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November 30, 2016
& URINE FORMATION
REVIEW!
November 30, 2016
200 litres of blood are filtered daily by the kidneysUsable material: reabsorbed back into bloodWaste: drained into the bladder
Urinary/Renal System
away from the heart
to the heart
a filter to
kidneysbladder
November 30, 2016
There are 2 kidneys in the human body
Each kidney has three layers:• The outer layer : cortex• The inner layer : medulla• Hollow chamber: renal pelvis
The functional unit of the kidneys is called the nephrons (1 million per kidney)
renal pelvis
renal vein
renal artery
ureter
medulla
nephroncortex
November 30, 2016
Functions/ResponsibilitiesThe kidneys are responsible for:• Ion regulation and osmoregulation: regulation
of salt and water balance
• Waste management: excretion of metabolic wastes like urea, excess H+ ions and drugs
• Hormone production: function as an endocrine gland releasing hormones like Vitamin D
• Gluconeogensis: glucose production from non-carbohydrate sources
• Blood pressure regulation
• Blood pH
November 30, 2016
Nephron
The unit of a kidney is the nephron – it carries out the process of removing waste and saving certain molecules from excretion
Flow of nephron:Glomerulus -> Bowman’s Capsule -> Proximal Convoluted Tubule -> Descending Loop of Henle -> Ascending Loop of Henle -> Distal Convoluted Tubule -> Collecting Duct
November 30, 2016
Urine FormationUrine formation depends on three functions:i) filtration: the movement of fluids from the blood into the Bowman’s capsule
ii) reabsorption: the transfer of essential solutes and water from the nephron back into the blood
iii) secretion: the movement of materials from the blood back into the nephron
November 30, 2016
FiltrationAfferent arteriole carries blood to a knot of capillaries called the glomerulus
Efferent arteriole drains from each glomerulus into the vasa recta which wraps around the nephron for further reabsorption later
Blood pressure forces water and small molecules that need to be filtered, out of the glomerulus and are collected by the Bowman's Capsule
Blood cells and proteins behind in the efferent arteriole
vasa recta
November 30, 2016
November 30, 2016
Reabsorption600mL/min of fluid flows through the kidneys • 120mL is filtered into the nephrons
(Would produce 120mL of urine every minute)> In order to maintain homeostasis,
you would have to consume 1L of fluid every 10 min of your day.
Actually, 1mL of the 120mL forms urine. The other 119mL of fluids and solutes are reabsorbed.
Reabsorption occurs until a threshold level is reached. Any excess NaCl is excreted with urine.
November 30, 2016
Secretion
Nitrogen-containing wastes, excess H+, and even drugs like penicillin can be secreted (moved from blood into the nephron)
ex. OAT (organic anion transporter)
November 30, 2016
Flashback: Cellular TransportActive transport• Na+ • ATP is used
Passive transport• Cl- through protein channel• No energy needed
Osmosis• Movement of water down the
concentration gradient
November 30, 2016
Proximal convoluted tubuleResponsible for most of the reabsorption of water and solutes from the filtrate
Na+, Cl-, glucose and amino acids are transported out of the filtrate
• Water will follow by osmosis
• These molecules are returned to the venous blood leaving the kidney
November 30, 2016
Loop of HenleThe kidneys produce urine that is hypertonic to the blood plasma • Loop of Henle functions as a
countercurrent multiplier creating a concentration gradient in the medulla
*Let’s start in reverse to understand….Thick ascending Loop of Henle:• Thick Loop is NOT permeable to
water
• Water is forced to stay inside the tubule.
• This means that the medulla fluid has a higher concentration of Na+ and Cl- than the cells of the tubule.
November 30, 2016
Loop of Henle cont.Descending Loop of Henle: *is permeable to water but not very permeable to Na+ and Cl-
Due to osmosis, water will move out of the tubule due to the medulla fluid being more concentrated in Na+ because of the ascending loop
Tubule fluid is less concentrated than the blood plasma, and solutes that have been left behind in the medulla create a concentration gradient
November 30, 2016
Distal convoluted tubuleFluid entering is less concentrated than the surrounding cortex fluid so
the tubule will lose water by osmosis
In presence of aldosterone (hormone), Na+ will be reabsorbed while K+ or H+ will be secreted (secretion of H+ important for acid-base balance)
November 30, 2016
Collecting ductFluid entering the collecting duct is at the same concentration as blood plasma, but NaCL has been moved out of the tubule fluid so urea and other waste products make up the solute content
The concentration gradient established by the Loop of Henle increases, so more and more water is absorbed from the tubule fluid and this leaves a very concentrated urine in the collecting duct.
November 30, 2016
Formation of Urea
Excess amino acids cannot be stored in the bodyThe liver breaks down nitrogenous compounds (amino acids mostly)This is called deaminationThis produces urea which must be removed from the body
November 30, 2016
Dehydration and SweatingA hormone called antidiuretic hormone (ADH) helps kidneys increase water reabsorption
When ADH is released, more concentrated urine is produced so this conserves body water
When you sweat, blood solutes become more concentrated and ADH (made by hypothalamus) is released from pituitary gland where it is stored
Only happens in collecting duct!
November 30, 2016
Disease and IssuesDiabetes Insipidus• Destruction of ADH producing cells of the hypothalamus• Urine output increases dramatically (up to 20L of dilute urine/day) = strong
thirst response• Must drink large quantities of water to replace what they were not able to
reabsorb
Diabetes Mellitus• Inadequate amount of insulin so blood sugar levels rise.• The proximal tubule can reabsorb 0.1% blood sugar, so all this excess sugar
stays in the nephrons.• Water remains in the nephron because osmotic pressures are altered due to
the excess sugar. • This water is lost as urine so these people are also excessively thirsty.
November 30, 2016
Dialysis• Kidneys are not able to do their work by themselves so the use
of a machine is needed• A unit called a dialyzer mimics the action of a nephron
Kidney Transplant• 85% effective in restoring function• Issue: immune response of the recipient
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