminated; forms urea

Deamination: Forming Urea• What are our major sources of

energy?– Carbohydrates, Fats, and Proteins

• How are carbs and fats stored? Proteins?– Glycogen and fat (adipose tissue)

• Deamination removal of for amino group from an amino acid to form a keto acid and ammonia (NH3)– Keto acids can form glucose and

fat– Ammonia is toxic

Deamination: Forming Urea• To prevent damage from

ammonia build up, ammonia instantly combines with CO2 and produce urea and H2O

• Urea passes from the liver into the blood plasma and then filtered out through the kidneys

• Uric Acid minor nitrogenous excretory product made from the breakdown of DNA

Structure of the Urinary System• Renal artery takes unfiltered

blood to kidneys• Renal vein takes filtered

blood from kidneys• Kidney bean-shaped network

of filtering units called nephrons

• Ureter carries urine from kidneys to bladder

• Bladder elastic storage area for urine

• Urethra carries urine from bladder to outside the body

Layers of a Kidney• 2 main roles of kidneys:1) Removal of urea2) Regulating water levels, ion levels, and

pH of blood (homeostasis)• Capsule tough outer layer to protect

kidney from damage• 3 main areas of a Kidney• Cortex contains all glomerulus, renal

capsules, and area where ultrafiltation occurs

1) Medulla contains kidney tubules and collecting ducts, and area where reabsorbtion occurs

2) Pelvis where all collecting ducts meet to carry waste away through ureters

K

L

M

N

O

Glomeruli

Cortex

Collecting ducts

Medulla

Pelvis

Structure of a Nephron• Nephron (kidney tubule)

filtration unit a kidney• Renal (Bowman’s) capsule

cup-shaped site where arterial blood is filtered– Blood comes in from arteriole– Glomerulus splitting

capillaries in capsule to increase filtering rate

– Filtered blood leaves through the arteriole

Ultrafiltration • Renal capsule filters urea, H2O,

and small molecules from the blood– Reabsorption pulls important

molecules and H2O back into blood

• 3 layers of Filtration walls inside renal capsule have small gaps; only small molecules get through– Blood cells are too big

• Blood pressure helps force waster material through filter and out of the blood (125 ml/min)

Reabsorption• What inside the filtrate?

– Urea– Water– Glucose– Na + / Cl-; Ions

• What do we need back?– Glucose and Ions

• Capillaries wrapped about nephrons reabsorb glucose and ions into the blood

• Water is reabsorbed in the collecting ducts depending on your blood water levels– Hydrated clear/light yellow– Dehydrated dark yellow

Kidney Failure• What happens when the kidneys shut

down?– Urea builds up in body– Toxic levels effect organs; death

• What can cause kidneys to fail?– Physical damage– Blood clots; blockage in tubes– Kidney Stones– Toxins; Alcohol and Drugs– Genetics; DNA– Disease

• How do we know kidneys are damaged?– Blood in urine– Large proteins in urine– Pain and illness

Living With One Kidney• What does living with one

kidney mean?– More urea in blood– Higher blood pressure– More stress on remaining kidney– Toxins have longer effects; alcohol

and drugs– Greater chance of losing other

kidney• What options do you have if you

lose both kidneys?1) Dialysis2) Kidney Transplant

Kidney Dialysis • Kidney dialysis machine filtering

blood outside the body1) Machine draws out blood from vein2) Inside machine; blood passes by

several dialysis membranes; Urea drawn out of blood into dialysis fluid (dialysate). How?– Diffusion

3) Dialysis fluid is contains salt and sugar. Why?– No diffusion; glucose/salts stays in blood

4) Filtered blood returns to body vein• 3-4 hours; 2-3 times a week• What diet must you have?

– Low-Protein = Less Urea

Kidney Transplant• Kidney Transplant surgically replacing

the damaged kidney with the healthy kidney of a donor

• What are the major difficulties with transplants?

1) Donor match kidney must be excepted by body (donor should be related to you or similar in DNA)– Drugs can lower white blood count to

help kidney acceptance– Might get really sick

2) Dangerous surgeries always have a risk of killing the patient

3) Expensive lots of money needed to get kidney and pay the hospital; plus after hospital care