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SECTION 11.3
The Human Excretory System
excretion - the process by which organisms remove metabolic wastes and excess substances
Major Metabolic Wastes
1.
carbon dioxide -> created as a product of aerobic cellular respiration in every cell
2.
water -> created as a product of aerobic cellular respiration in every cell
3.
mineral salts -> created as a product of the many chemical reactions occurring in the cell (metabolism)
- e.g. sodium chloride, potassium sulfate
4.
nitrogenous wastes -> created from the breakdown of amino acids
- e.g. ammonia, urea, uric acid
5.
heat -> most chemical reactions are exothermic and release heat which must be released by the organism to maintain a constant
temperature
Structures involved:
liver, lungs, skin, urinary system
Role of the Liver in Excretion
The liver removes toxic metabolic wastes (ammonia to urea), toxins, drugs, and hormones and converts them to less
poisonous forms. These are all removed permanently by the kidneys.
Lungs
The lungs remove carbon dioxide, water (vapor), and heat.
Skin
One of the skin’s functions is to regulate temperature.
If it is too cold, the muscles connected to hair follicles contract to make hairs stand up and trap warm air against body (results in
goose bumps).
If it is too hot and the skin releases sweat. Sweat is composed of water, mineral salts, and a small amount of urea. Due to the
presence of metabolic wastes, sweat is an excretory product.
 Know diagram of skin
Urinary System
Organ
2 kidneys
Structure & Function
- bean shaped organs about 10 cm long which lie against the back muscles in the abdominal cavity
- function is to filter metabolic wastes from the blood and to regulate the concentrations of substances in the blood and
body fluids (sodium, potassium, calcium, bicarbonate ions)
- secrete the hormone erythropoietin which stimulates red blood cell production, activate vitamin D
production in the skin
- each kidney is made up of 1.25 million nephrons which are the filtering unit of the kidney
- has 3 parts:
1 cortex - outer part of the kidney which contains most of the filtering/reabsorbing part of the nephron
2 medulla - middle layer formed from collecting ducts of the nephrons
3 pelvis - inner part where fluid from collecting ducts empty and drain into the ureters
2 ureters
- tubes leading from each kidney which carries urine from the pelvis of the kidney to the urinary bladder
urinary bladder- thin walled muscular sac where urine collects and is stored
- when full, voluntary muscles will contract to squeeze the urine out through the urethra (urination)
urethra - a tube leading from the bottom of the urinary bladder and carries urine out of the body
How the nephron works
1.
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Blood enters each kidney through the renal artery which branches off the descending aorta.
The renal artery divides smaller and smaller forming arterioles. The arterioles branch smaller to form a ball of capillaries called a
glomerulus found inside Bowman’s capsule.
Blood pressure is high in arteries which increases even more when the blood reaches the glomerulus inside Bowman’s capsule.
This is due to the fact that there is no room for the blood vessels to expand.
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Due to the high blood pressure, the filtration of blood occurs. WAGSU (water, amino acids, glucose, mineral salts, and urea)
leave the blood and enter Bowman’s capsule. This material is called nephric filtrate. Red blood cells, white blood cells, platelets,
plasma proteins, and fats remain in the blood. About 180 litres of fluid is filtered by the kidneys each day and the total body
volume of blood (5 L) goes through the kidneys every 20 minutes.
The blood leaves the glomerulus and enters a second arteriole which will branch to form a capillary network around the renal
tubule and loop of Henle.
The filtrate leaves Bowman’s capsule and enters the renal tubule and then the loop of Henle.
The reabsorption of WAGS occurs in the renal tubule and loop of Henle. WAGS consists of 99% of the filtered water, all of the
amino acids and glucose nd most of the mineral salts. Water is reabsorbed by osmosis (passive transport). Amino acids, glucose
and mineral salts are actively transported or absorbed by facilitated diffusion. The amounts are determined by threshold levels ->
maximum amount of material which can be reabsorbed. - e.g. diabetics excrete glucose in urine because threshold level is lower
than the blood glucose level (only so much can be reabsorbed).
Microvilli are present to increase surface area for reabsorption.
The capillary network fuse to form venules which eventually fuse to form renal veins. These drain blood from the kidney and
empty it into the inferior vena cava.
The material remaining in the loop of Henle is urine which is composed of WUSU - water, urea, mineral salts, and a small
amount of uric acid. Uric acid is formed due to the high concentration of the urine
The urine is drained from the loop of Henle into the collecting duct. It then enters the pelvis, the ureter, and finally the urinary
bladder until urination occurs.
Control of Urine Production
- Anti-Diuretic Hormone (ADH) from pituitary gland in the brain controls permeability of distal tubule and collecting duct.
- ADH causes more water to be reabsorbed and reduces urine volume when body needs to conserve water.
- Inhibition of ADH will cause increased secretion of water and thus increased urination.
- Alcohol and caffeine block ADH release from pituitary gland to cause increased urination.
- Diabetics have increased glucose levels in their blood but there is a limit to how much can be reaborbed in the renal tubule. As a result,
the filtrate has higher glucose levels than normal which draws water into the filtrate as well. Thus, the presence of glucose in the urine is a
test for diabetes and increased urination is a symptom.
Describe how dialysis works as well as the following kidney disorders in terms of causes, their effect, and treatments:
urinary tract infection, kidney stones.
Kidney Stones
Dialysis – know two types of dialysis, why a person needs dialysis
Urinary Tract Infection (UTI)
- usually more common in females than males due to anatomical differences and easier entry for bacteria
- may occur in urethra (urethritis), urinary bladder (cystitis), kidneys (pyelonephritis - caused by blocked prostate in older men, spread
infection from elsewhere, ureter/urinary bladder connection problems in children)
- symptoms include painful urination (burning), feel need to urinate (little or no volume), upper abdomen/lower back pain, chills, nausea,
vomiting
- treated with antibiotics and surgery if serious
a) cystitis - infected bladder
b) urethritis  - infected urethra
c) pyelonephritis - infection in the kidneys
Kidney Stones
- usually more common in males than females and are caused by the precipitation of chemicals in the urine due to recurrent UTI's, too little
water consumption, too much vitamins C or D
- most are made of calcium oxalate but may be made of uric acid or cystine crystals
- symptoms include severe abdominal/lower back pain, blood in urine, nausea, vomiting
- treatment varies with size of stone
 -> small stones will pass on own with increases water consumption and dietary changes
 -> larger stones that are less than 2 cm may need lithotripsy (ultrasound to break up stone
then pass it) or medications to break up stones
 -> stones larger that 2 cm will likely require surgery
Know organ transplant info we discussed in class