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Lecture notes for Friday April 19 and Monday April 22, 2002
Outline
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Finish digestive system
Urinary system
Structure of nephron
Function of nephron: glomerular filtration; tubular reabsorption; tubular secretion
Regulation
Kidney dialysis
Digestive system
Small Intestine
•Long convoluted tube, 21 feet => increase surface area
•Divided into three parts: duodenum; jejunum; ileum
Histology
•Same 4 basic layers
•Modified mucosa – heavily folded, intestinal glands that secrete INTESTINAL
JUICE (slightly alkaline)
•Many projections (VILLI) out of mucosa towards lumen => increase surface area
for absorption.
•Villi contain capillary network
Digestion in Small Intestine
•Mechanical:
o Segmentation = localized contractions in areas containing food =>
mixes chyme with digestive juices AND brings food particles into
contact with mucosa for absorption
o Peristalsis => pushes chyme forward
•Chemical: chmye entering Small Intestine contains partially digested carbs,
partially digested proteins and undigested lipids. These meet up with bile,
pancreatic juice and intestinal juice => hydrolysis (break down) of carbs to
monosaccarides, proteins to amino acids and lipids to fatty acids/monoglycerides.
Once broken down food is ready for absorptions.
Absorption
•90% of all food particles are absorbed in small intestine.
•Food particles move from GI tract across GI tract wall and capillary walls into
blood stream by diffusion and active transport
Large Intestine
•Structure
•5 feet
•Histology – same 4 basic layers; no major modifications; increased mucus
secretion to reduce friction
Digestion
•Mechanical
o Peristalsis
o Mass movements
•Chemical
o NO ENZYMES secreted in large intestine => no hydrolysis
o Breakdown of remaining carbs by local bacteria => CO2, hydrogen &
methane gas => flatulence
•Absorption
o remaining water is absorbed, very little else
•Chmye => feces
• What variables does the body need to be concerned about with regard to
maintaining homeostasis?
Functions of urinary system
• Regulates composition and volume of blood
• Regulates the composition and volume of extracellular fluid
• Removes cellular metabolic wastes from blood to external environment
Structure
• 2 kidneys - produce urine
• 2 ureters - carry urine to
• 1 bladder - stores urine
• 1 urethra - transports urine to external environments
Terminology
• Ur = urine
• Urology; urologist
• Renal = kidney
• Nephr = kidney
• Nephrology; nephrologist
Gross structure
• Renal capsule
• Renal cortex
• Renal medulla
• Renal pelvis
Microscopic structure
• Nephron = functional unit of the kidney
• Nephron =
1. renal corpuscle: glomerulus + Bowman’s capsule (glomerular capsule)
2. renal tubule
Functions of nephron
• Glomerular filtration:
filtration of H20 & plasma solutes from glomerular capillaries into Bowman’s capsule
(not including formed elements & proteins)
Glomerular Filtration Rate
• Filtration = forcing fluid & solutes through a membrane by PRESSURE.
• GFR = amount of filtrate that flows into Bowman’s capsule every minute: 125
mL/min = 180 L/day
Factors affecting GFR
• Diameter of afferent & efferent glomerular arterioles:
– autoregulation due to changes in glomerular BP
Tubular reabsorption
= reabsorption of important substances from the filtrate back to the peritubular capillaries
• E.g. H20, glucose, amino acids, Na, Ca, K, etc.
• 99% of filtrate is reabsorbed (active & passive diffusion)
• H20 reabsorption is regulated by ANTIDIURETIC HORMONE
• Increase in blood osmolarity => increase in ADH secretion
• Diuretics = substances that slow down the reabsorption of water in the nephron &
collecting ducts. E.g. caffeine & alcohol
Tubular secretion
= Removal of certain chemicals from peritubular capillaries back to filtrate
• E.g. ammonia, H+, creatinine, drugs, toxins
• Mainly active transport
• maintians blood pH
Review
• Kidneys produce 180 L/day of filtrate
• Kidneys filter entire volume of plasma x60/day
• Kidney produces 1L/day of urine
Kidney failure
• Dialysis