the excretory system. the body has 2 kidneys they hold ~ ¼ of our blood at any one time they...
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The Excretory System
The body has 2 kidneys
They hold ~ ¼ of our blood at any one time
They play a major role in homeostasis
Each has a mass of ~ 500 g
are made up of about 1 million nephrons
1. Remove Wastes
2. Balance Blood pH
3. Maintain Water Balance
4. Blood Pressure
Such as urea and uric acid from the blood
Uric acid is formed from the breakdown of DNA (nucleic acids)
Urea is formed in a process called deamination
It occurs in the liver
It is the conversion of amino acids in the blood to carbohydrates (urea is produced)
1.) NH3 is removed from amino acids (ammonia – highly toxic…0.005
mg can kill you)
2.) 2 molecules of NH3 combine with CO2 to form urea
(urea is 1000X less toxic)
Both urea and uric acid enter the blood and will be removed from the body by the kidneys
The build up of uric acid is called gout
Kidneys remove ions (E.g. H+) from the blood keeping the pH in normal range between 7.3 and 7.5
CO2 from the peritubular capillaries combines with H20 in the cells that line the nephon producing carbonic acid….
Carbonic acid breaks apart to form H+ and HCO3
- ions
CO2 + H2O H2 CO3 H2CO3 H + + HCO3
-
If the blood is too acidic the H+ is excreted in the urine and HCO3
- is reabsorbed back to the blood …buffering the blood
If the blood is too basic The HCO3
- is excreted in the urine and H+ is reabsorbed back to the blood
This is aided by changes in breathing rate
180 L moves through kidneys in one day
~ 2L of water is lost per day from perspiration, exhaling, urine
178 L are reabsorbed!
we can only survive a few days without water 1% loss of H2O = thirst,
5% loss of H2O = pain, collapse,
10% loss of H2O = death…E.g. heat exhaustion
Two hormones regulate water concentration in the blood:
antidiuretic hormone (ADH) aldosterone
Hormones are chemicals that travel in the blood and target cells in the body…. eliciting a response
Targets the nephrons distal tubule and collecting duct
It increases H2O reabsorption into the
bloodstream
It is produced by nerve cells in the hypothalamus
it is stored in the posterior pituitary gland and secreted when it is needed
Hypothalamus
Pituitary
H2O lost in the body causes H2O to move from the tissues into the bloodstream (shrinking body cells)
osmoreceptors in the hypothalamus detect low osmotic (H2O) pressure
The hypothalamus responds by: triggering thirst sending a nerve message to the
pituitary gland ….stimulating the release of ADH
ADH travels in the blood and targets the nephron
No ADH
ADH Present
ADH causes the distal tubule and collecting duct to become permeable to H2O
The kidneys reabsorb more H2O a more concentrated urine (dark yellow) is
produced
Cold weather, caffeine and alcohol all inhibit the release of ADH
reabsorption of the H2O can’t take place and
urine volume is increased
The kidneys help regulate blood pressure
Aldosterone: is produced and secreted by the
adrenal glands
It targets the ascending Loop of Henle, distal tubule and collecting duct
It increases the amount of Na+ reabsorption.. therefore increasing the reabsorption of H2O
This increases blood pressure
It is detected by osmoreceptors in the juxtaglomerular apparatus ………cells located in the afferent arteriole near the glomerulus
cells in the juxtaglomerular apparatus release rennin
Rennin converts angiotensinogen (a plasma protein secreted by the liver) to angiotensin (active form)
Produces and releases aldosterone
Aldosterone Increases Sodium reabsorption
Na+
Na+
Na+Na+
Na+Na+ Na+
Na+
Na+
Na+
Na+
angiotensin: constricts blood vessels causes aldosterone to be released from
the adrenal glands (both of which increase BP)
Aldosterone causes an increase in Na+ reabsorption from the ascending loop, distal tubule and collecting duct (nephron)
H2O follows by osmosis and moves into the bloodstream therefore increasing blood volume and BP
Draw and label the structures of the Urinary System
Renal arteries: branch from the abdominal aorta they supply the kidneys with
oxygenated, unfiltered blood
Renal veins: remove deoxygenated, filtered blood
Filter wastes from the blood
Are made up of 3 layers:
a.) the cortex: outer layer of connective tissue
b.) the medulla: inner layer..contains the nephrons (beneath the cortex)
c.) the pelvis: hollow chamber joining kidney to ureter
Are 2 tubes that filtered wastes from the kidneys passes through to reach the bladder
storage for urine
holds about 200 mL of urine
at 400mL stretch receptors signal the brain that it is “time to go….”
after 600 mL is collected all voluntary control is lost!
urine leaves the bladder through the urethra
sphincter muscles relax and urine is
voided
It is shorter in women and as a result women are more susceptible to bladder infections…..closer contact to the outside
The Nephron Handout: fill in structures
Note: the cortex contains: the afferent, efferent
arterioles and the Bowman’s capsule
The medulla contains: the Loop of Henle
are the functional units of the kidney
Afferent arterioles supply the nephrons with blood branch into the capillary bed called the
glomerulus
Blood leaving the glomerulus: Passes through the efferent arterioles travels to the peritubular capillaries
(they wrap around the tubules) to the venule then to the renal vein
The glomerulus is surrounded by the Bowman’capsule (funnel-like part)
This tapers into the proximal tubule
The proximal tubule connects to the loop of Henle
The loop of Henle connects to the distal tubule
The distal tubule empties into the collecting duct …these ducts merge in the renal pelvis
Your Assignment: Page 380, 1-3
It depends on 3 steps: Filtration Reabsorption Secretion
Filtration: the movement of fluid from the blood
(glomerulus) into the Bowman’s capsule
Reabsorption: is the movement of essential solutes and water
from the nephron back to the blood
Secretion: involves the transport of materials from the
blood into the distal tubule of the nephron
Filtration
Occurs at the glomerulus
filtration rate: if the pressure then filtration rate
blood enters nephron through the afferent arteriole (pressure is 2 kPa)
Then blood enters the glomerulus (pressure is 8 kPa) which acts like a high pressure filter
Proteins, blood cells and platelets are too large to filter through glomerulus and move into the efferent arteriole
Plasma passes through the glomerulus into the Bowman’s capsule (E.g. Na+, Ca2+, glucose, urea, uric acid etc.)
Reabsorption
Solutes move from nephron into bloodstream
Most reabsorption (85%) occurs in the proximal tubule
It also occurs in the Loop of Henle and distal tubule
it occurs till the threshold level is reached
600 mL of fluid moves through kidney per minute… about 120 mL of that is filtered into the nephron…and from that only 1 mL of urine is made
Both active and passive transport occur (large molecules require active transport)
glomerular filtrate (dissolved solutes) travels through the proximal tubule
the proximal tubule contains a rich supply of mitochondria (ATP production) and microvilli
as the filtrate moves through the proximal
tubule, Loop of Henle and distal tubule, H2O and certain ions are reabsorbed back into the bloodstream
This maintains proper water and ion balance
Na+, glucose and amino acids are actively transported out of the nephron into the peritubular capillaries (bloodstream)
in the descending loop the filtrate is hypertonic and water diffuses out of nephron into bloodstream (osmosis)
At the ascending loop, the filtrate is hypotonic Na+ is actively transported out …..to keep water from moving the wrong way
Cl- and HCO3- ions follow the Na+ ions…
due to charge attraction (passive transport)
There is limited energy for active transport so some solutes (E.g. NaCl) stay …..
once the ions move out, an osmotic gradient is set up so water diffuses from tubules and Loop of Henle into bloodstream
filtrate becomes more concentrated as it moves along towards the distal tubule
Secretion
movement of wastes from the bloodstream into nephron
Occurs at the distal tubule and involves active transport
urea, histamine, NH3, K+ ions, H+ ions, HCO3 ions, minerals, drugs such as penicillin etc. move from the blood into the distal tubule
After secretion the urine moves into the collecting ducts
The collecting ducts lead to the renal pelvis then on to the ureters and bladder
Filtration glomerulus and Bowman’s capsule passive transport
Reabsorption proximal tubule (mainly), loop of Henle, distal
tubule active and passive transport
Secretion distal tubule active transport
water (95%) urea uric acid trace amino acids electrolytes: Na+, K+, Cl-, SO4
2-, PO4 +3
excess vitamins, minerals, etc
The pH of urine ranges from 4 to 5 but can get as high as 8.5
Remains in Blood
Filters into Capsule
Reabsorbed
RBC Water Water (most of)
WBC Amino acids Amino acids (all)
Platelets Glucose Glucose (all)Fats Salts Salts (some)
Blood Protein Urea, uric acid
Urea, uric acid (none)
Component
Plasma Filtrate Urine
Urea 0.03 0.03 2.0
Uric Acid 0.004 0.004 0.05
Glucose 0.10 0.10 0 to trace
Amino Acid
0.05 0.05 -----
Salt 0.72 0.72 ~1.5
Protein 8.00 ----- ----
Comparing Solutes in plasma, Nephron, and Urine
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