Vertebrate kidney structure and function ap biology chapter 44.
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Transcript of Vertebrate kidney structure and function ap biology chapter 44.
Nephron Functional unit of the kidney 3 main jobs:
Filtration of water and solutes from blood
Reabsorption of water and molecules back into blood or interstitial fluid
Secretion of ions and other waste products from capillaries
Remember: the idea is to concentrate the fluids (filtrate) in the tubes of the kidney to produce urine that has higher osmolarity than that of blood
Filtration: Glomerulus Bowman’s capsule
Reabsorption Proximal convoluted tubule
Reabsorbs 75% of the water, salts, glucose, and amino acids
Reabsorption/Secretion Loop of Henle
Countercurrent exchange, which maintains the gradient
Distal convoluted tubule Tubular secretion of H ions, potassium, and certain
drugs
Overview: Flow of Filtrate Bowman’s capsule proximal
convoluted tubule descending loop of Henle ascending loop of Henle distal convoluted tubule collecting duct renal pelvis ureter bladder urethra
Urine production through filtration, secretion, and reabsorption 1. Blood pressure in
glomerulus forces fluid into Bowman’s capsule (BC) [example of bulk flow!] Blood is now called filtrate
and is composed of glucose, salts, vitamins, nitrogenous wastes (urea)
The osmolarity of blood and filtrate are about equal at this point since both water and salt are removed
2. As the blood flows from BC to proximal convoluted tubule (PCT) solutes are reabsorbed from the tubule Water and salts are
reabsorbed back into interstitial fluid
Ammonia, drugs, ions (H+) are secreted into tubule
Some ions are actively transported
Water flows passively out of PCT
3. From the PCT filtrate moves down the descending loop of Henle Water is reabsorbed by the
interstitial fluid out of the tubule This section is permeable to
water but not to solutes As water is reabsorbed, the
concentration within the tubule increases and is at its maximum at the elbow of the loop
4. As the filtrate makes the turn at the bottom of the loop, the epithelium is change and becomes permeable to salt but not to water Salt is transported out of the
ascending loop of Henle, which makes the interstitial fluid on the inner medulla of the kidney very saline
The filtrate within the loop is less concentrated
Through the thick portion of the loop, salt is actively pumped out and the filtrate continues to decrease in osmolarity
5. Filtrate enters the distal convoluted tubule (DCT) where ions are secreted into the tubule; water and bicarbonate are reabsorbed by the interstitial fluid Concentration of the filtrate is at its
lowest point along the DCT
6. From the DCT the filtrate again turns toward the inner medulla down through the collecting duct Water is reabsorbed and the filtrate
becomes increasingly more concentrated
Interstitial fluid increases in osmolarity from the cortex to the inner medulla so what is constantly diffusing out of the tube back into the interstitial fluid
This creates a urine that is hypertonic to most of the body fluids (since urea is present), becoming more concentrated as the water diffuses out of the duct